David Bennett

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since Jan 13, 2013
Stockholm, Sweden
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Recent posts by David Bennett

I just put together a winter ready equivalent of the fridge. 2" polystyrene insulation behind 0.5" wooden panels.
I won't be trying carcasses. I'be been thinking about humanure but if the neighbours (maybe even my wife) got wind of it I'd get even stranger looks.
A visitor to next door asked if the mulch piles were compost
3 years ago
I was wondering about David's conclusions about the ultimate way to compost everything on a small suburban plot in a cold climate.

Through a few years of experimenting I've gotten it down to bokashi and then into an insulated, rat proof worm bin. The bokashi takes care of milk and dairy and to some extent pre-processes the contents for the worms. Of course the bokashi gets slightly acidic so it takes a week or so for the pH to level out before worms can tuck in but using these methods together I've composted chicken bones, dairy etc. in the middle of winter (-15 C/5 F) without it freezing. Although that time, the rats found their way in so to keep the neighbourly peace, I took that bin apart and had a raised tumbler for a while. But that was too wet and heavy to rotate so it never really worked as I wanted it to.

The current bin is raised 12 inches off the ground so the rats don't have a cosy spot to hang out - we'll see whether it works when the weather turns cold in a month or two.

Although I am in love with my worms, I'd be one less step to just bury the bokashi directly, and some time I do, between plantings. Although the volume of waste from the family would be too much to just do that I think. What thoughts or experience do you have regarding critter proof, small scale urban extreme composting when combined with as many perennial plantings as possible?

3 years ago

Peter Berg wrote:
This is one of the fundamentals: the port (or gate) is 70% of the riser diameter, so according to Bernoulli's theorem, in the opening itself the speed is higher and the pressure comparatively lower. The secondary air channel is right in front of the port so this lower pressure will feed air in automatically. Behind the port both the pressure and the speed do go back to normal which in turn causing a lot of turbulence. The flames inside the riser are forming a double ram's horn pattern, coming back onto itself and spiralling up, thus lengthening the time in the riser.

Your explanation is clear and that video is awesome, explains everything perfectly. Thank you.
4 years ago
Awesome sketchUp file - great resource for learning and great that you've shared it and the test results.

Some questions (most yes/no):
  • are the diagonal bricks in the feed area fastened in any way?
  • have you knocked them by accident when adding feed stock yet?
  • is the fuel fed in through the top of the feed area?
  • ... by removing the ceramic glass cover?
  • ... that constrains the dimensions of the feed stock to longer (say 16") sticks, right?
  • the opening to the riser is tall and thin and instead of the usual long low burn tunnel - what is the reasoning behind that?
  • the flange on the bottom of the riser is there to direct the gases upwards, right?
  • seeing as the burn doesn't have to be at the bottom of the feed area (due to exhaust leaving at almost any height) - does it stay there?
  • there is a secondary air intake behind the ceramic glass top, right?
  • is the front "free-standing"?
  • ... and made of metal?
  • ... doesn't it get crazy hot?
  • what temperatures are you getting on the top of the third barrel?
  • are you welding the connecting tubes (between the barrels)

  • Cheers!
    4 years ago
    Great stuff Paul!

    What size tenons are you cutting at most? E.g. for the table legs.

    An article in New Scientist about whirlwind power.

    65% cheaper than solar, made from non-exotic materials (probably) and self-sustaining sounds like a good combo.

    Watch that space!
    6 years ago
    Thanks Garry

    I wasn't familiar with the Keith Gasifier until you mentioned it. Looks like a guy with a lot of experience to learn from.

    A YouTube channel (that I found this morning) along the same lines is Mr Teslonian. He's got loads going on and he seems to share it all. I started watching this long film while on the underground to work.

    A learning journey is also described here (mdpub.com) where the guy goes from tar-stained failure to clean-burning success. With pictures and explanations of why things happened. He also talks about fuel - pellets are ideal as they burn consistently fast and hot.

    There was another method I read about a while ago where they preheated the air taken in. They claimed a much higher efficiency but it was mostly just theory. That does however coincide with one insight the guy at mdpub.com had - he added air feed tubes through the barrel to preheat the intake air.

    With regards to elegance, steam does have a cool charm but is just too fiddly and dangerous for a layman like me to play with. Stirling engines are elegant to my mind but sadly fiddly and with fairly low output.
    6 years ago
    Ah good find. I was citing Bentley "the compost guy" Christie from memory. The systems linked to in this thread are all (I think) water flushing systems which would dilute the waste. I wouldn't put undilute urine in my worm compost.
    6 years ago
    Without having read the solviva.com link I can say that once the worms are done with anything, it won't work in a hot compost. Also, urine would cause problems because the salts and probable build up of ammonia (through anaerobic digestion) would kill the worms pretty much straight away.

    What may work would be: me > hot composting > worms > food plants/trees. Add an extra mulch step depending on your exposure to environmental toxins over the past few months/years or as desired. I think I'd probably trust that process if the hot composting step got hot enough for long enough. According to this site batch composting would provide the oomph required to reach the higher temperatures (60 C/140 F). Not sure how that would work in an outhouse situation...

    I did read somewhere that worms are good at removing heavy metals from compost materials (waste food in that case) but I'm not sure what happened to the heavy metals... If they ended up in the worms then they'll either end up in the chickens or the compost if they die there.
    6 years ago
    TEG is fairly costly and then you'll have the problem of the heat differential - you need heat on one side and cold on the other to generate current. Do you get cold much where you are? Generating cold will also cost you.

    There's loads of stuff on YouTube about gasification. You may also want to check out FEMAs plans for a gasifier and the Gasifier Experimenters Kit for getting started quickly. All I've seen about gasifiers has required moderate/advanced metalworking skills and equipment which could be a bit of a hurdle.

    Search results for FEMA gasifier plans: Google search results
    Gasifier Experimenters Kit: www.gekgasifier.com

    There's also some Combined Heat and Power projects out there that combine biochar production (and therefore woodgas) with Stirling like this one in Denmark. With CHP and gasifiers, the critical thing seems to be cleaning the gas so as not to fill the generator in tar and other gunk.

    Let us know what happens and good luck!
    6 years ago