JP3150497B2 - Dry purification method of exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing environmental pollutants such as sulfur oxides (hereinafter referred to as "SOx") from exhaust gas, and more particularly to a method of blowing a powdery absorbent into an exhaust gas stream to absorb the pollutant. The present invention relates to a so-called exhaust gas dry purification method for purifying exhaust gas by dry-separating the absorbed absorbent together with dust in exhaust gas.

[0002]

2. Description of the Related Art The dry purification method of exhaust gas has the advantages that no waste water is generated and the temperature of exhaust gas is not lowered.
As for desulfurization, in-furnace desulfurization in which calcium carbonate is injected into a combustion furnace and a method of spraying slaked lime into a flue are partially used, but the removal rate is low. In addition, various methods such as an activated manganese oxide method and an activated carbon method have been studied so far, but have not yet been industrially used.

On the other hand, studies on activated carbon adsorption / NH ₃ catalytic reduction method and copper oxide adsorption reduction method have been found as dry simultaneous desulfurization and denitration methods. However, these methods have complicated regeneration steps and require expensive absorbents. There are problems such as high processing costs. In addition, since these methods are used on a fixed bed and a moving bed, there are many problems that must be solved in a reactor in order to treat high-dust exhaust gas as in the case of coal-fired combustion.

As a measure for improvement, Japanese Patent Laid-Open No. 01-80425 is disclosed.
No. method is proposed. In this method, a substance capable of supplying calcium oxide and one or more substances selected from a group of substances capable of supplying a sulfate compound, a halogen element compound, silicon dioxide, aluminum oxide, sulfide, and a hydroxide of an alkali metal are kneaded with water. After curing in the presence of water,
Basically, it is pulverized into a powder and sprayed into exhaust gas, and the absorbent has a characteristic that the exhaust gas purifying performance is excellent.

[0005] However, the absorbent obtained by this method cures a kneaded solid having a relatively small amount of water without stirring, so that the hydration reaction for obtaining a highly active absorbent is not sufficiently performed, and therefore, such as SOx, etc. It has been said that it is difficult to increase the content of alkaline Ca necessary for absorbing the acid gas. For example, the addition ratio of calcium hydroxide, which is a Ca source, is at most 30% by weight, and if added more, inactive Ca will remain in excess, and the utilization rate of Ca will decrease.

Japanese Patent Application No. Hei 4-1992 discloses that when this is cured with stirring in hot water having a large amount of water, calcium hydroxide as a Ca source is further increased and an absorbent having high activity can be obtained.
No. 299642. However, the absorbent obtained by this method is in the form of a slurry, and it is necessary to dehydrate and dry it in order to turn this into powder and purify the exhaust gas by the dry method.
This requires enormous energy. In particular, absorbent slurries that have been cured with hot water have poor mechanical dewatering properties, and are at most 50%.
wt% or less, and if this is dehydrated more than necessary, there is a problem that the activity is reduced because the absorbent particles are compacted.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned state of the art, and has as its object to provide an economical dry purification method of exhaust gas which has solved the conventional disadvantages.

[0008]

According to the present invention, there are provided (1) a first raw material composed of a substance capable of supplying calcium hydroxide, a second raw material composed of a substance capable of supplying calcium sulfate, and silicon dioxide and aluminum oxide; Adjusting the slurry of the mixture with the third raw material consisting of the obtained substance,
Curing the slurry under a temperature condition of 90 to 100 ° C.,
A powder mixture of the second raw material and the third raw material is added to an absorbent precursor obtained by dehydrating the slurry that has been cured with hot water, and the mixture is kneaded to form a kneaded body. After being introduced into a disintegrator, the disintegration and the pulverization are simultaneously performed to form a solid-gas multiphase flow of the powdery absorbent and the hot gas. After the solid-gas multiphase flow is supplied into the exhaust gas stream, the exhaust gas and the powdery A dry purification method for exhaust gas, comprising introducing a mixed fluid of an absorbent into a dust collector and separating and recovering a powdery absorbent and fly ash entrained in the exhaust gas from the exhaust gas. (2) The method for dry purification of exhaust gas as described in (1) above, wherein the used powdery absorbent and fly ash separated and recovered from the exhaust gas in the dust collector are used as the second raw material and the third raw material. . (3) The exhaust gas according to the above (1) or (2), wherein the water dehydrated from the hot water cured slurry is circulated for adjusting the slurry and / or adjusting the temperature of the exhaust gas upstream of the dust collector. Dry purification method. (4) Whether the temperature of the hot gas blown into the crusher for drying and transporting the kneaded body is 400 to 600 ° C, and at least a part of the hot gas is taken out of the high temperature zone of the facility for generating the exhaust gas to be purified. The method for dry-purifying exhaust gas according to any one of claims 1 to 3, wherein the temperature of the exhaust gas before blowing in the powdery absorbent is raised by a duct burner. It is.

[0009]

The substance capable of supplying calcium hydroxide, which is the first raw material of the present invention, includes, for example, quicklime, slaked lime, calcium carbonate, cement, slag, dolomite plaster, and the like. Examples of the substance that can be obtained include dihydrate gypsum, hemihydrate gypsum and quicklime, slaked lime, a combination of calcium carbonate and sulfuric acid, and calcium sulfite, and a substance that can supply silicon dioxide, which is one of the third raw materials. As, for example, silica, metasilicate, aluminum silicate, calcium silicate and cristobalite, tridymite, kaolin, bentonite, talc, perlite, shirasu, diatomaceous earth, compounds containing reactive silicon dioxide such as water glass, and the like,
Examples of the substance that can supply aluminum oxide as one of the third raw materials include alumina, aluminum hydroxide, aluminum silicate, sodium sulfate, alum, aluminum sulfide, aluminum sulfate, aluminum chloride, bentonite, kaolin, and diatomaceous earth. Examples thereof include compounds containing reactive aluminum, such as zeolite and perlite.

Examples of other substances which can simultaneously supply two or more of the above four compounds are coal ash (calcium oxide, silicon dioxide, aluminum oxide source) and cement (calcium oxide, calcium sulfate). , Silicon dioxide,
Aluminum oxide source) Minerals containing reactive silicon dioxide, aluminum, calcium, etc. such as slag, shirasu, andesite, chert, quartz trachyte, opal, zeolite, feldspar, clay mineral, etrin guide and the like.

First, as a powdery absorbent to be dispersed in an exhaust gas containing contaminants such as SOx and oxygen, silicon oxide (SiO ₂ ): aluminum oxide (Al ₂
O ₃ ): Calcium oxide (CaO): Calcium sulfate (CaSO ₄ ) = 10 to 30%: 5 to 12%: 30 to 5
0%: 5% to 30% is preferable.

[0012] By combining various substances capable of providing the third raw material from the first raw material, and by sprinkling an absorbent into exhaust gas containing contaminants such as SOx and oxygen, S
Granules that absorb contaminants such as Ox and are collected by a dust collector. The general composition of the granules is unreacted Ca (O
_{H) 2: 10~20%, CaSO} 4: 50~70%, S
iO ₂ : 12 to 18%, Al ₂ O ₃ : 5 to 7%.
Of water and water to make a slurry,
After curing in hot water, the water was squeezed out by a dehydrator, and then a part of the powder and granules collected by a dust collector was added and kneaded, and then introduced into a crusher under hot gas flow. By performing crushing and pulverization at the same time, a powdery absorbent is obtained. Here, it is the water content after dehydration, but since the absorbent precursor cured by hot water is microscopically porous and the water contained therein is extremely large, centrifugal dehydration, vacuum dehydration, mechanical dehydration operations such as filter press, etc. It is at most 50% by weight or less. If water is squeezed out more than necessary in this dehydration operation, the absorbent particles are compacted and the micropores are crushed, which in turn causes a decrease in activity. Therefore, the water concentration after dehydration in this operation is preferably about 60% by weight.

In order to reduce the remaining water as much as possible, a dry used absorbent collected by a dust collector is added and kneaded, and the remaining water is removed by a hot gas as a kneaded material having a low water concentration. If this is the case, the energy required for drying and crushing can be greatly reduced. Another advantage of adding the used absorbent is that the unreacted Ca can be effectively used.

[0014]

The details of the present invention will be described based on embodiments.
FIG. 1 is a schematic system diagram showing an embodiment of the present invention, and illustrates a dry purification method of exhaust gas generated from a coal-fired boiler. In FIG. 1, reference numeral 10 denotes a mixing tank for an absorbent slurry for hot water curing, which includes a slurry of a first raw material supplied from a supply line 11 of a first raw material and a supply line 14 of a second raw material and a third raw material. Each raw material to be supplied is mixed with water supplied from the water supply line 12 and filtered water of the dehydrator 30 supplied from the filtered water supply line 15 to prepare a slurry having a predetermined concentration, and supplied from the steam supply line 13. The temperature is raised to the hot water curing temperature by the generated steam.

The slurry of the first raw material supplied from the line 11 is preferably calcium hydroxide obtained by slaking quicklime, and the second and third raw materials supplied from the line 14 are collected by a dust collector 90. The collected spent absorbent and fly ash in the exhaust gas are used.
The absorbent containing calcium hydroxide is SOx in the exhaust gas.
To produce calcium sulfate, and fly ash of a coal-fired boiler contains a considerable amount of silicon dioxide and aluminum oxide, and the requirements as the second and third raw materials of the absorbent used in the present invention are considered. Have.

The solid concentration of the absorbent slurry in the mixing tank 10 is suitably from 10 to 25% by weight. If the solid concentration is low, not only the capacity of the device for curing becomes large, but also the curing temperature of hot water is lowered. To ensure this, the consumption of steam supplied from the steam supply line 13 increases. On the other hand, if the solid content is too high, the slurry viscosity becomes high, making uniform stirring of the slurry difficult. In addition, the line becomes blocked during the transportation of the slurry, making it impossible to operate the equipment smoothly.

The slurry adjusted in the mixing tank 10 is supplied to the line 2
1 is sent into the hot water curing device 20 and is subjected to hot water curing at 90 to 100 ° C. for 6 to 12 hours. During this time, a gel-like substance consisting of four components of CaO, Al ₂ O ₃ , CaSO ₄ and SiO ₂ is generated. This gel-like substance has a specific surface area of 50 to 100 m ² / g and is transformed into a very porous substance.

As the hot water curing device 10, a stirring tank can be used, and a plurality of units may be used if necessary. Further, in order to maintain the curing temperature, the curing device 20 is subjected to steam tracing or a small amount of steam blowing. The absorbent slurry after curing is supplied from a line 31 to a dehydrator 30, where it is dehydrated to a solid concentration of about 40% by weight. The dehydrated absorbent cake is supplied from line 41 to kneader 40. A pug mill can be used as the kneading machine 40, where it is mixed with the powdery second and third raw materials supplied from the line 42 to form a kneaded body having a solid content concentration of 50% by weight or more.
The higher the solids concentration is, the better the drying calorie can be saved, but the capacity of the kneader is limited,
0 to 70% by weight.

Next, the kneaded material is supplied to a crusher 50 from a line 51, crushed and dried by a hot gas blown from a line 52, and is formed into a solid-gas mixed phase flow of the powdery absorbent and the hot gas. It is blown into the exhaust gas in the duct 91 from the line 71. If necessary, a solid-gas separator 70 such as a cyclone may be installed in the line 71 to separate the coarse powder of the absorbent that is insufficiently disintegrated, and then return to the kneader 40 from the line 43.

The absorbent blown into the exhaust gas flow in the duct 91 is suspended and dispersed in the exhaust gas to absorb and remove pollutants in the exhaust gas, but the contact time between the two is maintained for 10 seconds or more. Preferably, a reactor 80 can be provided in the duct 91 to secure this contact time.

The duct 91 is connected to a dust collector 90, and the absorbent and fly ash in the exhaust gas are separated from the exhaust gas.
And used as a second raw material and a third raw material to be supplied to the kneading machine 40, and the rest is taken out of the system from a line 94.
Contaminants in the exhaust gas are also absorbed by the absorbent during the process in which the absorbent is separated by the dust collector 90. Therefore, it is preferable to use a bag filter as the dust collector 90.

The amount of the absorbent blown into the exhaust gas is SO
It is blown in such a manner that the Ca content in the absorbent that reacts with pollutants such as x becomes 1 to 3 mol per mol of the pollutants in the exhaust gas. The exhaust gas temperature is 80 to 1 at the outlet of the dust collector 90.
Adjusted to 30 ° C. Generally, the exhaust gas temperature is 1
Since the temperature is as high as about 50 ° C., the temperature is adjusted by water spray or the like. For this purpose, a filtrate discharged from the dehydrator 30 can be used.

A crusher 5 for drying and transporting the absorbent.
The hot gas blown into the exhaust gas in the high temperature region of the exhaust gas generating equipment, for example, in the case of the boiler 100 in FIG. 1, a method of blowing high temperature exhaust gas at the inlet of the economizer (not shown) or exhaust gas before blowing the absorbent in the duct 91 into a line 54
A method of raising the gas temperature to a predetermined gas temperature and blowing it by adjusting the fuel supplied from the line 61 and the air supplied from the line 62 by introducing into the duct burner 60 incorporated between the line 52 and the exhaust gas purification cost. Leads to a reduction in However, when the exhaust gas is used in this way, the exhaust gas temperature needs to be in the range of 400 to 600 ° C. At exhaust gas temperatures below this, not only does the drying of the absorbent fail, but also a decrease in the activity of the absorbent, which is thought to be due to contaminants in the exhaust gas. At a higher temperature, the crusher must be made of a special material, and this is disadvantageous in terms of thermal economy.

(Experimental Example 1) Quick lime was poured into water, and coal ash and SiO ₂ containing 60 wt% and 23 wt% respectively of SiO ₂ and Al ₂ O ₃ were added to slaked lime slurry obtained by digestion on a dry basis. The mixture was mixed so that the weight ratio was 50:30:20. The amount of water at this time was equivalent to 5 times the total weight of the powder. The slurry was aged while being stirred in hot water at 95 ° C. for 12 hours, and then dehydrated by filtration under reduced pressure to obtain a precursor of an absorbent containing 60% by weight of water.

A powder mixture containing 50% by weight of gypsum dihydrate and 50% by weight of coal ash was added to this precursor in an amount of 60% by weight based on the total weight of the precursor to form a kneaded product. The kneaded product was introduced into a disintegrator under hot gas flow using kerosene as a fuel, and was brought into contact with a hot gas at a temperature of 550 ° C. for several minutes to obtain a powdery absorbent containing 0.8 wt% of water. The average particle size of this absorbent is 2
It was 0 μm, and it was confirmed from the X-ray diffraction peak that there was a substance similar to ettringite. When the specific surface area was measured, it was 63 m ² / g.

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

As a result of measuring SO ₂ and NO at the outlet of the bag filter while spraying the absorbent, the SO ₂ removal rate was 58%.
% And NOx removal rate of 43%. When the reaction product attached to the bag filter was analyzed after the test, almost all sulfates and some nitrates were detected. For comparison, a similar test was performed using slaked lime powder.
The O ₂ removal rate was 5%, and NOx was only slightly less than 2%.

(Experimental Example 2) The powder of the collected bag filter (used absorbent) after the absorbent evaluation test obtained in Experimental Example 1 was used as the precursor of the absorbent obtained in Experimental Example 1. 20, 60, and 100% by weight based on the total weight of the absorbent precursor were added to form kneaded bodies 1, 2, and 3. The kneaded product was introduced into a crusher under a hot gas flow, dried and pulverized with a hot gas at a temperature of 550 ° C. to obtain powdered absorbents 1 ′, 2 ′ and 3 ′.
Using each of these powdery absorbents, in the same manner as in Experimental Example 1,
When the Ca / SO ₂ molar ratio was sprayed on the test apparatus so as to be 2, the results shown in Table 1 were obtained.

[0029]

[Table 1]

(Experimental Example 3) Slaked lime and dihydrate gypsum were added to the coal ash used in Experimental Example 1 in an autoclave at a ratio of 30:50:20 (weight ratio), and mixed with 5 times as much water as a slurry. After changing the temperature from 70 to 120 ° C,
The mixture was agitated and cured in hot water for 時間 12 hours. The slurry after curing was dehydrated so as to have a solid content concentration of 50 wt% to obtain precursors 4 to 14 of the absorbent. 50% by weight of a powder mixture containing hemihydrate gypsum: 60% by weight and coal ash: 40% by weight with respect to the total weight of each precursor was added to form a kneaded body, and each kneaded body was crushed under a hot gas flow. And dried and pulverized with a hot gas at a temperature of 500 ° C. to obtain powdered absorbents 4 ′ to 14 ′. Using this powdery absorbent, Ca /
When sprayed on a test apparatus so that the SO ₂ molar ratio was 2, the results shown in Table 2 were obtained.

[0031]

[Table 2]

(Experimental Example 4) The dehydrated filtrate of the hydrothermally cured slurry obtained in Experimental Example 3 and coal ash, slaked lime, and hemihydrate gypsum were mixed in a weight ratio of 5%.
Mix at a ratio of 00: 25: 50: 25 and at 95 ° C. for 12
After curing for an hour, dehydration was performed so that the solid content concentration became 50 wt%, and a precursor of the absorbent was obtained. 40% by weight of a powder containing 50% by weight of gypsum and 50% by weight of coal ash based on the total weight of this precursor was added to form a kneaded body, and this kneaded body was introduced into a crusher under hot gas flow. The powder was dried with a hot gas at a temperature of 550 ° C. and pulverized to obtain a powdery absorbent. Using this powdery absorbent, Ca / SO ₂ was produced in the same manner as in Experimental Example 1.
It was sprayed on the test apparatus so that the molar ratio was 2. At this time, dehydrated filtrate was supplied from the absorbent supply line as cooling water for setting the gas temperature to 110 ° C.
_{2 The} removal rate was 60%, and the NOx removal rate was 44%.

(Experimental Example 5) Using the kneaded body 2 obtained in Experimental Example 2, the temperature of the crusher was set to 3 under a hot gas flow using kerosene as fuel.
The temperature was changed from 00 ° C. to 700 ° C., and the kneaded body was supplied thereto to obtain a dry powder absorbent at each temperature. The specific surface area and X-ray diffraction were measured for each of the absorbents,
Further, it was sprayed into an exhaust gas containing SO ₂ and NO under the same conditions and method as in Experimental Example 1, and the removal performance of each was measured. The results shown in Table 3 were obtained.

[0034]

[Table 3] Among the X-ray diffraction peaks, VS represents a very strong peak, S represents a strong peak, and W represents a weak peak. From the results shown in Table 3, when the hot gas temperature is 300 ° C., drying takes a long time and calcium carbonate is generated by the carbon dioxide gas in the hot gas, and a decrease in activity is observed. it can be seen that SO ₂ and NOx removal rate decreases.

[0035]

According to the present invention, a novel absorbent can be employed to remove environmental pollutants such as SOx in a dry manner, and a drying heat for forming a slurry-like absorbent into powder. Energy can be saved.

[Brief description of the drawings]

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

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroaki Doai 461-6, Satozuka, Toyohira-ku, Sapporo-city, Hokkaido Inside the Hokkaido Electric Power Research Institute (72) Inventor Hiroshi Fujita 4--22 Kannonshinmachi, Nishi-ku, Hiroshima, Hiroshima, Japan No. Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Atsushi Atani, 4-4-2 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (56) References JP-A-3-213122 (JP, A) JP-A-6-198127 (JP, A) JP-A-6-99025 (JP, A) JP-A-4-197419 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) B01D 53/34-53/83 B01J 20/16

Claims (4)

(57) [Claims] 1. A mixture of a first raw material composed of a substance capable of supplying calcium hydroxide, a second raw material composed of a substance capable of supplying calcium sulfate, and a third raw material composed of a substance capable of supplying aluminum oxide and aluminum oxide. Of the second raw material and the third raw material to an absorbent precursor obtained by dehydrating the slurry subjected to hot water curing under a temperature condition of 90 to 100 ° C. A powder mixture is added and kneaded to form a kneaded body. The kneaded body is introduced into a crusher under a hot gas flow so that crushing and pulverization are performed simultaneously to obtain a solid-gas mixed phase of the powdery absorbent and the hot gas. After the solid-gas multiphase flow is supplied into the exhaust gas stream, a mixed fluid of the exhaust gas and the powdery absorbent is introduced into the dust collector, and the exhaust gas is accompanied by the powdery absorbent and the exhaust gas. Characterized by separating and collecting fly ash Dry purification method of exhaust gas. 2. The used powdery absorbent and fly ash separated and recovered from the exhaust gas in the dust collector,
The dry purification method for exhaust gas according to claim 1, wherein the method is used as a raw material and a third raw material. 3. The exhaust gas according to claim 1, wherein the water dehydrated from the slurry cured with hot water is circulated for adjusting the slurry and / or adjusting the temperature of the exhaust gas upstream of the dust collector. Dry purification method. 4. The temperature of a hot gas blown into a crusher for drying and transporting the kneaded body is 400 to 600 ° C., and at least a part of the hot gas is taken out of a high temperature zone of a facility for generating an exhaust gas to be purified. The method for dry purification of exhaust gas according to any one of claims 1 to 3, wherein the temperature of the exhaust gas before being blown or before blowing in a powdery absorbent is raised by a duct burner.