Rankine cycle power generation system adopting cascade steam boiler

Abstract

The invention relates to a Rankine cycle power generation system adopting a cascade type steam boiler, the cascade type steam boiler comprises an internal circulation steam boiler and an external circulation steam boiler, a steam-water mixture generated by the internal circulation steam boiler enters a steam-water separator, and discharged steam is fed into a phase change heat exchanger through a main steam valve to heat feed water of the external circulation steam boiler; feed water of an external circulation steam boiler is fed into a phase change heat exchanger through a feed pump and a coal economizer to generate saturated steam, the saturated steam enters a superheater to form superheated steam, a generator is driven by a turbine to generate electricity, and steam exhaust of the turbine passes through condensate water formed by a condenser, passes through a condensate pump and a deaerator and then returns to the feed pump; high-temperature flue gas generated by combustion of a waste heat source or fuel in the combustor is cooled by the internal circulation boiler body, the superheater and the economizer and then treated by subsequent equipment to obtain a product or discharged as three wastes.

Description

Technical Field

[0001] This invention belongs to the field of power plant boiler technology, and specifically relates to a steam Rankine cycle power generation system using a cascade steam boiler. Background Technology

[0002] Traditional power plant boilers employ an open-loop circulation system. Clean water, after being purified by water treatment equipment, is pumped into the boiler's water circulation loop (such as the deaerator or condenser) to compensate for steam and water losses during the boiler's water circulation process. The generated superheated steam drives the turbine generator unit to generate electricity. During operation, scale and oxygen corrosion inevitably occur in the boiler drum or steam-water separator, and in the furnace water-cooled wall tubes. Scale formation and oxygen corrosion are two core issues threatening the safe and economical operation of the unit. They often reinforce each other, forming a vicious cycle of "scale formation - corrosion - more severe scale formation." Only a three-pronged strategy of "strict deaeration + scale prevention + water quality regulation" can fundamentally prevent tube rupture accidents. Furthermore, tube rupture accidents in the furnace water-cooled wall tubes of power plant boilers are classified as catastrophic according to the hazard and severity classification.

[0003] Scale formation in power plant boilers is a complex physicochemical process, with the following main mechanisms: Boiler feedwater contains hardness ions such as calcium and magnesium, as well as dissolved oxygen, which are difficult to completely remove with water treatment equipment. During boiler heating, these ions precipitate due to decreased solubility, chemical reactions, and concentration, forming insoluble carbonates, sulfates, or silicates as solid deposits that adhere to the heating surface tube walls and gradually accumulate as scale. Even with deoxygenation by a deaerator, a small amount of dissolved oxygen remains and is introduced into the boiler's water circulation system, leading to corrosion of the boiler's metal heating surfaces and the formation of oxides. Poor water quality, malfunctioning water treatment equipment, inadequate management, improper selection of chemicals, and oxides generated from corrosion of the boiler's metal heating surfaces all contribute to exacerbating scaling and under-scale corrosion, creating a vicious cycle that affects the safe and economical operation of waste heat power plant boilers and can even lead to major safety accidents.

[0004] Steam Rankine cycle generator sets operating with medium and low pressure parameters inevitably experience scale buildup and oxygen corrosion on their boiler heating surfaces during the absorption of heat from high-temperature heat sources. How to solve this problem and ensure the stable, economical, and efficient operation of the associated steam turbine generator sets is a question worthy of in-depth research by professionals in the power industry. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problem of scale and oxygen corrosion on the heating surface of the boiler body in newly built medium and low pressure combined heat and power units or medium and low pressure waste heat power generation units that use fuel. By adopting cascade steam boiler technology, the occurrence of scale and oxygen corrosion is transferred from the high-temperature heat source to the safer and easier-to-manage external phase change heat exchanger, thereby providing a reliable guarantee for the safe, stable and efficient operation of the entire combined cycle power generation unit.

[0006] The objective of this invention is achieved through the following measures:

[0007] A Rankine cycle power generation system employing a cascade steam boiler is characterized in that: the cascade steam boiler comprises an internal circulation steam boiler and an external circulation steam boiler; the internal circulation steam boiler includes an internal circulation boiler body 3, a steam-water separator 4, and a phase changer 7; the external circulation steam boiler includes a feedwater pump 17, an economizer 18, the phase changer 7, a superheater 19, and connecting pipes; the internal circulation steam boiler and the external circulation steam boiler form a cascade steam boiler through the phase changer 7.

[0008] The steam-water mixture generated by the contact between the internal circulation boiler body 3 and the high-temperature heat source enters the steam-water separator 4, where steam and water are separated. The separated liquid water returns to the internal circulation boiler body 3, while the separated steam 6 is sent to the phase change heat exchanger 7 via the main steam valve 5 to heat the feedwater of the external circulation steam boiler. The resulting condensate 8 returns to the internal circulation boiler body 3 directly or after being pressurized by the circulating water pump 9.

[0009] The feedwater from the external circulation steam boiler is pumped into the phase changer 7 via feedwater pump 17 and economizer 18. In the phase changer 7, saturated steam is generated by heat absorption. This saturated steam then enters the superheater 19 for further heating, forming superheated steam 20. The superheated steam 20 enters the turbine 21, driving the generator 28 to generate electricity. The exhaust steam from the turbine 21 is condensed in the condenser 22 to form condensate, which is then pumped into the deaerator 16 via condensate pump 23. The deaerated water in the deaerator 16 then re-enters the feedwater pump 17, thus forming the water circulation loop of the external circulation steam boiler.

[0010] After the high-temperature heat source is cooled by the internal circulation boiler body 3, superheater 19, and economizer 18, it enters the subsequent equipment (such as dust collector, desulfurization or denitrification equipment, etc.) for processing, and is then transported to the subsequent equipment for further processing or discharged (such as being discharged from the chimney by an induced draft fan).

[0011] The internal circulation boiler body 3 and the steam-water separator 4 adopt an integrated structure, and are listed as separate components only to highlight the steam-water separation function of the steam-water separator 4.

[0012] The high-temperature heat source is either waste heat or high-temperature flue gas generated by fuel combustion.

[0013] When the high-temperature heat source is high-temperature flue gas generated by fuel combustion, the internal circulation steam boiler includes an internal circulation boiler body 3, a steam-water separator 4, a phase change heat exchanger 7, a burner 1, and an air preheater 25; the external circulation steam boiler includes a feedwater pump 17, an economizer 18, a phase change heat exchanger 7, and a superheater 19.

[0014] The steam-water mixture generated during combustion in the furnace of the internal circulation boiler body 3 enters the steam-water separator 4 for steam-water separation. The separated liquid water returns to the internal circulation boiler body 3, while the separated steam 6 is sent to the phase change heat exchanger 7 via the main steam valve 5 to heat the feedwater of the external circulation steam boiler. The resulting condensate 8 returns to the internal circulation boiler body 3 directly or after being pressurized by the circulating water pump 9.

[0015] The feedwater from the external circulation steam boiler is pumped by feedwater pump 17 and economizer 18 into phase changer 7, where it absorbs heat to produce saturated steam. This steam then enters superheater 19, where it is heated by high-temperature flue gas in the furnace or flue to form superheated steam 20. The superheated steam 20 enters turbine 21 to drive generator 28 to generate electricity. The exhaust steam from turbine 21 is condensed in condenser 22 to form condensate, which is then pumped by condensate pump 23 into deaerator 16. The deaerated water in deaerator 16 then returns to feedwater pump 17, thus forming the water circulation loop of the external circulation steam boiler.

[0016] Air is blown by blower 24 and air preheater 25 to form hot air 26, which is mixed with combustible material 2 and burned in burner 1. The high-temperature flue gas produced by combustion heats the condensate 8 in the internal circulation boiler body 3, and the resulting steam-water mixture then enters steam-water separator 4.

[0017] The high-temperature flue gas generated by burner 1 is cooled by the internal circulation boiler body 3, superheater 19, economizer 18 and air preheater 25, and the resulting low-temperature flue gas 27 is transported to subsequent equipment (such as dust collector, desulfurization or denitrification equipment, etc.) for treatment, and then discharged from the chimney by induced draft fan.

[0018] The phase change heat exchanger 7 is equipped with continuous and periodic sewage discharge pipelines. After being purified by the water treatment equipment 13, the clean water 12 enters the purified water tank 14 and is then fed into the deaerator 16 or condenser 22 by the water supply pump 15 to compensate for the steam and water loss of the external circulation steam boiler.

[0019] The phase change heat exchanger 7 adopts a shell-and-tube heat exchange method. Preferably, the phase change heat exchanger 7 adopts a shell-and-tube heat exchanger, in which the steam generated by the internal circulation steam boiler flows through the shell side and the feedwater of the external circulation steam boiler flows through the tube side. The phase change heat exchanger 7 is equipped with a safety valve to prevent the saturated steam generated by the internal circulation steam boiler from entering the tube side and causing overpressure.

[0020] The internal circulation boiler body 3 includes water-cooled wall tubes, downcomers, and headers, and is designed according to the conventional natural circulation or forced circulation principle.

[0021] Preferably, the heating surface of the internal circulation boiler body 3 adopts enhanced heat transfer technology, such as finned tubes.

[0022] The combustible material 2 used in the burner 1 is one or more of gaseous, liquid or solid fuels, such as coal, biomass fuel, liquid fuel such as petroleum oil, and gaseous fuel such as natural gas.

[0023] The air preheater 25 is a rotary air preheater or a partitioned air preheater; when a partitioned heat exchange method is used, the heat exchange tubes are plain tubes, turbulence tubes, finned tubes or spiral groove tubes, etc.

[0024] A water replenishment line is provided: demineralized water or purified water is replenished into the water circulation loop of the internal circulation boiler body 3 via a booster pump to compensate for the steam and water loss generated by the internal circulation steam.

[0025] The steam space of the steam-water separator 4 leads out a safety valve connection pipe to prevent the internal circulation boiler body 3 from operating under overpressure.

[0026] Furthermore, a water jet ejector and a low-pressure heater are provided between the condensate pump 23 and the deaerator 16. The water jet ejector is used to extract the gas generated in the condenser 22 and maintain the vacuum level at the condenser 22.

[0027] Furthermore, a high-pressure heater is provided between the water pump 17 and the economizer 18, using the extracted steam from the turbine 21 as a heat source to form a regenerative cycle, thereby improving the power generation efficiency of the generator set.

[0028] The internal circulation steam boiler adopts a closed water circulation loop, with minimal steam and water loss. Pure water is used to replenish the steam and water loss. The pure water can be obtained by cooling the saturated steam generated by the phase change heat exchanger 7, or by using the condensate generated at the low-pressure heater and high-pressure heater. The pure water obtained by condensation has very little dissolved oxygen, thus eliminating the possibility of oxygen corrosion in the internal circulation steam boiler from the source.

[0029] An external air preheater is provided: heating steam is drawn from the extraction steam pipe of the steam turbine 21 and sent to the external air preheater through the regulating valve to heat the air delivered by the blower 24. The condensate generated at the external air preheater returns to the purification water tank 14 or the deaerator 16. The air with increased temperature coming out of the external air preheater enters the air preheater 25 in the flue gas duct to ensure that the metal wall temperature of the air preheater 25 in the flue gas duct is higher than the acid dew point temperature of the flue gas.

[0030] When the high-temperature heat source is a waste heat source, the waste heat source can be in one or more states, including gaseous, liquid, or solid. For example, 202520172730.3 - Waste heat recovery device for sensible heat of high-temperature magnesium slag, 202310573665.0 - Waste heat recovery device and method for sensible heat of molten calcium carbide, 202122078113.1 Energy-saving device for waste heat boiler tail gas of dry quenching coke flue gas, 201911143005.9 - Cooling system and method for cement clinker, etc., provide waste heat recovery devices and methods for recovering waste heat sources in three states: gas, solid, and liquid.

[0031] The economizer 18 employs enhanced heat transfer measures, such as using finned tubes or spiral grooved tubes.

[0032] The phase change heat exchanger 7 is equipped with continuous and periodic sewage discharge pipelines. After being purified by the water treatment equipment 13, the clean water 12 enters the purified water tank 14 and is then fed into the deaerator 16 or condenser 22 by the water supply pump 15 to compensate for the steam and water loss of the external circulation steam boiler.

[0033] The phase change heat exchanger 7 adopts a shell-and-tube heat exchange method. Preferably, the phase change heat exchanger 7 adopts a shell-and-tube heat exchanger. The steam generated by the internal circulation boiler body 3 flows through the shell side, and the feedwater of the external circulation steam boiler flows through the tube side. The phase change heat exchanger 7 is equipped with a safety valve to prevent the high-pressure saturated steam generated by the internal circulation steam boiler from entering the tube side and causing overpressure.

[0034] The internal circulation boiler body 3 includes water-cooled wall tubes, downcomers, and headers, and is designed according to the conventional natural circulation or forced circulation principle.

[0035] Preferably, the heating surface of the internal circulation boiler body 3 adopts enhanced heat transfer technology, such as finned tubes.

[0036] A water replenishment line is provided: demineralized water or purified water is replenished into the water circulation loop of the internal circulation boiler body 3 via a booster pump to compensate for the steam and water losses generated by the internal circulation steam boiler.

[0037] The steam space of the steam-water separator 4 leads out a safety valve connection pipe to prevent the internal circulation boiler body 3 from operating under overpressure.

[0038] Furthermore, a water jet ejector and a low-pressure heater are provided between the condensate pump 23 and the deaerator 16. The water jet ejector is used to extract the gas generated in the condenser 22 to maintain the vacuum at the condenser 22. The low-pressure heater uses the steam extracted from the turbine 21 as a heat source to heat the condensate pump 23.

[0039] Furthermore, a high-pressure heater is provided between the water pump 17 and the economizer 18, using the extracted steam from the turbine 21 as a heat source to form a regenerative cycle, thereby improving the power generation efficiency of the generator set.

[0040] The internal circulation steam boiler adopts a closed water circulation loop, with minimal steam and water loss. Pure water is used to replenish the steam and water loss. The pure water can be obtained by cooling the saturated steam generated by the phase change heat exchanger 7, or by using the condensate generated at the low-pressure heater and high-pressure heater. The pure water obtained by condensation has very little dissolved oxygen, thus eliminating the possibility of oxygen corrosion in the internal circulation steam boiler from the source.

[0041] In actual operation: condenser condensate is treated with ion exchange mixed bed or other precision filtration systems such as permeation membranes to remove dissolved copper ions; or water treatment equipment uses a combined operation process of anion and cation exchange resins and permeation membranes to ensure high water quality requirements for external circulation steam boiler makeup water; or the continuous wastewater from the phase change heat exchanger is cooled and then the harmful ions are removed before being returned to the external circulation steam boiler system for makeup water use.

[0042] The parts not mentioned in this invention are implemented using existing steam Rankine cycle power generation technology. That is, existing, well-known, mature, reliable and reasonable technical measures can be introduced into this system, such as setting up necessary pressure gauges, temperature control instruments, water level gauges, alarm instruments, automatic control facilities, etc.

[0043] The present invention has the following advantages over the prior art:

[0044] 1. Employing cascade steam boiler technology, the internal circulation steam boiler uses a closed-loop pure water circulation process, unlike the open circulation process in traditional power plant boilers which requires continuous water replenishment to compensate for steam and water losses caused by continuous blowdown, turbine steam leakage, and deaeration by the deaerator. The internal circulation steam boiler's heating surfaces are free from scale formation and oxygen corrosion accumulation, thus avoiding the possibility of scale and oxygen corrosion on the water-cooled wall tubes, convection heat exchange surfaces, and steam condensation side heat exchange surfaces of the phase change heat exchanger. The steam-water separator achieves high efficiency due to the pure water circulation, essentially removing the main areas of scale and oxygen corrosion from the internal circulation steam boiler. The harsh environment of the high-temperature heat source is transferred to the phase change heat exchanger of the external circulation steam boiler. The scale and oxygen corrosion transferred to the phase change heat exchanger can be safely controlled through methods such as blowdown, cleaning, feedwater deoxygenation, and adding deoxygenating agents to the phase change heat exchanger. Because the phase change heat exchanger operates in the medium-temperature range below the critical temperature of water, the regulatory risks for national regulatory authorities, as well as the safety risks for users and operators, are greatly reduced. This also results in economic benefits from long-term safe operation of the equipment and a significant reduction in related costs due to convenient maintenance and repair, thus ensuring the safe, economical, and long-term operation of the power plant boiler and its supporting generator sets. How to reduce or even eliminate scale and oxygen corrosion on the water-cooled wall tubes of the power plant boiler furnace and avoid accidents caused by this is a global technical challenge. The technical solution provided by this invention eliminates the possibility of scale and oxygen corrosion on the water-cooled wall tubes and convective heat exchange surfaces of power plant boilers at the source.

[0045] 2. An innovative economizer feedwater and superheater external circulation process is adopted. The economizer effluent, after being heated, is no longer supplied to the main body of the traditional power plant boiler and then enters the superheater to generate superheated steam to drive the turbine generator set. Instead, it enters the phase change heat exchanger and becomes an integral part of the external circulation steam boiler's water circulation loop. The saturated steam generated by the phase change heat exchanger 7 enters the superheater located in the high-temperature heat source of the internal circulation steam boiler. The generated superheated steam then drives the turbine generator set to generate electricity. Therefore, this is fundamentally different from the working fluid circulation of traditional power plant boilers. Because the feedwater heated by the economizer reaches or approaches saturation temperature, the heat transfer process of the phase change heat exchanger 7 is more efficient.

[0046] 3. The phase change heat exchanger adopts a shell-and-tube heat exchanger, in which steam flows through the shell side and feedwater from the external circulation steam boiler flows through the tube side. The tube side is easy to clean, and it is a phase change heat exchange process. By selecting appropriate internal circulation steam boiler pressure and external circulation steam boiler pressure, the heat transfer temperature difference of the phase change heat exchanger 7 can be ensured, thereby ensuring that the phase change heat exchanger 7 has a compact structure and high heat transfer efficiency.

[0047] 4. The internal circulation steam pipeline adopts a closed-loop circulation method. If a circulating water pump is installed, the circulating water pump does not need to be a multi-stage pump. Only the pressure resistance, temperature resistance and overcoming friction resistance need to be considered, and the power consumption is minimal.

[0048] 5. By adding an external air preheater (i.e., a warm air blower) to the flue, the metal wall temperature of the air preheater in the flue of the steam boiler is made higher than the acid dew point temperature of the flue gas, which effectively avoids low-temperature corrosion of the air preheater in the flue and maximizes the utilization of flue gas waste heat, thereby achieving the goal of energy saving and consumption reduction.

[0049] 6. Cascade steam boilers offer a variety of possibilities for the optimized design of boiler heating surfaces, such as adopting high circulation ratio once-through boiler technology and using internal straight fins for water-cooled wall tubes to enhance heat transfer, thus providing a reliable guarantee for the safe, stable and efficient operation of the entire combined cycle generator unit.

[0050] 7. The present invention is applicable to newly built medium and low pressure waste heat power generation units or medium and low pressure cogeneration units using fuel. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the process flow of the Rankine Cycle power generation system using a cascade steam boiler, according to the present invention.

[0052] Figure 1In the diagram, 1-burner, 2-combustible material, 3-internal circulation boiler body, 4-steam-water separator, 5-main steam valve, 6-steam, 7-phase change heat exchanger, 8-condensate, 9-circulating water pump, 10-first safety valve, 11-second safety valve, 12-clean water, 13-water treatment equipment, 14-purified water tank, 15-water supply pump, 16-deaerator, 17-feed water pump, 18-economizer, 19-superheater, 20-superheated steam, 21-steam turbine, 22-condenser, 23-condensate pump, 24-blower, 25-air preheater, 26-hot air, 27-low temperature flue gas, 28-generator.

[0053] Figure 2 This is a schematic diagram of the process flow of the Rankine cycle power generation system using a cascade steam boiler (high-temperature flue gas waste heat recovery) of the present invention.

[0054] Figure 2 In the middle, 3-internal circulation boiler body, 4-steam-water separator, 5-main steam valve, 6-steam, 7-phase change heat exchanger, 8-condensate, 9-circulating water pump, 10-first safety valve, 11-second safety valve, 12-clean water, 13-water treatment equipment, 14-purified water tank, 15-water supply pump, 16-deaerator, 17-feed water pump, 18-economizer, 19-superheater, 20-superheated steam, 21-steam turbine, 22-condenser, 23-condensate pump, 27-low temperature flue gas, 28-generator, 29-high temperature flue gas. Detailed Implementation

[0055] The following is in conjunction with the appendix Figure 1 Appendix Figure 2 The present invention will be further described in detail with reference to specific embodiments.

[0056] Example 1:

[0057] As attached Figure 1 As shown, a Rankine cycle power generation system employs a cascade steam boiler. The cascade steam boiler includes an internal circulation steam boiler and an external circulation steam boiler. The internal circulation steam boiler includes an internal circulation boiler body 3, a steam-water separator 4, a burner 1, and an air preheater 25. The external circulation steam boiler includes a feedwater pump 17, an economizer 18, a phase change heat exchanger 7, a superheater 19, and their connecting pipes.

[0058] The steam-water mixture generated by the internal circulation boiler body 3 enters the steam-water separator 4, where steam and water are separated. The separated liquid water returns to the internal circulation boiler body 3, while the separated steam 6 is sent to the phase change heat exchanger 7 via the main steam valve 5 to heat the feedwater of the external circulation steam boiler. The resulting condensate 8 returns to the internal circulation boiler body 3 directly or after being pressurized by the circulating water pump 9.

[0059] The feedwater from the external circulation steam boiler is pumped by feedwater pump 17 and economizer 18 into phase changer 7, where it absorbs heat to produce saturated steam. This steam then enters superheater 19, where it is heated by high-temperature flue gas in the furnace or flue to form superheated steam 20. The superheated steam 20 enters turbine 21 to drive generator 28 to generate electricity. The exhaust steam from turbine 21 is condensed in condenser 22 to form condensate, which is then pumped by condensate pump 23 into deaerator 16. The deaerated water in deaerator 16 then returns to feedwater pump 17, thus forming the water circulation loop of the external circulation steam boiler.

[0060] Air is blown by blower 24 and air preheater 25 to form hot air 26, which is mixed with combustible material 2 and burned in burner 1. The high-temperature flue gas produced by combustion heats the condensate 8 in the internal circulation boiler body 3, and the resulting steam-water mixture then enters steam-water separator 4.

[0061] The high-temperature flue gas generated by burner 1 is cooled by the internal circulation boiler body 3, superheater 19, economizer 18 and air preheater 25, and the resulting low-temperature flue gas 27 is transported to subsequent equipment (such as dust collector, desulfurization or denitrification equipment, etc.) for treatment, and then discharged from the chimney by induced draft fan.

[0062] The phase change heat exchanger 7 is equipped with continuous and periodic sewage discharge pipelines. After being purified by the water treatment equipment 13, the clean water 12 enters the purified water tank 14 and is then fed into the deaerator 16 or condenser 22 by the water supply pump 15 to compensate for the steam and water loss of the external circulation steam boiler.

[0063] The phase change heat exchanger 7 adopts a shell-and-tube heat exchange method. Preferably, the phase change heat exchanger 7 is a shell-and-tube heat exchanger, with steam flowing through the shell side and boiler feedwater flowing through the tube side. The phase change heat exchanger 7 is equipped with necessary safety valves.

[0064] The internal circulation boiler body 3 includes water-cooled wall tubes, downcomers, and headers, and is designed according to the conventional natural circulation or forced circulation principle.

[0065] Preferably, the heating surface of the internal circulation boiler body 3 adopts enhanced heat transfer technology, such as finned tubes.

[0066] The combustible material 2 used in the burner 1 is natural gas.

[0067] The air preheater 25 is a partitioned air preheater, and the heat exchange tubes are made of bare tubes, turbulence-disrupting tubes, finned tubes or spiral groove tubes, etc.

[0068] A water replenishment line is provided: demineralized water or purified water is pumped into the liquid water circulation loop of the internal circulation boiler body 3 or the steam-water separator 4 to replenish the steam and water losses generated by the internal circulation steam.

[0069] The steam space of the steam-water separator 4 has a safety valve connecting pipe, which is equipped with a first safety valve 10 and a second safety valve 11 to prevent the internal circulation boiler body 3 from operating under overpressure.

[0070] Because the internal circulation steam uses a closed water circulation loop, the steam and water loss is minimal, and pure water is used to replenish the steam and water loss. The pure water is produced by cooling the saturated steam generated by the phase change heat exchanger 7, thus basically eliminating the possibility of oxygen corrosion from the source.

[0071] A water jet ejector and a low-pressure heater are provided between the condensate pump 23 and the deaerator 16. The water jet ejector is used to extract the gas generated in the condenser 22 and maintain the vacuum at the condenser 22.

[0072] A high-pressure heater is provided between the water pump 17 and the economizer 18, using the extracted steam from the turbine 21 as a heat source to form a regenerative cycle, thereby improving the power generation efficiency of the generator set.

[0073] Preferably, the internal circulating steam adopts a closed water circulation loop, with minimal steam and water loss, and pure water is used to replenish the steam and water loss; the pure water can be obtained by cooling the saturated steam generated by the phase change heat exchanger, or by using the condensate generated at the low-pressure heater and high-pressure heater. The pure water obtained by condensation has very little dissolved oxygen, thus eliminating the possibility of oxygen corrosion from the source.

[0074] The purified water can also be produced by cooling the steam extracted from the steam turbine 21: the steam extracted from the steam turbine is cooled by the purified water from the water treatment equipment 13 or the purified water tank 14 to produce purified water, and the heated purified water is returned to the purified water tank 14.

[0075] An external air preheater is provided: heating steam is drawn from the extraction steam pipe of the steam turbine 21 and sent to the external air preheater through the regulating valve to heat the air delivered by the blower 24. The condensate generated at the external air preheater returns to the purification water tank 14 or the deaerator 16. The air with increased temperature coming out of the external air preheater enters the air preheater 25 in the flue gas duct to ensure that the metal wall temperature of the air preheater 25 in the flue gas duct is higher than the acid dew point temperature of the flue gas.

[0076] Example 2:

[0077] As attached Figure 2 As shown, the high-temperature heat source is the waste heat from high-temperature flue gas: a Rankine cycle power generation system employing a cascade steam boiler, characterized in that: the cascade steam boiler includes an internal circulation steam boiler and an external circulation steam boiler; the internal circulation steam boiler includes an internal circulation boiler body 3, a steam-water separator 4, and a phase changer 7; the external circulation steam boiler includes a feedwater pump 17, an economizer 18, a phase changer 7, a superheater 19, and connecting pipes; the internal circulation steam boiler and the external circulation steam boiler form a cascade steam boiler through the phase changer 7.

[0078] The steam-water mixture generated by the contact between the internal circulation boiler body 3 and the high-temperature heat source enters the steam-water separator 4, where steam and water are separated. The separated liquid water returns to the internal circulation boiler body 3, while the separated steam 6 is sent to the phase change heat exchanger 7 via the main steam valve 5 to heat the feedwater of the external circulation steam boiler. The resulting condensate 8 returns to the internal circulation boiler body 3 directly or after being pressurized by the circulating water pump 9.

[0079] The feedwater from the external circulation steam boiler is pumped into the phase changer 7 via feedwater pump 17 and economizer 18. In the phase changer 7, saturated steam is generated by heat absorption. This saturated steam then enters the superheater 19 for further heating, forming superheated steam 20. The superheated steam 20 enters the turbine 21, driving the generator 28 to generate electricity. The exhaust steam from the turbine 21 is condensed in the condenser 22 to form condensate, which is then pumped into the deaerator 16 via condensate pump 23. The deaerated water in the deaerator 16 then re-enters the feedwater pump 17, thus forming the water circulation loop of the external circulation steam boiler.

[0080] After being cooled by the internal circulation boiler body 3, superheater 19, and economizer 18, the high-temperature flue gas enters the subsequent equipment (such as dust collector, desulfurization or denitrification equipment, etc.) for treatment, and is then discharged from the chimney by the induced draft fan.

[0081] The economizer 18 employs enhanced heat transfer measures, such as using finned tubes or spiral grooved tubes.

[0082] The phase change heat exchanger 7 is equipped with continuous and periodic sewage discharge pipelines. After being purified by the water treatment equipment 13, the clean water 12 enters the purified water tank 14 and is then fed into the deaerator 16 or condenser 22 by the water supply pump 15 to compensate for the steam and water loss of the external circulation steam boiler.

[0083] The phase change heat exchanger 7 adopts a shell-and-tube heat exchange method. Preferably, the phase change heat exchanger 7 adopts a shell-and-tube heat exchanger. The steam generated by the internal circulation boiler body 3 flows through the shell side, and the feedwater of the external circulation steam boiler flows through the tube side. The phase change heat exchanger 7 is equipped with a safety valve to prevent the high-pressure saturated steam generated by the internal circulation steam boiler from entering the tube side and causing overpressure.

[0084] The internal circulation boiler body 3 includes water-cooled wall tubes, downcomers, and headers, and is designed according to the conventional natural circulation or forced circulation principle.

[0085] Preferably, the heating surface of the internal circulation boiler body 3 adopts enhanced heat transfer technology, such as finned tubes.

[0086] A water replenishment line is provided: demineralized water or purified water is replenished into the water circulation loop of the internal circulation boiler body 3 via a booster pump to compensate for the steam and water losses generated by the internal circulation steam boiler.

[0087] The steam space of the steam-water separator 4 leads out a safety valve connection pipe to prevent the internal circulation boiler body 3 from operating under overpressure.

[0088] Furthermore, a water jet ejector and a low-pressure heater are provided between the condensate pump 23 and the deaerator 16. The water jet ejector is used to extract the gas generated in the condenser 22 to maintain the vacuum at the condenser 22. The low-pressure heater uses the steam extracted from the turbine 21 as a heat source to heat the condensate pump 23.

[0089] Furthermore, a high-pressure heater is provided between the water pump 17 and the economizer 18, using the extracted steam from the turbine 21 as a heat source to form a regenerative cycle, thereby improving the power generation efficiency of the generator set.

[0090] The internal circulation steam boiler adopts a closed water circulation loop, with minimal steam and water loss. Pure water is used to replenish the steam and water loss. The pure water can be obtained by cooling the saturated steam generated by the phase change heat exchanger 7, or by using the condensate generated at the low-pressure heater and high-pressure heater. The pure water obtained by condensation has very little dissolved oxygen, thus eliminating the possibility of oxygen corrosion in the internal circulation steam boiler from the source.

[0091] The parts not mentioned in this invention are implemented using existing steam Rankine cycle power generation technology. That is, existing, well-known, mature, reliable and reasonable technical measures can be introduced into this system, such as setting up necessary pressure gauges, temperature control instruments, water level gauges, alarm instruments, automatic control facilities, etc.

[0092] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention, and these modifications and modifications also fall within 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 Rankine cycle power generation system employing a cascade steam boiler, characterized in that: The cascade steam boiler includes an internal circulation steam boiler and an external circulation steam boiler. The internal circulation steam boiler includes an internal circulation boiler body (3), a steam-water separator (4), and a phase change heat exchanger (7). The external circulation steam boiler includes a feedwater pump (17), an economizer (18), a phase change heat exchanger (7), and a superheater (19). The internal circulation steam boiler and the external circulation steam boiler form a cascade steam boiler through the phase change heat exchanger (7). The steam-water mixture generated by the contact of the internal circulation boiler body (3) with the high-temperature heat source enters the steam-water separator (4), where steam and water are separated. The separated steam is sent to the phase change heat exchanger (7) through the main steam valve (5) to heat the feedwater of the external circulation steam boiler. The condensate (8) generated is returned to the internal circulation boiler body (3) directly or after being pressurized by the circulating water pump (9). The feedwater from the external circulation steam boiler enters the phase changer (7) via the feedwater pump (17) and economizer (18). In the phase changer (7), saturated steam is generated by absorbing heat and then enters the superheater (19) to form superheated steam (20). The superheated steam (20) enters the turbine (21) to drive the generator (28) to generate electricity. The exhaust steam from the turbine (21) is condensed in the condenser (22) to form condensate, which is then pumped by the condensate pump (23) to the deaerator (16) to remove dissolved oxygen. The deoxygenated water in the deaerator (16) returns to the inlet of the feedwater pump (17), thus forming a water circulation loop for the external circulation steam boiler. After the high-temperature heat source is cooled by the internal circulation boiler body (3), superheater (19), and economizer (18), it is transported to subsequent equipment for processing.

2. The Rankine cycle power generation system according to claim 1, characterized in that: The high-temperature heat source is either waste heat or high-temperature flue gas generated by fuel combustion.

3. The Rankine cycle power generation system according to claim 2, characterized in that: When the high-temperature heat source is high-temperature flue gas generated by fuel combustion, the internal circulation steam boiler includes an internal circulation boiler body (3), a steam-water separator (4), a burner (1), and an air preheater (25). The steam-water mixture generated by the internal circulation boiler body (3) in the furnace enters the steam-water separator (4) for steam-water separation. The separated steam is sent to the phase change heat exchanger (7) through the main steam valve (5) to heat the feedwater of the external circulation steam boiler. The generated condensate (8) is returned to the internal circulation boiler body (3) directly or after being pressurized by the circulating water pump (9). The feed water of the external circulation steam boiler is sent into the phase change heat exchanger (7) through the feed water pump (17) and the economizer (18). It absorbs heat in the phase change heat exchanger (7) to generate saturated steam, and then enters the superheater (19). After being heated by the high-temperature flue gas in the furnace or flue, superheated steam (20) is formed. The superheated steam (20) enters the steam turbine (21) to drive the generator (28) to generate electricity. The exhausted steam from the steam turbine (21) is condensed by the condenser (22) to form condensate water, which is sent into the deaerator (16) through the condensate pump (23) to remove dissolved oxygen. The deaerated water in the deaerator (16) then enters the feed water pump (17), thus forming the water circulation loop of the external circulation steam boiler. Air passes through the blower (24) and the air preheater (25) to form hot air (26), which is mixed and burned with the combustible (2) in the burner (1). The high-temperature flue gas generated by the combustion heats the condensate water entering the internal circulation boiler body (3), and the generated steam-water mixture then enters the steam-water separator (4). The high-temperature flue gas generated by the burner (1) is cooled after passing through the internal circulation boiler body (3), the superheater (19), the economizer (18), and the air preheater (25). After being processed by subsequent equipment, it is discharged through the chimney by the induced draft fan.

4. The Rankine cycle power generation system according to claim 3, wherein: A water replenishment line is provided: Demineralized water or pure water is replenished into the water circulation loop of the internal circulation boiler body (3) through a booster pump.

5. The Rankine cycle power generation system according to claim 4, wherein: The pure water is the condensate water generated at the low-pressure heater and the high-pressure heater, or the pure water obtained by cooling the steam extracted from the steam turbine (21): The steam extracted from the steam turbine is cooled by the purified water coming out of the water treatment equipment (13) or the purification water tank (14) to obtain pure water, and the heated purified water then returns to the purification water tank (14).

6. The Rankine cycle power generation system according to claim 3, wherein: The combustible (2) uses one or more of gaseous, liquid, or solid fuels; the phase change heat exchanger (7) adopts a shell-and-tube heat exchange method; the air preheater (25) adopts a rotary air preheater or a shell-and-tube air preheater.

7. The Rankine cycle power generation system according to claim 3, wherein: An air preheater outside the furnace is provided: A heating steam pipeline is led out from the steam extraction pipeline of the steam turbine (21), sent into the air preheater outside the furnace through a regulating valve to heat the air sent by the blower (24). The condensate water generated at the air preheater outside the furnace returns to the purification water tank (14) or the deaerator (16), and the air with increased temperature coming out of the air preheater outside the furnace enters the air preheater (25) in the flue, making the metal wall temperature of the air preheater (25) in the flue higher than the acid dew point temperature of the flue gas.

8. The Rankine cycle power generation system according to claim 2, wherein: The form of the waste heat source includes one or more of gaseous, liquid, or solid; The phase change heat exchanger (7) adopts a shell-and-tube heat exchange method.

9. The Rankine cycle power generation system according to claim 8, wherein: A water replenishment line is provided: demineralized water or pure water is replenished into the water circulation loop of the internal circulation boiler body (3) via a booster pump.

10. The Rankine cycle power generation system according to claim 9, characterized in that: The purified water is condensate generated by the low-pressure heater and the high-pressure heater, or purified water obtained by steam extraction and cooling from the steam turbine (21): purified water is obtained by cooling the purified water from the steam extraction from the steam turbine through the water treatment equipment (13), and the heated purified water is returned to the purified water tank (14).

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