JPH11248142A - Method and device for treating waste gas of combustion furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To permit sending of gas, having the optimum temperature, into a bag filter and a catalyst tower by a method wherein the waste gas of the outlet port of a boiler and the exhaust gas of a hot-water generating boiler are cooled to a specified temperature while gas, discharged out of a bag filter, is reheated to another specified temperature and refuse in the gas is decomposed to remove the same under catalyst. SOLUTION: A waste heat recovering boiler 2, arranged in the rear stage of a combustion furnace 1, generates hot-water or steam by effecting heat exchange between exhaust gas of 800 deg.C or higher and cold water to regulate the temperature of the exhaust gas so as to become lower than 250 deg.C. Heat exchange between the exhaust gas of the boiler 2 and waste gas discharged out of a bag filter 5 is effected in a heat exchanger 3 whereby the exhaust gas is cooled to about 250-220 deg.C or preferably to 200 deg.C or lower. On the other hand, the gas, discharged out of the bag filter 5, is passed through a pipeline installed in the heat exchanger 3 whereby the gas is reheated to about 160-180 deg.C or preferably 200 deg.C. The reheated gas enters into a catalyst tower 6 and denitration as well as the removal of dioxins are effected in the catalyst tower 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas treatment device provided to be attached to a combustion furnace, and more particularly to heat recovery of exhaust gas from a solid fuel combustion furnace using solid matter such as municipal solid waste as a fuel, and dioxin. The present invention relates to an exhaust gas treatment device capable of effectively removing toxic substances such as species.

[0002]

2. Description of the Related Art There are many proposals for an exhaust gas treatment device provided in association with a combustion furnace as disclosed in Japanese Patent Publication No. 6-35888 or Japanese Patent Application Laid-Open No. 7-75720. As shown in FIG.
A boiler 2 that cools high-temperature exhaust gas generated from the combustion furnace and collects useful heat in the form of steam or the like in a stage subsequent to the combustion furnace 1. The gas from the boiler 2 is brought into contact with water for cooling and coarsening. Cooling tower 10 for washing off fine dust, a bag filter 5 for removing fine dust floating in the gas discharged from the water cooling tower 10, and the gas discharged from the bag filter 5 is re-used by heat of steam or the like obtained by the boiler 2. It comprises a heat exchanger 11 to be heated and a catalyst tower 6 for reacting a gas reheated by the heat exchanger 11 in the presence of a catalyst to decompose toxic substances such as NOx and dioxin and unburned matters.

In such an exhaust gas treatment apparatus, exhaust gas generated from a combustion furnace is cooled by a waste heat boiler 2 and then enters a catalyst tower 6 via a bag filter 5. In order to remove dust and dioxins in the above, it is efficient that the temperature of the gas is low, so that the gas temperature at the inlet of the bag filter 5 is generally 180 ° C.
On the other hand, it is necessary to set the temperature to 180 ° C. or higher in the catalyst tower provided at a later stage from the relation of the activity of the catalyst. Therefore, once cooled gas is supplied to the heat exchanger 11 at the catalyst tower inlet side. For example, a high-temperature heat medium must be prepared and the temperature of the tube wall of the heat exchanger must be 250 ° C. or more.
In such a case, there is a risk that dioxins are resynthesized on the tube wall.

Further, in the apparatus shown in FIG. 2, gas is washed and water-cooled by the water-cooling tower 10. However, since moisture is mixed in the exhaust gas, white smoke may be generated from a chimney which finally discharges the exhaust gas into the atmosphere. Also, there is a problem that dew condensation occurs in the bag filter. Furthermore, there is also a problem that the water cooling tower cannot be installed when it is difficult to secure a water source or when the wastewater treatment facilities are not fully equipped.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems of the prior art, and does not use a water cooling tower and effectively utilizes the heat energy of exhaust gas. The present invention proposes a method and a specific device for feeding gas at an appropriate temperature to a bag filter and a catalyst tower.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for treating exhaust gas from a combustion furnace, comprising obtaining exhaust gas discharged from the combustion furnace through a boiler to obtain hot water or steam.
At that time, the temperature of the exhaust gas at the outlet of the boiler was set to 250 ° C.
Performing the following steps: cooling the gas discharged from the hot water generating boiler to 220 ° C. or lower, and performing heat exchange to heat the gas discharged from the bag filter to 180 ° C. or higher; and cooling by the heat exchange. Further cooling the cooled gas to 180 ° C. or lower, and removing the gas cooled by the above step through a bag filter,
Reheating the gas discharged from the bag filter to 180 ° C. or higher by the heat exchange, and decomposing the gas reheated by the heat exchange in the presence of a catalyst to decompose harmful substances.
Performing the removal.

[0007] Further, as an apparatus for carrying out the above method, an exhaust gas treatment device of a combustion furnace is provided with a boiler for obtaining hot water or steam by waste heat of exhaust gas discharged from the combustion furnace, and a gas discharged from the boiler. A heat exchanger that cools and reheats the gas discharged from the bag filter,
A cooler for further cooling the gas cooled by the heat exchanger to a certain temperature, a bag filter for removing dust through the gas cooled to a certain temperature by the cooler, and a catalyst for cooling the gas reheated by the heat exchange. And a catalytic tower reaction that decomposes and removes harmful substances in the presence.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on its embodiments. FIG. 1 is a layout diagram showing an example of an apparatus for implementing the present invention. A waste heat recovery boiler 2 is placed downstream of the combustion furnace 1. The boiler 2 has a capability of generating hot water or steam by exchanging the exhaust gas of 800 ° C. or more with cold water, and adjusting the exhaust gas temperature to 250 ° C. or less to operate the bag filter 5 and the catalyst tower 6. A gas at a temperature that matches the conditions can be supplied. However, if the outlet temperature is too low, the bag filter 5
Because the gas flowing out of the furnace cannot be heated sufficiently.
It is necessary to maintain the temperature above 00 ° C.

A heat exchanger 3 is placed downstream of the boiler 2. The heat exchanger 3 exchanges heat between the exhaust gas discharged from the boiler 2 and the exhaust gas discharged from the bag filter 5, and cools the gas before entering the bag filter 5 to a certain limit.
It has a function of reheating the gas discharged from the bag filter 5. By passing through this heat exchanger 3, the exhaust gas is cooled down from about 250 ° C. to 220 ° C., preferably below 200 ° C., while the gas leaving the bag filter 5 is cooled by the heat exchanger 3
About 1 by passing through the pipeline installed in
It is reheated from 60 ° C to 180 ° C or more, preferably to 200 ° C.

Following the heat exchanger 3, a cooler 4 is placed. The cooler 4 may be an air cooler having a cooling pipe inside. This air cooler 4 is provided with an air fan 6 and cools exhaust gas by adjusting the air volume thereof.
The exhaust gas temperature at the inlet of the bag filter 5 is 140 to 180 ° C.
It is controlled at a low temperature. Since the air that has passed through the cooler 4 is heated air, it can be used as combustion air for solid fuel, a dry heat source for external equipment, and the like.

Following the cooler 4, a bag filter 5 is placed. This bag filter 5 does not need to be particularly limited.
Although a normal one may be used, in the present invention, since the exhaust gas is cooled to its operating temperature and does not contain excessive steam from the water cooling tower, a relatively low heat-resistant temperature can be used.

The gas exiting the bag filter 5 is reheated by the heat exchanger 3 as described above and enters the catalyst tower 6. At this time, since the gas is heated by the heat exchanger 3 to about 200 ° C., which is the optimum operating temperature of the catalyst tower 6, the activity is high, and the denitration and the dioxins can be efficiently performed. As such a catalyst, an improved denitration catalyst mainly composed of titanium oxide and vanadium oxide can be used.

[0013] A flue (not shown) and a chimney are placed at the subsequent stage of the catalyst tower via an induction fan 7 so that the exhaust gas purified by the present invention is released into the atmosphere.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention was carried out in a solid waste fuel combustion furnace having an exhaust gas treatment facility as shown in FIG. The capacity of the hot water boiler is about 500,000 kcal / h. At the entrance of the bag filter, slaked lime was blown in for the purpose of removing hydrogen chloride in the exhaust gas. As the catalyst, an improved denitration catalyst mainly composed of titanium oxide and vanadium oxide was used.

In a combustion furnace, a lower heating value of 4,000 kc
al / kg refuse solid fuel is burned at 200 kg / h,
Exhaust gas (water content: 7%) was generated at a temperature of about 800 ° C. and a generation amount of about 2,000 Nm ³ / h. The exhaust gas temperature at the outlet of the hot water boiler is 246 ° C.
° C. This was cooled to a bag filter inlet temperature of 160 ° C. by passing it through an air cooler, and then introduced into the heat exchanger as a fluid to be heated and reheated to 187 ° C.
The exhaust gas after reheating passed through the catalyst tower, and then was released to the atmosphere via an induction fan.

In this embodiment, the dioxin removal rate at the bag filter was 97%, and there was no resynthesis of dioxin by reheating with a heat exchanger. This is due to the fact that since the temperature of the fluid on the heating side of the heat exchanger is 250 ° C. or lower, the operation is performed at a temperature lower than the temperature at which dioxin is resynthesized. The dioxin removal rate of the catalyst was 91%, and approximately 88% of dioxin could be removed by the entire exhaust gas treatment facility.

[0017]

Since the present invention is constructed as described above, there is no place where the tube wall temperature becomes 250 ° C. or higher in the entire exhaust gas treatment system, and the resynthesis of dioxins can be reduced. In addition, since the water cooling tower is not used, the risk of white smoke and dew condensation in the bag filter and chimney is small,
Since the bag filter can be operated at a low temperature, dioxins (removal rate of about 95%) and hydrogen chloride (removal rate of about 90%) can be effectively removed. Furthermore, bag filter cloths with low heat resistance can be used,
Contribute to cost reduction. In addition, the activity of the catalyst is high, and the removal of dioxins and denitration can be performed with high efficiency. Furthermore, since the exhaust gas contains little water, the catalyst is less liable to be condensed and condensed by dust, so that the life of the catalyst can be extended, and the catalyst can be sufficiently applied to a combustion furnace that operates intermittently. When the exhaust gas is treated according to the present invention, the moisture in the exhaust gas finally discharged is 10% or less, and there is no generation of white smoke throughout the year.

[Brief description of the drawings]

FIG. 1 is a layout view of an exhaust gas treatment apparatus according to the present invention.

FIG. 2 is a layout view of a conventional exhaust gas treatment device.

[Explanation of symbols]

 1: Combustion furnace 2: Boiler: 3: Heat exchanger 4: Cooler 5: Bag filter 6: Catalyst tower 7: Induction fan 8: Air cooling fan 10: Water cooling tower 11: Heat exchanger

Claims (2)

[Claims] 1. A step of obtaining hot water or steam from exhaust gas discharged from a combustion furnace through a boiler to reduce the temperature of the exhaust gas to 250 ° C. or less; cooling the gas discharged from the boiler to 220 ° C. or less; 180
Performing a heat exchange by heating to a temperature of not less than 180 ° C .; further cooling the gas cooled by the heat exchange to a temperature of not more than 180 ° C .; removing the gas cooled by the above step through a bag filter; Reheating the discharged gas to 180 ° C. or higher by the heat exchange, and decomposing and removing harmful substances in the presence of the catalyst on the gas reheated by the heat exchange. A method for treating exhaust gas from a combustion furnace. 2. A boiler for obtaining hot water or steam by waste heat of exhaust gas discharged from a combustion furnace, and a heat exchanger for cooling gas discharged from the boiler and reheating gas discharged from a bag filter. A cooler for further cooling the gas cooled by the heat exchanger to a certain temperature; a bag filter for removing dust through the gas cooled to a certain temperature by the cooler; and a gas reheated by the heat exchange. A catalytic tower for decomposing and removing harmful substances in the presence of a catalyst.