Enhancing FCC reliability: The impact of cyclone technology developments
How optimising cyclone design and implementing advanced internal hardware enhance operational reliability, illustrated with three real-world examples
Mohammad Umer Ansari, Todd Foshee and Robert A Ludolph Shell Catalysts & Technologies
C yclones are indispensable components in the fluid catalytic cracking (FCC) unit, crucial for separating solid catalyst particles from gases. This enables catalyst retention within the FCC unit, facilitating cracking reactions and subsequent regeneration, while also averting the transfer of contaminants to the main fractionator and reducing particulate emissions into the flue gas system. By maintaining optimal catalyst particle size distribution and fluidisation conditions, cyclones increase catalyst circula - tion capacity, collectively enhancing catalytic cracking effi - ciency and yielding valuable gasoline and olefinic products. However, cyclones operate within an intensely harsh envi - ronment, and their reliability has been a consistently high pain point for FCC operators, a message supported by an industrial survey conducted in 2022. This supports the find - ings of an earlier Grace Davison survey, which found that catalyst losses from cyclones were the number one problem in FCC operation. Furthermore, after longer durations in ser - vice, cyclones frequently suffer from erosion, leading to hole formation and dipleg-related plugging events. The severity of these problems is different for primary and secondary cyclones, which operate within different solid loading and particle velocity environments. Primary and secondary cyclones are usually installed in series, located within both reactor and regenerator vessels above the dense fluidised beds. This arrangement is shown in Figure 1 . In particular, the issues are exacerbated in secondary cyclones, which contain a very intense vortex and where higher particle velocities are endured. The scenario of reduced particle loading subsequently causing higher ero - sion may appear counter-intuitive at first. In a secondary cyclone, although the particle loading is reduced, the vortex pathway is greater, more energetic, and prone to instability. These factors combine to cause faster erosion of the cone and the top of the dipleg. This effect is illustrated in Figure 2 . Common issues The impact this can have on an FCC plant operator is not trivial. Extensive erosion can lead to holes at the inlet and the bottom of cyclones, resulting in high catalyst losses and leading to reduced throughput, which consequentially has a big impact on margins. Reduced FCC throughputs create a bottleneck for the refinery, with subsequent loss
Reactor
Regenerator
Secondary cyclone
Primary cyclone
Secondary cyclone
Primary cyclone
in crude processing rate. Additionally, inefficient cyclone operation will exacerbate catalyst loss and create environ - mental compliance issues in the regenerator as the flue gas from the regenerator becomes progressively harder to treat. Additionally, operational and product quality issues emerge from the reactor as more catalyst escapes to the main frac - tionator, impacting column operation and bottoms products. Catalyst loss of between 3-5 tonnes per day (TPD) is not uncommon and is linked to a substantial increase in oper - ational costs. An unresolved issue could result in a step change in catalyst loss, with the potential for rates to rise by two to three times. Higher catalyst loss may lead to poor Figure 1 Typical arrangement of primary and secondary cyclone pairs in reactor and regenerator vessels of an FCC unit
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