JPS5898125A - Desulfurization of stack gas - Google Patents

Abstract

PURPOSE:To maintain high desulfurization ratio as well as to form gypsum in an absorbing tower, by mixing an exhaust gas after desulfurization treatment in an absorbing liquid containing CaCO3 to enhance the solubility and the dissolving speed of CaCO3. CONSTITUTION:An exhaust gas 1 exhausted from a boiler is introduced into an absorbing tower 2 and an absorbing liquid 3 containing CaCO3 accumulated in a liquid accumulating tank 12 provided to the lower part in the tower 2 is sprayed from spray nozzles 11 to subject the exhaust gas to desulfurization treatment while the purified exhaust gas 4 is discharged out of a system. During this time, a part of the exhaust gas 4a taken from the exhaust gas 4 is mixed in the absorbing liquid 3 in the tank 12 through an aeration fan 14 and a sparger 15 to subject the absorbing liquid 3 to aerating treatment. By this aerating treatment, the solubility and the dissolving speed of CaCO3 are raised and the part of calcium sulfite in the absorbing liquid 3 is further oxidized to form gypsum. In this case, the part of the absorbing liquid 3 among the absorbing liquid 3 containing formed gypsum is branched from a recirculating system 10 to be introduced into an oxidizing tower 5 and contacted with air from a line 16 to form gypsum by oxidizing treatment of calcium suboxide.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a smoke removal method, in particular, in order to desulfurize exhaust gas, an absorbent containing carbonate is dissolved to generate a total absorbent liquid, and this absorbent liquid is In the flue gas desulfurization method, which desulfurizes by contacting with flue gas while circulating, the flue gas after desulfurization treatment is mixed with the above absorption liquid and the whole is aerated, thereby increasing the solubility and dissolution rate of cal/rum carbonate. The present invention relates to a flue gas desulfurization method in which a high desulfurization rate can be maintained and all gypsum can be produced in an absorption tower.

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

As an example of these flue gas desulfurization methods, a method is known in which an absorption liquid containing dissolved carbonate, etc. is brought into contact with the exhaust gas, and the generated sulfite is oxidized to turn gypsum. .

This conventional method will be explained based on FIG. 1. This is exhaust gas exhausted from combustion equipment such as burners. This Nori 1. The gas 1 is brought into contact with the absorption liquid 3 circulating therein in the absorption tower 2, and the yellow oxide in the flue gas and the calcium carbonate in the absorption liquid 3 react as shown in the following formula. to produce calcium sulfite.

S02+CaCO3+y2H20-+CaSO3・%H
20+CO2-(R) The exhaust gas 4 that has been desulfurized in this manner will be released outside the system as clean gas.

On the other hand, the generated absorption liquid containing calcium sulfite is appropriately branched, extracted, and transferred to the oxidation tower 5. In this branched @receiving liquid 3aI'i oxidation tower 5, air is mixed and gypsum is produced as shown in the following formula (2).

CaSO3・y2f(20-)'/2024-u/2
H20-+ CaSO4・2H20-(2) Saranko, above contrary 1; i: L! The produced stone/11 slurry 6 is extracted and then sequentially transferred to the γi-filtration rock 7 to recover gypsum, and the furnace liquid 8 is returned to the absorption liquid 3 in the absorption tower 2. Become.

By the way, in the conventional method as described above,
The solution 8 discharged when collecting gypsum is returned to the absorption solution 3 and used for circulation.
Chloride and hydrogen, which are removed together with sulfur oxides during desulfurization treatment, gradually accumulate in the absorption liquid 3, resulting in a high Ct concentration.As a result, the solubility and dissolution rate IW of calcium carbonate decrease, and the desulfurization rate gradually decreases. There was a problem that the value was decreasing.

This is because the chlorine compound has a high solubility and cannot be recovered as a solid content, so it inevitably accumulates in the liquid.

In order to solve this problem, it is conceivable to drain the filtrate 8 out of the yarn without recycling it, but in this case there is a risk of causing secondary pollution and the effectiveness of the water. It has not been implemented from a usage standpoint.

The present invention was devised in order to effectively solve the above-mentioned problems with VC, and its purpose is to circulate an absorption liquid in which an absorbent containing calcium carbonate is dissolved, and to absorb this absorption liquid. In a lid smoke desulfurization method in which the desulfurization treatment is carried out by bringing the liquid into full contact with the gas, all the exhaust gas after the desulfurization treatment is mixed into the absorption liquid and aerated, thereby increasing the solubility and dissolution rate of calcium carbonate, To provide a +#l□ smoke desulfurization method that can maintain a high desulfurization rate and generate gypsum in an absorption tower.

Even if the solubility and dissolution rate of calcium carbonate tend to decrease as the Ct concentration in the absorption liquid increases, the present invention can improve the ρ solubility and dissolution rate by mixing gas into the absorption liquid and aerating it. U7J shows that the dissolution rate can be maintained high.
This was done by

A preferred embodiment of the present invention will be described below with reference to accompanying drawings.

FIG. 2 is a diagram showing an apparatus for explaining the method according to the first 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. This absorption tower 2
In the lower VC, an absorbing liquid 3 produced by dissolving an absorbent containing carbonate is stored. Then, this absorption liquid 3 is passed through a circulation pump 9 to a Q circulation system 1o to an absorption tower 2.
The spray 11 is transferred to the upper part of the
The air is sprayed into the tower 2. This one-hole atomized absorption liquid comes into contact with the exhaust gas 1 introduced into this tower 2, and the carbonic acid in the absorption liquid and the sulfur oxide in the 1'J1-gas are as shown in the following formula (3). The reaction produces calcium sulfite.

S02+-CaC03-1-3/2f (20→CaSO
3・3//! H2O-1-CO2- (3) In this way, the exhaust gas is desulfurized and the cleaned exhaust gas 4 is discharged outside the system.

Unfortunately, along with the desulfurization process described above, the hydrogen chloride gas in the sushi gas is also removed, and the absorption liquid containing this hydrogen chloride and the produced Lfc calcium sulfite flows down to the liquid storage tank 1.
2vc will be accumulated. Then, calcium carbonate 13 is appropriately added to this absorption liquid 3, and the absorption liquid 3 is circulated again to contribute to the desulfurization process.

On the other hand, part of the exhaust gas 4a of the cleaned exhaust gas 4 after the desulfurization treatment is mixed into the absorption liquid 3 in the liquid storage tank 12 via the aeration fan 14 and the suction fan 15. The absorption liquid 3 is subjected to aeration treatment. This aeration treatment, which is a feature of the present invention, can increase the solubility and dissolution rate of calcium carbonate as described below, and also reduce the amount of sulfite in the absorption liquid 3 as shown in the following formula (4). It can be oxidized to produce stone.

CaSO3・1//2H20-1-y202 +%H2
O-+CaSO4・2H20-(4) At this time, this 1'
Since the J exhaust gas 4a has been desulfurized and is sufficiently moist, gypsum does not dry and precipitate in the exhaust gas inlet 15, which prevents clogging.

In this way, the solubility of calcium carbonate is increased,
Among the generated absorption liquid 3 containing gypsum, a part of the absorption liquid 3a is branched from the circulation system 10 and introduced into the oxidation tower 5. The absorption liquid introduced into the oxidation tower 5 is brought into contact with the air 16, and all of the calcium sulfite in the absorption liquid is oxidized as shown in the above formula (4) to produce soot.

At this time, since some gypsum is precipitated in the liquid storage tank 3 as described above, the gypsum can be used as a core in the oxidation tower 5 to further promote the precipitation of gypsum.

Then, the gypsum slurry 6 generated in the oxidation tower 5 is transferred to the Oki-filter 7, where gypsum is recovered.

In addition, the E liquid 8 in the offshore filter 7 is returned to the liquid storage tank 12 of the absorption Jf2 in a state containing Ct-1, and contributes to the dissolution of the calcium carbonate 7-out 13 again.
・.

Therefore, the Cta degree in the absorbent liquid 3 circulating in the absorption tower 2 will gradually rise by 2, but from the experimental facts shown in FIGS. By mixing the exhaust gas after the desulfurization treatment and aerating this liquid 3, the solubility and dissolution rate of calcium carbonate can be maintained or increased.

In other words, Fig. 4 shows P in a state where no gas is mixed.
It is a graph showing the relationship between the solubility of calcium carbonate in an absorption liquid with an M value of 6 and time.

Curve a of Ct concentration Oppm, Ctilii degree 5,000
ppm song, %+b and Ct concentration 20,000 pp
Comparing the curves c of m, it can be seen that as the Ct concentration in the absorption liquid increases, the solubility and dissolution rate of calcium carbonate, which is an absorbent, decreases, and this means that as the Ct concentration increases, This means that the desulfurization rate decreases.

Further, FIG. 5 is a graph showing the relationship between the solubility of calcium carbonate in an absorption liquid with PI (value 6) and time in a state where nitrogen gas is mixed.

According to this, the curve d of Cta degree Oppm and the Ct concentration 2
0.000 ppm's song Se also depicts almost the same life f, C
It shows high solubility and dissolution rate regardless of the ctH degree, and even if the ctH degree increases, it shows higher solubility and dissolution M rate than when no aeration treatment is performed (Figure 1). (See middle curve a). This is because the calcium carbonate dissolved in the liquid completely separates CO2 as shown by the following equation (5), and bubbles that have been aerated by 15'JE are released into the gas together with this CO21.
If the ram is CaO with a high melting degree or as shown in the following formula (6) (
This is because Ca(OH)2 VC promotes the dissolution of carbonic acid.

CaCO3-+ CaO-1-CO2↑
, , (5) CaO-1-H2O-+ C
a (OH) 2 -(6
) Therefore, the gas mixed into the absorption liquid or the aeration gas is not limited to nitrogen gas, and the same effect can be obtained even if all exhaust gas such as the exhaust gas after desulfurization treatment is used.

From the above experimental facts, even if the Ct concentration increases due to circulating absorption liquid during desulfurization treatment,
It has been found that by mixing exhaust gas into this absorption liquid and subjecting it to aeration treatment, it is possible not only to prevent the solubility and dissolution rate of calcium carbonate, which is an absorbent, from decreasing, but also to increase the solubility and dissolution rate.

Therefore, according to the present invention, the Ct concentration in the absorption liquid increases 1-
However, a high desulfurization rate can be maintained.

In addition, when all gypsum is produced in the oxidation tower 5, the gypsum precipitation is further promoted using the gypsum precipitated in the liquid storage tank 12 as a core, so the oxidation tower 5 can be made smaller.
In addition, it is possible to recover all of the gypsum of good quality with large particle size.

Furthermore, by using damp exhaust gas after desulfurization treatment as the gas to be mixed into the absorption liquid, there is no possibility that gypsum will be deposited on the supertower 15, which is the exhaust gas introduction part, and the exhaust gas will become clogged. The absolute amount also does not increase.

Next, the second invention will be explained based on FIG.

3 is a diagram showing an apparatus for explaining the method according to the second invention, and the feature of the present invention is that a part 4a of the exhaust gas after the desulfurization treatment is transferred into the liquid storage tank 12. The calcium carbonate is mixed not only in the absorption liquid 3 but also in the absorption liquid flowing in the circulation system 10, thereby further increasing the solubility and dissolution rate of calcium carbonate compared to the first invention. be.

That is, a part 4ak of the exhaust gas 4 after the desulfurization treatment is branched, and the branched exhaust gas 4a is further branched,
One of the exhaust gases 4b is mixed into the absorption liquid 3 in the liquid storage tank 12 in the same manner as in the first invention. Then, the other branched exhaust gas 4C' (c) is introduced into the gas-liquid mixing tank 17 provided in the circulation system 10, and the absorption liquid 3b flowing in this system 10 is
VC is mixed in and this absorption liquid 3b is aerated.

According to this invention, compared to the first invention, the solubility and dissolution rate of calcium carbonate as an absorbent can be further improved by one level, and therefore the desulfurization rate can be further improved.

In addition, since there are many gypsum precipitation limits on the absorption tower side,
Furthermore, the precipitation of gypsum within the oxidation tower 5 can be completely promoted. Furthermore, when spraying the absorption liquid into the absorption tower 2, since a mixture of the absorption liquid and the exhaust gas is sprayed, finer droplets can be formed, and therefore, the contact area with the exhaust gas during desulfurization treatment can be reduced. You can make the dog listen more clearly.

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

(Li) Even if the Ct concentration in the absorbent increases, the solubility and dissolution rate of calcium carbonate, which is the absorbent, can be maintained high, and therefore, not only can a decrease in the desulfurization rate be prevented, but also can be kept high at all times.

(2) Since the damp exhaust gas after desulfurization treatment is mixed into the absorption liquid, there is no possibility that gypsum will precipitate in the exhaust gas introduction area and cause clogging. The absolute amount also does not increase.

(3) Since the production of gypsum within the oxidation tower is promoted,
This oxidation tower can be made small and small in capacity, and moreover, it is possible to recover all of the gypsum with large particle size and good quality.

(4) 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 7bth diagram showing an apparatus for explaining a conventional flue gas desulfurization method, and Fig. 2 shows an apparatus for explaining a preferred embodiment of the flue gas desulfurization method according to the first invention. Figure 3, South is a diagram showing an apparatus for explaining a preferred embodiment of the flue gas desulfurization method according to the second invention, and Figure 4 is a diagram showing the solubility of calcium carbonate in the OPHPCO2 harvested liquid in a state where no gas is mixed. FIG. 5 is a graph showing the relationship between the solubility of calcium carbonate in an absorption liquid with 1) II value of 6 and time in a state where nitrogen gas is mixed. In addition, in the figure, 1 is the gas tank, and 2 is the absorption tower 3, 3a. 3b is an absorption liquid, 4.4a, 4b, 4C is an exhaust gas after desulfurization treatment, 5 is an oxidation tower, 10 is a circulation system, 12 is a liquid storage tank, 13 is calcium carbonate, 14 is an aeration fan, 1
7 is a gas-liquid mixing tank. Figure 4 Figure 5

Claims (2)

[Claims] (1) It has a liquid storage tank for storing an absorption liquid in which an absorbent containing calcium carbonate is dissolved, and while the absorption liquid in the tank is circulated, this circulating absorption liquid and exhaust gas from combustion equipment such as a boiler are collected. In a flue gas desulfurization method in which exhaust gas is desulfurized by a catalytic reaction, the flue gas after the desulfurization treatment is mixed into the absorption liquid in the liquid storage tank to increase the solubility of carbonic acid in the absorption liquid. A flue gas desulfurization method characterized by: (2) It has a liquid storage tank for storing an absorption liquid in which an absorbent containing calcium carbonate is dissolved, and the absorption liquid in the tank is circulated through a circulation system, and the circulating absorption liquid and a boiler etc. In a flue gas desulfurization method that desulfurizes exhaust gas by causing a contact reaction with exhaust gas from combustion equipment, the desulfurization treatment is applied to the absorption liquid in the liquid storage tank and the absorption liquid flowing in the circulation system. A flue gas desulfurization method characterized in that the solubility of carbonic acid in these absorbing liquids is increased by mixing in the latter flue gas.