Plant and method for vacuum distillation of hydrocarbon liquids

Abstract

A vacuum distillation system and method utilizing an auxiliary, low capacity vacuum producing ejector operated in parallel with a primary ejector during the winter months enables significant reduction in the absolute pressure of a vacuum distillation column. Operation of a vacuum distillation tower at lower absolute pressures results in increased yield of desirable vacuum distillation products.

Description

CROSS-REFERENCED AND RELATED APPLICATIONS [0001] This application is a divisional application of U.S. patent application Ser. No. 10 / 401,617 filed in the United States Patent and Trademark Office on Mar. 26, 2003. Said U.S. patent application Ser. No. 10 / 401,617 is, in its entirety, incorporated into this application by reference.FIELD OF THE INVENTION [0002] The present invention relates to the field of hydrocarbon refining by the method of vacuum distillation. BACKGROUND OF THE INVENTION [0003] Vacuum distillation of petroleum hydrocarbons is a well known refining process commonly utilized in the art to minimize thermal cracking of heavier fractions of crude oil and obtain lighter desired products. Di-stilling these heavier materials under vacuum, that is lower pressure, decreases the boiling temperature of the various hydrocarbon fractions in the feed and therefore minimizes thermal cracking of these fractions. In conventional vacuum distillation systems, distillation is carried ...

AI Technical Summary

Benefits of technology

The present invention is about a plant and method for vacuum distillation of a liquid. The invention includes a vacuum distillation column, a first condenser, a primary vacuum producing ejector, an auxiliary vacuum producing ejector, and at least one second stage vacuum producing ejector. The second stage ejector can be connected in series to form condensate product that is discharged to a condensate collection vessel. The invention also includes an auxiliary ejector, which is a capacity of about 2.0 percent to 20 percent of the capacity of the primary ejector. The auxiliary ejector is operated in parallel with the primary ejector during the cool season months when the average temperature of available cooling water is about 70 °F or about 15 degrees lower than average cooling water temperatures during the warm season months. The invention reduces the load to the primary ejector, resulting in decreased pressure to the vacuum distillation column and increased recovery of heavy gas oil from heavy petroleum hydrocarbon feeds.

Problems solved by technology

This extra condensing capacity results in a lower than design backpressure in the primary ejector.

Thus, the primary ejector is not typically designed to take advantage of lower backpressures available as a result of lower temperature cooling waters available during the cooler season months.

Under this circumstances lowering the backpressure will not have any measurable effect on the ejectors suction pressure.

Available methods to reduce the column pressure, such as decreasing the suction load by decreasing the column stripping steam injection rate or reducing the furnace lift steam injection rate, has the effect of decreasing efficiency of the vacuum column and reduces the recovery of desirable gas oil product.

Installation of such systems would, of course, involve undesirable capital expenditure.

Images