JPH01208503A - Operation method for compound power generation plant - Google Patents

Abstract

PURPOSE:To restrict generation of MOx, when exhaust gas to be delivered from a gas turbine facility to an exhaust heat recovery boiler passes through a denitration device, by changing over the turbine facility from sliding pressure operation to constant pressure operation when the efficiency of the denitration device becomes a lower limit value. CONSTITUTION:A compound power generation plant is composed of a gas turbine facility 12 consisting of a compressor 2, a combustor 3 and a gas turbine 4, a steam turbine facility 5 having each of high/intermediate/low pressure turbines 9, 8, 12,, and an exhaust heat recovery boiler 18. The exhaust heat recovery boiler 18 is constituted by mounting a superheater 6, a reheater 7, an evaporator 17, a denitration device 14, and an coal economizer 15 in order. When a load is reduced by the command from an electric power system, said plant is under sliding pressure operation. At the time of the sliding pressure operation, denitration efficiency relating to an exhaust gas temperature is monitored so as to change over the operation of plant from sliding pressure operation to constant pressure operation, namely, from the constant opening condition of a regulating valve 16 to the variable opening condition, when denitration efficiency becomes a lower limit value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) This invention relates to an improvement in the method of operating a combined cycle power plant.

(Prior Art) Conventionally, steam turbine equipment has two types: constant pressure operation during base load and variable pressure operation during intermediate load. Transformer voltage operation is applied when the power system load is relatively low, and the heat loss of the entire power plant is relatively small. Transformer voltage operation is originally used to reduce heat loss during intermediate loads (partial loads). It was invented.

When the load drops from the rated load to a partial load, adjusting the amount of steam from the boiler with the steam control valve will inevitably increase the loss, so the opening degree of the steam control valve should be kept constant regardless of the load, and the boiler side This is a driving method that attempts to control the amount of fuel provided.

This operating method is also applied to combined power generation equipment that combines gas turbine equipment, waste heat recovery boiler, and steam turbine equipment into one assembly, and provides high power generation efficiency.

(Problems to be Solved by the Invention) Power plants are subject to strict control over pollution issues, particularly NOx control, and combined cycle power generation facilities are no exception. For this reason, the exhaust heat recovery boiler is equipped with a denitrification device to remove as much NOx as possible from the exhaust gas of the gas turbine equipment.

However, when the combined power generation equipment is in variable voltage operation,
The temperature of the exhaust gas sent from the gas turbine equipment to the exhaust heat recovery boiler is decreasing, and the temperature of the drum water in the exhaust heat recovery boiler, which is proportional to the exhaust gas temperature, is also decreasing. FIG. 2 is a graph showing exhaust gas temperature characteristics and drum water temperature characteristics, with the vertical axis representing exhaust gas temperature and drum water temperature, and the horizontal axis representing drum water pressure. As can be understood from this figure,
The exhaust gas temperature at 50% load is significantly lower than at rated conditions. When the load is 50%, when the exhaust gas temperature decreases, the denitrification efficiency when the exhaust gas passes through the denitrification device decreases further compared to the rated value, as shown in FIG.

Therefore, the load is 40%.

When it gradually decreases to 30%, the denitrification efficiency becomes worse and worse. As a result, the amount of NOx generated becomes higher and higher, causing an environmental pollution problem.

Therefore, in view of the above-mentioned circumstances, it is an object of the present invention to provide a method for operating a combined power generation plant that attempts to suppress the generation of NOx as much as possible.

[Structure of the invention]

(Means and effects for solving the problem) This invention has the following features:
The gas turbine equipment and the steam turbine equipment are arranged directly connected to one shaft or separately, and are equipped with an exhaust heat recovery boiler that generates steam using the exhaust gas sent out from the gas turbine equipment as a heat source and sends the steam to the steam turbine equipment. Inside the recovery boiler, exhaust gas is collected sequentially from the upstream side to the downstream side.

In systems equipped with a superheater, reheater, evaporator, denitrification equipment, and energy saver, when the exhaust gas sent from the gas turbine equipment to the exhaust heat recovery boiler passes through the denitrification equipment, the efficiency of the denitrification equipment reaches its lower limit. The steam turbine equipment is characterized in that the steam turbine equipment can be switched from variable pressure operation to constant pressure operation when

In this invention, during variable pressure operation, the exhaust gas temperature decreases, deteriorating the efficiency of the denitrification equipment, and increasing the amount of NOx generated. Therefore, in this invention, the exhaust gas temperature is monitored, and when the temperature drops extremely, the exhaust gas temperature is changed from variable pressure operation to constant pressure operation. Switch.

In this way, the amount of NOx generated can be kept at an extremely low value.

(Example) An embodiment of the invention will be described with reference to the drawings.

FIG. 1 is a schematic system diagram of the present invention. The combined power generation plant includes a gas turbine facility 12, a steam turbine facility 5, and an exhaust heat recovery boiler 18, and the gas turbine facility 12 and the steam turbine facility 8 are directly connected to one shaft or are arranged separately.

The gas turbine equipment 12 includes a compressor 2, a combustor 3, and a gas turbine 4. The steam turbine equipment 5, which is directly connected to the gas turbine equipment 12 or arranged separately, has a high-pressure turbine 9, an intermediate-pressure turbine 8, and a low-pressure turbine 12, which are connected by a common shaft. The exhaust heat recovery boiler 18 is
From the upstream side of the exhaust gas to the downstream side, the superheater 6,
Reheater 7, evaporator 17. Denitrification device 14 and economizer 15
The evaporator 17 is equipped with a drum 13.
is connected.

The behavior of the combined power generation plant based on the above configuration will be explained.

The air 1 sent to the compressor 2 is increased in pressure here,
Entering the combustor 3, fuel is added to produce working gas. The working gas is sent to the gas turbine 4, expands, and performs work. The exhaust gas 19 exiting the gas turbine 4 becomes a heat source for producing steam in the exhaust heat recovery boiler 18.

On the other hand, the condensate discharged from the condenser 12a of the steam turbine equipment 5 passes through the energy saver 15 of the exhaust heat recovery boiler 18, and then passes through the drum 13.
The water is temporarily stored in the evaporator 17, and then sent to the evaporator 17. The evaporator 17 partially vaporizes the condensate and returns it to the drum 13.

The drum 1113 sends only the steam to the superheater 6, from where it is sent as main steam 10 through the control valve 16 to the high pressure turbine 9.
flow to. The steam that has done work in the high pressure turbine 9 is transferred to the heat exchanger 2
0, intermediate pressure turbine 8 as reheated steam 11 via reheater 7
flows to Steam from the intermediate pressure turbine 11 enters the low pressure turbine 12, where it performs expansion work and is condensed in the condenser 12a, becoming condensed water.

The exhaust gas 19 sent out from the gas turbine equipment 12 is
As described above, while passing through the superheater 6, reheater 7, heat exchanger 20, and evaporator 17, heat is exchanged with water or steam and the heat energy is lost. Exhaust gas 1 leaving the evaporator 17
7 suppresses the generation of NOx when passing through the denitrification device 14.

By the way, when the combined cycle power plant is in rated operation, the denitrification equipment 1
The temperature of the exhaust gas 19 passing through the exhaust gas 19 is approximately 400° C. or higher, and the denitrification efficiency of the denitrification device 14 has reached 90% as seen in FIG. However, when the load is reduced due to a request from the power grid, the combined cycle plant enters variable voltage operation. In this case, as can be seen in FIG. 3, the denitrification efficiency decreases significantly. For example, when the exhaust gas temperature reaches 300° C., the denitrification efficiency drops to about 80%. Generally, it is said that the denitrification device 14 is preferably applied when its efficiency is 80% or more. Therefore, when the load decreases, the denitrification device 14 no longer performs its desired function. Therefore, when the load decreases, we monitor the exhaust gas temperature and watch for a decrease in the efficiency of the denitrification equipment, and when the efficiency reaches the lower limit, we switch from variable pressure operation to constant pressure operation, that is, from the constant opening state of the regulator valve 16 to the Switch to degree change state.

By doing this, the exhaust gas temperature increases, and as a result,
The efficiency of the denitrification device 14 is also increased, and the amount of NOx generated can be kept within the regulation value.

〔Effect of the invention〕

As explained above, according to the present invention, the amount of NOx generated can be stabilized and reliably suppressed.

Contribute to air pollution prevention.

[Brief explanation of the drawing]

Fig. 1 is a schematic system diagram showing an embodiment of a combined power generation plant to which this invention is applied, Fig. 2 is a characteristic diagram of exhaust gas temperature and drum water temperature accompanying changes in operation, and Fig. 3 is a diagram of the characteristics of the denitrification equipment. It is a characteristic line diagram showing efficiency. 5...Steam turbine equipment 6...Superheater 7...Reheater 12...Gas turbine equipment 14...
・Denitrification equipment 15...Cost saving device 17...Evaporator 18...Exhaust heat recovery boiler agent Patent attorney Noriyuki Noriyuki Ken Daishimaru 1 Figure 0 50 100 /! ;0
200F'te 47 ni no five (kuttL) 2nd cause

Claims (1)

[Claims] The gas turbine equipment and the steam turbine equipment are connected directly to one shaft or are placed separately, and are equipped with an exhaust heat recovery boiler that generates steam using the exhaust gas sent out from the gas turbine equipment as a heat source and sends the steam to the steam turbine equipment. In the recovery boiler, a superheater, reheater, evaporator, denitrification device, and energy saver are arranged sequentially from the upstream side to the downstream side of the exhaust gas, and the exhaust gas is sent from the gas turbine equipment to the exhaust heat recovery boiler. A method for operating a combined power generation plant, characterized in that when exhaust gas passes through a denitrification device, steam turbine equipment is switched from variable pressure operation to constant pressure operation when the efficiency of the denitrification device reaches a lower limit value.