A method for eliminating large differential expansion during cold start of an ultra-high temperature subcritical unit

Abstract

The present invention relates to a method for eliminating large differential expansion during cold start of an ultra-high temperature subcritical unit, and the specific steps are as follows: (I) Ignite and boost pressure, evacuate, and send shaft seal steam source for preheating; (II) Rotor start-up and warm-up, 1. Select start-up parameters, 2. Control the back pressure of the unit, 3. When the speed rises to 500 r / min, conduct a 10-minute friction inspection, and directly raise the speed to 1300 r / min for medium-speed warm-up for about 30 min; 4. Raise the speed to 2500 r / min for high-speed warm-up; (III) Constant speed warm-up, when the speed rises to 3000 r / min, the warm-up time is 20 - 30 minutes; (IV) Grid connection and initial load warm-up, connect to the grid and carry an initial load of 5 - 10% of the rated load, and continue to warm up; (V) Load increase and warm-up, when the cylinder temperature rises to be less than 40 °C different from the main steam temperature, continue to raise the main and reheat steam temperatures by 20 - 30 °C, and continue to warm up. This method solves the problems that have troubled the cold start of ultra-high temperature subcritical generator sets, such as large differential expansion, slow start-up speed, and even unit tripping, improves the efficiency of the unit to quickly carry load, and significantly reduces economic losses.

Description

Technical Field

[0001] The present invention belongs to the field of power equipment, and particularly relates to a method for eliminating large differential expansion during cold start-up of an ultra-high temperature subcritical unit. Background Technique

[0002] Currently, during the cold start-up process of the ultra-high temperature subcritical unit of Taigang's gas power generation, the differential expansion of the high-pressure cylinder gradually increases. After taking various control measures, the effect is not obvious. After grid connection, the differential expansion protection action occurs within less than 1 hour of operation, forcing the unit to trip. It cannot be started temporarily, affecting the balance of the gas system, resulting in a large amount of gas being vented, and seriously directly affecting the safety of the gas system and the safe operation of the unit.

[0003] Cause Analysis:

[0004] ① Improper selection of starting parameters; ② Premature input of the steam seal system or improper parameter control; ③ Excessive parameter fluctuations in each link; ④ Failure to promptly input the interlayer heating and conduct regular drainage; ⑤ Too low or unstable back pressure; ⑥ Too fast load increase or insufficient warm-up time. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a method for eliminating large differential expansion during cold start-up of an ultra-high parameter steam turbine unit. By comprehensively analyzing and judging the entire cold start-up process, the key links and key control parameters are found, and the key control points of each are clarified for control.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for eliminating large differential expansion during cold start-up of an ultra-high parameter steam turbine unit, the specific steps are as follows:

[0008] (I) Ignition and pressure rise

[0009] The boiler is ignited and the pressure is raised. When the cold unit waits for the boiler pressure to start changing, vacuum is pumped, and at the same time, the shaft seal steam source is sent for preheating. During preheating, all the supply branches of the steam seal must be closed. When the temperature at the monitoring point of the steam seal system rises to 200 °C, steam is supplied to the high, medium, and low steam seals, and vacuum pumping continues. At this time, the supply steam temperature of the steam seal is controlled at 180 °C, specifically close to the cylinder temperature, and the differential expansion increases in the positive direction.

[0010] (II) Starting and warm-up

[0011] 1. Selection of starting parameters: The pressure is 3.5 MPa, the temperature is 340 ± 10 °C, the reheat pressure is 0.68 MPa, and the temperature is 325 ± 5 °C.

[0012] 2. Control the back pressure of the unit at 25 ± 2 KPa, and control it by means of putting into and withdrawing the vacuum pumping system to ensure that the parameters are basically constant and slightly higher, and the maximum does not exceed 30 KPa.

[0013] When the speed is increased to 500 r / min, conduct a 10-minute friction inspection, then directly increase the speed to 1300 r / min for medium-speed warm-up for about 30 min. The differential expansion continues to increase in the positive direction, and the vibration parameters are normal after the warm-up is completed.

[0014] 4. Directly increase the speed to 2500 r / min for high-speed warm-up. The warm-up time is 30 - 60 minutes. The differential expansion continues to increase in the positive direction. After the warm-up is completed, the cylinder temperature continues to increase while remaining around 250 °C.

[0015] (III)Constant-speed warm-up

[0016] When the speed is increased to 3000 r / min, keep the steam temperature and steam pressure constant and continue to warm up. The warm-up time is 20 - 30 minutes. After the warm-up is completed, the cylinder temperature is basically at 280 - 300 °C, and prepare for grid connection.

[0017] (IV)Grid connection and initial load warm-up

[0018] Connect to the grid and carry an initial load of 5 - 10% of the rated load, and continue to warm up. When the difference between the cylinder temperature and the main steam temperature is less than 30 °C, increase the temperature by 30 °C. When the differential expansion is constant and does not increase, appropriately increase the load and continue to warm up.

[0019] (V)Load increase warm-up

[0020] Keep the back pressure of the steam turbine stable. When the cylinder temperature rises to a difference less than 40 °C from the main steam temperature, continue to increase the temperature of the main and reheat steam by 20 - 30 °C and continue to warm up to complete the load increase warm-up work. When the high-pressure differential expansion of the steam turbine is stable and shows a downward trend, open the valve position and increase the boiler pressure to achieve load increase. At the same time, when the absolute expansion is greater than 40 mm, continue to increase the parameters and carry the load until the differential expansion decreases and the absolute expansion reaches the normal operating value, and then quickly carry the load to complete the warm-up work for the entire cold start. At this time, important parameters such as the main steam parameters, cylinder temperature, and differential expansion are all close to the normal operating parameters.

[0021] The key control links in each step are:

[0022] ① The selection of each parameter is very important. The selection principle is to ensure that the main steam temperature is 50°C higher than the cylinder temperature (regulating stage metal temperature) and is strictly prohibited from exceeding 60°C. ② The back pressure should be slightly higher than the rated value and constant. ③ Auxiliary steam must be used as the steam source for the cold startup steam seal. Fresh steam is strictly prohibited for the steam seal before the load drops below 20MW. ④ Ensure that the cylinder body drain is open normally. When the differential expansion exceeds 3.5mm, inject heating steam from the external cylinder interlayer to heat the outer cylinder. Ensure that the high-pressure cylinder startup drain is drained for 30 seconds every 5 minutes and then closed. When the differential expansion is less than 3mm, remove the interlayer heating steam. ⑤ Control the load increase rate after grid connection and ensure the initial load warm-up. The conditions for load increase are that the high-pressure cylinder differential expansion tends to stabilize and the cylinder temperature approaches the main steam temperature. Increase the main steam temperature and continue warming up. Pay attention to absolute expansion to ensure that the outer cylinder expansion is in place. Otherwise, do not increase the load rapidly. ⑥ If the differential expansion increases too quickly during the warm-up process, quickly and appropriately reduce the main reheat steam temperature to curb the increase rate. However, the steam superheat must be ensured to be no less than 50°C.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] By selecting various parameters, putting the steam seal system into operation and controlling the warm-up time, the difficult problems that plagued ultra-high temperature subcritical generator sets, such as large cold start expansion difference, slow start speed and even unit tripping, were solved. The damage to the unit caused by frequent start and stop of the unit was eliminated, the efficiency of the unit in quickly taking on load was improved, the frequency of frequent operation of the unit was reduced, and the safe and stable operation of the unit was ensured; the friction of the unit engine was avoided, and the startup time was greatly shortened. Generally, the rated load of the unit can be reached within 10 hours, reducing economic losses. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to specific embodiments.

[0026] A method for eliminating large expansion difference during cold start of ultra-high temperature subcritical units, comprising the following specific steps:

[0027] (1) Ignition boost

[0028] The boiler is ignited and the pressure is increased. When the boiler pressure of the cold unit begins to change, vacuum is drawn and steam is supplied to the shaft seal for preheating. During preheating, all steam seal supply branches must be closed. When the temperature of the steam seal monitoring point rises to 200℃, steam is supplied to the high, medium and low steam seals and vacuum is continued. The steam supply temperature of the steam seal is controlled at 180℃, which should be as close to the cylinder temperature as possible. The expansion difference increases in the positive direction.

[0029] Note: ① The steam seal system shall not be put into operation too early, as it is likely to cause too rapid increase in differential expansion. The steam seal system shall be put into operation when the boiler starts to have pressure changes or when the main steam pressure is 0.2 - 0.5 MPa. Before the steam seal and vacuum systems are put into operation, it must be ensured that the boiler's atmosphere vent is open, the high and low bypasses are closed, and the main steam pipeline drain to the exhaust device is closed; ② The high and low bypasses shall be put into operation as early as possible. They shall be put into operation when the main steam pressure is 0.5 MPa. Otherwise, the boiler's temperature and pressure increase shall be stopped. At the same time, the condition for putting the high and low bypasses into operation is that the steam seal and vacuum systems must be put into normal operation.

[0030] (II) Rotor impulse and warm-up

[0031] 1. Selection of impulse parameters: Select a pressure of 3.5 MPa, a temperature of 340 ± 10 °C, a reheater pressure of 0.68 MPa, and a temperature of 325 ± 5 °C.

[0032] 2. Control the back pressure of the unit at 25 ± 2 KPa. Control it by putting the vacuum system into or out of operation to ensure that the parameters are basically constant and slightly higher, with a maximum not exceeding 30 KPa.

[0033] 3. When the speed is increased to 500 r / min, conduct a 10-minute friction inspection, and then directly increase the speed to 1300 r / min for medium-speed warm-up for about 30 min. The differential expansion continues to increase in the positive direction, and the vibration parameters are normal after the warm-up ends.

[0034] 4. Directly increase the speed to 2500 r / min for high-speed warm-up. The warm-up time is 30 - 60 minutes. The differential expansion continues to increase in the positive direction. After the warm-up ends, the cylinder temperature is around 250 °C and continue to increase the speed.

[0035] Note: ① The selection of impulse parameters is quite crucial. The main and reheater temperatures are 30 - 50 °C higher than the metal temperature of the governing stage and ensure a superheat degree of more than 60 °C. During cold start-up, desuperheating water is not used to avoid water hammer; ② It is not advisable to stay at 500 r / min for a long time. After the friction inspection is completed, directly increase the speed to medium-speed warm-up; ③ The medium-speed warm-up is carried out according to the time required in the instruction manual. After it is completed and the parameters are normal, directly increase the speed to high speed; ④ During the entire warm-up process, it must be ensured that the parameters of the main steam, reheater steam, turbine back pressure, steam seal pressure and temperature remain stable and do not fluctuate suddenly. The steam pressure is adjusted through the high and low bypasses; ⑤ During the speed increase process, it must be ensured that the cylinder body drains are open. It is strictly prohibited to increase the speed and warm up without opening the drains. If the vibration of the unit is still high after the warm-up ends, the warm-up time should be extended or even the speed should be reduced for warm-up.

[0036] (III) Constant-speed warm-up

[0037] When the speed is increased to 3000 r / min, keep the steam temperature and pressure constant and continue to warm up. The warm-up time is 20 - 30 minutes. After the warm-up ends, the cylinder temperature is basically above 280 °C, and prepare for synchronization.

[0038] (IV) Synchronization and initial load warm-up

[0039] Connect to the grid with an initial load of 5 - 10% of the rated load and continue warming up the machine. When the temperature difference between the cylinder temperature and the main steam temperature is less than 30°C, raise the temperature by 30°C. If the differential expansion remains constant without increasing, appropriately increase the load and continue warming up the machine.

[0040] (V) Load increase and warm-up

[0041] Maintain the stability of the turbine back pressure. When the temperature difference between the cylinder temperature and the main steam temperature rises to less than 40°C, continue to raise the temperature of the main and reheat steam by 30°C and continue warming up the machine. Based on this standard, complete the load increase and warm-up work. When the high-pressure differential expansion of the turbine is stable and shows a downward trend, appropriately open the valve position and increase the boiler pressure to achieve load increase. At the same time, when the absolute expansion is greater than 40 mm, continue to increase the parameters and carry the load until the differential expansion decreases and the absolute expansion reaches the normal operating value, then quickly carry the load to complete the warm-up work of the entire cold start. At this time, important parameters such as the main steam parameters, cylinder temperature, and differential expansion are all close to the normal operating parameters.

[0042] Loss of benefit during unit shutdown: 30h * 7 * 0.4 * 2 = 1.68 million yuan (calculated based on 30h).

[0043] Loss during unit startup = 200,000 yuan * 2 = 400,000 yuan

[0044] Cost of personnel organization for startup and shutdown: 2 times * 20,000 yuan = 40,000 yuan

[0045] ① + ② + ③ = Total: 2.12 million yuan / year.

[0046] This method solves the problems that have troubled the cold start of ultra-high temperature subcritical generator units, such as large differential expansion, slow startup speed, and even unit tripping, eliminates the damage caused by frequent unit startups and shutdowns to the unit, improves the efficiency of the unit to quickly carry the load, and significantly reduces the economic loss.

Claims

1. A method for eliminating large expansion differences during cold start of an ultra-high temperature subcritical unit, characterized by the following specific steps: (1) Ignition boost The boiler is ignited and the pressure is increased. When the boiler pressure of the cold unit begins to change, vacuum is drawn and the steam source for the shaft seal is supplied for preheating. During preheating, all the steam seal supply branches must be closed. When the temperature of the steam seal system monitoring point rises to 200℃, steam is supplied to the high, medium and low steam seals and vacuum drawing continues. At this time, the steam supply temperature of the steam seal is controlled at 180℃, which should be close to the cylinder temperature. The expansion difference increases in the positive direction. Auxiliary steam must be used as the steam source for the cold start-up steam seal. It is strictly forbidden to use new steam source to supply the steam seal before the load is lower than 20MW. (2) Warming up 1. The selection of the punching parameters is as follows: pressure 3.5MPa, temperature 340±10℃, reheating pressure 0.68MPa, temperature 325±5℃; 2. Control the back pressure of the unit at 25±2KPa by switching the vacuum system on and off to ensure that the parameters are basically constant and slightly higher, with a maximum value not exceeding 30KPa; 3. When the speed is increased to 500r / min, conduct a 10-minute friction check, then directly increase the speed to 1300r / min and warm up at medium speed for about 30 minutes. The expansion difference continues to increase in the positive direction, and the vibration parameters are normal after the warm-up.

4. Directly increase the speed to 2500r / min for high-speed warm-up. The warm-up time is 30-60 minutes. The expansion difference continues to increase in the positive direction. After the warm-up, the cylinder temperature is around 250℃ and the speed continues to increase. (3) Constant speed warm-up When the speed reaches 3000r / min, keep the steam temperature and pressure constant and continue to warm up. The warm-up time is 20-30 minutes. After the warm-up, the cylinder temperature is basically 280-300℃, and it is ready for grid connection. (IV) Grid-connected initial load warm-up Connect to the grid with an initial load of 5-10% of the rated load and continue warming up. When the difference between the cylinder temperature and the main steam temperature is less than 30°C, increase the temperature by 30°C. If the expansion difference remains constant and does not increase, increase the load appropriately and continue warming up. (5) Load increase and warm-up Keep the turbine back pressure stable. When the cylinder temperature rises to a temperature less than 40°C different from the main steam temperature, continue to increase the main and reheat steam temperatures by 20-30°C, continue to warm up, and complete the load increase warm-up work. When the high-pressure expansion difference of the turbine is stable and shows a downward trend, appropriately open the valve position and increase the boiler pressure to achieve load increase. At the same time, when the absolute expansion is greater than 40mm, continue to increase the parameters and carry the load until the expansion difference drops and the absolute expansion reaches the normal operating value and quickly carry the load to complete the entire cold start warm-up work. At this time, important parameters such as main steam parameters, cylinder temperature, expansion difference, etc. are all close to normal operating parameters.

2. The method for eliminating large expansion difference during cold start of ultra-high temperature subcritical units according to claim 1, characterized in that: In step (1), the steam seal system should not be put into operation too early, as this may cause the expansion difference to increase too quickly. The steam seal system should be put into operation when the boiler pressure begins to change or when the main steam pressure is between 0.2 and 0.5 MPa. Before the steam seal and vacuum system are put into operation, it must be ensured that the boiler exhaust is open, the high and low bypasses are closed, and the main steam pipeline drain to the exhaust device is closed.

3. The method for eliminating large expansion difference during cold start of ultra-high temperature subcritical units according to claim 1, characterized in that: In step (2), the main reheating temperature is 30-50°C higher than the metal temperature of the regulating stage and the superheat degree is ensured to be above 60°C.

4. The method for eliminating large expansion difference during cold start of ultra-high temperature subcritical units according to claim 1, characterized in that: During the entire warm-up process of step (2), the main steam, reheat steam, turbine back pressure, steam seal pressure and temperature parameters must be kept stable. Fluctuations are strictly prohibited and the steam pressure is adjusted through the high and low bypass.

5. The method for eliminating large expansion difference during cold start of ultra-high temperature subcritical units according to claim 1, characterized in that: Ensure that the cylinder body drain is opened normally. When the expansion difference is greater than 3.5mm, input the external cylinder interlayer heating steam to heat the outer cylinder. Ensure that the high-pressure cylinder drain is started and drained for 30s every 5 minutes, and then closed. Exit the interlayer heating steam when the expansion difference is less than 3mm.

6. The method for eliminating large expansion difference during cold start of ultra-high temperature subcritical units according to claim 1, characterized in that: The step (IV) controls the load increase speed after grid connection and performs initial load warm-up. The conditions for load increase are that the high-pressure cylinder expansion difference tends to be stable and the cylinder temperature is close to the main steam temperature. Increase the main steam temperature and continue warming up. Pay attention to absolute expansion to ensure that the outer cylinder expands to the right position. Otherwise, do not increase the load quickly.

7. The method for eliminating large expansion difference during cold start of ultra-high temperature subcritical units according to claim 1, characterized in that: If the expansion difference increases too quickly during the warm-up process, the growth rate can be curbed by quickly and appropriately lowering the main reheat steam temperature, but it must be ensured that the superheat of the steam is not lower than 50℃.