JPS5892452A - Flue gas desulfurization method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flue gas desulfurization method, in particular, in order to desulfurize flue gas, air is mixed into a circulating absorption liquid in which lime such as calcium carbonate is dissolved, thereby improving the solubility and dissolution of calcium carbonate. The present invention relates to a flue gas desulfurization method that increases speed, maintains a high desulfurization rate, and generates gypsum in an absorption tower.

In general, various methods have been researched, developed, and are already in operation as flue gas desulfurization methods for removing sulfur oxides contained in flue gas discharged from combustion equipment such as boilers.

As an example of these flue gas desulfurization methods, a method is known in which an absorption liquid in which lime such as calcium carbonate is dissolved is brought into contact with the flue gas, and the produced calcium sulfite is oxidized to recover gypsum.

This conventional method will be explained based on FIG. 1. First, 1 is exhaust gas exhausted from combustion equipment such as a boiler. This exhaust gas 1 is brought into countercurrent contact with the absorption liquid 3 circulating therein in the absorption tower 2, and the sulfur oxides in the exhaust gas and the calcium carbonate in the absorption liquid 3 are expressed by the following formula (1). It reacts to produce calcium sulfite.

S02+CaCO3+1/2H20→CaSO3・L/
2 H2O+ CO2- (1) The exhaust gas 4 that has been desulfurized in this way is discharged to the outside of the system. on the other hand,
The generated absorption liquid containing calcium sulfite is extracted as appropriate, and air oxidized in the oxidation tower 5 as shown in the following formula 2 to generate gypsum.

CaSO3-1/2 H2O+ 1/202+ 3/2
H2O4CaSO4-2H20- (2) Furthermore, the gypsum slurry 6 produced by the above reaction is extracted and then sequentially transferred to the filter 7 to recover the gypsum, and the F liquid 8 is returned to the absorption tower 2. It will be returned to the absorption liquid 3.

By the way, in the conventional method as described above, the E liquid 8 discharged when recovering gypsum in the filter 1 is returned to the absorption liquid 3 and used for circulation. Hydrogen chloride, which is removed together with sulfur oxides, gradually remains in the absorption liquid 3, increasing the CE concentration, resulting in a decrease in the solubility and dissolution rate of calcium carbonate, and the problem that the desulfurization rate gradually decreases. there were.

In order to solve this problem, it is conceivable to discharge ν liquid 8 outside the system without recycling it, but in this case there is a risk of secondary pollution and it is difficult to use water effectively. It has not been implemented from this point of view.

In view of the above-mentioned problems, the present invention was devised to effectively solve the problems. , air or air after treatment is mixed in and aerated, thereby increasing the solubility and dissolution rate of calcium carbonate, thereby making it possible to maintain a high desulfurization rate and to generate gypsum in the absorption tower. To provide a flue gas desulfurization method.

The present invention provides that even if the solubility and dissolution rate of calcium carbonate tend to decrease as the concentration in the absorbent increases, the solubility and dissolution rate can be maintained high by aerating the absorbent with air (gas). This was done by discovering the following.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 shows an apparatus for explaining the method according to the invention. First, 1 is exhaust gas exhausted from combustion equipment such as a boiler, and this exhaust gas 1 is introduced into an absorption tower 2 for desulfurization treatment. In this absorption tower 2, an absorption liquid 3 produced by dissolving an absorbent containing calcium carbonate is circulated by a circulation pipe 9.
The k-absorbing liquid 3a and the exhaust gas are brought into countercurrent contact, and the sulfur oxide in the exhaust gas and the calcium carbonate in the absorbing liquid are combined according to the following formula (
Calcium sulfite is produced by the reaction shown in 3).

So2+ CaCO3+ 1/2 H2O→CaSO3
-1/2 H2O+ Co2 (3) Along with this desulfurization treatment, hydrogen chloride gas in the exhaust gas will also be removed, and the desulfurized exhaust gas 4 will be released to the outside of the system. Further, the desulfurized absorption liquid containing the produced calcium sulfite flows down and remains in the liquid retaining tank 10, and calcium carbonate 11 is added thereto as appropriate.

Then, in order to increase the solubility and dissolution rate of calcium carbonate, the absorbent liquid 3 in the liquid retaining tank 10 is mixed with humid air discharged from the oxidation tower 5 and subjected to aeration treatment. Due to this aeration, the absorption liquid 3
A large amount of calcium carbonate is dissolved, and some calcium sulfite is still oxidized as shown in the following formula (4) to produce gypsum.

CaSO3・1/2H20+1/202+3/2H20
→CaSO4.2H20 (4) In this way, the absorption liquid 3 containing calcium carbonate, calcium sulfite, and gypsum is circulated again and contributes to the desulfurization process.

On the other hand, a part of the absorption liquid 3b of the circulating absorption liquid 3a is extracted and introduced into the oxidation tower 5.

The absorption liquid 3c introduced into the oxidation tower 5 is brought into contact with air 12, and the calcium sulfite in this absorption liquid is expressed by the above formula (4
), all are oxidized to produce gypsum.

At this time, since some gypsum is precipitated in the retaining tank 10 as described above, the precipitation of gypsum is further promoted in the oxidation tower 5 using this gypsum as a core.

After the oxidation treatment is completed in the oxidation tower 5, the discharged treated air 12a is directly introduced into the absorption liquid 3 in the retention tank 10 as described above. On this occasion,
Since the air after this treatment is sufficiently moist, gypsum does not dry and precipitate in the air introduction section 13, and no clogging occurs.

On the other hand, the gypsum produced in the oxidation tower 5 becomes a slurry and is transferred to the filter 7, where the gypsum is recovered.

Further, the filtrate 8 from the filter 7 is returned to the retention tank 10 of the absorption tower 2 in a state containing ■- ions, and contributes to the dissolution of calcium carbonate 11 again. Therefore, the Q concentration in the absorption liquid 3 will gradually increase, but from the experimental facts shown in Figures 3 and 4, the Q concentration in the absorption liquid 3 after treatment (
By introducing gas 12a and aerating this liquid 3, the solubility and dissolution rate of calcium carbonate can be maintained or increased.

That is, FIG. 3 is a graph showing the relationship between the solubility of calcium carbonate and time in the case where air is not mixed into the absorption liquid of part 6. ■Concentration Oppm curve 31 Last concentration 5
000 ppm curve b1 and Q concentration 20000 ppm
Comparing the curves C of m, it can be seen that as the side concentration increases, the solubility and dissolution rate of calcium carbonate decrease, which means that as the Q concentration increases, the desulfurization rate decreases. do.

FIG. 4 is a graph showing the relationship between the solubility of calcium carbonate and time in a state where nitrogen gas is mixed (aerated) into the absorption liquid of part 6. According to this, the curve d for the Q concentration Oppm and the curve e for the CI3 concentration 20000 ppm draw approximately the same line, and ■ they maintain high solubility and dissolution rate regardless of the concentration; rather, even if the Q concentration increases, there is no It shows higher solubility and dissolution rate than the case without aeration treatment (see curve a in FIG. 3). This is because calcium carbonate dissolved in water separates <C02 as shown in equation (5) below, and the bubbles generated by aeration dissipate into the gas with this C02. When 7um is expressed as CaO, which has a high solubility, and expressed by the following formula (6), (C
This is because the dissolution of calcium carbonate is promoted because it becomes a(OH)2.

CaCO3→CaO+CO2↑ ・・・・・・(5)C
aO+ H20→Ca(OH)2−・−(6) Therefore,
The gas for mixing or aeration is not limited to nitrogen gas, and blank paper may also be used. Also, since nitrogen gas is an inert gas, any other gas will have the same effect.

From the above experimental facts, by mixing air into the absorption liquid or aerating it, the solubility and dissolution rate of calcium carbonate can be reduced even when the Q concentration increases due to the circulation use of the absorption liquid. It turns out that it is possible to increase the amount without increasing the amount. Therefore, even if the C2 concentration in the absorption liquid increases, a high desulfurization rate can be maintained.

In addition, the air mixed in the absorption liquid 3 in the liquid holding tank 10 oxidizes some calcium sulfite to produce gypsum, which allows the oxidation tower 5 to be made smaller and to produce high-quality gypsum. It can be recovered.

Furthermore, since the absorbed liquid 3 in the liquid holding tank 10 is stirred by the mixed air, the power of the stirrer 14 can be saved.

In summary, according to the present invention, the following excellent effects can be achieved.

(1) Even when the ■ concentration in the absorption liquid increases, the solubility and dissolution rate of calcium carbonate can be maintained high, and therefore the desulfurization rate can be prevented from decreasing and always maintained at a high level. I can do it.

(2) Since a portion of gypsum can be generated even in the liquid storage tank, the oxidation tower can be made small with low capacity.

(3) Since the gypsum produced in the retention tank is used as a core and further crystallized in the oxidation tower, it is possible to recover gypsum with a large particle size and good quality.

(4) Since moist air discharged from the oxidation tower is used as air to be mixed into the absorption liquid, gypsum does not dry and precipitate in the sparger, which is the air introduction part, and clogging does not occur.

(5) Since the air mixed into the absorption liquid stirs the absorption liquid, the power of the stirrer in the absorption tower liquid retention tank can be saved.

(6) Since the method is simple, it can be easily adopted without making major changes to existing equipment.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an apparatus for explaining a conventional flue gas desulfurization method, FIG. 2 is a diagram showing an apparatus for explaining a preferred embodiment of the flue gas desulfurization method according to the present invention, and FIG. Figure 4 is a graph showing the relationship between the solubility of calcium carbonate and time (when no air is mixed into the absorption liquid in the circulation section 6), and Figure 4 shows the value 6.
3 is a graph showing the relationship between the solubility of calcium carbonate and time in a state in which nitrogen gas is mixed into the absorption liquid of FIG. In the figure, 1 is the exhaust gas, 2 is the absorption tower, 3 is the absorption liquid, and 3a
is a circulating absorption liquid, 5 is an oxidation tower, 10 is a liquid retainer, 12
12a is the oxidizing air, and 12a is the air after the oxidation treatment. Patent Applicant Ishikawajima-Harima Heavy Industries Co., Ltd. Representative Patent Attorney Nobuo Kinutani Figure 3 Time opening (minutes)

Claims (1)

[Claims] It has a retention tank for storing an absorption liquid in which an absorbent containing calcium carbonate is dissolved, and while circulating the absorption liquid in the tank, the circulating absorption liquid is mixed with exhaust gas from combustion equipment such as a boiler. In a flue gas desulfurization method, the flue gas is desulfurized by a contact reaction, and the absorption liquid after the desulfurization treatment is oxidized with air to recover gypsum,
A flue gas desulfurization method characterized in that the air after the oxidation treatment is mixed into the absorption liquid in the liquid storage tank to increase the solubility of calcium carbonate in the absorption liquid.