JPH02152520A - Dry treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To enable desulfurization and denitration by grinding an Si source and a Ca source added to water with a mill and by aging the resulting slurry to prepare an absorbent slurry. CONSTITUTION:In a slurrying stage 101, an Si compd. and a Ca compd. are added to water and ground to <=5mum average grain size with a mill. The resulting slurry is sent to a stage 106 for preparing an absorbent slurry through a feed path 105. In the stage 106, the slurry is aged by heating and stirring to partially modify the Si compd. and to produce a Ca-contg. gelled substance. An absorbent slurry obtd. by the aging is sent to a slurry pump 109 through a duct 108 and transferred through a slurry duct 110. Air is fed from a gas feed path 111 under high pressure, mixed with the slurry from the duct 110 and sprayed as fine particles from a spray nozzle 114 in a drying chamber 113.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a dry exhaust gas treatment method for dry removing sulfur oxides (hereinafter referred to as SOx) and nitrogen oxides (hereinafter referred to as NOx) from combustion exhaust gas. Regarding.

[Conventional technology]

The prior art (Patent Publication No. 58-76127) will be explained with reference to FIG. 1 is a feed adjustment system, 2 is a supply path for an absorbent containing an alkaline earth metal compound as a main component, and 3 is a water pipe, through which the suspension is dried from the supply path 13 for the aqueous suspension of the absorbent. The chamber 4 is sprayed.

A hot waste gas containing sulfur oxides (SOX) and nitrogen oxides (NoX) is introduced into the drying chamber 4 through a conduit 11. In the drying chamber 4, the atomized droplets of absorbent are dried into a powder and at the same time most of the sulfur oxides in the waste gas are absorbed and converted into sulphites and sulphates. A portion of the powder is recovered via a conduit 5 provided at the bottom of the drying chamber 4 together with a portion of the fly oxide present in the waste gas to be treated.

On the other hand, the waste gas entrained by the remainder of the powder and the remainder of the fly lysis is led via conduit 6 to a particle separator 7 . As this particle separator 7, a p cloth filter bag house or an electric precipitator is used.

The amount of the absorbent is adjusted to less than the nitrogen oxide concentration at this stage so that the sulfur oxides in the waste gas are not completely removed, but the nitrogen oxides are removed in the particle separator 7. . Further, the amount of water evaporated in the drying chamber 4 is adjusted so that the temperature of the waste gas and particles in the particle separator 7 is 85 to 145°C.

The waste gas depleted in nitrogen oxides and sulfur oxides from the separator 7 is led via a conduit 8 to a chimney (not shown) K. The particles separated from the waste gas in the particle separator 7 are composed of fly ash and a substance produced by the spray drying/absorption reaction in the drying chamber 4, and are taken out through the conduit 9. Part or all of the particles collected via conduits 5 and 9 are discharged out of the system via conduit 10. The remainder of the particles are recycled to the feed conditioning system IK via conduit 12 and recycled to the absorbent.

[Problem to be solved by the invention]

The above conventional method has the following drawbacks.

(1) The particles of the absorption reaction product contain sulfite. This sulfite is unstable and causes COD, so
This will impede the disposal of particles.

(2) Even if an attempt is made to improve SOx absorption performance by spraying a suspension of an absorbent (calcium hydroxide), there is a limit to the reactivity of the absorbent, and it is not possible to sufficiently remove SOx and NOx in a drying room. Can not.

Additionally, in order to increase the reactivity between SOx and NOx, it is necessary to increase the amount of suspension sprayed, which results in a drop in exhaust gas temperature and increases scale adhesion on the drying chamber walls and inside the particle separator. Corrosion occurs in the drying chamber and particle separator, which poses a problem.

On the other hand, as a dry method for simultaneous desulfurization and denitrification, activated carbon adsorption/N
Research has been done on the H3 catalytic reduction method and the copper oxide adsorption reduction method, but these methods have problems such as complicated regeneration steps, expensive absorbents, and high processing costs. Additionally, since these methods are used in fixed beds and moving beds, there are many problems that must be resolved, such as measures to prevent pressure loss from increasing in the reactor, in order to treat high-dust exhaust gases such as those from coal-fired reactors. .

The present invention solves the above problems, can simultaneously process SOx and NOx, enables desulfurization and denitration in the dry dusting process, allows waste to be reused as raw material for absorbent, and It is possible to avoid an increase in pressure drop in the absorption device, and furthermore, the product after absorbing Sox does not contain sulfite and is substantially converted to sulfate, making it easy to dispose of it. , which attempts to provide a dry exhaust gas treatment method.

[Means to solve the problem]

In the present invention, an absorbent slurry is atomized into exhaust gas containing sulfur oxides, nitrogen oxides, and oxygen, and granules that have absorbed sulfur oxides and nitrogen oxides are collected in a dry dusting process. The dry exhaust gas treatment method includes a step of adding a silicon source, a calcium source, and water and grinding with a wet mill to form a slurry, a step of curing the slurry while stirring to prepare an absorbent slurry, and a step of preparing the absorbent slurry. This is a dry exhaust gas treatment method characterized by including a step of spraying into the exhaust gas.

[Effect]

In the present invention, metal smelting/iron slag, pickling waste liquid treatment sludge, and fly ash. Kaolin, bentonite, silica sand,
At least one Si source selected from diatomite, zeolite, various silicate glasses, etc. and CaCO3, Ca, (
OH)2. Cab, CaSO4・2H20゜CaS
A small amount of Ca compound selected from O3・L/2H20, CaCl2, etc. is wet-milled with water to form a slurry, and this is cured while stirring the alkaline aqueous slurry to form an amorphous form. An absorbent consisting of calcium silicate is obtained.

This absorbent is not only an excellent SOx and NOx absorbent, but also 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. Furthermore, since the absorbent according to the present invention has high activity, the amount of slurry to be sprayed is small, the exhaust gas temperature is less likely to decrease, and equipment corrosion is less likely to occur. On the other hand, since the slurry is spray-dried and solidified into the exhaust gas, and the dried solids are collected together with the dust in the downstream dry multiplication device, there is no increase in pressure drop due to dust in the reactor, which is a drawback of fixed bed and moving bed. .

〔Example〕

An embodiment of the present invention will be explained with reference to FIG.

101 is a supply path 102 for supplying granular solids containing 81 compounds such as slag 9, fly assier, clay, etc.;
a*Ca(OH)2- CaOr C'aSO4a
2H201CaS03-1/2 H2O, CamQ2
While supplying Ca compounds such as from the supply path 103,
This is a step in which powder and granules collected from exhaust gas (described later) are supplied to a conduit 122, water is added through a water conduit 104, and wet milling is performed to mix absorbent raw materials to form a slurry.

Here, the specific surface area of the Sl source, which is the raw material, is increased, and C
In order to improve the reactivity with compound a, the average particle size is 5 μm.
Hereinafter, it is preferable that the powder be pulverized to about 1 μm.

The mixed and pulverized slurry is sent to an absorbent slurry preparation step 106 via a supply path 105. In the same step 106, the slurry is heated to 80°C to 150°C, preferably 105°C to 120°C, using a heating medium such as steam from the heat source supply path 107.
C. for several hours to several tens of hours, preferably 10 to 30 hours, and cured by stirring with a device not shown, whereby the $1 compound is partially denatured and a gel-like substance containing Ca is produced. In this slurry adjustment process by curing, it is important to maintain an atmosphere that does not contain SOx or NOx. That is, during the formation of a gel-like substance, which is a relatively slow reaction, alkaline components cause SOx and NOx.
It is important to ensure that it is not consumed. This gel-like material has a specific surface area of 80 to 150 m"/H, and changes into an extremely porous material compared to the 5 to 20 mVg of powder solids before curing, so its SOx and NOx absorption capacity is lower than that of the conventional This results in high activity that could not be achieved using other methods.

After curing, the absorbent is sent to a slurry pump 109 via a conduit 108 and transported by a slurry conduit 110. Air, steam, or exhaust gas is supplied from the gas supply line 111 at a high pressure of 1 to 10 k&/i G, and mixed with the slurry from the slurry conduit 110 to the conduit 117.
It is sprayed as fine particles from the spray nozzle 114 into the drying chamber 113 via the spray nozzle 114. This drying chamber 113 contains SOx and N.
The thermal exhaust gas containing Ox, or the exhaust gas containing some NOx and SOx after most of the NOx has been removed by combustion improvement or a separately provided denitrification device, is transferred to the thermal exhaust gas conduit 11.
It is derived from 5. In this drying chamber 113, the spray slurry is dried by the exhaust gas introduced from 115, and the S
Ox and NOx are removed simultaneously.

Here, since the absorbent in the present invention has good activity, no sulfite compounds are contained in the absorbent after absorption, and all of the absorbent is oxidized to sulfuric compounds. In the conventional method, the absorbed powder collected as a by-product contains sulfites, so when disposing of this, the by-product has a high COD and is an unstable substance, which poses a problem in terms of disposal. It had become inevitable.

The reason why the absorbent of this example shows high activity is that it contains a gel-like substance with a high specific surface area that is produced by the reaction of Si compounds and Ca compounds in the slurry adjustment process by curing. Containing a large amount of the substance means that the amount of slurry sprayed is small, the exhaust gas temperature decreases little, and scale adhesion to the drying chamber wall surface can be reduced. - Process of wet milling to form slurry in this example In No. 101, the absorbent raw material is made fine and Si
It has the role of increasing the reactivity between the Ca source and the Ca source, and increasing the content of highly active gel-like substances.

A portion of the reaction product solids are recovered via a conduit 120 provided at the bottom of the drying chamber 113. On the other hand, the remainder of the reaction product solids, unreacted absorbent, and exhaust gas accompanied by fly assy are led to a dry dust multiplication device 117 via a conduit 116. This device 117 uses a P cloth filter Meghouse. In the device 117, unreacted absorbent reacts with the SOx and NOx remaining in the drying chamber 113. The exhaust gas from which NOx and SOx have been removed is passed through a conduit 118 in a device 117 that includes a chimney (not shown). A conduit 119 consisting of a
is retrieved via. A part or all of the powder collected through conduits 120 and 119 is discharged from the system through conduit 121. The remainder of the powder is recycled via conduit 122 to the wet milling slurry process 101 of the absorbent raw material to increase the effective utilization of the absorbent and reduce the amount of fresh feed.

(Experimental Example 1) Water was added to the composition S1 compound shown in Table 1, and the mixture was ground in a wet ball mill for 12 to 24 hours.
Add at a ratio of 40.50wt and add water to 20-25wt.
Adjusted to chisulary. This slurry was charged into an autoclave and cured at 105° C. while stirring with a stirrer for a period of time, and absorbent slurries 1 to 4 (Sl compound average particle size 15 μm) and 5 to 8 (Sl compound average particle size 1.5 μm) were prepared.
2μ) was obtained. This absorbent slurry was dried in a dryer at 110°C for 12 hours, and then formed into a size of 4 to 5 mφ.
The absorption and removal performance of SOx and NOx was measured under the activity evaluation conditions shown in 2. The results are shown in Table-3.

Table-I Si compound composition table-2 Activity evaluation conditions table-3 Activity test results Note that the SO□ and NO absorption amounts are expressed as the absorption amounts up to the time when the reactor outlet concentration leaks 20% of the inlet concentration. Ta. Further, the residual rate of slaked lime after curing of the absorbent was determined from the X-ray peak intensity of Ca(OH)2 before and after curing of the absorbent.

In this example, the prepared absorbent was found to have a
1 It has changed into a porous gel-like substance that has a completely different shape from compound particles and slaked lime particles, and the specific surface area of the powdered solid before curing is 5 to 20 m3'j, while after curing it is 80 to 150 m3'j.
m'/g.

In addition, by using a Sl compound with a fine particle size,
It was found that the reactivity with slaked lime increased, and when the particle size of the Sl compound was 1.2 μm, even 40 grams of slaked lime completely reacted with Sl.

Furthermore, when the reaction product solids were analyzed, sulfite compounds were not detected in absorbents with a slaked lime residual rate of 10% or less.
It was confirmed that everything was oxidized to sulfuric acid compounds.

It should be noted that a higher proportion of slaked lime will absorb more SO2 and No, but the more unreacted slaked lime remains in the absorbent after curing, the worse the Ca utilization rate will be, so this is not a special measure.

(Experiment Example 2) Mix slaked lime and gypsum in the proportions shown in Table 4 with 81 Compound B in Table 1 above, grind for a while in a wet ball mill, adjust to a 15-20% slurry of each, and hold the mixture at 80-150°C. The mixture was cured in an autoclave for 5 to 30 hours while being stirred with a stirrer to obtain an absorbent slurry. 1 of this absorbent
After drying at 10°C for 12 hours, SO
The absorption and removal performance of x and NOx was measured. Table the results.
4.

According to this experimental example, it was found that although the activity of the absorbent depends on the amount of slaked lime mixed, the reactivity of slaked lime varies depending on the curing temperature for one hour. The curing temperature and time with 20% slaked lime are 105 to 120° C., preferably about a heating time. If the temperature is low, it is difficult to form a highly active gel-like substance, whereas if the temperature is high, a calcium silicate compound with a small specific surface area that is different from the gel-like substance is produced, and the activity decreases.

(Experimental Example 3) Absorbent slurries 6 and 10 prepared in Experimental Examples 1 and 2 were adjusted to a slurry concentration of 10% KII, and NOx1001
1%SO□600111+11. Co210%,)1
When sprayed into a pyrolysis chamber into which 150°C coal combustion exhaust gas consisting of 2010L remaining N2 (volume ratio) flows, and the dry solids were brought into contact with the exhaust gas for a solid-gas contact time of 1 second,
S02 and NOx in the outlet exhaust gas continued to decrease to below 50(9), respectively, until sO2 equivalent to slaked lime was absorbed.

When the solids produced by the reaction were analyzed, no sulfite compounds were detected, and it was confirmed that all of the solids had been oxidized to sulfur oxides.

In the method according to the present invention, compared to a fixed bed that uses an absorbent with a diameter of 4 to 5101 φ, since an absorbent slurry with small particles is used, the Ca utilization rate is higher, and the highly active gel contained in the absorbent is It was found that the amount of spraying was small because there was a large amount of such substances, and the exhaust gas temperature did not decrease much.

〔Effect of the invention〕

By adopting the above configuration, the present invention employs a novel absorbent slurry made from waste, etc., as explained above, and can simultaneously perform dry flue gas desulfurization and denitrification. , the absorption form of SOx can all be converted to sulfate, and its disposal can be facilitated.

Furthermore, by increasing the content of highly active gel-like substances in the absorbent slurry, it is possible to reduce the amount of slurry sprayed.

[Brief explanation of the drawing]

Figure 1 is a flow diagram of a dry exhaust gas treatment method according to an embodiment of the present invention, and Figure 2 is a flowchart of a conventional dry exhaust gas treatment method.
-Illustration. 101...Slurry process by wet mill grinding. 102...S1 compound powder/grain solid material supply path. 103... Oa compound supply path, 1o4... Water conduit pipe. 105... Supply path, 106... Slurry adjustment process. 107...Heat source supply path, 11o...Slurry conduit. 109... Slurry pump, 111... Gas supply path. 113...Drying room, 114...Spray nozzle. 115... Heat waste gas conduit, 117... Dry dust collector. 118, 119.120.122... Conduit. Figure 1

Claims (1)

[Claims] In a dry exhaust gas treatment method in which an absorbent slurry is sprayed into exhaust gas containing sulfur oxides, nitrogen oxides, and oxygen, and granules that have absorbed sulfur oxides and nitrogen oxides are collected in a dry dust collection step, A step of adding a silicon source, a calcium source, and water and wet milling to form a slurry, a step of curing the slurry while stirring to prepare an absorbent slurry, and a step of spraying the absorbent slurry into the exhaust gas. A dry exhaust gas treatment method comprising: