Low-side heating gradient utilization system and operation method

Abstract

The embodiment of the invention provides a low-side heating gradient utilization system and an operation method, the system comprises a boiler and a steam turbine, and the steam turbine comprises a high-pressure cylinder, an intermediate-pressure cylinder and a low-pressure cylinder which are connected in sequence; the heat supply system comprises a first steam pipeline and a heat supply network heater; the low-side cascade heat supply subsystem comprises a second steam pipeline, and a first shut-off valve, a first check valve and a pressure reducing valve are sequentially arranged on the second steam pipeline in the steam flowing direction. A steam side inlet of the heat exchanger is connected with an outlet of the second steam pipeline; an inlet of the third steam pipeline is connected to a steam side outlet of the heat exchanger, an outlet of the third steam pipeline is connected to the first steam pipeline, and a second check valve and a second shut-off valve are arranged on the third steam pipeline; an inlet of the water side bypass is connected to a heat supply network water return main pipe, an outlet of the water side bypass is connected to a heat supply network water supply main pipe, the water side bypass penetrates through the water side of the heat exchanger, and a flow adjusting device is arranged on the water side bypass.

Description

Technical Field

[0001] The embodiments disclosed herein belong to the field of combined heat and power technology, specifically relating to a low-level bypass heating cascade utilization system and its operation method. Background Technology

[0002] In recent years, to adapt to the rapid growth of installed capacity of new energy power generation, various regions have successively introduced policies requiring a comprehensive improvement in the power system's regulation capabilities. As an important component of the new power system, the regulation capabilities of thermal power units (especially combined heat and power units) have attracted much attention, as they bear the key responsibility of promoting the efficient consumption of new energy.

[0003] With increasingly stringent grid peak-shaving requirements, the minimum load rate of combined heat and power (CHP) units during the heating season is required to be reduced to around 25%, further exacerbating the conflict between power supply and heating. To balance heating demand with deep peak-shaving, most units are currently being retrofitted using a combined high- and low-pressure bypass heating system. While this approach alleviates the CHP conflict to some extent, the use of high-grade steam for heating before it has been fully utilized results in significant thermal losses, negatively impacting the unit's operational economy.

[0004] Therefore, solving the problem of limited peak-shaving capacity of cogeneration units under the traditional "heat-driven power generation" operation mode, meeting the grid's deep peak-shaving requirements without affecting residents' heating and steam supply needs, and further improving the heating economy of the units have become technical problems that urgently need to be solved by those skilled in the art. Summary of the Invention

[0005] The embodiments disclosed herein aim to at least solve one of the technical problems existing in the prior art, and provide a low-level bypass heating cascade utilization system and its operation method.

[0006] A first aspect of the embodiments of this disclosure provides a low-side heating cascade utilization system, comprising: A boiler and a steam turbine connected to the boiler, the steam turbine comprising a high-pressure cylinder, an intermediate-pressure cylinder and a low-pressure cylinder connected in sequence; The heating system includes a first steam pipeline extending from a connecting pipe between the intermediate-pressure cylinder and the low-pressure cylinder, and a heat network heater disposed on the first steam pipeline; and, The low-level bypass heating subsystem includes: a second steam pipeline whose inlet is connected to a reheat steam pipeline, and a first shut-off valve, a first check valve and a pressure reducing valve are sequentially installed on the second steam pipeline along the steam flow direction; The heat exchanger has its steam-side inlet connected to the outlet of the second steam pipeline; A third steam pipeline, its inlet connected to the steam-side outlet of the heat exchanger and its outlet connected to the first steam pipeline, is equipped with a second check valve and a second shut-off valve; and... The water-side bypass has its inlet connected to the return water header of the heating network and its outlet connected to the supply water header of the heating network. The water-side bypass passes through the water side of the heat exchanger and is equipped with a flow regulating device.

[0007] Optionally, the first and second shut-off valves are electric valves; and / or, a regulating valve is further provided on the second steam pipeline before the pressure reducing valve.

[0008] Optionally, a third check valve and a third shut-off valve are also provided on the water-side bypass after the water-side outlet of the heat exchanger.

[0009] Optionally, on the first steam pipeline of the heating system, between the connecting pipe between the intermediate-pressure cylinder and the low-pressure cylinder and the steam-side inlet of the heating network heater, a fourth shut-off valve, a fourth check valve, and a first regulating valve are sequentially provided.

[0010] Optionally, the drain outlet of the heating network heater is connected to the condensate system of the unit through a drain pipe, and a fifth shut-off valve is installed on the drain pipe.

[0011] A second aspect of the embodiments of this disclosure provides a low-bypass heating operation method, the operation method being implemented according to the low-bypass heating cascade utilization system described above, the method including a conventional heating mode and a low-bypass cascade heating mode; the conventional heating mode is suitable for high-load operation of the unit, in which case only the heating system is put into operation for heating; the low-bypass cascade heating mode is suitable for low-load peak-shaving operation of the unit, in which case both the heating system and the low-bypass cascade heating subsystem are put into operation for coordinated heating.

[0012] Optionally, the conventional heating mode includes: opening the fourth shut-off valve, the fourth check valve, the first regulating valve, and the fifth shut-off valve in the heating system; starting the heating network circulation pump and ensuring that all the heating network circulation water flows through the heating network heater; and simultaneously keeping the second steam pipeline and the third steam pipeline in the low-level bypass heating subsystem shut off.

[0013] Optionally, the low-bypass cascade heating mode includes: maintaining the operation of the heating system; opening the first shut-off valve, the second shut-off valve, and the third shut-off valve in the low-bypass cascade heating subsystem, so that reheat steam enters the heat exchanger through the second steam pipeline, and after heat exchange, flows into the first steam pipeline through the third steam pipeline; simultaneously, by adjusting the flow regulating device on the water-side bypass, controlling a portion of the heating network circulating water to flow through the heat exchanger to be heated, and then flowing into the main heating network water supply header.

[0014] Optionally, the flow rate ratio of the circulating water flowing through the heat exchanger and the circulating water flowing through the heating network heater can be allocated by coordinating the flow rate regulation device on the water-side bypass and the second regulating valve on the main heating network water pipeline.

[0015] Optionally, in the low-pressure bypass cascade heating mode, the reheated steam flowing through the heat exchanger is de-heated and depressurized until its pressure and temperature parameters are basically matched with the steam parameters from the medium-low pressure connecting pipe, and then it is incorporated into the first steam pipeline.

[0016] The beneficial effects of the embodiments of this disclosure include: This application achieves deep thermal-electric decoupling of the combined heat and power (CHP) unit. Through an innovative "low-pass cascade" design, the unit can be completely unconstrained by the "heat-driven power generation" mode when responding to the grid's deep peak-shaving command and reducing the power generation load to an extremely low level. While significantly reducing power generation, it maintains or even increases the external heat supply capacity, fundamentally resolving the contradiction between power supply and heat supply.

[0017] Compared to traditional technologies that directly depressurize and cool high-grade steam for heating, resulting in significant energy losses, this system achieves tiered and grade-matched utilization of steam energy. The newly added heat exchanger is a key piece of equipment; it allows high-grade reheat steam to first heat part of the heat network return water, and then the waste heat after depressurization is mixed with the exhaust steam from the low-pressure cylinder in the system for further heating. This tiered utilization method significantly reduces the work capacity loss of high-grade steam, greatly improving the unit's overall thermal economy and operating benefits.

[0018] The technical solution proposed in this application has the significant advantages of small modification scope, low investment cost, and high system integration. It mainly utilizes the existing low-pressure bypass concept for expansion, requiring few new pipelines and equipment, minimizing the impact on the main system, and facilitating implementation. Simultaneously, the multiple shut-off valves and check valves installed in the system ensure controllable flow of steam and water when switching between the two operating modes, effectively preventing media cross-contamination and guaranteeing the safe and stable operation of the unit.

[0019] The system in this application operates flexibly, seamlessly switching between "conventional" and "cascaded" modes according to load demand, giving the units greater operational flexibility and grid adaptability. Ultimately, this technology enables thermal power units to better fulfill their roles of "bottom-line supply guarantee" and "regulation backup," significantly improving the power system's ability to absorb intermittent renewable energy sources such as wind and solar power, resulting in substantial social and environmental benefits. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a low-level bypass heating cascade utilization system according to an embodiment of the present disclosure.

[0021] In the diagram, 1. Reheat steam pipeline; 2. Main steam pipeline; 3. High-pressure cylinder; 4. Intermediate-pressure cylinder; 5. Low-pressure cylinder; 6. Heat exchanger; 7. Heat network heater; 8. First heat network circulation pump; 9. Second heat network circulation pump; 01. First shut-off valve; 02. First check valve; 03. Pressure reducing valve; 04. Second shut-off valve; 05. Second check valve; 21. Fourth shut-off valve; 22. Fourth check valve; 23. First regulating valve; 24. Fifth shut-off valve; 41. Third check valve; 42. Third shut-off valve; 43. Flow regulating device; 51. First electric valve; 52. Second electric valve; 53. Third electric valve; 54. Fourth electric valve; 55. Second regulating valve; 56. Fifth electric valve. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] The embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. The detailed descriptions and accompanying drawings of the following embodiments are used to exemplarily illustrate the principles of this application, but should not be used to limit the scope of this application; that is, this application is not limited to the described embodiments. In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicating orientation or positional relationships 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. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. "Vertical" is not strictly vertical, but within the allowable error range. "Parallel" is not strictly parallel, but within the allowable error range.

[0024] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "joining" 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 direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application depending on the specific circumstances.

[0025] like Figure 1As shown, a low-pressure bypass heating cascade utilization system includes: a boiler and a steam turbine connected to the boiler. The steam turbine includes a high-pressure cylinder 3, an intermediate-pressure cylinder 4, and a low-pressure cylinder 5 connected in sequence. The main steam pipeline 2 is connected to the high-pressure cylinder 3.

[0026] The heating system includes a first steam pipeline extending from the connecting pipe between the intermediate-pressure cylinder 4 and the low-pressure cylinder 5, and a heat network heater 7 installed on the first steam pipeline. Additionally, a low-pressure bypass cascade heating subsystem includes a second steam pipeline, the inlet of which is connected to the reheat steam pipeline 1, and a first shut-off valve 01, a first check valve 02, and a pressure reducing valve 03 sequentially installed along the steam flow direction on the second steam pipeline.

[0027] The heat exchanger 6 has its steam-side inlet connected to the outlet of the second steam pipeline.

[0028] The third steam pipeline has its inlet connected to the steam side outlet of the heat exchanger 6 and its outlet connected to the first steam pipeline. The third steam pipeline is equipped with a second check valve 05 and a second shut-off valve 04. The water-side bypass has its inlet connected to the return water main pipe of the heating network and its outlet connected to the supply water main pipe of the heating network. The water-side bypass passes through the water side of the heat exchanger 6 and is equipped with a flow regulating device 43.

[0029] In some embodiments, the first shut-off valve 01 and the second shut-off valve 04 are electric valves, and / or, a regulating valve is also provided on the second steam pipeline before the pressure reducing valve 03.

[0030] In some embodiments, a third check valve 41 and a third shut-off valve 42 are provided on the water-side bypass after the water-side outlet of the heat exchanger 6.

[0031] In some embodiments, a fourth shut-off valve 21, a fourth check valve 22, and a first regulating valve 23 are sequentially arranged on the first steam pipeline of the heating system, from the connecting pipe between the intermediate-pressure cylinder 4 and the low-pressure cylinder 5 to the steam-side inlet of the heating network heater 7.

[0032] In some embodiments, the drain outlet of the heat network heater 7 is connected to the condensate system of the unit via a drain pipe, and a fifth shut-off valve 24 is provided on the drain pipe.

[0033] A second aspect of the embodiments of this disclosure provides a low-bypass heating operation method, the method being implemented according to the aforementioned low-bypass heating cascade utilization system, the method comprising a conventional heating mode and a low-bypass cascade heating mode. The conventional heating mode is suitable for high-load operation of the unit, in which case only the heating system is activated for heating. The low-bypass cascade heating mode is suitable for low-load peak-shaving operation of the unit, in which case both the heating system and the low-bypass cascade heating subsystem are activated simultaneously for coordinated heating.

[0034] In some embodiments, the conventional heating mode includes: opening the fourth shut-off valve 21, the fourth check valve 22, the first regulating valve 23, and the fifth shut-off valve 24 in the heating system; starting the heating network circulation pumps (including the first heating network circulation pump 8 and the second heating network circulation pump 9); and ensuring that all the circulating water in the heating network flows through the heating network heater 7. Simultaneously, the second and third steam lines in the low-level bypass heating subsystem are kept shut off.

[0035] In some embodiments, the low-bypass cascade heating mode includes: maintaining the operation of the heating system; opening the first shut-off valve 01, the second shut-off valve 04, and the third shut-off valve 42 in the low-bypass cascade heating subsystem, allowing reheat steam to enter the heat exchanger 6 via the second steam pipeline, and after heat exchange, to flow into the first steam pipeline via the third steam pipeline. Simultaneously, by adjusting the flow regulating device 43 on the water-side bypass, a portion of the heating network circulating water is controlled to flow through the heat exchanger 6 to be heated, and then flows into the main heating network water supply header.

[0036] In some embodiments, the flow rate ratio of the circulating water flowing through the heat exchanger 6 to that flowing through the heating network heater 7 is distributed by coordinating the flow rate regulation device 43 on the water-side bypass and the second regulating valve 55 on the main heating network water pipeline.

[0037] In some embodiments, in the low-pressure bypass cascade heating mode, the reheat steam flowing through the heat exchanger 6 is de-cooled and depressurized until its pressure and temperature parameters are basically matched with the steam parameters from the medium-low pressure connecting pipe, and then it flows into the first steam pipeline.

[0038] This application achieves deep thermal-electric decoupling of the combined heat and power (CHP) unit. Through an innovative "low-pass cascade" design, the unit can be completely unconstrained by the "heat-driven power generation" mode when responding to the grid's deep peak-shaving command and reducing the power generation load to an extremely low level. While significantly reducing power generation, it maintains or even increases the external heat supply capacity, fundamentally resolving the contradiction between power supply and heat supply.

[0039] Compared to traditional technologies that directly depressurize and cool high-grade steam for heating, resulting in significant energy losses, this system achieves tiered and grade-matched utilization of steam energy. The newly added heat exchanger 6 is a key piece of equipment; it allows high-grade reheat steam to first heat part of the heat network return water, and then the residual heat after cooling and depressurization is mixed with the exhaust steam from the low-pressure cylinder 5 in the system for heating. This tiered utilization method significantly reduces the work capacity loss of high-grade steam, greatly improving the unit's overall thermal economy and operating benefits.

[0040] The technical solution proposed in this application has the significant advantages of small modification scope, low investment cost, and high system integration. It mainly utilizes the existing low-pressure bypass concept for expansion, requiring few new pipelines and equipment, minimizing the impact on the main system, and facilitating implementation. Simultaneously, the multiple shut-off valves and check valves installed in the system ensure controllable flow of steam and water when switching between the two operating modes, effectively preventing media cross-contamination and guaranteeing the safe and stable operation of the unit.

[0041] The system in this application operates flexibly, seamlessly switching between "conventional" and "cascaded" modes according to load demand, giving the units greater operational flexibility and grid adaptability. Ultimately, this technology enables thermal power units to better fulfill their roles of "bottom-line supply guarantee" and "regulation backup," significantly improving the power system's ability to absorb intermittent renewable energy sources such as wind and solar power, resulting in substantial social and environmental benefits.

[0042] In the heating system of the relevant technology, a tee is connected between the medium-pressure cylinder and the low-pressure cylinder, and a steam pipeline is connected through the tee. The steam pipeline is connected in sequence to a shut-off valve, a check valve and a regulating valve. After entering the heat exchanger of the heating network heater, the condensate returns to the unit's condensate system through the shut-off valve.

[0043] Traditional low-level bypass heating mode generally uses hot reheat steam extraction + desuperheating and pressure reducing valve for heating to meet the heating load of the unit under deep peak shaving conditions. However, since the high-grade steam is used for heating without fully performing work, there is a large thermal economic loss. Therefore, this solution proposes a low-level bypass heating cascade utilization system where the reheat steam pipeline 1 is connected to a tee, and the second steam pipeline is sequentially equipped with a first shut-off valve 01, a first check valve 02, and a pressure reducing valve 03. At the same time, a heat exchanger 6 is added. The reheat steam bypass enters the heat exchanger 6 after passing through the first shut-off valve 01, the first check valve 02, and the pressure reducing valve 03. After heat exchange, it enters the heating network steam header after passing through the second check valve 05 and the second shut-off valve 04 to supply heat to the heat users.

[0044] Condensate system: After being pressurized by the first heating network circulation pump 8 and the second heating network circulation pump 9, the return water from the heating network is bypassed at the outlet of the return water header. After passing through the flow regulating device 43, it enters the heat exchanger 6 for heating, and then passes through the third check valve 41 and the third shut-off valve 42 before entering the heating network supply water header. The flow regulating device 43 includes a regulating valve.

[0045] An operation mode of a low-level bypass heating cascade utilization system includes the following steps: 1. Conventional heating mode When the unit is operating at medium to high load, deep peak shaving is not required. At this time, the steam supply from the middle exhaust can meet the needs of low-pressure users. That is, the fourth shut-off valve 21, the fourth check valve 22, the first regulating valve 23, and the fifth shut-off valve 24 are opened. The heating network circulation pumps (including the first heating network circulation pump 8 and the second heating network circulation pump 9) are started. The first electric valve 51, the second electric valve 52, the third electric valve 53, the fourth electric valve 54, the second regulating valve 55, and the fifth electric valve 56 are all opened. The heating network circulating water is heated by the heating network heater 7 and then supplied to the heat users.

[0046] 2. Low-level bypass cascade heating mode When the unit is operating at low load, the intermediate discharge heat supply cannot meet the needs of heat users as the load decreases. Simultaneously, supplementary heat supply is required through the low-pressure bypass. At this time, the intermediate discharge steam supply system remains operational, meaning the fourth shut-off valve 21, the fourth check valve 22, the first regulating valve 23, and the fifth shut-off valve 24 are opened. The heat network circulation pumps (including the first heat network circulation pump 8 and the second heat network circulation pump 9) are started, and the first electric valve 51, the second electric valve 52, the third electric valve 53, the fourth electric valve 54, and the second regulating valve 55 are all opened. The heat network circulating water is heated by the heat network heater 7 and then supplied to heat users. Simultaneously, the first shut-off valve 01, the first check valve 02, and the pressure reducing valve 03 are opened, and reheat steam enters the heat exchanger 6 through the second steam pipeline. When the bypass of the heating network circulating water system is put into operation, the third check valve 41 and the third shut-off valve 42 are opened. By controlling the flow regulating device 43 and the second regulating valve 55, the water flow entering the heat exchanger 6 is adjusted. After the reheat steam is de-cooled by the heat exchanger 6, its pressure and temperature are basically matched with the intermediate discharge steam. After passing through the second check valve 05 and the second shut-off valve 04, it is connected to the intermediate discharge steam supply header and supplies steam to the heating network heater 7.

[0047] In the operation mode of this application, low-level bypass heating is only a measure to meet the heating demand to a certain extent. If it is necessary to further improve the heating capacity, the unit can also be modified to high-level bypass and intermediate valve joint adjustment heating according to the actual situation. The system operation mode is basically consistent with this system.

[0048] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A low-level bypass heating cascade utilization system, characterized in that, include: A boiler and a steam turbine connected to the boiler, the steam turbine comprising a high-pressure cylinder, an intermediate-pressure cylinder and a low-pressure cylinder connected in sequence; The heating system includes a first steam pipeline leading out from the connecting pipe between the intermediate pressure cylinder and the low pressure cylinder, and a heat network heater installed on the first steam pipeline. as well as, The low-level bypass heating subsystem includes: a second steam pipeline whose inlet is connected to a reheat steam pipeline, and a first shut-off valve, a first check valve and a pressure reducing valve are sequentially installed on the second steam pipeline along the steam flow direction; The heat exchanger has its steam-side inlet connected to the outlet of the second steam pipeline; A third steam pipeline, its inlet connected to the steam-side outlet of the heat exchanger and its outlet connected to the first steam pipeline, is equipped with a second check valve and a second shut-off valve; and... The water-side bypass has its inlet connected to the return water header of the heating network and its outlet connected to the supply water header of the heating network. The water-side bypass passes through the water side of the heat exchanger and is equipped with a flow regulating device.

2. The low-level bypass heating cascade utilization system according to claim 1, characterized in that, The first and second shut-off valves are electric valves; and / or, a regulating valve is also provided on the second steam pipeline before the pressure reducing valve.

3. The low-level bypass heating cascade utilization system according to claim 1, characterized in that, On the water-side bypass, a third check valve and a third shut-off valve are also provided after the water-side outlet of the heat exchanger.

4. The low-level bypass heating cascade utilization system according to claim 1, characterized in that, On the first steam pipeline of the heating system, a fourth shut-off valve, a fourth check valve, and a first regulating valve are sequentially installed between the connecting pipe between the intermediate-pressure cylinder and the low-pressure cylinder and the steam inlet of the heating network heater.

5. A low-level bypass heating cascade utilization system according to claim 1, characterized in that, The drain outlet of the heating network heater is connected to the condensate system of the unit through a drain pipe, and a fifth shut-off valve is installed on the drain pipe.

6. A method for operating low-level bypass heating, wherein the method is implemented using the low-level bypass heating cascade utilization system according to any one of claims 1-5, characterized in that, The method includes a conventional heating mode and a low-bypass cascade heating mode; the conventional heating mode is suitable for high-load operation of the unit, in which only the heating system is put into operation for heating; the low-bypass cascade heating mode is suitable for low-load peak-shaving operation of the unit, in which both the heating system and the low-bypass cascade heating subsystem are put into operation for coordinated heating.

7. The operating method according to claim 6, characterized in that, The conventional heating mode includes: opening the fourth shut-off valve, the fourth check valve, the first regulating valve, and the fifth shut-off valve in the heating system; starting the heating network circulation pump and ensuring that all the circulating water in the heating network flows through the heating network heater; and simultaneously keeping the second and third steam pipelines in the low-level bypass heating subsystem shut off.

8. The operating method according to claim 6, characterized in that, The low-bypass cascade heating mode includes: maintaining the operation of the heating system; opening the first shut-off valve, the second shut-off valve, and the third shut-off valve in the low-bypass cascade heating subsystem, so that reheat steam enters the heat exchanger through the second steam pipeline, and after heat exchange, it flows into the first steam pipeline through the third steam pipeline; at the same time, by adjusting the flow regulating device on the water-side bypass, a portion of the heating network circulating water is controlled to flow through the heat exchanger to be heated, and then flows into the main heating network water supply header.

9. The operating method according to claim 8, characterized in that, The flow rate ratio of the circulating water flowing through the heat exchanger and the circulating water flowing through the heating network heater is distributed by coordinating the flow rate regulation device on the water-side bypass and the second regulating valve on the main heating network water pipeline.

10. The operating method according to claim 6, characterized in that, In the low-pressure cascade heating mode, the reheated steam flowing through the heat exchanger is de-heated and depressurized until its pressure and temperature parameters are basically matched with the steam parameters from the medium-low pressure connecting pipe, and then it flows into the first steam pipeline.

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