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Residuum & Vacuum Bottoms
From the base of the atmospheric distillation tower, the fractionated atmospheric residuum or heavier ends from the first stage refining process are conveyed to the vacuum tower. Due to the high viscosity of this residual fluid a charge pump is required to boost this byproduct to the vacuum tower. At this next refinery unit the medium is once again pre-heated prior to its introduction into the base of this vessel. The hot process stream is exposed to a hard vacuum. The sub-atmospheric pressure promotes vaporization of the heavier materials at temperatures below cracking conditions. Greater amounts of light ends are removed, including light and middle fractions of fuel oils, gas oils and a residuum called Vacuum Bottoms. The resulting vacuum residue, now even more viscous than the original residuum feedstock, again requires boosting to either the facility coking unit or asphalt plant, where the medium is cooked to produce coke for use in steel and aluminum production.
Nasty: a word which aptly describes these two fluid-handling services. Even at elevated process temperatures the extracted, residual fluids are highly viscous. Dispersed, solid contaminants that accompanied the crude oil feedstock are now concentrated by distillation in this byproduct, exposing the Residuum & Vacuum Bottoms pumps to an abrasive process fluid. In both applications NPSH / NPIP is at an absolute minimum due to the high vapor pressure of the process stream. Proper heat tracing and insulation of the pumps, and in particular their shaft seal(s), is essential to achieve good pump life. Operating the pumps at reduced speeds will also help to extend the design life of the pump rotating assembly and mechanical seals, while also affording the best suction lift capabilities.
Have You Considered The Value Of Using Rotary PD Pumping Technology?
Refinery production managers and operators around the globe have experienced the benefits that volumetric, rotary PD pumps can bring to these services. Having one machine that can efficiently transport heavy, medium and lightweight products simplifies the number of pieces of fluid-handling equipment required at these facilities. Controlling the rotary PD pumps with an adjustable speed drive allows operations to be performed in a “timed” manner without the need for flow control valves, eliminating the need for the recirculation of surplus process fluid. This reliable system control method takes full advantage of the tremendous turndown flow range of rotary PD pumps and their inherent high suction lift capability, making them an ideal fluid-conveying solution for your Residuum & Vacuum Bottoms handling systems.