CN111520204A - A system and method for improving the steam supply capacity and unit efficiency of a reheat steam turbine - Google Patents

Abstract

The invention discloses a system and method for improving the steam supply capacity and unit efficiency of a reheat steam turbine. The system includes a feedwater bypass heat exchange system, a heat supply system and a feedback control system. The present invention simultaneously adjusts the opening of the heat-extraction regulating valve of the medium-pressure cylinder and the steam regulating valve of the cold and reheated steam to the pressure matcher, so that the steam pressure and flow at the outlet of the steam-water heat exchanger can meet the user's requirements at the same time. According to the user's temperature requirements, combined with the heat exchange characteristics of the steam-water heat exchanger, the water flow rate corresponding to the outlet of the feed pump to the inlet pipe of the steam-water heat exchanger is controlled. Finally, select the return water position in the return water pipeline of the steam-water heat exchanger according to the temperature measurement value and open the corresponding electric valve. Provides a system that is universal and has a strong ability to adjust the temperature parameters of heating steam, and does not need to set up a water spray desuperheating device, which can be used for heating transformation of in-service units to improve its industrial steam supply capacity and unit efficiency.

Description

A system and method for improving the steam supply capacity and unit efficiency of a reheat steam turbine

technical field

The invention belongs to the technical field of steam extraction and heat supply of steam turbines, and in particular relates to a system and method for improving the steam supply capacity and unit efficiency of a reheat steam turbine.

Background technique

In recent years, in order to achieve energy saving and emission reduction and make full use of the advantages of cogeneration, more and more reheating condensing units have been transformed into heating units. In some existing heating systems, when the steam temperature parameter required by the user is low, the temperature of the heating steam is quite different from the heating temperature required by the user, and it is necessary to use water spray to reduce the temperature of the high-temperature heating steam. , the energy of high-temperature heating steam is not fully utilized.

At present, there are also some devices that use the superheat of the heating steam to increase the temperature of the feed water and reduce the heat absorption per unit of feed water in the boiler, so as to improve the comprehensive energy utilization efficiency of the power plant. For example, in the Chinese patent with the authorization date of August 31, 2016 and the authorization announcement number CN205535722U, an energy cascade utilization device for steam extraction and heating system is disclosed. The principle of matching the heating and extraction steam temperature directly replaces part of the regenerative heater. If the heating unit is retrofitted, this scheme may cause parameter mismatch, resulting in the overall thermal efficiency of the unit not being optimal or even decreasing. The low temperature of feed water during operation leads to unqualified out-of-stock indicators, and the universality of the system is limited. Therefore, the device is more suitable for the design of new heating units (the system affected by it needs to be greatly improved and designed), and is not suitable for heating renovation of in-service units. For example, the authorization date is February 15, 2017, and the Chinese patent with the authorization announcement number CN205957140U discloses a heating system with high heat utilization rate. The heating system utilizes the partial superheat of high temperature steam by adding a steam cooler to heat the final feed water of the boiler. The steam cooler of this system only heats the final feed water, and the system is relatively simplified, but it has certain limitations on the scope of application and adjustment capability of the heating steam temperature, so it is still necessary to set up a water spray desuperheating device.

To sum up, for the heating transformation of in-service units, there is currently no universal and heating steam temperature parameter adjustment ability that is strong, and does not need to set up a water spray desuperheating device, which can be used to improve industrial steam supply. system of capacity and unit efficiency.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a system and method with strong applicability and parameter adjustment ability, which can be used for heating renovation of in-service reheat steam turbine units to improve their industrial steam supply capacity and unit efficiency.

The present invention adopts following technical scheme to realize:

A system for improving the steam supply capacity and unit efficiency of a reheat steam turbine, comprising a steam turbine unit steam-water system, a feedwater bypass heat exchange system, a heating system and a feedback control system; wherein, the steam turbine unit steam-water system includes a boiler, a boiler The outlet of the superheated steam pipe is connected with the steam inlet of the high-pressure cylinder, the exhaust port of the high-pressure cylinder is connected with the inlet of the reheated steam pipe of the boiler, the outlet of the reheated steam pipe of the boiler is connected with the steam inlet of the medium-pressure cylinder, and the high-pressure cylinder is connected with the steam inlet of the medium pressure cylinder. The first-stage and second-stage extraction ports of the medium-pressure cylinder are respectively connected with the steam inlets of the first-stage high-pressure cylinder and the second-stage high-pressure cylinder; The steam inlet and outlet of the deaerator, the feed pump, the third-stage high-pressure feeder, the second-stage high-pressure feeder and the first-stage high-pressure feeder are connected in turn, and the water outlet of the first-stage high-pressure feeder is connected with the boiler feed water. The inlet of the pipeline is connected;

The feedwater bypass heat exchange system includes the feedwater pump outlet to the steam-water heat exchanger inlet pipe, the feedwater pump outlet to the steam-water heat exchanger water inlet pipe is drawn from the branch from the feedwater pump to the third-stage high feed water pipe, and The water inlet of the steam-water heat exchanger is connected, and the feed water bypass to the water inlet electric valve of the steam-water heat exchanger is installed on the outlet of the feed pump to the water inlet of the steam-water heat exchanger, and the water outlet of the steam-water heat exchanger and the return water of the steam-water heat exchanger The pipes are connected, the return water pipe of the steam-water heat exchanger is connected with the electric valve of the first-stage high addition outlet through the steam-water heat exchanger, and the water-supply pipe of the first-stage high is added to the boiler, and the return water pipe of the steam-water heat exchanger passes through the steam-water exchange. The electric valve from the heater outlet to the second-stage high feeder outlet is connected with the feedwater pipeline from the second-stage high-feed to the first-stage feeder, and the return water pipe of the steam-water heat exchanger passes the water from the steam-separation-water heat exchanger to the third-stage high-pressure feeder. The outlet electric valve is connected with the water supply pipeline from the third stage to the second stage;

The heating system includes a pressure matching device, the inlet of the pressure matching device is respectively connected with the heating and extraction pipeline of the medium-pressure cylinder and the steam pipeline of the cold reheat steam to the pressure matching device, and the heating and extraction pipeline of the medium-pressure cylinder is installed on the heating and extraction pipeline. There is a medium-pressure cylinder heating and extraction steam regulating valve, and a steam regulating valve is installed on the steam pipeline from cold reheat steam to pressure matcher, and the outlet of the pressure matcher is connected to the steam inlet of the steam-water heat exchanger. The steam outlet of the steam-water heat exchanger is connected with the steam pipeline from the steam-water heat exchanger to the user;

A first temperature measuring point is installed on the steam pipeline from the steam-water heat exchanger to the user, a second temperature measuring point is installed on the feed water pump to the third-stage high feed water pipeline, and a second temperature measuring point is installed on the return pipeline of the steam-water heat exchanger. Three temperature measuring points;

The feedback control system includes a feedback controller, the inlet of the feedback controller is connected with the first temperature measurement point, the second temperature measurement point and the third temperature measurement point, and the outlet of the feedback controller is connected to the outlet of the steam-water heat exchanger to the first temperature measurement point. The first-stage high plus outlet electric valve, the steam-water heat exchanger outlet to the second-stage high-outlet electric valve, the steam-water heat exchanger outlet to the third-stage high-outlet electric valve and the feed water bypass to the steam-water heat exchanger inlet electric valve connected.

A further improvement of the present invention is that holes are made on the cylinder block of the medium pressure cylinder according to the pressure requirements of the user.

A method for improving the steam supply capacity and unit efficiency of a reheated steam turbine, the method is based on the above-mentioned system for improving the steam supply capacity and unit efficiency of a reheated steam turbine, and includes the following operation steps:

Step 1: When the load of the unit is high and the heating and extraction steam of the medium-pressure cylinder can meet the pressure demand of the user, close the steam regulating valve of the pressure matcher to close the cold reheat steam, and adjust the opening of the heating and extraction regulating valve of the medium-pressure cylinder , so that the outlet steam flow of the steam-water heat exchanger can meet the user's needs; when the unit load is low, and the heat-extraction steam supply of the medium-pressure cylinder cannot meet the pressure demand of the user, adjust the heat-extraction control valve and cold reheating of the medium-pressure cylinder at the same time. The opening degree of the steam-to-pressure matcher steam regulating valve enables the steam pressure and flow rate of the steam-water heat exchanger to meet the user’s needs at the same time;

Step 2: setting the target value of the first temperature measuring point in the feedback controller according to the user's temperature requirements, and simultaneously transmitting the measured values of the first temperature measuring point and the second temperature measuring point to the feedback controller;

Step 3: According to the heat exchange characteristics of the steam-water heat exchanger and the measured values of the first temperature measuring point and the second temperature measuring point, processing is performed in the feedback controller, and the feed water bypass is controlled to the steam-water heat exchanger water inlet electric valve. The opening degree to control the feed water flow corresponding to the outlet of the feed pump to the inlet pipe of the steam-water heat exchanger;

Step 4: Send the measured value of the third temperature measuring point to the feedback controller, and select the return water position in the return water pipe of the steam-water heat exchanger according to the temperature measurement value as the first-stage high-feeding to the boiler feed water pipeline or the second-stage high-pressure adding To the first-stage high feed water pipeline or the third-stage high-feed to the second-stage high-feed water pipeline, after confirming the position, open the corresponding control valve steam-water heat exchanger to output water to the first-stage high-add outlet electric valve or steam-water heat exchanger The water is discharged to the second-stage high-plus-outlet electric valve or the steam-water heat exchanger, and the water is discharged to the third-stage high-plus-outlet electric valve and the other two control valves are closed.

The present invention at least has the following beneficial technical effects:

The present invention provides a system and method for improving the steam supply capacity and unit efficiency of a reheated steam turbine. First, by simultaneously adjusting the openings of the heat-extraction regulating valve of the medium-pressure cylinder and the steam regulating valve of the cold reheated steam to the pressure matcher , so that the steam pressure and flow rate of the steam-water heat exchanger outlet can meet the needs of users at the same time. Then, set the target value of the first temperature measuring point in the feedback controller according to the user's temperature requirements, and transmit the measured values of the first temperature measuring point and the second temperature measuring point to the feedback controller. Heat exchange characteristics, control the water flow rate corresponding to the outlet of the feed pump to the inlet pipe of the steam-water heat exchanger. Finally, the measured value of the third temperature measuring point is sent to the feedback controller, and the return water position in the return water pipeline of the steam-water heat exchanger is selected according to the temperature measured value and the corresponding electric valve is opened. Provides a system that is universal and has strong ability to adjust the temperature parameters of heating steam, and does not need to set up a water spray desuperheating device, which can be used for heating transformation of in-service units to improve its industrial steam supply capacity and unit efficiency.

Description of drawings

Figure 1 is a schematic structural diagram of the present invention.

Description of reference numbers:

1. Boiler, 2. High-pressure cylinder, 3. Medium-pressure cylinder, 4. Feed water pump, 5. Deaerator, 6. Pressure matching device, J1, first-stage high-pressure cylinder, J2, second-stage high-pressure cylinder, J3, The third stage is added, J4, steam water heat exchanger, L1, the first stage is added to the boiler feed water pipeline, L2, the second stage is added to the first stage and the feed water pipeline, L3, the third stage is added to the first stage Secondary high feed water pipeline, L4, feed water pump to the third high feed water pipeline, L5, cold reheat steam to pressure matcher steam pipeline, L6, medium pressure cylinder heating and extraction steam pipeline, L7, feed pump outlet to The water inlet pipe of the steam-water heat exchanger, L8, the water outlet of the steam-water heat exchanger to the return water pipe of the first-stage high-pressure addition outlet, L9, the steam-water pipe of the steam-water heat exchanger to the user, V1, the water-outlet of the steam-water heat exchanger to the first-stage high-pressure heater Outlet electric valve, V2, water from steam-water heat exchanger to the second-stage high plus outlet electric valve, V3, steam-water heat exchanger water to the third-stage high and outlet electric valve, V4, feed water bypass to steam-water heat exchanger inlet water Electric valve, V5, steam regulating valve for cold reheat steam to pressure matcher, V6, regulating valve for heating and extraction steam of medium pressure cylinder, T1, first temperature measuring point, T2, second temperature measuring point, T3, third temperature Measuring point, C1, feedback controller.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings.

Referring to Figure 1, the present invention provides a system for improving the steam supply capacity and unit efficiency of a reheat steam turbine, including a steam turbine unit steam-water system, a feedwater bypass heat exchange system, a heating system and a feedback control system.

The steam turbine unit steam-water system includes a boiler 1, the outlet of the superheated steam pipe of the boiler 1 is communicated with the steam inlet of the high-pressure cylinder 2, the steam outlet of the high-pressure cylinder 2 is communicated with the inlet of the reheated steam pipe of the boiler 1, and the boiler The outlet of the reheat steam pipe of 1 is connected with the steam inlet of the medium pressure cylinder 3, and the first and second stage extraction ports of the high pressure cylinder 2 are respectively connected with the steam inlets of the first-stage high-pressure cylinder J1 and the second-stage high-pressure cylinder J2. , the first-stage and second-stage steam extraction ports of the medium-pressure cylinder 3 are respectively connected with the steam inlet of the third-stage high-add J3 and the deaerator 5. The deaerator 5, the feed pump 4, the third-stage high-add J3, the first The water inlet and outlet of the second-stage high-rise J2 and the first-stage high-grade J1 are connected in turn, and the water outlet of the first-stage high-grade J1 is connected with the inlet of the water supply pipe of the boiler 1.

The feedwater bypass heat exchange system includes a branch from the feedwater pump outlet to the steam-water heat exchanger inlet pipe L7, and the feedwater pump outlet to the steam-water heat exchanger inlet pipe L7 from the feed pump to the third-stage high feed water pipe L4. It leads out and is connected with the water inlet of the steam-water heat exchanger J4. The feed water bypass to the steam-water heat exchanger inlet electric valve V4 is installed on the outlet of the feed pump to the steam-water heat exchanger inlet pipe L7, and the water outlet of the steam-water heat exchanger J4 It is connected with the return water pipe L8 of the steam-water heat exchanger, and the return water pipe L8 of the steam-water heat exchanger passes the water from the steam-water heat exchanger to the first-stage height plus outlet electric valve V1 and is connected with the first-stage height and the boiler feed water pipe L1 , the steam-water heat exchanger return water pipeline L8 is connected with the second-stage high-fill to the first-stage high-fill water pipeline L2 through the steam-water heat exchanger outlet to the second-stage high addition outlet electric valve V2, and the steam-water heat exchanger return water pipeline L8 is connected with the water supply pipeline L3 from the third stage to the second stage through the steam-separation water heat exchanger to the third-stage high-fill outlet electric valve V3.

The described heating system includes a pressure matcher 6, and the inlet of the pressure matcher 6 is respectively connected with the medium-pressure cylinder heat-extraction pipeline L6 and the cold reheat steam-to-pressure-matcher steam pipeline L5, and the medium-pressure cylinder heat-extraction pipeline L5 is connected. The medium-pressure cylinder heating and extraction steam regulating valve V6 is installed on the steam pipeline L6, the cold reheat steam to the pressure matcher steam pipeline L5 is installed with the cold reheat steam to the pressure matcher steam regulating valve V5, the outlet of the pressure matcher 6 It is communicated with the steam inlet of the steam-water heat exchanger J4, and the steam outlet of the steam-water heat exchanger J4 is communicated with the steam pipeline L9 from the steam-water heat exchanger to the user.

The feedback control system includes a feedback controller C1, the inlet of the feedback controller C1 is connected with the first temperature measuring point T1, the second temperature measuring point T2 and the third temperature measuring point T3, and the outlet of the feedback controller C1 is connected with the soda water. The water from the heat exchanger goes to the first stage with the electric valve V1, the steam-water heat exchanger goes to the second stage and the electric valve V2, the steam-water heat exchanger goes to the third stage with the electric valve V3 and the feed water bypass. It is connected to the water inlet electric valve V4 of the steam-water heat exchanger.

In addition, a first temperature measuring point T1 is installed on the steam-water heat exchanger to the user steam pipeline L9, and a second temperature measuring point T2 is installed on the feed pump to the third-stage high feed water pipeline L4. A third temperature measuring point T3 is installed on the water pipeline L8.

According to the user's pressure requirements, holes are made on the cylinder block of the medium pressure cylinder, and the heat supply and extraction pipeline L6 of the medium pressure cylinder is led out. The pipe size is calculated according to the user's flow demand.

A method for improving the steam supply capacity and unit efficiency of a reheat steam turbine provided by the present invention includes the following operation steps:

Step 1: When the unit load is high and the medium pressure cylinder heating and extraction steam can meet the pressure demand of the user, close the cold reheat steam to the pressure matcher steam regulating valve V5, and adjust the heating and extraction regulating valve V6 of the medium pressure cylinder. opening, so that the outlet steam flow of the steam-water heat exchanger 6 can meet the needs of the user; when the unit load is low and the heat supply and extraction of the medium-pressure cylinder cannot meet the pressure demand of the user, adjust the heat-extraction control valve V6 of the medium-pressure cylinder at the same time. And the opening degree of the steam regulating valve V5 of the pressure matcher and the cold reheat steam, so that the outlet steam pressure and flow rate of the steam-water heat exchanger 6 can meet the needs of users at the same time.

Step 2: Set the target value of the first temperature measuring point T1 in the feedback controller C1 according to the user's temperature requirements, and simultaneously transmit the measured values of the first temperature measuring point T1 and the second temperature measuring point T2 to the feedback controller C1.

Step 3: According to the heat exchange characteristics of the steam-water heat exchanger J4 and the measured values of the first temperature measuring point T1 and the second temperature measuring point T2, processing is performed in the feedback controller C1, and the feed water is bypassed to the steam-water heat exchanger by controlling The opening of the water inlet electric valve V4 controls the water supply flow corresponding to the outlet of the water supply pump to the water inlet pipe L7 of the steam-water heat exchanger.

Step 4: Send the measured value of the third temperature measuring point T3 to the feedback controller C1, and select the return water position in the return water pipe L8 of the steam-water heat exchanger according to the temperature measured value as the first level and add it to the boiler feed water pipe L1 or the first level. Add the second-stage high to the first-stage high water supply pipeline L2 or the third-stage high-fill to the second-stage high-fill water pipeline L3. After confirming the position, open the corresponding control valve, and the water from the steam-water heat exchanger will flow out to the first-stage high-fill outlet. The valve V1 or the steam-water heat exchanger outputs water to the second-stage high-plus-outlet electric valve V2 or the steam-water heat exchanger outputs water to the third-stage high-plus-outlet electric valve V3 and closes the other two control valves.

In the system for improving the steam supply capacity and unit efficiency of the reheat steam turbine provided by the present invention, the flow rate of the bypass feed water can be comprehensively adjusted, and the position of the return water in the return water pipe of the steam-water heat exchanger can be set, so it is universal. The ability to adjust the temperature parameters of heating steam and heating steam is strong, and there is no need to set up a water spray desuperheating device, which can be used for heating transformation of in-service units to improve their industrial steam supply capacity and unit efficiency.

Claims (3)

1. A system for improving the steam supply capacity and the unit efficiency of a reheat steam turbine is characterized by comprising a steam-water system of the steam turbine unit, a water supply bypass heat exchange system, a heat supply system and a feedback control system; wherein,

the steam-water system of the steam turbine set comprises a boiler (1), an outlet of a superheated steam pipeline of the boiler (1) is communicated with a steam inlet of a high-pressure cylinder (2), a steam outlet of the high-pressure cylinder (2) is communicated with an inlet of a reheated steam pipeline of the boiler (1), an outlet of the reheated steam pipeline of the boiler (1) is communicated with a steam inlet of an intermediate-pressure cylinder (3), a first-stage steam extraction port and a second-stage steam extraction port of the high-pressure cylinder (2) are respectively communicated with steam inlets of a first-stage high pressure booster (J1) and a second-stage high pressure booster (J2), a first-stage steam extraction port and a second-stage steam extraction port of the intermediate-pressure cylinder (3) are respectively communicated with steam inlets of a third-stage high pressure booster (J3) and a deaerator (5), the water inlets and the water outlets of the third-stage high-pressure boiler (J3), the second-stage high-pressure boiler (J2) and the first-stage high-pressure boiler (J1) are communicated in sequence, and the water outlet of the first-stage high-pressure boiler (J1) is communicated with the inlet of a water supply pipeline of the boiler (1);

the water supply bypass heat exchange system comprises a water supply pump outlet to a steam-water heat exchanger water inlet pipeline (L7), a water supply pump outlet to steam-water heat exchanger water inlet pipeline (L7) is led out from a water supply pump to a branch of a third-level high pressure water supply pipeline (L4) and is communicated with a water inlet of a steam-water heat exchanger (J4), a water supply bypass to steam-water heat exchanger water inlet electric valve (V4) is installed on the water supply pump outlet to the steam-water heat exchanger water inlet pipeline (L7), a water outlet of the steam-water heat exchanger (J4) is communicated with a steam-water heat exchanger water return pipeline (L8), the steam-water heat exchanger water return pipeline (L8) is communicated with a first-level high pressure water supply outlet electric valve (V1) and a first-level high pressure boiler water supply pipeline (L1) through a steam-water heat exchanger water outlet to a second-level high pressure water supply outlet electric valve (V2) and a second-level high pressure water supply pipeline, a water return pipeline (L8) of the steam-water heat exchanger is communicated with a third-level high-pressure water feeding pipeline (L3) through an electric valve (V3) of a third-level high-pressure water feeding outlet of the steam-water heat exchanger;

the heat supply system comprises a pressure matcher (6), wherein the inlet of the pressure matcher (6) is respectively communicated with a heat supply steam extraction pipeline (L6) of an intermediate pressure cylinder and a steam pipeline (L5) for conveying cold reheat steam to the pressure matcher, an intermediate pressure cylinder heat supply steam extraction regulating valve (V6) is installed on the heat supply steam extraction pipeline (L6) of the intermediate pressure cylinder, the steam pipeline (L5) for conveying cold reheat steam to the pressure matcher is provided with a steam regulating valve (V5) for conveying cold reheat steam to the pressure matcher, the outlet of the pressure matcher (6) is communicated with the steam inlet of a steam-water heat exchanger (J4), and the steam outlet of the steam-water heat exchanger (J4) is communicated with a steam pipeline (L9) for conveying steam from the;

a first temperature measuring point (T1) is arranged on a pipeline from the steam-water heat exchanger to user steam (L9), a second temperature measuring point (T2) is arranged on a pipeline from a water feed pump to a third-level high pressure feed water (L4), and a third temperature measuring point (T3) is arranged on a water return pipeline (L8) of the steam-water heat exchanger;

the feedback control system comprises a feedback controller (C1), wherein an inlet of the feedback controller (C1) is communicated with a first temperature measuring point (T1), a second temperature measuring point (T2) is communicated with a third temperature measuring point (T3), an outlet of the feedback controller (C1) is communicated with a steam-water heat exchanger water outlet to first-stage high-pressure water outlet electric valve (V1), a steam-water heat exchanger water outlet to second-stage high-pressure water outlet electric valve (V2), a steam-water heat exchanger water outlet to third-stage high-pressure water outlet electric valve (V3) and a water supply bypass to steam-water heat exchanger water inlet electric valve (V4).

2. The system according to claim 1, wherein the opening is made in the intermediate pressure cylinder block according to a pressure requirement of a user.

3. A method for improving the steam supply capacity and the unit efficiency of a reheat steam turbine, which is based on the system for improving the steam supply capacity and the unit efficiency of a reheat steam turbine according to claim 1 or 2, comprising the following steps:

the method comprises the following steps: when the load of the unit is high and the heat supply steam extraction of the intermediate pressure cylinder can meet the pressure requirement of a user, closing a steam regulating valve (V5) of the pressure matcher for cold reheat steam, and regulating the opening degree of the heat supply steam extraction regulating valve (V6) of the intermediate pressure cylinder to enable the flow of the outlet steam of the steam-water heat exchanger (6) to meet the requirement of the user; when the load of the unit is low and the heat supply steam extraction of the intermediate pressure cylinder cannot meet the pressure requirement of a user, the opening degrees of a heat supply steam extraction regulating valve (V6) of the intermediate pressure cylinder and the steam regulating valve (V5) of a cold reheat steam to a pressure matcher are simultaneously adjusted, so that the outlet steam pressure and the flow of the steam-water heat exchanger (6) can simultaneously meet the requirement of the user;

step two: setting a target value of the first temperature measuring point (T1) in a feedback controller (C1) according to the temperature requirement of a user, and simultaneously transmitting the measured values of the first temperature measuring point (T1) and the second temperature measuring point (T2) to the feedback controller (C1);

step three: processing in a feedback controller (C1) according to the heat exchange characteristics of the steam-water heat exchanger (J4) and the measured values of a first temperature measuring point (T1) and a second temperature measuring point (T2), and controlling the feed water flow corresponding to the feed water pump outlet to a steam-water heat exchanger water inlet pipeline (L7) by controlling the opening degree of a feed water bypass to a steam-water heat exchanger water inlet electric valve (V4);

step four: and transmitting the measured value of the third temperature measuring point (T3) to a feedback controller (C1), selecting a water return position in a water return pipeline (L8) of the steam-water heat exchanger as a first-level high water feeding pipeline (L1), a second-level high water feeding pipeline (L2) or a third-level high water feeding pipeline (L3), opening a corresponding control valve to enable water to flow out of the steam-water heat exchanger to a first-level high water outlet electric valve (V1) or to enable water to flow out of the steam-water heat exchanger to a second-level high water outlet electric valve (V2) or to flow out of the steam-water heat exchanger to a third-level high water outlet electric valve (V3) after confirming the position, and closing the other two control valves.

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