JPH06137516A - Method for operating pressure fluidized bed composite generator plant - Google Patents

Abstract

PURPOSE:To reduce an NOx generation amount at the time of burning in a composite plant for generating high temperatures gas for driving a gas turbine by burning coal, etc., in a pressure fluidized bed and generating steam by a heat transfer tube arranged in the bed. CONSTITUTION:Only minimum amount of air necessary for burning the discharge air of a compressor 15 to be driven by a gas turbine 12 is supplied to a fluidized bed 7, and the residual air is bypassed to a burning exhaust gas conduit 4. It prevents an increase in NOx generation amount due to excess oxygen in the bed 7 at the time of partial load of the turbine 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel such as coal or a coal-based paste or slurry (hereinafter,
In the combined plant that generates high-temperature gas for driving the gas turbine, and also generates steam in the heat transfer tubes arranged in the pressurized fluidized bed, It relates to a method of reducing nitrogen oxide when (hereinafter referred to as NO _x).

[0002]

2. Description of the Related Art In pressurized fluidized bed combustion, it is necessary to keep the fluidized bed temperature at 800 to 900 ° C. in order to basically perform desulfurization in a furnace. On the other hand, as a characteristic of the gas turbine, the air supplied from the gas turbine compressor is about 60 to 70% of the rated load even if the load on the gas turbine decreases. In this state, in order to reduce the plant load, that is, to reduce the heat absorption of the heat transfer tubes in the fluidized bed to reduce the amount of generated steam, it is necessary to reduce the bed height of the pressurized fluidized bed and the amount of coal supplied. Becomes However, since the amount of air supplied is too large, the residual oxygen concentration after combustion will increase significantly compared to when the rated load is applied. As a result, there is a problem that the generated NO _x also greatly increases when the load is low.

[0003]

PROBLEM TO BE SOLVED BY THE INVENTION Pressurized fluidized bed composite plan
NO generated in_xTo reduce the free board
As a method, those who burn by adding fuel to the freeboard
There is a law, but there is a drawback that the system becomes complicated. Stone again
There is also a method of burning the fine powder in charcoal with a freeboard,
Combustion temperature changes as the proportion of fines in coal changes.
So stable NO _xIt has the drawback of being difficult to control. Change
In addition, both plans to use additional fuel will
It has the biggest drawback of reduced plant efficiency.

[0004]

In order to solve the above-mentioned conventional problems, the present invention supplies a fuel to a pressurized fluidized bed in which a heat transfer tube is arranged to burn the fuel, and steam is generated in the heat transfer tube. In the combined power generation plant that generates a gas and drives the gas turbine by the combustion exhaust gas to generate electric power, the oxygen concentration in the fluidized bed is the fuel in the discharge air of the compressor driven by a part of the output of the gas turbine. Is supplied to the lower part of the fluidized bed, and the remaining air is introduced into the combustion exhaust gas line between the freeboard above the fluidized bed and the gas turbine. The present invention proposes an operating method of a pressurized fluidized bed combined cycle power plant characterized by the following.

[0005]

[Operation] When the load on the gas turbine decreases, the discharge of the compressor
Since the amount of air discharged does not decrease in proportion to the load,
When air is supplied to the fluidized bed as it is, oxygen becomes excessive.
NO_xIncrease the amount of. In the present invention, it is necessary to burn the fuel.
Only the minimum amount of oxygen required is supplied to the fluidized bed, the rest is bypassed.
NO is generated as it is introduced into the combustion exhaust gas pipeline. _xQuantity
Will be reduced.

[0006]

1 is a flow chart showing an example of equipment for carrying out the method of the present invention. In the figure, 1 is a pressurized fluidized bed boiler, which includes a primary air supply pipe 2, a high temperature and high pressure combustion gas discharge pipe 4, a heat transfer pipe 5 in a fluidized bed, a coal / limestone supply pipe 6, a pressurized fluidized bed 7, air dispersion. Board 8, wind chamber 10, freeboard 11
And so on. The high-temperature high-pressure combustion gas discharge pipe 4 is connected to the gas turbine 12, and a cyclone 13 and a high-temperature dust removing device 14 are provided in the middle thereof. 9 is an ash storage bin. The low temperature combustion gas pipe 22 at the outlet of the gas turbine 12 is equipped with a denitration device 23 and an exhaust heat recovery heat exchanger 24 up to the chimney 25.

The gas turbine 12 is connected to an air compressor 15 and a generator 16. The outlet air pipe of the air compressor 15 is branched into a primary air supply pipe 2 and a bypass air supply pipe 3, and a control valve 17 is provided in the bypass air supply pipe 3. An oxygen concentration measuring device 20 is attached to the high-temperature high-pressure combustion gas discharge pipe 4 at the outlet of the pressurized fluidized bed boiler 1, and its signal is sent to an oxygen concentration controller 21. Then, the opening degree of the control valve 17 is controlled so that the measurement value of the oxygen concentration measuring device 20 is always a fixed value or less. In FIG. 1, 26 is a steam turbine, 27 is a generator, 28 is a condenser, 29 is a pump, and 30 is a feed water heater.

In the pressurized fluidized bed combustion, when the load of the gas turbine is reduced due to the characteristics of the positive displacement air compressor,
The amount of air supplied to the fluidized bed does not decrease in proportion to the load,
Even in the vicinity of the minimum load, it is 60 to 70% of the rated load. On the other hand, in order to reduce the amount of heat absorbed in the fluidized bed, that is, the amount of generated steam, the pressurized fluidized bed boiler operates by lowering the height of the fluidized bed to match the amount of generated steam. Under this condition, the coal input is reduced and the bed temperature is operated at 800-900 ℃. In the past, however, the supplied air volume was excessive compared to the air volume required for combustion. Therefore, the residual oxygen concentration reached about three times the rated load as shown in FIG.

Generally, if the temperature of the fluidized bed is the same, the generated NO _x has an inverse relationship with the residual oxygen concentration after combustion.
To reduce the NO _x , the residual oxygen concentration after combustion should be reduced. Therefore, as in the present embodiment, a means for bypassing a part of the amount of air supplied to the fluidized bed so as to keep the residual oxygen concentration after combustion constant from a certain partial load is effective. The effect of this bypass is shown in FIG. From this figure, it can be seen that the NO _x reduction effect by the method of the present invention is remarkable.

[0010]

According to the present invention, NO generated from the fluidized bed
_x decreases. Therefore, the capacity of the denitration device installed in the low temperature gas piping system downstream of the gas turbine can be reduced, and the amount of catalyst used can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a flowchart showing an example of equipment for carrying out the method of the present invention.

FIG. 2 is a diagram showing a relationship between a gas turbine load and a residual oxygen concentration after combustion.

FIG. 3 is a diagram showing the relationship between the load of the gas turbine and the generated NO _x , comparing the present invention and the conventional case.

[Explanation of symbols]

 1 Pressurized Fluidized Bed Boiler 2 Primary Air Supply Pipe 3 Bypass Air Supply Pipe 4 High Temperature High Pressure Combustion Gas Release Pipe 5 Heat Transfer Pipe 6 Coal / Limestone Supply Pipe 7 Pressurized Fluidized Bed 8 Air Dispersion Plate 9 Ash Storage Bin 10 Air Chamber 11 Free Board 12 Gas turbine 13 Cyclone 14 High temperature dedusting device 15 Air compressor 16 Generator 17 Control valve 20 Oxygen concentration measuring device 21 Oxygen concentration regulator 22 Low temperature combustion gas pipe 23 Denitration device 24 Exhaust heat recovery heat exchanger 25 Chimney 26 Steam Turbine 27 Generator 28 Condenser 29 Pump 30 Water heater

Claims (1)

[Claims] 1. A combined power generation system in which fuel is supplied to a pressurized fluidized bed having a heat transfer tube disposed therein for combustion to generate steam in the heat transfer tube and a combustion exhaust gas drives a gas turbine to generate electricity. In the plant, of the discharge air of the compressor driven by a part of the output of the gas turbine,
Supplying below the fluidized bed only air in an amount such that the oxygen concentration in the fluidized bed is kept at the minimum required for combustion of the fuel,
A method for operating a pressurized fluidized bed combined cycle power plant, characterized in that the remaining air is introduced into a combustion exhaust gas pipe line between the freeboard above the fluidized bed and the gas turbine.