Improve FCCU Profitability- Bottoms System Upgrades
SUMMARY
A review of process flow scheme fundamentals and basic equipment operating and design principles that have improved unit operating profitability through better use of capacity, higher conversion and lower cost maintenance.
TEXT
Many refiners continue to face significant problems with reliability of the FCCU main column bottoms (MCB) system. Poor reliability reduces unit capacity, lowers conversion and increases the cost of maintenance. Reliability troubles include MCB pump head-flow loss, exchanger tube-side fouling, debutanizer reboiler shell-side fouling, and coke accumulation in the bottom of the main column. Because many FCCU product recovery sections are based on inherently unsound process and equipment design, only rarely can operating changes alone materially improve reliability. Thus, a revamp involving some capital expense is almost always needed to correct the basic shortcomings that lie at the root of the problem. This paper discusses process flow scheme fundamentals and basic equipment operating and design principles that have improved unit operating profitability through better capacity utilization, higher conversion, and lower cost of maintenance.
Superheated vapor enters the main column at 930-1025ºF (500-550ºC) where it contacts a portion of the main column bottoms stream. The MCB system removes heat from and scrubs catalyst fines from the reactor effluent stream. Consequently, the system operates at high temperature and contains solids that can erode and plug equipment not specifically designed for such difficult conditions.
MCB is pumped from the liquid pool in the bottom of the main column through an exchanger network where the temperature is reduced from 680-700ºF (360-370ºC) to 440-560ºF (225-295ºC) to meet the main column overall heat balance requirements...