Combined heat and power generation energy gradient utilization heat supply system based on low-pressure cylinder separation

Abstract

The invention provides a combined heat and power generation energy gradient utilization heat supply system based on low-pressure cylinder separation. The system comprises an intermediate-pressure cylinder, a first low-pressure cylinder section, a second low-pressure cylinder section, a first heat exchanger, a second heat exchanger, a first pipeline, a second pipeline, a third pipeline and a fourth pipeline. The pipe sides of the first heat exchanger and the second heat exchanger are sequentially connected to a heating return water pipeline in series in the flowing direction of heating return water, an outlet of the medium-pressure cylinder communicates with an inlet of the first section of the low-pressure cylinder through the first pipeline, and an outlet of the medium-pressure cylinder communicates with an inlet of the second section of the low-pressure cylinder through the second pipeline. An outlet of the low-pressure cylinder section 1 is communicated with a shell side inlet of the first heat exchanger through a third pipeline, and an outlet of the medium-pressure cylinder is communicated with a shell side inlet of the second heat exchanger through a fourth pipeline. The system can solve the problems that in the prior art, combined heat and power generation efficiency and flexibility are difficult to consider, low-temperature waste heat utilization is insufficient, and system modification economy is poor.

Description

Technical Field

[0001] This application relates to the field of thermoelectric technology, and more specifically, to a cogeneration energy cascade utilization heating system based on a low-pressure cylinder sub-cylinder. Background Technology

[0002] In the field of heating in coal-fired power plants, typical technical solutions include: 1) Medium and low pressure connecting pipe steam extraction heating technology, which involves adding regulating valve groups to the medium and low pressure connecting pipes of the steam turbine to extract steam from the medium-pressure cylinder exhaust or the low-pressure cylinder intake for heating the heating network as needed. This technology is mature, but it suffers from the problem of high-pressure steam (around 0.4 MPa) directly heating the heating water, resulting in a waste of high-quality capacity; 2) Absorption heat pump coupling technology, which uses steam extracted from the steam turbine as a driving heat source and raises the temperature of the heating network return water through a heat pump device, realizing deep utilization of low-temperature waste heat. However, this method has limited deep adjustment capability of the unit; 3) Low-pressure cylinder zero-output modification technology, by cutting off the steam inlet of the low-pressure cylinder to achieve full steam exhaust from the intermediate-pressure cylinder for heating, significantly improves the unit's heating capacity and has a high deep adjustment capability, but there is a phenomenon of high-pressure steam (around 0.4MPa) directly heating the heating water, resulting in a waste of high-quality capacity; 4) High back-pressure circulating water heating technology, which uses the condensate heat of exhaust steam to heat the circulating water, to achieve energy cascade utilization, but the unit's operation and adjustment capability is very weak due to the matching limitation between the return water temperature of the heating network and the unit's back pressure. Although the above technologies have improved the level of waste heat utilization on the turbine side in different dimensions, they still face common technical bottlenecks such as the difficulty in balancing the efficiency of cogeneration and the flexibility of unit operation, insufficient improvement of low-temperature waste heat quality, and poor economic efficiency of system modification. Summary of the Invention

[0003] This application provides at least one heating system based on the energy cascade utilization of cogeneration energy from a low-pressure cylinder. This system can improve the problems in the prior art, such as the difficulty in balancing the efficiency and flexibility of cogeneration, insufficient utilization of low-temperature waste heat, and poor economic efficiency of system modification.

[0004] This application provides a combined heat and power (CHP) energy cascade utilization heating system based on a low-pressure cylinder. The system includes an intermediate-pressure cylinder, a first low-pressure cylinder (section 1), a second low-pressure cylinder (section 2), a first heat exchanger, a second heat exchanger, a first pipe, a second pipe, a third pipe, and a fourth pipe. The first and second heat exchangers are connected in series along the flow direction of the heating return water in the heating return water pipeline. The inlet of the first pipe is connected to the outlet of the intermediate-pressure cylinder, and the outlet of the first pipe is connected to the inlet of the first low-pressure cylinder (section 1). The inlet of the second pipe is connected to the outlet of the intermediate-pressure cylinder, and the outlet of the second pipe is connected to the inlet of the second low-pressure cylinder (section 2). The inlet of the third pipe is connected to the outlet of the first low-pressure cylinder (section 1). The third pipe is connected to the shell-side inlet of the first heat exchanger, the fourth pipe is connected to the outlet of the intermediate-pressure cylinder, and the fourth pipe is connected to the shell-side inlet of the second heat exchanger. During the non-heating phase, the first section of the low-pressure cylinder maintains a minimum steam flow rate, and both the first and second heat exchangers stop receiving steam. During the heating phase, the second section of the low-pressure cylinder maintains a minimum steam flow rate. The first heat exchanger uses the exhaust steam from the first section of the low-pressure cylinder to heat the heating return water, and the second heat exchanger uses the exhaust steam from the intermediate-pressure cylinder to further heat the heating return water. The unit's electrical load frequency is adjusted by regulating the steam intake of the first and second heat exchangers.

[0005] In one optional implementation, during the heating phase, the exhaust steam from the low-pressure cylinder 1 heats the heating return water to 80-90°C, and the exhaust steam from the medium-pressure cylinder heats the heating return water to 90-110°C.

[0006] In one optional embodiment, the system further includes a first flow regulating valve, a second flow regulating valve, a third flow regulating valve, and a fourth flow regulating valve, wherein the first flow regulating valve is disposed at the outlet of the first pipeline, the second flow regulating valve is disposed at the second pipeline, the third flow regulating valve is disposed at the third pipeline, and the fourth flow regulating valve is disposed at the fourth pipeline.

[0007] In one optional embodiment, a condenser is also included, wherein the shell-side inlet of the condenser is connected to the outlet of the low-pressure cylinder section 2, and the shell-side outlet of the condenser is connected to the main steam inlet of the boiler.

[0008] In one alternative embodiment, a deaerator is further included, which is connected in series between the shell-side outlet of the condenser and the main steam inlet of the boiler.

[0009] In an alternative embodiment, a condensate pump is further included, which is connected in series between the condenser shell-side outlet and the deaerator inlet.

[0010] In one alternative embodiment, a feedwater pump is further included, which is connected in series between the outlet of the deaerator and the main steam inlet of the boiler.

[0011] In one optional embodiment, the system further includes multiple low-pressure heaters, the tube sides of which are sequentially connected in series between the shell-side outlet of the condenser and the inlet of the deaerator. The temperature of the heating medium in the shell-side of the multiple low-pressure heaters gradually increases along the condensate flow direction, and the heating medium in each stage of the low-pressure heater flows into the previous stage of the low-pressure heater after heat exchange, and finally flows into the tube side of the condenser. The heating medium includes the extraction steam of the second stage of the low-pressure cylinder, the exhaust steam of the first stage of the low-pressure cylinder, and the exhaust steam of the intermediate-pressure cylinder.

[0012] In one optional embodiment, the low-pressure heater includes a first heater, a second heater, a third heater, and a fourth heater. The shell-side outlet of the condenser is sequentially connected to the inlet of the deaerator via the tube sides of the first heater, the second heater, the third heater, and the fourth heater. The shell-side inlet of the first heater is connected to a first extraction port located in the second section of the low-pressure cylinder, and the shell-side outlet of the first heater is connected to the shell side of the condenser. The shell-side inlet of the second heater is connected to a second extraction port located in the second section of the low-pressure cylinder, and the shell-side outlet of the second heater is connected to the shell side of the first heater. The shell-side inlet of the third heater is connected to the outlet located in the first section of the low-pressure cylinder, and the shell-side outlet of the third heater is connected to the shell side of the second heater. The shell-side inlet of the fourth heater is connected to the outlet located in the intermediate-pressure cylinder, and the shell-side outlet of the fourth heater is connected to the shell side of the condenser.

[0013] In one alternative embodiment, the shell-side outlets of the first heat exchanger and the second heat exchanger are respectively connected to the shell-side inlet of the low-pressure heater or the shell side of the condenser.

[0014] The above-mentioned technical solution of this application has the following beneficial technical effects:

[0015] The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder of this application embodiment effectively solves the problems of contradiction between thermoelectric efficiency and flexibility, insufficient utilization of low-temperature waste heat, and poor system economy in traditional cogeneration technology by decomposing the low-pressure cylinder into two parts (low-pressure cylinder section 1 and low-pressure cylinder section 2) and combining it with cascade heating method.

[0016] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. These drawings are incorporated in and constitute a part of this specification. They illustrate embodiments conforming to this application and, together with the specification, serve to explain the technical solutions of this application. It should be understood that the following drawings only show some embodiments of this application and should not be considered as limiting the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This illustration shows a schematic diagram of a cogeneration energy cascade utilization heating system based on a low-pressure cylinder sub-cylinder, provided in an embodiment of this application.

[0019] In the picture:

[0020] 1. Intermediate-pressure cylinder; 2. Low-pressure cylinder section 1; 3. Low-pressure cylinder section 2; 4. First heat exchanger; 5. Second heat exchanger; 6. First pipeline; 7. Second pipeline; 8. Third pipeline; 9. Fourth pipeline; 10. First flow regulating valve; 11. Second flow regulating valve; 12. Third flow regulating valve; 13. Fourth flow regulating valve; 14. Condenser; 15. Deaerator; 16. Condensate pump; 17. Feedwater pump; 18. First heater; 19. Second heater; 20. Third heater; 21. Fourth heater. Detailed Implementation

[0021] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present application.

[0022] The embodiments of this application will now be described in detail. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0023] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise stated, "multiple" means two or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0024] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0025] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0026] refer to Figure 1 This application provides a combined heat and power (CHP) energy cascade utilization heating system based on a low-pressure cylinder. The system includes a medium-pressure cylinder 1, a low-pressure cylinder section 1 2, a low-pressure cylinder section 2 3, a first heat exchanger 4, a second heat exchanger 5, a first pipe 6, a second pipe 7, a third pipe 8, and a fourth pipe 9. The first heat exchanger 4 and the second heat exchanger 5 are connected in series along the flow direction of the heating return water in the heating return water pipeline. The inlet of the first pipe 6 is connected to the outlet of the medium-pressure cylinder 1, and the outlet of the first pipe 6 is connected to the inlet of the low-pressure cylinder section 2. The inlet of the second pipe 7 is connected to the outlet of the medium-pressure cylinder 1, and the outlet of the second pipe 7 is connected to the inlet of the low-pressure cylinder section 2 3. The inlet of the third pipe 8 is connected to the outlet of the low-pressure cylinder section 2. The outlet of the third pipe 8 is connected to the shell-side inlet of the first heat exchanger 4, the inlet of the fourth pipe 9 is connected to the outlet of the intermediate-pressure cylinder 1, and the outlet of the fourth pipe 9 is connected to the shell-side inlet of the second heat exchanger 5. During the non-heating stage, the low-pressure cylinder 1 section 2 maintains minimum steam flow, and both the first heat exchanger 4 and the second heat exchanger 5 stop steam intake. During the heating stage, the low-pressure cylinder 2 section 3 maintains minimum steam flow, the first heat exchanger 4 uses the exhaust steam from the low-pressure cylinder 1 section 2 to heat the heating return water, and the second heat exchanger 5 uses the exhaust steam from the intermediate-pressure cylinder 1 to further heat the heating return water. The unit's electrical load frequency is adjusted by regulating the steam intake of the first heat exchanger 4 and the second heat exchanger 5.

[0027] While traditional methods of heating using zero-output low-pressure cylinders or extraction steam from medium-pressure cylinder 1 can improve heating capacity, the direct use of high-pressure steam (0.4MPa) for heating hot water results in inefficient energy utilization and low thermal efficiency. Furthermore, while technologies like absorption heat pumps can improve waste heat utilization, they limit the unit's deep peak-shaving capabilities. This system employs a split-cylinder design for the low-pressure cylinder, dedicating section 2 of low-pressure cylinder 1 to heating and section 3 of low-pressure cylinder 2 to power generation. This allows for flexible switching between heating and power generation, addressing the existing problem of balancing combined heat and power (CHP) efficiency with operational flexibility. Specifically, in pure condensing mode, section 2 of low-pressure cylinder 1 operates at a low flow rate, while section 3 of low-pressure cylinder 2 carries most of the steam to ensure power generation efficiency. In heating mode, section 2 of low-pressure cylinder 1 operates at a high flow rate, while section 3 of low-pressure cylinder 2 retains only a small amount of cooling steam (approximately 20t / h) to ensure the unit still has peak-shaving capabilities. Simultaneously, by adjusting the steam flow rates of the first and second stage heaters, the electrical load can be flexibly adjusted, enabling real-time frequency regulation and improving operational flexibility. Therefore, it retains the peak-shaving capability of zero output of the low-pressure cylinder while avoiding energy waste caused by direct heating of high-pressure steam, thus balancing high flexibility and high energy efficiency.

[0028] Traditional high-back-pressure circulating water heating technology is limited by the matching of the heating network return water temperature and the unit back pressure, making it difficult to efficiently utilize low-temperature waste heat (such as 45°C return water). This system, however, employs a tiered heating method to heat the heating return water in two stages, effectively addressing the problem of insufficient improvement in the grade of low-temperature waste heat. Specifically, the first stage of heating utilizes the second exhaust steam from the first stage of the low-pressure cylinder (lower-grade heat energy) to heat the heating return water, while the second stage utilizes the first exhaust steam from the medium-pressure cylinder (higher-grade heat energy) to further heat the heating return water. Clearly, by using steam of different grades to heat the heating return water in stages, the problem of insufficient improvement in the grade of low-temperature waste heat in existing units can be addressed, while also avoiding the waste of high-grade steam and improving overall thermal efficiency.

[0029] Traditional technological upgrades (such as absorption heat pumps and high back-pressure heating) often require complex equipment or significant modifications to the turbine structure, resulting in high investment costs and complex operation and maintenance. This system, based on a partial cylinder modification of the low-pressure cylinder, only requires the addition of two heat exchangers and related valves, without replacing the main turbine structure. The upgrade is simple, and the system can flexibly switch operating modes, adapting to pure condensing or heating conditions without additional equipment, thus reducing operation and maintenance costs. This addresses the issue of poor economic efficiency in upgrading existing unit systems.

[0030] In some embodiments, during the heating supply phase, the steam exhaust from section 2 of the low-pressure cylinder heats the heating return water to 80–90°C, and the steam exhaust from section 1 of the medium-pressure cylinder heats the heating return water to 90–110°C. Of course, the above temperature parameters can be selected according to actual conditions and are not limited to the methods discussed above.

[0031] In some embodiments, the system further includes a first flow regulating valve 10, a second flow regulating valve 11, a third flow regulating valve 12, and a fourth flow regulating valve 13. The first flow regulating valve 10 is disposed at the outlet of the first pipeline 6, the second flow regulating valve 11 is disposed at the second pipeline 7, the third flow regulating valve 12 is disposed at the third pipeline 8, and the fourth flow regulating valve 13 is disposed at the fourth pipeline 9. In actual operation, by controlling the opening degrees of the first flow regulating valve 10, the second flow regulating valve 11, the third flow regulating valve 12, and the fourth flow regulating valve 13, the steam intake of the low-pressure cylinder section 1 2, the low-pressure cylinder section 2 3, the first heat exchanger 4, and the second heat exchanger 5 can be adjusted.

[0032] In some embodiments, the system further includes a condenser 14, the shell-side inlet of which is connected to the outlet of the low-pressure cylinder section 3, and the shell-side outlet of which is connected to the main steam inlet of the boiler. During operation, the condenser 14 can be used to release heat from the exhaust steam of the low-pressure cylinder section 3 and condense it into water. Simultaneously, the heat released from the exhaust steam of the low-pressure cylinder section 3 can be used to heat fluids passing through the condenser 14 tubes, such as heating return water.

[0033] In some embodiments, the system further includes a deaerator 15 connected in series between the shell-side outlet of the condenser 14 and the main steam inlet of the boiler. During operation, the deaerator 1511 removes dissolved oxygen and other non-condensable gases from the condensate and supplies deaerated water to the main steam inlet of the boiler.

[0034] In some embodiments, the system further includes a condensate pump 16 connected in series between the shell-side outlet of the condenser 14 and the inlet of the deaerator 15. During operation, the condensate pump 16 is used to deliver condensate to the deaerator 15.

[0035] In some embodiments, the system further includes a feedwater pump 17 connected in series between the outlet of the deaerator 15 and the main steam inlet of the boiler. During operation, the feedwater pump 17 is used to deliver deaerated water to the main steam inlet of the boiler.

[0036] In some embodiments, the system further includes a plurality of low-pressure heaters, the tube sides of which are sequentially connected in series between the shell-side outlet of the condenser 14 and the inlet of the deaerator 15. The temperature of the heating medium in the shell-side of the plurality of low-pressure heaters gradually increases along the condensate flow direction, and the heating medium in each stage of the low-pressure heater flows into the previous stage of the low-pressure heater after heat exchange, and finally flows into the tube side of the condenser 14. The heating medium includes the extraction steam of the low-pressure cylinder 2 section 3, the exhaust steam of the low-pressure cylinder 1 section 2, and the exhaust steam of the intermediate-pressure cylinder 1. For example, the low-pressure heater includes a first heater 18, a second heater 19, a third heater 20, and a fourth heater 21. The shell-side outlet of the condenser 14 is sequentially connected to the inlet of the deaerator 15 via the tube side of the first heater 18, the second heater 19, the third heater 20, and the fourth heater 21. The shell-side inlet of the first heater 18 is connected to the first extraction port located in the low-pressure cylinder section 2 3. The shell-side outlet of the first heater 18 is connected to the shell side of the condenser 14. The second heater... The shell-side inlet of the second heater 19 is connected to the second extraction port located in section 3 of the low-pressure cylinder 2. The shell-side outlet of the second heater 19 is connected to the shell side of the first heater 18. The shell-side inlet of the third heater 20 is connected to the outlet located in section 2 of the low-pressure cylinder 1. The shell-side outlet of the third heater 20 is connected to the shell side of the second heater 19. The shell-side inlet of the fourth heater 21 is connected to the outlet located in the intermediate-pressure cylinder 1. The shell-side outlet of the fourth heater 21 is connected to the shell side of the condenser 14. In actual operation, the steam temperature entering the fourth heater 21 is the highest, followed by the steam temperature entering the third heater 20, then the steam temperature entering the second heater 19, and the steam temperature entering the first heater 18 is the lowest. These heaters can utilize the waste heat from extraction and exhaust steam to heat the condensate in stages, thus improving the overall system efficiency and reducing boiler fuel consumption. In addition, the condensate from each stage of the heater can be discharged into the previous stage heater (low temperature side), thereby fully recovering the waste heat in the condensate, reducing the consumption of high-grade steam extraction, and avoiding the waste of heat caused by the direct discharge of condensate into the condenser 14.

[0037] In some embodiments, the shell-side outlets of the first heat exchanger 4 and the second heat exchanger 5 are respectively connected to the shell-side inlet of the low-pressure heater or the shell side of the condenser 14. For example, the shell-side outlet of the third heater 20 is connected to the shell-side outlet of the first heat exchanger 4, and the shell-side outlet of the fourth heater 21 is connected to the shell-side outlet of the second heat exchanger 5.

[0038] The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder of this application effectively solves the problems of contradiction between thermoelectric efficiency and flexibility, insufficient utilization of low-temperature waste heat, and poor system economy in traditional cogeneration technology by decomposing the low-pressure cylinder into two parts (low-pressure cylinder 1 section 2 and low-pressure cylinder 2 section 3) and combining it with the cascade heating method.

[0039] One or more embodiments in this specification are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this specification should be included within the protection scope of this application.

[0040] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder, characterized in that, The system includes a medium-pressure cylinder, a low-pressure cylinder section 1, a low-pressure cylinder section 2, a first heat exchanger, a second heat exchanger, a first pipe, a second pipe, a third pipe, and a fourth pipe. The first and second heat exchangers are connected in series along the flow direction of the heating return water in the heating return water pipeline. The inlet of the first pipe is connected to the outlet of the medium-pressure cylinder, the outlet of the first pipe is connected to the inlet of the low-pressure cylinder section 1, the inlet of the second pipe is connected to the outlet of the medium-pressure cylinder, the outlet of the second pipe is connected to the inlet of the low-pressure cylinder section 2, the inlet of the third pipe is connected to the outlet of the low-pressure cylinder section 1, the outlet of the third pipe is connected to the shell-side inlet of the first heat exchanger, the inlet of the fourth pipe is connected to the outlet of the medium-pressure cylinder, and the outlet of the fourth pipe is connected to the shell-side inlet of the second heat exchanger. During the non-heating phase, the low-pressure cylinder section 1 maintains a minimum steam flow rate, and both the first heat exchanger and the second heat exchanger stop receiving steam. During the heating supply phase, the low-pressure cylinder section 2 maintains minimum steam flow. The first heat exchanger uses the exhaust steam from the low-pressure cylinder section 1 to heat the heating return water, and the second heat exchanger uses the exhaust steam from the medium-pressure cylinder to further heat the heating return water. The unit's electrical load frequency is adjusted by regulating the steam intake of the first and second heat exchangers.

2. The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder as described in claim 1, characterized in that, During the heating season, the exhaust steam from the first stage of the low-pressure cylinder heats the heating return water to 80-90°C, and the exhaust steam from the intermediate-pressure cylinder heats the heating return water to 90-110°C.

3. The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder as described in claim 1, characterized in that, It also includes a first flow regulating valve, a second flow regulating valve, a third flow regulating valve and a fourth flow regulating valve, wherein the first flow regulating valve is disposed at the outlet of the first pipeline, the second flow regulating valve is disposed at the second pipeline, the third flow regulating valve is disposed at the third pipeline and the fourth flow regulating valve is disposed at the fourth pipeline.

4. The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder as described in claim 1, characterized in that, It also includes a condenser, the shell-side inlet of which is connected to the outlet of the low-pressure cylinder section 2, and the shell-side outlet of which is connected to the main steam inlet of the boiler.

5. The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder as described in claim 4, characterized in that, It also includes a deaerator, which is connected in series between the shell-side outlet of the condenser and the main steam inlet of the boiler.

6. The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder as described in claim 5, characterized in that, It also includes a condensate pump connected in series between the condenser shell-side outlet and the deaerator inlet.

7. The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder as described in claim 5, characterized in that, It also includes a feedwater pump, which is connected in series between the outlet of the deaerator and the main steam inlet of the boiler.

8. The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder as described in claim 5, characterized in that, It also includes multiple low-pressure heaters, the tube sides of which are connected in series between the shell-side outlet of the condenser and the inlet of the deaerator. The temperature of the heating medium in the shell side of the multiple low-pressure heaters gradually increases along the condensate flow direction, and the heating medium in each stage of the low-pressure heater flows into the previous stage of the low-pressure heater after heat exchange, and finally flows into the tube side of the condenser. The heating medium includes the extraction steam of the second stage of the low-pressure cylinder, the exhaust steam of the first stage of the low-pressure cylinder, and the exhaust steam of the intermediate-pressure cylinder.

9. The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder as described in claim 8, characterized in that, The low-pressure heater includes a first heater, a second heater, a third heater, and a fourth heater. The shell-side outlet of the condenser is sequentially connected to the inlet of the deaerator via the tube sides of the first heater, the second heater, the third heater, and the fourth heater. The shell-side inlet of the first heater is connected to the first extraction port located in the second section of the low-pressure cylinder, and the shell-side outlet of the first heater is connected to the shell side of the condenser. The shell-side inlet of the second heater is connected to the second extraction port located in the second section of the low-pressure cylinder, and the shell-side outlet of the second heater is connected to the shell side of the first heater. The shell-side inlet of the third heater is connected to the outlet located in the first section of the low-pressure cylinder, and the shell-side outlet of the third heater is connected to the shell side of the second heater. The shell-side inlet of the fourth heater is connected to the outlet located in the intermediate-pressure cylinder, and the shell-side outlet of the fourth heater is connected to the shell side of the condenser.

10. The cogeneration energy cascade utilization heating system based on low-pressure cylinder sub-cylinder as described in claim 8, characterized in that, The shell-side outlets of the first heat exchanger and the second heat exchanger are respectively connected to the shell-side inlet of the low-pressure heater or the shell-side outlet of the condenser.

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