JPH0326318A - Waste gas treating device - Google Patents

Abstract

PURPOSE:To easily regenerate a deteriorated denitration catalyst by providing a device for coating the surface of the catalyst deteriorated by the deposition of a noble-metal oxidation catalyst scattered from an oxidation device with a denitration catalyst composition. CONSTITUTION:The oxidation device 2 provided with a noble-metal oxidation catalyst of platinum, rhodium or >=1 kind between them is arranged on the upstream side of a passage 1 for waste gas contg. unburnt carbon monoxide, etc., and nitrogen oxides, and the denitration device 3 provided with a denitration catalyst and an ammonia injector 4 are arranged on the downstream side of the passage 1. The surface of the denitration catalyst deteriorated by the deposition of the noble-metal oxidation catalyst scattered from the oxidation device 2 is coated with the denitration catalyst composition by a spray nozzle 6. Consequently, the deteriorated denitration catalyst is easily regenerated, a boiler and a gas turbine need not be operated at a low load to clear the waste gas-related law, and the exchange of the denitration catalyst at an early stage is obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a combustion exhaust gas treatment device, and more particularly to a combustion exhaust gas treatment device that regenerates a denitrification device whose performance has deteriorated.

[Conventional technology]

Exhaust gas from boilers and gas turbines fluctuates to some extent depending on the fuel used and the condition of the combustion equipment, but unburned fuel such as carbon monoxide (CO) There are nitrogen oxides (hereinafter referred to as NOx) such as No and NO2. Since the amount of these exhaust gases is enormous, if CO and NOx are emitted as they are, they will pollute the atmosphere and cause pollution problems.

Therefore, in such cases, conventionally, an oxidizer equipped with a catalyst for promoting combustion (hereinafter referred to as a combustion catalyst) and an oxidizer to combust unburned substances such as GO and turn them into harmless gases such as CO2 and NOx are used. It has been practiced to co-locate a denitrification device for reducing N2 and H20 in the presence of a denitrification catalyst using ammonia as a reducing agent.

The oxidation catalyst used is a carrier having a honeycomb-like structure with many slots parallel to the flow, coated with a metal catalyst such as platinum, rhodium, or platinum-rhodium.

Further, as a denitrification catalyst, a catalyst composition containing one or more types of oxides such as titanium, vanadium, molybdenum, tungsten, iron, etc. is shaped into a honeycomb shape or a plate shape,
Alternatively, honeycomb or plate-shaped carriers impregnated or coated with these catalyst compositions are often used.

In the above-mentioned exhaust gas treatment device, the oxidizing device is arranged on the upstream side of the high temperature exhaust gas, and the denitrification device is arranged on the downstream side. This is because the amount of precious metal catalyst used can be reduced by placing an expensive precious metal catalyst in the exhaust gas upstream of high temperature to increase its activity. Furthermore, the temperature of the exhaust gas increases due to unburned components in the exhaust gas burned in the oxidizer, which has the effect of improving catalyst activity when treated in the denitrification device.

[Problem to be solved by the invention]

When the above-mentioned conventional device was operated for a long period of time, a phenomenon occurred in which the performance of the denitrification device decreased much more rapidly than initially expected, although the cause was unknown.

As a result, the total amount of exhaust gas NOx stipulated by law cannot be complied with, and the output of boilers and gas turbines may be reduced, or the amount of ammonia used as a reducing agent may be increased to increase the amount of residual ammonia. Furthermore, no fundamental solution had been found, forcing the company to take measures such as replacing the denitrification catalyst early. The present invention has been made to solve the problems of the prior art described above.

[Means for Solving the Problems] The problem with the prior art described above is that platinum, rhodium, or one or more of these is present in the upstream region of the exhaust gas line containing unburned substances such as carbon monoxide and nitrogen oxides. In an exhaust gas treatment device having an oxidation device equipped with a noble metal oxidation catalyst, a denitration device equipped with a denitration catalyst downstream of the passage, and an ammonia injection device, performance may be degraded due to adhesion of the precious metal oxidation catalyst scattered from the oxidation device. The problem is solved by an exhaust gas treatment device characterized by being provided with a device for coating the deteriorated surface of the denitrification catalyst with a denitrification catalyst composition.

〔Example〕

The inventors conducted various tests and studies to find out why the performance of the denitration equipment deteriorates more than expected when conventional equipment is operated for a long period of time. It was presumed that this was due to peeling off from the honeycomb carrier due to changes in load, or becoming gaseous and scattering downstream, and depositing on the catalyst of the denitrification equipment. In other words, if platinum or the like adheres to the denitration catalyst, platinum acts as a catalyst to oxidize the ammonia used in the denitration equipment to reduce NOx to NOx, so the apparent performance of the denitration equipment will deteriorate. It was thought that this would decrease. The present invention has been made based on the above knowledge, and the content of the invention will be specifically explained below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention, in which an oxidizer 2 having an oxidation catalyst such as platinum is provided on the upstream side of the exhaust gas in an exhaust gas passage 1 containing both unburned components such as CO and NOx. A denitrification unit N3 equipped with a denitrification catalyst is provided on the downstream side. An ammonia injection nozzle 4 is provided in the exhaust gas passage upstream of the denitrification device, and a required amount of ammonia is supplied to this from an ammonia supply pipe 5 and mixed with the exhaust gas. 9 is a catalyst compound solution such as ammonium metavanadate, vanadyl sulfate or ammonium molybdate, which is mixed with compressed air from the compressed air supply pipe 7 and mixer 8
The mixture is mixed in the spray nozzle 6 installed upstream of the denitrification device 3.
sprayed by. The sprayed catalyst mixture is applied to the surface of the denitrification catalyst, covering platinum and other substances adhering to the catalyst to prevent it from exerting its oxidation catalytic function. In this way, the denitrification catalyst can be restored to close to its initial performance.

Catalyst & 11 A certain solution is applied when the denitrification rate is measured and has decreased by about 3% from the initial value, but the concentration of the solution applied depends on the amount of platinum etc. attached to the surface of the denitrification catalyst. Although the amount of application depends on the amount of application, the above spray application is repeated 2 to 3 times. Although platinum and the like attached to the denitrification catalyst cannot be easily removed, it can be easily rendered harmless by coating it with a denitrification catalyst composition as in the present invention.

In addition, as a method for applying and covering the catalyst with platinum attached with the denitrification catalyst composition, it is possible to immerse the catalyst itself in the catalyst composition solution, apart from the above-mentioned example, but spray coating is also possible. is more convenient.

〔Effect of the invention〕

According to the present invention, it is possible to easily recover from deterioration in the performance of the denitrification catalyst, for which the cause was previously unknown and appropriate treatment could not be taken. It is possible to prevent operation at a reduced temperature or premature replacement of the denitrification catalyst.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention. ■... Exhaust gas passage, 2... Oxidizer, 3... Denitration device, 4... Ammonia injection nozzle, 5... Ammonia supply pipe, 6... Spray nozzle, 7... Compressed air Supply pipe, 8...Mixer, 9...Catalyst composition solution.

Claims (1)

[Claims] (1) An oxidizer equipped with platinum, rhodium, or a precious metal oxidation catalyst of one or more of these in the upstream region of an exhaust gas passage containing unburned substances such as carbon monoxide and nitrogen oxides, and the downstream region of the passage. In an exhaust gas treatment device having a denitrification device equipped with a denitrification catalyst and an ammonia injection device, the device applies a denitration catalyst composition to the surface of the denitration catalyst whose performance has deteriorated due to the adhesion of precious metal oxidation catalysts scattered from the oxidation device. An exhaust gas treatment device characterized by being provided with.