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We have two sets of desalters and each set has 2 stages i.e., 2 desalters in series. Our crude oil props input to desalter mainly BS&W, API, Salt Content, Filterable solids, Viscosity and Residence time are within (or equal to, in case of R.Time) the design conditions. But we are unable to obtain the desired outlet parameters even though these are within the design parameters. For Ex: Salt ptb (o/l) - Design:1, Desired: <0.4, but actual is 0.6-0.8, like that there are variations in all parameters viz., BS&W, Filterable solids & Oil in water etc.
How can we improve these parameters in the existing train so that we can reduce the severe pre heat train fouling that is very frequently happening and overhead corrosion. Would effective demulsifying and anti foulant agents will be helpful in this regard? If so, please recommend?
 
Answers
02/03/2009 A: Berthold Otzisk, Kurita Europe GmbH, Berthold.Otzisk@kurita-water.com
The different types of crudes require special adjustment of the electrical desalter system. A change of deltaP at the mixing valve or change of the level of the oil and water phase often help to improve the performance. It is useful to find the optimum deltaP range for the desalting of a crude oil blend. Starting with a low deltaP stepwise increase the deltaP every hour. Check the salt concentration of the desalted oil frequently and carefully observe the desalter effluent. No problem, if the desalter effluent becomes black, but it should not become oily.
Powerful emulsion breakers will help to improve the dehydration of the crude oil. This will result in lower salt concentration and reduced corrosion potential in the top pumparound and overhead system.
Depending which crude blend is treated it could be helpful to change the emulsion breaker program.
Kurita's ACF technology is a very interesting tool to reduce the corrosion potential timely before corrosion problems can occur. The additives used for this technology are chemical liquid formulations based on a very strong organic base. These additives can be injected directly after desalting to react with the chlorides before entering the furnace section. This is an alternative to caustic injection and reduces the chloride concentration in the overhead system significantly.
Asphaltene precipitation is often observed to be the main reason for preheat train fouling. Powerful antifoulants stabilise the asphaltenes and avoid further precipitation.
19/02/2009 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Any number of things could be causing your problems. Inadequate wash water rate or poor water quality can have a significant impact on desalter performance. On the water quality side, high pH/NH3 can cause bad emulsions, especially if your crude has naphthenic acids in it. Hard water sources going to the desalter can cause solids to form in the desalter, which can hurt desalter performance and increase fouling. Poor mudwashing practices can lead to problems. If you have not gone through an exercise recently to optimize your mix valve DP, that should be done.
If your desalter has a lot of crystalline salt, that will make it harder to meet desalter performance objectives and can contribute to fouling and corrosion problems. It's also possible that your desalter is doing all it can do without spending capital to upgrade it. If I read your note correctly it was designed to achieve 1 ptb salt out. Your target is <0.4 ptb and you are actually achieving 0.6-0.8 ptb (I'm not sure what your o/l abbreviation stands for). That looks to me like your desalter is doing better than design. At that level of salt out, it takes a lot more work to achieve each incremental .1ptb reduction in salt out.
Changing your chemical treatment program - new emulsion breaker and/or adjunct chemistries - may or may not help. Antifoulants can work but are usually expensive. If you want to try antifoulant make sure that you have good baseline operating history on your preheat train and a good monitoring program in place so that you can make an accurate assessment of whether antifoulant program is providing enough benefit to justify cost.