Micro-gasification: Cooking with gas from biomass - Amper

Micro-gasification: Cooking with gas from dry biomass
3.4.3 Densification
The most important processing need is densification of bulky low-grade biomass materials,
available as wastes and in high volume that can otherwise not be used well as cooking fuel.
Compacted and densified fuel has several advantages:
It has a higher heating value per volume (more carbon per volume).
It reduces transport costs (more fuel, less air to be transported)
It has more predictable performance in a stove due to more uniform size, shape, density
etc.
It is often easier and cleaner to handle (less dust, easier packing etc.)
It is more convenient as it comes in the right size ready-to-use (no chopping required)
It has better storability (less moisture absorption, less mould, less spontaneous fires
through self-ignition, less insect-infestation than natural fuel)
It can be a solution to waste management problems
It adds value to low-value residues, often creating employment in the process
However, densified biomass is not the magic bullet! Additional equipment and labor are
required. To establish this capability locally, outside investments are recommended.
Only where fuel is already a commodity (like in many urban areas)
Only where households have purchasing power
Only where there is a large source of un-used ‗wasted‘ residual biomass (do not compete
with the use as manure or compost)
Only where there is a feasible link between the source of biomass and the market of the
densified fuel (relation of distance, transport costs and the value of the fuel)
Only where fuel densification can be run as an income generating business
Only where there is electricity so that larger scale operations can be done without electricity
only manual production at a small scale is feasible
How can materials be densified for use in micro-gasifiers?
Various binding and compaction methods are used to ‗glue‘ the loose biomass material
together to form a compact dense shape, which does not immediately fall apart during drying,
handling and use a fuel. The intended use of the product and the envisaged scale of
operation determine size, shape and the needed degree of compaction of the product.
The processes of biomass densification can be clustered in three main groups 23 :
The wet, ambient temperature, low pressure (10-15 bar) process: an added binder is
optional, as binding is effected through random rearrangement of softened and detached
natural fibres in a wide variety of agricultural residues and in other waste feedstock. The
process accepts sawdust, rice husks, bagasse, coffee/ peanut shells, and other granular
feedstock as well as charcoal dust and crumbs -or purposefully charred agricultural residues-
as part of the matrix, as long as the fibres can encapsulate them into a tight nonelastic
mass when compressed. Emphasis is on careful blending and pre-preparation of
feedstock for pliability, combustibility and other behaviours. Once the principles are mastered,
a far wider variety of ingredients are possible as compared to other processes. Densification
and shaping can be done using a hand to squeeze the material into shape, or
human force to press the material in a mould. Over 25 designs of hand operated or mechanized
versions of presses are in use, based on various ways to create pressure: levers,
hydraulic jacks, screw platens, treadle/peddles etc.
Costs range from $50 to $750. The density of product is commonly 0.3 to 0.5 gm/cc.
23 based on an email by Richard Stanley from the Legacy Foundation in May 2010.
HERA – GIZ Manual Micro-gasification Version 1.01 January 2011
81