Micro-gasification: Cooking with gas from biomass - Amper

Micro-gasification: Cooking with gas from dry biomass
1.4 Micro-gasifiers for cooking applications
Because gasifiers require high temperatures and heat transfer into cold biomass, making
them small is difficult. As such, it has been a challenge to make biomass gasification suitable
for domestic cooking! Commercially viable gasifiers have long been understood and
used in large industry and even in transportation: over one million vehicles were fueled by
biomass (mainly charcoal) gasification during WWII, when liquid fuel was hard to come by.
But there was nothing similar for small applications such as a household stove. The most
common and best known industrial applications are downdraft gasifiers, where the gases
are generated and removed from the reactor (gas-generator), then combusted in a remote
burner, e.g. in an internal combustion engine or in a street-lamp supplied by town gas.
Fundamentally, the challenge in cooking is a question of scale; how to gain control over the
pyrolysis, gasification and combustion in a small enough (vertical) space to be used by individual
households.
Micro-gasification refers to gasifiers small enough in size to fit under a cooking pot at a
convenient height. It was conceptualised as a top-lit up-draft (abbreviated TLUD) process in
1985 and developed to laboratory prototype stages by Dr. Thomas B. Reed in the USA.
Independently in the 1990s the Norwegian Paal Wendelbo developed stoves based on the
same TLUD principle in refugee camps in Uganda. TLUD devices have always been intended
as biomass-burning cook-stoves and there were some early Do-It-Yourself backpacker
efforts, but it was only in 2003 that the first micro-gasifier was commercially made
available by Dr. Thomas B. Reed when he presented the Woodgas Campstove to the outdoor
camping niche market in the USA. 7
Commercially available models are still scarce, though there is growing interest. Module 2 of
this book attempts to give an overview on the current ‗state of the art‘ of gasifiers appropriate
for domestic use.
1.4.1 Comparative advantages of micro-gasfiers for cooking
Small-scale micro-gasifiers offer good opportunities for the use in cook-stove applications
and/or for domestic heating, because they can
Cleanly burn the woodgas in mainly smoke-free combustion (unlike conventional burning
of solid fuel)
Provide a steady hot flame shortly after ignition (no waiting, as with charcoal)
Have high fuel-efficiency due to complete combustion of the fuel (little smoke)
Be operated batch-fed over extended periods without attention (no tending of fire)
Utilise a wide variety of solid biomass fuels, even inexpensive often discarded small
biomass residues, that other stoves cannot easily handle (no stick-wood)
Give the user the freedom to decide individually when to use the device, as biomass fuel
is often locally available, within reach of most people. It can be collected or bought directly
by the stove user. Hence it makes biomass-gasifiers ‗ready-to-use‘ options, independent
from external factors beyond the control of the user that determine the availability
of other energy sources like electricity, fossil fuel supply, or sunlight for solar cooking.
7 More details in Module 2 and on http://www.woodgas.com/, where the stove can also be ordered.
HERA – GIZ Manual Micro-gasification Version 1.01 January 2011
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