Refiners, particularly in Asia and the Middle East target FCC unit operation for maximum propylene production. With global chemical markets expanding, it is expected that more chemical and polymer grade propylene production will be produced from the on-purpose propane dehydrogenation (PDH) units that have started up in China over the past two years. PDH units have also been announced since late 2013 in the U.S., due to the abundance of shale based propane feedstock. At the same time, modern ethane feedstock-based ethylene steam crackers produce significantly less propylene “byproduct” compared to naphtha- based steam crackers. This is a problem because as a chemical building block, propylene is second in demand only to ethylene. But the most cost-effective way to produce incremental production of this important polyolefin is from the refinery cat cracker (FCCU).
Of course, FCCU hardware upgrades and higher severity operating conditions coincide with the noticeable increase in ZSM-5 inventory. Some of the operating changes coinciding with increased ZSM-5 additive usage include:
- Higher reactor-riser cracking temperatures (e.g., 980 °F back in the 1990s to 1020 °F in today’s propylene targeted mode)
- Higher catalyst circulation rates and higher cat-to-oil ratios
- Higher E-cat activity
- Better feed quality.
Better FCC hardware has been developed to coincide with higher FCC operating severity, such as redesigned feed injectors for promoting low delta coke. Other related improvements revolve around the FCC regenerator. Without improved regenerator heat removal efficiency required with the higher reactor temperatures, the regenerator temperature can increase to unacceptable levels resulting in accelerated catalyst deactivation and degraded cracking selectivity. The corresponding developments in FCC catalyst cooling systems have given refiners a flexible option to deal with the heat balance challenges encountered with maximum propylene FCC operations.
ZSM-5 catalyst additives, FCCU regenerator and related heat removal technologies are just part of the matrix of solution sets refiners need to hedge against feedstock volatility that polyolefins value uplift provides refiners, while simultaneously producing transportation fuels. More on this value uplift available from the FCCU will be discussed in more detail during the Cat Cracking session at the November RefComm Bahrain 2015 Conference.