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We are experiencing excessive backwash frequency on our auto backwash filters (25 micron size) on the feed to the diesel hydrotreater unit.The hot feed is a blend of straight run kero, LDO and HDO which is fed directly from the crude unit with no makeup from intermediate storage. The feed when analyzed indicates a particulate level of about 6 ppm which in my opinion is low to cause such a problem. Has anyone experienced similar phenomena when the moisture levels in the feed are high? Moisture when analyzed was observed to be about 750 ppm in the feed.
 
Answers
10/08/2010 A: Christopher Turner, Snamprogetti Ltd, chris.turner@snampro.co.uk
6ppm may not sound much - but convert it into kg/day and think about the size of your filters and it may turn out to be quite significant.
31/05/2009 A: Reenamol Nirmala, Engineers India Limited, reenamol.n@eil.co.in
If the straight run feed to your DHT is coming from stripper (steam as stripping medium), there will be chances of high frequency of backwash. A coalescer common to both hot and cold feed can reduce the backwash frequency. The performance of coalescer at higher temperature needs to be evaluated.
18/03/2009 A: Prabhat Choudhary , IOCL, prabhatchoudhary26@gmail.com
I will go with you as same problem we are experiencing in our DHDT unit. I think some emulsion may form because of water presence and may cause the filter choking and excessive backwash. I also need clarification in this regard.