Vacuum Unit Design Effect on Operating Variables



To revamp vacuum units, process modelling and equipment design know-how are needed, and the understanding of connected equipment performance can lead to higher gasoil quality and yields, with fewer unscheduled shutdowns.



Process modelling errors and failure to design vacuum unit equipment as an integrated system has caused yield loss, poor gasoil quality, and unscheduled shutdowns. The vacuum unit charge pump, fired heater, transfer line, column internals, and ejector system must be evaluated and designed together so that operating temperature and pressure can be optimised to meet economic goals. Revamps need to push major equipment to its intrinsic limits to minimise investment.

Real equipment performance should be the basis of a revamp, not office-based assumptions or cursory reviews of the original equipment manufacturer's data sheets. Even though vacuum unit equipment is often highly constrained by existing equipment, an experienced revamp engineer can often manipulate heater outlet temperature, column flash zone pressure, coil steam injection, or vacuum bottoms stripping to achieve revamp yield and reliability targets.

The challenge is to accomplish these ojectives while meeting stringent investment criteria or Capex restrictions. Vacuum unit heater-inlet-through-ejector-outlet must be considered a single system when a practical, operable, and cost-effective revamp is to be implemented...


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Tags: CDU, VDU