JP3025111B2 - Exhaust gas treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of treating exhaust gases to remove sulfur oxides (hereinafter referred to as SO _X) from the exhaust gas. More specifically, the present invention relates to an improvement in a so-called semi-dry desulfurization method for purifying exhaust gas by spray-drying a desulfurizing agent slurry in an exhaust gas stream and dry-separating the absorbent absorbing SO _X with dust.

[0002]

2. Description of the Related Art The semi-dry desulfurization method is mainly carried out using calcium hydroxide as an absorbent, but simply spraying a slurry of calcium hydroxide alone into exhaust gas has a poor desulfurization rate.
As a remedy, a method of activating a desulfurizing agent as introduced in JP-A-61-209038 and U.S. Pat. No. 4,931,264 has attracted attention.

[0003] In these methods, an aqueous slurry of calcium hydroxide, a mixture of calcium sulfate or calcium sulfite formed by absorption of SO _X by calcium hydroxide, and a fly ash containing silicon dioxide and aluminum oxide is subjected to high-temperature conditions. This is a method of adjusting the desulfurizing agent by hydrothermal curing under the following conditions.

[0004] The desulfurizing agent prepared by this method has a desulfurization performance that is 1.3 to 1.6 times higher than that of calcium hydroxide alone. Calcium consumption can be reduced. However, the biggest drawback of this method is that the capacity of the apparatus for hydrothermal curing and the amount of heat required for hydrothermal curing are increased, and economical exhaust gas treatment cannot be performed.

The reason for this is that the slurry of this type of absorbent has a slurry concentration of not more than 25% by weight, preferably not more than 25% by weight, because the viscosity of the slurry increases remarkably with the increase of the slurry concentration.
This is because a slurry having a low concentration of not more than% by weight must be added, and more than four times the amount of water must be added per weight of the absorbent, and the amount increases accordingly.

Therefore, in order to secure the hydrothermal curing time, the capacity of the apparatus must be increased, and in order to secure the hydrothermal curing temperature, the amount of heat for heating steam and the like is increased by the increase in the slurry flow rate. Increase.

Another major problem is that this absorbent slurry is not only a non-Newtonian fluid exhibiting pseudoplastic flow properties, but also has hydraulic properties similar to cement. Therefore, uniform stirring of the slurry in the hydrothermal curing apparatus is an important issue, but when the capacity of the apparatus is large, the uniform stirring is extremely difficult, and the stirring power is consumed more than necessary.

[0008]

SUMMARY OF THE INVENTION The present invention provides a first raw material which can supply calcium hydroxide and a second raw material which can supply at least one of calcium sulfate and calcium sulfite. And using a highly active desulfurizing agent obtained by hydrothermal curing an aqueous slurry of a mixture of a third raw material that can supply silicon dioxide and aluminum oxide, while using a compact hydrothermal curing device that has long been desired. It is an object of the present invention to provide a method capable of reducing the amount of heat required for securing the hydrothermal curing temperature and enabling the treatment of large-capacity exhaust gas from a power plant or the like.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides at least one of the first raw material, calcium sulfate and calcium sulfite, which can supply calcium hydroxide as described above. And a highly active desulfurizing agent slurry obtained by hydrothermal curing an aqueous slurry of a mixture of a second raw material that can supply silicon dioxide and a third raw material that can supply silicon dioxide and aluminum oxide. Add two raw materials and a third raw material.

In this case, the present invention defines an appropriate range for the amounts of the second raw material and the third raw material to be added to the desulfurizing agent slurry obtained by the hydrothermal curing.

[0011]

Conventionally, the adjustment of a highly active desulfurizing agent by hydrothermal curing
The first raw material, the second raw material, and the third raw material to be supplied to the exhaust gas system are mixed in total from the beginning, and the mixed slurry is subjected to hydrothermal curing. This is because the activation of the desulfurizing agent by hydrothermal curing requires that the first raw material, the second raw material, and the third raw material react to form sulfur-reactive calcium silicate and calcium aluminate. Considering that, the first raw material, the second raw material and the third raw material were mixed in their entirety from the beginning.

However, as a result of the inventor's intensive experiment and research, the first raw material, the second raw material, and the third raw material do not need to be mixed in their entirety from the beginning to be hydrothermally cured.
After hydrothermal curing with an aqueous slurry of a mixture of the second raw material and the third raw material (spent desulfurizing agent and fly ash) of 30 to 70% by weight, preferably 40 to 60% by weight of the first raw material,
Immediately before spraying the desulfurizing agent slurry after curing into the exhaust gas, the second raw material and the third raw material are mixed with the first raw material by 30 to 8 times.
It has been found that if 0% by weight, preferably 40 to 60% by weight is added and stirred, a highly active desulfurizing agent can be obtained which is not inferior to a desulfurizing agent which has been mixed and hydrothermally cured from the beginning.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an embodiment of an exhaust gas treatment method according to the present invention will be described. In FIG. 1, reference numeral 10 denotes a spray dryer for spraying a desulfurizing agent slurry into an exhaust gas to be desulfurized to dry the slurry and absorb and remove SO _X in the exhaust gas. 1 shows a dry dust collector (preferably a bag filter) for separating fly ash from purified exhaust gas.

Exhaust gas generated from a coal-fired boiler or the like (not shown) is introduced into a spray dryer through a flue 11, and a desulfurizing agent slurry is introduced through a conduit 12. The desulfurizing agent slurry introduced from the conduit 12 is sprayed into the spray dryer 10 by a rotary atomizer or the like, contacts the exhaust gas, is dried by the sensible heat of the exhaust gas, and absorbs SO _X in the exhaust gas. SO _X in spray dryer 10
Most of the desulfurizing agent that has absorbed and dried is introduced from the conduit 13 into the dry dust collector 20 together with the exhaust gas and fly ash in the exhaust gas, and the remaining desulfurizing agent deposited on the bottom of the spray dryer 10 is solid. Dispensing line 14
Taken out of

The desulfurizing agent introduced into the dry dust collector 20 is separated from the exhaust gas together with fly ash in the exhaust gas, and also absorbs SO _X in the exhaust gas during the separation process. The purified exhaust gas separated by the dry dust collector 20 is passed through a flue 21
, And the used desulfurizing agent and fly ash are taken out of the solids extraction line 22 of the dry dust collector 20. In FIG. 1, reference numeral 30 denotes a mixing tank for a desulfurizing agent slurry for hydrothermal curing, 40 denotes a hydrothermal curing device, and 50 denotes a final mixing tank for the desulfurizing agent slurry.

A desulfurizing agent slurry for hydrothermal curing is continuously supplied with a slurry of calcium hydroxide prepared by a scraper (not shown) or the like at a predetermined flow rate from a conduit 31 to a slurry desulfurizing agent slurry. And fly ash is supplied from the supply line 32. The input amount is conduit 3
The amount is 30 to 70% by weight (preferably 40 to 60% by weight) based on the dry basis weight of the calcium hydroxide to be charged from No. 1, and the calcium hydroxide is continuously charged at a constant rate.

Further, water is supplied from the conduit 33, and the slurry concentration in the mixing tank is 10 to 25% by weight (preferably 15 to 25% by weight).
(25% by weight). From the conduit 34, the slurry temperature in the slurry in the mixing tank 30 is 60 to 100 ° C. (preferably 8 to 100 ° C.).
0 to 100 ° C.). The desulfurizing agent slurry adjusted to a predetermined composition and slurry concentration in the mixing tank 30 is supplied from a conduit 41 to a hydrothermal curing device 40,
Hydrothermal curing is performed for an average residence time of 30 minutes to 15 hours (preferably 6 to 12 hours).

A stirring tank can be adopted as the hydrothermal curing device.
In order to make the residence time distribution of the desulfurizing agent uniform, a plurality of stirring tanks can be provided. In addition, a steam trace (not shown) or a small amount of steam blowing (not shown) is performed in the hydrothermal curing device to prevent a temperature drop due to heat loss, and the hydrothermal curing temperature is maintained at a predetermined value.

The hydrothermally cured desulfurizing agent slurry is continuously supplied from a conduit 51 to a final desulfurizing agent slurry preparation tank 50, and a used desulfurizing agent and a fly ash supply line 52 are supplied from a supply line 52. Fly ash is added. The additional amount is 30 to 80% by weight based on the dry weight of calcium hydroxide supplied to the mixing tank.
(Preferably 40 to 60% by weight). Further, water is continuously supplied from the conduit 53 so that the concentration of the desulfurizing agent slurry in the final mixing tank becomes 10 to 25% by weight.

Thus, in the final mixing tank 50, the hydrothermally cured desulfurizing agent slurry and the additionally used spent absorbent and fly ash are uniformly stirred and mixed.
A desulfurizing agent slurry having a predetermined concentration is supplied to the spray dryer 10 through the conduit 12.

Excess used desulfurizing agent and fly ash not reused as a desulfurizing agent are taken out of the system through a dust transport line 23. As described above in detail, the method of the present invention is completely different from the conventional method in that the second raw material and the third raw material for adjusting the desulfurizing agent, that is, the used absorbent and fly ash are added. Next, an experimental example of the exhaust gas treatment method according to the present invention will be described. The desulfurization experiment of the coal-fired boiler exhaust gas was carried out using the exhaust gas treatment equipment shown in the system diagram shown in FIG. The average specifications of the exhaust gas used in the experiment are as follows.

Exhaust gas flow rate: 10,000 m ³ N / h
r (dry basis) Exhaust gas temperature: 136 ° C Moisture concentration in exhaust gas: 7.9 vol% SO _X concentration in exhaust gas: 800 ppm (dry basis) Fly ash concentration in exhaust gas: 6.57 g / m ³ N (wet standard) Composition of fly ash (wt%): SiO ₂ (57.2), Al ₂ O ₃ (1
9.6), Fe ₂ O ₃ (3.2), CaO (5.7), MgO (1.0) The equipment uses a spray dryer equipped with a rotary atomizer as the spray dryer 10 and has a capacity of 10 seconds of residence time of exhaust gas. In addition, as the dry dust collector 20,
A pulse jet type bag filter was used. The mixing tank 30 for the desulfurizing agent slurry for hydrothermal curing and the final mixing tank 50 for the desulfurizing agent slurry were stirring tanks equipped with paddle blades, and both had a capacity of 30 minutes for the residence time of the slurry.

The hydrothermal curing tank 40 is also a stirring tank equipped with paddle blades, and the hydrothermal curing time (average residence time of the slurry in the hydrothermal curing tank) is 8 hours in each experiment according to the flow rate of the slurry. The liquid level of the slurry in the hydrothermal curing was adjusted. The hydrothermal curing temperature was set to 95 ° C., the temperature of the slurry was raised by blowing steam into the mixing tank, and the outer wall of the curing tank was subjected to steam tracing to prevent a temperature decrease due to heat loss.

The calcium hydroxide slurry was adjusted to a purity of 9%.
5% by weight (dry basis) of slaked granular quicklime was used. In each experiment, 165% of the slurry having a slurry concentration of 20% by weight was used.
The mixture was supplied from the conduit 31 to the mixing tank 30 at a rate of kg / hr. The slurry concentration in the mixing tank 30, the hydrothermal curing tank 40, and the final mixing tank 50 were all set to 16.7% by weight, and water was separately supplied into the spray dryer 10 so that the exhaust gas temperature at the bag filter outlet became 65 ° C. (Not shown).

In the experiment, in order to see the difference between the conventional method and the method of the present invention, the total amount of the second raw material and the third raw material to be added to the desulfurizing agent, namely, the total amounts of the used desulfurizing agent and fly ash were made equal. Was compared. That is, in the conventional method, the second raw material and the third raw material to be added to the desulfurizing agent are all added to the mixing tank 30, and in the method of the present invention, the total addition amount is the same as that of the conventional method. And final mixing tank 5
It was divided into 0 and charged.

In order to examine the effect of coexistence of deliquescent chloride in the experiment, in experiment No. 4, the desulfurizing agent slurry sprayed into the exhaust gas contained 0.5% by weight of deliquescent chloride as chlorine. Then, salt was added to the mixing tank 30. The experimental results are summarized in Table 1.

[0027]

[Table 1]

[0028]

In the method for treating exhaust gas according to the present invention, the second raw material which is a substance capable of supplying at least one of calcium sulfate and calcium sulfite, which is added to prepare an aqueous slurry to be subjected to hydrothermal curing. And the amount of the third raw material capable of supplying silicon dioxide and aluminum oxide is 30 to 7 per dry weight of the first raw material capable of supplying calcium hydroxide supplied to the preparation tank.
It is 0% by weight, and the amount of the desulfurizing agent slurry supplied to the hydrothermal curing device is reduced, and the conventional disadvantage is improved accordingly.

That is, as described above, the concentration of the desulfurizing agent slurry during hydrothermal curing must be 25% by weight or less, and if the amount of solids added during hydrothermal curing decreases, the amount of solids reduced by 4 times. As described above, the amount of the desulfurizing agent slurry decreases.

The capacity of the hydrothermal curing device can be represented by the product of the hydrothermal curing time (residence time in the curing device) and the volume flow rate of the desulfurizing agent slurry, and the capacity of the device decreases in proportion to the decrease in the flow rate of the desulfurizing agent slurry. I do. In addition, the hydrothermal curing time requires a long time of 30 minutes to 15 hours, preferably 6 to 12 hours, and the capacity of the hydrothermal curing device is reduced by a decrease in the desulfurizing agent flow rate expressed in (m ³ / hr). The amount will be reduced by 6 to 12 times.

Further, the hydrothermal curing temperature is required to be 60 ° -100 ° C., preferably 80 ° -100 ° C. In order to heat the desulfurizing agent slurry from near normal temperature to the hydrothermal curing temperature, the flow rate of the desulfurizing agent slurry is required. A corresponding amount of heat is required, and the amount of heat for heating can be reduced in proportion to the amount of reduction in the desulfurizing agent slurry flow rate.

As is clear from the experimental results in Table 1, the method of the present invention, that is, the method of dividingly adding the second raw material and the third raw material to be added to the desulfurizing agent before and after the hydrothermal curing is adopted. It is evident that the amount of water vapor blown in for reducing the capacity of the hydrothermal curing tank and for maintaining the hydrothermal curing temperature is reduced without substantially impairing the desulfurization rate in comparison with the conventional method.

This effect is also exhibited when a desulfurizing agent is contained in the desulfurizing agent to achieve a high desulfurization rate.

The reduction of the capacity of the hydrothermal curing tank and the reduction of the amount of used steam means that large-scale exhaust gas purification in a power plant or the like can be economically performed, and it is clear that this contributes to environmental conservation.

[Brief description of the drawings]

FIG. 1 is a schematic system diagram showing an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Spray dryer 20 Dry dust collector 23 Dust transport line 30 Mixing tank 40 Hydrothermal curing tank 50 Final mixing tank 32,52 Supply line of used desulfurizing agent and fly ash

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroaki Doai 461-6 Satozuka, Toyohira-ku, Sapporo City, Hokkaido Research Institute of Electric Power Company (72) Inventor Hiroshi Fujita 6-22, Kannonshinmachi, Nishi-ku, Hiroshima-shi Inside the Hiroshima Research Laboratory of Heavy Industries, Ltd. (72) Atsushi Atani 4-6-1, Kannonshinmachi, Nishi-ku, Hiroshima-shi Inside the Hiroshima Research Laboratory of Mitsubishi Heavy Industries, Ltd. (72) Shinichiro Kotake 2-5-1, Marunouchi, Chiyoda-ku, Tokyo No. Mitsubishi Heavy Industries, Ltd. (56) References JP-A-4-197419 (JP, A) JP-A-63-12321 (JP, A) JP-A-55-8889 (JP, A) JP-A-2-152520 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/50 B01D 53/34 B01D 53/81

Claims (4)

(57) [Claims] A substance capable of supplying calcium hydroxide is defined as a first raw material, a substance capable of supplying at least one of calcium sulfate and calcium sulfite is defined as a second raw material, and a substance capable of supplying silicon dioxide and aluminum oxide are defined as a first raw material. The aqueous slurry of the mixture as the three raw materials is hydrothermally cured to obtain a sulfur oxide absorbent slurry, and the absorbent slurry is sprayed into the exhaust gas, and the solid particulate matter having absorbed the sulfur oxide is subjected to frying in the exhaust gas. In the exhaust gas treatment method using the solid particulate matter and fly ash separated as ash as the second raw material and the third raw material, the second raw material and the third raw material are added to the absorbent slurry after the hydrothermal curing. A method for treating exhaust gas, wherein a raw material is added to adjust an absorbent slurry. 2. The amount of the second raw material and the third raw material to be added to the hydrothermally cured aqueous slurry is 30 to 70% by weight of the added amount of the first raw material. 2. The exhaust gas treatment method according to claim 1, wherein the amount of the second raw material and the third raw material to be added is 30 to 80% by weight of the amount of the first raw material. 3. The exhaust gas treatment method according to claim 1, wherein the solid concentration of the absorbent slurry sprayed into the exhaust gas is 10 to 25% by weight. 4. The exhaust gas treatment method according to claim 1, wherein 0.1 to 1% by weight of deliquescent chloride as chlorine is added to the absorbent slurry sprayed into the exhaust gas.