JPH0321804B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for burning pulverized coal, and particularly to a pulverized coal combustion device that can reduce nitrogen oxides in combustion exhaust gas.

Most large-scale boilers for business use, including large-scale boilers for power plants, that use coal as fuel use powdered coal (hereinafter referred to as "pulverized coal"), which is obtained by pulverizing coal to a predetermined particle size. use By using this pulverized coal, the surface area per unit of coal increases and the combustibility is greatly improved, and controllability is also improved accordingly.

On the other hand, even in boilers that use such pulverized coal as fuel, the need to reduce nitrogen oxides (NOx) is the same as in other combustion devices, and various low NOx combustion methods are being implemented. In the case of coal combustion, compared to petroleum, the fuel contains a higher amount of N, so-called fuel NOx, and the current switch to coal as a fuel has actually made the NOx problem more serious. is also occurring.

There are two methods of removing NOx: the low NOx combustion method, which suppresses the generation of NOx in the combustion stage and removes the generated NOx, and the method where the generated NOx is removed from the exhaust gas using a denitrification device. One of the combustion methods is the gas phase reduction method. This method performs combustion by dividing the air ratio (the ratio of the amount of air actually supplied to the theoretical amount of air), and performs combustion with the air ratio of about 1 to bear the heat load of the combustion device. By keeping the ratio low (usually 0.6 or less), reducing intermediate products such as ・CH ₃ , CO, and ・H are produced, and the NOx generated by these products is reduced in the gas phase and converted into harmless N. ₂ .

Conventionally, this method involves changing the air ratio of each burner and mixing a reducing flame with a low air ratio with a main burner flame burned with a high air ratio to reduce NOx in the gas phase. However, according to this method, the mixing of both flames is not necessarily good, and there are cases where the gas phase reduction of NOx is insufficient. For this reason, the inventors have proposed a burner structure in which each burner can constitute a main combustion flame and a reduction flame, thereby achieving a high gas phase reduction rate.

An object of the present invention is to provide a pulverized coal combustion apparatus that can perform gas phase reduction well and is particularly effective as a combustion apparatus in which each burner forms a main combustion flame and a reduction flame, respectively, as described above.

In short, this invention provides a pulverized coal combustion device for supplying pulverized coal pulverized by a coal pulverizer to a burner and combusting it, in which the burner is formed to have a main fuel cylinder and an auxiliary fuel cylinder that is coaxial within the cylinder, The main fuel cylinder and the auxiliary fuel cylinder are located at the burner throat with their ends aligned, and a plurality of coal crushers are provided, and one or more burner main fuel cylinders are connected to each coal crusher through a pipe. In addition, some of the plurality of coal crushing devices are connected via a pulverized coal separator to a pulverized coal storage tank, and further, the pulverized coal storage tank and the auxiliary fuel cylinder of each burner are respectively connected to each other through a duct. This pulverized coal combustion device is characterized in that a pipe is provided with means for supplying gas having a lower O ₂ partial pressure than the primary air supplied to the main fuel cylinder.

Examples of the present invention will be described below.

FIG. 1 shows the structure of a burner used in the combustion apparatus of the present invention. In the figure, reference numeral 2 is a main fuel cylinder, and 4 is an auxiliary fuel cylinder arranged coaxially within the main fuel cylinder 2. The open end portions are formed so as to be aligned together and located at the burner throat portion (opening 9) as shown. The main fuel 1 is injected into the furnace from the annular injection port at the open end by the air for air transport (primary air) supplied from the mill, and passes through the wind box 5 and swirl vanes 7 into the furnace from the opening 9. Combined with the swirl-supplied secondary air, combustion is performed at an air ratio of approximately 1 as a whole. On the other hand, the auxiliary fuel 3 is injected into the furnace from the auxiliary combustion tube 4 with low O ₂ gas such as exhaust gas, and is combusted at a low air ratio to produce reducing intermediate products and NOx.
is reduced in the vapor phase.

FIG. 2 shows the supply path of pulverized coal to the burner described above (designated 10).

In the figure, three mills 12a, 12b, and 12c are arranged. A main fuel supply pipe 19 supplies pulverized coal as the main fuel to each burner, and is connected to the main fuel combustion section of each burner, that is, the main fuel cylinder 2 shown in FIG. Numeral 13 is a pulverized coal extraction pipe line, and each pipe line 13 joins the extraction main pipe 23 and is connected to a separator 14 such as a cyclone. Reference numeral 21 denotes a control valve provided in each extraction pipe 13, which controls the amount of extraction from each mill. 15 is a pulverized coal storage tank connected to the separator 14; 20 is an auxiliary fuel combustion section of each burner;
In other words, it is an auxiliary fuel supply pipe that connects the auxiliary fuel cylinder 4 in FIG. 1 and this pulverized coal storage tank 15.

In this apparatus, each of the mills 12a to 12c pulverizes the supplied coal to a predetermined particle size. Due to the primary air A supplied into the mill, this pulverized coal is supplied as the main fuel to the main combustion section of each burner through the pipe 19, and together with the secondary air supplied directly to the burners, the air ratio is approximately 1. be burned.

On the other hand, a part of the pulverized coal from each mill reaches the separator 14 via the extraction pipe 13 and the extraction main pipe 23, and the separated pulverized coal is stored in a pulverized coal storage tank 15. Note that the gas (primary air A) from which the pulverized coal has been separated is further removed by another dust collector or the like to remove the remaining pulverized coal, and then is dispersed into the atmosphere or, as the case may be, is introduced into a combustion equipment furnace. The pulverized coal in the storage tank is supplied to the auxiliary fuel supply pipe 20 via the feeder 16, and each burner 10 is
is supplied to the auxiliary fuel combustion section. As a result, a reduction flame is formed, and the NOx generated in the main combustion flame is reduced in the gas phase. Note that the gas for airflow transporting the auxiliary fuel may be N ₂ or Ar in addition to the exhaust gas. In addition, by mixing air with these inert gases, the O ₂ partial pressure in the gas is adjusted, and the timing of generation of intermediate products in the reduction flame is adjusted to control the gas phase reduction of NOx. It's okay.

Further, when the combustion device is in a partial load state, operation of some of the mills is stopped, but in this case, the valve 21 provided in the extraction pipe 13 of the stopped mill is kept closed. If it is desired to rapidly increase the load from this partial load, supply auxiliary fuel from the storage tank 15 to the stopped burner, and also increase the O ₂ partial pressure of the gas for air flow transport, thereby increasing the auxiliary fuel combustion section. It may be used as the main burner to supply fuel until the stopped mill reaches steady operation.

By carrying out this invention, a certain amount of pulverized coal is always stored, so even if some of the mills stop operating due to partial load, the burners in operation can stably burn.

Further, since the main fuel supply system and the auxiliary fuel supply system are separated and each burner performs gas phase reduction, it is possible to always perform good gas phase reduction of NOx regardless of the load on the combustion device.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a burner used in a combustion apparatus according to the present invention, and FIG. 2 is a system diagram of the combustion apparatus according to the invention. 10...burner, 12a, 12b, 12c...
Coal crusher, 13...extraction pipe, 14...separator, 15...pulverized coal storage tank, 19...main fuel supply pipe, 20...auxiliary fuel supply pipe.

Claims (1)

[Claims] 1. In a pulverized coal combustion device that supplies pulverized coal pulverized by a coal pulverizer to a burner and burns it, the burner is formed to have a main fuel cylinder and an auxiliary fuel cylinder that is coaxial within the cylinder, and the main fuel cylinder and the auxiliary fuel cylinders are located in the burner throat portion with their ends aligned, and a plurality of coal crushers are provided, and one or more burner main fuel cylinders are connected to each coal crusher by a pipe, and A part of the coal crushing equipment, which has multiple units, is connected via a pulverized coal separator to a pulverized coal storage tank through a pipe, and the pulverized coal storage tank and the auxiliary fuel cylinder of each burner are connected through a pipe, respectively. A pulverized coal combustion device characterized by providing means for supplying gas having a lower O ₂ partial pressure than primary air supplied to a fuel cylinder.