Makeup H 2 is added as required to replace the H 2 consumed by the reactions.
Conversion higher than 95% is achieved by recycling the heavier unconverted fraction through the reactor, so that only this fraction remains in the reactor for a longer residence time.
A northern California refinery recently switched from fluid coking to delayed coking since fluid coke is less valuable, and a more difficult byproduct to handle, than delayed coke.