JPS60226403A - Method for adjusting sulfite concentration - Google Patents

Abstract

PURPOSE:To keep the concentration of the residual sulfites in a product sulfate at a desired low value rapidly and economically in spite of variation in load, by measuring the sulfite concentration in an absorbing solution continuously to adjust the amount of an oxidizing agent, etc. to be fed on the basis of the measured value. CONSTITUTION:A waste gas 100, containing SO2, and fed to the body of an absorption column 101 is brought into contact with an absorbing solution to remove the SO2, and the resultant gas is discharged as a purified gas 102 to the outside of the column 101. On the other hand, the absorbing solution, formed by absorbing the SO2, and containing sulfites is dropped into a tank 103, brought into contact with air (oxidizing agent) fed from nozzles 107, oxidation catalyst fed from a pipe 108 and CaCO3 fed from a pipe 106 and neutralized. The sulfites are simultaneously oxidized into sulfates, which are passed through a centrifuge 119 to take out by-product gypsum 120. In the above-mentioned method, the sulfite concentration in the absorbing solution in the tank 103 is measured by a sulfite concentration detector 109, and the amount of the air and/or oxidation catalyst is controlled to adjust the resultant measured values to the set value. (Symbols 111 and 112 are controllers.)

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to 0aS03.l/1H20 and 0a(H8O3).
2, H2SO3, Na2SO3, NaH8Ox, MgS
O3 and Mg(H8O3)z and 2 S Oa and K1-l
This relates to a method for controlling the concentration of sulfites such as SO3 and hydrogen sulfites (hereinafter collectively referred to as sulfites, including sulfurous acid). collectively referred to as absorption liquid.)
The present invention provides an extremely effective method for adjusting the supply amount of the oxidizing agent and oxidation catalyst when oxidizing the sulfite contained in the sulfite to sulfate.

Conventionally, in the wet flue gas desulfurization method, since the absorption liquid that has absorbed 802 contains sulfite, a method of blowing air into the absorption liquid to oxidize it to sulfate was proposed in Japanese Patent Publication No. 45-12.
No. 005, No. 50-17318, No. 51-12479
No., JP-A-50-159897, JP-A No. 53-88694
As described in No. 57-71819 and others, it is widely used. Further, the case where additives such as catalysts are used in combination to promote oxidation is also described in the above cited reference.

In these conventional methods, the oxidation rate of sulfite is determined experimentally, and the supply amount of the oxidizing agent (mostly air is used) and oxidation catalyst are adjusted accordingly to control the sulfite concentration. The method used was to sample a small amount of the liquid and manually analyze it in accordance with JIS K 0102VC to determine the sulfite concentration and check whether the oxidizing agent was in the appropriate amount.

Therefore, it goes without saying that when operating a reaction tank that oxidizes sulfite to sulfate in a continuous operation that changes from time to time, manual analysis is required to adjust the supply amount of the oxidant and oxidation catalyst from time to time. It has the disadvantage that it requires a lot of manpower and time.

Furthermore, sulfite 1JIsK01.
02, there was also a problem with interference from iron ions, which sometimes caused problems in controlling the concentration of sulfite.

Now, when the operation of oxidizing sulfite to form sulfate is carried out on an industrial scale, it is usually carried out in a continuous operation. That is, while a sulfite-containing liquid is continuously supplied to the reaction tank, an oxidizing agent is also continuously supplied to the reaction tank, and according to the material balance,
An operation is adopted in which the liquid is continuously extracted from the reaction tank. The liquid extracted from the reaction tank mainly contains sulfate, with some sulfite mixed therein. This is a characteristic of continuous operation, and control of sulfite concentration becomes an important issue if sulfate is desired as a product. Although manual analysis data based on JIS K 0102 mentioned above is important as a management method, it requires manpower and time, and in addition, it is difficult to supply oxidizing agent to the reaction tank in response to constantly changing load conditions. In practice, it has been extremely difficult to adjust the amount appropriately. Therefore, in the conventional method, an excess oxidizing agent is constantly supplied regardless of the increase or decrease in the oxidation load in the reaction tank, thereby reducing the residual concentration of sulfite in the sulfate product.

However, in recent years, it has become a problem to continue supplying wasteful oxidizing agents from the viewpoint of resource and energy conservation, and it has become difficult to maintain an optimal supply of oxidizing agents and oxidizing catalysts even in response to sudden changes in oxidation load.
There is a strong demand to maintain tk and control the sulfite concentration to a desired level. However, there are limits to manual analysis, and this requirement has not been met.

The present invention has been developed in view of the current situation, and provides a method for constantly and quickly supplying an appropriate amount of oxidizing agent and oxidation catalyst without waste even in response to load fluctuations, and adjusting the sulfite concentration to a desired value. By developing a sulfite detector that continuously and instantaneously detects sulfite concentration online, we have developed a sulfite detector that detects the sulfite concentration in the reaction tank liquid and the sulfite concentration setting value. This paper proposes a method for adjusting sulfite concentration, which is characterized in that the amount of oxidizing agent and/or oxidizing catalyst supplied to the reaction tank is adjusted based on a deviation signal between the oxidizing agent and the oxidizing catalyst.

Note that the sulfite concentration can also be adjusted by adjusting the amount of sulfite supplied to the reaction tank instead of the oxidizing agent, and the amount of sulfite supplied to the oxidizing agent, oxidation catalyst, and sulfite can be adjusted at the same time. It can also be done by

An example embodiment in which the method of the present invention is applied to a wet lime-gypsum flue gas desulfurization apparatus will be described below with reference to FIG.

The present invention was achieved by developing a method for continuously and instantaneously detecting sulfites in liquid online without relying on manual analysis.
The detection method will be specifically explained with reference to FIG.

Figure 2 is an explanatory diagram showing the configuration of the sulfite detector used in the present invention. In Figure 2, A is a sample liquid, B is air or nitrogen, and C is a sulfite detector such as sulfuric acid or hydrochloric acid. acid, D is waste liquid, E is extraction gas containing SO2, F is exhaust, G is exhaust, and H is drain. Furthermore, 1 is a metering pump, 2 is a heater, 3 is a temperature controller, 4 is a temperature detector, and 5 is an acid decomposition container, which is a stirring type continuous acid decomposition container that is isolated from the outside air.

6 is the retained liquid, 7 is the stirrer, 8 is the blowing pipe, 9 is the sealing material,
10 is a motor, 11 is a flow rate indicator, 12 is a minute pump, 13 is a liquid seal, 14 is one electrode, 15 is a controller, 16
is air, 17 is a flow rate controller, 18 is an air pump, 22 is an S02 analyzer, 23 is a sulfite concentration calculator, 24 is a sulfite concentration indicator, 25 is an overflow pipe, 26 is a square,
27 indicates a dehumidifier, and -X-1 and ■2 indicate signals.

A sample liquid A containing sulfite is collected by a metering pump 1, and the temperature of the retentate liquid 6 in the acid decomposition container 5 is set to a predetermined temperature (70°C).
C) or higher) via the heater 2, and then supplied to the reaction vessel 5. The heat source of the heater 2 is controlled by detecting the temperature of the retained liquid 6 with a detector 4 and by a signal output from the temperature regulator 3 so that the retained liquid 6 reaches a predetermined temperature (70° C. or higher).

The staying liquid 6 in the acid decomposition container 5 is stirred with a stirrer 7 so that the solid content in the staying liquid 6 does not settle.
The pH of the retained liquid 6 is detected by the detector 14, and according to the result, a signal output from the controller 15 is used to control the trace pump 12.
An acid 0 for decomposing sulfites, such as sulfuric acid or hydrochloric acid, is injected into the acid decomposition container 5 by controlling K11! to the required value -(3 or less). (Control.

When an acid that decomposes sulfites, such as sulfuric acid or hydrochloric acid, is injected into the retentate 6, the sulfites in the sample solution A will be dissolved according to the following formula (1
) to (2), reacts with acid to form So.

occurs. (When the sulfite is 0aSO3, the formula +
11 and +21, but the same applies to salts other than Oa salt. ) (in case of sulfuric acid addition) OaSO3+H! E30a →0aSO4+H20+
8021...mark (1) (in case of adding hydrochloric acid) OaSO3+ 2HO1" 0aO1x + Hz O
+802 f -"' (21 The generated S02 is adjusted to the required flow rate with the flow controller 17 as a carrier gas, and part or all of the air (or nitrogen) is distributed to the distribution 9f2.
6, the remaining liquid 6 is blown into the remaining liquid 6 through the flow rate indicator 11 and the blowing pipe 8, and the remaining liquid 6 is blown into the remaining liquid 6. , it is vented as a vented gas E which is a mixture of air (or nitrogen) and moisture.

On the other hand, the remaining air (or nitrogen) used for blowing
16 merges with the extracted gas E coming out of the acid decomposition container 5, and the combined gas is used for the SO2 analyzer 22, which will be described later.
The remaining part is discharged as exhaust gas F, except for a part of it which is sucked and collected by the air pump 18.

Next, the stagnant liquid 6 is supplied with the sample liquid A from the metering pump 1.
The increased amount is discharged from the overflow pipe 25 to the liquid seal 13, and the liquid seal 13 maintains a liquid depth sufficient to overcome the internal pressure of the acid decomposition vessel 5 and removes solids in the overflow liquid from the acid decomposition vessel 5. The structure is such that liquid does not settle, and the excess amount of overflow liquid flowing into the liquid sealing vessel 13 is discharged as waste liquid. The S02, air (or nitrogen), and moisture extraction gas E generated according to the above reaction formulas (1) and (2) is combined with the remaining air (or nitrogen) 16 as described above, and then released as the exhaust gas F. However, a part of the exhaust gas F is removed by a dehumidifier 27 to remove moisture contained therein as a drain H, and then sucked by an air pump 18 to be drained 802.
The SO gas is sent to the analyzer 22, and the SO concentration is measured by the analyzer 22, and then released as exhaust G. 802 analyzer 22
The signal is sent to the sulfite concentration calculator 23, and the sulfite concentration calculator 23 further receives the flow rate signal from the air (or nitrogen) flow rate controller 17 and the sample liquid A sampling flow rate signal ■2 from the metering pump 1. Using these input signals, the computing unit 23 performs the following theoretical calculations to calculate the sulfite concentration in the sample liquid A and outputs it to the sulfite concentration indicator 24.

(Calculation of sulfite concentration) Sulfite concentration (+nol/l) = 0aSO3 as sulfite using the apparatus shown in Diameter Example Figure 2.
The concentration was measured. This case will be specifically explained using numerical values.

FIG. 3 shows the measurement results when the test apparatus shown in FIG. 2 was used under the following conditions.

0aSO3 concentration in sample slurry: 0.05, 0.1
, 0.2mo1/ as sample slurry supply flow rate '0.
12t/am Carrier gas type: air, nitrogen flow rate: 20t/m Set reaction temperature: 70, 80℃ Set reaction pi (: 3 total air flow rate + 10t/WiR Reaction vessel capacity: 15 Figure 3 shows the A detected value of Q a 8 O3 concentration,
This is a graph showing the comparison of analytical values obtained by manual analysis. The horizontal axis shows the 0aSO3 concentration obtained by manual analysis, and the vertical axis shows the measured value using water droplets. The black circle indicates 70℃, and the white circle indicates 80℃. The measurement results indicated by triangles indicate the results at 80° C. using nitrogen. Furthermore, Table 1 shows some examples from the test results regarding SOW measurement values, manual analysis values of Ca5Os concentration in sample liquid, and water droplet measurement values.
are summarized in

As is clear from Table 1, water droplets can be measured continuously for samples whose concentrations change rapidly with almost the same accuracy as manual analysis.

Above, we have specifically shown an example of the sulfite detection method when the sulfite is 0aSO3, but when the sulfite is HzSOz
, Na2803, NaH8Os, MgSO
3, Mg (H8O3)2. 2SO3゜KHSO3,
Ca(H8O3)2 could also be detected in the same way.

FIG. 1 is an illustration of an embodiment of the method of the invention. In FIG. 1, exhaust gas 100 containing SO is led to an absorption tower main body 101, contacts an absorption liquid within the tower, removes So, and is then discharged to the outside of the tower as purified gas 102. At the bottom of the absorption tower main body 101 is a tank 103 for storing absorption liquid.
The absorbent is stirred by a stirrer 104, and the absorbent is sent to the top of the tower by an absorption tower circulation pump 105, spread inside the tower, and brought into contact with exhaust gas.30. be absorbed. A part of the sulfite generated when the absorbent absorbs So, 'i is oxidized by 02 in the exhaust gas in the gas-liquid contact zone, so the acidic absorption liquid containing sulfite and sulfate and having a low - It falls into tank 103. In the tank 103, 0a003 as an SO2 absorbent is supplied from the 0aOO3 supply Lyle 106 in proportion to the amount of SO2 absorbed, and in order to neutralize the absorption liquid and oxidize the sulfite in the absorption liquid to sulfate. Air is blown through the provided air nozzle 107, or a liquid containing an oxidation catalyst such as manganese salt or cobalt salt is supplied from the oxidation catalyst supply line 108. Of course, air and an oxidation catalyst may be used together. When processing boiler exhaust gas, the load on the boiler and the sulfur component content in the fuel used vary, so the amount of exhaust gas 100 processed and the SO2 and O2 concentrations also vary, and eventually the absorption liquid in the tank 103 changes. The amount of oxidation of the sulfite in it begins to fluctuate.

That is, if the amount of exhaust gas 100 to be processed increases, the SO2 concentration increases, or the O2 concentration decreases, this can be dealt with by increasing the amount of air from the air nozzle 107 or increasing the concentration of the oxidation catalyst. On the other hand, if the oxidation load decreases, this is dealt with by reducing the amount of air or reducing the supply of oxidation catalyst. In the present invention, the tank 10
In order to instantaneously detect the sulfite concentration in the absorption liquid in the sulfite detector 109 on-line, the sulfite detector 109 has the configuration shown in FIG. 2.
is provided and sends the concentration signal to the sulfite controller 110.

The sulfite controller 110 receives a deviation signal between the detected value and the sulfite concentration set value set in the relationship between the permissible sulfite concentration value in by-products and the permissible sulfite concentration value related to S02 absorption performance. It is sent to an air flow controller 111 and/or an oxidation catalyst flow controller 112.

The air flow controller 111 receives the signal from the air flow meter 113 and the signal from the sulfite controller 110, and adjusts the opening and closing of the pulp 114 to open and close the air nozzle 107.
Adjust the amount of air blown in from the tank and operate at the minimum amount of air that can maintain the desired sulfite concentration.

On the other hand, in the oxidation catalyst flow rate controller 112, a signal from the flow meter 115 of the liquid containing the oxidation catalyst and a signal from the sulfite controller 11 are used.
By receiving the signal from 0 and adjusting the opening and closing of the pulp 116, the concentration of the oxidation catalyst is adjusted, and the operation is performed at the minimum catalyst supply amount that can maintain the desired sulfite concentration.

Here, the oxidation catalyst and air may be used alone or in combination. If the sulfite concentration in the absorption liquid is adjusted using the oxidation catalyst alone, the oxidation caused by 02 in the exhaust gas will be promoted, so if the inlet 802 concentration is very high and the oxidation load is large, the oxidation catalyst alone will be used. There may be cases where this is not possible. When adjusting the sulfite concentration in the absorption liquid by blowing air alone, if the oxidation load increases, the oxidation function may deteriorate due to the generation of large air bubbles, which also increases the power cost for air blowing. It will be a waste of money. Therefore, when an oxidation catalyst and air are used together, it is easiest to cope with large fluctuations in oxidation load. That is, in the present invention, it is possible to select whether to use the air as an oxidizing agent and the oxidation catalyst alone or in combination depending on the oxidation load amount. The absorption liquid whose sulfite concentration has been adjusted to the desired value through oxidation becomes a suspension mainly composed of sulfate gypsum particles, so the pump 1
The absorbent liquid is sent from the absorbent extraction line 118 to the centrifugal separator 119 via the absorbent line 17, where the by-product gypsum 120 is recovered.

The filtrate is drained from line 121 or recycled.

In Fig. 1, a case in which the sulfite concentration adjustment method of the present invention is applied to a wet lime-gypsum method flue gas desulfurization equipment that uses Oa O03 as an absorbent and produces gypsum as a by-product is specifically explained.
H'p Na2303 with Na2SO4 as absorbent,
The present invention can be similarly applied to a soda method in which NaH8O3 sulfite and Na2SO4f sulfate are discharged, and a flue gas desulfurization method in which a magnesium compound or a potassium compound is used alone or in combination. In short, the compounds that react with acid and emit SC+ in the sulfite detector shown in FIG. 2 are not limited to the above compounds, but can be applied as appropriate.

As explained in detail above, in the past, sulfite concentration was detected by manual analysis in accordance with JIS K 0102, which required labor and time. It is almost impossible to adjust the supply amount of oxidation catalyst and oxidation catalyst to the optimum value, that is, the most economical amount.
When recovering high-purity gypsum as a by-product, the solution is to supply excess air and oxidation catalyst to prevent the sulfite concentration from increasing.This is done from the perspective of energy and resource conservation. Although this is undesirable, the method of the present invention can instantly respond to rapidly fluctuating load conditions and supply the optimal amount of oxidizing agent (air, etc.) and oxidation catalyst without waste to reduce the sulfite concentration. It can be adjusted to a desired value and has the unique effect of being extremely economical.

The present invention will be explained in more detail with reference to Examples below.

Example 1 The equipment used is shown in Figure 1.

4,000rr of exhaust gas emitted from coal-fired boilers
1Wh is collected from the outlet of the electrostatic precipitator and transferred to the absorption tower main body 1.
It was introduced in 2001. Exhaust gas 100 is 8022,0004.

Dust 50 (IW1wyr/N, HOIlooPF
, had an average composition of HF30-. The absorbent 0aOO3 is made by crushing limestone into a powder of 325 mesh or less, and suspending it in water to obtain 2 mol/l of 0a.
It was supplied to tank 103 from line 106 as OO3 slurry. The tank 103 that stores the absorption liquid has a capacity of 2,00 (1
+s+ diameter, the liquid depth was 2,000 IN, and the liquid level was controlled so that the amount of absorbed liquid was approximately 6,000 tons. Absorption tower circulation pump 105, 60ff1'/
The absorption liquid of h was sprayed from the top of the absorption tower 101, and the tower was filled with a grid to clean the exhaust gas. S02.
Most of the dust, Hoe, and HF are collected in the absorption liquid, and the purified gas 102 has an average composition of 50% S02.
泗、dust 60m97m'N, Hoe, , HF
were included below KIIF. So.

The absorbent liquid was absorbed to form sulfite and the acidic absorption liquid flowed down to the tank 103, so OaQO3 was supplied as an alkali from the line 106 so that the absorption liquid became neutral. The absorption liquid is used in a sulfite detector 109 having the configuration shown in FIG.
was continuously sampled at 0.121 min/min and the sulfite concentration was immediately indicated. When neither the air from the air nozzle 107 nor the oxidation catalyst from the oxidation catalyst supply line 108 is supplied, the indicated value of the sulfite detector 109 is 0.
The aSOs varied in the range of 0.3 to Q, 5 mol/l, and the average Q, 4 mol/l. 0aSO3
The concentration fluctuations were due to fluctuations in the SO2 concentration and 02 concentration contained in the exhaust gas 100. The absorption liquid containing 0aSO3 as sulfite was extracted from the pump 117 according to the material balance between So and the absorbed amount. Next, set the sulfite concentration to 0.05m using the sulfite controller 110.
oi/z and sends the deviation signal to the air flow controller 111, air flow meter 113, pulp 114, air nozzle 10
Air was blown into the absorbent via 7. In the steady state, the air flow rate was 80 m''N/h, and the sulfite concentration in the absorption liquid could be maintained at the set value. /7, and continuous operation tests were conducted for each, but in steady state,
The sulfite concentration in each absorption liquid was 0.047 mo1/l.

The detected values were 0.093 mol/l and 0.194 mol/l. The sulfite concentration management according to the present invention is shown in Table 1 of a medical examination example in comparison with manual analysis data. Furthermore, when operating with the sulfite concentration set value k O, 0005 mol/l, the air flow rate reached a steady state at 250 m''N7h (manual analysis of the absorption liquid showed that it was less than 0.001 mol/l). High purity. 120 pieces of by-product gypsum were recovered.

Example 2 In Example 1, the signal from the sulfite controller 110 was sent to the air flow controller 111, but this time it was switched to the oxidation catalyst flow controller 112, and air blowing into the absorption liquid was stopped. did? SO contained in Gas 100! is 1,200
F and was operated for about 18 hours without adding an oxidation catalyst.

The record of the indicated value of the sulfite detector 109 indicating the sulfite concentration in the absorption liquid at this time is shown in area (A) of FIG. The sulfite concentration in the absorption liquid reached a steady state at about 0.03 mol/l.

Next, a 2Qwt% Mn5Oa aqueous solution as an oxidation catalyst is started to be supplied to the tank from the line 108, and at the same time, the sulfite concentration setting value of the sulfite controller 110 is adjusted to 0.001 mo.
It was set to l/l and operated. The record of the sulfite concentration in the absorption liquid at this time is shown in area (B) of FIG.

In both cases, the sulfite concentration could be controlled by controlling the supply amount of the MnSO4 aqueous solution at the desired sulfite concentration setting value. As described above, the present invention has a remarkable effect of being able to control even a concentration range that is considered to be a trace concentration compared to the accuracy of conventional manual analysis.

Example 3 Continuing from Example 2, an example will now be described in which a method of blowing air through the air nozzle 107 is used in combination with the supply of the MnSO4 aqueous solution. In this embodiment, the exhaust gas 1
00K included F30xFi, 3.000F.

The sulfite concentration setting value of the sulfite controller 110 is set to 0.03.
mol/l, OD1msl/l, 0.0005mo
The records of the indicated values of the sulfite detector 109 when expressed as l/l are shown in the areas (0), (D), (E), (0), (E), and (0), respectively, in FIG. ) There is a correlation between the Mn concentration in the absorption liquid and the amount of air blown from the air nozzle 107, and if the amount of 20 wt% MnSO4 aqueous solution supplied from the line 108 is increased so that the Mn concentration increases, Correspondingly, the air flow rate was reduced.The method of simultaneously sending the signal from the sulfite controller 110 to the air flow controller 111 and the oxidation catalyst flow controller 112 is difficult because the response to the oxidation catalyst concentration is slow. It is better to control the sulfite concentration by sending a signal mainly to

[Brief explanation of the drawing]

FIG. 1 is an illustrative diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the configuration of a sulfite detector used in the present invention, and FIG. 3 is a measurement value obtained by the sulfite detector shown in FIG. 2. ★Correlation diagram with manual analysis values. FIG. 4 is a graph showing the change in sulfite concentration over time, showing the effects of the present invention. 2... Heater, 5... Acid decomposition container, 17... Flow rate controller, 22... So2 analyzer, 23... Sulfite concentration calculator, 24... Sulfite concentration indicator, 27... Dehumidifier, 100... Exhaust gas, 101... Absorption tower main body, 1
05...Absorption tower circulation pump, 109...Sulfite detector, 110...Sulfite controller, 111...Air flow rate controller, 112...Oxidation catalyst flow rate controller, 119...
・Centrifugal separator, 120...By-product gypsum Fig. 3 Midoz) Analysis r; prayer b Ca 303Xl'J rrno
No//70 and 14 sulfate concentration (mol/1) 1st
Continuation of page [Phase] Int, CI, 4 Identification symbol Placed within the agency @ Inventor Susumu Okino No. 4-6-n, Onshin-cho, Kuruhiroshima Research Institute, Nishi-ku, Hiroshima Mitsubishi Heavy Industries, Ltd. ) July 1980 (,c Fl Case Display 1988 Patent Application No. 079668 Name of the invention Relationship with the famous case for amending the sulfite concentration adjustment method Patent applicant (1 location Marunouchi, 1st Ta-ku, Tokyo) 1-Item No. 5 IIj Name (620) Mitsubishi Heavy Industries Co., Ltd. Agent 1 Correct the "total air flow rate" on page 11, line 5 of the specification to 1 injected carrier Ganu flow rate. 2 In Figure 2. Correct the yellow color of the sampling flow rate signal for sample liquid A as ■2 so that it is not distributed.

Claims (1)

[Claims] In a method of oxidizing sulfite in a liquid or suspension containing sulfite, a signal detecting the sulfite concentration of the liquid;
A method for adjusting sulfite concentration, comprising adjusting the supply amount of an oxidizing agent and/or oxidation catalyst for oxidizing sulfite in the liquid based on a deviation signal from a sulfite concentration setting value.