Temperatures of extraction from the first pressure reduction stage and the second pressure reduction stage in the operation of a vacuum distillation tower?

The operational balance of the vacuum distillation tower involves a reaction process, and it is also necessary to monitor whether there are any fluctuations in the properties of the raw materials. Changes in product distribution?

This post was last edited by mpcchuang on 2010-5-31 at 09:37. You have also observed this situation; it should be understood in this way: when the temperature of the fluid drawn from line 1 increases, more heat energy accumulates at the top of the tower. This results in an increasing flow rate of fluid returning from the top of the tower in order to keep the temperature there under control. At the same time, the temperature of the fluid drawn from line 1 also rises. As more cold fluid is circulated back to the top of the tower, heat is absorbed as well. Where does this heat come from? It can only come from the vapor temperature in line 1. As heat moves upward, the temperature of the fluid drawn from line 1 actually decreases. This is not a normal phenomenon; it disrupts the temperature gradient throughout the tower and disturbs the balance between the vapor and liquid phases as well as the material balance. If this continues, enough heat will accumulate at the top of the tower, which can lead to accidents in large-scale installations. At the beginning of the year, I saw on this forum operational data from Guangxi Petrochemical Plant, where one set of vacuum distillation units shared the same infrastructure as two sets of atmospheric distillation units. On March 17th, an oil leakage incident occurred due to a problem with the seal of a pump used in the vacuum distillation unit – the fire that resulted was quite severe. It’s not clear whether this incident happened in that plant with an annual production capacity of 8 million tons. If so, it’s necessary to investigate the causes not only in terms of the equipment but also in terms of operating procedures. To maintain the balance between the vapor and liquid phases as well as the material balance in the vacuum distillation tower, it’s important to pay attention to the flow rates in both the atmospheric distillation unit and line 1

Reply to 3# mpcchuang: Hello, our top temperature is very low, generally not exceeding 45 degrees. The temperature of the material drawn from line 1 varies between 80 and 120 degrees. Very little product comes out of line 1; most of it goes back into the system through reflux. The top temperature is also low in this case, and we rarely adjust the amount of reflux. The density of the material on line 1 is currently only 860, while that on line 2 is 880. Have you encountered a similar situation? Please give me your advice. At our plant, the temperature ranges from 163 to 200 degrees – of course, this is relative to the temperature at the main extraction point. It seems that production is normal and the quality of the asphalt is fine, but I still feel something is off. At least, as you said, there seems to be an imbalance in the tower, and a temperature gradient should exist. Another issue is that the temperature drawn from stage 2 of the reduction process is basically 200 degrees, with the liquid level kept at its maximum level. Since part of the stream goes to stage 2 of the reduction process, it is necessary to operate the tower at full capacity in order to maintain stability. The gas phase from stage 2 returns to the tower at around 210 degrees; will there be some liquid phase flowing back as well? I would like to ask if this has any impact on not reducing the first line? It should be almost time to pull it out at normal pressure; pulling more will affect the color~! It’s been reduced by more than one degree; the top circulation liquid level will drop. That’s a problem. I’m worried – will something really go wrong? I’m scared...

This post was last edited by mpcchuang on 2010-6-1 at 11:16. Does your unit have a capacity of over 500 tons per year? If it’s a smaller unit, accidents are less likely to occur. We’ve encountered situations where the backflow at the top of the column was too high; the automatic temperature control system wasn’t sufficient, and the reduction in flow rate wasn’t timely, which led to the tearing of the valve cover at the inlet of the bottom pump and resulting oil spraying and fire. Keep in mind that the inlet pressure is zero, so it’s the stress that causes these problems. Regarding the issue you raised, too low a temperature at the top of the column can cause corrosion of the trays or packing in that area. A low top temperature also hinders the production of more diesel fuel in the first extraction line. Your side stream probably produces fractionated oil; with such a configuration, the range of the produced oil might be wide. We once had a system similar to yours, but we later changed it to an independent intermediate reflux system. Generally speaking, the vapor temperature for the second extraction should be higher than the temperature of the liquid returning to the column. After extraction in the second line, the liquid should be sent in two directions: one path goes out of the unit, while the other is used as the intermediate reflux returning to the column. The temperature of this intermediate reflux should be lower than the extraction temperature. However, the vapor temperature returning to the column in your case is around 210 degrees, which confuses me. If you need my help with analysis, just send me the operational data via email

We have a vacuum distillation unit with a capacity of 1 million units. Our vacuum tower is structured as follows: 1. The tower consists of 7 stages of packing; in the top vapor recovery section (the first stage of vacuum distillation), part of the vapor is used to produce products while another part is recycled； 2. At Min-1 Medium and Min-2 Medium, remove the lines on the second, third, and fourth sides as well as the associated stripping tower ； 3. Neither the washing oil nor the superheated oil came out. 4. Vacuum -93; top temperature below 45°. Extraction at 115° in the first stage of reduction; reflux rate of 30,000 kg/h, with no external discharge. Extraction at 173° in the second stage of reduction; flow rate of 20,000 kg/h; return to the tower at 167°. Distillation in the second stage occurs at 207°, with return to the tower at 215°. The gas phase returns to the tower below the distillation point. Part of the material from the second stage is sent to another unit, while part goes to the second intermediate stage of reduction; extraction there is at 275°, with return to the tower at 200°. The reflux rate is 33,000 kg/h. 5. The processing capacity is 2800 T/d; if the oil removal isn’t adequate, it will affect the bottom pump. If you can, please help me resolve this issue. I also had an interesting problem with deformation in the vacuum tower before.

How can the top cooling temperature be controlled at 45 degrees? In our facility, it’s kept around 110 degrees

It is normal to keep the degassing temperature at 45 degrees; under such conditions, the gas produced during degassing consists mainly of steam and non-condensable gases. If the temperature reaches 110 degrees, it indicates that the gas contains a large amount of diesel components, which is not favorable for vacuum creation and also reduces the yield of diesel from the first distillation stage. I also have a question: with a top pressure reduction of 110°C, is it a lubricating oil-type vacuum distillation tower? What is the temperature of the liquid circulating back from the top pressure reduction process? Also, is the amount of dirty oil in the top pressure reduction water seal tank relatively large? Is there an oil-water separator downstream?

Our secondary vapor return column temperatures are all at 220°C. The dry point of the paraffin oil reaches 600–605℃

I suggest that if you have the chance, stop and check the internal components of the Chata. We’ve encountered similar issues before; upon opening it, we found problems with the reduction line