Several issues regarding catalytic cracking unit shutdowns (online, etc.)
Thread Content
This post was last edited by oxygenhust on 2009-8-10 17:12. 1. What is the sequence for opening the manholes on the tower after the unit is shut down? What should be kept in mind? 2. What precautions should be taken to ensure stable oil removal after stopping the feed? 3. What conditions must be met after the shutdown before a large oil and gas blind flange can be installed? Looking forward to a reply. Thank you :)
First question: When opening manholes, it should start from the reaction area; it’s best to do this from top to bottom； When opening the manhole, it is important to ensure that the catalyst in both reactors is completely removed. A vacuum pump can be used for this purpose; in particular, the regeneration line and the standby line should be operated by repeatedly opening and closing the valves, so that all the catalyst is transferred to the regenerator and then removed completely. The catalyst in the external heat exchanger also needs to be completely removed ； When opening the manholes in the settler system, it is essential to ensure that the oil and gas within the system have been completely removed, and that the system temperature has dropped. Do not rush; in the past, our company experienced a fire accident due to incomplete removal of oil and gas, after the manholes were opened. A proper blind flange must be installed when opening the manholes ； Second question: When draining oil from a stable system, it is necessary to carefully check the process to prevent accidents such as oil leakage, spills, or cross-contamination ； Shut down the heat source of the system in a timely manner; when the system pressure drops too low, a steam stabilizing pump can be used to force pressure out. Third question: Two essential conditions for removing the large oil-gas blind flange: 1. The reaction settler system must be thoroughly purged with steam ； 2. Purge the oil from the fractionation tower, re-refining tank, and crude oil tank, and use steam to purge the system thoroughly.
For the third question, the poster can refer to this —— Cessation of operations due to catalyst issues, and the time required for installing large oil and gas blind flanges: http://bbs.hcbbs.com/viewthread.php?tid=248730&highlight=%CD%A3%B9%A4%2B%D3%CD%C6%F8%B4%F3%C3%A4%B0%E5
Stabilize the oil removal process by using water to push it away. Open the manholes in sequence, from top to bottom.
1. The manhole on the tower should be opened from top to bottom; note that it should be opened only when the temperature drops below 100 degrees. For the regenerator, there is a lot of catalyst at the manhole; since the system is under pressure, care must be taken when opening the manhole to avoid the catalyst possibly spraying out and causing injury. 2. The timing of stable oil removal is quite important; it is best to start oil removal at the stage when the reaction rate drops significantly. As for whether water pressure is needed, it is generally required according to the operating procedures, but in practice, direct steam purging is also acceptable. 3. What is mentioned on the second floor regarding the two necessary conditions for removing the large oil and gas blind flange: 1. The reaction settler system must be thoroughly purged using steam ； 2. Purge the oil from the fractionation tower, re-refining tank, and crude oil tank, and use steam to purge the system thoroughly. ”That’s completely correct; strictly speaking, it should be done that way. In practice, after the distillation tower has been purged with steam for a certain period of time, it is possible to install the blind flange; the re-refining tank can be ignored for now.