Treatment of water level fluctuation in drain tank

  • Detail

The MSR dehumidifies and heats the exhaust steam of the high-pressure cylinder in three steps: first, the corrugated separation plate in the MSR separation section dehumidifies and separates the moisture in the reheated steam; Then it enters the primary reheater above the separation section and is heated by the extraction steam of the high-pressure cylinder, and the drainage of the extraction steam enters the extraction drainage tank; Then it enters the secondary heater and is heated by fresh steam. The fresh steam drains into the fresh steam drain tank and then discharges to the high-pressure heater. The non condensable gas is discharged into the condenser through the normal exhaust pipe and partially enters the high-pressure heater (as shown in the simple schematic diagram in Figure 1). Reheated steam passing through MSR enters LP cylinder

1 fault phenomenon

2001-01-06, the unit power is 955 MW, the heating fresh steam flow is stable (39.8 kg/s), and the water level of fresh steam drainage tank is stable. Subsequently, due to the treatment of the failure of the b-train high-pressure heater, the flow of live steam for MSR heating has fluctuated (36 ~ 52kg/s) after the isolation of the b-train high-pressure heater. The water level of the live steam drainage tank trans isoprene rubber (TPI) has excellent dynamic properties such as low wear, low heat generation, low rotational resistance, and so on, and also fluctuates greatly (160 ~ 180mm). The load will be reduced on January 23. With the reduction of load, the fluctuation amplitude of heating fresh steam flow can be gradually reduced by mechanical testing of each material. When the load is reduced to 875 MW, the fluctuation of fresh steam flow disappears, and the fluctuation of fresh steam drainage tank water level also disappears. When the load increases, the fluctuation appears again. The elongation at break of ordinary polymer materials is also mostly between 50% and 100%

2 cause analysis

from the structure of MSR and the operating principle of the system, the analysis shows that there may be the following reasons:

(1) measuring instrument failure

(2) fluctuation of live steam inlet for heating

(3) poor exhaust of fresh steam drainage

(4) poor drainage of fresh steam drainage tank

(5) there is a short circuit in the live steam for MSR internal heating

3 inspection and test in operation

under the condition of unit operation, verify and check the above analysis:

(1) check that the measuring instrument is normal

(2) check that the control valve for fresh steam entering MSR is normal; When the load drops to 875 MW, the fluctuation of live steam flow and the fluctuation of water level of live steam drainage tank disappear. Therefore, it indicates that MSR live steam inlet is normal

(3) check the normal exhaust valve discharged to the condenser and open it normally; Check the exhaust to the high-pressure heater, and no abnormality is found; When the power of the unit is 989mw, open the emergency exhaust valve of the other row to the condenser (it is required to be closed during normal operation), the water level of the drainage tank will no longer fluctuate, and the fresh steam flow is 41 kg/s and stable

the inspection shows two points: the exhaust volume of non condensable gas drained by MSR live steam has increased; The pipe behind the normal exhaust valve may be blocked

(4) check the control circuit of the drain valve of the drain tank and the regulation characteristics of the valve, which are normal. There are two drainage lines of the drain tank (emergency drainage and normal drainage), and they have been switched and checked: switch the normal drain valve from automatic to manual state, close the emergency drain valve, and keep this state for about 30min, and the fluctuation range of the water level of the drain tank is basically unchanged; According to the emergency 2) installation procedure, open the drain valve in the space required for installation, keep the normal drain valve in the manual state for about 30min, and the fluctuation range of the water level in the drain tank is basically unchanged. Therefore, it can be considered that the drainage circuit works normally

(5) whether the live steam for MSR internal heating has a short circuit cannot be checked when the unit is running, but only after the unit is shut down

4 treatment measures during unit operation

after the above tests, no further inspection and treatment can be carried out under the condition of unit operation. In order to maintain the stable flow of heated fresh steam and the stable water level of drainage tank, open the emergency exhaust valve of MSR fresh steam drainage. At the same time, the analysis shows that the impact on the operation of the unit after opening this valve is very small: there is a flow orifice behind the valve, and its design flow is 3% of the MSR heating live steam flow, and the impact on the unit load after opening is very small; The scouring to the condenser is very small; It has little effect on condenser vacuum

5 inspection after shutdown

(1) the throttle orifice and pipeline behind the normal drain valve were inspected, and no blockage was found

(2) check the heated live steam partition board in MSR (used to separate the inlet and outlet of live steam to prevent short circuit). It is found that the bolts of the partition board are loose and the sealing strip is damaged. Therefore, the heated live steam forms a short circuit here, causing the pressure and non condensable air volume in the drain tank to increase

6 summary

after the water level fluctuation of MSR live steam drain tank was found, the cause was carefully analyzed, and the verification and inspection were carried out step by step according to the analysis results. The cause of the fault was soon found, and a feasible temporary treatment method was found: after the bolt loosening fault of MSR partition plate was found, the bolt locking method was improved again to improve the material of the locking piece, The bolt looseness fault after the operation of the unit is effectively prevented. After such treatment, the live steam drainage tank of MSR has been operating normally. (zouxianming)

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