What happens if we do not use steam for streaping and neither the slop lateral cut draw from the tower in our Vacuum tower? I would like to know the consequences for this type or operation.
Answers
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31/01/2012
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Rajkumar Chate, Sulzer, rajkumar.chate@sulzer.com
Vacuum columns without stripping steam are called dry vacuum columns. Columns using stripping steam operates at a COT temperature of 390-400 deg C while dry vacuum column operates at higher COT temperature (410-430 deg C). without increasing the COT temperature if we cut the stripping steam then quantity of VR will increase (some gas oil escapes with VR). For deep cut vacuum columns (Higher HVGO end point) people prefer to go with dry operation, this will reduce your vacuum system load. Without using the stripping steam if we increase the COT then there is high chance of CCR carryover in HVGO and sever coking of wash bed, to avoid carry over of CCR fraction (either bed height or higher surface area packing) shall be increased. To avoid coking of the bed 2-3 layers of coke resistant packing (grid) shall be fitted in bottom of wash bed.
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25/05/2011
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Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
DRY, WET and DAMP vacuum column designs exist in refineries. Vacuum distillation columns that does not use stripping steam are known as DRY VACUUM columns. Slop distillate / Slop cut is highly polymeric in nature and gets polymerized in to coke in the low velocity zones of equipment / piping. So if the slop cut is not withdrawn / kept live the coking will start and engulf the column internals / packed bed slowly. Coked up packed bed will lead to the entrainment of Asphaltenes / heavier ends into the Vacuum Gas Oil (FCC feed) raising the CCR values that leads to higher Carbon deposits on the Catalyst etc., adverse effects on FCC operations.
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18/11/2010
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Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Without the stripping steam, the cut point will be lower, in other words, for the same con carbon and metals contents in the heavy gas oil, the bottoms product flow rate will increase.
If the “slop lateral cut draw” is the spent wash oil, aka slop wax, and if it is drawn from a chimney tray, the liquid will reach the top of the chimneys, overflow , and experience serious entrainment in the vapor. To achieve the same con carbon and metals content in the gas oil, the flash zone temperature will need to be reduced, resulting in an increase in bottoms flow rate.
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