Revamps 2025 Issue

Fluid catalytic cracking (FCC) revamp opportunities

Changes to fluid catalytic cracking unit input parameters may require upgrades for maximum unit value

Warren Letzsch Warren Letzsch Consulting

T he fluid catalytic cracking unit (FCCU) represents an opportunity to increase the refinery’s profita - bility because of its large capacity and processing flexibility. It can convert heavy oils into gasoline and die - sel, produce olefins for alkylation and petrochemicals, and process a wide variety of feeds. The FCCU is usually oper - ated within multiple limits, which are based on existing feedstocks and product demands with its current equip - ment. When changes occur in the input parameters, a revamp might be necessary to extract the most value from the unit. FCC equipment revamps are frequently not considered for future turnarounds because capital is limited or the eco - nomics do not seem to justify a change. With FCCU run lengths spread out to four to seven years, the operator is ‘playing a pat hand’ for eight to 14 years if no improve - ments are made to the cracker. A revamp producing $0.20/ bbl will yield $10,000/day for a 50,000 bpd unit. This is $3.65 million/year. Therefore, a revamp with a simple pay - back of one to two years is worth considering. Justifying a project The benefits are usually largest for increased feed capac - ity, followed by improved yields and/or product properties. Reducing operating costs normally provides the smallest payback but can still pay dividends. While the FCCU model may show the required value to justify a project, a model of the entire refinery needs to confirm that the benefits will be realised. Optimisation of the FCC operation must be done such that all units impacted by the change, including the alkylation and reforming units, are not bottlenecks to the overall plan. Every refinery unit should be examined to determine capacity and identify bottlenecks preventing a more prof - itable operation. Good mass, heat, and pressure balances are required around the FCCU and individual sections of the cracker for the analysis. FCC units can be broadly classified as gas oil, resid, or petrochemical units. Some designs are a combination of these classifications. A hydrotreater in front of the cracking unit can be part of the cracking complex in that it provides a more desirable feedstock that can allow more versatility regarding yield structure and operating parameters.

Gas oil crackers downstream from a hydrotreater have a feedstock that does not need to produce much coke to sat - isfy the heat balance. Delta cokes can become low enough that the regenerator temperatures stay very low even when full CO combustion is desired. Maximum feed temperatures should be used to lower the coke make, which requires a fired heater for the feed. Maximum feed temperatures using only heat integration with the main column are about 550ºF, while a fired heater increases the feed temperature to about 720ºF. The feed end point will determine how high the feed tem - perature can be raised without the occurrence of coking in the heater tubes. Moving bed catalytic crackers processed gas oils with an end point of about 950ºF with feed heaters that approached 800ºF. A higher feed temperature lowers the coke required by the heat balance. CO₂ emissions are reduced from the process because the hydrogen content of the heater fuel is higher than that in the coke. Coke makes of 4 to 4.5 wt% are possible, translating to higher liquid yields. Higher reactor temperatures can be accommodated with low delta coke operations because the regenerator temper - ature stays within the normal operating range. In the future, refining complexes may turn into petrochemical plants and sites for recycling plastics. Reactor temperatures of 1,000 to 1,150ºF may be common for optimal performance and minimal catalyst deactivation. A hydrotreater designed for high pressures can provide a low delta coke feed regardless of the crude oil choice. Guard beds for these hydroproces - sors can remove impurities that might interfere with FCC yields and/or product properties. Petrochemicals include light olefins and aromatics, which are the main components from a petrochemical cracker. The gasoline from the catalytic cracker and the reformer produce aromatics. Switching the reformer to a benzene, toluene, and xylenes (BTX) operation (special catalyst and Research Octane Numbers (RONs) >100) can greatly increase the desired aromatics. FCCUs make higher yields of xylenes and less benzene than steam crackers, adding extra value to an integrated refinery/petrochemical com - plex. The unconverted hydrocarbons (paraffins and naph - thenes) from the reformer can be recycled to the catalytic cracker to produce more olefins.

Revamps 2025