JPS5824398A - Reduction of alkaline scale - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to scale reduction, and more particularly, the present invention relates to scale reduction and, more particularly, to a method for substantially reducing or eliminating the rate and extent of calcium carbonate scale and magnesium hydroxide scale formation in a water distillation apparatus. METHODS AND APPARATUS.

Dissolved magnesium salts and (
or) Numerous studies have been carried out to exclude the formation of alkaline scale during the distillation of waters containing calcium salts. For all types of seawater distillation equipment, approximately 82
Heating seawater to temperatures up to about 180 degrees Fahrenheit produces scale that is primarily calcium carbonate (CaCO3).

At temperatures of about 200” F., magnesium hydroxide (Mg(OH)2) scale increases.
At temperatures between about 180 and 200"F, either type of scale or a mixture thereof is seen.

Calcium carbonate scale and magnesium hydroxide scale are collectively called alkaline scale.

Because scale is an insulator, even thin layers of scale on heat transfer surfaces or other components of process equipment can significantly reduce the heat transfer capabilities of these components. Scale build-up on evaporator tubes can significantly reduce processing capacity and/or increase energy manpower per unit of processing capacity. Scale build-up often results in shutdowns and is costly due to the direct cost of cleaning scaled pipes.

Various steps have been taken in attempts to reduce or eliminate scale formation in seawater distillation equipment, with limited success. Total alkalinity in the evaporator line [bicarbonate ions (HCO) and carbonate ions (CO
i2) and hydroxyl ion (n)],
An acid (generally a mineral acid) is added to the feed stream to the distillation unit. However, it is difficult to achieve effective control of scale formation by one continuous acid addition because mineral acids are highly corrosive and the scaling reaction is sensitive to acid concentration. Accurate control of the amount of acid introduced is necessary since too much introduced into the seawater feed stream will cause corrosion of the equipment, whereas insufficient introduction of acid will result in rapid scale formation.

Hard acid addition is an expensive process, and the carbon dioxide produced by the chemical reaction between sea alkalinity and acid must be almost completely removed by degassing. Rapid corrosion of equipment components occurs. Therefore, this is impractical for many seawater installations.

The use of non- or organic chemical scale-inhibiting additives to prevent alkaline scale formation has had limited success and is often ineffective at relatively high prine temperatures. Thus, while many commercial scale control additives provide good control over calcium carbonate scale formation, such chemicals are only marginally effective at controlling magnesium hydroxide scale formation at relatively high temperatures. Only.

- It has long been recognized that acids promote the decomposition of carbonic acid, hydrogen salts, and carbonates in acids, ultimately producing hydroxide ions and insoluble magnesium hydroxide at high temperatures. Thus, the water in a multi-stage flash evaporator is heated under non-boiling conditions, as in the case of an acid line, by adding pressurized carbon dioxide to the hydroxide ion production reaction, thereby suppressing the hydroxyl ion formation reaction. Plans are being made to try to curb the generation.

Steaming is a multi-stage fludge machine that heats the ply under pressure and flashes it in a separate room from the heating stage.
Although there has been some success on a pilot scale in a steam evaporator, this method has not been successful in other types of evaporators where the boiling ply/heat transfer surface is in direct contact with the heat transfer surface. Furthermore, the addition of carbon dioxide in all types of evaporation equipment is not commercially practical, since the presence of free (not chemically bound) carbon dioxide promotes corrosion.

Checkovlch
No. 3,218,241 (November 1965)
16th of the month) will be pressurized and heated.
A method for inhibiting scale formation in a multi-stage flash (MSF) freshwater recovery unit by maintaining the concentration of carbon dioxide in a prine at a level sufficient to inhibit hydrolysis of bicarbonate ions to carbonate ions. is listed. The Czech Pitch patent states that this can be accomplished by recycling the carbon dioxide released during the distillation of the feed seawater.

The Czewicz patent states that scale formation can be retarded by the addition of glassy phosphates or other chelating or wetting agents.

Addition of acid may be necessary at high temperatures.

However, Czechovic U.S. Patent No. 5.218.241
The method of this issue uses relatively low pH (e.g. 7.5 or higher) and very high free carbon dioxide concentrations (e.g. 4-15 ppp).
m) is required. Such conditions achieve scale reduction only at the expense of relatively high corrosion rates of commonly used steel and copper alloy process equipment components.

As a result, this solution to the problem of controlling alkaline scale formation is rarely or never used commercially.

In summary, the problem of controlling alkaline scale formation in commercial seawater distillation plants has been addressed in several ways. Relatively low temperature [i.e. approximately 88℃ (approximately 190℃)
) Plants operated below may use the addition of polyphosphates or other chemical scale-inhibiting additives to suppress calcium carbonate scale formation. Approximately 8
Operations above 8C (approximately 190F) required continuous addition of acid to the feedwater followed by degassing to destroy the alkali metallurgy of the feedwater and remove carbon dioxide from the system. .

Alternatively, the continuous addition of chemical scale-inhibiting additives
Mechanical means for removing soft scale from heat transfer surfaces
For example, in combination with sponge pomgor of the Taprogge type, or with partial destruction of the alkalinity of the feed water by continuous addition of acid and subsequent removal of carbon dioxide by degassing.

Prior art systems generally required periodic shutdowns and acid circulation to remove accumulated scale. The frequency of shutdowns was inversely proportional to the effectiveness of the chemical and/or mechanical treatments used. in general,
the cost, complexity and corrosion hazards of the scale control pretreatment methods used and the costs associated with shutdowns and periodic acid cleaning;
Plans are being made to balance production losses and corrosion.

One object of the invention is to overcome one or more of the problems mentioned above.

According to the present invention, the concentration of free, unbound carbon dioxide in the prine can be reduced to extraordinary levels (e.g., about 1
ppm) and at the same time (in the case of seawater operations) maintain the pH of the prine at about 8.7 to 9.3 and keep the P alkalinity of the pline at about 20 to 90 ppm, expressed as f CaCO3. so that at least 1
High temperature effects of species
threshold eff@ct) The chemical scale control additive and carbon dioxide are dissolved in one line of a water distillation unit or similar equipment. Rather than reducing the total alkalinity of the prine, such treatment effectively reduces the hydroxyl and carbonate ion concentrations of the prine to levels that would exist if chemical additives were used alone, thus , substantially eliminates cisscale by significantly reducing the conversion of bicarbonate ion/ to carbonate ion and ultimately to hydroxyl ion/.

The present invention is particularly useful in evaporators, such as vapor compression seawater distillation devices, where the prine is boiled by contact with a high temperature heat transfer surface. Some co2 as a result of the evaporation process
Dissolving carbon dioxide into a line that has lost CO2 reduces the effective loss of CO2, indicating that the presence of chemical scale-inhibiting additives almost completely eliminates the formation of calcium carbonate scale and magnesium hydroxide scale. By inhibiting the decomposition of bicarbonate ions to the extent that they are removed, the upward shift in hydroxide ion concentration is reduced. Thus, the two major sources of alkaline earth metal formation are negated.

As a result, currently commercially available chemical scale control additives are effective in almost completely eliminating alkaline scale formation.

The total alkalinity of the prine does not decrease and the pH of the prine
The above reciprocal benefits are obtained without a significant increase in the corrosion rate, since the reduction in the corrosion rate is not sufficient to significantly increase the corrosion rate of the materials of construction commonly used in distillation equipment. This results in the maintenance of maximum throughput over long periods of operation and a substantial reduction in the frequency of outages. Distillate and prine are subjected to threshold chemical treatment.
It is less corrosive than carbon dioxide treatment alone and much less corrosive than carbon dioxide treatment alone.

Other objects and advantages of the invention will be apparent from the following detailed description of the accompanying drawings and from the claims.

The present invention is useful in various types of process equipment in which water containing dissolved magnesium and/or calcium, which can precipitate as scale in the presence of bicarbonate decomposition products, contacts the surfaces of the processing equipment during the evaporation process. Provided are methods and apparatus for reducing or substantially eliminating alkaline scale formation in. Although the invention is particularly advantageous for seawater desalination brands, it can also be utilized in various other types of grossing equipment and can be applied to the production of bottled distilled water or water for medicinal purposes. Alternatively, it can be applied, for example, to the condensation of cooling tower blowdowns by evaporation.

In this specification, the term "seawater" includes water. The term ply/l refers to water that contains dissolved magnesium and/or calcium salts and has been subjected to an evaporation process. As used herein, the term ply/l means that a large amount of water is pure water. It refers to a process in which carbon dioxide is also lost at the same time.

Calcium carbonate scale results from the thermal decomposition of bicarbonate (at relatively low temperatures) and the reaction of the resulting carbonate with calcium present in seawater as follows.

28CO3-2co2↑+CO3" + 820
(1) Ca+2+ CO52';i CaCO3↓
(2) Carbonate ions appear in the prine at pH levels above about 8.3t.

When seawater is heated to high temperatures, the carbonates react with the water, releasing more carbon dioxide and producing hydroxide ions, which precipitate as magnesium hydroxide as described below.

C0f2+ 820 d C02↑+20H-+3)M
g+2+ 20"'22Mg(OH)-2↓
(4) Boiling seawater promotes scale formation due to the above reaction. The degree to which the above reaction occurs increases by increasing the boiling temperature, increasing the holding time, and increasing the concentration factor. The CO2 released from one line by boiling is typically removed from the evaporator to the atmosphere by exhaust gas along with non-condensable gases such as nitrogen and oxygen.

According to the present invention, in contrast to prior art methods, 002 is added to the pline simultaneously with or after the evaporation of a portion of the pline and the pline is heated at a selected high temperature under certain conditions as shown below. Plines that have been or are being subjected to an evaporation process and thus contain substantial amounts of carbonate ions resulting from the decomposition of bicarbonate present in the feed water, if they also contain chemical scale control additives. It has been discovered that by dissolving 002 in K, scale formation on heat transfer surfaces and other Norocess equipment components can be substantially eliminated or minimized.

The added co2 is preferably added to the ply/co2 by boiling.
At least a portion of the C02 released from the air is recycled and filtered to the pline.

C02 is adjusted to reduce the concentration of free (not chemically bound) C02 in the prine to approximately 1 p by the method detailed below.
It is dissolved into the prine to keep it below pm, preferably below about 0.5 ppm. This is essential since the presence of free 002 increases the tendency for dissolved C02 to be stripped during boiling. The stripped CO□ is carried into the vapor space and into the distillate collection space, thus tending to increase the corrosion rate.

The presence of dissolved carbon dioxide in the boiling line of the evaporator shifts the parallelism of equations (1), +2), +3) above to the left, thus suppressing the decomposition of bicarbonate ions. In effect, the carbonate ions act as a sponge I for carbon dioxide, preventing its loss in free form. Thus, the tendency of magnesium to precipitate as magnesium hydroxide is reduced or substantially eliminated. Additionally, the presence of chemical scale-inhibiting additives generally enhances the solubility of calcium carbonate over long periods of time at elevated temperatures,
Thus, precipitation reaction 2 is inhibited by substantially inhibiting or minimizing the formation of calcium carbonate.

Although the presence of chemical additives alone eliminates or reduces calcium carbonate formation, chemical A true synergistic effect between the additive and the dissolved carbon dioxide is achieved. As suggested in Czechovic U.S. Pat. No. 3,218,241, treatment with carbon dioxide alone to the extent necessary to suppress alkaline school formation significantly lowers the line pH and increases the free carbon dioxide concentration. This results in an intolerable corrosion rate.

In accordance with the present invention, chemical scale-inhibiting additives provide a high rate of reduction in alkaline scaling rate (e.g., about 7 O
-751) is achieved, but carbon dioxide addition in combination with chemical additives to establish prine P alkalinity and pH within a specified range achieves almost complete elimination of scale formation.

A feature of the system using the method of the present invention is that the total prine alkalinity, measured as the total concentration of hydroxide ions, carbonate ions, and bicarbonate ions, This means that it will not be lowered by adding it.

However, the concentrations of hydroxide and carbonate and salt ions are reduced by the addition of carbon dioxide, which suppresses the decomposition of bicarbonate ions to carbonate ions. Removal of bicarbonate ion decomposition is not necessary.

Alkalinity as defined above is usually IM alkalinity I
and is expressed as ppm of equivalent CaCO3 determined by titration with standard mineral acids using a methylole/no indicator at room temperature and pH 4.5. (Some standard textbooks require an end point pH of 4.6, but in seawater distillation technology it is customary to use an end point pH of 4.5.) Prine's #P Alkalinity l is /p at room temperature
Equivalent CaCO determined by titration with standard mineral acids using a phenolphthalein indicator in H8.3
Expressed as 3 ppm.

The standard method for measuring Prine's P and M alkalinity is described by Powell, Industrial Page (McGraw-Hill, 1954).
, which is incorporated herein by reference.

When practicing the invention for seawater distillation, the addition of a high temperature effect chemical scale control additive in combination with carbon dioxide increases the P alkalinity of the prine by about 20 to 90 p.
pmx is preferably kept at about 30-80 ppm and pHt of the prine is kept at about 8.7-9.5. Prine's M
Alkalinity is not reduced.

When applying the invention to a distillation unit operating on fresh water, the addition of carbon dioxide to a prine treated with a threshold chemical additive may cause little or no reduction in P alkalinity, but A small pH decrease (e.g. about 0
．． (2 to 0.5 units), a significant increase in M alkalinity can occur.

The selection of P alkalinity and pH within the above ranges depends on operating variables such as the type of evaporator, the materials of construction of the evaporator, the operating temperature, the degree of dilution with one line of feed in the multi-flash unit, etc. do.

It has been found that by operating according to the invention, the value (2P-M) is kept below zero.

Although carbon dioxide gas is preferably injected directly into the pline, other means of supplying diacid or carbon to the pline can also be used. For example, excellent results have been obtained by dissolving carbon dioxide gas in a water stream, such as a small portion of a feed seawater stream, and then directing this treated water stream to a pline in an evaporator. Thus, although a small portion of the feed may be treated with carbon dioxide prior to evaporation, it should generally be assumed that the prine is treated with carbon dioxide at about the same time as or after evaporation.

Carbon dioxide can be obtained from a variety of carbon dioxide sources, such as bottled CO2, flue gas, which removes pollutants, and the like. However, it is preferred to recirculate the carbon dioxide released from the pline during boiling or flushing. However, large amounts of non-condensable gases other than CO2, such as N2, can form blanket traps on heat transfer surfaces and impede heat transfer within the evaporator, limiting the amount of non-condensable gas removed from the system. Only that amount should be recycled.

an amount sufficient to prevent (and thus substantially inhibit) the decomposition of bicarbonate ions, but insufficient to result in the presence of a substantial amount of free (not chemically bound) CO2. CO2 must be introduced into the pline. In fact, for a vapor compression (VC) distillation unit with a distillate rate of about 11,361 (approximately 500 gallons) 7 hours, chemical additives equal to or less than the manufacturer's recommended addition rate. Approximately 200SF- (approximately o
, 44 zb,) 7 was found to be sufficient to reduce the P alkalinity from t-1279 pm to 86 ppm. The pH was reduced from 9.5 to 9.25 without recirculating exhaust gas.

Free CO2 in the prine should be less than about 1 ppm, preferably less than 0.5 ppm.

The introduction of C02 into one line tends to decrease the pH of the line, but does not increase the P alkalinity of the line to the desired 20%.
CO required to bring within -9.0 ppm
It was found that only about 0.2 to 1.0 units of g)H reduction occurred from the addition of 2.

98 of prine treated with chemical additives and CO2
should be about 8.7 to 9.3 measured at room temperature.

Of course, the efficiency of the CO2 injector is one factor that determines how effectively CO2 is absorbed into the ply.

The process of the present invention operates at temperatures as low as 88°C (190°F), such as that typically encountered in multi-stage flash (MSF) type distillation equipment.
It is particularly applicable to seawater distillation processes operating at prine temperatures above. However, the method of the present invention is suitable for vapor compression (VC) type distillation equipment, which can operate at much lower prine temperatures than MSF type equipment but may experience a relatively harsh environment with respect to scaling. Also applied with excellent results.

As mentioned above, the present invention provides a method for applying one or more selected high temperature chemical scales that provides a threshold scale inhibition effect by keeping high concentrations of carbonate ions in solution in the presence of calcium and magnesium ions. Consists of dissolving CO2 into the prine in combination with a suppressor additive.

Chemical additives having only wetting and sequestering properties are not suitable.

It is believed that the scaling suppression according to the present invention is, at least in part, a result of the scale crystal surfaces being modified by chemical additives during the scale formation process, thereby reducing the crystallization rate. Microscopic studies have revealed that there is substantial crystal deformation when threshold effect chemical scale-inhibiting compounds are present.

A variety of suitable additives are commercially available, including polymers and copolymers of maleic acid, polyphosphonates, phosphonic acid derivatives, aminophosphonic acid derivatives, I-lyacrylic acid and polymethacrylic acid derivatives, and polyol esters. is included.

However, polyphosphate is about 88°C (about 190'l = "
), it is not suitable for use in connection with the present invention because it can revert to the orthophosphate form and precipitate with the calcium or iron present in the prine. Polyphosphates also fail to inhibit magnesium hydroxide scale formation.

Mineral acids are not suitable for use in the present invention.

A preferred chemical additive is Ciba Geigy (ctb''a-
Gslgy Corporation) from Allesley, New York (＾rsley) to Belgard (
BELGARD) EV and hydrolyzed polymaleic anhydride (poly ma
Another highly effective chemical treatment is American Cyanamid Co.
American CyanamldCompany
), which is sold under the trade name P2O, and is believed to consist of a copolymer of maleic acid and sodium allylsulfonate. Other suitable chemical treatments include Monsanto (Mon5ant).

COMP any) to DEQUES
There is a compound sold under the trade name T. One example is the commercially available product DEQUEST 2010 (consisting of 1-hydroxyethyl IJ 7" to 1-diphosphonic acid).
Inc.'s FLOCON (e.g. 70: F'LOCON 247) product and Mechanical Equipment Company's (FLOCON) 247 product.
Products M2O9 and M235 from Cal Equlpmsnt Co., New Orleans, LA are also suitable.

Among the above products, BELGARO M2O
9 (Mechanical Equipment Company) and Dekunis)
(DEQUEST) products are preferred. Although those skilled in the art will recognize that the performance of various suitable chemical additives will vary, the process of the present invention improves the performance of all polymer manifolds of the type described above.

The addition rates of the chemical scale-inhibiting additives described above can be easily determined experimentally and are recommended by the respective additive manufacturers when used in combination with added carbon dioxide according to the method of the present invention. It has been found that acceptable results can be obtained at lower addition rates.

The following detailed examples are intended to illustrate the implementation of the present invention, but the scope of the present invention is not limited by these examples.

Example 1 - Vapor Compression Distillation Figure 1 is a vapor compression seawater evaporator modified to use the method of the present invention. Although the apparatus of FIG. 1 will be described in detail, the method of the present invention is not limited to the use of the particular apparatus of FIG. Needless to say, it is also possible to implement the method.

The vapor compression distillation apparatus shown in FIG.
U.S. Pat.
No. 254, No. 4.002,558, No. 4.260,4
No. 61, the disclosure of which is hereby incorporated by reference.

The distillation apparatus includes a multi-stage evaporator, generally indicated at 10, and an associated vapor compressor 12. In such a system, water on the tube side of the calandria or tube bundle 14 consisting of a plurality of tubes 15 is evaporated by heat exchange with the condensing steam on the shell side of the evaporator 10. The steam generated in the tube is sent downward through the downtake from the upper end of the calandria 14,
and is sent upward through the demister 20 to the compressor 1.
2 is sent to the suction side. The vapor is compressed in compressor 12 and then discharged through conduit 22 to the shell side of evaporator 10, where most of the vapor is condensed by contact with tube 15'. The distillate (condensate) is removed through line 24 by distillate pump f25.

The distillate flows through the meter 26 and the heat exchanger 321,
stored.

The filtered feed water is sent to the heat exchanger 32 through a line 35 with an integrated mixing device 36 at a feed pump 7D34. The feed water is high temperature distillate and! low down
It is heated by heat exchange with the air conditioner (down) and sent to the deaerator 42. At some point prior to injection into the mixing device 36,
The feed water is metered at 44, as is known in the art. and a tank (indicated schematically at 45) by addition of the chemical scale inhibiting additive described above.

The feed water is preferably heated in a heat exchanger to a temperature several degrees below its boiling point.

In the deaerator 42, non-condensable gases, including nitrogen, oxygen and small amounts of carbon dioxide, are removed from the feed water by scrubbing, preferably against steam. Deaerator 42 is preferably a packed column, and the feed water is delivered to column 42 at a spray head 46 or other water distribution device.
injected into.

The steam exhausted from the calandria 14 and containing the CO2 released by the decomposition of the bicarbonate present in the feed water is injected into the bottom of the column through 47, preferably into the evaporator 10.
It is supplied to the deaerator through a line 48 leading from an exhaust valve 49 on the shell side.

The steam to the bottom of the deaerator 42 assists in the release of non-condensable gases from the descending feed water and is approximately equal to or preferably the temperature of the circulating water in the evaporator 10. Preheat the feed water to a temperature above the water temperature. By contacting the exhaust stream in line 48 with a relatively cold seawater feed, the CO2 present in line 48 is concentrated into the gas stream in lie 150 exiting deaerator 42.

Non-condensable gases and a small amount of steam flow from deaerator 42 through line 50 to exhaust valve 51.

A small portion of the non-condensable gas is exhausted from line 50 through exhaust valve 51, but a large portion (e.g. about 80 degrees) of non-condensable gas is generally exhausted through valve 52, line 60. 61
(best shown in FIG. 2).

Carbon dioxide injector 61 includes a perforated tube 62 attached to one end of line 60 and below the level of the pline within evaporator 10 .

In another embodiment, a small portion of the seawater feed stream is sent from line 35 through line 63 (shown in dotted line) to tank 64 in which the feed water is passed from deaerator 42 to line 6.
It absorbs the carbon dioxide sent in step 5. Non-condensable gas is vented from column 64 in line 66 and carbon dioxide-containing water is pumped in line 68 to a carbon dioxide injector by pump 67.

In either embodiment, degassed feed water flows from the bottom of deaerator 42 through line 70 to the bottom of evaporator 10. There is a slight pressure drop from the deaerator 42 to the evaporator lO to allow fluid flow. A liquid level control device 72 in the deaerator controls a valve 74f in the lie/70 so that the liquid level in the deaerator 42 is maintained substantially constant.

[Alternatively, a liquid seal between the deaerator and the evaporator may include a flow-limiting orifice.] (not shown) can be used to restrict the flow of steam from the deaerator to the evaporator. ] By controlling the valve 52 in the gas line 61 in combination with the exhaust valve 51, the device 10 for evaporating carbon dioxide and small amounts of other incompressible gases
The injection rate into the prine is controlled.

The pressure inside the evaporator 10 is set to a pressure slightly higher than atmospheric pressure [for example, about 0.0703 Kg/cm2-gauge pressure (1 psl
g)), and the pline is approximately 102.6C (216C).
,7°F) (boiling point elevated 0.94°C (1.7°F)), and the vapor in tube 14 reaches approximately 106.1°C (223°F).
) to give a net ΔT of 3.5°C (6.3°F).

The parts of the evaporator that are in contact with the ply are generally aluminum brass or copper-nickel (90/10) alloy!
Made.

The vapor compression distillation apparatus shown in Figures 1 and 2 [Mechanical Equipment Co., Ltd.
1136 t (300 gallons) at a distillation rate of 7 hours (nominal distillate distillation rate). A series of seawater distillate tests were conducted with the addition of chemical scale control additives and with and without carbon dioxide injection (the carbon dioxide source was the exhaust from deaerator 42).

The P alkalinity of the cold seawater feed was approximately zero, and the M alkalinity of the feed was approximately 110-120 ppm during the test.
It remained almost unchanged. The pH of the feed is approximately 7.8-
It changed between 8.2.

Table 1 shows test results for run time, average ply/density factor, fouling factor (Rd), pline pH % P alkalinity, blowdown and copper content in the distillate.

Table 1 shows that for runs 5 and 6 with CO2 injection and chemical scale control additives, the P alkalinity was relatively low and the fouling factor for 100 hours of run time was the same as that without CO2 injection. This shows that there is no substantial increase in blowdown or distillate copper content (such copper content is a measure of corrosion rate).

/ / Example 2 - Vapor Compression Distillation with Co2 Addition via Feed Sidestream A preferred means of dissolving carbon dioxide in a side stream of a seawater feed is shown. (Components common to both FIG. 1 and FIG. 3 are designated by the same reference numerals.

Some components of FIG. 1, such as the compressor, various valves, and the distillate and blowdown lines running through the heat exchanger 32, have been omitted in FIG. be. ) In the apparatus shown in FIG.
? ] After the addition of chemical additives at point 44, the seawater feed is transferred to the side stream (line 80) and the main feed stream (line 35).
It can be divided into Feed pH is approximately 8.3. The respective flow rates in line 80 and line 35 are, for example, approximately 1 gallon (6.8 rpm) and approximately 45 rpm (approximately 12 gallons).
gallon) can be 7 minutes. The water feed in line 35 is pumped by pump 34 to heat exchanger 32 and
After being heated in 2 by heat exchange with the distillate and a blowdown run (not shown), it is sent to the spray head 46 of the defiler 42.

Side stream 80 is split at point 82 into two streams, stream 84 and stream 86, and stream 84 is directed to eductor 90 at a rate of about 0.8 gallons per minute. Line 86 is directed through valve 92 to spray head 94 of C02/seawater contacting tower 96 at a rate of about 0.7574 (about 0.2 gallons) 7 minutes.

[Alternatively, the spray head 94 may be replaced by a water inlet pipe (
(not shown) can be used. ] A suitable eductor is a Penberthy LM type 1/2# eductor.

Eductor 90 contains incompressible gas (02 and N2)
, CO2 and a small amount of water vapor.

In eductor 90, the water feed in stream 84 is pressurized;
It is mixed with the exhaust gas from line 50 and is injected into a flood line whose end is below the surface of the bulk seawater [02] in column 96.

When injected into the seawater 102, most of the water vapor in the line 100 and the CO2 are dissolved in the seawater 102. The non-condensable gas and a small amount of CO2 do not dissolve and collect in the vapor space 103 above the surface of the seawater 1020 in the column 96.

The cold seawater introduced into the column by the spray head 94 absorbs most of the CO2 present in the vapor space 103. Undissolved CO2 and non-condensable gas are removed from the exhaust valve 104.
The vapor space 103 is evacuated from the vapor space 103 and released into the atmosphere via line 106. (Valve 04 is shown as a float-type valve, but may be a nail-type manual reed valve or other suitable type of valve.) The diacid carbon-enriched water feed is supplied to column 96. From line 11
A pump (not shown in the diagram) passes through the evaporator 10 to the snow mother 112 below the liquid level of the syline in the evaporator 10.
Sent by (The evaporator is supplied with degassed seawater from line 70 as described with respect to the apparatus of FIG. 1 above.) Example 3 - Multi-stage and multi-effect evaporator As described above, the invention The method described above is also applicable to other types of seawater distillation apparatuses than the vapor compression apparatus shown in FIG. Examples of distillation apparatuses to which the method of the invention can be applied include multi-stage flash apparatuses and multi-effect vertical or horizontal tube evaporators.

Various types of multi-stage and multi-effect distillation equipment are known to those skilled in the art. For example, Czechovic U.S. Patent No. 3.21
No. 8.241 describes two embodiments of a multistage flash evaporator for seawater desalination, both once-through (no recirculation) and recirculation.

Generally, multi-stage and multi-effect evaporators include a series of leading and trailing stages, each stage including a ply/holding space and a vapor condensation space. The pline holding space is defined as the area where the plies of each tier are or are about to boil (or flash). Each subsequent stage operates at a lower pressure than the preceding stage.

When applying the method of the invention to a multi-stage flash evaporator, the recycled lit CO2 is introduced into one line of the last stage rather than in the preceding stage, and only after the absorbed CO2 has been sent into the heat exchanger. It is desirable not to let it boil.

In this way, CO2 is conserved for the primary task of reducing scale formation in the stage condenser (steam condensation space). However, since the pline conditions in the flushing chamber (pline holding space) tend to generate magnesium hydroxide scale on the chamber walls operating at relatively high temperatures, some It may be desirable to introduce 002.

Because each succeeding stage of a multi-stage flash evaporator operates at a lower pressure level compared to its respective preceding stage, each stage condenser is evacuated into the pline section of the immediately succeeding stage, thereby causing the plines in the preceding stage to evacuate. Much of the released carbon dioxide can be replaced. In this way, extreme chemical conditions in the pline that tend to promote the formation of magnesium hydroxide scale throughout the distillation apparatus can be prevented. However, in some cases, with some types of multi-stage flash apparatus, Since the pressure drop with the immediately succeeding stage is relatively small, carbon dioxide is transferred from the stage condenser to the second stage in order to provide a sufficient pressure effect and make the carbon dioxide injection practical.
It may be necessary to evacuate to the pline of a 3rd or 3rd subsequent stage. Since it is preferable to inject carbon dioxide at a deep pline depth, the kernel problem is exacerbated.

Another solution in a multi-stage flash evaporator is to collect the carbon dioxide-rich stream from a series of stages and inject the collected carbon dioxide into the pline at some point at low pressure within the device.

In the case of multi-effect vertical tube or horizontal tube evaporators, CO
The 2-enriched stream must be exhausted from the vapor condensing section of each effect tube and mixed into the pline of the subsequent effect tube.

As will be apparent to those skilled in the art, the above method and apparatus may include:
Desalination of seawater or other evaporation operations on brackish water can be carried out with little increase in the corrosive properties of the distillate and the line, and with the formation of alkaline scales eliminated or substantially reduced. Thus, there is no loss of throughput caused by snarling of tubes or other surfaces, and the output capacity can be maintained substantially over the operating time.

From the above detailed description, it can be seen that the present invention has been developed by adding carbon dioxide to the chemical additive treated prine, thereby greatly enhancing the scale control performance of the chemical additive. It will be clear to those skilled in the art that a limited reduction in the P alkalinity and pH of the brine will result in an undesirable increase in the corrosion tendency of the prine, since the concentration of free carbon dioxide in the brine will be limited. This effect is achieved without significant side effects. The desired pH and P alkalinity ranges set forth herein are within the desired range for the currently commercially available chemical additives listed herein. be.

If in the future chemical additives are developed that are capable of inhibiting alkaline scale formation at higher P alkalinity and pH levels, treatment by the method described herein, i.e., with such chemical additives. It is believed that the objects of the present invention can be achieved with such chemical additives by reducing the P alkalinity and pH of the treated prine by the addition of carbon dioxide. The alkaline scale control properties of such chemical additives will thereby be enhanced.

The foregoing detailed description is presented for ease of understanding only, as various modifications will be apparent to those skilled in the art, and the invention is not unnecessarily limited by such details. It goes without saying.

[Brief explanation of the drawing]

FIG. 1 is a partially cross-sectional schematic diagram of a vapor compression distillation apparatus embodying the present invention; FIG. -to->v
FIG. 5 is a schematic diagram, partially in section, of a preferred embodiment of a vapor compression distillation apparatus embodying the present invention. In the figure, 10...multi-tube evaporator, 12... vapor compressor, 14... calandria or tube bundle, 16...
Downtake, 20...r mister-122...conduit, 24...distillate pump, 32...heat exchanger, 34
...Supply bong! , 36... integrated mixing device, 42...
... Deaerator (tower), 44 ... Chemical scale inhibiting additive, addition point, 61 ... Carbon dioxide injection device, 62.
...Porous pipe, 64...Unsuitable, 72...Liquid level control device.

Claims (1)

[Claims] Contacting the evaporating alkaline silane containing at least one high temperature chemical scale inhibiting additive to achieve alkaline scale inhibition during +11; A method of reducing or substantially eliminating chemical decomposition in the brine after or concurrently with evaporation of the brine. dissolving into the prine an amount insufficient to provide a substantial amount of unbound carbon dioxide to prevent corrosive conditions and alkaline scale formation. . (2) The wrinkle high temperature scale inhibiting additive is a polymer of maleic acid, a copolymer of maleic acid, a polyphosphonate, a phosphonic acid derivative, an aminophosphonic acid derivative, a polymethacrylic acid derivative, an I-lyacrylic acid derivative, a boryl ester, or a mixture thereof. The method according to claim 1, characterized in that the method comprises: (3) The amount of carbon dioxide dissolved is between 20 and 90 expressed as the equivalent calcium carbonate of the P alkalinity of the brine.
ppm K and brine pH of about 8.7-9.
(4) The concentration of chemically unbound carbon dioxide in the prine is maintained at less than about 1 ppm. Claims characterized in that the method according to paragraph (3). (5) The concentration of the chemically unbound carbon dioxide in the syline is less than about 0.5 ppm. The method according to claim (4). (6) The alkaline brine is heated to 88°C (below 190°C).
The method according to claim 13, characterized in that the evaporation occurs at a temperature above or above. (7) The presence of a high temperature chemical scale control additive in the brine to be evaporated that achieves threshold scale control during M evaporation prevents the formation of alkaline scale in the brine. A method of suppressing
#i the prine after the evaporation and simultaneously with the evaporation in order to reduce the P alkalinity and pH of the pline compared to plines treated with the additive, thereby enhancing the scale control ability of the additive. (8) A method characterized in that the brine contains a substantial amount of carbonate ions produced by decomposition of bicarbonate ions present in the brine and a threshold scale in the brine. A method of inhibiting the formation of alkaline scale in a pline by the presence of a high temperature chemical scale inhibiting additive that achieves inhibition, the method comprising: adding carbon dioxide to the prine after or simultaneously with the decomposition to lower P alkalinity and pH and thereby enhance the scale control ability of the additive; A method characterized in that it is carried out by dissolving carbon dioxide gas in a relatively cold water stream and mixing it with the carbon dioxide-containing water stream t-the prine. (9) A method according to claim (8), characterized in that the water stream consists of a side stream of the feed water stream. tl[l Characterized by collecting non-condensable gases generated from the pline during the evaporation step and adding carbon dioxide to the feedwater side stream by directing the bulk gas to the prine and mixing with the side stream. The method according to claim (9)6. The mixing of the feed water side stream and the gas is carried out in an eductor.
Claim 1 (1) characterized in that the process is carried out by mixing and pressurizing the carcass gas and the side stream in a container and then contacting the gas and side stream mixture with relatively low temperature water.
The method described in section. α2 #The method according to claim (8) or (9) or 11 (1 or (11)), characterized in that the relatively low-temperature water consists of seawater. 0 a shell-and-tube heat exchanger having a shell side and a tube side; means for delivering alkaline brine to either the shell side or the cough tube side; means for boiling the nuclear prine in contact with the surface; means for sending steam to the other of the body side and limb side to boil the brine portion in contact with the heat transfer surface; a source of carbon dioxide; a source of high temperature chemical scale control additive capable of achieving intermediate scale control in the pline; A distillation apparatus that communicates with the brine transfer means and has means for applying a predetermined amount of nucleating agent to the skeleton prine during boiling of the pline. The device according to claim 03, characterized in that it includes means for communicating with the space. (2) The device according to claim (a), characterized in that the nuclear injector consists of a porous tube. αNo. The device according to claim (a), wherein the deaerator is disposed in the conduit between the #tline collection side of the heat exchanger and the skeleton injector. ) each of the carbon dioxide source and the first water source communicate with a first mixing means for mixing the carbon dioxide and water to produce a first stream of carbon dioxide-containing water; and wherein the nuclear mixing means is also in communication with a second mixing means for mixing the first stream of carbon dioxide-containing water with a second water source that is in communication with the heat exchanger plines. The device according to claim α4. α the first mixing means comprises an eductor and the second mixing means comprises an eductor;
2. The apparatus according to claim 1, wherein the mixing means comprises a gas-liquid contact tower. Apparatus according to any one of claims 1 to 3, characterized in that the first water source comprises a side stream of the feed seawater stream that feeds the line to the nuclear heat exchanger. +21+ A series of pre-stages and post-stages, each stage including a pline holding space and a vapor condensing space, wherein there is a pressure drop between adjacent preceding stages and subsequent stages; to an adjacent subsequent stage, a portion of the pline is evaporated in the subsequent stage, and a portion of the prine is evaporated with at least one high temperature chemical scale control additive that achieves threshold alkaline scale control; a substantial amount of carbonate ions resulting from the decomposition of bicarbonate ions in the prine. during evaporation, sufficient to substantially reduce the rate and extent of bicarbonate ion decomposition within the pline, but with a substantial amount of carbon dioxide not chemically bound within the pline. A method comprising the step of dissolving sufficient carbon dioxide into the pline to provide a sufficient amount of carbon dioxide to prevent corrosive conditions and alkaline scale formation. (2z By recirculating the carbon dioxide from the vapor condensation space of the preceding stage to the pline holding space of the subsequent stage,
A method according to claim 2D, characterized in that at least a portion of the carbon dioxide is dissolved into the ply. c! 3) the chemical scale inhibiting additive is a polymer of maleic acid, a copolymer of maleic acid, a polyphosphonate, a phosphonic acid derivative, an aminophosphonic acid derivative, a polymethacrylic acid derivative, a polyacrylic acid derivative, an I-liol ester, or The method according to claim C2υ, characterized in that the method is selected from the group consisting of mixtures of. @ The amount of carbon dioxide dissolved is approximately 20 to 20% of the P alkalinity of the prine expressed as equivalent calcium carbonate
Keep the pH of the prine at 90 ppm and about 8.7 to 9.
The method according to claim 21, characterized in that the amount is such that the amount is maintained at @3. (Characterized by keeping the concentration of chemically unbound carbon dioxide in the 251 prine below about 1 ppm~59
9. The method according to claim (2). 252. The method of claim C251, wherein the concentration of chemically unbound carbon dioxide in the gripping line is less than about 0.5 ppm. 127) transferring the carbon dioxide from the vapor condensation spaces of the plurality of preceding stages to at least one subsequent stage of each of the plurality of preceding stages;
22. A method according to claim 21, characterized in that the pline is recycled to two stages of pline holding spaces. +21 A series of steps, each stage including a pline holding space and a vapor condensing space, having a pressure drop relative to an adjacent succeeding stage between adjacent leading and trailing legs to evaporate a portion of the pline in the adjacent succeeding stage. A multi-stage evaporator comprising leading and trailing stages and means for delivering a first stage of the stages, a source of carbon dioxide, at least one prine holding space or vapor condensing space and a source of carbon dioxide. communication means for communicating carbon dioxide from the carbon dioxide source to the pline; A source of high temperature chemical crystalline scale control additives capable of achieving threshold scale control in the prine. and introducing means for introducing an amount of the additive from the additive source into the pline prior to evaporation of the prine in the first stage. +21. The evaporator of claim 1, wherein the carbon dioxide source includes means for communicating the vapor condensation space of the preceding stage with the pline holding space of the subsequent stage. (') wherein the carbon dioxide source includes means for communicating with the vapor condensation space of the plurality of preceding stages to the pline holding space of at least one subsequent stage of each of the plurality of preceding stages. Scope No. (an evaporation device according to item a).