JPS6030911A - Pulverized coal combustion device - Google Patents

Abstract

PURPOSE:To enable production of a minimum unburnt content in ash by means of a minimum mill power, by constituting a pulverized coal combustion device such that coal crushed by a crushing part is separated as pulverized coal by a classifier, and the separated coal is conveyed to a burner. CONSTITUTION:When fire-retardant pulverized coal is burnt, a unburnt content produced in the vicinity of an exhaust gas passage is increased, resulting in an increase in the metal temperature of a superheater 4. Detection of such metal temperature by means of a temperature detector 6 permits discrimination of burning coal being fire-retardant. In which case, through opening of a damper 23, a flow rate of a slit air F is increased. As the flow rate of the slit air F increases, a bypass amount shown by an arrow mark G increases, and thereby, a time, for which pulverized coal stays in a mill 9, is increased, the grain size of the pulverized coal is decreased according to the staying time, and a unburnt content in ash is decreased. On the contrary, flammable coal is burnt early and therefore, the metal temperature of the superheater 4 is decreased over that in the case of fire-retardant coal. The metal temperature is detected by a temperature detector 6, and this enables to discriminate that coal under combustion is flammable, and in this case, with the damper 23 closed, the flow rate of the slit air F is decreased and a flow rate of a throat air B is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulverized coal combustion device, and more particularly to a pulverized coal combustion device in which pulverized coal pulverized in a mill is burned in a furnace.

The problem of emitting unburned matter in ash in pulverized coal combustion is a combustion problem determined by the amount of ash in the coal and the combustion efficiency of the coal. Studies are being conducted based on combustion theory.

The following equation is known as an arrangement of factors that affect the unburned content in the ash.

Here, Y is an index indicating the degree of combustion, and the larger Y is, the more the combustion progresses and the unburned content decreases. The others are as follows.

α: Coal expansion rate.

Ks: Burning rate coefficient of coal P: 01 Partial pressure d: Particle size of char In the equation, α, f(FR), and ρ8 are constants determined by the coal, and θ is determined by the furnace shape. In addition, is determined by the properties of the coal and the ambient temperature; the higher the temperature, the faster the combustion rate;
In terms of partial pressure, the higher the 02 partial pressure, the faster the combustion rate. but,
Generally, when the temperature and partial pressure are high, NOx is high (because
There are of course limits to that.

Therefore, the only variables for Y are the fine particle sizes shown by d and xw, and the unburned content in the ash increases or decreases depending on the size of the fine particles.

FIG. 1 shows the influence of the sieve passage percentage on the unburned content in the ash. From this graph, it can be seen that the larger the pass percentage and the finer the particle size, the lower the unburned content in the ash. Therefore, in the case of flame-retardant coal, the mill power should be increased (
Reducing the particle size by reducing the particle size is an effective means to independently reduce the amount of unburned matter in the ash.

Incidentally, the properties of available coal vary widely, and the combustion characteristics and crushability vary greatly depending on the properties. In general, coal with a high combustion ratio, or flame retardancy, has the property of being easily pulverized, and conversely, coal with a low fuel ratio, or flammability, has the property of being difficult to pulverize. In conventional pulverized coal combustion equipment, the mill is operated under constant operating conditions regardless of the properties of the coal, so when using coal with a high fuel ratio that is easy to crush, the mill power is reduced, but the pulverized particle size cannot be made sufficiently fine. As a result, the amount of unburned matter in the ash after combustion increases significantly.

On the other hand, in the case of low-fuel coal that has poor pulverization properties, making the fineness of the powder finer than necessary is a waste of mill power. It is economical to assemble the car.

In this way, in conventional pulverized coal combustion equipment, the mill is operated at full capacity under constant operating conditions regardless of the properties of the coal, which results in wasted mill power. There were drawbacks such as not being able to do so.

An object of the present invention is to provide a pulverized coal combustion apparatus which eliminates the above-mentioned drawbacks of the prior art and obtains a minimum amount of unburned content in the ash with a minimum mill power. To achieve this objective, the present invention provides a mill for pulverizing the supplied coal into pulverized coal, which is equipped with a pulverizing section and a classifier, a furnace for burning the pulverized coal, a burner, and the pulverized coal in the pulverized section. In a pulverized coal combustion apparatus that separates coal into coarse powder coal and pulverized coal by the classifier and transports the separated pulverized coal to the burner, the pulverized coal is transported to the mill and the pulverized coal to the classifier 6 A conveying gas jetting means and a bypass gas jetting means for re-supplying the crushed coal to the crushing section without going through the classifier are provided, and the amount of gas discharged by the bypass gas jetting means is controlled by the exhaust gas temperature of the furnace. It is characterized by the fact that it is made to do so.

Hereinafter, the present invention will be explained in detail based on FIGS. 2 to 4.

FIG. 2 is a schematic diagram of the pulverized coal combustion apparatus according to the present invention. In this figure, 1 is a furnace, and 2 is II+l of the furnace 1.
3 is a wind box for supplying combustion air; 4 is a super heater provided in the exhaust gas passage; 5 is a reheater also provided in the exhaust gas passage; 6 is the metal temperature of the super heater 4; This is a temperature detection device that detects temperature.

Further, 7 is a hopper that supplies raw coal, 8 is a coal feed pipe leading to the hopper 7, 9 is a mill that grinds the coal supplied from the coal feed pipe 8 into pulverized coal, and 10 is pulverized coal that has been pulverized by the mill 9. to the burner 2 (a conduit).

FIG. 3 is a sectional view showing the internal structure of the mill 9, in which the mill 9 includes the coal feed pipe 8, the crushing section 11, and the power transmission section 12.
, a classifier 13, a fine/pulverized coal outlet pipe 14, a foreign matter discharge port 15, and an air supply pipe 16. Said hopper 7
The supplied coal is supplied to the inside of the crushing section 11 through the coal feed pipe 8 as shown by arrow A. This crushing section 11 includes a lower ring 1 which is fixedly rotated and connected to the power transmission section 12.
7, a plurality of balls 18 that revolve and rotate on the lower ring 17, and a fixed upper ring 19 that is pressurized by a spring or the like above the ball 18. The feed coal supplied from the lower end of the coal feed pipe 8 is transported to the crushing section 11
It is pulverized by the lower ring 17 and the pole 18, and airflow-carried upward by the primary air from the air supply a16.

As shown in FIG. 4, the inside of this air supply pipe 16 is divided into two by a partition plate, and between this partition plate and the lower ring 17 there is a throat 2 which generates a vertical flow, and Oblique flow occurs on the side slope part.S') ノ) 2
2 are formed respectively. In the air supply pipe 16, primary air with a low partial pressure, which is a mixture of exhaust gas from the furnace 1 and cooling air, is supplied, and this primary air is blown upward through the throat 21 as shown by arrow B. and the crushing section 1
The coal pulverized in step 1 is passed through the classifier 13 as shown by arrow C.
Send it inside.

The pulverized coal fed into the classifier 13 is separated into pulverized coal and coarse pulverized coal.
The coarse coal is conveyed to the burner 2 from the lower part of the classifier 13 through specific gravity separation as shown by arrow E.
It is re-supplied to the inside of 1 and crushed into pulverized coal.

On the other hand, the primary air supplied into the air supply pipe 16 is
As shown by the arrow), the ball 18 passes through the slit 22.
It is also ejected diagonally towards the direction. The air flow ejected from this slit 22 causes the coal crushed in the crushing section 11 to be crushed into the classifier 13-! : without being conveyed, it is re-supplied inside the crushing section 11 through a bypass path shown by arrow G. When the flow rate of pear air F ejected from the slit η increases, the bypass amount of the crushed coal also increases, so the classification efficiency of the 5-classifier 13 improves, and conversely, the flow rate of the slit air F decreases and the flow rate of the throat air B increases. If the amount increases, the classification efficiency of the classifier 13 will deteriorate (and a part of the coarse pulverized coal will be conveyed to the burner 2 together with the pulverized coal.The flow rate adjustment of this slit air/F is performed by a damper shown in Fig. 2. This damper swamp is connected to the temperature detection device 6.

In the pulverized coal combustion apparatus as described above, when pulverized coal of IE combustibility is being combusted, the metal temperature of the superheater 4 increases because the amount of unburned coal near the exhaust gas passage increases. By detecting this metal temperature with the temperature detection device 6, it can be determined that the burning coal is flame retardant, so in this case, the damper is opened to increase the flow rate of the slit air by 1. . When the flow rate of slit air 1゛ increases, the amount of bypass shown by arrow G in Fig. 3 increases, so the residence time of the pulverized coal in the mill 9 becomes longer, the particle size of the coarse pulverized coal becomes finer, and the unburned content in the ash increases. decreases.

On the other hand, since easily flammable coal burns quickly, the metal temperature of the superheater 4 is lower than when using flame-retardant coal. By detecting this metal temperature with the temperature detection device 6, it can be determined that the burning coal is easily combustible, so in this case, the damper 23 should be closed and the slit air
1 and increase the flow rate of throat air B. When the visibility of the throat air B increases, a portion of the coarse pulverized coal blown upward by the throat air H is also mixed with the pulverized coal and conveyed to the burner 2, so the residence time of the pulverized body in the mill 9 is shortened. As a result, the motion of Mill 9 is low, and the signal is heard.

In addition, in the above-mentioned embodiment, a method for determining the flame retardance and combustibility of coal is described as detecting the metal temperature of Super Heat ←4, but the invention is not limited to the above-mentioned embodiment. It is also possible to detect the metal temperature of the reheater 5 or the gas temperature of the air heater, etc., and adjust the flow rate under the slit air based on this temperature.

In addition, if the primary air supplied to the air supply pipe 16 is limited to a mixed air of υ gas and cooling air, the heating air raid heated by an air heater etc.
6 may be supplied.

As described in detail above, the pulverized coal combustion device of the present invention detects the metal temperature of the super heater or reheater, the exhaust gas temperature at the air heater inlet, etc., and controls the Temir bypass gas ejection amount based on this temperature. The amount of unburned matter in the ash can be kept to a minimum with the minimum necessary mill power.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the relationship between the percentage passing through the sieve and the unburned content in the ash, Fig. 2 is a schematic diagram of the pulverized coal combustion apparatus according to the present invention, and Fig. 3 is the internal structure of the mill according to the present invention. FIG. 4 is an enlarged sectional view of the main part of FIG. 3. 1...furnace, 2...burner, 4...
...Super heater, 5... Reheater, 6.
...temperature detection device, 9...mil, 10.
...Conduit, 11...Crushing section, 13...
...Classifier, 16...Air supply pipe, addition...
・Partition plate, 21...S0-), 22...
Slit, le... song damper. Figure 1

Claims (1)

[Claims] A mill for pulverizing the supplied coal into pulverized coal is provided with a pulverizing section and a classifier, a burner is provided in a furnace for burning the pulverized coal, and the coal pulverized in the pulverizing section is separated into coarse pulverized coal and pulverized coal by the classifier. In the pulverized coal combustion apparatus, the pulverized coal is separated into pulverized coal and the separated pulverized coal is conveyed to the burner. The pulverized coal combustion is characterized in that a bypass gas jetting means is provided to re-supply the pulverized gas to the pulverizing section without using a vessel, and the amount of gas discharged from the bypass gas jetting means is controlled by the exhaust gas temperature of the furnace. Device.