PTQ Q3 2023 Issue

pt q&a

More answers to these questions can be found at www.digitalrefining.com/qanda

Q What are the optimal routes to valorisation of olefins- rich FCC unit and coker unit off-gas? A Carel Pouwels, Global FCC Specialist Light Olefins, Ketjen, carel.pouwels@ketjen.com Valorisation routes greatly depend on refinery configura - tions. FCC units that typically operate in ‘conventional’ gasoline mode are distinctly different from FCC units that operate in max propylene mode or even in very high sever - ity mode. Therefore, it depends on the level of observed olefins. Refiners that aim to maximise propylene, whereby propylene yields are achieved at 9 wt% or higher, com - monly operate a C 3 splitter. The amount of ethylene pro - duced may be too low for economic recovery, especially in an environment where gasoline demand is relevant. However, not only does ethylene yield count but so do the scale and capacity of the FCC unit. As refiners pivot to serve the petrochemical market, greater severity can drive both propylene and ethylene yields. In such cases, ethylene recovery may be used to enhance FCC prof - itability. For those refiners who doubt the economics of their own assets and question whether there is more potential, it is worthwhile to investigate the status quo. Benchmarking against industry peers, as illustrated in the following chart (see Figure 1 ), provides a health check and valuable insight into a refiner’s current position. To benefit optimally from such configurations, we strongly recommend working closely with partners to maximise the units in operation. It is advantageous to use the expertise of the licensor of process equipment and supplier of FCC cata - lysts to tune the operation conditions and reformulate to the optimal FCC catalyst. A Celso Pajaro, Head Engineered Solutions Refinery, Sulzer Chemtech, USA, 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 down - stream 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. Q What optimal hydrocracking catalysts and operating strategies are needed to co-hydroprocess waste oils with VGO? A Andrew Layton, Principal Consultant, KBC, Andrew. layton@kbc.global There are several steps involved in co-processing waste oils. The levels of sulphur aromatics and N2 are exception - ally low, but fatty acids – unsats/oxygenates and pour point – are high. When the feed boils in the kero/diesel range at 5-10% in total reactor feed, the considerations for process - ing are less severe than when processing 100% waste oils. However, considerations apart from catalysts include:  Feed quality/storage • Flowability at temperature. Waste oils have a flowability problem at ambient temperatures • Contaminant removal/metals content. Feed contamina - tion removal from solids to metals occurs at several distinct levels dependent on the upstream pretreatment of the pur - chased feedstock. v Concentration of the waste oil in total feed • Impacts materials; reactor heat rise control; corrosion con - trol; metals build-up • Typically, around 5-10% maximum on an existing unit. w Number of reactors; beds available; heat rise control. This may not be a major issue at low concentrations, especially in VGO service. x Product quality target • O₂; olefins removal; cloud reduction y COx control (as discussed in the following). The question targets co-processing with VGO rather than diesel. Thus, cloud and flowability control may not be a main concern when sending it to an FCC or VGO hydrocracker.

Conventional Max GLN FCC High severity FCC Conventional Max C = FCC

Propylene, wt%

Figure 1 FCC operations at three different modes

PTQ Q3 2023