Micro-gasification: Cooking with gas from biomass - Amper

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Micro-gasification: Cooking with gas from dry biomass c) Wooden presses by Richard Stanley and the Legacy Foundation Richard Stanley and the Legacy Foundation are probably the most active promoters of manual biomass briquetting all over the world. The website http://www.legacyfound.org/ has comprehensive resources on manual briquette-making and numerous publications (for sale) There are various versions of the common ram-type press, cheaper ones from wood, stronger lever-presses can also be made from more durable metal at a higher cost. Samples of biomass briquettes from all over the world Source: http://www.legacyfound.org/html/photoGallery.html HERA – GIZ Manual Micro-gasification Version 1.01 January 2011 87
Micro-gasification: Cooking with gas from dry biomass III) Briquetting options: medium pressure, moist-dry feedstock This category comprises versions of presses, that can be either mechanically powered, e.g. by a large fly-wheel or electrically, with electricity requirements depending on the pressure and the intended throughput. The speed of densification or achievable throughput per hour, the energy consumption of the press and the quality of the briquettes produced depend largely on the properties of the feed material (flow ability, cohesion, particle size and distribution, etc.) The moving parts, which generate the pressure against a die are either rotating screws or back-and-forth-moving pistons. Typically outputs per hour are limited by the diameter of the die. Operation times depend on temperature build-up, with stopping required before the machine gets overheated. a) Screw-type extruder presses In a screw press / extruder a rotating, often conical screw takes the biomass feedstock from the hopper and compacts it against a die which assists in the build-up of pressure against the screw. The friction between the material and the die cause the material to heat to 300 ° C when the lignin gets mobilised as a binder. A heating mantle around the die is common to enhance this. The created log-shape briquette exits at the front in a continuous stream and needs to be broken off to the correct size. The screw is subject to wear-and-tear and the material quality of the screw greatly influences its life-span. In developing countries extruders can often be manufactured by skilled artisans. Figure and text quoted from: http://www.gate-international.org/documents/techbriefs/webdocs/pdfs/e019e_2003.pdf, page 5 Depending on the shape of the die, the log is usually cylindrical or hexagonal. The produced briquette typically has a hole in the centre from the screw (hollow-core). From the partial torrefaction of the biomass by heat (‗toasting‘) and the high degree of mobilisation of the lignin the surface of the briquette becomes dark and shiny like wax (‗waxed log‘). This type of briquette is becoming increasingly popular in urban areas of Asia like in Bangladesh. HERA – GIZ Manual Micro-gasification Version 1.01 January 2011 Briquette sale by bicycle in Dacca (Photo Robert Heine, 2010) Hollow-core briquettes have been used in micro-gasifiers, but no test results for performance or emissions are known. They are expected to perform slightly better than the compact briquettes produced by piston presses described in the next section. More testing is needed to judge the behaviour of these fuels in micro-gasifiers. 88
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Micro-gasification: Cooking with gas from biomass - Amper

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