NO850160L - PROCEDURE AND APPARATUS FOR ANALYSIS AND MANAGEMENT OF CARBONATE AND SULFIDE IN GREENLIFE SUSPENSION AND CUSTOMIZATION - Google Patents

Description

The present invention relates to the analysis of green liquor, slurry and causticization cells, and white liquor chemicals as well as the management of pulp factory operations from the analysis.

A good diagram of the causticization process can be found

in Pulp and Paper Manufacture, 2nd Edition, Volume I, The Pulping of Wood, 1969, prepared under the direction of The Joint Textbook Committee of the Paper Industry, R. G. MacDonald, Publisher, and J. N. Franklin, Technical Publisher, McGraw Hill Book Company, New York, publisher. The diagram is Figure 9-72 on page 535.

The process actually starts with the recovery furnace. The black liquor consisting of organic and inorganic chemicals and water is fed to the furnace where the water is evaporated, the organic components are burned and the inorganic components are recovered in the form of a molten melt. The molten melt containing mainly sodium carbonate and sodium sulphide is continuously decanted from the furnace layer and dissolved in water (gentle wash) at the dissolution tank or tanks to form green liquor. A typical green liquor composition is approx. 60-65% sodium carbonate and 25-28% sodium sulphide calculated by weight (% solids) expressed as Na20. A typical solids content in green liquor is around 18% of the total liquid weight. The green liquor is pumped from the dissolution tank or tanks to a green liquor clarification device where the precipitate is sedimented out. The sediment is impurities, i.e. undissolved, solid substances from the furnace. These are mainly carbon, calcium, magnesium and iron compounds.

After clarification, the green liquor is mixed with slaked lime or mesa from the calcining furnace in the slurry. Usually, the amount of lime is adjusted to maintain a specified white liquor concentration. Supplementary lime in the form of fresh lime (or limestone burnt in the calcining kiln) is added to the burnt lime to replace lime loss in the system. Grinding stone sand (large, unreacted lime particles) is removed from the slurry of slaked lime in the slurry's sorting section. In the slurry, the lime or calcium oxide reacts with the water in the green liquor to form calcium hydroxide and this in turn reacts with the sodium carbonate in the green liquor to form sodium hydroxide and calcium carbonate, which then flows to the causticization cells. Caustic cells are used to give the caustic reaction that starts in the slurry sufficient time to reach completion. From the caustics, 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 clarified white liquor is pumped to storage and then to the digester to convert wood chips into pulp. 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 washing water and this is used in the dissolution tank or tanks to dissolve the smelt to form raw green liquor.

In the usual process, the thin wash water is then used at the dissolution tank or tanks to dissolve the molten sodium salts coming from the recovery digester. The resulting raw green liquor is then clarified to remove the sediment and then pumped to the slurryer. Lime supplied to the slurryer is usually based on the total flow of green liquor and the slurry temperature, the slurry temperature specification 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 the white liquor taken from a caustic cell or from the overflow from the white liquor clarification device. Lime feed, green liquor density at the dissolution tank or tanks, or a combination of the two are usually changed to maintain a white liquor strength within specification for a plant. The specification is usually expressed as the sodium hydroxide and sodium sulphide concentration in the white liquor, ie AA (active alkali) or EA (effective alkali). These expressions are defined and discussed on pages 358-363 of MacDonald and Franklin, supra.

White liquor AA or EA concentration varies significantly due to changes in lime availability (CaO content), reactivity (hydration rate), mass flow rate of lime to the slurry or combinations thereof. Sodium carbonate concentration changes. in the green liquor feed will also affect the resulting white liquor strength. The presence of this number of uncontrolled variables makes it very difficult to control the slimming/causticization reaction.

Current practice uses a total titratable alkali (TTA) measurement to control fluid strength and caustic efficiency. TTA is a measure of sodium hydroxide, sodium carbonate and sodium sulphide and is therefore only an indirect, approximate determination of the Na2CC>2 concentration in the liquid.

Another variable that makes slurry management difficult is the colorimetric titration (ABC test) used to analyze the liquid. The ABC test can be found in TAPPI test T624 OS-68 (Parts 9, 10 and 11). It can be modified to adapt to specific plant conditions. Titration endpoints are not identified by a sharp color change. Instead there is a gradual change in colour, e.g. from orange to red or from green to blue, depending on which indicator is used. This "diffuse" endpoint determination results in great uncertainty in the fluid concentrations, which are the only variables regularly measured.

Attempts have been made to solve these problems. Hultman, et al, US Patents 4,236,960 and 4,311,666 describe a different type of process for controlling the degree of causticization. Sutinan and Haapoja, "Causticizing Plant and Lime Kiln Computer Control" describes a Nokia Autolime system.

TAPPI test T624 OS-68 describes tests for the analysis of soda ash and sulphite white liquor and green liquor. Test 12 describes the sodium carbonate (assessment method) test. ;

The invention relates to a method and an apparatus for measuring carbonate and sulphide concentrations in white and green cooking liquid and in the slurry and causticisation cells and 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 power plant slurry is in reality a carbonate reactor, i.e. carbonate ions in the green liquor are crystallized from solution with hydrated lime, and sodium hydroxide is evolved in the process. In particular, the causticization control logic is based on determining the concentration of sodium carbonate and sodium sulphide in the green liquor, in the white liquor sludge slurry at the slurryer or first causticizing device and in the white liquor that is fed to the cooker 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/causticisation process, but to indicate inefficiencies in the process and to take steps to control them. An increase in sulfide concentration will tend to decrease the efficiency of the causticization reaction. Knowledge of the concentration of sodium sulfide entering the slurry will alert the operator or process computer to the optimum causticization efficiency that can be expected from the recaustic plant. The changes in sulphide concentration will also indicate changes in sodium sulphide reduction efficiency in the recovery digester and will enable steps to be taken to achieve better control of the sodium sulphide reduction efficiency in the digester.

It is desirable that as much of the sodium carbonate in the green liquor as possible is converted to sodium hydroxide in the slurry and the causticizing devices. It is impossible to completely convert all of the sodium carbonate into sodium hydroxide - some sodium carbonate will remain in the lye. The ultimate limit on how much sodium carbonate can be converted to sodium hydroxide is controlled by the equilibrium causticization efficiency. A discussion of the factors governing equilibrium causticization efficiency can be found at pages 532-534 of MacDonald and Franklin, supra.

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 done correctly, the beneficial effects will be high operating efficiency due to the effective conversion of sodium carbonate to sodium hydroxide, and low sodium carbonate "dead" content in the white liquor, which has many beneficial effects during boiling, evaporation due to recycling. 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 to lime will result in low conversion efficiency of sodium carbonate to sodium hydroxide. An excess of lime for green liquor will weaken the sedimentation

and the filtration properties of the calcium carbonate "sludge",

which must be removed from the white liquor before it can be used in the cookers.

Variations in the Na2C02_concentration in the liquid at 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 T^ a^ CO-^ concentration in the liquor in the slurry/caustic device, but is very difficult to measure and control. However, the concentration and flow rate of the green liquor can be measured and controlled rather easily. The proposed strategy will control the green liquor flow rate to the slurry to maintain the desired Na^O^ concentration in the slurry/causticizer liquor despite variations occurring in the lime. The green liquor concentration is also controlled in a control loop. The advantages of this strategy are the following: 1. A constant, desired concentration of Na-^CO^ is controlled early in the slurry/caustic acid reaction, ensuring safe, efficient operation. 2. The slurry/causticization process is controlled by regulating the flow rate and concentration of the green liquor, which is technically quite easy to achieve. Controlling the concentration, activity and flow rate for the lime is technically difficult and is therefore allowed to vary within normal limits and the green liquor flow rate is regulated depending on these variations. This strategy provides much more accurate control than is the case with strategies that attempt to regulate lime flow rate in response to changes in liquid flow rate and concentration. 3. This strategy will control the process based on direct measurements of the critical component in the system, sodium carbonate. This provides much more accurate management than is the case with strategies based on TTA liquid conductivity, liquid density or other indirect, approximate indications of Na2CC>2 in process liquids.

The total fluid-space production rate (amount of

white liquor developed per minute) will be controlled by the flow rate of lime to the slurry. As the production rate must be increased or decreased in order to maintain a total liquid balance in the plant, the flow rate of lime that is added to the slurry is correspondingly increased or decreased. The flow rate for the green liquor will be automatically adjusted using a control loop to maintain the desired Na2C02_concentration in the white liquor. Both chemical inventory (lime and liquid stock levels) and plant production rates can be maintained using this strategy. Chemical inventory and/or production rate can be controlled either manually or automatically.

The last measurement is to determine the concentrations of sodium hydroxide, sodium carbonate and sodium sulphide in the white liquor which is taken to the boiler room for use in the cooking process. It is important to measure the sodium hydroxide and sodium sulphide concentrations in the white liquor so that the amount of liquid to be supplied to the boiler(s) can be determined correctly. Changes in the sodium sulfide concentration (developed at the reboiler) can affect the white liquor AA/EA concentration.

The device takes a sample from an appropriate line

- green liquor, slurry/caustic liquid, or white liquor

the digester - filters the sample if necessary, takes a measured amount, reacts the measured amount with an acid to produce hydrogen sulfide and carbon dioxide and measures the amounts 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 device is to analyze liquid from the slurry or the causticisation cells. A number of operations or methods are performed in each of these circuits during the test cycle. These methods are set up in different order depending on the different operations in the plant.

The device must work uniformly over a long period of time and must provide reproducible results. The liquid is e.g. corrosive and can also clog wires. The inventors have constructed a device that eliminates corrosion and reduces clogging of wires to a minimum. This necessitated extensive laboratory and facility testing and new construction. During the testing, it was found that the liquid being analyzed, the degree of completion of the reaction and the temperature of the reactive gases, would cause changes in the results, which would lead to an unfeasible control of the process. Again, considerable time and laboratory and plant testing were required before the problem was recognized, the sources of the problem discovered, and corrective steps taken. The present device and control logic are the result of work by several people over a number of years and the present application represents the inventors' understanding of the problem and the solution at the time of application. The work continues. Figure 1 is a diagram of the main components of the test unit. Figure 2 is a diagram of the filter circuit for the apparatus. Figure 3 is a diagram of a three-filter circuit assembly for the apparatus when operating in a three-component configuration. Figure 4 is a diagram of the sludge separation circuit. Figure 5 is a cross-section of the reactor for the apparatus. Figure 6 is a top view of the reactor for the apparatus. Figure 7 is an internal side view partly in section and shows the drive device for the magnetic stirring rod and the stirring rod in the reactor chamber. Figure 8 is a cross-section along line 8-8 in Figure 7. Figure 9 is a graphical representation of a voltage output for a gas chromatograph during gas analysis resulting from a typical green liquor sample. Figure 10 is a schematic diagram of a data collection circuit. Figure 11 is a diagram of a single loop apparatus in a pulp mill. Figure 12 is a diagram of a double loop apparatus in a pulp mill. Figure 13 is a diagram of a triple loop apparatus in a pulp mill. Figure 14 is a diagram of a cascaded 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 device is to be used to analyze liquid from the slurry or causticisation cells. Each of these circuits has a series of operations or methods that are performed during a test cycle. These methods are sequenced in different ways depending on the particular operation in a plant. The parts and methods will be described for each of the circuits. A possible sequence will then be described.

It should be pointed out that most of the operable valves in the unit are two-position valves. This is for convenience and simple operation. Three-position valves or multi-port valves are used in several specific applications. Where this is the case, the use of these valves is noted.

Filter circuit

The purpose of the filter circuit is to remove particulate material from the liquid to prevent both clogging of the test equipment and chemical side reactions that could mask the liquid's real composition.

The following description is directed to the filter circuit in Figures 2 and 3. Each of the filter circuits in the three-circuit arrangement shown in Figure 3 will have the same parts and operating sequence, and therefore 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.

Wires

ML - Plant liquid line in the caustic system between the green liquor clarifier and the slurryer, between the slurryer and the first causticizer, between the first and second causticizers or between the storage tank for clear white liquor and the boiler, depending on the liquid being sampled.

L22 - Sampling line from the filter outlet line

L30A for the sampling lrets.

L28 - Liquid return line from the filter circuit to the clarifier, the slurryer or the causticizer depending on the liquid during sampling.

L2 9 - Liquid supply line from plant liquid line ML

to the filter circuit.

L30 - Filter outlet line from the upper part of the filter F to the liquid return line L28. L30A - Filter outlet line from 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 filter outlet line L30B to liquid return line L28.

L31 - Filter backwash line from valve V28

to the filter outlet line L30C.

L32 - Filter bypass line from the filter circuit inlet line L29 to the liquid return line L28.

L33 - Air inlet line to the top of the filter shock dome FS.

L33A Air inlet line from the air supply

to the 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 line and filter backwash outlet line between valve V28 and bottom of filter F.

L35 - Inlet line from filter circuit liquid feed line L29 to valve V28.

L36 - Water supply line.

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

Valves

Operating valves (solenoid operated)

V21 - Valve in filter outlet line L30A. Two positions: Open; close.

V22 - Valve in sampling line L22. Two positions: Open; close.

V24 - Valve in the filter bypass line L32. Two positions: Open; close.

V26 - Valve in the air inlet line L33A. Two positions: Open; close.

V28 - Filter inlet-backwash-three-way T-valve at the connection point of filter backwash line L31, filter inlet line L34 and inlet line L35. Two positions: Position one (backwash) (1B) - open to filter backwash line L31 and filter backwash outlet line L34, closed to inlet line L35; position two (filter)(2F) - open to filter inlet line L34 and inlet line L35, closed to filter backwash line L31.

V29 - Valve in the water backwash line L37. Two positions: Open; close.

Control valves

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

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

into 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 the filter F and to induce selective current into the sampling line L22 when the valve V22 is open. Pressure relief valve (normally closed, can be opened automatically)

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

V19 - Repair valve in liquid return line L28. V25 - Repair valve in filter circuit liquid supply line L2 9.

The filter circuit has several methods of operation.

Circulation method (no liquid to filter) ( Circulation)

The first method is a liquid circulation method whereby the liquid is taken from the plant liquid line, through the circulation line and returned to the slurryer or causticizer without passage through the filter.

Wires involved

ML - Plant liquid line.

L28 - Liquid return line from the filter circuit.

L2 9 - Liquid supply line from the plant liquid line ML

to the filter circuit.

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

Valves involved

Operating valves/ position

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 the air inlet line L33A/closed.

V28 - Filter inlet backwash valve/position one (backwash) (1B) - open to filter backwash line L31 and filter backwash outlet line L34, closed to inlet line

L35.

V29 - Valve in the water backwash line L37/

close.

Control valves

V18 - Control valve in filter outlet line L30B

to prevent current passing through line L30 into filter F.

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

into the filter F.

Repair valves

V19 - Repair valve in the liquid return line L28. V25 - Repair valve in filter circuit fluid supply line L29.

Current

ML through V25 through L29 through V24 through L32

through V19 through L28.

Time

The time will vary.

Liquid filtration method (filter)

The second method is a liquid filtration method whereby the liquid is taken from the plant liquid line, filtered in the filter F and returned to the return line to establish stable filtration of the liquid.

Main components involved

F - Filter

Wires involved

ML - Plant liquid line.

L28 - Return line from the filter circuit.

L29 - Liquid supply line from the plant liquid 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 bottom of filter F.

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

Valves involved

Operating valves/ position

V21 - Valve in filter outlet line L30A/open.

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

V29 - Valve in water backwash line L37/closed.

Control valves

V18 - Control valve in filter outlet line L30B

to prevent current passing through line L30 into filter F.

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

into the filter F.

Pressure valve

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

Repair valves

V19 - Repair valve in filter circuit fluid return line L28.

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

Current

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 the analyzer is first started, a filter cycle is immediately carried out to provide a liquid sample for the first reaction. For all subsequent reactions, the filter cycle is started at a time that is determined by a mechanism elsewhere in the system. It can be initiated by means of a sequencer output which is activated when a new liquid sample is desired. This could be signaled by completion of filling of the acid pump AP2 or opening of the valve which applies pressure to the reactor R1.

Time

60 seconds - will vary depending on the time required to fill the lower part of the filter with liquid and provide a sufficient current in L30 to provide a uniform liquid sample to the sampling line L22.

Liquid sampling method (sample)

The third method is a liquid sampling method where the liquid is taken from the plant liquid line, filtered and sent to the sampling circuit to provide the test sample. The 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

Wires involved

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

Valves involved

Operating valves/ position

V22 - Valve in sampling line L22/open.

Pressure valves

V20 - Back pressure valve in the filter outlet line L30B

provides back pressure to effect selective diversion of the filtered liquid into sampling line L22.

Current

ML through V25 through L2 9 through L35 through V28 through L34 through F through V21 through L30A: part through V22 through L22 to sampling circuit.

Divide through V20 through L30B through V18 through L30C through V19 through L28.

Time

60 seconds - will vary depending on the time

necessary to completely flush and fill the sampling circuit with new fluid.

Stop sampling method (stop)

The fourth method is a stop sampling method which is a pause to allow the sampling valve V22 in the sampling circuit to change position. The parts, wiring, valves, valve positions and currents are the same as in the second method - the filter method.

Time

5 seconds or as needed to ensure shutdown

the valve V22.

Liquid backwash method

The fifth method is a liquid backwash method whereby the liquid is used to backwash or backwash particulate material in the filter from the filter to the return line. It is carried out in two stages.

Stage 1 (backwash 1)

In step 1, the filter outlet valve V21 is closed and liquid from the plant liquid line ML fills the filter to the center of the filter shock dome FS.

Main components involved

F - Filter

FS - Filter shock.

Wires involved

ML - Plant liquid line.

L2 9 - Liquid supply line from the plant liquid line ML

to the filter circuit.

L33 - Air inlet line to the top of the filter shock dome FS.

L34 - Filter inlet line from valve V28 to bottom

of the filter F.

L35 - Inlet line from filter circuit liquid feed line L29 to valve V28.

Valves involved

Operating valves/ position

V21 - Valve in the filter outlet line L30A/closed.

V22 - Valve in sampling line L22/closed. V24 - Valve in the filter bypass line L32/closed. V26 - Valve in the air inlet line L33A/closed. V28 - Filter inlet backwash valve/position two (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 liquid supply line L2 9.

Current

ML through V25 through L29 through L35 through. V28

through L34 into F to the middle of FS.

Time

10 seconds or as needed for provisioning

of sufficient liquid to backwash the filter.

Stage 2 (backwash 2)

In stage 2, air entering at the top of the filter dome FS will drive the liquid through the filter element of 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 liquid return line L28.

Main components involved

F - Filter

Wires involved

L28 - Liquid return line from the filter circuit.

L30C- Filter outlet line from filter backwash line L31 to filter circuit fluid return line L28.

L31 - Filter backwash line from valve V28

to the filter outlet line L30C.

L33 - Air inlet line to the top of the filter shock dome FS.

L34 - Filter backwash outlet line from bottom

of the filter F to the valve V28.

Valves involved

Operating valves/ stiIling

V21 - Ventili filter outlet line L30A/closed. V22 - Valve in sampling line L22/closed. V24 - Valve in filter bypass line L32/open. V26 - Valve in the air inlet line L33A/open. V28 - Filter inlet backwash valve/position one (backwash) (1B) - 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

VI8 - Control valve in filter outlet line L30B to prevent flow through line L30 into filter F.

V23 - Control valve in the backwash line L31

to prevent current through wire L31 into

the filter F.

Repair valves

V19 - Repair valve in the filter circuit liquid return line L2 8.

Current

Air

V26 through L33 into F.

Liquid

F through L34 through V28 through V23 through L31

through L30C through V19 through L28.

Time

15 seconds or as needed for i sufficient

degree to backwash filter.

Water backwash method

The sixth method is a water backwash method whereby 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 liquid return line L28. The water backwash method would normally occur instead of a first method, a bypass method, and would follow a fifth method, the liquid backwash method. It is used whenever the filter is heavily soiled with particulate matter. The liquid supply would normally be cut off. The parts, lines, valves and valve positions are the same as in Step 2 of the Fifth Method, Step 2 of the Liquid Backwash Method, with the following additions and changes.

Wires involved

L33A- Air line to the filter shock dome is not used. L33B- Inlet line from water backwash line

L37 to the top of the filter shock dome FS.

L36 - Water supply line.

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

Valves involved

Operating valves/ position

V26 - Valve in the air inlet line L33A/closed.

V29 - Valve in water backwash line L37/open.

Current

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 for provisioning

of a complete washing of the filter element. Sludge separation circuit - slurry/ causticizer - white liquor

It is often desirable to control applications for obtaining liquid samples directly from the slurry or caustic acid for analysis. This liquid contains 8-10% by weight of suspended calcium carbonate sludge solids, which must be removed prior to analysis. The level of solids content present in this liquid is too high to be introduced immediately to the filter circuit since severe clogging of the filter element would result. The purpose of the sludge separation unit is to remove the bulk of the solids from the liquid and provide a "clear" liquid containing 1% or less suspended sludge solids. This "clear" liquid is filterable and becomes the liquid supply to the filter circuit. It should be noted that the sludge separation unit in no way interferes with subsequent operation of the analyzer system. The filter, sample, reactor and gas chromatograph circuits operate exactly the same as they do when no sludge separation circuit is used. The sludge separation circuit only ensures that an acceptable liquid sample is provided to the filter circuit.

It has been found that the best method of sludge separation involves the use of a continuous settling cone. This device receives uncleared liquid from the slurryer or caustic acid, separates the sludge from the liquid, returns the sludge to the slurry or caustic acid, and feeds a continuous supply of "clear" liquid to the filter circuit. The advantages of this apparatus and method are simplicity, reliability, ease of operation and a fresh, uninterrupted supply of liquid to the filter circuit so that operation of the filter circuit is not disturbed.

The sedimentation cone itself is a non-mechanical thickener of a type that is usually used for continuous liquid-solid separations in low-volume applications. The details of the construction and operation of these devices are well known and will not be detailed here, but may be found in Perry, J. H. (publisher) Chemical Engineers Handbook, 3rd ed., McGraw-Hill Book Co., Inc. New York, 1950, pages 940-941. The sludge separation unit should be designed for a capacity that will deliver a desired flow of "clear" liquid (about 2-3 litres/minute) to the filter circuit.

The following description is of the sludge separation circuit shown in figure 4. The circuit consists of the following components: Main components

T1 - Continuous sedimentation cone.

T2 - Clear liquid tank.

SP1 - Feed pump for unclarified liquid from supply line L39 for unclarified liquid to supply line L40 for unclarified liquid.

SP2 - Feed pump for clear liquid in filter circuit liquid feed line L2 9.

B1 - "Bustle" pipe and "launder" ring apparatus from settling cone T1 to feed line L43 for

clear liquid.

Wires

L29 - Fluid supply line to the filter circuit.

L3 9 - Feed line for uncleared liquid from slurry (or causticizer) to feed pump SP1 for uncleared liquid.

L40 - Feed line for uncleared liquid from feed pump SP1

for uncleared liquid to the meeting point for sedimentation cone inlet line L41 and sedimentation cone bypass line L42.

L41 - Sedimentation cone inlet line from feed line L40 for uncleared liquid to sedimentation cone T1.

L42 - Sedimentation cone bypass line from feed line L40 for uncleared liquid to slurry (or causticizer) return line L50.

L43 - Supply line for clear liquid from "bustle" tube/-

"launder" ring device B1 to meeting point for inlet line L44 for clear liquid tank and bypass line L46 for clear liquid tank.

L44 - Inlet line for clear liquid tank from feed line L43 for clear liquid to clear liquid tank T2.

L45 - Overflow line for clear liquid tank from clear liquid tank T2 to bypass/overflow line L48 for clear liquid.

L46 - Bypass line for clear liquid tank from supply line L43 for clear liquid to bypass/overflow line L48 for clear liquid.

L47 - Outlet line for clear liquid tank from clear liquid tank T2 to meeting point for filter circuit liquid supply line L29 and drainage line L51 for clear

liquid tank.

L48 - Bypass/overflow line for clear liquid tank from meeting point for bypass line L46 for clear liquid tank and overflow line L45 for clear liquid tank to slurry (caustic) return line L50.

L49 - Sedimentation cone sludge discharge line from sedimentation cone T1 to slurry (caustic south) return line L50.

L50 - Sludger (causticizer) return line that returns flows from clear tank bypass/overflow line L48, sludge discharge line L49, and sedimentation cone bypass line L42 to the slurryer (or causticizer).

L51 - Clear liquid tank drain line from clear liquid tank outlet line L47 to return line L50.

L52 - Water flushing line from plant water supply to supply line L39 for uncleared liquid.

Operation and repair valves (manually operable)

V30 - Sedimentation cone inlet valve in sedimentation cone inlet line L41. Two positions:

Open, closed.

V31 - Sedimentation cone bypass valve in sedimentation cone bypass line L42. Two positions:

Open, closed.

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

V33 - Clear liquid tank inlet valve in clear liquid tank inlet line L4 4. Two positions: Open, closed.

V34 - Clear liquid tank outlet valve in filter circuit liquid supply line L29. Two positions: Open, closed.

V35 - Clear liquid tank drain valve in clear liquid tank drain line L51. Two positions: Open, closed.

V36 - Water backwash valve in water backwash line L52. Two positions: Open, closed.

V37 - Feed valve for uncleared liquid in feed line L39

too cloudy liquid. Two positions: Open, closed.

The sludge separation unit has five operation methods and these are the normal operation method, the clear liquid tank bypass method, the sedimentation cone bypass method, the circuit shutdown/water backwash method, and the circuit shutdown/ready-to-start method.

Normal operating method

The first method is the normal operation method. The circuit will normally remain in this method. The circuit will be removed from this method only as needed when it is necessary to repair the sludge separation or filter circuits, or when shutting down the slurry/causticizer process.

Main parts involved

T1 - Continuous sedimentation cone.

T2 - Clear liquid tank.

SP1 - Feed pump for uncleared liquid/on.

SP2 - Clear liquid feed pump/on.

B1 - "Bustle" tube/"launder" ringer.

Wires involved

L29 - Liquid supply line to filter circuit.

L39 - Feed line for uncleared liquid.

L40 - Feed line for uncleared liquid.

L41 - Sedimentation cone inlet line.

L43 - Supply line for clear liquid.

L44 - Clear liquid tank inlet line.

L45 - Clear liquid tank overflow line.

L48 - Clear liquid 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 liquid tank bypass valve/closed (or choked).

Can be throttled partially open when the circuit is in operation to direct some clear liquid to the return line L50 to ensure that L50 does not become clogged.

V33 - Clear liquid tank inlet valve/open.

V34 - Clear liquid tank outlet valve/open.

V35 - Clear liquid tank drain valve/closed.

V36 - Water flush valve/closed.

V37 - Feed valve for uncleared liquid/open.

Current

Cloudy liquid

From slurry (or caustic) through V37 through L39 through SP1 through L40 through V30 through L41

into T1.

Clear liquid

From T1 through B1 through L43 through V33 through L44 into T2 through L47 through V34 through SP2 through

L29.

Sludge

From T1 through L49 through L50 to slurry (or

caustician).

Time

The time will vary. The circuit will normally be in this method, being removed from this method only for maintenance of this circuit or the filter circuit or

when shutting down the slurry and causticizer process.

Clear liquid tank circulation method

This second method is the clear liquid tank bypass method. This method is used when it is necessary to stop the flow of clear liquid to the clear liquid tank. This may be necessary when repair of this part of the circuit is required, or when repair of the filter circuit is required, requiring the flow of clear liquid to the filter circuit to be stopped.

Main components involved

T1 - Continuous sedimentation cone.

T2 - Clear liquid tank.

SP1 - Feed pump for uncleared liquid/on.

SP2 - Feed pump for clear liquid/off.

B1 - "Bustle" tube/"launder" ringer.

Wires involved

L39 - Feed line for uncleared liquid.

L40 - Feed line for uncleared liquid.

L41 - Sedimentation cone inlet line.

L43 - Supply line for clarified liquid.

L46 - Clear liquid tank bypass line.

L47 - Clear liquid tank outlet line.

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

L51 - Clear liquid tank drain line.

Operating valves/ position

V30 - Sedimentation cone inlet valve/open. V31 - Sedimentation cone bypass valve/closed. V32 - Clear liquid tank bypass valve/open.

V33 - Clear liquid tank inlet valve/closed. V34 - Clear liquid tank outlet valve/closed.

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

V37 - Feed valve for uncleared liquid/open.

Streams

Cloudy liquid

From slurry or causticizer through V37 through L39 through SP1 through L40 through V30 through L41

into T1.

Clear liquid

From T1 through B1 through L43 through V32 through L46 through L48 through L50 to upslemmer or kausti-sør.

From T2 through L47 through L35 through L51 through

L50 into slurry or caustic.

Sludge

From T1 through L49 through L50 to slurry or

caustician.

Time

Varies as needed to correct maintenance problems that require clear liquid tank circulation.

Sedimentation cone recirculation method

The third method is the sedimentation cone recirculation 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 liquid will be stopped in this method and there will be no sample flow to the filter circuit and analyzer.

Main components involved

SP1 - Feed pump for uncleared liquid/on.

SP2 - Feed pump for clear liquid/off.

Wires involved

L3 9 - Feed line for uncleared liquid.

L40 - Feed line for uncleared liquid.

L42 - Sedimentation tank bypass line.

L47 - Clear liquid tank outlet line.

L50 - Op<p>slemmer or causticizer return line.

L51 - Clear liquid tank drain line.

Operating valves/ position

V30 - Sedimentation tank inlet valve/closed.

V31 - Sedimentation tank bypass valve/open.

V32 - Clear liquid tank bypass valve/closed.

V33 - Clear liquid tank inlet valve/open.

V34 - Clear liquid feed valve/open.

V35 - Clear liquid tank drain valve/open.

V36 - Water flush valve/open.

V37 - Feed valve for uncleared liquid/open.

Streams

Cloudy liquid

From slurry or causticizer through V37 through L39 through SP1 through L40 through V31 through L42

through L50 to slurry or causticizer.

Time

Varies as needed to complete maintenance repairs that require settling cone recirculation.

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 shut down the circuit for maintenance or as a reaction to a shutdown of the slurry/causticization process. The flow of cloudy liquid 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

T1 - Cone of sedimentation.

T2 - Clear liquid tank.

SP1. - Feed pump for uncleared liquid/on.

SP2 - Feed pump for clear liquid/on.

B1 - "Bustle" tube/"launder" ring.

Wires involved

L40 - Feed line for uncleared liquid.

L41 - Sedimentation tank inlet line.

L42 - Sedimentation tank bypass line.

L43 - Clear liquid feed line.

L44 - Clear liquid tank inlet line.

L45 - Clear liquid tank overflow line.

L46 - Clear liquid tank bypass line.

L47 - Clear liquid tank outlet line.

L48 - Clear liquid tank bypass/overflow line.

L49 - Sedimentation cone sludge discharge line. L50 - Return line to slurry or causticizer. L51 - Clear liquid tank drain line.

L52 - Water flush line.

Operating valves/ position

V30 - Sedimentation cone inlet valve/open.

V31 - Sedimentation cone bypass valve/open.

V32 - Clear liquid tank bypass valve/open.

V33 - Clear liquid tank inlet valve/open.

V34 - Clear liquid tank outlet valve/open.

V35 - Clear liquid tank drain valve/open.

V36 - Water flush valve/open.

V37 - Feed valve for uncleared liquid/closed.

Current

Water

Through L52 through V36 through L39 through SP1 through L40 through: V31 through L42 through L50 into slurry or causticizer.

V30 through L41 into T1.

From T1 through L49 through L50 into slurry or caustic.

From T1 through B1 through L4 3 through:

V32 through L46 through L48 through L50 into slurry or causticizer.

V33 through L44 into T2 through L47 through:

V34 through SP2 through L29.

V35 through L51 through L50 into slurry or

caustician.

Time

15 minutes or as needed for complete manner

to flush the circuit with water.

Note

This operation, as described, will completely flush the entire circuit with water. Selected valves can be closed at will to direct wash water only through selected lines and parts of the circuit. It is not always necessary or desirable to flush the entire circuit.

The circuit shutdown/ready-to-start method

The fifth method is the circuit shutdown/ready-to-start method. This method is used after the circuit has been flushed with water. The circuit is in a "ready to start" state and will remain in this state until restarted.

Main components involved

All components are in a "ready to go" state.

All tanks are drained and all pumps are off.

Wires

All lines have been flushed and drained and are located

itself in a ready-to-go state.

Operation valves/position

V30 - Sedimentation tank inlet valve/open.

V31 - Sedimentation tank bypass valve/closed.

V32 - Clear liquid tank bypass valve/closed.

V33 - Clear liquid tank inlet valve/open.

V34 - Clear liquid feed valve/open.

V35 - Clear liquid tank drain valve/closed.

V36 - Water flush valve/closed.

V37 - Feed valve for uncleared liquid/closed.

Current

No current in the circuit once tanks and lines are empty and drained. To restart the circuit and return to the first or normal mode of operation, the turbid liquid feed valve V2 9 is opened and pumps SP1 and SP2 are started. The circuit will then resume normal operation. The circuit should be started and run for at least 30 minutes before starting the rest of the analyzer system to ensure that all tanks are filled and

the circuit has reached equilibrium.

Sampling circuit

The purpose of the sampling circuit is to obtain a measured liquid 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 sections, a sample valve and an associated sample loop shown in the upper central part of Figure 1, and an acid section shown on the right side of Figure 1. The sample loop receives a 10 cm 3 sample of the filtered liquid and the acid pump obtains a 50 cm 3 sample of 10 volume-% sulfuric acid

(about 2.2 N). The acid pump works so that it delivers a full 50 cm 3 of acid, but only 40 cm 3 goes to the reactor. The rest is left in the sample loop SL2 and is washed out when fresh liquid replaces the acid in the liquid sampling method.

It has the following components:

Main components

SL2 - Sample loop to obtain 10 cm 3 filtered

\liquid sample. It is connected to ports P5 and P6 in the sampling valve V14.

AP1 - The air piston for operation of 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 for achieving 3

a 50 cm sample of 10% sulfuric acid. Two positions: Position one (acid filled and ready to go)(1F);

Position two (acid out or transfer) (2T).

Wires

L9 - Antiflocculant line from antiflocculant supply to acid feed line L20.

L14 - Air line from air supply line L27 to

the valve V11.

L15 - Air line from valve V11 to port P1 in sample valve V14 for supplying air to move sample valve V14 to position one (sampling) (1 S) .

L16 - Air line from valve V11 to port P2 in test valve V14 for supplying air to move test valve V14 to position two (transfer) (2T) .

L17 - Test line from port P4 in test valve V14

to port R9 in reactor R1.

L19 - Acid line from acid line L21 to port P3

in the test valve V14.

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

L21 - Acid line from the meeting point for acid lines

L19 and L20 to the acid pump AP2.

L22 - Test lead from filter system to port P8

in the test valve V14.

L23 - Sample line from port P7 to sample valve

V14 to the drain.

L24 - Air line from valve V17 to the inside of the piston in AP1 to move the piston outwards to position one (acid fill)(1F).

L25 - Air line from valve V17 to the outside of the piston in AP1 to move the piston inward to position two (acid transfer)(2T).

L26 - Air line from air supply line L27 to

the valve V17.

L27 - Air supply line.

Valves

Operating valves

V11 - Solenoid operated air valve connecting air line L14 to either air line L15 or air line L16 to position test valve V14. Two positions: Position one (sampling) (1S) - air line L14 connected to air line L15; position two (transfer) (2T)

- air line L14 connected to the air line

L16.

V14 - Air operated test valve has two operating ports.

P1 - Connected to air line L15 to allow air to move the valve to position one (sampling), and

P2 - connected to the air line L16 to allow air to move the valve to position two (transfer).

And six test ports:

P3 - Connected to the acid line L19,

P4 - Connected to test lead L17,

P5 - Inlet to the test loop SL2,

P6 - Outlet from the test loop SL2,

P7 - Connected to drain line L23,

P8 - Connected to test lead L22.

It has two positions:

Position one (sampling) (1S) - reception of the sample from the filter circuit into the sample loop SL2. Connects ports P5, P6, P7 and P8.

Position two (transfer) (2T) - leading the sample from the sample loop SL2 to the reactor R1. Connects ports P3, P4, P5 and P6 and sends acid supply from AP2 through test loop SL2 to reactor R1.

V17 - Solenoid operated air valve connecting air line L26 to either air line L24 or air line L25. Two positions: Position one (acid fill)(1F); air line L26 connected to air

the wire L25; position two (acid transfer)(2T): Air line L26 connected to the air line

L24.

Control valves

V12 - Control valve in the sample line L17 prevents material or gas from returning through the line L17 from the reactor R1 to the sampling circuit.

V15 - Control valve in the acid line L19 prevents backflow of acid from L19 through L20 into AP2 during the acid pump filling method.

V16 - Control valve in the acid feed line L20 prevents the backflow of acid through the acid feed line

L20 under the acid transfer method.

Pressure control valves

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

The sample valve and associated sample loop receive and hold a measured liquid sample. The acid system receives and holds a measured amount of acid separately from the liquid sample. These are held until the reactor can receive the sample and the acid. The circuit then transports the sample, full of the acid, to the reactor R1. During this latter step, the acid passes through the sample loop SL2. This achieves two goals: (1) The sample is transported to the reactor system by the acid and (2) the sample loop is cleaned by the acid during injection. After the transfer, some acid remains in the loop and will dissolve any residue that may be left in the loop. Cleaning the sample loop before each liquid analysis is important because the liquid being handled has a tendency to crystallize on any surfaces with which it comes into contact. During the next sample reception, the sample is circulated through the sample loop SL2 and out of the system through line L23. This requires 60 to 100 seconds to ensure that all the acid and any residue that may be present is removed from the sample loop, and that the new sample is a representative sample of the liquid currently used in the process. The sampling circuit has several methods of operation. In many of these methods, the valve processing arrangement is the same.

An initial acid flush cycle (methods 1-4) is carried out at start-up to ensure that the sample system is clean and filled with acid before sample analysis begins.; At start-up there may be a sample in the sample loop depending on the status of the sample system at shutdown.

Ready to go method ( Ready to go 1)

The first method is a ready-to-start method whereby there is acid or liquid in the test loop SL2, depending on the status of the test circuit at shutdown.

Main components involved

SL2 - Sample loop/filled with 10 cm<3> acid or liquid. AP1 - Air operated piston for operating the piston i

the acid pump/position one (acid fill) (1F).

AP2 - Acid pump/position one (acid filling) (1F).

Wires involved

L14 - Air line from air supply line L27 to

the valve V11.

L15 - Air line from valve V11 to port P1 i

the test valve V14.

L24 - Air line from valve V17 to the inside of

the stamp in AP1.

L26 - Air line from air supply line L27 to

the valve V17.

L27 - Air supply line.

Valves involved

Operating valves/ stiIling

V11 - Solenoid operated air valve/position one (sampling) ( 1 S) : Connects the air lines L14 and L1 5 .

V14 - Air operated sample valve/position one (sampling) (1S): 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 holds acid

in line L19.

V16 - Control valve in the acid supply line L20 keeps acid in the acid lines L2 0 and L21.

Pressure control valves

AR2 - Pressure regulating valve in air line L26.

AR3 - Pressure regulating valve in air line L1 4 .

Current

Air

L27 through AR3 through L14 through V11 through L15 through P1 into V14.

L27 through AR2 through L26 through V17 through L24

into AP1.

Liquid

No electricity.

Test valve repositioning method (repositioning 1)

The second method is a test valve repositioning method. The sample valve is moved from the sample receiving position to the sample transfer position.

Main components involved

SL2 - Sample loop/10 cm acid present.

AP1 - Air driven piston for operation of the piston i

the acid pump/position one (acid fill) (1F).

AP2 - Positive displacement acid pump/position one (acid fill)(1F).

Wires involved

L14 - Air line from air supply line L27 to

the valve V11.

L16 - Air line from valve V11 to port P2 i

the test valve V14.

L24 - Air line from valve V17 to the inside of

the stamp in AP1.

L26 - Air line from air supply line L27 to

the valve V17.

L27 - Air supply line.

Valves involved

Operating valves/ position

V11 - Solenoid operated air valve/position two (transmission)(2T): Connects air lines L14 and L16.

V14 - Air operated test valve/position two (over-flow) (2T) : Connects ports P3, P4, P5 and P6.

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

Cont ro Unexpected i le r

V15 - Control valve in the acid line L19 holds acid

in wire 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.

Current

Air

L27 through AR3 through L14 through V11 through L16 through P2 into V14.

L27 through AR2 through L26 through V17 through L24

into AP1.

Time

5 seconds or as needed to ensure that V14 has

completed shift.

Acid transfer method (transfer 1)

The third method is a transfer method whereby the acid pump pushes the 50 cm 3 of acid in the acid pump AP2 through the sample loop SL2 and into the reactor. An initial flush of the system with acid is performed to ensure that the system is purged and filled with acid before sample analysis begins.

Main components involved

SL2 - Trial loop.

AP1 - Air driven piston for operation of the piston.

in the acid pump/position two (acid transfer) (2T).

AP2 - Positive displacement acid pump/position two

(acid transfer)(2T).

Wires involved

L14 - Air line from air supply line L27 to

the valve V11.

L16 - Air line from valve V11 to port P2 i

the test valve V14.

L17 - Test line from port P4 in test valve V14

to port R9 in reactor R1.

L19 - Acid line from acid line L21 to port P3

in the test valve V14.

L21 - Acid line from the acid pump AP2 to the acid line

L19.

L25 - Air line from valve V17 to the outside of

the stamp in AP1.

L26 - Air line from air supply line L27 to

the valve V17.

L27 - Air supply line.

Valves involved

Operating valves/ position

V11 - Solenoid operated air valve/position two (overdrive) (2T): Connects air lines L14 and L1 6 .

V14 - Air Operated Test Valve/Position Two (Transmission)

(2T): Connects ports P3, P4, P5 and P6.

V17 - Solenoid operated air valve/position two (acid transfer)(2T): Connects the air lines L26 and

L24.

Control valves

V12 - Control valve in the test line L17 prevents the liquid and the acid from returning to the test circuit once it has entered the reactor.

V15 - Control valve in the acid line L19 allows the acid to flow from AP2 through L21 through L19 into V14.

V16 - Control valve in the 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.

Current

Air

L27 through AR3 through L14 through V11 through L16 through P2 into V14.

L27 through AR2 through L26 through V17 through L25

into AP1 to move piston upwards.

Liquid

AP2 through L21 through V15 through L19 through P3 through P5 through SL2 through P6 through P4 through

V12 through L17 into R1.

Time

30 seconds or as needed to ensure AP2 has

completed his stroke.

Test valve repositioning method 2 (repositioning 2)

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

With the correct choice of antiflocculation agent stock concentration and the correct size of antiflocculation lines L9 and acid feed line L20, the proportions of acid and antiflocculation agent drawn into the acid pump AP2 will be such that it ensures a desired concentration of antiflocculation agent in the reaction mixture. Sufficient turbulence exists in L20, L21 and AP2 during the acid filling step to ensure sufficient dissolution of antiflocculating agent in the acid.

Main components involved

SL2 - Sample loop/about 10 cm 3 acid.

AP1 - Air driven piston for operation of the piston

in the acid pump/position one (acid fill) (1F).

AP1 - Positive displacement acid pump/position one (acid fill) (1F).

Wires involved

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

L14 - Air valve from the air supply line to valve V11.

L15 - Air line from valve V11 to port P1 i

the test valve V14.

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

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

L24 - Air line from valve V1 7 to the inside of

the stamp in AP1.

L26 - Air lines from the air supply line L27

to valve V17.

L27 - Air supply line.

Valves involved

Operating valves/ stiIling

V11 - Solenoid operated air valve/position one (testing) (1 S) .

V14 - Air operated sample valve/position one (sampling) (1S): Connects ports P5, P6, P7 and P8.

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

Control valves

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

V16 - Control valve in the acid feed line L20 allows acid to flow from L20 through L21 into AP2.

Pressure control valves

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

Current

Air

L27 through AR3 through L14 through V11 through L15 through P1 into V14.

L27 through AR2 through L26 through V17 through L26

into AP1.

Acid

L20 through V16 through L21 into AP2.

Antiflocculating agent

L9 through L20 through V1 6 through L21 into AP2. Time

5 seconds.

Note: Time not really important - a large excess of time (about 12 minutes for the described system) is available for the pump to fill and the valve to turn.

Ready-to-go method (ready-to-go 2)

The fifth method is another ready-to-start method (ready-to-start 2) whereby the sample valve waits to receive a sample from the filter circuit. It is identical to the first method (ready to go 1) and will not be given in detail again. Its 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 whereby a sample is collected from the filter circuit.

Main components involved

SL2 - Sample loop/initially filled with 10 cm 3 of acid

from last sample transfer method.

AP1 - Air driven piston for operation of the piston i

the acid pump/position one (acid fill) (1F).

AP2 - Positive displacement acid pump/position one (acid fill) (1F).

Wires involved

L14 - Air line from air supply line L27 to

the valve V11.

L15 - Air supply line from valve V11 to port P1 in test valve V14.

L22 - Liquid sample line from the filter system to the port

P8 in the test valve V14.

L2 3 - Sample line from port P7 to sample valve

V14 to the drain.

L24 - Air line from valve V17 to the inside of

the stamp in AP1.

L26 - Air line from air supply line L27 to

the valve V17.

L27 - Air supply line.

Valves involved

Operating valves/ position

V11 - Solenoid operated air valve/position one (sampling) (1S): Connects the air lines L14 and L15.

V14 - Air operated sample valve/position one (sampling) (1S): Connects ports P5, P6, P7 and P8.

V17 - Solenoid operated air valve/position one (acid fill)

(1F): Connects air lines L26 and L25.

Control valves

V15 - Control valve in the acid line L19 holds the acid

in line L19.

V16 - Control valve in the acid feed line L20 keeps the acid in the lines L2 0 and L21.

Pressure control valves

AR2 - Pressure regulating valve in air line L26.

AR3 - Pressure regulating valve in air line L14.

Current

Air

L27 through AR3 through L14 through V11 through L15 through P1 into V14.

L27 through AR2 through L26 through V17 through L24

into AP1.

Liquid

L22 through P8 through P5 through SL2 through P6 through P7 through L23.

Time

60 seconds or as needed to ensure complete flushing by filling the sample loop with a fresh one

liquid sample.

Ready to go method ( Ready to go 3)

The seventh method is a third ready-to-start method (Start-ready 3) whereby the sample circuit waits for the reactor circuit to receive the sample. It is identical to the first and fifth methods (Start Ready 1 and Start Ready 2) and will not be given in detail. The sample loop is filled with liquid instead of acid at this step.

Test valve repositioning method (Repositioning 3)

The eighth method is a third sample valve repositioning method (Repositioning 3) whereby the sample valve V14 is moved from position one (sampling) to position two (transfer). It is identical to the second method (Repositioning 1) and will not be given in detail. Its time is the same as Repositioning 1.

Acid transfer method ( Transfer 2)

The ninth method is another transfer method (Transfer 2) whereby the acid pump pushes 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 sample loop to clean the sample loop of any material that may have settled on the pipe material during the seventh method (Start Ready 3). This acid and residue will be removed from the system during the next sample collection method. It is identical in operation to the third method (Transfer 1) and will not be given in detail.

Test valve repositioning method (Repositioning 4)

The tenth method is a fourth repositioning method (Repositioning 4) whereby the sample valve V14 is moved from position two (transfer) to position one (sampling) and the acid pump AP2 is filled with acid and antiflocculation agent. It is identical to the fourth method (Repositioning 2) and its time is the same.

Reactor circuit

The reactor is shown in Figures 5 and 6 and the reactor circuit is shown in the lower left part of Figure 1.

As can be seen in Figure 5, the reactor R1 has a reactor space R2 which is delimited by a cover element R3, side walls R4 and a base R5. The cover element R3 has four ports: R6 for the exhaust gas from the reactor to the drain line, R7 for the washing water to the reactor, R8 both for the reactor gas from the reactor to the gas chromatograph and for gas under pressure to pressurize the reaction chamber, and R9 for the sample and the acid to the reactor. The base R5 defines the bottom R10 in the chamber R2. The bottom R10 is sloped towards the middle outlet valve V13 so that the reaction chamber R2 can be easily washed and drained after each reaction. The magnetic stir bar V13 provides turbulence and mixing of the reaction mixture. The base R5 rests on a pressure chamber R11 and the pressure in the chamber R11 is maintained by means of the rubber membrane R12 between the base R5 and the pressure chamber R11. Air enters the pressure chamber R11 through air line L1 and the air pressure keeps the valve V13 in its upper closed position to keep liquid in the reaction chamber R2. When the air pressure is released from the line L1, the valve V13 falls into its lower position so that the reaction chamber R2 can be drained. The liquid enters the outlet line L18 for drainage or treatment in another way.

The reactor circuit has the following components:

Main components

R1 - Reactor.

M1 - Drive device for magnetic stirring rod for reactor mixer.

Wires

L1 - Air line from valve V10 to reactor outlet pressure chamber R11.

L2 - Lead to gas chromatograph GC.

L2A - Line between the reactor gas line L6 and

the gas chromatograph GC.

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

L3 - Air line between the air supply line L27

and the wire L11.

L4 - Water supply line between the water supply and

IN

the port R7 in the reactor R1.

L5 - Outflow line from port R6 in the reactor

R1 to the drain.

L6 - Reaction gas line from line L13 to line L2A.

L7 - Air line between air line L14 and the stirring rod drive device M1.

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

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

L11 - Connecting line between air line L3 and meter line L12, and reactor gas line L6, air pressure line L8 and reactor line L13.

L12 - Meter line between the air line L3 and the connection line L11, and the meter protector G1 and the pressure gauge G2.

L13 - Reactor line between port R8 in reactor R1

and the meeting point for the reactor gas line L6, the reactor pressurization line L3 and the connection line L11.

L14 - Air line between the air supply line L27

and the valve V10.

L17 - Test line between the test valve V14 and the port

R9 in the reactor R1.

L18 - Outlet line from valve V13 in reactor R1.

Valves

Operating valves (solenoid operated)

V3 - Valve in air line L3. Two positions: Open;

close.

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

close.

V5 - Valve in the outflow line L5. Two positions:

Open; close.

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

V8 - Valve in reactor pressurization line L8. Two

positions: Open; close.

V10 - Valve between air line L14 and air line L1. Two positions: Open; close.

Operating valves (air operated)

V13 - Outlet valve in the reactor R1 between the reaction chamber R2 and the outlet line L18. It is operated by air pressure from line L1. Two positions : Closed - when the air is on; open when the air

is off.

Control valves

V12 - Control valve in the sample line L17 which prevents either the sample, the reaction gas or the air from entering

flow back through test lead L17.

Pressure control valves

AR1 - Pressure regulating valve in air line L1. AR3 - Pressure regulating valve in air line L14. AR4 - Pressure regulating valve in air line L3. AR5 - Pressure control valve in reactor pressurization line L10.

Repair valves (normally open, manually operable)

V7 - Repair valve in air line L7.

Gates

R6 - Port in the reactor R1 for the outflow line

L5.

R7 - Port in the reactor R1 for the water line L4.

R8 - Port in the reactor R1 for the reactor line L13.

R9 - Port in the reactor R1 for the test line L17. The operating sequence for the reactor is as follows:

(1) The reactor is cleaned:

(a) The reactor is drained.

(b) The reactor is filled with water.

(c) The reactor is drained again.

(d) The reactor is refilled with water.

(e) The reactor is drained again.

(f) The reactor is refilled with water.

(g) The reactor is drained again.

(2) The reactor is vented for 5 seconds and then sealed. (3) The acid and the sample are placed in the reactor and the reaction starts. (4) After about 11 minutes, pressurize the reactor using an accurate air pressure regulator. This is important if a direct relationship between gas chromatograph outlet and liquid concentration is to be achieved. The final reactor pressure should be approx. 0.14 kg/cm<2> above the highest total reactor pressure resulting from the sum of all the partial pressures or expected components or 1.83 kg/cm 2 above the ambient pressure. This is to compensate for the dependence of reactor pressure on liquid concentration, which would give an incorrect reading if there was no compensation.

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

(6) The reaction gas is transferred to the gas chromatograph. The time for transfer must be long enough to obtain a representative sample of gas in the sample loop SL1 in the gas chromatograph. This usually takes 40-50 seconds.

The cycle takes about 19 minutes, but will vary depending on the characteristics of each individual system.

Ready to go method ( Ready to go)

The first method for the reactor circuit is a ready-to-start method whereby the reactor waits to receive the sample. It usually only occurs at startup. The reactor contains whatever was present in it at shutdown. This can be an old reaction mixture, wash water, etc.

Main components involved

R1 - Reactor.

Wires involved

L1 - Air line from valve V10 to valve V13. L14 - Air line from air supply line L27

to 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 outflow line L5/closed.

V6 - Valve in reaction gas line L6/closed.

V8 - Valve in air pressure line L8'/closed. ;

V10 - Valve between air lines L14 and Li/open.

V13 - Outlet valve in reactor R1/closed.

Pressure control valves

AR1 - Pressure regulating valve in air line L1.

AR3 - Pressure regulating valve in air line L14.

Current

Air

L27 through AR3 through L14 through V10 through L1

through AR1 into R11 to keep V13 closed.

Venting method ( Venting)

The second method is a venting method. The reactor is vented when the sample valve V14 is repositioned from position one (sampling) to position two (transfer). This allows the pressure in the reaction chamber to reach atmospheric pressure prior to sample injection. The gas in the reactor contains at most small amounts of carbon dioxide and hydrogen sulphide.

Main components involved

R1 - Reactor.

Wires involved

L1 - Air line from valve V10 to chamber R11

in the reactor R1.

L5 - Vent line from port R6 in reactor R1

to the atmosphere.

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 vent line L5/open.

V6 - Valve in reaction gas line L6/closed.

V8 - Valve in pressure line L8/closed.

V10 - Valve between air lines L14 and L1/open to keep outlet valve V13 in reactor R1 closed.

V13 - Outlet valve from reactor R1/closed.

Pressure control valves

AR1 - Pressure regulating valve in air line L1.

AR3 - Pressure regulating valve in air line L14.

Current

Air

R1 through R6 through V5 through L5 to outflow line to drain.

L27 through AR3 through L14 through V10 through L1

through AR1 into R11 to keep V13 closed.

Time

5 seconds as needed for air in the reactor to reach

equilibrium with atmospheric pressure. In the venting method prior to the introduction of the sample, the venting method must end prior to the introduction of the sample into the reactor for

to ensure that no reaction gas products are lost.

Drainage method (Drainage)

The third method is a reactor drainage method. During the washing cycle, the reactor is drained either for reaction products or for washing water.

Main components involved

R1 - Reactor.

Wires involved

L1 - Air line from valve V10 to outlet valve

V13 in reactor R1.

L3 - Air line from air supply line L27 to

connecting wire L11.

L11 - Connection cable from air line L3 to

the reactor line L13.

L13 - Reactor line from connection line L11 to

port R8 in the reactor R1.

L18 - Outlet line from reactor R1.

L27 - Air supply line.

Valves involved

Operating valves/ position

V3 - Valve in air line L3/open.

V4 - Valve in the water line L4/closed.

V5 - Valve in outflow line L5/closed. V6 - Valve in reaction gas line L6/closed. V8 - Valve in Air pressure line L8/closed. V10 - Valve between air lines L14 and L1/closed to release air from line L1 to open valve V13.

V13 - Outlet valve in the reactor R1/open to drain the reactor through the outlet line L18.

Control valves

V12 - Control valve in test line L17 prevents air from escaping through test line L17.

Pressure control valves

AR4 - Pressure regulating valve in air line L3.

Current

Air

No current in wire L1.

L27 through AR4 through L3 through V3 through L11

through L13 through R8 into R1.

Liquid

R1 through V13 through L18.

Time

10 seconds or as needed to drain the reactor

complete.

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

R1 - Reactor

Wires involved

L1 - Air line from valve V10 to chamber R11

in the reactor R1.

L4 - Water line between the water supply and port R7

in the reactor R1.

L5 Vent line from port R6 in reactor R1

to the atmosphere.

L14 - Air line from air supply line L27 to

the valve V10.

L27 - Air supply line.

Valves involved

Operating valves/ position

V3 - Valve in air line L3/closed.

V4 - Valve in water line L4/open.

V5 - Valve in outflow line L5/open. V6 - Valve in reaction gas line L6/closed. V8 - Valve in air pressure line L8/closed. V10 - Valve between air lines L14 and L1/open.

V13 - Outlet valve in reactor R1/closed.

Cont ro Unexpected i ler

V12 - Control valve in test line L17 prevents air from entering the test circuit.

Pressure control valves

AR1 - Pressure regulating valve in air line L1.

AR3 - Pressure regulating valve in air line L14.

Current

Air

R1 through R6 through V5 through L5 to outflow line to drain.

L27 through AR3 through L14 through V10 through L1

through AR1 into R11 to keep V13 closed.

Water

L4 through V4 through R7 into R1.

Time

20 seconds or as needed for on sufficient

way to fill the reactor with water.

Sample transfer method ( Transfer)

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

Main components involved

R1 - Reactor.

Wires involved

L1 - Air line from valve V10 to outlet valve V13 in reactor R1.

L14 - Air line from the air supply line'L27

to valve V10.

L17 - Test lead from test circuit to port R9 i

the reactor R1.

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 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 L14 and L1/open.

VI3 - Outlet valve from reactor R1/closed.

Control valves

V12 - Control valve in sample line L17 prevents i. the sample or reaction gases from returning through line L17.

Pressure control valves

AR1 - Pressure regulating valve in air line L1.

AR3 - Pressure regulating valve in air line L14.

Current

Air

L27 through AR3 through L14 through V10 through L1

through AR1 into R11 to keep V13 closed.

Liquid

SL2 through V14 through L17 through V12 through R9

into R1 .

Acid

AP2 through L21 through V15 through L19 through V14 through SL2 through L17 through V12 through R9 into

R1.

Time

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

Reaction method ( Reaction)

The seventh method is the reaction method. The reaction between the acid and the sample takes place in the reaction chamber. The! are two steps in the reaction method, reaction 1 and reaction 2. Reaction 2 is the continuation of reaction 1 after pressure has been applied to the reaction chamber and is identical to reaction 1.

Main components involved

R1 - Reactor

Wires involved

L1 - Air line from valve V10 to outlet valve

V13 in reactor R1.

L14 - Air line from air supply line L27 to

the valve V10.

L27 - Air supply line.

Valves involved

Operating valves/ stiIling

V3 - Valve in air line L3/closed.

V4 - Valve in the water line L4/closed.

V5 - Valve in outflow line L5/closed.

V6 - Valve in reaction gas line L6/closed.

V8 - Valve in air pressure line L8/closed.

V10 - Valve between air lines L14 and L1/open.

V13 - Outlet valve in reactor R1/closed.

Control valves

V12 - Control valve in test line L17 prevents the reaction gas from entering the test circuit

through the test lead L17.

Pressure control valves

AR1 - Pressure regulating valve in line L1.

AR3 - Pressure regulating valve in air line L14.

Current

Air

L27' through AR3 through L14 through V10 through L1

through AR1 into R11 to keep V13 closed.

Time

The total time for the reaction is about 15 minutes. It is divided into two parts before and after pressure is applied.

Pressure setting method ( Pressure)

The eighth method is a pressure setting method. Eleven minutes after the reaction begins, air pressure is applied through a precise regulator to the reaction chamber to maintain a constant final reactor pressure.

It was decided to pressurize eleven minutes into the reaction because at this time: 1) the reaction is substantially complete and no further pressure rise is expected; 2) four minutes of the reaction time remain, which allows the air which has been added in the pressurization step to be well mixed with the reaction gases to obtain a homogeneous reaction gas sample at the end of the reaction.

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

The pressurization stage was added in response to observations made during the development of the system. In order to make valid comparisons between samples, it is necessary to have a constant end gas pressure. If this is not done, the experience from previous attempts will be repeated. In these experiments, the final gas pressure inside the reactor was allowed to remain whatever pressure existed due to the release of carbon dioxide and hydrogen sulfide from the reaction. This pressure varied according to the amounts of sodium carbonate and sodium sulphide in the liquid sample. It was observed that although an increase in sodium carbonate concentration in the liquid caused an increase in the carbon dioxide peak area developed by the gas chromatograph, the relationship was not directly proportional. Furthermore, the carbon dioxide peak area was affected by the amount of Na2S in the liquid, resulting in erroneous sodium carbonate measurements due to changes in the sodium sulfide concentration in the liquid. The measurement of sodium sulphide in the liquid was affected in the same way.

After this was recognized, it was decided to adjust the pressure so that there would be the same 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 upon completion of the reaction. 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 that existed in the reactor will not exceed 1.69 kg/cm 2. By adding additional air to achieve a pressure of 1.83 kg/cm 2, it is possible to obtain gas samples each containing a constant total number of moles of gas. The air has essentially no carbon dioxide or hydrogen sulfide and does not affect the readings for carbon dioxide or hydrogen sulfide developed in the reaction. The peak areas for carbon dioxide and hydrogen sulphide will then be directly proportional to the concentrations of sodium carbonate and sodium sulphide, respectively, in the liquid. Furthermore, sodium carbonate measurements will not be affected by the sodium sulfide concentration in the liquid, nor will the sodium sulfide 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

R1 - Reactor.

Wires involved

L1 - Air line between the valve V10 and the outlet valve V1 3 in the reactor R1.

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

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

L11 - Connection line between reactor pressurization line L8 and pressure gauge line L12.

L12 - Pressure gauge line from connection line L11

to gauge protector G1 and air pressure gauge G2.

L13 - Reactor line between reactor pressurization line L8 and port R8 in reactor R1.

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 outflow line L5/closed.

V6 - Valve in reaction gas line L6/closed.

V8 - Valve in reactor pressurization line L8/open. V10 - Valve between air lines L14 and Li/open.

V13 - Outlet valve in reactor R1/closed.

Control valves

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

through the test line.

Pressure control valves

AR1 - Pressure regulating valve in air line L1.

AR3 - Pressure regulating valve in air line L14. AR5 - Pressure control valve that has a precision of - 0.014 kg/cm^ in the reactor pressurization line

L10.

Current

Air

L27 through AR2 through L14 through V10 through L1 through AR1 through R11 to keep V13 closed.

L27 through AR5 through L10 through V8 through L8

through L13 through R8 into R1.

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 sufficient time to allow a representative sample to be received in the sample loop SL1 of the gas chromatograph.

Main components involved

R1 - Reactor.

Wires involved

L1 - 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 port R8 in reactor R1

and the reaction gas line L6.

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 outflow line L5/closed. V6 - Valve in reaction gas line L6/open. V8 - Valve in air pressure line L8/closed. V10 - Valve between air lines L14 and L1/open.

V13 - Outlet valve in reactor R1/closed.

Control valves

V12 - Control valve in test line L17 prevents reaction gas from entering the test circuit

through the test lead L17.

Pressure control valves

AR1 - Pressure regulating valve in air line L1.

AR3 - Pressure regulating valve in air line L14.

Current

Air

L27 through AR3 through L14 through V10 through L1

through AR1 into R11 to keep V13 closed.

Reaction gas

R1 through R8 through L13 through V6 through L6 through L2A to gas chromatograph.

Time

40 seconds or as needed to ensure that the gas chromatograph has received a representative reaction gas sample.

Stop Transfer Method ( Stop)

The tenth method is the stop transfer method. The reaction gas valve V6 is closed. Allow time for the pressure in the gas chromatograph system to equalize.

Main components involved

R1 - Reactor.

Wires involved

L1 - 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.

Valves involved

Operating valves/ position

V3 - Valve in air line L3/closed.

V4 - Valve in the water line L4/closed.

V5 - Valve in outflow line L5/closed.

V6 - Valve in reaction gas line L6/closed.

V8 - Valve in air pressure line L8/closed.

V10 - Valve between air lines L14 and L1/open.

V13 - Outlet valve in reactor R1/closed.

Control valves

V12 - Control valve in the sample line L17 prevents reaction gas from entering the sampling system through the sample line.

Pressure control valves

AR1 - Pressure regulating valve in air line L1.

AR3 - Pressure control valve in air line L14.

Current

Air

L27 through AR3 through L14 through V10 through L1

through ART into R11 to keep V13 closed.

Time

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

Drive device for magnetic stirring rod

The liquid in the reactor chamber R2 is stirred by the mixing rod R13 in the reactor and rests on the drain valve V13 at the bottom of the reactor. This rod is magnetically connected with and rotated by the drive device M2 for the magnetic stirring rod in the chamber M1.

The drive device for the magnetic stirring rod is shown in figures 7 and 8. A powerful horseshoe magnet M3 faces upwards towards the stirring rod R13. The horseshoe magnet M3 is mounted on

a rotating plate M4. Any type of mounting can be used. It can be fixed to the plate M4 with epoxy or another type of adhesive. It is shown mounted in an arc-shaped recess in the upper surface of plate M4.

The plate M4 rests on a base M5. Both the rotating plate M4 and the base M5 are shown as circular in cross-section. The base M5 has an upper flat, horizontal bearing surface M6 around its periphery. A circular recessed part M7 is located within the periphery. The recessed part M7 also has a flat, horizontal surface below the surface M6 and a vertical side wall extending from its surface to the bearing surface M6. A circular further recessed part M8 is located within the part M7. The surface of the recessed part M8 is also flat and below the surface of the part M7. The part M8 also has a vertical side wall extending from its surface to the surface of the part 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 holds a nylon and glass ball bearing M9. The plate M4 has a cylindrical shaft M10 which fits and rotates in the bearing M9. A motor part M11 in the plate M4 fits and rotates in the recessed part M7 in the base M5. There is a clearance between the motor part M11 and the surfaces of the recessed part M7. The motor part M11 is circular and concentric with both the cylindrical shaft M10 and the outer circular periphery M12 of the plate M5. The periphery M13 of the engine part M11 is broken by radial slits or incisions M14 at equal distances from each other.

An air duct M15 runs through the base M5 under the recessed part M8. Two secondary air passages M16 extend from air line M15 at an angle upwards to 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 rotate the disc M4. The outlets of the secondary air passages M16 are shown as 180° apart on opposite sides of the air line M15. The outlets can be parallel to a tangent to the periphery for countersunk part M7 or angled towards the periphery. The outlets can be, as shown, close to the periphery of recessed part M7.

Air from air line L7 passes through line M15 and passage M16 to impinge on the walls of the radial slots M14 to rotate the disc M4. The 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 opening between the base and the rotating plate.

The rotation of the plate M4 rotates the magnet M3. The rotating magnet M3 rotates the stirring rod R13.

The drive device for the magnetic stirring rod has the following components and operation:

Main components involved

M1 - Magnetic stirrer-mixing chamber.

M2 - Drive for magnetic stir bar mixer.

Wires involved

L7 - Air line from air inlet L14 to the chamber

M1.

L14 - Air line from air supply line L27 to

air line L7.

L27 - Air supply line.

Valves involved

Pressure control valves

AR3 - Pressure regulating valve in air line L14.

Repair valves

V7 - Repair valve in air pressure line L7.

Current

L27 through AR3 through L14 through V7 through L7

into M1 for operation of M2.

It will be understood that the drive device for the magnetic stirrer can also be shut off depending on whether the reactor chamber is filled or empty by changing valve V7 to a solenoid operated on/off valve and operating it on the same cycle as valve V10 which controls the outlet valve V13 to the reactor. Valves V7 and V10 would open and close together.

Gas chromatograph system

In the reactor, the 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 a gas chromatograph. The chromatograph emits a continuous analog signal corresponding to the flow rate of the 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 liquids of known concentration allows the carbon dioxide and hydrogen sulphide measurements to be converted directly into a determination of sodium carbonate and sodium sulphide in the liquid sample.

The analysis process takes around four minutes for both carbon dioxide and hydrogen sulphide. It may only be necessary to analyze for carbon dioxide in the green liquor and the caustic acid white liquor samples. This would reduce the analysis time for these samples to one and a half minutes.

The gas chromatograph can be used for successive analysis of the reaction gas from a number of reactors. For a slurry/causticizer line, three liquid samples should be analyzed, resulting in a three-reactor analyzer system. For this reason, the valve V1 is a four-way valve which has four inlets from the reactors or other external sources and an outlet to the gas chromatograph. It cycles through the four positions until it is at the correct position for receiving reaction gas from the selected reactor.

It requires about five seconds to move from one position to the next. A further five seconds are available for electronic control of the valve's position.

The internal details of a gas chromatograph will not be stated. It represents a standard equipment and its details, J other than that it is given time to review its procedure and the results of its analysis are not important here. There are a number of valves in the gas chromatograph which ensure that the sample loop is filled, that the gas sample is fed to the analysis column, and that the sample loop and the analysis column are cleaned and backwashed. This discussion will not include the standard helium purge and backpurge that occurs in the gas chromatograph itself because these are normal functions of the instrument. It will only be noted that these valves and operations exist in any gas chromatograph and will only give a general overview of the process and apparatus. The only methods that will be described in detail are the external methods.

The chromatograph circuit has few parts. These are: Components

Main components

GC - Gas chromatograph/two positions: Position one (ready to start) is used in three different methods - method 1A (circulation); method 1B (gas transfer);

method 1C (purification) - position two (analyses).

SL1 - Sample loop for the gas chromatograph.

Wires

L2 - Lead to the gas chromatograph.

L2A - Line from reaction gas line L6

to the gas chromatograph GC.

L2B - Line from calibration gas line L7

to the gas chromatograph line L2A.

L2C - Line from the air pressure line L10 to the gas chromatograph line L2B.

L6 - Reaction gas line from the reactor R1 to the gas chromatograph line L2A.

L7 - Calibration gas line from the calibration gas supply 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 V1

for operation of the valve.

Valves

Operating valves

V1 - Valve in the gas chromatograph line L2A. Four positions for bringing sample into 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 control valve in air line L14.

AR5 - Pressure regulating valve in high-pressure air line

L1 0 .

In the sequence of operations, the gas chromatograph takes a gas sample into the sample loop SL1, analyzes the gas sample, purges the sample from the system and backflushes the system. It then waits for the supply of a new sample.

Ready to go method ( Ready to go)

The first method is a ready-to-go method. The gas chromatograph is waiting for a sample from the reactor circuit.

Main components involved

GC - Gas chromatograph/position one (ready to start) Valves involved

Operating valves/ position

V1 - Valve in gas chromatograph line L2A/position four (closed). This is an example. The valve can be in any position at startup. It will depend on the valve position when the system was switched off.

V2 - Valve in high-pressure air line L2C/closed.

V6 - Valve in reaction gas line L6/closed.

V7 - Valve in calibration gas line L7/closed.

Current

No flow of reaction gases.

Repositioning method ( Repositioning)

The second method is a repositioning method (re-positioning). The valve V1 is repositioned around its four positions until it is aligned with the right reactor. It moves in the same direction, either clockwise or counterclockwise, taking five seconds to move. A further five seconds are allocated for the system to check the position of the valve. If its position 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.

Ready to go method ( Ready to go 2)

The third method is a new ready-to-start method (Start-ready 2) whereby all the valves remain in their positions until the reactor circuit is ready for transfer of a gas sample.

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

The fourth method is a reaction gas transfer method. The gas chromatograph is valve controlled internally so that the reactive ion gas passes through the sample loop and then to the vent to the drain. The time for this transfer is long enough for a representative sample to be received. The initial gas entering the sample loop SL1 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 the previous air purification method. Air must be purged from these lines and the sample loop to ensure that a representative sample of reaction gas is obtained. It takes time to achieve a stable sample in the sample loop. Consequently, the time will vary depending on several factors affecting the gas transfer to the sample loop. These factors may include the arrangement and dimensions of the pipe material between the reactor and the sample loop, the sample purification conditions, and the conditions of pressure, gas composition, etc. existing in the reactor itself at the time of gas transfer. The time is usually between 40 and 60 seconds.

Main components involved

GC - Gas chromatograph/method 1A (Gas transfer).

SL1 - Sample loop for the gas chromatograph.

Wires involved

L2A - Gas chromatograph line from reaction gas line L6 to sample loop SL1.

L6 - Reaction gas line from the reactor to line L2A.

L13 - Reactor line from port R8 in reactor R1 to line L6.

Valves involved

Operating valves/ position

V1 - Valve in gas chromatograph line L2A/position one

(reactor circuit one).

V2 - Valve in high-pressure air line L2C/closed.

V6 - Valve in reaction gas line L6/open.

V7 - Valve in calibration gas line L7/closed.

Current

Reaction gas

R1 through R6 through L13 through V6 through L6 through L2A through V1 through SL1 to drain.

Time

40 seconds or as needed to achieve one

representative sample of reaction gas in the sample loop. The time of 40 seconds is representative. The length of time is the time it takes to achieve a representative

sample of reaction gas in the sample loop SL1.

Stop test method ( Stop)

The fifth method is a stop sampling method whereby the reaction gas to the gas chromatograph is stopped and the gas pressure in the sample loop is made equal to atmospheric pressure.

Main components involved

GC - Gas chromatograph/method 1B (gas transfer). SL1 - Sample loop in the gas chromatograph.

Valves involved

Operating valves/ position

V1 - Valve in 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.

Current

No electricity.

Time

5 seconds or as needed for equality of conditions in test loop.

Analysis method ( Analyse)

The sixth method is an analysis method whereby 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 changes from position two (transfer gas) to position three (analyses).

Main components involved

GC - Gas chromatograph/position two (analyses).

SL1 - Sample loop in the gas chromatograph.

Valves involved

Operating valves/ position

V1 - Valve in 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.

Current

Helium through test loop leads reactor gas through

column past the detector out outflow.

Time

4 minutes depending on elution time for carbon dioxide

and hydrogen sulfide through the column. The time may be longer or shorter than 4 minutes depending on the length of the column, column packing characteristics, helium flow rate, etc. The time will be one and a

half a minute if the analysis is only of carbon dioxide. Again, the time can be longer or shorter than one and

half a minute due to other factors.

Sample purification method ( Purification)

The seventh method is a gas cleaning method whereby high-pressure air is used to clean the sample from the sample loop and the lines between the sample loop and the reactor.

Main components involved

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

SL1 - Sample loop for gas chromatograph.

Wires involved

L2 - Gas chromatograph line from high-pressure air line L10 to sample loop SL1. Includes wires L2A, L2B and L2C.

L10 - High pressure line between air supply line

L27 and the gas chromatograph line L2.

L27 - Air supply line.

Valves involved

Operating valves/ position

V1 - 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.

Current

Air

L27 through AR5 through L10 through V2 through L2

through SL1 to outflow to drain.

Time

1 minute 5 seconds or as needed to sufficiently clean the wires and loop.

During the time that the liquid sample in reactor 1 completes its reaction, the valve V1 would move to positions 2 and 3, and the gas chromatograph would analyze the gas samples

from the second and third reactors.

Data collection and analysis

The gas chromatograph output circuit develops voltage "spikes" corresponding to the appearance of each gas component at the gas chromatograph's detector. The time interval (from the start of the analysis) during which each component (air, carbon dioxide and hydrogen sulphide) will pass through the detector,

is a characteristic for each component gas. This time interval during which each component appears at the detector is very reproducible and easy to establish for each gas. The gas chromatograph output circuit develops a continuous 0-1 volt analog signal proportional to the flow of gas through the detector. During the time interval each component passes through the detector, a voltage "peak" develops in response to the behavior of the component. Figure 9 is a graphical representation of G.C. voltage output during a gas analysis resulting from a typical green liquor sample. Each component of the gas sample is identified and the time interval during which it appears is noted. The voltage "peaks" for each component can be easily observed from the figure. 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, the carbon dioxide and hydrogen sulfide integrated stresses are proportional to the sodium carbonate and sodium sulfide stresses in the liquid. The integrated peak areas for C02 and E^ S are therefore a measure of the ^2003 and Na2S concentrations in the liquid sample.

The data acquisition circuit enables the carbonate/sulphide analyzer to convert the voltage peaks developed by the gas chromatograph into values corresponding to the concentrations of Na2C02 and Na2S in the liquid. The data acquisition circuit consists of the following main components:

GC - Gas Chromatograph Output Circuit.

VCO - Voltage-to-frequency converter.

M - Microcomputer.

A diagram of the data acquisition circuit is shown in Figure 10. The associated wiring and components required to join the main components are known and are therefore not illustrated.

To calculate the concentration of Na-^CO^ and Na,,S in the liquid sample, the CO,,- and H,,S voltage peaks must be integrated. There are many methods that can be used to achieve the integration. The preferred method of peak integration is to use a voltage-to-frequency converter (VCO) to convert the 0-1 volt G.C. the output signal to a 0-10,000 HZ frequency signal. The continuous series of electronic pulses thus developed is used as input to a digital microcomputer. The time intervals corresponding to the appearance of the CO,,- and H,,S peaks are programmed into the microcomputer software.

During the separate time intervals corresponding to the peak

for each component, the microcomputer counts the total number of pulses developed by the VCO for the peak period. The number of pulses thus counted is a measure of the peak area. The thus obtained peak area measurements for CO^ and H2S are proportional to the concentrations for Na2CO. and Na2S, respectively, in the liquid sample.

The microcomputer allows additional calibration

of the analyzer by providing the ability to convert the pulse count measurements into direct determinations of Na^O^ and Na,,S in the liquid. The pulse count is directly proportional to the concentration of the chemical in the liquid. By analyzing several liquids with known concentrations and measuring the pulse counts developed from these known liquids, one can easily establish correct conversion factors for converting the pulse counts into concentration measurements. These conversion factors are then stored in the microcomputer program equipment. The conversion factors are applied to the pulse counts for all subsequent liquid samples to provide direct determinations of Na2CO.j and Na,,S in the liquid. The liquid concentrations can be given as printed data or converted into analogue signals for use as input to control devices. Methods for developing such outputs are varied and are well known.

Reactor temperature measurement system

It has been observed that the measurement of sodium carbonate and sodium sulfide developed by the carbonate/sulfide analyzer is affected by the temperature at which the reaction takes place. The reaction temperature is mainly controlled by the temperature inside the analyzer cabinet. The measurements developed by the analyzer vary in direct proportion to the cabinet temperature. As the enclosure temperature increases, the resulting measurements of sodium carbonate and sodium sulfide will increase accordingly. This phenomenon must be compensated for if accurate measurements are to be obtained for all samples despite reactor temperature variations.

It has been decided that the best method for eliminating measurement errors due to reactor temperature variations is to use a correction factor for each measurement based on the cabinet temperature during the reaction. To determine the correct factor for each measurement, the enclosure temperature is measured at the completion of each reaction. The appropriate correction factors, based on cabinet temperature, are then automatically calculated for each sample and applied to the "raw" or "uncorrected" values developed by the gas chromatograph. This strategy has been found to be an effective method for eliminating errors caused by reaction temperature variations.

It has been found that for every 1°C deviation from a reference temperature, the G.C. measured area for ^200^ increase or decrease 0.4% and the G.C. measured area for Na2S increase or decrease 0.7%. The correction for Na2C0^er: and for Na2S is:

CA = corrected area

MA = G.C. measured area

Two = reference temperature

T = real temperature of gas from reactor As an example, if the reference temperature is 30°C and the real temperature is 27°C, then applies to Na2CC>2

and for Na2S

The temperature measurement system uses a resistance temperature detector (RTD) mounted inside the cabinet, and a relay that closes to ensure that the detector can be subjected to sampling by the analyzer data acquisition system. The relay closes to ensure sampling of the detector immediately upon completion of the 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 signature is converted to a temperature measurement in the data acquisition software.

A resistance temperature detector has been found to be the most suitable temperature measuring device. The detector element has an electrical resistance that varies directly with temperature. This resistance can easily be measured electronically and can easily be converted into a temperature reading because the calibration of these elements is well documented. Other devices, such as thermocouples or thermistors, which have electrical characteristics that vary as a function of temperature, may also be used in this application.

Construction materials

All materials are selected to ensure maximum serviceability and resistance to the effects of heat, pressure and the corrosive properties of the liquid and gas streams. The following materials have been found to be the best for the specific applications listed below: The reactor top and base is made of P.V.C.(Poly-Vinyl Chloride) The accessories on top of the pump are P.V.C.The mounting plate for all solenoids, etc. is P.V.C.The drive device for the magnetic stirrer is P.V.C.

The reactor cylinder and the acid pump cylinder are made of glass.

All pipe materials that are in direct contact with acid or the gases are made of Teflon, while all other pipe materials are made of nylon. All connections that are in direct contact with acid or the gases are made of nylon. The connection between the reactor gas and the gas chromatograph and the outflow solenoids is made of Teflon. All control valves are made of Teflon. The test loop is made of nylon.

The acid pump piston is Teflon coated with 316 S.S.

(stainless steel). The couplings that come into indirect contact with gases or those that are flushed with air or water are of 316 S.S. All fittings, piping, valves, columns, etc. in the gas chromatograph are of 316 S.S. The gas isolation valve mounted in front of the gas chromatograph is of 316 S.S. The air, water, pressurization and purge solenoids are 304 S.S.

All connections on the air and water lines located on the inlet sides of the solenoid or regulators are made of brass. All regulators are made of aluminium. The liquid/acid test valve is of Hastalloy C.

Operation

In a total system, these circuits will operate together. The exact operation will depend on the plant's configuration. A typical operation for a reactor circuit is shown in the following table. In this table, the operating valves, the valve positions - open (0), closed (C) or position (1, 2) -, the change of position (<*>), and the time, are given. For an analyzer using multiple reactor circuits, the start-up time of each circuit would be staggered, thereby resulting in no overlap of gas chromatograph operation. Otherwise, the logic and sequencing of each circuit will generally be identical, although minor modifications may be made to each individual reactor circuit in response to differences in fluid strength or other properties without adversely affecting overall system operation.

Continues Continues Continues

Use

Figures 11, 12 and 13 are schematic diagrams showing the use of the apparatus in the causticization system.

Control loop 1 seen in Figure 11 describes the use of the analyzer with regard 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 plant liquid line ML1 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 an additional line in this diagram. It is line L40 that leads part of the thin washing water into the plant liquid line ML1.

The line L28/2 9 denotes two lines, L29 which leads the liquid from the plant liquid line ML1 to the reactor system RS1 and L28 which returns the liquid from the reactor system RS1 to the plant liquid line ML1. 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 Figures 1-3. Line L2 leads the reaction gas from the reactor system RS1 to the gas chromatograph/analyser GC/A in which the gas is analyzed for carbon dioxide (resulting from sodium carbonate in the liquid) and hydrogen sulphide (resulting from sodium sulphide) as described above. The analyzer, which uses the carbon dioxide analysis, outputs a signal through control line CL1 to the control device that operates valve V40 to increase or decrease the amount of thin wash flowing through line L40 into ML1 to maintain a constant sodium carbonate concentration in the green liquor going to the slurryer .

The hydrogen sulphide analysis has several applications. It is an indication of the reduction efficiency of the recovery digester. The sodium sulphide concentration can be given to the reboiler operator to confirm to him that the reduction efficiency is good or to give him the opportunity to make corrections to improve the reduction efficiency. It is also an indication of the potential efficiency of the causticization operation. As the concentration of sodium carbonate or sodium sulphide in the green liquor increases, the efficiency of the caustic operation decreases. This will give the operator information about the caustic reaction and what the green liquor is going through and allow the caustic operator to take corrective action.

The second control loop in this system is shown in Figure 12. This loop controls the balance of green liquor and lime, and actually controls the entire slurrying operation. A "clear" liquid sample is taken from the calcium carbonate sludge separator at either the slurryer or the first causticizer. This "clear" liquid is then filtered to remove any remaining calcium carbonate sludge. The sodium carbonate and sodium sulfide concentration in this filtered liquid is then measured in GC/A from the reaction gas from the second reactor system, RS2. The control loop logic will contain a reference value for the desired sodium carbonate concentration in the liquid. This reference value for Na2C02_concentration will, as shown by plant experience, result in the best combination of high Na2C03 to NaOH conversion efficiency, low Na2C03 "dead load", and acceptable sludge settling properties. The loop will then control the slurry operation via mass flow of sodium carbonate to the slurry in order to thereby maintain and control this concentration of Na^O^ in the liquid leaving the slurry. There are two ways to control 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 which the inventors consider to be significantly better, is shown in Figure 12. In this method, the amount of sodium carbonate in the green liquor is controlled by 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 the sodium carbonate, is then sent through control line CL2 to the control device that operates valve V41 to increase or decrease the amount of green liquor flowing through ML1 into slurryer S.

The measurement of the chemical concentrations in the white liquor is taken from the line between the clear white liquor 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 amount of sodium hydroxide in the white liquor must be determined indirectly. There are three elements of information that must be combined to obtain the sodium hydroxide concentration in the white lye. 1. The sodium carbonate concentration in the white liquor; 2. The sodium carbonate concentration in the green liquor; 3. The sodium hydroxide concentration in the green liquor. Measurements 1 and 2 are used to determine the amount of carbonate

in the green liquor which, in the slurry/caustic operation, has

been converted to sodium hydroxide in the white liquor. The difference between the amount of Na2C03 entering the system with the green liquor and the amount of Na2C03 leaving with the white liquor is the concentration of NaOH that has been formed in the white liquor due to the causticization reaction. All chemical concentrations are expressed on a sodium oxide (Na2O) basis. 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 accounted for. This source of NaOH in the system is relatively stable - a periodic (every eight hours) determination of NaOH in the green liquor can be made manually by an operator and entered into the analyzer software.

The determination of NaOH in the green liquor can be made 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 developed by recausting is the amount of NaOH that has entered together with the green liquor. It is recommended that the NaOH material in the green liquor be determined by the indirect method, which has the advantage of reducing errors caused by time delays in the process. The amount of NaOH associated with the green liquor is then stored in the microprocessor memory until updated with another titration. This value is used to update each subsequent white liquor sodium hydroxide determination.

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

NaOH (white liquor) = Na2C03(green liquor) - Na2C03(white liquor)

+ NaOH (green 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 when this is necessary, usually every 8 hours. An up-to-date, complete analysis of clarified white liquor (determination of sodium hydroxide, sodium sulfide and sodium carbonate) is provided to the operator of the digester or the digester process computer

every 12-19 minute.

The system software must also take into account the time delays in the slurrying, causticizing and clarifying operations in order to correctly determine the current NaOH concentration in the white liquor. This will determine the amount of chemicals to be added to the digester to control the digestion process.

Cascaded management options

In many applications it will be sufficient and desirable to utilize carbonate/sulphide analyzer measurements as the primary input to process control devices. In some applications, however, it may be advantageous to control the process directly with a measuring device which provides a more immediate, but less accurate (in terms of sodium carbonate concentration) response to process changes. If these devices are used, measurements from the carbonate/sulphide analyzer should be used as reference value control signals for the primary control devices. This control system of the "cascaded" type will greatly improve the accuracy of the primary control measuring devices and improve control of the process.

Several measuring devices such as conductivity probes, density meters, etc., provide rapid response to process changes. However, these devices provide only indirect measurements of sodium carbonate concentration - they respond 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 determinations of sodium carbonate concentration and less accurate control of the process than could be achieved if sodium carbonate were measured directly. However, the changes that affect the calibration of these devices when measuring the sodium carbonate concentration take place slowly; certainly longer than the 15-20 minute sampling period developed by the carbonate/sulfide analyzer.

The direct measurements of sodium carbonate developed by the carbonate/sulphide analyzer can be used as a reference value control input to each primary control device. This practice will have the effect of regulating the calibration of the primary device (conductivity probe, density meter, etc.) every 15-20 minute so that it is an accurate indicator of Na2CO.j concentration despite the previously mentioned variations in the ratio for Na2C03/total chemicals. A cascaded management strategy of this type will have the advantage that it has both an accurate method for determining sodium carbonate concentrations in the process and the ability to react immediately to changes in the process.

This is illustrated in figure 14. The main items are the dissolution tank DT, the green liquor clarifier GLC, the green liquor pump GLP, the slurry S and the first causticizer C1. Plant liquid line ML1 carries green liquor from dissolution tank DT to the green liquor clarifier GLC, and plant liquid line ML2 carries green liquor from the green liquor clarifier GLC to. the slurryer S. The main line L42 for thin wash solution leads weak thin wash solution to lines L40 and L41.

The thin wash solution in line L41 is used to dissolve the melt in the solution tank DT. The amount of thin wash solution that goes from the solution tank DT through line L41 is controlled by valve V41. The amount of thin wash solution is determined by the density of the green liquor from the solution tank DT. This is monitored in plant line ML1 by the density meter DM1. The signal from the density meter DM1 is fed through control line CL1 to the valve controller CN1. Valve V41 is controlled by CN1 with a signal that passes through control line CL2. This is a standard local control loop in which a local direct measurement is used to monitor the process conditions.

Figure 14 also illustrates the use of local conditions to monitor and control the amount of thin wash solution entering ML2 to maintain the carbonate level in the green liquor. In this case, however, the gas chromatograph/analyzer is used to determine the reference values for this local control.

The valve V4 0 is used to control the flow of thin wash solution in line L42, which is the amount of thin wash solution that will enter the plant liquid line ML2. This is controlled locally using a density meter DM2 which sends a signal through control line CL3 to the control unit CN2. CN2 operates the control valve V40 to increase or decrease the flow of thin wash solution to maintain the density in ML2 at a specified level. However, the density of the liquid is not a direct indication of sodium carbonate in the liquid. A sample of the density controlled liquid from ML2 is taken and analyzed for sodium carbonate concentration by the reactor system RS1 and the gas chromatograph/analyser unit GC/A. This direct determination of sodium carbonate is used to send a reference value signal through control line CLS to CN2 to adjust the density reference value so that the density more accurately reflects the sodium carbonate concentration in the liquid.

Claims (39)

1. Procedure, characterized in that it includes clarification of pulp factory green liquor, transporting said clarified green liquor to a slurryer, adding thin wash solution to said clarified green liquor while transporting the clarified green liquor to the slurryer, mixing thin wash solution with the clarified green liquor before the slurryer to provide a green liquor with controlled sodium carbonate concentration, determining the concentration of sodium carbonate in the controlled green liquor after said mixing and before the slurryer, and adjusting the volume of thin wash solution added to the clarified green liquor in response to changes in the concentration of sodium carbonate in the controlled green liquor to maintain a substantially constant concentration of sodium carbonate in said ruled green liquor, adding lime to the controlled green liquor in the slurry to react sodium carbonate in the green liquor with calcium hydroxide developed from said lime to form a reaction mixture of green liquor, lime and their reaction products, transporting said reaction mixture from the slurry, determining the concentration of sodium carbonate in the reaction mixture, adjusting the flow of controlled green liquor into the slurry in response to a change in sodium carbonate concentration in said reaction mixture. 2. Method according to claim 1, characterized in that each of the steps for determining the concentration of sodium carbonate includes taking a sample from the appropriate liquid stream, and determining the concentration of sodium carbonate in the sample. 3. Method according to claim 2, characterized in that it further includes removal of the suspended solids from each sample before said determination of sodium carbonate concentration is carried out. 4. Method according to claim 1, characterized in that it further includes transporting said reaction mixture through several series-connected causticizing vessels to allow the reaction to continue. 5. Method according to claim 4, characterized in that each of the steps for determining the concentration of sodium carbonate includes taking a sample from the appropriate liquid stream, and determining the concentration of sodium carbonate in the sample. 6. Method according to claim 5, characterized in that it further includes the removal of suspended solids from each sample before said determination of sodium carbonate concentration is carried out. 7. Procedure, characterized in that it includes burning pulp factory digestate in a furnace to develop an organic melt, dissolution of said melt to develop a pulp factory green liquor comprising sodium carbonate, sodium sulphide, soluble impurities and insoluble impurities, clarification of said pulp factory green liquor to remove said insoluble impurities, transporting said clarified green liquor to a slurry, adding lime to the green liquor in the slurry to react sodium carbonate in the green liquor with calcium hydroxide developed from said lime to form a reaction mixture of green liquor, lime and their reaction products, transporting said reaction mixture from the slurryer through several series-connected causticizing vessels to allow said reaction to proceed; then separating said reaction mixture into a clarified white liquor and a calcium carbonate sludge, return of said clarified white liquor to the mass digestion process, transporting said calcium carbonate sludge to a washing tank, washing said calcium carbonate sludge with water to form a thin washing liquid, IN use of part of said thin washing liquid for dissolving said melt, addition of part of said thin washing liquid to said clarified green liquor while the clarified green liquor is transported to the slurryer, mixing of the thin washing liquid and the clarified green liquor before the slurry to provide a green liquor with controlled sodium carbonate concentration, determination of the concentration of sodium carbonate in the controlled green liquor after said mixing and before the slurry, adjusting the volume of said thin washing liquid that is added to the clarified green liquor in response to changes in the concentration of sodium carbonate in the controlled green liquor to maintain a substantially constant concentration of sodium carbonate in the controlled green liquor, determination of the concentration of sodium carbonate in the reaction mixture, adjusting the flow of controlled green liquor into the slurry in response to changes in the sodium carbonate concentration in said reaction mixture. 8. Method according to claim 7, characterized in that each of the steps for determining the concentration of sodium carbonate includes taking a sample from the appropriate liquid stream, and determining the concentration of sodium carbonate in the sample. 9. Method according to claim 8, characterized in that it further includes removing the suspended solids from each sample before the determination of sodium carbonate concentration is carried out. 10. Procedure, characterized in that it includes clarification of pulp factory green liquor, transporting the clarified green liquor to a slurryer, adding water to the clarified green liquor while transporting the clarified green liquor to the slurryer, mixing the water with the clarified green liquor before the slurry to provide a green liquor with controlled sodium carbonate concentration, determination of the concentration of sodium carbonate in the controlled green liquor after said mixing and before said slurry, and adjusting the volume of water added to the clarified green liquor in response to changes in the concentration of sodium carbonate in the controlled green liquor to maintain a substantially constant concentration of sodium carbonate in the controlled green liquor, adding lime to the controlled green liquor in the slurry to react sodium carbonate in the green liquor with calcium hydroxide developed from the lime to form a reaction mixture of green liquor, lime and their reaction products, transport of the reaction mixture from the slurry, determination of the concentration of sodium carbonate in the reaction mixture, adjusting the flow of controlled green liquor into the slurry in response to a change in sodium carbonate concentration in said reaction mixture. 11. Method according to claim 10, characterized in that each of the steps for determining the concentration of sodium carbonate includes taking a sample from the appropriate liquid stream, and determining the concentration of sodium carbonate in the sample. 12. Method according to claim 11, characterized in that it further includes removing the suspended solids from each sample before the determination of sodium carbonate concentration is carried out. 13. Method according to claim 10, characterized in that it further includes transport of said reaction mixture through several series-connected causticizing containers to give the reaction the opportunity to continue. 14. Method according to claim 13, characterized in that each of the steps for determining the concentration of sodium carbonate includes taking a sample from the appropriate liquid stream, and determining the concentration of sodium carbonate in the sample. 15. Method according to claim 14, characterized in that it further includes the removal of suspended solids from each sample before the determination of sodium carbonate concentration is carried out. 16. Procedure, characterized in that it includes clarification of pulp factory green liquor, transporting the clarified green liquor to a slurry, adding lime to the green liquor in the slurry to react sodium carbonate in the green liquor with calcium hydroxide developed from the lime to form a reaction mixture of green liquor, lime and their reaction products, transport of the reaction mixture from the slurry, determination of the concentration of sodium carbonate in the reaction mixture, adjusting the volume of the clarified green liquor added to the slurry in response to changes in the concentration of sodium carbonate in the reaction mixture. 17. Method according to claim 16, characterized in that the step for determining the concentration of sodium carbonate includes taking a sample from the reaction mixture, and determining the concentration of sodium carbonate in the sample. 18. Method according to claim 17, characterized in that it further includes removal of the suspended solids from said sample before the determinations of sodium carbonate concentration are carried out. 19. Method according to claim 16, characterized in that it further includes transport of the reaction mixture through several series-connected causticizing containers to allow said reaction to continue. 20. Method according to claim 19, characterized in that the step for determining the concentration of sodium carbonate includes taking a sample from the reaction mixture, and determining the concentration of sodium carbonate in the sample. 21. Method according to claim 20, characterized in that it further includes removing the suspended solids from the sample before the determination of sodium carbonate concentration is carried out. 22. Apparatus, characterized in that it includes a clarification device for pulp factory green liquor, a slurry, first device for transporting clarified green liquor from the green liquor clarification device to the slurryer, other device for adding liquid to said first device, the length of the first device between the second device and the slurryer allows the green liquor and the liquid to mix and form a controlled green liquor, third device between the second device and the slurryer for determining the sodium carbonate concentration in the controlled green liquor in said first device, fourth device responsive to the third device for adjusting flow of liquid in the second device, fifth device for adding lime to the slurry, sixth device for transporting a reaction mixture of green liquor, lime and reaction products from the slurry, seventh device for determining sodium carbonate concentration -tras ion in the reaction mixture, eighth device responsive to the seventh device for adjusting current in the first device. 23. Apparatus according to claim 22, characterized in that each of said third device and said seventh device includes device for sampling the appropriate liquid, and a further device for determining the sodium carbonate concentration in said sample. 24. Apparatus according to claim 23, characterized in that each of said sampling devices further includes a device for removing suspended solids from the sample. 25. Apparatus according to claim 22, characterized in that it further includes several causticizing vessels connected in series to allow the reaction between the green liquor and the lime to continue, the sixth device transports the reaction mixture from the slurryer through the causticizing vessels. 26. Apparatus according to claim 25, characterized in that each of said devices for determining the sodium carbonate content includes device for sampling the appropriate liquid, and device for determining the sodium carbonate concentration in the sample. 27. Apparatus according to claim 26, characterized in that said sampling device has devices for removing suspended solids from the sample. 28. Apparatus, characterized in that it includes a slurryer for reaction of clarified green liquor with lime, first device for transporting the clarified green liquid to the slurryer, second device for adding lime to the slurry, third device for transporting a reaction mixture of green liquor, lime and reaction products from the slurry, fourth device for determining the sodium carbonate concentration in the reaction mixture, fifth device that reacts to said fourth device for adjusting the flow of green liquor in the first device. 29. Apparatus according to claim 28, characterized in that said device for determining the sodium carbonate content includes device for sampling the reaction mixture, and device for determining the sodium carbonate concentration in the sample. 30. Apparatus according to claim 29, characterized in that it further includes device for removing suspended solids from the sample. 31. Apparatus according to claim 30, characterized in that it further includes several causticizing vessels connected in series to allow the reaction between the green liquor and the lime to continue, as said third device transports the reaction mixture from the slurryer through the causticizing containers. 32. Apparatus according to claim 31, characterized in that the device for determining the sodium carbonate content includes device for sampling the reaction mixture, and device for determining the sodium carbonate concentration in the sample. 33. Apparatus according to claim 32, characterized in that said sampling device has a device for removing suspended solids from the sample. 34. Apparatus, characterized in that it includes first device for clarifying pulp factory green liquor, other device for reaction of the clarified green liquor with lime, third device for transporting the clarified green liquor from the first device to the second device, fourth device for adding liquid to the third device, the length of the third device between the fourth and second devices allowing the green liquor and the liquid to mix and form a controlled green liquor, fifth means for determining the sodium carbonate concentration in the controlled green liquor in the third means at a point between the fourth means and the second means, sixth means responsive to the fifth means for adjusting the flow of liquid in the fourth means, seventh means for adding lime to the slurry, eighth device for transporting a reaction mixture of green liquor, lime and reaction products from the slurry, ninth device for determining the sodium carbonate concentration in the reaction mixture, tenth device responsive to the ninth device for adjusting current in the first device. 35. Apparatus according to claim 34, characterized in that each of said fifth and ninth devices includes device for sampling the appropriate liquid, and a further device for determining the sodium carbonate concentration in the sample. 36. Apparatus, characterized in that it includes a recovery furnace for burning pulp mill digestate to form inorganic melt, a melt dissolution tank for the formation from said melt of particulate material and a green liquor comprising sodium carbonate and sodium sulphide, first device for transporting the smelt from the recovery furnace to the melt dissolution tank, a green liquor clarification tank, second device for transporting the green liquor from said melt-dissolution tank to said green liquor clarification tank, a slurry for reaction of the clarified green liquor with lime to form a reaction mixture of green liquor, lime and reaction products, third device for transporting the clarified green liquor from the green liquor clarification tank to the slurryer, fourth device for adding said lime to the slurry, Causticizing vessels to allow the reaction between the green liquor and the lime to continue, fifth device for transporting the reaction mixture from the slurryer through the causticizing vessels, sixth device for separating the reaction mixture into a clarified white liquor and a calcium carbonate sludge, seventh device for transporting the reaction mixture from the causticizing containers to said separation device, eighth device for transporting the clarified white liquor to a boiler, ninth device for washing the chemical from the calcium carbonate sludge to form a thin washing outlet, tenth device for transporting the calcium carbonate sludge from said separation device to said ninth device, eleventh device for transporting said thin wash outlet from said ninth device to the melt dissolution tank, twelfth device for transporting part of said thin wash outlet to the third device, thirteenth device for determining the sodium carbonate concentration in a mixture of said clarified green liquor and said thin wash outlet at a point before the slurryer, fourteenth device responsive to the thirteenth device for adjusting the flow of thin washing material in the twelfth device, fifteenth device for determining the sodium carbonate concentration in the reaction mixture, sixteenth means responsive to the fifteenth means for adjusting the current in said third means. 37. Apparatus according to claim 36, characterized in that each of said devices for determining the sodium carbonate content includes device for sampling the appropriate liquid, and device for determining the sodium carbonate concentration in said sample. 38. Apparatus, characterized in that it includes a first device for burning pulp mill digestate to form an inorganic melt, second device for dissolving the melt to form particulate material and a green liquor comprising sodium carbonate and sodium sulphide, third device for transporting the smelt from the first device to the second device, fourth device for clarifying the green liquor, fifth device for transporting the green liquor from said second device to said fourth device, sixth arrangement for reaction of the clarified green liquor with lime to form a reaction mixture of green liquor, lime and reaction products, seventh device for transporting the clarified green liquor from said fourth device to said sixth device, eighth device for adding the lime to the sixth device, ninth arrangement for allowing the reaction between the green liquor and the lime to continue, tenth device for transporting the reaction mixture from the sixth device to the ninth device, eleventh device for separating the reaction mixture into a clarified white liquor and a calcium carbonate slurry, twelfth device for transporting the reaction mixture from the ninth device to the eleventh device, thirteenth device for transporting the clarified white liquor to a pulp factory boiler, fourteenth device for washing chemicals from the calcium carbonate sludge to form a thin washing outlet, fifteenth device for transporting the calcium carbonate sludge from said eleventh device to said fourteenth device, sixteenth device for transporting said thin wash outlet from said fourteenth device to said second device, seventeenth device for transporting part of said thin wash outlet from the seventeenth device to the fifth device, eighteenth device for determining the concentration of sodium carbonate in the mixture of the clarified green liquor and said thin washing material in said fifth device, nineteenth device responsive to said eighteenth device for adjusting the flow through said seventeenth device, twentieth device for determining the sodium carbonate concentration in the reaction mixture, twenty-first device responsive to said twentieth device for adjusting current in said seventeenth device. 39. Apparatus according to claim 38, characterized in that each of said devices for determining the sodium carbonate content includes device for sampling said appropriate liquid, and device for determining the sodium carbonate concentration in said sample.