Combined heat and power generation system capable of efficiently and flexibly supplying heat through double-machine combined supply

Abstract

The invention relates to the technical field of energy utilization, in particular to a double-unit combined supply efficient and flexible heat supply combined heat and power generation system which comprises a high back pressure unit and a conventional unit and further comprises a first-stage heating unit, a second-stage heating unit, a third-stage heating unit and a fourth-stage heating unit. Four stages of different heating units are arranged and communicate with a conventional backpressure unit and a high backpressure unit at the same time, and a low-pressure cylinder communicating pipe heat supply mode and a low-pressure cylinder zero-output heat supply mode are flexibly selected according to the total steam demand quantity of a third-stage heater and a fourth-stage heater in combination with the real-time electric load condition of the conventional backpressure unit; the heat supply load of the unit can be adjusted more flexibly, under the condition that the electric load is determined, the external heat supply load of a conventional high-back-pressure unit can fluctuate between + / -50%, and the thermoelectric decoupling capacity is high.

Description

Technical Field

[0001] The present invention relates to the technical field of energy utilization, and in particular to a heat and power cogeneration system for efficient and flexible heating with dual machines. Background Art

[0002] High back pressure heating means increasing the pressure of the exhaust steam in the condenser and using circulating water from the heat network to cool the exhaust steam, thereby using the latent heat of vaporization of the exhaust steam from the steam turbine unit to heat the circulating water and achieve heating. This technology has low heating energy consumption, but has the following disadvantages: (1) Strong coupling between heat and electricity and poor operational flexibility. When the heat supply is constant, the electrical load regulation capacity is less than 5%; (2) High requirements for the operational stability of the heat network. When the circulating water from the heat network leaks, it may lead to insufficient cooling water for the unit and an increase in the exhaust steam temperature, thereby threatening the safe operation of the unit.

[0003] Both the medium- and low-pressure interconnecting pipe heating and the low-pressure cylinder zero-output heating technology use the medium-pressure cylinder exhaust steam to heat the circulating water of the heat network. Under this method, the unit operation flexibility is greater, but the energy quality of the medium-pressure cylinder exhaust steam is relatively high. If it is directly used to heat the circulating water of the heat network, there will be a loss of work capacity and high heating energy consumption.

[0004] Since both have their own shortcomings, the units are unable to strike a balance between power generation flexibility and heating energy consumption, resulting in energy waste. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the problem that the operating flexibility and heating energy consumption of the above-mentioned heating unit cannot be well balanced, the present invention is proposed.

[0007] Therefore, the object of the present invention is to provide a cogeneration system with dual-machine cogeneration for efficient and flexible heating.

[0008] To solve the above technical problems, the present invention provides the following technical solutions: a dual-unit cogeneration system with efficient and flexible heating, comprising a high back pressure unit unit and a conventional unit unit, and also comprising a primary heating unit, a secondary heating unit, a tertiary heating unit and a quaternary heating unit; the primary heating unit is connected to the high back pressure unit unit for preliminarily heating the heating return water, the secondary heating unit is connected to the high back pressure unit unit and the primary heating unit for further heating the heating return water, the tertiary heating unit is simultaneously connected to the high back pressure unit unit, the conventional unit unit and the secondary heating unit, and uses the exhaust steam of the unit to further heat the heating return water, the quaternary heating unit is connected to the conventional unit unit and the tertiary heating unit, and uses the exhaust steam of the conventional unit unit to perform the final heating on the heating return water.

[0009] As a preferred solution of the cogeneration system with efficient and flexible heating of dual-machine cogeneration described in the present invention, the high back pressure unit includes a high back pressure medium pressure cylinder, a high back pressure low pressure cylinder, a high back pressure connecting steam pipe, a high back pressure generator, a high back pressure condenser, a condensate pump, a low-pressure heating module and a deaerator. The high back pressure medium pressure cylinder and the high back pressure low pressure cylinder are supplied with steam through a high back pressure connecting steam pipe. The high back pressure medium pressure cylinder, the high back pressure low pressure cylinder and the high back pressure generator are coaxially arranged. The exhaust port of the high back pressure low pressure cylinder is connected to the high back pressure condenser, the drain port of the high back pressure condenser is connected to the condensate pump, the water outlet of the condensate pump is connected to the low-pressure heating module, and the water outlet of the low-pressure heating module is connected to the deaerator.

[0010] As a preferred solution of the cogeneration system with efficient and flexible heating by dual-machine cogeneration described in the present invention, the conventional unit includes a conventional medium-pressure cylinder, a conventional low-pressure cylinder, a conventional connecting steam pipe, a conventional generator and a conventional condenser. The conventional medium-pressure cylinder and the conventional low-pressure cylinder are supplied with steam through a conventional connecting steam pipe. The conventional medium-pressure cylinder, the conventional low-pressure cylinder and the conventional generator are coaxially arranged, and the exhaust port of the conventional low-pressure cylinder is connected to the conventional condenser.

[0011] As a preferred solution of the cogeneration system with efficient and flexible heating of dual-machine combined supply described in the present invention, the first-level heating unit includes a heating return water pipe, an addition inlet, and a addition outlet. The input end of the heating return water pipe is connected to the external heating return water, and the output end of the heating return water pipe is connected to the addition inlet. The addition inlet and the addition outlet are arranged on the high back pressure condenser.

[0012] As a preferred solution of the cogeneration system with efficient and flexible heating of dual-machine combined supply described in the present invention, wherein: the secondary heating unit includes a secondary heater, a second water supply pipe, a second heating pipe, a second drainage pipe, and a second water outlet pipe. The secondary heater is provided with a cold side and a hot side. The second water supply pipe is respectively connected to the first outlet and the cold side water inlet of the secondary heater, the second heating pipe is respectively connected to the low-pressure module and the hot side heating port of the secondary heater, the second drainage pipe is connected to the hot side of the secondary heater and the input end of the low-pressure module, and the second water outlet pipe is connected to the cold side water outlet of the secondary heater.

[0013] As a preferred solution of the cogeneration system with efficient and flexible heating of dual-machine combined supply described in the present invention, the three-stage heating unit includes a three-stage heater, a medium-pressure cylinder steam supply pipe, a low-pressure cylinder steam supply pipe, a three-stage water supply pipe, and a three-stage drainage pipe. The three-stage heater is provided with two hot sides and one cold side. The input end of the cold side is connected to the two-stage water outlet pipe, and the output end of the cold side is connected to the four-stage heating unit.

[0014] As a preferred solution of the cogeneration system with efficient and flexible heating of dual machines described in the present invention, one hot side of the three-stage heater is connected with the conventional intermediate pressure cylinder exhaust steam through the intermediate pressure cylinder steam supply pipe, the other hot side of the three-stage heater is connected with the high back pressure low pressure cylinder exhaust steam through the low pressure cylinder steam supply pipe, and the two hot side output ends of the three-stage heater are connected with the condensate pump output end.

[0015] As an optimal solution for the cogeneration system with efficient and flexible heating of dual machines described in the present invention, the four-stage heating unit includes a four-stage heater, four-stage water supply pipes, four-stage drainage pipes, four-stage steam supply branches, a water supply bypass and four-stage water outlet pipes.

[0016] As a preferred solution of the cogeneration system with efficient and flexible heating of dual machines described in the present invention, the four-stage heater is connected to the three-stage heater through a four-plus water supply pipe, and the output end of the four-stage heater is connected to the external heating water supply through a four-plus drainage pipe.

[0017] As an optimal solution for the cogeneration system with efficient and flexible heating of dual machines described in the present invention, the four-pressure steam supply branch is connected to the medium-pressure cylinder steam supply pipe, and the two ends of the water supply bypass are respectively connected to the three-pressure water supply pipe and the four-pressure drainage pipe.

[0018] The beneficial effects of the present invention are as follows: the present invention sets four different heating units and connects with the conventional back-pressure unit and the high back-pressure unit at the same time. The exhaust steam of the medium-pressure cylinder of the conventional back-pressure unit is used as the heat source of the fourth-stage heater to heat the water in the heating network. According to the total steam demand of the third-stage and fourth-stage heaters and the real-time electric load of the conventional back-pressure unit, the low-pressure cylinder connecting pipe heating mode and the low-pressure cylinder zero-output heating mode are flexibly selected, so that the heating load of the unit can be adjusted more flexibly. When the electric load of the conventional high back-pressure unit is determined, the fluctuation degree of the general heat load does not exceed 5%. Under the scheme of the present invention, when the electric load is determined, the external heating load of the conventional high back-pressure unit can fluctuate between ±50%, and it has a higher thermoelectric decoupling capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0020] Figure 1 The overall schematic diagram of a combined heat and power system with dual units for efficient and flexible heating. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0024] Secondly, the present invention is described in detail with reference to the schematic diagram. When describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0025] Example 1

[0026] Reference Figure 1 , is the first embodiment of the present invention, which provides a dual-machine cogeneration system for efficient and flexible heating, including a high back pressure unit unit 100 and a conventional unit unit 200, and also including a primary heating unit 300, a secondary heating unit 400, a tertiary heating unit 500 and a quaternary heating unit 600; the primary heating unit 300 is connected to the high back pressure unit unit 100, and is used for preliminarily heating the heating return water, the secondary heating unit 400 is connected to the high back pressure unit unit 100 and the primary heating unit 300, and is used for further heating the heating return water, the tertiary heating unit 500 is simultaneously connected to the high back pressure unit unit 100, the conventional unit unit 200 and the secondary heating unit 400, and uses the exhaust steam of the unit to further heat the heating return water, the quaternary heating unit 600 is connected to the conventional unit unit 200 and the tertiary heating unit 500, and uses the exhaust steam of the conventional unit unit 200 to perform the final heating on the heating return water.

[0027] Specifically, the high back pressure unit 100 includes a high back pressure medium pressure cylinder 101, a high back pressure low pressure cylinder 102, a high back pressure connecting steam pipe 103, a high back pressure generator 104, a high back pressure condenser 105, a condensate pump 106, a low pressure module 107 and a deaerator 108. The high back pressure medium pressure cylinder 101 and the high back pressure low pressure cylinder 102 are supplied with steam through the high back pressure connecting steam pipe 103. The high back pressure medium pressure cylinder 101, the high back pressure low pressure cylinder 102 and the high back pressure generator 104 are coaxially arranged. The exhaust port of the high back pressure low pressure cylinder 102 is connected to the high back pressure condenser 105. The drain port of the high back pressure condenser 105 is connected to the condenser. The condensate pump 106 is connected, and the outlet of the condensate pump 106 is connected to the low-pressure heating module 107. The outlet of the low-pressure heating module 107 is connected to the deaerator 108. The high back-pressure condenser 105 serves as the first-stage heater. The heating return water (generally 40-50°C) is added to the first-stage heater. When the exhaust back pressure of the low-pressure cylinder of the turbine is 54 kPa, the water temperature of the heating water at the outlet of the first-stage heater can reach about 80°C. After the heating water is heated from the first-stage heater, it enters the second-stage heater 401. The low-pressure heating module 107 is provided with four low-pressure heaters, and the four low-pressure heaters are connected to each other and to the high back-pressure low-pressure cylinder 102.

[0028] Furthermore, the conventional unit 200 includes a conventional intermediate pressure cylinder 201, a conventional low pressure cylinder 202, a conventional connecting steam pipe 203, a conventional generator 204 and a conventional condenser 205. The conventional intermediate pressure cylinder 201 and the conventional low pressure cylinder 202 are supplied with steam through the conventional connecting steam pipe 203. The conventional intermediate pressure cylinder 201, the conventional low pressure cylinder 202 and the conventional generator 204 are coaxially arranged. The exhaust port of the conventional low pressure cylinder 202 is connected to the conventional condenser 205. The conventional unit 200 does not participate in the primary heating and the secondary heating. The conventional unit is operated in a conventional back pressure state or a low pressure cylinder zero output state.

[0029] Furthermore, the first-stage heating unit 300 includes a heating return water pipe 301, an addition inlet 302, and an addition outlet 303. The input end of the heating return water pipe 301 is connected to the external heating return water, and the output end of the heating return water pipe 301 is connected to the addition inlet 302. The addition inlet 302 and the addition outlet 303 are arranged on the high back pressure condenser 105, and the exhaust steam from the high back pressure low pressure cylinder 102 enters the high back pressure condenser 105 to heat the heating return water.

[0030] Furthermore, the secondary heating unit 400 includes a secondary heater 401, a second water supply pipe 402, a second heating pipe 403, a second drainage pipe 404, and a second water outlet pipe 405. The secondary heater 401 is provided with a cold side and a hot side. The second water supply pipe 402 is respectively connected to the first outlet 303 and the cold side water inlet of the secondary heater 401, the second heating pipe 403 is respectively connected to the low-pressure module 107 and the hot side heating port of the secondary heater 401, the second drainage pipe 404 is connected to the hot side of the secondary heater 401 and the input end of the low-pressure module 107, and the second water outlet pipe 405 is connected to the cold side water outlet of the secondary heater 401.

[0031] Specifically, the secondary heater 401 adopts the first type of absorption heat pump, which can achieve that the outlet water temperature of the heat pump driven hot water is lower than the inlet water temperature of the hot water network that needs to be heated. In the secondary heater 401, the condensed water before the inlet of the deaerator 108 of the unit heat recovery system is used as the high-temperature driving hot water (about 150°C). The water temperature of the driving hot water drops to about 65°C after heat exchange in the secondary heater 401, and then it is pumped back to the unit heat recovery system through an electric pump. By recycling the high-temperature condensed water of the heat recovery system, the low-pressure cylinder to each level of the heat recovery system can be realized. The extraction volume of the low-pressure heater increases, which indirectly realizes the energy application of low-grade extraction steam at each stage (the energy consumption of heating through low-pressure cylinder extraction steam is lower than that of heating through medium-pressure cylinder exhaust steam, where the energy consumption indicators are medium-pressure cylinder exhaust steam > No. 4 low-pressure heater extraction steam > No. 3 low-pressure heater extraction steam > No. 2 low-pressure heater extraction steam > No. 1 low-pressure heater extraction steam), achieving orderly and efficient energy utilization. The temperature of the hot network water in the second-stage heater 401 can be increased by 5°C, that is, the outlet water temperature reaches 85°C. The outlet water temperature depends on the ratio of the water extraction volume of the heat recovery system to the water volume of the hot network.

[0032] Example 2

[0033] Reference Figure 1 , which is the second embodiment of the present invention. This embodiment is different from the first embodiment in that: the three-stage heating unit 500 includes a three-stage heater 501, a medium-pressure cylinder steam supply pipe 502, a low-pressure cylinder steam supply pipe 503, a three-addition water supply pipe 504, and a three-addition water discharge pipe 505. The three-stage heater 501 is provided with two hot sides and one cold side. The input end of the cold side is connected to the two-addition water outlet pipe 405, and the output end of the cold side is connected to the four-stage heating unit 600.

[0034] Specifically, the three-stage heater 501 adopts the second type absorption heat pump, the exhaust steam of the conventional medium pressure cylinder 201 of the conventional unit unit 200 is used as the driving heat source of the three-stage heater 501, and the exhaust steam of the high back pressure low pressure cylinder 102 of the high back pressure unit unit 100 is used as the low-temperature heat source, and the condensate drain after heat recovery is recovered to the front pipeline of the condensate pump 106 of the high back pressure unit unit 100.

[0035] Furthermore, one hot side of the three-stage heater 501 is connected to the exhaust steam of the conventional intermediate pressure cylinder 201 through the intermediate pressure cylinder steam supply pipe 502, and the other hot side of the three-stage heater 501 is connected to the exhaust steam of the high back pressure low pressure cylinder 102 through the low pressure cylinder steam supply pipe 503, and the two hot side output ends of the three-stage heater 501 are connected to the output end of the condensate pump 106.

[0036] During operation, whether to put the third-stage heater 501 into operation is determined based on whether the return water volume of the heating network fully utilizes the waste heat of high back pressure exhaust steam in the first-stage heater. If the return water volume of the heating network is small and the waste heat of high back pressure unit exhaust steam is not fully utilized in the first-stage heater, the third-stage heater 501 is turned on and the heating network water is heated in the third-stage heater 501; otherwise, the fourth-stage heater 601 is directly connected through the bypass, and the temperature of the heating water increases by 1 to 10°C after being heated in the third-stage heater 501, which mainly depends on the unutilized exhaust steam heat in the first-stage heater.

[0037] Example 3

[0038] Reference Figure 1 , which is the third embodiment of the present invention. This embodiment is different from the above embodiments in that: the four-stage heating unit 600 includes a four-stage heater 601, a four-addition water supply pipe 602, a four-addition drainage pipe 603, a four-addition steam supply branch 604, a water supply bypass 605 and a four-addition water outlet pipe 606.

[0039] Specifically, the four-stage heater 601 is connected to the three-stage heater 501 through the four-stage water supply pipe 602, and the output end of the four-stage heater 601 is connected to the external heating water supply through the four-stage drainage pipe 603. The four-stage heater 601 adopts a surface heat exchanger. The temperature of the heating water can reach 100-110°C after being heated in the four-stage heater 601, meeting the external heating load requirements.

[0040] Furthermore, the fourth steam supply branch 604 is connected to the medium pressure cylinder steam supply pipe 502, and both ends of the water supply bypass 605 are connected to the third water supply pipe 504 and the fourth water discharge pipe 603 respectively.

[0041] The exhaust steam of the medium-pressure cylinder of the conventional unit unit 200 is used as the heat source of the four-stage heater 601 to heat the water in the hot network; the drain water after steam heat exchange cooling is collected in the pipeline before the condensate pump 106 of the high back-pressure unit unit 100. The conventional unit unit 200 flexibly selects the low-pressure cylinder connecting pipe heating mode and the low-pressure cylinder zero-output heating mode according to the total steam demand of the three-stage heater 501 and the four-stage heater 601 and the real-time power load of the conventional unit unit 200.

[0042] Assume that the total coal consumption of the two units corresponding to the total power generation P1 is B1; the total coal consumption of the two units corresponding to power generation P1 and heat supply Q1 is B2; then the heating energy consumption corresponding to heat supply Q1 is (B2-B1) / Q1. The heating energy consumption index can reach 13kg standard coal / GJ, which is much lower than the heating index of 23kg standard coal / GJ in the zero output mode of the low-pressure cylinder. For two 350MW supercritical units, after adopting this system, the heating capacity of the two units can reach 3600GJ / h.

[0043] Importantly, it should be noted that the construction and arrangement of the present application shown in a plurality of different exemplary embodiments are only exemplary. Although only a few embodiments are described in detail in this disclosure, it should be readily understood by those who refer to this disclosure that many modifications are possible (e.g., the size, scale, structure, shape and proportion of various elements, and parameter values ​​(e.g., temperature, pressure, etc.), installation arrangement, use of materials, color, directional changes, etc.) without substantially departing from the novel teachings and advantages of the subject matter described in the application. For example, the element shown as integrally formed can be composed of multiple parts or elements, the position of the element can be inverted or otherwise changed, and the nature or number or position of the discrete element can be changed or changed. Therefore, all such modifications are intended to be included in the scope of the present invention. The order or sequence of any process or method steps can be changed or reordered according to alternative embodiments. In the claims, any "device plus function" clause is intended to cover the structure of performing the function described herein, and is not only structurally equivalent but also equivalent structure. Without departing from the scope of the present invention, other replacements, modifications, changes and omissions can be made in the design, operating conditions and arrangement of the exemplary embodiments. Therefore, the invention is not limited to a specific embodiment, but extends to numerous modifications still falling within the scope of the appended claims.

[0044] Additionally, in order to provide a concise description of exemplary embodiments, all features of an actual embodiment (ie, those features that are not relevant to the best mode presently contemplated for carrying out the invention or those that are not relevant to implementing the invention) may not be described.

[0045] It will be appreciated that in the development of any actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but will be a routine task of design, fabrication, and production for those of ordinary skill having the benefit of this disclosure without undue experimentation.

[0046] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A heat and power cogeneration system with high efficiency and flexible heating by dual-unit cogeneration, comprising a high back pressure unit (100) and a conventional unit (200), characterized in that: Also includes, A primary heating unit (300), a secondary heating unit (400), a tertiary heating unit (500) and a quaternary heating unit (600); The first-stage heating unit (300) is connected to the high back-pressure unit unit (100) and is used for preliminarily heating the heating return water. The second-stage heating unit (400) is connected to the high back-pressure unit unit (100) and the first-stage heating unit (300) and is used for further heating the heating return water. The third-stage heating unit (500) is simultaneously connected to the high back-pressure unit unit (100), the conventional unit unit (200) and the second-stage heating unit (400) and uses the exhaust steam of the unit to further heat the heating return water. The fourth-stage heating unit (600) is connected to the conventional unit unit (200) and the third-stage heating unit (500) and uses the exhaust steam of the conventional unit unit (200) to perform final heating on the heating return water.

2. The heat and power cogeneration system with high efficiency and flexible heating of dual-machine cogeneration as claimed in claim 1 is characterized by: The high back pressure unit (100) comprises a high back pressure medium pressure cylinder (101), a high back pressure low pressure cylinder (102), a high back pressure connecting steam pipe (103), a high back pressure generator (104), a high back pressure condenser (105), a condensate pump (106), a low pressure heating module (107) and a deaerator (108). The high back pressure medium pressure cylinder (101) and the high back pressure low pressure cylinder (102) are supplied with steam via the high back pressure connecting steam pipe (103). The medium-pressure cylinder (101), the high-back-pressure low-pressure cylinder (102), and the high-back-pressure generator (104) are coaxially arranged, the exhaust port of the high-back-pressure low-pressure cylinder (102) is connected to the high-back-pressure condenser (105), the drain port of the high-back-pressure condenser (105) is connected to the condensate pump (106), the water outlet of the condensate pump (106) is connected to the low-pressure heating module (107), and the water outlet of the low-pressure heating module (107) is connected to the deaerator (108).

3. The heat and power cogeneration system with high efficiency and flexible heating according to claim 2, characterized in that: The conventional unit (200) comprises a conventional intermediate pressure cylinder (201), a conventional low pressure cylinder (202), a conventional connecting steam pipe (203), a conventional generator (204) and a conventional condenser (205); the conventional intermediate pressure cylinder (201) and the conventional low pressure cylinder (202) are supplied with steam via a conventional connecting steam pipe (203); the conventional intermediate pressure cylinder (201), the conventional low pressure cylinder (202) and the conventional generator (204) are coaxially arranged; and the exhaust port of the conventional low pressure cylinder (202) is connected to the conventional condenser (205).

4. The heat and power cogeneration system with high efficiency and flexible heating according to claim 3 is characterized by: The primary heating unit (300) comprises a heating return water pipe (301), a feed inlet (302), and a feed outlet (303); the input end of the heating return water pipe (301) is connected to external heating return water; the output end of the heating return water pipe (301) is connected to a feed inlet (302); and the feed inlet (302) and the feed outlet (303) are arranged on a high back pressure condenser (105).

5. The heat and power cogeneration system with high efficiency and flexible heating of dual-machine cogeneration as claimed in claim 4 is characterized by: The secondary heating unit (400) comprises a secondary heater (401), a second heating water supply pipe (402), a second heating heating pipe (403), a second heating drainage pipe (404), and a second heating water outlet pipe (405). The secondary heater (401) is provided with a cold side and a hot side. The second heating water supply pipe (402) is respectively connected to the first heating outlet (303) and the cold side water inlet of the secondary heater (401). The second heating pipe (403) is respectively connected to the low temperature heating module (107) and the hot side heating outlet of the secondary heater (401). The second heating drainage pipe (404) is connected to the hot side of the secondary heater (401) and the input end of the low temperature heating module (107). The second heating water outlet pipe (405) is connected to the cold side water outlet of the secondary heater (401).

6. The heat and power cogeneration system with high efficiency and flexible heating according to claim 5, characterized in that: The three-stage heating unit (500) comprises a three-stage heater (501), a medium-pressure cylinder steam supply pipe (502), a low-pressure cylinder steam supply pipe (503), a three-stage water supply pipe (504), and a three-stage water discharge pipe (505). The three-stage heater (501) is provided with two hot sides and one cold side. The input end of the cold side is connected to the two-stage water outlet pipe (405), and the output end of the cold side is connected to the four-stage heating unit (600).

7. The heat and power cogeneration system with high efficiency and flexible heating according to claim 6, characterized in that: One hot side of the three-stage heater (501) is connected to the exhaust steam of the conventional medium-pressure cylinder (201) through the medium-pressure cylinder steam supply pipe (502), and the other hot side of the three-stage heater (501) is connected to the exhaust steam of the high back-pressure low-pressure cylinder (102) through the low-pressure cylinder steam supply pipe (503). Both hot side output ends of the three-stage heater (501) are connected to the output end of the condensate pump (106).

8. The heat and power cogeneration system with high efficiency and flexible heating according to claim 7, characterized in that: The four-stage heating unit (600) comprises a four-stage heater (601), four-addition water supply pipes (602), four-addition drainage pipes (603), four-addition steam supply branches (604), a water supply bypass (605) and four-addition water outlet pipes (606).

9. The heat and power cogeneration system with high efficiency and flexible heating according to claim 8, characterized in that: The four-stage heater (601) is connected to the three-stage heater (501) via a four-addition water supply pipe (602), and the output end of the four-stage heater (601) is connected to the external heating water supply via a four-addition drainage pipe (603).

10. The heat and power cogeneration system with high efficiency and flexible heating according to claim 9, characterized in that: The four-pressure steam supply branch (604) is connected to the medium-pressure cylinder steam supply pipe (502), and the two ends of the water supply bypass (605) are respectively connected to the three-pressure water supply pipe (504) and the four-pressure water discharge pipe (603).

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