JPH0117045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for operating a combustion furnace, and particularly to a method for reducing nitrogen oxides (hereinafter referred to as NOx) in exhaust gas when starting up a combustion furnace such as a boiler or at low load. Concerning how to operate a combustion furnace.

Conventionally, NOx in exhaust gas from boiler combustion furnaces
As a method of reducing
A method is being used to reduce the combustion temperature by recirculating the fuel, and to lower the oxygen partial pressure to suppress the generation of NOx.

However, although this method is certainly effective in reducing NOx during steady operation or under high load, when starting the boiler and under low load, the air flow rate at the burner throat, which has a constant opening cross-sectional area, due to problems with stable combustion of the burner. It is necessary to maintain the fuel at a certain speed or higher, and for this reason, the burner section is supplied with more air than the required amount of air corresponding to the amount of fuel, making it impossible to avoid a combustion state with a high oxygen concentration, resulting in a high NOx concentration. .

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to avoid deteriorating the combustion condition of the burner.
An object of the present invention is to provide a method for operating a combustion furnace that can reduce the generation of NOx.

In order to reduce the oxygen concentration in the combustion furnace and ensure the necessary gas flow rate at the burner throat, the present invention not only recirculates the exhaust gas from the bottom of the combustion furnace into the furnace, but also recirculates the exhaust gas at the burner throat. The combustion chamber is circulated in the burner section to perform combustion with low oxygen concentration.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is an apparatus system diagram showing an embodiment in which the present invention is applied to a boiler combustion furnace. In the figure, the equipment system includes a boiler 1, a burner 3 and a burner throat 4 provided through the side wall of a furnace 2 of the boiler 1, a window box 5 provided to cover the burner throat 4, and a device connected to the boiler 1. The installed exhaust gas flue 6 and the boiler 1 branched from the flue gas flue 6
a recirculating gas duct 7 leading to the bottom of the furnace;
It is mainly composed of branch ducts 8, 8A and 8B which further branch from the wind box 3 and reach the wind box 3. Gas recirculation fans 9 and 10 are installed in the ducts 7 and 8, respectively, and each duct has dampers 10A, 11, 10 for adjusting air volume, respectively.
12 and 13 are arranged.

In the above configuration, an amount of fuel corresponding to the boiler load is supplied to the burner 3, and air corresponding to this amount of fuel is introduced into the wind box 5, so that the fuel is stably combusted. On the other hand, the recirculated gas passes through the gas recirculation duct 7 as shown by the arrow, and is injected into the boiler furnace 2 through the gas recirculation fan inlet damper 10A and the furnace bottom inlet damper 11. On the other hand, after exiting the gas recirculation fan 9, the exhaust gas mixed into the wind box 5 is boosted in pressure by the gas recirculation gas boost up fan 10, and is sent to the wind box 5 before and after the boiler via the inlet dampers 12 and 13. After being supplied, it is injected into the furnace 2 through the burner throat 4. When starting the boiler and under low load, a portion of the recirculating gas branched from the recirculating gas fan 9 is diverted to the fan 1 in order to ensure the burner throat speed.
The pressure is increased by 0 and supplied into the wind box 5, and the combustion air is further supplied to the burner throat 4.
Inject into the furnace. The exhaust gas circulation amount when the boiler load is 25 to 75% is, for example, in the range of 50 to 25%.

By the above operation, it is possible to obtain stable combustion in the furnace and suppress the generation of NOx without increasing the amount of combustion air more than necessary. Note that the recirculating gas injected into the furnace 2 through the furnace bottom inlet damper 11 cools the flame, lowers the oxygen partial pressure in the burner zone, and has the effect of suppressing the generation of NOx. In addition, by injecting a large amount of recirculated gas into the furnace 2, the oxygen concentration in the exhaust gas is reduced, which is advantageous as an oxygen equivalent value of NOx.

The present invention is not limited to the above-mentioned boiler combustion furnace, but can equally be applied to other industrial furnaces, incinerators, etc.

As described above, according to the present invention, by recirculating a portion of the exhaust gas to the burner throat portion of the combustion furnace, it is possible to easily suppress the generation of NOx at the time of startup of the furnace and at low load.

[Brief explanation of drawings]

FIG. 1 is an apparatus system diagram showing an embodiment of the present invention. 1...boiler, 2...furnace, 3...burner, 4
... Burnus Throat, 5 ... Widbox, 7
...Gas recirculation duct, 8, 8A, 8B... Branch duct.

Claims (1)

[Claims] 1. In operation of a combustion furnace that aims to reduce nitrogen oxides by recirculating exhaust gas from the bottom of the combustion furnace equipped with a burner and a burner throat, the burner throat is A method of operating a combustion furnace, characterized in that part of the exhaust gas is recirculated through the burner throat so that the air passing through it has a velocity above a certain value for combustion stabilization. 2. The method of operating a combustion furnace according to claim 1, wherein the combustion furnace is a boiler.