JPH0579364B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a wet flue gas desulfurization method, and particularly to a method for efficiently collecting solid particulates and sulfur oxides in combustion flue gas in a single-column absorption tower. This invention relates to a wet flue gas desulfurization method that can desulfurize and recover as gypsum.

[Background of the invention]

The mainstream wet flue gas desulfurization equipment currently in use uses calcium-based absorbents and recovers gypsum as a byproduct. That is, limestone, which uses limestone, quicklime, and slaked lime as absorbents.
This is the plaster method (or lime/gypsum method).

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 discharged from a boiler etc. is sent to a dust removal tower 2
After being cooled and dust removed here and some of it is desulfurized, it is led to the absorption tower 3, where it comes into contact with the circulating fluid slurry, the mist is removed by the demister 4, and the mist is discharged from the absorption tower 3. be done.

On the other hand, limestone slurry 20 which is an absorbent slurry
is supplied to the absorption tower circulation tank 5 by the limestone slurry pump 21. The slurry is supplied by the absorption tower circulation pump 7 to the spray nozzle 22 installed in the absorption tower 3, and is sprayed from there into the absorption tower 3, comes into contact with the exhaust gas 1, and absorbs and removes sulfur oxides in the exhaust gas 1. It is returned to the absorption tower circulation tank 5 and used for circulation.

After absorption, the slurry in the absorption tower circulation tank 5 is transferred from the absorption tower bleed pump 8 to the dust removal tower circulation tank 6.
supplied to Spray nozzle 22 inside dust removal tower 2
The slurry is sprayed from the slurry, further comes into contact with the exhaust gas 1, and reduces the amount of unreacted limestone in the slurry by removing sulfur oxides in the exhaust gas 1, and is supplied to the byproduct recovery system, that is, the oxidation tower supply tank 10. be done.

In the oxidation tower supply tank 10, unreacted limestone is adjusted to a pH value suitable for oxidation by adding sulfuric acid, and is recovered as gypsum. The pH-adjusted slurry is supplied to the oxidation tower 12 by the oxidation tower supply pump 11, where the calcium sulfite is air oxidized to become gypsum. Thereafter, the gypsum slurry is led to a syringe 14 through a conduit 13, concentrated in a tank 15 and a pump 16, and then dehydrated in a centrifuge 17 to recover powdered gypsum 18.

In addition, the above-mentioned shaker 14 and centrifugal separator 17
The filtered water 19 is circulated and reused. In the figure, 20 is a limestone slurry, and 21 is a limestone slurry pump.

However, in this conventional technology, the absorption tower 3 and the dust removal tower 2 are installed separately, and there is a device for neutralizing unreacted limestone in the slurry extracted from the absorption system (sulfuric acid tank, sulfuric acid pump, etc.) and an oxidation device for calcium sulfite. This has the disadvantage that the site area is large and the equipment is complicated. In addition, utility of reacted limestone (excess limestone) and sulfuric acid to be added was required.

As described above, 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 in the case of a suspension containing calcium carbonate is as follows.

Considering SO ₂ as a sulfur oxide in combustion exhaust gas, SO ₂ gas is physically absorbed into a suspension and produces sulfurous acid.

SO ₂ (gas) SO ₂ (absorbed in suspension) (1) SO ₂ (in liquid) + H ₂ OH ₂ SO ₃ (2) Sulfurous acid in the liquid dissociates and reacts as shown below.

H ₂ SO ₃ H ⁺ +HSO ₃ ^- (3) On the other hand, limestone is often used as calcium carbonate, but the calcium carbonate in limestone dissolves in suspension.

CaCO ₃ CaCO ₃ (in liquid) (4) Dissolved calcium carbonate reacts with sulfite in suspension to form calcium sulfite.

CaCO ₃ +H ⁺ +HSO ₃ ^- →CaSO ₃ +H ₂ O+CO ₂ ↑
(5) Also, the calcium sulfite produced by formula (5) reacts with sulfite in the suspension to produce calcium hyposulfite.

CaCO ₃ +H ⁺ +HSO ₃ ^- Ca(HSO ₃ ) ₂ (6) On the other hand, calcium hyposulfite produced by the reaction of equation (6) undergoes a reaction with calcium carbonate in the suspension as shown in the equation below, and becomes calcium sulfite. generate.

2CaCO ₃ +Ca(HSO ₃ ) ₂ →2CaSO ₃ +Ca(HCO ₃ ) ₂
(7) Weakly acidic calcium bicarbonate Ca (HCO ₃ ) ₂ ,
Generates weakly acidic Ca(HCO ₃ ) ₂ of formula (6). _CaCO3
Even if HCO ₃ ^- and HSO ₃ ^- are supplied, they act as buffering agents and the pH value remains relatively stable.

In the conventional wet flue gas desulfurization method, a part of the tactical suspension is led to an oxidation tower to proceed with the oxidation reaction of calcium sulfite and become 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.

CaCO ₃ +H ₂ SO ₄ +H ₂ O→CaCO ₄・2H ₂ O+CO ₂ ↑
(8) Also, calcium sulfite is 2CaSO ₃ +H ₂ SO ₄ +2H ₂ O→ CaSO ₄・2H ₂ O + Ca(HSO ₃ ) ₂ (9) When air is supplied to the oxidation tower, oxygen dissolves in the liquid and becomes dissolved oxygen. Most calcium sulfites are (9), (10)
Reacts with calcium hyposulfite in the formula to produce gypsum.

Ca(HSO ₃ ) ₂ + 1/2O ₂ +2H ₂ O→ CaSO ₄・2H ₂ O+H ₂ SO ₃ (10) In this way, in conventional wet flue gas desulfurization equipment, unreacted calcium carbonate is extracted from the absorption tower. Therefore, it is necessary to supply an excessive amount of calcium carbonate, and sulfuric acid is also required for pH adjustment in the oxidation tower, resulting in high utility costs.

In addition, there was a drawback that equipment costs were high due to auxiliary equipment for installing dust removal towers, oxidation towers, etc.

Therefore, in order to reduce utility costs and equipment costs, in order to carry out the oxidation reaction of formula (10) in the absorption tower, Japanese Patent Publication No. 58-28206 and Japanese Patent Application Laid-Open No. 58-92451
No., JP 58-92452, JP 58-95543, JP 58-98125, JP 58-98126, JP 58
−104619, Unexamined Japanese Patent Publication No. 104620, Unexamined Japanese Patent Publication No. 1983-
No. 91428 and others have already been proposed.

However, in both cases, the PH value of the suspension is high;
Although it is preferable for the absorption of sulfite gas in combustion exhaust gas, the oxidation reaction rate is slow due to the high pH value, 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 installing a separate oxidation tower, it is necessary to adjust the pH of the calcium sulfite oxidation system and to remove SO ₂ It is necessary to adjust the total SO ₃ ion concentration in the absorption system.

[Purpose of the invention]

The purpose of the present invention is to integrate an absorption tower and a gypsum recovery device for oxidizing calcium sulfite in an absorption tower and recovering gypsum without installing an oxidation tower, which was carried out in the conventional wet flue gas desulfurization method. The object of the present invention is to provide a wet flue gas desulfurization method that is carried out in a column type and has high desulfurization efficiency.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention brings a suspension containing calcium carbonate or calcium hydroxide into gas-liquid contact with combustion exhaust gas containing sulfur oxide to desulfurize it, as well as cooling the exhaust gas, removing dust and sulfur. The target is a wet flue gas desulfurization method in which oxides are absorbed and removed in the same tower and gypsum is recovered as a byproduct.

The suspension after being brought into contact with the exhaust gas is then stored in an oxidation reactor at the bottom of the same tower, and air is supplied to the oxidation reactor in accordance with the PH value of the suspension in the oxidation reactor. It is characterized by controlling the amount.

[Embodiments of the invention]

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

Figure 1 is a principle diagram of a wet flue gas desulfurization device according to an embodiment of the present invention, Figures 2 to 5 are characteristic diagrams obtained through experiments by the inventors, and Figure 2 shows a suspension PH of
Figure 3 is a characteristic diagram showing the relationship between the PH value of the suspension and _{the SO 2 absorption} rate, and Figure 4 is the PH value of the suspension. and _CaCO3
FIG. 2 is a characteristic diagram showing the relationship between the oxidation rate of Figure 5 is a cross-sectional view showing a calcium sulfite oxidation reaction device;
6 and 7 are cross-sectional views showing the air atomizer, and FIGS. 8 and 9 are oxidation performance characteristic diagrams of the air atomizer showing the relationship between air supply amount and oxidation rate.
Figure 10 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, and Figure 12 is a characteristic diagram showing the relationship between suspension PH value and desulfurization performance. Figure 13 is a characteristic diagram showing the relationship between the total SO ₃ ion concentration in the suspension and the SO ₂ absorption rate ratio. Figure 14 is a characteristic diagram showing the relationship between the PH value and the total SO ₃ ion concentration. FIG. 15 is a characteristic diagram showing the relationship between gypsum particle size and cumulative weight distribution.

Before explaining the embodiments of the present invention, the inventors' experimental results will be explained using FIGS. 2 to 4.

The present inventors have been studying the rationalization and efficiency improvement of equipment for a wet flue gas desulfurization method for some time. As a result of basic studies and tests conducted at a pilot plant, the absorption tower and oxidation tower of the wet flue gas desulfurization system were integrated to reduce the amount of suspension.
It has been discovered that a wet desulfurization method that does not require sulfuric acid for pH adjustment, can reduce consumption of calcium carbonate, can recover marketable by-product gypsum, and has high desulfurization efficiency can be obtained.

To oxidize calcium sulfite in a suspension that has absorbed sulfur oxides in combustion exhaust gas, the method described above (10) is mainly used.
Although the oxidation reaction follows the formula, it has become clear that the oxidation reaction is highly dependent on the hydrogen ion concentration in the suspension, that is, the PH value. This means that when the pH in the suspension changes, the dissolution rate of calcium sulfite increases, and the rate of calcium sulfite oxidation increases.

FIG. 4 is a characteristic diagram showing the relationship between the PH value in a suspension and the oxidation rate of calcium sulfite CaSO ₃ , which was clarified by the results of basic studies. When the pH value in the suspension is around 7, oxidation of calcium sulfite hardly occurs. Adjust the pH of the suspension by adding sulfite or sulfuric acid.
It has become clear that when the value is gradually lowered, the oxidation reaction rate of calcium sulfite increases rapidly, and becomes almost constant when the pH value is around 4 and below.

On the other hand, as shown in Figure 2, when the pH value of the suspension decreases, the oxidation rate of calcium sulfite tends to increase as explained in Figure 4, but SO ₂ is desorbed in the gas phase. I'll let you go. Therefore, in the oxidation reaction process of calcium sulfite, the pH value of the suspension is 3.8 to 5.0.
It turns out that it is more economical to do it within the range of .

Figure 2 shows the results when the air supply rate is constant. In the oxidation reaction in the high pH value range, the dissolution rate of calcium sulfite is the rate-determining step, whereas in the low pH value range, It can be seen that the oxidation reaction progresses with the rate of oxygen dissolution being the rate-determining step. In other words, when oxidizing calcium sulfite in the PH range of 3.8 to 5.0, increasing the dissolution rate of oxygen, that is, adjusting the amount of air supplied per unit suspension if the air atomization is the same. It has become clear that the amount of calcium sulfite oxidation can be adjusted using

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, it is clear from basic study results that the dissolution rate of limestone containing calcium carbonate is affected by the hydrogen ion concentration in the suspension, calcium carbonate concentration, limestone particle size, calcium ion concentration, carbonate ion concentration, temperature, etc. It became clear that the dependence on the hydrogen ion concentration was particularly large.

In other words, by lowering the pH value, the dissolution rate of limestone can be adjusted to a reaction order of 2 with respect to the hydrogen ion concentration.
It became clear that there was a strong dependence on the degree and PH. This is because conventional wet flue gas desulfurization equipment was operated with the suspension PH value in the absorption tower in the vicinity of 5.5 to 6, which suppressed the dissolution rate of limestone and caused excessive limestone to be supplied. Ta. This also caused a vicious cycle in which the amount of sulfuric acid consumed in the next oxidation tower increased.

Next, the inventors found that when simultaneously oxidizing calcium sulfite in an absorption tower and gradually lowering the PH value of the suspension, the absorption rate of SO ₂ into the suspension, that is, the PH value of the suspension The SO ₂ absorption capacity per unit suspension volume was investigated. This corresponds to (1), (2), and (3) mentioned above.
As shown in the equation, as the hydrogen ion concentration in the suspension increases, the SO ₂ absorption rate naturally decreases, and the desulfurization performance in the absorption tower deteriorates.

FIG. 3 is a diagram showing the relationship between the PH value and the SO ₂ absorption rate at the suspension interface. As is clear from the figure, when the PH value is 3.5 or less, the SO ₂ absorption rate decreases rapidly and the desulfurization performance in the absorption tower decreases, but when the PH value of the suspension is 3.8 or higher, the SO ₂ absorption rate decreases. It became clear that there was no sudden decrease in the desulfurization performance and that the desulfurization performance could be maintained as before when the PH value was 3.8 or higher.

Next, in order to perform oxidation and dust removal in the absorption tower, the present inventors investigated whether solid particles corresponding to submicron size contained in the combustion exhaust gas could be collected using the gas-liquid contact method. . We adopted a spray-type gas-liquid contact device that can maintain low ventilation loss and has excellent gas-liquid contact effects, and achieved low pressure loss and high desulfurization performance. The spray method has high dust removal performance, and eliminates the need for a dust removal tower installed outside the absorption tower in the conventional method, making it possible to absorb sulfur oxides and remove dust inside the absorption tower.

In order to completely oxidize calcium sulfite in an absorption tower system, it is important to use a refinement method that has a high air utilization rate. In conventional oxidation towers, calcium sulfite was oxidized by atomizing air under conditions in which the inside of the system was maintained at about 2 to 3 atm. In other words, the conventional method promotes highly efficient oxidation with an air utilization rate of 50 to 70%, but when proceeding with the oxidation reaction in the absorption tower, the pressure in the system is approximately atmospheric pressure, and the air atomization method (fine air atomization method) (legalization) became important. Furthermore, the important thing about air atomizers is that the power consumption for miniaturization is small, and we have studied various atomizers and developed a low-power, high-efficiency atomizer.

As a result of the above studies, we were able to rationalize the equipment as shown in the present invention, leading to the development of an energy-saving wet flue gas desulfurization method.

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 supplying calcium carbonate or calcium hydroxide to the absorption tower 3. 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, etc.

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 contact device 22, solid particles and sulfur oxides are collected in the suspension and becomes a treated gas 34. . The suspension in contact with the gas and liquid falls naturally and is stored in the oxidation reactor 23. A part of calcium sulfite is absorbed by oxygen 5 in combustion exhaust gas 1.
7% and some of it becomes gypsum. Air sent from the air supply line 27 to the oxidation reaction device 23 is atomized by an atomizer, which will be described later, and oxygen is dissolved in the suspension to become dissolved oxygen. Most of the calcium sulfite reacts with this dissolved oxygen in the oxidation reactor 23 and is oxidized into gypsum.

A suspension stirrer 33 is installed at the bottom of the oxidation reactor 23.
is installed, and the solids in the suspension 24 are stirred to prevent them from settling.

A suspension of calcium carbonate or calcium hydroxide in water is supplied to the oxidation reactor 23 and the supply line 26 through supply lines 28 and 29. The PH value of the suspension 24 in the oxidation reaction device 23 is detected by the PH detector 31, and in conjunction with the detected value, the air supply amount is adjusted by the flow regulator (not shown) of the air supply line 32. It's starting to be controlled.

In other words, as mentioned above, when the PH value of the suspension changes, the oxidation rate of calcium sulfite changes greatly.In other words, when the PH value of the suspension increases, the oxidation rate of calcium sulfite slows down, and conversely, when the PH value of the suspension increases, the oxidation rate of calcium sulfite slows down. As the pH value of the liquid decreases, the oxidation rate of calcium sulfite increases (see Figure 4).

Therefore, if the PH value of the suspension increases, the amount of air supplied will be decreased accordingly, and if the PH value of the suspension is decreased, the amount of air supplied will be increased accordingly. The oxidation reaction proceeds in just the right amount.

After the generated gypsum remains in the oxidation reaction device 23 for a certain period of time, it is extracted from the extraction line 102 and sent to a gypsum recovery device (not shown).

The air necessary to oxidize the calcium sulfite in the suspension is atomized by an atomizer, but increasing the efficiency of this atomizer increases the power cost, so it is directed to the stirring blades of the suspension stirrer 33. A suitable example is a method in which air is blown onto the mixture using a stirring blade, and the air is atomized by the shear force of the stirring blades.

Further, as shown in FIG. 6, a constrictor 35 is installed in the piping system 36 for the suspension 24, and an air supply line 27 is connected to the upstream side of the constrictor in the suspension flow direction. Another suitable example is a method in which the two fluids, the suspension 24 and air, are mixed on the upstream side of the constriction part 35 and the air is made fine by passing through the constriction part 35.

If this two-fluid air atomizer is installed in the circumferential direction of the oxidation reaction device 23 as shown in FIG. 7, it will also have a stirring effect on the suspension 24. Representative examples of the results of basic experiments regarding the oxidation performance of the air atomizer shown in FIG. 6 are shown in FIGS. 8 and 9.

As shown in these figures, the oxidation rate is determined by the flow rate of the two fluids in the constriction section 35 in FIG. It is an air atomizer.

In the wet desulfurization equipment of the present invention, when the combustion exhaust gas and the suspension are brought into gas-liquid contact, whether or not solid particles in the combustion exhaust gas can be collected is investigated. The results of the dust removal performance are shown in Figure 10. In this test, the suspension droplet size ranged from 800 to 2300 μm, and the superficial gas flow rate was
It was varied in the range of 1.3 to 3.1 m/s. It also shows typical dust removal performance when the ratio of suspension to gas amount is varied from 1.5 to 6.

As is clear from this figure, higher performance was obtained than the conventional dust removal performance that collected solid particulates in combustion exhaust gas. That is, solid fine particles in the combustion exhaust gas in the absorption tower according to the present invention can be collected with high efficiency.

When the PH value of the suspension was set to be in the range where calcium sulfite is easily oxidized, it became clear that the PH value of 4 or higher did not have a large effect as shown in Figure 3, but as shown in Figure 11. Absorption experiments were carried out using a 150 mm absorption tower as shown in Figure 1 to examine the SO ₂ removal performance.
The suspension contains CaCO ₃ , CaSO ₃ and CaSO ₄ ,
The SO ₂ concentration in the simulated combustion exhaust gas was 1000 ppm, and the gas flow rate was 1.2 m/s.

FIG. 12 is a diagram showing the relationship between suspension pH and desulfurization performance based on this study. As is clear from the figure, when the PH value is around 4 or less, the desulfurization performance tends to decrease, but when the PH value is around 4 or more, the desulfurization performance is not affected much, and as shown in Figure 13. The total SO ₃ ion concentration in the suspension is 100 m−mol/
It has been found that when the pH value is around 4, the desulfurization performance decreases, but if the SO ₃ ions are kept below this value, the wet desulfurization method of the present invention can obtain high desulfurization performance.

In addition, the oxidation rate of calcium sulfite shown in Figure 4 is very fast in the pH range of 5.0 or less, and the rate of oxygen absorption is the rate-limiting process. Speed is increased.

FIG. 14 is a characteristic diagram showing the PH value and the saturation solubility curve of all SO ₃ ions. 70 when the PH value is around 4
~80 m-mol/, but it is preferable to oxidize the entire amount in the oxidation reactor 23 shown in FIG. 4 from the viewpoint of desulfurization performance. However, the experimental results of the absorption tower shown in Figure 11 show that the total sulfite ion concentration, including solid calcium sulfite, is approximately
It was revealed that desulfurization performance does not change if it is 1.3 times or less.

As shown in FIG. 5, in order to increase the amount of dissolved oxygen, it is efficient to supply air from multiple locations along the height direction of the oxidation reaction device 23. Further, in order to recover large particles of gypsum, the bottom of the oxidation reaction device 23 is made into a cone shape, and coarse gypsum can be recovered by slow stirring action.

FIG. 15 is a diagram for confirming the performance of the present invention, and is a diagram showing the particle size distribution of recovered gypsum in an experiment using actual gas (coal-fired boiler) with an exhaust gas amount of 600 Nm ³ /h.

As impurities in the gypsum, CaSO ₃ 1/2H ₂ O was found to be 0.00002 mol/CaCO ₃ was not detected.
From the purity of the gypsum thus recovered, it is clear that the wet flue gas desulfurization method according to the present invention has the same high quality as the conventional method.

Depending on the content of sulfur oxides in the flue gas,
The amount of limestone to be supplied is adjusted, but since the pH value is low, calcium hyposulfite is generated as a buffer, and the pH value of the suspension does not change significantly and can be operated in the pH range suitable for the specified oxidation reaction. . In addition, if the amount of air is increased and the oxidation reaction rate of calcium hyposulfite is accelerated, the PH value tends to decrease, so the air supply should be adjusted in conjunction with the PH value of the suspension in the oxidation reaction device 8 shown in Fig. 4. The amount has been adjusted. However, when the amount of air is increased, decarboxylation reactions occur simultaneously, which tends to increase the PH value, but it has become clear that these effects are small.

〔Effect of the invention〕

According to the present invention, solid fine particles in combustion exhaust gas,
Since sulfur oxides can be collected in suspension, a conventional dust removal tower is not required, and by integrating the tower into one, a conventional oxidation tower is also not required. Therefore, it is possible to downsize the device and reduce equipment costs.

In addition, since the amount of air supplied to the oxidation reactor is controlled in conjunction with the PH value of the suspension, there is no excess or deficiency of air in the oxidation reactor, which allows the oxidation system of calcium sulfite to be properly controlled. PH adjustment and appropriate adjustment of the total SO ₃ ion concentration in the SO ₂ absorption system are performed at the same time, resulting in high desulfurization performance and high gypsum recovery.

Furthermore, it becomes unnecessary to replenish sulfuric acid to the calcium sulfite oxidation reaction system, making it possible to reduce utility costs.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of a wet flue gas desulfurization apparatus according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between the PH value of the suspension and the SO ₂ concentration in the separated gas phase, and Fig. Figure 3 is a characteristic diagram showing the relationship between the PH value of the suspension and the SO ₂ absorption rate, Figure 4 is a characteristic diagram showing the relationship between the PH value of the suspension and the oxidation rate of CaCO _{3, and Figure 5 is a characteristic diagram showing the relationship between the PH value of the suspension and the oxidation rate of CaCO 3} . , FIGS. 6 and 7 are sectional views showing an oxidation reaction apparatus for calcium sulfite, FIGS. 6 and 7 are sectional views showing an air atomizer, and FIGS.
9 and 9 are oxidation performance characteristic diagrams of air atomizers showing the relationship between air supply amount and oxidation rate.
The figure 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, and Figure 12 is a graph showing the relationship between the PH value of the suspension and desulfurization performance. The characteristic diagram, Figure 13, shows the total SO ₃ in the suspension.
Figure 14 is a characteristic diagram showing the relationship between ion concentration and SO ₂ absorption rate ratio. Figure 14 is a characteristic diagram showing the relationship between PH value and total SO ₃ ion concentration. Figure 15 is the relationship between gypsum particle size and cumulative weight distribution. FIG. 16 is a schematic diagram of a conventional wet flue gas desulfurization device. DESCRIPTION OF SYMBOLS 1... Exhaust gas, 3... Absorption tower, 5... Circulation tank, 23... Oxidation reactor, 24... Suspension, 2
7...Air supply line, 31...PH detector.

Claims (1)

[Claims] 1 Desulfurization by bringing a suspension containing calcium carbonate or calcium hydroxide into gas-liquid contact with combustion exhaust gas containing sulfur oxides, cooling the exhaust gas, removing dust, and absorbing and removing sulfur oxides. In the wet flue gas desulfurization method in which gypsum is recovered as a by-product by performing both in the same tower, the suspension after contacting with the flue gas is stored in the oxidation reactor in the lower part of the same tower, and A wet flue gas desulfurization method characterized in that the amount of air supplied to the oxidation reactor is controlled in conjunction with the PH value of the suspension.