The SR reformer is one of several different types of reformer technology used in refining. A semi-regen unit is a reformer with a fixed bed catalyst that has to be taken out of operation periodically in order to regenerate the catalyst as its activity declines. This is in contrast to a continuous catalytic reformer (CCR) in which the catalyst is continuously withdrawn, regenerated, and fed back into the unit, keeping activity high.

For more detail see: reformer