Story Two: An unforgettable incident from the tower operation.

Catalytic fractionation results in a high dry point for the crude gasoline; reducing the top of tower temperature to 105 degrees solves this issue and makes the dry point acceptable. However, the recycle stream from the top of the tower contains water, and the pump used for this recycle stream is prone to cavitation, which can lead to tower flooding； It kept happening for several days without any solution.

At that time, there was no pressure indicator on the top of the tower; only on-site gauges were available, and they were installed at a high location. Routine inspections are hardly carried out, and no one pays attention to the pressure at the top of the tower; everyone assumes that it remains stable. Since we don’t have any means to control it, we simply ignore it. Several consecutive days of failing tests, with evaluation forms from the production department arriving every day – the poster is really frustrated ； That day, the poster, being in a bad mood, went up to the reflux tank at the top of the distillation tower to take a look. He checked the pressure there – wow, 64 kPa ； It used to be a steady 50 kPa; why is it so high now? Nothing has changed again. But the reason for the failure was finally identified: excessive pressure at the top of the tower!

Continuing the story: The pressure at the top of the tower is too high. Why? It has been working normally all along, and there haven’t been any major changes recently either! Feed rate, reflux rate, top temperature, temperature after cooling... each of these is checked individually; even the composition of the rich gas and the boiling range of the crude gasoline remain relatively stable ； I’m completely baffled.

This post was last edited by altpage on 2016-12-25 at 17:27. It’s been many days; I almost forgot about this post. Today, I uncovered the mystery: I was in a bad mood that day, so I went up to the top of the distillation column and the reflux tank. The pipes at the top of the tank were quite complex. Suddenly, my hand touched the pressure supply line that carried gas back to the top of the distillation column; it felt slightly hot to the touch. That was strange – the control valve for that pressure supply line was already closed, and both the upstream and downstream valves were also shut. So why was there still flow of material in that pipeline? Going down to the ground level and checking the control valve assembly, I found that the bypass was warm, which clearly indicated that material was flowing through it. A \"F\" wrench was used to tighten the bypass valve a couple of times; the sound of fluid flowing in the pipeline ceased immediately. The control room was promptly informed to adjust the operation of the distillation tower by raising its top temperature to 110. Two hours later, the reflux stream no longer contained water, and its flow rate became stable. Another hour passed before samples were taken, and the dry point of the crude gasoline met the required standards ； The problem that had been plaguing the device for three days was accidentally solved.

Over a decade ago, during distillation operations, a malfunction in the level control of the flash tower caused heavier components to enter the top of the tower, resulting in discoloration of the naphtha; timely adjustments were made to prevent contamination of the semi-finished product tanks.