JPH0510128B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention provides a solution or suspension (hereinafter collectively referred to as a liquid) containing carbonates such as CaCO ₃ , Na ₂ CO ₃ , MgCO ₃ , and dolomite that contains sulfurous acid, sulfuric acid,
In a tank where acid such as hydrochloric acid, nitric acid, or acetic acid is added to cause a reaction between carbonate and acid, the carbonate concentration in the liquid extracted from the tank is detected and the carbonate and acid are supplied to the tank. It concerns a method of adjusting the amount. (Conventional technology) Chemical operations using the neutralization reaction of acids and alkalis have been widely put into practical use, and
It is known that a reaction product is obtained by adding an acid such as sulfuric acid, hydrochloric acid, nitric acid, or acetic acid to a liquid containing a carbonate such as CaCO ₃ , Na ₂ CO ₃ , MgCO ₃ , or dolomite. For example, an operation in which sulfuric acid is added to a liquid containing CaCO ₃ to recover calcium sulfate, ie, gypsum, as a product is used in wet lime-gypsum smoke desulfurization equipment. More specifically, gypsum is recovered by adding CaCO ₃ to sulfate produced by desulfurization, or calcium sulfite produced by absorbing SO ₂ in the absorption tower of flue gas desulfurization equipment is collected in an oxidation tower. send to
At the same time as gypsum through air oxidation in an oxidation tower,
The above reaction is used when nitric acid is added in an oxidation tower and the residual CaCO ₃ is converted to gypsum so that the SO ₂ absorbent CaCO ₃ does not remain and reduce the purity of the gypsum. In the operation of obtaining gypsum through the reaction of CaCO ₃ and sulfuric acid, the amount of carbonate and acid can be adjusted depending on the amount of acid supplied to the tank and the amount of carbonate supplied.
In fact, as a way to control the concentration of CaCO ₃ in the tank, a small amount of liquid is sampled from the tank.
Through manual analysis in accordance with JIS R-9101,
Because it detected the residual concentration of CaCO ₃ , it was unsuitable for continuous operation where it changes from moment to moment, and it had the disadvantage of requiring manpower and time. Therefore, in order to improve continuous operability, PH
A meter is used to continuously detect the pH of the liquid.
The supply amounts of CaCO ₃ and sulfuric acid were being adjusted. That is,
A method was used to empirically manage the CaCO ₃ concentration in the liquid by utilizing the phenomenon that the pH shifts to the alkaline side when CaCO ₃ increases, and conversely to the acidic side when sulfuric acid increases. (Problems to be Solved by the Invention) In the above conventional method, CaCO ₃ is a poorly soluble solid, and the PH and CaCO ₃ concentration change due to variations in particle size and changes in residence time in the tank. Since the correlation is not uniquely determined and therefore the residual CaCO ₃ concentration varies, CaCO ₃ in the plaster
This may cause a problem in which . In order to avoid this, a method of supplying sulfuric acid in excess has always been adopted, but when the pH of the liquid is between 2 and 6, significant hunting often occurs, resulting in material corrosion due to acid and acidification of plaster. The problem remained unresolved.
It is an object of the present invention to solve these drawbacks and provide a method for adjusting carbonate concentration that can quickly respond to momentary changes and can be operated continuously. (Means for Solving the Problems) In order to solve the above-mentioned drawbacks, the present invention has been achieved as a result of intensive research and has developed a carbonate detector that continuously and instantaneously detects carbonates online. relates to a carbonate concentration adjustment method characterized by adjusting the amount of acid supplied to a tank based on a deviation signal between a detection signal of the carbonate concentration of a tank internal liquid and a carbonate concentration set value. . Of course, it is also possible to adjust the supply amount of carbonate instead of acid, and the supply amounts of acid and carbonate may be adjusted simultaneously. That is, the present invention provides a method for controlling the carbonate concentration of a mixture obtained by mixing a carbonate-containing liquid or suspension and an acid-containing liquid or suspension. Supply of the liquid or suspension containing the carbonate to be added to the mixed liquid based on the deviation signal between the signal from the device that detects the carbon dioxide concentration and converts it to the carbonate concentration in the liquid and the carbonate concentration setting value. The present invention relates to a method for adjusting carbonate concentration, characterized in that the amount and the amount of the acid-containing liquid or suspension to be supplied are adjusted simultaneously or separately. The present invention was made possible by the development of a method for continuously and instantaneously detecting carbonates in liquid online without manual analysis. Here, the method for detecting carbonate will be specifically explained with reference to FIG. 1 in the case where the carbonate is CaCO ₃ . The carbonate detection method described here was proposed in Japanese Patent Application No. 58-144893 (Japanese Unexamined Patent Publication No. 60-36955) previously filed by the present inventors.
Other methods for detecting carbonates include Japanese Patent Application No. 58-23741 (Japanese Unexamined Patent Publication No. 59-237), which was previously filed by the present inventors.
No. 150339), No. 58-144894 (Unexamined Japanese Patent Publication No. 60-36956)
No. 58-144895 (Japanese Unexamined Patent Publication No. 60-36957)
The method proposed in the previous issue can also be used. A sample slurry A containing CaCO ₃ is collected by a metering pump 1, and the temperature of the staying liquid 6 in the reaction vessel 5 is adjusted so that the temperature of the staying liquid 6 becomes a predetermined temperature.
It is detected by a detector 4, heated through a heater 2 whose heat source is controlled by a signal from a temperature controller 3, and then supplied to a reaction vessel 5. Considering the detection efficiency of CaCO ₃ , the temperature of the retained liquid 6 should preferably be 50°C or higher;
Possible up to the boiling point of the retentate. The PH of the stagnant liquid 6 in the reaction vessel 5 is detected by the PH detector 14, and the trace pump 12 is controlled by the signal from the PH controller 15 to react with an acid C that decomposes carbonates such as sulfuric acid or hydrochloric acid. Pour into container 5 and adjust to the specified pH.
The PH is controlled so that From the viewpoint of CaCO ₃ detection efficiency, the pH of the retained liquid 6 is controlled to 4 or less, preferably 2 to 4. _{In addition ,} according _{to the} following _{reaction , the} generated CO ₂ can be _smoothly removed _. In order to control the flow rate, a part or all of the air B controlled to a predetermined flow rate by the flow rate controller 11 is supplied to the flow rate indicator 1 by operating the distribution valve 22.
7 and the air blowing pipe 8 into the staying liquid 6, and in order to prevent the solid content in the staying liquid 6 in the reaction vessel 5 from settling, the staying liquid 6 is blown into the staying liquid 6 through a sealing material 9 by a motor 10. The mixture is stirred by a driven stirrer 7. Next, the increase in the amount of the retained liquid 6 due to the supply of the sample slurry A from the metering pump 1 is discharged from the overflow pipe 23 to the liquid seal 13, and in the liquid seal 13, the amount of liquid in the reaction vessel 5 is increased.
A structure in which the liquid depth is maintained relative to the internal pressure of the reaction vessel 5 so that the CO ₂ -containing gas E does not leak along with the overflow liquid, and the solid content in the overflow liquid from the reaction vessel 5 does not settle. It is becoming. Further, the excess amount of overflow liquid flowing into the liquid seal 13 is discharged as waste liquid D. occurred according to reaction formula (1) [or (2)]
CO ₂ and the mixed gas E of air and evaporated water from the air blowing pipe 8 are combined with the air 16 bypassing the reaction vessel 6 and then released as exhaust F, but a part of the exhaust F is After the moisture contained in the dehumidifier 24 is removed as drain H, it is sucked in by the air pump 18 and sent to the CO ₂ analyzer 19.
The CO ₂ concentration is measured by the CO ₂ analyzer 19 and then released as exhaust gas. CO ₂ analyzer 19
The detection signal that gives the CO ₂ concentration
It is sent to a computing unit 20 for calculating the concentration of CaCO ₃ in the water. The calculator 20 also receives a flow rate signal *1 that gives the air flow rate Q from the air flow meter 11 and a flow rate signal *2 that gives the slurry sampling flow rate A from the slurry sampling metering pump 1.
Using the two input signals, the computing unit 20 performs the following theoretical calculation to calculate the CaCO ₃ concentration in the collected slurry A, and causes the CaCO ₃ concentration indicator 21 to indicate the CaCO ₃ concentration. _Q × X: CO ₂ concentration [%] In this way, the CaCO ₃ concentration in the liquid containing CaCO ₃ can be detected continuously and instantaneously, but the detection accuracy will be described in Example 1 below. (Example) Example 1 Using the test equipment shown in Figure 1, under the following conditions.
The _CaCO3 concentration in the _CaCO3- containing slurry was measured continuously. _CaCO3 concentration in sample slurry
: 0.05, 0.1, 0.2mol/l Sample slurry collection flow rate : 0.12l/min Blow air flow rate : 7Nl/min Reaction temperature setting : 50℃ Reaction PH setting : 4 Setting CO ₂ concentration : 2vol% Total air flow rate : 20Nl/min Reactor capacity: 1 The results are shown in Figure 2. Figure 2 is a correlation diagram between the detected value by the method of the present invention and the analytical value by conventional manual analysis.
is the case using sulfuric acid. In addition, CO ₂ measurement value,
Typical examples of manual analysis values of CaCO ₃ and values detected by the present invention are shown in Table 1 below.

[Table] Above is a specific example of the carbonate detection method when the carbonate is CaCO _3. However, when the carbonate is Na ₂
Similar detection was possible for CO ₃ , MgCO ₃ , K ₂ CO ₃ and dolomite. Also, _NaHCO3 and
Bicarbonate of Ca(HCO ₃ ) ₂ was also detectable. Next, a carbonate concentration adjustment method (method of the present invention) using a carbonate detector having the configuration shown in FIG.
A case in which the method is applied to a wet lime plaster method flue gas desulfurization equipment will be specifically explained with reference to FIG. 3 as an example. Exhaust gas 100 containing SO ₂ is sent to the absorption tower main body 101
The SO 2 gas is introduced into the column, comes into contact with the absorption liquid in the column, removes SO ₂ , and is then discharged to the outside of the column as purified gas 102. A tank 103 for storing the absorption liquid is provided at the lower part of the absorption tower main body 100. The absorption liquid is stirred by a stirrer 104, and an absorption tower circulation pump 105 is used to stir the absorption liquid.
The absorption liquid is sent to the top of the column and dispersed inside the column, where it comes into contact with the exhaust gas and absorbs SO ₂ . The absorbent
Sulfites produced by absorbing SO ₂ are oxidized by O ₂ in the exhaust gas in the gas-liquid contact zone, so
The acidic absorption liquid containing sulfites and sulfates and having a low pH falls into the tank 103. If sulfite remains, air is blown from an air nozzle 106 provided in the tank to bring the absorption liquid into contact with O ₂ in order to oxidize it into sulfate. On the other hand, the SO ₂ absorbent CaCO ₃ is
The CaCO ₃ concentration is detected by the carbonate detector 107, and the SO ₂ absorption ability of the absorption liquid can be known.
The carbonate detector 107 can be configured as described above, and its concentration signal is sent to the carbonate controller 108.
sent to. The carbonate controller 108 sends a deviation signal between the set CaCO ₃ concentration required for SO ₂ absorption and the detected value to the flow controller 109.
The opening and closing of the valve 111 is adjusted based on the deviation signal from the signal No. 10, and the liquid in which CaCO ₃ particles are suspended is supplied from the line 112 to the tank 103. The absorption liquid in the tank 103 is a suspension of gypsum and CaCO ₃ particles, but in order to control the tank liquid level and gypsum concentration, the absorption liquid is drawn from the absorption liquid extraction line 114 to the neutralization tank 115 via the pump 113. Remove the absorption liquid. In the neutralization tank 115, CaCO ₃ remaining in the absorption liquid is turned into gypsum by adding sulfuric acid.
Instead of the conventional PH control to adjust the amount of sulfuric acid added, the method of the present invention directly removes residual CaCO ₃
It is possible to detect the concentration and convert just the right amount of carbonate to sulfate. That is, the carbonate concentration in the liquid is detected by the carbonate detector 116 having the above-described configuration, and the concentration signal is sent to the carbonate controller 117.
A deviation signal between the desired concentration of CaCO ₃ particles mixed in the gypsum particles and the carbonate concentration setting value is sent to the flow rate controller 118. Flow regulator 118 also receives the signal from flow meter 110 and uses the deviation signal to adjust the amount of sulfuric acid supplied from sulfuric acid supply line 121 via valve 120. The liquid containing gypsum whose carbonate concentration has been adjusted to a desired value is sent to a centrifugal separator 123 via a pump 122, where by-product gypsum 124 is recovered, and the filtrate is drained through a line 125 or recycled. Used cyclically. Here, an example of a method of using the concentration signal from the carbonate detector 116 to adjust the sulfuric acid supply amount in the neutralization tank 115 is shown in FIG. 3, but the signal used for adjusting the sulfuric acid supply amount is This can be done using only the carbonate concentration, or it is of course possible in the present invention to use the carbonate concentration signal and other flow rate signals in combination. Furthermore, the carbonate concentration signal is used not only for adjusting the sulfuric acid supply amount, but also for the absorption liquid extraction line 11.
It can be used to adjust the amount of carbonate supplied from 4, or it is also possible to adjust the amount of carbonate and sulfuric acid supplied at the same time. Similarly, tank 1
03, it is also possible to use the carbonate concentration signal from the carbonate detector 107 alone to adjust the carbonate CaCO ₃ supply amount from the CaCO ₃ supply line 112, or to adjust the amount of exhaust gas processed and the inlet SO ₂ , exit
Each concentration of SO ₂ and the pH of the absorption liquid in the tank 103
The carbonate supply amount is adjusted using a calculation signal that combines the pH of the flowing absorption liquid in the absorption tower main body 101, and
It is also possible to control the carbonate concentration in the absorption liquid. (Effect of the invention) In this way, it is not possible to supply sulfuric acid in excess as in the past,
In addition, problems with pH control such as an increase in CaCO ₃ concentration can be resolved. In particular, if the dissolution rate of CaCO ₃ differs depending on the shape of CaCO ₃ particles or the residence time in the tank varies, the correlation between PH and residual CaCO ₃ concentration cannot be determined unambiguously. In the neutralization reaction between acid and carbonate, it has been difficult to adjust the residual CaCO ₃ concentration to the desired value using PH control and prevent excess or deficiency of acid supply, but the method of the present invention overcomes this drawback. It can be resolved. (Example) Example 2 The apparatus used is shown in FIG. 4000m of exhaust gas emitted from coal-fired boilers
³ N/h was collected from the outlet of the electrostatic precipitator and introduced into the absorption tower main body 101. Exhaust gas 100 is SO ₂
2000ppm, dust 500/m ³ N, HCl 100ppm HF
It had an average composition of 30 ppm. CaCO ₃ , which is an absorbent, is made by crushing limestone into a powder of 325 mesh or less and adding it to water at a concentration of 2 mol/l.
CaCO ₃ slurry containing CaCO ₃ was added to line 1.
The CaCO ₃ concentration in the absorption liquid in the tank 103 is detected by the same carbonate detector 107 as shown in FIG. 1, and the concentration signal is detected. Carbonate controller 10
8, a deviation signal from the carbonate concentration set value is transmitted to the flow rate controller 109, and at the same time, control is performed by opening and closing a valve 111 based on the deviation signal from the flowmeter 110 signal. Set carbonate concentration to 0.025mol/l, 0.05mol/
1 and 0.1 mol/l, CaCO ₃ in the absorption liquid could be operated at the set concentration, and the data shown in Table 2 below was obtained.

[Table] CaCO ₃ concentration at this time (m mol/l), absorption liquid
Figure 4 shows the changes over time in PH (-), outlet SO ₂ concentration (ppm), and inlet SO ₂ concentration (ppm). Note that test numbers 1 to 3 were conducted successively as shown in FIG. The CaCO ₃ concentration signal of the carbonate detector according to the present invention is shown by line (A) in FIG. 4, demonstrating that continuous control is possible. Line (B) in FIG. 4 shows the PH meter detection value of the absorption liquid. (Although not shown in Figure 3, a commercially available PH meter was installed in the absorption liquid sampling line of the carbonate detector 107.) Even though the CaCO ₃ concentration shown by line (A) is almost constant, First, the PH of the absorption liquid fluctuated because the amount of air blown from the air nozzle 106 fluctuated, which is impossible to do with conventional PH control.
The excellent effect of CaCO ₃ concentration control (invention) was demonstrated. In other words, with conventional PH control, the absorbent is
Fluctuations in the supply amount of CaCO ₃ were unavoidable, but with the present invention, the supply amount is stable even against pH fluctuations.
_CaCO3 concentration control was achieved. Entrance SO ₂
Stable CaCO ₃ concentration control is possible even with changes in the concentration (D) line, and this stabilizes the titer of the absorption solution, so the outlet SO ₂ concentration (C) line also does not change significantly and remains stable. Desulfurization performance was demonstrated. Next, the absorption liquid is continuously sent from the absorption liquid extraction line 114 to the neutralization tank ₁₁₅ , and during the test period shown in _FIG . supplied. The CaCO ₃ concentration in the liquid in the neutralization tank 115 is set to 0.001,
Control operation was possible at 0.005 and 0.010 mol/l, respectively. As a result, unlike conventional PH control, residual CaCO ₃ in by-product gypsum could be stably controlled, and neutral by-product gypsum of good quality could be recovered. Table 3 below shows a comparison of the CaCO ₃ concentration in the by-product gypsum with data measured by manual analysis.

[Table] Example 3 The filtrate from the filtrate line 125 obtained in the experiment of Example 2 is a gypsum saturated liquid,
A portion of this filtrate is continuously collected to collect dissolved Ca ²⁺
Ion softening experiments were conducted according to the method of the present invention. The experimental apparatus is shown in FIG.
The gypsum permeate was supplied from 01 at a rate of 200/h. The Ca ²⁺ ion concentration in the gypsum permeate was 0.045 mol/l, as determined by manual analysis. tank 2
In order to detect carbonate contained in the liquid in 00, the first
A carbonate detector 202 having the configuration shown in the figure is installed, and a valve 204 is adjusted using a deviation signal from the carbonate concentration setting value from a carbonate controller 203.
Aqueous Na ₂ CO ₃ solution was supplied from 05. CaSO ₄ + Na ₂ CO ₃ → CaCO ₃ + Na ₂ SO ₄ When performing the substitution reaction, only the dissolved carbonate Na ₂ CO ₃ is sent to the carbonate detector 202 as a carbonate, excluding the precipitated CaCO ₃ particles through a filter. Since we made it possible to detect it, we were able to supply just the right amount of Na ₂ CO ₃ . As described above, the present invention utilizes the carbonate detector having the configuration shown in FIG. 1 in the experimental apparatus shown in FIGS. 3 and 5, thereby detecting It has been demonstrated that carbonate can be controlled to the desired level. As already mentioned, the carbonate detector used in the method of the present invention is not limited to the configuration shown in FIG.
Carbonate detectors using any of the methods proposed in No. 58-144895 can be used.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of a carbonate detector used in the present invention. FIG. 2 shows a correlation diagram between the CaCO ₃ concentration measured by the carbonate detector of FIG. 1 and conventional manual analysis. FIG. 3 shows an embodiment diagram of the present invention. FIG. 4 shows data showing the effects of the present invention, and shows records during carbonate concentration management operation. A is the concentration signal recorder reading from the CaCO ₃ concentration detector in the absorption liquid, B is the absorption liquid PH recorder reading, C is the SO ₂ concentration recording value in the purified gas, and D is the exhaust gas reading. The graph shows the changes over time in the indicated values of the SO ₂ concentration recorder. FIG. 5 shows another embodiment of the invention.

Claims (1)

[Claims] 1. In a method for controlling the carbonate concentration of a mixed liquid obtained by mixing a liquid or suspension containing a carbonate and a liquid or suspension containing an acid, the carbon dioxide concentration of the mixed liquid is detected. The supplied amount of the carbonate-containing liquid or suspension to be added to the mixed liquid and the acid A method for adjusting carbonate concentration, characterized by adjusting the supply amount of a containing liquid or suspension at the same time or separately.