A system and control method for cutting off a single low-pressure cylinder of a double low-pressure cylinder middle-row heating unit

Abstract

The present invention discloses a system and control method for switching a double low-pressure cylinder middle row heating unit to a single low-pressure cylinder. The system comprises a middle-pressure cylinder (1), a low-pressure cylinder (2), a low-pressure cylinder (3), a connecting pipe butterfly valve (4), a connecting pipe butterfly valve (5), and a regulating subsystem for switching the double low-pressure cylinders to a single low-pressure cylinder. The regulating subsystem for switching the double low-pressure cylinders to a single low-pressure cylinder comprises a cooling steam regulating valve (6), a check valve (8), and a check valve (9). When the middle row industrial heating is performed at low load, the connecting pipe butterfly valve (5) is fully closed. By adjusting the openings of the butterfly valve (4) and the cooling steam regulating valve (6), the middle row industrial heating pressure is regulated when the low-pressure cylinder (3) is switched off, and the unit operates safely and efficiently. The control method comprises a design parameter collection step, a single-cylinder connecting pipe butterfly valve regulating step, and a cooling steam regulating valve control step. The system and control method of the present invention can improve the operating economy of the steam turbine system and ensure the safe operation of the steam turbine unit.

Description

Technical Field

[0001] The present invention belongs to a center-row industrial heating steam turbine system and control method, and relates to a system and control method for cutting a single low-pressure cylinder of a center-row heating unit with two low-pressure cylinders. The system and control method can improve the operating economy of the steam turbine system and ensure the safe operation of the steam turbine unit. Background Art

[0002] In existing technology, industrial heating units with two low-pressure cylinders (LPCs) typically utilize a connecting pipe butterfly valve for regulation. Adjusting the valve opening maintains the central heating pressure in front of the valve. The pressure behind the valve is generally proportional to the flow rate entering the LPC, while a pressure differential exists across the valve, which is inversely proportional to the flow rate. When the unit load is low, the pressure differential across the butterfly valve is large, leading to valve instability and vibration. Simultaneously, each LPC operates at low load, resulting in low efficiency and poor unit economics. To address the issues of butterfly valve instability and vibration, conventional solutions employ a connecting pipe cooling bypass, directing steam from the central outlet to the LPC inlet to cool the disconnected LPC, maintaining efficient operation of one LPC and eliminating the other. However, this cooling method only throttles and reduces pressure, not generating power. Furthermore, the inlet temperature of the cooling steam is high, requiring water spraying for cooling and steam-water separation before it can enter the LPC, complicating the system. Inadequate water atomization or subsequent incomplete steam-water separation also poses a safety risk of water entering the LPC.

[0003] Attachment of prior art Figure 1 The mutual cooperation of the regulating valve and the water spray cooling device shown in the figure solves the economic and safety problems of switching from dual low-pressure cylinders to single low-pressure cylinders. However, at the same time, it also causes insufficient water spray atomization or incomplete subsequent steam-water separation, and there is also a safety hazard of water ingress into the low-pressure cylinder, and the system is complex. Summary of the Invention

[0004] The purpose of the present invention is to overcome the economic and safety problems of switching from double low-pressure cylinders to single low-pressure cylinders in the above-mentioned prior art, especially the technical problems of insufficient water spray atomization or incomplete subsequent steam-water separation, and the potential safety hazard of water entering the low-pressure cylinder, and to provide a single low-pressure cylinder switching system and control method for a double low-pressure cylinder mid-row heating unit.

[0005] The content of the present invention is: a double low-pressure cylinder middle row heating unit switching single low-pressure cylinder system, characterized in that: the system consists of: a medium-pressure cylinder (1), a low-pressure cylinder one (2), a low-pressure cylinder two (3), a connecting pipe butterfly valve one (4), a connecting pipe butterfly valve two (5) and a regulating subsystem for switching the double low-pressure cylinders to a single low-pressure cylinder; wherein the connecting pipe butterfly valve one (4) is connected to the low-pressure cylinder one (2), the low-pressure cylinder two (3) is connected to the butterfly valve two (5), and the medium-pressure cylinder (1) is connected to the low-pressure cylinder one (2) and the low-pressure cylinder two (3) through steam.

[0006] Furthermore, for safer and more economical operation, the regulating subsystem for switching from the double low-pressure cylinder to the single low-pressure cylinder is composed of a cooling steam regulating valve 1 (6), a check valve 1 (8) and a check valve 2 (9); when the middle-row industrial heating is performed at low load, the connecting pipe butterfly valve 2 (5) is fully closed, and by adjusting the opening of the butterfly valve 1 (4) and the cooling steam regulating valve 1 (6), the middle-row industrial heating pressure regulation and the safe and efficient operation of the unit are achieved when the low-pressure cylinder 2 (3) is cut off.

[0007] Furthermore, in order to increase safety and economical operation, the regulating subsystem for switching from the double low-pressure cylinder to the single low-pressure cylinder is composed of a cooling steam regulating valve 1 (6), a cooling steam regulating valve 2 (7), a check valve 1 (8) and a check valve 2 (9); when the middle-discharge industrial heating is performed at low load, the connecting pipe butterfly valve 2 (5) is fully closed, and by adjusting the opening of the butterfly valve 1 (4), the cooling steam regulating valve 1 (6) or the cooling steam regulating valve 2 (7), the middle-discharge industrial heating pressure is regulated when the low-pressure cylinder 2 (3) is cut off and the unit is operated safely and efficiently.

[0008] The double low-pressure cylinder operation is switched to the single low-pressure cylinder operation, which means that low-pressure cylinder 1 (2) operates normally, and low-pressure cylinder 2 (3) also operates, but at this time low-pressure cylinder 2 (3) only passes a small amount of steam for cooling, and does not do work and has zero output.

[0009] Furthermore, in order to expand the application of the system, the double low-pressure cylinder middle row heating unit single low-pressure cylinder switching system is characterized in that: the system also includes a heat recovery system, low-pressure heater extraction steam 6 extraction and low-pressure heater extraction steam 7 extraction, as well as low-pressure heater 5# and low-pressure heater 6#. The system adopts the principle of "pressure higher than 5% of the low-pressure cylinder inlet steam pressure under pure condensing THA conditions, and priority at the back" to select the low-pressure cylinder second (3) cooling steam source between extraction 6 or extraction 7, determine the switching operating point, and perform the regulating valve cooling steam regulating valve 1 (6) or cooling steam regulating valve 2 (7). "Priority at the back" means that if extraction 7 meets the requirements, extraction 7 will be selected first, and if it does not meet the requirements, extraction 6 will be selected.

[0010] Furthermore, the double low-pressure cylinder middle row heating unit switching single low-pressure cylinder system is characterized in that: when the load is low, a cooling pipeline (including a regulating valve) is provided from the appropriate heat recovery extraction pipe (6 extraction or 7 extraction) of the low-pressure cylinder one (2) to the inlet of the low-pressure cylinder two (3). When the cylinder is switched, the steam after the front flow of the low-pressure cylinder one (2) is used to cool the low-pressure cylinder two (3). There is no need to add a cooling steam desuperheating water system and working equipment, so that the cooling steam of the low-pressure cylinder two (3) can be used to work without the risk of water ingress, thereby improving the economy and safety of the unit.

[0011] At present, for large units with two low-pressure cylinders and a power of more than 600MW, the industrial heating of the middle row is limited by the temperature of the middle row. The main steam flow rate generally cannot be too low, and it is extremely difficult to cut off the double cylinders. Therefore, the setting of A low-pressure cylinder cooling bypass is not considered, and the system is simple.

[0012] Another aspect of the present invention is: a control method for switching off a single low-pressure cylinder of a heating unit with a double low-pressure cylinder middle row, the control method comprising the following steps:

[0013] Step A: Step A is a design parameter collection step, which is used to collect industrial heating operation data of the middle row of the steam turbine unit, Y heat balance diagrams and the power plant's annual load PW distribution, and low-load operation parameters DFC;

[0014] Step B is a step for adjusting the butterfly valve of the connecting pipe of a single cylinder. In step B, the opening of the connecting pipe butterfly valve is adjusted according to Y heat balance diagrams calculated based on a certain amount of heating boundary.

[0015] Step C is the cooling steam regulating valve control step: according to the principle of "pressure higher than 5% of the low-pressure cylinder inlet steam pressure under pure condensing THA conditions, priority given to the rear", select the low-pressure cylinder two (3) cooling steam source between 6 pumping or 7 pumping, determine the switching operating point, and control the cooling steam regulating valve one (6) or the cooling steam regulating valve two (7).

[0016] Another aspect of the present invention is: a control method for cutting off a single low-pressure cylinder of a double low-pressure cylinder middle row heating unit, the control method includes the following three modes: mode 1, mode 2 and mode 3;

[0017] Mode 1: When the unit is started, shut down or not in operation, butterfly valve 1 (4) and butterfly valve 2 (5) are fully open, cooling steam regulating valve 1 (6) and cooling steam regulating valve 2 (7) are fully closed, check valve 1 (8) and check valve 2 (9) are in the natural state (fully open or fully closed), and neither of them participates in the regulation;

[0018] Mode 2: When the unit starts to supply heat to the middle row and before the single cylinder is cut off, the cooling steam regulating valve 1 (6) and the cooling steam regulating valve 2 (7) are fully closed, the check valve 1 (8) and the check valve 2 (9) are naturally fully opened and do not participate in the regulation; the butterfly valve 1 (4) and the butterfly valve 2 (5) are synchronously closed (opened) to regulate the middle row heating pressure;

[0019] Mode 3: When the unit starts to cut off a single cylinder, cooling steam regulating valve 1 (6) and cooling steam regulating valve 2 (7) participate in regulating the cooling steam according to the principle of "pressure higher than 5% of the low-pressure cylinder inlet steam pressure under pure condensing THA conditions, priority at the back" and "one open and one closed". The cooling steam flow is regulated based on the exhaust temperature of the low-pressure cylinder 2 (3) of the conventional cylinder cutting; check valve 1 (8) and check valve 2 (9) are naturally fully closed; butterfly valve 2 (5) is fully closed and butterfly valve 1 (4) is gradually opened to regulate the heating pressure separately.

[0020] Compared with the prior art, the present invention has the following characteristics and beneficial effects:

[0021] (1) The present invention provides a single low-pressure cylinder switching system and control method for a double low-pressure cylinder center-row heating unit. The system is simple and can improve the operating economy of the steam turbine system and ensure the safe operation of the steam turbine unit.

[0022] (2) By adopting the present invention, taking a subcritical air-cooled 600MW unit as an example, when the medium-range industrial heating capacity is 1.0MPa / 400t / h and the system disclosed in the embodiment of the present invention is used for single-cylinder operation, the unit output can be stably increased by more than 3MW compared with the conventional single-cylinder cooling system when the load is not higher than 420MW. Based on an annual single-cylinder operation of 6000h and an electricity price of 0.4 yuan / kWh, the annual additional power generation income can be more than 7.2 million yuan; compared with the dual-cylinder operation, the unit output can be stably increased by more than 13MW when the load is not higher than 360MW, and the annual additional power generation income can be more than 30 million yuan; the investment payback period is less than 1 year. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the principle of the prior art;

[0024] Figure 2 It is a schematic diagram of the principle of the single low-pressure cylinder switching system of the double low-pressure cylinder middle row heating unit of the present invention.

[0025] In the figure: 1-medium pressure cylinder, 2-low pressure cylinder 1, 3-low pressure cylinder 2, 4-butterfly valve 1, 5-butterfly valve 2, 6-cooling steam regulating valve 1, 7-cooling steam regulating valve 2, 8-check valve 1, 9-check valve 2. DETAILED DESCRIPTION

[0026] The following embodiments are intended to further illustrate the present invention, but should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above-mentioned contents of the present invention still fall within the scope of protection of the present invention.

[0027] Example 1: See the accompanying drawings.

[0028] A system for switching a double low-pressure cylinder middle row heating unit to a single low-pressure cylinder, the system comprising: an intermediate-pressure cylinder 1, a low-pressure cylinder 1 2, a low-pressure cylinder 2 3, a connecting pipe butterfly valve 1 4, a connecting pipe butterfly valve 2 5, and a regulating subsystem for switching a double low-pressure cylinder to a single low-pressure cylinder; wherein, the connecting pipe butterfly valve 1 4 is connected to the low-pressure cylinder 1 2, the low-pressure cylinder 2 3 is connected to the butterfly valve 2 5, and the intermediate-pressure cylinder 1 is connected to the low-pressure cylinder 1 2 and the low-pressure cylinder 2 3 via steam.

[0029] Example 2: See the accompanying drawings.

[0030] A system for switching from a dual-low-pressure cylinder center-row heating unit to a single low-pressure cylinder. The regulating subsystem for switching from dual low-pressure cylinders to a single low-pressure cylinder comprises a cooling steam regulating valve 1 (6), a check valve 1 (8), and a check valve 2 (9). During low-load center-row industrial heating, the connecting pipe butterfly valve 2 (5) is fully closed. By adjusting the openings of butterfly valve 1 (4) and cooling steam regulating valve 1 (6), the center-row industrial heating pressure is regulated when the low-pressure cylinder 2 (3) is switched off, ensuring safe and efficient operation of the unit. Other components are the same as in Example 1 and are omitted.

[0031] Example 3: See the accompanying drawings.

[0032] A system for switching from a dual-low-pressure cylinder center-row heating unit to a single low-pressure cylinder. The regulating subsystem for switching from dual low-pressure cylinders to a single low-pressure cylinder comprises cooling steam regulating valve 1 (6), cooling steam regulating valve 2 (7), check valve 1 (8), and check valve 2 (9). During low-load center-row industrial heating, the connecting pipe butterfly valve 2 (5) is fully closed. By adjusting the opening of butterfly valve 1 (4), cooling steam regulating valve 1 (6), or cooling steam regulating valve 2 (7), the center-row industrial heating pressure is regulated when the low-pressure cylinder 2 (3) is switched off, ensuring safe and efficient operation of the unit. Other components are the same as in Example 1 and are omitted.

[0033] Example 4: See the accompanying drawings.

[0034] A system for switching a single low-pressure cylinder from a dual-low-pressure cylinder center-row heating unit includes a heat recovery system, low-pressure heater extraction steam extractions 6 and 7, and low-pressure heaters 5 and 6. The system selects the cooling steam source for low-pressure cylinder 23 between extractions 6 and 7, determines the switching operating point, and controls the cooling steam control valve 16 or cooling steam control valve 27, based on the principle of "pressure higher than 5% of the low-pressure cylinder inlet steam pressure under pure condensing (THA) conditions, with later-stage steam sources prioritized." Other aspects are the same as those of any of Embodiments 1-3 and are omitted.

[0035] Example 5: See the accompanying drawings.

[0036] A method for controlling a single low-pressure cylinder of a heating unit with a double low-pressure cylinder middle row, the method comprising the following steps:

[0037] Step A: Step A is a design parameter collection step, which is used to collect industrial heating operation data of the middle row of the steam turbine unit, Y heat balance diagrams and the power plant's annual load PW distribution, and low-load operation parameters DFC;

[0038] Step B is a step for adjusting the butterfly valve of the connecting pipe of a single cylinder. In step B, the opening of the connecting pipe butterfly valve is adjusted according to Y heat balance diagrams calculated based on a certain amount of heating boundary.

[0039] Step C is the cooling steam regulating valve control step: according to the principle of "pressure higher than 5% of the low-pressure cylinder steam inlet pressure under pure condensing THA conditions, and priority given to the rear", select the low-pressure cylinder 23 cooling steam source between 6 pumping or 7 pumping, determine the switching operating point, and regulate the cooling steam regulating valve 16 or the cooling steam regulating valve 27.

[0040] For other examples, see Examples 1-4.

[0041] Example 6: See the accompanying drawings.

[0042] A control method for cutting off a single low-pressure cylinder of a double-low-pressure cylinder middle-row heating unit, the control method includes the following three modes: mode 1, mode 2 and mode 3;

[0043] Mode 1: When the unit is started, shut down or operating without heating, butterfly valve 14 and butterfly valve 25 are fully open, cooling steam regulating valve 16 and cooling steam regulating valve 27 are fully closed, check valve 18 and check valve 29 are in the natural state (fully open or fully closed), and neither valve participates in the regulation.

[0044] Mode 2: When the unit starts supplying heat to the middle row and before single-cylinder operation is cut off, cooling steam regulating valve 16 and cooling steam regulating valve 27 are fully closed, check valve 18 and check valve 29 are naturally fully opened and do not participate in regulation; butterfly valve 14 and butterfly valve 25 are synchronously closed (opened) to adjust the middle row heating pressure;

[0045] Mode 3: When the unit starts to cut off a single cylinder, cooling steam regulating valve 16 and cooling steam regulating valve 27 participate in regulating the cooling steam by "one open and one closed" according to the principle of "pressure higher than 5% of the low-pressure cylinder inlet steam pressure under pure condensing THA conditions, and priority given to the rear", and adjust the cooling steam flow rate based on the exhaust steam temperature of the low-pressure cylinder 23 during conventional cylinder cutting; check valve 8 and check valve 29 are naturally fully closed; butterfly valve 25 is fully closed, and butterfly valve 14 is gradually opened to adjust the heating pressure separately.

[0046] For other examples, see Examples 1-5.

[0047] The control principle in the embodiment may be specifically as follows:

[0048] (1) Collecting industrial heating operation data of steam turbine units, relevant heat balance diagrams and annual load distribution of power plants;

[0049] (2) Calculate the heat balance diagram for each working condition by adjusting a certain amount of heating boundary by cutting the butterfly valve of the single cylinder connecting pipe;

[0050] (3) According to the principle of "pressure higher than 5% of the low-pressure cylinder inlet steam pressure under pure condensing THA conditions, and priority given to the rear", select the low-pressure cylinder 23 cooling steam source between 6 or 7 pumping, determine the switching operating point, and select the relevant cooling steam regulating valves 6 and 7 and design the pipeline; or only one cooling steam regulating valve 16 cooling steam source can be set according to the situation;

[0051] (4) According to the operating parameters of double and single low-pressure cylinders, the connecting pipe butterfly valves 4 and 5 are selected and the related pipelines are designed. Among them, the butterfly valve 14 is considered to pass the double cylinder cooling flow at full close, and the butterfly valve 25 is considered to be fully closed and zero flow;

[0052] (5) Select and design the check valves 8 and 9 for isolating the heat recovery steam extraction pipelines 5 and 6 of the low-pressure cylinder 1 2 and low-pressure cylinder 2 3 according to the pure condensing and heating working conditions;

[0053] (6) Control strategy for turbine exhaust heat supply cut-off single cylinder operation:

[0054] a) When the unit is started, shut down or operating without heating, butterfly valves 4 and 5 are fully open, cooling steam regulating valves 6 and 7 are fully closed, and check valves 8 and 9 are in the natural state (fully open or fully closed) and do not participate in regulation;

[0055] b) When the unit starts to supply heat to the middle row and before single cylinder operation is cut off, cooling steam regulating valves 6 and 7 are fully closed, check valves 8 and 9 are naturally fully opened and do not participate in regulation; butterfly valves 4 and 5 are synchronously closed (opened) to adjust the middle row heating pressure;

[0056] c) When the unit starts to cut off a single cylinder, cooling steam regulating valves 6 and 7 are operated in accordance with the principle of "pressure higher than 5% of the low-pressure cylinder inlet steam pressure under pure condensing THA conditions, with priority given to the rear part" and "one open and one closed" to regulate the cooling steam. The cooling steam flow is regulated based on the exhaust steam temperature of low-pressure cylinders 2 and 3 during normal cylinder cutting; check valves 8 and 9 are naturally fully closed; butterfly valve 2 and 5 are fully closed, and butterfly valve 1 and 4 are gradually opened to regulate the heating pressure separately;

[0057] d) During the cylinder cutting process, the steam temperature at the inlet of low-pressure cylinder 1-2 should not exceed the limit. If it does, the main steam pressure, main steam temperature and reheat temperature need to be adjusted.

[0058] The above specific technical solutions are intended only to illustrate the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above specific technical solutions, those skilled in the art should understand that they may modify the above specific technical solutions or replace some of the technical features therein with equivalents; and such modifications or replacements do not deviate from the spirit and scope of the present invention.

[0059] The technical contents not specifically described in the present invention and the above embodiments are the same as the prior art, and the raw materials are all commercially available products.

[0060] The present invention is not limited to the above embodiments, and all of the contents of the present invention can be implemented and have the above good effects.

Claims

1. A system for switching a single low-pressure cylinder from a double low-pressure cylinder middle row heating unit, characterized by: The system consists of: a medium-pressure cylinder (1), a low-pressure cylinder 1 (2), a low-pressure cylinder 2 (3), a butterfly valve 1 (4), a butterfly valve 2 (5) and a regulating subsystem for switching from a double low-pressure cylinder to a single low-pressure cylinder; Among them, the medium-pressure cylinder (1) is connected to the low-pressure cylinder one (2) and the low-pressure cylinder two (3) through a steam connecting pipe, the butterfly valve one (4) is arranged on the steam connecting pipe between the medium-pressure cylinder (1) and the low-pressure cylinder one (2), the butterfly valve one (4) is connected to the low-pressure cylinder one (2), the butterfly valve two (5) is arranged on the steam connecting pipe between the medium-pressure cylinder (1) and the low-pressure cylinder two (3), and the low-pressure cylinder two (3) is connected to the butterfly valve two (5); The regulating subsystem for switching from the double low-pressure cylinder to the single low-pressure cylinder is composed of a cooling steam regulating valve 1 (6), a check valve 1 (8) and a check valve 2 (9), and the cooling steam regulating valve 1 (6) is arranged on the cooling steam pipeline of the low-pressure cylinder 2 (3); or, the regulating subsystem for switching from the double low-pressure cylinder to the single low-pressure cylinder is composed of a cooling steam regulating valve 1 (6), a cooling steam regulating valve 2 (7), a check valve 1 (8) and a check valve 2 (9), and the cooling steam regulating valve 1 (6) and the cooling steam regulating valve 2 (7) are arranged in parallel on the cooling steam pipeline of the low-pressure cylinder 2 (3); The check valve 1 (8) is arranged on the pipeline of the low-pressure heater 5#; The check valve 2 (9) is arranged on the pipeline of the low-pressure heater 6#.

2. The single low-pressure cylinder switching system for a double low-pressure cylinder middle row heating unit according to claim 1 is characterized in that: The system also includes a heat recovery system, low-pressure heater extraction steam 6 extraction and low-pressure heater extraction steam 7 extraction, as well as low-pressure heater 5# and low-pressure heater 6#.

3. The single low-pressure cylinder switching system for a double low-pressure cylinder middle row heating unit according to claim 2 is characterized in that: At low load, the steam extracted from the low-pressure heater 6 or the low-pressure heater 7 of the low-pressure cylinder 1 (2) is used as the cooling steam source for the low-pressure cylinder 2 (3) and goes to the inlet of the low-pressure cylinder 2 (3). When the cylinder is cut, the steam after the front part of the low-pressure cylinder 1 (2) is used to cool the low-pressure cylinder 2 (3).

4. A control method for switching a single low-pressure cylinder from a heating unit with a double low-pressure cylinder and a middle row, the control method comprising the system for switching a single low-pressure cylinder from a heating unit with a double low-pressure cylinder and a middle row according to any one of claims 1 to 3; The control method includes the following steps: Step A: Step A is a design parameter collection step, which is used to collect industrial heating operation data of the middle row of the steam turbine unit, Y heat balance diagrams and the power plant's annual load PW distribution, and low-load operation parameters DFC; Step B is a step for adjusting the butterfly valve of the connecting pipe of a single cylinder. In step B, the opening of the connecting pipe butterfly valve is adjusted according to Y heat balance diagrams calculated based on a certain amount of heating boundary. Step C is the cooling steam regulating valve control step: according to the principle of "pressure higher than 5% of the low-pressure cylinder inlet steam pressure under pure condensing THA conditions, priority given to the rear", select the low-pressure cylinder two (3) cooling steam source between 6 pumping or 7 pumping, determine the switching operating point, and control the cooling steam regulating valve one (6) or the cooling steam regulating valve two (7).

5. A control method for switching a single low-pressure cylinder from a heating unit with a double low-pressure cylinder and a middle row, the control method comprising the system for switching a single low-pressure cylinder from a heating unit with a double low-pressure cylinder and a middle row according to any one of claims 1 to 3; The control method includes the following three modes: Mode 1, Mode 2 and Mode 3; Mode 1: When the unit is started, shut down or not in operation, butterfly valve 1 (4) and butterfly valve 2 (5) are fully open, cooling steam regulating valve 1 (6) and cooling steam regulating valve 2 (7) are fully closed, check valve 1 (8) and check valve 2 (9) are in the natural state (fully open or fully closed), and neither of them participates in the regulation; Mode 2: When the unit starts to supply heat to the middle row and before the single cylinder is cut off, the cooling steam regulating valve 1 (6) and the cooling steam regulating valve 2 (7) are fully closed, the check valve 1 (8) and the check valve 2 (9) are naturally fully opened and do not participate in the regulation; the butterfly valve 1 (4) and the butterfly valve 2 (5) are synchronously closed (opened) to regulate the middle row heating pressure; Mode 3: When the unit starts to cut off a single cylinder, cooling steam regulating valve 1 (6) and cooling steam regulating valve 2 (7) participate in regulating the cooling steam according to the principle of "pressure higher than 5% of the low-pressure cylinder inlet steam pressure under pure condensing THA conditions, with priority given to the rear", and adjust the cooling steam flow rate based on the exhaust temperature of the low-pressure cylinder 2 (3) during conventional cylinder cutting; check valve 1 (8) and check valve 2 (9) are naturally fully closed; butterfly valve 2 (5) is fully closed, and butterfly valve 1 (4) is gradually opened to regulate the heating pressure separately.

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