How can we minimise gas and coke make with heavy feed to our FCC?

First published in PTQ Q4 2018

Pierre Bellet, Axens

Catalytic systems towards better coke and/or dry gas selectivities will certainly help, especially to face contaminant metals which catalyse side reactions. If not limited by catalyst circulation, low delta coke catalysts will increase cat/oil but coke yield should stay constant. Yet, we will focus here on process and hardware solutions. We assume you have already explored adjusting the unit’s operating conditions to reach the best compromise. Nevertheless, other areas can be explored to reach your target:

  • Feed injection optimisation: the atomisation steam rate might not be optimum or your current technology might not be best nor adapted to your heavier feed. Poor feed distribution will naturally result in unnecessarily high coke and dry gas yields. The FCC Alliance’s FIT G-Series or FIT R-Series feed injectors have been specifically designed to address the challenges associated with heavier feedstocks.
  • Riser termination device: a replacement can also be investigated in order to improve the unit’s yields towards reduced coke make.
  • Catalyst stripping optimisation: in case your coke make issue is due to a bottleneck on your regenerator (too high operating temperature, limited burning air injection capacity or limitation on regenerator velocity to avoid catalyst entrainment to flue gas lines), the catalyst stripping should probably be optimised. Indeed, hydrogen is responsible for most of the temperature elevation in the regenerator during combustion of coke and unstripped hydrocarbons. The FCC Alliance’s state-of-the-art stripper packing will ensure maximal hydrocarbons removal, leaving mostly coke to be burnt. A reduction in regenerator temperature of about 10-15°C is typically reached, allowing the refiner to operate away from the current constraint and therefore not minding about this high coke make.
  • Heat balance tuning: finally, the usage of catalyst cooler or riser quench will also help to achieve your objective.

Whatever the current constraint on your unit, a process solution most certainly exists.

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