NO850151L - CARBONATE / SULFIDE ANALYSIS AND MANAGEMENT METHOD - Google Patents

Abstract

A method and apparatus for measuring carbonate and sulfide concentrations in white and. green mass mill liquor, and in slurry and caustic cells, and to control the caustic reaction and other steps using this information. In particular, the caustic control logic is based on determining the concentration of sodium carbonate and sodium sulfide in the green liquor. in white liquor sludge slurry in the slurry (S) or the first caustic (C1), and in white liquor as. is transferred to the cooking house, and to use this information to control the whole process. measures the amount of these gases in a gas chromium two-graph GC. The apparatus has four main circuits: the filter circuit, the sampling circuit, the reactor circuit and the gas chromatograph circuit. A sludge separation circuit is also used if the apparatus is to analyze liquor from the slurry or causticizing cells.

Description

The present invention relates to the analysis of green liquor, slurry and causticization cells as well as white liquor chemicals and control of the operation of pulp boiling mills based on analyses.

A good diagram for the causticization process can be found in

"Pulp and Paper Manufacture", second' edition, vol. 1, "The Pulping of Wood", 1969, prepared under the direction of the "Joint Textbook Committee of the Paper Industry", publisher R.G. MacDonald and Technical Publisher J.N.Franklin, McGraw Hill

Book Company, New York. The diagram is fig. 9-72 on page

535 .

The process starts with the recycling furnace. Black liquor consists of

end of organic and inorganic chemicals and water are charged to the furnace where water evaporates, organic components are burned and inorganic components are recovered in the form of a melt. This melt, which mainly contains sodium carbonate and sodium sulphide, is continuously decanted from the furnace layer and dissolved in water (gentle washing) in a dissolution tank or tanks and forms green liquor. A typical green-lye composition is approx. 60-65% sodium carbonate and 25-28% sodium sulfide, calculated by weight (% solids), expressed as Na20. A typical solids content for green liquor is approx.

18% of the total lye weight. The green liquor is pumped from the dissolution tank or tanks to a green liquor clarifier, where sediment is sedimented. The precipitate is impurities, e.g. undissolved solids from the furnace. These are mainly carbon, calcium, magnesium and iron compounds.

After clarification, the green liquor is mixed with quicklime

from the oven in the slurry. Usually the amount of lime is adjusted to maintain a specified white liquor concentration. Refreshing lime in the form of fresh lime (or limestone burnt in the kiln) is added to the slaked lime to replace lime loss in the system. Grains (large, unreacted lime particles) are removed from the leached lime slurry in the classer section of the slurryer. Lime reacts in the slurry or

calcium oxide with the water in the green liquor and forms calcium hydroxide which in turn reacts with sodium carbonate in the green liquor and forms sodium hydroxide and calcium carbonate which then flows to the causticization cells. The caustic cells are used to allow sufficient time for the caustic reaction which starts in the slurry and approaches completion. From the causticizers, the slurry is pumped to the white liquor clarifier (or a pressure filter) to separate the white liquor from the lime sludge, calcium carbonate. The clearer white liquor is pumped to storage and then to the digester for cooking wood chips. The sludge or calcium carbonate at the bottom of the clarifier is pumped to a sludge washer, where it is washed with water from the sludge filter and sediment washer. The overflow water from the sludge washer is called thin liquor, and this is used in the dissolution tank or tanks to dissolve the smelt to form the raw green liquor.

In the usual process, the thin liquor is thus used in the dissolution tank or tanks to dissolve molten sodium salts from the recovery digester. The resulting raw green liquor is then clarified to remove sediment and then pumped to the slurryer. Lime supply to the slurryer is generally based on the total flow of green liquor and the slurry temperature, the temperature specifications being such that a specified white liquor strength and safe operating conditions are maintained.

The caustic reaction is usually controlled by chemical analysis (titration) of white liquor from a caustic cell or from white liquor clears the overflow. The lime feed, the green liquor density at the dissolving tank or tanks, or a combination of the two, is usually changed to maintain a white liquor strength within a paper mill's specifications. The specifications are usually expressed as the sodium hydroxide and sodium sulphide concentration in the white liquor, ie AA (active alkali) or EA (effective alkali). These terms are defined and discussed on pages 358-363 of the above-mentioned MacDonald and Franklin reference.

White liquor AA or -EA concentration varies considerably

due to changes in lime availability (CaO content), reactivity (hydration rate), mass flow rate of lime to the slurry or combinations of these. Sodium carbonate concentration changes in the green liquor feed also affect the resulting white liquor strength. The presence of this number of uncontrolled variables makes it very difficult to control the slurry-caustic reaction.

Current practice uses a total titratable alkali (TTA) measurement to check alkali strength and caustic efficiency. TTA is a measurement of sodium hydroxide, sodium carbonate and sodium sulphide, and is therefore only an indirect, approximate determination of the Na2C0^ concentration in the lye.

Another variable that makes slurry management difficult is the colorimetric titration (ABC test) used to analyze the lye. The ABC sample can be found in TAPPI sample T624 OS-68 (parts 9, 10 and 11). It can be modified to

to be adapted to specific mill conditions. The titration end points are not identified by an abrupt color change. Rather, it is a gradual color change from e.g. orange to red, or from green to blue, depending on which indicator is used. This "diffuse" endpoint determination results in a lot of uncertainty in the lye concentrations, which are the only variables that are regularly measured.

Attempts have been made to solve these problems.

Hultman et al., in US-PS 4,236,960 and 4,311,666, have described another type of process for controlling the degree of causticisation. Sutinan and Haapoja describe in "Causticizing Plant and Lime Kiln Computer Control" a Nokia Autolime system.

TAPPI sample T624 OS-68 describes samples for analysis of

soda and sulphite white and green liquors. Test 12 describes the sodium carbonate (assessment method) test.

The present invention proposes a method and an apparatus for measuring carbonate and sulphide concentrations in white and green pulp cooking liquors and in slurry and causticisation cells as well as control of the causticisation reaction and other steps which use this information.

The proposed process control logic reduces or eliminates most of the above-mentioned process control problems. It is based on the idea that a coke slurry is in reality a carbonate reactor, i.e. that carbonate ions in the green liquor are crystallized from the solution with hydrated lime, and sodium hydroxide is formed by this process. Specifically, the causticization control logic is based on determining the concentration of sodium carbonate and sodium sulfide in the green liquor, in the white liquor sludge slurry in the slurryer or the first causticizer, and in the white liquor sent to the digester, and uses this information to control the entire process. This logic is very different from current practice.

The reason for measuring the concentration of sodium sulphide

in the green liquor is not to control the slurry-causticization process, but to indicate inefficiencies in the process and to take steps to regulate these. An increase in sulphide concentration will tend to reduce the efficiency of the causticisation reaction. Knowledge of the concentration of sodium sulfide entering the slurry indicates to the operator or process computer the optimum caustic efficiency that can be expected from his recaustic plant. The changes in sulphide concentration will also indicate changes in the efficiency of the reboiler sodium sulphide reduction, and will allow precautions to be taken to improve control of the reboiler sodium sulphide reduction efficiency.

It is desirable that as much as possible of the sodium carbonate

in the green liquor is converted to sodium hydroxide in the slurry

and the causticians. It is impossible to completely convert all sodium carbonate to sodium hydroxide, which sodium carbonate will remain in the white lye. The ultimate limit to how much sodium carbonate can be converted to sodium hydroxide is governed by the equilibrium causticization efficiency. A discussion of the factors governing equilibrium causticization efficiency can be found on pages 532 - 534 of the aforementioned MacDonald and Franklin reference.

It is desirable to maintain the final white liquor at a composition very close to that determined by the equilibrium causticization efficiency. If this is carried out correctly, the benefits will be high operating efficiency due to the efficient conversion of sodium carbonate to sodium hydroxide,

and low sodium carbonate "dead weight" in the white liquor, which has many advantages for boiling, evaporation and recovery.

To achieve this, it is necessary to accurately balance the amounts of lime and green liquor added to the slurry.

An excess of green liquor in relation to lime will result

in a low conversion efficiency of sodium carbonate to sodium hydroxide. An excess of lime in relation to green liquor will impair the sedimentation and filtration properties of calcium carbonate "sludge", which must be removed from the white liquor before it can be used in the boilers.

Variations in the Na2C0^ concentration in the liquor in the slurryer or causticizer are the result of variations in the concentration and flow rate of lime and green liquor. Lime quality and quantity can be variable and difficult

to regulate, changes in mass flow rate, availability (% CaO) and lime reactivity (where rapid hydration occurs) affect the Na2C0^ concentration in the slurry caustic liquid, but are extremely difficult to measure and control. However, the concentration and flow rate of the green liquor can be measured and controlled relatively easily. The proposed strategy will control the green liquor flow rate to the slurry in order to

maintain the desired Na2CC>2 concentration in the slurry-caustic acid liquor despite variations that occur in the lime. The green liquor concentration is also controlled in a control loop. The advantages of this strategy are as follows: 1. A constant, desired concentration of Na2C0^ is controlled early in the slurry causticization reaction, ensuring safe and efficient operation. 2. The slurry-causticization process is controlled by adjusting the flow rate and concentration of the green liquor, which is technically rather easy to implement. Controlling the concentration, activity and flow rate of the lime is technically difficult, and is therefore allowed to vary within normal limits, and the green liquor flow rate is adjusted in response to these variations. This strategy provides much more accurate control than strategies that attempt to adjust the lime flow rate in response to changes in air flow rate and concentration. 3. This strategy will control the process based on direct measurements of the critical component of the system, the sodium carbonate. This provides much more accurate control than strategies based on TTA liquid-conductivity, liquid-density or other indirect, approximate indications of Na2C03

in the process fluids.

The total liquor room production rate (the amount of white liquor formed per minute) will be controlled by the flow rate of the lime to the slurryer. When the production rate must be increased or decreased to maintain a total mill-liquor balance, the flow rate of lime added to the slurry is correspondingly increased or decreased. The green liquor flow rate is automatically adjusted by a control loop to maintain the desired Na2C0^ concentration in the white liquor. Both chemical inventory (lime and liquid storage levels) and mill production rates can be maintained by this strategy. Chemical inventory and/or production speed can be controlled either manually or automatically.

The safest measurement is to determine the concentrations of sodium hydroxide, sodium carbonate and sodium sulphide in the white lye that is sent to the boiler to be used for cooking.

It is important to measure the sodium hydroxide and sodium sulphide concentrations in the white liquor, so that the amount of liquid charged to the boiler or boilers can be correctly determined. Changes in the sodium sulphide concentration (formed at the reboiler) can affect the white liquor AA-EA concentration.

The apparatus takes a sample from a suitable pipeline, green liquor, slurry caustic liquor, or a white liquor to the digester, filters the sample if necessary, withdraws a measured amount, reacts the measured amount with an acid to form hydrogen sulfide and carbon dioxide, and measures the quantities of these gases in a gas chromatograph. The apparatus has four main circuits: the filter circuit, the sampling circuit, the reactor circuit and the gas chromatograph circuit. A sludge separation circuit is also used if the equipment is to analyze the lye from the slurry or causticisation cells. A number of operations or methods are carried out in each of these circuits during a test cycle. These methods are time-shifted depending on different operation of the mill.

The unit must work consistently over a long period of time and

gives reproducible results. E.g. lye is corrosive and can also clog pipelines. An apparatus has now been constructed which eliminates corrosion and reduces line clogging to a minimum. This required a good deal of laboratory and plant testing, and reconstructions. During testing, it was found that the liquor being analyzed, the degree of completion of the reaction, and the temperature of the reactive gases would cause changes in the results that would lead to an inability to control the process.

Again, a good deal of time and laboratory and facility testing was required before the problem was recognised, the source of the problem discovered and corrective measures taken. The present apparatus and control logic are the result of several man-years of work over a period of several years, and the present application represents the inventors' understanding up to the date of the application of the problem and the solution. However, the work continues.

The invention shall be explained in more detail with reference to

the accompanying drawings.

Fig. 1 is a diagram of the main components of the test unit.

Fig. 2 is a diagram of the filter circuit for the apparatus.

Fig. 3 is a diagram of a three-filter circuit unit for appa-. the raw ride when working in a three-component configuration.

Fig. 4 is a diagram of the sludge separation circuit.

Fig. 5 is a cross-section of the reactor for the apparatus.

Fig. 6 is a top view of the reactor for the apparatus.

Fig. 7 is an internal side view, partially in cross-section, showing the drive mechanism for the magnetic stirring rod, and the stirring rod in the reactor chamber.

Fig. 8 is a cross-section along the line 8-8 in fig. 7.

Fig. 9 is a diagram of a gas chromatograph voltage output during gas analysis as a result of a typical green liquor sample.

Fig. 10 is a schematic diagram of a data acquisition circuit.

Fig. 11 is a diagram of a single loop apparatus in a

pulp mill.

Fig. 12 is a diagram of a double loop apparatus in a pulp mill. Fig. 13 is a diagram of a triple loop apparatus in a pulp mill.

Fig. 14 is a diagram of a cow damage control.

The apparatus has four main circuits: the filter circuit, the sampling circuit, the reactor circuit and the gas chromatograph circuit. A sludge separation circuit is also used if the apparatus is to be used to analyze lye from the slurry or causticisation cells. Each of these circuits has a number of operations or modes of operation that are carried out during a test cycle. These are sequenced differently, depending on the particular operation of the mill. Parts and methods will be described for each of the circuits. A possible sequence must then be described.

It should be pointed out that most of the operating valves in the unit are two-way valves. This is for the sake of simplicity. Three-way valves or multi-way valves are used in several specific applications. Where this is the case, the use of the valves is indicated.

The filter circuit.

The purpose of the filter circuit is to remove particulate matter from the lye to prevent both clogging of the sample equipment and chemical side reactions that will mask the true composition of the lye.

The following description is directed to the filter circuit in fig. 2 and 3. Each of the filter circuits in the three circuit pattern shown in fig. 3, will have the same parts and operation sequence, and thus the same reference numbers will be used for the individual elements in these circuits.

The circuit has the following components:

Main components.

F - filter.

FS - filter shock dome.

Pipelines.

ML - mill liquor pipeline in the causticization system between the green liquor clarifier and the slurryer, between the slurryer and the first causticizer, between the first and second causticizer or between the clear white liquor storage tank and the boiler,

depending on the lye being sampled.

L22 - Sampling line from the filter outlet line L30A to the sampling circuit.

L28 - Lye return line from the filter circuit to the clarifier, suspender or causticizer, depending on the lye being sampled.

L29 - Lye feed line from mill lye line

ML to the filter circuit.

L30 - Filter outlet line from the upper part of the filter F to the lye return line L28.

L30A - Filter outlet line from the filter

F to sampling line L22.

L30B - Filter outlet line from filter outlet line L30A to filter backwash line L31.

L30C - Filter outlet line from the filter outlet line L30B to the lye return line

L28.

L30 - Filter backwash line from valve

V28 to filter outlet line L30C.

L32 - Filter bypass line from the filter circuit inlet line L29 to the lye return line L28. L33 - Air inlet line to top of filter shock dome FS.

L33A - Air inlet line from air supply to water backwash line

L37.

L33B - Air and water inlet line between water backwash line L37 and top of filter shock dome FS.

L34 - Filter inlet and filter backwash outlet line between valve V28 and bottom of filter F.

L35 - Inlet line from filter circuit lye feeder

wire L29 to valve V28.

L36 -;;.Water supply line.

L37 - Water backwash line from water supply line L36 to inlet line L33B.

Valves.

Operating valves (powered solenoid).

V21 - Valve in filter outlet line L30A. Two

positions: open; close.

V22 - Valve in sampling line L22. Two

positions: open; close.

V24 - Valve in filter bypass line L32. Two

positions: open; close.

V26 - Valve in air inlet line L33A. Two

positions: open; close.

V28 - Filter inlet-return three-way T-valve at the connection between filter return line L31, filter inlet line L34 and inlet line L35. Two positions: position 1 (backwash) (IB) - open to filter return line L31 and filter backwash outlet line L34, closed to inlet line L35; position 2 (filter) (2F) - open to filter inlet line L34 and inlet line L35, closed to filter backwash line

V29 - Valve in water backwash line L37.

Two positions: open; close.

Control valves.

V18 - Control valve in the filter outlet line

L30B to prevent flow through the pipeline L30 to the filter F.

V23 - Check valve in the filter return line L31 to prevent flow through the pipeline L31 to the filter F.

Pressure valve (open or partially open, manually operable).

V20 - Back pressure valve in the filter outlet line

L30B to provide pressure in filter

F and to induce preferred flow to the sampling line 22 when the valve V22

is open.

Pressure relief valve (normally closed, can open automatically)

V27 - Pressure relief valve on filter F. Repair valves (normally open, manually operable).

V19 - Repair valve in the lye return line

L28.

V25 - Repair valve in filter circuit lut supply line L29.

The filter circuit has several operating methods.

The circulation method (no liquid to the filter) (circulation).

The first method is a lye circulation method where the lye is taken

from the mill lead the line through the bypass line and is returned to the slurryer or causticizer without going through the filter.

Wiring involved.

ML - Møllelut line.

L28 - Lute return line from the filter circuit.

L29 - Lye feed line from the mill lye line

ML to the filter circuit.

L32 - Filter circuit line from filter circuit inlet line L29 to filter circuit outlet line L28.

Involved valves.

Operating valves/ position on.

V21 - Valve in filter outlet line L3OA/closed. V22 - Valve in sampling line L22/closed. V24 - Valve in filter bypass line L32/open. V26 - Valve in the air inlet line L33A/closed. V28 - Filter inlet/backwash valve/position 1 (backwash) (IB) - open to filter backwash line L31 and filter backwash outlet L34, closed to inlet line L35.

V29 - Valve in water backwash line L37/closed.

Control valves.

V18 - Check valve in filter outlet line L30B to prevent flow through line L30 to filter F.

V23 - Check valve in filter backwash line L31 to prevent flow through line L31 to filter F.

Repair valves.

V19 - Repair valves in the lye return line

L28.

V25 - Repair valve in filter circuit lut supply line L29.

Flow

ML through V25 through L29 through V24 through L32 through V19 through L28.

Time

The time will vary.

The lye filtration method ( filter).

The second method is a lye filtration method where the lye is taken from the mill discharge, filtered in the filter F and returned to the return line to create stable filtration of the lye.

Main components involved.

F - Filter.

Wiring involved.

ML - mill lead wire.

L28 - Return line from the filter circuit.

L29 - Lute feed line from mill lute the line

ML to the filter circuit.

L30 - Filter outlet line from the upper part of

the filter F to the return line L28.

L34 - Filter inlet line from valve V28

to the bottom of the filter F.

L35 - Inlet line from filter circuit lut supply line L29 to valve V28.

Involved valves.

Operating valves/ position on.

V21 - Valve in filter outlet line L30A/open. V22 - Valve in sampling line L22/closed. V24 - Valve in filter bypass line L32/closed. V26 - Valve in air inlet line L33A/closed. V28 - Filter inlet backwash valve/position 2 (filter) (2F) - open to filter inlet line L34 and inlet line L35, closed to filter backwash line L31.

V29 - Valve in water backwash line L37/closed.

Control valves.

V18 -Check valve in filter outlet line L30B to prevent flow through

wire L30 to filter F.

V23 - Check valve in filter backwash line L31 to prevent flow through line L31 to filter F.

Pressure valve.

V20 - Back pressure valve in the filter outlet line L30B.

Repair valve.

V19 - Repair valve in filter circuit lye return

wire L28.

V25 - Repair valve in filter circuit lut supply line L29.

Flow.

ML through V25 through L29 through L35 through V28 through L34 through F through V21 through

L30 through V20 through V18 through V19 through L28 .

Note:

When first starting up the analyzer, a filter cycle is immediately performed to provide a liquid sample for the first reaction. For all subsequent reactions, the filter cycle is started at a time which is determined by an action elsewhere in the system. It can be started by a sequencer output which is activated when a new lye sample is desired. This could be achieved by completing the filling of the acid pump AP2 or opening the valve which puts pressure on the reactor Ri.

Time.

60 seconds, will vary depending on the time required to fill the lower portion of the filter with lye and provide an adequate current in L30 to provide a consistent lye sample to sample line L22.

The sampling method ( sample).

The third method is a lye sampling method where the lye

is taken from the mill liquor line, filtered and sent to the sampling circuit to provide the sample. Parts, lines, valves and valve positions are the same in this method as in the other method, the filter method, except for the following change.

Main components involved.

F - Filter.

Wiring involved.

L22 - Sampling line from the filter outlet line L30A to the sampling circuit.

Involved valves.

Operating valves/ positions.

V22 - Valve in sampling line L22/open.

Pressure valves.

V20 - Back pressure valve in the filter outlet line L30B provides back pressure to give preferential separation of filtered lye to the sampling line L22.

Flow

ML through V25 through L29 through L35 through V28 through L34 through F through V21 through L30A; part through V22 through L22 to the sampling circuit. Part through V20 through L30B through V18 through L30C through V19 through L28.

Time.

60 seconds, will depend on the time necessary to complete flushing and filling the sampling circuit with new lye.

Method for stopping sampling (stop).

The fourth method is a sampling stop method which is a pause to allow the sampling valve B22 in the sampling circuit to change position. Parts, wiring, valves, valve positions and flows are the same as in the second method, the filter method.

Time.

5 seconds or as needed to ensure closure of valve V22.

The lye backwash method.

The fifth method is a lye backwashing method where the lye is used for backwashing or backwashing of particulate substances in the filter from the filter to the return line. It takes place in two stages.

Stage 1 (backwash 1).

In step 1, the filter outlet valve V21 is closed and lye from the mill lye line ML fills the filter to the middle of the filter shock dome FS.

Main components involved

F - Filter

FS - Filter shock dome.

Wiring involved

ML - Mill lye wire.

L29 - Lute feed line from mill lute the line

ML to the filter circuit.

L33 - Air inlet line to top of filter

shock dome FS.

L34 - Filter inlet line from valve V28

to the bottom of the filter F.

L35 - Inlet line from filter circuit lut supply line L29 to valve V28.

Involved valves

Operating valves/position.

V21 - Valve in filter outlet line L30A/closed. V22 - Valve in sampling line L22/closed. V24 - Valve in filter bypass line L32/closed. V26 - Valve in air inlet line L33A/closed. V28 - Filter inlet backwash valve/position 2 (filter) (2F) - open to filter inlet line L34 and inlet line L35, closed to filter backwash line L31.

V29 - Valve in water backwash line L37/closed.

Repair valves.

V25 - Repair valve in filter circuit lut supply line L29.

Flow.

ML through V25 through L29 through L35 through V28 through L34 to F to mid FS.

Time.

10 seconds or as needed to provide sufficient lye to backwash the filter.

Step 2 (backwash 2).

In stage 2, air entering the top of the filter-shock dome FS drives lye through the filter element in the filter F, out the inlet of the filter element, through the filter backwash outlet line L34, the backwash line L31, the filter outlet line L30C and the filter circuit lye return line L28.

Main components involved.

F - Filter.

Wiring involved.

L28 - Lute return wire from the filter circuit. L30C- Filter outlet line from filter backwash line L31 to filter circuit lye return line L28.

L31 - Filter backwash line from valve

V28 to filter outlet line L30C.

L33 - Air inlet line to top of filter

the shock dome FS .

L34 - Filter backwash outlet line from bottom of filter F to valve V28.

Involved valves.

Operating valves/ position on.

V21 - Valve in the filter outlet line L30A/closed. V22 - Valve in sampling line L22/closed. V24 - Valve in filter bypass line L32/open. V26 - Valve in air inlet line L33A/open. V28 - Filter inlet backwash valve/position 1 (backwash) (IB) - open to filter backwash line L31 and filter backwash outlet line L34, closed to inlet line L35.

V29 - Valve in water backwash line

L37/closed.

Control valves.

V18 - Check valve in filter outlet line L30B to prevent flow through line L30 to filter F.

V23 - Check valve in backwash line L31 to prevent flow through line L31 to filter F.

Repair valves.

V19 - Repair valves in filter circuit lut return line 2 8 .

Flow

Air

V26 through L33 to F.

Lye

F through L34 through V28 through V23 through through"L31'through L30C through V19 through L28 .

Time.

15 seconds or as needed to adequately backwash the filter.

Water backwash method.

The sixth method is a water backwash method where water is introduced at the top of the filter shock dome FS and washes particulate matter from the filter element, out the bottom of the filter through the filter backwash outlet line L34, the backwash line L31, the filter outlet line L30C and the filter circuit liquor return line L28. The water backwash method will usually replace a first method, a bypass method, and will follow a 5th method, the lye backwash method. It is used at all times when the filter is excessively dirty with particulate matter. The lye feed will usually be stopped. Parts, lines, valves and valve positions are the same as in step 2 of the 5th method, step 2 of the lye backwash method, with the following additions and changes.

Wiring involved.

L33A - Air line to filter shock dome

is not used.

L33B - Inlet line from water backwash line L37 to top of filter shock dome FS.

L36 - Water supply line.

L37 - Water backwash line from water supply line L36 to inlet line L33B.

Involved valves.

Operating valves/ position on.

V26 - Valve in air inlet line L33A/closed. V29 - Valve in water backwash line L37/open.

Flow

Water

L36 through V29 through L37 through L33B through

F through L34 through V28 through V23 through

L31 through L30C through V19 through L28.

Time

60 seconds or as needed to provide a total wash of the filter element.

Sludge separation circuit - slurry/caustic white liquor.

It is often desirable for control purposes to obtain lye samples directly from the slurryer or causticizer for analysis. This lye contains 8-10% by weight of suspended calcium carbonate sludge solids which must be removed before analysis. The level of solids loading present in this liquor is too high to be immediately fed to the filter circuit because severe clogging of the filter element would result. The purpose of the sludge separation unit is to remove the bulk of solids from the liquor, and to provide a "clear"

lye, containing 1% or less suspended solids. This "clear" lye is filterable and becomes the lye feed to the filter circuit. It should be pointed out that the sludge separation unit does not interfere in any way with subsequent operation of the analyzer system. The filter, sample, reactor and gas chromatograph circuits work exactly as they do when no sludge separation circuit is used. The sludge separation circuit only ensures that an acceptable lye sample is provided to the filter circuit.

The best method of sludge separation has been found and involves the use of a continuous sedimentation cone. This device receives uncleared liquor from the slurryer or causticizer, separates the sludge from the liquor, returns the sludge to the slurryer or causticizer, and feeds a continuous "clear" liquor to the filter circuit. The advantages of this apparatus and method are simplicity, reliability, ease of operation and a fresh and uninterrupted supply of lye to the filter circuit,

so that operation of the filter circuit is not disturbed.

The settling cone itself is a non-mechanical thickener

of a type that is usually used for continuous liquid-solid separation in low volume applications. Details of the construction and operation of these units are well known and will not be detailed here, but can be found in J.H.Perry, Chemical Engineers Handbook, 3rd ed. McGraw-Hill Book Co. Inc., New York, 1950, pp. 940-941. The sludge separation unit should be designed for a capacity that will provide a desirable flow of "clear" lye (approx. 2-3 litres/min.) to the filter circuit.

The following description is of the sludge separation circuit

which is shown in fig. 4. The circuit consists of the following components:

Main components:

Tl - Continuous sedimentation cone.

T2 - Clear liquor tank.

SPl - Feed pump for uncleared lye from feed line L39 for uncleared lye to feed line L40

for unclarified lye.

SP2 - Feed pump for clear liquor in filter circuit liquor

feed line L29.

Bl - "Bustle tube" and "launder ring" apparatus

from settling cone Tl to clear liquor feed line L43.

Wires:

L29 - Connect supply line to filter circuit.

L39 - Feed line for uncleared lye from slurryer (or caustic) to feed pump SLI for

unclarified lye.

L40 - Feed line for uncleared liquor from feed pump SPl for uncleared liquor to the connection for sedimentation cone inlet line L41 and

sedimentation cone bypass line L42.

L41 - Sedimentation cone inlet line from feed line L40 for uncleared lye to sedimentation cone Tl.

L42 - Sedimentation cone bypass line from feed line L40 for uncleared lye to slurry

(or caustic) return line L50.

L43 - Clear liquor feed line from Bustle pipe-launder ring apparatus Bl to the connection for clear liquor tank inlet line L44 and clear liquor tank bypass line L46.

L44 — Clear liquor tank inlet line from clear liquor

feed line L43 to clear liquor tank T2.

L45 - Clear liquor tank overflow line from clear liquor tank T2 to clear liquor circulation-overflow line

L48.

L46 - Clear liquor tank circulation line from clear liquor feed line L43 to clear liquor circulation-overflow line L48.

L47 - Clear liquor tank outlet line from clear liquor tank T2 to the connection for filter circuit lye supply line L29 and clear liquor tank drain line L51.

L48 - Clear liquor tank bypass-overflow line from the connection for the clear liquor tank bypass line L46 and clear liquor tank overflow line L45 to the slurry/caustic return line

L50.

L49 - Sedimentation cone sludge discharge line from sedimentation cone Tl to slurry/causticizer return line L50.

L50 - Slurry (caustic) return line returns flows from clear liquor tank bypass/overflow line L48, sludge discharge line L49 and sedimentation cone bypass line L42 to slurry (or caustic).

L51 - Clear liquor tank tap line from clear liquor tank outlet line L47 to return line L50.

L52 - Water flushing line from mill water supply to feed line L39 for uncleared lye.

Operating and repair valves (manually operable.

V30 - Sedimentation cone inlet valve in the sedimentation cone inlet line L41. Two positions: open, closed.

V31 - Sedimentation cone bypass valve in the sedimentation cone bypass line L42. Two positions: open, closed.

V32 - Clear liquor tank bypass valve in clear liquor tank bypass line L46. Two positions: open, closed.

V33 - Clear liquor tank inlet valve in clear liquor tank inlet line L44. Two positions: open, closed.

V34 - Clear liquor tank outlet valve in filter circuit liquor supply line L29. Two positions:

open, closed.

V35 - Clear liquor tank drain valve in clear liquor tank drain line L51. Two positions:

open, closed.

V36 - Water flush valve in the water flush line L52.

Two positions: open, closed.

V37 - Feed valve for uncleared lye in feed line L39 for uncleared lye. Two positions: open, closed.

The sludge separation unit has five working modes, as these

is the normal working mode, clear liquor tank circulation mode, sedimentation cone circulation mode, circuit shutdown/water flush mode and circuit shutdown/emergency mode.

Normal mode of operation.

The first working method is the usual working method. The circuit will usually stay like this. The circuit will work differently only if repairs are required to the sludge separation or filter circuits, or when the slurrying/causting process is shut down.

Main parts involved.

Tl - continuous sedimentation cone.

T2 - Clear liquor tank.

SP1 - Feed pump for uncleared lye/on.

SP2 - Feed pump for clear liquor/on.

Bl - Bustle tube/launder ring apparatus.

Wiring involved.

L29 - Lye supply line to the filter circuit.

L39 - Feed line for uncleared lye.

L40 - Feed line for uncleared lye.

L41 - Sedimentation cone inlet line.

L43 - Feed line for clear liquor.

L44 - Tank inlet line for clear liquor.

L45 - Overflow line for the clear water tank.

L48 - Clear liquor tank bypass/overflow line.

L49 - Sedimentation cone sludge discharge line.

L50 - Slurry (caustic) return line.

Operating valves/ position■

V30 - Sedimentation cone inlet valve/open.

V31 - Sedimentation cone bypass valve/closed.

V32 - Clear liquor tank bypass valve/closed (or choked). Can be throttled partially open when the circuit is in operation to feed some clear liquor to the return line L50 to ensure that L50 does not become clogged.

V33 - Clear liquor tank inlet valve/open.

V34 - Clear liquor tank outlet valve/open.

V35 - Clear liquor tank drain valve/closed.

V36 - Water flush valve/closed.

V37 - Feed valve for uncleared liquor/open.

Flow.

Unclarified lye.

From slurry (or causticizer) through V37 through L39 through SPl through L40 through V30 through L41 to Tl.

Clear liquor.

From Tl through Bl through L43 through V33 through L44 to T2 through L47 through V34 through SP2 through L29.

Sludge.

From Tl through L49 through L50 to slurry (or caustic).

Time.

The time will vary, the circuit will usually be ~"on"this "yearly mode7~f jéf nes ~ from "'deri "Run""for maintenance of the Rretsen or filter circuit or when shutting down the slurrying or causticization process.

Clear liquor tank circulation method.

The second method is the clear liquor tank circulation method. This method is used when it is necessary to stop the flow of clarified liquor to the clarified liquor tank. This may be necessary because of repairs to this part of the circuit, or because of the need for repairs to the filter circuit, which requires that the flow of lye to the filter circuit be stopped.

Main parts involved.

Tl - Continuous sedimentation cone.

T2 - Clear liquor tank.

SPl - Feed pump for uncleared lye/on.

SP2 - Feed pump for clear liquor/on.

Bl - Bustle tube/launder ring apparatus.

Wiring involved.

L39 - Feed line for uncleared lye.

L40 - Feed line for uncleared lye.

L41 - Sedimentation cone inlet line. L43 - Clear liquor supply line.

L46 - Clear liquor tank bypass line.

L47 - Clear liquor tank outlet line.

L48 - Clear liquor tank bypass/overflow line. L49 - Sedimentation cone sludge discharge line. L50 - Slurry (or caustic) return line. L51 - Clear liquor tank drain line.

Operating valves/ position on.

V30 - Sedimentation cone inlet valve/open. V31 - Sedimentation cone bypass valve/closed. V32 - Clear liquor tank bypass valve/closed. V33 - Clear liquor tank inlet valve/open. V34 - Clear liquor tank outlet valve/open.

V35 - Clear liquor tank drain valve/closed. V36 - Water flush valve/closed.

V37 - Feed valve for uncleared liquor/open.

Flow path.

Cloudy liquid.

From slurry or causticizer through V37 through L39 through SPl through L40 through V30 through L41 to Tl.

Clear liquor.

From Tl through Bl through L43 through V32 through

L46 through L48 through L50 to slurry or causticizer.

From T2 through L47 through L35 through L51 through L50 to slurry or caustic.

Sludge.

From Tl through L49 through L50 to slurry or causticizer.

Time.

Varies as needed to remedy maintenance problems that necessitate clear liquor tank circulation.

The sedimentation cone circulation method.

The third method is the sedimentation cone circulation method. This method is used when it is necessary to stop the operation of the sedimentation cone in order to repair this part of the circuit. The flow of clear liquor will be interrupted in this way and there will be no sample flow to the filter circuit and analyzer.

Main components involved.

SPl - Feed pump for uncleared lye/on.

SP2 - Feed pump for clear liquor/off.

Wiring involved.

L39 - Feed line for uncleared lye.

L40 - Feed line for uncleared lye.

L42 - Sedimentation tank bypass line.

L47 - Clear liquor tank outlet line.

L50 - Slurry or causticizer return line. L51 - Clear liquor tank drain line.

Operating valves/position.

V30 - Sedimentation tank inlet valve/closed. V31 - Sedimentation tank bypass valve/open.

V32 - Clear liquor tank bypass valve/closed.

V33 - Clear liquor tank inlet valve/open.

V34 - Clear liquor feed valve/open.

V35 - Clear liquor tank drain valve/open.

V36 - Water flush valve/open.

V37 - Feed valve for uncleared liquor/open.

Flow.

Unclarified lye.

• Unclarified lye from slurry or causticizer through V37 through L39 through SPl through L40 through V31 through L42 through L50 to slurry or causticizer.

Time.

Varies according to the need to complete maintenance repairs that necessitate circulation of the sedimentation cone.

Circuit shutdown/ water flushing method.

The fourth method is the circuit shutdown/water flush method. This method is used when it is necessary to completely close the circuit for maintenance or due to a shutdown of the slurry/causticization process. The flow of cloudy lye to the system is stopped and all lines and main parts are flushed with water to ensure they are clean and unclogged.

Main components involved.

Tl - Continuous sedimentation cone.

T2 - Clear liquor tank.

SPl - Feed pump for uncleared lye/on.

SP2 - Feed pump for clear liquor/on.

Bl - Bustle tube/launder ring apparatus.

Wiring involved.

L40 - Feed line for uncleared lye.

L41 - Sedimentation cone inlet line.

L42 - Sedimentation tank bypass line.

L42 - Clear liquor supply line.

L44 - Clear liquor tank inlet line.

L45 - Clear liquor tank overflow line. L46 - Clear liquor tank bypass line.

L47 - Clear liquor tank outlet line.

L48 - Clear liquor tank bypass/overflow line. L49 - Sedimentation cone sludge discharge line. L50 - Slurry (or caustic) return line. L51 - Clear liquor tank drain line.

L52 - Water flush line.

Operating valves position.

V30 - Sedimentation tank inlet valve/closed. V31 - Sedimentation tank bypass valve/open. V32 - Clear liquor tank bypass valve/closed. V33 - Clear liquor tank inlet valve/open. V34 - Clear liquor feed valve/open.

V35 - Clear liquor tank drain valve/open. V36 - Water flush valve/open.

V37 - Feed valve for uncleared liquor/open.

Flow.

Water.

Through L52 through V36 through L39 through SPl through L40 through: V31 through L42 through L50 to slurry or causticizer.

V30 through L41 to Tl.

From Tl through L49 through L50 to slurry or causticizer.

From Tl through Bl through L43 through: V32 through L46 through L48 through L50 to slurry or causticizer. V33 through L44 to T2 through L47 through: V34 through SP2 through L29. V35 through L51 through L50 to slurry or causticizer.

Time.

15 minutes or as needed to completely flush the circuit with water.

Remark.

As described, this method will completely flush the circuit with water. Selected valves can be closed as desired to direct the washing water only through other selected lines and parts of the circuit. It is not always desirable or necessary to flush the entire circuit.

Circuit shutdown/ emergency response method.

The fifth method is the circuit shutdown/standby method. This is used after the circuit is flushed with water. The circuit is in a "standby" state, and remains in this state until a new start.

Main components involved.

All components are in "standby". All tanks are drained

and all pumps are off.

Wires.

All lines are flushed and drained, and remain in standby condition.

Operating valves.

V30 - Sedimentation tank inlet valve/closed.

V31 - Sedimentation tank bypass valve/open.

V32 - Clear liquor tank bypass valve/closed.

V33 - Clear liquor tank inlet valve/open.

V34 - Clear liquor feed valve/open.

V35 - Clear liquor tank drain valve/open.

V36 - Water flush valve/open.

V37 - Feed valve for uncleared liquor/open.

Flow.

There is no flow in the circuit when tanks and wires

are empty and drained.

To restart the circuit and return to the first or normal mode of operation, the cloudy liquid feed valve V29 is opened and the pumps SP1 and SP2 are turned on. The circuit then resumes its normal mode of operation. The circuit should be started and running at least 30 minutes before starting the rest of the analyzer system to ensure that all tanks are filled and that the circuit has reached equilibrium.

Sampling circuit.

The purpose of the sampling circuit is to obtain a measured alkali sample and a measured amount of acid, and keep them separate until the reactor can receive them, and to transport them to the reactor. It has two main parts, a sampling valve and a connected sampling loop, shown in the upper, central part of fig. 1, and an acid part shown in the right part of fig. 1. The sampling loop collects a 10 cm^ sample of the filtered lye and the acid pump delivers a 50 cm 3 sample of 10% sulfuric acid by volume (approx. 2.2N). The acid pump turns on and discharges

3 3

a full 50 cm sample, but only 40 cm goes to the reactor. The rest remains in the sample loop LS2 and is washed out when fresh lye displaces the acid by the lye sampling method.

It has the following components.

Main components.

SL2 - Sampling loop to obtain a 10 cm<3>

filtered lye sample. It is connected to the openings P5 and P6 in the sampling valve V14.

API - Air piston for operating the piston in the positive displacement acid pump AP2. Two positions: position one (acid in or filling) (1F); position two (acid out or transfer) (2T).

AP2 - Positive displacement acid pump to achieve

a 50 cm 3 sample of 10% sulfuric acid.

Two positions: (acid filling and preparedness)

(1F); position two (acid out or transfer)

(2T) .

Wires.

L9 - Antiflocculation line from antiflocculation source to acid feed line L20.

L14 - Air line from air supply line L27 to

the valve Will.

L15 - Air line from the valve Vil to the opening Pl in the sampling valve V14 for admitting air to move the sampling valve V14 to position one (sampling) (IS).

L16 - Air line from valve Will to port P2 in sampling valve V14 for admitting air to move sampling valve V14 to position two (transfer) (2T).

L17 - Sampling line from opening P4 in sampling valve V14 to opening R9 in reactor RI.

L19 - Acid line from acid line L21 to opening P3 in sampling valve V14.

L20 - Acid supply line from the acid source to the acid line L21.

L21 - Acid line from the connection between the acid lines L19 and L20 to the acid pump AP2.

L22 - Sampling line from the filter system to the opening P8 in the sampling valve V14.

L23 - Feed line from opening P7 in sampling valve V14 to sewer.

L24 - Air line from valve V17 to inside piston API to move piston outwards towards position one (acid filling) (1F).

L25 - Air line from valve V17 to the outside of the piston in API to move the piston inward to position two (acid transfer)

(2T) .

Wiring involved.

L14 - Air line from air supply line L27 to

the valve Will.

L15 - Air line from the valve Will to the opening

Pl in sampling valve V14.

L24 - Air line from valve V17 to the inside

of the stamp in API.

L26 - Air line from air supply line L27 to

the valve V17.

L27 - Air supply line.

Involved valves.

Operating valves/position.

Will - Solenoid operated air valve/position one (sampling) (IS): connected to air lines L14 and L15.

V14 - Air operated sampling valve/position one (sampling) (IS): connects ports P5, P6, P7 and P8.

V17 - Solenoid operated air valve/position one (acid fill) (1F): connects air lines L26 and L24.

Control valves.

V15 - Control valve in the acid line L19 holder

acid in line L19.

V16 - Control valve in the acid supply line L20

keeps acid in the acid lines L20 and L21.

Pressure control valves.

AR2 - Pressure regulating valve in air line L26. AR3 - Pressure regulating valve in air line L14.

Flow.

Air.

L27 through AR3 through L14 through Vil through L15 through Pl to V14.

L26 - Air line from air supply line L27 to

the valve V17.

L27 - Air supply line.

Valves.

Operating valves.

Will - Solenoid operated air valve connecting air lines L14 to either air line L15 or air line L16 to position sampling valve V14. Two positions: position 1 (sampling) (IS) - air line L14 connected to air line L15;

position two (transmission) (2T) - air line L14 connected to air line L16. V14 - Air-operated sampling valve has two operating openings.

Pl - Connected to air line L15 for

to allow air to move the valve to position one (sampling) and

P2 - Connected to air line L16 for

to allow air to move the valve to position two (transfer).

And six sampling openings:

P3 - Connected to acid line L19,

P4 - Connected to the sampling line L17, P5 - Inlet to the sampling loop SL2,

P6 - Outlet from sampling loop SL2,

P7 - Connected to sewer line L23,

P8 - Connected to sampling lead L22. It has two positions: Position one (sampling) (IS) - receives the sample from the filter circuit to sampling loop one SL2.

Connects openings P5, P6, P7 and P8. Position two •(transferint) (2T) - sends the sample from the sampling loop SL2 to the reactor Ri. Connecting the openings P3,

L27 through AR2 through L26 through V17 through L24 to API.

Lye.

No flow.

Sampling valve repositioning method (repositioning 1) The second method is a repositioning method for the sampling valve. It is moved from the sample receiving position to the sample transfer position.

Main components involved.

SL2 - Sampling loop/10 cm 3 acid present.

API - Air operated piston to drive the piston

in the acid pump/position one (acid filling)

(1F) .

AP2 - Positive displacement acid pump/position

one (acid replenishment) (1F).

Wiring involved.

L14 - Air line from air supply line L27 to

valve Will.

L16 - Air line from the valve Will to the opening

P2 in the sampling valve V14.

L24 - Air line from valve V17 to the inside

of stamped API.

L26 - Air line from air supply line L27 to

the valve V17.

L27 - Air supply line.

Involved valves.

Operating valves/ position on.

Will - Solenoid operated air valve/position two (transmission) (2T): connects air lines L14 and L16.

V14 - Air operated sampling valve/position

two (transmission (2T): connects openings P3 , P4, P5 and P6.

V17 - Solenoid operated air valve/position one (oxygen filling) (1F): connects air lines L26 and L25.

Control valves.

V15 - Control valve in the acid line L19 holder

acid in line L19.

V16 - Control valve in the acid supply line L20

keeps acid in the acid lines L20 and L21.

Pressure control valves.

AR2 - Pressure regulating valve in air line L26. AR3 - Pressure regulating valve in air line L14.

Flow.

Air.

L27 through AR3 throughm L14 through Vil through L16 through P2 to V14.

L27 through AR2 through L26 through V17 through L24 to API.

Time.

5 seconds or as needed to ensure V14 has the changeover.

The acid transfer method ( transfer 1).

The third method is a transfer method where the acid pump forces the 50 cc of acid in the acid pump AP2 through the sampling loop SL2 and to the reactor. An initial flush of the system with acid is carried out to ensure that the system is clean and filled with acid before the sample analysis begins.

Main components involved.

SL2 - Sampling loop.

API - Air operated piston to drive the piston

in the acid pump/position two (acid transfer)

(2T).

AP2 - Positive displacement acid pump/position two (acid transfer) (2T).

Wiring involved.

L14 - Air line from air supply line L27 to

the valve Will.

L16 - Air line from the valve Will to the opening

P2 in the sampling valve V14.

L17 - Sampling line from the opening P4 at the sampling valve V14 to the opening R9 in the reactor Ri.

L19 - Acid line from acid line L21 to opening P3 in sampling valve V14.

L21 - Acid line from acid pump AP2 to acid line L19.

L25 - Air line from valve V17 to outside

of the stamp in API.

L26 - Air line from air supply line L27 to

the valve V17.

L27 - Air supply line.

Involved valves.

Operating valves/position.

Will - Solenoid operated air valve/position two (transmission)(2T): connects air lines L14 and L16.

V14 - Air Operated Sampling Valve/Position Two (Transfer)(2T): connects ports P3, P4, P5 and P6.

V17 - Solenoid operated air valve/position one (acid fill) (1F): connects air lines L26 and L25.

Control valves.

V12 - Control valve in sampling line L17

prevents lye and acid from returning to the sampling circuit after being in the react-

tower.

V15 - Check valve in acid line L19 which allows acid to flow from AP2 through L21 through L19 to V14.

V16 - Check valve in acid line L20 prevents acid from returning to the acid feed system when AP2 transfers the acid.

Pressure control valves.

AR2 - Pressure regulating valve in air line L26. AR3 - Pressure regulating valve in air line L14.

Flow.

Air.

L27 through AR3 through L14 through Vil through L16 through P2 to V14.

L27 through AR2 through L26 through V17 through L25 to API to move the piston up.

Lye.

AP2 through L21 through V15 through L19 through P3 through P5 through SL2 through P6 through P4 through V12 through L17 to

RIDE.

Time.

30 seconds or as needed to ensure AP2 has completed its stroke.

Sampling valve repositioning method 2 (repositioning 2).

The fourth method is a second sampling valve repositioning method to move the sampling valve from position two (transfer) to position one (sampling), and to move the acid pump from position two (acid transfer) to position one (acid filling), to fill the acid pump with acid and anti-flocculant. It is necessary to add anti-flocculation agent to the reaction mixture to prevent flocculation and deposition of sulfur in the reactor. It is best to add a known amount of anti-flocculant to each reaction by mixing anti-flocculant solution with acid when the acid pump is primed.

By suitable choice of anti-flocculating agent concentration

and correct dimensioning of the anti-flocculating agent lines L9 and the acid feed line L20, the amounts of the acid and anti-flocculating agent drawn into the acid pump AP2 will be such that a desired concentration of anti-flocculating agent in the reaction mixture is ensured. Sufficient turbulence exists in L20, L21 and AP2 during the acid filling step to ensure adequate dissolution of anti-flocculant in the acid.

Main components involved.

SL2 - Sampling loop/approx 10 cm 3.

API - Air operated piston for operating the piston

in the acid pump/position one (acid filling)

(1F) .

API - Positive Displacement Acid Pump/Position

one (acid replenishment) (1F).

Wiring involved.

L9 - Anti-flocculant feed line from anti-flocculant storage to acid feed line L20 .

L14 - Air valve from air supply line to valve

Want.

L15 - Air line from valve Wil to the opening

Pl in sampling valve V14.

L20 - Acid supply line from acid source to the line

L21.

L21 - Acid line from the acid feed line L20 to the acid pump AP2.

L24 - Air line from valve V17 to the inside

of the stamp in API.

L26 - Air lines from the air supply line L27

to valve V17.

L27 - Air supply line.

Involved valves.

Operating valves/ position on.

Will - Solenoid operated air valve/position one

(sampling) (IS).

V14 - Air operated sampling valve/position one (sampling) (IS): connects ports P5, P6, P7 and P8.

V17 - Solenoid operated air valve/position one (acid filling) (1F): connects air lines L26 and L25.

Control valves.

V15 - Control valve in the acid line L19 prevents backflow of the acid from L19 through L21 to AP2.

V16 - Control valve in the acid supply line L20

allowing acid to flow from L20 through L21 to AP2.

Pressure control valves.

AR2 - Pressure regulating valve in air line L26. AR3 - Pressure regulating valve in air line L14.

Flow.

Air.

L27 through AR3 through L14 through Vil through L15 through Pl to V14.

L27 through AR2 through L26 through V17 through V24 to API.

Acid

L20 through V16 through L21 to AP2.

Anti-flocculant.

L9 through L20 through V16 through L21 to AP2.

Time.

5 seconds.

Remark.

Time not really important, large surplus of time (approx.

12 minutes for the system described) is available to fill the pump and reconnect the valve.

Preparedness method (preparedness 2).

The fifth method is a second preparedness method (preparedness

2) where the sampling valve waits to receive a sample from the filter cartridge. It is identical to the first method (preparedness 1) and shall not be given in detail again. The time is 12 minutes, but can be changed depending on the operation of a particular system.

Sample collection method ( sample).

The sixth method is a sample collection method, where a sample is collected from the filter circuit.

Main components involved.

SL2 - sampling loop (initially filled with 10 cm 3 of acid from the last sample transfer method.

API - Air operated piston to drive the piston

in the acid pump/position one (acid filling)

(1F) .

AP2 - Positive displacement acid pump/position

a (acid replenishment)(1F).

Wiring involved.

L14 - Air line from air supply line L27 to

the valve Will.

L15 - Air supply line from the valve Vil to the opening Pl in the sampling valve V14.

L22 - Lye sample line from the filter system to

the opening P8 in the sampling valve V12.

L23 - Sampling line from opening P7 on

sampling valve V14 to drain.

L24 - Air line from valve V17 to the inside

of the stamp in API.

L26 - Air line from air supply line L27 to

the valve V17.

L27 - Air supply line.

Involved valves.

Operating valves/ position on.

Will - Solenoid operated air valve/position one (sampling) •( IS ) : connects air lines L14 and L15.

V14 - Air operated sampling valve/position one (sampling)(IS): connects ports P5, P6, P7 and P8.

V17 - Solenoid operated air valve/position one (acid filling) (1F): connects air lines L26 and L25.

Control valves.

V15 - Control valve in the acid line L19 prevents backflow of the acid from L19.

V16 - Control valve in the acid supply line L20

allowing acid to flow in lines L20 and L21.

Pressure control valves.

AR2 - Pressure regulating valve in air line L26. AR3 - Pressure regulating valve in air line L14.

Flow.

Air.

L27 through AR3 through L14 through Vil through L15 through Pl to V14.

L27 through AR2 through L26 through V17 through

L24 through API.

Lye.

L22 through P8 through P5 through SL2 through

P6 through P7 through L23.

Time.

60 seconds or as needed to ensure total

flushing and filling the sample loop with a fresh lye sample.

Preparedness method (preparedness 3).

The seventh method is a third preparedness method (preparedness

3) in which the sample circuit waits for the reactor circuit to receive the sample. It is identical to the first and fifth methods (preparedness 1 and preparedness 2), and shall not be described in detail. The sample loop is filled with lye instead of acid at this stage.

Sampling valve repositioning method (repositioning 3). The eighth method is a third sampling valve repositioning method (repositioning 3), in which the sampling valve V14 is moved from position 1 (sampling) to position 2 (transfer). It is identical to the second method (repositioning 1) and will not be given in detail. The time is the same as repositioning 1.

Acid transfer method ( transfer 2).

The ninth method is a second transfer method (transfer-

ing 2) where the acid pump forces the 50 cm 3 of acid through the sample loop and into the reactor. This also leads the sample into the reactor. Acid remains in the test loop to clean it of material that may have coated the pipe system during the seventh method (preparedness 3). This acid and the residue are removed from the system during the next sample collection method. It is identical to the way of working in the third (transfer 1) and

shall not be described in detail.

Sampling valve repositioning method ( repositioning- 4). The tenth method is a fourth repositioning method (repositioning 4) in which the sampling valve V14 is moved from position 2 (transfer) to position 1 (sampling), and the acid pump AP2 is filled with acid and anti-flocculating agent. It is identical to the fourth method (repositioning

2) and the time is the same.

Reactor circuit.

The reactor is shown in fig. 5 and 6, and the reactor circuits are

shown at the bottom left in fig. 1.

As can be seen from fig. 5, the reactor Ri has a reactor chamber

R2 which is defined by a lid R3, side walls R4 and a bottom

R5. Lid R3 has four openings: R6 for deaeration gas

from the reactor to drain, R7 for washing water to the reactor,

R8 both for reactor gas from the reactor to the gas chromatograph and for pressurized gas to pressurize the reaction chamber, R9 for the sample and acid to the reactor. The bottom R5 defines the bottom RIO in the reaction chamber R2. Bottom RIO

is inclined towards the central outlet valve V13, so that the reaction chamber R2 can be washed and emptied easily after each reaction. Magnetic rod R13 provides turbulence and mixing in the reaction chamber. The bottom R5 rests on a pressure chamber Ril,

and the pressure in the chamber Ril is maintained by means of a rubber diaphragm R12 between the bottom R5 and the pressure chamber Ril. Air enters the pressure chamber Ril through the air line

LI, and the air pressure keeps the valve V13 in the upper, closed position to keep the lye in the reaction chamber R2. When air-pressure is drained from the pipeline Li, the valve V13 falls

to the lower position and allows the reaction chamber R2 to empty. The lye goes via the outlet line L18 to the drain or is treated in another way.

The reactor circuit has the following parts:

Main ingredients:

RI - Reactor.

Ml - Drive device for the magnetic rod in the reactor-mixer.

Wires:

LI - Air line from valve V10 to reactor outlet running pressure chamber Ril.

L2 - Lead to the gas chromatograph GC.

L2 - Line between the reactor gas line

L6 and the gas chromatograph GC.

L2B- Line between reactor pressure line L10 and line L2A.

L3 - Air line between the air supply line L27

and the line LII.

L4 ■ - Water supply line between the water source and the opening R7 in the reactor RI.

L5 Air line from opening R6 in the reactor

Ride to drain.

L6 Reactor gas line from line L13 to

the wire L2A.

L7 Air line between air line L14 and

the magnetic rod drive device Ml.

L8 — Reactor pressure line between reactor pressure line L10 and reactor line L13.

L10 - Reactor pressure line between air supply line L27 and lines L8 and L2B.

LII - Connection line between the overhead line

L3 and the measuring line L12, and the reactor gas line L6, the air pressure line L8 and the reactor line L13.

Ll2 - Measuring lead between the air line L3 and the connecting line LII, and the measuring protector

Gl and the pressure gauge G2.

L13 - Reactor line between the opening R8 in the reactor Ri and the connection between the reactor gas line L6, the reactor pressure line L8 and the

the connecting line LII.

L14 - Air line between the air supply line L7

and the valve V10.

L17 - Sampling line between the sampling valve V14 and the opening R9 in the reactor

RIDE.

L18 - Outlet line from valve V13 in the reactor

RIDE.

Valves.

Operating valves (solenoid driven).

V3 - Valve in air line L3. Two positions:

open; close.

V4 - Valve in the water line L4. Two positions:

open; close.

V5 - Valve j air line L5. Two positions:

open; close.

V6 - Valve in reaction gas line L6. Two

positions: open; close.

V8 - Valve in reactor pressure line L8. Two

positions: open; close.

V10 - Valve between air line L14 and air line Li. Two positions: open; close.

Operating valves. (air driven).

V13 - Outlet valve in the reactor Ri between the reaction chamber R2 and the outlet line L18. This is operated by air pressure from line LI. Two positions: closed when air is on; open when air is off.

Control valves.

V12 - Control valve in the sampling line L17 which prevents either the sample, reaction gas or air from flowing back through the sampling line L17.

Pressure control valves.

ARI - Pressure regulating valve in the air line Li.

AR3 - Pressure regulating valve in air line L14. AR4 - Pressure regulating valve in air line L3. AR5 - Pressure control valve in the reactor pressure line L10.

Repair valves (normally open, manually operable).

V7 - Repair valve in air line L7.

Openings.

Rfi - Opening in reactor RI for air line L5. R7 - Opening in reactor RI for water line L4.

R8 - Opening in the reactor Ri for reactor line L13. R9 - Opening in reactor Ri for sampling line

L17.

The operating sequence for the reactor is as follows:

(1) The reactor is cleaned:

(a) The reactor is emptied.

(b) The reactor is filled with water.

(c) The reactor is emptied again.

(d) The reactor is refilled with water.

(e) The reactor is emptied again.

(f) The reactor is refilled with water.

(g) The reactor is emptied again.

(2) The reactor is vented for 5 seconds and closed again. (3) Acid and sample are placed in the reactor and the reaction starts. (4) After approx. 11 minutes, the reactor is pressurized using a precise air pressure regulator. This is important if you want to achieve a direct relationship between gas chromatography outlet and lye concentration. The final gas pressure should be approx. 2 psi above the highest total reactor pressure which

arises from the sum of all the partial pressures of the expected components, or 26 psi above ambient pressure. This tends to compensate for the reactor pressure's dependence on the lye concentration, which will again give an incorrect reading if it

The calm was not compensation.

(5) The reaction is allowed to run to completion.

(6) The reaction gas is transferred to the gas chromatograph.

The transfer time must be long enough to obtain a representative gas sample in the sample loop SLI

in the gas chromatograph. This usually takes 40-

50 seconds.

The cycle takes approx. 19 minutes, but will vary according to the characteristics of each individual system.

The preparedness method (preparedness).

The first method for the reactor circuit is the standby method where the reactor waits to receive the sample. It usually only happens at startup. The reactor contains what may be present at shutdown. This can be an old reaction mixture, washing water, etc.

Main components involved.

RI - Reactor.

Wiring involved.

LI - Air line from the valve V10 to the valve

V13.

L14 - Air line from air supply line L27 to

the valve V10.

L27 - Air supply line.

Involved valves. host valves.

Operating valves/ position on.

V3 - Valve in air line L3/closed.

V4 - Valve in the water line L4/closed.

V5 - Valve in the air line L5/closed.

V6 - Valve in reaction gas line L6/closed. V8 - Valve in air pressure line L8/closed. V10 - Valve between air line ne L14 and L]/apen. V13 - Outlet valve in the reactor Rl/closed.

Pressure control valves.

ARI - Pressure regulating valve in the air line LI. AR3 - Pressure regulating valve in air line L14.

Flow.

Air.

L27 through AR3 through L14 through V10 through Li through ARI to Ril to keep V13 closed.

Aeration method (aeration).

The second method is an air method. The reactor is vented when the sample valve V14 is repositioned from position 1, sampling, to position 2, transfer. This allows that. the pressure in the reaction chamber may reach atmospheric pressure before sample injection. The gas in the reactor contains at most small amounts of carbon dioxide and hydrogen sulphide.

Main components involved.

RI - Reactor.

Wiring involved.

LI - Air line from the valve V10 to the chamber

Ril in the reactor RI.

L5 - Air line from opening R6 in the reactor

Ride to the atmosphere.

L14 - Air line between the air supply line L27

and the valve V10.

L27 - Air supply line.

Involved valves.

Operating valves/position.

V3 - Valve in the air line 1.3/closed.

V4 - Valve in the water line L4/closed.

V5 - Valve in the air line L5/open.

V6 Valve in reaction gas line L6/closed. V8 - Valve in pressure line L7/closed.

V10 - Valve between the air lines L14 oo L15/ open to keep the outlet valve V13 in the reactor RI closed.

V13 - Outlet valve from reactor Rl/closed.

Pressure control valve.

ARI - Pressure regulating valve in the air line Li. AR3 - Pressure control valve in air line L14.

Flow.

Air.

Ride through R6 through V5 through L5 to the vent line to drain.

L27 through AR3 through L14 through V10 through LI through ARI to Ril to keep V13 closed.

Time.

5 seconds for air in the reactor to reach equilibrium

with atmospheric pressure. In the venting method before introducing the sample, the venting method must end before introducing the sample to the reactor to ensure that no loss of reaction ion gas products occurs.

The emptying method ( emptying).

The third method is a reactor emptying method. During the wash cycle, the reactor is emptied, either of reaction products or of wash water.

Main components involved.

RI - Reactor.

Wiring involved.

Li - Air line from the valve V10 to the outlet valve V13 in the reactor Ri.

L3 - Air line from the air supply line L27 to

connecting line LII.

LII - Connecting wire from air line L3

to the reactor line L13.

L13 - Reactor line from the connection line

to the opening R8 in the reactor RI.

L18 - Outlet line from reactor RI. L27 - Air supply line.

Involved valves.

Operating valves/ position on.

V3 - Valve in air line L3/open.

V4 - Valve in the water line L4/closed. V5 - Valve in the air line L5/closed. V6 - Valve in reaction gas line L6/closed. V8 - Valve in air pressure line L8/closed. V10 - Valve between air lines L4 and Ll/closed to drain air from line Li to open valve V13.

V13 - Outlet valve from the reactor Rl/open to drain the reactor through the outlet line L18.

Control valves.

V12 - Control valve in sampling line L17

prevents air from escaping through sampling line L17.

Pressure control valves.

AR4 - Pressure regulating valve in air line L3.

Flow

Air

No flow in line LI.

L27 through AR4 through L3 through V3 through LII through L13 through R8 to Ri.

Lye

Ride through V13 through L18.

Time.

10 seconds or as needed to complete emptying the reactor.

The filling method (filling).

The fourth method is the reactor filling method. During the washing cycle, the reactor is filled with washing water.

Main components involved.

RI - Reactor.

Wiring involved.

LI - Air line from the valve V10 to the outlet valve V13 in the reactor RI.

L4 - Water line between the water source and the opening

R7 in the reactor Ri.

L5 - Air line from opening R6 in the reactor

RI to the atmosphere.

L14 - Air line from air supply line L27 to

the valve V10.

L27 - Air supply line.

Involved valves.

Operating valves/ position on.

V3 - Valve in air line L3/closed.

V4 - Valve in the water line L4/open.

V5 - Valve in the air line L5/open.

V6 - Valve in reaction gas line L6/closed. V8 - Valve in air pressure line L8/closed.

V10 - Valve between air line L14 and Ll/open. V13 - Outlet valve in the reactor Rl/closed.

Control valves.

V12 - Control valve in the sampling line

L17 prevents air from entering the test circuit.

Pressure control valves.

ARI - Pressure regulating valve in the air line Li.

AR3 - Pressure regulating valve in air line L14.

Flow.

Air.

Ride through R6 through V5 through L5 to air line to drain.

L27 through AR3 through L14 through V10 through LI through ARI to Ril to keep V13 closed.

Water.

L4 through V4 through R7 to Ri.

Time.

20 seconds or as needed to sufficiently fill the reactor with water.

The sample transfer method ( transfer).

The sixth method is the sample transfer method. The sample is received from the sampling circuit.

Main components involved.

RI - Reactor.

Wiring involved.

LI - Air line from the valve V10 to the outlet valve V13 in the reactor Ri.

L14 - Air line from air supply line L27 to

the valve V10.

L17 - Sampling lead from sample circuit to

the opening R9 in the reactor RI.

L27 - Air supply line.

Involved valves.

Operating valves/position.

V3 - Valve in air line L3/closed. V4 - Valve in the water line L4/closed. V5 - Valve in the air line L5/closed. V6 - Valve in reaction gas line L6/closed. V8 - Valve in air pressure line L8/closed. V10 - Valve between air line L14 and Ll/open. V13 - Outlet valve in the reactor Rl/closed.

Control valves.

V12 - Sampling line L7 prevents sample or reaction gas from returning through line L17.

Pressure control relief valves.

ARI - Pressure regulating valve in the air line LI. AR3 - Pressure regulating valve in air line L14.

Flow

Air

L27 through AR3 through L14 through V10 through LI through ARI to Ril to keep V13 closed.

Lye.

SL2 through V14 through L17 through V12 through R9 to RI.

Acid.

AP2 through L21 through V15 through L19 through V14 through SL2 through L17 through V12 through R9 to RI.

Time.

30 seconds or as needed to ensure complete transfer of acid and sample.

Mode of reaction (reaction).

The seventh way is the way of reaction. The reaction between acid and sample takes place in the reactor chamber. There are two step 1 reaction method, reaction 1 and reaction 2. Reaction

2 is the continuation of reaction 1 after the pressure has been applied to the reaction chamber, and is identical to reaction 1.

Main components involved.

RI - Reactor.

Wiring involved.

LI - Air line from the valve V10 to the outlet valve V13 in the reactor Ri.

L14 - Air line from air supply line L27 to

the valve V10.

L27 - Air supply line.

Involved valves.

Operating valves/ position on.

V3 - Valve in air line L3/closed. V4" - Valve in water line L4/closed. V5 - Valve in air line L5/closed. V6 - Valve in reaction gas line L6/closed. V8 - Valve in air pressure line L8/closed. V10 - Valve between air line L14/ and lL/open. V13 - Outlet valve in the reactor Rl/closed.

Control valves.

V12 - Sampling line L7 prevents sample or reaction gas from returning through line L17.

Pressure control valves.

ARI - Pressure regulating valve in line LI. AR 3 - Pressure control valve in the air line L14.

Flow.

Air.

L27 through AR3 through L14 through V10 through LI through ARI to Ril to keep V13 closed.

Time.

Total time for the reaction is approx. 15 minutes. It splits into two parts before or after printing

is hung up.

The pressure method (pressure).

The eighth method is a pressure method. Eleven minutes after the reaction begins, pressure is applied through a precision regulator to the reaction chamber to maintain a constant reactor end pressure.

It was decided to pressurize for 11 minutes into the reaction, because at this point: 1) the reaction was essentially complete and no further pressure rise was expected; 2) there was 4 minutes of reaction time remaining, allowing air added in the pressure step to be well mixed with the reaction gases to give a homogeneous reaction gas sample at the end of the reaction.

The time of pressurization can be changed as needed in response to the characteristics of individual reactor systems.

The pressure step was added in response to observations made during the development of the system. In order to be able to make correct comparisons between samples, it is necessary to have a constant gas end pressure. If this is not the case, the applicant's experience from the trials will be repeated. In these experiments, the gas end pressure in the reactor was allowed to remain at whatever pressure existed due to the release of carbon dioxide and hydrogen sulfide from the reaction. The pressure varied according to the amount of sodium carbonate and sodium sulphide in the lye sample. It was observed that although an increase in the sodium carbonate concentration in the liquor caused an increase in the carbon dioxide peak from the gas chromatograph, the relationship was not directly proportional. Furthermore, the carbon dioxide peak area was affected by the amount of Na^S in the air,

which resulted in erroneous sodium carbonate measurements due to changes in the sodium sulfide concentration in the liquor. The measurements for sodium sulphide in the lye were affected

Similarly.

After this was realized, it was decided to adjust the pressure so that there would be the same total number of moles of gas in the system for each measurement. This can be done by maintaining the reaction gas in the reactor at a constant pressure, when the reaction is finished. The addition of air will act as a diluent, and the total number of moles of gas will remain fixed among a number of samples. It has been found that the total pressure of air, carbon dioxide and hydrogen sulphide under the conditions existing in the reactor will not exceed 24 psi. By adding additional air to achieve a pressure of 26 psi, it is possible to obtain gas samples that each contain a constant total number of moles of gas. The lye has essentially no carbon dioxide or hydrogen sulphide and does not affect the readings for carbon dioxide or hydrogen sulphide which are formed by the reaction. The peak areas for carbon dioxide and hydrogen sulphide are thus directly proportional to the concentration of sodium carbonate and sodium sulphide respectively in the lye. Furthermore, the sodium carbonate measurements will not be affected by the sodium sulphide concentration in the air, nor will the sodium sulphide measurements be affected by the sodium carbonate concentration. The measurements of sodium carbonate and sodium sulphide are then used to control the process.

Main components involved.

RI - Reactor.

Wiring involved

LI - Air line between the valve VlO and the outlet valve V13 to the reactor Ri.

L8 - Reactor pressure line between reactor pressure line L10 and reactor line L13.

L10 - Reactor pressure line between reactor pressure line L8 and air supply line L27.

LII - Connection line between the reactor pressure line L8 and the pressure measurement line L12.

L12 - Pressure measuring line from the connecting line LII to the measuring protector Gl and the air pressure gauge G2.

L13 - Reactor line between the reactor pressure line

L8 and the opening R8 in the reactor Ri.

L14 - Air line between the air supply line L27

and the valve V10.

L27 - Air supply line.

Valves involved:.'

Operating valves/position.

V3 - Valve in air line L3/closed. V4 - Valve in the water line L4/closed. V5 - Valve in the air line L5/closed. V6 - Valve in reaction gas line L6/closed. V8 - Valve in reactor pressure line L8/open. V10 - Valve between air line L14 and Ll/open. V13 - Outlet valve in the reactor Rl/closed.

Control valves.

V12 - Control valve in the test line L17 prevents reaction gases from entering the test circuit through the test line.

Pressure control valves.

ARI - Pressure regulating valve in the air line LI. AR3 - Pressure regulating valve in air line L14. AR5 - Pressure control valve with an accuracy of + 0.02 psi in reactor pressure line L10.

Flow.

Air.

L27 through AR2 through L14 through V10 through LI through ARI to Ril to keep V13 closed. L27 through AR5 through L10 through V8 through L8 through L13 through R8 to Ri.

Reaction gas transfer method (gas to G.C.).

The ninth method is the reaction gas transfer method. The reaction gas is transferred to the gas chromatograph, G.C. This requires enough time to allow a representative sample to receive in the sample loop SLI in the gas chromatograph.

Main components involved.

RI - Reactor.

Involved wiring.

LI - Air line between valve V10 and reactor outlet valve V13.

L2A - Line between reaction gas line L6

and the gas chromatograph.

L6 - Reaction gas line between the reactor line

L13 and the gas chromatograph line L2A.

L13 - Reactor line between the opening R8 in the reactor Ri and the reaction gas line L6.

L14 - The air line between the air supply line

L27 and valve V10.

Involved valves.

Operating valves/ position on.

V3 - Valve in air line L3/closed.

V4 - Valve in the water line L4/closed.

V5 - Valve in the air line L5/closed.

V6 - Valve in reaction gas line L6/open. V8 - Valve in air pressure line L8/closed.

V10 - Valve between air line L14 and Ll/open. V13 - Outlet valve in the reactor Rl/closed.

Control valves.

V12 - Control valve in the test line L17 prevents reaction gases from entering the test circuit through the test line.

Pressure control valves.

ARI - Pressure regulating valve in the air line Li. AR3 - Pressure regulating valve in air line L14.

Flow.

Air.

L27 through SAR3 through L14 through V10 through Li through ARI to Ril to keep V13 closed.

Reaction gas.

Ride through R8 through L13 through V6 through

L6 through L2A to gas chromatograph.

Time.

40 seconds or as needed to ensure that

the chromatograph has received a representative reaction s gas brittle ve .

Stop the transfer method ( stop).

The tenth method is the stop-transfer method. The reaction gas valve V6 closes. Time is allowed for the pressure in the gas chromatograph to equalize.

The main ingredients.

RI - Reactor

Wiring involved.

LI - The air line between valve V10 and reactor

outlet valve V13.

L14 - Air line between the air supply line L27

and the valve V10.

L27 - Air supply line.

Involved valves.

Operating valves/position.

V3 - Valve in air line L3/closed.

V4 - Valve in the water line L4/closed.

V5 - Valve in the air line L5/closed.

V6 - Valve in reaction gas line L6/closed. V8 - Valve in air pressure line L8/closed.

V10 - Valve between air line L14 and lL/open. V13 - Outlet valve in the reactor Rl/closed.

Control valves.

V12 - Check valve in the test line L17 prevents gas from entering the test line through the test line.

Pressure control valves.

ARI - Pressure regulating valve in the air line LI. AR3 - Pressure regulating valve in air line L14.

Flow.

Air.

L27 through AR3 through L14 through V10 through LI through ARI to Ril to keep V13 closed.

Time.

5 seconds or as needed for the pressure to equalize in the gas chromatograph sample chamber.

Drive device for the magnetic rod.

The liquid in the reaction chamber R12 is stirred by means of the mixing rod R13 in the reactor, which rests on the drain valve V13 at the bottom of the reactor. This rod is magnetically connected to and driven by a drive device M2 in the chamber M1.

The drive device is shown in fig. 7 and 8. A powerful horseshoe magnet M3 faces upwards towards rod R13. The horseshoe magnet M3 is mounted on a rotating plate M4. Any type of assembly can be used. It can be attached to the plate M4 using epoxy or another type of adhesive. It is shown mounted in a precise recess i

the upper surface of the plate M4.

The plate M4 rests on a base M5. Both the rotating plate M4 and the base M5 are shown in circular cross section. The base M5 has an upper, flat horizontal bearing surface M6 around the periphery. A circular, recessed part M7 lies within this periphery. The recessed part M7 also has

a flat, horizontal surface below the surface M6 and a vertical side wall extending from the surface to the bearing surface M6. A circular further recessed part M8 is located on the part M7. This surface M8 is also flat, and below the surface of the part M7. The section M8

also has a vertical sidewall extending from its surface to the surface of portion M7. The periphery of the base M5, the periphery of the part M7 and the periphery of the part M8

are concentric.

The part M8 is equipped with a nylon and glass ball bearing M9. The plate M4 has a cylindrical shaft M10 that fits into it

and rotates in bearing M9. A motor part Mil in the plate M4 fits and rotates in the recessed part M7 in the base M5. There is a clearance between the motor part Mil and the surface of the recessed part M7. The motor part Mil is circular and concentric, both with the cylindrical shaft M10 and with the outer circular periphery M12 of the plate M5. The periphery M13 of the engine part Mil is interrupted by evenly spaced, radial slits or notches M14.

The air duct M15 extends through the base M5 under the recessed part M8. Two secondary air passages M16 extend from the air line M15 at an angle upwards towards the surface of the recessed part M7. The outlets of the secondary air passage M16 are aligned with the radial slots M14 to allow air to impinge on the side walls of the radial slots M14

and turn plate M4. The outlet of the secondary air passages M16 is shown 180° apart and on opposite sides of the air line M15. The outlets can be parallel to one

tangent to the periphery of the recessed part M1, or angled towards the periphery. As shown, the outlets can be close to the periphery of the cut-out part M7.

Air from the air line L7 passes through the line M15 and the passages M16, and impinges on the walls of the radial slots M14 to turn the slot M4. Escaping air from the secondary air passages M16 also acts as a bearing for the plate M5 between the surface M17 of the plate M4 and the bearing surface M6 of the base M5. The air finally escapes along the surface M6 and out through the gap between the base and the rotating plate.

The rotation of the plate M4 results in the rotation of the magnet M3. Turning the magnet M3 causes the magnetic stirrer R13 to turn.

The drive device for the magnetic stirrer has the following components and mode of operation:

Main components involved.

Ml - Mixing chamber with magnetic stirring rod.

M2 - Drive device for magnetic stirring rod.

Wiring involved.

L7 - Air line from air line L14 to chamber Ml.

L14 - Air line from air supply line L27 to

air line L7.

L27 - Air supply line.

Involved valves.

Pressure control valves.

AR3 - Pressure regulating valve in air line L14. Repair valves.

V7 - Repair valve in air pressure line L7.

Flow.

L27 through AR3 through L14 through V7 through

L7 to Ml to drive M2.

It should be clear that the drive device for the magnetic stirring rod can also be switched on and off, depending on whether the reactor chamber is filled or empty, by changing the valve V7

to a solenoid operated on/off value, and to operate it on the same cycle as valve V10, which controls outlet valve V13 to the reactor. Valves V7 and V10 could be opened and closed together.

The gas chromatograph system.

In the reactor, green liquor or white liquor is reacted with acid

to form carbon dioxide and hydrogen sulphide gases. The concentration of these gases is measured in the gas chromatograph. The chromatograph emits a continuous, analogue signal, corresponding to the flow rate of gas through the chromatograph's detector. By integrating this signal for the correct time intervals (corresponding to the time for the appearance of carbon dioxide and hydrogen sulphide at the detector), the concentrations of carbon dioxide and hydrogen sulphide in the reaction gas are measured. Calibration of the reactor/gas chromatograph system using lye of known concentration allows the carbon dioxide and hydrogen sulphide measurements to be directly converted into a determination of the sodium carbonate and sodium sulphide content in the liquid sample.

The analysis process takes approx. 4 minutes, both for carbon dioxide and hydrogen sulphide. It may be necessary to analyze only carbon dioxide in green liquor or caustic white liquor samples. This reduces the analysis time for these samples to 1% minute.

The gas chromatograph can be used to successively analyze reaction gases from a number of reactors. For a slurry/caustic line, three liquor samples should be analyzed, resulting in a three-reactor analyzer system. For this reason, valve VI is a four-position valve with four inlets from reactors or other external sources, and one outlet to the gas chromatograph. It moves through the four positions until it is at the correct position to receive reaction gas from the selected reactor. It requires approx. 4 seconds to move from one position to the next. A further 5 seconds are used to electronically check the valve's position.

The internal details of a gas chromatograph shall not be given here. It is a standard piece of equipment, and its details, other than allowing it time to go through the procedure and the results of the analysis, are not important here. There are a number of valves in the gas chromatograph that allow the sample loop to be filled, the gas sample to be carried to the analysis column,

and that the sample loop and analysis column are flushed and rinsed. The discussion will not include standard helium flushing

and backwash that enters the gas chromatograph itself because these are common functions of this instrument.

It should only be pointed out that these valves and this operation are present in every gas chromatograph and only give a general overview of the process and the apparatus. The two procedures to be described in detail are the external procedures.

The chromatograph circuit has few parts. These are:

Components.

Main components.

GC - Gas chromatograph/two positions: position

one (preparedness) is used by three different methods - method IA (circulation); method IB (gas transfer); method 1C (flushing) - position two (analysis).

SLI - Sample loop for the gas chromatograph.

Wires.

L2 - Lead to the gas chromatograph.

L2A - Line from the reaction gas line

L6 to the gas chromatograph GC.

L2B - Line from the calibration gas line

L7 to the gas chromatograph line L2A.

L2C - Line from air pressure line L10

to the gas chromatograph line L2B.

L6 - Reaction gas line from the reactor RI to

the gas chromatograph line L2A.

L7 - Calibration gas line from the calibration gas source to the gas chromatograph line L2B.

L10 - Air pressure line from the air supply line

L27 to gas chromatograph line L2C.

L14 - Air line from air supply line L27 to

air line L53.

L27 - Air supply line.

L53 - Air line from air line L14 to .valve VI to drive the valve.

Valves.

Operating valves.

VI - Valve in the gas chromatograph line L2A.

Four positions to bring the sample to the gas chromatograph: position one (reactor one); position two (reactor two); position three (reactor three); position four (reserve).

V2 - Valve in the high-pressure air line L2C.

Two positions: open; close.

V6 - Valve in reaction gas line L6. Two positions: open; close.

V7 - Valve in calibration gas line L7.

Two positions: open; close.

Pressure control valves.

AR3 - Pressure regulating valve in air line L14. AR5 - Pressure regulating valve in high-pressure air-

wire L10.

In the operating sequences, the gas chromatograph takes a gas sample to the sample loop SLI, analyzes it, flushes the sample from the system and backwashes the system. It then waits for the supply of a new sample.

The preparedness method/ preparedness.

The first method is a contingency method. The gas chromatographs are waiting for a sample from the reactor circuit.

Main components involved.

GC - Gas chromatograph/position one (standby).

Involved valves.

Operating valves/ position on.

VI - Valve in the gas chromatograph line L2A/position four (closed). This is an example. The valve can have any position at start-up. This depends on the valve position when the system was shut off.

V2 - Valve in the high-pressure air line L2C/closed. V6 - Valve in reaction gas line L6/closed. V7 - Valve in calibration gas line L7/closed.

Flow.

No flow of reaction gases.

The repositioning method (repositioning).

The second method is a repositioning method (repositioning). The valve VI is repositioned around its four positions, until it is in line with the correct reactor. It moves in the same direction, either clockwise or counterclockwise, and takes five seconds to move. An additional 5 seconds is allowed for the system to check the valve's position. If the localization is not correct, it will move again and be checked again. This will continue until it is in the correct position.

The other valves and the gas chromatograph remain as they are.

Preparedness method (preparedness 2).

The third method is a new preparedness method (preparedness

2) where all valves remain in position until the reactor circuit is ready to transfer a gas sample.

The reaction gas transfer method (gas to G.C.)

The fourth method is a reaction gas transfer method. The gas chromatograph has internal valves, so that the reaction gas passes through the sample loop and then to deaeration to drain. The transfer time is long enough to receive a representative sample. The original gas entering the sample loop Li will not usually be representative of the mass of gas in the reactor. The lines from the reactor to the gas chromatograph are initially filled with air from a previous air purge. The air must be purged from these lines and the sample loop, to ensure that a representative sample of the reaction gas is obtained. It takes some time to achieve a stable sample in the sample loop. As a consequence, the time will vary, depending on the various factors affecting gas transfer to the sample loop. These factors may include the arrangement and dimensions of the piping between the reactor and the sample loop, the sample flushing conditions, pressure conditions, gas compositions, etc., present in the reactor itself at the time of the gas transfer. The time is usually between 40 and 60 seconds.

Main components involved.

GC - Gas chromatograph/method IA (gas transfer). SLI- Sample loop for the gas chromatograph.

Wiring involved.

L2A - Gas chromatograph line from reaction gas line L6 to sample loop SLI.

L6 - Reaction gas line from the reactor to

the wire L2A.

L13 - Reactor line from opening R8 in reactor RI to line L6.

Involved valves.

Operating valves/ position on.

VI - Valve in the gas chromatograph line L2A/

position one (reactor circuit one).

V2 - Valve in the high-pressure air line L2C/closed. V6 - Valve in reaction gas line L6/open. V7 - Valve in calibration gas line L7/closed.

Flow.

Reaction gas.

RI through R6 through L13 through V6 through L6 through L2A through VI through SLI to drain.

Time.

40 seconds or as needed to achieve one

representative sample of reaction gas in the sample loop. A time of 40 seconds is representative. The length of time is the time required to obtain a representative sample of reaction gas in the sample loop SLI.

Stop the sampling method ( stop).

The fifth method is a stop sampling method where the reaction gas to the gas chromatograph is stopped and the gas pressure in the sample loop is allowed to equalize with atmospheric pressure.

Main components involved.

GC - Gas chromatograph/method IB (gas transfer). SLI- Sample loop for the gas chromatograph.

Involved valves.

Operating valves/ position on.

VI - Valve in the gas chromatograph line L2A/

position one (reactor circuit one).

V2 - Valve in the high-pressure air line L2A/closed. V6 - Valve in reaction gas line L6/closed. V7 - Valve in calibration gas line L7/closed.

Flow.

No flow.

Time.

5 seconds or as needed for equilibrium conditions in the test loop.

Analysis method ( analyzed).

The sixth method is an analysis method where the sample is analyzed in the gas chromatograph. There is no change in the outer circuit. The change is in the internal system of the gas chromatograph. It connects from position two (gas transfer), to position three (analysis).

Main components involved.

GC - Gas chromatograph/position two (analysis).

SLI- Sample loop for the gas chromatograph.

Involved valves.

Operating valves/ position on.

VI - Vent the gas chromatograph line L2A/position one (reactor circuit one).

V2 - Valve in high-pressure air line L2A/closed. V6 - Valve in reaction gas line L6/closed. V7 - Valve in calibration gas line L7/closed.

Flow.

Helium through the sample loop carries reactor gas through the column, because the detector and out for venting.

Time.

4 minutes depending on the movement time of carbon dioxide and hydrogen sulphide through the column. The time can be more or less than 4 minutes, depending on the length of the column, the packing characteristics of the column, the helium flow rate, etc. The time will be 1% minute if only carbon dioxide is analyzed. Again, the time may be more or less than 1^ minutes due to other factors.

The test flushing method (flushing).

The seventh method is a gas flushing method where high-pressure air is used to flush the sample from the sample loop and the lines between the sample loop and the reactor.

Main components involved.

GC - Gas chromatograph/method 1C (flushing).

SLI - The gas chromatograph sample loop.

Wiring involved.

L2 - Gas chromatograph line from high pressure air line L10 to sample loop SL. Includes wires L2A, L2B and L2C.

L10 - High pressure line between the air supply line

L27 and the gas chromatograph line L2.

L27 - Air supply line.

Involved valves.

Operating valves/position.

VI - Valve in the gas chromatograph line L2A/position one (reactor circuit one).

V2 - Valve in the high-pressure air line L2C/open. V6 - Valve in reaction gas line L6/closed. V7 - Valve in calibration gas line L7/closed.

Pressure control valves.

AR5 - Pressure regulating valve in the high-pressure air line L10.

Flow.

Air.

L27 through AR5 through L10 through V2 through

L2 through SLI to vent to drain.

Time.

1 minute and 5 seconds or as needed to adequately flush wires and loop.

During the time the lye sample in the reactor completes its reaction, the valve VI will move to positions two and three, and the gas chromatograph analyzes gas samples from the second and third reactors.

Data collection and analysis.

Gas chromatograph output circuit forms voltage "peaks"

which corresponds to the appearance of each gas component in the detector in the gas chromatograph. The time interval (from the start of the analysis) during which each component (air, carbon dioxide and hydrogen sulphide) takes to pass through the detector is a characteristic of each component gas. This time interval during which each component appears in the detector is very reproducible, and can be easily determined for each gas. The gas chromatograph output circuit produces a continuous 0-1 volt analog signal that is proportional to the flow of gas through the detector. During the time interval each component passes through the detector in, a voltage peak is formed in response to the component's behavior.

Fig. 9 is a diagram of a G.C. voltage output during a gas analysis, from a typical green liquor sample.

Each component of the gas sample is identified, and the time interval during which it occurs is noted. The voltage peaks for each component are easily observed from fig. The integrated voltage for each component (which is equal to the area under each peak) is proportional to the amount of the component in the gas sample. Furthermore, carbon dioxide and hydrogen disulphide are integrated stresses, proportional to the sodium carbonate and sodium sulphide concentration in the lye. The integrated peak areas for C02 and r^S are therefore measures of a Na^O^ and Na2S, the concentrations in the sample.

The data acquisition circuit enables the carbonate/sulphide analyzer to convert the voltage peaks from the gas chromatograph into values corresponding to the concentrations of Na2CC>3 and Na2S

in the lye. The data acquisition circuit consists of the following main components:

GC - Gas chromatograph output circuit.

VCO - Voltage-frequency converter.

M - Mini calculator.

A schematic of the data acquisition circuits is shown in

fig. 10. The associated interconnection and components necessary to interconnect the main components are known and therefore not shown.

To calculate the concentrations of Na2CO^ and Na2S in the lye sample, the C02~ and H2S voltage peaks must be integrated. There are many methods that can be used to accomplish this. The preferred method of peak integration is to use

a volt-frequency converter, VCO, to convert the 0-1 voltage gas chromatograph output signal to a 0-10,000 Hz frequency signal. The continuous series of electronic pulses thus formed is used as input into a digital micro-calculator. The time intervals corresponding to the appearance of the C02 and H2S peaks are programmed into the microcomputer's software. During the discrete time intervals corresponding to the peak of each component, the microcomputer counts the total number of pulses generated by the VCO for the peak period. The number of pulses thus counted is a measure of the peak area. The peak area measurements thus obtained for C02 and H2S are proportional to the concentrations of Na-jCO^, respectively Na2S in the lye sample.

The microcalculators allow further calibration of the analyzer to obtain an opportunity to convert the pulse count measurements into direct determinations of Na2C03 and Na2S in the lye. The pulse count is directly proportional to the concentration of a chemical in the lye. By analyzing different liquors of known concentration and measuring the pulse counts obtained from these known liquors, one can easily determine the correct conversion factors for converting the pulse counts into the concentration measurement. These conversion factors are then stored in the microcomputer's software. The conversion factors are applied to pulse counts for all subsequent lye samples to give a direct determination of Na2C03 and Na2S in the lye. The lye concentrations can be given as pre-written information, or converted into analogue signals for use as input to control devices. Methods for obtaining such data are varied and well known.

Reactor temperature measurement system.

The measurements of sodium carbonate and sodium sulphide obtained with the aid of the carbonate sulphide analyzer are observed and affected by the temperature at which the reaction takes place. The reaction temperature is primarily controlled by the temperature in the analyzer chamber. The measurements obtained from the analyzer vary in direct proportion to the temperature. As the temperature is increased, the resulting measurements of sodium carbonate and sodium sulfide are increased accordingly. This phenomenon must be compensated for if accurate measurements are to be obtained for all samples, despite temperature variations.

It has been determined that the best method to eliminate measurement errors due to reactor temperature variations is to apply a correction factor to each measurement, based on the temperature during the reaction. To determine the correct factor for each measurement, the temperature is measured at the end of each reaction. The correct correction factors, calculated for the temperature, are then used automatically for each sample, and applied to the uncorrected values on the gas chromatograph. This strategy has been found to be an effective method for eliminating errors caused by variations in the reaction temperature.

It has been found that for every degree C deviation from a reference temperature, the measured gas chromatography range for Na2CO increases or decreases by 0.4%, while the corresponding value for Na2S is 0.7%.

The correction for Na_C0_. is:

and for Na S it is:

CA = corrected area,

MA = G.C. measured area,

To = reference temperature,

T = actual gas temperature from the reactor.

If, as an example, the reference temperature is 30°C, and the real temperature is 27°C, one gets for Na9C0-. : and for Na2S The temperature measurement system uses a resistance temperature detector, RTD, measured inside the room, and a relay that closes to allow the detector to be sampled by the analyzer data collection system. The relay closes to allow testing of the detector immediately after completion of transfer of reactor gases to the gas chromatograph sample chamber. It remains closed for 20 seconds or as needed to obtain an accurate temperature measurement. The RTD signal is converted into a temperature measurement in the data collection material.

A resistance temperature detector has been found to be the most suitable temperature measuring device. The detector element exhibits an electrical resistance that varies directly with temperature. This resistance is easily measured electronically, and easily converted

to a temperature reading, because the calibration of these

elements are well documented. Other devices, such as thermocouples or thermistors, which show electrical properties that vary as a function of temperature, can also be used for this.

Construction materials.

All materials have been chosen to ensure maximum performance and resistance to the effects of heat, pressure and the corrosive properties of lye and gas streams. The following materials have been found to be the best for the specific applications listed below: Reactor top and bottom are constructed of PVC (polyvinyl chloride). The fastening on the top of the pump is PVC. The mounting plate

for all solenoids etc. is PVC. The drive device for the magnetic stirring rod is PVC.

Reactor cylinder and acid pump cylinder are made of glass. Everyone

pipes that are in direct contact with acid or gases are Teflon, all other pipes are nylon. All couplings that are in direct contact with acid or gases are nylon. Reactor gas for the gas chromatograph and the air solenoids are Teflon. All control valves are made of Teflon. The test loop is made of nylon.

The acid pump piston is Teflon-coated 316S.S., (stainless steel). The connections that come into direct contact with gases or

those flushed with air or water are 316 S.S. All fittings, pipes, valves, columns, etc., in the gas chromatograph are 216 S.S. The gas isolation valve mounted on the front of the gas chromatograph is 316 S.S. Air, water, pressure

and flush solenoids are 304 S.S.

All connections on air and water lines located on the inlet side of the solenoid or regulators are made of brass. All regulators are made of aluminium. The lye-acid sample valve is "Hastalloy C".

Operation.

In a total system, these circuits will work together. The exact operation will depend on the mill configuration. A typical operation for a reactor circuit is shown in the following table. In this table are given the operating valves, the valve positions with open (0), closed (C) or position (1,

2), change of position (<*>), and the time. For an analyzer that uses multiple reactor circuits, the start-up time for each circuit will be shifted so as not to regulate overlapping of the gas chromatograph operation. Otherwise, logic and sequencing for each circuit will generally be identical, although minor modifications may be made in each individual reactor circuit in response to differences in lute strength or other characteristics without adversely affecting the operation of the overall system.

Use.

Fig. 11, 12 and 13 are schematic diagrams showing use of the apparatus in the causticization system. The control loop 1 in fig. 11 describes the use of the analyzer with a view to controlling the sodium carbonate concentration in the green liquor of the slurry. In this diagram, green liquor flows from the green liquor clarifier GLC through the mill outlet MLl and is pumped by the green liquor pump GLP to the slurryer S. Lime is added to the green liquor at slurryer S. There is a further line in this diagram. It is the line L40 that carries a portion of the weak liquor to the mill discharge' ML1.

The line L28/29 indicates two lines, L29 carrying lye

from the mill discharge line MLl to the reactor system RS1, and L28 which returns the liquor from the reactor system RS1 to the mill liquor line MLl. Each of the reactor systems, RS1, RS2 and RS3, includes a filter circuit, a sample circuit and a reactor circuit. These circuits are shown in fig. 1-3. Line L2 carries reaction gas from the reactor system RS1 to the gas chromatograph analyzer GC/A, in which gas is analyzed for carbon dioxide (from the sodium carbonate in the lye) and hydrogen sulfide (from sodium sulfide) as described above. The analyzer utilizing carbon dioxide analysis issues a signal through control line CL1 to the controller which controls valve V40 to increase or decrease the amount of weak liquor flowing through line L40 to ML1 to maintain a constant sodium carbonate concentration in the green liquor of the slurryer.

The hydrogen sulphide analysis has various applications. It is an indication of the reduction efficiency of the recovery digester. The sodium sulfide concentration can be given to the reboiler operator to confirm that the reduction efficiency is good, or to allow him to make corrections to improve the reduction efficiency. It is also an indication of the potential efficiency of causticisation. When the concentration of sodium carbonate or sodium sulphide in the green liquor is increased, the efficiency of causticisation is reduced. This gives the operator information about the causticization reaction the green liquor will be subjected to, and allows the causticization operator to take corrective measures.

The second control loop in this system is shown in fig.

12. This loop controls the balance of green liquor and lime, and thus controls the entire slurry. A "clear" lye sample is taken from the calcium carbonate sludge separator at either the slurryer or the first causticizer. This clear liquor is then filtered to remove any remaining calcium carbonate sludge. The sodium carbonate and sodium sulphide concentration in the filtered lye is then measured in GC/A from the reaction gas from the second reactor system, RS2.

The control loop logic will contain a set point for

the desired sodium carbonate concentration in the lye. This set point for the Na 2 CO 3 concentration will, as shown by mill experience, result in the best combinations of high conversion efficiency for Na 2 CO 3 to NaOH, low Na 2 CO 3 "dead weight", and acceptable sludge settling characteristics. The loop will then control the slurry operation via the mass flow of sodium carbonate to the slurry to maintain and control this concentration of Na2C^

in the lye leaving the slurry. There are two ways of controlling the sodium carbonate concentration in the slurry or the first causticizer. One is the usual method of controlling the amount of lime added to the slurry. The second and the method considered by the present inventors

to be significantly better, is shown in fig. 12. In this method,

the amount of sodium carbonate in the green liquor is controlled using a loop 1 as described above. The amount of this green liquor added to the slurry is controlled by loop 2. The amount of sodium carbonate and sodium sulfide in the white liquor, from the first caustic or slurry, is determined by GC/A from the reaction gases from RS2. A signal, based on sodium carbonate, is sent through control line CL2 to the control that operates valve V41 to increase or decrease the amount of green liquor flow through ML1 into slurryer S.

The measurement of the chemical concentrations in the white liquor is taken

from the line between the clear liquid storage tank and the boiler or boilers. The concentrations of sodium sulphide and sodium carbonate in the white liquor are determined directly by GC/A analysis of the reaction gases from the third reaction system, RS3. However, the amounts of sodium hydroxide in the white liquor must be determined indirectly. There are three pieces of information that must be combined to give the sodium hydroxide concentration in the white lye:

1. Sodium carbonate concentration in the white liquor; 2. Sodium carbonate concentration in the green liquor; 3. Sodium hydroxide concentration in the green liquor.

Measurements 1 and 2 are used to determine the amount of carbonate

in the green liquor which, during the slurrying/causticization, is converted to sodium hydroxide in the white liquor. The difference between the amount of Na2CO-j entering the system with the green liquor and the amount of Na^CO^ leaving it with the white liquor is the concentration of NaOH produced in the white liquor due to causticization. All chemical concentrations are expressed as sodium oxide, Na20. Some sodium hydroxide also enters the system with the green liquor. This sodium hydroxide passes unchanged through the system to the white liquor, and must be taken into account. This NaOH source in the system is relatively stable, a periodic, e.g. every 8 hours, determination of NaOH in the green liquor can be carried out manually and entered into the analyzer

the software material.

The determination of NaOH in the green liquor can be carried out directly by titrating a green liquor sample. Alternatively, it can be determined indirectly by titrating NaOH in the white liquor. The amount of NaOH in the white liquor that cannot be accounted for by the amount of NaOH formed during recausting is the amount of NaOH that has gone in with the green liquor. It is recommended that the NaOH content in the green liquor be determined by the indirect method, which has the advantage of reducing errors due to time differences in the process. The amount of NaOH associated with the green liquor is then stored in the microprocessor memory, until it is updated by a new titration. This value is used to update each subsequent white liquor sodium hydroxide determination.

The analyzer solves the following equation for each subsequent sample to determine the sodium hydroxide concentration in the white liquor:

The carbonate analysis is updated with each sample every 19 minutes. The determination of sodium hydroxide in the green liquor is updated by manual titration of a green or white liquor sample,

if necessary, usually every 8 hours. An updated and complete analysis of clarified white liquor (determination of sodium hydroxide, sodium sulphide and sodium carbonate) is sent to the digester operator or digester process computer every 12 to 19 minutes.

The system software material must also take into account time delays during slurrying, causticization and clarification in order to correctly determine the current NaOH concentration in the white liquor. This will determine the amount of chemicals added to the cooker to regulate the cooking process.

Cascade control options.

In many applications, it will be sufficient and desirable to use carbonate-sulphide analyzer measurements as primary information for the process control equipment. However, in some applications it may be advantageous to control the process directly with a measuring device which gives a more immediate, but less accurate (expressed as the sodium carbonate concentration) response to process changes.

If these devices are used, the measurements from the carbonate-sulphide analyzer should be used as set-point control signals for the primary controls. This "cascade" type of control system will greatly improve the accuracy of the primary control measurement devices, and improve process control.

Several measuring devices, such as conductivity probes, density meters, etc., provide quick responses to process changes. However, these devices only provide indirect measurements of the sodium carbonate concentration, they provide in response to the concentration of all chemicals in the process stream. The ratio of sodium carbonate to total chemicals

in the process stream will vary with time, resulting in incorrect determination of sodium carbonate concentration and less accurate control of the process than can be achieved if sodium carbonate is measured directly. However, changes that affect the calibration of these devices when measuring the sodium carbonate concentration occur slowly, and certainly slower than the 15-20 minute sampling period created by the carbonate-sulphide analyzer.

The direct measurements of sodium carbonate produced by the carbonate-sulphide analyzer can be used as a set point control information for each primary control device. This practice will have the effect of adjusting the calibration of the primary device, (conductivity probe, density meter, etc.), every 15 to 20 minutes, so that there is an accurate Na^ CO^ indicator concentration despite the previously mentioned variations in the ratio between Na2C0^and total chems. A cascade control strategy of this type will have the advantage of both an accurate method for determining the sodium carbonate concentrations in the process and the ability to respond immediately to process changes.

This is shown in fig. 14. The main point is the dissolution tank DT, the green liquor clarifier GC, the green liquor pump GLP, the slurryer S and the first causticizer Cl. The mill discharge ML1 carries green liquor from the dissolution tank DT to the green liquor clarifier GLC, and the mill discharge ML2 carries green liquor from the green liquor clarifier GLC to the slurryer S. The main soft liquor line L42 carries soft liquor to the lines L40 and L41.

The lye in line L41 is used to dissolve the smelt

in the dissolution tank DT. The amount of soft liquor that goes to the dissolution tank DT through line L41 is controlled by valve V41. The amount of soft liquor is determined by the density of the green liquor from the dissolution tank DT. This is monitored in the mill line MLl by the density meter DM1. The signal from the density meter DM1 passes through the control line CL1 to the valve control CN1. The valve V41 is checked

of CN1 with a signal passing through control line CL2. This is a standard local control loop, where a local, direct measurement is used to monitor the process conditions.

Fig. 14 also shows the use of local conditions to monitor and control the amount of soft liquor entering ML2 to maintain the carbonate level in the green liquor. However, at this time the gas chromatograph analyzer is used to determine the set points for this local control.

The valve V40 is used to control the flow of soft liquor in line 40, which is the amount of soft liquor that enters the mill outlet ML2. This is monitored locally by a density meter DM2 which sends a signal through the control line CL3 to the control unit CN2. CN2 drives control- . the valve V40 to increase or decrease the flow of soft liquor to keep the density in ML2 at a specified level. However, the density of the lye is not a direct indication of the sodium carbonate content in the lye. A sample of the density-controlled liquor from ML2 is taken and analyzed for sodium carbonate concentration by the reactor system RS1,

and the gas chromatograph-analyzer unit GC/A. This direct determination of sodium carbonate is used to send a set point signal through the control line CLS to CL2

to adjust the density setpoint so that the density more accurately reflects the sodium carbonate concentration in the lye.

Claims (76)

1. Procedure for determining the carbonate content in a lye, characterized in that it includes: to remove suspended solids from the liquor to obtain a filtered liquor, placing the filtered lye in a sample container to sample a specific quantity of the filtered lye, to use a measured amount of acid to remove and purify said sample from said sample container, and to transfer the sample to a closed reaction chamber, to allow acid and try to react in the reaction chamber for a first period of time, to collect in the reaction chamber a first gas, obtained from the reaction of the acid and the sample, the first gas comprising carbon dioxide, providing a constant pressure in the reaction chamber at the completion of the first time period, by adding a second gas to the reaction chamber, this being substantially free of carbon dioxide, to continue the reaction between acid and sample in the reaction chamber for a second period of time, and to continue collecting said first gas from the reaction in the reaction chamber, wherein the first and second gases comprise a gas mixture, transferring said gas mixture in the reaction chamber to a gas chromatograph, analyze the gas mixture for the carbon dioxide content, and purge the gas mixture from the gas chromatograph. 2. Method according to claim 1, characterized in that it further comprises allowing a second amount of the acid to remain in the sample container after transfer of the sample, in order to further remove residues that may remain in the sample container. 3. Method according to claim 2, characterized in that it further comprises removing suspended solids from a new feed of the lye to form a second filtered lye, using the second filtered lye to remove said second amount of acid and said residue from the sample container, and as others try to obtain a measured amount of said other filtered lye in the sample container. 4. Method according to claim 1, characterized in that it further comprises removing suspended solids from a new feed of the liquor to form a second filtered liquor, to place the second filtered lye in the sample container, in order as a second sample to obtain a specific amount of said second filtered lye, the second sample amount being equal to the first sample amount, to use a second measured amount of acid, to remove and clean the second sample from the sample container and transfer the second sample to the closed reaction chamber, the second amount of acid being equal to the first amount of acid, allowing the second amount of acid and the second sample to react in a second reaction in the reaction chamber for a third period of time equal to the first period of time, in the reaction chamber to collect a third gas, obtained from the second reaction, this comprising carbon dioxide, providing a constant pressure in the reaction chamber at the end of the third time period by adding a second amount of the second gas; the second gas addition for each sample providing a 2 molar amount in the gas in the reaction chamber which is the same for all samples, and which is greater than the total potential number of moles of gas that can be formed from the reaction between each sample and each amount of acid, to continue the second reaction in the reaction chamber for a fourth time period, equal to the second time period, and to continue in the reaction chamber and collect the third gas from the second reaction, as the second and third gases constitute a second gas mixture, transferring the second gas mixture in the reaction chamber to the gas chromatograph, analyzing the second gas mixture for carbon dioxide content, and to purge the second gas mixture from the gas chromatograph. 5. Method according to claim 4, characterized in that it further comprises allowing a third amount of the acid to remain in the sample container after transfer of the first sample, in order to further remove residues that may remain in the sample container. 6. Method according to claim 5, characterized in that it further comprises using a second filtered lye to remove the third amount of acid and the rest from the sample container. 7. Method according to claim 1, characterized in that it further comprises, before the transfer of acid and sample to the reaction chamber, the reaction chamber containing a gas containing a small amount of carbon dioxide, and the pressure of the contained gas is allowed to equal atmospheric, just before transfer of acid and sample to the reaction chamber. 8. Method according to claim 1, characterized in that it further comprises to wash the reaction chamber after transferring the gas mixture to the gas chromatograph. 9. Method according to claim 1, characterized in that it comprises the addition of an anti-flocculating agent to the sample. 10. Method according to claim 9, characterized in that the anti-flocculation agent is added to the acid. 11. Method according to claim 1, characterized in that it further comprises converting the amounts of carbon dioxide gas into sodium carbonate liquor concentrations. 12. Method according to claim 1, characterized in that the lye is selected from pulp mill green liquor, pulp mill slurry liquor, pulp mill causticization liquor and pulp mill clarified white liquor. 13. Method according to claim 12, characterized in that it further comprises allowing a second amount of the acid to remain in the sample container to further remove residues that may remain in it. 14. Method according to claim 13, characterized in that it further comprises removing suspended solids from a new supply of the lye to form a second filtered lye, to use this to remove the second quantity of acid and the residue from the sample container, to obtain as a second sample a measured amount of the second filtered lye in the sample container. 15. Method according to claim 12, characterized in that it further comprises removing suspended solids from a new supply of liquor to form a second filtered liquor, to place this in the sample container to, as a second sample, obtain a specific amount of the second filtered lye, the second sample amount being equal to the first sample crowd, using a second measured amount of the acid to remove and purify the second sample from the sample container; and to transfer the second sample to the closed reaction chamber, the second amount of acid being equal to the first amount of acid, allowing the second amount of acid and the second sample to react in a second reaction in the reaction chamber for a third period of time equal to the first period of time, in the reaction chamber to collect a third gas obtained from the second reaction, the third gas comprising carbon dioxide, providing a constant pressure in the reaction chamber after the third time period is completed by adding a second quantity of the second gas; the second addition of gas for each sample gives a total molar amount of gas in the reaction chamber that is the same for all samples, and is greater than the total potential number of moles in the gas that can be formed from the reaction of each sample and the acid, to continue the second reaction in the reaction chamber for a fourth time period equal to the second time period, and to continue in the reaction chamber to collect the third gas from the second reaction, as the second and third gases constitute a second gas mixture, transferring the second gas mixture in the reaction chamber to a gas chromatograph, analyzing the second gas mixture for the carbon dioxide content, and flushing the second gas mixture from the gas chromatograph. 16. Method according to claim 15. characterized in that it further comprises allowing a third amount of the acid to remain in the sample container after transfer of the first sample, to further remove residues that may remain in the sample container. 17. Method according to claim 16, characterized in that it further comprises using said second filtered lye to remove the third amount of acid and the rest from the sample container. 18. Method according to claim 12, characterized in that it further comprises before the transfer of acid and sample to the reaction chamber, the reaction chamber containing a gas containing a small amount of carbon dioxide, and the pressure in the contained gas is allowed to become exactly equal to the atmospheric pressure before the transfer of acid and sample to the reaction chamber. 19. Method according to claim 12, characterized in that it further comprises washing the reaction chamber after the transfer of the gas mixture to the gas chromatograph. 20. Method according to claim 12, characterized in that it further comprises the addition of an anti-flocculation agent to the sample. 21. Method according to claim 20, characterized in that the anti-flocculation agent is added to the acid. 22. Method according to claim 12, characterized in that it further comprises converting the amount of carbon dioxide gas into sodium carbonate liquid concentrations. 23. Method according to claim 22, characterized in that it further comprises determining the sodium carbonate concentration in the green liquor and the white liquor, and to determine part of the sodium hydroxide concentration in the white liquor by determining the difference between the sodium carbonate concentration in the green liquor and the sodium carbonate concentration in the white liquor. 24. Method according to claim 12, characterized in that the liquid is selected from pulp mill slurry liquor and pulp mill caustic liquor, and further comprises removing ■ suspended solids from the lye by sedimentation followed by filtration. 25. Method according to claim 24, characterized in that it further comprises allowing a second amount of the acid to remain in the sample container after transfer of the first sample to further remove any residue present that may remain in the sample container. 26. Method according to claim 25, characterized in that it further comprises removing suspended solids from a new feed of the liquor to form a second filtered liquor, using the second filtered liquor to remove the second amount of acid and the residue from the sample container, and to obtain as a second sample, a measured amount of the second filtered lye in the sample container. 27. Method according to claim 24, characterized in that it further comprises removing suspended solids from a new feed of the liquor to form a second filtered liquor, to place the second filtered lye in the sample container in order to obtain as a second sample a specific amount of the second filtered lye, the second amount being equal to the first amount, using a second measured amount of the acid to remove and purify the second sample from the sample container and transfer the sample to the closed reaction chamber, the second amount of acid being equal to the first amount of acid, allowing the second amount of acid and the second sample to react in a second reaction in the reaction chamber for a third period of time equal to the first period of time, collecting in the reaction chamber a third gas obtained from the second reaction, the third gas comprising carbon dioxide, providing a constant pressure in the reaction chamber at the end of the third time period by adding a second amount of the second gas, the other gas for each sample providing a total molar amount of gas in the reaction chamber that is equal for all samples, and is greater than the total potential number of moles of gas that can be formed from each reaction of each sample and each amount of acid, to continue the second reaction in the reaction chamber for the fourth time period equal to the second time period, and to continue collecting in the reaction chamber the third gas from the second reaction, as the second and third gases constitute a second gas mixture, transfer of the second gas mixture in the reaction chamber to the box chromatograph, analyze the second gas mixture for the carbon dioxide content, and flushing the second gas mixture from the gas chromatograph. 28. Method according to claim 27, characterized in that it further comprises allowing a third quantity of the acid to remain in the sample container after the transfer of the first sample, to further remove any residue present that may remain in the sample container. 29. Method according to claim 28, characterized in that it further comprises using the second filtered lye to remove the third amount of acid and the rest from the sample container. 30. Method according to claim 24, characterized in that it further comprises before the transfer of acid and sample to the reaction chamber, where the reaction chamber contains a gas containing a small amount of carbon dioxide, and the pressure of the contained gas is allowed to equal atmospheric pressure just prior to the transfer of the acid and sample to the reaction chamber. 31. Method according to claim 24, characterized in that it further comprises washing the reaction chamber after transferring the first and second gas to the gas chromatograph. 32. Method according to claim 24, characterized in that it further comprises to wash the reaction chamber after transferring the gas mixture to the gas chromatograph. 33. Method according to claim 32, characterized in that it comprises the addition of an anti-flocculating agent to the sample. 34. Method according to claim 24, characterized in that the anti-flocculation agent is added to the acid. 35. Method according to claim 1 for determining the carbonate and sulphide content in a lye, characterized in that it further comprises that the gases from the reaction chamber containing carbon dioxide and hydrogen sulphide, that the second gas is essentially free of carbon dioxide and hydrogen sulphide, and analyzing the gas mixture for the carbon dioxide and hydrogen sulphide content. 36. Method according to claim 35, characterized in that it further comprises allowing a second amount of the acid to remain in the sample container to further remove any residue that may remain in the sample container. 37. Method according to claim 36, characterized in that it further comprises removing suspended solids from a new feed of the lye to form a second filtered lye, using the second filtered lye to remove the second amount of acid and residue from the sample container, and as a second sample to obtain a measured amount of said second filtered lye in the sample container. 38. Method according to claim 35, characterized in that it further comprises removing suspended solids from a new feed of the liquor to form a second filtered liquor, to place the second filtered lye in the sample container in order as a second sample to obtain a specific amount of said second filtered lye, this being equal to the first sample amount, to use a second measured amount of said acid to remove and purify said second sample from the sample container and to transfer the second sample to the closed reaction chamber, the second amount of acid being equal to the first amount of acid, allowing the second amount of acid and the second sample to react in a second reaction in the reaction chamber for a third period of time equal to the first period of time, in the reaction chamber to collect a third gas obtained from the second reaction in that this third gas comprises carbon dioxide and hydrogen sulphide, providing a constant pressure in the reaction chamber at the end of the third time period by adding a second amount of the second gas, the second gas addition for each sample providing a total molar amount of gas in the reaction chamber that is equal for all samples, and is greater than the total potential number of moles of gas that can be formed from the reaction of each sample and each amount of acid, to continue the second reaction in the reaction chamber for a fourth time period equal to the second time period, and to continue in the reaction chamber to collect the third gas from the second reaction, the second and third gases comprising a second gas mixture, transferring the second gas mixture in the reaction chamber to the gas chromatograph, analyzing the second gas mixture for the carbon dioxide and hydrogen sulphide content, and to flush. the second gas mixture from a gas chromatograph. 39. Method according to claim 38, characterized in that it further comprises allowing a third quantity of the acid to remain in the sample container after transfer of the first sample, in order to further remove any residue present that may remain in the sample container. 40. Method according to claim 39, characterized in that it further comprises using the second filtered lye to remove the second amount of acid and the rest from the sample container. 41. Method according to claim 35, characterized in that it further comprises before the transfer of acid and sample to the reaction chamber, the reaction chamber containing a gas containing a small amount of carbon dioxide and hydrogen sulphide, and the pressure of the contained gas is allowed to equal atmospheric pressure just prior to the transfer of acid and sample to the reaction chamber. 42. Method according to claim 35, characterized in that it further comprises washing the reaction chamber after transferring the gas mixture to the gas chromatograph. 43. Method according to claim 35, characterized in that it comprises the addition of an anti-flocculating agent to the sample. 44. Method according to claim 43, characterized in that the anti-flocculation agent is added to the acid. 45. Method according to claim 35, characterized in that it further comprises converting the amount of carbon dioxide gas into sodium carbonate liquid concentrations. 46. Method according to claim 35, characterized in that the lye is selected from pulp mill green liquor and pulp mill clarified white liquor. 47. Method according to claim 46, characterized in that it further comprises to allow a second quantity of the acid to remain the sample container after transferring the sample to further remove any residue that may remain in the sample container. 48. Method according to claim 47, characterized in that it further comprises removing suspended solids from a new feed of the lye to obtain a second filtered lye, using the second filtered liquor to remove the second amount of acid and the residue from the sample container, and to obtain as a second sample a measured amount of the second filtered lye in the sample container. 49. Method according to claim 46, characterized in that it further comprises removing suspended solids from a new feed liquor to form a second filtered liquor, placing the second filtered lye in the sample container to obtain as a second sample a specific quantity of the second filtered lye, with the second sample amount being equal to the first sample amount, to use a second measured amount of the acid to remove and purify the second sample from the sample container, and to transfer the second sample to the closed reaction chamber, the second amount of acid being equal to the first amount of acid, allowing the second amount of acid and the second sample to react in a second reaction in the reaction chamber for a third period of time equal to the first period of time, to collect in the reaction chamber a third gas obtained from the second reaction, this comprising carbon dioxide and hydrogen sulphide, providing a constant pressure in the reaction chamber at the end of the third time period by adding a second amount of the second gas, the second gas addition for each sample providing a total molar amount of gas in the reaction chamber that is equal for all samples, and is greater than the total potential number of moles of gas that can be obtained from the reaction between each sample and each amount of acid, to continue said reaction in the reaction chamber for a fourth time period equal to the second time period, and to continue collecting in the reaction chamber the third gas from the second reaction, the second and third gases comprising a second gas mixture, transferring the second gas mixture in the reaction chamber to the gas chromatograph, analyzing the second gas mixture for the carbon dioxide and hydrogen sulphide content, and flushing the second gas mixture from the gas chromatograph. 50. Method according to claim 49, characterized in that it further comprises allowing a third amount of the acid to remain in the sample container after the acid transfer of the first sample, to further remove any residue that may remain in the sample container. 51. Method according to claim 50, characterized in that it further comprises using the second filtered lye to remove the third amount of acid and the rest from the sample container. 52. Method according to claim 46, characterized in that it further comprises before the transfer of acid and sample to the reaction chamber, the reaction chamber contains a gas containing smaller amounts of carbon dioxide and hydrogen sulphide, and the pressure of the contained gas is allowed to equal atmospheric pressure just prior to the transfer of acid and sample to the reaction chamber. 53. Method according to claim 46, characterized in that it further comprises washing the reaction chamber after transferring the gas mixture to the gas chromatograph. 54. Method according to claim 46, characterized in that it comprises the addition of an anti-flocculating agent to the sample. 55. Method according to claim 54, characterized in that the anti-flocculation agent is added to the acid. 56. Method according to claim 46, characterized in that it further comprises converting the amount of carbon dioxide gas into sodium carbonate liquid concentrations. 57. Method according to claim 35, characterized in that the lye is selected from pulp mill slurry liquor and pulp mill causticization liquor, in that it further comprises removing suspended solids from the liquor by sedimentation followed by filtration. 58. Method according to claim 57, characterized in that it further comprises allowing a second amount of the acid to remain in the sample container after transferring the sample to further remove any residue that may remain in the sample container. 59. Method according to claim 58, characterized in that it further comprises removing suspended solids from a new feed of the liquor to form a second filtered liquor, using the second filtered liquor to remove the second amount of acid and the residue from the sample container, and as a second sample to obtain a measured amount of the second filtered lye in the sample container. 60. Method according to claim 57, characterized in that it further comprises removing suspended solids from a new feed of the liquor to form a second filtered liquor, to place the second filtered lye in the sample container in order as a second sample to obtain a specific amount of the second filtered lye, this sample amount being equal to the first sample amount, to use a second measured amount of acid to remove and purify the second sample from the sample container, and to transfer the second sample to the reaction chamber, the second amount of acid being equal to the first amount of acid, allowing the second amount of acid and the second sample to react in a second reaction in the reaction chamber for a third period of time equal to the first period of time, collecting in the reaction chamber a third gas obtained from the second reaction, the third gas comprising carbon dioxide and hydrogen sulphide, providing a constant pressure in the reaction chamber at the end of the third time period by adding a second amount of the second gas, the second gas addition for each sample providing a total molar amount of gas in the reaction chamber that is equal for all samples and is greater than the total potential number of moles of gas that can be obtained from the reaction in each sample and each amount of said acid, to continue the second reaction in the reaction chamber for a fourth time period equal to the second time period, and to continue collecting in the reaction chamber the third gas from the second reaction, as the second and third gases constitute a second gas mixture, transferring the second gas mixture in the reaction chamber to the gas chromatograph, analyzing the second gas mixture for the carbon dioxide and hydrogen sulphide content, and to purge the second gas mixture from the gas chromatograph. 61. Method according to claim 60, characterized in that it further comprises allowing a third amount of acid to remain in the sample container after transfer of the first sample to further remove any residue that may be present in the sample container. 62. Method according to claim 61, characterized in that it further comprises using the second filtered lye to remove the third amount of acid and the rest from the sample container. 63. Method according to claim 57, characterized in that it further comprises, that, prior to transfer of acid and sample to the reaction chamber, the reaction chamber contains a gas containing minor amounts of carbon dioxide and hydrogen sulfide, and the pressure of the contained gas is allowed to equal atmospheric pressure, just before transferring the acid and sample to the reaction chamber. 64. Method according to claim 57, characterized in that it further comprises washing the reaction chamber after transferring the gas mixture to the gas chromatograph. 65. Method according to claim 57, characterized in that it comprises the addition of an anti-flocculating agent to the sample. 66. Method according to claim 65, characterized in that the anti-flocculation agent is added to the acid. 67. Method according to claim 57, characterized in that it further comprises converting the amount of carbon dioxide gas into sodium carbonate liquid concentrations. 68. Apparatus for determining the carbonate and sulphide content in a lye, characterized in that it comprises first devices for removing suspended solids from the liquor, other devices to obtain a measured sample liquor from the first device, third devices to allow reaction between an acid and the sample, and to collect gases from the reaction, fourth devices for collecting a measured sample of acid and transferring the contents from the second and fourth devices to the third devices, fifth devices connecting the first and second devices, sixth devices connecting the second and fourth devices, seventh devices for alternatively connecting the other devices to either the fifth or sixth devices, eighth devices for connecting the second and third devices, ninth devices for adding a gas to the third devices, a gas chromatograph to analyze the constituents of the gases from the reaction, tenth devices for connecting third devices and the gas chromatograph. 69. Apparatus according to claim 68, characterized in that it further comprises eleventh devices eleventh devices for equalizing & v dot internal pressure in the third devices for atmospheric pressure. 70. Apparatus according to claim 68, characterized in that it further comprises eleventh devices for connecting the other devices to a drain, and the seventh devices connect the second and eleventh devices when they connect the second and fifth devices and also connect the eighth and second devices when they connect the sixth and second devices. 71. Apparatus according to claim 68, characterized in that it further comprises eleventh devices for connecting washing water with the third devices, and twelfth devices for emptying the third devices. 72. Apparatus according to claim 68, characterized in that it further comprises eleventh means for connecting an anti-flocculation agent to the fourth means. 73. Apparatus for determining the carbonate and sulphide content in a lye, characterized in that it comprises first devices for removing suspended solids from the liquor, other devices to obtain a measured sample liquor from the first devices, third devices to allow reaction between an acid and the sample, and collection of gases from the reaction, fourth devices for collecting a measured sample of acid and transferring the contents of the second and fourth devices to the third device, fifth devices connecting the first and second devices, sixth devices for connecting the other devices to the drain, seventh devices connecting the second and fourth devices, eighth devices for connecting the second and third devices, ninth devices to alternatively connect the other devices with either the fifth or seventh devices, as the ninth devices connect the second and sixth devices when they connect the second and fifth devices, and also connect the eighth and second devices when they connect the seventh and second devices, devices for adding a gas to the third devices, a gas chromatograph for analyzing the components in the gas from the reaction, and eleventh devices for connecting the third devices and the gas chromatograph. 74. Apparatus according to claim 73, characterized in that it further comprises twelfth devices for connecting washing water with the third devices, and thirteenth devices for bottling the third devices. 75. Apparatus according to claim 73, characterized in that it further comprises twelfth means for connecting an anti-flocculation agent to the fourth means. 76. Apparatus according to claim 73, characterized in that it further comprises twelfth devices for bringing the internal pressure in the third devices and atmospheric pressure into equilibrium.