Introduction VDU Feed/Products Different Types Of Vacuum Distillation VDU Flow Diagram Process Equipments - Heater - Vacuum Tower - Vacuum System
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Crude Vacuum Distillation Unit •Objective To distill the long residuum crude from the atmospheric tower at higher temperatures and reduced pressure. The VDU takes the long residuum from the ADU (Atmospheric Distillation Unit) and separates the heavier end products such as vacuum gas oils, vacuum distillate, slop wax, and residue at reduced pressure and high temperature.
•Feed •Long Residuum (Reduced Crude) from CDU
•Products •Light Vacuum Gas Oil, •Heavy Vacuum Gas Oil, •Residuum, • Slop wax, •Asphalt.
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Different Types Of Vacuum Distillation Dry Vacuum Distillation Low energy consumption, applicable to fuel type vacuum towers. Do not utilize stripping steam. Pressure profile • Flash zone: 20 mm Hg abs • Top of tower: 5-l5 mm Hg abs
Wet Vacuum Distillation High product quality, applicable to lube type vacuum towers and utilize stripping steam. Pressure profile • Flash zone: 65 - 75 mm Hg abs • Top of tower: 50-65 mm Hg abs
Damp Vacuum Distillation Low energy consumption and high product quality. Stripping steam is appreciably reduced and the ejector system is a three-stage system. Pressure profile • Flash zone: 35 mm Hg abs • Top of tower: 15-25 mm Hg abs
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VDU Flow Diagram
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Vacuum Heater
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Vacuum Heater Vacuum Heater •Vacuum heater is a cylindrical furnace having convection zone and radiation zone. •The heater operates at outlet temperature of 750F. •The furnace is fired by fuel gas and pilot gas.
Coke formation Reason: •Conditions in the radiant tubes cause the reduced crude to thermally decompose to coke and gas.
Avoiding coke formation: •By minimizing oil film temperature. •By reducing the residence time of the oil in the tubes of the radiant section. •Steam can be used to lower oil residence time.
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Vacuum Tower
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Vacuum Tower Sections: •Three different section of different diameter and height •Large diameter columns are used to maintain comparable vapor velocities at the reduced pressures.
Type of Trays and Packed beds: •Three packed beds for three draw off cuts and three draw off trays are used •Packed bed – Structural packing
Tray – Chimney type for draw off trays
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– Sieve trays for the bottom section
Vacuum System
Typical Vacuum system •Steam Ejectors •Condensers •Condensate receiver
•To convert pressure energy of high pressure motive steam into velocity. •Motive steam expands to a pressure below the suction fluid pressure creating the driving force to bring suction fluid into an ejector. •High velocity motive steam entrains and mixes with the suction fluid. The resulting mixture is supersonic. •Then the mixture passes through the converging, throat, and diverging sections of a diffuser, high velocity is converted back into pressure. •In the diffuser’s diverging section, cross-sectional flow area is increased and velocity is further converted to pressure.
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Vacuum System Ejector System for different types of towers
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Vacuum System Vacuum Condensers The primary purpose of a condensers in an ejector system is to condense as much steam and hydrocarbons as possible. By condensing steam and hydrocarbon vapors, the load handled by a downstream ejector is reduced. This maintains energy usage (motive steam consumption) for driving the ejectors, to a minimum.
