Friday, August 13, 2010

Reusing water to wash biodiesel

I mentioned in my previous post that the waterfall from the back of the building inspired me to pursue alternative water sources for use in making biodiesel. I haven't started collecting rainwater yet, but I bumped into one of my totes and realized I have another resource for the time being. The totes in the picture above are water from the spigot which is used during methanol recovery to chill the methanol vapors and condense back into the methanol tank pictured below.

So, I generally water the plants in the STARworks garden that are not watered with drip irrigation, but often there is more water used than the plants need. I redirect this water into totes for Anne or anyone else to use in the garden. I finally realized today that I should be using this water to wash biodiesel, rather than pulling more water from the spigot.

I pieced together the necessary hoses and fitting to make this work and commenced washing a small batch of biodiesel recovered from wash water and glycerol totes. I should explain that a little biodiesel is inevitably drained in the process of removing glycerol and/or wash water from the reactor and wash tanks. Since biodiesel is less dense than either of those, it will eventually settle to the top of totes. I carefully drain this biodiesel and put it in a tote or barrel until I've accumulated enough to wash and polish it into finished fuel. You don't want this unwashed biodiesel to sit around too long as it will eventually oxidize and become unusable as fuel. All is not lost as you can re-react the oxidized biodiesel, but that's not efficient use of time, money and other resources, so its time to wash some fuel!

When washing biodiesel to remove soaps created in the reactor, I typically add, then drain water a few times to get the soap content in the biodiesel down to less than 200 parts per million before drying and sending to the ion exchange column for polishing. The wash water can also be reused from one batch to the next allowing me to further reduce resource utilization. After I empty one of these totes of water, I will connect it to one or more of the downspouts to use rainwater instead for washing and perhaps chilling during the methanol recovery process. I will need to setup some sort of filter for the detritus in the runoff from the roofs. Until next time....

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