Right. So saving the world isn’t all about cute seals, swanky organic clothes, and sexy Tesla electric cars. We’ve built a gasifier that can burn just about any carbon source from wood chips to cow pies to straw if its pelletized. We also have alot of diversity in our CSE which is one of its primary strengths. Put those two together, add some beer and weird things are bound to happen. So a few weeks ago we were talking about available local waste resources that could be potential feedstocks, and one of our members happens to run my town Wastewater Treatment plant…. You can see where this is going and I don’t blame you if you stop reading now. But for those looking for ,erm, unique solutions to the coming energy crisis, please do read on!
This past Monday I got together with several of the more intrepid members of my CSE and met up at our local Sewage Treatment plant to see if we could find a better mix of the leftover sludge that wold burn. Weeks ago we ran about 10#’s of sludge through the gasifier and the results were not the greatest – it was too wet and our plant treats the leftover solids with lime to kill off the ecoli, etc and the high mineral content didn’t agree with the gasifier -rock dust doesn’t burn so good.
We hope that adding in some other carbon sources that the village has in abundance (chips and leaves) we can raise the carbon content and it will burn better. Here is yours truly shlepping chips into the augers (BIG augers… like 18″ diameter!) that they use to move the Bio Solids around.
About the sludge. Lets be clear about this: these are Class A Biosolids, which means they are clean enough to be certified for use as fertilizer for food crops if need be. The Biosolids are thoroughly processed, and are now no more human waste than my finished compost is still a melon rind. Still, I get it that its gross…
The issue is that due to the lime, it funks around with the soil PH if you add too much or too often.
So we are sitting on alot of it. Like enough to fill the All Purpose Room at my kids school – and that is just since November in a town of 2000 souls. If we can get this crap (pun intended) to burn we could literally power the entire Municipal yard on sh/t. [The jokes alone almost make this job worth it –they just never get old!] So that is why 5 relatively normal men are throwing perfectly good wood chips into an auger full of perfectly good Biosolids on a bright Monday Morning. No one ever said saving the world was easy.
We struggled to get the mix right for awhile. The augers were set to move the Solids expeditiously filling each gap in the auger almost completely, so there wasn’t enough room to mix in the chips. Once we slowed the intake of the sheets of drying solids, we were able to get something closer to a 50:50 mix of chips to processed waste which was our goal. The scale of this study is getting significant, we are rapidly moving from backyard tinkerer to players on a municipal scale. If we are able to make the recipe work, we could be only months away from setting up a test scale gasifier on site. How exciting! But I am getting ahead of myself.
The steam coming off the mixed pile shows how wet the mix still is – we estimate it to be over 70% moisture. That is about 4x too wet to burn – we like our fuels to be in the 15-18% moisture range. We were able to mix up this good sized pile in about 30 minutes, so the equipment is certainly efficient enough. Next up will be to set up some solar stills to see how rapidly we can dry the mixture without any energy inputs, and then see if it can burn well.
In the mean time, we have 2 concerns. The Biosolds are about 1-2% nitrogren and adding all that carbon will almost certainly turn this into a giant compost pile – the piles of pure BioSolids are already sitting at 90 F all winter on their own as a result of residual benign bacteria chewing on it – and we just inoculated our solids with all sorts of good bugs. That would mean we would be losing carbon to the air in the exhalations of the bacteria until it dries. If that becomes an issue then we will need to dry the Solids before we mix them to prevent the bacteria from firing up. The second concern that many of us voiced is that in taking the wet BioSolid and mixing in leaves, straw, and chips we end up with a mixture that looks remarkably like cob. Depending on the binding strength present in the sludge we may very well have just made a 2 ton impressionist sculpture on the municipal grounds when this all dries/hardens. Let’s hope not!
This may end up being one of our more notable failures, but Edison managed to create 10,000 ways to *not* make a lightbulb so we are due for some flops. But if we pull this off we may be on to something.
Seriously, I wouldn’t sh/t you on this…
Filed under: CSE, Gasifier, Renewable Energy | 8 Comments »