To convert a wide range of hydrocarbon feedstocks, from ethane to vacuum gasoils (VGOs), into high-value light olefins. High olefins fluid catalytic cracking (HO FCC) processes, such as catalytic pyrolysis process (CPP) and deep catalytic cracking (DCC) are technologies that produce higher yields of ethylene and propylene than fluidized catalytic cracking (FCC). Both steam cracking and HO FCC reactor systems can be operated separately but are designed with a shared recovery system to reduce capital cost.
HO FCC technologies are fluidized cracking processes that convert heavy feedstocks, including vacuum and atmospheric gasoils, to gasoline, diesel and light olefins. The HO FCC reactor systems produce 15 wt%–25 wt% propylene or 10 wt%–20 wt% ethylene. Steam cracking is commonly used on feedstocks from ethane to light GOs. The higher cracking temperatures of pyrolysis will result in higher ethylene yield than the HO FCC processes. Heavy GO feedstocks would foul the cracking furnace too quickly to be economical. To process both heavy GOs and light feeds, both fluidized catalytic cracking and steam cracking reactor systems are applied.
The HO FCC unit effluent must first be processed in an FCC style main fractionator. The main fractionator must remove catalyst fines from the heavy-oil product. The main fractionator also produces a light cycle oil and an overhead gas that is primarily light hydrocarbons and gasoline. The overhead of the main fractionator can be further processed via a wet-gas compressor. The gas is then stripped with the gasoline absorbed via a lean-oil absorber, followed by amine treatment and finally a caustic wash. The combined effluents are sent to compression and into a series of contaminant removal beds and hydrogenation steps.
The heavy GO feedstocks always include contaminants that foul subsequent purification processes like the driers and hydrogenation reactors. Therefore, the HO FCC effluent needs to be processed through contaminant removal beds prior to entering the ethylene recovery unit. If both steam cracking and the HO FCC reactor are processing contaminated
feeds, the caustic system, oxygen and NOx hydrogenation, mercaptan, mercury, COS and arsine removal beds can also be shared, as shown in the figure.
This integrated technology is suitable for revamps of ethylene plants, as well as grassroots applications. The figure shows a maximum integration scenario for an HO FCC and steam cracking. The level of integration is a function of contaminant levels, HO FCC effluent gas composition and other capital reduction considerations.
Licensor: The Shaw Group
