JPH05261244A - Method for removing hydrogen chloride in combustion gas - Google Patents

Abstract

PURPOSE:To effectively remove HCl in high temp. exhaust gas with equipment which is manufactured at low cost. CONSTITUTION:In the 1st reactor 3, high temp. exhaust gas is cooled to a low temp. and simultaneously humidified by cold water spraying and given dry desalting by spraying a powdery desalting agent from nozzles 5, 6. Next, in the 2nd reactor 8, after the exhaust gas is given semi-dry desalting by spraying (9) dilute anionic alkaline water solution, it is given solid-gas separation by a bag filter 11 together with the reactional product and unreacted material.

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 hydrogen chloride gas in high temperature exhaust gas discharged from a refuse incinerator or the like.

[0002]

2. Description of the Related Art Many methods for scientifically removing hydrogen chloride gas in high-temperature exhaust gas by using a desalting agent have been proposed, and a method using slaked lime and an alkaline aqueous solution as the desalting agent is known. (For example, Japanese Unexamined Patent Publication No. 59-127656) In this method, slaked lime powder is used in a dry type in the front stage of an electrostatic precipitator, and an alkaline solution is allowed to act in a wet stage in the rear stage. In this removal method, an electrostatic precipitator is indispensable, and the desalting agent acted in the previous stage is captured by the electrostatic precipitator, and the contact time in the reaction system is short, so that the efficiency is low. Further, since the alkaline liquid which acts in the latter stage is acted in a wet manner, a wastewater treatment facility is required and the cost becomes high. Moreover, it is difficult to remove organic chlorine compounds such as dioxins by this method.

Further, as another method, JP-A-60-227
It is also known to act the desalting agent in a dry manner before the dust collector as proposed in 817, and then to act an aqueous solution or water slurry of the desalting agent in a semi-dry manner. This method has the advantage that the desalting agent used in the dry type and the semi-dry type are the same substance, so that the temperature and desalting degree can be controlled separately, but on the other hand, the size and complexity of the device are inevitable and a large amount of Since a desalting agent is necessary (Ca / Cl equivalent ratio of about 3), the running cost becomes high. In addition, it is necessary to increase the moisture content in the combustion gas in order to increase the degree of desalination, which causes a drawback that corrosion of the device is likely to occur.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a desalting method capable of highly desalting with a small amount of a desalting agent and free from the risk of corrosion even in an ordinary apparatus that does not use a special or high-grade machine. Is.

[0005]

According to the method of the present invention, high temperature exhaust gas discharged from a combustion apparatus is introduced into the bottom of a first reactor, and cold water is sprayed to perform quenching and humidification, and then an alkali is discharged from the top of the reactor. A step of injecting a powder desalting agent comprising a hydroxide of an earth metal or a salt thereof, and introducing gas from the first reactor into the upper part of the second reaction vessel to bring it into contact with atomized fine particles of an alkaline aqueous solution. The process comprises a step of lowering and a step of releasing from the bottom of the second reactor into the atmosphere through a filter cloth type dust collector, the total amount of the desalting agent used is smaller than in the conventional method, and the operation is It's easy.

In the present invention, the unreacted powder desalting agent in the first reactor can not only exert the desalting action in the second reactor but also leave a desalination reserve in the filter cloth type dust collector. A membrane is formed and the desalination function is maintained until the end. For this reason, the total amount of the desalting agent used becomes small, and economical operation becomes possible.

In the present invention, the dry section of the first reactor,
The desalination degree of each of the semi-dry section of the second reactor can be adjusted as desired, but in the dry section, chemical neutralization of the chloride containing exhaust gas is possible from the viewpoints of adhesion to the equipment for reducing running cost and prevention of corrosion trouble. The desalting agent is added in an amount larger than the equivalent amount, and the amount of the desalting agent in the semi-dry type portion is smaller than the chemical neutralization equivalent amount. That is,
In normal exhaust gas treatment, the powder desalting agent in the dry part has a neutralization chemical equivalent of 1.0 to 2.0, and the alkaline liquid added in the semi-dry part has a neutralization chemical equivalent of 0.1 to 0.5. is there.

Further, in the present invention, water is ejected mainly at the bottom of the first reactor, that is, the high temperature exhaust gas introduction region for the purpose of suppressing the generation of oxidant, while cooling and humidification are carried out, whereby the reaction in the dry desalination section is carried out. The property is enhanced and a high degree of desalination is achieved. Further, since the second reactor is a semi-dry desalination section, it can be operated at a temperature higher than the corrosion limit temperature, and as a result, high desalination can be performed, and additional equipment such as drainage treatment is not required at all.

[0009]

[Explanation of apparatus] In FIG. 1, HCl from the rotary incinerator 1
The contained (1000 to 2000 mg / Nm3) high-temperature exhaust gas is introduced into the bottom portion 3b of the first reactor 3 through the post-combustion chamber 2, and is rapidly cooled to 300 ° or less by cold water spray from the nozzle 4. Slaked lime (Ca (oH) ₂ powder is injected from a desalting agent injection nozzle 5.6 provided in the upper part 3a of the reactor. The amount of Ca (OH) ₂ added is a chemical equivalent ratio to HCl in exhaust gas. The gas passing through the desalting agent injection region has a temperature of 200 ° to 300 ° C. and a moisture content of about 19 to 24% by weight. It is introduced into the upper portion 8a of the second reactor 8 and sprayed with 0.1-10 wt% of NaOH liquid from the spray nozzle 9. The amount of NaOH charged is HC in the exhaust gas.
The chemical equivalent ratio is 0.5 to 0.1 with respect to 1. In the bottom portion 8b of the second reactor, the gas temperature drops to 150 to 200 ° C and the moisture content becomes 22 to 26% by weight. The low temperature desalted exhaust gas is further introduced into the filter cloth type dust collector 11 through the cooling conduit 10 and solid-gas separated, and the desalted exhaust gas is discharged into the atmosphere by the fan 12. Although the inner surface of the first reactor is caster-tensioned, the inner surface of the second reactor is preferably Teflon-coated, and its volume is preferably at least twice as large as that of the first container.

[0010]

Example: Temperature 830 ° C, Hcl content 1700 mg
/ Nm ³ of high temperature exhaust gas into the first reactor 3 by 1050 Nm ³
/ Hr. Temperature in the middle of the reactor is 280 °
Cooled to C. Ca (OH) ₂ from the injection nozzle 5.6
After spraying the powder at a Ca / cl equivalent ratio of 1.3 to perform primary desalting, 0.5% Na was discharged from the nozzle 9 of the second reactor 8.
Aqueous OH was sprayed at a Na / cl ratio of 0.2 volume. The temperature of the bottom part 8b of the reactor was 180 ° C. The solid content in the solid-gas mixture of the reactants and unreacted materials that have passed through the reactor is removed by the bag filter 11, and the HCl concentration before being released into the atmosphere is 5 on average.
It was 2 mg / Nm ³ .

[0011]

[Effect] According to the present invention, since the powder desalting agent is used in the first reactor and the liquid desalting agent is used in the second reactor, both of them are handled individually, which facilitates the operation and causes no trouble. Less. Since the desalination performance is improved to about twice as much as the chemical neutralization equivalent, the amount of desalting agent used is reduced and the running cost is reduced. Since the reaction product in each reactor and the unreacted desalting agent-containing material can be taken out of the system as a powdery product, the work is simplified. Further, there is an advantage that an auxiliary equipment such as a slurry forming device is not required and the entire structure of the device can be simplified.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an apparatus for carrying out the method of the present invention.

[Explanation of symbols]

 3 is a first reactor 5, 6 is a powder desalting agent injection nozzle 8 is a second reactor 9 is an alkaline aqueous solution spray nozzle 11 is a bag filter

Claims (2)

[Claims] 1. A method for removing hydrogen chloride in a combustion gas using a powder desalting agent and an alkaline aqueous solution, wherein hot exhaust gas is introduced into the bottom of a first reactor and cold water is sprayed to quench and humidify. And then injecting a powdered desalting agent consisting of an alkaline earth metal hydroxide or its salt from the upper part of the reactor, and introducing the gas from the first reactor to the upper part of the second reaction vessel. Contacting with the sprayed fine particles of the alkaline aqueous solution to lower it, and introducing the powder-containing gas in the second reactor into the filter cloth type dust collector to release the passing desalted exhaust gas into the atmosphere. Method for removing hydrogen chloride from combustion gas. 2. The amount of the powder desalting agent is 1.0 to 2.0 chemical equivalents to the hydrogen chloride in the exhaust gas, and the amount of the sprayed alkaline aqueous solution is 0.1 to 0.5 chemical equivalents. The method according to item 1.