Biodiesel and SVO Forums Home
Is dry wash Temp sensitive?

This topic can be found at:

March 04, 2014, 11:01 AM
Is dry wash Temp sensitive?
I'm getting mixed results with dry washing. I currently use a 65 gal cone bottom drum that is 3/4 full of mixed shavings/dust from various hardwoods. I'm recirculating with a constant rate of about 2 gallons/minute. Sometimes I can get soaps down to 60 ppm after 24 hrs of pumping and sometimes it's not dropping at all from 1000 ppm.
I'm doing 50 gal batches with KOH. I whole batch demeth to recover about 4.5 gallons of methanol, then separate the glyc for 24 hrs before I send it to dry wash. My processing space is subject to wide temperature variations with the winter weather. Right now its changing between 20-30*F and 70*F
March 04, 2014, 11:11 AM
I don't dry wash, so you can take my comments with a big grain of salt.

My understanding is that the key is dwell time. It sounds like you are recirculating at a pretty fast rate, pumping the fuel through the chips multiple times. Most people seem to get better results by moving the fuel very slowly, passing it through the chips (or media) just once or twice. I have also heard that once the chips become saturated with soap, they will actually release it back into the fuel -- there is a limited lifespan to the media before you need to replace or regenerate whatever you're using.

I just wonder if those factors are having more of an effect than temperature. I don't recall ever reading anything about temp effects on dry washing.

Cheers, John
March 04, 2014, 11:39 AM
Hi Biopac,

After bio sits in a cone bottom tank for at least a week to allow the bulk of soaps to naturally drop out...and to minimize all this excess soap saturating your dry wash media...
March 04, 2014, 11:51 AM
Ryan P.
My dry washing isn't with wood chips, but with the KOH soap there is a temperature effect on my filter bags. The KOH soap is a jelly, so the warmer it is, the thinner the jelly and the more that the bags miss. I try to keep my fuel during soap filtered between 60-75F, warm enough for the fuel to move through the filter bags but not so warm to allow the soap to thin out and move through, too.

When I was brewing in small garden shed, I had left the final bag hanging over the empty cone tank and had the shed get so hot in the July sun that the soap flowed out of the bag and collected in the cone bottom. Not a lot, but a cup's worth.
March 04, 2014, 01:59 PM
Jon Heron
Further to what the others have said, yes, the colder the better, the colder the fuel the less soap it can have in solution.
Also upflow is the way to go, the soap all settles to the bottom of the chips so by using downflow you are reducing the effectiveness and longevity of the chips by a large margin. Particularly if you are feeding out the bottom of a cone, that will guarantee the soap will be coming out with the fuel as it accumulates.
The other large factor is methanol content, it takes very little methanol to trap a lot of soap in the fuel, you may try bubbling dry air through the fuel overnight before sending it through the chips.


Simple schematic for a pump and heater control with a high limit
Sensor for the biodiesel/glycerin layer
March 04, 2014, 07:54 PM
Thanks for the feedback. I forgot to mention that sometimes I start dry washing with the bio still quite warm from the whole batch demeth. (120*F) So maybe that's my problem. I will let it cool off and then run the process after letting it cool. ....I usually use the fuel as fast as I make since I drive a lot! so I'm hoping to dry wash it as quick as possible. Driving an 05 liberty CRD and an 01 Excursion 7.3 and the nearest gas station is 20 miles from where I live.
March 31, 2014, 03:17 PM
Yes. As mentioned, Dry wash is temp sensitive. I now let the Bio cool down, then send it through the tank "down flow" style and it comes out testing 0 ppm from my untreated batch of sawdust chips. So, glad it's working better.
March 31, 2014, 11:51 PM
Just a thought as I looked at your post.
Since you demeth and spend the energy dollars
to heat it, IMO after demeth it would be worthwhile to bubble
and circulate the batch if you can. Just a bit of insurance to drive of the residual
methanol while in the cooling process.
We then let it settle for a couple of days before
it hits the chips.
Glad to hear 0 PPM,, the trick now is how long will it stay there before
you need a re-fresh.
Good Luck

1999 K3500 Dually with a new AMG 6.5TD turned up a bit by John Kennedy
Chevy DMax Totaled thanks to a 20 year old in a Mustang
Mercedes 300CDT
John Deere
On B99.?