Several questions regarding the vacuum distillation tower

Coking at the bottom of the vacuum distillation tower is likely caused by a heavier composition of your feed material, with a higher residue value. During operation, the temperature in the bottom of the vacuum distillation tower is too high, and the circulation volume is insufficient. Additionally, given that the pressure at the feed section of the tower and the pressure at the top are not very different, it’s quite possible that the tower is experiencing flooding. It is recommended to adjust the operating conditions and reduce the reflux rate. Hehe, I’m just offering my thoughts here; please correct me if there are any mistakes :handshake :handshake

It needs to be cleaned regularly to prevent clogging. There is not much difference in the vacuum feed inlet either at the top of the tower; it doesn’t need to be considered – as long as the vacuum level remains stable is sufficient

In modern vacuum distillation towers, there is generally a process in which cold residue oil is returned to the bottom of the tower, thereby reducing the temperature at the bottom and minimizing coking. Does your plant have such a process? The differential pressure for pressure reduction in your unit is low; if it is a packed tower, could it be that the packing is not properly installed, or that it has been damaged due to corrosion? However, if the side-line temperatures of each tower are normal, then everything should be fine.

I agree with what bingyu252 said

The common causes of reduced bottom coking include high furnace exit temperature, heavy crude oil (high in resins and asphalts), and long residence time at the bottom of the tower. It affects the vacuum level in terms of operation, and furthermore, it impacts the operation of the bottom suction pump. Regarding the issue of a very small difference in vacuum level between the feed section and the tower top, I believe it is a problem related to the accuracy of the instrument readings. After our plant was converted into a high-efficiency packed vacuum tower, the vacuum level in the vaporization section was only 95 kPa

What are the consequences of a flooded vacuum tower?

The consequences of a vacuum distillation column being flooded are extremely serious. Normal oil refineries absolutely will not allow such a situation to occur in their vacuum and atmospheric distillation columns; once this happens, it constitutes a major accident. The residue at the bottom of the column ends up at the top, while the light components from the top spread everywhere, resulting in chaos inside the column. It takes more than two days to restore normal operations, leading to issues with feed distribution and defective product output, which necessitates an immediate shutdown

As for making connections, there’s not much to say about that. The pressure difference inside the tower is low; it’s likely that there is a problem with the packing inside the tower, so it’s recommended to check it during maintenance. It’s also possible that the feed temperature is too high, resulting in a backflow rate that isn’t sufficient, which leads to the coking issue mentioned above. Consider reducing the feed temperature and increasing the backflow rate at the same time – this should help resolve such problems

I am very grateful for the answers from all of you; I have learned a great deal from them :) My plant does not have the process described on page 4, where the residue from the bottom of the vacuum distillation tower is sent back into the tower. As a result, there is a high likelihood of coking at the bottom of the tower. We suspect that coking has already begun there and is gradually spreading, which is a source of great concern for us. As for what one gentleman said regarding the small difference between the pressure at the feed section of the tower and the top pressure, which suggests that there might be a risk of flooding in the vacuum tower, I think this still needs further investigation; after all, the temperatures at the side streams of the tower are within normal ranges, and the operation of the entire tower is relatively stable. The vacuum tower in my unit does indeed have the problem of packing falling off; some of it even makes its way to the pump’s inlet filter via the bottom suction pump, which sometimes causes the pump to fail to deliver flow. However, if the vacuum difference between the tower top and the inlet is so small, is the pressure drop across the packing in the tower really that small as well? The large-scale loss of packing should have a significant impact on the operation of the tower; could it be that the entire tower is now empty?:funk: I’m not quite sure about this.

I learned a lot; I think it’s Yanta

Is the product qualified now? Since the packing can be seen even in the bottom-reduction pump, it means the packing needs to be replaced.

I don’t know if it’s because your factory is too large or what else, but it only takes a few hours to deal with a tower flooding issue! However, a tower flood is a major accident that can lead to emergency shutdowns and contamination of product tanks!

What is coking at the bottom of a vacuum distillation tower, its analysis, causes, and countermeasures? ?