Used with permission (© SAIT Polytechnic, MacPhail School of Energy, 2009)
The Crude Plant serves three purposes:
The salts and solid contaminants are removed by desalting, a process which consists of adding make-up water low in contaminants to the feedstock stream, passing the combined feedstock and water stream through a mixing valve to disperse the water into extremely small droplets, and passing the combined stream at low velocity through a vessel containing an electrical field. When the mixture contacts the electrical field, the water carrying the contaminants coalesces and separates from the crude oil. This procedure is repeated in a second stage where a further reduction of the contaminants occurs. The brine effluent containing the contaminants is routed to the Waste Water Treatment Unit for treatment and disposal.
After desalting, the diluted crude is fractionated into various boiling-range products in a single crude oil fractionation column. Fractionation is accomplished by heating the diluted crude oil stream in a fired heater to vaporize the lighter components. The two phase mixture is fed to the flash zone of the crude tower where the vaporized gas oil and lighter components flow up the tower and are condensed at various stages and removed.
Gas oil and jet kerosene are removed as side draws while a naphtha/jet diluent is removed from the tower overhead. The naphtha/jet and gas oil streams are routed to the Naphtha/Jet Hydrotreater for further processing; the diluent is returned to the production fields for reuse. The unvaporized residuum, which contains the majority of the contaminants and is similar to tar in composition, is stripped of light ends in the bottom section of the tower and routed to the Hydrocracker Reaction Unit for conversion to lighter components.