An accident occurred during evaporation shutdown; please provide an analysis
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This morning, while shutting down Phase 3 of the evaporation process – with Phases 2 and 3 being fed by a single stream of medium-temperature, medium-pressure steam split into two paths – the operator informed me that the vacuum level in Phase 2’s second effect was at -0.05 kPa, while the vacuum level in Phase 2’s first effect was increasing (between -90 and -87 kPa). I tried to adjust the vacuum level, but it continued to rise. The operator then said that the temperature of the surface condenser had increased; I noticed that the vacuum pump was hot and no cooling water was flowing out. After informing the operator of this, I shut down the vacuum pump, but restarting it didn’t help, so I shut it down again. By this time, the evaporation process had entered interlock mode. The operator instructed me to start the circulation system and close the steam valves on the second floor. Ten minutes later, the pressure in the main pipeline for medium-temperature, medium-pressure steam rose sharply to 8.7 MPa. I opened the steam valves for Phase 2 and also opened the pressure relief valve at the top of unit 1301 in Phase 2 to release pressure. At that point, the pressure inside Phase 2’s second effect had dropped to 0.47 MPa, while the pressure in the medium-temperature, medium-pressure steam pipeline decreased； Please analyze it – what is the reason?
There is no lye left in the second-effect evaporator
Is your evaporation a three-effect counterflow process?
It’s not detailed enough; it would be best to explain the process
Based on the available information, it’s indeed difficult to judge. The continuous changes in pressure are most likely caused by the instability in the pumping capacity of the vacuum system and the amount of gas generated (which may also be secondary steam); if these factors were stable, then the system pressure should remain relatively constant. If the vacuum pump heats up, the efficiency of the vacuum system will inevitably decrease, the pumping capacity will drop, and the pressure ahead will increase – this is a logical consequence ； Why does a vacuum pump get hot? One of the reasons is poor performance of the condenser; if it’s a water ring pump, a lack of cooling for the pump itself is also a cause. In your case, it’s likely due to poor performance of the condenser. But why is the vacuum level keeping dropping as we move forward? This contradicts the poor performance of the condenser; it’s unclear when this reversal occurs and what actions are taken in between, so it can only be guessed.