Dear Colleagues
In case that the salinity of oilfield or brackish water is high, a possible method is blending the treated flow with high saline feed water (to dilute the input salinity). Is there any other more intelligent process available? - Any data or experience about / with High Efficiency Reverse Osmosis (HERO)?
Thank you in advance!
Ruediger
I'm not certain what you are trying to achieve. What would you do with the permeate blended with feed water? If your question is motivated by a desire to only partially desalinate the feed stream, producing a somewhat saline "permeate" stream, there are some possibilities. As you are aware, RO in conventional form only produces a rather pure permeate. Historically, the development of RO membranes has proceeded in the direction of ever higher salt rejection. It is possible to partially desalinate (some salt goes through the membrane) using a nanofiltration (NF) membrane. NF membranes preferentially reject divalents, thus are better known for reducing hardness. However, they can also be used to desalinate in stages. They are commercially available. It is also possible to modify a commercial RO membrane to let some salt through (the details may be proprietary). The advantage of using an NF or modified RO membrane is that because there is some salt in the permeate, the pressure across the membrane need not be so high. This can allow one to start with a feed water salinity that would require a pressure exceeding the membrane strength if one were doing conventional RO. The salty permeate could then be used as the feed water in another instance of the process to produce less salty permeate, possibly terminating with a conventional RO instance (if a highly pure permeate is desired). Although I have been involved in some research on the feasibility of such staged desalination (as distinct from pressure staging, which is done to increase efficiency in the conventional RO process), I am not aware of any commercial application.
Dear Thomas,
thank you. NF-Filtration is a good suggestion.
From what I understand, currently high salinity raw feed water is pretreated with RO to a lower efficiency level and the permeate then blended with the raw water again separately to produce a lower salinity feed water before RO/NF again in the next stage. This would allow using the membranes within it its limitations and prolong the use of membrane useful life and reduce pressure use. Well a hybrid system with energy recovery has been used though there are some offering RO systems which vary its approach for treating very high saline feed water. Check out some links below:
http://www.membranes.com/docs/papers/New%20Folder/BRACKISH%20WATER%20RO%20AND%20NF%20OPERATIONS%20AMTA%202010%20Final%20071610.pdf
http://idadesal.org/wp-content/uploads/2013/05/BANFF2013_SESSION5.pdf
http://www.lenntech.com/abstracts/2104/treatment-by-nanofiltration-and-reverse-osmosis-of-high-salinity-drilling-water-for-seafood.html
http://www.twdb.texas.gov/publications/reports/numbered_reports/doc/r363/c6.pdf
http://www.hydranautics.com/docs/papers/New%20Folder/Effect%20of%20Feed%20Ionic%20Strength.pdf
http://web.mit.edu/emilytow/www/Desal_2015_Thieletal.pdf
http://www.dhptraining.com/pdfs/dohs_details_website%202014-1-17.pdf
http://www.wrri.nmsu.edu/conf/conf11/reverse_osmosis_deep.pdf
http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_003b/0901b8038003b4a0.pdf?filepath=liquidseps/pdfs/noreg/609-02010.pdf&fromPage=GetDoc
Mohan - Thanks for posting the list of links.
Peter - Thanks for the reminder about FO. FO is described in some of Mohan's links.
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