DHT unit feed filters backwashing frequency increases

[Abu noor]

In our DHT unit back washing increases every 20 -30 minutes per cycle. The feed to this unit are SRGO and LCGO cold and hot. Currently we are facing back pressure and feed controls get fully open and flow is less . What is the issues and how we can solve it?
Thanks

[Nasir Hussain]

There may be many reasons for the increase in backwashing frequency;
1. Most of the time, it is due to the problem at the upstream units. Changes in trays level of CDU/VDU columns, flow disturbance in the feeds, change over of Feed supply pumps at the upstream units, heavy particles from upstream units, contaminants in the feed from storage, sudden adjustments made at upstream units due to change in the crude oil recipe or any other problem, Storage tank contaminated with Oxygen because Oxygen forms gum when reacting with diesel.
2. Backwashing can also be increased due to Backwash material not draining properly into the backwash rundown collection vessel.
3. Unstable flow from the upstream units like a sudden increase in the feed rate.

[Nasir Hussain]

Some suggested solutions are;
1.Reduce flow rate to control the back washing time as we discussed.
2. Cascade the tray level with storage tank and dix the feed flow to the unit. So that any variation in level will be sent to tank.
3. Flow increments to the unit should be gradual.

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