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Hydrotreater feed filter

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This topic contains 3 replies, has 3 voices, and was last updated by  Hedewandro Lucredi 2 months, 1 week ago.

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  • #21876

    Hedewandro Lucredi
    Participant

    In our diesel hydrotreater, we have a feed filter and the feed is Diesel from DCU. The feed is coker naphta and gasoil. Sometimes, after switch we have some plugging and the automatic backwash is increased. The backwash time is reduced from 2 h to 15-20 min. Also we inject LCO (light cycle oil from FCCU) in order to remove some gums from the DCU streams and straight diesel that was stored in tank. Is it common in other hydrotreater (plugging)? And what about gums ? Why do we need to use LCO ? What happens if we do not use LCO ? What is it the plugging products (coke fines, rusts).

  • #25239

    Mike Kimbrell
    Participant

    Coke fines should be captured by the HCGO and should not end up in the LCGO that is typically routed to a Diesel hydrotreater. What range of gas oil is routed to this hydrotreater? For the filter fouling rate to increase after the drum switch is unusual for a diesel unit. It is more common for a HCGO hydrotreater.

    The problems I have had with LCGO fouling has been oxygen intrusion causing polymerization of the olefins in the LCGO. A very low level of oxygen can catalyze this polymerization. In one case, the source of oxygen was the straight run diesel that was stored in a tank that was vented to the atmosphere. Oxygen diffused into the straight run diesel. When that stream was blended with the LCGO from the Coker, the oxygen catalyzed the polymerization of the olefins as the feed was preheated.

    This does not seem to fit your case. If adding LCO from an FCC helps, then a potential cause is entrainment of asphaltenes into the gas oil that you are routing to this hydrotreater. What is the MCR (or CCR) of this feed? Is the feed clear or is it dark? LCGO should not be dark. It will turn dark as it reacts with oxygen, so you need to look at it right after it is sampled. Asphaltenes will eventually blind the feed filter and you will need to disassemble them to remove them as they will not backflush off at some point.

  • #25301

    cjaviervarela
    Participant

    Mike make a great resume.

    In our older DCU, we suffer similar problem (but not that often) because of poor fractionation between LCGO & HCGO as consequence of multiple revamp of the Units. When we change the main tower those problem disappear

    What do you see at the filters? do yo make any analysis of the at your laboratory?

  • #27363

    Hedewandro Lucredi
    Participant

    We observe corrosion products mainly. It seems that when we have any flow variation some corrosion products are carry over from the system (tower, pipes, etc) and goes to the filter.

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