JPS591910A - Combustion method of fluidized-bed boiler - Google Patents

Abstract

PURPOSE:To improve the quality of combustion of an unburnt coal, to increase an utilizing factor of coal, and simultaneously to sharply lower a content rate of NOX in an exhaust gas, by a method wherein an ash content accompanied with a combustion exhaust gas is separated from the combustion exhaust gas to crush it, and the crushed ash content is fed in a space above a fluidized bed. CONSTITUTION:After an ash content 6 separated by a cyclone 5 is crushed by a crusher 11, is fed by the air or a combustion exhaust gas 13 into a space 4 above a fluidized bed 2 in a fluidized bed boiler 1. Since the ash content is crushed, an unburnt coal is increased in the surface area, in respect to a calcium series grain, an unreacted lime is brought to an exposing state, and when the unburnt coal is fed in the space 4, it is further burned, and the unreacted lime is used again for reaction on SOX. Further, through the reaction of NOX, generated by burning the coal, on an unburnt coal in the fine-crushed ash content, the NOX can be reduced to N2, and this permits the sharp reduction in the NOX content in an exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion method for a fluidized bed boiler, and more specifically, the present invention relates to a combustion method for a fluidized bed boiler, which improves the combustibility of unburned coal, the reaction rate of SO□ and lime, and enhances the NOx reduction effect. Concerning boiler combustion methods.

Conventionally, when burning coal in a fluidized bed boiler 1, as shown in FIG. For example, cyclone 6
Separate this separated ash into its! The fuel was returned to the fluidized bed 2 of the fluidized bed boiler together with air or combustion exhaust gas in a still state.

However, such conventional combustion methods have the following drawbacks.

(b) Despite attempts to return the ash separated by the cyclone to the fluidized bed to further burn the unburned coal in the ash, the combustion efficiency hardly improves.

(b) Furthermore, there is almost no improvement in the utilization rate of unreacted lime in the ash.

(c) There is almost no effect of lowering the NOX content in the combustion exhaust residue.

Therefore, the present invention has been made to eliminate such conventional drawbacks, and improves the combustibility of unburned waste, increases the utilization rate of lime, and at the same time reduces the NOX content in exhaust gas. It has the advantage of being able to significantly reduce the

That is, the fluidized bed boiler combustion method of the present invention is a fluidized bed boiler combustion method in which air is blown into lime powder containing coal to form a fluidized bed of the lime powder and the coal powder is combusted. This method is characterized in that the entrained ash is separated and pulverized, and the pulverized ash is supplied to the space above the fluidized bed while the coal powder is combusted.

The present invention will be described below based on embodiments shown in the drawings.

FIG. 2 shows the process of the present invention. Lime and coal powder, each having a particle size of 10 mm or less, are usually supplied in a mixed state or separately onto the gas distribution plate 6 of the fluidized bed boiler 1. On the other hand, a part of the air required for combustion is supplied through the gas distribution plate 3, and the coal powder is combusted in the presence of a large amount of lime while forming a fluidized bed 2, and the remaining air is used as secondary air to form the fluidized bed 2. upper space 4
Then, it is supplied to the downstream side of the supply position of the pulverized ash 6, which will be described later. Usually, a heat transfer tube 14 is embedded in the fluidized bed 2, and a heated fluid such as water is passed through the fluidized bed 2 to generate steam. The combustion exhaust gas 12 is sent to the upper space 4 of the boiler.
The ash 6 entrained in the exhaust gas is separated in the cyclone 5. The exhaust gas 7 from which the ash content has been separated is further removed by an electrostatic precipitator or a bag filter 8 to remove remaining ash content 9, and then released into the atmosphere as a clean exhaust gas 10.

On the other hand, the ash 6 separated by the cyclone 5 is transported to the crusher 11.
After being crushed in , it is supplied to the space 4 above the fluidized bed 2 of the fluidized bed boiler 1 by means of an air volume or flue gas 16 . Incidentally, the ash 9 can also be crushed in the same manner as the ash 6 and supplied to the boiler 1 in the same manner. Among the particles of ash 6 separated by cyclone 5, the outer layer is usually covered with caso formed by the reaction between lime and SOX, and the inner layer is covered with remaining unreacted calcium such as CaCO3 and CaO. There are coal-based particles and unburned coal-based particles (char).

In the present invention, since such ash is pulverized, the surface area of unburned coal increases, and unreacted lime of calcium-based particles is exposed, and in this state, the coal is introduced into the space 4 above the fluidized bed. Ru.

By the way, inside the fluidized bed, coal powder is burned under fluidized bed conditions using a part of the theoretical amount of air required for combustion, so reducing gas is generated, and the remaining air introduced further reduces the amount of reducing gas. It is being burned. In other words, the space above the fluidized bed is entirely reducing in the area close to the fluidized bed, and completely transitions to oxidizing after the introduction of secondary air.

When pulverized ash is supplied to the reducing part of the space N in such an atmosphere, NOx generated by combustion of coal in the fluidized bed 2 will be absorbed into the space 4 above the fluidized bed 2, especially in the part near the fluidized bed 2. N2, which is a reducing gas in a reducing atmosphere.
NH3 is reduced to N2 by reacting with CO, etc., and NOx +
C-+cox 10N2 Reduces NOX content in exhaust gas. NOx
The effect of lowering the content is more effective when the pulverized coal is supplied to the boiler using combustion exhaust gas, since the space above the fluidized bed is easily maintained in a reducing state. Next, the unburned coal is combusted again by the secondary air supplied to the space 4 on the downstream side above the fluidized bed 2, and the unreacted lime reacts with SOx generated by coal combustion and becomes caso4. form.

As described above, according to the present invention, the ash entrained in the flue gas of the fluidized bed boiler is separated and pulverized, and the coal powder is combusted while being supplied to the space above the fluidized bed. The unburned coal is further combusted, thus the coal combustion efficiency is significantly improved. However, since the unreacted lime in the ash particles is again subjected to the reaction with SOx, the utilization rate of lime is improved and the desulfurization effect of exhaust gas can be enhanced. Furthermore, in the present invention, NOx generated by coal combustion can be reduced to N2 by reacting with unburned coal in the pulverized ash, thereby significantly reducing the NOx content in exhaust gas. I can do it.

In this way, the present invention increases the combustion rate of coal supplied to a fluidized bed boiler, and at the same time reduces SOX and NOx in exhaust gas.
It has a remarkable effect of reducing

[Brief explanation of drawings]

Figure 1 shows the operating process of a conventional fluidized bed boiler, Figure 2 shows the operating process of a conventional fluidized bed boiler.
The figure is a diagram showing the operation process of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Fluidized bed boiler, 2... Fluidized bed, 4... Space above fluidized bed, 11... Pulverizer. Agent: Patent Attorney Shin Ogawa − Patent Attorney Ken Noguchi Teru Patent Attorney Kazuhiko Saishita

Claims (1)

[Claims] 1. In a fluidized bed boiler combustion method in which air is blown into lime powder containing coal and the coal powder is combusted while forming a fluidized bed of the lime powder. A combustion method for fluidized bed poultry 2, characterized in that the ash is separated and pulverized, and the pulverized ash is supplied to a space above the fluidized bed while the coal powder is combusted. 2. Claims that supply air less than the theoretical amount of air required for combustion of coal into the fluidized bed, and supply the remaining air to the space above the fluidized bed on the downstream side of the supply position of the crushed ash. The combustion method for a fluidized bed boiler according to item 1.