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In VDU we are facing problem in HVGO SECTION, that HVGO pump suction strainer periodically choking?
What’s the causes?
 
Answers
07/11/2018 A: keith bowers, B and B Consulting, kebowers47@gmail.com
Mr Ragsdale has posted a cogent response. I agree 100%. Some coke particle formation in the hottest section of a VDU is to be expected. This is why adequate overflash (down flowing liquid) is necessary to keep the the coke from fouling the internals and decreasing HVGO production. Either remove the pump suction strainer(s) permanently or revise to dual strainers with valving to allow periodic and routine cleaning of the (plugged) strainers.
Reducing the coke formation rate may not be economically optimum as that will require decreasing the temperature and residence time of the HVGO and Vacuum Tower bottoms (VTB) in the tower. Normally maximizing the yield of HVGO vs VTB is economically better.
07/11/2018 A: NS Murthy, Suez, murthy.ns.ext@suez.com
Check the entrainment aspects in VDU column. Also, analyze the strainer material for type of fouling - organic or inorganic. Look for any major shift in crude mix diet including acidity of HVGO stream. Additionally the colour of HVGO needs an quick assessment. Typically it should be D5 and when it crosses D8, then there is heavy asphaltenes 'lift' in the column. Control the "C" factor then. Also look for wetting velocity in Slop wax bed below. Good luck.
07/11/2018 A: James Chacko, Suez Water Tecnologies & Solutions, james.chacko@suez.com
Please check the TAN number of the VDU Feed and side cuts, like LVGO, VGO and HVGO. There is a possibility that it might be higher than 0.5!. If so then go to a High Acid Corrosion corrective mode. Check also the adequate flow for wash oil section PA below. Next is the strainer Micron size. A root cause can be arrived at post these minimum checks.
07/11/2018 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Pump suction strainers are for startup only. Leave the strainer out. This is a service where some solids are expected. The strainer on the reflux (pumparound) line is intended to keep the packed section from plugging. Bypass and clean regularly.