JPH02217703A - Combustion of coal of low volatile matter - Google Patents

Abstract

PURPOSE:To make it possible to regulate the concentration of pulverized coal in a fluid stagnation zone by providing a sleeve of cone shape with its end being larger than its inner portions in the throat of a main burner, forming the fluid stagnation zone on the side of the central axis of the sleeve, and separating the pulverized coal that is through the sleeve and pouring it into the fluid stagnation zone through a slit. CONSTITUTION:A mixture gas of pulverized coal produced by pulverizing a coal of low volatile matter and carrier air is conveyed to a cyclone 10 through a piping 30, and after part of the air that is separated in the cyclone 10 is extracted through a piping 32, the air is mixed with high temperature air and the flow rate and temperature of the air in the mixture gas are regulated to specified set values and then the mixture gas is delivered to a main burner 100 via a piping 33. And, a sleeve 600 that is connected to the piping 33 which delivers the mixture gas and cone-shaped with the diameter increasing along the central axis of the piping 33 as the diameter comes nearer to the end is provided in the throat of the main burner throat 100. The sleeve 600 forms a fluid stagnation zone 90 on the side of the central shaft and at the same time it is provided with a slit 601 in the shape of a louver which communicates with the fluid stagnation zone 90. The pulverized coal in the mixture gas which has passed through the sleeve 600 via the slit 601 is poured into the fluid stagnation zone 90.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the combustion of low-volatile coal, and particularly to low-volatile coal that is suitable for obtaining stable ignition and flame holding of low-volatile solid fuels such as anthracite. Concerning methods of burning coal.

[Conventional technology]

C in conventional combustion methods of low volatile coal such as anthracite.
In this case, 10 to 30% auxiliary fuel (mainly 1JJ) is used. In this case, 1 ignition and flame holding are maintained stably and continuously by the auxiliary fuel, so the means for transporting the anthracite and feeding it into the furnace are as follows: Without special consideration, it is usually fed downward into the furnace at low velocity by means of a stream with a slit shaped like a fish's tail.This method allows the anthracite to be used as a fuel for power generation boilers etc. without any problems. However, it uses a large amount of expensive oil fuel, which affects the power generation cost.Recently, attempts have been made to use a cyclone or a rotating burner.

However, since treatment for the extremely difficult-to-ignite characteristics of low-volatile coal is insufficient, it is necessary to take full advantage of the greatest feature of swirl burners, which is ``maintaining a stable combustion flame through the recirculation region within the flame.'' It wasn't.

In other words, in order to burn low-volatile coal such as anthracite, it depends on how quickly the temperature of the fine coal powder can be raised to the ignition temperature, but there is no technology that takes this point into consideration. There wasn't.

In other words, the problem with stable ignition and flame retention of anthracite coal is that its ignition temperature is extremely high, with some kinds of anthracite reaching over 800°C, and the ignition temperature of normal bituminous coal depending on the measurement method, being 400 to 450°C. On the other hand, the time required for ignition (hereinafter referred to as ignition time) is more than twice as long as when anthracite coal is thrown into a furnace using the same burner as bituminous coal.

Therefore, ignition can be reached within the recirculation region of the swirling burner jet, and it is extremely difficult to maintain the flame without the aid of auxiliary fuel.In order to compensate for this delay in ignition time and maintain stable combustion, oil The use of auxiliary fuels such as fuels has become essential for a wide range of boiler loads.

(Problem to be solved by the invention) In the conventional combustion method of low-volatile coal, the ignition temperature of anthracite coal is extremely high, causing a delay in ignition time, so auxiliary fuel is used, which is not economical. There was a problem with the quality.

The purpose of the present invention is to mix and supply high-temperature air at the minimum flow rate necessary for ignition to a group of fine particles of low-volatile coal, and to adjust the concentration of fine coal in a stagnation area near the burner throat. The object of the present invention is to provide a method for burning low-volatile coal.

[Means for solving the invention]

In order to achieve the above-mentioned objects, 1) the method of combustion of low-volatile coal according to the present invention is to transport a mixture of pulverized coal obtained by pulverizing low-volatile coal to a cyclone and air for transport, and to separate the air by the cyclone; After extracting at least a portion of the mixture, the mixture is configured to mix with high temperature air, adjust the flow rate and temperature of the air in the mixture to a predetermined set value, and send the mixture to the main burner.

Then, a cone-shaped sleeve connected to the pipe for feeding the air-fuel mixture and expanding toward the end along the center axis of the pipe is arranged inside the main burner throat, and the sleeve forms a stagnation area on the side of the center axis and a stagnation area. The pulverized coal in the mixture that has passed through the sleeve is injected into the stagnation area through the slit.

[Effect]

According to the present invention, as a combustion method for low-volatile coal, excess air in the mixture separated by a cyclone is extracted and high-temperature air is mixed, so that the air in the mixture is maintained at predetermined flow rates and temperature settings. is adjusted to A stagnation area is formed on the central axis side of the sleeve by providing a cone-shaped sleeve that widens toward the main burner throat and connected to a conduit for feeding the air-fuel mixture. On the other hand, the pulverized coal in the mixture that has passed through the sleeve is separated and injected into the stagnation area through a slit provided in the sleeve.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. 1 to 4.

As shown in Fig. 1, a mixture of pulverized coal obtained by pulverizing low-volatile coal and conveying air is conveyed to the cyclone 10 via a pipe 30, and a small amount of the air separated by the cyclone After some of the mixed gas is extracted through pipe 32, high-temperature air is mixed with the air mixture, the flow rate and temperature of the air in the mixture are adjusted to predetermined set values, and the mixture is sent to the main burner (main burner) via pipe 33. burner throat) 1oO.

Then, as shown in FIG. 2, a cone-shaped sleeve 600 connected to the pipe line 33 for feeding the air-fuel mixture and expanding toward the end along the central axis of the pipe line 33 is arranged inside the main burner throat 100. 600 forms a stagnation area 90 on the central axis side and is provided with a louver-shaped slit 601 communicating with the stagnation area 90, and the pulverized coal in the mixture that has passed through the sleeve 600 is injected into the stagnation area 90 through the slit 601. shall be taken as a thing.

The pulverized anthracite coal crushed in Mill 20 has a temperature of 80 to 110°C.
The coal is conveyed through the conduit 30 by low-temperature conveying air. The weight ratio of this mixture of pulverized coal and air is, for example, 0.
3 to 1.0 kg/kg, most of the pulverized coal is collected by the cyclone 10 installed on the downstream side, but dampers installed in each of the pipes 31 and 32 (not shown) The amount of air blown down to the pipe line 31 side is adjusted to 5 to 30% of the conveyance air flowing through the pipe line 3o. In this state, the temperature of the mixture flowing through the pipe 31 is 80 to 90°C, and the weight ratio of pulverized coal to air is 1.
5 to 5.0 kg/kg. This state quantity is a numerical value determined by the respective performances of the mill 20 and the cyclone 10, and cannot necessarily be said to be an appropriate state quantity when considering the turndown ratio of the burner and the optimum throat flow velocity. In order to improve this state quantity, high-temperature air supplied by the booth-up fan 50 via the conduit 51, for example from an air heater, becomes effective. By supplying this high temperature air.

For example, the state quantities of the air (high-temperature air) passing through the pipe 33 are set to a temperature of 200 to 300°C and a weight ratio of pulverized coal to air of 0.
It can be 5 to 2.0 kg/kg.

Optimal ignition conditions are obtained for at least the main burner 100. On the other hand, since the vent air flowing through the pipe 32 is not only unnecessary for ignition but also obstructs the formation of various ignition atmospheres, one solution is to supply it to the pair burner 200, for example, as shown in FIG. It is. Main burner 10
0 and the pair burner 200 are cell type operated bare, and due to the flame holding effect of the main burner 100, the pair burner 2
00 flame holding is supported.

As shown in FIG. 2, the main burner 100 has a stagnation area (dead space) 90 in its center.
It includes a cone-shaped sleeve 600 that widens toward the end (bluff body sleeve that widens toward the end), a louver-shaped slit (louver-type suction slit) 601, and a flame-holding ring 700 below the slit. In addition, since the pulverized coal particles develop in the pipe line 33 due to drifting and agglomeration (plowing between particles due to static electricity in a dry atmosphere), wear-resistant materials such as ceramics are used to disperse the particles unevenly. A dispersion plate 50 formed of
0 is set. And the main burner throw l-i-0
A turning register 70 is provided on the upper surface of the air conditioner 0, and an inner peripheral secondary air 71 and an outer peripheral secondary air 72 are separated by a guide sleeve 800 on the downstream side thereof.

Next, the operation of this embodiment will be explained.

First, the minimum required amount of air (-order air) is obtained by classification and collection in the cyclone. As shown in Figures 3 and 4, this flow rate is determined by the characteristics of the cyclone classification efficiency, and only the minimum flow rate of air necessary for igniting the pulverized coal particles is supplied to the area near the burner throat. This eliminates wasted time in heating excess air to the ignition temperature of the fuel. For this reason, the cyclone separates the pulverized coal/air mixture (usually N amount ratio <1.kg/kg) into gas and solids downstream of the mill, and the blowdown ratio is 5 to 30 with good cyclone classification efficiency. %, the pulverized coal particles are concentrated and separated in the cyclone without remaining in excess.

Next, by adding a hot air line, the temperature of the mixture of pulverized coal and conveying air is increased to minimize one ignition time, and sufficient momentum of the conveying air necessary for burner turndown is obtained. In other words, by mixing high-temperature air of 300"C or more, high-temperature and concentrated pulverized coal
air mixture can be obtained. This effect can be conceptually explained by the following equation.

Pulverized coal particle temperature; conveying air temperature = tp Mi1+, (initial condition) Furnace gas temperature = t4 1# Average radius of pulverized coal particles = γ Specific heat of pulverized coal particles = C Density of pulverized coal particles = ρ Pulverized coal Heat transfer coefficient of particles = α Ignition temperature of pulverized coal particles = Heat received by pulverized coal particles = Q If time is dz, dQ = α4πγ2θdz (0 = tg - tp) Also, as a result, pulverized coal particles When dQ temperature increases, d Q = -4, / 3πγ1Cρdθ, therefore a4ycy”θdz=-4/3sy3cρd 8dz=
-cpY/3a-dO/8 Therefore, ignition time 2 depends on the value of γ, but for ignition time 1, the conveying air temperature is 100℃
It can be seen from both equations that when the temperature is 300°C, the temperature is reduced by about half.

Furthermore, by creating an annular flared nozzle with a cone-shaped sleeve connected to the pipe line (high-temperature primary area) 33, a stagnation area (dead space) having a flared shape is formed on the side of the main burner central axis of the sleeve. , it becomes a high temperature stagnation area suitable for ignition and flame holding. The separated microparticles can then be selectively injected through the Roux suction slit.

In this manner, the internal secondary air and the fine particles mix in the recirculation region stabilized by the action of the strongly swirling secondary air that swirls strongly through the swirl register, and a stable flame is maintained.

The main burner shown in FIG. 2 is an embodiment in which the present invention is applied to a rotating burner, but it can also be easily developed into a conventional Finspur type intertube burner.

Further, although the cyclone and burner are placed separately in the above embodiment, it is also possible to incorporate the cyclone in the burner as long as the function is not lost.

〔Effect of the invention〕

According to the low-volatile coal combustion method of the present invention, by adjusting the amount of air in the air-fuel mixture to the minimum necessary amount and raising the temperature to a high temperature, the ignition time can be shortened without using auxiliary fuel, and the main burner throat can be Stable combustion is obtained by forming a stagnation area with the sleeve.

In addition to realizing oilless combustion of anthracite, the piping for auxiliary fuel can be reduced, and the width of the furnace can also be expected to be reduced.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is an enlarged cross-sectional view of the main part of the figure, FIG. 3 is an external view of the cyclone shown in FIG. 1, and FIG. 4 is a graph explaining the cyclone efficiency. lO...Cyclone, 33...Pipeline (mixture). 34.High temperature air, 90.Stagnation area, 1oO...
Main burner, 600...sleeve. 601 ・Slit. Figure 1

Claims (1)

[Claims] 1. A mixture of pulverized coal obtained by pulverizing low-volatile coal and air for transportation is conveyed to a cyclone, and after extracting at least a portion of the air separated by the cyclone, A method for combustion of low-volatile coal, comprising mixing air, adjusting the flow rate and temperature of the air in the mixture to predetermined set values, and feeding the mixture to a main burner. 2. A cone-shaped sleeve connected to a conduit for feeding the air-fuel mixture and expanding toward the end along the central axis of the conduit is arranged in the main burner throat, and the sleeve forms a stagnation area on the side of the central axis. 2. The low-volatile fuel according to claim 1, further comprising a louver-shaped slit communicating with the stagnation area, through which the pulverized coal in the mixture that has passed through the sleeve is injected into the stagnation area. Method of burning coal.