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FLUID CATALYTIC CRACKING, AND ISOMERIZATION
Publication date:4Q 2014
Fluid Catalytic Cracking and Isomerization
Fluid Catalytic Cracking
The fluid catalytic cracking unit (FCCU) has long been considered the backbone of the modern refinery. Since the first unit was installed in 1942, the FCCU continues to perform "miracles" for refiners in meeting challenges of increasingly stringent fuel standards, changing market conditions, and competing technologies. These new challenges that are consistently presented to refiners are what instigate evolution in FCCU design and operation. Changes in hardware, control schemes, catalysts, maintenance strategies, etc. are all driven by current or anticipated changes to the refining landscape.
Once seen mainly as a gasoline-producing unit, the role of the FCCU has developed for a wide array of feedstocks and products. Continued FCC technology developments have focused on widening the boiling range of the feed that can be processed in the unit, maximizing LCO yields, becoming reliable manufacturers of petrochemicals like BTX and light olefins, and providing operational flexibility in order to allow the unit to take advantage of favorable market opportunities to maximize unit profitability. Novel catalyst formulations and production methods will be oriented towards handling increasingly difficult feedstocks with improved activity and selectivity while coping with volatile prices of raw materials. Residual feedstocks have been playing an increased role in the FCCU, which can greatly impact operation due to the particularly heavy hydrocarbons and presence of different contaminants.
The progression of FCC technology expands further in response to environmental regulations that aim to limit emissions from the products developed in the FCCU, and from the unit itself. Fuel reformulation and sulfur reduction and advanced emissions control technologies are being developed so that the process remains capable of meeting regulatory targets concerning both fuel quality standards and environmental emissions. Additives and adsorbents are seeing extensive research in order to better collect unwanted heteroatoms and prevent them from being released into the atmosphere. Additional regulations call for the inclusion of biofuels into the blending pool for refined products, leading to development in processing renewable feedstocks in the FCCU.
A study and analysis of both the most up-to-date technological offerings from companies and licensers, and the R&D work carried out over the past year indicate several technological trends present for FCC. FCCUs are becoming more-relied upon for the production of multiple transportation fuels and petrochemical products, and for the processing of a variety of different feedstocks. These trends can be placed in varying categories, which include: tight oil processing, resid FCCUs (RFCCUs), biological/renewable feeds processing, gasoline quality and production, LCO yield and quality, light olefins production, aromatics (BTX) production, emissions reduction from the FCCU, and process monitoring and control.
Additionally, the fluid catalytic cracking section features the latest trends and technology offerings, including:
Isomerization, in itself, has become somewhat less desirable in recent years due to the mandate to increase ethanol in gasoline and the restrictive RVP specifications on finished gasoline with the isomerate share in the gasoline pool declining to about 3%. C5-C6 isomerization units increase octane by as much as 25 points, though octane is not as desirable as it used to be given declining gasoline demand around the world, and increase RVP, which is a major constraint particularly in the summer months. As a result of these factors, isomerization unit economics have suffered greatly and a number of units in the US and Europe have either been shut down completely or seen operating rates reduced greatly.
Refiners that are continuing to operate isomerization units are looking to increasingly saturate benzene in these units due to the more restrictive benzene limits being placed on gasoline around the globe. C5-C6 isomerization has become even more integral in helping refiners manage benzene in the gasoline pool given these tighter specifications.
Basically, four different types of isomerization process schemes are available for use. These include a once-through isomerization scheme, a once-through isomerization scheme with prefractionation, a scheme that recycles low-octane hexanes, and a scheme that combines recycle of low-octane hexanes with an upstream prefractionation step. Each scheme will give a different yield and octane number and refiners must choose a scheme based on specific product goals. These schemes can be used with either a zeolite or chlorided alumina catalyst. Refiners that are continuing to operate isomerization units are looking to increasingly saturate benzene in these units due to the more restrictive benzene limits being placed on gasoline around the globe. C5-C6 isomerization has become even more integral in helping refiners manage benzene in the gasoline pool given these tighter specifications.
Additionally, the isomerization section features the latest trends and technology offerings, including:
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primary conversion process, gasoline, diesel, LCO, propylene, butylenes, light olefins, LPG, fluidized bed, riser, ULSD, ULSG, ultra low sulfur, rare earth, dieselization, SOX, NOX, slurry oil, fuel oil, fuel specifications, gasoline benzene, reformulated gasoline, RFG, CO, particulate matter, mild FCC, dual-riser, multiple riser, ZSM-5, additives, zeolite, matrix, co-catalysts, RFCC, biofeeds, catalyst regenerator, power recovery, advanced process control, opportunity crudes, energy efficiency, electrostatic precipitators, ESP, flue gas scrubber, tight oil, residual feeds, isomerization, gasoline, MTBE, ethanol, naphtha, light naphtha, reformate, isomerate, octane, MON, RON, RVP, Reid Vapor Pressure, benzene, sulfur, condensate, methyl pentane, normal butane, normal pentane, normal hexane, isobutane, cyclohexane, platinum, palladium, zeolite, chlorided alumina, sulfated zirconia, tungstated zirconia, borosilicates, silicoaluminophosphate, SAPO, molecular sieve, membrane, stripper, deisobutanizer, deisopentanizer, deisohexanizer