RU2767677C1 - Method of reducing the power of a gas turbine plant below its permissible lower limit of the control range - Google Patents

Abstract

FIELD: heat power engineering.

SUBSTANCE: invention relates to heat engineering and can be used to convert a power gas turbine unit (GTU) as part of a combined-cycle gas turbine unit (CCGT) to maximum permissible minimum power. Method of reducing power of power gas turbine plant for its transfer to mode of minimum electric load as part of combined-cycle plant consists in fact, that reducing the supply of fuel and air compressed in the compressor to the combustion chamber to the permissible lower limit of the adjustment range, which is determined by the maximum permissible excess air coefficient. At that, after reaching the lower limit of the control range, the power of the gas turbine unit is further reduced by further reducing the supply of fuel to the combustion chamber and heating the air before the compressor due to the heat of the steam taken from the low-pressure cylinder of the steam turbine, further reducing its power and heat loss in the condenser, at that, controlling the level of air heating upstream of the compressor by the minimum allowable temperature of exhaust gases of the gas turbine unit and allowable emissions of nitrogen oxides into the atmosphere.

EFFECT: reduced air flow through the compressor, reduced power of the CCGT steam turbine and prevention of cold brittleness of compressor parts at ambient temperature below -20 °C when GTU operates under load below its permissible lower limit of control range as part of CCGT.

1 cl, 1 dwg

Description

Scope of use

The invention relates to the field of thermal power engineering, and can be used to transfer a power gas turbine plant (GTP) as part of a combined cycle plant (CTP) to the maximum allowable minimum power.

State of the art

Over the past 10 years, the share of renewable energy sources (solar and wind) has significantly increased in the structure of generating capacities in developed countries. These energy sources are naturally variable and the periodic loss of their power, primarily during the daytime, is compensated by powerful gas turbines as part of the STP.

The power reduction of the power gas turbine to transfer it to the minimum electrical load mode can be carried out by reducing the supply of fuel and air compressed in the compressor to the combustion chamber to the permissible lower limit of the control range, determined by the maximum permissible excess air coefficient. To maintain within acceptable limits the temperature of the gases before and after the gas turbine with a decrease in the power of the gas turbine, it is necessary, together with a decrease in the fuel supply to the combustion chamber, to reduce the consumption of compressed air injected into it by the compressor so as not to exceed the specified ratio between them (the specified maximum possible excess coefficient air). For this, the inlet guide vane (VNA) regulates the amount of air entering the compressor inlet. However, the possibilities of using VNA to reduce the power of gas turbines are limited. The adjustment range of GTU power due to the use of VNA is 60-100% of its nominal power.

Modern gas turbines are subject to requirements for increased maneuverability: they must be started and loaded at high speed, while they must be able to unload below 60% of their rated power while maintaining high efficiency and environmental safety while reducing the electrical load of the power grid. Working in the deep unloading mode, but without cooling down the steam part of the STP, the GTP can, if necessary, be loaded immediately at maximum speed, continuously up to 100% of its rated power. At the same time, energy costs for the rotation of the GTU shaft as part of the STP and heat losses from the initial steam discharge from the STP waste-heat boiler to the condenser of its steam turbine are eliminated. However, as the gas turbine is unloaded below its permissible lower limit of the control range, which is 60% of its rated power, due to an increase in the excess air ratio with a further decrease in the fuel supply to the combustion chamber due to the limitation of the possibility of reducing the flow of compressed air supplied from the compressor to the chamber combustion of gas turbines, by using VNA, the emission of environmentally harmful substances and the specific heat consumption of gas turbines increase.

Known from the prior art adopted as a prototype of the claimed invention is a method for reducing the power of a power gas turbine to transfer it to the minimum electrical load mode as part of a PTU, which consists in reducing the supply of fuel and compressed air in the compressor to the combustion chamber to the permissible lower limit of the adjustment range, determined by the maximum allowable excess air coefficient, while the power of the gas turbine plant, after reaching the lower limit of the control range, is further reduced by controlled bypass of a part of the air compressed in the compressor to its inlet, controlling the degree of bypass according to the minimum allowable exhaust gas temperature of the gas turbine plant and allowable emissions of nitrogen oxides into the atmosphere (patent RU 2536458 C1, published on December 27, 2014 (hereinafter - [1])).

According to the method known from [1] for transferring the GTP as part of the STP to the minimum electric load mode, the supply of fuel and air compressed by the compressor into the combustion chamber is first reduced to the permissible lower limit of the control range, determined by the specified maximum allowable excess air coefficient. After reaching the lower limit of the control range, the power of the gas turbine is additionally reduced by bypassing a part of the air compressed in the compressor to its inlet, controlling the degree of air bypass using the regulator for the minimum allowable temperature of the exhaust gases of the gas turbine and with the help of the operator on the control panel of the gas turbine for permissible emissions of nitrogen oxides into the atmosphere . The method known from [1] can reduce the flow rate of air supplied to the combustion chamber to lower values than by using an adjustable VHA compressor for this purpose. In addition, with this method of reducing the power of the gas turbine, the adjustment possibilities are expanded in establishing the required fuel-air ratio.

The main disadvantage of the method known from [1] for reducing the power of a power gas turbine to transfer it to the minimum electrical load mode as part of a STP is that the reduction in power of the gas turbine and STP due to air bypass is much greater than the reduction in fuel consumption in the combustion chamber, and therefore the efficiency GTU and PTU decreases with deep unloading.

Disclosure of invention

The objective of the invention is to provide the possibility of reducing the power of the gas turbine when operating under load below its permissible lower limit of the adjustment range as part of the STU without bypassing part of the compressed air to the compressor inlet, and the technical results are to reduce the air flow through the compressor, reduce the power of the steam turbine of the STP and prevent cold brittleness of parts compressor at an outdoor air temperature below -20°C when the GTU is operating under load below its permissible lower limit of the control range as part of the PTU.

The solution to this problem by achieving these technical results is ensured by the fact that the method of reducing the power of a gas turbine power plant to transfer it to the minimum electrical load mode as part of a combined cycle plant consists in reducing the supply of fuel and compressed air in the compressor to the combustion chamber to an acceptable lower limit adjustment range, determined by the maximum allowable coefficient of excess air. Moreover, the power of the gas turbine plant, after reaching the lower limit of the control range, is further reduced by further reducing the fuel supply to the combustion chamber and heating the air in front of the compressor due to the heat taken from the steam turbine, further reducing its power and heat loss in the condenser, while controlling the level of air heating in front of the compressor according to the minimum allowable temperature of the gas turbine exhaust gases and allowable emissions of nitrogen oxides into the atmosphere. Moreover, the heating of the air in front of the compressor is carried out due to the heat of the steam taken from the low pressure cylinder (LPC) of the steam turbine.

The causal relationship between the above technical results and the totality of the essential features of the claims of the claimed invention is as follows.

An additional reduction in the power of the GTU after reaching the lower limit of its control range by further reducing the fuel supply to the combustion chamber and heating the air in front of the compressor due to the heat of the steam taken from the low pressure cylinder stage of the steam turbine, further reducing its power and heat loss in the condenser, makes it possible to reduce air consumption through the compressor and reduce the power of the steam turbine of the STP when the GTP is operating below its permissible lower limit of the control range as part of the STP. Since the power of the gas turbine is directly proportional to the mass of the volumetric air flow, in order to reduce the power of the gas turbine, it is necessary to preheat the air in front of the compressor to reduce the volumetric air flow in the combustion chamber, which also reduces the exhaust gas flow through the waste heat boiler, thus reducing its steam output and , as a result, further reducing the power of the steam turbine STP. Air preheating in front of the compressor also helps to prevent cold brittleness of compressor parts at outdoor air temperatures below -20°C.

With the above method of reducing the power of the gas turbine to transfer it to the minimum electrical load mode, the STP expands the adjustment capabilities in setting the required fuel-air ratio, which makes it possible to satisfy all the requirements associated with maintaining the required values of the excess air coefficient, the amount of nitrogen oxide emissions and the temperature of the exhaust gases. gases at the outlet of the gas turbine by controlling the level of air heating in front of the compressor according to the minimum allowable temperature of the gas turbine exhaust gases and allowable emissions of nitrogen oxides into the atmosphere.

Brief description of the drawing

The drawing shows a diagram of a PTU with air heating in front of the compressor due to the heat of the steam taken from the steam turbine.

Description of drawing items

1 - compressor;

1.1 - VNA;

1.2 - VNA turning actuator;

2 - combustion chamber;

2.1 - fuel control valve;

2.2 - fuel line;

3 - gas turbine;

3.1 - exhaust gas line;

4 - electric generator;

5 - waste heat boiler;

5.1 - flue gas line;

5.2 - high pressure steam line;

5.3 - low pressure steam line;

6 - chimney;

7 - steam turbine;

7.1 - exhaust steam line;

7.2 - line of selected steam;

7.3 - steam control valve;

8 - electric generator;

9 - capacitor;

10 - steam-water heat exchanger;

11 - air-to-water heat exchanger;

11.1 - chilled water line;

11.2 - heated water line;

11.3 - control valve;

12 - circulation pump;

13 - air supply line;

14 - outdoor air temperature sensor;

15 - air temperature sensor before the compressor;

16 - exhaust gas temperature sensor;

17 - regulator;

ShRM - standard power regulator.

Implementation of the invention

Below is a particular example of a STP scheme with air heating in front of the compressor due to the heat of steam taken from a steam turbine to implement a method for reducing the power of a power gas turbine to transfer it to the minimum electrical load mode as part of a STP.

The PTU contains a compressor 1 with a VNA 1.1 containing a turning actuator 1.2 connected to the SHRM. The compressor 1 is connected through the air line to the combustion chamber 2, which is connected to the fuel line 2.2 with the control valve 2.1 installed on it, connected to the SHRM. Combustion chamber 2 is connected to gas turbine 3. At the same time, compressor 1 is installed on the same shaft with gas turbine 3 and electric generator 4. Gas turbine 3 is connected via exhaust gas line 3.1 to waste heat boiler 5, which is connected via exhaust gas line 5.1 to chimney 6. At the same time, the waste heat boiler 5 is connected via a high-pressure steam line 5.2 and a low-pressure steam line 5.3 with a steam turbine 7, which is installed on the same shaft with an electric generator 8. The steam turbine 7 is connected via an exhaust steam line 7.1 with a condenser 9 and using the bleed steam line 7.2, on which the steam control valve 7.3 connected to the regulator 17 is installed, with the steam-water heat exchanger 10. In this case, the steam-water heat exchanger 10 is connected via the cooling water line 11.1, on which the circulation pump 12 and the control valve 11.3 are installed, and heated water lines 11.2 with an air-to-water heat exchanger 11, which is installed on the supply line during air 13 connected to the VHA 1.1 of compressor 1. The regulator 17 is connected to the outdoor air temperature sensor 14 installed on the air supply line 13 before the air-to-air heat exchanger 11, to the air temperature sensor before the compressor 15 installed on the air supply line 13 before the VHA 1.1 of the compressor 1 , and to the exhaust gas temperature sensor 16 installed on the exhaust gas line 3.1 in front of the waste heat boiler 5 (Fig.).

The way to reduce the power of the power gas turbine to transfer it to the minimum electrical load mode as part of the STP is as follows.

When the gas turbine is operating at partial loads within its control range, power control is carried out using the SHRM by acting on the fuel control valve 2.1 to control the fuel flow entering the combustion chamber 2, and then by acting on the turning actuator 1.2 VNA 1.1 of the compressor 1 to regulate the flow rate of compressed air entering the combustion chamber 2 is not lower than the permissible lower limit of the adjustment range, determined by the maximum permissible excess air coefficient.

If it becomes necessary to reduce the power of the GTU below the border of its control range when operating under load, as part of the STU, the fuel consumption entering the combustion chamber 2 is first reduced by acting on the fuel control valve 2.1, and then the consumption of air compressed in the compressor 1 is reduced , entering the combustion chamber 2, by the action of the SHRM on the actuating mechanism of rotation 1.2 VNA 1.1, which is transferred to the extreme covered position, at which the lower limit of the adjustment range determined by the specified maximum allowable excess air coefficient is acceptable. Then, a further reduction in the fuel consumption entering the combustion chamber 2 is carried out by the action of the CRM on the fuel control valve 2.1. When the set value of the exhaust gas temperature is reached with its further decrease, the air flow entering the combustion chamber 2 is reduced by heating it with the help of the regulator 17, controlling the degree of opening of the steam control valve 7.3. In this case, the input signal of the regulator 17 is the signal of the exhaust gas temperature sensor 16, averaged over time, in order to maintain the set value of the exhaust gas temperature. To increase the speed of the controller 17, other parameters of the GTU can be used as additional input values, for example, a signal from the outdoor air temperature sensor 14 and/or a signal from the air temperature sensor before the compressor 15.

When the gas turbine operates below its permissible lower limit of the control range, the air entering through the air supply line 13 is first heated in the air-to-water heat exchanger 11, and then passes through the VHA 1.1 and is compressed in the compressor 1. After that, the air compressed in the compressor 1 enters the combustion chamber 2 , in which it is mixed with the fuel supplied through the fuel line 2.2, and the resulting air-fuel mixture is ignited. Then, the gases obtained as a result of the combustion of the air-fuel mixture enter from the combustion chamber 2 into the gas turbine 3, rotating its blades and the shaft on which the compressor 1 and the electric generator 4 are installed. After passing through the gas turbine 3, the exhaust gases enter through line 3.1 into the waste heat boiler 5 , in which water is heated due to the heat of the exhaust gases. After that, the exhaust gases enter from the waste heat boiler 5 into the chimney 6, and the steam obtained as a result of heating the water in the waste heat boiler 5 enters through the high pressure steam line 5.2 and the low pressure steam line 5.3 into the steam turbine 7, rotating its blades and shaft on which the electric generator 8 is installed. Then the steam exhausted in the steam turbine 7 enters the condenser 9 through the exhaust steam line 7.1. steam-water heat exchanger 10, in which its heat exchange with water is carried out, pumped by means of a circulation pump 12 through the cooling water line 11.1 and the heated water line 11.2 with a control valve 11.3 through the steam-water heat exchanger 10 and the air-to-air heat exchanger 11, in which the air supplied through the line 13 is heated due to the heat of hot water.

The combined action of the SHRM and the regulator 17 makes it possible to reduce the GTU power below its permissible lower adjustment limit due to the additional, in comparison with the capabilities of the VNA 1.1, reducing the air flow by heating it and reducing the fuel consumption in the combustion chamber 2. In this case, air heating, in addition to the maintenance condition temperature of the exhaust gases of the GTU is not lower than the maximum allowable, is limited by the maximum allowable content of nitrogen oxides in the exhaust gases, which is controlled by the operator on the control panel of the GTU according to the readings of the relevant standard instruments (not shown in Fig.) with the possibility of making manual adjustments to the degree of opening of the steam control valve 7.3.

Industrial Applicability

The method for reducing the power of a power gas turbine plant to transfer it to the minimum electrical load mode as part of a combined cycle plant according to the patented invention meets the condition of "industrial applicability". The essence of the technical solution is disclosed in the formula, description and drawing clearly enough for understanding and industrial implementation by the relevant specialists on the basis of the state of the art in the field of thermal power engineering.

Claims (2)

1. A method for reducing the power of a gas turbine power plant to transfer it to the minimum electrical load mode as part of a combined cycle gas plant, which consists in reducing the supply of fuel and compressed air in the compressor to the combustion chamber to the permissible lower limit of the control range, determined by the maximum permissible excess air coefficient , characterized in that the power of the gas turbine plant, after reaching the lower limit of the control range, is further reduced by further reducing the fuel supply to the combustion chamber and heating the air in front of the compressor due to the heat taken from the steam turbine, further reducing its power and heat loss in the condenser, while controlling the level of air heating in front of the compressor according to the minimum allowable temperature of the exhaust gases of the gas turbine plant and allowable emissions of nitrogen oxides into the atmosphere. 2. The method according to p. 1, characterized in that the heating of the air in front of the compressor is carried out due to the heat of the steam taken from the low pressure cylinder of the steam turbine.

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