Fluor's approach of simulating a crude vacuum column provides the right basis for new designs or revamps involving the wash section of crude vacuum units to prevent coke formation in the wash bed and ensure its proper performance.
Coke formation can cause unscheduled and costly shutdowns, loss of distillate to resid, poor distillate quality, and poisoning of FCC and hydrocracker catalysts. To prevent dry out, during the design or revamp of crude vacuum column, the minimum net liquid flow rate at the bottom of the wash packed bed (net over flash) must be correctly determined. This net over flash does not include the liquid entrained from the vacuum column flash zone. Fluor has developed simulation models that can predict net over flash flow rate to help prevent net over flash, which has been identified as the prime cause of wash bed coking.