Wide-load efficient steam turbine set provided with double-flow middle balance piston type intermediate pressure cylinder and operation method of wide-load efficient steam turbine set

Abstract

According to the wide-load efficient turboset provided with the double-flow middle balance piston type intermediate-pressure cylinder and the operation method of the wide-load efficient turboset, on the basis that the arrangement mode of the turboset and a steam extraction system of the turboset is not changed, the unique double-flow middle balance piston type intermediate-pressure cylinder is designed, and a steam extraction heat regeneration system is adaptively designed; two operation modes of a conventional mode and pressure-building cylinder switching are provided, the temperature field change of a high-temperature metal part of the turboset before and after mode switching is small, safety and reliability are high, the metal service life of the set is not affected, and meanwhile the problem of blade flutter caused by insufficient steam exhaust flow of a low-load cylinder of the set under the low-load working condition is solved. Compared with a conventional mode that two steam inlet valves of the medium-pressure cylinder are combined for pressure building heat supply, the throttling loss of the medium-pressure cylinder and the steam exhaust loss of the low-pressure cylinder can be reduced, the efficiency of the medium-pressure cylinder and the low-pressure cylinder is greatly improved, and the wide-load and high-efficiency unit is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of new generation coal-fired power wide load high efficiency technology, and particularly relates to wide load high efficiency operation of extraction heating condensing steam turbine unit. Specifically, it relates to wide load high efficiency steam turbine unit with double-flow intermediate balanced piston type intermediate pressure cylinder and operation method thereof. BACKGROUND

[0002] Under the background of building a new energy system, thermal power plants are accelerating the transformation into comprehensive energy suppliers, and extraction heating condensing steam turbine unit has become the mainstream type of thermal power unit. The preferred extraction point for high-pressure industrial heating extraction is cold re-steam, which has high heating economy. At present, it is commonly used. The "Implementation Plan for New Generation Coal-fired Power Upgrading Special Action" clearly requires wide load high efficiency indicators for units. Extraction heating condensing steam turbine unit currently faces the following problems: (1) After deep peak shaving of the unit, the cold re-steam pressure cannot meet the unit heating pressure requirement, and the extraction cannot be performed. The conventional use of two intermediate connecting doors for pressure holding and heating will greatly reduce the efficiency of the intermediate pressure cylinder by 15-20%. The boiler superheated steam heating cannot utilize the high-grade energy of high-pressure steam, which greatly weakens the heating benefit on the unit coal consumption after deep peak shaving. The thermal cycle efficiency is also reduced, and the unit low load power generation efficiency is greatly reduced.

[0003] (2) After extraction heating of the unit at low load, the low-pressure cylinder exhaust flow is reduced, not only the low-pressure cylinder efficiency is greatly reduced, but also the low-pressure cylinder exhaust flow is prone to enter the flow range of exciting the last stage blade flutter, which exists a major safety hazard, and limits the extraction heating flow of the unit, which restricts the heating benefit on the unit coal consumption.

[0004] (3) The current scheme of changing the steam flow of the thermal system or separately removing the low-pressure cylinder during deep peak shaving will cause the temperature field of the high-temperature metal parts of the steam turbine unit to change dramatically before and after the operation mode switching, which not only affects the service life of the unit, but also may cause safety hazards such as dynamic and static rubbing, poor expansion, etc. Under the background of frequent peak shaving, the practical value is not great.

[0005] In order to solve the above-mentioned defects and improve the wide load high efficiency capability of the extraction heating condensing steam turbine unit, a unique double-flow intermediate balanced piston type intermediate pressure cylinder and thermal system are designed without changing the arrangement of the unit steam turbine and extraction system. The unit low load heating capability is improved, and the low load economy of the unit is improved by improving the efficiency of the intermediate pressure cylinder and the low pressure cylinder. At the same time, the problem of small flow blade flutter of the last stage blade of the low pressure cylinder is solved. SUMMARY

[0006] The application provides a wide-load high-efficiency steam turbine unit with a double-flow intermediate balanced piston type medium-pressure cylinder, which does not change the overall arrangement structure of a conventional steam turbine unit and can be applied to the modification of an existing unit in service, and is based on the most widely used four-cylinder, four-steam-exhaust, once intermediate reheat, eight-stage steam extraction, double back pressure, single-shaft condensing type existing steam turbine structure, and the steam turbine unit is composed of a high-pressure cylinder, a medium-pressure cylinder, a first low-pressure cylinder, a second low-pressure cylinder and a generator which are connected in series.

[0007] The pressure drop of the first-stage nozzle of the medium-pressure cylinder first flow and the medium-pressure cylinder second flow is designed to be different, so that a certain pressure difference is maintained on both sides of the intermediate balanced piston, a small amount of steam flow is kept, the heat generated by the friction of the rotor is taken away, and the temperature in the region is prevented from exceeding the limit.

[0008] Further, the wide-load high-efficiency steam turbine unit with a double-flow intermediate balanced piston type medium-pressure cylinder has two operation modes of the medium-pressure cylinder first inlet valve and the medium-pressure cylinder second inlet valve, one of which is a conventional mode in which both inlet valves are fully opened, at this time, the steam of the medium-pressure cylinder first flow and the medium-pressure cylinder second flow is symmetrically divided, and the steam flow is consistent; and the other mode is a pressure holding mode in which the medium-pressure cylinder first inlet valve is fully opened and the medium-pressure cylinder second inlet valve is partially opened, at this time, the steam of the medium-pressure cylinder first flow and the medium-pressure cylinder second flow is asymmetrically divided, and the steam flow of the medium-pressure cylinder first flow is greater than that of the medium-pressure cylinder second flow.

[0009] Further, the axial forces generated by the steam flow inconsistency of the medium-pressure cylinder first flow and the medium-pressure cylinder second flow are mainly balanced by the thrust generated by the intermediate balanced piston. Specifically, when the steam flow of the medium-pressure cylinder first flow and the medium-pressure cylinder second flow is consistent, the pressure on both sides of the intermediate balanced piston is also consistent, and no thrust is generated, at this time, the axial forces of the steam of the medium-pressure cylinder first flow and the medium-pressure cylinder second flow acting on the rotor can be self-balanced. When the steam flow of the medium-pressure cylinder first flow is greater than that of the medium-pressure cylinder second flow, the pressure on both sides of the intermediate balanced piston is inconsistent, and a thrust is generated to balance the axial forces generated by the steam flow inconsistency of the medium-pressure cylinder first flow and the medium-pressure cylinder second flow.

[0010] Further, the wide load high efficiency steam turbine unit with double flow intermediate balanced piston type medium pressure cylinder is configured as follows: the main steam from the boiler is connected to the high pressure cylinder inlet through the main steam valve, the high pressure cylinder exhaust port is connected to the boiler cold re-steam pipe through the high pressure cylinder exhaust check valve and the cold re-steam valve. The external heat supply branch pipe of the unit is connected to the boiler cold re-steam pipe after the high pressure cylinder exhaust check valve through the external heat supply adjusting valve. The reheated steam from the boiler is connected to the first and second medium pressure cylinder inlets through the first and second medium pressure cylinder inlet valves respectively, the exhaust port of the first medium pressure cylinder is directly connected to the first low pressure cylinder inlet, the exhaust port of the first low pressure cylinder is connected to the first condenser, the exhaust port of the second medium pressure cylinder is connected to the second low pressure cylinder inlet through the second low pressure cylinder inlet valve, and the exhaust port of the second low pressure cylinder is connected to the second condenser.

[0011] Further, the process of the extraction regenerative system of the wide load high efficiency steam turbine unit with double flow intermediate balanced piston type medium pressure cylinder is as follows: the condensate outlet of the first and second condensers is connected to the condensate pump inlet through the condensate pump inlet valve, and the condensate pump outlet is divided into two branches: one branch is connected to the condensate water inlet of the eighth heater through the condensate pump first outlet valve; the other branch is connected to the condensate water inlet of the medium pressure cylinder exhaust cooler through the condensate pump second outlet valve. The condensate water outlets of the eighth heater and the medium pressure cylinder exhaust cooler are combined and then connected to the condensate water inlet of the seventh heater, and then sequentially connected to the condensate water inlets and outlets of the sixth heater, the fifth heater, and the deaerator. The feedwater outlet of the deaerator is sequentially connected to the feedwater inlets and outlets of the feedwater pump, the third heater, the second heater, and the first heater. The eighth stage extraction branch pipe of the second low pressure cylinder is connected to the eighth heater steam inlet through the eighth stage extraction check valve. The seventh stage extraction branch pipe of the first low pressure cylinder is connected to the seventh heater steam inlet through the seventh stage extraction check valve. The sixth stage extraction branch pipe of the first low pressure cylinder is connected to the sixth heater steam inlet through the sixth stage extraction check valve and the sixth heater steam valve. The fifth stage extraction branch pipe of the second split flow of the medium pressure cylinder is divided into two branches: one branch is connected to the third heater steam inlet through the fifth stage extraction third check valve and the third heater second steam valve; the other branch is combined with the fifth stage extraction branch pipe of the first split flow of the medium pressure cylinder through the fifth stage extraction second check valve and the fifth stage extraction first check valve of the first split flow fifth stage extraction branch pipe of the medium pressure cylinder, and then connected to the fifth heater steam inlet through the fifth heater steam valve. The fourth stage extraction branch pipe of the first split flow of the medium pressure cylinder is connected to the deaerator steam inlet through the fourth stage extraction check valve and the deaerator steam valve. The third stage extraction branch pipe of the second split flow of the medium pressure cylinder is connected to the third heater steam inlet through the third stage extraction check valve and the third heater first steam valve. The second stage extraction branch pipe of the boiler cold re-evaporation steam pipe is connected to the second heater steam inlet through the second stage extraction check valve and the second heater steam valve. The first stage extraction branch pipe of the high pressure cylinder is connected to the first heater steam inlet through the first stage extraction check valve and the first heater steam valve. The drain outlet of the first heater is connected to the drain inlet of the second heater. The drain outlet of the second heater is divided into two branches: one branch is connected to the drain inlet of the third heater through the second heater drain first regulating valve; the other branch is connected to the drain inlet of the deaerator through the second heater drain second regulating valve. The drain / steam outlet of the third heater is divided into two branches: one branch is connected to the drain inlet of the deaerator through the third heater drain regulating valve; the other branch is directly connected to the steam inlet of the medium pressure cylinder exhaust cooler through the third heater exhaust valve, and a bypass is arranged after the third heater exhaust valve of the branch pipe, which is connected to the first condenser through the medium pressure cylinder second split flow exhaust pressure regulating valve. The drain inlets and outlets of the fifth, sixth, seventh, and eighth heaters are sequentially connected, and finally connected to the second condenser. The drain outlet of the medium pressure cylinder exhaust cooler is directly connected to the second condenser.

[0012] Further, the wide-load high-efficiency steam turbine unit with a double-flow intermediate balanced piston type intermediate pressure cylinder has operation modes including a conventional mode and a pressure holding and cylinder cutting mode, and respectively as follows. The conventional mode has the operation mode that the first intermediate pressure cylinder inlet valve, the second intermediate pressure cylinder inlet valve and the second low pressure cylinder inlet valve are fully opened, the second heating device drain second regulating valve is closed, the second heating device drain first regulating valve is opened, the third heating device second inlet valve is closed, the third heating device first inlet valve is opened, the third heating device drain regulating valve is opened, the third heating device exhaust valve is closed, the first condensate pump outlet valve is opened, the second condensate pump outlet valve is closed, and other valves are operated according to the conventional mode. The mode is a commonly used operation mode of the current steam turbine system, and is applied when the unit load is high and the cold re-pressing pressure can meet the heating demand.

[0013] The pressure holding and cylinder cutting mode has the operation mode that the first intermediate pressure cylinder inlet valve is fully opened, the second intermediate pressure cylinder inlet valve and the second low pressure cylinder inlet valve are closed to the lowest limit, the second heating device drain second regulating valve is opened, the second heating device drain first regulating valve is closed, the third heating device second inlet valve is opened, the third heating device first inlet valve is closed, the third heating device drain regulating valve is closed, the third heating device exhaust valve is opened, the first condensate pump outlet valve is closed, the second condensate pump outlet valve is opened, the second intermediate pressure cylinder second split exhaust pressure regulating valve is adjusted to make the second intermediate pressure cylinder second split exhaust pressure consistent with the first intermediate pressure cylinder second split exhaust temperature, so as to maintain the stability of the temperature field of the intermediate pressure cylinder metal parts, and other valves are operated according to the conventional mode.

[0014] Further, the first intermediate pressure cylinder inlet valve is fully opened, the second intermediate pressure cylinder inlet valve is closed to the lowest limit to improve the cold re-steam main pipe pressure to meet the heating requirement, and the second low pressure cylinder inlet valve is closed to the lowest limit to cut off the second low pressure cylinder operation, and only a small steam flow is kept to cool the relevant metal parts. The mode is a unique mode different from the conventional thermal system, and is applied when the cold re-steam pressure cannot meet the heating demand in the low load range.

[0015] Before and after the unit operation mode switching, the temperature fields of the intermediate pressure cylinder, the first low pressure cylinder and the high temperature metal of the cut-off second low pressure cylinder inlet are basically consistent, and have no significant influence on the unit life and safety reliability.

[0016] When the conventional mode is switched to the pressure-holding cylinder-cutting mode, the third heater continues to operate, its drain changes to superheated steam, its function changes to a pre-cooler for the medium-pressure cylinder exhaust cooler, and the medium-pressure cylinder exhaust cooler recovers the heat of the second split flow of the medium-pressure cylinder. The pressure of the second split flow of the medium-pressure cylinder is much lower than that of the first split flow, and the steam source of the fifth heater changes to the first split flow of the medium-pressure cylinder. After the second low-pressure cylinder is cut off, the eighth heater loses the heating steam source, and its function is replaced by the medium-pressure cylinder exhaust cooler.

[0017] When the conventional mode is switched to the pressure-holding cylinder-cutting mode, the second low-pressure cylinder is cut off as a whole, which can greatly increase the exhaust flow of the first low-pressure cylinder, improve its operating efficiency, and solve the problem of blade flutter caused by insufficient exhaust flow of the low-pressure cylinder due to heating extraction at low load, thereby indirectly improving the heating capacity of the unit at low load.

[0018] The disclosed wide-load high-efficiency steam turbine unit with a double-flow intermediate balanced piston type medium-pressure cylinder has the following innovations: (1) The present application designs a unique double-flow intermediate balanced piston type medium-pressure cylinder and a thermal system without changing the arrangement of the steam turbine unit and the extraction system, proposes two operating modes, and has small changes in the temperature field of the high-temperature metal parts of the steam turbine unit before and after switching, high safety and reliability, no effect on the metal life of the unit, and solves the problem of blade flutter caused by insufficient exhaust flow of the low-pressure cylinder at low load, which can indirectly improve the extraction heating capacity. It is especially suitable for the modification of active extraction heating condensing steam turbine units.

[0019] (2) Compared with the pressure-holding mode of the conventional medium-pressure cylinder with two inlet valves, most of the steam entering the medium-pressure cylinder flows through the first split flow of the medium-pressure cylinder without throttling loss, and the overall efficiency of the medium-pressure cylinder is high. At the same time, due to the cutting off of the second low-pressure cylinder, the exhaust flow of the first low-pressure cylinder increases, and the efficiency of the low-pressure cylinder is greatly improved, thereby realizing wide-load high-efficiency of the unit. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The flow chart of the wide-load high-efficiency steam turbine unit with a double-flow intermediate balanced piston type medium-pressure cylinder of the present application; Fig. 1: 1, high-pressure cylinder; 2, intermediate-pressure cylinder; 3, first intermediate-pressure cylinder split flow; 4, second intermediate-pressure cylinder split flow; 5, intermediate-pressure cylinder middle balance piston; 6, first low-pressure cylinder; 7, second low-pressure cylinder; 8, generator; 9, second condenser; 10, first condenser; 11, condensate pump; 12, eighth heater; 13, seventh heater; 14, sixth heater; 15, fifth heater; 16, deaerator; 17, feed water pump; 18, third heater; 19, second heater; 20, first heater; 21, intermediate-pressure cylinder exhaust cooler; 22, main steam valve; 23, second intermediate-pressure cylinder inlet valve; 24, first intermediate-pressure cylinder inlet valve; 25, second low-pressure cylinder inlet valve; 26, high-pressure cylinder exhaust check valve; 27, cold re-vaporization valve; 28, external heat supply adjustment valve; 29, first stage extraction check valve; 30, first heater inlet valve; 31, second stage extraction check valve; 32, second heater inlet valve; 33, third stage extraction check valve; 34, first third heater inlet valve; 35, fourth stage extraction check valve; 36, deaerator inlet valve; 37, fifth stage extraction first check valve; 38, fifth stage extraction second check valve; 39, fifth heater inlet valve; 40, fifth stage extraction third check valve; 41, second third heater inlet valve; 42, third heater exhaust valve; 43, second intermediate-pressure cylinder second split flow exhaust pressure adjustment valve; 44, sixth stage extraction check valve; 45, sixth heater inlet valve; 46, seventh stage extraction check valve; 47, eighth stage extraction check valve; 48, condensate pump inlet valve; 49, condensate pump first outlet valve; 50, condensate pump second outlet valve; 51, third heater drain adjustment valve; 52, second heater drain second adjustment valve; 53, second heater drain first adjustment valve. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0022] The application is based on the most widely used four-cylinder, four-exhaust, once intermediate reheat, eight-stage extraction, double back pressure, single shaft condensing type existing steam turbine structure, and the steam turbine generator unit is composed of a high-pressure cylinder 1, a medium-pressure cylinder 2, a first low-pressure cylinder 6, a second low-pressure cylinder 7 and a generator 8 in series. The high-pressure cylinder 1, the first low-pressure cylinder 6 and the second low-pressure cylinder 7 all adopt a conventional structure, wherein the second low-pressure cylinder 7 can be completely cut off for operation. The through-flow structure of the medium-pressure cylinder 2 adopts a conventional symmetrical double-flow arrangement, which is composed of a medium-pressure cylinder first flow 3 and a medium-pressure cylinder second flow 4, and independent steam inlets are designed for the two, which are connected to the reheat steam pipeline through a medium-pressure cylinder first steam inlet valve 24 and a medium-pressure cylinder second steam inlet valve 23. The medium-pressure cylinder 2 is divided by a medium-pressure cylinder intermediate balance piston 5, and the two sides of the medium-pressure cylinder intermediate balance piston 5 are respectively connected with the space behind the first-stage nozzle of the medium-pressure cylinder first flow 3 and the medium-pressure cylinder second flow 4.

[0023] The wide-load high-efficiency steam turbine unit with a double-flow intermediate balance piston type medium-pressure cylinder is configured as follows: the main steam from a boiler is connected to the steam inlet of the high-pressure cylinder 1 through a main steam valve 22, and the steam outlet of the high-pressure cylinder 1 is connected to the boiler cold reheat steam pipe through a high-pressure cylinder exhaust check valve 26 and a cold reheat steam valve 27. The unit external heat supply branch pipe is connected to the boiler cold reheat steam pipe after the high-pressure cylinder exhaust check valve 26 through an external heat supply adjusting valve 28. The reheat steam from the boiler is connected to the steam inlets of the medium-pressure cylinder first flow 3 and the medium-pressure cylinder second flow 4 through the medium-pressure cylinder first steam inlet valve 24 and the medium-pressure cylinder second steam inlet valve 23 respectively. The steam outlet of the medium-pressure cylinder first flow 3 is directly connected to the steam inlet of the first low-pressure cylinder 6, the steam outlet of the first low-pressure cylinder 6 is connected to the first condenser 10, the steam outlet of the medium-pressure cylinder second flow 4 is connected to the steam inlet of the second low-pressure cylinder 7 through a second low-pressure cylinder steam inlet valve 25, and the steam outlet of the second low-pressure cylinder 7 is connected to the second condenser 9.

[0024] The process of the extraction regenerative system of the wide load high efficiency steam turbine unit with double flow intermediate balanced piston type medium pressure cylinder is as follows: the condensate outlet of the first condenser 10 and the second condenser 9 is connected to the inlet of the condensate pump 11 through the inlet valve 48 of the condensate pump, and the outlet of the condensate pump 11 is divided into two branches: one branch is connected to the condensate inlet of the eighth heater 12 through the first outlet valve 49 of the condensate pump; the other branch is connected to the condensate inlet of the medium pressure cylinder exhaust cooler 21 through the second outlet valve 50 of the condensate pump. The condensate outlets of the eighth heater 12 and the medium pressure cylinder exhaust cooler 21 are connected to the condensate inlet of the seventh heater 13, and then connected to the condensate inlets and outlets of the sixth heater 14 and the fifth heater 15 in sequence; and then connected to the condensate inlet of the deaerator 16. The feedwater outlet of the deaerator is connected to the feedwater pump 17, the third heater 18, the second heater 19 and the first heater 20 in sequence. The eighth extraction branch pipe of the second low pressure cylinder 7 is connected to the steam inlet of the eighth heater 12 through the eighth extraction check valve 47. The seventh extraction branch pipe of the first low pressure cylinder 6 is connected to the steam inlet of the seventh heater 13 through the seventh extraction check valve 46. The sixth extraction branch pipe of the first low pressure cylinder 6 is connected to the steam inlet of the sixth heater 14 through the sixth extraction check valve 44 and the steam inlet valve 45 of the sixth heater. The fifth extraction branch pipe of the second flow of the medium pressure cylinder is divided into two branches: one branch is connected to the steam inlet of the third heater 18 through the third extraction check valve 40 and the second steam inlet valve 41 of the third heater; the other branch is connected to the steam inlet of the fifth heater 15 through the second extraction check valve 38 and the fifth extraction branch pipe of the first flow of the medium pressure cylinder 3, and the first extraction check valve 37 is arranged on the fifth extraction branch pipe of the first flow of the medium pressure cylinder 3, and then connected to the steam inlet of the fifth heater 15 through the steam inlet valve 39 of the fifth heater. The fourth extraction branch pipe of the first flow of the medium pressure cylinder 3 is connected to the steam inlet of the deaerator 16 through the fourth extraction check valve 35 and the steam inlet valve 36 of the deaerator. The third extraction branch pipe of the second flow of the medium pressure cylinder 4 is connected to the steam inlet of the third heater 18 through the third extraction check valve 33 and the first steam inlet valve 34 of the third heater. The second extraction branch pipe of the cold re-steam pipe of the boiler is connected to the steam inlet of the second heater 19 through the second extraction check valve 31 and the steam inlet valve 32 of the second heater. The first extraction branch pipe of the high pressure cylinder 1 is connected to the steam inlet of the first heater 20 through the first extraction check valve 29 and the steam inlet valve 30 of the first heater.

[0025] The first heater 20 is connected to the second heater 19. The second heater 19 is connected to the third heater 18 and the deaerator 16. The third heater 18 is connected to the deaerator 16 and the first condenser 10. The fifth, sixth, seventh and eighth heaters 15, 14, 13 and 12 are connected to the second condenser 9. The deaerator 16 is connected to the second condenser 9.

[0026] The first stage nozzle pressure drop of the first and second streams of the intermediate balance piston type intermediate pressure cylinder is designed to be different, so that a pressure difference is maintained on both sides of the intermediate balance piston 5, a small amount of steam flow is maintained, and the heat generated by the friction of the rotor is removed to prevent the temperature in the area from exceeding the limit.

[0027] The first and second inlet valves 24 and 23 of the intermediate balance piston type intermediate pressure cylinder are designed to have two operating modes: one is the conventional mode in which both inlet valves are fully open, and the steam is symmetrically distributed in the first and second streams, and the steam flow is consistent. The other mode is the pressure holding mode in which the first inlet valve 24 is fully open and the second inlet valve 23 is partially open, and the steam is asymmetrically distributed in the first and second streams, and the steam flow in the first stream is greater than that in the second stream.

[0028] The axial force generated by the inconsistent steam flow in the first and second streams of the intermediate pressure cylinder is mainly balanced by the thrust generated by the intermediate balance piston 5. Specifically, when the steam flow in the first and second streams is consistent, the pressure on both sides of the intermediate balance piston 5 is also consistent, and no thrust is generated. At this time, the axial force of the steam in the first and second streams acting on the rotor can be self-balanced. When the steam flow in the first stream is greater than that in the second stream, the pressure on both sides of the intermediate balance piston is inconsistent, and a thrust is generated to balance the axial force generated by the inconsistent steam flow in the first and second streams.

[0029] The wide-load high-efficiency steam turbine unit with the double-flow intermediate balanced piston type medium-pressure cylinder has operation modes of a conventional mode and a pressure holding and cylinder cutting mode, and respectively as follows. The conventional mode: the operation mode is that the first medium-pressure cylinder inlet valve 24, the second medium-pressure cylinder inlet valve 23 and the second low-pressure cylinder inlet valve 25 are fully opened; the second heater drain second regulating valve 52 is closed, the second heater drain first regulating valve 53 is opened, the third heater second inlet valve 41 is closed, the third heater first inlet valve 34 is opened, the third heater drain regulating valve 51 is opened, the third heater exhaust valve 42 is closed, the first condensate pump outlet valve 49 is opened and the second condensate pump outlet valve 50 is closed. The mode is an operation mode commonly applied to the current steam turbine system, and is applied to the working condition that the load of the unit is high and the cold re-pressing force can meet the heating demand.

[0030] The pressure holding and cylinder cutting mode: the operation mode is that the first medium-pressure cylinder inlet valve 24 is fully opened, the second medium-pressure cylinder inlet valve 23 and the second low-pressure cylinder inlet valve 25 are closed to the lowest limit; the second heater drain second regulating valve 52 is opened, the second heater drain first regulating valve 53 is closed, the third heater second inlet valve 41 is opened, the third heater first inlet valve 34 is closed, the third heater drain regulating valve 51 is closed, the third heater exhaust valve 42 is opened, the first condensate pump outlet valve 49 is closed and the second condensate pump outlet valve 50 is opened. The second medium-pressure cylinder split flow exhaust pressure regulating valve 43 adjusts the second medium-pressure cylinder split flow 4 exhaust pressure to make the exhaust temperature consistent with the first medium-pressure cylinder split flow 3 exhaust temperature, so as to maintain the stability of the metal part temperature field of the second medium-pressure cylinder 2.

[0031] The first medium-pressure cylinder inlet valve 24 is fully opened, the second medium-pressure cylinder inlet valve 23 is closed to the lowest limit to improve the cold re-steam main pipe pressure to meet the heating requirement, and the second low-pressure cylinder inlet valve 25 is closed to the lowest limit to cut off the operation of the second low-pressure cylinder 7, and only a small steam flow is kept to cool the related metal parts. The mode is a unique mode different from the conventional thermal system, and is applied when the cold re-steam pressure cannot meet the heating demand in the low load range.

[0032] Before and after the unit operation mode is switched, the temperature fields of the second medium-pressure cylinder 2, the first low-pressure cylinder 6 and the high-temperature metal of the cut-off second low-pressure cylinder 7 are basically consistent, and there is no significant influence on the unit life and safety reliability.

[0033] When the conventional mode is switched to the pressure holding and cylinder cutting mode, the third heater 18 continues to operate, the drain thereof is changed to superheated steam, the function thereof is changed to a pre-cooler of the intermediate pressure cylinder exhaust cooler 21, and the intermediate pressure cylinder exhaust cooler 21 is combined to recover the heat of the second split flow 4 of the intermediate pressure cylinder. The pressure of the second split flow 4 of the intermediate pressure cylinder is far lower than that of the first split flow of the intermediate pressure cylinder, and the steam source of the fifth heater 15 is changed to the fifth stage extraction steam of the first split flow 3 of the intermediate pressure cylinder. After the second low pressure cylinder 7 is cut off, the eighth heater 12 loses the heating steam source, and the function thereof is replaced by the intermediate pressure cylinder exhaust cooler 21.

[0034] When the conventional mode is switched to the pressure holding and cylinder cutting mode, the second low pressure cylinder 7 is cut off as a whole, the exhaust flow of the first low pressure cylinder 6 can be greatly improved, the operation efficiency is improved, the blade flutter problem caused by insufficient low pressure cylinder exhaust flow due to heating extraction steam in the low load condition of the unit is solved, and the low load heating capacity of the unit is indirectly improved. Compared with the conventional method of simultaneously closing the first inlet valve 24 of the intermediate pressure cylinder and the second inlet valve 23 of the intermediate pressure cylinder to improve the heating pressure, the efficiency of the intermediate pressure cylinder 2 can be greatly improved because most of the steam entering the intermediate pressure cylinder 2 flows through the first split flow 3 of the intermediate pressure cylinder, the first inlet valve 24 of the intermediate pressure cylinder is always fully open, there is no throttling loss, and a small part of the steam flows through the second split flow 4 of the intermediate pressure cylinder, there is throttling loss, and the overall efficiency of the intermediate pressure cylinder 2 can be greatly improved. The improvement of the efficiency of the intermediate pressure cylinder and the low pressure cylinder and the increase of the cold re-extraction heating flow can greatly improve the low load economy of the extraction heating condensing steam turbine unit, and realize the goal of wide load and high efficiency of the new generation coal-fired turbine unit.

[0035] The steam turbine unit provided in the application mainly improves the structure of the existing double-flow intermediate pressure cylinder, and designs an intermediate balance piston type intermediate pressure cylinder, which can adjust the flow of two split flows of the intermediate pressure cylinder online. On this basis, through adaptive improvement of the extraction heat recovery system, two operation modes are designed, which are used in the high load and low load stages of the unit respectively. The improved steam turbine unit can change the steam flow according to the characteristics of the operating condition, reduce the throttling loss of the inlet valve of the intermediate pressure cylinder and the exhaust loss of the low pressure cylinder in the low load condition of the conventional structure, and improve the wide load performance of the unit.

[0036] The technical scheme provided in the application has the following specific effects in solving the problems of the prior art in the background art: (1) After the unit is deeply peak-regulated, the cold re-pressure cannot meet the heating pressure requirement of the unit, and the unit cannot extract steam externally. The conventional method uses the two inlet valves of the intermediate pressure cylinder to simultaneously hold pressure and improve the heating pressure. At this time, the throttling loss of the inlet valve of the intermediate pressure cylinder is large, which causes the efficiency of the intermediate pressure cylinder to be reduced by 15-20%. In the pressure holding and cylinder cutting mode of the present scheme, most of the steam flowing through the intermediate pressure cylinder enters the first split flow of the intermediate pressure cylinder through the fully open first inlet valve of the intermediate pressure cylinder, and there is no throttling loss. Compared with the conventional scheme, the efficiency of the intermediate pressure cylinder can be improved by more than 10%.

[0037] (2) For the problem that the low-pressure cylinder efficiency is sharply reduced after the unit low-load extraction heating, and it is easy to enter the flow range of exciting the last stage blade flutter, the two low-pressure cylinder flows of the conventional scheme are always consistent, and they are simultaneously reduced with the unit load reduction. In the pressure blocking and cylinder cutting mode of the scheme, the second low-pressure cylinder can be cut off as a whole, at this time, its flow is transferred to the first low-pressure cylinder, the flow of the first low-pressure cylinder is increased, and it reenters the safe and stable high-efficiency range operation, and it is calculated that the scheme can improve the low-pressure cylinder efficiency by more than 2%.

[0038] (3) If the conventional double-flow intermediate-pressure cylinder is not improved in structure, and the second low-pressure cylinder is directly cut off for operation, the exhaust temperature of the two split flows of the intermediate-pressure cylinder will sharply rise, which can reach more than 70 DEG C, which not only affects the unit life, but also can cause safety hazards such as dynamic and static rubbing, poor expansion, etc. After the technical scheme described in the application is switched to the pressure blocking and cylinder cutting mode, the exhaust temperature of the first split flow of the intermediate-pressure cylinder basically does not change due to the synchronous rise of the inlet steam pressure and the exhaust pressure, and the exhaust temperature of the second split flow of the intermediate-pressure cylinder can be adjusted through the intermediate-pressure cylinder second split exhaust pressure regulating valve, and it is always maintained stable.

Claims

1. A wide load high efficient steam turbine unit configured with dual flow intermediate balanced piston type intermediate pressure cylinder, characterized in that, The high-efficiency steam turbine unit is composed of a high-pressure cylinder (1), a medium-pressure cylinder (2), a first low-pressure cylinder (6), a second low-pressure cylinder (7) and a generator (8) in series.

2. A wide load high efficient steam turbine set with double flow intermediate balanced piston type intermediate pressure cylinder as claimed in claim 1 wherein, The pressure drop of the first-stage nozzle of the first medium-pressure cylinder (3) and the second medium-pressure cylinder (4) is designed to be different, so that a certain pressure difference is maintained on both sides of the medium-pressure cylinder intermediate balance piston (5), and a small amount of steam flow is kept to take away the heat generated by the friction of the rotor.

3. A double flow intermediate balanced piston type wide load high efficient steam turbine unit with medium pressure cylinder as claimed in claim 2 wherein, The operation mode of the first medium-pressure cylinder inlet valve (24) and the second medium-pressure cylinder inlet valve (23) is divided into two types: one is the conventional mode in which the first medium-pressure cylinder inlet valve (24) and the second medium-pressure cylinder inlet valve (23) are both fully open, at this time the steam of the first medium-pressure cylinder (3) and the second medium-pressure cylinder (4) is symmetrically divided, and the steam flow is consistent; the other mode is the pressure holding mode, the first medium-pressure cylinder inlet valve (24) is fully open, and the second medium-pressure cylinder inlet valve (23) is partially open, at this time the steam of the first medium-pressure cylinder (3) and the second medium-pressure cylinder (4) is asymmetrically divided, and the steam flow of the first medium-pressure cylinder (3) is greater than that of the second medium-pressure cylinder (4).

4. A double flow intermediate balanced piston type wide load high efficient steam turbine unit with medium pressure cylinder as claimed in claim 3 wherein, The axial force generated by the steam flow inconsistency of the first medium-pressure cylinder (3) and the second medium-pressure cylinder (4) is balanced by the thrust generated by the medium-pressure cylinder intermediate balance piston (5).

5. A wide load high efficient steam turbine set with double flow intermediate balanced piston type intermediate pressure cylinder as claimed in claim 1 wherein, The flow of the steam turbine side system component is as follows: the main steam from the boiler is connected to the inlet of the high-pressure cylinder (1) through the main steam valve (22), the exhaust port of the high-pressure cylinder (1) is connected to the boiler cold re-steam pipe through the high-pressure cylinder exhaust check valve (26) and the cold re-steam valve (27); the unit external heating branch pipe is connected to the boiler cold re-steam pipe after the high-pressure cylinder exhaust check valve (26) through the external heating adjusting valve (28); the reheat steam from the boiler is connected to the inlet of the first medium-pressure cylinder (3) and the second medium-pressure cylinder (4) through the first medium-pressure cylinder inlet valve (24) and the second medium-pressure cylinder inlet valve (23), respectively; the exhaust port of the first medium-pressure cylinder (3) is directly connected to the inlet of the first low-pressure cylinder (6), the exhaust port of the first low-pressure cylinder (6) is connected to the first condenser (10), the exhaust port of the second medium-pressure cylinder (4) is connected to the inlet of the second low-pressure cylinder (7) through the second low-pressure cylinder inlet valve (25), and the exhaust port of the second low-pressure cylinder (7) is connected to the second condenser (9).

6. A double flow intermediate balanced piston type wide load high efficiency steam turbine unit with interstage pressure cylinder as claimed in claim 5 wherein, The specific flow of the extraction regenerative system components is as follows: the condensate outlets of the first condenser (10) and the second condenser (9) are connected to the condensate pump (11) inlet through the condensate pump inlet valve (48); the condensate pump (11) outlet is divided into two branches: one branch is connected to the condensate inlet of the eighth heater (12) through the condensate pump first outlet valve (49); the other branch is connected to the condensate inlet of the intermediate pressure cylinder exhaust cooler (21) through the condensate pump second outlet valve (50); the condensate outlets of the eighth heater (12) and the intermediate pressure cylinder exhaust cooler (21) are combined and connected to the condensate inlet of the seventh heater (13), and then sequentially connected to the condensate inlets and outlets of the sixth heater (14) and the fifth heater (15); then connected to the condensate inlet of the deaerator (16); the deaerator feedwater outlet is sequentially connected to the feedwater pump (17), the third heater (18), the second heater (19), and the first heater (20) feedwater inlets and outlets; the eighth extraction branch pipe of the second low pressure cylinder (7) is connected to the eighth heater (12) steam inlet through the eighth extraction check valve (47); the seventh extraction branch pipe of the first low pressure cylinder (6) is connected to the seventh heater (13) steam inlet through the seventh extraction check valve (46); the sixth extraction branch pipe of the first low pressure cylinder (6) is connected to the sixth heater (14) steam inlet through the sixth extraction check valve (44) and the sixth heater steam inlet valve (45); the fifth extraction branch pipe of the second flow division (4) of the intermediate pressure cylinder is divided into two branches: one branch is connected to the third heater (18) steam inlet through the fifth extraction third check valve (40) and the third heater second steam inlet valve (41); the other branch is combined with the fifth extraction branch pipe of the first flow division (3) of the intermediate pressure cylinder through the fifth extraction second check valve (38), the fifth extraction first check valve (37) is arranged on the fifth extraction branch pipe of the first flow division (3) of the intermediate pressure cylinder, and then connected to the fifth heater (15) steam inlet through the fifth heater steam inlet valve (39); the fourth extraction branch pipe of the first flow division (3) of the intermediate pressure cylinder is connected to the deaerator (16) steam inlet through the fourth extraction check valve (35) and the deaerator steam inlet valve (36); the third extraction branch pipe of the second flow division (4) of the intermediate pressure cylinder is connected to the third heater (18) steam inlet through the third extraction check valve (33) and the third heater first steam inlet valve (34); the second extraction branch pipe of the boiler cold re-steam pipe is connected to the second heater (19) steam inlet through the second extraction check valve (31) and the second heater steam inlet valve (32); the first extraction branch pipe of the high pressure cylinder (1) is connected to the first heater (20) steam inlet through the first extraction check valve (29) and the first heater steam inlet valve (30); the drain outlet of the first heater (20) is connected to the drain inlet of the second heater (19); the drain outlet of the second heater (19) is divided into two branches: one branch is connected to the drain inlet of the third heater (18) through the second heater drain first regulating valve (53); the other branch is connected to the drain inlet of the deaerator (16) through the second heater drain second regulating valve (52).The drain / steam outlet of the third heater (18) is divided into two branches: one branch is connected to the drain inlet of the deaerator (16) through the third heater drain regulating valve (51); the other branch is directly connected to the steam inlet of the medium-pressure cylinder exhaust cooler (21) through the third heater exhaust valve (42), and a bypass is arranged after the third heater exhaust valve (42) in the branch, which is connected to the first condenser (10) through the second medium-pressure cylinder exhaust pressure regulating valve (43); the drain inlets and outlets of the fifth heater (15), the sixth heater (14), the seventh heater (13) and the eighth heater (12) are sequentially connected, and finally connected to the second condenser (9); the drain outlet of the medium-pressure cylinder exhaust cooler (21) is directly connected to the second condenser (9).

7. A method of operating a wide load high efficient steam turbine unit configured with double flow intermediate balanced piston type intermediate pressure cylinder as claimed in any of the claims 1 to 6, wherein It is divided into a conventional mode and a pressure holding cylinder mode, respectively as follows: Normal mode: the operation mode is that the first admission valve (24) of the intermediate pressure cylinder, the second admission valve (23) of the intermediate pressure cylinder, and the second admission valve (25) of the second low pressure cylinder are all opened; the second drain valve (52) of the second heater is closed, the first drain valve (53) of the second heater is opened, the second admission valve (41) of the third heater is closed, the first admission valve (34) of the third heater is opened, the drain valve (51) of the third heater is opened, the exhaust valve (42) of the third heater is closed, the first outlet valve (49) of the condensate pump is opened, and the second outlet valve (50) of the condensate pump is closed; Pressure holding and cylinder cutting mode: the operation mode is that the first admission valve (24) of the intermediate pressure cylinder is fully opened, the second admission valve (23) of the intermediate pressure cylinder and the second admission valve (25) of the second low pressure cylinder are closed to the lowest limit; the second drain valve (52) of the second heater is opened, the first drain valve (53) of the second heater is closed, the second admission valve (41) of the third heater is opened, the first admission valve (34) of the third heater is closed, the drain valve (51) of the third heater is closed, the exhaust valve (42) of the third heater is opened, the first outlet valve (49) of the condensate pump is closed, and the second outlet valve (50) of the condensate pump is opened; the second split flow exhaust pressure regulating valve (43) of the intermediate pressure cylinder adjusts the exhaust pressure of the second split flow (4) of the intermediate pressure cylinder to make the exhaust temperature consistent with the exhaust temperature of the first split flow (3) of the intermediate pressure cylinder, so as to maintain the stability of the temperature field of the metal parts of the intermediate pressure cylinder (2).

8. A method of operating a wide load high efficient steam turbine unit configured with dual flow intermediate balanced piston type intermediate pressure cylinder as claimed in claim 7 wherein, Before and after the switching of the operation mode of the unit, the temperature field of the intermediate pressure cylinder (2), the temperature field of the first low pressure cylinder (6), and the temperature field of the high-temperature metal of the cut-off second low pressure cylinder (7) are consistent.

9. A method of operating a wide load high efficient steam turbine unit configured with dual flow intermediate balanced piston type intermediate pressure cylinder as claimed in claim 7 wherein, When the normal mode is switched to the pressure holding and cylinder cutting mode, the third heater (18) continues to operate, the drain outlet thereof is changed to superheated steam, the function thereof is changed to a pre-cooler of the intermediate pressure cylinder exhaust cooler (21), and the heat of the exhaust of the second split flow (4) of the intermediate pressure cylinder is recovered in combination with the intermediate pressure cylinder exhaust cooler (21); the exhaust pressure of the second split flow (4) of the intermediate pressure cylinder is much lower than that of the first split flow (3) of the intermediate pressure cylinder, and the steam source of the fifth heater (15) is changed to the fifth stage extraction steam of the first split flow (3) of the intermediate pressure cylinder; after the second low pressure cylinder (7) is cut off, the eighth heater (12) loses the heating steam source, and the function thereof is replaced by the intermediate pressure cylinder exhaust cooler (21).

10. A method of operating a wide load high efficient steam turbine unit configured with dual flow intermediate balanced piston type intermediate pressure cylinder as claimed in claim 7 wherein, When the normal mode is switched to the pressure holding and cylinder cutting mode, the second low pressure cylinder (7) is cut off as a whole, which can greatly increase the exhaust flow of the first low pressure cylinder (6), not only improving the operation efficiency, but also solving the problem of blade flutter caused by insufficient low pressure cylinder exhaust flow due to heating extraction steam in the low load condition of the unit, and indirectly improving the low load heating capacity of the unit.

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