Micro-gasification: Cooking with gas from biomass - Amper

Micro-gasification: Cooking with gas from dry biomass
3.4.1 Drying
Drying by sun and wind are feasible and cheap options in most scenarios where drying of
biomass cooking fuel is needed. Subsequent dry storage complements the efforts to keep
the fuel from regaining moisture from the elements.
One has to differentiate between core moisture of a fuel and surface moisture. Surface
moisture (when e.g. a core-dry fuel got wet in a rain shower, but the moisture has not penetrated
to the core of the fuel) can be removed in a couple of hours, while core-moisture
needs days, weeks and even months to be removed, depending on the diameter of the fuel
pieces.
Biomass fuel can easily be pre-heated with the effect to remove residual moisture if the fuel
is kept close to the stove before use. Some stoves offer special options like a warmingdrawer
for fuel underneath the stove for that purpose. Drying by kilns and ovens is typically
irrelevant for household fuels, so it is not discussed here.
3.4.2 Sizing
Sizing is understood here as Size reduction of compact, high-energy fuels to microgasifier-compatible
size by chopping, cutting, chipping, grinding, breaking, sawing, etc. This
applies mainly to wood or other solid predominantly woody biomass that comes in too big
chunks to fit in the fuel container of a micro-gasifier for cooking.
For ‗up-sizing‘ to create bigger chunks from small or inhomogeneous particle sizes the
processing needed is ‗Densification‘ which is dealt with in the next paragraph.
A word of caution: in an area with abundant supply of wood in the form of big logs or sticks,
it has to be considered carefully, if down-sizing of fuel to a micro-gasifier-friendly format is
the most feasible option, or if there are other alternatives to burn that type of biomass
cleanly. Chopping of wood by hand is a big physical effort which most people dislike and
therefore complain about. In a scenario where there is no scarcity of big-sized wood, other
stove-models like e.g. rocket stoves, that can burn stick-wood well and cleanly, might be
more acceptable and appropriate for household cooking. If the production of biochar is the
major interest and household cooking not required, bigger units such as the Adam Retort
should be considered.
Sizing-requirements by hand can be a make-or-break- factor for the acceptance of microgasifiers
in an area. If too much additional effort is required to prepare the fuel, gasifier
stoves will not be liked and successful adaptation is less likely.
If possible, it is recommended that a fuel-supply chain of down-sized wood (e.g. woodchips)
be established at reasonable cost and convenience using mechanised equipment.
For areas without other smaller sized naturally occurring fuels, this will improve the acceptance
of micro-gasifier for cooking.
The main tools for manual sizing operations are knives, axes and splitters. For mechanical
operation there are some shredders and chippers with fly-wheels driving rotating blades
and grinders. Hammer-mills use mainly impact forces, whereas cutting-mills cut the material
to pieces with rotating cutting ‗teeth‘ out of hard metal 22 .
The most common equipment for larger-scale operations depend on external power by
combustion engines or electricity: Larger equipment might be needed as a pre-processing
step for densification: the input material has to be smaller than the densified output product.
In other words, to produce a pellet of 6 mm diameter, the feedstock has to be smaller. Industrial
equipment is based on shredders, grinders, or hammer mill-type choppers. Equipment
of all sorts of sizes exists and has to be selected according to the specific needs of a
location and scale of operation.
22 http://wiki.gekgasifier.com/w/page/6123688/Chippers,-chunkers,-loppers,-splitters,-shredders,disintegrators,-etc
gives a good overview on available wood-sizing equipment
HERA – GIZ Manual Micro-gasification Version 1.01 January 2011
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