Question
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How can the FCC unit be upgraded to benefit petrochemical integration?
Feb-2025
Answers
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Carel Pouwels, Ketjen, carel.pouwels@ketjen.com
For petrochemical integration, the maximisation of light olefins by the FCC unit is essential. Within a given unit configuration, the first choice is to enhance process conditions that maximise unit severity. Maximising reactor outlet temperature is one of the first independent process variables to consider; preferably, the temperature is enhanced to the range of 545-550°C. More extreme process conditions can be applied when the FCC unit is upgraded to so-called ‘high-severity’ FCC units, whereby reactor temperatures up to 600°C are possible.
Depending on the metallurgy, a revamp might be needed. Due to the increased dry gas and LPG production, the refinery needs to address the wet gas compressor handling too. If not yet present in the current downstream configuration, the refinery needs to expand with deC2, deC3, and deC4 recovery units while also building a C₃ splitter to make chemical-grade propylene.
Next to the enhanced severity by a higher reactor temperature, conversion can also be enhanced by increased catalytic cracking reactions through more catalyst circulation (or cat-to-oil ratio). Consequently, more gasoline molecules are generated, which can be cracked to light olefins. Note, however, that hydrogen transfer reactions will also increase and can negatively impact C3=/LPG. The key to a high olefins yield is control of the various competing reactions. Hence, the reduction of hydrocarbon partial pressure through enhanced dispersion and lift steam is also of importance. This way, light olefins are preserved, and reactions to paraffins by unwanted hydrogen transfer are minimised.
While dedicated unit hardware and process conditions for high-severity operations are needed, the third element of importance is the FCC catalyst that is optimised for such application. While every FCC unit with its specific feed is unique, it thus requires a unique catalyst solution, preferably from a repository of expertise with a wealth of industrial experience in high-severity FCC applications, ranging from the lightest to the heaviest feedstocks. With decades of supply to various FCC units of all licensors, Ketjen’s max propylene catalysts AFX and Denali AFX with optional usage of its DuraZOOM-MA additive, have achieved record olefins yields. Ketjen’s new ZSM-5 investment at its Bayport site will support the industry in this move to petrochemical integration.
Jan-2025
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