Improve FCC yields to meet changing environment -- Part 2.

This article suggests that to optimize performance and comply with environmental mandates, refiners should balance many operating parameters of the fluid catalytic cracking (FCC) unit. In a traditional FCC unit, increasing the catalyst-to-oil ratio to raise conversion also increases the coke yield and catalyst circulation to the regenerator. The new technology provides the ability to increase both conversion and selectivity by recycling a portion of the carbonized catalyst back to the base of the reactor riser. The carbonized catalyst circulated from the stripper to the base of the riser is at the same temperature as the reactor. With no heat being added to the system the recycle is heat-balance neutral. Thus the catalyst circulation up the riser can be varied independently front the catalyst circulation rate without increasing the catalyst circulation rate to the regenerator.