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I am working in a Diesel Hydrotreating unit. I would like to know how much should be the wash water flow.
I also look after Sour water stripping unit. Why are the feed valves to SWS stripper located near the tower.
Is there any specific reason for it? The same is the case with Amine recovery unit stripper.
 
Answers
08/09/2010 A: Egbert van Hoorn, Hocon B V, Egbertvh@hotmail.com
A guideline that can be used is the the level of NH4SH (amoniumbisulphide) in the wash water should not exceed 2-4% to avoid corrosion. 2% is conservative. 4% is somewhat more aggressive. The level of salts which is acceptable also depends on the type of material used in the HDS/hydrocracking unit.
Another reason for the location of the valves on the SWS and amine unit is to minimise the length of piping which is exposed to significant corrosion. The two phase flow is potentially corrosive because the vapours will be mostly H2S.
01/09/2010 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
The various hydroprocessing licensors have different recommendations for wash water flow, and it is dependent on the quantity of ammonia in the reactor effluent and the quality of the fresh wash water. But a quick check rule of thumb is that the wash water flow (fresh+recycled - if you are recycling some from the cold separator) should ensure a liquid volume fraction of 0.20-0.25 in the feed to the effluent air cooler. This should give you good contact between the water and gas. The question of fresh and recycle water ratios depends on the ammonia, H2S, and chloride concentrations.
On the subject of the feed valves to the SWS and amine regen columns - they are located close to the tower to minimize the length of pipe that will experience two-phase flow and thus reduce the risk of vibration.