JPS6148042B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for reducing nitrogen oxides from gas containing nitrogen oxides such as exhaust gas from a coal combustor,
In particular, the present invention relates to a method of effectively reducing nitrogen oxides from exhaust gas using solid fuel or a carbon-containing substance similar thereto. Conventionally, methods for reducing and removing nitrogen oxides from the exhaust gas of coal combustors include reducing and distributing the supply of oxygen-containing gas such as air required for combustion, and improving fuel supply methods to maintain a uniform temperature in the combustion area. Combustion control methods that reduce the generation of nitrogen oxides by lowering the maximum temperature and reducing the maximum temperature, flue gas denitrification methods that remove generated nitrogen oxides from exhaust gas by gas phase reaction or solution absorption, and methods that combine the two. etc. have been used. Combustion control methods are mainly used for gases and
When liquid fuel is burned using a gas containing nitrogen gas such as air as an oxygen source, it is possible to suppress the nitrogen in the air from turning into nitrogen oxides (so-called thermal NOx) in the high temperature region of the flame. Although it is effective, it has drawbacks such as a high reduction rate cannot be expected and it is not very effective in suppressing nitrogen oxides (so-called fuel NOx) generated from nitrogen contained in fuel. On the other hand, the flue gas denitrification method is highly effective in removing nitrogen oxides, but has the disadvantage of being expensive, such as requiring new equipment and auxiliary agents such as a solution (wet method) or ammonia gas (dry method). The purpose of the present invention is to bring coal combustor exhaust gas into contact with solid carbon-containing substances to reduce and remove nitrogen oxides from the exhaust gas, and at the same time to reduce and remove the low concentration of hydrogen and by-products.
The aim is to re-burn flammable gases such as carbon monoxide and methane to economically reduce and remove nitrogen oxides from exhaust gas. The present invention applies the principle that nitrogen oxides are effectively reduced to nitrogen gas by carbon at a temperature of 400°C or higher in coal combustion gas, and when coal is used as the carbon source, the above reduction reaction occurs. At the same time, some of the volatile content in the coal is carbonized and mixed into the gas, and nitrogen compounds such as ammonia and cyanide contained in this volatile content become a new cause of nitrogen oxide formation during the subsequent reburning process. The objective is to realize a high overall nitrogen oxide removal rate by reducing the generation of nitrogen compounds from the carbon source. Specifically, a carbon-containing solid substance that has been carbonized in advance is used as a carbon source. An embodiment of the present invention will be described below with reference to the drawings. The figure shows an example of the present invention, with a column diameter of 50 mm.
This is an example of application to coal combustion using a fluidized bed of φ. Coal having the properties shown in Table 1 (A) is supplied from the coal supply pipe 2 to the combustion fluidized bed 1, while air supplied from the air introduction pipe 5 is uniformly distributed within the combustion fluidized bed 1 by the disperser 4. It is dispersed in the coal particles and fluidizes the coal particles in the bed, and at the same time serves as a source of oxygen necessary for coal combustion. In order to maintain a smooth fluidized state, the combustion fluidized bed 1 may be filled with reactively inactive alumina particles in addition to coal. In steady-state operation, the inert particles are replaced by ash produced from the combustion of coal. Furthermore, it is also possible to remove sulfur oxides generated by combustion within the combustion fluidized bed 1 by using limestone or the like crushed to an appropriate particle size.

[Table] The ash produced by combustion is taken out from the overflow pipe 3, and the bed height of the combustion fluidized bed 1 is kept almost constant. From the carbonaceous supply pipe 7, carbonized coal coal having the properties shown in (B) as a carbon-containing solid material previously carbonized in Table 1 is supplied to form a fluidized bed 6 for denitrification. The combustion exhaust gas from the combustion fluidized bed 1 is sent to the disperser 9
The nitrogen oxides are uniformly dispersed in the denitrification fluidized bed 6, and the nitrogen oxides that have reacted with the char are removed there. In this embodiment, in order to maintain the bed height of the denitrification fluidized bed 6,
Although the overflow pipe 8 was provided to take out the excess chia out of the system, the outlet of the overflow pipe 8 may be introduced into the combustion fluidized bed 1. The denitrification fluidized bed 6 is selected by selecting an appropriate value and dropping the chires from the openings of the disperser 9 into the combustion fluidized bed 1, and adjusting the speed of supplying the chires from the carbonaceous supply pipe 7.
The overflow pipe 8 may be omitted if the bed height can be maintained substantially constant. Since the gas that has passed through the denitrification fluidized bed 6 contains trace amounts of flammable components such as hydrogen, carbon monoxide, and methane, a sufficient amount of air is introduced from the secondary air introduction pipe 10 to burn off the combustible components. supply,
The secondary air distributor 11 distributes the air uniformly onto the freeboard 12. The gas containing combustible components leaving the denitrification fluidized bed 6 is burned by the secondary air while rising within the freeboard 12 and is exhausted to the outside of the system through the exhaust pipe 13. Coal supply amount from coal supply pipe 2 55g/h, air supply amount from air introduction pipe 5
400Nl/h, amount of chir supplied from carbonaceous supply pipe 7
10g/h, keeping the temperature of the combustion fluidized bed 1 and the denitrification fluidized bed 6 at 1,000°C, and changing the flow rate of air preheated to about 300°C from the secondary air introduction pipe 10,
Table 2 shows the analysis results of the gas sampled directly below the disperser 9 and at the outlet of the exhaust pipe 13.

[Table] For comparison, using the same equipment as in Example 1, 10 g/h of the coal shown in Table 1 (A) was fed from the carbonaceous supply pipe 7.
When a similar experiment was carried out by supplying the same, the results shown in Table 3 were obtained.

[Table] According to the present invention, it is possible to prevent the generation of new nitrogen oxides through re-combustion after reducing nitrogen oxides, and it is possible to maintain a high nitrogen oxide removal rate as a whole.

[Brief explanation of the drawing]

The figure is a diagram showing an aspect of an embodiment of the present invention. 1...Fluidized bed for combustion, 2...Coal supply pipe, 3,
8... Overflow pipe, 4,9... Distributor, 5... Air introduction pipe, 6... Fluidized bed for denitrification, 7... Carbonaceous supply pipe, 10... Secondary air introduction pipe, 11... Secondary air distributor, 12...freeboard, 13...exhaust pipe.

Claims (1)

[Claims] 1. Introducing high-temperature coal combustion gas containing nitrogen oxides produced by a fluidized bed for coal combustion into the granular carbon provided on the fluidized bed to form a fluidized bed of the granular carbon, and The temperature of the fluidized bed of granular carbon is maintained at 400° C. or higher to reduce the concentration of nitrogen oxides in the combustion gas, and the temperature of the fluidized bed of granular carbon is maintained at 400° C. or higher to reduce the concentration of nitrogen oxides in the combustion gas, and A method of supplying air to the hot coal combustion gas containing combustible components that has come out and burning and removing it, which can be carbonized in advance as the granular carbon and converted into nitrogen oxides among the volatile components. A method for reducing nitrogen oxides in coal combustion gas, characterized by using carbon with reduced nitrogen compounds and burning the coal while maintaining the bed height of the fluidized bed at a constant value and using it as a heating source.