Steam Rankine-organic Rankine combined cycle power generation system

Abstract

The invention relates to a steam Rankine-organic Rankine combined cycle power generation system, which cools positive pressure exhaust steam of a steam turbine in a steam Rankine cycle through an organic working medium in the organic Rankine cycle, and recovers latent heat of vaporization of steam in the steam Rankine cycle for organic Rankine cycle power generation. The steam Rankine cycle and the organic Rankine cycle are combined together, meanwhile, an internal circulation high-pressure water flue gas waste heat recovery system is adopted, the problem of low-temperature corrosion of flue gas waste heat of a power station boiler is solved, and the whole combined cycle power generation device is reasonable in process setting and high in heat utilization efficiency.

Description

Technical Field

[0001] The present invention relates to a steam Rankine - organic Rankine combined cycle power generation system, and particularly to a combined cycle generating unit in which the steam Rankine cycle uses a positive - pressure condenser, the positive - pressure condenser serves as the ORC heat source, and the hot - water type waste heat recovery device and the regenerative heating technology of the air pre - heater outside the furnace are adopted, specifically belonging to the technical field of power plant power devices in thermal power plants. Background Art

[0002] In the article "Organic Rankine Cycle Pure Low - Temperature Waste Heat Power Generation Technology with Low - Boiling - Point Working Fluids" by Zhang Hong (Cement. 2006. No.8), taking n - pentane as an example, the respective characteristics of the conventional steam Rankine cycle and the organic Rankine cycle in recovering low - and medium - enthalpy heat are compared. For low - and medium - enthalpy heat, the ORC technology has many advantages over the conventional steam Rankine cycle. The main advantage is that it has a higher efficiency in recovering sensible heat. Since the ratio of sensible heat to latent heat in the cycle is not equal, this ratio is larger in the ORC technology. Therefore, more heat can be recovered by using the ORC technology than the steam cycle.

[0003] Compared with the conventional steam Rankine cycle, the ORC has the following advantages:

[0004] (1) Since the boiling point of the organic working fluid is lower than that of water, the evaporation pressure at the same temperature is higher. Therefore, the ORC system has a higher efficiency in utilizing medium - and low - temperature heat sources. In practical applications, the same ORC system can be applied to heat sources at different temperatures with only minor modifications.

[0005] (2) Taking n - pentane as an example, the density of n - pentane is greater than that of steam and its specific volume is smaller than that of steam (see Table 1), resulting in smaller pipe sizes in the steam turbine (especially the height of its last - stage blades), the exhaust pipe, and the air - cooled condenser.

[0006] Table 1 Comparison of pressures and densities of steam and n - pentane

[0007] Temperature / °C Vapor pressure / kPa <![CDATA[Water vapor density / (kg / m 3 )]]> n-Pentane pressure / kPa <![CDATA[Density of n-pentane / (kg / m 3 )]]> 50 12 0.08 160 4.57 100 101 0.60 589 16.49 150 476 2.55 1600 47.77

[0008] (3) Different from steam, n - pentane remains in a dry state throughout the expansion work process, which eliminates the possibility of forming moisture and the possibility of damage to the expander impeller when high - speed small droplets impact. Therefore, the ORC can more effectively adapt to part - load operation and large power fluctuations than a steam turbine and does not require a superheater.

[0009] (4) In water - scarce areas, air - cooled condensers are preferentially used. The air - cooled condensers used in ORC power plants are much smaller in volume and much lower in price than those used in steam power plants.

[0010] (5) Compared with water vapor, due to the low sonic velocity of organic working fluids, favorable aerodynamic matching can be obtained at low blade speeds. The turbogenerator can achieve high efficiency at 50 Hz and does not require a gearbox.

[0011] (6) The condensation pressure of organic working fluids is high, and the entire system operates at a pressure close to and slightly higher than atmospheric pressure, which greatly reduces the leakage of organic working fluids.

[0012] (7) The freezing point of organic working fluids is very low (for example, n-pentane is lower than -73 °C), and it can still operate normally at lower temperatures. In this way, the output can be increased in cold weather, and the condenser does not require additional anti-freezing facilities. In addition, most components of the ORC system are from mature refrigeration components, which reduces the development difficulty of the ORC system.

[0013] Chinese patents such as 201320042189.1 - Steam Rankine - Organic Rankine combined cycle power generation device, 201310029372.2 - Steam Rankine - Organic Rankine combined cycle power generation device, 201310029366.7 Brayton - Steam Rankine - Organic Rankine combined cycle thermoelectric co - generation method and device, 201320042188.7 Brayton - Steam Rankine - Organic Rankine combined cycle thermoelectric co - generation device, etc. combine the advantages of ORC and propose a combined cycle power generation device that uses a positive - pressure condenser, external - cycle water replenishment, and efficiently recovers flue - gas waste heat using a composite phase - change heat exchanger. The positive - pressure condenser used in this device has prominent advantages: effectively avoiding the disadvantages of traditional negative - pressure condensers such as air leakage, large volume, poor heat - transfer effect, and the need to set up a water - jet air ejector; the steam turbine avoids a large tail impeller and cylinder block, and its safety performance is greatly improved; the positive - pressure condenser is small in volume and has high heat - transfer efficiency, and the relative prices of the steam turbine and condenser equipment are reduced a lot, etc. However, the above - mentioned technologies also have many disadvantages, such as complex process settings, using distilled water in the water - replenishment circuit, not considering the large amount of water replenishment during thermoelectric co - generation, and defects in the water - treatment process for water replenishment. In addition, when the temperature changes in winter and summer, due to the use of organic working fluids for low - temperature flue - gas waste heat, the overall performance of the entire unit is affected by various factors, and it is very difficult to optimize the linkage operation and regulation.

[0014] However, ORC technology also has its inherent disadvantages: Since organic working fluids may have characteristics such as flammability and explosiveness, when using flue - gas waste heat in the boiler tail flue to organize ORC, explosion protection and environmental and work - site protection resulting from this must be considered. This is a difficult problem that must be solved when ORC technology is used to recover flue - gas waste heat containing dust and corrosive substances in the power - station system.

[0015] Steam boilers use coal, oil, natural gas, etc. as fuels. Since the fuels contain sulfur, sulfur oxides will be produced during combustion. The sulfur oxides combine with water vapor to form sulfurous acid or sulfuric acid vapor. For the air preheater arranged in the tail flue of the steam boiler, if the metal wall temperature is lower than the condensation point of the sulfuric acid vapor (acid dew point), liquid sulfuric acid (referred to as acid dew) will be formed on its surface. Acid dew corrosion and ash blockage phenomena often occur due to the too low wall temperature. Acid dew corrosion will occur after the air preheater operates for one to two years, and even perforation and scrapping will occur. This is a worldwide problem that plagues steam boilers.

[0016] Existing power station boilers use corrosion-resistant low-temperature economizers, air heaters - low-temperature economizers or phase change heat exchangers to recover the waste heat of flue gas, achieving certain effects, but there are also some problems: for example, the generated hot water needs to have a reasonable consumption place, which is suitable for cogeneration units with a relatively large heat supply, and it is not easy to organize the heat balance.

[0017] For the air preheater arranged in the tail flue of the steam boiler to recover the waste heat of flue gas, the air duct arrangement for the air to enter and exit the air preheater needs to occupy space. The air and flue gas in the air preheater need to adopt cross-flow and rotary methods for heat exchange to effectively avoid the heat transfer deviation of the air preheater. The distance from the air duct to the boiler burner is relatively long, and the volume of the air preheater is relatively large. While for the economizer that uses low-temperature boiler feed water to recover the waste heat of flue gas, the liquid-phase feed water pipes for the feed water to enter and exit the economizer are arranged compactly, conveniently and occupy less space. As the heat-carrying medium, the liquid-phase feed water has a large heat capacity, and the heat transfer coefficient between the flue gas and the liquid-phase feed water in the economizer is much larger than the heat transfer coefficient between the flue gas and the air in the air preheater. For the economizer and the air preheater under the same heat exchange conditions, the volume of the economizer is much smaller than that of the air preheater.

[0018] Chinese Patent 2025104203840 - A steam boiler uses high-pressure water as the heat carrier for recovering the waste heat of the steam boiler flue gas, combines the gas-water heat exchanger and the external air preheater heat recovery technology, effectively avoids the low-temperature corrosion of the steam boiler flue gas, and realizes the safe and efficient recovery and utilization of the waste heat of the flue gas in the internal cycle. It is suitable for the partial renovation or new construction of industrial steam boilers and power station boilers, but does not fully consider the overall optimization advantages of simple operation adjustment and easy heat balance organization when this technology is applied in the combined cycle power generation system.

[0019] Therefore, how to reasonably recycle the waste heat of the flue gas of a power station boiler, adopt a high-pressure water waste heat recovery system, utilize the characteristic that the corresponding saturation temperature of high-pressure water is relatively high, use high-pressure water as the heat-absorbing medium of the flue gas-water heat exchanger, and use the high-temperature water lower than the saturation temperature of the waste heat recovery system pressure coming out of the gas-water heat exchanger as the heat source of the air preheater outside the furnace, so as to achieve the compact and convenient layout of the flue gas-water heat exchanger at the tail of the power station boiler, achieve the compact and simple layout of the air preheater outside the power station boiler furnace, effectively avoid the low-temperature corrosion of the flue gas-water heat exchanger at the tail while reducing the flue gas temperature, and solve the problems existing in the existing steam Rankine-organic Rankine combined cycle technology, which has become a research hotspot in this field. Summary of the Invention

[0020] The object of the present invention is to solve the above-mentioned technical disadvantages and propose a new steam Rankine-organic Rankine combined cycle power generation system, which can replace the traditional steam Rankine cycle, and at the same time solve the key problems of the safe operation of the ORC unit, recover the latent heat of vaporization of the steam in the steam Rankine cycle for power generation in the low-temperature organic Rankine cycle, realize the efficient internal circulation heat utilization of the low-temperature waste heat of the flue gas, and achieve the purpose of effectively improving the operation thermal efficiency, optimizing the operation regulation and safety of the entire combined cycle unit.

[0021] The object of the present invention is achieved by the following measures:

[0022] A steam Rankine-organic Rankine combined cycle power generation system, which includes a steam Rankine cycle, an organic Rankine cycle and a high-pressure water flue gas waste heat recovery system.

[0023] The so-called steam Rankine cycle refers to that the saturated steam 5 coming out of the furnace heating surface 2 of the boiler body 1 forms superheated steam 7 after passing through the superheater 6, and is sent to the steam turbine 8 to drive the steam turbine generator 9 to generate electricity. The exhaust steam coming out of the steam turbine 8 has a pressure higher than the atmospheric pressure and is condensed in the positive-pressure condenser 10. The formed condensate 11 enters the furnace heating surface 2 of the boiler body 1 through the boiler feed pump 12 and the economizer 13, and then generates saturated steam 5, thus forming a steam Rankine cycle loop.

[0024] The so-called organic Rankine cycle refers to that the liquid organic working medium 37 forms a gaseous organic working medium 33 through the organic working medium circulation pump 32 and the positive-pressure condenser 10, enters the gas turbine 34, drives the gas turbine generator set 35 to generate electricity. The organic working medium discharged from the gas turbine 34 is cooled by the organic working medium condenser 36 to form a liquid organic working medium 37, and then enters the organic working medium circulation pump 32, thus forming an organic Rankine cycle loop.

[0025] The high-temperature flue gas generated by the burner 3 of the boiler body 1 is cooled after passing through the furnace heating surface 2, the superheater 6, the economizer 13 and the gas-water heat exchanger 19, and then forms low-temperature flue gas 31 after passing through the dust collector 29 and the desulfurization device 30, and is discharged from the chimney through the boiler induced draft fan.

[0026] The air passes through the blower 15 and the air preheater 16 to form hot air 17, which is then transported to the burner 3 of the boiler body 1 as a combustion aid and burns with the fuel 4 to form high-temperature flue gas.

[0027] The high-temperature water coming out of the air-water heat exchanger 19 enters the external air preheater 16 through the high-temperature water pipeline 20, and serves as the heat source of the external air preheater 16. The low-temperature water coming out of the external air preheater 16 enters the buffer water tank 21. The low-temperature water in the buffer water tank 21 is pressurized by the circulating water pump 18 and then enters the air-water heat exchanger 19. Alternatively, the high-temperature water coming out of the air-water heat exchanger 19 enters the buffer water tank 21 through the high-temperature water pipeline 20 and then is transported into the external air preheater 16 through the circulating water pump 18 to heat the air transported by the blower 15, and then returns to the air-water heat exchanger 19, thereby forming a high-pressure water flue gas waste heat recovery system.

[0028] The liquid organic working medium 37 is a single-component organic working medium, or a mixed solution with a low-boiling-point component as a single component and a high-boiling-point component as an absorbent, constituting an organic Rankine basic cycle of a low-boiling-point component.

[0029] The liquid organic working fluid 37 includes liquid carbon dioxide, which is regarded as an organic working fluid in the present invention.

[0030] A feed water system matching the steam Rankine cycle is provided: boiler feed water 40 passes through a water treatment unit 41 to form primary desalted water 42, enters a deaerator 43 to remove gas components in the primary desalted water 42, and then passes through a feed water booster pump 44 to feed into the water circulation system of the steam Rankine cycle.

[0031] The make-up water system matched with the steam Rankine cycle is used to supplement the gas-water drainage loss, steam leakage loss, heating steam water consumption, etc. in the steam Rankine cycle.

[0032] The primary desalted water 42 meets the use requirements of the furnace heating surface 2 of the boiler body 1 after being deoxygenated.

[0033] The water treatment unit 41 includes thermal desalination, chemical desalination (anion and cation exchange method) or membrane separation technology desalination.

[0034] The deoxidizer 43 includes thermal deoxidation, chemical deoxidation, desorption deoxidation, electrochemical deoxidation or deoxidation resin deoxidation, etc. Preferably, a normal temperature deoxidizer is used.

[0035] The furnace heating surface 2 adopts water treatment measures such as adding medicine in the pot and continuous or regular sewage discharge.

[0036] The buffer water tank 21 is provided with a pressure regulator 23: the inert gas coming out of the pressure regulator 23 enters the buffer water tank 21 through a pressure regulating valve 25, maintaining the liquid water in the gas-water heat exchanger 19, the air preheater 16 outside the furnace, the buffer water tank 21 and their connecting pipelines at a relatively high pressure, so that the saturation temperature corresponding to the heat-carrying medium, i.e., water, in the high-pressure water and flue gas waste heat recovery system is relatively high, meeting the water temperature requirement for heating the air preheater outside the furnace.

[0037] Preferably, the water temperature coming out of the gas-water heat exchanger 19 is 10°C to 30°C lower than the saturation water temperature corresponding to the system pressure.

[0038] The pressure regulator 23 is a high-pressure gas storage tank or a compressor.

[0039] The inert gas coming out of the pressure regulator 23, including nitrogen, argon, etc., has excellent thermal inertia and is extremely difficult to chemically corrode the heat exchange surface material in the high-pressure water and flue gas waste heat recovery system.

[0040] Preferably, nitrogen is used to displace the gas in the high-pressure water and flue gas waste heat recovery system, and the system is sealed after the displacement; feed water is led out from the outlet pipeline of the boiler feed pump and injected into the high-pressure water and flue gas waste heat recovery system, and the pressure of the high-pressure water and flue gas waste heat recovery system is slowly controlled to the set value. At this time, the buffer water tank 21 is equivalent to a gas-water coexistence chamber.

[0041] The fuel 4 of the burner 3 of the boiler body 1 is pulverized coal, biomass fuel, fuel oil or combustible gas, etc.

[0042] The water and air in the air preheater 16 outside the furnace adopt an indirect heat exchange method, and the heat exchange tubes are smooth tubes, fin tubes or spiral groove tubes, etc. Preferably, heat transfer enhancement measures are adopted.

[0043] The water and flue gas in the gas-water heat exchanger 19 adopt an indirect heat exchange method, and the heat exchange tubes are smooth tubes, fin tubes or spiral groove tubes, etc.

[0044] Control the inlet water temperature of the gas-water heat exchanger 19 (for example, above 85°C, and determine the appropriate temperature according to the sulfur content of the fuel), so that the average value of the inlet water temperature and the exhaust gas temperature of the gas-water heat exchanger 19, that is, the metal wall temperature, is higher than the flue gas acid dew point temperature, which can effectively avoid the low-temperature corrosion of the gas-water heat exchanger 19. On the premise of avoiding condensation, the flue gas waste heat is utilized to the maximum extent, enabling the flue gas waste heat recovery device to operate economically and with high thermal efficiency, achieving the purpose of energy conservation and consumption reduction.

[0045] The buffer water tank 21 is provided with an exhaust valve 26, a pressure gauge, a safety valve, etc.

[0046] The steam Rankine-organic Rankine combined cycle power generation system adopts a denitration facility for removing nitrogen oxides in the flue gas formed during the fuel combustion process.

[0047] The described organic working fluid condenser 36 is arranged according to conventional techniques, using water or air as the cooling medium and adopting a closed or open cooling water circulation mode.

[0048] The heat exchange elements of the aforementioned equipment mentioned in the present invention can adopt tubular, finned, serpentine or helical groove tubes, or tubes with other heat transfer enhancement measures or other types of hollow cavity heat exchange elements.

[0049] For the equipment, its standby system, pipelines, instruments, valves, thermal insulation, bypass facilities with adjustment functions, etc. not described in the present invention, well-known and mature technologies are used for supporting.

[0050] The present invention has the following advantages compared with the prior art:

[0051] 1. Simple process setting and remarkable energy-saving effect: The steam Rankine - organic Rankine combined cycle power generation system designed in the present invention is different from the traditional steam Rankine cycle based on the Rankine cycle principle, the organic Rankine cycle system using the indirect heat exchange between flue gas and organic working fluid, and the steam Rankine - organic Rankine combined cycle power generation technology. It adopts a positive pressure operation mode for the condenser, uses the exhaust steam of the steam turbine as the heat source of the organic Rankine cycle, and makes use of the characteristic that the organic Rankine cycle system has higher efficiency in utilizing medium and low temperature heat sources. The condenser in the steam Rankine cycle and the evaporator in the organic Rankine cycle are ingeniously combined. The latent heat of vaporization of steam is effectively utilized. The organic Rankine cycle has a simple, safe and efficient process; because the back pressure operates in a positive pressure mode, the exhaust steam at the outlet of the steam turbine can ensure a certain degree of superheat, and the initial steam pressure of the newly built unit can adopt supercritical or ultra-supercritical pressure, further improving the thermal efficiency of the power generation cycle;

[0052] 2. Low equipment investment and significant reduction in operating costs:

[0053] (1) It eliminates the inevitable air leakage and water leakage phenomena in the traditional negative pressure operation technology of the condenser, and there is no need to set up deaerators, air extractors, low-pressure heaters in the steam Rankine cycle loop, avoiding the steam and water losses caused by the operation of traditional deaerators, air extractors, etc.; the make-up water system for the external cycle has high deaeration efficiency and good effect, and the process flow selection is flexible;

[0054] (2) Since the specific volume of the exhaust steam of the steam turbine is much smaller than that of the traditional condenser, the volume of the condenser can be greatly reduced. Since the back pressure of the steam turbine in the steam Rankine cycle operates in a positive pressure mode, the exhaust steam at the outlet of the steam turbine can ensure a certain degree of superheat, overcoming the design, operation and safety problems brought by the wet steam to the last stage blades of the steam turbine in the traditional Rankine cycle unit. After removing the blades and impellers at the low-pressure end of the steam turbine, the entire steam turbine generator set is compact and safe, and the vibration of the steam turbine generator set is significantly improved compared with before, fundamentally eliminating the design, manufacturing and operation problems brought by the wet steam to the last stage blades of the steam turbine in the traditional steam Rankine cycle, and optimizing the operating conditions of the steam turbine; therefore, the relative prices of the steam turbine and condenser equipment are reduced a lot;

[0055] 3. The operating safety is significantly improved:

[0056] Compared with the traditional organic Rankine combined cycle power generation technology, the heat source of the organic Rankine cycle unit directly uses the positive pressure exhaust steam of the steam turbine in the steam Rankine cycle, which is led to a safe place with reliable protection measures through pipelines. The organic Rankine cycle process is simple in setting, effectively avoiding many problems caused by the leakage of organic working medium and the direct interlacing with the steam Rankine cycle system. The safety of the organic Rankine cycle system is reliably guaranteed, further eliminating potential safety hazards for its industrial application;

[0057] 4. For the high-pressure water deep recovery and internal circulation heat utilization system of flue gas waste heat, the equipment layout is simple, the operation adjustment is convenient, and it is less affected by external factors. The flue gas discharge temperature can be reduced to about 110°C (determined according to the acid dew point of the flue gas). Through the bypass adjustment of the high-pressure water flue gas waste heat recovery system, the low-temperature corrosion at the end of the gas-water heat exchanger can be avoided, which is beneficial to the safe operation of the dust collector (such as a bag filter), and the water-saving effect of the desulfurization device is obvious;

[0058] 5. The setting of the makeup water system can meet the combined heat and power generation requirements of the combined cycle power generation system. The deaeration effect of the deaerator is efficient and reliable, avoiding problems such as poor deaeration effect caused by the leakage of oxygen into the condenser under negative pressure and the dilution of the oxygen concentration by the condensate water in the traditional process. The setting of the makeup water system is more reasonable and effective;

[0059] 6. The interlocking cycle regulation of the system is simpler, safer and more efficient compared with the existing technology, and the heat balance organization is easy;

[0060] 7. The installation and layout of the system equipment are significantly optimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a schematic structural diagram of the steam Rankine - organic Rankine combined cycle power generation system of the present invention.

[0062] Figure 1Among them, 1 - boiler body, 2 - furnace heating surface, 3 - burner, 4 - fuel, 5 - saturated steam, 6 - superheater, 7 - superheated steam, 8 - steam turbine, 9 - steam turbine generator, 10 - positive pressure condenser, 11 - condensate, 12 - boiler feed water pump, 13 - economizer, 14 - boiler feed water, 15 - blower, 16 - air preheater outside the furnace, 17 - hot air, 18 - circulating water pump, 19 - gas-water heat exchanger, 20 - high-temperature water pipeline, 21 - buffer water tank, 22 - low-temperature water pipeline, 23 - pressure regulator, 24 - pressure regulating pipeline, 25 - pressure regulating valve, 26 - exhaust valve, 27 - heating steam, 28 - flue, 29 - dust collector, 30 - desulfurization device, 31 - low-temperature flue gas, 32 - organic working fluid circulation pump, 33 - gaseous organic working fluid, 34 - gas turbine, 35 - gas turbine generator, 36 - organic working fluid condenser, 37 - liquid organic working fluid, 38 - cooling water inlet, 39 - cooling water outlet, 40 - boiler make-up water, 41 - water treatment unit, 42 - primary demineralized water, 43 - deaerator, 44 - make-up water booster pump, 45 - make-up water pipeline. Detailed implementation mode

[0063] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0064] Embodiment 1:

[0065] As Figure 1 shown, a steam Rankine - organic Rankine combined cycle power generation system, which includes a steam Rankine cycle, an organic Rankine cycle and a high-pressure water flue gas waste heat recovery system.

[0066] The so-called steam Rankine cycle refers to the saturated steam 5 coming out of the furnace heating surface 2 of the boiler body 1, passing through the superheater 6 to form superheated steam 7, being sent into the steam turbine 8 to drive the steam turbine generator 9 to generate electricity. The exhaust steam coming out of the steam turbine 8 has a pressure higher than the atmospheric pressure and is condensed in the positive pressure condenser 10. The formed condensate 11 enters the furnace heating surface 2 of the boiler body 1 through the boiler feed water pump 12 and the economizer 13, and then generates saturated steam 5 again. The extraction steam of the steam turbine is used as heating steam 27 and is supplied externally through the heating pipeline to achieve combined heat and power generation, thus forming a steam Rankine cycle loop.

[0067] The described organic Rankine cycle means that the liquid organic working fluid 37 forms a gaseous organic working fluid 33 through an organic working fluid circulation pump 32 and a positive pressure condenser 10, enters a steam turbine 34, drives a steam turbine generator set 35 to generate electricity. The organic working fluid discharged from the steam turbine 34 is cooled by an organic working fluid condenser 36 to form a liquid organic working fluid 37, and then enters the organic working fluid circulation pump 32, thus forming an organic Rankine cycle loop. The organic working fluid condenser 36 is cooled by cooling water, and a conventional open or closed circulating cooling water system is adopted. The cooling water inlet 38 with a lower temperature enters the organic working fluid condenser 36 to liquefy the exhaust gas of the steam turbine 34, and the cooling water outlet 39 with a higher temperature formed is discharged.

[0068] The high-temperature flue gas generated by the burner 3 of the boiler body 1 is cooled by the furnace heating surface 2, superheater 6, economizer 13, and gas-water heat exchanger 19, and then forms a low-temperature flue gas 31 through a dust collector 29 and a desulfurization device 30, and is discharged from the chimney through a boiler induced draft fan.

[0069] The air forms hot air 17 through a blower 15 and an air preheater outside the furnace 16, and is transported to the burner 3 of the boiler body 1 as a combustion-supporting substance, and burns with the fuel 4 to form high-temperature flue gas.

[0070] The high-temperature water coming out of the gas-water heat exchanger 19 enters the air preheater outside the furnace 16 through a high-temperature water pipeline 20 and serves as the heat source of the air preheater outside the furnace 16. The low-temperature water coming out of the air preheater outside the furnace 16 enters a buffer water tank 21. The low-temperature water in the buffer water tank 21 is boosted by a circulating water pump 18 and then enters the gas-water heat exchanger 19, thus forming a high-pressure water flue gas waste heat recovery system.

[0071] The described liquid organic working fluid 37 adopts a single-component organic working fluid.

[0072] The described liquid organic working fluid 37 includes liquid carbon dioxide, and carbon dioxide is regarded as an organic working fluid in the present invention.

[0073] A make-up water system supporting the steam Rankine cycle is provided: the boiler make-up water 40 forms primary demineralized water 42 through a water treatment unit 41, enters a deaerator 43 to remove the gas components in the primary demineralized water 42, and then is supplemented into the outlet pipeline of a boiler feed water pump 12 through a make-up water booster pump 44 through a make-up water pipeline 45, or is supplemented into the water circulation system of the steam Rankine cycle from the inlet pipeline of the boiler feed water pump 12.

[0074] The make-up water system supporting the steam Rankine cycle is used to supplement the gas-water blowdown loss, steam leakage loss, heat supply steam water consumption, etc. in the steam Rankine cycle.

[0075] After being deoxidized, the primary demineralized water 42 meets the use requirements of the furnace heating surface 2 of the boiler body 1.

[0076] The water treatment unit 41 uses chemical desalination (cation and anion exchange method) or membrane separation technology for desalination, etc.

[0077] The deaerator 43 uses a normal temperature deaerator.

[0078] The furnace heating surface 2 adopts water treatment measures such as adding medicine in the boiler, continuous or periodic blowdown, etc.

[0079] The buffer water tank 21 is provided with a pressure regulator 23: The inert gas coming out of the pressure regulator 23 is nitrogen, which enters the buffer water tank 21 through the pressure regulating pipeline 24 and the pressure regulating valve 25, maintaining the liquid water in the gas-water heat exchanger 19, the air preheater 16 outside the furnace, the buffer water tank 21 and their connecting pipelines at a relatively high pressure, so that the saturation temperature corresponding to the heat-carrying medium, i.e., water, in the high-pressure water-gas flue gas waste heat recovery system is relatively high, meeting the water temperature requirement for heating the air preheater outside the furnace.

[0080] Preferably, the water temperature coming out of the gas-water heat exchanger 19 is 10°C to 30°C lower than the saturation water temperature corresponding to the system pressure.

[0081] The pressure regulator 23 is a high-pressure gas storage tank.

[0082] Preferably, nitrogen is used to displace the gas in the high-pressure water-gas flue gas waste heat recovery system, and the system is sealed after the displacement is completed; Feed water is led out from the outlet pipeline of the boiler feed pump and injected into the high-pressure water-gas flue gas waste heat recovery system, and the pressure of the high-pressure water-gas flue gas waste heat recovery system is slowly controlled to the set value. At this time, the buffer water tank 21 is equivalent to a gas-water coexistence cavity.

[0083] The fuel 4 of the burner 3 of the boiler body 1 adopts pulverized coal, biomass fuel, fuel oil or combustible gas, etc.

[0084] The water and air in the air preheater 16 outside the furnace adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, fin tubes or spiral groove tubes, etc. Preferably, heat transfer enhancement measures are adopted.

[0085] The water and flue gas in the gas-water heat exchanger 19 adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, fin tubes or spiral groove tubes, etc.

[0086] Control the inlet water temperature of the gas-water heat exchanger 19 (for example, above 85°C, and determine the appropriate temperature according to the sulfur content of the fuel), so that the average value of the inlet water temperature and the exhaust gas temperature of the gas-water heat exchanger 19, that is, the metal wall temperature, is higher than the flue gas acid dew point temperature, which can effectively avoid the low-temperature corrosion of the gas-water heat exchanger 19. On the premise of avoiding condensation, the flue gas waste heat is utilized to the maximum extent, enabling the flue gas waste heat recovery device to operate economically and with high thermal efficiency, achieving the purpose of energy conservation and consumption reduction.

[0087] The buffer water tank 21 is provided with an exhaust valve 26, a pressure gauge, a safety valve, etc.

[0088] The steam Rankine - organic Rankine combined cycle power generation system adopts a denitration facility for removing nitrogen oxides in the flue gas formed during the fuel combustion process.

[0089] The described organic working fluid condenser 36 is arranged according to conventional techniques, using water or air, etc. as the cooling medium and the closed - cooling water circulation mode of the cooling tower for temperature reduction.

[0090] The heat exchange elements of the aforementioned equipment mentioned in the present invention can adopt tube - in - tube, finned tube, serpentine tube or helical groove tube, or tubes with other heat transfer enhancement measures or other types of hollow cavity heat exchange elements.

[0091] For the equipment, its standby system, pipelines, instruments, valves, thermal insulation, bypass facilities with adjustment functions, etc. not described in the present invention, well - known and mature technologies are used for matching.

[0092] Although the present invention has been disclosed above with preferred embodiments, they are not used to limit the present invention. Any person skilled in this art can make various changes or modifications without departing from the spirit and scope of the present invention, and they also belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims of this application.

Claims

1. A steam Rankine - organic Rankine combined cycle power generation system, characterized in that: The steam Rankine - organic Rankine combined cycle power generation system includes a steam Rankine cycle, an organic Rankine cycle, and a high - pressure water flue gas waste heat recovery system. The steam Rankine cycle refers to that the saturated steam (5) coming out from the furnace heating surface (2) of the boiler body (1) forms superheated steam (7) through the superheater (6), and is sent into the steam turbine (8) to drive the steam turbine generator (9) to generate electricity. The exhaust steam coming out from the steam turbine (8) has a pressure higher than the atmospheric pressure and is condensed in the positive - pressure condenser (10). The formed condensate (11) enters the furnace heating surface (2) of the boiler body (1) through the boiler feed water pump (12) and the economizer (13), and then generates saturated steam (5), thus forming a steam Rankine cycle loop. The organic Rankine cycle refers to that the liquid organic working medium (37) forms gaseous organic working medium (33) through the organic working medium circulation pump (32) and the positive - pressure condenser (10), enters the gas turbine (34), drives the gas turbine generator set (35) to generate electricity. The organic working medium discharged from the gas turbine (34) is cooled by the organic working medium condenser (36) to form liquid organic working medium (37), and then enters the organic working medium circulation pump (32), thus forming an organic Rankine cycle loop. The high - temperature flue gas generated by the burner (3) of the boiler body (1) is cooled after passing through the furnace heating surface (2), the superheater (6), the economizer (13), and the gas - water heat exchanger (19), and then forms low - temperature flue gas (31) through the dust collector (29) and the desulfurization device (30), and is discharged from the chimney through the boiler induced draft fan. Air forms hot air (17) through the blower (15) and the air pre - heater outside the furnace (16), and is transported to the burner (3) of the boiler body (1) as a combustion aid, and burns with the fuel (4) to form high - temperature flue gas. The high - temperature water coming out from the gas - water heat exchanger (19) enters the air pre - heater outside the furnace (16) through the high - temperature water pipeline (20) and serves as the heat source of the air pre - heater outside the furnace (16). The low - temperature water coming out from the air pre - heater outside the furnace (16) enters the buffer water tank (21). The low - temperature water in the buffer water tank (21) is boosted by the circulation water pump (18) and then enters the gas - water heat exchanger (19), or the high - temperature water coming out from the gas - water heat exchanger (19) enters the buffer water tank (21) through the high - temperature water pipeline (20), and then is transported by the circulation water pump (18) into the air pre - heater outside the furnace (16) to heat the air transported by the blower (15), and then returns to the gas - water heat exchanger (19), thus forming a high - pressure water flue gas waste heat recovery system.

2. The steam Rankine - organic Rankine combined cycle power generation system according to claim 1, characterized in that: The liquid organic working medium (37) is a single - component organic working medium, or a mixed solution with a low - boiling - point component based on a single component and a high - boiling - point component as an absorbent.

3. The steam Rankine - organic Rankine combined cycle power generation system according to claim 2, characterized in that: The liquid organic working medium (37) includes liquid carbon dioxide.

4. The steam Rankine - organic Rankine combined cycle power generation system according to claim 1, characterized in that: A make-up water system is provided: The boiler make-up water (40) of the make-up water system forms primary demineralized water (42) through a water treatment unit (41), enters a deaerator (43), and is then supplemented into the water circulation system of the steam Rankine cycle through a make-up water booster pump (44).

5. The steam Rankine - organic Rankine combined cycle power generation system according to claim 4, characterized in that: The water treatment unit (41) includes thermal demineralization, chemical demineralization (cation and anion exchange method), or desalination by membrane separation technology.

6. The steam Rankine - organic Rankine combined cycle power generation system according to claim 4, characterized in that: The deaerator (43) includes thermal deaeration, chemical deaeration, desorption deaeration, electro-chemical deaeration, or deaeration by deaeration resin.

7. The steam Rankine - organic Rankine combined cycle power generation system according to claim 1, characterized in that: A pressure regulator (23) is provided: The inert gas coming out of the pressure regulator (23) enters a buffer water tank (21) through a pressure regulating valve (25) to maintain the liquid water in the gas - water heat exchanger (19), the air preheater outside the furnace (16), the buffer water tank (21), and their connecting pipelines at a set pressure.

8. The steam Rankine - organic Rankine combined cycle power generation system according to claim 7, characterized in that: The inert gas coming out of the pressure regulator (23) includes nitrogen and argon.

9. The steam Rankine - organic Rankine combined cycle power generation system according to claim 1, characterized in that: Nitrogen is used to displace the gas in the high - pressure water flue gas waste heat recovery system. After the displacement is completed, the system is sealed; Feed water is led out from the outlet pipeline of the boiler feed water pump (12) and injected into the high - pressure water flue gas waste heat recovery system, and the pressure of the high - pressure water flue gas waste heat recovery system is slowly controlled to a set value.

10. The steam Rankine - organic Rankine combined cycle power generation system according to claim 1, characterized in that: The buffer water tank (21) is provided with an exhaust valve (26), a pressure gauge, and a safety valve.

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