Steam-starved residual heat cascade heating system and method

Abstract

The embodiment of the present application provides a kind of full steam exhaust waste heat cascade heat supply system and method, belong to waste heat utilization technical field.The full steam exhaust waste heat cascade heat supply system, including the multistage heating device connected in series, the input end of multistage heating device is connected with heat network circulating water backwater, the output end of multistage heating device is connected with heat network circulating water supply, and the heat source of multistage heating device comes from the steam exhaust of 600MW and above grade supercritical direct air cooling three-cylinder four-steam unit, multistage heating device carries out heat exchange with steam exhaust and heat network circulating water backwater, to realize the purpose of heating heat network circulating water backwater.Multistage heating device receives different steam exhaust from unit respectively, and heat network circulating water backwater is heated by the heat source of steam exhaust, to improve heating capacity, heating economy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste heat utilization, in particular to a full-deaerated-steam cascade heat supply system and a full-deaerated-steam cascade heat supply method. BACKGROUND

[0002] The cold end loss of a thermal power plant is the largest loss of the thermal system of the power plant. The steam turbine exhaust loss of a pure condensing unit can account for more than 40% of the total fuel heat. The steam turbine exhaust loss is waste heat emission for a thermal power plant, but constitutes a huge energy waste for low-grade building heating. If the steam turbine deaerated-steam waste heat can be fully recovered for heating, the heating capacity and energy utilization efficiency of the power plant will be greatly improved, bringing huge energy-saving, environmental protection and social benefits. Strengthening waste heat recovery and utilization and improving energy utilization rate are fundamental measures for energy saving, carbon emission reduction and environmental protection. Due to the high price of coal, thermal power plants are facing extremely severe operating conditions. Under such circumstances, supplying heat to cities and supplying industrial extraction steam to enterprises have become important means for power enterprises to increase income.

[0003] 600MW and above units, especially supercritical units, have gradually become the main unit type in the current thermal power industry in China, and are air-cooled units in most northern regions. Compared with conventional 300MW heat supply units, the middle exhaust pressure of the steam turbine is higher, direct extraction for heating affects the economy, and for some 600MW units with low-pressure cylinder high-back pressure or double-back pressure modification, the deaerated-steam waste heat cannot be fully utilized, and part of the exhaust steam still needs to be continuously exhausted to the cold island, causing a loss of cold source. Moreover, when running at low load, there are problems such as inflexible operation mode and poor heating economy.

[0004] The present application provides a full-deaerated-steam cascade heat supply system and a full-deaerated-steam cascade heat supply method, which fully recovers and utilizes the deaerated-steam generated by a 600MW and above supercritical direct air-cooled three-cylinder four-exhaust steam turbine unit, heats the heat network circulating water return water with the heat source of the deaerated-steam, assists in heating, and improves the heating economy. SUMMARY

[0005] The purpose of the embodiments of the present application is to provide a full-deaerated-steam cascade heat supply system and a full-deaerated-steam cascade heat supply method, which fully recovers and utilizes the deaerated-steam generated by a 600MW and above supercritical direct air-cooled three-cylinder four-exhaust steam turbine unit, heats the heat network circulating water return water with the heat source of the deaerated-steam, assists in heating, and improves the heating economy.

[0006] In order to achieve the above-mentioned purpose, the embodiment of the first aspect of the present application provides a full-deaerated steam residual heat cascade heating system, which is applied to a 600MW and above grade supercritical direct air cooling three-cylinder four-exhaust steam unit. The full-deaerated steam residual heat cascade heating system comprises a plurality of cascade-connected multi-stage heating devices. The input end of the multi-stage heating device is connected to the heat network circulating water return water. The output end of the multi-stage heating device is connected to the heat network circulating water supply. The heat exchange heat source of the multi-stage heating device comes from the deaerated steam of the 600MW and above grade supercritical direct air cooling three-cylinder four-exhaust steam unit. The multi-stage heating device exchanges heat between the deaerated steam and the heat network circulating water return water, so as to achieve the purpose of heating the heat network circulating water return water.

[0007] Preferably, the multi-stage heating device comprises:

[0008] a first-stage heating device, wherein the heat exchange heat source of the first-stage heating device comes from the conventional back pressure deaerated steam of the conventional back pressure low-pressure cylinder of the supercritical direct air cooling three-cylinder four-exhaust steam unit;

[0009] a second-stage heating device, wherein the heat exchange heat source of the second-stage heating device comes from the high back pressure deaerated steam of the high back pressure low-pressure cylinder of the supercritical direct air cooling three-cylinder four-exhaust steam unit;

[0010] a third-stage heating device, wherein the heat exchange heat source of the third-stage heating device comes from the high back pressure deaerated steam of the high back pressure low-pressure cylinder of the supercritical direct air cooling three-cylinder four-exhaust steam unit after quality treatment;

[0011] a fourth-stage heating device, wherein the heat exchange heat source of the fourth-stage heating device comes from the deaerated steam of the small steam turbine of the supercritical direct air cooling three-cylinder four-exhaust steam unit after work;

[0012] a fifth-stage heating device, wherein the heat exchange heat source of the fifth-stage heating device comes from the deaerated steam of the medium-pressure cylinder of the supercritical direct air cooling three-cylinder four-exhaust steam unit after temperature and pressure reduction treatment;

[0013] a heat network circulating pump, which is used to circulate the heated heat network circulating water return water and the heat network circulating water return water after the pressure of the first-stage heating device and the second-stage heating device is increased;

[0014] The first-stage heating device, the second-stage heating device, the heat network circulating pump, the third-stage heating device, the fourth-stage heating device and the fifth-stage heating device are connected in series, and are used to converge and output the heat network circulating water return water heated by the first-stage heating device, the heat network circulating water return water heated by the second-stage heating device, the heat network circulating water return water heated by the third-stage heating device, the heat network circulating water return water heated by the fourth-stage heating device and the heat network circulating water return water heated by the fifth-stage heating device to the heat network circulating water supply.

[0015] Preferably, the primary heating device comprises a primary heat network heater and a primary heat network inlet valve, the primary heat network heater is connected with the conventional back pressure low pressure cylinder through a primary heat network inlet pipeline, the primary heat network inlet pipeline is provided with the primary heat network inlet valve, and the primary heat network inlet valve is used to control the flow of the conventional back pressure exhaust steam entering the primary heat network heater.

[0016] Preferably, the secondary heating device comprises a secondary heat network heater and a secondary heat network inlet valve, the secondary heat network heater is connected with the high back pressure low pressure cylinder through a secondary heat network inlet pipeline, the secondary heat network inlet pipeline is provided with the secondary heat network inlet valve, and the secondary heat network inlet valve is used to control the flow of the high back pressure exhaust steam entering the secondary heat network heater.

[0017] Preferably, the tertiary heating device comprises a tertiary heat network heater, a steam compressor, a first tertiary heat network inlet valve and a second tertiary heat network inlet valve.

[0018] The tertiary heat network heater is connected with the high back pressure low pressure cylinder through a tertiary heat network inlet pipeline, and the steam compressor is arranged between the high back pressure low pressure cylinder and the tertiary heat network heater.

[0019] The steam compressor is used to compress and upgrade the high back pressure exhaust steam output by the high back pressure low pressure cylinder, and the high back pressure exhaust steam after the compression and upgrading enters the tertiary heat network heater for heat exchange.

[0020] The first tertiary heat network inlet valve is used to control the flow of the high back pressure exhaust steam entering the steam compressor, and the second tertiary heat network inlet valve is used to control the flow of the high back pressure exhaust steam entering the tertiary heater.

[0021] Preferably, the quaternary heating device comprises a quaternary heat network heater, a small steam turbine, a first quaternary heat network inlet valve and a second quaternary heat network inlet valve.

[0022] The quaternary heat network heater is connected with the intermediate pressure cylinder of the supercritical direct air cooling three-cylinder four-exhaust steam unit through a quaternary heat network inlet pipeline, and the small steam turbine is arranged between the intermediate pressure cylinder and the quaternary heat network heater.

[0023] The small steam turbine receives steam from the intermediate pressure cylinder and uses the steam of the intermediate pressure cylinder to do work, and the exhaust steam generated after the work is output to the quaternary heat network heater for heat exchange.

[0024] The first quaternary heat network inlet valve is used to control the flow of the steam entering the small steam turbine for work, and the second quaternary heat network inlet valve is used to control the flow of the exhaust steam entering the quaternary heat network heater for heat exchange.

[0025] Preferably, the five-stage heating device comprises a desuperheater, a five-stage heat network heater, a first five-stage heat network inlet valve and a second five-stage heat network inlet valve.

[0026] The five-stage heat network heater is connected to the intermediate-pressure cylinder of the supercritical direct air-cooling three-cylinder four-exhaust steam unit through a five-stage heat network inlet pipeline, and the desuperheater is arranged between the intermediate-pressure cylinder and the five-stage heat network heater.

[0027] The desuperheater receives steam from the intermediate-pressure cylinder and performs desuperheating and pressure reduction on the steam, and the steam after the desuperheating and pressure reduction enters the five-stage heat network heater for heat exchange.

[0028] The first five-stage heat network inlet valve is used to control the steam flow entering the desuperheater, and the second five-stage heat network inlet valve is used to control the steam flow entering the five-stage heat network heater for heat exchange.

[0029] Preferably, the full-steam-exhaust residual heat cascade heating system further comprises a plate heat exchanger, which is used to receive the first converged drain from the four-stage heating device and the five-stage heating device and exchange heat between the first converged drain and the heat network circulating water return.

[0030] Preferably, the full-steam-exhaust residual heat cascade heating system further comprises an auxiliary vacuum pumping system, which is arranged on a vacuum pumping communication pipeline of the air-cooling radiator of the supercritical direct air-cooling three-cylinder four-exhaust steam unit, and is in communication with the multi-stage heating device and used to pump out air from the multi-stage heating device.

[0031] In the second aspect, the embodiments of the present application provide a 600MW and above grade supercritical direct air-cooling three-cylinder four-exhaust steam unit, which comprises a conventional back-pressure low-pressure cylinder, a high-back-pressure low-pressure cylinder and a full-steam-exhaust residual heat cascade heating system as described above.

[0032] In the third aspect, the embodiments of the present application provide a full-steam-exhaust residual heat cascade heating method, which is implemented by using the full-steam-exhaust residual heat cascade heating system as described above, and the method comprises the following steps:

[0033] When the supercritical direct air-cooling three-cylinder four-exhaust steam unit is in the initial and final stages of heating, the heat network circulating water return is heated by the first-stage heating device and the second-stage heating device to meet the heating demand.

[0034] When the supercritical direct air-cooling three-cylinder four-exhaust steam unit is in the middle stage of heating, the heat network circulating water return is heated by the first-stage heating device, the second-stage heating device and the third-stage heating device to meet the heating demand.

[0035] When the supercritical direct air cooling three-cylinder four-steam turbine unit is in the heating extreme cold period, the heat network circulating water return water is heated by the first heating device, the second heating device, the third heating device, the fourth heating device and the fifth heating device to meet the heating demand.

[0036] When the supercritical direct air cooling three-cylinder four-steam turbine unit is in deep peak regulation operation, the conventional back pressure low pressure cylinder is in micro power operation, and the second heating device, the third heating device, the fourth heating device and the fifth heating device heat the heat network circulating water return water to meet the heating demand.

[0037] The application comprises a multi-stage heating device, which respectively receives different exhaust steam from the unit, heats the heat network circulating water return water by the heat source of the exhaust steam, and improves the heating capacity and the heating economy.

[0038] Other features and advantages of the embodiments of the application will be described in detail in the following specific implementation part. BRIEF DESCRIPTION OF DRAWINGS

[0039] The accompanying drawings are included to provide a further understanding of the embodiments of the application, and constitute a part of the specification, and are used together with the following specific implementation to explain the embodiments of the application, but do not constitute a limitation on the embodiments of the application. In the drawings:

[0040] Figure 1 is a structural schematic diagram of the full exhaust steam waste heat cascade heating system provided by the embodiment 1 of the application.

[0041] EXPLANATION OF REFERENCE NUMERALS

[0042] 1-first heat network heater, 2-second heat network heater, 3-third heat network heater, 4-fourth heat network heater, 5-fifth heat network heater, 6-heat network circulating pump, 7-conventional back pressure low pressure cylinder, 8-high back pressure low pressure cylinder, 9-steam compressor, 10-first third heat network steam inlet valve, 11-second third heat network steam inlet valve, 12-small steam turbine, 13-first fourth heat network steam inlet valve, 14-second fourth heat network steam inlet valve, 15-temperature and pressure reducer, 16-first fifth heat network steam inlet valve, 17-second fifth heat network steam inlet valve, 18-assisted vacuum pumping system, 19-medium pressure cylinder, 20-plate heat exchanger, 21-first drain pump, 22-second drain pump, 23-first heat network steam inlet valve, 24-second heat network steam inlet valve. DETAILED DESCRIPTION

[0043] The specific implementation of the embodiments of the application will be described in detail below in combination with the drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the embodiments of the application, and is not used to limit the embodiments of the application.

[0044] In the embodiments of the present application, the orientation words such as "upper", "lower", "left", "right" used without the opposite description generally refer to the orientation or positional relationship shown in the drawings or the orientation or positional relationship commonly used when the product of the present application is used. The terms "first", "second", "third" and the like are only used for differentiation and cannot be understood as indicating or implying relative importance.

[0045] The terms "parallel", "vertical" and the like do not mean that the components must be absolutely parallel or vertical, but can be slightly inclined. For example, "parallel" only means that its direction is more parallel relative to "vertical", and does not mean that the structure must be completely parallel, but can be slightly inclined.

[0046] The terms "horizontal", "vertical", "overhanging" and the like do not mean that the components must be absolutely horizontal, vertical or overhanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0047] In addition, the terms "approximately", "substantially" and the like are intended to indicate that the relevant content is not required to be absolutely accurate, but can have some deviation. For example, "approximately equal" does not only mean absolute equality, because in actual production and operation processes, it is difficult to achieve absolute "equality", and generally there is some deviation. Therefore, in addition to absolute equality, "approximately equal" also includes the above-mentioned case of having some deviation. For example, in other cases, unless otherwise specified, the terms "approximately", "substantially" and the like have similar meanings as described above.

[0048] In the description of the present application, it should also be noted that unless otherwise explicitly specified and limited, the terms "arrangement", "installation", "connection", "connection" should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0049] "Connection" described herein is used to express the electrical power connection or signal connection between two components; "connection" can be the direct connection of two elements, or can be connected through an intermediate medium (such as a wire), or can be indirectly connected through a third element.

[0050] "Signal connection" described herein is used to express the signal connection between two components, such as control signals and feedback signals; "electrical connection" is used to express the electrical power connection between two components; "connection" can be the direct connection between two parts, or can be indirectly connected through a third part.

[0051] Embodiment 1

[0052] Please refer to Figure 1 In a first aspect, the embodiment provides a full-steam exhaust residual heat cascade heating system, which is applied to a 600 MW and above supercritical direct air cooling three-cylinder four-steam exhaust unit. The full-steam exhaust residual heat cascade heating system comprises a plurality of cascade-connected multi-stage heating devices. An input end of the multi-stage heating device is connected to a heat network circulating water return water, and an output end of the multi-stage heating device is connected to a heat network circulating water supply. A heat exchange heat source of the multi-stage heating device comes from steam exhaust of the 600 MW and above supercritical direct air cooling three-cylinder four-steam exhaust unit. The multi-stage heating device exchanges heat between the steam exhaust and the heat network circulating water return water to achieve the purpose of heating the heat network circulating water return water.

[0053] Specifically, according to a heat balance calculation equation, the steam exhaust discharged by the supercritical direct air cooling three-cylinder four-steam exhaust unit is calculated, and the number of stages of the multi-stage heating device is determined according to the calculation result to achieve the purpose of minimizing the heat loss of the steam exhaust island.

[0054] For two 600 MW low-pressure cylinder four-steam exhaust units, when the units are operated at double back pressure through cold end system modification, the number of stages of high back pressure operation can be increased to form a cascade "full-steam exhaust" heating system. The multi-stage heating device receives different steam exhausts from the units respectively, and heats the heat network circulating water return water through the heat source of the steam exhaust to improve the heating capacity and heating economy.

[0055] In the embodiment, the multi-stage heating device comprises:

[0056] A first-stage heating device, a heat exchange heat source of the first-stage heating device comes from conventional back pressure steam exhaust of a conventional back pressure low-pressure cylinder 7 of the supercritical direct air cooling three-cylinder four-steam exhaust unit;

[0057] A second-stage heating device, a heat exchange heat source of the second-stage heating device comes from high back pressure steam exhaust of a high back pressure low-pressure cylinder 8 of the supercritical direct air cooling three-cylinder four-steam exhaust unit;

[0058] A third-stage heating device, a heat exchange heat source of the third-stage heating device comes from high back pressure steam exhaust of the high back pressure low-pressure cylinder 8 of the supercritical direct air cooling three-cylinder four-steam exhaust unit after quality treatment;

[0059] A fourth-stage heating device, a heat exchange heat source of the fourth-stage heating device comes from steam exhaust after work of a small steam turbine 12 of the supercritical direct air cooling three-cylinder four-steam exhaust unit;

[0060] A fifth-stage heating device, a heat exchange heat source of the fifth-stage heating device comes from steam exhaust discharged from a medium-pressure cylinder 19 of the supercritical direct air cooling three-cylinder four-steam exhaust unit after desuperheating and pressure reduction treatment;

[0061] A heat network circulating pump 6 is used to circulate the heated heat network circulating water return water and the heat network circulating water return water after the confluence of the first-stage heating device and the second-stage heating device;

[0062] The first-stage heating device, the second-stage heating device, the heat network circulating pump 6, the third-stage heating device, the fourth-stage heating device and the fifth-stage heating device are connected in series, and are used to confluence and output the heat network circulating water return water heated by the first-stage heating device, the heat network circulating water return water heated by the second-stage heating device, the heat network circulating water return water heated by the third-stage heating device, the heat network circulating water return water heated by the fourth-stage heating device and the heat network circulating water return water heated by the fifth-stage heating device to the heat network circulating water supply.

[0063] Specifically, the heat network circulating water return water is exchanged with the conventional back pressure waste steam in the first-stage heating device to obtain first-stage heat network circulating water return water; the first-stage heat network circulating water return water is input into the second-stage heating device, the second-stage heating device exchanges the first-stage heat network circulating water return water with the first high back pressure waste steam to output second-stage heat network circulating water return water; the second-stage heat network circulating water return water is input into the third-stage heating device, the third-stage heating device exchanges the second-stage heat network circulating water return water with the second high back pressure waste steam after quality improvement treatment to output third-stage heat network circulating water return water; the third-stage heat network circulating water return water is input into the fourth-stage heating device, the fourth-stage heating device exchanges the third-stage heat network circulating water return water with the waste steam after the work of the small steam turbine 12 to output fourth-stage heat network circulating water return water; the fourth-stage heat network circulating water return water is input into the fifth-stage heating device, the fifth-stage heating device exchanges the fourth-stage heat network circulating water return water with the waste steam after temperature reduction and pressure reduction to output fifth-stage heat network circulating water return water.

[0064] The heat network circulating water return water is heated in the fifth-stage heating device, and the heat gradually increases to become fifth-stage heat network circulating water return water to meet the standard of the heat network circulating water supply, the water temperature required by the external network, and become the heat network circulating water supply to supply heat to the user.

[0065] In the embodiment, the first-stage heating device comprises a first-stage heat network heater 1 and a first-stage heat network steam inlet valve 23, the first-stage heat network heater 1 is connected with the conventional back pressure low-pressure cylinder 7 through a first-stage heat network steam inlet pipeline, the first-stage heat network steam inlet pipeline is provided with the first-stage heat network steam inlet valve 23, and the first-stage heat network steam inlet valve 23 is used to control the flow of the conventional back pressure waste steam entering the first-stage heat network heater 1.

[0066] Specifically, the exhaust valve of the conventional back pressure low-pressure cylinder 7 to the air cooling radiator is closed, and the first-stage heat network steam inlet valve 23 is opened, the waste steam of the conventional back pressure low-pressure cylinder 7 enters the first-stage heat network heater 1 from the first-stage heat network steam inlet pipeline to heat the heat network circulating water return water, and the heat network circulating water return water is heated to become first-stage heat network circulating water return water and is output to the second-stage heating device.

[0067] In the embodiment, the secondary heating device comprises a secondary heat network heater 2 and a secondary heat network inlet valve 24, the secondary heat network heater 2 is connected with the high-back-pressure low-pressure cylinder 8 through a secondary heat network inlet pipeline, the secondary heat network inlet pipeline is provided with the secondary heat network inlet valve 24, and the secondary heat network inlet valve 24 is used for controlling the flow of the high-back-pressure exhaust steam entering the secondary heat network heater 2.

[0068] Specifically, the exhaust valve of the high-back-pressure low-pressure cylinder 8 to the air cooling radiator is closed, the secondary heat network inlet valve 24 is opened, the first high-back-pressure exhaust steam of the high-back-pressure low-pressure cylinder 8 enters the secondary heat network heater 2 from the secondary heat network inlet pipeline, is used for heating the primary heat network circulating water return, and the primary heat network circulating water return is heated into the secondary heat network circulating water return and then is output to the tertiary heating device.

[0069] In the embodiment, the tertiary heating device comprises a tertiary heat network heater 3, a steam compressor 9, a first tertiary heat network inlet valve 10 and a second tertiary heat network inlet valve 11.

[0070] The tertiary heat network heater 3 is connected with the high-back-pressure low-pressure cylinder 8 through a tertiary heat network inlet pipeline, the steam compressor 9 is arranged between the high-back-pressure low-pressure cylinder 8 and the tertiary heat network heater 3.

[0071] The steam compressor 9 is used for performing compression upgrading treatment on the high-back-pressure exhaust steam output by the high-back-pressure low-pressure cylinder 8, and the high-back-pressure exhaust steam after the compression upgrading treatment enters the tertiary heat network heater 3 for heat exchange.

[0072] The first tertiary heat network inlet valve 10 is used for controlling the flow of the high-back-pressure exhaust steam entering the steam compressor 9, and the second tertiary heat network inlet valve 11 is used for controlling the flow of the high-back-pressure exhaust steam entering the tertiary heater.

[0073] Specifically, the exhaust valve of the high-back-pressure low-pressure cylinder 8 to the air cooling radiator is closed, the first tertiary heat network inlet valve 10 and the second tertiary heat network inlet valve 11 are opened, the steam compressor 9 performs compression upgrading treatment on the second high-back-pressure exhaust steam of the high-back-pressure low-pressure cylinder 8, the second high-back-pressure exhaust steam after the compression upgrading enters the tertiary heat network heater 3 through the tertiary heat network inlet pipeline, is used for heating the secondary heat network circulating water return, and the secondary heat network circulating water return is heated into the tertiary heat network circulating water return and then is output to the quaternary heating device.

[0074] The full exhaust steam waste heat cascade heat supply system should adopt steam compression upgrading technology, increase the exhaust steam usage, and reduce the cold source loss. A certain proportion of high-grade high-backpressure exhaust steam is extracted for compression upgrading, and is discharged into the heat supply heater to heat the heat supply circulating water. After this method is adopted, under a certain low-pressure cylinder exhaust steam flow, the operation back pressure is reduced, and the unit operation economy is improved. After the operation back pressure is reduced, the minimum cooling flow required by the low-pressure cylinder is reduced, and the base load of the full recovery of high-backpressure operation exhaust steam can be obviously reduced, and the unit peak shaving capacity is also enhanced. Meanwhile, the upgrading of the high-grade exhaust steam can increase the recovery amount of low-grade exhaust steam, and improve the utilization efficiency of the low-grade exhaust steam. The steam compression device can be an electric centrifugal steam compressor 9, which has the advantages of simple system and convenient operation and maintenance.

[0075] The three-stage heating device is an exhaust steam upgrading compression system. The water temperature rise of the main engine exhaust steam can be increased by about 7℃. Based on the input steam heat, the COP value of the exhaust steam upgrading compression system can reach 5-7, which is 2-4 times that of the absorption heat pump and the steam injection heat pump. In the high-backpressure range, the driving power required by the exhaust steam upgrading compression system is only 20-50% of the power increase of a single low-pressure cylinder output. Therefore, when the heating temperature is low, the exhaust steam upgrading system can also achieve good energy-saving effect.

[0076] In the embodiment, the four-stage heating device comprises a four-stage heat supply heater 4, a small steam turbine 12, a first four-stage heat supply inlet valve 13, and a second four-stage heat supply inlet valve 14.

[0077] The four-stage heat supply heater 4 is connected with the intermediate-pressure cylinder 19 of the supercritical direct air-cooled three-cylinder four-exhaust steam unit through a four-stage heat supply inlet pipeline. The small steam turbine 12 is arranged between the intermediate-pressure cylinder 19 and the four-stage heat supply heater 4.

[0078] The small steam turbine 12 receives steam from the intermediate-pressure cylinder 19 and uses the steam of the intermediate-pressure cylinder 19 to do work. The exhaust steam generated after the work is output to the four-stage heat supply heater 4 for heat exchange.

[0079] The first four-stage heat supply inlet valve 13 is used to control the steam flow entering the small steam turbine 12 for work, and the second four-stage heat supply inlet valve 14 is used to control the exhaust steam flow entering the four-stage heat supply heater 4 for heat exchange.

[0080] Specifically, the first four-stage heat supply inlet valve 13 and the second four-stage heat supply inlet valve 14 are opened. The steam discharged from the intermediate-pressure cylinder 19 first enters the small steam turbine 12 to do work. The exhaust steam after the work enters the four-stage heat supply heater 4 through the four-stage heat supply inlet pipeline, and is used to heat the three-stage heat supply circulating water return. After the three-stage heat supply circulating water return is heated to become the four-stage heat supply circulating water return, it is output to the five-stage heating device.

[0081] The full-deaerated steam residual heat cascade heat supply system is provided with a high back pressure small turbine 12 generator unit, steam extraction is taken from the middle pressure cylinder 19 exhaust steam of the turbine, and the exhaust steam is used for heating the heat network circulating water. The capacity of the steam extraction power generation is determined according to the difference between the outlet water temperature of the three-stage heat network heater 3 and the outlet water temperature of the heat network circulating water after the exhaust steam is extracted. The capacity and stage number of the steam extraction small turbine are determined. The small turbine 12 should be designed to have the conditions of wide load operation and good back pressure adaptability, so as to ensure that the heat supply capacity and the power generation capacity are relatively stable when the inlet steam pressure and the back pressure change. Therefore, the inlet steam of the small turbine 12 is preferably selected to be regulated by a nozzle. According to the network regulation policy and the actual situation of most power plants, one small turbine 12 of 20 MW level or two small turbines 12 of 10 MW level in series can be selected for exhaust steam heat supply configuration.

[0082] Through optimization of the flow passage of the small turbine 12, a special small turbine 12 machine with a large inlet steam flow regulation range, a wide inlet steam pressure range, a strong exhaust steam pressure adaptability and a good back pressure adaptability can be realized. The small turbine 12 can be selected to have a two-in-series operation mode of two small turbines 12 of 10 MW level. The four-stage heating device is used for heating. Essentially, it is used for increasing the stage number of the low-pressure cylinder. Within the high back pressure heat supply temperature range of the main machine, the bypass small turbine 12 is put into heat supply, a multi-stage high back pressure system is formed, the bypass small machine is designed to have a large capacity and high efficiency, and better cascade high back pressure effect can be achieved, and the economy of the unit heat supply is improved as a whole.

[0083] Above the high back pressure heat supply range of the main machine, the exhaust steam bypass heat supply small turbine 12 can effectively convert the energy level difference between the high-quality steam extracted from the 600 MW turbine and the low-parameter heat supply into electric power, which is equivalent to increasing the work capacity of the middle pressure cylinder 19. For example, under the same heat supply, the small turbine 12 generates 10 MW of power, and the extraction amount needs to be increased to make up for it. The extraction needs to supplement 36 GJ / h of heat. According to the calculation, 1 GJ of extraction heat supply increases 23.3 kg of standard coal. The power supply coal consumption of the condensing condition of the steam turbine is 324 g / kwh. The small turbine 12 can save 2.4 t / h of standard coal per 10 MW of power generation. If all the extraction heat supply is first used for power generation, the energy-saving effect will be very obvious. If the average power generation output of the small turbine 12 reaches 70 MW, the coal saving amount can reach 36,000 t during the heat supply period.

[0084] In the embodiment, the five-stage heating device includes a desuperheater 15, a five-stage heat network heater 5, a first five-stage heat network inlet valve 16 and a second five-stage heat network inlet valve 17.

[0085] The five-stage heat network heater 5 is connected with the middle pressure cylinder 19 of the supercritical direct air-cooled three-cylinder four-exhaust turbine unit through a five-stage heat network inlet pipeline. The desuperheater 15 is arranged between the middle pressure cylinder 19 and the five-stage heat network heater 5.

[0086] The desuperheater 15 receives steam from the intermediate pressure cylinder 19, and desuperheats and depressurizes the steam from the intermediate pressure cylinder 19, and the desuperheated and depressurized steam enters the fifth heat network heater 5 for heat exchange;

[0087] The first fifth heat network inlet valve 16 is used for controlling the steam flow entering the desuperheater 15, and the second fifth heat network inlet valve 17 is used for controlling the steam flow entering the fifth heat network heater 5 for heat exchange.

[0088] Specifically, the first fifth heat network inlet valve 16 and the second fifth heat network inlet valve 17 are opened, the steam discharged from the intermediate pressure cylinder 19 first enters the desuperheater 15 for desuperheating and depressurizing, and the desuperheated and depressurized steam enters the fifth heat network heater 5 through the fifth heat network inlet pipeline for heating the fourth heat network circulating water return water, and the fourth heat network circulating water return water is heated to become fifth heat network circulating water return water and then output to the heat network circulating water supply.

[0089] The steam discharged from the intermediate pressure cylinder 19 of the steam turbine is directly desuperheated and depressurized and then discharged into the newly added fifth heat network heater 5 to perform peak heating on the heat network circulating water, thereby meeting the heating temperature requirement.

[0090] In the embodiment, the full-steam waste heat cascade heating system further comprises a plate heat exchanger 20, which is used for receiving the first converged drain water from the fourth heating device and the fifth heating device and performing heat exchange between the first converged drain water and the heat network circulating water return water.

[0091] Further, the heat network circulating water is divided into two paths, one path of the heat network circulating water enters the first heat network heater 1 for step-by-step heating to meet the outer network water temperature, and the other path of the heat network circulating water enters the plate heat exchanger 20, and the heat network circulating water is output to the outlet pipeline of the first heat network heater 1 after heat exchange with the first converged drain water in the plate heat exchanger 20.

[0092] In the embodiment, the full-steam waste heat cascade heating system further comprises an auxiliary vacuum pumping system 18, which is arranged on the air cooling radiator vacuum pumping communication pipeline of the supercritical direct air cooling three-cylinder four-steam turbine unit, and is in communication with the multi-stage heating device, and is used for pumping out air of the multi-stage heating device, thereby facilitating the exhaust steam of the unit to enter the first heat network heater 1, the second heat network heater 2, the third heat network heater 3, the fourth heat network heater 4 and the fifth heat network heater 5.

[0093] Valves are added on the connection pipeline of the exhaust pipe of the steam turbine conventional back pressure low pressure cylinder 7 and the high back pressure low pressure cylinder 8 to the air cooling radiator, the valve of the steam turbine conventional back pressure low pressure cylinder 7 and the steam turbine high back pressure low pressure cylinder 8 inlet valve are changed into full sealing small opening adjustable butterfly valves, and the air cooling vacuum pipe and the steam turbine 1# and 2# air cooling radiator vacuum connection pipe are optimized and reconstructed, an auxiliary vacuum system 18 is added, the steam turbine low pressure cylinder micro power operation can be realized, the peak shaving requirement in the heating period is met, and the heating flexibility of the unit is improved.

[0094] The drain flow process of the full-steam exhaust residual heat cascade heating system is as follows:

[0095] The drain flow of the fifth heat network heater 5 flows to the fourth heat network heater 4, the drain flow of the fourth heat network heater 4 and the fifth heat network heater 5 is combined as first combined drain flow, the first combined drain flow is input into the plate heat exchanger 20, is heat-exchanged with the heat network circulating water return water, and is sent to the chemical fine treatment device inlet through the first drain pump 21 and is treated by the chemical fine treatment device.

[0096] The drain flow of the third heat network heater 3 flows to the second heat network heater 2, the drain flow of the third heat network heater 3 and the second heat network heater 2 is combined, flows to the first heat network heater 1, the drain flow of the third heat network heater 3, the second heat network heater 2 and the first heat network heater 1 is combined as second combined drain flow, and the second combined drain flow is sent to the steam turbine 7# low pressure heater outlet through the second drain pump 22.

[0097] In the second aspect, the embodiment provides a 600MW and above grade supercritical direct air cooling three-cylinder four-exhaust steam turbine unit, which comprises a conventional back pressure low pressure cylinder 7, a high back pressure low pressure cylinder 8 and the full-steam exhaust residual heat cascade heating system as described above.

[0098] In the embodiment, the conventional back pressure low pressure cylinder 7 operates at 29kpa, and the high back pressure low pressure cylinder 8 operates at 55kpa.

[0099] In the embodiment, the high back pressure low pressure cylinder 8 is a transformation of the conventional low pressure cylinder of the 600MW and above grade supercritical direct air cooling three-cylinder four-exhaust steam turbine unit. The low pressure cylinder rotor of the unit is optimized and designed, under the premise of not obviously affecting the economy in the non-heating period, the long blade rotor can adapt to the super-high back pressure operation by increasing the blade root strength and optimizing the blade type design, therefore, one of the low pressure cylinder rotors needs to be transformed to adapt to the super-high back pressure operation, so as to increase the high back pressure operation pressure and improve the recovery amount of the steam exhaust, and the low pressure cylinder operating at the super-high back pressure can realize 50-60kPa operation under the condition of the unit 70% load above the pure condensation working condition.

[0100] Compared with the unmodified supercritical direct air-cooled three-cylinder four-exhaust unit, the modified double-cylinder single-high back pressure has lower average operating back pressure, higher economic efficiency, and higher heating and peak regulation capacity.

[0101] In a third aspect, the embodiment provides a full exhaust waste heat cascade heating method, which is implemented by using the full exhaust waste heat cascade heating system as described above, and the method comprises the following steps:

[0102] When the supercritical direct air-cooled three-cylinder four-exhaust unit is in the initial and final stages of heating, the heating network circulating water return is heated by the first and second heating devices to meet the heating demand.

[0103] When the supercritical direct air-cooled three-cylinder four-exhaust unit is in the middle stage of heating, the heating network circulating water return is heated by the first, second, and third heating devices to meet the heating demand.

[0104] When the supercritical direct air-cooled three-cylinder four-exhaust unit is in the extreme cold stage of heating, the heating network circulating water return is heated by the first, second, third, fourth, and fifth heating devices to meet the heating demand.

[0105] When the supercritical direct air-cooled three-cylinder four-exhaust unit is in deep peak regulation operation, the conventional back pressure low-pressure cylinder operates at a micro output, and the second, third, fourth, and fifth heating devices heat the heating network circulating water return to meet the heating demand.

[0106] The full exhaust waste heat cascade heating system can be designed into different heating modes according to the heating capacity and parameters when the low-pressure cylinder of the steam turbine has double back pressure operation conditions. For example, the low-pressure cylinder of the steam turbine is modified to operate at a micro output and has ultra-low back pressure operation conditions, thereby increasing the steam extraction amount for heating the heating network circulating water to meet the heating demand during peak regulation. This modification mode has good operation flexibility and relatively simple system switching.

[0107] Under the heating condition, the two low-pressure cylinders can be switched between single back pressure and double back pressure operation, the corresponding exhaust devices are operated in two groups, the vacuum extraction system is also divided into two systems, the exhaust steam is exchanged with the heating network circulating water, the condensed water enters the corresponding exhaust device, and then enters the condensed water system through the condensed water pump.

[0108] The steam turbine 2nd low-pressure cylinder is reformed into a high-back-pressure low-pressure cylinder 8, and the selection of the last-stage blade is optimized, so that the operation back pressure is further improved, and the recovery amount of exhaust steam is improved, and under the condition of the unit above 70% load in the pure condensation condition, the low-pressure cylinder in the ultra-high back pressure operation can realize the operation of 50-60kPa, and meanwhile, the economic operation in the pure condensation condition can be considered.

[0109] Through the reform of the system in the application to the 600MW supercritical unit, the exhaust steam waste heat of the steam turbine can be maximally utilized to heat the circulating water of the heat network, a cascade heat supply system is formed, the cold end loss is reduced, the unit peak shaving demand is considered, the system in the application is flexible in operation, and the energy-saving effect is remarkable.

[0110] In the full-exhaust steam waste heat cascade heat supply system, each heating device is designed according to the structure type of condensing heat exchange, is equipped with a vacuum pumping system, has the function of recovering negative pressure exhaust steam, and is designed according to a small end difference. The steam entering the heat network heater needs to be desuperheated to ensure that the superheat degree of the inlet steam does not exceed 30-50 degrees, the exhaust steam of the small steam turbine 12 can be directly desuperheated by spraying water, and the exhaust steam of the medium-pressure cylinder 19 passes through a desuperheating and pressure reducing device and then enters the heat network heater for peak heating.

[0111] In the full-exhaust steam waste heat cascade heat supply system, the cascade recovery of the drain heat of each heating device, the design of the system considers the safe operation of the polishing treatment system, the drain of the heat network heater corresponding to the main engine low-pressure cylinder can be directly recovered to the exhaust device, the drain heat of the exhaust steam of the small steam turbine 12 and the peak extraction of the desuperheating and pressure reducing device 15 is recovered after being heat-exchanged with the condensate water by increasing the plate heat exchanger 20, and the cooled drain is returned to the chemical polishing treatment inlet.

[0112] In the full-exhaust steam waste heat cascade heat supply system, within a certain range, the relative flow of the two low-pressure cylinders can be controlled through the opening adjustment of the heat supply butterfly valve newly installed at the inlet of the two low-pressure cylinders, and the proportion of the total inlet steam and extraction amount of the low-pressure cylinder can be distributed through the overall control of the intermediate discharge pressure. Generally, the exhaust steam pressure of the medium-pressure cylinder 19 should be changed within the range of 20% of the exhaust steam flow corresponding to the exhaust steam flow of the medium-pressure cylinder 19.

[0113] The full-exhaust steam waste heat cascade heat supply system in the application can meet the heat supply demand of 12000t / h circulating water of the heat network with a temperature rise of 65 DEG C through 5-stage heating under the design circulating water amount and the maximum heat supply amount, and the water supply temperature can reach 105 DEG C and the heat supply amount is 907MW considering the return water temperature of 40 DEG C, and the heat supply index is 45w / m2, so that 2000 million m2 heat supply area can be met.

[0114] Through the optimization of the cold end system of a 600 MW supercritical direct air-cooling double low-pressure cylinder unit, double back pressure operation of the low-pressure cylinder can be realized, the flexibility of step high back pressure operation is improved, and the exhaust steam recovery capacity can be significantly increased. Compared with double cylinder single back pressure operation, the energy saving effect of double cylinder double back pressure operation is very obvious. For example, under the condition of the same main steam flow, compared with double cylinder single back pressure operation of 34 kPa, the unit output of double back pressure operation (17 kPa and 34 kPa respectively) can be increased by 14.5 MW.

[0115] Compared with the traditional extraction heating system, the actual heating coal consumption of the full exhaust heating system is significantly reduced. The average heating coal consumption during the heating period is 23.3 kg / GJ. If the heating network circulating water return water temperature is averaged at 42°C, compared with pure extraction heating, the double cylinder single back pressure operation + conventional extraction heating can save coal by 35%, the double cylinder double back pressure operation + conventional extraction heating can save coal by 45%, and on this basis, the exhaust steam upgrading + small steam turbine 12 power generation exhaust heating + conventional extraction heating can save coal by 55% compared with pure extraction heating, and the average heating coal consumption during the heating period is 9 kg / GJ. Based on a single 600 MW three-cylinder four-exhaust unit, the annual heating capacity is 60 million GJ, and compared with the conventional double-machine series high back pressure system, the system can save 35,000 tons of standard coal.

[0116] The above describes the optional implementation of the embodiments of the application in detail in combination with the drawings, but the embodiments of the application are not limited to the specific details in the above implementation, and various simple modifications can be made to the technical solutions of the embodiments of the application within the technical concept of the embodiments of the application, and these simple modifications all belong to the protection scope of the embodiments of the application.

[0117] In addition, it should be noted that various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations are not described again in the embodiments of the application.

[0118] Those skilled in the art can understand that all or part of the steps of the above-mentioned embodiment methods can be completed by programs instructing related hardware, the programs are stored in a storage medium, and the storage medium includes a plurality of instructions for making a single-chip microcomputer, a chip or a processor execute all or part of the steps of the method described in various embodiments of the application. The foregoing storage medium includes a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk and various program code storage media.

[0119] Besides, the various different embodiments of the embodiments of the present application can also be combined arbitrarily, as long as the idea of the embodiments of the present application is not violated, which should be considered as the disclosed content of the embodiments of the present application.

Claims

1. A full-deaeration waste heat cascade heat supply system, applied to a 600 MW and above grade supercritical direct air cooling three-cylinder four-exhaust unit, characterized in that, The full-deaerated steam waste heat cascade heat supply system comprises a plurality of cascade-connected multi-stage heating devices, the input end of the multi-stage heating device is connected with the heat network circulating water return water, the output end of the multi-stage heating device is connected with the heat network circulating water supply, the heat exchange heat source of the multi-stage heating device comes from the deaerated steam of a 600 MW and above supercritical direct air cooling three-cylinder four-exhaust unit, the multi-stage heating device exchanges heat between the deaerated steam and the heat network circulating water return water to heat the heat network circulating water return water. The multi-stage heating device comprises: a first-stage heating device, the heat exchange heat source of the first-stage heating device comes from the conventional back pressure deaerated steam of the conventional back pressure low-pressure cylinder (7) of the supercritical direct air cooling three-cylinder four-exhaust unit; a second-stage heating device, the heat exchange heat source of the second-stage heating device comes from the high back pressure deaerated steam of the high back pressure low-pressure cylinder (8) of the supercritical direct air cooling three-cylinder four-exhaust unit; a third-stage heating device, the heat exchange heat source of the third-stage heating device comes from the high back pressure deaerated steam of the high back pressure low-pressure cylinder (8) of the supercritical direct air cooling three-cylinder four-exhaust unit after quality improvement treatment; a fourth-stage heating device, the heat exchange heat source of the fourth-stage heating device comes from the deaerated steam after work of the small steam turbine (12) of the supercritical direct air cooling three-cylinder four-exhaust unit; a fifth-stage heating device, the heat exchange heat source of the fifth-stage heating device comes from the deaerated steam of the medium-pressure cylinder (19) of the supercritical direct air cooling three-cylinder four-exhaust unit after temperature and pressure reduction treatment; a heat network circulating pump (6) arranged between the second-stage heating device and the third-stage heating device; the first-stage heating device, the second-stage heating device, the heat network circulating pump (6), the third-stage heating device, the fourth-stage heating device and the fifth-stage heating device are connected in series, and the heat network circulating water return water heated by the first-stage heating device, the heat network circulating water return water heated by the second-stage heating device, the heat network circulating water return water heated by the third-stage heating device, the heat network circulating water return water heated by the fourth-stage heating device and the heat network circulating water return water heated by the fifth-stage heating device are converged and output to the heat network circulating water supply; the system further comprises a plate heat exchanger (20) for receiving the first converged condensate from the fourth-stage heating device and the fifth-stage heating device and exchanging heat between the first converged condensate and the heat network circulating water return water.

2. The total-steam-deprivation cascade heat-providing system according to claim 1, wherein The first-stage heating device comprises a first-stage heat network heater (1) and a first-stage heat network steam inlet valve (23), the first-stage heat network heater (1) is connected with the conventional back pressure low-pressure cylinder (7) through a first-stage heat network steam inlet pipeline, the first-stage heat network steam inlet pipeline is provided with the first-stage heat network steam inlet valve (23), and the first-stage heat network steam inlet valve (23) is used to control the flow of the conventional back pressure deaerated steam entering the first-stage heat network heater (1).

3. The total-steam-deprivation cascade heat-recovery step heat-provision system of claim 1, wherein, The second-stage heating device comprises a second-stage heat network heater (2) and a second-stage heat network steam inlet valve (24), the second-stage heat network heater (2) is connected with the high back pressure low-pressure cylinder (8) through a second-stage heat network steam inlet pipeline, the second-stage heat network steam inlet pipeline is provided with the second-stage heat network steam inlet valve (24), and the second-stage heat network steam inlet valve (24) is used to control the flow of the high back pressure deaerated steam entering the second-stage heat network heater (2).

4. The total-steam- starve cascade heat-providing system according to claim 1, wherein, The third heating device comprises a third heat network heater (3), a steam compressor (9), a first third heat network steam inlet valve (10) and a second third heat network steam inlet valve (11); The third heat network heater (3) is connected with the high-back-pressure low-pressure cylinder (8) through a third heat network steam inlet pipeline, and the steam compressor (9) is arranged between the high-back-pressure low-pressure cylinder (8) and the third heat network heater (3); The steam compressor (9) performs compression upgrading treatment on the high-back-pressure exhaust steam output by the high-back-pressure low-pressure cylinder (8), and the high-back-pressure exhaust steam after the compression upgrading treatment enters the third heat network heater (3) for heat exchange; The first third heat network steam inlet valve (10) is used for controlling the flow of the high-back-pressure exhaust steam entering the steam compressor (9), and the second third heat network steam inlet valve (11) is used for controlling the flow of the high-back-pressure exhaust steam entering the third heat network heater.

5. The total-steam- starve cascade heat-providing system according to claim 1, wherein, The fourth heating device comprises a fourth heat network heater (4), a small steam turbine (12), a first fourth heat network steam inlet valve (13) and a second fourth heat network steam inlet valve (14); The fourth heat network heater (4) is connected with the intermediate-pressure cylinder (19) of the supercritical direct air cooling three-cylinder four-exhaust steam unit through a fourth heat network steam inlet pipeline, and the small steam turbine (12) is arranged between the intermediate-pressure cylinder (19) and the fourth heat network heater (4); The small steam turbine (12) receives steam from the intermediate-pressure cylinder (19) and uses the steam of the intermediate-pressure cylinder (19) to do work, and the exhaust steam generated after the work is output to the fourth heat network heater (4) for heat exchange; The first fourth heat network steam inlet valve (13) is used for controlling the steam flow entering the small steam turbine (12) for work, and the second fourth heat network steam inlet valve (14) is used for controlling the exhaust steam flow entering the fourth heat network heater (4) for heat exchange.

6. The total-steam- starve cascade heat-providing system according to claim 1, wherein, The fifth heating device comprises a desuperheater (15), a fifth heat network heater (5), a first fifth heat network steam inlet valve (16) and a second fifth heat network steam inlet valve (17); The fifth heat network heater (5) is connected with the intermediate-pressure cylinder (19) of the supercritical direct air cooling three-cylinder four-exhaust steam unit through a fifth heat network steam inlet pipeline, and the desuperheater (15) is arranged between the intermediate-pressure cylinder (19) and the fifth heat network heater (5); The desuperheater (15) receives steam from the intermediate-pressure cylinder (19) and performs desuperheating and pressure reducing treatment on the steam of the intermediate-pressure cylinder (19), and the steam after the desuperheating and pressure reducing treatment enters the fifth heat network heater (5) for heat exchange; The first fifth heat network steam inlet valve (16) is used for controlling the steam flow entering the desuperheater (15), and the second fifth heat network steam inlet valve (17) is used for controlling the steam flow entering the fifth heat network heater (5) for heat exchange.

7. The total-steam- starve cascade heat-providing system according to claim 1, wherein, The full-exhaust-steam waste heat cascade heat supply system further comprises an auxiliary vacuum pumping system (18), the auxiliary vacuum pumping system (18) is arranged on an air cooling radiator vacuum pumping communication pipeline of the supercritical direct air cooling three-cylinder four-exhaust steam unit, the auxiliary vacuum pumping system (18) is in communication with the multi-stage heating device, and is used for pumping out air of the multi-stage heating device.

8. A 600 MW and above class supercritical direct air-cooling triple-cylinder four-exhaust unit characterized by, The system comprises a conventional back pressure low-pressure cylinder (7), a high back pressure low-pressure cylinder (8), and the full-deaerated-steam waste heat cascade heating system according to any one of claims 1-7.

9. A method of full-steam-depletion cascade heat supply, characterized by The method is implemented by using the full-deaerated-steam waste heat cascade heating system according to any one of claims 1-7, and the method comprises: When the supercritical direct air cooling three-cylinder four-exhaust steam unit is in the initial and final stages of heating, the heating network circulating water return water is heated by the first and second heating devices to meet the heating demand; When the supercritical direct air cooling three-cylinder four-exhaust steam unit is in the middle stage of heating, the heating network circulating water return water is heated by the first, second and third heating devices to meet the heating demand; When the supercritical direct air cooling three-cylinder four-exhaust steam unit is in the extreme cold stage of heating, the heating network circulating water return water is heated by the first, second, third, fourth and fifth heating devices to meet the heating demand; When the supercritical direct air cooling three-cylinder four-exhaust steam unit is in the deep peak regulation operation, the conventional back pressure low-pressure cylinder (7) is operated at a small power, and the second, third, fourth and fifth heating devices heat the heating network circulating water return water to meet the heating demand.

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