Q & A > Question Details
We have a Kerosene hydrotreater which is processing straight run light kerosene from crude unit to produce ATF. My feed conditions are : Temp at battery limit: 80-100 Deg C, pressure: 6.5 kg/cm2. Density: 0.804 @ 15 Deg C. Kerosene is being filtered by two basket type filter having 100 mesh (one stand by) (Filter temp around: 135-145 Deg C). We are facing a problem of frequent filter chocking, but filter element is clear, no dirt, no scale, no corrosion particles, you can say crystal clear like clean filter element, still having high DP.
what may be the reason of higher DP across filter?
Is there any chance of gum formation/ polymerisation (Because of additives in crude unit), which u can not see by naked eye, but may create DP?

Additional info:
Filter is getting chocked frequently. i.e. sometimes in 3-4 hrs (best achieved life 15-20 days). Once filter got chocked 16 times in 2.5 days. Dirty filter baskets are being cleaned by hydrojetting and followed by steaming.
Original design was of 25 micron (500 mesh), but because of frequent chocking filter mesh has been changed to 74 micron (200 mesh) temporarily. Filter element is of stainless steel.
Till date no adverse effect observed in reactor DP or heat exchanger fouling.
LK feed is straight run from crude unit, no feed from tankage.
which feed characterization study can be carried out to identify problem.
 
Answers
23/02/2011 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
You say ' frequent filter choking'. How frequent is that?
Probably the basket strainer effective surface area is too low. Basket strainers generally have very little surface area and therefore have very little dity holding capacity. They are designed mostly for removal of course material only - such as protecting pumps for instance. It is unlikely to be gums as there should not be olefins to polymerise if this is SR kero from CDU. At the operating temperature you advise of 135-145 DegC it is not very likely to be wax either. (Should be in solution at this sort of operating temperature and should not be in the kero cut anyway). The apparent lack of corrosion products in the blocked basket strainer is strange as that is what I'd usually expect to see as the main contaminant type.
We would suggest to undertake a feed characterisation study. Pall Corporation offers such consulting services to identify feed contaminants type, amount and behavior.
To protect Naphtha / Kero HT reactor and feed exchancer and reactor from premature fouling, we would typically recommend 2um, 10um or perhaps 20um rated filter elements. Are you seeing any premature reactor dO increase or heat excahnger fouling currently?
Note: 100mesh strainer is equivalent to in terms of 149um micron rating. So it's not really protecting your reactor very much anyway. Suggest you consider to bypass the basket strainers altogether until you can work out what the issue is. You might want to consider installing a high capacity cartridge filter with high surface area, and appropriate temperature tolerance to protect the feed exchanger & reactor. We have had excellent results supplying such feed filters for naphtha/ kero and GO hydrotreaters.
22/02/2011 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
Is the kerosene wet? It is possible in these filters, although usually at sub-50 micron, that entrained water can coat the filter elements and impose DP by reducing the sizes of the holes through which the hydrocarbon may pass.
22/02/2011 A: Muhammad Muzaffar Malik Sarfaraz Ahmed Malik, BPPL, muzaffar_malik1@yahoo.com
If the feed is coming to hydrotreater from storage tank then there are obvious chances for gum formation as a result of oxidation of olefins present in Kero(especially at the temperature above 100C) since the air is contaminated in storage tanks of Kero.
22/02/2011 A: keith bowers, B and B Consulting, kebowers47@gmail.com
I have not heard of this phenomenon before. What materials are the basket strainer constructed of? How do you clean and return the strainers to service? What is removed? 100 mesh is a relatively coarse strainer, not really a 'filter.' Generally speaking, a 'polymer' would squeeze through (extrude) through a 100 mesh screen with modest pressure drop.
Anything solid which is trapped by the 100 mesh screen, and is causing a pressure drop problem should remain there until removed by back-flushing or washing.
The 'gas-to-gasoline and 'gas-to-diesel' can produce small amounts of 'durene' which is insoluble in hydrocarbons and will plug filters and fine screens in fuel systems. I am not aware of any material normally present in crudes or crude unit kero that would 'disappear' when a basket strainer is taken out of service.
22/02/2011 A: Mark Willingham, Purolator Advanced Filtration, mark.willingham@purolator-afg.com
I believe there could be two possibilities here.
One would be as you suggest some type of gum formation/polymerization which would not reveal itself when looking at the filter.
The other could be an chemical incompatibility issue with your basket material, if your material is synthetic such as polypropylene (PP). If it is PP, there could be some "swelling" of the media which would show itself in the form of a higher dp.
If you are using a stainless steel mesh basket, my guess is that it is some type of gum formation/polymerization.
Our company does manufacture 316ss sintered wire cloth baskets in a variety of micron ratings. We also offer a fully automatic backwash filter system which may be useful in this application. But first, we need to know the material of construction of the currently used basket filter.