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In a hydrotreater plant, water carry over in diesel is giving a problem. Is there any possibility that oxygenates are forming water in reaction?
 
Answers
13/02/2018 A: Abhay Raj Mishra, Iocl, mishraar@indianoil.in
Oxygenated compound like naphthenic acid/phynol produces water during course of hydro processing reaction but that water normally separated in high pressure and low pressure separators. the main cause for the water in diesel product is the steam being used in steam /diesel stripper. the obvious solution is coalescer followed with salt dryer.
Also check your steam and stripper bottom temperature and try to maintain stripper bottom temperature about 20-30 Deg C higher than the steam temperature.
20/06/2008 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@ap.pall.com
Is there a steam stripper also in this HDS? This is often source of water contamination in diesel rundown. As diesel is cooled, water condenses and the droplets are quite fine and the emulsion can be quite stable. High efficiency Pall Phasesep or Aquasep liquid coalescers can be used to remove virtually all free water from diesel rundown ( to <15 ppmw free water in diesel). This is often done to protect salt drier and prevent excessive salt usage and also prevent salty water breakthrough.
It is also important to consider the run down temperature. Run down temperature should be not more than 20 deg C higher than tank storage temperature to prevent water condensation in the tank and haze formation.
The other alternative to LL coalescer and salt drier is to use vacuum drier of course but that is significantly more expensive in capital cost.
19/06/2008 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Oxygenated compounds such as naphthenic acids are readily hydrogenated in a hydrotreater reactor with water being one of the reaction products. Other sources to consider: If you have a water wash, carryover from the water wash is an obvious place to look. Also many diesel hydrotreaters have steam strippers. The diesel leaving the stripper is saturated with water at stripper temperature. When the oil is cooled on the way to storage the water solubility decreases, which causes a free water phase to form. Most refineries I've seen have either vacuum or salt driers to manage the diesel moisture issues.
18/06/2008 A: Raghavendra Sangam, Libra Techcon Ltd., rsangam0504@yahoo.co.in
Check hydrotreater feed composition for oxygenates and calculate water formation rate that may be possible (assuming all oxygen is converted to water). Compare with the quantity of moisture you are getting in the product.
Reactor outlet stream will be injected with water, before cooling, to wash the salts that are formed as reaction by-product. Check the injection rate versus the operation/design requirement.
Check whether the downstream coalescer is working properly or not.
As a final product treatment, there may be a salt dryer. If so, check its performance. Change/top-up the salt in the dryer if required.