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I am working in UOP hydrocracker unit. In our feed filter backwash frequency is very high since one month. We have cleaned the filter elements one by one. After cleaning of filter some improvement seen for some days but then filter starts backwashing again. we have also checked CCR and asphaltene and all are within range. we process VGO and HCGO in our hydrocracker unit . It is recycle type with 97% conversion. please suggest remedy.
 
Answers
26/09/2017 A: Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Also check for inorganic particulates, which can also cause a problem .
24/09/2017 A: RAUL FLORES, PDVSA INTEVEP, fraulf@hotmail.com
Please pick up a good sample of the filtrate/solids/mud sticked to the filter element. Analyse it and crosscheck in function of the results: HC, Si, Fe, Al, and so on. That will help you to start.
20/09/2017 A: Vijay Beleri, Rateau energy systems, v_beleri@hotmail.com
Believe the feed filter is internally backwashed (filtrate used for backwashing filters in reverse direction) wedge wire filters. Have seen higher dirt load coming from following 2 sources.
Cold feed coming from tankages instead of direct, have normally resulted in higher dirt load, and frequent backwashes.
upset in operation of cokers resulting in higher dirt being carried over.
do you also have a product filter for HCGO in the coker unit?.
Please advise if you are able to
1) increase the backwash flow rate. If it is internal backwash the downside could be reduced feed going to the reactors. If you can indicate approx m3/hr being used for backwash.
2) Increased delta P for backwash. what is the present delta P during backwash.
3) can you physically verify that all the valves - especially drain valves are opening like they should during backwash cycle. have seen at times that some of the valves are stuck (especially of these valves done have limit switches), some of the housings/ banks may not be backwashing completely. leading to quicker backwash cycles.
4) has there been any change in temperature of feed, or its constituents. especially hcgo
20/09/2017 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
Here are a few things you may wish to consider:
1) One common cause for BW filter plugging is dirty backwash fluid which reverse plus the elements leading to short cycle time and high BW fluid generation. Is your backwash fluid filtered feed? ( i.e. filtrate)
2) If one or more filter elements are damaged or bypassing due to poor sealing or inconsistent pore size then dirty backwash fluid and reverse plugging can result. Sintered woven mesh filter elements can provide more consistent filtration quality and also longer cycle times compared to slotted V wire type of filter element.
3) Has anything changed with your feed composition or source? If so then OCT (Oil Compatability Test) could be useful to conduct to check feed compatability.
4) Have you determined what is blocking the filter elements? Is this particulate matter only, asphaltenes or gums?
5) if HCGO feed is coming via tanks are the tanks nitrogen blanketed?
6) Has there been any changes to feed temperatures? Is cold feed from tanks or imported feed being processed perhaps?
19/09/2017 A: Abdulkarim Aldabass, Saudi Aramco, dabassaa@yahoo.com
The problem might be related to the free water with the GO as this would carry out corrosion material in the pipes. A sample analysis for corrosion products will indicate the system cleaning
19/09/2017 A: Dave Collings, Jacobs, dave.collings@jacobs.com
Consider a higher HCGO wash oil rate which will create more recycle at the Coker (and incrementally hurt yields) but possibly improve your issue.
19/09/2017 A: Raghavendra Sangam, Larsen and Toubro Ltd, rsangam0504@yahoo.co.in
(1) First confirm the correctness of sensors in the feed and filter system (temperatures, dP setting for the back-wash initiation etc.) (2) Check for any change in viscosity / temperature of the filter feed since the problem began. Adjust the filter feed temperature to reduce viscosity within operational flexibility. (3) CCR and asphaltene are "within range" of what? Are they within range of filter design parameters? Check the flow rate is within design value and address suitably. (4) After certain period of time, filter elements lose their efficiency. Then the deterioration is exponential. Check with filter manufacturer. Re-visit the procedure for cleaning the filter elements. Chemical cleaning or 'burn' the deposit in thermal process? Or combination?
19/09/2017 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Coker gas oil solids can vary significantly. Many units have a filter in the coker. Some also have a sand filter OSBL on the line between the coker and the hydrocracker.