[Stoves] Charcoal from waste - home cooking or other markets? (Re: Crispin, Anand Karve)

[Ken Boak]

Dear Crispin, Anand, and stoves list,

Regarding waste charcoal and other uses of charcoal fuel:

I have recently restarted a project I was first involved in back in 2010,
which is the production of a biomass gasifier for village scale power
generation.

This involved the conversion of a Lister 6hp engine to spark ignition to
allow it to run on syn-gas from a wood chip gasifier.

My experiments were conducted at a workshop held at All Power Labs, of
Berkeley, California,  in February of 2010 and later in Spring of 2012 -
when I was fortunate enough to be working at APL for six months of 2012.

During that time myself and a team of fellow enthusiasts converted the
Lister to spark ignition and proved that it would run at the elevated
compression ratio of 17:1 - as common in small diesel engines. This allowed
the Lister to perform well on syn-gas without the usual loss of performance
associated with running a standard low compression engine on gas.

Since the initial experimental phase, I have come to believe that the
woodchip gasifier is a hard beast to tame, and that a charcoal gasifier is
a much simpler and forgiving technology and better suited to construction
and operation and repair - particularly in the rural setting.

So this opens up the question of supplying charcoal in a form that is
compatible with the gasifier and in a quantity that satisfies the demand of
village scale distributed heat and power systems.

The solution that I am currently researching is a charcoal gasifier that
has a pre-pyrolyser - as a means of producing the charcoal as an
intermediate fuel from assorted biomass.  The pyrolyser is initially driven
from the waste heat of the diesel exhaust and supplemented by the heat from
burning the pyrolysis gases, volatiles and tars - which otherwise would
potentially cause a problem later in the valve gear of the diesel engine.

Whilst some say that converting biomass to char is wasteful in terms of
energy, and also prone to generating high levels of noxious pollutants,
 the solution of having a closed torrefier, closely coupled to the charcoal
gasifier, that consumes all pyrolysis gases - and makes the associated heat
available for other purposes - such as water heating, drying, roasting,
cooking, boiling etc  reduces the pollution to a minimum.

It also allows a wide range of otherwise "difficult" agricultural waste
products to the converted to charcoal fuel in a form that can be used for
running the converted engine.  This includes the leaves, tree trimmings,
nut shells, husks, stones/pits, sawdust etc and any other wide variety of
waste products to be converted and used effectively as fuel for heat and
electrical and/or mechanical  power for running small agri-processing
machines

In my estimation somewhere between 1.5 and 2kg of dry biomass will be
needed to produce 1kWh of electricity using a charcoal gasifier.

For every kWh of electrical power produced about 4kWh of high grade waste
heat either as hot air for drying or hot water at 60C + will be available.

For those requiring a refresher on the design of the charcoal gasifier - I
recommend a paper from 1942 "The Making of the Kalle Gasifier"  submitted
to the list by Tom Miles nearly 10 years ago

http://gasifiers.bioenergylists.org/kallegas

Additionally for small scale charcoal gasifiers made from scrap materials -
I suggest Gary Gilmore's design from 2010/11 - which is described in a 3
part YouTube series

https://www.youtube.com/watch?v=srLETKDrwto


And from 2013 - his Simple-Fire gasifier

https://www.youtube.com/watch?v=KAJXdaCQ6uQ




regards


Ken

London
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