Economics

The previously discussed pressure curve shows that reducing the flash zone pressure from 50 mm Hg to 20 mm Hg can reduce the resid production from 35% to 30% of the crude charge rate. If the crude unit charge rate is 100 MBPSD, then the resid rate would drop from 35,000 BPSD to 30,000 BPSD. Depending upon the differential between HVGO and resid, the economics table provides a simple calculation for the economic value of the reduced resid. For example, if HVGO is worth $1/bbl more than resid, the 5,000 BPSD of increased HVGO production is worth $1.8 MM/yr. If the revamp costs for the unit in question is less than this $1.8 MM, the project payout is less than a year to reduce the flash zone pressure from 50 to 20 mm Hg. Other incentives can be calculated from the presented material specific to each refiner’s crude slate and operating pressure.

In the non-optimized furnace example previously discussed, the flash zone temperature probably could be increased almost 50° F to experience a similar coking tendency as the non-optimized design. The previously discussed resid production chart indicates that increasing the flash zone temperature from 700° F to 750° F reduces the Arab Heavy resid production from 32 to 27% of crude. Assuming a 100,000 BPSD crude rate, the resid production will drop by 5,000 BPSD. The previously mentioned economics table shows that a 5,000 BPSD reduction in resid production is worth $1.8 MM/yr. assuming a $1/bbl differential between HVGO and resid. This incentive could justify furnace and transfer line modifications allowing better deep cut operation.

It should be noted that this furnace temperature incentive ignores the increased cost for the heater duty since much of the heat is recovered by the exchanger train. A detailed engineering study should include the heater duty cost. Similarly, the cost differentials between HVGO and resid should consider that the heaviest HVGO can contain higher concentrations of metals and asphaltenes which may somewhat reduce incentives.