Micro-gasification: Cooking with gas from biomass - Amper

Micro-gasification: Cooking with gas from dry biomass
3.1 Solid biomass suitable as fuel in a micro-gasifier
Micro-gasifiers can handle a great variety of biomass that must be solid, relatively dry, and
of sizes that allow the proper passage of primary air. Although mineral coal could be used
in a significantly altered micro-gasifier, the focus here is on the vast resource-base of RE-
NEWABLE SOLID BIOMASS FUELS that other burners cannot handle. A wide range of
renewable biomass residues beyond conventional firewood sticks or charcoal can be used
as cooking-fuel in a properly designed micro-gasifier.
...using biomass that does not require the destruction of timber resources means
less stress on the local environment 17 :
For optimal fuel use and combustion efficiency the biomass fuel should
1) Be dry: moisture content preferably below 20%. High moisture content results in less
stable stove operation and decreased available energy output of the fuel because more
energy is used simply to evaporate the moisture.
2) Be slightly chunky to allow air/gas passage: particle size should exceed 4 mm in the
smallest dimension. For finer feedstock like sawdust and rice husk, a fan-powered micro-gasifier,
using forced convection to control the flow of air, is advisable
3) Have relatively uniform particle size distribution to avoid compacted zones or oversized
voids in the fuel container which would prevent the uniform progression of the pyrolysis
front through the fuel-bed
4) Be sufficiently energy-dense enough to achieve a reasonable balance of the ‗burnable
mass‘ in a given volume of a fuel-container with cooking duration and refueling efforts.
There are some general issues about choices of biomass fuels to be considered:
The fuel should not compete with resources necessary for food production (like land,
water, labour etc.) or a higher value use, such as a building material.
Fast growing fuels should not negatively impact the biodiversity of the locality.
Any fuel must be economically available in the long-term.
Fuel must be convenient to use and appropriate for the intended use.
The supply of any biomass should be sustainably managed, so that it can be a truly
renewable energy source
The fuel should not contain or release any toxic or harmful substances. In general, any
previously living material is non-toxic when combusted, but some fuels may have been
treated with toxic substances required by a previous use, such as treated lumber for insect
and rot resistance. Such treated materials should be avoided, especially in cooking
applications where humans are often in close proximity of the combustion gases.
In areas with irregular and scarce rainfall, drought tolerant species are preferred. Many
‗anti-desertification plants‘ that are suitable for restoring vegetation cover in arid areas can
also provide good biomass fuels. A selection of suitable plants is found on
http://desertification.wordpress.com/3-interesting-plant-species/. Some examples mentioned
are pigeon peas, flax, jatropha, bamboo, switchgrass etc.
Here are some examples of biomass successfully used as cooking-fuel in gasifier stoves in
Haiti e.g. peanut shells, rice and coconut husks, corn stalks and stover, small twigs and
branches, sugar cane bagasse, wheat chaff, animal waste, bamboo, citrus fruit rinds,
17 Partially quoted from http://www.charcoalproject.org/2010/05/a-man-a-stove-a-mission/
HERA – GIZ Manual Micro-gasification Version 1.01 January 2011
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