Online cleaning prevents NHT production stoppage
Background
A Western European refinery was experiencing severe flooding problems in the debutaniser column of a naphta hydrotreater unit (NHT). The root cause analysis showed the presence of high amounts of formed ammonium chloride and bisulphide salts. While hydrogen sulfides are coming from the hydrotreating process, the main chloride source in this case was off-gas, discharged from the reformer debutaniser. The ammonium salts were deposited on the NHT debutaniser top section due to low temperature and absence of sufficient water. The liftable caps of the valve trays in the debutaniser top section didn’t work properly anymore causing flooding and high levels of C5 in the C4 section were observed due to a decline in separation (off-spec production). The steam production by debutaniser bottom reboilers had to be stopped because this increased the flooding problems. High Reid vapour pressure of isomerate and a significant throughput reduction of about 10m3/h were additional drawbacks.
Previously the NHT was shut down for 1-2 days, performing a water wash with shutdowns of the reformer unit and isomerisation unit. Since water washing didn’t remove all salts that time, such a situation should be avoided due to production losses and significant extra costs for an external cleaning company.
Objectives
- No shutdowns of the NHT, reformer and isomerisation unit required.
- Online cleaning without additional costs for hiring an external cleaning company.
- Non off-spec production during online cleaning.
- Recovery of operating situation to original condition.
- Safe and smooth plant operation.
Kurita’s Technology:
