Gasifier, as distinct from Digester.

8 years 9 months ago #39674 by Kiwi303
From the other thread, just to keep it from going off the tracks with talking about different technologies.

So I thought a post about a Methane Digester BioGas discussion was actually about Wood as Gasifying via Pyrolysis.

Spark asked if it would be better to run a gasifier off charcoal rather than Wood, Personally I see the wood gasifier leaving charcoal as a byproduct as a plus since that charcoal can then be crushed and used for Terra Preta style carbon addition to soils and gardens.

We already add charcoal to the gardens here on the farm by adding the ashes from the fire, complete with the small bits of unburnt charcoal.

Fires don't actually burn the wood, they heat the wood until the wood offgases and then burn the wood gas, hence why fires seem to float above the wood :D

On the other hand, a Charcoal Gasifier can be made just as well as a Wood Gasifier, and in fact a well made wood gasifier, once the wood gas is exhausted leaving a charcoal bed would then become a charcoal gasifier and continue to decompose the charcoal into CO and burn that. As I understand it, a poorly built wood gasifier would not manage the change from CO + H2 + H2O vapors to CO only and would die leaving charcoal.

Here's an instructable to a charcoal gasifier.

You Live and Learn, or you don't Live Long -anon

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8 years 9 months ago #507130 by Anakei
I love the idea of low tech alternative energy especially for cooking but when you look into them they seem so complicated to set up, and you are using 2 processes to create the energy - eg make the charcoal then burn the charcoal, or make the gas then burn the gas.

What is the advantage of this as opposed to some thing more direct eg a rocket stove?

Urban mini farmer and guerilla gardener

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8 years 9 months ago #507134 by Kiwi303
The gasifier creates gas which can be burnt in a spark ignition engine, AKA a petrol engine, and hence turn a generator or pump or other system which requires rotary input.

Ideal for areas without water flow sufficient to power a turbine or a wheel.

For direct heat application such as a stove then yes, it's not the best, but for an application where you want to run an engine without being reliant on imported fuel, just your coppiced wood clippings etc, then it would provide that engine power.

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8 years 9 months ago #507137 by spark

My thoughts for lsb-scale charcoal production are along the lines of a wood fired batch kiln.
Basically, you put carbon rich (plant) material into a retort, shut the door. Light a fire undneath it to start it, and the heat from the fire will pyrolyse the the material in the retort. I understand that the vapours given off by the airless pyrolysis of wood are sufficient to drive the process to completion should they be directed to the firebox under the retort and combusted (so you only need to light a wood fire to start it, and then it will run on its own gas until it is finished). I'd probably build it out of firebrick around a steel retort. It probably makes sense to put some kind of heat exchanger in the smokestack to heat water for domestic hot water and or radiators. The retort should probably have some kind of "explosion vent" so that unintended explosive combustion in the retort will simply say lift the lid and vent a gout of flame instead of tearing the retort apart like a bomb. I'd expect that maintenance requirements would be almost nil (ash removal, flue sweeping, etc).
I would expect the end product to be a high-grade charcoal that is almost entirely carbon and ash.

Why make high grade charcoal?
It's arguably better than coke for blacksmithing and steel making (coke is what you get when you use coal instead of wood to make "charcoal").

It's a clean burning cooking fuel (for a rocket stove or BBQ etc) - but only safe for use outside (unless you have a proper flued appliance eg a coal range) because charcoal combustion produces lots of carbon monoxide, and the smoke is far less iritating than that from wood, it's much easier to overexpose yourself to carbon monoxide by burning charcoal than it is with wood [xx(]

Because all of the tar has been cooked out of the wood, the charcoal is clean burning - no tar to clog up the pipes or filters of a gas generator (from what I have read, tar and the removal thereof is a big maintenance issue with wood gas generators). A gas generator lets you run a spark ignition engine without petrol, either as stationary power for electricity generation, water pumping, powering machinery like a lathe, or mobile machinery like a tractor or running your ute into town and back again.

As an aside, I understand that a few hundred years ago, the use of coal took off in a big way in the UK due to depletion of England's forests (why do you think the british navy was so interested in our giant Kauri?) due to population growth and mis-management. Firewood got expensive, so the poor people started burning coal (the wealthy perfered wood). The first coal mines were coal that was relatively easy to get at, scrape off the top soil and shovel it into your wheel barrow, etc, but as the easy coal was used up, the miners had to dig deeper and deeper, which raised the problem of digging below the water table. A man named Newcomen invented a "steam" engine that was put to work pumping water out of coal mines and the rest is history...


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