Thermodynamic system based on regenerative steam extraction energy gradient absorption
By constructing a thermodynamic system for the cascade absorption of regenerative extraction steam energy, and using low-pressure extraction steam to heat medium-pressure feedwater, the problem of insufficient utilization of turbine extraction steam energy is solved, thereby reducing cold source losses and improving thermal economy.
Patent Information
- Application Number
- CN202520955264.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-15
- Publication Date
- 2026-03-06
- Estimated Expiration
- 2035-05-15
AI Technical Summary
In existing technologies, the utilization of steam extraction energy from steam turbines is not yet sufficient, resulting in significant cold source losses and affecting the unit's thermal efficiency.
By constructing a thermodynamic system based on the energy cascade absorption of regenerative extraction steam, the superheated section of low-pressure extraction steam is used to heat the medium-pressure feedwater, thereby displacing the high-pressure cylinder extraction steam, reducing cold source losses, and improving thermal economy under medium and low loads.
This technology enables the extraction of more low-pressure steam and the discharge of high-pressure steam, reducing cold source losses, improving the thermal economy of the unit at low and medium loads, and reducing the design pressure of equipment and pipelines, thus reducing costs.
Smart Images
Figure CN223975168U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of coal-fired power generation technology, specifically relating to a thermodynamic system based on the cascade absorption of regenerative steam extraction energy. Background Technology
[0002] To reduce cold source losses and improve unit thermal efficiency, modern generating units are equipped with turbine extraction steam regeneration systems. This involves extracting a portion of the steam used for power generation and utilizing its latent heat to heat condensate and feedwater, reducing the amount of latent heat discharged to the cold-end condensing unit. This is a typical application for reducing cold source losses and improving unit thermal efficiency. To further improve unit thermal efficiency, in recent years, steam coolers (hereinafter referred to as external steam coolers) have been added downstream of the final stage (highest pressure stage) high-pressure heater. Considering cost, single-stage reheat units have one stage of external steam cooler, while double-stage reheat units have two stages of external steam coolers connected in parallel. The steam source comes from the first-stage extraction steam after reheating. After passing through the external steam cooler, the low-superheat extraction steam is then connected to its corresponding regeneration heater, releasing its latent heat and becoming condensate before entering the relevant system. External steam coolers contribute approximately 15 kJ / kWh to reducing power generation heat rate, equivalent to a reduction of approximately 0.5 g / kWh in coal consumption. Research and comparison revealed that the superheat of extraction steam in other stages of the intermediate-pressure cylinder and the high-pressure section of the low-pressure cylinder remains very high under rated operating conditions and medium-low load conditions. Directly using it as a heat source for the regenerator results in significant heat loss, thus requiring further optimization to reduce cold source losses. Utility Model Content
[0003] The technical problem to be solved by this utility model is to provide a thermodynamic system based on the cascade absorption of regenerative steam extraction energy, which solves the problem of insufficient utilization of steam extraction energy in the existing technology. Through system structure innovation, the cascade absorption of regenerative steam extraction energy enables the extraction of more low-pressure steam and the discharge (less extraction) of high-pressure steam, thereby reducing cold source losses and improving the thermal economy of the unit at low and medium loads.
[0004] According to the technical solution of this utility model, this utility model provides a thermodynamic system based on the cascade absorption of regenerative steam extraction energy. In the boiler feedwater pipeline of the boiler, a multi-stage low-pressure heater, a deaerator, a pre-pump, a feedwater pump, a multi-stage high-pressure heater, and an external steam cooler before the boiler are sequentially arranged along the feedwater delivery direction. The intermediate-pressure cylinder of the steam turbine is connected to an intermediate-pressure cylinder high-pressure extraction steam pipeline and multiple intermediate-pressure cylinder low-pressure extraction steam pipelines. The intermediate-pressure cylinder high-pressure extraction steam pipeline is sequentially connected to the external steam cooler before the boiler and the feedwater pump. The adjacent high-pressure heaters are connected; the low-pressure cylinder of the turbine is connected to the low-pressure cylinder extraction steam pipe; multiple intermediate-pressure cylinder low-pressure extraction steam pipes and low-pressure cylinder extraction steam pipes are connected to the deaerator and low-pressure heater respectively in order of extraction steam pressure from high to low; the booster pump and the feedwater pump are also connected through an intermediate-pressure feedwater heating pipe; an external intermediate-pressure feedwater heater is installed in the intermediate-pressure cylinder low-pressure extraction steam pipe and the low-pressure cylinder extraction steam pipe; the intermediate-pressure feedwater heater connects the external intermediate-pressure feedwater heater in parallel.
[0005] In some implementations, the number of external evaporators for medium-pressure water supply heating is three, four, or five.
[0006] In some embodiments, the multi-stage low-pressure heater includes a No. 8 low-pressure heater, a No. 7 low-pressure heater, and a No. 6 low-pressure heater arranged sequentially along the feedwater delivery direction; the medium-pressure cylinder low-pressure steam extraction pipeline includes a five-section steam extraction pipeline, a six-section steam extraction pipeline, and a seven-section steam extraction pipeline, and the low-pressure cylinder steam extraction pipeline includes an eight-section steam extraction pipeline; the five-section steam extraction pipeline, the six-section steam extraction pipeline, the seven-section steam extraction pipeline, and the eight-section steam extraction pipeline are respectively connected to the deaerator, the No. 6 low-pressure heater, the No. 7 low-pressure heater, and the No. 8 low-pressure heater, and each of the five-section steam extraction pipeline, the six-section steam extraction pipeline, the seven-section steam extraction pipeline, and the eight-section steam extraction pipeline is equipped with an external medium-pressure feedwater heater evaporator.
[0007] In some embodiments, the multi-stage low-pressure heater also includes a ninth and a tenth low-pressure heater positioned before the eighth low-pressure heater.
[0008] In some embodiments, the multi-stage high-pressure heater includes a fourth high-pressure heater, a third high-pressure heater, a second high-pressure heater, and a first high-pressure heater arranged sequentially along the water supply direction.
[0009] In some embodiments, the medium-pressure water supply heating pipeline connects the medium-pressure water supply heating external evaporators in parallel; in the medium-pressure water supply heating pipeline, valves are provided on the output side and input side of each medium-pressure water supply heating external evaporator.
[0010] In some implementations, the boiler is connected in sequence to an air preheater, a dust collector, an induced draft fan, a desulfurization unit, and a chimney via boiler flue gas ducts.
[0011] Compared with the prior art, the beneficial technical effects of this utility model are as follows:
[0012] This utility model discloses a thermodynamic system based on the cascade absorption of regenerative extraction steam energy. It employs thermodynamic system reconstruction and efficiency improvement technology. By constructing a thermodynamic system for the cascade absorption of regenerative extraction steam energy, it fully utilizes the steam turbine extraction energy and reduces cold source losses. Specifically, an external evaporator cooler is added upstream of the deaerator and low-pressure heater in the regenerative extraction steam pipeline. The superheated section of this low-pressure extraction steam is then used to heat the intermediate-pressure feedwater at the outlet of the booster pump, increasing the intermediate-pressure feedwater temperature and displacing the extraction steam from the first-stage high-pressure heater (the stage with the lowest extraction pressure). The low-superheated steam then returns to its respective regenerative heater. This scheme not only increases the extraction steam from the original low-pressure heater but also heats the superheated section. The high-grade feedwater system utilizes higher-grade extraction steam to achieve energy-saving goals. Designed as heated medium-pressure feedwater rather than high-pressure feedwater, it significantly reduces the design pressure of external steam coolers, pipelines, valves, and other equipment and fittings, thus lowering costs. To facilitate layout and reduce extraction steam pressure loss, the medium-pressure feedwater is connected to the extraction steam of each unit according to heat and temperature matching principles. To reduce system layout complexity, multiple external steam coolers can be arranged in parallel. This system can operate under all unit operating conditions, improving overall thermal economy. To further reduce costs, it can be designed for low to medium loads and operated only under these conditions, providing low to medium load thermal economy. Attached Figure Description
[0013] Figure 1 This is a schematic diagram of the system structure provided by this utility model.
[0014] Explanation of reference numerals in the attached figures:
[0015] 1. Boiler; 11. Boiler feedwater pipeline; 111. Medium-pressure feedwater heating pipeline; 12. Boiler flue gas pipeline; 121. Air preheater; 122. Dust collector; 123. Induced draft fan; 124. Desulfurization unit; 125. Chimney; 21. No. 6 low-pressure heater; 22. No. 7 low-pressure heater; 23. No. 8 low-pressure heater; 24. No. 9 low-pressure heater; 25. No. 10 low-pressure heater; 3. Deaerator; 4. Pre-pump; 5. Feedwater pump; 61. 62. High-pressure heater No. 1; 63. High-pressure heater No. 3; 64. High-pressure heater No. 4; 7. External steam cooler in front of the boiler; 81. High-pressure cylinder; 82. Medium-pressure cylinder; 821. High-pressure extraction steam pipeline of medium-pressure cylinder; 822. Five-section extraction steam pipeline; 823. Six-section extraction steam pipeline; 824. Seven-section extraction steam pipeline; 83. Low-pressure cylinder; 831. Low-pressure cylinder extraction steam pipeline; 84. Generator; 9. External steam cooler for medium-pressure feedwater heating. Detailed Implementation
[0016] This invention provides a thermodynamic system based on the cascade absorption of regenerative steam extraction energy, which solves the problem of insufficient utilization of steam extraction energy in existing technologies. Through system structural innovation, the cascade absorption of regenerative steam extraction energy enables the extraction of more low-pressure steam and the discharge (less extraction) of high-pressure steam, thereby reducing cold source losses and improving the thermal economy of the unit at low and medium loads.
[0017] Please see Figure 1 This utility model discloses a thermal system based on the cascade absorption of regenerative steam extraction energy. In the boiler feedwater pipeline 11 of boiler 1, a multi-stage low-pressure heater, a deaerator 3, a pre-pump 4, a feedwater pump 5, a multi-stage high-pressure heater, and an external steam cooler 7 are sequentially arranged along the feedwater delivery direction. There are multiple low-pressure heaters and high-pressure heaters, all of which are regenerative heaters of the regenerative system.
[0018] The steam turbine includes a high-pressure cylinder 81, an intermediate-pressure cylinder 82, a low-pressure cylinder 83, and a generator 84 connected together. The intermediate-pressure cylinder 82 is connected to an intermediate-pressure cylinder high-pressure extraction steam pipe 821 and multiple intermediate-pressure cylinder low-pressure extraction steam pipes. The intermediate-pressure cylinder high-pressure extraction steam pipe 821 is sequentially connected to the external steam cooler 7 before the boiler and the high-pressure heater adjacent to the feedwater pump 5. The high-pressure steam extracted from the intermediate-pressure cylinder first heats the feedwater before the boiler and then continues to be used in the high-pressure heater. It is understood that "before" and "after" in this text refer to the direction of feedwater delivery, i.e., "upstream side" and "downstream side."
[0019] The low-pressure cylinder 83 of the steam turbine is connected to a low-pressure cylinder extraction steam pipe 831. Multiple intermediate-pressure cylinder low-pressure extraction steam pipes and low-pressure cylinder extraction steam pipes 831 are connected to the deaerator 3 and the low-pressure heater respectively in order of extraction steam pressure from high to low. In other words, the steam pressure input to the deaerator 3 and each stage of the low-pressure heater in the boiler feedwater pipe 11 gradually increases along the feedwater (condensate) flow direction, thereby gradually heating the feedwater.
[0020] The pre-pump 4 and the feedwater pump 5 are also connected via a medium-pressure feedwater heating pipe 111; in other words, on the boiler feedwater pipe 11, the medium-pressure feedwater heating pipe 111 is led out from the output end of the pre-pump 4, and the end of the medium-pressure feedwater heating pipe 111 is connected to the input end of the feedwater pump 5. A medium-pressure feedwater heating external evaporator 9 is installed in the medium-pressure cylinder low-pressure extraction steam pipe and the low-pressure cylinder extraction steam pipe 831, so that the extracted steam first passes through the medium-pressure feedwater heating external evaporator 9 before entering the deaerator and low-pressure heater of the regenerative system; the medium-pressure feedwater heating external evaporator 9 heats the extracted feedwater with a portion of the heat (superheated portion) of the extracted steam, and the medium-pressure feedwater heating pipe 111 connects the medium-pressure feedwater heating external evaporator 9 in parallel, such as... Figure 1 As shown. The number of external evaporators 9 for medium-pressure water supply heating can be set according to actual conditions and needs, preferably three, four or five.
[0021] like Figure 1 In the specific embodiment shown, the multi-stage low-pressure heater includes at least a No. 8 low-pressure heater 23, a No. 7 low-pressure heater 22, and a No. 6 low-pressure heater 21 arranged sequentially along the feedwater delivery direction; further, the multi-stage low-pressure heater also includes a No. 9 low-pressure heater 24 and a No. 10 low-pressure heater 25 arranged before the No. 8 low-pressure heater 23. The intermediate-pressure cylinder low-pressure steam extraction pipeline includes a five-section steam extraction pipeline 822, a six-section steam extraction pipeline 823, and a seven-section steam extraction pipeline 824. The low-pressure cylinder steam extraction pipeline 831 includes an eight-section steam extraction pipeline. The five-section extraction steam pipeline 822, the six-section extraction steam pipeline 823, the seven-section extraction steam pipeline 824, and the eight-section extraction steam pipeline are respectively connected to the deaerator 3, the No. 6 low-pressure heater 21, the No. 7 low-pressure heater 22, and the No. 8 low-pressure heater 23. Each of the five-section extraction steam pipeline 822, the six-section extraction steam pipeline 823, the seven-section extraction steam pipeline 824, and the eight-section extraction steam pipeline is equipped with a medium-pressure feedwater heating external steam cooler 9. The multi-stage high-pressure heaters include the No. 4 high-pressure heater 64, the No. 3 high-pressure heater 63, the No. 2 high-pressure heater 62, and the No. 1 high-pressure heater 61, arranged sequentially along the feedwater delivery direction. The steam drawn from the medium-pressure cylinder high-pressure extraction steam pipeline 821 first passes through the boiler-front external steam cooler 7 and then through the No. 4 high-pressure heater 64.
[0022] As a supplementary explanation, steam will enter the steam side of the high-pressure heater and the low-pressure heater, and become condensate after heat exchange. The condensate will eventually enter the boiler feedwater pipe 11 as condensate to form a water circulation. The specific settings of the existing components in the regenerative system can be selected by using existing technology or other feasible methods, which are not improvements of this invention, so they will not be described in detail and are not shown in the figure or are only simple illustrations.
[0023] More specifically, each pipeline will have corresponding valves as needed to control the opening and closing of the pipeline. For example... Figure 1 As shown, for the scheme of connecting the medium-pressure water supply heating external evaporators 9 in parallel via the medium-pressure water supply heating pipeline 111, it is preferable to install valves on both the output and input sides of each medium-pressure water supply heating external evaporator 9 in the medium-pressure water supply heating pipeline 111. More specifically, these valves are electric valves, capable of being manually or automatically controlled by a control system.
[0024] Furthermore, such as Figure 1 In the specific embodiment shown, the boiler 1 is connected in sequence to the air preheater 121, the dust collector 122, the induced draft fan 123, the desulfurization device 124, and the chimney 125 via the boiler flue gas duct 12.
[0025] The following examples further illustrate the content, concept, and beneficial technical effects of this solution.
[0026] Taking a certain 1,000 MW double reheat unit as an example, the superheat of steam extracted from other stages of the intermediate-pressure cylinder (excluding those with external evaporators), the steam extracted from the high-pressure section of the low-pressure cylinder, and the intermediate-pressure feedwater temperature under various operating conditions are shown in the table below:
[0027]
[0028]
[0029]
[0030] This shows that the superheat of the extraction steam in other stages of the intermediate-pressure cylinder and the high-pressure section of the low-pressure cylinder is still very high under rated operating conditions and medium-low load conditions. Directly using it as a heat source for the regenerator results in large losses, which provides a possibility for optimization.
[0031] To further improve the thermal efficiency of the unit, this utility model proposes to install an external evaporator to heat high-grade feedwater before returning it to the corresponding regenerative heater for units with high superheat. Through system structural innovation, the energy of the regenerative extraction steam is absorbed in stages, realizing the extraction of more low-pressure steam and the discharge (less extraction) of high-pressure steam, reducing cold source losses and improving the thermal economy of the unit at low and medium loads.
[0032] The main innovations and concepts of this plan include:
[0033] 1. The superheated section of the low-pressure extraction steam is used to heat the medium-pressure feedwater (outlet of the pre-pump) first, increasing the temperature of the medium-pressure feedwater and displacing the steam extracted by the first-stage high-pressure heater (the stage with the lowest extraction steam pressure). The low-superheated steam is returned to its respective regenerator.
[0034] 2. This solution not only increases the original low-pressure heater extraction steam, but also heats the high-grade feedwater in the superheater section and discharges higher-grade extraction steam, thus achieving the energy-saving goal.
[0035] 3. Heating medium-pressure water supply instead of high-pressure water supply can significantly reduce the design pressure of external evaporators, pipes, valves and other equipment and fittings, thus reducing costs.
[0036] 4. To facilitate layout and reduce steam extraction pressure loss, medium-pressure feedwater is connected to the steam extraction of each unit according to the principles of heat matching and temperature matching.
[0037] 5. This system can be put into operation under all operating conditions of the unit, improving thermal economy under all operating conditions. To reduce costs, it can be designed to operate only under medium and low loads, providing thermal economy under medium and low loads.
[0038] Furthermore, taking a 1,000 MW unit as an example, the system setup and benefits are explained. Using a 50% THA (Total Heat Amount) operating condition as the design point, external evaporative coolers are installed in sections 5, 6, 7, and 8 of the unit. Four feedwater lines are drawn from the pre-pump outlet and connected to the corresponding medium-pressure feedwater heating external evaporative coolers. The four sets of external evaporative coolers operate in parallel. The superheat of the steam after passing through the evaporative coolers is controlled at approximately 50°C and is then connected to the corresponding regenerative heater. After releasing latent heat, it becomes condensate and enters the relevant system. Calculations show that each set of external evaporative coolers reduces power generation heat consumption by approximately 5 kJ / kWh, and the four sets of external evaporative coolers can reduce power generation heat consumption by approximately 20 kJ / kWh.
[0039] When the unit is operating at 50% THA or higher, close the valves on the output and input sides of the external evaporator 9 for medium-pressure feedwater heating and disconnect the external evaporator.
[0040] In specific engineering applications, the number of external evaporator stages can be flexibly set according to the unit conditions and energy saving requirements, and the benefits vary depending on the unit conditions and system settings.
[0041] In summary, this utility model, by constructing a thermodynamic system for the cascade absorption of regenerative steam extraction energy, fully utilizes the steam extraction energy of the turbine and reduces cold source losses, aiming to improve the thermal economy of the unit at low and medium loads and even at rated loads. It is technically and economically feasible and worthy of development and promotion.
Claims
1. A thermal system based on regenerative extraction steam energy cascade absorption, characterized in that, A plurality of low-pressure heaters, a deaerator (3), a pre-pump (4), a feedwater pump (5), a plurality of high-pressure heaters and a boiler front external steam cooler (7) are sequentially arranged in a boiler feedwater pipeline (11) of a boiler (1) in the feedwater conveying direction. A high-pressure steam extraction pipeline (821) and a plurality of low-pressure steam extraction pipelines of the intermediate-pressure cylinder of the steam turbine are connected to the intermediate-pressure cylinder (82), the high-pressure steam extraction pipeline (821) is sequentially connected to the boiler front external steam cooler (7) and a high-pressure heater adjacent to the feedwater pump (5) after the feedwater pump (5); a low-pressure cylinder (83) of the steam turbine is connected to a low-pressure cylinder steam extraction pipeline (831); the plurality of low-pressure steam extraction pipelines of the intermediate-pressure cylinder and the low-pressure cylinder steam extraction pipeline (831) are sequentially connected to the deaerator (3) and the low-pressure heater in the order of the extraction pressure from high to low. The pre-pump (4) and the feedwater pump (5) are further connected through a medium-pressure feedwater heating pipeline (111), the medium-pressure feedwater heating external steam cooler (9) is arranged in the low-pressure steam extraction pipeline of the intermediate-pressure cylinder and the low-pressure cylinder steam extraction pipeline (831), and the medium-pressure feedwater heating pipeline (111) connects the medium-pressure feedwater heating external steam coolers (9) in parallel.
2. The thermodynamic system based on regenerative extraction steam energy cascade absorption according to claim 1, characterized in that, The number of the medium-pressure feedwater heating external steam coolers (9) is three, four or five.
3. The thermodynamic system based on regenerative extraction steam energy cascade absorption according to claim 1, characterized in that, The plurality of low-pressure heaters include an eighth low-pressure heater (23), a seventh low-pressure heater (22) and a sixth low-pressure heater (21) arranged in the feedwater conveying direction in sequence; the low-pressure steam extraction pipeline of the intermediate-pressure cylinder includes a fifth steam extraction pipeline (822), a sixth steam extraction pipeline (823) and a seventh steam extraction pipeline (824), and the low-pressure cylinder steam extraction pipeline (831) includes an eighth steam extraction pipeline; the fifth steam extraction pipeline (822), the sixth steam extraction pipeline (823), the seventh steam extraction pipeline (824) and the eighth steam extraction pipeline are connected to the deaerator (3), the sixth low-pressure heater (21), the seventh low-pressure heater (22) and the eighth low-pressure heater (23) respectively, and one medium-pressure feedwater heating external steam cooler (9) is arranged in each of the fifth steam extraction pipeline (822), the sixth steam extraction pipeline (823), the seventh steam extraction pipeline (824) and the eighth steam extraction pipeline.
4. The thermodynamic system based on regenerative extraction steam energy cascade absorption according to claim 3, characterized in that, The plurality of low-pressure heaters further include a ninth low-pressure heater (24) and a tenth low-pressure heater (25) arranged in front of the eighth low-pressure heater (23).
5. The thermodynamic system based on regenerative extraction steam energy cascade absorption according to claim 4, characterized in that, The plurality of high-pressure heaters include a fourth high-pressure heater (64), a third high-pressure heater (63), a second high-pressure heater (62) and a first high-pressure heater (61) arranged in the feedwater conveying direction in sequence.
6. The thermodynamic system based on regenerative extraction steam energy cascade absorption according to any one of claims 1-5, characterized in that, The medium-pressure feedwater heating pipeline (111) connects the medium-pressure feedwater heating external steam coolers (9) in parallel; a valve is arranged on the output side and the input side of each medium-pressure feedwater heating external steam cooler (9) in the medium-pressure feedwater heating pipeline (111).
7. The thermodynamic system based on regenerative extraction steam energy cascade absorption according to any one of claims 1-5, characterized in that, The boiler (1) is sequentially connected to an air preheater (121), a dust remover (122), an induced draft fan (123), a desulfurization device (124) and a chimney (125) through a boiler flue gas pipeline (12).