JPH05180413A - Fluidized bed combustion boilers - Google Patents

Abstract

PURPOSE:To obtain a fluidized bed boiler which is capable of inhibiting the generation of NOx and SOx and controlling the temperature of a fluidized bed. CONSTITUTION:A denitration area is formed according to each function in a gasification primary combustion area 22, a secondary denitration combustion area 23, a third high temperature perfect combustion area 24 and a furnace upper part outlet 25 laid out in a furnace 21 having a fluidized bed 28 which serves as a foam type fluidized bed where all the areas are directed from the lover part of the furnace at the upper part of the furnace. For example, coal, oil, gas and other various kinds of wastes are used as a fuel 26 under the optimum condition of each process while Line stone or the like is used as a desulfurizing agent 27, which makes it possible to carry out excellent forming type fluidized bed combustion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluidized bed combustion boiler of a fluidized bed type for a prime mover product.

[0002]

2. Description of the Related Art In bubble-type fluidized bed combustion, conventionally, it was possible to suppress the generation of NOx by introducing air in multiple stages, but since desulfurization is carried out in the bed, it is difficult to suppress both NOx and SOx. there were. Further, there was no control mechanism for the fluidized bed temperature, and it was difficult to cope with changes in fuel, boiler load, etc.

FIG. 2 shows an embodiment of a conventional fluidized bed boiler. As shown in FIG.
Is charged and the fluidized bed 13 is formed. Coal 14 as fuel is put into the fluidized bed 13 and desulfurization agent (limestone etc.)
Combustion and desulfurization reaction proceed in the layer with 15.

The secondary air 16 is introduced from the middle point of the furnace 11. However, if this amount is increased to suppress NOx, the air ratio in the fluidized bed is lowered and the desulfurization reaction is difficult to occur. The combustion gas exiting the furnace 11 is cooled by the furnace upper heat transfer surface 17 and the convection heat transfer surface 18, and is discharged to the atmosphere through the dust collector. On the other hand, the unburned matter separated from the gas is
It is put into the fluidized bed through the unburned ash recycling 19.
Inside the fluidized bed 13, an in-bed tube 20 is installed to control the bed temperature.

[0005]

By the way, in the bubble type fluidized bed combustion system, the two-stage combustion is conventionally adopted as the NOx reducing means. However, when the two-stage combustion is performed, the air ratio in the fluidized bed is increased. There is a problem that the desulfurization reaction due to limestone, which is a reaction in an oxidizing atmosphere, is reduced.
Further, since fluidized bed combustion is generally low temperature combustion at 800 to 900 ° C., there is a problem that a large amount of N ₂ O is generated and the temperature is not sufficient for decomposition of dioxin.

In view of the above problems, the present invention is NOx, SOx
An object of the present invention is to provide a fluidized bed combustion boiler capable of controlling the temperature of the fluidized bed while suppressing the occurrence of

[0007]

The structure of the fluidized bed combustion boiler according to the present invention which achieves the above-mentioned object is composed of oil, oil, gas,
A fluidized bed combustion type boiler that uses various wastes as fuel and uses limestone as a desulfurizing agent, and has a dense layer that becomes a bubble type fluidized bed at the bottom of the furnace, and the air ratio of the rich layer is theoretically burned. A gasification primary combustion zone in which a reducing atmosphere having an air content of 0.5 to 0.8 is formed, and a secondary air inlet is provided on the layer,
The air ratio after the secondary air is charged is 0.8 to the theoretical combustion air amount.
A secondary denitration combustion region in which a NOx decomposition region is formed as 1.0, and a tertiary air inlet is provided above the secondary denitration combustion region,
A third high temperature complete combustion region in which N ₂ O and dioxin decomposition regions are formed due to an increase in atmospheric temperature due to unburned gas combustion
A heat transfer tube group is installed at the exit of the furnace so that the gas flow velocity of the heat transfer tube is higher than the superficial velocity of the lower combustion furnace, and the superficial velocity at the exit of the heat transfer tube group is set to be slower than the superficial velocity of the lower combustion furnace. It is characterized in that it comprises a desulfurization zone in which a region where particles are retained is formed in the upper part of the heat tube group and a desulfurization reaction zone having an atmospheric gas temperature of 800 ° C to 900 ° C is formed by appropriately selecting a heat transfer area. .

[0008]

In the aforesaid construction, in the bubbling fluidized bed region, 0.5 to 0.8 times as much primary air as theoretical combustion air is introduced and gasification combustion is carried out in a reducing atmosphere. The unburned gas guided to the upper side of the fluidized bed is partially burned by the secondary air introduced into the bed to form a high-temperature reducing atmosphere with an air ratio of 0.8 to 1.0, and the NOx reduction decomposition reaction is performed. proceed. The residual unburned gas after the introduction of the secondary air is burned by the introduction of the tertiary air to form a high temperature oxidizing atmosphere, and promotes the decomposition of N ₂ O and dioxin. The combustion gas at the furnace outlet contains oxygen, but is in a high temperature state, and needs to be cooled to a temperature suitable for the desulfurization reaction. The cooling surface installed at the furnace outlet has the purpose of cooling this gas and the role of dividing the combustion furnace and the desulfurization section. The fine particles containing limestone that have risen from the lower part of the furnace pass through the cooling surface of the furnace outlet and reach the desulfurization zone in the upper part of the furnace. The gas velocity in the cooling surface is dimensioned to be faster than that in the lower part of the furnace, and the gas velocity at the outlet of the cooling surface is dimensioned to be slower than that in the lower part of the furnace. The part repeatedly falls and rises above the cooling surface. Then, a group of dense fine particles containing limestone is formed in the upper part of the furnace, and the temperature atmosphere in this part is adjusted to 8
By maintaining the temperature at 00 to 850 ° C, the desulfurization reaction can be promoted.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a fluidized bed boiler according to the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram of a fluidized bed boiler according to this embodiment. As shown in the figure, in the furnace 21 having a dense layer that is a bubble type fluidized bed, the gasification primary combustion zone 22, the secondary denitration combustion zone 23, and the tertiary high temperature complete combustion zone from the lower furnace to the upper furnace. A combustion zone 24 and a desulfurization zone 25 are formed at the upper outlet of the furnace for each function. For example, coal, oil, gas, various wastes, etc. are used as fuel 26, and limestone etc. are used as desulfurization agent 27. Burning.

In the gasification primary combustion zone 22, a bubble type fluidized bed 28 is formed as a rich layer, and the injected fuel such as coal 26 is combusted by the primary air 29 introduced therein. Here, the amount of the primary air 29 to be introduced is such that the air ratio of the rich layer is 0.5 to 0.8 of the theoretical combustion air amount,
A reducing atmosphere is formed, and the coal 26 undergoes reducing combustion.
This range of air ratio is desirable for low NOx combustion.

The secondary denitration combustion zone 23 is provided with a secondary air inlet which is introduced from above the fluidized bed 28, and the secondary air ratio after injection is 0.8 to 1.0 of the theoretical combustion air amount. Air 3
0 is charged, a part of the unburned gas rising from the fluidized bed 28 is burned, and an optimal atmosphere for the denitration reaction is formed until the tertiary air is charged.

The tertiary high temperature complete combustion zone 24 is provided with a tertiary air injection port, and N due to an increase in atmospheric temperature due to unburned gas combustion.
₂ O and dioxin form a high temperature oxidizing atmosphere between the furnace upper heat transfer surface 32 by introducing the tertiary air 31,
It is completely burned.

The desulfurization zone 25 has a furnace upper heat transfer surface 32 composed of a heat transfer tube group provided near the furnace outlet, and the gas flow velocity of the heat transfer tubes is made faster than the superficial velocity of the lower combustion furnace and By making the superficial velocity of the heat tube outlet slower than the superficial velocity of the lower combustion furnace, a region where particles are retained is formed in the upper part of the heat transfer tube group. In other words, some of the particles that have risen in the furnace will fall and rise repeatedly above the cooling surface. Then, by appropriately selecting the heat transfer area, the desulfurization reaction zone having the optimum atmospheric gas temperature of 800 to 900 ° C. for the desulfurization reaction is formed up to the cyclone 33.

Therefore, the desulfurizing agent 27 scattered from the fluidized bed 28
Passes through the furnace 21 and the upper heat transfer surface 32 of the furnace and is decelerated in the desulfurization zone 25 at the outlet of the furnace to form a high-concentration desulfurization atmosphere, and SOx is adsorbed by the desulfurizing agent.

Particles scattered from the desulfurization zone 25 at the outlet of the furnace are collected by a cyclone 33 having a circulating particle hopper 34 at the lower end, stored in the circulating particle hopper 34, and then provided at the outlet of the circulating particle hopper 34. The circulating fluidized bed is controlled by the circulating particle adjusting valve 35, and the fluidized bed heat exchanger is introduced to the fluidized bed heat exchanger 37 for introducing the flowing gas 36.

Inside the fluidized bed heat exchanger 37, the inner tube 3
8 is installed, and the combustion temperature can be controlled by returning the circulating ash to the fluidized bed 28 after cooling.

The gas from the outlet of the cyclone 33 is guided to the dust collector and the chimney after cooling through the convection heat transfer surface 39. This is particularly effective in preventing corrosion of the heat exchanger when using as the fuel 26, for example, one that generates a corrosive gas when discarded.

[0018]

As described above with reference to the embodiments, the fluidized bed combustion boiler according to the present invention is configured to convert the combustion process of fuel into the gasification primary combustion zone, secondary denitration combustion zone, tertiary high temperature complete combustion zone and The process is divided into a desulfurization zone, and optimum conditions are realized for each process, and it is possible to control the fluidized bed temperature while suppressing the generation of NOx and SOx.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a fluidized bed combustion boiler according to this embodiment.

FIG. 2 is a conceptual diagram of a fluidized bed combustion boiler according to a conventional technique.

[Explanation of symbols]

 21 furnace 22 gasification primary combustion zone 23 secondary denitration combustion zone 24 third high temperature complete combustion zone 25 desulfurization zone 26 fuel 27 desulfurization agent 28 fluidized bed 29 primary air 30 secondary air 31 tertiary air 32 heat transfer over furnace Surface 33 Cyclone 34 Circulating particle hopper 35 Circulating particle adjusting valve 36 Fluidized bed heat exchanger Gas for fluidized bed 37 Fluidized bed heat exchanger 38 Inner layer tube 39 Convection heat transfer surface

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukihisa Fujima 5-717-1, Fukahori-cho, Nagasaki-shi, Nagasaki Sanhishi Heavy Industries Ltd. Nagasaki Research Institute (72) Kenji Tagashi, 5-717, Fukahori-cho, Nagasaki-shi, Nagasaki No. 1 Sanryo Heavy Industries Ltd. Nagasaki Research Institute

Claims (4)

[Claims] 1. A fluidized bed combustion type boiler that uses petroleum, oil, gas, various wastes, etc. as fuel, and uses limestone, etc. as a desulfurizing agent, and has a dense layer that forms a bubble type fluidized bed at the bottom of the furnace. Then, the air ratio of the rich layer is set to a gasification primary combustion region in which a reducing atmosphere having a theoretical combustion air amount of 0.5 to 0.8 is formed, and a secondary air inlet is provided on the layer to provide secondary air. The secondary denitration combustion region where the NOx decomposition region is formed by setting the air ratio after injection to the theoretical combustion air amount of 0.8 to 1.0, and the tertiary air injection port is provided at the upper part of the secondary denitration combustion region. A high temperature complete combustion region where N ₂ O and dioxin decomposition regions are formed due to an increase in ambient temperature due to combustion of combustion gas, and a heat transfer tube where the gas flow velocity of the heat transfer tube at the furnace outlet is faster than the superficial velocity of the lower combustion furnace Group, and set the superficial velocity at the heat transfer tube group outlet to be slower than that of the lower combustion furnace. A desulfurization zone is formed in which an area where particles are retained is formed in the upper portion of the heat transfer tube group, and a desulfurization reaction zone having an atmospheric gas temperature of 800 ° C. to 900 ° C. is formed by appropriately selecting a heat transfer area. Fluidized bed combustion boiler. 2. The fluidized bed combustion boiler according to claim 1, wherein a cyclone for collecting the desulfurizing agent and unburned components scattered from the desulfurization reaction zone at the desulfurization zone outlet, and a hopper for storing these particles under the cyclone. And a circulating particle adjusting valve for controlling a circulating amount of particles at the outlet of the hopper. 3. The fluidized bed combustion boiler according to claim 1, wherein the cyclone trapped particles are guided to a fluidized bed heat exchanger, and the combustion temperature can be controlled by recharging the cyclone particles into the furnace while controlling the amount of cooling particles. A fluidized bed combustion boiler characterized in that 4. The fluidized bed combustion boiler according to claim 1, wherein when a fuel generating corrosive gas is used, the high temperature part of the superheater is installed in a fluidized bed heat exchanger to generate particles and heat. A fluidized bed combustion boiler, which is replaced to prevent corrosion of the heat transfer tubes.