JPH08131775A - Dry treatment method for exhaust gas - Google Patents

Abstract

PURPOSE: To obtain a proper dry treatment method for removing acid gas, heavy metals, and dioxins in exhaust gas. CONSTITUTION: The following processes are set up: in the first process, high temperature combustion exhaust gas is led to the first bag filter 1, calcium hydroxide powder and a reaction auxiliary are added into the gas, the concentrations of HCl, SOx, and dust in the gas are decreased so that the gas can pass through an ammonia-reduction selective denitration catalyst in the next process, and part of heavy metals and dioxins are removed; in the second process, the high temperature exhaust gas treated in the first process is led to an ammonia-reduction selective denitration catalyst apparatus, and ammonia is added into the gas to remove NOx; in the third process, the exhaust gas, which was treated in the second process and is still hot, is introduced into a cooler 3, and water or calcium hydroxide slurry is supplied to cool the gas; in the fourth process, the exhaust gas cooled in the third process is led to the second bag filter 4, and calcium hydroxide powder and a reaction auxiliary are added into the gas, and residual HCl, SOx, heavy metals, dioxins, and dust are removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry exhaust gas treatment method applicable to an exhaust gas treatment apparatus for municipal waste incinerators and other incinerators, and particularly to removing acid gas, heavy metals and dioxins in exhaust gas. In this case, the method can be advantageously applied.

[0002]

2. Description of the Related Art One aspect of a conventional dry exhaust gas treatment method will be described with reference to FIG. In FIG. 3, in order to improve the removal efficiency of heavy metals and dioxins, the exhaust gas temperature reducing device 3
The exhaust gas is treated by the bag-type gas heater 6 up to the catalyst activation temperature range in order to increase the removal efficiency in the denitration device 2 installed downstream of the catalyst. Since it was heated and denitration processing was performed by the denitration device 2, energy for heating the exhaust gas was required.

[0003]

In the conventional dry exhaust gas treatment, the removal efficiency of HCl, SOx, heavy metals, and dioxins in the bag filter is better as the exhaust gas temperature is lower, and the NOx removal rate in the denitration unit is the exhaust gas. There was a conflicting problem that the higher the temperature, the better.

In order to avoid the above problems, if a denitration device is installed on the upstream side of the bag filter, the alkaline component in the dust and the acidic ammonium sulfate or ammonium sulfate produced by the reaction between ammonia and SOx will deteriorate the catalyst. was there. Therefore, as mentioned above,
The exhaust gas is cooled and treated with a bag filter, and the exhaust gas is reheated and treated with a denitration device.

In view of the above-mentioned state of the art, the present invention solves the conventional problems and provides a method for eliminating the step of reheating exhaust gas which has been performed before the denitration treatment step without deteriorating the removal performance of harmful substances. Is what you are trying to do.

[0006]

According to the present invention, (1) the combustion exhaust gas is introduced into a high temperature first bag filter, and slaked lime powder and a reaction aid are blown into the exhaust gas to remove H in the exhaust gas.
Cl, SOx, soot and dust are removed to the concentration at which the ammonia reduction selective denitration catalyst of the next step can pass, and some heavy metals,
First step for removing dioxins, high-temperature exhaust gas treated in the first step is led to an ammonia reduction selective denitration catalyst device, and ammonia is added to remove NOx
The third step of guiding the still-high-temperature exhaust gas treated in the step and the second step to the temperature reducing device to supply water or slaked lime slurry to reduce the temperature, and the exhaust gas reduced in the third step to the second bag A dry exhaust gas treatment method comprising a fourth step of introducing a slaked lime powder and a reaction auxiliary agent into the filter to remove the remaining HCl, SOx, heavy metals, dioxins and soot and dust. (Hereinafter, referred to as the first invention) (2) The combustion exhaust gas is introduced into a first bag filter equipped with a high temperature ammonia selective selective denitration catalyst, and ammonia is added to remove NOx, and slaked lime powder and a reaction aid The first step in which most of the HCl, SOx, soot and dust, and some heavy metals and dioxins in the gas are blown in to remove the high-temperature exhaust gas treated in the first step to a temperature reducer and water is introduced. Or second to supply slaked lime slurry to reduce temperature
The second step is to introduce the exhaust gas cooled in the second step to the second bag filter, and blow a slaked lime powder and a reaction aid to remove the remaining HCl, SOx, heavy metals and soot from the third step. The dry exhaust gas treatment method. (Hereinafter referred to as the second invention).

[0007]

[Action]

(1) Operation of the first invention: In the first bag filter into which the combustion exhaust gas on the upstream side flows, slaked lime and a reaction aid (a material containing diatomaceous earth as a main component, and when the bag filter is backwashed, the surface of the bag filter) Of the reaction product and soot and dust to facilitate the separation of the reaction product) and the reaction product of slaked lime and some of the acidic gases (HCl, SOx), soot, heavy metals and dioxins are removed by filtration, The ammonia reduction selective denitration catalyst (hereinafter, simply referred to as a denitration catalyst) in the next step is prevented from deteriorating. (First step) Since not all the acidic gas is removed in the first step, a small amount of acidic ammonium sulfate and ammonium sulfate is produced in the denitration catalyst treatment by adding ammonia in the next step.
Ox is sufficiently removed, and the catalyst hardly deteriorates. (Second step) Next, the exhaust gas from which NOx has been removed is brought into contact with water or slaked lime slurry to be cooled. This temperature reduction is sufficient with water, but it is preferable to use slaked lime slurry in order to prevent low temperature corrosion of the temperature reducing device. This temperature reduction operation is performed in the next step in order to increase the removal rate of the remaining acidic gas, heavy metals, and dioxins.
(Third step) Finally, in the second bag filter, the slaked lime slurry and the reaction aid are added to the exhaust gas whose temperature has been reduced to remove the remaining acidic gas, heavy metals, and dioxins. In particular, dioxins are removed with high efficiency in a reduced temperature state. (4th process)

(2) Operation of the second invention: In this second invention, the first step and the second step of the first invention are performed in one step, and the operation and effect are the same as those of the first step of the first invention. It is almost the same as the combination of the second step (the first step). Also, the second step and the third step of the second invention are the third step of the first invention.
The process is the same as the fourth process. (Second step, third step)

[0009]

Embodiments of the present invention will be specifically described below with reference to the drawings.

(Embodiment 1) An embodiment of the first invention is shown in FIG.
Therefore, it will be described. Incineration scale of municipal waste is 300 tons / day
Degrees, the combustion exhaust gas has a temperature of approximately 230 ° C and a flow rate of approximately
85,000 Nm ³/ H (wet) of the combustion exhaust gas
The composition is HCl concentration: 800 ppm, SOx concentration: 100
ppm, NOx concentration: 120 ppm, mercury concentration: 0.5
mg / Nm ³, Dioxin concentration: 2ng / Nm³,
Dust concentration: 3g / Nm³It is a degree.

Combustion exhaust gas of this property is supplied to the first bag filter 1, and at the same time, slaked lime powder (of special grade or higher):
250 kg / h, a reaction aid whose main component is diatomaceous earth:
60 kg / h is supplied. By doing so, about 80% of HCl and about 60% of SOx in the combustion exhaust gas can be obtained.
%, About 99.8% of the soot and dust are removed and the temperature of the flue gas is still maintained at about 220 ° C.

Exhaust gas of this property is then supplied to the denitration reactor 2, where ammonia (25%): 18 kg / h
Is supplied, and the denitration reaction is performed by the denitration catalyst containing V ₂ O ₅ as the main component, and about 60% of NOx in the exhaust gas is removed.

Further, the exhaust gas after the above treatment is cooled by the temperature reducing device 3.
Slaked lime slurry (concentration: 1%): 3,500
After the temperature is reduced to about 160 ° C. by kg / h, it is finally supplied to the second bag filter 4. Here, as in the first bag filter 1, slaked lime powder: 60 kg /
h, reaction aid: 6 kg / h is supplied, about 90% of mercury in exhaust gas, about 95% of dioxins and about 85% of HCl at the outlet of the first bag filter 1, similarly SO.
About 75% of x is removed.

(Embodiment 2) An embodiment of the second invention will be described with reference to FIG. The same amount and properties of the combustion exhaust gas as in Example 1 were supplied to the first bag filter 5 with the denitration catalyst, and at the same time, slaked lime powder (special grade or higher): 250 kg / h, a reaction aid containing diatomaceous earth as a main component. : 60 kg / h and ammonia (25%): 18 kg / h. By doing this, about 80% of the HCl in the combustion exhaust gas can be obtained.
%, SOx approximately 60%, NOx approximately 60%, soot and dust approximately 9
9% are removed. Hereinafter, as in Example 1, the same result as in Example 1 was obtained by reducing the temperature with the temperature reducer 3 and processing with the second bag filter.

[0015]

EFFECTS OF THE INVENTION According to the present invention, it is possible to achieve both high efficiency removal of NOx and high efficiency removal of heavy metals and dioxins without reheating exhaust gas.
x and the like can also be removed. Conventionally, the steam required to reheat the exhaust gas can be used for other residual heat utilization. In addition, by using a two-stage bag filter, HCl, S
The removal efficiency of Ox etc. can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory view of a dry exhaust gas treatment method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a dry exhaust gas treatment method according to another embodiment of the present invention.

FIG. 3 is an explanatory diagram of one embodiment of a conventional dry exhaust gas treatment method.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01D 53/81 B01D 53/34 124 Z

Claims (2)

[Claims] 1. The combustion exhaust gas is introduced into a high temperature first bag filter, and slaked lime powder and a reaction aid are blown into the exhaust gas to allow HCl, SOx and soot in the exhaust gas to pass through an ammonia reduction selective denitration catalyst in the next step. The first step of removing some heavy metals and dioxins as well as removing to a concentration, the high temperature exhaust gas treated in the first step is led to an ammonia reduction selective denitration catalyst device, and ammonia is added to remove NOx. In the second step, the high temperature exhaust gas treated in the second step is introduced into a temperature reducing device to supply water or slaked lime slurry to reduce the temperature, and the exhaust gas reduced in the third step is discharged into the second step. A dry exhaust gas comprising a fourth step of introducing a slaked lime powder and a reaction auxiliary agent into a bag filter and removing the remaining HCl, SOx, heavy metals, dioxins and soot and dust. Processing method. 2. The combustion exhaust gas is led to a high temperature first bag filter equipped with an ammonia reduction selective denitration catalyst, ammonia is added to remove NOx, and slaked lime powder and a reaction aid are blown into the gas. Most of HCl, SO
x, soot and dust and some heavy metals and dioxins are removed in the first step, and the high temperature exhaust gas treated in the first step is introduced into a temperature reducer to reduce the temperature by supplying water or slaked lime slurry. The second step is to introduce the exhaust gas cooled in the second step to the second bag filter, and blow a slaked lime powder and a reaction aid to remove the remaining HCl, SOx, heavy metals and soot from the third step. The dry exhaust gas treatment method.