Biomass burner idea
Burning biomass, especially something like grass clippings which are really easy to get, is a lovely idea.
Solar is great but it’s not always the best way to get your energy, and if you need a fuel biomass is the cheapest and most readily available. Unlike waste veggie oil, it also scales up very well and is inherently low carbon.
The main problem that I was seeing when thinking about how you might design an easy to build biomass burner is:
1. Safety, a hopper of dried grass clippings is a fire hazard
2. Feed mechanism.
3. If you want to make electricity efficiently by burning fuel, you need to capture the heat produced with good efficiency using a heat exchanger of some sort.
4. Ash needs to be handled.
A biomass burner for electricity production is the hardest, and I just thought up an idea for it that seemed pretty good and I though I’d share it.
Basically the heat exchanger is vertical, and the fuel is dropped down the intake of it. The heat exchanger could be shaped in a slight helix shape if you wanted rather than straight, but you get the idea.
To increase the efficiency of the exchanger it would be as long as possible, and the walls could be textured in an appropriate way, or fluted or otherwise enhanced.
The interesting thing is that it could be used for a wide variety of different biomass types. With a large center tube chopped would could be used. Having metal flaps protrude radially into the center of the tube could help a bit to improve heat exchanger efficiency here maybe.
With an auger or other feed mechanism grass clippings or pellets could be used.
BTW the intake of air is still convection powered, and it might need some start up procedure or some more clever designing in some way to make sure the hot air goes up the right way, not up the intake. A one way valve on the exhaust?
It could also help with safety a bit because the high temperatures are normally kept away from the fuel input. Although potential reversal of the siphon could be a small problem, potentially releasing sparks, the exhaust gasses should be relatively cool in any case.
BTW I recently discovered the Harwell Thermo mechanical generator which sounds pretty cool. No bearings, no accurate machining (or I think hard to make flexures depends on how easy the flexure is to make) needed.
If you could make a more efficient one that didn’t have rubber in the engine (which limits the operating temperature and therefore efficiency) that could be awesome with a burner like this. I think we can afford some wire gauze or steel wool here.
Way cheaper than solar panels, and the waste heat can still be used.