Most S&W liquids crackers employ a high-temperature (220°C +)
quench oil tower design (Fig. 6.2.5). This system recovers heat from the cracked gas at optimal levels
by using circulating quench oil, pan oil, and quench water at successive temperature levels. Hot
quench oil is pumped from the bottoms of the quench oil tower and used to supply heat to the dilution
steam reboilers. A slipstream from the tower bottom to the heavy fuel oil stripper is fed to the quench
fitting on the recycle furnace effluent. Viscosity of the quench oil is controlled by recycling the middle
boiling fuel oil components, via the stripper overheads recycle, back into the quench oil. This recycle
allows for the operation of the quench oil tower at a hotter bottoms temperature, thus maximizing use
of the furnace effluent heat. The fuel oil product from the stripper bottoms is pumped through a cooler
to tankage.