RU2827760C1 - Combined cycle gas turbine with waste-heat boiler and feed water instant boiling evaporators - Google Patents

Abstract

FIELD: heat power engineering; power engineering.

SUBSTANCE: invention can be used in development of power CCGT units for production of electric energy at thermal power plants. Combined cycle gas turbine with a waste heat boiler and high and low pressure instant boiling evaporators comprises expansion stages in a gas turbine plant, high and low pressure expansion stages in a steam turbine, high and low pressure steam superheaters, an economiser and a gas condensate heater in a waste heat boiler, wherein between condensate outlet in low-pressure instant boiling evaporator and gas heater of condensate in waste heat boiler there is a steam heater is arranged in the intermediate low pressure expansion stage of a steam turbine.

EFFECT: increased efficiency of combined cycle gas turbine due to usage of heat removed in water-to-water heat exchanger for steam heating in steam heater in intermediate stage of low pressure expansion of steam turbine.

1 cl, 1 dwg

Description

The invention relates to thermal power engineering and power engineering and can be used in the development of power combined cycle gas turbines for the production of electrical energy at thermal power plants.

A combined cycle gas turbine unit (CCGT) is known [RU patent No. 2121118, IPC F24J 3/08, published on 27.10.1998], which includes a gas turbine unit (GTU) and a steam turbine, a waste heat boiler with a gas condensate heater, an economizer, a low-pressure steam superheater, a non-contact evaporator, and a low-pressure flash evaporator.

Due to the presence of a non-contact evaporator, this combined cycle gas turbine unit has insufficiently high reliability, is difficult to operate, is expensive, and due to weak superheating of the steam, has low efficiency.

A closer technical solution, selected as a prototype, is a combined cycle gas turbine unit with a waste heat boiler and high and low pressure flash boiling evaporators [RU patent No. 2674822, IPC F02C 6/00, published on 13.12.2018], containing expansion stages in the gas turbine unit, high and low pressure expansion stages in the steam turbine, high and low pressure steam superheaters, an economizer and a gas condensate heater in the waste heat boiler.

In the prototype, due to the removal of part of the condensate heat obtained in the low-pressure flash boiling evaporator in the water-to-water heat exchanger, the efficiency of the plant is reduced. An additional decrease in efficiency and a decrease in the reliability of the last stages of the steam turbine expansion occurs due to an increase in the humidity of the steam in these stages.

The technical result of the invention is an increase in the efficiency of a combined-cycle plant by using heat removed in a water-to-water heat exchanger to heat steam in a steam heater in an intermediate low-pressure expansion stage of a steam turbine.

The technical result of the claimed invention is achieved due to the fact that in a combined-cycle plant with a waste-heat boiler and high- and low-pressure flash boiling evaporators, containing expansion stages in a gas turbine plant, high- and low-pressure expansion stages in a steam turbine, high- and low-pressure steam superheaters, an economizer and a gas condensate heater in the waste-heat boiler, in contrast to the prototype, a steam heater is installed in an intermediate low-pressure expansion stage of the steam turbine between the condensate outlet in the low-pressure flash boiling evaporator and the gas condensate heater in the waste-heat boiler.

The figure shows a diagram of a combined cycle gas turbine unit with a waste heat boiler and instantaneous boiling evaporators for feed water.

The proposed CCGT unit includes a power gas turbine unit, the main elements of which are a compressor 1, a combustion chamber 2 and a turbine 3. The waste heat boiler of the CCGT unit includes a high-pressure steam superheater 4, a low-pressure steam superheater 5, an economizer 6 and a gas condensate heater 7. The CCGT unit includes a high-pressure flash evaporator 8, a low-pressure flash evaporator 9, high-pressure 10 and low-pressure 11 expansion stages of the steam turbine, a deaerator 12, a steam heater 13 in the low-pressure expansion stages of the steam turbine, a water-to-water heat exchanger for cleaning 14, a chemical water cleaning unit 15, a condenser 16, a feedwater pump 17, a condensate pump 18, a recirculation pump 19, a cleaning unit pump 20, and a circulating water pump 21.

The CCGT operates as follows. Atmospheric air enters the compressor 1 of the power GTU. Fuel is fed into the combustion chamber 2. The GTU generates part of the useful electric power taken from the generator buses connected to the gas turbine 3. The exhaust gases of the GTU are sent to the waste heat boiler, where they successively transfer heat to steam and water in the high-pressure 4 and low-pressure 5 steam superheaters, economizer 6, and gas condensate heater 7.

Steam generation in the high-pressure circuit is performed in the high-pressure flash evaporator 8, and in the low-pressure circuit - in the low-pressure flash evaporator 9. Steam from the high-pressure flash evaporator 8, after superheating in the high-pressure superheater 4, is directed to the high-pressure expansion stages 10 of the steam turbine. From them, the exhaust steam enters the low-pressure flash evaporator 9, for example, through a bubbling plate, into which water from the high-pressure flash evaporator 8 also enters. Steam from the low-pressure flash evaporator 9, after superheating in the low-pressure superheater 5, is directed to the low-pressure expansion stages 11 of the steam turbine. The steam turbine, consisting of the high-pressure 10 and low-pressure 11 expansion stages, generates the remaining portion of the useful electric power. Water from the low-pressure flash evaporator 9 is directed to the steam heater 13 in the low-pressure expansion stages 11 of the steam turbine, and from it to the deaerator 12 and the gas condensate heater 7. Part of the water from the steam heater 13 is directed to the water-to-water heat exchanger for cleaning 14, from it to the chemical water cleaning unit 15, and then with the help of the pump of the cleaning unit 20 to the deaerator 12. The exhaust steam from the low-pressure expansion stages 11 of the steam turbine enters the condenser 16. Water from the deaerator 12 and the condenser 16 is pumped out, respectively, by the feedwater pump 17 and the condensate pump 18. The recirculation pump 19 ensures the recirculation of water in the circuit of the gas condensate heater 7 in order to regulate the temperature of the condensate at its inlet. Circulating water is pumped through condenser 16 by circulating water pump 21.

The increase in the efficiency of the combined cycle plant by 0.95% compared to the prototype is confirmed by the results of one of the variants of calculations of the thermal schemes of the prototype and the proposed combined cycle plant with similar initial parameters of the gas at the inlet to the waste heat boiler and the same pressures of the feedwater and steam in the condenser included in the initial calculation data.

Thus, the proposed invention makes it possible to increase the efficiency of the plant by using the heat removed in the water-water heat exchanger to heat the steam in the steam heater in the intermediate low-pressure expansion stage of the steam turbine, which increases the operation of the steam turbine, as well as reducing the humidity of the steam in the last expansion stages of the steam turbine.

Claims (1)

A combined-cycle plant with a waste-heat boiler and high- and low-pressure flash-boiling evaporators, comprising expansion stages in a gas turbine plant, high- and low-pressure expansion stages in a steam turbine, high- and low-pressure steam superheaters, an economizer and a gas condensate heater in the waste-heat boiler, characterized in that a steam heater in an intermediate low-pressure expansion stage of the steam turbine is installed between the condensate outlet in the low-pressure flash-boiling evaporator and the gas condensate heater in the waste-heat boiler.