JPS61293528A - Wet stack-gas desulfurization method - Google Patents

Abstract

PURPOSE:To perform the recovery of gypsum in one tower by bringing a suspension into contact with an O2-contg. gas in the inside of a circulation tank incorporated in an absorption tower, regulating the amount of all Ag2SO3 contained in the suspension and thereafter adding CaCO3 or Ca(OH)2 to keep pH in a prescribed range and performing the gas-liquid contact with an exhaust gas. CONSTITUTION:An exhaust gas 1 contg. SOx is introduced into an absorption tower 3 and the solid fine grains and SOx are collected in a suspension. One part of CaSO3 is brought into contact with O2 contained in the exhaust gas to make one part thereof gypsum and the amount of all Ag2SO3 is regulated so that it is made to <=1.3 times of the saturated dissolved amount of CaSO3 in 3.8 pH. The greater parts of CaSO3 are oxidized with air in an oxidation reaction apparatus 23 to produce gypsum. On the other hand, the suspension of CaCO3, Ca(OH)2 and H2O is sent to the oxidation apparatus 23 through the feed lines 28, 29 and pH is kept to 3.8-5.0 and pH, the feed amount of limestone and SOx are detected to control the feed amount of air. After gypsum is retained in an oxidation reaction apparatus 8 for a specified time, it is recovered through a drawing-out line 102.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a wet flue gas desulfurization method, and in particular, it collects solid fine particles and sulfur oxides in the combustion flue gas in a tower-type absorption tower and efficiently removes gypsum from the flue gas. The present invention relates to a wet flue gas desulfurization method that enables the recovery of waste gases as waste gas.

[Background of the invention]

The mainstream wet flue gas desulfurization equipment currently in use uses calcium-based absorbents and recovers gypsum as a byproduct. In other words, limestone, quicklime,
This is the limestone/gypsum method (or lime/gypsum method), which uses slaked lime. FIG. 16 shows a conventional flue gas desulfurization device that uses limestone as an absorbent and recovers gypsum as a by-product.

Exhaust gas 1 from a boiler, etc. is led to a dust removal tower 2, where it is cooled and removed, and a part of it is desulfurized, and then led to an absorption tower 3, where it comes into contact with circulating fluid slurry, and is passed through a demister 4. The mist is removed from the water and discharged from the absorption tower 3. On the other hand, limestone slurry 20, which is an absorbent slurry, is supplied to the absorption tower circulation tank 5 by a limestone slurry pump 21, and the slurry is supplied to a spray nozzle 22 installed in the absorption tower 3 by an absorption tower circulation pump 7. It is sprayed into the absorption tower 3, contacts the exhaust gas 1, absorbs and removes sulfur oxides in the exhaust gas 1, returns to the absorption tower circulation tank 5, and is recycled and used. The slurry in the absorption tower circulation tank 5 after absorption is supplied from the absorption tower bleed pump 8 to the scrubbing tower circulation tank 6, is sprayed from the spray nozzle 22 in the scrubbing tower 2, and further comes into contact with the exhaust gas 1, By removing the sulfur oxides in the exhaust gas 1, the amount of unreacted limestone in the slurry is reduced and the slurry is supplied to the byproduct recovery system, that is, the oxidation tower supply tank 10. In the oxidation tower supply tank 10, unreacted limestone is converted into gypsum by adding sulfuric acid, and the pH is adjusted to a value suitable for oxidation. The pl-1 prepared slurry is supplied to the oxidation tower 12 by the oxidation tower supply pump 11, where the calcium sulfite is air oxidized to gypsum, and then passed through the conduit 1.
3 to Shirafuna 14, and tank 15. After being concentrated by pump 16, the gypsum slurry is passed through centrifuge 17.
The gypsum 18 is dehydrated and powdered gypsum 18 is recovered. Shirafuna 14
The filtered water 19 from the centrifugal separator 17 is circulated and reused.

In addition, 20 is a limestone slurry, and 21 is a limestone slurry pump.

However, in this prior art, the absorption tower 3 and the removal tower 2
is located separately, a device for neutralizing unreacted limestone in the slurry extracted from the absorption system (sulfuric acid tank, sulfuric acid pump, etc.) and a device for oxidizing calcium sulfite are required, resulting in a large site area and equipment. It has the disadvantage that it is complicated. Additionally, the utility of reacting limestone (excess limestone) and adding sulfuric acid was required.

In this manner, the combustion exhaust gas 1 is led to the absorption tower 3, where it is brought into gas-liquid contact with a suspension containing calcium carbonate or calcium hydroxide, and the suspension absorbs sulfur oxides. The absorption reaction process for a suspension containing calcium carbonate is as follows.

Considering SO2 as a sulfur oxide in combustion exhaust gas, SO□ gas is physically absorbed into a suspension to generate sulfurous acid.

SO bagasse)== Niji 5O (absorbed in suspension) (1)
SO2 (in liquid) +1lz01=kol1zSO+
(2) Sulfurous acid in the liquid dissociates and reacts as shown below.

HzSOs;=GoH"+ll5Ot-<31 On the other hand, limestone is often used as calcium carbonate, and the calcium carbonate in limestone is dissolved in the suspension.

CaC0t 4? ::2CaCOz (in liquid) (4) Dissolved calcium carbonate reacts with sulfite in suspension to produce calcium sulfite.

CaC0t + It" +ll501-→Ca5Oa
＋! IzO+ C(h↑(5) Also, the calcium sulfite produced by formula (5) reacts with sulfite in the suspension to produce calcium hyposulfite.

CaSO3+ H" +l!SO3-a, -koCa 0
1S(h) 2 (6) On the other hand, calcium hyposulfite produced by the reaction of formula (6) undergoes a reaction with calcium carbonate in the suspension as shown in the following formula to produce calcium sulfite.

2CaCOs+Ca(lIsO*)z →2CaS0.
3+Ca01COs)z (71 Weakly acidic calcium bicarbonate Ca (llcO+) 2 , +6) produces weakly acidic Ca (IICOaL). It acts as an agent and keeps the pH relatively stable.

In the conventional wet flue gas desulfurization method, a portion of the above-mentioned suspension is led to an oxidation tower to proceed with the oxidation reaction of calcium sulfite to form gypsum, but in the oxidation tower, sulfuric acid is added to adjust the pH of the suspension. to proceed with the oxidation reaction to form calcium hyposulfite. On the other hand, when sulfuric acid is added to the suspension, a neutralization reaction occurs with unreacted calcium carbonate and gypsum is produced.

CaC0z + HtSOa + lzQ → Ca5Oa
・211zO+ Cot↑(8) Also, calcium sulfite is 2CaSO3+ +12SO4+ 2H□0→CaSO
4.2020 + Ca (IISOi) When air is supplied to the oxidation tower, oxygen is dissolved in the liquid, and the dissolved oxygen and most of the calcium sulfite react with calcium hyposulfite (formula 91,001) to form gypsum. .

Ca () ISO3) z + % Ot+ 2820
−→Ca5Oa・28zO+ H2SO+ In this way,
In conventional wet flue gas desulfurization equipment, unreacted calcium carbonate is removed from the absorption tower, so it is necessary to supply an excessive amount of calcium carbonate, and sulfuric acid is also required for pH adjustment in the oxidation tower. There was a problem in that the utility cost was high, and the equipment cost was high due to the auxiliary equipment for installing the oxidation tower.

Therefore, Japanese Patent Publication No. 58-28206 and Japanese Patent Application Laid-open No. 58-92451 have been proposed in order to carry out the 01 type oxidation reaction in an absorption tower for the purpose of reducing the utility cost and equipment cost.

JP-A-58-92452, JP-A-58-95543
, JP-A-58-98125, JP-A-58-98126
, JP-A-58-104619° JP-A-58-1046
20. Utility Model Application No. 588-91428 has already been proposed. However, in both cases, the pH of the suspension is high;
Although it is preferable for the absorption of sulfite gas in the combustion exhaust gas, the oxidation reaction rate is slow due to the high pH, and the concentration of sulfite radicals in the suspension gradually increases.

In other words, in order to smoothly perform dust removal, absorption, and oxidation in the absorption tower, and to efficiently recover gypsum and obtain high desulfurization performance without separately installing it in the oxidation tower, it is necessary to adjust the pH of the calcium sulfite oxidation system and to absorb SOz. It is necessary to adjust the total SO3-'' concentration of the system.

[Purpose of the invention]

The purpose of the present invention is to provide an absorption tower and a gypsum recovery device that can be used to oxidize calcium sulfite in an absorption tower and recover gypsum without installing an oxidation tower, which was done in the conventional wet flue gas desulfurization method. This is done in a ceremony.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention aims to reduce the amount of total sulfite radicals in the suspension by contacting with oxygen-containing gas in a circulation tank in a column, thereby reducing the amount of saturated calcium sulfite dissolved at pH 3.8. After that, calcium carbonate or calcium hydroxide is added to maintain the pH of the suspension between 3.8 and 5.0 to separate combustion exhaust gas and gas liquid. It is designed so that they are in contact with each other.

[Embodiments of the invention] Embodiments of the present invention will be described below with reference to the drawings.

Fig. 1 is a principle diagram of a wet flue gas desulfurization device according to an embodiment of the present invention, Figs. 2 to 5 are data obtained by experiments by the inventors, and Fig. 2 shows suspension pH and separation. S in the gas phase
Figure 3 shows the relationship between the O□ concentration, Figure 3 shows the relationship between suspension pH and SO2 absorption rate, and Figure 4 shows the relationship between suspension pH and CaSO3 oxidation rate. Figure 5 is a sectional view showing a calcium sulfite oxidation reaction device, Figures 6 and 7 are sectional views showing an air atomizer, and Figures 8 and 9 are air atomizers showing the relationship between air supply amount and oxidation rate. Oxidation performance characteristic diagram, 1st
Figure 0 is a spray dust removal performance characteristic diagram showing the relationship between dust particle size and dust removal rate, Figure 11 is a schematic diagram of the experimental equipment, Figure 12 is a characteristic diagram showing the relationship between suspension pH and desulfurization performance, 13th
The figure is a characteristic diagram showing the relationship between the absorption rate ratio of total 5(h- and 5(lz) in the suspension. Figure 14 is a characteristic diagram showing the relationship between pH and total 5O1-. Figure 15 is the gypsum particle size. It is a characteristic diagram which shows the relationship between and cumulative weight distribution.

Before explaining the embodiments of this structure, the experimental results of the inventors will be introduced using FIGS. 2, 3, and 4.

The inventors of the present invention have been studying equipment rationalization and efficiency improvement for wet flue gas desulfurization equipment for some time, and as a result of basic studies and tests at a pilot plant, the conventional wet flue gas desulfurization equipment Integrate the oxidation tower and! We have discovered a wet desulfurization device and a gypsum recovery method that do not require the amount of sulfuric acid for adjusting the pH of the temperature control liquid, can reduce the amount of calcium carbonate consumed, and can recover marketable by-product gypsum.

To oxidize calcium sulfite in a suspension that has absorbed sulfur oxides in combustion exhaust gas, the above-mentioned formula C11 is mainly followed, but the oxidation reaction depends on the hydrogen ion concentration in the suspension, that is, pH
It has become clear that there is a strong dependence on This is because when the pH in the suspended S solution changes, the dissolution rate of calcium sulfite increases, and the rate of calcium sulfite oxidation increases.

Figure 4 shows what was revealed from the basic study results.
These are the results of determining the pH and oxidation rate in the suspension. Oxidation hardly occurs when the pH in the suspension is around 7. Therefore, when sulfurous acid or sulfuric acid is added to gradually lower the pH, the oxidation reaction rate of calcium sulfite increases rapidly, and the pH
It has become clear that H becomes constant from around 4 to below.

On the other hand, as shown in Figure 2, as the pH of the suspension decreases, the oxidation concentration of calcium sulfite tends to increase as explained in Figure 4, but SO2 is desorbed into the gas phase. come. That is, in the oxidation reaction process of calcium sulfite, pH 3,
It is more economical to set the value around 8 to 5.0.

Figure 2 shows the results when the amount of supplied air is constant.
It can be seen that the dissolution rate of calcium sulfite is the rate-determining step in the oxidation reaction in a high pH region, whereas in the low pH region, the rate of oxygen dissolution is the rate-determining step in the oxidation reaction. That is, the pHjW range is 3.8 to 5.0.
When oxidizing calcium sulfite in , increasing the dissolution rate of oxygen, that is, keeping the air atomization the same,
It has become clear that the amount of calcium sulfite oxidation can be adjusted by adjusting the amount of air supplied per unit suspension.

In theory, by supplying calcium carbonate to the absorption system in an amount equivalent to the chemical equivalent of sulfur oxides contained in the combustion exhaust gas, the calcium balance during gypsum recovery can be balanced.

However, basic research has shown that the dissolution rate of limestone containing calcium carbonate is affected by the hydrogen ion concentration in the suspension, the calcium carbonate concentration 1 right limestone particle size, the calcium 11 ion concentration, the carbonate ion concentration, and the temperature. It is clear from the results that
In particular, it became clear that the dependence on hydrogen ion concentration was large. In other words, it has been revealed that by lowering the pH, the dissolution rate of limestone has a reaction order of about 2 with respect to the hydrogen ion concentration, which is highly dependent on pH. This means that the suspension p in the absorption tower in conventional wet flue gas desulfurization equipment
Since H was operated at around 5.5 to 6, the dissolution rate of limestone was suppressed and excessive limestone was supplied.

This caused a vicious cycle in which the amount of sulfuric acid consumed in the next oxidation tower increased.

Next, the inventors determined that when simultaneously oxidizing calcium sulfite in an absorption tower and sequentially lowering the pH of the suspension, the absorption rate of SOt into the suspension, ie! ! ! It was necessary to study the pH of the suspension and the SO□ absorption capacity per unit volume of suspension. This is +11 mentioned above. (2),
As shown in Equation 431, as the hydrogen ion concentration in the suspension increases, the SOz absorption rate naturally decreases, and the desulfurization performance in the absorption tower deteriorates.

Figure 3 shows the pH and SO2 absorption rate at the suspension interface, and the SO2 absorption rate decreases rapidly from the pH range of 3.5 to 3.8, and the desulfurization rate in the absorption tower decreases. Although the performance deteriorates, when the suspension pH is around 4 or higher, the SO□ absorption rate does not drop sharply, and when the suspension pH is around 4 or higher, the desulfurization performance can be maintained as before. Ta.

Next, in order to carry out oxidation and dust removal in the absorption tower, the present inventors needed to investigate whether submicron particles contained in the combustion exhaust gas could be collected by the gas-liquid contact method. The present inventors have conventionally adopted a spray type gas-liquid contacting device that can maintain low ventilation loss and have excellent gas-liquid contact efficiency, and have achieved low pressure loss and high desulfurization performance. The dust removal performance of the one-spray system is high, and the conventional dust removal tower installed outside the absorption tower has been eliminated, allowing the absorption of sulfur oxides and the dust removal function to be performed within the absorption tower.・Absorption tower system In order to completely oxidize calcium sulfite, it is important to refine the amount of air required and use a refinement method that has a high air utilization rate. In the conventional oxidation tower, calcium sulfite was oxidized by atomizing air under conditions in which the inside of the system was maintained at about 2 to 3 ats+.

In other words, in the conventional method, highly efficient oxidation was carried out with an air utilization rate of 50 to 70%, but when the oxidation reaction is carried out in an absorption tower, the pressure in the system is almost atmospheric pressure, and the air atomization method (
(miniaturization method) became important.

Furthermore, the important thing about air atomizers is that the power consumption for miniaturization is small, and we have verified various atomizers and developed a low-power, high-efficiency atomizer.

As a result of the above studies, we have developed an energy-saving wet flue gas desulfurization device that can streamline equipment as shown in the present invention.

An embodiment of the present invention will be described below with reference to FIG.

The absorption tower 3 includes an oxidation reaction device 23, a gas-liquid contact device 22, circulation lines 25 and 26 for the suspension 24, a supply line 27 for air serving as an oxygen source, and a supply line for sending calcium carbonate or calcium hydroxide to the absorption tower 3. It has built-in lines 28 and 29, a suspension line 30 for extracting a suspension containing gypsum, a suspension pH detector 31, a detection line 32, a suspension stirrer 33, a mist collector 4, and the like. The combustion exhaust gas 1 containing sulfur oxides is introduced into the absorption tower 3 and comes into gas-liquid contact with a suspension in a gas-liquid contactor 22, and solid particles and sulfur oxides are collected in the suspension to become a treated gas 34. . The suspension is collected in the oxidation reactor 23 and becomes a suspension 24.

A part of calcium sulfite is oxygen 5 to 7 in combustion exhaust gas 1.
% and some of it becomes gypsum. Most of the calcium sulfite is transferred to the oxygen source supply bag 2 in the oxidation reaction device 23.
The air sent from 27 is atomized and oxygen is dissolved in the suspension, which reacts with the dissolved oxygen and is oxidized to gypsum. A suspension stirrer 33 is installed at the bottom of the oxidation reaction device 23 to stir the solids in the suspension 24 to prevent them from settling.On the other hand, calcium carbonate or calcium hydroxide is mixed with water. The suspension is fed to the oxidation reactor 23 via the feed line 28.29, and the suspension 24 or the suspension 24 circulation line 25. Circulation pump 7° feeds into supply line 26. The suspension 24 of the oxidation reaction device 23 is detected by the pH detector 31
In conjunction with the flow rate regulator of the air supply line 32, the optimum pH1 limestone supply amount for the oxidation reaction and sulfur oxides in the combustion exhaust gas are detected, and the air supply amount is controlled. After staying in the oxidation reactor 8 for a certain period of time, the gypsum is transferred to the extraction line 10.
2 and sent to a gypsum recovery device (not shown).

The amount of air required to oxidize the calcium sulfite in the suspension to a total concentration or less than a predetermined concentration varies depending on the efficiency of the air atomizer, but increasing the efficiency of the atomizer increases the power cost. Therefore, an effective method is to blow air into the suspension stirrer 33 and use the shear force of the stirring blades to atomize the air.

In addition, a constriction part 3 is provided in the piping system 36 for the suspension 24 shown in FIG.
5 is installed, and an air supply line 27. When the two liquids are mixed in the suspension 24 at a certain flow rate in the constriction section 35, the air becomes finer. If these two-liquid air atomizers are ejected in the cylindrical circumferential direction of the oxidation reactor 23 as shown in FIG. 7, the suspension 24 can also be stirred. Figures 8 and 9 show representative examples of basic experimental results regarding the oxidation performance of the air atomizer shown in Figure 6.
As shown in the figure.

As shown in FIGS. 8 and 8, the oxidation rate is determined by the flow rate of the two liquids in the constriction section 35 in FIG. This is an air atomizer suitable for

Next, in the wet desulfurization equipment of the present invention, when the combustion exhaust gas and the suspension are brought into gas-liquid contact, it is checked whether the solid particles in the combustion exhaust gas can be collected or not. Figure 10 shows the dust removal performance results. Figure 10 shows that the droplet diameter of the suspension varied from 800 to 2300 μm, and the superficial gas flow velocity varied from 1.3 to 3.1 m/S.
It also shows typical removal performance when the ratio of suspension to gas amount is varied from 1.5 to 6. Higher dust removal performance was obtained than the conventional dust removal performance that collected solid particulates in combustion exhaust gas. That is, it has become clear that solid particles in the combustion exhaust gas can be collected with high efficiency in the absorption tower according to the present invention.

Furthermore, when the pH of the suspension is set to a region where calcium sulfite is easily oxidized, it is clear that the absorption rate of SO□ is not significantly affected at pH 4 or higher, as shown in Figure 3. 150m as shown in Figure 11.
Absorption experiments were carried out using an absorption tower in the middle of the experiment, and the S02 removal performance was investigated. Suspension is CaC0.0.4wt%, Ca5Ot%
, Ca5O,%, the SOz concentration in the simulated combustion exhaust gas was 11000 pp, and the gas flow rate was 1.2 m/S.

As shown in Figure 12, the suspension pH and desulfurization performance are as follows:
Desulfurization performance tends to decrease slightly in the vicinity, but at pH 4 or higher, desulfurization performance is not affected much, and as shown in Figure 13, the total 5Off-? J1 degree is 100
+-mol/(1) Desulfurization performance decreases near pH 4, but it was found that if the pH value is maintained below 30.3''-, high desulfurization performance can be obtained in the wet desulfurization method of the present invention.

Further, the oxidation reaction apparatus 2 shown in the configuration of the present invention shown in FIG.
The oxidation rate of calcium sulfite in pH 3 is very fast in the pH range of around 4, and the rate of oxygen absorption is the rate-determining process, and the oxidation rate can be increased by adjusting the amount of air and improving the air atomization method. Figure 14 shows the pH and saturation solubility curves of all 503-.

At around pH 4, it is 70 to 80 mmol/1, but it is preferable from the viewpoint of desulfurization performance to oxidize the entire amount in the oxidation reactor ff123 shown in FIG. However, the experimental results of the absorption tower shown in Figure 11 show that the desulfurization performance remains unchanged as long as the total sulfite ion concentration, including solid calcium sulfite, is approximately 1.3 times or less than the saturated dissolved amount near pH 4. was made into

Also, as shown in Figure 5, in order to increase the amount of dissolved oxygen,
It is efficient to supply air from multiple locations in the height direction of the oxidation reactor 23, and in order to recover large gypsum,
The bottom of the oxidation reactor 23 is shaped like a Yune, and coarse gypsum can be recovered by slow stirring.

Figure 15 shows exhaust gas it60 to confirm the performance of the present invention.
The particle size distribution of the recovered gypsum was confirmed using actual gas (coal-fired boiler) of ONm3/b. As impurities in gypsum, CaSO3・%1120 is 0.00002 mol
/l, CaC0t was not detected. The purity of the gypsum recovered in this way also revealed that the wet flue gas desulfurization method according to the present invention has marketable quality as well as the conventional method.

Particularly, in the oxidation reaction apparatus according to the method of the present invention, the pH range can be adjusted by adjusting the air supply amount depending on the content of sulfur oxides in the combustion exhaust gas. The amount of limestone supplied is adjusted according to the sulfur oxide content in the combustion exhaust gas, but since the pH is low, calcium hyposulfite is produced as a buffer, and the pH of the suspension remains at the specified level without major fluctuations. It can be operated at a pH suitable for oxidation reactions. In addition, increasing the amount of air and accelerating the oxidation reaction rate of calcium hyposulfite will reduce p.
Since H tends to decrease, the pH of the suspension in the oxidation reactor 8 shown in FIG. 4 can be adjusted by adjusting the amount of air supplied. However, when the amount of air is increased, decarboxylation reactions occur simultaneously, which tends to increase the pH, but it has become clear that these effects are small.

〔Effect of the invention〕

According to the present invention, solid fine particles and sulfur oxides in combustion exhaust gas are collected in a suspension, and a pH range suitable for the oxidation reaction of calcium sulfite and a sulfite group that does not reduce the So2 absorption rate of the suspension are obtained. Smooth oxidation of calcium sulfite can be achieved by limiting the content of Sot, and since the amount of oxidation of sulfite radicals is adjusted by the amount of air blown, the desulfurization rate remains the same as the Sot absorption rate of the conventional method. Performance can be obtained.

In addition to absorption and removal of sulfur oxides in the combustion exhaust gas, it has also become clear that solid particles in the combustion exhaust gas can be collected in a suspension, making the conventional dust removal tower unnecessary. In the calcium sulfite oxidation reaction system installed at the bottom of the absorption tower, the amount of calcium sulfite oxidized can be adjusted by adjusting the air supply amount, so the amount of sulfite radicals in the suspension supplied to the gas-liquid contact section can be adjusted to a predetermined amount or less. As a result, high desulfurization performance can be obtained.

By integrating the functions of dust removal, absorption, and oxidation mechanisms into one tower as described above, it is possible to reduce the oversupply rate of limestone and have the effect of increasing the utilization rate of limestone. In addition, the pH can be adjusted by adjusting the amount of air supplied to the calcium sulfite oxidation reaction system, making it unnecessary to replenish sulfuric acid to the calcium sulfite oxidation reaction system, making it possible to reduce nutrition.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of a wet flue gas desulfurization device according to an embodiment of the present invention, Figs. 2 to 5 show experimental data;
The figure shows the relationship between suspension p) (and the desorbed gas phase) SOt: a degree, Figure 3 shows the relationship between suspension pH (!: soz absorption rate), and Figure 4 shows the relationship between suspension pH and CaC0. : Shows the relationship between the oxidation rate of +.Figure 5 is a cross-sectional view showing a calcium sulfite oxidation reaction device, Figures 6 and 7 are cross-sectional views showing an air atomizer, and Figures 8 and 9 are air supply. Oxidation performance characteristic diagram of air atomizer showing the relationship between amount and oxidation rate, 1st
Figure 0 is a spray dust removal performance characteristic diagram showing the relationship between dust particle size and dust removal rate, Figure 11 is a schematic diagram of the experimental equipment, Figure 12 is a characteristic diagram showing the relationship between suspension pH and desulfurization performance, 13th
The figure is a characteristic diagram showing the relationship between the absorption rate ratio of total 803- and S(h) in the suspension, and Figure 14 shows the relationship between pH and total 503-
FIG. 15 is a characteristic diagram showing the relationship between gypsum particle size and cumulative weight distribution. FIG. 16 is a schematic system diagram of a conventional wet flue gas desulfurization apparatus. DESCRIPTION OF SYMBOLS 1... Exhaust gas, 3... Absorption tower, 5... Circulation tank, 23... Oxidation reaction device, 24... Suspension, 27.
...Oxygen source supply device. Figure 1 Figure 3 Figure → View 4 pH at the liquid interface (-) Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 □ 12 R1 I5! -Supply amount (Kg) 9th
Figure I % M Di (Nrr?/h) Figure 10: I/z Tomb 1 (m a-5) No. 1 of Taste 4'i Net
Figure 1 Figure 13 0 50 100 +50 ZOO → Suspension *v+I
C age o, - (m-moQ/view) Fig. 14 - pH (-) Fig. 15 - Ichi Uhikunemurakaki (Table m)

Claims (1)

[Claims] A suspension containing calcium carbonate or calcium hydroxide is brought into gas-liquid contact with combustion exhaust gas containing sulfur oxides to desulfurize it, and the exhaust gas is also cooled, dust removed, and sulfur oxides absorbed and removed in the same tower. In a wet flue gas desulfurization method for recovering gypsum as a living organism, the amount of total sulfite in the suspension is reduced to saturation of calcium sulfite at pH 3.8 by contacting it with an oxygen-containing gas in a circulation tank in the tower. Adjust the amount to be 1.3 times or less of the dissolved amount, then add calcium carbonate or calcium hydroxide to maintain the pH of the suspension at 3.8 or more and 5.0 or less and remove it from the combustion exhaust gas. A wet flue gas desulfurization method characterized by bringing gas into liquid contact.