GB2159507A - Method for regulating concentration of carbonate - Google Patents

Abstract

The present invention is directed to a method for regulating a concentration of a carbonate contained in a solution or a suspension, the method being characterised by adjusting a feed rate (via valve 128) of the carbonate to be added to the solution or the suspension (in tank 103) in accordance with a signal regarding a deviation (controller 125) of a detection signal (detector 124) of a carbonate concentration in the solution or the suspension from a predetermined carbonate concentration. <IMAGE>

Description

SPECIFICATION Method for regulating concentration of carbonate The present invention relates to a method for controlling a concentration of a carbonate such as CaCO3, Na2CO3, MgCO3 or dolomite which is contained in a solution or a suspension (hereinafter referred to generically as the solution), and more particularly, the present invention relates to a method for remarkably effectively controlling a concentration of a carbonate which is a remaining alkali, for example, when CaCO3 is fed to an absorbing solution with which an exhaust gas containing SO, is desulfurized, or when an acidic solution is neutralized with an alkaline source such as NA2CO3, MgCO3 or dolomite.Particularly in a wet smoke desulfurizing apparatus, a concentration of CaCO3 present in an absorbing solution or a suspension (hereinafter referred to generically as the absorbing solution) which will be sprayed into an absorbing tower for treating SO, is one of important factors having influence on an SO, absorption performance. In this case, it is of consequence to properly control the concentration of CaCO3 in the absorbing solution, and the present invention can regulate the concentration of CaCO3 very effectively.

Heretofore, the concentration of CaCO3 in the absorbing solution has been controlled by sampling a small amount of the absorbing solution and detecting its concentration with the aid of a manual analysis in conformity with JIS R-9101, but such a control way takes much labor and time disadvantageously.

Therefore, it is extremely difficult to successively detect the CaCO3 concentration varied with time, which fact makes it impossible to regulate an amount of desulfurizing agent CaCO3 to be fed to an absorbing tower on the basis of data obtained by the manual analysis.

Thus, a commercially available pH meter has been used reluctantly as an on-line detector to continuously detect a pH of the absorbing solution and to thereby presume excess and deficiency of the desulfurizing agent, CaCO3. That is to say, the concentration of CaCO 3 in the absorbing solution which will be sprayed into the absorbing tower has been supposed by the utilization of the phenomenon that if an amount of Caco3 is great, a pH of the absorbing solution will be on an alkaline side and if its amount is small, the pH will be shifted to an acidic side. In such a case, the regulation of the CaCO3 concentration in the absorbing solution is inevitably inaccurate, and the manual analysis which requires much labor and time has to be carried out in order to seek an interconnection between a pH value and the CaCO3 concentration and to thereby correct gaps therebetween.

The control of the CaCO3 concentration in the absorbing solution which will be sprayed into the absorbing tower is very important from the viewpoints of reducing a consumption of the desulfurizing agent, CaCO3, and preventing a purity deterioration of the by-product, gypsum, which deterioration is caused by leaving CaCO3 therein. However, such a concentration control has been carried out only by indirectly detecting the CaCO3 concentration control still remains unsolved.

Heretofore, a feed rate of the absorbing solution in a wet lime method has been regulated in accordance with a signal regarding a deviation of a detected pH value of the absorbing solution in the absorbing tower from a pH value which has been set to obtain a desired efficiency of desulfurization. Such methods have been widely employed and are disclosed in Japanese Patent Provisional Publication Nos 30783/1977, 32895/1977, 24277/1979 and 177123/1983. However, any of these methods is insufficient in point of the adjustment of the CaCO3 concentration in the absorbing solution to a desired level.

Moreover, in the treatment of a waste liquid, a neutralization reaction of an acid with an alkali has often been utilized, and a Ph meter has been employed to grip a progressive degree of the neutralization reaction. In the case that a carbonate such as Na2CO3, MgCO3 or CaCO3 is used as an alkaline source, it is naturally desired for the sake of cost savings to reduce an excessive amount of the carbonate, but such an excessive amount of the remaining carbonate has merely been presumed experientially and experimentally from pH values detected. In the case of this method, the concentration of the carbonate has been sought by the manual analysis and a correction of the interconnection between the pH value and the concentration must often be carried out. Therefore, much labor has been required and it has been difficult to accurately regulate the concentration of the carbonate.

Furthermore, when a CaCO3 concentration in a slurry prepared merely by suspending a CaCO3 powder in water is regulated, a gravimeter or a solid suspension desimeter has been utilizied, but if solids other than CaCO3, for example, a crystalline gypsum, a sand and a fly ash are coexistent therewith, they will bring about an error, which fact makes it difficult to accurately regulate the CaCO3 concentration in a direct manner. A similar problem will occur also in regulating a sparingly soluble carbonate such as dolomite or MgCO3, in addition to the CaCO3 powder. Also for the concentration regulation of the readily soluble carbonate such as Na3CO3, a gravimeter, a pH meter or a flowmeter has been used to carry out the indirect regulation, or the manual analysis which requires labor and time has been depended upon.

In order to eliminate the above-mentioned drawbacks, the present invention has now been accomplished as a result of intensive researches, and its object is to provide a method for regulating a feed rate of a carbonate in accordance with a signal regarding a deviation of a detection signal of a carbonate concentration from a predetermined concentration level on the basis of a developed carbonate detector for detecting a carbonate concentration successively and instantaneously on line.

That is to say, the present invention is connected with a method for regulating a concentration of a carbonate contained in a solution or a suspension, the method being characterized by adjusting a feed rate of the carbonate to be added to the solution or the suspension in accordance with a signal regarding a deviation of a detection signal of a carbonate concentration in the solution or the suspension from a predetermined carbonate concentration.

The present invention has been completed by developing a process for detecting a carbonate concentration in a solution successively and instantaneously on line instead of a manual analysis.

The above-mentioned and other objects as well as features and benefits of the present invention will become apparent from the following detailed description and accompanying drawings, in which.

Figure 1 shows a constitution of a carbonate detector used in the present invention; Figure 2 shows an interconnection between CaCO3 concentrations measured by the carbonate detector of Fig. 1 and concentrations obtained by a manual analysis; and Figures 3 and 4 show embodiments of the present invention.

Now, a process for detecting a concentration of the carbonate CaCO3 will be described in detail in ref erence to Fig. 1 This detection process which will be here explained is-suggested in the specification of Japanese Patent Application No 144893/1983 which the inventors of the present application have already filed, and is also utilizable in detection processes of the carbonate concentration described in Japanese Patent Application Nos 23741/1983, 144894/1983 and 144895/1983 which the present inventors have al ready filed.

In Fig. 1, a sample slurry A containing CaCO3 is taken by a constant delivery pump 1 and is then heated by a heater 2 so that a temperature of a stagnant solution 6 in a reaction container 5 may be on a predetermined level, and the heated slurry A is afterward fed to the reaction container 5. In this case, the heat ing control of the slurry is carried out by detecting the temperature of the stagnent solution 6 with the aid of a detector 4 to produce a signal and applying the temperature signal via a temperature controller 3 connecting to the detector 4 to the heater 2. In view of a detection efficiency of CaCO3, the temperature of the stagnant solution 6 is preferably 500C or more and is acceptable within the range under a boiling point of the stagnant solution 6.

A pH value of the stagnant solution 6 in the reaction container 5 is detected by a pH detector 14, and under the control by a signal from a pH controller 15, a micropump 12 allows sulfuric acid (or hydrochlo ric acid) to flow into solution 6 may be on a predetermined level. In view of a detection efficiency, the pH of the stagnant solution should be adjusted to 4 or less, preferably 2 to 4.

Reactions at this time make progress as follows: CaCO3 + H2SO4 < CaSO4 + H20 + C02 t (1) CaCO3 t 2HCI - > CaCI 2 + H3O + CO2 t (2) For the purpose of smoothly giving off the generated CO3, a distributing valve 22 is controlled by a flow rate controller 11 so that all or a controlled part of air B may be allowed to run into the stagnant solution 6 through a flow rate indicator 17 and an air blow pipe 8.For the prevention of a solid precipitation in the stagnant solution 6 in the reaction container 5, the stagnant solution 6 is stirred by means of a stirrer 7 which can be driven by a motor 10, a position where the motor 10 is connected to the reaction container 5 being sealed with a sealant 9.

The stagnant solution 6 is discharged from the reaction container 5 through an overflow pipe 23 to a trap 13 as much as an amount of the sample slurry A fed to the container 5 through the constant delivery pump 1. The trap 13 has a solution depth opposable to an internal pressure in the reaction container 5 so as to prevent that a gas E containing CO,i2 accompanies the overflowed solution and leaks out from the trap 13, and the structure of the trap 13 is designed so that a solid content in the overflowed solution may not precipitate. The overflowed solution is discharged from the trap 13 as a waste liquid D as much as an amount of the new inflow solution.

A mixed gas E consisting of a CO2 gas generated in accordance with the reaction formula (1) (or formula (2)), the air fed through the air blow pipe 8 and an evaporated water content is caused to run into air 16 which has by-passed the reaction container 5, and a part of the joined gas E is discharged as an exhaust gas F and the remaining gas is delivered to a dehumidifier 24, where water is removed as a drain H from the gas. Afterward, the gas is sucked by an air pump 18 and is forwarded to a CO2 analytical instrument 19, by which a concentration of CO2 present in the gas is measured, and the gas is then discharged as an exhaust gas G.

A signal regarding a CO2 concentration X which has been produced in the CO2 analytical instrument 19 is delivered to a calculator 20 for calculating a CaCO3 concentration in the sample slurry A. In the calculator 20, a flow rate signal "q" regarding an air flow rate Q and a flow rate signal "f" regarding a slurry flow rate F have already been inputted from an air flowmeter 11 and the constant delivery pump 1 for taking the slurry, respectively. By the use of these three input signals, the calculator 20 carries out a theoretical calculation of the following formula (3) to seek a concentration of CaCO2 in the sample slurry A and a sought concentration of CaCO3 is then indicated on a CaCO,.i3 concentration indicator 21.

Concentration (mol/liter) of CaCO3 = Q x X (3) (~00 - X) x 22.4 x F werein Q: Flow rate (N4min) of air F : Flow rate (f/min) of slurry x ; Concentration (%) of CO, In such a way, the concentration of CaCO2 in the solution can be detected successively and instantaneously. Next, Example 1 will be described to inspect a detection accuracy.

Example 1 A concentration of CaCO2 in a slurry was measured continuously under the following conditions by the use of a test apparatus shown in Fig. 1.

Conc. of CaCO2 in sample slurries : 0.05, 0.1 and 0.2 mol/liter Feed flow rate of sample slurries : 0.12 liter/min Blow flow rate of air : 7 Cumin Predetermined raction temp. : 500C Predetermined pH :4 Predetermined conc. of CO2 : 2 vol% Total flow rate of air : 20 Cumin Volume of reaction container : 1 liter The measured results are shown in Fig. 2 with a graph denoting the interconnection between values detected by the present invention and analytical values obtained by a conventional manual analysis, and in this drawing, black and white circles indicate results in the cases of using hydrochloric acid and sulfuric acid, respectively.The following table sets forth some typical examples of measured values of CO2 concentrations as well as analytical values of the CaCO2 concentrations by the manual analysis and the present invention.

Case number No. 1 No.2 No.3 Concentration (mol/liter) of CaCO2 Manual analysis 0.056 0.104 0.192 Present method 0.053 0.100 0.195 Conc. (%) of CO2 0.71 1.32 2.55 Used acid H S S In this table, H and S represent hydrochloric acid and sulfuric acid, respectively.

The above-mentioned concrete example is connected with the procedure of detecting the concentration of the carbonate which was CaCO2, but such a concentration detection was also practicable in the cases that the carbonates were Na2CO2, MgCO2, K,.i2CO2 and dolomite. Moreover, concentrations of hydrogencarbonates such as NaHCO2 and Ca(HCO2)2 could be likewise detected, and hence in this specification, the term "carbonate" is to be understood to also include the hydrogencarbonate in its category.

Next, a method for regulating the carbonate concentration (the present invention) will be described in detail in reference to a smoke desulfurizing apparatus for a wet lime process shown in Fig 3, the method being associated with the carbonate detector comprising the construction shown in Fig 1.

An exhaust gas was delivered from a coal-fired boiler 94 through a flue 95 to a dry dust collector 98, where most of a dust 97 was removed from the exhaust gas. A concentration of the dust in the exhaust gas was about 10 g/m3N at an inlet and was about 500 mg/m3N at an outlet of the dry dust collector 98.

Next, the exhaust gas was forwarded via a flue 99 to a heat exchanger 100, in which the exhaust gas was cooled from about 140 to about 80,dgC, whereby heat was recovered. The exhaust gas containing about 500 mg/m3N of the dust and about 1,500 ppm of SO2 was guided to an absorbing tower 102 through a flue 101. In the lower portion of the absorbing tower 102, there was provided a tank for receiving a solution in which a Ca compound was suspended. Inside the tank 103 shown in Fig. 3, the suspension slurry was divided by partitions 122 and 123, but these partitions may be omitted. Particularly in the case that the partitions were provided, the solution had to be stirred by a stirrer 104 to prevent a solid therein from precipitating, but in the case of no partitions, the stirrer 104 was omitted since air bubbles generated could stir the solution.The solution suspended with the Ca compound was forwarded to the top of the absorbing tower by means of a circulating pump 105 and was sprayed into the tower, and it dropped while brought into contact with the exhaust gas and returned to the tank 103. The SO2-free smoke which had been brought into contact with the absorbing solution was delivered to a mist eliminator 106, in which it was cleaned, and the clean gas was then carried via a flute 107 to the heat exchanger 100, where the clean gas was heated and discharged therefrom to the atmosphere. The cleaned gas in the flue 107 contained about 100 ppm or less of SO2 and 50 mg/m3N or less of the dust, which fact meant that the absorbing solution slurry had caught SO, and the dust.Most of HCI and HF which were present in an amount of several tens ppm in the exhaust gas were also caught simultaneously.

A concentration of the carbonate CaCO2 in the absorbing solution which was being delivered to the top of the tower by the circulating pump 105 was detected by a carbonate detector 124. The latter was constituted as described above, and a concentration signal produced by the carbonate detector 124 was sent to a carbonate controller 125 and a signal regarding a deviation of the concentration signal from a predetermined carbonate concentration was produced and then sent to a flow rate controller 126. Further, the flow rate controller 126 received a signal from a flowmeter 127 and in accordance with the deviation signal, an opening and shutting adjustment of the valve 128 was regulated in order to control a feed of the CaCO2 suspension, which was the absorbing agent for SO2, to the tank 103 through a line 108.

A sulfite which resulted from the absorption of SO2 by the absorbing agent was oxidized with oxygen present in the exhaust gas in the gas-liquid contact zone, and additionally, air was fed to the contact zone through an air nozzle 109 to oxidize the remaining sulfite to gypsum which was a sulfate. As was definite from the above, the solution in the tank 103 contained the Ca compounds of gypsum and CaCO2, and in the solution, the caught dust was also contained.The dust had a grain diameter of about 1 micron which was much smaller than that of the crystalline gypsum and CaCO2, and therfore the solution mainly containing the dust was taken out by the utilization of a difference of sedimentation rate and was sprayed, as a waste liquid, into the high-temperature exhaust gas of about 150 C in the flue 95 from a spray nozzle 96 provided therein via a line 117 and a pump 118 Then, the dry solid mainly comprising the dust was caught by the dry dust collector 98.

On the other hand, the absorbing solution was guided to a separator 111 through an absorbing solution outlet 110 and a pump 119 and a by-product gypsum 112 was obtained there. The result filtrate and the overflowed solution were returned to the tank 103 through a line 113. The concentration of CaCO3 in the absorbing solution was to be as low as possible in order to inhibit the contamination of the by-product gypsum 112 with the CaCO2 grains, but when the gypsum scarcely contained the CaCO2 which was the absorbing agent for SO2, a percent absorption of SO2 naturally deteriorated. Therefore, a regulation of this reciprocal function was necessary.

Heretofore, such a reciprocal function has been balanced by the use of a pH meter as mentioned above, but it has been difficult to regulate the CaCO2 concentration to a desired level since the conventional manner cannot detect its concentration directly. Therefore, a stable percent absorption of SO2 cannot be kept up in response to a load fluctuation of the boiler 94, and there have been inconveniences such as the deterioration in a quality of the by-product gypsum and the increase in a consumption of the absorbing agent. However, according to the present invention, such problems can be overcome, and the concentration of CaCO3 can be thus regulated to a desired level.

Inside the tank 103, a partition 114 was provided so as to define a liquid chamber 115 isolated from the absorbing solution which was being stirred, and the bottom portion of the liquid chamber 115 was opened. Further, an inclined plate 120 was provided as a part of the bottom of the tank 103, and baffles 116 were provided in the liquid chamber 115 so that the slurry mainly containing the dust in the liquid chamber 115 might not be agitated by the turbulence of the absorbing solution which was being stirred.

In the wet smoke desulfurizing apparatus, a washing water, a sealing water of a pump or the like was jetted through a washing nozzle 121 in order to prevent gas flow paths from narrowing due to adhesion and accumulation of a solid in the mist whcih was caught by the mist eliminator 106, and in this way, a great deal of water was used. Moreover, when the high-temperature exhaust gas had been brought into contact with the absorbing solution, water evaporated owing to a humidification cooling phenomenon of the exhaust gas. Such a feed and an evaporation of water became a disturbance for concentrations of CaCO2 and gypsum grains accumulated in the tank 103. Thus, in the method of the present invention, water mainly containing the dust was discharged through the line 117 and the absorbing agent containing the Ca crystalline compound at a high concentration was discharged through the line 110, and by virtue of the two simultaneous treatments, the concentration of the Ca crystalline compound could be controlled. Additionally, in order to singly regulate the concentration of CaCO2 grains, which were effective as the absorbing agent for SO2, among the Ca compounds, the above-mentioned carbonate concentration regulation was necessary. Accordingly, a combination of these mechanisms permited functional effects of the present invention to be built up.

The present invention will be described about an embodiment for regulating a concentration of a carbonate in the following example.

Example 2 In this example, an apparatus shown in Fig. 4 was employed. In Fig. 4, the same reference numerals as in Fig. 3 represent corresponding members and devices.

A tank 103 for storing an absorbing solution had a sectional area of 2,000 mm x 2,000 mm and a solution depth of 2,000 mm. The absorbing solution was sprayed into an absorbing tower 102 from the top thereof at a feed rate of 120 m3/h by means of a circulating pump 105, the absorbing tower being packed with grids. An exhaust gas discharged from a coal4ired boiler 94 was taken at a feed rate of 8,000 m3Níh by an electrical dust collector 98 through its outlet, and was then guided to the absorbing tower 102 via a heat exchanger 100. The exhaust gas at an inlet of the absorbing tower contained 1,500 ppm of SO, and 500 mg/m3N of a dust on the average.

Inside the tank 103, partitions 122 and 123 were provided to divide the solution in the tank into two portions thereof, so that a circulating slurry which had dropped while absorbing SO2 was first brought into contact with air bubbles temporarily and was then forwarded to the circulating pump 105 in order indicated by arrows in the drawing. Further, inside the tank 103, there was provided a cylindrical parting chamber 114 having an internal diameter of 400 mm and a length of 1,500 mm, the chamber 114 being opened at the bottom thereof. A cylindrical upper lid is linked to a line 117 directly connecting to a (sunction) pump 118, and a waste liquid maily containing the dust was taken out through the line 117.A concentration of a solid in the waste liquid was about 1% by weight, and it was confirmed by a microscope that the solid was principally composed of a spherical dust having a grain size of about 1 micron.

On the other hand, air was continuously blown through an air nozzle 109 in a feed rate of 250 m2N/h, so that a concentration of a sulfite in the absorbing solution was maintained at a level of less than 1 millimol/liter. Further, a flow rate of the absorbing solution discharged from the tank 103 through an outlet 110 was controlled to adjust a concentration of solids principally comprising gypsum and CaCO2 in the absorbing solution in the tank 103 to a level of about 20% by weight. The concentration of the solids was detected by the use of a gravimeter.

The SO2 absorbing agent, CaCO3, was prepared by grinding limestone to 325 meshes or less and was put in a silo 132 and was then thrown, through a rotary valve 131, into a tank 133 for storing a CaCO2 suspension therein. In order that a concentration of CaCO2 in the tank 133 might be 2 mol/liter, a signal produced in a carbonate detector 129 was sent to a carbonate controller 130, and a signal regarding a deviation of the above signal from a predetermined value was transmitted to a revolution regulating system of the rotary valve 131. As a solvent for the suspension, city water was employed, a feed of water was carried out in a conventional manner by means of a level detector 135, a level regulator 136 and a valve 137.As the carbonate detector 129, an apparatus described in reference to Fig. 1 was adopted in order to control the concentration of the CaCO2 suspension in the tank 133. The CaCO2 suspension was fed to the tank 103 via a pump 134, a valve 128 and a line 108, and its feed rate was controlled by regulating an open degree of the valve 128 in accordance with a signal regarding a deviation of a concentration signal from a predetermined carbonate concentration. The aforesaid concentration signal was that which was produced by detecting a concentration of the carbonate CaCO2 in the absorbing solution with the aid of a carbonate detector 124 and was then sent to a carbonate controller 125.Under the predetermined carbonate concentrations of 0.05, 0.1 and 0.2 mol/liter, each continuous operation test was carried out, and at this time, concentrations of the carbonate in the absorbing solution was 0.053, 0.100 and 0.195 mol/liter, which results indicated that the satisfactory concentration control was accomplished.

Comparisons between the results of the present invention and data obtained by a manual analysis are as set forth in Example 1.

Next, the solution mainly containing the dust which had been taken out through the line 117 by means of the pump 118 was divided into two portions, and one portion of the solution was sprayed through the spray nozzle 96 into the flue 95 in which the exhaust gas having a temperature of about 1500C was flowing. A flow rate of the sprayed solution was 50 liter/h, and the solution was dried in the flue 95 for about 3 seconds and the dried dust was then caught by the electrical dust collector 98. On the other hand, another portion of the aforesaid divided solution was guided to a neutralizing treatment tank 138 through a line 143.A concentration of the carbonate in a solution in the neutralizing treatment tank 138 was detected by a carbonate detector 139 similar to the detector which had been described in reference to Fig 1, in order to produce a concentration signal, and the latter signal was sent to a carbonate controller 140, where a signal of a deviation of the concentration signal from a predetermined carbonate concentration was produced. A valve 141 was controlled by the produced deviation signal to adjust a feed rate of an aqueous Na2CO2 solution which was a neutralizing agent and which was fed to the tank 138 through a line 142. For the purpose of removing dissolved Ca2 ions, i e., softening, a deposition reaction of CaCO2 was carried out in accordance with the following reaction formula (4) in the neutralizing treatment tank 138: Ca2+ + Na2CO3 < CaCO2 + 2Na (4) The solid CaCO2 carbonate was separated by a filter and the resultant filtrate was guided to the carbonate detector 139, whereby Na2CO2 could be fed neither too much nor too less.

As understood from the foregoing, the functional effect of the present invention has been verified by the apparatus shown in Fig. 4. That is to say, it is apparent that the feed rate of the carbonate can be regulated in accordance with the signal regarding the deviation of the detection signal of the carbonate concentration in the solution from the predeteremined concentration level.

In the above description, the carbonate detector shown in Fig. 1 is adopted as one typical example, but there can also be utilized carbonate detectors having structures disclosed in Japanese Patent Application Nos. 23741/1983, 14489411983 and 144895/1983.

In the conventional method of using a pH meter, it is difficult that a response to the concentration of CaCO2 is promptly accomplished and the concentration is adjusted to a desired level. As is definite from the above description and examples, however, according to the method of the present invention, the concentration of CaCO2 can always be regulated to the level of a desired concentration effectively.

Claims (7)

1. A method for regulating a concentration of a carbonate contained in a solution or suspension, the method being characterized by adjusting a feed rate of said carbonate to be added to said solution or suspension in accordance with a signal regarding a deviation of a detection signal of a carbonate concentration in said solution or suspension from a predetermined carbonate concentration.

2. The method for regulating a concentration of a carbonate according to Claim 1 wherein said method is applicable to a process by which CaCO2 is fed to an exhaust gas containing SO2 to carry out a desulfurizing treatment.

3. A method for regulating a concentration of a carbonate according to Claim 1 wherein said method is applicable to a process by which an acidic solution is neutralized by an alkaline source such as Na2CO3, MgCO2, CaCO2, K2CO2 and dolomite.

4. The method for regulating a concentration of a carbonate according to Claim 1 or 2 wherein said method is applicable to a control of said carbonate concentration in a suspension in a device for feeding said suspension to a tank which is provided in the lower portion of an absorbing tower in a smoke desulfurizing apparatus for a wet lime gypsum process.

5. The method for regulating a concentration of a carbonate according to any one of Claims 1, 2 and 4 wherein said method is applicable to a control of a carbonate concentration in a solution in a neutralizing treatment tank in a smoke desulfurizing apparatus for a wet lime gypsum process.

6. The method for regulating a concentration of a carbonate according to any one of Claims 1 to 5 wherein in said method, a signal regarding a deviation of a detection signal of a carbonate concentration from a predetermined carbonate concentration is taken out from a carbonate controller via a carbonate detector.

7. A method for regulating a concentration of a carbonate contained in a solution or suspension substantially as herein described with reference to the accompanying drawings and the given examples.