A coal power plant

Abstract

The utility model relates to a coal power unit. Coal power unit, include: boiler, heat circulation system, back pressure machine and feedwater heater, the steam output end of boiler is connected with the steam input end of back pressure machine and the steam input end of heat circulation system respectively, the steam output end of back pressure machine is connected with the steam input end of feedwater heater, to steam output to feedwater heater, the feedwater output end of heat circulation system is connected with the feedwater input end of feedwater heater, to feedwater output to feedwater heater, the feedwater output end of feedwater heater is connected with the feedwater end of boiler, to steam heated after the feedwater output to boiler. Adopt the utility model can reduce coal power unit coal consumption.

Description

Technical Field

[0001] This application relates to the field of coal-fired power unit technology, and in particular to a high-efficiency thermal system for coal-fired power units. Background Technology

[0002] With the continuous increase in the installed capacity of new energy sources and the development of new-generation coal-fired power, the application of coal-fired power units is becoming more and more widespread, and there is a need to continuously improve the flexibility of these units. Typically, coal-fired power units generate steam by burning coal, which drives a steam turbine to power a generator.

[0003] In current coal-fired power unit systems, waste heat from flue gas is typically used to heat boiler feedwater in order to reduce unit coal consumption. However, because the flue gas temperature is not high, the feedwater heating location is usually before the high-pressure heater, meaning the final feedwater cannot be heated. As a result, the boiler feedwater temperature remains unchanged, failing to achieve a significant reduction in unit coal consumption. Utility Model Content

[0004] Therefore, it is necessary to provide a high-efficiency thermal system for coal-fired power generating units that can reduce coal consumption, addressing the aforementioned technical problems.

[0005] In a first aspect, this application provides a coal-fired power unit, including: a boiler, a thermal cycle system, a back pressure turbine, and a feedwater heater;

[0006] The steam output end of the boiler is connected to the steam input end of the back pressure turbine and the steam input end of the thermal cycle system, respectively. The steam intake of the back pressure turbine meets the feedwater heating requirements of the coal-fired power unit.

[0007] The steam output end of the back pressure unit is connected to the steam input end of the feedwater heater to output steam to the feedwater heater;

[0008] The feedwater output end of the thermal circulation system is connected to the feedwater input end of the feedwater heater to output feedwater to the feedwater heater;

[0009] The feedwater heater's feedwater output end is connected to the boiler's feedwater end to output steam-heated feedwater to the boiler.

[0010] In one embodiment, the thermal cycle system includes a high-pressure cylinder and a high-pressure regenerating component. The steam input end of the thermal cycle system includes the steam input end of the high-pressure cylinder and the steam input end of the high-pressure regenerating component. The water supply output end of the thermal cycle system includes the water supply output end of the high-pressure regenerating component.

[0011] The steam inlet of the high-pressure cylinder is connected to the steam outlet of the boiler;

[0012] The steam input end of the high-pressure regenerative component is connected to the steam output end of the high-pressure cylinder, and the water supply output end of the high-pressure regenerative component is connected to the water supply input end of the water supply heater.

[0013] In one embodiment, the coal-fired power unit further includes a connection component for controlling the connection status between the back pressure machine and the high-pressure cylinder; the connection component is disposed between the back pressure machine and the high-pressure cylinder.

[0014] In one embodiment, the connecting component is a clutch.

[0015] In one embodiment, the coal-fired power unit further includes a first valve for controlling the opening and closing of the steam transmission channel between the boiler and the back pressure turbine; the first valve is located between the boiler and the back pressure turbine.

[0016] In one embodiment, the coal-fired power unit further includes a second valve that controls the opening and closing of the steam transmission channel between the back compressor and the feedwater heater; the second valve is located between the back compressor and the feedwater heater.

[0017] In one embodiment, the coal-fired power unit further includes a condensing device for condensing the steam discharged from the back pressure turbine; the steam input end of the condensing device is connected to the steam output end of the back pressure turbine.

[0018] In one embodiment, the coal-fired power unit further includes a third valve for controlling the opening and closing of the steam transmission channel between the back compressor and the condensing device; the third valve is located between the back compressor and the condensing device.

[0019] In one embodiment, the coal-fired power unit further includes a fourth valve for controlling the steam intake of the thermal cycle system; the fourth valve is located between the boiler and the thermal cycle system.

[0020] In one embodiment, the back pressure compressor is connected in parallel with the thermodynamic cycle system.

[0021] The aforementioned coal-fired power unit, by installing a back-pressure turbine between the boiler's steam outlet and the inlet of the thermal cycle system, and adding a feedwater heater between the back-pressure turbine and the boiler feedwater side, allows for the extraction of a portion of boiler steam matching the feedwater heating demand into the back-pressure turbine when the unit's load is below its rated load—that is, when the unit is operating at medium to low load conditions. The back-pressure turbine can then supply this portion of boiler steam to the feedwater heater, which further heats the boiler feedwater. This allows the feedwater to be heated to a higher temperature than the conventional system feedwater under this load condition, thereby improving the thermal cycle efficiency of the coal-fired power unit, reducing coal consumption, and achieving economical operation across a wide load range.

[0022] The first steam supplied by the boiler to the back pressure turbine is located before the throttling valve, therefore the first steam does not undergo throttling and there is no throttling loss. This reduces the overall throttling loss of the unit, resulting in economic benefits. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of a coal-fired power unit in one embodiment;

[0025] Figure 2 This is a structural block diagram of a coal-fired power unit in one embodiment;

[0026] Figure 3 This is a schematic diagram of the optimized coal-fired power unit structure in one embodiment.

[0027] Explanation of icon numbers:

[0028] Boiler-101; High-pressure cylinder-102; Intermediate-pressure cylinder-103; Low-pressure cylinder-104; Condenser-105; Low-pressure heater-106; Deaerator-107; First high-pressure heater-110; Second high-pressure heater-109; Third high-pressure heater-108; Thermal cycle system-201; Back pressure compressor-202; Feedwater heater-203; Connecting assembly-205; Condensing device-204; First valve-206; Second valve-207; Third valve-208; Fourth valve-209; Generator-20 Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0030] Coal-fired power generation is a complex energy conversion process involving the interconversion of multiple energy forms. The unit mainly consists of a boiler, turbine, generator, and auxiliary systems. In the boiler, coal is fed into the combustion chamber for combustion, releasing a large amount of heat energy. Feedwater in the boiler is heated and evaporated through heating surfaces, forming high-temperature, high-pressure steam. After entering the turbine, the steam expands on the blades, driving them to rotate and thus converting heat energy into mechanical energy. The mechanical energy output from the turbine is converted into electrical energy by the generator and transmitted to the outside world through power lines.

[0031] Steam turbine cylinders can be classified into high-pressure cylinders, intermediate-pressure cylinders, and low-pressure cylinders based on different steam inlet parameters. Figure 1A schematic diagram of a coal-fired power unit is shown. The coal-fired power unit 10 includes a boiler 101, a high-pressure cylinder 102, an intermediate-pressure cylinder 103, a low-pressure cylinder 104, a condenser 105, a low-pressure heater 106, a deaerator 107, a third high-pressure heater 108, a second high-pressure heater 109, and a first high-pressure heater 110. The third high-pressure heater, the second high-pressure heater, and the first high-pressure heater are connected sequentially via feedwater channels, and the steam extraction temperature of the third high-pressure heater, the second high-pressure heater, and the first high-pressure heater increases sequentially.

[0032] Specifically, the main steam discharged from boiler 101 enters high-pressure cylinder 102. The exhaust steam from high-pressure cylinder 102 enters the reheater of boiler 101 for reheating, forming reheated steam. Simultaneously, the second high-pressure heater 109 and the first high-pressure heater 110 extract exhaust steam from high-pressure cylinder 102 at different temperatures for reheating. The reheated steam discharged from boiler 101 enters intermediate-pressure cylinder 103. The intermediate-pressure exhaust steam from intermediate-pressure cylinder 103 enters low-pressure cylinder 104, while the third high-pressure heater 108 extracts a portion of the exhaust steam from intermediate-pressure cylinder 103 for reheating. The exhaust steam that performs work in low-pressure cylinder 104 enters condenser 105 and condenses into water. The condensate then sequentially enters low-pressure heater 106, deaerator 107, third high-pressure heater 108, second high-pressure heater 109, and first high-pressure heater 110, finally returning to boiler 101, thus realizing the boiler's thermal cycle. The power generated by generator 20 comes from the combined work of high-pressure cylinder 102, medium-pressure cylinder 103 and low-pressure cylinder 104. The condensers in this scheme can all be replaced by air-cooled islands.

[0033] In current coal-fired power unit systems, to reduce coal consumption, waste heat from flue gas is typically used to heat boiler feedwater. Based on Figure 1 As illustrated, the structure suggests that the feedwater temperature from the first high-pressure heater is relatively high. If the flue gas temperature is low, the feedwater is typically heated before the high-pressure heater, meaning the final feedwater cannot be heated. This results in no change in the boiler feedwater temperature, failing to significantly reduce the unit's coal consumption. Furthermore, when the unit is operating at medium to low loads, throttling losses increase, and heating with waste heat from the flue gas cannot reduce these losses. Therefore, how to increase the boiler feedwater temperature while simultaneously reducing throttling losses under medium to low load conditions, thereby achieving economic efficiency in wide-load operation of coal-fired power units, is a key focus for current coal-fired power unit development.

[0034] Based on this, this plan selects to add one back-pressure turbine and one feedwater heater. A back-pressure turbine is a steam turbine with an exhaust pressure higher than atmospheric pressure, significantly higher than that of a condensing steam turbine. A feedwater heater is a steam-water heat exchange device that uses extracted steam to heat boiler feedwater; by further heating the boiler feedwater, it can improve the overall thermal cycle efficiency of the coal-fired power unit.

[0035] In some embodiments, Figure 2 A structural block diagram of a coal-fired power unit is shown, wherein the coal-fired power unit 10 includes: a boiler 101, a thermal cycle system 201, a back pressure machine 202, and a feedwater heater 203.

[0036] The steam output of boiler 101 is connected to the steam input of back pressure compressor 202 and the steam input of thermal circulation system 201, respectively. The steam intake of back pressure compressor 202 meets the feedwater heating requirements of the coal-fired power unit. The steam output of back pressure compressor 202 is connected to the steam input of feedwater heater 203, and the feedwater output of thermal circulation system 201 is connected to the feedwater input of feedwater heater 203. The steam output of feedwater heater 203 is connected to the feedwater end of boiler 101.

[0037] In some embodiments, Figure 3 A schematic diagram of the optimized coal-fired power unit is shown. The thermal cycle system 201 may include a high-pressure cylinder 102, an intermediate-pressure cylinder 103, a low-pressure cylinder 104, a condenser 105, a low-pressure heater 106, a deaerator 107, and a high-pressure regeneration assembly (a third high-pressure heater 108, a second high-pressure heater 109, and a first high-pressure heater 110).

[0038] Specifically, the back-pressure turbine is located before the high-pressure cylinder of the steam turbine and is connected in parallel with it. The main steam from the boiler is split before throttling; part flows into the back-pressure turbine, and the other part flows into the high-pressure cylinder after throttling. Thus, the main steam flowing into the back-pressure turbine is not throttled, reducing some of the throttling losses. The feedwater heater is located between the high-pressure regenerator assembly and the boiler feedwater side, connected to the first high-pressure heater, and is used to further heat the feedwater supplied by the first high-pressure heater via the exhaust steam from the back-pressure turbine. This further heats the feedwater, thereby reducing unit coal consumption and achieving economical operation of the coal-fired power unit across wide load ranges.

[0039] In the above embodiments, by adding a back-pressure turbine and a feedwater heater, when the unit is operating at low to medium loads, a portion of the boiler main steam required for feedwater heating can be extracted and fed into the back-pressure turbine to perform work, reducing the amount of steam entering the thermal cycle system. Furthermore, the back-pressure turbine can discharge steam into the feedwater heater to further heat the feedwater, thereby increasing the feedwater temperature and reducing the unit's coal consumption. This further reduces the amount of steam entering the high-pressure cylinder under low to medium load conditions, avoiding excessive throttling and thus reducing the unit's throttling losses, achieving economic efficiency for wide-load operation of the coal-fired power unit.

[0040] It should be understood that the main steam flow rate entering the back pressure turbine is equal to the exhaust steam flow rate of the back pressure turbine, and the exhaust steam from the back pressure turbine will enter the newly added feedwater heater to heat the feedwater. That is, the exhaust steam flow rate of the back pressure turbine required for heating the feedwater determines the flow rate entering the back pressure turbine. Therefore, the main steam flow rate entering the back pressure turbine can be dynamically adjusted based on the feedwater heating demand of the coal-fired power unit to achieve the purpose of heating feedwater on demand.

[0041] In some embodiments, the steam input terminal of the thermal circulation system 201 may include the steam input terminal of the high-pressure cylinder 102 and the steam input terminal of the high-pressure regeneration component, specifically the steam input terminal of the first high-pressure heater 110 and the steam input terminal of the second high-pressure heater 109. Similarly, the water supply output terminal of the thermal circulation system 201 may include the water supply output terminal of the high-pressure regeneration component, specifically the water supply output terminal of the first high-pressure heater 110 and the water supply output terminal of the second high-pressure heater 109.

[0042] The steam input end of the high-pressure cylinder 102 is connected to the steam output end of the boiler 101 to receive the main steam supplied by the boiler. The steam output end of the high-pressure cylinder 102 is connected to the steam input ends of the first high-pressure heater 110 and the second high-pressure heater 109, respectively, to discharge steam to the first high-pressure heater 110 and the second high-pressure heater 109. The feedwater output end of the first high-pressure heater 110 is connected to the feedwater input end of the feedwater heater 203 to supply heated feedwater to the feedwater heater 203 through the feedwater channel.

[0043] Specifically, after the low-pressure heater heats the condensate, the heated feedwater is processed by a deaerator and then sent to the third high-pressure heater. The third high-pressure heater then reheats the feedwater using steam extracted from the intermediate-pressure cylinder, and the reheated feedwater is sent to the second high-pressure heater through the feedwater channel. The second high-pressure heater also reheats the feedwater using steam extracted from the high-pressure cylinder, and the reheated feedwater is sent to the first high-pressure heater through the feedwater channel. After the first high-pressure heater heats the feedwater using extracted steam, the reheated feedwater is sent to a newly added feedwater heater through the feedwater channel. The feedwater heater further heats the feedwater using steam extracted from the back pressure turbine and then sends the heated feedwater to the boiler.

[0044] In the above embodiments, by adding a feedwater heater between the high-pressure regenerative component and the boiler to further heat the feedwater, it is possible to ensure the precise increase of the feedwater temperature and improve the overall circulation thermal efficiency of the unit.

[0045] In some embodiments, the coal-fired power unit 10 may further include a connection assembly 205 disposed between the back pressure machine 202 and the high-pressure cylinder 102 to control the connection status between the back pressure machine and the high-pressure cylinder.

[0046] In some embodiments, the connecting component is a clutch. It is understood that in this embodiment, the back pressure compressor and the high-pressure cylinder are coaxially arranged via a clutch; that is, the back pressure compressor and the high-pressure cylinder share the same shaft or mechanical transmission system. The clutch can dynamically connect or disconnect the back pressure compressor and the high-pressure cylinder to achieve flexible engagement / disengagement of the back pressure compressor.

[0047] In some embodiments, if the back pressure machine is not used for a long period of time, it can be considered that the back pressure machine is in a shutdown state. In this case, the connection between the back pressure machine and the high pressure cylinder can be disconnected by connecting components. At this time, the back pressure machine stops running completely and the high pressure cylinder runs independently.

[0048] In some embodiments, if the back pressure machine is not put into use for a short period of time or temporarily, it can be considered to be in standby mode, and it can be determined whether to disconnect the connection between the back pressure machine and the high-pressure cylinder according to the actual situation.

[0049] In this context, the back pressure turbine being in standby mode refers to the back pressure turbine being able to quickly start up without participating in power generation, typically within a few minutes, by maintaining its operating temperature and minimum steam supply. This is a transitional state between "operation" and "shutdown".

[0050] In some embodiments, in order to facilitate steam bypass (such as exhaust steam to the condenser), prevent pressure buildup inside the back pressure compressor, and save energy, the connection between the back pressure compressor and the high-pressure cylinder can be disconnected.

[0051] In some embodiments, for systems requiring high response speed, it may be possible to maintain the connection between the back pressure unit and the high-pressure cylinder.

[0052] In the above embodiments, on the one hand, by setting a connecting component between the back pressure unit and the high-pressure cylinder, the back pressure unit and the high-pressure cylinder can be arranged coaxially, eliminating the need for an additional generator, saving unit space, and simplifying transmission. On the other hand, by flexibly switching the connection state between the back pressure unit and the high-pressure cylinder through the connecting component, the back pressure unit can be dynamically engaged or disengaged without affecting the operation of the main unit.

[0053] In some embodiments, the coal-fired power unit 10 may further include a first valve 206 between the boiler 101 and the back pressure unit 202, and a second valve 207 between the back pressure unit 202 and the feedwater heater 203.

[0054] The first valve 206 controls the opening and closing of the steam transmission channel between the boiler and the back pressure turbine, as well as the steam intake of the back pressure turbine. The second valve 207 controls the opening and closing of the steam transmission channel between the back pressure turbine and the feedwater heater.

[0055] Specifically, when the coal-fired power unit is operating at low to medium load, the feedwater temperature is low, requiring the back pressure turbine to be started. At this time, both the first and second valves are fully open, allowing main steam to flow from the boiler to the back pressure turbine, and then from the back pressure turbine into the feedwater heater. Furthermore, the steam flow rate into the back pressure turbine can be controlled by adjusting the opening of the first valve. It is understood that since the ultimate goal is to increase the feedwater temperature, only the main steam flow rate sufficient to meet the temperature increase requirement needs to be drawn into the back pressure turbine.

[0056] In some embodiments, when the back pressure compressor is in a shutdown state, both the first valve and the second valve may be in a closed state. When the back pressure compressor is in a hot standby state, the first valve is open to control the steam flow into the back pressure compressor to a minimum, and the second valve is closed so that the exhaust steam from the back pressure compressor does not enter the new heater.

[0057] In the above embodiments, by installing valves between the boiler and the back pressure unit, and between the back pressure unit and the feedwater heater, the opening or closing of the steam transmission pipeline is precisely controlled, thereby improving the accuracy of steam transmission control.

[0058] In some embodiments, the coal-fired power unit 10 may further include a condensing device 204 connected to the back pressure turbine, specifically a condenser. The steam input end of the condensing device 204 is connected to the steam output end of the back pressure turbine 202 to condense the steam discharged by the back pressure turbine 202 in standby mode. The condensing device 204 may also be a coal-fired power unit condenser 105, which is connected to a low-pressure heater. After condensing the exhaust steam from the back pressure turbine 202 and the low-pressure cylinder 104 into water, the condensate is transported to the low-pressure heater for heating via a feedwater pipeline. After being treated by a deaerator, it is then transported to the third high-pressure heater, the second high-pressure heater, the first high-pressure heater, and the feedwater heater for further heating before being delivered to the boiler feedwater side. A third valve 208 is provided between the back pressure turbine 202 and the condensing device 204 to control the opening and closing of the steam transmission channel between them.

[0059] Specifically, when the back pressure compressor is in hot standby mode, although its main functions are temporarily disabled, a certain amount of steam flow and temperature control still need to be maintained to prevent equipment damage and ensure rapid response capability. Therefore, to avoid steam accumulation inside the back pressure compressor, which could lead to a sudden pressure surge and potentially damage the equipment, this embodiment adds a condenser connected to the back pressure compressor. By opening the third valve, the exhaust steam from the back pressure compressor is directed into the condenser, maintaining a low pressure at the back pressure compressor outlet and thus preventing overpressure.

[0060] In some embodiments, the third valve is closed when the back pressure unit is in a stopped state.

[0061] In some embodiments, the condensing device 204 can condense the steam discharged from the back pressure unit into water. The condensate can be returned to the low-pressure regenerator assembly, and after being treated by the deaerator, it is sent to the third high-pressure heater, the second high-pressure heater, the first high-pressure heater, and the feedwater heater for heating before being sent to the boiler feedwater side.

[0062] In the above embodiments, by connecting the condenser to the back pressure unit, steam can be prevented from accumulating inside the back pressure unit, thereby preventing equipment damage and ensuring the safety and operational stability of the back pressure unit.

[0063] In some embodiments, the coal-fired power unit 10 further includes a fourth valve between the boiler 101 and the thermal cycle system 201, specifically a fourth valve 209 between the boiler 101 and the high-pressure cylinder 102, which controls the steam intake of the thermal cycle system, or in other words, controls the steam intake of the high-pressure cylinder.

[0064] In some embodiments, the fourth valve 209 is a throttle valve, which can control the flow rate of the fluid by adjusting the cross-sectional area of ​​the channel, thereby achieving precise control of the fluid flow rate.

[0065] Specifically, the main steam of the boiler is diverted before entering the throttling valve. Based on the feedwater heating requirements of the coal-fired power unit, the portion of the main steam that meets the feedwater heating requirements is used to do work in the back pressure turbine, and the generated electricity is used for the unit's grid-connected electricity.

[0066] Based on the above, this solution, by adding a back-pressure turbine, allows some of the main steam to be supplied to the back-pressure turbine when the unit is operating at low to medium loads, reducing the throttling losses of the main steam and thus lowering the unit's coal consumption. This solution also adds a feedwater heater, with the heating steam sourced from the back-pressure turbine's exhaust steam. On one hand, this allows for dynamic increases in feedwater temperature based on heating demand, achieving on-demand feedwater heating and further reducing coal consumption, resulting in energy savings. On the other hand, it improves steam utilization.

[0067] Furthermore, this solution achieves coaxial arrangement of the back pressure unit and the high-pressure cylinder by setting a connecting component between them, eliminating the need for an additional generator, saving unit space, and simplifying transmission. On the other hand, the connection state between the back pressure unit and the high-pressure cylinder can be flexibly switched by the connecting component, allowing for dynamic activation and deactivation of the back pressure unit without affecting the operation of the main unit.

[0068] Moreover, by connecting the condenser to the back pressure unit, this solution can prevent steam from accumulating inside the back pressure unit, thereby avoiding equipment damage and ensuring the safety and operational stability of the back pressure unit.

[0069] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0070] The embodiments described above are merely illustrative of several implementations of this utility model, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A coal-fired power unit, characterized in that, The coal-fired power unit includes: a boiler, a thermal circulation system, a back pressure turbine, and a feedwater heater; The steam output terminal of the boiler is connected to the steam input terminal of the back pressure unit and the steam input terminal of the thermal cycle system, respectively. The steam output end of the back pressure unit is connected to the steam input end of the feedwater heater to output steam to the feedwater heater; The water supply output terminal of the thermal circulation system is connected to the water supply input terminal of the water supply heater to supply water to the water supply heater; The feedwater heater's feedwater output end is connected to the boiler's feedwater end to output feedwater heated by the steam to the boiler.

2. The coal-fired power unit according to claim 1, characterized in that, The thermal circulation system includes a high-pressure cylinder and a high-pressure regeneration component. The steam input end of the thermal circulation system includes the steam input end of the high-pressure cylinder and the steam input end of the high-pressure regeneration component. The water supply output end of the thermal circulation system includes the water supply output end of the high-pressure regeneration component. The steam input end of the high-pressure cylinder is connected to the steam output end of the boiler; The steam input end of the high-pressure regenerative component is connected to the steam output end of the high-pressure cylinder, and the water supply output end of the high-pressure regenerative component is connected to the water supply input end of the water supply heater.

3. The coal-fired power unit according to claim 2, characterized in that, The coal-fired power unit also includes: A connection assembly for controlling the connection status between the back pressure machine and the high-pressure cylinder; the connection assembly is disposed between the back pressure machine and the high-pressure cylinder.

4. The coal-fired power unit according to claim 3, characterized in that, The connecting component is a clutch.

5. The coal-fired power unit according to claim 1, characterized in that, The coal-fired power unit also includes: A first valve that controls the opening and closing of the steam transmission channel between the boiler and the back pressure unit; the first valve is located between the boiler and the back pressure unit.

6. The coal-fired power unit according to claim 1, characterized in that, The coal-fired power unit also includes: A second valve controls the opening and closing of the steam supply channel between the back pressure unit and the feedwater heater; the second valve is located between the back pressure unit and the feedwater heater.

7. The coal-fired power unit according to claim 1, characterized in that, The coal-fired power unit also includes a condensing device for condensing the steam discharged from the back pressure machine; the steam input end of the condensing device is connected to the steam output end of the back pressure machine.

8. The coal-fired power unit according to claim 7, characterized in that, The coal-fired power unit also includes: A third valve controls the opening and closing of the steam supply channel between the back pressure unit and the condensing device; the third valve is located between the back pressure unit and the condensing device.

9. The coal-fired power unit according to claim 1, characterized in that, The coal-fired power unit also includes: A fourth valve for controlling the steam intake of the thermal cycle system; the fourth valve is located between the boiler and the thermal cycle system.

10. The coal-fired power unit according to claim 1, characterized in that, The back pressure machine is connected in parallel with the thermodynamic circulation system.

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