JPH065125B2 - Method for controlling unburned matter in fluidized bed combustion boiler - Google Patents

Description

The present invention relates to a method for controlling unburned components in a fluidized bed combustion boiler.

[Background of the Invention]

Generally, in this type of fluidized bed combustion boiler, when the load decreases, the temperature in the fluidized bed also decreases, the gas temperature also decreases, and the gas flow rate passing through the freeboard, that is, the flow velocity decreases, and the gas temperature further decreases. The phenomenon occurs. This means that the unburned amount of unburned material is reduced when the load is low, and when the load is low, the efficiency of the cyclone, which is governed by the flow velocity, deteriorates, and the collection efficiency cannot be secured, and the circulation amount decreases. By doing so, it will be further accelerated.

Therefore, in the conventional fluidized bed combustion boiler, there is a problem that when the load changes, the amount of combustion in the freeboard portion and the heat exchange action with the heat transfer surface become unbalanced and the temperature of the freeboard portion decreases. , Which will reduce the overall combustion efficiency of the boiler.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and solves the problems of the prior art by a simple and rational means, controls the gas flow rate according to the fluctuation of the load, and always obtains a constant flow velocity. Therefore, it is intended to provide a control method for maintaining the efficiency of any one of the cyclones and maintaining the temperature of the freeboard portion at the optimum temperature for desulfurization and denitration according to the load.

[Structure of Invention]

The configuration of the present invention that solves the problems of the prior art eliminates all or part of the contact heat transfer section to the cyclone of the fluidized bed combustion boiler, and eliminates the freeboard peripheral wall, the exhaust gas duct, and the high temperature cyclone at the furnace outlet connected to this. All or
Part of it has an adiabatic structure, and particles containing unburned ash scattered from the fluidized bed are kept at a high temperature until they enter the cyclone from the freeboard through the exhaust gas duct, and the particles of a relatively large size captured by the cyclone are retained. Repeatedly returning large particles to the freeboard via the circulation path at high temperature,
A means for reburning the unburned matter in the particles scattered from the fluidized bed, the high temperature cyclone at the furnace outlet and the rear heat transfer surface of the freeboard are connected to each other through a plurality of exhaust gas ducts, and the cyclone and rear transfer surfaces are connected to each other. The amount of gas passing through the hot surface is controlled by the damper for controlling the flow rate provided in the low temperature gas passage connected to the lower side of the rear heat transfer surface, and the amount of gas passing through is controlled by the freeboard section. Gas flow rate and cyclone collection efficiency should not change significantly even at low load,
A method for controlling unburned components in a fluidized bed combustion boiler characterized by controlling the temperature pattern of the freeboard part to a temperature suitable for desulfurization and denitration, and all or all of the contact heat transfer parts up to the cyclone of the fluidized bed combustion boiler. Part of the high temperature cyclone at the peripheral wall of the freeboard, exhaust gas duct and the furnace outlet connected to it, or part of it, has an adiabatic structure to free particles containing unburned ash scattered from the fluidized bed. It is kept at a high temperature from the board through the exhaust gas duct until it enters the cyclone, and the particles with a relatively large particle size captured by the cyclone are repeatedly returned to the freeboard through the circulation path in a high temperature state, and the fluidized bed A means for reburning the unburned components in the scattered particles, the freeboard is divided into a plurality of parts, and each of the divided freeboard parts has the exhaust gas A low temperature gas flow path for connecting a high temperature cyclone at the exit of the furnace and a rear heat transfer surface separately through a duct, and connecting the amount of gas passing through the cyclone and the rear heat transfer surface to the lower side of the rear heat transfer surface. By means of controlling the amount of passing gas for each by the damper for controlling the flow rate provided in the freeboard, it is possible to prevent the gas flow velocity in the freeboard part and the cyclone collection efficiency from changing significantly even under a low load. It is characterized by controlling the temperature pattern of the part to a temperature suitable for desulfurization and denitration.

〔The invention's effect〕

 According to the present invention, the following effects can be obtained.

(a) By adding a system to the freeboard part, which collects unburned ash scattered from the fluidized bed at high temperature and circulates it to the freeboard part, effective combustion of unburned ash can be measured, and the freeboard part is By keeping it at high temperature, desulfurization and denitration reactions are promoted, NOx emission value can be remarkably controlled, and desulfurization agent can be saved.

(b) By reducing the number of cyclones used during partial load, the gas flow velocity can be maintained within an appropriate range and the collection efficiency can be secured.

(c) Since the damper is installed in the low temperature part on the lower side of the rear heat transfer surface, the reliability of flow rate control is high.

(d) When the load changes, even if the balance between the combustion amount and the heat transfer surface is disturbed, the use of the freeboard part corresponding to the damper is interrupted by closing one of the dampers. And use the remaining freeboard part as it is, desulfurize the temperature pattern of the freeboard part,
The temperature can be controlled to be suitable for denitration.

[Embodiment I] (FIGS. 1 and 2) An embodiment of the configuration of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing the structure of a fluidized bed combustion boiler plant for carrying out the method of the present invention, FIG. 2 is a perspective view of the same as above, and FIG. 3 is a schematic view of an embodiment in which the freeboard portion is divided into a plurality of parts. The figure is a perspective view of the same as above.

First, the embodiment shown in FIGS. 1 and 2 will be described. 1 is a fluidized bed combustion boiler having a fluidized bed 2 (abbreviated as boiler), and 4 is a freeboard section. The free board 4
High temperature cyclones 6a and 6b are connected to the upper part of the high temperature cyclones 6a and 6b through a plurality of exhaust gas ducts 5a and 5b.
The particle discharge port provided in the lower part of the above and the freeboard section 4 are connected by the circulation paths 7a and 7b. Then, all or a part of the peripheral wall of the freeboard portion 4 has a heat insulating structure such as a furnace construction 8 that does not absorb heat, and a contact heat transfer portion up to the high temperature cyclones 6a, 6b continuing to the lower side of the freeboard portion 4. The heat insulating material 9 is lined on all or a part of the above. In addition, the circulation paths 7a and 7b are also provided with the heat insulating structure as described above.

On the lower side of each of the high temperature cyclones 6a, 6b, the rear heat transfer surfaces 11a, 11b of a boiler such as an economizer and an air heater are connected via exhaust gas ducts 10a, 10b having a heat insulating structure,
Flow rate control dampers 13a and 13b are respectively provided in the low temperature exhaust gas passages 12a and 12b connected to the lower side of the rear heat transfer surfaces 11a and 11b. The exhaust gas flowing through the exhaust gas passages 12a and 12b reaches a chimney through a second multi-cyclone, an air heater, a dust collector, etc. though not shown. Of course, the flow rate control dampers 13a and 13b are configured to detect load fluctuations and automatically control the opening degree by this control signal.

[Action]

Based on the above-mentioned boiler plant, the unburned-content control method of the fluidized bed combustion boiler according to the present invention will be described.

When the boiler 1 is operated and the fluidized bed combustion is started, the fluidized bed 2
Particles including unburned ash scattered from the freeboard portion 4 toward the freeboard portion 4 have no temperature drop because the entire or part of the peripheral wall of the freeboard portion 4 has the furnace construction structure 8. After a part of it is burned, the high temperature cyclone 6a, 6b passes through the exhaust gas duct 5a, 5b together with the exhaust gas.
, Where only relatively large particles are trapped. At this time, the exhaust gas duct 5 connected to the freeboard section 4
Since the heat insulating material 9 is lined in the a, 5b and the high temperature cyclones 6a, 6b, the temperature drop of the scattered particles in the exhaust gas is small.

Particles captured by the high temperature cyclones 6a and 6b are 800-1000 ℃
Circulating path 7 by gravity from high temperature cyclones 6a and 6b
It is returned to the lower part of the freeboard section 4 through a and 7b, and is reburned in the freeboard section 4. After that, this process is repeated, and the unburned components that jump out of the fluidized bed 2 are burned in the freeboard unit 4, and the unburned components that are sent to the high temperature cyclones 6a and 6b and captured are returned to the freeboard unit again. Is almost completely burned, and in addition to the heat insulation effect of the furnace construction 8 and the heat insulating material 9 described above, the freeboard portion 4 is kept at a high temperature to effectively perform desulfurization and denitration reactions, and SOz in exhaust gas The NOx emission value is greatly reduced.

Exhaust gas with fine particles captured by the high temperature cyclones 6a and 6b is
Through the exhaust gas ducts 10a, 10b having a heat insulating structure, the exhaust gas that reaches the rear heat transfer surfaces 11a, 11b of the boiler and undergoes heat exchange at low temperature (about 300 to 400 ° C) is exhaust gas flow paths 12a, 12b.
After that, processing is carried out in a known manner and the operation is continued.

If, for example, the load is reduced by 50% during such operation, the fluidized bed temperature is reduced, the exhaust gas flow velocity and the exhaust gas amount are halved, and the circulation amount by the high temperature cyclones 6a and 6b is decreased. As a result, the combustion amount and the rear heat transfer surface become unbalanced.

Therefore, the present invention uses one of the dampers according to the load detection signal.
Operate 13a or 13b so that one exhaust gas flow path 12a or 1
Blocks 2b and interrupts exhaust gas resulfurization.

As a result, the flow of exhaust gas becomes slow, but if the endothermic structure in the freeboard section 4 is small, it will not be affected so much and temperature control will not be performed while ensuring the collection efficiency of the high temperature cyclones 6a, 6b. sell.

[Example II] (Figs. 3 and 4) Reference numeral 1 in this example is a fluidized bed combustion boiler (abbreviated as "boiler") having a fluidized bed 2, and the freeboard of the boiler 1 is composed of a plurality of vertical partition walls 3. 4 freeboard parts
It is divided into a and 4b, and the following structure is the same as that of the first embodiment, so detailed description will be omitted.

[Action]

Based on the above-mentioned boiler plant, the unburned-content control method of the fluidized bed combustion boiler according to the present invention will be described.

When the boiler 1 is operated and the fluidized bed combustion is started, the fluidized bed 2
Particles containing unburned ash scattered from the freeboard parts 4a, 4b toward the freeboard parts 4a, 4b are free from the temperature drop because the whole or part of the peripheral wall of the freeboard parts 4a, 4b is the furnace construction structure 8. After a part of it burns in the board parts 4c and 4d,
Together with the exhaust gas, they enter the high temperature cyclones 6a, 6b through the exhaust gas ducts 5a, 5b, where only particles having a relatively large particle size are captured. At this time, since the heat insulating material 9 is lined in the exhaust gas ducts 5a, 5b and the high temperature cyclones 6a, 6b connected to the freeboard portions 4a, 4b, the temperature drop of the scattered particles in the exhaust gas is small.

Particles captured by the high temperature cyclones 6a and 6b are 800-1000 ℃
Circulating path 7 by gravity from high temperature cyclones 6a and 6b
It is returned to the lower part of the freeboard parts 4a and 4b through a and 7b, and re-burned separately in the freeboard parts 4a and 4b. After that, the high and low levels are repeated, and the unburned components that jump out from the fluidized bed 2 are burned in the freeboard units 4a and 4b, and the unburned components sent to the high temperature cyclones 6a and 6b are captured again in the freeboard unit. It is returned and burned almost completely, and in addition to the heat insulation effect by the furnace construction 8 and the heat insulating material 9 described above, the freeboard portions 4a and 4b are kept at a high temperature to effectively perform desulfurization and denitration reactions, SOx and NOx emission values in exhaust gas are greatly reduced.

Exhaust gas with fine particles captured by the high temperature cyclones 6a and 6b is
Through the exhaust gas ducts 10a, 10b having a heat insulating structure, the exhaust gas flow paths 12a, 12b reach the rear heat transfer surfaces 11a, 11b of the boiler, where heat is exchanged to lower the temperature (about 300 to 400 ° C).
After that, processing is carried out in a known manner and the operation is continued.

If, for example, the load is reduced by 50% during such operation, the temperature of the fluidized bed is reduced, the flow velocity of exhaust gas and the amount of exhaust gas are halved, and the circulation amount by the high temperature cyclones 6a and 6b is reduced, so that the freeboard section is reduced. As a result, the combustion amount and the rear heat transfer surface become unbalanced.

Therefore, the present invention uses one of the dampers according to the load detection signal.
Operate 13a or 13b so that one exhaust gas flow path 12a or 1
Block 2b and interrupt the flow of exhaust gas.

As a result, the operation of the freeboard 4a or 4b on the side where the flow of exhaust gas is interrupted is interrupted, and only the remaining freeboard unit 4a or 4b continues to operate 100%. Therefore, even if the use of one is stopped, the other continues to be used normally and the gas flow rate is maintained, so there is no overcooling in the freeboard section and the collection efficiency of the high temperature cyclone 6a or 6b is secured. The temperature can be controlled under the condition.

[Brief description of drawings]

FIG. 1 is a schematic view showing the structure of a fluidized bed combustion boiler plant for carrying out the method of the present invention, FIG. 2 is a perspective view of the same as above, and FIG. 3 is a schematic view showing the structure of another freeboard divided by partition walls,
FIG. 4 is a perspective view of the same. DESCRIPTION OF SYMBOLS 1 ... Fluidized bed combustion boiler, 2 ... Fluidized bed, 3 ... Partition, 4a, 4b
Freeboard part, 5a, 5b ... Exhaust gas duct, 6a, 6b ... High temperature cyclone, 7a, 7b ... Circulation path, 8 ... Furnace construction, 9 ... Insulation material, 10a, 10b ... Exhaust gas duct, 11a, 11b ... Rear transmission Hot side, 12
a, 12b ... Exhaust gas flow path, 13a, 13b ... Flow control damper.

Claims (2)

[Claims] (A) All or part of a contact heat transfer part to a cyclone of a fluidized bed combustion boiler is eliminated, and all or one of a freeboard peripheral wall, an exhaust gas duct and a high temperature cyclone at a furnace outlet connected to the peripheral wall. The part has an adiabatic structure and particles containing unburned ash scattered from the fluidized bed are kept at high temperature until they enter the cyclone from the freeboard through the exhaust gas duct, and the particles with a relatively large particle size are captured by the cyclone. Is repeatedly returned to the freeboard through the circulation path in a high temperature state, a means for reburning the unburned components in the particles scattered from the fluidized bed, (b) via the plurality of exhaust gas ducts in the freeboard. A high temperature cyclone at the furnace outlet and a rear heat transfer surface were separately connected, and the amount of gas passing through the cyclone and the rear heat transfer surface was provided in a low temperature gas flow path that was connected to the lower side of the rear heat transfer surface. By means of controlling the amount of passing gas separately with a damper for controlling the flow rate, and so on, the gas flow velocity in the freeboard section and the cyclone collection efficiency do not change significantly even under low load, and the temperature of the freeboard section A method for controlling unburned components in a fluidized bed combustion boiler, which is characterized by controlling a pattern to a temperature suitable for desulfurization and denitration. 2. (a) All or part of the contact heat transfer part to the cyclone of the fluidized bed combustion boiler is eliminated, and all or one of the freeboard peripheral wall, the exhaust gas duct, and the high temperature cyclone at the furnace outlet connected to it. The part has an adiabatic structure and particles containing unburned ash scattered from the fluidized bed are kept at high temperature until they enter the cyclone from the freeboard through the exhaust gas duct, and the particles with a relatively large particle size are captured by the cyclone. Is repeatedly returned to the freeboard through the circulation path in a high temperature state to reburn the unburned matter in the particles scattered from the fluidized bed, (b) the freeboard is divided into a plurality of parts, and The high temperature cyclone at the furnace outlet and the rear heat transfer surface are separately connected to the freeboard portions, respectively, through the exhaust gas duct, and the gas passing through the cyclone and the rear heat transfer surface is separately connected. The amount of passing gas is controlled by a damper for controlling the flow rate, which is provided in the low temperature gas passage connected to the lower side of the rear heat transfer surface. A method for controlling unburned components in a fluidized bed combustion boiler, characterized in that the collection efficiency does not change significantly even under a low load, and the temperature pattern of the freeboard part is controlled to a temperature suitable for desulfurization and denitration.