Energy cascade utilization system and method applied to condensing back supply heat unit

Abstract

The present application belongs to the technical field of coal-fired unit energy saving, and particularly relates to an energy gradient utilization system and method applied to a condensing-extraction back heating unit. On the high-pressure bypass, the main steam is used to drive the steam circulating water pump to operate in the small back pressure turbine, so that the small capacity circulating water pump is used to meet the circulating water demand of the condenser in the standby state during the heating period, which is conducive to reducing the plant power rate during the heating period. On the low-pressure bypass, the reheated steam first enters the steam-water heat exchanger to heat the boiler feed water. The reheated steam after heat exchange enters the desuperheater to adjust the steam temperature to the required parameters of the heat user, and is then sent to the heat network. When the system is de-energized, the corresponding low-pressure heater is also de-energized. The pressure matching device is used to mix the high-discharge steam and the medium-discharge steam to improve the heating parameters, so that the heating regulation and the turbine load regulation are separated, which is conducive to the safe operation of the unit. The flexibility of the unit is further improved, and the operation condition of low-load heating and the requirement of deep peak shaving are more suitable.

Description

Technical Field

[0001] This invention belongs to the field of energy-saving technology for coal-fired power units, specifically relating to an energy cascade utilization system and method for condensing-extraction back-heating units. Background Technology

[0002] Combined heat and power (CHP) offers comprehensive benefits such as energy conservation and environmental improvement, making it a crucial component in building an energy-saving society. However, with rising energy prices and accelerating urbanization, problems such as insufficient heating capacity and insignificant energy-saving effects in some CHP units are becoming increasingly prominent. As residential and industrial users' demand for heating load continues to increase, the power grid is placing higher demands on the heating capacity of these units at low to medium load rates. It is essential to improve the heat-to-power ratio and flexibility of CHP units, maximizing their wide-range peak-shaving capabilities while ensuring adequate heating capacity. Therefore, research on heating system retrofitting and energy-saving technologies for CHP units has significant social benefits and practical value. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide an energy cascade utilization system and method for condensing-extraction back-heating units, so as to solve the technical problems of achieving thermoelectric decoupling and improving the hot spot ratio.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] In a first aspect, the present invention provides an energy cascade utilization system for condensing-extraction-back heating units, comprising: a high-pressure cylinder, a high-pressure bypass, a low-pressure bypass, a pressure matching device, and a boiler reheater;

[0006] The high-pressure bypass includes: a small back-pressure steam turbine and a steam-driven circulating water pump;

[0007] The main steam pipeline is divided into two paths: one path connects to the steam inlet of the small back-pressure steam turbine, the output shaft of the small back-pressure steam turbine is connected to the steam-driven circulating water pump, and the exhaust port of the small back-pressure steam turbine is connected to the steam inlet of the boiler reheater. The other path of the main steam pipeline connects to the steam inlet of the high-pressure cylinder, one exhaust port of the high-pressure cylinder is connected to the steam inlet of the boiler reheater, and the other exhaust port of the high-pressure cylinder is connected to one inlet of the pressure matching device.

[0008] The low-pressure bypass includes: a low-pressure bypass valve, a steam-water heat exchanger, a second desuperheating and pressure reducing device, a check valve, a second regulating valve, and a shut-off valve;

[0009] The other exhaust port of the boiler reheater is connected to the steam-water heat exchanger. The low-pressure bypass valve is connected to the boiler reheater and the steam-water heat exchanger. The steam-side outlet of the steam-water heat exchanger is connected in sequence to the second desuperheating and pressure reducing device, the check valve, the second regulating valve, and the shut-off valve.

[0010] Furthermore, it also includes: intermediate pressure cylinder and low pressure cylinder;

[0011] One exhaust port of the boiler reheater is connected to the steam inlet of the intermediate pressure cylinder. The first exhaust port of the intermediate pressure cylinder is connected to the steam inlet of the low pressure cylinder. The second exhaust port of the intermediate pressure cylinder is connected to the other inlet of the pressure matching device.

[0012] Furthermore, it is characterized by further including: an automatic synchronization clutch;

[0013] One end of the automatic synchronizing clutch is connected to the high-medium pressure rotor in the intermediate pressure cylinder, and the other end of the automatic synchronizing clutch is connected to the low pressure rotor in the low pressure cylinder.

[0014] Furthermore, it also includes: a butterfly valve, a first regulating valve, a first gate valve, a second gate valve, an electric gate valve, a high-pressure bypass valve, and a first desuperheating and pressure reducing device;

[0015] The butterfly valve connects the first exhaust port of the intermediate pressure cylinder and the inlet port of the low pressure cylinder;

[0016] The first regulating valve is connected to another exhaust port of the high-pressure cylinder and one inlet of the pressure matching device;

[0017] The first gate valve is connected to the second exhaust port of the intermediate pressure cylinder and the pressure matching device;

[0018] The second gate valve is connected to the third exhaust port of the intermediate pressure cylinder;

[0019] The electric gate valve and the high-pressure bypass valve are connected to the main steam pipeline and the small back-pressure steam turbine.

[0020] The first desuperheater and pressure reducer is connected to the small back pressure steam turbine and the boiler reheater.

[0021] Secondly, the present invention provides a method for energy cascade utilization applied to a condensing-extraction back-heating unit, based on an energy cascade utilization system for a condensing-extraction back-heating unit as described in any one of the claims, comprising:

[0022] First operating condition: Before the heating season begins, the main steam pipeline is connected to the steam inlet of the high-pressure cylinder, one exhaust port of the high-pressure cylinder is connected to the steam inlet of the boiler reheater, one exhaust port of the boiler reheater is connected to the steam inlet of the intermediate-pressure cylinder, and the first exhaust port of the intermediate-pressure cylinder is connected to the steam inlet of the low-pressure cylinder.

[0023] Second operating condition: When the heating season begins, the automatic synchronous clutch operates, disengaging the intermediate and high-pressure rotors in the intermediate-pressure cylinder from the low-pressure rotor in the low-pressure cylinder; at the same time, the butterfly valve closes, cutting off the steam circuit from the intermediate-pressure cylinder to the low-pressure cylinder.

[0024] Furthermore, the electric gate valve and the high-pressure bypass valve open, and the high-pressure bypass starts working. The main steam enters the small back-pressure steam turbine through the high-pressure bypass to do work, driving the steam-driven feedwater pump during the heating season. After doing work, the exhaust steam passes through the first desuperheater and pressure reducer and then enters the boiler reheater to increase the steam parameters. The low-pressure bypass valve, check valve, regulating valve, and shut-off valve open, and the low-pressure bypass starts working. Steam enters the steam-water heat exchanger from the boiler reheater through the low-pressure bypass valve to heat the boiler feedwater. After the steam parameters are adjusted by the second desuperheater and pressure reducer, it passes through the check valve, regulating valve, and shut-off valve in sequence and is sent to the heating network for heating.

[0025] Furthermore, the main steam passes through the high-pressure cylinder, the boiler reheater, and the intermediate-pressure cylinder. The steam that has done work is discharged from the third exhaust port of the intermediate-pressure cylinder. The regulating valve is closed, the first gate valve is closed, and the second gate valve is opened. The intermediate-pressure steam is then sent to the heating network for heating.

[0026] Furthermore, when the electrical load continues to decrease and the steam parameters from the intermediate-pressure cylinder cannot meet the requirements of the heating network, the first regulating valve opens, the first gate valve opens, the second gate valve closes, and the pressure matching device starts to work. The exhaust steam from the high-pressure cylinder and the exhaust steam from the intermediate-pressure cylinder are mixed in the pressure matching device, and the steam parameters are increased before being sent to the heating network for heating.

[0027] Furthermore, the first and second desuperheating pressure reducers adjust the steam parameters by adding desuperheating water.

[0028] Furthermore, once the heating season begins, the automatic synchronous clutch disengages the high-pressure and intermediate-pressure rotors from the low-pressure rotor, the butterfly valve closes, and the low-pressure rotor stops operating; with the butterfly valve closed, steam no longer enters the low-pressure cylinder.

[0029] The present invention has at least the following beneficial effects:

[0030] 1. This invention provides an energy cascade utilization system for condensing-extraction back-pressure heating units, comprising: a high-pressure cylinder, a high-pressure bypass, a low-pressure bypass, a pressure matching device, and a boiler reheater; the high-pressure bypass includes: a small back-pressure turbine and a steam-driven circulating water pump; the main steam pipeline is divided into two paths: one path connects to the steam inlet of the small back-pressure turbine, the output shaft of the small back-pressure turbine connects to the steam-driven circulating water pump, the exhaust port of the small back-pressure turbine connects to the steam inlet of the boiler reheater, and the other path of the main steam pipeline connects to the steam inlet of the high-pressure cylinder. One exhaust port of the high-pressure cylinder is connected to the steam inlet of the boiler reheater, and the other exhaust port of the high-pressure cylinder is connected to one inlet of the pressure matching device. The low-pressure bypass includes: a low-pressure bypass valve, a steam-water heat exchanger, a second desuperheating and pressure reducing device, a check valve, a second regulating valve, and a shut-off valve. The other exhaust port of the boiler reheater is connected to the steam-water heat exchanger, and the low-pressure bypass valve connects the boiler reheater and the steam-water heat exchanger. The steam-side outlet of the steam-water heat exchanger is sequentially connected to the second desuperheating and pressure reducing device, the check valve, the second regulating valve, and the shut-off valve. In the high-pressure bypass, the main steam performs work in the small back-pressure turbine to drive the steam-driven circulating water pump, thereby using a small-capacity circulating water pump to meet the circulating water demand of the condenser in standby mode during the heating season, while also helping to reduce the plant's power consumption rate during the heating season. The exhaust steam of the main steam after performing work then enters the desuperheating and pressure reducing device to adjust the steam parameters, reducing the required desuperheating water volume and reducing losses. In the low-pressure bypass, the reheated steam first enters the steam-water heat exchanger to heat the boiler feedwater. After heat exchange, the reheated steam enters the desuperheater and pressure reducer to adjust the steam parameters to the parameters required by the heat user before being sent to the heating network. On the one hand, when the low-pressure cylinder is disconnected from the system, the corresponding low-pressure heater is also disconnected at the same time. By utilizing the steam-water heat exchanger, the reheated steam is effectively used to raise the boiler feedwater temperature, offsetting the excessively low feedwater temperature caused by the lack of a low-pressure heater. On the other hand, the reheated steam enters the desuperheater and pressure reducer after heat exchange, reducing the required amount of desuperheating water and lowering losses.

[0031] 2. This invention provides a method for energy cascade utilization applied to a condensing-extraction back-heating unit, comprising: First operating condition: Before the heating season, the main steam pipeline is connected to the inlet of the high-pressure cylinder, one exhaust port of the high-pressure cylinder is connected to the inlet of the boiler reheater, one exhaust port of the boiler reheater is connected to the inlet of the intermediate-pressure cylinder, and the first exhaust port of the intermediate-pressure cylinder is connected to the inlet of the low-pressure cylinder; Second operating condition: When the heating season begins, an automatic synchronization clutch operates, disconnecting the high- and intermediate-pressure rotors in the intermediate-pressure cylinder from the low-pressure rotor in the low-pressure cylinder; simultaneously, the butterfly valve closes, cutting off the steam path from the intermediate-pressure cylinder to the low-pressure cylinder. During the heating season, the main steam passes through the high-pressure cylinder, boiler reheater, and intermediate-pressure cylinder. The steam after performing work is discharged from the third exhaust port of the intermediate-pressure cylinder. The regulating valve is closed, the first gate valve is closed, and the second gate valve is open, allowing the intermediate-exhaust steam to be sent to the heating network for heating. When the unit operates at low load, there may be situations where the intermediate-exhaust steam cannot meet the heating requirements. By using a pressure matching device, the high-pressure exhaust steam and the intermediate-exhaust steam are mixed to improve the heating parameters. This separation of heating regulation and turbine load regulation facilitates safe unit operation. It further enhances the unit's flexibility, making it more adaptable to low-load heating conditions and meeting the requirements of deep peak shaving. Attached Figure Description

[0032] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0033] Figure 1 This is a system diagram of an energy cascade utilization system applied to a condensing-extraction back-heating unit according to the present invention;

[0034] The components are as follows: 1. High-pressure cylinder; 2. Medium-pressure cylinder; 3. Automatic synchronous clutch; 4. Low-pressure cylinder; 5. Butterfly valve; 6. First regulating valve; 7. Pressure matching device; 8. First gate valve; 9. Second gate valve; 10. Electric gate valve; 11. High-pressure bypass valve; 12. Small back-pressure steam turbine; 13. Steam-driven circulating water pump; 14. First desuperheating and pressure reducing device; 15. Boiler reheater; 16. Low-pressure bypass valve; 17. Steam-water heat exchanger; 18. Second desuperheating and pressure reducing device; 19. Check valve; 20. Second regulating valve; 21. Shut-off valve. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0036] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this invention is for describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0037] Example 1

[0038] Please see Figure 1 As shown, the present invention provides an energy cascade utilization system for condensing-extraction-back pressure heating units, comprising a high-pressure cylinder 1, a medium-pressure cylinder 2, an automatic synchronization clutch 3, a low-pressure cylinder 4, a butterfly valve 5, a first regulating valve 6, a pressure matching device 7, a first gate valve 8, a second gate valve 9, an electric gate valve 10, a high-pressure bypass valve 11, a small back-pressure steam turbine 12, a steam-driven circulating water pump 13, a first desuperheating and pressure reducing device 14, a boiler reheater 15, a low-pressure bypass valve 16, a steam-water heat exchanger 17, a second desuperheating and pressure reducing device 18, a check valve 19, a second regulating valve 20, and a shut-off valve 21. The high-pressure bypass connects the main steam path to the steam inlet of the small back-pressure turbine 12 via an electric gate valve 10 and a high-pressure bypass valve 11. The output shaft of the small back-pressure turbine 12 is connected to a steam-driven circulating water pump 13, driving the pump to operate. The steam outlet of the small back-pressure turbine 12 is connected to the inlet of the first desuperheater 14. The outlet of the first desuperheater 14 and one exhaust port of the high-pressure cylinder 1 are connected to the boiler reheater 15. The boiler reheater 15 is connected to the inlet of the steam-water heat exchanger 17 via a low-pressure bypass valve 16. The outlet of the steam-water heat exchanger 17 is connected to the inlet of the second desuperheater 18. The outlet of the second desuperheater 18 is sequentially connected to a check valve 19, a second regulating valve 20, and a shut-off valve 21 to supply heat to the heating network. One exhaust port of the high-pressure cylinder 1 is connected to the steam inlet of the intermediate-pressure cylinder 2 via the boiler reheater 15, and the other is connected to one inlet of the pressure matching device 7 via the first regulating valve 6. One end of the automatic synchronizing clutch 3 is connected to the high- and intermediate-pressure rotor in the intermediate-pressure cylinder 2, and the other end of the automatic synchronizing clutch 3 is connected to the low-pressure rotor in the low-pressure cylinder 4. The first exhaust port of the intermediate-pressure cylinder 2 is connected to one side of the butterfly valve 5, and the other side of the butterfly valve 5 is connected to the steam inlet of the low-pressure cylinder 4. The second exhaust port of the intermediate-pressure cylinder 2 is connected to the inlet of the pressure matching device 7 through the first gate valve 8. After the steam is mixed, it is used to supply heat to the heating network. The third exhaust port of the intermediate-pressure cylinder 2 is used to supply heat to the heating network through the second gate valve 9.

[0039] Example 2

[0040] This invention provides a method for energy cascade utilization in a condensing-extraction back-pressure heating unit. After the heating season begins, as needed, an automatic synchronous clutch 3 operates to disengage the high-pressure and intermediate-pressure rotors from the low-pressure rotor, butterfly valve 5 closes, and the low-pressure rotor stops operating. Main steam passes through high-pressure cylinder 1, boiler reheater 15, and intermediate-pressure cylinder 2. The steam after performing work is discharged from the third exhaust port of intermediate-pressure cylinder 2. At this time, the first regulating valve 6 is closed, the first gate valve 8 is closed, and the second gate valve 9 is open, and the intermediate-pressure steam is sent to the heating network for heating. High-pressure bypass and low-pressure bypass are respectively set on both sides of boiler reheater 15. In the high-pressure bypass, main steam passes through electric gate valve 10 and high-pressure bypass valve 11, enters the small back-pressure turbine 12 for expansion and work, driving the small-capacity steam-driven circulating water pump 13, which operates during the heating season. The exhaust steam after performing work enters the first desuperheater and pressure reducer 14 to adjust the steam parameters, making them consistent with the exhaust parameters of high-pressure cylinder 1, and then enters boiler reheater 15 together. The low-pressure bypass involves hot steam from the boiler reheater 15 outlet passing through the low-pressure bypass valve 16, entering the steam-water heat exchanger 17 to heat the boiler feedwater, and then entering the second desuperheater and pressure reducer 18 to adjust the steam parameters to meet the heat user's needs. The steam then passes sequentially through the check valve 19, the second regulating valve 20, and the shut-off valve 21 before being sent to the heating network. When the electrical load continues to decrease and the steam parameters from the intermediate-pressure cylinder 2 cannot meet the heating network requirements, the first regulating valve 6 opens, the first gate valve 8 opens, the second gate valve 9 closes, and the pressure matching device 7 starts working, mixing the exhaust steam from the high-pressure cylinder 1 and the intermediate-pressure cylinder 2 to increase the steam parameters before sending it to the heating network.

[0041] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An energy cascade utilization system applied to a condensing-extraction back-heating unit, characterized in that, include: High-pressure cylinder (1), high-pressure bypass, low-pressure bypass, pressure matching device (7) and boiler reheater (15); The high-pressure bypass includes: a small back-pressure steam turbine (12) and a steam-driven circulating water pump (13). The main steam pipeline is divided into two paths: one path is connected to the steam inlet of the small back pressure turbine (12), the output shaft of the small back pressure turbine (12) is connected to the steam-driven circulating water pump (13), the exhaust port of the small back pressure turbine (12) is connected to the steam inlet of the boiler reheater (15), the other path of the main steam pipeline is connected to the steam inlet of the high pressure cylinder (1), one exhaust port of the high pressure cylinder (1) is connected to the steam inlet of the boiler reheater (15), and the other exhaust port of the high pressure cylinder (1) is connected to one inlet of the pressure matching device (7); The low-pressure bypass includes: a low-pressure bypass valve (16), a steam-water heat exchanger (17), a second desuperheating and pressure reducing device (18), a check valve (19), a second regulating valve (20), and a shut-off valve (21). The other exhaust port of the boiler reheater (15) is connected to the steam-water heat exchanger (17). The low-pressure bypass valve (16) is connected to the boiler reheater (15) and the steam-water heat exchanger (17). The steam-side outlet of the steam-water heat exchanger (17) is connected in sequence to the second desuperheating and pressure reducing device (18), the check valve (19), the second regulating valve (20), and the shut-off valve (21).

2. The energy cascade utilization system applied to a condensing-extraction back-heating unit according to claim 1, characterized in that, Also includes: Medium-pressure cylinder (2) and low-pressure cylinder (4); One exhaust port of the boiler reheater (15) is connected to the steam inlet of the intermediate pressure cylinder (2). The first exhaust port of the intermediate pressure cylinder (2) is connected to the steam inlet of the low pressure cylinder (4). The second exhaust port of the intermediate pressure cylinder (2) is connected to the other inlet of the pressure matching device (7).

3. The energy cascade utilization system applied to a condensing-extraction back-heating unit according to claim 2, characterized in that, Also includes: Automatic synchronizing clutch (3); One end of the automatic synchronizing clutch (3) is connected to the high-medium pressure rotor in the medium-pressure cylinder (2), and the other end of the automatic synchronizing clutch (3) is connected to the low-pressure rotor in the low-pressure cylinder (4).

4. The energy cascade utilization system applied to a condensing-extraction back-heating unit according to claim 3, characterized in that, Also includes: Butterfly valve (5), first regulating valve (6), first gate valve (8), second gate valve (9), electric gate valve (10), high-pressure bypass valve (11) and first desuperheating pressure reducer (14); The butterfly valve (5) is connected to the first exhaust port of the medium-pressure cylinder (2) and the inlet port of the low-pressure cylinder (4); The first regulating valve (6) is connected to another exhaust port of the high-pressure cylinder (1) and one inlet of the pressure matching device (7); The first gate valve (8) is connected to the second exhaust port of the intermediate pressure cylinder (2) and the other inlet of the pressure matching device (7); The second gate valve (9) is connected to the third exhaust port of the intermediate pressure cylinder (2); The electric gate valve (10) and the high-pressure bypass valve (11) are connected to the main steam pipeline and the small back pressure steam turbine (12). The first desuperheater (14) is connected to the small back pressure steam turbine (12) and the boiler reheater (15).

5. A method for cascaded energy utilization applied to condensing-extraction back-heating units, characterized in that, An energy cascade utilization system for a condensing-extraction back-heating unit according to any one of claims 1 to 4 includes: First operating condition: Before the heating season begins, the main steam pipeline is connected to the steam inlet of the high-pressure cylinder (1), one exhaust port of the high-pressure cylinder (1) is connected to the steam inlet of the boiler reheater (15), one exhaust port of the boiler reheater (15) is connected to the steam inlet of the intermediate-pressure cylinder (2), and the first exhaust port of the intermediate-pressure cylinder (2) is connected to the steam inlet of the low-pressure cylinder (4). Second operating condition: When the heating season begins, the automatic synchronous clutch (3) operates, causing the high and medium pressure rotor in the medium pressure cylinder (2) to disconnect from the low pressure rotor in the low pressure cylinder (4); at the same time, the butterfly valve (5) closes, cutting off the steam circuit from the medium pressure cylinder (2) to the low pressure cylinder (4).

6. The energy cascade utilization method applied to a condensing-extraction back-heating unit according to claim 5, characterized in that, When the electric gate valve (10) and the high-pressure bypass valve (11) are opened, the high-pressure bypass starts to work. The main steam enters the small back-pressure steam turbine (12) through the high-pressure bypass to do work, driving the steam-driven circulating water pump (13) during the heating season. After doing work, the exhaust steam enters the boiler reheater (15) after passing through the first desuperheater (14) to increase the steam parameters. When the low-pressure bypass valve (16), check valve (19), second regulating valve (20) and shut-off valve (21) are opened, the low-pressure bypass starts to work. Steam enters the steam-water heat exchanger (17) from the boiler reheater (15) through the low-pressure bypass valve (16). After the steam parameters are adjusted by the second desuperheater (18), it passes through the check valve (19), the second regulating valve (20) and the shut-off valve (21) in sequence to be sent to the heating network for heating.

7. The energy cascade utilization method applied to a condensing-extraction back-heating unit according to claim 5, characterized in that, The main steam passes through the high-pressure cylinder (1), the boiler reheater (15) and the intermediate-pressure cylinder (2). The steam after doing work is discharged from the third exhaust port of the intermediate-pressure cylinder (2). The first regulating valve (6) is closed, the first gate valve (8) is closed, and the second gate valve (9) is opened. The intermediate-pressure steam is sent to the heating network for heating.

8. The energy cascade utilization method applied to a condensing-extraction back-heating unit according to claim 5, characterized in that, When the electrical load continues to decrease and the steam parameters from the intermediate discharge cannot meet the requirements of the heating network, the first regulating valve (6) opens, the first gate valve (8) opens, the second gate valve (9) closes, the pressure matching device (7) starts to work, the exhaust steam from the high-pressure cylinder (1) and the exhaust steam from the intermediate-pressure cylinder (2) are mixed in the pressure matching device (7), and the steam parameters are increased before being sent to the heating network for heating.

9. The energy cascade utilization method applied to a condensing-extraction back-heating unit according to claim 6, characterized in that, The first desuperheating and pressure reducing device (14) and the second desuperheating and pressure reducing device (18) adjust the steam parameters by adding desuperheating water.

10. A method for energy cascade utilization applied to a condensing-extraction back-heating unit according to claim 5, characterized in that, After the heating season begins, the automatic synchronous clutch (3) activates to disengage the high and medium pressure rotor of the medium pressure cylinder (2) from the low pressure rotor of the low pressure cylinder (4), and the low pressure rotor stops running; the butterfly valve (5) closes, and steam no longer enters the low pressure cylinder (4).

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