Flash vacuum distillation unit

Charge stock for the catalyst testing experiment was prepared by topping a sample of the in situ crude shale oil to 600°F in a batch still equipped with a column having 35 trays and then separating the 600°— 1000°F fraction in a vacuum flash distillation unit. Properties of the 600°-1,000°F fraction of in situ crude shale oil are shown in Table III. 

Cavitation occurs wherever irregular water flow takes place, particularly if high pressures and vacuum are involved in the flow systems. Cavitation is a serious problem in desalination plants. In multi-stage flash distillation units, cavitation occurs in ... 

In two stage units, it is often economical to distill more gas oil in the vacuum stage and less in the atmospheric stage than the maximum attainable. Gas formed in the atmospheric tower bottoms piping at high temperatures tends to overload the vacuum system and thereby to reduce the capacity of the vacuum tower. The volume of crude vaporized at the flash zone is approximately equal to the total volume of distillate products. Of course, the vapor at this point contains some undesirable heavy material and the liquid still contains some valuable distillate products. The concentration of heavy ends in the vapor is reduced by contact with liquid on the trays as the vapor passes up the tower. This liquid reflux is induced by removing heat farther up in the tower. 

Figure 1-11 General flow diagram for a distillation section (atmospheric and vacuum), including a primary flash unit, in a refinery. 

High temperature deep flashing and vacuum flashing of thermally cracked distillate also contributes to increasing the percentage of the crude, which can be routed to the FCC unit. 

The VPS is generally the first process unit. The VPS s goal is to fractionate the atmospheric resid or reduced crude so that the base stock will have the desired viscosity. The fractionation also controls the volatility and the flash point. The boiling point separation is accomplished by using high efficiency distillation/fractionation hardware. Secondary effects include asphalt segregation in the Vacuum Resid from the VPS (potential by-product), reduction in Conradson carbon and color improvement. 

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