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Currently we are using service water as wash water to our desalter in CDU. Heat exchanger has LP steam on tube side and wash water on shell side where the wash water gets heated to 120 deg C before going to desalter. When we are trying to use a mix of service water and stripped water as wash water, our exchanger is getting fouled (Scales of salts are being formed on tubes within 2 days). The metallurgy of tubes in CS. IN other CDUs we are able to use stripped water along with service water and no fouling of exchanger is observed. How to proceed to identify the cause of fouling?
 
Answers
09/05/2016 A: James Chacko, GE Power and Water, james.chacko@ge.com
Reasons are well known:
Scaling tendencies, O&G, Polymeric components, Particulates and Heat
If this is in the Middle East Region, GE Water & Process Technolgies could handle the unit through appropriate treatment techniques
We have treated such waters successfully and three such units are already under our treatment
26/04/2016 A: Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
Deposit composition analysis will provide some clues of the fouling process. Stripped water with high pH is observed to have foaming and sludge formation tendencies. Some units dose Organic acids to manage the Desalting water (either service water or Stripped water or mix) pH in the range of 6.5 - 7.5. High TDS levels of Service water (from RO / MED plants or Borewells) will aggravate the sludge deposition / precipitation tendencies at elevated temperatures. In one location we used DM water towards managing the desalting water pH.
23/04/2016 A: Marcello Ferrara, ITW SrL, mferrara@itwtechnologies.com
You might also consider SWS water might have some organic contaminants (which is the case, if the feed is phenolic water) which will eventually polimerize.
As already suggested, scale analysis will better give you an idea of the phenomenon.
In case of polymeric fouling ITW Online Cleaning will solve the problem.
21/04/2016 A: NS Murthy, Suez, murthy.ns.ext@suez.com
Look into the service water quality and measure the PSI value (both before and after mixing with stripped sour water) which can tell about the scaling tendency of the water at such elevated temperature. As stripped sour water had to be used as makeup in desalter, it would be appropriate to minimize or avoid mixing with service water. A few refiners even recycle the desalter brine so as to get adequate washing of crude (say 5 to 7% vol of wash water in crude) when they have inadequate stripped sour water for use. As another expert commented, get the salt analysed too to validate the scaling with mixed water.
Your query also mentioned that there is no such deposit in another unit. Presuming the water sources (stripped sour water and service water) are same for both crude trains, check the LMTD and degree of super heat of LP steam between units.
21/04/2016 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
The use of sour water stripper bottoms as desalter water has been historically spotty. Some refineries tried the procedure only to stop due to problems, even where there is no heat exchanger on the water. What is different where you are successfully using stripped water? Different sour water stripper? Different sources of sour water? In your case, the problem is not due to different crudes (if they are different}, as the problem appears before the crude and water are combined, if I understand the issue. As Mr. Rodwell said, the kind of scale may provide a clue.
21/04/2016 A: karthik ramesh, indian oil corporation, rameshkarthik810@gmail.com
Use fresh hot /cold Demineralised water for back flushing the fouled side in this type of exchangers. we had implemented the modification in one of our crude distilaltion unit and reduced the cleaning frequency of this exchanger.
20/04/2016 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
Get an analysis of the scale. Also take analysis of the two water streams. Not all service water and stripped waters are the same, and compatibility issues can result in scaling as the temperature increases. Some divalent cations can be very insoluble in water given the right anion appearance. The service water may not scale by inself, but the presence of sulfates or cyanides from the stripped water could result in depositions.