Diesel extraction temperature
Thread Content
There are two diesel extraction ports in the catalytic fractionation tower of our plant. The 13th layer from the top is the upper extraction port, and the 15th layer is the lower extraction port. Generally, we only open the lower pumping, but for some reason the pumping volume was very unstable some time ago. We tried stripping steam backflushing and washing the tower but could not effectively improve it, so we had to open some upper pumping outlets. My question is, which of the liquid phase temperature and gas phase temperature should be higher when pumping down? I think the gas phase should be high, but ours is the liquid phase. Can anyone analyze the reasons - including problems with pumping down and temperature difference?
Friend the original poster, how can the vapor and liquid phase temperatures be different at the same outlet?
I don’t know if the gas phase and liquid phase temperatures you mentioned are in the same layer. If they are in the same layer, it should be that the liquid phase temperature is higher than the gas phase temperature. Because the gas and liquid phases have gone through countercurrent contact mass transfer and heat transfer in the same layer, it should be normal for the gas phase temperature to decrease and the liquid phase temperature to increase. There are many reasons for unstable diesel output, such as changes in raw material properties, less diesel components, changes in reaction temperature, changes in catalyst activity, the size of the recycle ratio, and also related to the operation of the fractionation tower. Look at the pressure drop of the tower. If the temperature of the fractionation tower is low, the diesel components may be pushed back into the refining oil or to the bottom of the tower. If the temperature is high, it may rush upward, etc. Therefore, the reasons should be comprehensively analyzed.
What I'm talking about is the gas-liquid phase in the same layer. So if the gas phase is higher than the liquid phase, how do you explain it?
You can add a section and a middle section to fill with diesel. This can ensure the stability of diesel extraction and increase the yield of diesel!
How to add it specifically? How to ensure quality?
Lead a pipe from the middle section back to the tower and connect it to the diesel extraction pipe. The diameter of the pipe does not need to be too thick, 50 is enough. Because the return tower in the first middle section and the diesel extraction outlet are basically on the same platform or one platform apart, the required pipe length does not need to be very long. It is very helpful to adjust the quality of diesel and ensure the amount of diesel pumped out.
Well, what the brother above mentioned is worth studying.
Theoretically, the temperatures of the gas and liquid phases on the same tray are the same. The higher-temperature gas phase from the bottom of the tray and the liquid phase from the upper tray are in counter-current contact on the tray to transfer mass and heat. After reaching gas-liquid balance, the gas phase leaves the tray and flows to the upper tray, and the liquid phase flows to the next tray. You can refer to the book Principles of Chemical Engineering. As mentioned above, the gas phase temperature is high. I think the reason for this is that the gas and liquid phases are not fully contacted, or the board is partially dry. After the gas-liquid contact reaches equilibrium, the temperature of the liquid phase is high. I can't explain this situation. I imagine both situations would reduce the separation efficiency of the column. Can you check if there are any operational problems?
personal opinion: There are two diesel extraction ports in the catalytic fractionation tower. Normally, only one can be opened because they are all full extraction ports, so there cannot be throttling. In addition, we have always used diesel to replenish the middle section in production, but the amount is very small to ensure the stability of the return flow in the middle section and avoid the sloshing in the middle section that affects the amount of diesel.
It should be that the temperature of the liquid phase is higher than that of the gas phase. The diesel line is generally not blocked. It may be that the gate plate of the extraction valve has fallen off.
Most of the time, the temperature of the lower extraction layer of our diesel oil is slightly higher than the liquid phase temperature. In addition, we also have diesel oil to replenish the middle section line, but the amount of the middle section line is always very stable. It was only used once when the middle section pump broke down. We are now considering whether there is a problem with the extraction port.
Theoretically speaking, the liquid phase temperature should be higher than the gas phase temperature so that the liquid phase can be extracted. On the contrary, the liquid phase will decrease, which is also the reason for the decrease in diesel volume. The addition of the upper distillation outlet is the result of the upward movement of heavy components. If the gas phase is higher than the liquid phase, the gasoline component should become heavier without opening the extraction port. I wonder if this is actually the case?
This issue seems to be quite controversial, please continue to express more convincing opinions.