Summer switching single-cylinder operation system and method for 660MW double-low-pressure-cylinder unit

Abstract

The invention discloses a summer switching single-cylinder operation system and method for a 660MW double-low-pressure-cylinder unit. The summer switching single-cylinder operation system comprises an intermediate-pressure cylinder, a condenser, a butterfly valve, a temperature and pressure reducing valve set, a shut-off valve, a heater set and two low-pressure cylinders. Butterfly valves are mounted on pipelines for connecting the steam exhaust end of the intermediate-pressure cylinder with the steam inlet ends of the two low-pressure cylinders respectively, a temperature and pressure reducing valve group is mounted on a pipeline for connecting the steam exhaust end of the intermediate-pressure cylinder with the steam inlet end of one of the low-pressure cylinders, and shut-off valves are mounted on pipelines for connecting one of the low-pressure cylinders with the heater group respectively; the method comprises the following steps: determining unit-to-single-cylinder operation limiting conditions; before one low-pressure cylinder is cut off, the opening degrees of the two butterfly valves are adjusted at the same time, and the steam exhaust pressure of the medium-pressure cylinder is improved; and in the process of cutting off one low-pressure cylinder, the other low-pressure cylinder normally operates, and the deep peak regulation requirement of the unit is met. Under the condition that the low-pressure through-flow area is not changed, the operation deep adjustment capacity, the operation safety and the operation stability of the unit under the summer working condition can be improved.

Description

Technical Field

[0001] The invention relates to a heating steam turbine operation system and method, and in particular to a 660MW double low-pressure cylinder unit summer single-cylinder cut-off operation system and method, belonging to the technical field of steam turbines. Background Art

[0002] The new power system with new energy as the main body is gradually prompting coal-fired power to transform from a power supply type to a power regulation type. Coal-fired power units need to provide more auxiliary operation services such as peak-shaving and frequency regulation, reliable capacity reserve, etc. to the power system. At this stage, the peak-shaving capacity, total peak-shaving amount, and peak-shaving operation economy level of coal-fired power units are still quite different from the total installed capacity and the development needs of clean energy installed capacity. For example: the 660MW capacity-level wet-cooling unit is designed with a double low-pressure cylinder structure and a large low-pressure exhaust area. When the unit is operating in summer, the required minimum cooling flow is relatively large, and the unit's peak-shaving capacity is limited. In order to improve the unit's flexible deep peak-shaving operation capability and ensure the safety and reliability of the unit's operation under low-load conditions, it is necessary to carry out flexible deep peak-shaving adaptability technical transformation of the unit, and it is planned to adopt the low-pressure cylinder single-cylinder cutting technology route.

[0003] To sum up, how to accelerate the flexibility transformation of coal-fired power units of various capacity levels in service and the flexibility manufacturing of newly built high-efficiency coal-fired power units will play a role in flexibility regulation and emergency backup power supply capacity building and needs to be urgently addressed. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a 660MW dual low-pressure cylinder unit summer single-cylinder operation system and method, so as to meet the unit's summer deep peak-shaving operation requirements.

[0005] A summer single-cylinder cut-off operation system of a 660MW dual low-pressure cylinder unit comprises an intermediate-pressure cylinder, a condenser, a butterfly valve, a temperature-reducing and pressure-reducing valve group, a shut-off valve, a heater group and two low-pressure cylinders; the exhaust end of the intermediate-pressure cylinder is connected to the steam inlet ends of the two low-pressure cylinders, and the two low-pressure cylinders are respectively connected to the heater group; a butterfly valve is installed on the pipeline connecting the exhaust end of the intermediate-pressure cylinder to the steam inlet ends of the two low-pressure cylinders, a temperature-reducing and pressure-reducing valve group is installed on the pipeline connecting the exhaust end of the intermediate-pressure cylinder to the steam inlet end of one of the low-pressure cylinders, and a shut-off valve is installed on the pipeline connecting one of the low-pressure cylinders to the heater group;

[0006] When single cylinder operation is performed, the butterfly valve on the pipeline connecting the medium pressure cylinder and one of the low pressure cylinders is closed, the temperature and pressure reducing valve group is opened, the exhaust end of one of the low pressure cylinders is connected to the steam inlet of the condenser, and the shut-off valve is closed.

[0007] A summer single-cylinder operation method for a 660MW dual low-pressure cylinder unit includes:

[0008] S1. Determine the unit's single-cylinder operation restriction conditions, including the intermediate pressure cylinder exhaust pressure and the low pressure cylinder inlet steam temperature;

[0009] S2. Before cutting off one of the low-pressure cylinders, adjust the opening of the two butterfly valves at the same time to increase the exhaust pressure of the medium-pressure cylinder, thereby increasing the exhaust temperature of the medium-pressure cylinder before cutting off the cylinder;

[0010] S3. During the process of cutting off one of the low-pressure cylinders, the other low-pressure cylinder is operated normally, and the butterfly valve on the pipeline of the other low-pressure cylinder is fully opened. At the same time, the butterfly valve and the shut-off valve on the pipeline of one of the low-pressure cylinders are closed, and the temperature reduction and pressure reduction valve group is opened. The steam discharged from the medium-pressure cylinder is converted into cooling steam through the temperature reduction and pressure reduction valve group and sent to one of the low-pressure cylinders, ensuring that the temperature difference before and after the unit cylinder cutting meets the operating conditions and meets the unit's deep peak regulation requirements.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The low-pressure cylinder summer single-cylinder operation system of the present application can be widely used in units of the same type. Without changing the low-pressure flow area, it can improve the deep adjustment capability, operation safety and stability of the unit in summer operating conditions.

[0013] This scheme adopts two low-pressure cylinders, and the two low-pressure cylinders supply steam to the heater group at the same time. In summer, when the single-cylinder operation is cut off, after one of the low-pressure cylinders is cut off, in order to avoid the risk of overheating of the low-pressure cylinder, it is necessary to introduce about 60t / h of cooling steam into one of the low-pressure cylinders. The steam source is taken from the exhaust steam of the medium-pressure cylinder. At the same time, a shut-off valve and a check valve are added to the pipeline from one of the low-pressure cylinders to each heat recovery steam extraction pipeline to prevent steam from flowing back into the low-pressure cylinder.

[0014] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments: BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a system diagram of a 660MW dual low-pressure cylinder unit in summer with single cylinder cut off operation;

[0016] Figure 2 It is the relationship curve of back pressure to the minimum steam inlet pressure of the low-pressure cylinder;

[0017] Figure numerals: 1. Low-pressure cylinder 1, 2. Medium-pressure cylinder, 3. Condenser, 4. Butterfly valve, 5. Temperature and pressure reducing valve group, 6. Heater No. 6, 7. Heater No. 7, 8. Heater No. 8, 9. Heater No. 9, 10. Shut-off valve, 11. Check valve, 12. Heater group. DETAILED DESCRIPTION

[0018] The embodiments of the technical solution of the present application will be described in detail below in conjunction with the accompanying drawings. Unless otherwise specified, the technical terms or scientific terms used in the present application are generally understood by those skilled in the art to which the present invention belongs.

[0019] Figure 1 A 660MW dual low-pressure cylinder unit summer single-cylinder operation system is shown, which includes a heater group 12, an intermediate pressure cylinder 2, a condenser 3, a butterfly valve 4, a temperature and pressure reducing valve group 5, a shut-off valve 10 and two low-pressure cylinders 1; the exhaust end of the intermediate pressure cylinder 2 is connected to the steam inlet ends of the two low-pressure cylinders 1, and the two low-pressure cylinders 1 are connected to the heater group 12 respectively.

[0020] A butterfly valve 4 is installed on the pipes connecting the exhaust end of the medium-pressure cylinder 2 and the steam inlet ends of the two low-pressure cylinders 1, a temperature-reducing and pressure-reducing valve group 5 is installed on the pipe connecting the exhaust end of the medium-pressure cylinder 2 and the steam inlet end of one of the low-pressure cylinders 1, and a shut-off valve 10 is installed on the pipe connecting one of the low-pressure cylinders 1 and the heater group 12;

[0021] When single cylinder operation is performed, the butterfly valve 4 on the pipeline connecting the medium pressure cylinder 2 and one of the low pressure cylinders 1 is closed, the temperature reduction and pressure reducing valve group 5 is opened, the exhaust end of one of the low pressure cylinders 1 is connected to the steam inlet of the condenser 3, and the shut-off valve 10 is closed.

[0022] For example: The 660MW ultra-supercritical unit single reheat wet cooling unit adopts a two-low-pressure cylinder design (low-pressure cylinder No. 1 and low-pressure cylinder No. 2), and the two low-pressure cylinders simultaneously supply steam to the heater group 12. When the single cylinder is cut off in summer, the butterfly valve of the connecting pipe entering the No. 1 low-pressure cylinder is closed. After the No. 1 low-pressure cylinder is cut off and cut off, in order to avoid the risk of blast overheating of the No. 1 low-pressure cylinder, about 60t / h of cooling steam needs to be introduced into the No. 1 low-pressure cylinder, and the steam source is taken from the exhaust steam of the medium-pressure cylinder 2.

[0023] To prevent steam from flowing back into the No. 1 low-pressure cylinder, a shut-off valve 10 is installed on the pipeline connecting one of the low-pressure cylinders 1 and the heater group 12, and a check valve 11 is installed on the pipeline connecting one of the low-pressure cylinders 1 and the heater group 12.

[0024] The heater group 12 includes a sixth heater 6, a seventh heater 7, an eighth heater 8 and a ninth heater 9 arranged in series; the two low-pressure cylinders 1 are respectively connected to the sixth heater 6, the seventh heater 7, the eighth heater 8 and the ninth heater 9. The energy utilization of the exhaust steam of the low-pressure cylinder is realized by the arranged heaters.

[0025] The seventh heater 7 is connected to the pipeline connected to the sixth heater 6 and the seventh heater 7 through the drain pump. In this way, the recycling of drain water is realized.

[0026] The ninth heater 9 is connected to the condenser 3. In this way, the water after the heat exchange of the ninth heater 9 enters the condenser 3 to achieve condensation and recycling of the water.

[0027] Based on the summer single-cylinder cut-off operation system of the 660MW dual low-pressure cylinder unit in any of the above embodiments, a summer single-cylinder cut-off operation method is also provided, and the operation method comprises:

[0028] S1. Determine the unit's single-cylinder operation restriction conditions, including the intermediate pressure cylinder exhaust pressure and the low pressure cylinder inlet steam temperature;

[0029] S2. Before cutting off one of the low-pressure cylinders 1, adjust the openings of the two butterfly valves 4 at the same time to increase the exhaust pressure of the medium-pressure cylinder 2, thereby increasing the exhaust temperature of the medium-pressure cylinder 2 before cutting off the cylinder;

[0030] S3. During the process of cutting off one of the low-pressure cylinders 1, the other low-pressure cylinder 1 is operated normally, and the butterfly valve 4 on the pipeline of the other low-pressure cylinder 1 is fully opened. At the same time, the butterfly valve 4 and the shut-off valve 10 on the pipeline of one of the low-pressure cylinders 1 are closed, and the temperature reduction and pressure reduction valve group 5 is opened. The steam discharged from the medium-pressure cylinder 2 is converted into cooling steam through the temperature reduction and pressure reduction valve group 5 and sent to one of the low-pressure cylinders 1, ensuring that the temperature difference before and after the unit cylinder cutting meets the operating conditions and meets the unit's deep peak regulation requirements.

[0031] In order to achieve the unit's single-cylinder operation requirement in summer, the unit's single-cylinder operation restriction conditions are as follows:

[0032] 1. After the unit cuts off the No. 1 low-pressure cylinder, the No. 2 low-pressure cylinder is put into use, the low-pressure area is reduced, and when operating at high load, the middle row will be over-pressured, affecting the safety and stability of related equipment such as the steam turbine. During operation, high-load operation needs to be limited, and the middle row pressure needs to be controlled not to exceed 0.490MPa.

[0033] 2. Low-pressure cylinder steam inlet temperature limit

[0034] When the unit is running with a single cylinder cut off, it is necessary to monitor the low-pressure cylinder inlet steam temperature and make sure it does not exceed 350℃ to ensure the safe operation of the low-pressure cylinder. If it exceeds 350℃, the main steam and reheat temperature can be lowered. Combined with the middle row pressure limit and calculated based on the reheat temperature dropping to 595℃, the maximum load of the unit running with a single cylinder cut off in summer is 311.3MW.

[0035] 3. Limitation of the heating rate of the low-pressure cylinder

[0036] When the unit is running with a single cylinder cut off, the exhaust temperature of the intermediate pressure cylinder 2 and the steam inlet temperature of the No. 2 low pressure cylinder are close to 350℃. Under the same main steam flow, the operating parameters of the intermediate position when running normally with two low pressure cylinders and when running with one low pressure cylinder cut off are shown in the following table:

[0037]

[0038] From the operating parameters shown in the table above, it can be seen that when the unit is instantly switched to the single-cylinder operation state, the exhaust pressure of the intermediate pressure cylinder 2 increases, causing the exhaust temperature of the intermediate pressure cylinder 2 to instantly rise by 85.6℃. The temperature rise rate is too fast, which will cause the expansion difference of the unit to increase and reach the alarm limit value, affecting the safe operation of the unit. To solve this problem, the following measures can be taken:

[0039] (1) Before the unit cuts off a low-pressure cylinder, adjust the opening of the two connecting pipe butterfly valves at the same time to increase the exhaust pressure of the intermediate-pressure cylinder 2, thereby increasing the exhaust temperature of the intermediate-pressure cylinder before the cylinder is cut off; during the cylinder cut-off process, the steam inlet butterfly valve of the No. 2 low-pressure cylinder is fully opened during normal operation, and the steam inlet butterfly valve of the No. 1 low-pressure cylinder is closed at the same time to ensure that the temperature difference before and after the unit cylinder cut-off is within a reasonable range.

[0040] (2) Before the unit cuts off the cylinder, the steam inlet temperature of the intermediate pressure cylinder 2 is first reduced to avoid a large temperature difference before and after the unit cuts off the cylinder. According to preliminary calculations, the steam inlet temperature of the intermediate pressure cylinder 2 is reduced by 40°C and the exhaust temperature of the intermediate pressure cylinder 2 is reduced by 27.9°C.

[0041] 4. Minimum cooling flow control of No. 2 low-pressure cylinder

[0042] Under low load conditions, the exhaust volume flow of the steam turbine is small, which will directly lead to increased operating risks and life loss of the last two stages of blades, and easily cause increased erosion rate and dynamic stress of the last two stages of moving blades. When the back pressure is high, the exhaust cylinder outlet temperature will increase due to blade blasting. The exhaust volume flow of the low-pressure cylinder cannot be accurately detected. The minimum cooling flow of the low-pressure cylinder can be controlled by detecting the low-pressure cylinder inlet pressure. The relationship between back pressure and the minimum inlet pressure of the low-pressure cylinder is as follows: Figure 2 As shown in the curve.

[0043] According to the above operating restrictions, the summer back pressure is calculated to be 9.2kPa, the main steam temperature is 600℃, the intermediate pressure cylinder inlet steam temperature is calculated to be 600℃, and the minimum operating load is 137.2MW.

[0044] The unit's summer single-cylinder operation system can meet the unit's deep peak-shaving requirements. Based on the back pressure of 9.2kPa, the unit's peak-shaving operation range is 137.2MW-311.3MW.

[0045] For example: Combine Figure 1Note: If the No. 1 low-pressure cylinder is cut off, only 60t / h of cooling steam is considered; if the No. 2 low-pressure cylinder operates normally, the middle row pressure is not higher than 0.490MPa, the low-pressure cylinder steam inlet temperature is not higher than 350℃, the back pressure is 9.2kPa, and the medium-pressure cylinder steam inlet temperature is 600℃. The minimum operating load is calculated to be 137.2MW; if the back pressure is reduced, the minimum operating load will also be reduced. Conventionally, the two low-pressure cylinders operate at the same time in summer with back pressure of 9.2kPa, and the minimum operating load is 290MW. If a single cylinder is cut off in summer, the deep adjustment capacity of the unit increases by 152.8MW.

[0046] The present invention has been disclosed as above with preferred implementation cases, but it is not intended to limit the present application. Any technician familiar with the profession can make slight changes or modifications to equivalent implementation cases with equivalent changes by using the above-disclosed structures and technical contents without departing from the scope of the technical solution of the present application, which still fall within the scope of the technical solution of the present application.

Claims

1. A summer single-cylinder operation system for a 660MW dual-low-pressure cylinder unit, comprising a heater group (12), an intermediate-pressure cylinder (2) and two low-pressure cylinders (1); the exhaust end of the intermediate-pressure cylinder (2) is connected to the steam inlet ends of the two low-pressure cylinders (1), and the two low-pressure cylinders (1) are respectively connected to the heater group (12), characterized in that: It also includes a condenser (3), a butterfly valve (4), a temperature and pressure reducing valve group (5) and a shut-off valve (10); A butterfly valve (4) is installed on the pipelines connecting the exhaust end of the medium-pressure cylinder (2) and the steam inlet ends of the two low-pressure cylinders (1), a temperature-reducing and pressure-reducing valve group (5) is installed on the pipeline connecting the exhaust end of the medium-pressure cylinder (2) and the steam inlet end of one of the low-pressure cylinders (1), and a shut-off valve (10) is installed on the pipeline connecting one of the low-pressure cylinders (1) and the heater group (12); When single-cylinder operation is performed, the butterfly valve (4) on the pipeline connecting the medium-pressure cylinder (2) and one of the low-pressure cylinders (1) is closed, the temperature-reducing and pressure-reducing valve group (5) is opened, the exhaust end of one of the low-pressure cylinders (1) is connected to the steam inlet of the condenser (3), and the shut-off valve (10) is closed.

2. According to claim 1, a 660MW dual low-pressure cylinder unit summer single-cylinder operation system is characterized by: It also comprises a check valve (11), wherein the check valve (11) is installed on a pipeline connecting one of the low-pressure cylinders (1) and the heater (12).

3. According to claim 1, a 660MW dual low-pressure cylinder unit summer single-cylinder operation system is characterized by: The heater group (12) comprises a sixth heater (6), a seventh heater (7), an eighth heater (8) and a ninth heater (9) which are arranged in series; the two low-pressure cylinders (1) are respectively connected to the sixth heater (6), the seventh heater (7), the eighth heater (8) and the ninth heater (9).

4. According to claim 3, a 660MW dual low-pressure cylinder unit summer single-cylinder operation system is characterized by: The seventh heater (7) is connected to the pipeline connecting the sixth heater (6) and the seventh heater (7) through a drain pump.

5. According to claim 3, a 660MW dual low-pressure cylinder unit summer single-cylinder operation system is characterized by: The ninth heater (9) is connected to the condenser (3).

6. A summer single-cylinder operation method for a 660MW dual low-pressure cylinder unit, characterized in that: Based on the implementation of the operating system according to any one of claims 1 to 5, the operating method comprises: S1. Determine the unit's single-cylinder operation restriction conditions, including the intermediate pressure cylinder exhaust pressure and the low pressure cylinder inlet steam temperature; S2, before cutting off one of the low-pressure cylinders (1), the openings of the two butterfly valves (4) are adjusted simultaneously to increase the exhaust pressure of the medium-pressure cylinder (2), thereby increasing the exhaust temperature of the medium-pressure cylinder (2) before cutting off the cylinder; S3. During the process of cutting off one of the low-pressure cylinders (1), the other low-pressure cylinder (1) is operated normally, and the butterfly valve (4) on the pipeline of the other low-pressure cylinder (1) is fully opened. At the same time, the butterfly valve (4) and the shut-off valve (10) on the pipeline of one of the low-pressure cylinders (1) are closed, and the temperature reduction and pressure reduction valve group (5) is opened. The steam discharged from the medium-pressure cylinder (2) is converted into cooling steam through the temperature reduction and pressure reduction valve group (5) and sent to one of the low-pressure cylinders (1), so as to ensure that the temperature difference before and after the unit cylinder cutting meets the working condition requirements and meets the unit deep peak regulation requirements.

7. A summer single-cylinder operation method for a 660MW dual low-pressure cylinder unit according to claim 6, characterized in that: In step S1, the exhaust steam pressure of the intermediate pressure cylinder (2) is below 0.490 MPa, and the inlet steam temperature of the low pressure cylinder is below 350°C.

8. The summer single-cylinder operation method of a 660MW dual low-pressure cylinder unit according to claim 6 is characterized by: Before the unit cuts off the cylinder, the steam inlet temperature of the intermediate pressure cylinder (2) is first reduced. The steam inlet temperature of the intermediate pressure cylinder (2) is reduced by 40°C, and the exhaust temperature of the intermediate pressure cylinder (2) is reduced by 27.9°C.

9. A summer single-cylinder operation method for a 660MW dual low-pressure cylinder unit according to claim 6, characterized in that: The peak-shaving operation range of the unit is 137.2MW-311.3MW. The minimum load of the unit when operating with a single cylinder in summer is 137.2MW, and the maximum load of the unit when operating with a single cylinder in summer is 311.3MW.

10. A summer single-cylinder operation method for a 660MW dual low-pressure cylinder unit according to claim 6, characterized in that: When the two low-pressure cylinders (1) are in operation at the same time, the exhaust pressure of the medium-pressure cylinder (2) is 0.241 MPa, the exhaust temperature of the medium-pressure cylinder (2) is 261.6°C, and the exhaust flow rate of the medium-pressure cylinder (2) is 15.43 t / h. Under the highest load condition after cutting off a single cylinder in summer, the exhaust pressure of the medium-pressure cylinder (2) is 0.490 MPa, the exhaust temperature of the medium-pressure cylinder (2) is 347.2°C, and the exhaust flow rate of the medium-pressure cylinder (2) is 18.16 t / h.

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