JPS589693B2 - Catalytic reduction denitrification method for exhaust gas with a temperature of 300°C or less - Google Patents

Description

Detailed Description of the Invention The present invention provides a catalytic reduction denitrification method for exhaust gas that uses a titanium-based catalyst and reduces heat loss when removing nitrogen oxides (NOx) from exhaust gas by catalytic reduction denitrification using ammonia. Regarding.

Generally, harmful nitrogen oxides contained in exhaust gas from boilers, sintering machines, internal combustion engines, etc. are reduced in a reducing gas atmosphere and decomposed and removed into harmless components such as nitrogen, carbon dioxide, or water vapor.

In the reductive decomposition of nitrogen oxides contained in combustion furnace exhaust gas such as boiler exhaust gas, ammonia is generally injected into the gas because the above gas does not normally contain reducing gas, but It is known that catalysts are poisoned by chemical dust, alkalis, ammonia compounds, sulfide compounds, etc., making it impossible to achieve the intended purpose.

Poisoning of the catalyst is thought to be due to the effects of sulfur oxides (especially sulfur dioxide gas) and ammonia compounds contained in the combustion furnace exhaust gas, and this sulfur dioxide gas is oxidized and becomes sulfuric anhydride. It is believed that this acts on the metal oxide of the catalyst to form sulfate, changing the composition from a metal oxide that exhibits catalytic activity to one that does not exhibit catalytic activity.

By the way, when nitrogen oxides in exhaust gas are conventionally removed by catalytic reduction using a catalyst, an alumina-based catalyst is generally used as a catalyst. A process is required to regenerate the catalyst whose activity has decreased due to poison using high-temperature air.

For alumina-based catalysts, the catalyst with decreased activity is
There are examples of regeneration using high-temperature air above 0°C, but the high-temperature gas after regeneration is released as is along with the exhaust gas, and since catalyst regeneration is performed at a temperature above 500°C, a conveying means is used to move the catalyst from the regenerator. In order to transfer it to the reactor again, it must be cooled to protect the transfer equipment, resulting in a lot of energy loss.

Furthermore, there was a drawback that a cooler was required.

The present invention was made to eliminate the above-mentioned drawbacks, and does not use an alumina-based catalyst when denitrating exhaust gas at a relatively low temperature, that is, 300°C or less, and uses a titanium-based catalyst that is resistant to poisoning even at a relatively low temperature. A moving bed type regenerator is installed above the reaction tower and communicates with the moving bed of the reaction tower, and heating of 450°C or higher is generated in a heating furnace perpendicular to the moving direction of the catalyst inside the regenerator. A part of the gas is allowed to pass through to regenerate the catalyst, and the used heated gas and part of the heated gas from the heating furnace are added to the exhaust gas to raise the exhaust gas temperature to 300°C or less, and then the reaction is carried out. A catalyst supplied to the column and continuously or intermittently discharged from the bottom of the reaction column is refluxed to the top of the regeneration reactor by a conveying means, and
The present invention is characterized in that the proportion of heated gas flowing from the heating furnace into the regenerator and the exhaust gas to be treated can be adjusted.

An embodiment of the present invention will be described below with reference to the drawings.

1. The air sucked in by a combustion air fan is heated to approximately 500°C in 2 hot blast furnaces.

3 is a regenerator that removes ammonium sulfate salt, hydrocarbons, and combustible dust adhering to the catalyst.

The regenerator 3 is provided with a moving bed type catalytic reduction denitrification reactor 6 above the reaction tower 6, which will be described later, and communicates with the moving bed of the reaction tower 6. passing heated gas of 450°C or higher,
While regenerating the catalyst, the used heated gas and heated gas from the heating furnace are added to the exhaust gas to raise the exhaust gas temperature from 300°C or lower to 250°C to 300°C.

4 and 5 are hot air lines into which heated gas flows.

6 is a catalytic reduction denitrification reactor.

7 is an exhaust gas line for a boiler sintering machine internal combustion engine, etc.

Control valves 8 and 9 control the flow rates of the heating gas lines 4 and 5, respectively.

10 is an ammonia injection line, and after adding ammonia, the air sucked in by the combustion air fan 1 is passed through the hot air stove 2 to about 5
heated to 00°C.

A portion of the heated air is led to the regenerator 3, where ammonium sulfate salts, hydrocarbons, and combustible dust adhering to the catalyst are removed.

A portion of the heated air is also led to the exhaust gas flue 7 through the line 4 in order to participate in raising the temperature of the exhaust gas.

In order to cope with load fluctuations at the smoke source, a part of the high-temperature air used for regeneration is branched off and guided into the flue in front of the reactor, in cases where regeneration is not necessary or when a small amount of air is required. In this method, a portion of the hot air was branched and guided into the flue in front of the reactor inlet.

Therefore, in order to control the regeneration temperature and the reaction temperature, flow rate control valves 8 and 9 are provided to enable optimal temperature control.

For example, when a diesel engine is operating at full capacity, the temperature of the exhaust gas inside the denitration device is high, the NOx concentration is high, and the load per unit area of the catalyst is high.

Therefore, it is necessary to transfer a large amount of the moving bed catalyst, and a large amount of heat is passed through the regenerator 3. For this purpose, the control valve 8 of the exhaust gas line 4 is closed and the control valve 9 is opened.

When the exhaust gas temperature decreases, the NOx concentration decreases, and the load per unit area of the catalyst decreases.

For this reason, it is sufficient to keep the transfer amount of the moving bed catalyst small and to pass a small amount of heat to the regenerator 3 through the control valve 8.
and close control valve 9.

Since the present invention has the above configuration, the temperature of the heated gas sent to the regeneration system can be kept low.

Furthermore, since the fluidized bed between the regeneration reactor and the reaction tower is in communication, there is little heat loss and poisoning at the inlet of the reactor can be prevented.

Since the exhaust gas temperature is raised and the regeneration temperature is relatively low, energy economy is high, and ordinary steel can be used as the material for the regeneration system, resulting in low construction costs.

In addition, it is possible to perform long-term, high-performance continuous denitrification operation while preventing a decrease in catalyst activity against dirty exhaust gas containing large amounts of S02 and dust, and ammonium sulfate salts, hydrocarbons, etc. are relatively easy to adhere to the catalyst. High performance denitrification rates can be maintained even in exhaust gas denitrification in the temperature range.

Furthermore, since the regenerator is located at the top of the reactor, the catalyst is preheated in advance, which has the effect of preventing deterioration of the catalyst due to rapid temperature drop and corrosion of the equipment due to SO3 in the exhaust gas.

Experimental example Space velocity (SV) 7000hr-1, reaction temperature 260
A denitrification reaction experiment was conducted using the above catalytic reduction denitrification apparatus for 1000 hours under the conditions of .degree. C. and NH3/NOX=1.

After about 200 hours, the initial denitrification efficiency of 96% decreased to 66%.

It can be seen that when the titanium-based catalyst is regenerated and activated in this state at a regeneration reaction temperature of 420° C. for 3 hours, the denitrification rate increases to 95%.

(See Figure 2)

[Brief explanation of drawings]

FIG. 1 is a diagram showing a specific process flow of the catalytic reduction denitrification method of the present invention, and FIG. 2 is a graph showing changes over time in the denitrification rate and catalyst activity in the present invention. 1... Combustion air fan, 2... Hot air stove, 3... Regenerator,
4, 5...Hot air line, 6...Catalytic reduction denitrification reactor, 7
...Exhaust gas line, 8, 9...Control valve, 1
0...Ammonia injection line.

Claims (1)

[Claims] 1. In a method for catalytically reducing nitrogen oxides using a titanium-based catalyst filled in the reaction tower by passing nitrogen oxide-containing exhaust gas through a moving bed type ammonia catalytic reduction denitrification reaction tower orthogonally to the moving direction of the catalyst. A moving bed type regenerator is installed above the reaction tower and communicates with the moving bed of the reaction tower, and a part of the heated gas of 450°C or higher generated in the heating furnace passes through the regenerator so as to be perpendicular to the moving direction of the catalyst inside the regenerator. Seshime,
While regenerating the catalyst, the heated gas after use and a portion of the heated gas from the heating furnace are added to the exhaust gas to be treated, and the temperature of the exhaust gas is raised to 250°C to 300°C, and then supplied to the reaction tower. On the other hand, the catalyst continuously or intermittently discharged from the lower part of the reaction tower is made to flow to the top of the regenerator by means of a conveying means, and the inflow material required to be heated is introduced from the heating furnace into the regenerator and the gas to be treated. A catalytic reduction denitrification method for exhaust gas having a temperature of 300°C or less, characterized in that the ratio can be adjusted.