JPS58108306A - Method for low nox combustion of pulverized coal - Google Patents

Abstract

PURPOSE:To enable to burn pulverized coal in the state that the rate of NOx is low, by controlling the air ratio by providing a granulated coal burner, a pulverized coal burner, and an air feed port in turn from the upstream side of the flow of combustion gas. CONSTITUTION:A granulated coal burner 2, a pulverized coal burner 3, and an air feed port 4 are provided to a combustion furnace in turn from the lowest part which is the upstream side of the flow of combustion gas, and granulated coal and pulverized coal are fed to each burner from a pipeline 2a and a pipeline 3a respectively, together with combustion air being fed from a forced draft fan 5. On the other hand, the air to burn unburnt content in combustion gas is fed from an air feed port 4 passing through a line 6. In this case, about 50% of the whole feeding amount of fuel is fed from the granulated burner port 2, and the air ratio to fuel is determined to be from 0.85-1.1, which is larger than the air ratio to the pulverized coal burner 3.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method of pulverized coal combustion, particularly low nitrogen oxide (low NOx) combustion.

Recently, the combustion of pulverized coal, which is made by pulverizing coal, as an alternative to heavy oil is being considered again. This is due to its good controllability in response to load fluctuations and its suitability as a combustor for large thermal power generation boilers. However, from the viewpoint of environmental protection, it is required to solve problems such as dust, sulfur oxides, and NOx in the exhaust gas. Regarding the treatment of NOx, conventional means using chemicals such as NH3 to remove harmless nitrogen, and methods using catalysts have also been disclosed.

However, pulverized coal combustion has a different fuel ratio than heavy oil droplets,
The means of combustion, low NOx combustion, etc. had to be adapted to this and required consideration.

This invention is aimed at reducing N in exhaust gas from combustion of pulverized coal.
It is proposed that Ox reduction be achieved through a combination of the combustor's □ arrangement, structure, supply amount of combustion air, etc.

In a method of combusting coal that has been pulverized and separated into coarse powder and fine powder, a coarse powder burner is located upstream of the combustion gas flow, a fine powder burner is located downstream of the coarse powder burner, and an air supply port is further downstream of the coarse powder burner. and setting the air ratio of the coarse powder burner to be larger than the air ratio of the fine powder burner to measure NOx 8 yuan, and aiming the axis of the coarse powder burner diagonally downward to extend the combustion time of coarse powder combustion of coal. Low N
It is characterized by a low NOXi pulverized coal combustion method that performs Ox combustion.

A value of 70% or more passing through a 200 mesh is used as a numerical value to define the degree of pulverization of pulverized coal. - As an example, the relationship between the mesh and the opening of the sieve is as follows.

Table 1 The values for the fuel ratio (fixed carbon/volatile matter) of the pulverized coal that passed through this sieve are shown in Table 2 below.

Table 2 From the above table, the finer the coal is, the lower the ratio of fixed carbon to the volatile content is, and the larger the contact area with oxygen, meaning rapid combustion. This means that the amount of fixed carbon is large, which means that the combustion time, that is, the residence time in the furnace, needs to be increased.

Regarding a means for reducing NOx by separating pulverized coal into fine powder and coarse powder, an invention disclosed in JP-A-55-12311 is disclosed. This invention is a fine powder.

The coarse powder mixture is separated during pneumatic transport into two independent particles.
The present invention discloses a separation means for feeding individual burners.

The present invention proposed by the inventors takes this a step further and aims to achieve combustion with even lower NOx.

First, for the coarse powder that is separated and supplied, the air ratio (actual supplied air amount/theoretical combustion air amount) is set to 0.85 to 1.1, and the coarse powder is almost completely combusted.

In the fine powder burner located downstream of this coarse powder burner, more stable combustion is possible due to its high volatile content, so the air ratio is set to 0.6 to 0.8 to form a reducing atmosphere, and the nascent reducing components are generated. This reduces the NOx generated by the upstream coarse powder burner and turns it into harmless NJ. An air supply port is provided downstream of this fine powder burner to ensure complete combustion of unburned carbon in the exhaust gas.

In this case, it is desirable that the ratio of the amount of fuel supplied to the coarse powder burner and that of the fine powder burner is 50:50, that is, approximately the same amount of pulverized coal is supplied to each burner.

The present invention will be explained in detail below with reference to the drawings.

In FIG. 1, coarse powder burners 2. Fine powder burner 3.
An air supply port 4 is provided upward along the wall surface. Coarse powder of coal, which is the fuel, is supplied to each burner through a pipe 2a, and fine powder is supplied to each burner through a pipe 3a, together with combustion air from a forced air blower 5.

Further, air is supplied from the air supply port 4 through a pipe line 6 to combust unburned components in the combustion gas.

A part of the exhaust gas from the boiler 1 is sucked by the recirculation 7 and is supplied to the coarse powder burner 2 through the pipe 2b, and then to the supply air pipe of the air supply port 4 through the pipe 4b, thereby reducing the Ol pressure in the combustion atmosphere in the furnace. The aim is to achieve low NOx combustion. A part of the recirculating gas from the recirculating gas fan is supplied from blow-off nostles 8 and 9 in the gas retention section on the bottom side of the furnace. This has the effect of completely burning the coarse powder and preventing the generation of soot. In this case, approximately 50% of the total amount of supplied fuel is supplied from the coarse powder burner 2, and the air ratio (actual supplied air amount/theoretical combustion air amount) is 0.85.
or 1.1. As an example of the structure of the burner, as shown in FIG. 2, a flame-holding oil-fired burner 102 is located at the axis of the coarse powder burner 2, and a flame-holding plate 202 is attached to the end thereof. The exhaust gas drawn out from the exhaust gas duct of the boiler is ejected from an annular nozzle 302 surrounding the coarse powder burner by the recirculation fan 7 so as to surround the flame. Further, from the viewpoint of flame stabilization and to increase the combustion gas velocity, recirculation gas may be supplied to the combustion air supply line as is normally done.

Further, a pipe 51 having a damper 52 may be provided between the combustion air supply pipe and the recirculation gas supply pipe to supply a mixed gas of recirculation gas and combustion air.

Figure 3 shows a case in which the coarse powder burner 2' is mounted obliquely to the furnace wall so that its fine point is directed toward the bottom of the furnace, so that the flame path is long and the combustion time of unburned components in the flame is extended. The recirculating gas jet nozzle 10 is positioned above the coarse powder burner 2' to form a recirculating gas film between the flame of the fine powder burner 3 and reduce NOx.

Figure 4 shows the case where the coarse powder burner 2 is located at the lowest stage of the furnace wall, the medium-coarse powder burner 21 is placed above it, the fine powder burner 3 is further above it, and the air supply port 4 is placed above it. The aim is to make it easier to control burner combustion to reduce Hog. Approximately 30% of the total amount of fuel is supplied to the coarse powder burner 2 at the lowest stage, and the air ratio is adjusted to 0.85 to 1.
1, approximately 20% of the total fuel amount is supplied to the medium-coarse powder burner 21 to set the air ratio to 0.75 to 0.9, and approximately 50% of the total fuel amount is supplied to the fine powder burner 3 on the upper stage for reduction. The idea is to create an atmosphere and remove NOx. Figure 3,
Reference numeral 16 in FIG. 4 is a device for ensuring boiler safety by allowing immediate ignition even when the pilot burner (oil combustion) experiences load fluctuations and the flame is blown out.

FIG. 4 is a diagram showing a system of a pulverized coal supply device using a ball mill or the like. The coal is transferred from the coal hopper 13 to the weighing machine 13a.
is supplied to a mill, for example, a ball mill 12. Pressurized air from the forced air blower 11 supplies the fine powder pulverized by the ball mill 12 to the first cyclone 14 via the pipe 12a. The coarse powder collected by the first cyclone is supplied to the coarse powder burner 2 with combustion air from the forced air blower 5.

The medium-coarse pulverized coal and fine powder sent out from the first cyclone 14 are supplied to the second cyclone 15 via a pipe 14a, and the collected medium-coarse pulverized coal is supplied to the medium-coarse powder burner 21 via a pipe 21a. The pulverized coal is supplied from the second cyclone 15 to the pulverized burner 3 via the pipe line 15a and is combusted in the furnace.

Here, fine powder means 200 mesh passing pulverized coal, medium coarse pulverized coal means 1
Coarse powder coal that passes 00 mesh refers to fine powder coal that passes 50 mesh.

Figure 5 shows a furnace with a width of 4200 mm and a depth of 3000 mm, in which pulverized coal has been sieved in advance and separated into fine powder, medium-coarse powder, and coarse powder, and the burner arrangement is similar to that in Figure 4.

The diagram shows the case where the furnace outlet 02% is plotted on the horizontal axis and the % of unburned content is plotted on the vertical axis when the coal is supplied to an experimental furnace with a furnace height of 9600 mm and combusted. The curve (B) shows the measured values when pulverized coal is separated into fine powder and coarse powder by the means of the present invention and then burned. .

As can be seen from this figure, the burner arrangement shown in the embodiment allows low NOx combustion to be achieved by separating coarse powder and fine powder during pulverized coal combustion and burning the pulverized coal.

[Brief explanation of drawings]

FIG. 1 is a piping system reading diagram according to the present invention, and FIG. 2 is a vertical sectional view showing an example of a burner device used in the present invention.
Fig. 3 is a piping system reading diagram showing another embodiment of the present invention, Fig. 4 is a piping system reading diagram of an apparatus according to the present invention when using a medium-coarse powder burner, and Fig. 5 is similar to Fig. 4. It is a drawing showing numerical values of residual unburned matter in a corresponding experimental reactor. 1...Boiler 2...River/coarse powder burner 3...
...Fine powder burner 4...Air supply port 21
・・・・・・Medium coarse powder burner 5・・・・・・Forced blower 7・・・・・・Recirculation 7 ゛Figure 1Figure 3 (1, v

Claims (1)

[Claims] 1. In a method of combusting coal that has been pulverized and separated into coarse powder and fine powder, a coarse powder burner is located upstream of the combustion gas flow, a fine powder burner is located downstream of the coarse powder burner, and the A low NOx pulverized coal combustion method, characterized in that an air supply port is provided downstream, and the air ratio of the coarse powder burner is made higher than the air ratio of the fine powder burner. 2. The air ratio of the coarse powder burner is 0.85 to 1. ．． 1
and the air ratio of the fine powder burner is 0.6 to 0.85.
A low NOx pulverized coal combustion method according to claim 1, characterized in that: 3. The low NOx pulverized coal combustion method according to claim 1 or 2, characterized in that the ratio of the amount of fuel supplied to the fine powder burner and the coarse powder burner is approximately equal. 4. A patent characterized in that the coarse powder burner and the fine powder burner are provided on a vertical wall of a furnace, and the axis of the coarse powder burner is oriented obliquely downward with respect to the vertical wall to extend the residence time of combustion particles in the furnace. A low NOx pulverized coal combustion method according to any one of claims 1 to 3. 5. Coarse powder burners are provided in upper and lower stages on the vertical wall of the furnace, and coarse powder fuel is supplied to the lower burner, and medium-coarse powder fuel is supplied to the upper burner. 1
The low NOx pulverized coal combustion method according to any one of items 1 to 4. 6. The low NOx pulverized coal combustion method according to any one of claims 1 to 5, characterized in that recirculation gas is supplied to surround the coarse powder burner flame. 7. The low NOx pulverized coal combustion method according to any one of items 1 to 6, characterized by supplying combustion air and/or retifa gas from the bottom of the furnace.