pt q&a
More answers to these questions can be found at www.digitalrefining.com/qanda
Q What chemical treatment programmes can help limit FCC unit bottoms circuit coking and fouling? A Rainer Rakoczy, Technology Advisor Fuels, Clariant International Ltd, rainer.rakoczy@clariant.com While fluid catalytic cracking (FCC) technology offers valu - able flexibility in processing different feedstocks, this flex - ibility comes with inherent efficiency trade-offs. As refiners optimise their processes, they must balance the desire for maximum feedstock utilisation against the production of higher-value products, which often requires compromises in overall process efficiency. Many FCC unit operations can utilise the bottom residue product thanks to its comparable high carbon-to-hydrogen atomic ratio as a heat producer in the regenerator. Unfortunately, this residue remains highly active and can accumulate throughout the entire downstream process - ing, resulting in severe fouling, especially in cases where piping is not optimised from a hydraulic flow perspective. The application of small quantities of supporting chemicals may help keep overall residue homogenised and movable to reduce any laydown of debris in the machinery. A Ghoncheh Rasouli, Technical Presales Consultant, Technology/SIM Product Management, KBC (A Yokogawa Company), ghoncheh.rasouli@kbc.global FCC unit bottoms circuit coking and fouling occur through a combination of high coke precursors and thermal instabil - ity within the main fractionator bottoms, slurry exchangers, and pumparound loops. The primary drivers are heavy feed components with high aromatic content, asphaltenes, res - ins, and elevated Conradson carbon (CCR), such as vacuum gas oil (VGO) and slurry oil. Poor feed hydrotreatment allows sulphur, nitrogen, and metals (including nickel and vanadium) to enter the unit. These metals, either present in the slurry or deposited on the catalyst, promote dehydrogenation reactions that gen - erate hydrogen and unsaturated hydrocarbons, accelerat - ing polymerisation and coke growth. Catalyst fines carried into the bottoms stream provide nucleation sites for deposit formation, while localised hot spots, high temperatures, and long residence times encourage thermal cracking of heavy hydrocarbons into lighter gases and solid carbon. Stagnant or low-flow areas further increase contact time with hot surfaces, compounding the tendency for fouling. Prevention requires a combined approach of feed quality improvement, operating control, and chemical treatment. Upgrading hydrotreating to lower CCR, sulphur, nitrogen, and metal contaminants is fundamental, and blending or hydrocracking heavy aromatic streams helps limit high-CCR feed components. Controlling slurry recycle rates is essen - tial to prevent excessive accumulation of heavy aromatics, while effective catalyst stripping reduces entrained hydro - carbons and minimises heavy-end carryover. Maintaining
stable temperature profiles and eliminating hot spots limits thermal cracking and the formation of coke precursors. Chemical treatment complements these practices by neu - tralising or passivating metals that catalyse coke formation. Antimony (Sb) compounds are commonly used to passiv - ate nickel, suppressing its dehydrogenation activity, while magnesium or rare-earth compounds neutralise vanadium and prevent catalyst degradation. Through cleaner feed, controlled recycle, optimised oper - ation, and targeted chemical passivation, FCC unit bottoms coking and fouling can be significantly mitigated, ensuring more reliable and efficient unit performance. A Berthold Otzisk, Senior Product Manager, Process Chemicals, Kurita Europe GmbH, berthold.otzisk@kurita- water.com A chemical treatment programme can be a great help in keep - ing fouling in the slurry oil system to a minimum. To select a suitable additive, it is very important to carry out a stream analysis, stream characterisation, and deposit analysis. Stream analysis determines the proportion of polynuclear aromat - ics (PNAs), catalyst fines, solids, carbon content, metals, and catalyst fines content. Stream characterisation assesses the aliphatic and aromatic content to determine the fouling poten - tial. Deposit analysis provides very important information and quantifies the amount of organic vs inorganic foulants present. Several antifoulants can be used. They should remain thermally stable even at high temperatures >350°C to be effective. Coke suppressants inhibit the high-temperature reaction of condensed aromatic compounds, which may lead to unwanted agglomeration and coke formation. This kind of additive will stop or reduce the formation of coke, but cannot remove existing coke deposits from the system. Catalyst fines dispersants prevent agglomeration and react with the surface of catalyst fines. Depending on the product, they either keep the catalyst fines in suspension or prevent them from sticking together. Asphaltene stabilisers avoid agglomeration and pre - cipitation of large molecules by forming an artificial layer between the asphaltene molecules. Organic dispersants avoid agglomeration and deposition of condensed poly - nuclear aromatic compounds on heat exchanger surfaces. This type of chemistry often exhibits relatively poor thermal stability at the temperatures present in the fractionator bot - toms and should not be injected into the slurry return line. It is possible to combine different additives with various func - tions in one antifoulant product to achieve the best results. Q What cost-effective strategies are available to increase naphtha production? A Rainer Rakoczy, Technology Advisor Fuels, Clariant International Ltd, rainer.rakoczy@clariant.com Naphtha is an important intermediate for the chemical,
5
PTQ Q1 2026
www.digitalrefining.com
Powered by FlippingBook