(56c) Heat Transfer and Heat Removal in Flowing Dense Phase Fluidized Beds

As refiners considered the processing of less expensive atmospheric residues from crude oil in the early 1980s, the removal of excess heat from commercial Fluidized Catalytic Cracking (FCC) units became an important issue. In addition to the traditional vacuum gas oil portion of the crude (650?1050°F), these residues contained heavier 1,050+°F material that possess a higher concentration of coke precursors. Cracking of the heavier oil and its contaminant carbon residue posed an operating situation requiring higher than normal heat release in the FCC regenerator. In combination with higher regenerator temperatures, other contaminants in the heavier feedstocks such as nickel and vanadium cause both accelerated catalyst deactivation and poorer yield performance. A heat removal device was needed to remove excess heat from the circulating catalyst and allow the refinery operator a means of controlling the regenerator and the FCC unit's heat balance.

This paper relates the history and work process for the successful development of such a heat removal device and the key engineering and fluidization parameters to quantitatively determine the heat transfer coefficients and heat duties are examined. The pertinent heat transfer data and correlations from the literature and the mathematical treatment of the device are illustrated. The result is an understanding of flowing gas and emulsion phase influences, surprisingly high heat transfer capabilities and simple designs that are still valid, reliable and valuable 25 years later.