Question
-
What are the optimal routes to valorisation of olefins-rich FCC unit and coker unit off-gas?
Jun-2023
Answers
-
Celso Pajaro, Sulzer Chemtech, chemtech@sulzer.com
‘Optimal’ routes depend on the off-gas stream flow rate, composition, and refinery configuration. FCC unit off-gas can be sent to a cryogenic unit to recover the residual C₃+ and the C₂/C₂=. The C₂/C₂= rich stream can be injected downstream of the ethane cracking furnace, where ethylene will be recovered, and the ethane will be returned to the furnace. This arrangement requires the removal of water and other residual impurities.
If there is no steam cracker, recovering ethylene may not be profitable, and a conversion process is preferred. There are several processes in the market that convert olefins into aromatics or other processes that alkylate benzene with light olefins, producing ethyl benzene and cumene.
Coker off-gas has a lower olefin content than FCC off-gas but still has a significant amount of C₂+ material that can be recovered. It is not uncommon that coker off-gas is combined with FCC off-gas and fed to a cryogenic unit (as previously described). For small refineries, the previously mentioned options may not be economical. In this case, they may focus on recovering the C₃+ material in the off-gas by improving the efficiency of their gas plant. Changes in unit configuration, adding chilling cooling to absorbent naphtha, and other changes can reduce C₃+ in the off-gas by more than 2-3 mol% while increasing C₃/C₄ stream flow rate by 5% or more.
Jun-2023
SPONSORS