Detailed steps for shutting down the distillation unit, draining oil, and purging are as follows

This task should be assigned to the unit’s technicians; moreover, it is also specified in the unit’s operating procedures, which are also referred to as instructions for operation. It is best to refer to the relevant documents of your own organization, as production processes and equipment vary from one organization to another, which may lead to differences in details.

I think it should be more or less the same; I don’t understand it, so I’m asking. There’s no detailed explanation in the operating procedures

In my understanding, the process is carried out step by step along the various branches, with the oil lines being purged and sent to the tank area.

There’s nothing difficult about fractional sweeping: use steam to sweep the light oil and water mixture, and use steam repeatedly to sweep the heavy oil, moving from front to back towards the sludge line – be sure to prevent heavy oil from entering the light oil line. After scanning, drain the condensate point by point, verify the purging effect, and then drain the water. The key is to be familiar with the processes; once you’re familiar with them, there are no problems.

Are all side streams blown into the fractionation tower? After washing the top loop, do I need to drain the water and then blow it with steam?

During shutdown, lower all fractionation levels to produce as much qualified product as possible. After stopping the feed, each line sequentially pumps oil into its respective waste oil line leading to the tank farm. Once the pumps are depleted of oil, they are shut down. Then, the corresponding purging medium (water or steam) is introduced at the pump inlets and outlets to purge the fractionator tower. After a liquid level is established in the tower, the slurry pump is restarted to continue pumping out the remaining oil until the tower is completely emptied. The pumps are then turned off, and all circulation line block valves are closed. Finally, steam is introduced once again for external purging to remove any residual hydrocarbons; purging continues until no vapor remains and the discharge appears clear. After installing the blind flanges, steam is supplied to the fractionation tower from the steam tower; all towers and vessels are opened to vent and drain any remaining water. There are several related issues to consider: First, since the catalyst has not been completely unloaded, the slurry circulation cannot be stopped; therefore, it’s necessary to control both the external discharge rate and the liquid level in the fractionator. Second, pumps must not operate under vacuum conditions for extended periods; constant monitoring is required to prevent equipment damage. Third, the bottom vent of the tower tends to get clogged due to coke formation, so preparations for dealing with this issue should be made in advance. Fourth, during large-scale shutdowns, all purging personnel must communicate promptly with one another, and those responsible for connected pipelines should coordinate with other supervisors to determine the optimal timing for purging. Fifth, it’s difficult to completely purge heavy oil pipelines in a single attempt; thus, a method involving repeated depressurization and repressurization can be employed. Sixth, condensate must be drained prior to introducing steam. Seventh, personal safety is paramount; if condensate drainage proves impossible, do not attempt to handle the situation while pressure remains present.