JPS60227816A - Absorption tower of wet type stack gas desulfurization apparatus - Google Patents

Abstract

PURPOSE:To perform effectively the absorption and oxidation of SOX by dividing the liquid reservoir part of lower part of absorption tower into the liquid reservoir part of front stage free in contact with waste gas and the liquid reservoir part of rear stage incapable of contact with the waste gas by means of a partition board capable of overflow and a sealing separation plate. CONSTITUTION:The liquid reservoir part of absorption tower 800 is divided into front and rear stages with a partition board 500 and a separation plate 300 is provided in order to make the structure noncontacting with waste gas of the liquid reservoir part 200 of the rear stage. A suspension soln. is brought into contact with combustion waste gas 1 countercurrently in a gas- liquid contacting part 600 of the absorption tower 800 to absorb SOX and flowed down on the separation plate 300 and at first collected in the liquid reservoir part 100 of the front stage and thereafter overflowed on a partition board 500 between the separation plate 300 and the partition board 500 and entered the liquid reservoir 200 of the rear stage. In the front stage, the pH is low under contacting with the combustion waste gas high in CO2 partial pressure and the oxidation of SOX is accelerated and in the rear stage, the pH recovering velocity and the dissolving velocity of an alkaline absorbent are increased with the sealing effect of the separation plate 300 and the suspension soln. is made the state preferable for the circulation to the gas-liquid contacting part 600.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an absorption tower for a wet flue gas desulfurization system, and in particular to an absorption tower suitable for absorbing sulfur compounds contained in combustion exhaust gas and oxidizing the absorption products. It is related to the structure of

(Background of the Invention) The wet flue gas desulfurization method involves bringing a suspension of an alkaline absorbent such as calcium hydroxide or calcium carbonate into gas-liquid contact with combustion flue gas to remove sulfur oxides (mainly This method removes C3Oz) and ultimately recovers it as a by-product such as gypsum.

In this case, when calcium carbonate is used as an example of an alkaline absorbent, sulfur oxides in the combustion exhaust gas are absorbed into the suspension, and the following reaction E (1) to (6)
4').

SO2 (gas) + HxOd HzSOa -...”
・n1・・(1) HiSOm d H+ HsOs
・・・・・・・・・・・・・・・(2) H80s-d
H++5Os-・・・・・・・・・・・・・・・(3)
CaCO5+ H” # C Otori 0+ and σ1...
・・・・・・・・・(4) Ca + SOs = CaSO
s ・・・・・・・・・・・・・・・(5) CaSOs
+ 1/20x →Ca5Oa ---・”・”
(6) However, since all of the above reactions except for equation (6) are equilibrium reactions, the following considerations are required. One is that Cot in the combustion exhaust gas dissolves into a suspension to produce CO1, which is described in (7) and (8) below.
As shown in the equation, it is maintained in almost equilibrium with HCOs- and COs'-, while it is decarboxylated according to equation (9).

HnCOi HH” + HCOs−・・・・・・・・・・
・・・・・・・・・・・・・・・(7) Eα1d H” +
CO5-・・・・・・・・・・・・・・・・・・
・(8) HxC(h d HzO+CO!↑ ・・・・
・・・・・・・・・・・・・・・・・・(9) Therefore,
What is important through the series of desulfurization reactions described above is that if the decarboxylation reaction of formula (9) can be promoted, the equilibrium of formulas (1) to (8) will shift to the right, and the desulfurization reaction will be suitably performed. For this reason, various methods have been proposed for this purpose (Utility Model Application Publication No. 58-95217, Utility Model Application No. 11).
No. 858-95218, Japanese Utility Model Application No. 58-95216, Japanese Patent Application Publication No. 58-98125, Japanese Patent Application Publication No. 58-92452,
JP-A No. 58-95543, Utility Model Application No. 58-91428, l! #Kokai No. 58-104619, JP-A-58-98
No. 126, JP-A-58-104620, etc. viA).

The gist of all of these conventional methods is to supply air to the suspension to cause bubbling. In this way, the apparent 001 partial pressure in the upper gas phase (combustion exhaust gas) decreases, and (9 ) The decarboxylation reaction shown in the equation will be accelerated.

As a result, the equilibrium of equations (1) to (9) can be shifted to the right side, and as a result, the solubility of calcium carbonate is increased according to equation (4).

However, combustion exhaust gas generally contains a large amount of C (h gas) reaching 10 to 14-
ot gas has a high dissolution rate and is HxCOs shown in equation 9.
Therefore, if air aeration is performed under these conditions, the apparent partial pressure of Co2 in the gas phase will be lowered, but a large amount of air will be required to promote decarboxylation, and the power consumption will be reduced. A rise is inevitable.

Another reason is that the absorption of Soz into a suspension is more effective as the pH value of the suspension is higher, so it is usually carried out at pH > 6, but the oxidation reaction of CaOs in the suspension is It is most efficient when carried out at low pH values, such as around 4. Therefore, it is not efficient to proceed with the oxidation reaction at the same time as the absorption of Son in the liquid reservoir in the absorption tower, as in the prior art.

In order to eliminate such drawbacks, a method of dividing pH ranges has also been proposed. However, these improved methods have a structure in which the suspension that was in contact with the combustion exhaust gas is recycled to the gas-liquid contact section, so the pH recovery of the suspension, which undergoes a slow decarboxylation reaction, is also slow. , and the dissolution rate of calcium carbonate is also low. Furthermore, since the liquid reservoir is in a completely mixed state, an increase in pH value is unavoidable, which slows down the oxidation reaction, and there is also the problem that a large amount of air must be supplied.

(Objective of the Invention) The object of the present invention is to solve the above-mentioned drawbacks of the prior art. The purpose of the present invention is to provide an absorption tower for a desulfurization device.

(Summary of the Invention) In order to achieve the above object, the present invention involves spraying an absorbing liquid (hereinafter sometimes referred to as a suspension) containing an alkaline absorbent in the upper part and bringing it into contact with combustion exhaust gas. a gas-liquid contact section that absorbs and removes sulfur oxides, and a lower part that receives the suspension that has absorbed sulfur oxides that flows down after the above contact, and oxidizes the absorbed sulfur oxides while supplying air. 5 In an absorption tower of a wet flue gas desulfurization equipment equipped with a liquid reservoir, the liquid reservoir is arranged in front along the flow by a partition plate that allows overflow.
The rear stage is divided into at least two parts, reaches below the surface of the absorption liquid upstream of this partition plate, and seals the inside of the absorption tower into a part containing the first stage liquid reservoir and a part containing the second stage liquid reservoir. It is characterized by being provided with a separator plate.

In the present invention, the liquid reservoir can be provided with an air supply system for bubbling, an alkaline absorbent replenishment system, and the like. In this case, if a suspension circulation system equipped with an ejector is provided in the pre-stage liquid reservoir and air is supplied through the ejector, the mixing properties of the air will be improved and the oxidation reaction can be further promoted.

Further, it is desirable to replenish the alkaline absorbent to the latter liquid reservoir where its solubility is good.

With this configuration of the present invention, the suspension that has come into countercurrent contact with the combustion exhaust gas flows down on the separator and is first collected in the former liquid reservoir, and then passes between the separator and the partition plate before being collected in the latter. It overflows from the top of the tank and is collected in the latter stage liquid reservoir. While the liquid remains in each reservoir, it is subjected to bubbling treatment while being supplied with air, but at that time, the suspension in the previous stage reservoir is in contact with combustion exhaust gas having a high 001 partial pressure.
The pH value is generally as low as about 4, and therefore the oxidation reaction of absorbed sulfur oxides is suitably promoted. On the other hand, the suspension in the latter stage liquid reservoir is in a state where contact with the combustion exhaust gas is cut off due to the sealing effect of the separator (the partial pressure of Cox in the gas phase decreases), so that the decarboxylation reaction is carried out well. As a result, both the pH recovery (increase) rate and the dissolution rate of the prucaric absorbent improve, which is preferable when circulating to the gas-liquid contact area.

(Embodiments of the Invention) The present invention will be explained in more detail below with reference to embodiments shown in the drawings.

Figure s1 shows a side cross section of an absorption tower according to an embodiment of the present invention. In this absorption tower, the flue gas 1 is passed through the absorption tower 8.
00, and then in the gas-liquid contact section 600 is brought into countercurrent contact with the suspension that is circulated and sprayed via lines 4 and 3 as described later. The exhaust gas 2 from which the sulfur oxides contained therein have been absorbed and removed through this contact is discharged from the top of the absorption tower 800 to the atmosphere. On the other hand, the suspension that has absorbed sulfur oxides flows down through the dispersion plate 700, etc., but at that time,
The liquid flows down on the separator plate 300 provided to make the downstream liquid reservoir 200 partitioned by the partition plate 500 into a non-contact structure with respect to combustion exhaust gas, and is first collected in the preliminary liquid reservoir 100 . Note that the lower part 400 of the separator plate 300 is inserted below the liquid level of the pre-stage liquid reservoir 100 in order to enable liquid sealing, and the partition plate 500 is arranged as shown in FIG.
As is clear from FIG. 5, which is a view taken along the line, a groove 501 is provided in the center of the upper part to allow the liquid in the former liquid reservoir to overflow to the latter liquid reservoir.

The suspension stored in the front liquid reservoir A100 as described above is aerated by supplying air 6 in a conventional manner, but since this suspension is in contact with the combustion exhaust gas, the pH value is as low as about 4. Therefore, the oxidation reaction of the contained calcium sulfite is suitably promoted. However, if a more complete oxidation reaction is desired, the suspension is drained from the line 7 provided at the bottom of the pre-liquid reservoir 100.

After being sent to a normal oxidation system (not shown) equipped with an oxidation tower, Silafuna, etc. for treatment and recovering the generated gypsum, the suspension containing unreacted materials is passed through line 8 and sent to the former liquid reservoir 10 again.
Just set it back to 0. The suspension treated in this way is
The suspension then rises through the gap between the lower part 400 of the separator plate and the partition plate 5000, passes through the upper groove part (501 in FIG. 5) of the partition plate, and overflows into the subsequent liquid reservoir 200, and the thus collected suspension is It is aerated under a supply of air 5 and decarboxylated. In this case, since the suspension is insulated from the combustion exhaust gas by the sealing effect of the lower part 409 of the separator, efficient decarboxylation takes place, thereby promoting pH recovery and dissolution of CaCO5.

Note that the CaCO5 is replenished through the line 1o, and the degassed exhaust gas containing the COx gas generated by the decarboxylation reaction is also discharged through the line 9 and then merged with the exhaust gas 2 and the like. Furthermore, the suspension after the above treatment is extracted from line 4, and then pressurized by a pump or the like (not shown), then supplied to gas-liquid contact section 600 through line 3, and combusted in the same manner as described above. After the exhaust gas 1 and gas liquid are removed, this process is repeated.

Next, FIG. 2 shows another embodiment of the present invention, and as is clear from FIG. 6, which is a view taken along the line B-B', this device has a diametrical partition plate 500. A cylindrical partition plate 5oOA (501A indicates an overflow groove) and a lower part 400A of the separator plate are provided in place of the lower part 4°O of the p4 separation plate provided in parallel upstream thereof, and The structure is similar to that of the absorption tower shown in FIG. 1, except that a separator plate 300A extending in a funnel shape from the bottom of the plate is provided. Even with such a configuration, the front liquid reservoir 100 and the rear liquid reservoir 200 having similar functions can be formed independently of each other, so that the front liquid reservoir 100 can be It is possible to promote the oxidation of sulfur absorbed in the liquid, and in the latter stage liquid reservoir section 200, it is possible to promote both the pH recovery of the suspension based on the decarboxylation reaction and the dissolution of CaCO5.

In this case, if the partition plate 500A is provided with a box that reaches the inner wall of the absorption tower 800 as shown at 502 in FIG. Therefore, the decarboxylation reaction can be further promoted.

Further, FIG. 3 shows another embodiment of the present invention, and as is clear from FIG. It is the same as the absorption tower shown in Fig. 2, except that a lower separator plate 400AK of the same shape provided on the inside is replaced with a lower separator plate 400B of the same shape on the outside, and a separator plate 30oB extending in an umbrella shape from this is provided. This is a similar configuration, and similar effects can be achieved with such a configuration.

Furthermore, FIG. 4 shows an embodiment of the present invention, and this device has a first stage liquid circulation line 31 equipped with a pump 202 and an ejector 201 sequentially in the front stage liquid reservoir 100. The structure is similar to that of the absorption tower shown in the figure. With such a configuration, the line 3 in the ejector 201
Since it becomes possible to increase the contact efficiency between the air introduced from No. 2 and the circulating suspension, the oxidation reaction of the absorbed sulfur oxides can be further promoted.

Hereinafter, the present invention will be explained in more detail based on experimental examples conducted to confirm the effects of the present invention.

Experimental Example 1 Assuming the liquid reservoir part of the absorption tower shown in each of the above examples, calcium carbonate (saturated state, 18 ° C) o, oss tongue was 11
A suspension was prepared by adding C (h) to water at a rate of 0.03 h, 10 h and 100 h, respectively, through which a simulated gas was passed at a rate of 1.21/min per 11 of the suspension. When we calculated the relationship between the contact time and pH value at that time, we obtained the results shown in Figure 9. In the figure, for AoXBo and Co, Cot in the gas phase was 0.03, 10, and 100, respectively. The case is shown below.

From this result, it is clear that as the C(h partial pressure) in the simulated gas (gas phase) increases, the pH decreases, and that any C(h
Even in the case of partial pressure, as the contact time elapses, the above-mentioned (4)
, (7), (8) and (9) reactions reach equilibrium,
It can be seen that the pH value becomes constant.

Experimental Example 2 According to Experimental Example 1, HxSOs was added to the suspension that had reached an equilibrium state with Cot in the gas phase so that CaCO5/HxSOx = 20 (molar ratio), and the pH value changed. The results shown in Figure 11 were obtained. In addition, in the same figure,
A20.13!0 and Coo indicate the case where COt in the gas phase is 0.03%, 10% and 100%, respectively. This result shows that by adding HzSOa, the reactions of equations (1) to (9) described above occur and reach equilibrium over time, and that the lower the CO pressure in the gas phase, the lower the It is known that the pH value increases. This means that the lower the Cot partial pressure in the combustion exhaust gas, the higher the solubility of calcium carbonate in the suspension.
In other words, bubbling air into the suspension lowers the apparent CQz partial pressure in the gas phase, and the pH recovery rate and content of the suspension decrease. Ca
This suggests that the dissolution rate of CO3 is increased as well.

Experimental example 3 Bo case of experimental example 1 (co! partial pressure in the gas phase is 0゜l)
atw) for 60 minutes to confirm the equilibrium state, continue the B2o case of Experimental Example 2 for another 60 minutes to confirm the equilibrium reactions of equations (1) to (9), and then , the same treatment was carried out except that the partial pressure of C0w in the gas phase was changed to 0.05 atw, and thus the suspension.

When the pH value recovery status was investigated, the results shown in FIG. 11 were obtained.

As is clear from this figure, co! It is understood that after the point D, where the partial pressure is lowered, the decarboxylation reaction of formula (9) described above occurs, and calcium carbonate becomes easier to dissolve. As described above, the pH recovery rate and the dissolution rate of calcium carbonate are greatly affected by the partial pressure of Cot in the gas phase, so in order to promote this, it is necessary to It can be said that it is effective to throw away the latter stage liquid reservoir and aerate the suspension with air.

(Effects of the Invention) As described above, according to the present invention, the suspension liquid reservoir is divided into a front stage liquid reservoir that can freely come into contact with combustion exhaust gas and a rear stage liquid reservoir that cannot come into contact with the combustion exhaust gas. ,.

The former makes it possible to oxidize absorbed sulfur oxides in suspension under low pH conditions suitable for oxidation reactions, and the latter allows CO! in the gas phase to be oxidized. Since the partial pressure is low, the decarboxylation reaction of the suspension can be carried out efficiently5, which increases the pH recovery rate and the dissolution rate of the alkaline absorbent, making the suspension suitable for circulation to the gas-liquid contact area. It becomes possible to obtain liquid.

[Brief explanation of the drawing]

FIG. 1 is a side cross-sectional view of an absorption tower according to an embodiment of the present invention, FIGS. 2 and 3 are side cross-sectional views of an absorption tower according to other embodiments and rows of the present invention, and FIG. , a side sectional system diagram of an absorption tower according to another embodiment of the present invention, FIG. 5 is a sectional view of the absorption tower shown in FIG. FIG. 8 shows B − of the absorption tower shown in FIG. 2, respectively.
FIG. 7 is a cross-sectional view of the absorption tower shown in FIG. 3 in the direction of arrows taken along line C-C/, and FIG. Diagram showing how the pH of the suspension changes with the contact time when it is brought into contact with a CaCOx HzO-based suspension, depending on the CO2 concentration in the gas, '1
g10 diagram is CO! Containing gas x CaCO5'khsOs
- When brought into contact with a HzO-based suspension, the p of the suspension
Figure 11 shows how H changes with contact time for each CCh concentration in the gas.
-H2SOs After contacting with HxO suspension, C
It is a figure which shows how the pH of a suspension changes with contact time when the partial pressure of Ch is halved and it is brought into contact with the latter suspension in the same way. 1... Combustion exhaust gas, 3.4... Suspension circulation line,
5.6... Air, 7... Suspension extraction line, 8...
・Suspension return line, 9... Sharp exhaust gas line, 1o
. . . CaCO5 replenishment line, 31 . . . Suspension front stage circulation line, 32 . . . Air line, 100 . . . ...Pump, 300.300A, 300
B...Separation plate, 400.400A, 400B...Separation plate lower part, 5゜01500A...Partition plate, 501.5
01A... Partition plate upper groove, 502... Chest, 600
... Gas-liquid contact section, 800 ... Absorption tower. Agent Patent Attorney Takenaga KawakitaFigure 3Figure 4Figure 5Figure 6Figure 7Figure 8Figure 9

Claims (1)

[Claims] (1) A gas-liquid contact part in which an absorption liquid containing an alkaline absorbent is sprayed in the upper part and brought into contact with the combustion exhaust gas to absorb and remove sulfur oxides from the exhaust gas, and in the lower part, the absorption liquid flows down after the contact. In an absorption tower of a wet flue gas desulfurization equipment, the absorption tower is equipped with a liquid reservoir section that receives sulfur oxides and oxidizes the absorbed sulfur oxides while supplying air. , the rear stage is divided into at least two parts, and upstream of this partition plate [a part that reaches below the liquid level of the absorption liquid and that includes the above-mentioned front stage liquid reservoir part and a part containing the latter stage liquid reservoir part] An absorption tower for a wet flue gas desulfurization equipment, characterized by being provided with a separator for sealing. (In claim 1, the wet type is characterized in that the pre-stage liquid reservoir is provided with an absorption liquid circulation system equipped with a +1° ejector for bringing the absorption liquid into air contact.) Absorption tower of flue gas desulfurization equipment.