JPH06198127A - Waste gas treating device - Google Patents

Abstract

PURPOSE:To simultaneously desulfurize and denitrify waste gas by a by system by scattering a powder absorbent into the waste gas, collecting the granular body in which SOx and NOx are absorbed, discharging a part of it to outside the system, feeding specified chemicals to the remainder to form slurry and aging it with hot water before reusing it as the absorbent. CONSTITUTION:Coal ash, slaked lime, the collected granular body and water are added from a feeding path 11, a feeding path 12, a conduit 28 and a water conduit 13 respectively to prepare the slurry in a process 10. Then when the slurry is transferred by a conduit 14 to an aging process 15 where it is heated with a steam heating medium from a heat source feeding path 16 while agitating it, a gel-like substance is formed. The gel-like substance is transferred to a dehydration process 18 by a pump 31 and after dehydration, it is transferred by a transfer line 19 to a drying/cracking process 20 when it is dried by heating gas from a heating source feeding path 21 and finely pulverized. And when the pulverized material is pneumatically conveyed through a conduit 22 and scattered into a flue 29 for waste gas from a spray nozzle 23 as an absorbent, it is collected by a dust collector 25 while absorbing SOx and NOx and a part of it is released in the air from a flue 26 and tie remainder is reused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to sulfur oxides (hereinafter referred to as SOx) and nitrogen oxides (hereinafter referred to as NOx) from combustion exhaust gas.
(referred to as x) in a dry process.

[0002]

2. Description of the Related Art The dry purification method of exhaust gas has advantages such as no generation of waste water and reduction of exhaust gas temperature.
Regarding desulfurization, some methods such as in-furnace desulfurization by injecting calcium carbonate into the combustion furnace and spraying slaked lime on the flue are used, but the removal rate is low. Further, various methods such as the active manganese oxide method and the activated carbon method have been studied so far, but they have not yet been industrially spread.

On the other hand, as dry simultaneous desulfurization and denitration methods, research on activated carbon adsorption / NH ₃ catalytic reduction method and copper oxide adsorption reduction method can be seen, but these methods require complicated absorbent process and expensive absorbent. There are problems such as high costs. Further, since these methods are used in fixed beds and moving beds, there are many problems that must be solved, such as measures to prevent pressure loss increase in the reactor, in order to treat high-dust exhaust gas such as coal-fired.

[0004]

The present invention solves the above problems and enables simultaneous treatment of SOx and NOx, enables desulfurization and denitration in a dry dust collecting process, and a waste material as a raw material of an absorbent. Can be reused, and even SOx
It is intended to provide a dry exhaust gas treatment method in which the product that has absorbed is free of sulfite and is substantially converted into sulfate, which facilitates disposal.

[0005]

A dry exhaust gas treatment method of the present invention is a dry exhaust gas treatment method in which a powdery absorbent is dispersed in an exhaust gas containing SOx, NOx and oxygen to collect powder particles having absorbed SOx and NOx. The dust collecting step and a part of the collected powder and granules are discharged to the outside of the system, and the remainder is calcium oxide, calcium sulfate,
A step of adjusting the slurry by adding a substance capable of supplying aluminum oxide and silicon dioxide and water, a step of curing the slurry with hot water while stirring, a step of dehydrating the slurry after curing, and a dehydration step A dry exhaust gas treatment method comprising: a step of drying and crushing a solid material to give a powder, and a circulating step of spraying the powdery absorbent into the exhaust gas.

[0006]

The substance capable of supplying calcium oxide of the present invention includes, for example, quick lime, slaked lime, calcium carbonate, cement, slag, dolomite plaster and the like. Examples of substances that can supply calcium sulfate include gypsum dihydrate, gypsum hemihydrate, quick lime, slaked lime, a combination of calcium carbonate and sulfuric acid, and calcium sulfite. Further, as a substance capable of supplying silicon dioxide, for example, silica, metasilicic acid, aluminum silicate, calcium silicate and cristobalite, tridymite, kaolin, bentonite, talc, perlite, shirasu, diatomaceous earth, water glass and the like reactive silicon dioxide are contained. Further, examples of the substance that can supply aluminum oxide include, for example, alumina, aluminum hydroxide, aluminum silicate, alum sulfate, alum, aluminum sulfide, aluminum sulfate, aluminum chloride, bentonite, kaolin, diatom. Examples include compounds containing reactive aluminum such as soil, zeolite, and perlite.

[0007] Examples of other substances capable of simultaneously supplying two or more of the above-mentioned four kinds of compounds are coal ash (calcium oxide, silicon dioxide, aluminum oxide source), cement (calcium oxide, calcium sulfate, Silicon dioxide, aluminum oxide source) slag, and shirasu, andesite, chert, quartz trachyte, opal, zeolite, feldspar, clay mineral,
Reactive silicon dioxide, aluminum, etc.
Minerals including calcium are included.

First, as a powdery absorbent dispersed in exhaust gas containing SOx, NOx and oxygen, silicon oxide (SiO ₂ ): aluminum oxide (Al
₂ O ₃ ): Calcium oxide (CaO): Calcium sulfate (CaSO ₄ ) = 10-30%: 5-12%: 30-4
5%: 5 to 30% is preferable.

By combining various substances capable of providing the above-mentioned four kinds of compounds (calcium oxide, calcium sulfate, silicon dioxide and aluminum oxide), by sprinkling an absorbent into exhaust gas containing SOx, NOx and oxygen. Granules that absorb SOx and NOx and are collected in the dry dust collecting process {The general composition of this granule is% by weight of unreacted Ca.
(OH) ₂ : 10 to 20%, CaSO ₄ : 50 to 70
_{%, SiO 2: 12~18%,} Al 2 O 3: a slurry plus the portion of water is 5-7%}, which After curing in hot water, squeeze water in the dehydration step Then, by drying and crushing, CaO, Al ₂ O ₃ , C
A powdered absorbent composed of aSO ₄ and SiO ₂ components is obtained. Not only is this absorbent an excellent SOx and NOx absorbent, but it also has the function of oxidizing sulfite to convert it to sulfate, so that the exhaust gas treatment product does not contain sulfite. Further, since the absorbent according to the present invention has a high activity, the amount of dispersion in the exhaust gas is small, the temperature of the exhaust gas does not decrease, and there is no fear of corrosion of the device.

Particularly, in the dry method using the powder absorbent, unlike the semi-dry method in which the slurry-like absorbent is sprayed, there is almost no decrease in the temperature of the exhaust gas, so that there is no limit to the amount of the absorbent sprayed and exhaust gas with high SOx concentration Will also be applicable. In the semi-dry method, the temperature decreases due to the evaporation of water, so it is necessary to operate so that it does not fall below the gas dew point in order to prevent wetting of the ash discharged
If the concentration of SOx is high, the amount of slurry must be increased, and thus the gas dew point is restricted, but the method of the present invention does not have such a restriction.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. Numeral 10 supplies coal ash from the supply path 11 and slaked lime from the supply path 12 and also supplies the granular material collected from the exhaust gas described later from the conduit 28, and further introduces the water conduit 13
This is a slurry adjusting step in which water is added from the above and the slurry is adjusted while being stirred by a device (not shown). Generally conduit 2
10 to 30% by weight of the granular material supplied from No. 8, 20 to 30% of the coal ash supplied from the supply path 11,
CaO (as slaked lime) supplied from the supply channel 12 is 4
It is 0 to 60%. The slurry adjusted here is the conduit 14
Is transferred to the curing step 15 by the pump 30. In the step 15, the slurry is agitated by a steam heating medium from the heat source supply path 16 while being stirred by an apparatus (not shown).
Heated to 0 to 120 ° C, preferably 90 to 100 ° C,
If kept for 6 to 12 hours, hydrothermal cure during this period Ca
A gel-like substance composed of four components of O, Al ₂ O ₃ , CaSO ₄ , and SiO ₂ is produced. The gel-like substance has a specific surface area of 50 to 100 m ² / g and is transformed into a very porous substance.

The slurry that has been cured is transferred to the dehydration step 18 by the pump 31 via the conduit 17, and is dehydrated to a solid concentration of 50% or more by an apparatus (not shown). The dehydrated solid absorbent is dried on the transportation line 19.
It is sent to the crushing process. In the step 20, it is dried by the heating gas from the heat source supply path 21 and simultaneously finely pulverized.
Generally, gas or gas from an oil-fired combustion furnace is used as a heat source for drying, but it is also possible to introduce a part of high-temperature exhaust gas from a boiler. If the amount of heat is insufficient using this boiler exhaust gas, it is possible to raise the temperature with a duct burner. The temperature of the hot gas blown into the drying and crushing step 20 is 300 to 60.
It is 0 ° C, preferably 500 to 550 ° C. The reason is that in order to avoid a prior absorption reaction with SOx, NOx, carbon dioxide gas, etc. in the gas, it is dried at high temperature in the shortest possible time.

The dried and crushed powdered absorbent is in the conduit 2
2 is sent by air flow from the spray nozzle 23 to SOx, N
It is sparged into the exhaust gas flue 24 containing Ox and oxygen. The absorbent scattered here rides on the exhaust gas flow and becomes SO.
The gas, which is guided to the dust collector 25 while absorbing x and NOx, is further desulfurized and denitrated, and the purified gas is discharged from the flue 26 to the atmosphere. A bag filter, an electrostatic precipitator, or the like is used as the dust collector 25, but the bag filter is advantageous because it has a higher SOx and NOx absorption efficiency. The powder and granules separated from the exhaust gas by the dust collector 25 consist of reaction product solids, coal ash and unreacted absorbent, and are taken out through the conduit 27. The powder and granules collected from the conduit 27 are discharged from the conduit 29 to the outside of the system, but a part of them is discharged from the conduit 28.
Then, the process is returned to the step 10 of adjusting the raw material of the absorbent to increase the effective utilization rate of the absorbent and reduce the amount of the raw material to be newly supplied. In particular, since the recovered reaction product solid contains calcium sulfate as a useful absorbent raw material, this recovered product can be used.

Hereinafter, examples of the present invention will be described. (Experimental Example 1) Quicklime was added to water, and 60 wt% of SiO ₂ and Al ₂ O ₃ were added to the slaked lime slurry obtained by digestion.
% And 23 wt% of coal ash and dihydrate gypsum were mixed in a weight ratio of 50:30:20 on a dry basis. The amount of water at this time was set to 5 times the total weight of the powder. The slurry was cured in hot water of 95 ° C. for 12 hours while stirring. The cured slurry was filtered under reduced pressure and dehydrated, then heated in an electric furnace at 550 ° C. for several minutes to give a dry solid, which was then crushed with a crusher to obtain a powdery absorbent. The average particle size of this absorbent was 20 microns, and it was confirmed from the X-ray diffraction peak that there was a substance similar to ettringite. The specific surface area was measured and found to be 88 m ² / g. Here, dihydrate gypsum was used as gypsum, but either anhydrous or hemihydrate gypsum may be used.

This powdery absorbent was sprayed to a device having a gas amount of 20 m ³ N / h, which was connected to a bag equipped with a spray nozzle and a bag filter so that the Ca / SO ₂ ratio was 2. The composition of the inlet gas at this time was SO ₂ : 500 ppm, NO: 12
ppm, CO ₂ : 10 vol%, O ₂ : 5 vol%, H
₂ O: 8 vol%, N ₂ : adjusted so as to be in balance, and gas temperature was adjusted by a heater so as to be 110 ° C. Pressurized N ₂ gas was used for spraying the absorbent from the spray nozzle.

As a result of measuring SO ₂ and NO at the bag filter outlet while spraying the absorbent, the SO ₂ removal rate was 60.
%, The NOx removal rate was 45%. When the reaction products attached to the bag filter were analyzed after the test, most of them were sulfates and some nitrates were detected.

For comparison, the same test using slaked lime powder showed a SO ₂ removal rate of 5% and a NOx of just under 2%.

(Experimental Example 2) The coal ash used in Experimental Example 1 was charged with slaked lime and gypsum dihydrate at a ratio of 30:50:20 (weight ratio) into an autoclave and mixed with water equivalent to 5 times. The temperature was changed to 70 to 120 ° C. and the mixture was aged and cured in hot water for 6 to 12 hours to obtain a slurry of Table 1. Each of these was dehydrated, dried and crushed in the same manner as in Experimental Example 1 to obtain a powdery absorbent, and a SO ₂ and NOx removal test was conducted in the same manner as in Experimental Example 1 to obtain the results in Table 1.

[0019]

[Table 1]

(Experimental Example 3) Quicklime is a substance capable of supplying calcium oxide, the coal ash used in Experimental Example 1 is a substance capable of simultaneously supplying silicon dioxide and aluminum oxide, and a substance capable of further supplying calcium sulfate. As shown in Table 2, various kinds of gypsum dihydrate were mixed with 5 times the equivalent amount of water, and the slurry was adjusted by the following method. Hot water (70
First, quick lime was put into a 3 liter container equipped with a stirrer and hydrated to obtain a slaked lime slurry. Coal ash and gypsum dihydrate were added thereto, and the mixture was cured in hot water at 95 ° C for 12 hours with stirring.

The slurry after curing was dehydrated, dried and crushed in the same manner as in Experimental Example 1 to obtain a powdery absorbent. Using this absorbent, a SO ₂ and NOx removal test was conducted in the same manner as in Experimental Example 1, and the results shown in Table 2 were obtained.

[0022]

[Table 2]

(Experimental Example 4) Of the slurries prepared in Experimental Example 3, No. The absorbent powder was prepared in the same manner as in Experimental Example 1 except that the curing slurry of No. 13 was dehydrated and the drying temperature and time in the electric furnace were changed as shown in Table 3. Using this absorbent, a SO ₂ and NOx removal test was conducted in the same manner as in Experimental Example 1, and the results shown in Table 3 were obtained.

[0024]

[Table 3]

(Experimental Example 5) Using the powdery absorbent obtained in Experimental Example 1, the temperature of the bag filter was changed as shown in Table 4, and the SO ₂ and NOx contents were changed in the same manner as in Experimental Example 1. A removal test was performed and the results shown in Table 4 were obtained.

[0026]

[Table 4]

[0027]

EFFECTS OF THE INVENTION According to the present invention, it is possible to simultaneously perform dry flue gas desulfurization and denitration by using a novel absorbent, and it is possible to convert all the SOx absorption form to sulfate. It is possible to facilitate its disposal. further,
Since the highly active powder absorbent is sprayed, it can be carried out without limiting the spray amount of the absorbent as in the semi-dry method.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hiroaki Doi, 6 461 Satozuka, Toyohira-ku, Sapporo City, Hokkaido Research Institute of Electric Power Co., Ltd. (72) Hiroshi Fujita, 6-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima No. Mitsubishi Heavy Industries, Ltd. Hiroshima Research Institute (72) Inventor Jun Tatani 4-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute (72) Inventor Shinichiro Kotake 2 Marunouchi, Chiyoda-ku, Tokyo No. 5-1 Sanryo Heavy Industries Co., Ltd.

Claims (1)

[Claims] 1. A dry dust collecting step in which a powdery absorbent is dispersed in an exhaust gas containing sulfur oxides, nitrogen oxides, and oxygen to collect powders that have absorbed sulfur oxides and nitrogen oxides. ,
A step of discharging a part of the collected powder and granules out of the system and adding a substance capable of supplying calcium oxide, calcium sulfate, aluminum oxide and silicon dioxide and water to the rest to adjust the slurry, and the slurry. A step of curing with hot water while stirring, a step of dehydrating the slurry after curing, a step of drying and crushing the dehydrated solid matter to form a powder, and the powdery absorbent in the exhaust gas A method for treating dry exhaust gas, which comprises: