Thermodynamic system of deep backpressure small-sized combined heat and power generation unit

Abstract

The utility model discloses a thermodynamic system of a deep backpressure small-sized combined heat and power generation unit. The thermodynamic system comprises a steam turbine; the boiler is connected with the steam turbine and used for supplying steam to the steam turbine; the generator is connected with the turbine and used for converting energy and outputting electric energy; the water supply pipeline is communicated with the chemical water supply source and the boiler, and a steam seal heater, a low-pressure water supplementing heater, a low-pressure heater, a high-pressure deaerator, a first-stage high-pressure heater and a second-stage high-pressure heater are connected to the water supply pipeline; the steam extraction pipeline is a first-stage steam extraction pipeline which is connected with the medium-pressure heat supply end and is used for realizing medium-pressure heat supply; the second-stage steam extraction pipeline is communicated with the second-stage high-pressure heater; and the third-stage steam extraction pipeline is communicated with the first-stage high-pressure heater and / or the low-pressure heat supply end. The back pressure exhaust steam of the combined heat and power generation unit is reduced to be close to the atmospheric pressure value, the output of the steam turbine and the power generation efficiency of the unit are improved, and the goals of reducing coal consumption and saving energy in the whole plant are achieved.

Description

Technical Field

[0001] The utility model relates to the field of deep back pressure units, in particular to a thermal system of a deep back pressure small-scale cogeneration unit. Background Art

[0002] At present, in cogeneration projects, back-pressure cogeneration units are mostly preferred. Compared with conventional extraction condensing steam turbine units of the same scale, extraction back-pressure steam turbine units have lower engineering costs, and under the conditions of meeting the heat load and power load, the steam intake of the extraction back-pressure steam turbine is less, and the scale of the boiler matched with it is small, thereby reducing the total investment of the thermal power plant.

[0003] Cogeneration units are generally small in scale, and their main function when in use is to ensure heat supply. While ensuring that the heat supply meets the requirements, a certain amount of electricity is generated at the same time to achieve the effect of cogeneration.

[0004] In existing small back-pressure cogeneration units, the back-pressure exhaust steam of the steam turbine is mostly consumed for heating. Since the heating parameters are mostly 0.8-1.2MPa, the back-pressure exhaust steam pressure of the steam turbine is relatively high and the power generation capacity is poor.

[0005] The exhaust pressure of steam turbine is also called back pressure, which refers to the absolute pressure behind the last stage blades of steam turbine. The selection of steam turbine design back pressure is directly related to the economy and rationality of the whole generator set. Steam turbine back pressure is an important factor affecting the power generation efficiency and coal consumption rate of the unit. Reducing steam turbine back pressure can improve steam turbine output and unit power generation efficiency, thereby reducing power generation coal consumption. In other words, steam turbine operating back pressure is an important adjustment parameter for energy saving and coal consumption reduction in the whole plant.

[0006] When the turbine exhaust back pressure is high, the total power generation capacity of the turbine is also reduced. Summary of the invention

[0007] In order to solve the above technical problems, the utility model proposes a deep back pressure small cogeneration unit thermal system, which can be used to solve the above technical problems.

[0008] In order to achieve the above-mentioned utility model purpose, the utility model adopts the following technical solutions:

[0009] A deep back pressure small cogeneration unit thermal system, comprising:

[0010] Steam turbine;

[0011] A boiler connected to the steam turbine for supplying steam to the steam turbine;

[0012] A generator, connected to the steam turbine, is used for energy conversion and outputting electrical energy;

[0013] A water supply pipeline connects the chemical water supply source and the boiler, and is connected with a steam seal heater, a low-pressure chemical water supply heater, a low-pressure heater, a high-pressure deaerator, a first-stage high-pressure heater, and a second-stage high-pressure heater;

[0014] The steam extraction pipelines are arranged in sequence along the turbine cylinder toward the generator:

[0015] The first-stage steam extraction pipeline is connected to the medium-pressure heating end to realize medium-pressure heating;

[0016] The second stage steam extraction pipeline is connected to the second stage high pressure heater;

[0017] The third stage steam extraction pipeline is connected to the first stage high pressure heater and / or the low pressure heating end;

[0018] The fourth stage steam extraction pipeline is connected to the high pressure deaerator;

[0019] The fifth stage steam extraction pipeline is connected to the low pressure heater;

[0020] The exhaust steam pipeline, whose exhaust steam pressure is close to atmospheric pressure, is connected to the low-pressure feed water heater.

[0021] In some embodiments of the present application, it further includes: a drain tank and a drain pump;

[0022] wherein a first drain circuit is formed between the second-stage high-pressure heater, the first-stage high-pressure heater and the high-pressure deaerator;

[0023] A second drain circuit is connected between the low-pressure heater and the low-pressure feed water heater;

[0024] A drain circulation loop is formed between the low-pressure feed water heater, the steam seal heater, the drain water tank and the drain pump.

[0025] In some embodiments of the present application, the first hydrophobic circuit includes:

[0026] A first branch drain path is connected between the second stage high pressure heater and the first stage high pressure heater, and a second branch drain path is connected between the first stage high pressure heater and the high pressure deaerator.

[0027] In some embodiments of the present application, the hydrophobic circulation loop includes:

[0028] There are two drain discharge pipelines, one of which is connected to the low-pressure feed water heater and the drain tank, and the other is connected between the steam seal heater and the drain tank;

[0029] The drain return pipeline has one end connected to the drain tank and the other end connected to the inlet of the low-pressure feed water heater. The drain pump is arranged on the drain return pipeline.

[0030] In some embodiments of the present application, a feed water pump is provided between the high pressure deaerator and the first stage high pressure heater, and two feed water pumps are provided, arranged in parallel, one for use and one for backup. Between the first stage high pressure heater and the high pressure deaerator.

[0031] In some embodiments of the present application, a desalted water booster pump is provided between the chemical water supply source and the steam seal heater, and two desalted water booster pumps are provided and arranged in parallel, one for use and one for backup.

[0032] In some embodiments of the present application, the third-stage steam extraction pipeline is connected to the fourth-stage steam extraction pipeline to ensure the steam source required by the high-pressure deaerator when the unit load is low.

[0033] In some embodiments of the present application, the exhaust pressure of the exhaust pipeline is 0.15 MPa.

[0034] In some embodiments of the present application, the boiler and the steam turbine are connected via a main steam header.

[0035] In some embodiments of the present application, a first output pipeline is arranged on the main steam main pipe for standby medium-pressure heating, and a medium-pressure temperature and pressure reducer is arranged on the first output pipeline;

[0036] And a second output pipeline is used for backup low-pressure heating, and a low-pressure temperature and pressure reducer is arranged on the second output pipeline.

[0037] Compared with the prior art, the advantages and positive effects of the utility model are:

[0038] In the deep back pressure small cogeneration unit thermal system proposed in this embodiment, the steam turbine adopts a deep back pressure steam turbine structure, and the steam extraction pipeline of the steam turbine is set to six steam extraction pipelines, among which the steam extracted from the first stage steam extraction pipeline and the third stage steam extraction pipeline close to the front side of the steam turbine is used for medium pressure heating and low pressure heating to ensure the heating capacity of the entire cogeneration system;

[0039] The exhaust pipe on the rear side of the steam turbine is used to achieve back-pressure exhaust with lower back pressure. The pressure value of the back-pressure exhaust is close to atmospheric pressure, which is greatly reduced compared with the existing exhaust back pressure value. The reduced exhaust back pressure ensures that the steam entering the steam turbine is used for power generation as much as possible while ensuring heat supply, thereby increasing the overall power generation of the unit;

[0040] In order to realize the utilization of ultra-low pressure back-pressure exhaust steam and the adaptation to the low-pressure exhaust steam back pressure, the system of the utility model correspondingly arranges a low-pressure chemical feed water heater, which is connected to the exhaust steam pipeline, so that the back-pressure exhaust steam of the exhaust steam pipeline can enter the chemical feed water heater and exchange heat with the desalted water transported from the chemical water supply source to the boiler.

[0041] On the one hand, the desalted water can be heated by exchanging heat with the back pressure exhaust steam and the desalted water, thereby increasing the temperature of the desalted water, so that the desalted water can reach the optimal temperature required when entering the boiler through multi-stage heating, thereby improving the boiler efficiency;

[0042] On the other hand, by exchanging heat with desalted water, its heat can be fully utilized. After being absorbed by the desalted water, the heat re-enters the entire system, ensuring that the exhaust steam is not discharged, recovering the exhaust steam waste heat as much as possible, and reducing the cold end loss.

[0043] After reading the specific embodiments of the present invention in conjunction with the accompanying drawings, other features and advantages of the present invention will become more clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, a brief introduction will be given below to the drawings required for use in the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0045] Figure 1 This is a system schematic diagram of the thermal system of a deep back pressure small cogeneration unit in an embodiment of the utility model.

[0046] Among them, 100, steam turbine; 110, first stage steam extraction pipeline; 120, second stage steam extraction pipeline; 130, third stage steam extraction pipeline; 140, fourth stage steam extraction pipeline; 150, fifth stage steam extraction pipeline; 160, exhaust pipeline; 200, boiler; 300, generator; 410, steam seal heater; 420, low pressure feed water heater; 430, low pressure heater; 440, high pressure deaerator; 450, first stage high pressure heater; 460, second stage high pressure heater; 510 , drain tank; 520, drain pump; 610, first drain circuit; 611, first branch drain path; 612, second branch drain path; 620, second drain circuit; 630, drain circulation loop; 631, drain discharge pipeline; 632, drain return pipeline; 700, feed water pump; 800, desalted water booster pump; 910, main steam main pipe; 920, first output pipeline; 930, medium-pressure temperature and pressure reducer; 940, second output pipeline; 950, low-pressure temperature and pressure reducer. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0048] It should be noted that in the description of the present invention, the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings, which are only for the convenience of description, and do not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0049] The utility model provides an embodiment of a thermal system of a deep back pressure small cogeneration unit, including:

[0050] The steam turbine 100 is a deep back-pressure steam turbine 100 structure.

[0051] The boiler 200 is connected to the steam turbine 100 and is used to supply steam to the steam turbine 100;

[0052] Specifically, the main steam generated by the boiler 200 side is led from the boiler 200 superheater outlet header to the main steam header 910, and the header is connected to the main steam valve inlet of the steam turbine 100, leading the main steam to the steam turbine 100, and the steam performs work in the steam turbine 100. The steam generated by the boiler 200 becomes exhaust steam after performing work in the steam turbine 100.

[0053] The steam turbine 100 is provided with multiple stages of steam extraction pipelines and steam exhaust pipelines.

[0054] The generator 300 is connected to the steam turbine 100 and is used for energy conversion to output electrical energy.

[0055] A water supply pipeline connects the chemical water supply source and the boiler 200, and is connected to a steam seal heater 410, a low-pressure chemical water supply heater 420, a low-pressure heater 430, a high-pressure deaerator 440, a first-stage high-pressure heater 450, and a second-stage high-pressure heater 460;

[0056] The steam extraction pipelines are arranged in sequence along the turbine cylinder toward the generator:

[0057] The first stage steam extraction pipeline 110 is connected to the medium pressure heating end to realize medium pressure heating;

[0058] The second stage steam extraction pipeline 120 is connected to the second stage high pressure heater 460;

[0059] The third stage steam extraction pipeline 130 is connected to the first stage high pressure heater 450 and the low pressure heating end;

[0060] The fourth stage steam extraction pipeline 140 is connected to the high pressure deaerator 440;

[0061] The fifth stage steam extraction pipeline 150 is connected to the low pressure heater 430;

[0062] The exhaust steam pipeline 160 , whose exhaust steam pressure is close to atmospheric pressure, is connected to the low-pressure make-up water heater 420 .

[0063] The exhaust steam from the exhaust steam line 160 is back pressure exhaust steam.

[0064] In the deep back pressure small cogeneration unit thermal system proposed in this embodiment, the steam turbine 100 adopts a deep back pressure steam turbine 100 structure. At the same time, the steam extraction pipeline of the steam turbine 100 is set to six steam extraction pipelines, among which the steam extracted from the first stage steam extraction pipeline 110 and the third stage steam extraction pipeline 130 close to the front side of the steam turbine 100 is used for medium pressure heating and low pressure heating to ensure the heating capacity of the entire cogeneration system;

[0065] The exhaust pipe 160 on the rear side of the steam turbine 100 is used to achieve back-pressure exhaust with relatively low back pressure. The pressure value of the back-pressure exhaust is close to atmospheric pressure, which is greatly lower than the exhaust back pressure value of the existing mainstream units. The reduced exhaust back pressure improves the turbine output and the unit's power generation efficiency, thereby reducing coal consumption for power generation.

[0066] From the correlation between the thermal system of the steam turbine 100 and the cold end parameters, it can be seen that improving the initial parameters of steam and reducing the cold end parameters (back pressure) of the steam turbine 100 are the main ways to improve the thermal efficiency of the unit. When the initial parameters of the steam turbine 100 are constant, reducing the cold end parameters (back pressure) of the steam turbine 100 can increase the ideal enthalpy drop of the steam of the steam turbine 100, reduce the loss of the cold source, and improve the thermal efficiency of the cycle. After the back pressure of the steam turbine 100 is reduced, the exhaust parameters are reduced, and the overall power generation capacity of the steam turbine 100 is improved.

[0067] In this embodiment, the back pressure exhaust of the exhaust pipe 160 of the cogeneration system is reduced to a value close to the atmospheric pressure, thereby improving the output of the steam turbine 100 and the power generation efficiency of the unit, and achieving the goal of reducing coal consumption and saving energy in the entire plant.

[0068] The deep back-pressure small cogeneration unit thermal system in this embodiment, while ensuring that the main heating function of the entire unit meets the requirements, also achieves continuous power generation of the generator 300 by reducing the exhaust steam back pressure, thereby improving the power generation efficiency.

[0069] The steam turbine 100 of this embodiment is a deep back-pressure steam turbine 100. Since the pressure value of its back-pressure exhaust steam is only slightly higher than the atmospheric pressure value, the pressure is very low. When in use, it cannot enter some conventional medium-pressure heaters and high-pressure heaters for utilization, nor can it be used to provide heating to users. If this part of the steam is discharged, it will cause the exhaust steam to be lost, resulting in waste.

[0070] In order to realize the utilization of ultra-low pressure back-pressure exhaust steam and the adaptation to the low-pressure exhaust steam back pressure, the system of this embodiment is correspondingly provided with a low-pressure make-up water heater 420, which is connected to the exhaust steam pipeline 160, so that the back-pressure exhaust steam of the exhaust steam pipeline 160 can enter the low-pressure make-up water heater 420 and exchange heat with the desalted water transported from the desalted water supply source to the boiler 200.

[0071] On the one hand, the desalted water can be heated by exchanging heat with the back pressure exhaust steam and the desalted water, thereby increasing the temperature of the desalted water, so that the desalted water can reach the optimal temperature required for entering the boiler 200 through multi-stage heating, thereby improving the efficiency of the boiler 200;

[0072] On the other hand, the heat of the back-pressure exhaust steam can be fully utilized by exchanging heat with desalted water. After being absorbed by the desalted water, the heat re-enters the entire thermal system, ensuring that the exhaust steam is not discharged, recovering the exhaust steam waste heat as much as possible, and reducing the cold end loss.

[0073] In some embodiments, the steam in the first-stage extraction pipeline 110 of the steam turbine 100 is first-stage extraction steam (4.5 MPa, a), which is a medium-pressure heating steam source and is connected to the medium-pressure heating end to provide medium-pressure heating.

[0074] The second stage steam extraction pipeline 120 is a second stage steam extraction, which provides steam for the second stage high pressure heater 460 as the last stage heating of high pressure feed water;

[0075] The third-stage extraction steam pipeline 130 is a third-stage extraction steam, which is introduced into the first-stage high-pressure heater 450 as the first-stage heating of high-pressure feed water, wherein the third-stage extraction steam (1.7MPa, a) is also used as a low-pressure heating steam source, connected to the low-pressure heating end, for realizing low-pressure heating;

[0076] The third-stage steam extraction pipeline 130 is connected to the fourth-stage steam extraction pipeline 140. The third-stage steam extraction is also connected to the fourth-stage steam extraction pipeline 140 through a pipeline from the third-stage steam extraction pipeline 130 to supply steam to the high-pressure deaerator 440, which serves as an auxiliary steam source during the entire low-load condition, that is, a backup auxiliary steam source.

[0077] The fourth stage steam extraction pipeline 140 is a fourth stage steam extraction pipeline, which provides steam for the high pressure deaerator 440 to achieve heating and deoxygenation of the desalted water;

[0078] The fifth stage steam extraction pipeline 150 is a fifth stage steam extraction pipeline, which provides steam for the low pressure heater 430 to heat the desalted water;

[0079] The exhaust steam pipeline 160 corresponds to the back pressure exhaust steam (0.15MPa, a) leading to the low pressure make-up water heater for continuous heating of desalted water, ensuring that the deep back pressure exhaust steam does not overflow (i.e., discharge externally), and making full use of the exhaust steam waste heat to reduce the cold end loss;

[0080] The steam leakage from the steam turbine 100 is connected to the steam seal heater 410 as a preliminary heating source for the desalted water.

[0081] The steam leakage from the steam turbine 100 can be collected through a plurality of pipelines and connected to the steam seal heater 410 for heat exchange with the desalted water.

[0082] The desalted water drawn from the chemical water supply source first enters the steam seal heater 410 for heat exchange and is initially heated, then enters the low-pressure chemical feed water heater 420 to be heated by the back-pressure exhaust steam, then enters the low-pressure heater 430 for continuous heating, and then enters the high-pressure deaerator 440 for heating and deoxygenation. After being discharged from the high-pressure deaerator 440, it enters the first-stage high-pressure heater 450 for heating, and then enters the second-stage high-pressure heater 460 for heating. Finally, after reaching the optimal temperature for entering the boiler 200, it enters the economizer inlet of the boiler 200. Finally, the high-pressure feed water generates main steam in the boiler 200 for use by the steam turbine 100.

[0083] The desalted water flowing out from the chemical water supply source is heated by multiple heaters before entering the boiler 200. The heating heat source comes from the multi-stage extraction and exhaust steam of the steam turbine 100. While heating the desalted water, the exhaust steam heat is also recovered and utilized, thus avoiding heat loss in the system.

[0084] In some embodiments of the present application, a desalted water booster pump 800 is provided between the chemical water supply source and the steam seal heater 410 , and two desalted water booster pumps 800 are provided and arranged in parallel, one for use and one for backup.

[0085] The deionized water booster pump 800 can pump the deionized water in the chemical water supply source into the steam seal heater 410 and then into the high-pressure deaerator 440 .

[0086] Two desalted water booster pumps 800 are provided, one of which is used as a backup.

[0087] In some embodiments of the present application,

[0088] A feed water pump 700 is provided between the high pressure deaerator 440 and the first stage high pressure heater 450. Two feed water pumps 700 are provided between the first stage high pressure heater 450 and the high pressure deaerator 440. The two feed water pumps are arranged in parallel, one for use and one for backup.

[0089] The feed water pump 700 is mainly used to pump water in the high-pressure deaerator 440 into the first-stage high-pressure heater 450 and then to the economizer inlet of the boiler 200. Two feed water pumps are provided, and one is used as a backup.

[0090] In some embodiments of the present application, the small-scale deep back pressure cogeneration system further includes: a drain tank 510 and a drain pump 520;

[0091] A first drain circuit 610 is formed between the first-stage high-pressure heater 450 , the second-stage high-pressure heater 460 and the high-pressure deaerator 440 ;

[0092] In some embodiments of the present application, the first hydrophobic circuit 610 includes:

[0093] A first branch drain path 611 is connected between the second stage high pressure heater 460 and the first stage high pressure heater 450 , and a second branch drain path 612 is connected between the first stage high pressure heater 450 and the high pressure deaerator 440 .

[0094] In the second-stage high-pressure heater 460, the second-stage extraction steam from the second-stage extraction pipeline 120 of the steam turbine 100 is condensed into drain, and enters the first-stage high-pressure heater 450 through the first branch drain path 611 in a step-by-step reflux manner. In the first-stage high-pressure heater 450, the third-stage extraction steam from the third-stage extraction pipeline 130 of the steam turbine 100 is condensed into drain, and enters the high-pressure deaerator 440 through the second branch drain path 612 in a step-by-step reflux manner.

[0095] A drain circulation loop 630 is formed between the low-pressure make-up water heater 420 , the steam seal heater 410 , the drain water tank 510 , and the drain pump 520 .

[0096] A second drain circuit 620 is connected between the low-pressure heater 430 and the low-pressure make-up water heater 420;

[0097] In some embodiments of the present application, the hydrophobic circulation loop 630 includes:

[0098] There are two drain discharge pipes 631, one of which is connected to the low-pressure feed water heater 420 and the drain tank 510, and the other is connected between the steam seal heater 410 and the drain tank 510;

[0099] The drain return pipeline 632 has one end connected to the drain tank 510 and the other end connected to the outlet of the low-pressure make-up water heater 420 . The drain pump 520 is arranged on the drain return pipeline 632 .

[0100] Specifically, in the low-pressure heater 430 , the fifth-stage extraction steam from the fifth-stage extraction pipeline 150 of the steam turbine 100 is condensed into drain water, and enters the low-pressure feed water heater 420 through the second drain water circuit 620 in a step-by-step reflux manner.

[0101] The drain condensed from the back pressure exhaust steam from the exhaust pipe 160 of the steam turbine 100 in the low-pressure feed water heater 420 and the drain condensed from the steam leakage of the steam turbine in the steam seal heater 410 are introduced into the drain tank 510 through their corresponding drain discharge pipes 631, and then the drain pump 520 boosts the pressure of the drain in the drain tank 510 and pumps it into the feed water circulation behind the outlet of the low-pressure feed water heater 420, and the exhaust steam is pumped back to the water side of the thermal system in the form of drain, thereby reducing the exhaust steam working medium loss of the steam turbine 100.

[0102] In some embodiments of the present application, the exhaust pressure of the exhaust pipe 160 is 0.15 MPa.

[0103] In some embodiments of the present application, the boiler 200 and the steam turbine 100 are connected via a main steam header 910 .

[0104] In some embodiments of the present application, a first output pipeline 920 is provided on the main steam main pipe 910 for backup medium-pressure heating, and a medium-pressure temperature and pressure reducer 930 is provided on the first output pipeline 920 .

[0105] And the second output pipeline 940 is used for backup low-pressure heating, and a low-pressure temperature and pressure reducer 950 is arranged on the second output pipeline 940.

[0106] The first-stage extraction steam from the first-stage extraction pipeline 110 of the steam turbine 100 is used as a medium-pressure heating steam source; the third-stage extraction steam from the third-stage extraction pipeline 130 of the steam turbine 100 is used as a low-pressure heating steam source.

[0107] Under the condition of low load or shutdown for maintenance of the steam turbine 100, the main steam can be desuperheated and depressurized to ensure heat supply. One route is led out from the main steam main pipe 910 and connected to the medium-pressure desuperheater 930, and then sent to the heat user after desuperheating and depressurizing to the required heat supply parameters (temperature and pressure); another route is led out from the main steam main pipe 910 and connected to the low-pressure desuperheater 950, and then sent to the heat user after desuperheating and depressurizing to the required heat supply parameters.

[0108] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the above embodiments, or to replace some of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions claimed to be protected by the present invention.

Claims

1. A deep back pressure small cogeneration unit thermal system, characterized in that: Included are: Steam turbine; A boiler connected to the steam turbine for supplying steam to the steam turbine; A generator, connected to the steam turbine, is used for energy conversion and outputting electrical energy; A water supply pipeline connects the chemical water supply source and the boiler, and is connected with a steam seal heater, a low-pressure chemical water supply heater, a low-pressure heater, a high-pressure deaerator, a first-stage high-pressure heater, and a second-stage high-pressure heater; The steam extraction pipelines are arranged in sequence along the turbine cylinder toward the generator: The first-stage steam extraction pipeline is connected to the medium-pressure heating end to realize medium-pressure heating; The second stage steam extraction pipeline is connected to the second stage high pressure heater; The third stage steam extraction pipeline is connected to the first stage high pressure heater and / or the low pressure heating end; The fourth stage steam extraction pipeline is connected to the high pressure deaerator; The fifth stage steam extraction pipeline is connected to the low pressure heater; The exhaust steam pipeline, whose exhaust steam pressure is close to atmospheric pressure, is connected to the low-pressure feed water heater.

2. The deep back pressure small cogeneration unit thermal system according to claim 1 is characterized in that: It also includes: a drain tank and a drain pump; wherein a first drain circuit is formed between the second-stage high-pressure heater, the first-stage high-pressure heater and the high-pressure deaerator; A second drain circuit is connected between the low-pressure heater and the low-pressure feed water heater; A drain circulation loop is formed between the low-pressure feed water heater, the steam seal heater, the drain water tank and the drain pump.

3. The deep back pressure small cogeneration unit thermal system according to claim 2 is characterized in that: The first drain circuit includes: A first branch drain path is connected between the second stage high pressure heater and the first stage high pressure heater, and a second branch drain path is connected between the first stage high pressure heater and the high pressure deaerator.

4. The deep back pressure small cogeneration unit thermal system according to claim 2, characterized in that: The drain circulation loop includes: There are two drain discharge pipelines, one of which is connected to the low-pressure feed water heater and the drain tank, and the other is connected between the steam seal heater and the drain tank; The drain return pipeline has one end connected to the drain tank and the other end connected to the outlet of the low-pressure feed water heater. The drain pump is arranged on the drain return pipeline.

5. The deep back pressure small cogeneration unit thermal system according to claim 2, characterized in that: A feed water pump is arranged between the high-pressure deaerator and the first-stage high-pressure heater. Two feed water pumps are arranged in parallel between the first-stage high-pressure heater and the high-pressure deaerator.

6. The deep back pressure small cogeneration unit thermal system according to claim 2, characterized in that: A desalted water booster pump is arranged between the chemical water supply source and the steam seal heater. Two desalted water booster pumps are arranged in parallel.

7. The deep back pressure small cogeneration unit thermal system according to claim 2, characterized in that: The third-stage steam extraction pipeline is connected to the fourth-stage steam extraction pipeline, and is used to ensure the steam source required by the high-pressure deaerator when the unit load is low.

8. The deep back pressure small cogeneration unit thermal system according to claim 2, characterized in that: The exhaust pressure of the exhaust pipeline is 0.15MPa,a.

9. The deep back pressure small cogeneration unit thermal system according to claim 2, characterized in that: The boiler and the steam turbine are connected via a main steam header.

10. The deep back pressure small cogeneration unit thermal system according to claim 9, characterized in that: A first output pipeline is arranged on the main steam main pipe for standby medium-pressure heating, and a medium-pressure temperature and pressure reducer is arranged on the first output pipeline; And a second output pipeline is used for backup low-pressure heating, and a low-pressure temperature and pressure reducer is arranged on the second output pipeline.

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