JPH08159411A - Cogeneration system - Google Patents

Abstract

PURPOSE: To provide a cogeneration waste recombustion system in which even if a burner is turned down, a combustion state is prevented from becoming unstable or producing carbon monoxide, and low NOx is ensured. CONSTITUTION: There are formed a primary waste passage 4 where a passage 3 for waste supplied from a gas turbine to a waste heat boiler is branched upstream a burner 2 and the waste and a fuel to the burner are directly mixed to form a primary flame, and a secondary waste passage 5 which joins the passage 4 downstream the burner 2 and makes contact with the primary flame. There is further provided means 6 for controlling a flow rate ratio of both passages 4, 5 in response to an increase and a decrease of the supply amount of the fuel to the burner 2. Accordingly, upon the burner being turned down, the flow rate of the primary waste mixed with the fuel is also drawn so that there is eliminated the possibility of the amount of the mixing of the waste becoming excessive to secure stable combustion at all times, and also upon maximum combustion flame temperature is properly lowered to restrict the amount of production of NOx by controlling the flow rate ratio such that the amount of the primary waste is supplied in a slightly insufficient amount to ensure complete combustion with the secondary waste.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called cogeneration system that uses exhaust heat of a gas turbine or a gas engine generator as a heat source for a boiler or the like.

[0002]

2. Description of the Related Art In a cogeneration system, when a turbine is stopped for a periodic inspection of a gas turbine or the like, a high-temperature exhaust gas is not supplied to a waste heat boiler, so a preliminary heat source is required, and steam demand is relatively high. In a cogeneration system, since it is necessary to reheat the exhaust gas of the gas turbine to increase the steam generation capacity, an exhaust gas re-combustion system has been developed that uses the residual air in the exhaust gas to reheat. There is.

[0003]

In the above-mentioned exhaust gas re-combustion system, it is desirable to control the combustion amount of the reburning burner according to the fluctuation of the steam demand in order to improve the heat utilization efficiency. Since a certain amount of exhaust gas is supplied, if the turndown ratio is made too large, the exhaust gas supply amount becomes excessive when the fuel is throttled, combustion becomes unstable, and carbon monoxide is generated. There is a drawback that Further, the multi-burner system in which a plurality of burners are sequentially ignited according to steam demand has a drawback in that combustion is stable, but equipment cost is high. The present invention solves the above-mentioned problems, and does not cause unstable combustion or generation of carbon monoxide even if the turndown ratio is sufficient, and further, it is possible to reduce the amount of NOx generated. The purpose is to provide a cogeneration system of this kind.

[0004]

As shown in FIG. 1, a cogeneration system according to the present invention uses an exhaust burner 2 for heating an exhaust gas supplied from a gas turbine or a gas engine to a waste heat boiler 1 as combustion air. In the cogeneration system of re-combustion by means of the burner 2, the exhaust passage 3 is branched on the upstream side of the burner 2
And a primary exhaust passage 4 that directly mixes with the above fuel to form a primary flame A, and a secondary exhaust passage 5 that joins the passage 4 on the downstream side of the burner 2 and that contacts the primary flame A. , Both the passages 4, 5 according to the increase or decrease of the fuel supply amount of the burner 2.
It is provided with means 6 for controlling the flow rate ratio.

[0005]

In the conventional system shown in FIG. 1, when the fuel is throttled due to the decrease in steam demand, the exhaust flow rate becomes relatively large and the combustion temperature lowers, which causes the generation of carbon monoxide and unstable combustion. However, according to the present invention of FIG. 2, when the fuel supply amount of the burner 2 is throttled, the flow rate of the primary exhaust mixed with the fuel is also throttled, so that the exhaust amount supplied to the burner 2 becomes excessive. Therefore, stable combustion can always be ensured regardless of the size of the flame, and the primary exhaust volume can be supplied to a slightly insufficient amount even at maximum combustion, and the flow rate ratio must be controlled so that the secondary exhaust gas completely burns. As a result, the flame temperature can be appropriately lowered to suppress the NOx generation amount.

[0006]

EXAMPLE FIG. 2 shows a structure around a reburning burner of a cogeneration system according to the present invention.
The burner 2 is provided in the middle part of the exhaust passage 3 for supplying the high temperature exhaust gas from the gas turbine to the waste heat boiler 1. During the turbine operation, the burner 2 allows a large amount (13 to 15%) in the high temperature exhaust gas. The exhaust gas is reheated by burning the fuel gas using the contained oxygen, and the waste heat boiler 1
To improve the boiler efficiency. Exhaust passage 3
Is branched into two upstream of the burner 2 and directly mixed with the fuel of the burner 2 to form the primary flame A.
And a secondary exhaust passage 5 that rejoins the primary exhaust passage on the downstream side of the burner 2 and comes into contact with the primary flame A. The primary damper 7 and the secondary damper 7 are formed in the respective passages 4 and 5, respectively. By controlling the stepping motor 9 for opening and closing the primary damper 7 by the control device 6,
The flow rate ratio of both passages 4 and 5 is controlled. An air introduction pipe 10 is connected to the side wall of the primary exhaust passage 4, and when the turbine is stopped for maintenance or inspection, the damper 7 is closed so that the combustion air is blown from the air supply pipe 10 to the burner 2 by the blower 11. The waste heat boiler 1 is supplied with the necessary minimum amount of heat.

In the above structure, the fuel control valve 12 for supplying the fuel to the burner 2 is controlled by the output from the pressure sensor 13 for detecting the vapor pressure of the waste heat boiler 1, and the fuel supply amount is increased or decreased according to the increase or decrease of the fuel supply amount. When the opening of the primary damper 7 is controlled and the load of the waste heat boiler 1 is reduced and the fuel control valve 12 is throttled, the primary exhaust is also controlled so that the primary exhaust has a predetermined air-fuel ratio, and flame Is prevented from becoming unstable and carbon monoxide is generated. Further, at the time of maximum combustion, the flow rate of the primary exhaust is made slightly smaller than the theoretical air-fuel ratio (for example, 0.9), and the combustion temperature is lowered to suppress the NOx generation amount, and the secondary exhaust is flamed downstream of the burner 2. By contacting with A, complete combustion is achieved.

[0008]

According to the present invention, as described above, the burner 2
When the fuel supply amount of is reduced, the flow rate of the primary exhaust mixed with the fuel is also reduced. Therefore, there is no fear that the amount of exhaust gas supplied to the burner 2 becomes excessive, and therefore stable combustion is always performed regardless of the size of the flame. It has the advantage that it can be secured, and it supplies the primary displacement to a slightly shortage even during maximum combustion,
By controlling the flow rate ratio so as to completely burn the secondary exhaust gas, there is an advantage that the flame temperature can be appropriately lowered and the NOx generation amount can be suppressed.

[Brief description of drawings]

FIG. 1 is an overall system diagram of a conventional cogeneration system.

FIG. 2 is a longitudinal sectional view of a main part of a cogeneration system according to the present invention.

[Explanation of symbols]

 1 Waste Heat Boiler 2 Reheating Burner 3 Exhaust Passage 4 Primary Exhaust Passage 5 Secondary Exhaust Passage 6 Control Device or Flow Ratio Controlling Means 7 Primary Damper 8 Secondary Damper 9 Step Motor 10 Air Supply Pipe 11 Blower 12 Fuel Control Valve 13 Pressure sensor

[Procedure amendment]

[Submission date] April 15, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

[Fig. 1] Overall system diagram of conventional cogeneration system

FIG. 2 is a longitudinal sectional view of a main part of a cogeneration system according to the present invention.

FIG. 3 is a longitudinal sectional view of a main part of another embodiment of the present invention.

FIG. 4 is a graph showing the effect of the present invention.

[Explanation of symbols] 1 waste heat boiler 2 reheating burner 3 exhaust passage 4 primary exhaust passage 5 secondary exhaust passage 6 controller or flow rate control means 7 primary damper 8 secondary damper 9 step motor 10 air supply pipe 11 Blower 12 Fuel control valve 13 Pressure sensor

Claims (1)

[Claims] 1. A cogeneration system in which exhaust gas supplied from a gas turbine or a gas engine to a waste heat boiler is used as combustion air for re-combustion by a reburning burner, and the exhaust passage is branched upstream of the burner. And forms a primary exhaust passage that directly mixes with the fuel of the burner to form a primary flame, and a secondary exhaust passage that joins the passage on the downstream side of the burner and comes into contact with the primary flame, and
A cogeneration system comprising means for controlling the flow rate ratio of both passages according to the increase or decrease of the fuel supply amount of the burner.