Low NOX gas-steam combined cycle system and method adopting wet flue gas recirculation
Technical Field
The invention belongs to the technical field of gas-steam combined cycle, and particularly relates to low NO by wet flue gas recirculationXA combined gas-steam cycle system and method.
Background
A simple gas-steam combined cycle thermodynamic system comprises a gas compressor, a combustion chamber, a gas turbine, a waste heat boiler, a steam turbine, a condenser, a feed water pump and a generator. The method comprises the following steps of adiabatically compressing air in an air compressor, mixing the air with fuel, burning the air in a combustion chamber, enabling generated flue gas to enter a gas turbine for expansion and work application, converting part of energy in the flue gas into mechanical energy by using the gas turbine, enabling the flue gas to enter a waste heat boiler along a flue in order to recover the part of heat due to the fact that the exhaust temperature of the gas turbine reaches 450-600 ℃, absorbing the heat exhausted by the gas turbine by the waste heat boiler to generate steam, converting the heat of the steam into the mechanical energy by a steam turbine, and enabling the flue gas at the tail of the waste heat boiler to be exhausted to the atmosphere through a chimney.
The content of nitrogen in the air is up to 78 percent under the high-temperature condition (>At 1500 deg.C, the nitrogen in the air can react with oxygen to generate thermal NOXNO when the temperature exceeds 1500 DEG CXThe amount of the produced (C) increases rapidly with an increase in temperature. When the gas turbine takes the heated petroleum gas as fuel, the theoretical combustion temperature of the flame in the combustion chamber is 1950 ℃, and when the natural gas is taken as fuel, the theoretical combustion temperature of the flame in the combustion chamber is up to 2300 ℃, so that a large amount of thermal NO is generated under the conditionXAnd the discharge into the environment can cause serious pollution.
To satisfy the national low NOXThe emission requirements are mostly reduced by the prior art by taking more extreme measuresXAnd (4) discharging. E.g. wet low NOXCombustion techniques for reducing NO by injecting high concentrations of demineralized water or steam into the combustion chamber and by reducing the temperature of the combustion chamberXThe technology has great limitations, such as high preparation cost and shortened service life of hot parts of the gas turbine due to the adoption of high-concentration desalted water. Another can reduce NOXThe selective catalytic reduction technology of the tail flue of the emission can effectively reduce NO under the action of the catalystXThe cost is high, and the condition that the catalyst is invalid exists, so that ammonia gas is discharged into the environment and pollution is caused. Currently, the reduction of NO is relatively effectiveXThe method of emission is a staged combustion technique, which suppresses thermal NO by lowering the temperature of the combustion chamberXAnd (4) generating.
Currently, reducing NO in combined gas-steam cyclesXEmission technologies mostly suppress NO by lowering the temperature in the combustion chamberXGeneration or tail absorption of NOXTo reduce NOXAnd (4) discharging. The prior art often ignores the excess air ratio in the combustion chamber versus NOXInfluence of formation of NO during the actual reaction of nitrogen with oxygenXThe rate of formation is proportional to the square root of the oxygen concentration, thereby effectively reducing thermal NO when the excess air ratio is reducedXThereby reducing NOXAnd (4) generating.
Disclosure of Invention
The present invention is directed to provide a low NOX gas-steam combined cycle system and method using wet flue gas recirculation, which can greatly reduce NO from the perspective of reducing the excess air ratio and ensuring the efficiency of a gas turbine, in view of overcoming the above-mentioned disadvantages of the prior artXAnd (4) discharging.
The invention adopts the following technical scheme:
low NO with wet flue gas recirculationXThe gas-steam combined cycle system comprises a gas compressor, wherein a high-pressure gas outlet of the gas compressor is sequentially connected with a waste heat boiler through a combustion chamber and a gas turbine, the waste heat boiler is connected with a flue gas inlet of a spray tower through a flue gas recirculation pipe, a flue gas outlet of the spray tower is connected with an air pipeline of the gas compressor through a flue gas recirculation fan, the waste heat boiler is connected with a steam turbine through a pipeline, and the steam turbine is coaxially connected with a generator.
Specifically, a circulating water tank is arranged below the spray tower, and an outlet pipeline of the circulating water tank is connected with a circulating water inlet of a circulating water pipe through a circulating water pump; the circulating water outlet of the circulating water pipe is connected with the spraying device.
Furthermore, a second electric valve and a second flowmeter are arranged on the circulating water pipe, a plurality of circulating water pipe branches are arranged on the circulating water pipe at the rear end of the second flowmeter, and each circulating water pipe branch is provided with a regulating valve and a spraying device.
Specifically, one end of the flue gas recirculation pipe is connected with a tail flue of the waste heat boiler, and the other end of the flue gas recirculation pipe is connected with the spray tower; the flue gas recirculation pipe is sequentially provided with a first electric valve and a first flowmeter.
Specifically, a thermocouple thermometer is arranged on a pipeline between the spray tower and the flue gas recirculation fan.
In another aspect of the invention, a low NO process using wet flue gas recirculationXGas-steam combinationMethod of operating a circulation system with low NO with wet flue gas recirculationXThe gas-steam combined cycle system comprises a compressor, wherein the compressor comprises an air pipeline and a flue gas pipeline; an inlet of an air pipeline is connected with the atmosphere, a high-pressure gas outlet of the air compressor is sequentially connected with a waste heat boiler through a combustion chamber, a gas turbine and the waste heat boiler, the waste heat boiler is connected with a flue gas inlet of the spray tower through a flue gas recirculation pipe, a first electric valve and a first flowmeter are sequentially arranged on the flue gas recirculation pipe, a flue gas outlet of the spray tower is connected with the air pipeline of the air compressor through a flue gas recirculation fan, a thermocouple thermometer is arranged at the flue gas outlet of the spray tower, and a plurality of boiler heating surfaces are arranged inside the waste heat boiler; an outlet pipeline of the boiler heating surface is connected with an inlet pipeline of the boiler heating surface after sequentially passing through a steam turbine condenser and a feed pump, and the steam turbine is coaxially connected with a generator; a circulating water tank is arranged below the spray tower and is connected with a circulating water inlet of a circulating water pipe through a circulating water pump; a circulating water outlet of the circulating water pipe is divided into a plurality of circulating water pipe paths after passing through a second electric valve and a second flowmeter, and each circulating water pipe branch path is provided with a regulating valve and a spraying device;
air and recirculated flue gas enter the air compressor through the air inlet pipeline, enter the combustion chamber after adiabatic compression and burn with the fuel, the high-temperature flue gas that the combustion produces enters the gas turbine and expands and does work, introduce the exhaust into the exhaust-heat boiler; the exhaust gas exchanges heat with the boiler heating surface in the waste heat boiler, the generated high-temperature steam enters a steam turbine to expand and do work, the steam doing the work is condensed into condensed water in a condenser, and then the condensed water is sent to the boiler heating surface through a feed water pump;
one part of the tail flue gas of the waste heat boiler is discharged through a chimney, and the other part of the tail flue gas is divided through a flue gas recirculation pipe; the divided flue gas enters a spray tower through a flue gas recirculation pipe, spray water and the flue gas are subjected to countercurrent contact heat exchange under the action of a spray device and finally flow into a circulating water tank, and circulating water in the circulating water tank is sent to each circulating water pipe branch by a circulating water pump and enters the next circulation;
after heat exchange is carried out between the flue gas and the spray water, the low-temperature flue gas is sent into an air pipeline through a flue gas recirculation fan, and is mixed with air and then enters an air inlet pipeline of the air compressor; the first flowmeter is used for measuring the flow of the recirculated flue gas and controlling the opening degree of an inlet baffle of the flue gas recirculation fan to adjust the flue gas recirculation rate and reduce the excess air coefficient in the combustion chamber;
and measuring the temperature of the flue gas after temperature reduction by using a thermocouple temperature measuring meter, controlling the opening degree of the regulating valve of each circulating water pipe branch, and regulating the spraying water flow at any time.
Specifically, after the spray water and the flue gas are subjected to countercurrent contact heat exchange, the temperature of the flue gas is 15-30 ℃.
Compared with the prior art, the invention has at least the following beneficial effects:
the invention relates to a low NO with wet flue gas recirculationXA gas-steam combined cycle system is characterized in that from the perspective of reducing the excess air coefficient, partial smoke is divided from a tail flue of a waste heat boiler, a spray tower is utilized to remove dust in the smoke and reduce the temperature of the smoke, the opening degree of an inlet baffle of a smoke recirculation fan is adjusted to adjust the smoke recirculation rate so as to reduce the excess air coefficient in a combustion chamber, and therefore the NO in the combustion chamber is reducedXTo thereby achieve a reduction in NOXThe purpose of discharging.
Furthermore, a circulating water tank is arranged at the bottom of the spraying tower, and the spraying water exchanging heat with the flue gas can be cooled to the ambient temperature, so that the circulating water temperature is prevented from being continuously increased, and the heat exchange effect of the spraying water and the flue gas is prevented from being reduced. Through installing motorised valve and flowmeter, circulating pipe branch road installation governing valve at circulating pipe, can be according to flue gas flow, in time adjust spray water flow, avoid unnecessary circulating water pump to consume power.
Furthermore, when the unit operates under variable load, the flow of the recirculated flue gas is adjusted in time by adjusting the first electric valve and the first flow meter, and NO is reduced on the premise of ensuring the efficiency of the gas turbineXAnd (4) discharging.
Furthermore, a thermocouple thermometer is arranged to measure the temperature of the recirculated flue gas after heat exchange, and the flow of the recirculated flue gas is adjusted according to the measured temperature so as to reduce the temperature of the recirculated flue gas at the outlet of the spray tower.
In summary, the present invention can reduceThe excess air coefficient in the small combustion chamber effectively reduces NO on the premise of ensuring the efficiency of the gas turbineXDischarging of (3); meanwhile, under the condition of variable load, the efficiency of the gas turbine can be ensured, and unnecessary power consumption of the circulating water pump is reduced.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a schematic view of the system of the present invention
Wherein: 1. a compressor; 2. a combustion chamber; 3. a gas turbine; 4. a waste heat boiler; 5. a boiler heating surface; 6. a steam turbine; 7. a generator; 8. a condenser; 9. a feed pump; 10. a first electrically operated valve; 11. a first flow meter; 12. a flue gas recirculation pipe; 13. a spray tower; 14. a circulating water tank; 15. a water circulating pump; 16. a circulating water pipe; 17. a second electrically operated valve; 18. a second flow meter; 19. adjusting a valve; 20. a spraying device; 21. a thermocouple thermometer; 22. a flue gas recirculation fan.
Detailed Description
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Referring to FIG. 1, the present invention is a low NO with wet flue gas recirculationXThe gas-steam combined cycle system comprises a gas compressor 1, a combustion chamber 2, a gas turbine 3, a waste heat boiler 4, a boiler heating surface 5, a steam turbine 6, a generator 7, a condenser 8, a water feeding pump 9, an electric valve 10, a flow meter 11, a flue gas recirculation pipe 12, a spray tower 13, a circulation water tank 14, a circulation water pump 15, a circulation water pipe 16, an electric valve 17, a flow meter 18, a regulating valve 19, a spray device 20, a thermocouple thermometer 21 and a flue gas recirculation fan 22.
The air compressor 1 comprises an air pipeline and a flue gas pipeline, and the air inlet of the air compressor 1 comprises two parts, wherein one part is air, and the other part is part of flue gas which is branched from a tail flue of the waste heat boiler 4; the inlet of the air pipeline is connected with the atmosphere, high-pressure gas generated by the air compressor 1 sequentially passes through the combustion chamber 2, the gas turbine 3 and the waste heat boiler 4 and then is connected with the flue gas inlet of the spray tower 13 through the flue gas recirculation pipe 12, the flue gas outlet of the spray tower 13 is connected with the inlet of the flue gas recirculation fan 22 through the flue gas recirculation pipe, and the outlet of the flue gas recirculation fan 22 is connected with the air pipeline of the air compressor 1 through the flue gas recirculation pipe.
Wherein, a pipeline between the spray tower 13 and the flue gas recirculation fan 22 is provided with a thermocouple thermometer 21.
One end of the flue gas recirculation pipe 12 is connected with a tail flue of the waste heat boiler 4; the flue gas recirculation pipe 12 is sequentially provided with a first electric valve 10 and a first flowmeter 11.
A plurality of boiler heating surfaces 5 are arranged inside the waste heat boiler 4; an outlet pipeline of the boiler heating surface 5 is connected with an air inlet pipeline of the steam turbine 6; the steam turbine 6 is coaxially connected with the generator 7; an exhaust pipeline of the steam turbine 6 is connected with an inlet pipeline of the boiler heating surface 5 after sequentially passing through a condenser 8 and a feed pump 9.
A circulating water tank 14 is arranged below the spray tower 13, and an outlet pipeline of the circulating water tank 14 is connected with a circulating water inlet of a circulating water pipe 16 through a circulating water pump 15; the circulating water outlet of the circulating water pipe 16 is connected with a spraying device 20.
The circulating water pipe 16 is provided with a second electric valve 17 and a second flow meter 18, the circulating water pipe 16 at the rear end of the second flow meter 18 comprises a plurality of circulating water pipe branches, and each circulating water pipe branch is sequentially provided with a regulating valve 19 and a spraying device 20.
The invention relates to a low NO with wet flue gas recirculationXThe working process of the gas-steam combined cycle is as follows:
air and recirculated flue gas enter the air compressor 1 through an air inlet pipeline, enter the combustion chamber 2 after adiabatic compression to be combusted with fuel, and high-temperature flue gas generated by combustion enters the gas turbine 3 to expand and do work, and exhaust gas is introduced into the waste heat boiler 4;
the exhaust gas exchanges heat with a boiler heating surface 5 in the waste heat boiler 4, the generated high-temperature steam enters a steam turbine 6 to expand and do work, the steam doing the work is condensed into condensed water in a condenser 8, and then the condensed water is sent to the boiler heating surface 5 through a feed water pump 9;
the tail flue gas of the waste heat boiler 4 is divided into two parts, one part is directly discharged to the atmosphere through a chimney, and the other part is divided into partial flue gas through a flue gas recirculation pipe 12; when the unit is started and stopped, controlling the first electric valve 10 to be switched on and off; when the unit is operated, the divided flue gas enters a spray tower 13 through a flue gas recirculation pipe 12, spray water and the flue gas are subjected to countercurrent contact heat exchange under the action of a spray device 20, the temperature of the flue gas is reduced to 30 ℃, the flue gas finally flows into a circulating water tank 14, and circulating water in the circulating water tank 14 is sent into each circulating water pipe branch by a circulating water pump 15 and enters the next circulation;
after the heat exchange between the flue gas and the spray water, the temperature of the flue gas is greatly reduced; under the action of the flue gas recirculation fan 22, low-temperature flue gas is sent into an air pipeline, mixed with air and then enters an air inlet pipeline of the compressor 1; the first flowmeter 11 is used for measuring the flow of the recirculated flue gas and controlling the opening degree of an inlet baffle of the flue gas recirculation fan 22 to adjust the flue gas recirculation rate, so that the excess air coefficient in the combustion chamber is reduced;
the thermocouple thermometer 21 is used for measuring the temperature of the flue gas after temperature reduction, and the opening degree of the second regulating valve 19 of each circulating water pipe branch is controlled, so that the flow of spray water is regulated at any time, and the efficiency of the gas turbine is ensured.
In northern areas, in summer, the circulating water temperature is taken to be 20 ℃; in winter, the circulating water temperature is 5 ℃; at the moment, the range of the flue gas recirculation rate is 0-15%; correspondingly, the range of the spraying water flow is 300.5-845 t/h. Through the selection of the parameters, the temperature of the flue gas can be controlled within 15-30 ℃, so that NO is reducedXAnd meanwhile, the high temperature of the inlet of the gas compressor is avoided, and the efficiency of the gas turbine is reduced. The above data will vary somewhat depending on the region and season, and is only considered to be conservative, and for other circumstances, different circulating water temperatures are considered within the scope of this patent.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.