What is the purpose of the polishing column? What does it do? Is it used in the drying process?

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The polishing column takes excess methanol and soaps out and substitutes for a water wash. The advantage is a savings in time, and elimination of the waste water issues. There are several available absorbent materials available on the market. The material I use is based on refined hardwood chips. Thank you for your inquiry. I am happy to post additional documentation that you would find useful including process flow diagrams, bill of materials and more detailed component photos.
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From reading at journeytoforever.org I gathered that it is good to eliminate water-washing as it leaves the water contaminated. Can you direct me to a resource where I might read more about the polishing column's function? So you put the hardwood chips in the polishing column and press the methyl esters through like a filter? Thanks for your response.
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The base column was purchased from http://www.turnerbiodiesel.com/ but was then modified so that it could be rotated and reversed to backflow the filter media and also facilitate cleanout. I can post more images of the quick connects and frame that make that possible.
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That would be great! How many gallons before you need to change the media? Do you have an estimate of cost/gal to use this method? This source says 2-4 cents per gallon with DW-resin. http://www.biodieselmagazine.com/articles/8999/ion-exchange-resin-as-dry-wash-media
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I see now that the information I sought is on the turner biodiesel website. Thanks for uploading the diagram of your system, Dorn. Where are the filters and what sizes are they?