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Effects of Flash Zone Pressure Upon Resid Production and Cut Point

Reducing the flash zone pressure reduces the resid production for both Brent and Arabian Heavy crudes. The slopes of the curves are similar indicating that the benefits of low pressure operation should be similar for other crudes. Operation at 100 mm Hg flash zone pressure is typical of old, high pressure units. Operation at the lower range of 7 mm Hg typifies a modern, low pressure deep cut design. Reducing the flash zone pressure from 100 mm Hg to 7 mm Hg reduces the Arabian Heavy resid production from 40 to 25% of the crude charge rate. Brent shows similar resid reductions although Brent contains less resid material than Arabian Heavy.

 

 

Reducing the flash zone pressure increases the resid cut point for both crudes. As expected, the Brent and Arabian Heavy cut points are very close together for a given flash zone pressure. Therefore, the expected cut point for a refiner's crude can be compared to this graph. The graph assumes a constant flash zone temperature of 725° F. Operating at flash zone pressures below 20 mm Hg can yield resid cut points above 1000° F.