Abnormal pressure rise reason analysis and handling of the shaft sealing system

Shaft seal abnormal pressure rise reason analysis and handling 2019 - 03 - 25 huangxin operation strategy on July 9, a hot start-up, succession when researchers found that in the process of round plate MARKVie system STEAMSEAL page unit shaft seal pressure to zero. 34 kg/cm2, the load of 300 mw unit. After found abnormal shaft seal pressure, check the shaft seal pressure setting, confirm the shaft seal for Auto pressure control mode, the set value is 0. 25 kg/cm2, ruled out the possibility of accidentally set shaft seal pressure setting. Shaft with the fan running and vacuum is normal, rule out the possibility of a shaft with low vacuum. Shaft seal pressure control valve opening show was 0%, the pressure relief valve shows that 100% of the shaft sealing system. Knowledge theory guide turbine shaft seal system of the main equipment are shaft seal pressure control valve, the leakage of the shaft seal valve, shaft, shaft seal cooler and fan, etc. In the high pressure section of steam turbine, the normal function of the shaft sealing system is to prevent the steam leak outward, in order to ensure that the steam turbine with high efficiency; In the low pressure section of steam turbine, it is to prevent outside air into the steam turbine, guarantee the vacuum steam turbine is as high as possible, and to ensure the efficiency of steam turbine unit. At the beginning of the steam turbine unit start-up, shaft seal pressure control valve to control pressure, shaft seal steam mother tube shaft seal steam to high school low pressure cylinder of paragraphs, the shaft seal pressure relief valve closed. With the increase of load, the high pressure cylinder steam will overflow into the shaft seal mother tube, pressure is higher than the set value, the shaft seal mother tube shaft seal pressure control valve shut down gradually, shaft seal pressure relief valve gradually open the control pressure, shaft seal mother tube made redundant shaft seal steam entering the condenser, also called the seal at this stage. Shaft seal of the unit after cast shaft seal vacuum pressure should be controlled in 0. 25 kg/cm2, shaft seal pressure will lead to low vacuum, high and middle pressure cylinder gas leakage, shaft seal pressure can lead to high lubricating oil in the water, oil. Analytical processing strategy analysis after discussion, draw three possibilities. Within a shaft seal pressure control valve is leaking or the actual valve opening do not tally with the display, auxiliary steam, through the pressure control valve leakage of shaft seal to shaft sealing pipe, the shaft seal pressure. The second is the leakage of the shaft seal valve opening do not tally with the show actually, high-pressure gas leakage is pressure relief and the shaft seal pressure to zero. 34kg/cm2。 The deficiency in the high-pressure section three seal tile, high pressure steam leakage quantity larger than ever before and the leakage of the shaft seal when the valve is fully open still cannot maintain the shaft seal pressure to zero. 25公斤/平方厘米。 Two valve on-site inspection, the actual opening more difficult to judge. So run the researchers decided to manual operation to correct two road. First of all, the first possibility of illness. In situ after close the shaft seal pressure control valve isolation valves, observe whether the unit shaft seal pressure is falling. After close the isolation valve, the slow down shaft sealing pressure, and until the 0. 30 kg/cm2, the shaft seal pressure control valve is a certain degree of leakage phenomenon. But according to the experience of operators, this valve before there is also a small amount of leakage, and close the rear axle seal pressure have fallen, but they are still greater than the normal operation of unit value, internal leakage of shaft seal pressure regulator is not the main reason for the shaft seal pressure; Because the valve is not a serious defect, and the valve during downtime or load still need to use a lot of fall, so cannot isolate them, therefore reopened isolation valves, restore its normal use. Again for a second possibility. Shaft seal pressure relief valve with manual by-pass and before and after the isolation valve. Operators slightly open shaft seal pressure relief valve, by-pass valve gradually closing shaft seal before the pressure relief valve isolation valve. In front of the closed pressure relief valve of the shaft sealing isolation valves in the process of the strict observation of shaft seal pressure change trend, found that the shaft seal pressure basic no change, Explain the main valve basic original has been is closed state) 。 Open the bypass valve to around a third opening, unit shaft seal pressure back to normal pressure at runtime. The basic judging is the relief valve stem appear fall off of the shaft sealing system. Report long-term value, and try to hold the load, closely monitor the shaft sealing pressure, notify immediately after repair, restore valve is normal. Follow-up after emergency repair work, the shaft seal pressure relief valve is back to normal, the shaft seal pressure controlled to 0. 25公斤/平方厘米。 Under the same load, the shaft seal close to the relief valve opening and the historical data, according to rule out a third abnormal reason, unit seal tile damage is evil does not exist. Summarize strategy if the shaft seal appeared in the process of the equipment operation pressure is high, to determine whether a shaft seal pressure setting is wrong, first check valve status and feedback, can manually adjust appropriately shaft plus increase fan inlet valve shaft and vacuum. Shaft seal pressure control valve and the shaft seal has manual bypass pressure relief valves, manual adjustment of the opening of the by-pass control when necessary mother tube pressure of the shaft sealing system.