Analysis on the causes of abnormalities in the distillation tower of the urea plant

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The distillation tower is operating normally, the liquid level in the distillation tower is automatically controlled, the liquid level display drops, and the distillation tower outlet liquid regulating valve is closed from 56% to 40%. After 20 minutes, the central control found that the high-pressure load was 100%, the liquid level in the urine tank dropped, and the evaporation system load could only be maintained at 70%. Manually open the distillation tower outlet liquid regulating valve to 100%, and then the system load will be stable. Before and after comparison: 1. There is no change in the inlet liquid of the stripping tower, and the outlet liquid pressure and temperature are normal. 2. There is no significant change in the gas phase temperature of the distillation tower. 3. The liquid temperature of the distillation tower is automatically controlled at 135°C, which is 4% to 8% smaller than the previous evaporation heating regulating valve. 4. The liquid level of the distillation tower shows -1.26%. 5. The liquid outlet regulating valve of the distillation tower must be kept fully open and closed from 100% to 90%. The distillation tower is overpressured. 6. There is no obvious change in the low-pressure system, and the water inlet regulating valve of the temperature-regulated water heat exchanger is closed by 10%. Please help me analyze the reason. If the description is not clear, please add QQ81477112 to communicate.