JPS61285306A - Burning method for pulverized carbon fuel - Google Patents

Abstract

PURPOSE:To enable to make turn-down ratio large by supplying a part of high density fuel to a burner having a fuel injection cylinder in such manner that at the end of fuel supply tube, fuel separation unit is installed. CONSTITUTION:Pulverized coal and air in a supply tube 25 are swirled by a cyclone 19 as a fuel separation device and a part of gas flow containing ultrafine pulverized coal flows into a cyclone inner cylinder 30 and is injected and burnt from a vent burner 23 via a vent tube 20, however, most part of pulverized coal is centrifugally separated and gathered in the inner wall side of the cyclone and injected along the wall sirling toward an end opening part of a injection by cylinder 5. At this time, the density of pulverized coal is controlled by a flow controlling device with no relation to burner load variation. Also, as the vent tube is essentially an air vent, density of coal is controlled even when load is low or high.

Description

[Detailed Description of the Invention] <Industrial Field of Application> The present invention relates to a method for burning pulverized carbon fuel such as pulverized coal, and in particular, a method that performs a wide range of load control even when burning high fuel ratio coal or oil coke. Regarding combustion methods that can be used.

<Prior art and its problems> For example, in boilers for thermal power plants, conversion from petroleum fuel to coal fuel is actively being carried out due to changes in fuel conditions. In this case, the power generation load of the power station varies considerably due to fluctuations in the power demand of the power station, such as seasonal differences between summer and winter, and differences between weekdays and holidays. Recently, as the amount of power generated by nuclear power generation has increased, it has become necessary to use nuclear power generation as a base load and to vary the load of large boilers for thermal power plants, which have conventionally been operated at a constant load as a base load.

Figure 2 shows a conventional pulverized coal combustion system.

Fuel is supplied from the coal bunker 41 to the pulverizer 45 via the coal reducer 43. In the coal pulverizer 45, the fuel is pulverized and dried by hot air from the primary air 7 amp 51.
Transfer takes place. The pulverized coal is supplied to the furnace from the pulverized coal pipe 46 through the pulverized coal burner 48, and is mixed and burned with combustion air sent from the wind duct 47 and the wind box 50.

In the figure, numerals 32 and 33 are primary and secondary air preheaters, and 40 is a blower.

In the above device, fuel coal is supplied to the pulverizer in proportion to its load factor, as shown in Figure 3.
-The secondary air amount is controlled to maintain 70% of the maximum load air supply amount even when the pulverizer load rate is below 50%, in order to prevent pulverized coal from accumulating in the pulverized coal pipe and to prevent burner backfire. are doing.

Pulverized coal supplied into the furnace from some burners has a high ambient temperature in high load zones and a low ambient temperature in low load zones due to the influence of radiant heat from inside the furnace. Further, the ignition temperature and the time required to reach the ignition temperature (ignition time) vary depending on the properties of the fuel, that is, the volatile content, total moisture, and ash particle size contained in the fuel. FIG. 4 specifically shows these points.

In the high load area, the atmospheric temperature is high and the powdered coal concentration is high, so the ignition temperature is about 500% with the same volatile content, for example 30%.
Under the condition 'C, the ignition time is approximately 0.05 seconds, but in the low load range the ignition time is approximately three times as long as approximately 0.15 seconds. Here, the ambient temperature in the high load area is approximately 1200℃,
The powder coal concentration is o, 55, and the ambient temperature in the low load area is about 100.
0'c, and the powdered coal concentration is 0.3. In this way, in the low load range, the ignition time becomes longer, making it difficult to hold the flame, resulting in so-called blow-off combustion, resulting in a longer flame and unstable combustion, which further reduces the minimum load in pulverized coal-only combustion. Have difficulty. For this reason, it has sometimes become difficult to realize the lower loads required of boilers than ever before. In addition, it has been found that increasing the concentration of pulverized coal is more effective in terms of box reduction, but the pulverized coal concentration (0/A, coal/Air weight ratio) is
The limit is 0.6 to 0.7.

Purpose of the present invention The present invention was created in view of the above-mentioned problems, and can maintain an appropriate pulverized coal concentration at all times regardless of the burner load.
Therefore, it is an object of the present invention to provide a burner combustion method that can increase the turndown ratio.

Summary of the Invention In summary, the present invention provides a fuel separation device (especially preferably a cyclone separator) near the terminal end of a fuel supply pipe that conveys a mixture of powdered carbon fuel and a transportation gas, and in the separation device. The fuel mixture is separated into a mixture with a high fuel concentration and a mixture with a low concentration of the same, and the mixture with a high fuel concentration is supplied to the burner for combustion, so that the concentration of fuel supplied to the burner can be maintained at an appropriate level even under low load. This is a combustion method.

<Example> Examples of the present invention will be specifically described below.

In FIGS. 1A and 1B, reference numeral 5 denotes a pulverized coal injection cylinder, and numeral 19 denotes a cyclone separator provided at the base of this injection cylinder, that is, at the end on the pulverized coal inflow side.

Reference numeral 30 denotes a cyclone inner cylinder arranged within the cyclone separator 19 and configured to allow fluid in the separator to flow in the direction opposite to the flow of fluid in the pulverized coal injection cylinder 5. ° The cyclone inner cylinder 30 is connected to the pento burner z3 via the vent cylinder 20. 21 is a flow control device such as a damper disposed in the vent pipe, and 22 is a drive device for driving the flow control device. Further, the pulverized coal supply pipe 25 opens in the tangential direction of the side wall of the cyclone separator 19, as shown in FIG.

In addition, the code|symbol 3 is tertiary air, 4 is secondary air, 6 is a venturi formed in the injection cylinder, 11 is an ignition torch, 12 is a burner throat, 13 is a burner flame, 16 is a secondary swirl vane, 17 is 3 A secondary air register 18 is a secondary air register.

In the apparatus having the above configuration, the pulverized coal and conveying air (primary air) flowing from the pulverized coal supply pipe 25 form a swirling flow within the cyclone separator 19, and a part of the supplied pulverized coal has a particle size mainly of ultra-fine powder. It flows into the cyclone inner cylinder 30 as a gas flow containing distributed pulverized coal, passes through the bend pipe 2o, is injected from the pend burner 23, and is combusted. In addition, the mixture in the vent pipe 2° is filtered with a bag filter to recover the fuel.
The gas can be discharged into the atmosphere, or the mixture can be discharged into the coal bunker 41.

On the other hand, within the cyclone 19, most of the supplied pulverized coal is centrifuged and collected on the inner wall side of the cyclone separator 19. In this state, the separated pulverized coal flows along the wall surface while rotating toward the tip opening of the injection cylinder 5 and is injected. In other words, there are many ultrafine particles in the airflow flowing into the cyclone inner cylinder 30,
Moreover, the pulverized coal concentration becomes low, and conversely, the amount of gas from the injection tube 5 that flows into the inner tube 30 decreases, and the pulverized coal concentration relatively increases. Therefore, by adjusting the flow rate control device 21, the pulverized coal concentration can be maintained appropriately regardless of changes in burner load, and good combustion can be achieved. Note that since the vent pipe 20 is inherently capable of air venting, the pulverized coal concentration can be controlled not only during the above-mentioned low load but also during high load.

FIG. 5 shows an example of control using the above-described device.

In the figure, the pulverizer primary air volume is kept constant at about 70% when the load is 50% or less, as shown in FIG. Here, by adjusting the flow rate control device 21 to adjust the vent amount (flow rate supplied to the pento burner 23),
1), the amount of air at the burner port decreases, and the pulverized coal concentration relatively increases. Note that the symbol "a" indicates the case where the vent amount is larger than a, and the lower the load, the larger the vent amount is to maintain the pulverized coal concentration at a predetermined value.

With the above configuration, it is possible to widen the control range of the pulverized coal burner, and for example, in the case of the prior art, the minimum load can be reduced from about 40% to about 20%. Although the above embodiments have been described using pulverized coal as fuel, the present invention is not limited to pulverized coal fuel, but can be applied to oil≧ol coke, which is the residue obtained by extracting naphtha or gasoline from heavy oil. Needless to say.

<Effects> By implementing the present invention, the pulverized coal concentration in the burner can be adjusted regardless of the burner load, so the turndown ratio of the burner can be increased, and a burner with excellent controllability can be provided. .

In addition, the pulverized coal-containing gas is injected as a swirling flow from the injection tube, and the pulverized coal concentration is low in the center, and the surrounding area is supplied with a high concentration of pulverized coal, which has high ignitability and creates a high-temperature atmosphere in the center as well. Although the concentration is low, ignitability is improved, and the combustibility of the burner as a whole improves from this point as well.

The high-concentration fuel mixture separated by the separator passes through the venturi 6 to prevent the fuel from being uneven in the circumferential direction inside the injection tube 5, and to reduce the flow velocity of the mixture of fuel and gas (air) at the venturi section. rises, which helps prevent backfire.

The same purpose as described above can be achieved by narrowing the tip passage of the fuel injection tube 5 to increase the flow velocity.

[Brief explanation of the drawing]

FIG. 1(A) is a longitudinal sectional view of a burner for a fine powder bed showing an embodiment of the present invention, and FIG. 1(B) is a sectional view taken along line A-A in FIG.
Fig. 2 is a diagram showing the supply system of pulverized coal, Fig. 3 is a diagram showing the relationship between the amount of thermal coal and the amount of secondary air with the pulverizer load factor,
FIG. 4 is a diagram showing the relationship between ignition temperature and ignition time and volatile content, and FIG. 5 is a diagram showing the relationship between primary air volume and coal supply amount and pulverizer load factor. 5...Pulverized coal injection cylinder 19...Cyclone separator 20...
・Vent pipe 21...Flow rate adjustment device 23...Pent burner Figure 3 Figure 4 Volatile matter (momme daf

Claims (1)

[Claims] 1. In a method in which a mixture of powdered carbon fuel and a conveying gas is supplied to a burner and combusted, a fuel separation device is provided near the end of the fuel supply pipe that conveys the mixture, and a comparison is made in the separation device. The mixture is separated into a mixture with a high fuel concentration and a mixture with a low fuel concentration, and the mixture with a high fuel concentration is supplied to a burner with a fuel injection tube to be burned, and the mixture with a low fuel concentration is discharged through a vent pipe. A method of combustion of powdered carbon fuel characterized by: