JP3025081B2 - Dry exhaust gas treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to sulfur oxides from flue gas (hereinafter referred to as SO _x) and nitrogen oxides (hereinafter NO _x
) In a dry process.

[0002]

2. Description of the Related Art A conventional dry exhaust gas treatment method disclosed in Japanese Patent Application Laid-Open No. 58-76127 will be described with reference to FIG. 1 is a feed regulating system, 2 is a supply path of an absorbent mainly composed of an alkaline earth metal compound, and 3 is a water guide pipe, and the suspension is dried from a supply path 13 of an aqueous suspension of the absorbent. Room 4
Sprayed. The drying chamber 4 contains sulfur oxides (SO _x ).
Exhaust gas containing nitrogen and nitrogen oxides (NO _x )
More derived. In the drying chamber 4, the sprayed droplets of the absorbent are dried into powder, and at the same time, most of the sulfur oxides in the exhaust gas are absorbed and converted into sulfites and sulfates. A part of the powder is recovered together with a part of fly ash present in the exhaust gas to be treated via a conduit 5 provided at the bottom of the drying chamber 4.

On the other hand, the exhaust gas accompanying the remainder of the powder and the remainder of fly ash is led to a particle separation device 7 via a conduit 6. As the particle separator 7, a filter cloth filter bag house or an electric dust collector is used.

In the drying chamber 4, most of the sulfur oxides in the exhaust gas are absorbed. However, the amount of the absorbent sprayed into the drying chamber 4 does not completely remove the sulfur oxides in the exhaust gas at this stage, but removes the nitrogen oxides in the particle separator 7 in order to remove the nitrogen oxides. Adjusted to less than 1/3 of the density. The amount of water evaporated in the drying chamber 4 is adjusted so that the temperature of the exhaust gas and the particles in the particle separation device 7 becomes 85 to 145 ° C.

The exhaust gas having a reduced content of nitrogen oxides and sulfur oxides is led from a separator 7 via a conduit 8 to a chimney (not shown). The particles separated from the exhaust gas by the particle separation device 7 are made of a substance produced by the spray drying / absorption reaction in the drying chamber 4 and fly ash, and are taken out through the conduit 9. The particles collected via the conduits 5 and 9 are discharged out of the system from the conduit 10, but a part of the particles are discharged from the conduit 1.
It is circulated to the feed regulating system 1 via 2 and recycled to the absorbent.

[0006]

The above-mentioned conventional method has the following disadvantages. (1) Sulfite is contained in the particles of the absorption reaction product. This sulfite is unstable and has COD (chemical oxygen dema).
nd), which hinders the disposal of particles. (2) Even if a suspension of an absorbent (such as calcium hydroxide) is sprayed to improve the absorption performance of SO _x , the reactivity of the absorbent is limited, and SO _x and NO _x are reduced in a drying room. Cannot be removed sufficiently.

Further, in order to increase the reactivity between SO _x and NO _x, it is necessary to increase the spray amount of the suspension. As a result, the temperature of the exhaust gas decreases, and the scale adheres to the wall of the drying chamber and the particle separation device. Not only increases, but also corrosion occurs in the drying chamber and the particle separator, which is a problem.

On the other hand, as simultaneous dry desulfurization and denitration methods, studies on activated carbon adsorption / NH ₃ catalytic reduction method and copper oxide adsorption reduction method have been found, but these methods have complicated regeneration steps,
There are problems such as an expensive absorbent and a high processing cost. In addition, since these methods are used on a fixed bed and a moving bed, in order to treat high dust exhaust gas such as coal-fired,
There are many problems that need to be solved, such as measures to prevent pressure drop in the reactor.

[0009] The present invention is to solve the above, it is possible to simultaneously process the SO _x and NO _x, to allow the desulfurization and denitration in a dry precipitator step, the raw material of the absorbent recycling waste It is also possible to avoid an increase in pressure loss in the absorption device, and further, since the product that has absorbed SO _x contains no sulfite and is substantially converted to sulfate. Another object of the present invention is to provide a dry exhaust gas treatment method capable of facilitating disposal, shortening the time for producing the absorbent slurry, and increasing the activity of the absorbent slurry.

[0010]

SUMMARY OF THE INVENTION According to the dry exhaust gas treatment method of the present invention, sulfur oxides and nitrogen oxides are absorbed by spraying an absorbent slurry into an exhaust gas containing sulfur oxides, nitrogen oxides and oxygen. A dry dust collection process for collecting powder and granules,
A crushing step in which a part of the collected powder is discharged out of the system, and a substance capable of supplying calcium oxide, calcium sulfate, aluminum oxide and silicon dioxide and water are added to the remainder and crushed to form a slurry, A slurry adjusting step of preparing the absorbent slurry by curing the slurry while stirring, and a step of spraying the absorbent slurry into the exhaust gas,
The slurry is circulated in the slurry pulverizing step and the slurry adjusting step.

[0011]

The substance capable of supplying the calcium oxide of the present invention includes, for example, quicklime, slaked lime, carbonated lime, cement, slag, dolomite plaster (containing lime) and the like.

Examples of the substance that can supply calcium sulfate include gypsum dihydrate, hemihydrate gypsum, quicklime, slaked lime, a combination of lime carbonate and sulfuric acid, and calcium sulfite.

[0013] Substances that can supply silicon dioxide include:
For example, silica, metasilicic acid, aluminum silicate, calcium silicate and the like, and compounds containing reactive silicon dioxide such as cristobalite, tridymite, kaolin, bentonite, talc, perlite, shirasu, diatomaceous earth, glass and the like can be mentioned.

Examples of the substance capable of supplying aluminum oxide include alumina, aluminum hydroxide, aluminum silicate, sodium sulfate, alum, aluminum sulfide, aluminum sulfate, aluminum chloride, bentonite, kaolin, diatomaceous earth, zeolite, and pearlite. And other compounds containing reactive aluminum.

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

Various combinations of substances which can provide the above four compounds (calcium oxide, calcium sulfate, silicon dioxide and aluminum oxide) are combined with sulfur oxide (SO
_x ), by absorbing the SO _x and NO _x by spraying an absorbent slurry into an exhaust gas containing nitrogen oxides (NO _x ) and oxygen, and with a part of the powder and granules collected in the dry dust collection process. A slurry is obtained in a pulverizing step of adding water and pulverizing them, and the slurry is cured in a slurry adjusting step to obtain CaO, Al ₂ O ₃ , CaSO ₄ , S
An absorbent slurry consisting of the components of iO ₂ is obtained.

This absorbent slurry has excellent SO _x and N
In addition to being an absorbent for O _x , it has the effect of absorbing sulfite and converting it to sulfate at the same time, 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 the slurry to be sprayed can be small, the temperature of the exhaust gas is small, and the corrosion of the device is small. On the other hand, the slurry is spray-dried and solidified in the exhaust gas, and the dried solids are collected together with the dust by the downstream dry dust collector, so there is no pressure drop increase due to dust in the reactor, which is a drawback of fixed beds and moving beds. .

According to the present invention, in the dry exhaust gas treatment method described above, the slurry is circulated through the above-mentioned pulverizing step and slurry adjustment, whereby the collected powder and granules and the newly supplied raw material are pulverized and the slurry is cured. At the same time, saving time, and
There is no need for many curing tanks.

Further, by circulating the slurry pulverizing step and the slurry preparing step and simultaneously performing the pulverization and the curing, the material supplied as the raw material is atomized, the hydrothermal reaction is promoted, and the absorption performance of the absorbent slurry is improved. Can be

[0020]

FIG. 1 shows an embodiment of the present invention.

101 supplies fly ash from a supply channel 102 and calcium oxide from 103,
This is a pulverization step in which the powder and granules collected from the exhaust gas described later are supplied from a conduit 122, and water is further added from a water guide pipe 104 to mix the raw material of the absorbent while pulverizing to form a slurry.

The raw material slurry partially ground here is transferred to a slurry adjusting step 106 for an absorbent via a conduit 105. In the same step 106, the slurry is heated to 60 ° C. to 120 ° C., preferably 80 ° C. to 100 ° C. while being stirred by a device (not shown) by the steam heating medium from the heat source supply path 107, and again through the circulation path 122. It is sent to the crushing step 101. The circulation of the slurry between the pulverizing step 101 and the absorbent slurry adjusting step 106 can be performed either in a batch or continuous manner. This is a good idea.

In the case of continuous circulation, circulation is carried out for 2 to 20 hours, preferably 4 to 12 hours while maintaining the above-mentioned heating temperature, and during this time, it is cured with hot water and CaO, Al ₂ O ₃ , CaS
A gel-like substance composed of four components of O ₄ and SiO ₂ is generated.

This gel-forming reaction is a hydrothermal reaction caused by dissolved ions of the substance to be supplied as a raw material. In order to increase the reactivity, the raw material to be supplied is made as fine as possible, and the reaction product is produced in a high degree. The more active the absorbent, the higher the dispersion.

Therefore, in the pulverizing step 101 of this embodiment,
5 μm average particle size to improve the reactivity between raw materials
Hereinafter, it is desirable to pulverize to preferably about 1 μm.

The gel-like substance obtained as described above is
The specific surface area is also 80~150m ² / g, a specific surface area of the particulate solids before curing is transformed into a very porous material compared to a 5~20m ² / g, SO _x and NO _x Shows high activity which could not be achieved by the conventional method.

After the curing, the absorbent slurry is supplied to conduit 1
08 to a slurry pump 109 and transported by a slurry conduit 110. Air, steam or exhaust gas is supplied from the gas supply path 111 at a high pressure of 1 to 10 kg / cm ² G, mixed with the slurry from the slurry conduit 110, and supplied from the spray nozzle 114 through the conduit 112 to the drying chamber 11.
3 is sprayed as fine particles. The drying chamber 113, heat exhaust gas, or pre-NO _x exhaust gas heat mostly contain some of the NO _x and SO _x removed by a denitration apparatus provided with improved combustion and additional containing SO _x and NO _x It is led from an exhaust gas conduit 115. In this drying chamber 113,
The slurry sprayed by the exhaust gas introduced from the hot exhaust gas conduit 115 dries and simultaneously removes SO _x and NO _x .

Here, since the absorbent in the present invention has a high activity, the absorbent after absorption does not contain a sulfite compound and is entirely oxidized to a sulfate compound. In the conventional method, since the sulfite is contained in the absorbed granular material recovered as a by-product, when this is discarded, the by-product C
Since the OD is high and the substance is unstable, the problem of dumping has been inevitable.

The high activity of the absorbent of this embodiment is that the gel having a high specific surface area composed of four components of CaO, Al ₂ O ₃ , CaSO ₄ and SiO _{2 in} the slurry preparation step for curing the absorbent slurry. Inclusion of a large amount of this highly active gel-like substance can reduce the amount of slurry spraying, reduce the temperature of exhaust gas, and reduce the scale adhesion to the drying chamber wall. it can.

A part of the reaction product solid is supplied to the drying chamber 113.
It is collected via a conduit 120 provided at the bottom. Meanwhile, before
The remainder of the reaction product solids, unreacted absorbent and fly-up
Exhaust gas associated with gas
To the position 117. This device 117 is a filter cloth filter
A bag house, an electric dust collector or the like is used. Apparatus 1
In 17, unreacted absorbent is dried in the drying chamber 113.
Remaining SO_xAnd NO _xReacts with. NO in device 117
_xAnd SO_xThe exhaust gas from which the water has been removed is passed through a conduit 118.
And is discharged from a chimney (not shown). Exhaust gas with device 117
The solids separated from the reaction product
And unreacted sorbent, taken through conduit 119
Will be issued. Powder recovered via conduits 120 and 119
The granules are discharged out of the system from the conduit 121, and a part thereof is
Slurry by crushing absorbent material through circulation step 122
Recycled to the chemical conversion step 101 to increase the effective utilization rate of the absorbent.
To reduce the amount of newly supplied raw materials.

In particular, since the reaction product solid collected through the conduits 120 and 119 contains calcium sulfate which is a useful raw material of the absorbent slurry of the present invention, the recovered solid can be used.

Hereinafter, experimental examples performed for the present invention will be described.

(Experimental Example 1) FIG. 3 shows the flow of the apparatus used in the experiment. The present apparatus comprises a supply tank 201 for slurry to be charged and mixed with an absorbent material, a wet grinding mill 204 connected to this by a conduit 202 having a pump 203, and a slurry introduced from the grinding mill 204 via a conduit 205. It comprises a curing tank 206 with a stirrer for preparing the absorbent slurry, and a conduit 207 having a pump 203 ′ for circulating the slurry from the curing tank 206 to the supply tank 201.

[0034] Slaked lime and gypsum are put into a feed tank 201 at a ratio of 60:30:10 (weight ratio) to fly ash containing a large amount of SiO ₂ and Al ₂ O ₃ and having an average particle size of 5.5 μm as shown in Table 1. After adding water to adjust the slurry to 20%, the slurry was heated to 95 ° C. by the heater 208. The slurry is fed into a wet milling mill 204 (using zirconia 1φ bead) by a pump 203, and the ground slurry is sent to a pre-watered curing tank 206 with a stirrer at 95 ° C. Pump 20 from the part
At 3 ', it was returned to the supply tank 201. In addition, curing tank 206
A reflux condenser 209 for preventing the evaporation of water is provided above the
The slurry was circulated in the circulation loop for 6 hours to prepare an absorbent slurry 1.

[0035]

[Table 1]

This absorbent slurry 1 was mixed with Ca / S0_Tworatio
Spray dryer and bag fill to 2.0
20Nm combined gas volume^Three/ H, inlet gas composition
SO _Two: 400 ppm, NO: 200 ppm, CO_Two: 10
Vol%, O_Two: 5Vol%, H _TwoO: 8Vol%, N_Two: Ba
Spray into the drying chamber where gas at 150 ° C consisting of lance flows
SO after 30 minutes_TwoAnd NO_xMeasures absorption removal performance
did. At this time, the temperature of the drying chamber is 68 to 72 ° C._Two
85% removal rate, NO_xA removal rate of 20% was obtained.

For comparison, slaked lime slurry was prepared using Ca / S0
It was sprayed at a concentration adjusted the same conditions to be ₂ ratio 2.0, SO ₂ 30%, the NO _x is only 1%
The following removal rates were obtained.

Microscopic observation of the absorbent slurry 1 revealed that the absorbent slurry 1 had been transformed into a porous gel-like substance having a completely different shape from fly ash particles and slaked lime particles. Has a specific surface area of 5 to 20
While there was a m ² / g, grinding, surface area after curing ratio was 90~180m ² / g. The average particle size of the slurry was 1.0 μm.

Further, when the reaction product solid collected by the bag filter was analyzed, no sulfite was detected, and it was confirmed that all of the sulfite was oxidized to sulfate.

(Experimental Example 2) The fly ash used in Experimental Example 1 was mixed with slaked lime and gypsum at the ratios shown in Table 2, and pulverized by the same method as in Experimental Example 1 except that the temperature and the circulation time were changed. , Curing, absorbent slurry 2-1
0 was obtained.

The absorbent slurry was prepared at a Ca / SO ₂ ratio of 2.
It was sprayed into the drying chamber under the same conditions by the apparatus of Experimental Example 1 so that the value became 0, and the absorption and removal performance of SO ₂ and NO _x was measured after 30 minutes. Table 2 shows the results. In addition, when the temperature of the circulation condition was 105 ° C., the slurry was circulated in a pressure loop to adjust the absorbent.

[0042]

[Table 2]

As a comparative example, slaked lime and gypsum were mixed at a ratio of 40:40:20 with the fly ash used in Experimental Example 1 and pulverized to a mean particle size of 1.0 μm. Cured for 12 hours and 12 hours. The absorbent slurries 11 and 12 obtained here were evaluated in the same manner as in Experimental Example 1 to measure the absorption and removal performance of SO ₂ and NO _x . The results shown in Table 3 were obtained.

[0044]

[Table 3]

As described above, it has been found that in the method according to the present invention, the curing time can be shortened and an absorbent having high absorption and removal performance for SO ₂ and NO _x can be obtained.

[0046]

According to the present invention, as described above, the present invention adopts a novel absorbent slurry made from wastes and the like to adopt a dry flue gas desulfurization / Denitration can be performed at the same time, and SO
All of the absorption form of _x can be converted to sulfate, which can facilitate disposal. Further, by increasing the content of the highly active gel substance in the absorbent slurry, the spray amount of the slurry can be reduced.

In addition, the present invention is particularly directed to a substance capable of supplying calcium oxide, calcium sulfate, aluminum oxide and silicon dioxide to a particulate material which has absorbed sulfur oxides and nitrogen oxides collected in a dry dust collection step. Since the slurry is circulated through a pulverizing step of adding water and water and pulverizing to a slurry, and a slurry adjusting step of adjusting the absorbent slurry by curing the slurry while stirring, the time can be reduced. Also, since the substance supplied as a raw material is atomized and the reaction product is highly dispersed, the content of the substance mainly composed of CaO, Al ₂ O ₃ , CaSO ₄ and SiO ₂ in the absorbent slurry And the absorption capacity of the absorption slurry can be increased.

[Brief description of the drawings]

FIG. 1 is a flowchart of a dry exhaust gas treatment method according to one embodiment of the present invention.

FIG. 2 is a flowchart of a conventional dry exhaust gas treatment method.

FIG. 3 is a flow chart of an apparatus for pulverizing and curing an absorbent slurry raw material used in an experimental example of the present invention.

[Explanation of symbols]

 101 grinding step 102 supply path of Si compound powder solids 103 supply path of Ca compound 104 water guide pipe 105 supply path 106 slurry adjustment step 107 heat source supply path 110 slurry conduit 109 slurry pump 111 gas supply path 113 drying chamber 114 spray nozzle 115 Heat exhaust gas conduit 117 Dry dust collecting device 118, 119, 120, 122 Pipe 121 Circulation path 201 Raw material slurry supply tank 203, 203 'Pump 204 Crusher 206 Curing tank 208 Heat source 209 Refluxer 202, 205, 207 Conduit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Hiroshi Fujita Inventor Hiroshi Research Institute, Hiroshima City 4-4-2, Kannonshinmachi (72) Inventor Atsushi Tatani Atsushi Tani 4-chome Kannonshinmachi, Nishi-ku, Hiroshima City 22 Hiroshima Research Institute, Mitsubishi Heavy Industries, Ltd. (72) Inventor Naohiko Ugawa 6-22, Kannon Shinmachi, Nishi-ku, Hiroshima City Inventor Kenji Inoue 4-chome, Kannon Shinmachi, Nishi-ku, Hiroshima City No. 6-22, in the Hiroshima Laboratory, Mitsubishi Heavy Industries, Ltd. (56) References JP-A-63-12321 (JP, A) JP-A-2-152520 (JP, A) JP-A-56-137743 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/60 B01D 53/34 B01D 53/74

Claims (1)

(57) [Claims] 1. A dry dust collecting step of spraying an absorbent slurry into an exhaust gas containing sulfur oxides, nitrogen oxides and oxygen to collect powdery particles having absorbed the sulfur oxides and nitrogen oxides, A crushing step in which a part of the collected powder is discharged out of the system, and a substance capable of supplying calcium oxide, calcium sulfate, aluminum oxide and silicon dioxide and water are added to the remainder and crushed to form a slurry, Curing the slurry while stirring to prepare an absorbent slurry, and spraying the absorbent slurry into the exhaust gas, and circulating the slurry through the pulverizing step and the slurry adjusting step. A dry exhaust gas treatment method characterized by the above-mentioned.