Steam Rankine-organic Rankine combined cycle power generation system

Abstract

The utility model 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] This utility model relates to a steam Rankine-organic Rankine combined cycle power generation system, and more particularly to a combined cycle generator set that uses a steam Rankine cycle with a positive pressure condenser, a positive pressure condenser as an ORC heat source, a hot water type waste heat recovery unit, and an external air preheater for heat recovery technology, specifically belonging to the technical field of power equipment for thermal power plants. Background Technology

[0002] Zhang Hong's article, "Organic Rankine Cycle Pure Low-Temperature Waste Heat Power Generation Technology with Low-Boiling-Point Working Fluids" (Cement, 2006, No. 8), uses n-pentane as an example to compare the characteristics of conventional steam Rankine cycles and organic Rankine cycles in recovering low and medium enthalpy heat. For low and medium enthalpy heat, the ORC technology has many advantages over the conventional steam Rankine cycle, mainly in its higher efficiency in recovering sensible heat. Because the sensible heat / latent heat ratio is unequal in the cycle, the ORC technology has a larger ratio. Therefore, the ORC technology recovers more heat than the steam cycle.

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

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

[0005] (2) Taking n-pentane as an example, n-pentane has a higher density and a lower specific volume than water vapor (see Table 1), which results in smaller pipe sizes in the turbine (especially the height of its last stage blades), exhaust pipes and air-cooled condensers.

[0006] Table 1. Comparison of pressure and density of water vapor and n-pentane

[0007] Temperature / °C Water 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) Unlike water vapor, n-pentane remains dry throughout the expansion process, which eliminates the possibility of moisture formation and damage to the expander impeller from high-speed small droplets. Therefore, ORC can adapt to partial load operation and large power fluctuations more effectively than steam turbines and does not require a superheater.

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

[0010] (5) Compared with water vapor, organic working fluids have a lower sound velocity, which can achieve favorable aerodynamic matching at low blade speeds. The impeller can achieve higher efficiency at 50 Hz and does not require a gearbox.

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

[0012] (7) Organic working fluids have very low freezing points (e.g., n-pentane is below -73°C), allowing them to operate normally at lower temperatures. This increases output in cold weather, and the condenser does not require additional antifreeze measures. Furthermore, most components of the ORC system are derived from mature refrigeration components, thus reducing the development difficulty of the ORC system.

[0013] Chinese patents 201320042189.1 - Steam Rankine-Organic Rankine Combined Cycle Power Generation Device, 201310029372.2 - Steam Rankine-Organic Rankine Combined Cycle Power Generation Device, 201310029366.7 - Breton-Steam Rankine-Organic Rankine Combined Cycle Cogeneration Method and Device, and 201320042188.7 - Breton-Steam Rankine-Organic Rankine Combined Cycle Cogeneration Device, etc., combine the advantages of ORC (Organic Rankine Cycle) and propose a combined cycle power generation device that uses a positive pressure condenser, external circulation makeup water, and a composite phase change heat exchanger to efficiently recover waste heat from flue gas. The positive pressure condenser used in this device has outstanding advantages. This technology effectively avoids the drawbacks of traditional negative pressure condensers, such as air leakage, large size, poor heat transfer, and the need for water jet ejectors. It also avoids the bulky tail impeller and cylinder of the steam turbine, significantly improving safety. Positive pressure condensers are smaller and have higher heat transfer efficiency, and the relative prices of steam turbines and condensers are much lower. However, the technology also has several disadvantages, including complex process setup, the use of distilled water in the makeup water circuit, failure to consider the large makeup water volume during combined heat and power (CHP), and defects in the makeup water treatment process. Furthermore, due to the use of low-temperature flue gas waste heat from organic working fluids during winter and summer temperature changes, the overall performance of the entire unit is affected by various factors, making coordinated operation and optimization difficult.

[0014] However, ORC technology also has its inherent drawbacks: because organic working fluids may be flammable or explosive, when using waste heat from flue gas to organize ORC in the boiler tail flue, it is necessary to consider the resulting explosion protection as well as environmental and work site protection. This is a problem that ORC technology must solve when recovering waste heat from flue gas containing dust and corrosive substances in power plant systems.

[0015] Steam boilers use coal, petroleum, natural gas, etc. as fuel. Because the fuel contains sulfur, sulfur oxides are produced during combustion. These sulfur oxides combine with water vapor to form sulfurous acid or sulfuric acid vapor. If the metal wall temperature of the air preheater located in the tail flue of the steam boiler is lower than the condensation point (acid dew point) of sulfuric acid vapor, liquid sulfuric acid (called acid dew) will form on its surface. Acid dew corrosion and ash blockage caused by excessively low wall temperature often occur. After one to two years of operation, the air preheater will experience acid dew corrosion, and may even perforate and become unusable. This is a global problem that plagues steam boilers.

[0016] Existing power plant boilers use corrosion-resistant low-temperature economizers, warm air blowers-low-temperature economizers, or phase change heat exchangers to recover waste heat from flue gas, achieving certain results, but also having some problems: for example, the hot water produced needs to be disposed of in a reasonable location, is suitable for cogeneration units with a large heat supply, and is not easy to organize heat balance.

[0017] An air preheater for recovering waste heat from flue gas, located at the tail flue of a steam boiler, requires space for its air ducts. The air and flue gas in the air preheater need to exchange heat through cross-flow and rotation to effectively avoid heat transfer deviation. The ducts travel a long distance to the boiler burner, resulting in a large air preheater volume. In contrast, an economizer using low-temperature boiler feedwater to recover waste heat from flue gas has a compact, convenient, and space-saving installation of its liquid feedwater pipes. The liquid feedwater, as the heat transfer medium, has a large heat capacity, and the heat transfer coefficient between flue gas and liquid feedwater in the economizer is much greater than that between flue gas and air in the air preheater. Under the same heat exchange conditions, the economizer is much smaller than the air preheater.

[0018] Chinese Patent 2025104203840 - A steam boiler uses high-pressure water as the heat carrier for recovering waste heat from steam boiler flue gas. It combines gas-water heat exchanger and external air preheater regeneration technology to effectively avoid low-temperature corrosion of steam boiler flue gas while achieving safe and efficient internal circulation and recovery of waste heat from flue gas. It is suitable for partial modification or new construction of industrial steam boilers and power plant boilers. However, it does not fully consider the overall optimization advantages of this technology when applied to combined cycle power generation systems, such as simple operation and adjustment and easy thermal balance organization.

[0019] Therefore, how to rationally recover and utilize the waste heat from power plant boiler flue gas, adopting a high-pressure water flue gas waste heat recovery system, and utilizing the high saturation temperature of high-pressure water as the heat absorption medium in the flue gas-water heat exchanger, while using the high-temperature water from the heat exchanger (below the pressure saturation temperature of the waste heat recovery system) as the heat source for the external air preheater, has become a hot research topic in this field. This allows for a compact and convenient arrangement of the flue gas-water heat exchanger at the tail end of the power plant boiler, and a compact and simple arrangement of the external air preheater. It also reduces the exhaust gas temperature while effectively avoiding low-temperature corrosion of the flue gas-water heat exchanger, thus solving the problems existing in the current steam Rankine-organic Rankine combined cycle technology. Utility Model Content

[0020] The purpose of this invention is to overcome the shortcomings of the above-mentioned technologies and propose a new steam Rankine-organic Rankine combined cycle power generation system that can replace the traditional steam Rankine cycle. It also solves the key problems of safe operation of ORC units, recovers the latent heat of vaporization of steam in the steam Rankine cycle for power generation in the low-temperature organic Rankine cycle, and realizes the efficient heat utilization of the low-temperature waste heat of flue gas through internal circulation. This effectively improves the operating thermal efficiency of the entire combined cycle unit, optimizes operation regulation, and enhances safety.

[0021] The objective of this utility model is achieved through the following measures:

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

[0023] The steam Rankine cycle refers to the process where saturated steam 5 exiting from the furnace heating surface 2 of the boiler body 1 passes through the heat exchanger 6 to form superheated steam 7, which is then sent to the steam turbine 8 to drive the steam turbine generator 9 to generate electricity. The exhaust steam exiting the steam turbine 8 has a pressure higher than atmospheric pressure and is condensed in the positive pressure condenser 10. The condensate 11 formed enters the furnace heating surface 2 of the boiler body 1 via the boiler feed water pump 12 and the economizer 13, where it generates saturated steam 5 again, thus forming a steam Rankine cycle loop.

[0024] The organic Rankine cycle refers to the process where liquid organic working fluid 37 is converted into gaseous organic working fluid 33 by organic working fluid circulation pump 32 and positive pressure condenser 10, and then enters gas turbine 34 to drive gas turbine generator set 35 to generate electricity. The organic working fluid discharged from gas turbine 34 is cooled by organic working fluid condenser 36 to form liquid organic working fluid 37, and then enters organic working fluid 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 by the furnace heating surface 2, superheater 6, economizer 13, and gas-water heat exchanger 19, and then forms low-temperature flue gas 31 by the dust collector 29 and desulfurization device 30, which is then discharged from the chimney by the boiler induced draft fan.

[0026] Air passes through the blower 15 and the air preheater 16 outside the furnace to form hot air 17, which 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.

[0027] The high-temperature water coming out of the gas-water heat exchanger 19 enters the air preheater 16 outside the furnace through the high-temperature water pipeline 20 and serves as the heat source of the air preheater 16 outside the furnace. The low-temperature water coming out of the air preheater 16 outside the furnace enters the buffer water tank 21. The low-temperature water in the buffer water tank 21 is boosted by the circulating water pump 18 and then enters the gas-water heat exchanger 19. Or the high-temperature water coming out of 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 circulating water pump 18 into the air preheater 16 outside the furnace 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.

[0028] 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, constituting a low-boiling-point component organic Rankine basic cycle.

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

[0030] A makeup water system is provided for supporting the steam Rankine cycle: The boiler makeup water 40 forms primary demineralized water 42 through the water treatment unit 41. After entering the deaerator 43 to remove the gas components in the primary demineralized water 42, it is then supplemented into the water circulation system of the steam Rankine cycle by the makeup water booster pump 44.

[0031] The makeup water system for 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.

[0032] After being deoxygenated, the primary demineralized water 42 meets the use requirements of the furnace heating surface 2 of the boiler body 1.

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

[0034] The deaerator 43 includes thermal deaeration, chemical deaeration, desorption deaeration, electrochemcial deaeration, or deaeration by deaeration resin, etc. Preferably, a normal temperature deaerator is adopted.

[0035] The furnace heating surface 2 adopts water treatment measures such as adding medicine in the boiler, continuous or periodic blowdown, etc.

[0036] The buffer tank 21 is equipped with a pressure regulator 23: the inert gas from the pressure regulator 23 enters the buffer tank 21 through the pressure regulator valve 25, maintaining the liquid water in the gas-water heat exchanger 19, the external air preheater 16, the buffer tank 21 and its connecting pipes at a high pressure, so that the saturation temperature of the heat transfer medium, i.e. water, in the high-pressure flue gas waste heat recovery system is high, which meets the water temperature requirements for heating the external air preheater.

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

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

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

[0040] Preferably, nitrogen is used to replace the gas in the high-pressure water flue gas waste heat recovery system, and the system is then sealed after the replacement is completed. Feedwater is drawn from the boiler feedwater pump outlet pipe 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 the set value. At this time, the buffer tank 21 is equivalent to a gas-water co-containment chamber.

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

[0042] The water and air in the external air preheater 16 are exchanged indirectly. The heat exchange tubes are plain tubes, finned tubes or spiral groove tubes, etc. Preferably, enhanced heat transfer measures are adopted.

[0043] The water and flue gas in the gas-water heat exchanger 19 exchange heat indirectly, and the heat exchange tubes are made of plain tubes, finned tubes, or spiral grooved tubes, etc.

[0044] By controlling the inlet water temperature of the gas-water heat exchanger 19 (for example, above 85℃, the appropriate temperature is determined according to the sulfur content of the fuel), the average value of the inlet water temperature and the exhaust temperature of the gas-water heat exchanger 19, i.e., the metal wall temperature, is higher than the acid dew point temperature of the flue gas. This can effectively prevent low-temperature corrosion of the gas-water heat exchanger 19. Under the premise of avoiding condensation, the waste heat of the flue gas is utilized to the maximum extent, so that the waste heat recovery device of the flue gas can operate economically and with high thermal efficiency, thereby achieving the purpose of energy saving and consumption reduction.

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

[0046] The steam Rankine-organic Rankine combined cycle power generation system employs a denitrification facility to remove nitrogen oxides from the flue gas generated during fuel combustion.

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

[0048] The heat exchange elements of the aforementioned equipment mentioned in this utility model can be tubes, finned tubes, serpentine tubes or spiral grooved tubes, or tubes or other types of hollow cavity heat exchange elements that adopt other heat transfer enhancement measures.

[0049] Equipment and its backup systems, pipelines, instruments, valves, insulation, and bypass facilities with regulating functions not described in this utility model shall be equipped with known and mature technologies.

[0050] Compared with the prior art, the present invention has the following advantages:

[0051] 1. Simple process setup and significant energy-saving effect: The steam Rankine-organic Rankine combined cycle power generation system designed in this utility model differs from traditional steam Rankine cycles based on the Rankine cycle principle, organic Rankine cycle systems utilizing flue gas and organic working fluid through inter-wall heat exchange, and steam Rankine-organic Rankine combined cycle power generation technologies. It adopts a positive pressure operation mode for the condenser, using the turbine exhaust steam as the heat source for the organic Rankine cycle. Taking advantage of the higher efficiency of the organic Rankine cycle system in utilizing medium and low temperature heat sources, the condenser in the steam Rankine cycle and the evaporator in the organic Rankine cycle are cleverly combined together, effectively utilizing the latent heat of vaporization of steam. The organic Rankine cycle process is simple, safe, and efficient. Because the back pressure adopts a positive pressure mode, the exhaust steam at the turbine outlet can ensure a certain degree of superheat. The initial steam pressure of newly built units can use supercritical or ultra-supercritical pressure, further improving the thermal efficiency of the power generation cycle.

[0052] 2. Lower equipment investment and significantly reduced operating costs:

[0053] (1) It eliminates the unavoidable air and water leakage phenomena of traditional condenser negative pressure operation technology, and does not require the installation of deaerators, ejectors and low-pressure heaters in the steam Rankine loop, thus avoiding the steam and water loss caused by the operation of traditional deaerators and ejectors; the external circulation water supply system has high deoxygenation efficiency and good effect, and the process flow selection is flexible.

[0054] (2) Because 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. Because the back pressure of the steam turbine in the steam Rankine cycle is positive pressure, the exhaust steam at the turbine outlet can ensure a certain degree of superheat. This overcomes the design, operation and safety problems caused by wet steam in the last stage blades of the steam turbine in the traditional Rankine cycle unit. After the removal of the tail blades and impellers at the low pressure end of the steam turbine, the entire steam turbine generator set is compact and safe. The vibration of the steam turbine generator set is significantly improved compared to before. This fundamentally eliminates the design, manufacturing and operation problems caused by wet steam in the last stage blades of the steam turbine in the traditional steam Rankine cycle. The operating conditions of the steam turbine are optimized. Therefore, the relative price of the steam turbine and condenser equipment is greatly reduced.

[0055] 3. Operational safety is significantly improved:

[0056] Compared to traditional organic Rankine combined cycle power generation technology, the organic Rankine cycle unit directly uses the positive pressure exhaust steam from the turbine in the steam Rankine cycle as its heat source, which is then piped to a safe location with reliable protection measures. The organic Rankine cycle process is simple to set up and can effectively avoid many problems caused by leakage of organic working fluid and direct interaction with the steam Rankine cycle system. The safety of the organic Rankine cycle system is reliably guaranteed, further eliminating safety hazards for its industrial application.

[0057] 4. The high-pressure water deep recovery and internal circulation heat utilization system for flue gas waste heat has a simple equipment layout, convenient operation and adjustment, and is less affected by external factors. The exhaust temperature can be reduced to about 110℃ (depending on the acid dew point of the flue gas). By bypassing the high-pressure water flue gas waste heat recovery system, low-temperature corrosion at the end of the gas-water heat exchanger can be avoided, which is conducive to the safe operation of dust collectors (such as bag filters). The water-saving effect of the desulfurization unit is obvious.

[0058] 5. The water makeup system is designed to meet the cogeneration needs of the combined cycle power generation system. The deaerator has a high efficiency and reliable deoxygenation effect, avoiding problems such as oxygen leakage due to negative pressure in the condenser and poor deoxygenation effect caused by condensate dilution of oxygen concentration in the traditional process. The water makeup system is designed to be more reasonable and effective.

[0059] 6. The system's linkage and circulation adjustment is simpler, safer, and more efficient than existing technologies, and facilitates thermal equilibrium organization.

[0060] 7. The installation and layout of system equipment have been significantly optimized. Attached Figure Description

[0061] Figure 1 This is a schematic diagram of the steam Rankine-organic Rankine combined cycle power generation system of this utility model.

[0062] Figure 1In the diagram, 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 feedwater pump, 13-economizer, 14-boiler feedwater, 15-blower, 16-external air preheater, 17-hot air, 18-circulating water pump, 19-air-water heat exchanger, 20-high temperature water pipeline, 21-buffer tank, 22-low temperature water pipeline, 23-pressure stabilizer, 24-pressure stabilizer Pipeline, 25-Pressure regulating valve, 26-Exhaust valve, 27-Heating steam, 28-Flue duct, 29-Dust collector, 30-Desulfurization unit, 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 feedwater, 41-Water treatment unit, 42-Primary demineralized water, 43-Deaerator, 44-Make-up water booster pump, 45-Make-up water pipeline. Detailed Implementation

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

[0064] Example 1:

[0065] like Figure 1 As shown, a 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.

[0066] The steam Rankine cycle refers to the process where saturated steam 5 exiting the furnace heating surface 2 of the boiler body 1 passes through the heat exchanger 6 to form superheated steam 7, which is then sent to the steam turbine 8 to drive the steam turbine generator 9 to generate electricity. The exhaust steam exiting the steam turbine 8 has a pressure higher than atmospheric pressure and is condensed in the positive pressure condenser 10. The resulting condensate 11 enters the furnace heating surface 2 of the boiler body 1 via the boiler feed water pump 12 and the economizer 13, where it generates saturated steam 5 again. The steam extracted from the steam turbine is used as heating steam 27 and supplied externally through the heating pipeline to achieve combined heat and power, 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 the organic working fluid circulation pump 32 and the positive pressure condenser 10, enters the steam turbine 34, drives the steam turbine generator set 35 to generate electricity. The organic working fluid discharged from the steam turbine 34 is cooled by the organic working fluid condenser 36 to form a liquid organic working fluid 37, and then enters the organic working fluid circulation pump 32, thereby forming an organic Rankine cycle loop. The organic working fluid condenser 36 is cooled by cooling water, and a conventional open or closed cycle system of circulating cooling water is adopted. The relatively low-temperature cooling water inlet 38 enters the organic working fluid condenser 36 to liquefy the exhaust gas of the steam turbine 34, and the formed relatively high-temperature cooling water outlet 39 is discharged;

[0068] 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 a 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.

[0069] The air forms hot air 17 through the blower 15 and the air preheater 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.

[0070] The high-temperature water coming out of the gas-water heat exchanger 19 enters the air preheater outside the furnace 16 through the 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 the buffer water tank 21. The low-temperature water in the buffer water tank 21 is boosted by the circulating water pump 18 and then enters the gas-water heat exchanger 19, thereby 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 the water treatment unit 41, enters the deaerator 43 to remove the gas components in the primary demineralized water 42, and then is supplemented into the outlet pipeline of the boiler feed water pump 12 through the make-up water booster pump 44 through the 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 employs chemical desalination (cation and anion exchange method) or membrane separation technology for desalination.

[0077] The deaerator 43 is an ambient temperature deaerator.

[0078] The furnace heating surface 2 adopts water treatment measures such as adding chemicals inside the boiler and continuous or periodic sewage discharge.

[0079] The buffer tank 21 is equipped with a pressure regulator 23: the inert gas coming out of the pressure regulator 23 is nitrogen, which enters the buffer tank 21 through the pressure regulator pipeline 24 and the pressure regulator valve 25, maintaining the liquid water in the gas-water heat exchanger 19, the external air preheater 16, the buffer tank 21 and its connecting pipelines at a high pressure, so that the saturation temperature of the heat transfer medium, i.e. water, in the high-pressure flue gas waste heat recovery system is high, which meets the water temperature requirements for heating the external air preheater.

[0080] Preferably, the water temperature exiting the gas-water heat exchanger 19 is 10°C to 30°C lower than the saturated 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 replace the gas in the high-pressure water flue gas waste heat recovery system, and the system is then sealed after the replacement is completed. Feedwater is drawn from the boiler feedwater pump outlet pipe 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 the set value. At this time, the buffer tank 21 is equivalent to a gas-water co-containment chamber.

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

[0084] The water and air in the external air preheater 16 are exchanged indirectly. The heat exchange tubes are plain tubes, finned tubes or spiral groove tubes, etc. Preferably, enhanced heat transfer measures are adopted.

[0085] The water and flue gas in the gas-water heat exchanger 19 exchange heat indirectly, and the heat exchange tubes are made of plain tubes, finned tubes, or spiral grooved tubes, etc.

[0086] By controlling the inlet water temperature of the gas-water heat exchanger 19 (for example, above 85℃, the appropriate temperature is determined according to the sulfur content of the fuel), the average value of the inlet water temperature and the exhaust temperature of the gas-water heat exchanger 19, i.e., the metal wall temperature, is higher than the acid dew point temperature of the flue gas. This can effectively prevent low-temperature corrosion of the gas-water heat exchanger 19. Under the premise of avoiding condensation, the waste heat of the flue gas is utilized to the maximum extent, so that the waste heat recovery device of the flue gas can operate economically and with high thermal efficiency, thereby achieving the purpose of energy saving and consumption reduction.

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

[0088] The steam Rankine-organic Rankine combined cycle power generation system employs a denitrification facility to remove nitrogen oxides from the flue gas generated during fuel combustion.

[0089] The organic working fluid condenser 36 is set up according to conventional technology, using water or air as the cooling medium and a closed cooling tower cooling water circulation method.

[0090] The heat exchange elements of the aforementioned equipment mentioned in this utility model can be tubes, finned tubes, serpentine tubes or spiral grooved tubes, or tubes or other types of hollow cavity heat exchange elements that adopt other heat transfer enhancement measures.

[0091] Equipment and its backup systems, pipelines, instruments, valves, insulation, and bypass facilities with regulating functions not described in this utility model shall be equipped with known and mature technologies.

[0092] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the present invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the present invention, and these changes and modifications also fall within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined 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 comprises 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 saturated steam (5) from the furnace heating surface (2) of the boiler body (1), which forms superheated steam (7) through the heater (6), and is sent into the steam turbine (8) to drive the steam turbine generator (9) to generate electricity, the exhaust steam from the steam turbine (8) has a pressure higher than atmospheric pressure and is condensed in the positive pressure condenser (10) to form condensed water (11), which is sent into the furnace heating surface (2) of the boiler body (1) through the boiler feed water pump (12) and the economizer (13) to generate saturated steam (5) again, thereby forming a steam Rankine cycle loop; the organic Rankine cycle refers to liquid organic working medium (37), which forms gaseous organic working medium (33) through the organic working medium circulating pump (32) and the positive pressure condenser (10), and is sent into the gas turbine (34) to drive the gas turbine generator set (35) to generate electricity, the organic working medium discharged from the gas turbine (34) is cooled to form liquid organic working medium (37) through the organic working medium condenser (36), and then enters the organic working medium circulating pump (32), thereby forming an organic Rankine cycle loop; the high-temperature flue gas generated by the burner (3) of the boiler body (1) is cooled through the furnace heating surface (2), the superheater (6), the economizer (13) and the gas-water heat exchanger (19), and then passes through the dust remover (29) and the desulfurization device (30) to form low-temperature flue gas (31), which is discharged from the chimney through the boiler induced draft fan; the air passes through the air blower (15) and the external air preheater (16) to form hot air (17), which is delivered to the burner (3) of the boiler body (1) as a combustion-supporting material and burns with the fuel (4) to form high-temperature flue gas; the high-temperature water from the gas-water heat exchanger (19) enters the external air preheater (16) through the high-temperature water pipeline (20) as a heat source of the external air preheater (16), the low-temperature water from the external air preheater (16) enters the buffer tank (21), the low-temperature water in the buffer tank (21) is pressurized by the circulating water pump (18) and then enters the gas-water heat exchanger (19), or the high-temperature water from the gas-water heat exchanger (19) enters the buffer tank (21) through the high-temperature water pipeline (20), and then is delivered into the external air preheater (16) through the circulating water pump (18) to heat the air delivered by the air blower (15) and then returns to the gas-water heat exchanger (19), thereby 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 of a single-component low-boiling component and a high-boiling 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) comprises 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, wherein the boiler make-up water (40) of the make-up water system forms primary desalted water (42) through a water treatment unit (41), enters a deaerator (43), and then is 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) comprises thermal desalting, chemical desalting or membrane separation technology desalting.

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

7. The steam Rankine-organic Rankine combined cycle power generation system according to claim 1, characterized in that: A pressure stabilizer (23) is provided, wherein the inert gas from the pressure stabilizer (23) enters a buffer tank (21) through a pressure stabilizing valve (25), so as to maintain the liquid water in the gas-water heat exchanger (19), the air preheater (16) outside the furnace, the buffer tank (21) and the connecting pipelines thereof 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 from the pressure stabilizer (23) comprises 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 replace the gas in the high-pressure water flue gas waste heat recovery system, and the system is closed after the replacement is completed; the feed water from the outlet pipeline of the boiler feed water pump (12) is 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 tank (21) is provided with an exhaust valve (26), a pressure gauge and a safety valve.

Images