Micro-gasification: Cooking with gas from biomass - Amper

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Micro-gasification: Cooking with gas from dry biomass Table of content Module 1: 1.1 Gasifying solid biomass for cooking 8 1.1.1 Steps of biomass combustion 9 1.1.2 The ‗uncontrolled‘ open fire 11 1.1.3 Improving control in a gasifier device 11 1.2 Practical Applications of biomass gasifiers 13 1.3 Distinguishing features of biomass gasifiers 13 1.4 Micro-gasifiers for cooking applications 14 1.4.1 Comparative advantages of micro-gasfiers for cooking 14 1.4.2 Design features making micro-gasifiers suitable for cooking 15 1.5 Example: the Top-lit Up-draft TLUD gasifiers 15 1.6 Performance of micro-gasifiers for cooking 17 1.6.1 Performance factors influenced by design or user 17 1.6.2 Environmentally influenced performance factors 19 1.6.3 Performance results 20 1.7 Summary: biomass gasification in a nutshell 22 HERA – GIZ Manual Micro-gasification Version 1.01 January 2011 7
Micro-gasification: Cooking with gas from dry biomass 1.1 Gasifying solid biomass for cooking Understanding the difference between ―feeding an open fire‖ and ―controlling a combustion process in a gasifier‖ is one starting point for understanding the way biomass and fire are combined in cooking devices. Let‘s start with a familiar example: Everybody has seen a burning candle: once lit, it proceeds to slowly melt the wax and burn with a stable flame for a prolonged time. Notably, wax burns by a multi-step process where it first melts, then travels as a liquid up the wick, then vaporizes due to additional heat received by the wick. The flame provides heat to melt additional solid wax at the top of the candle by both radiant heat and proximity. The vaporized wax mixes with oxygen in the air – and the visible flame is present at the interface where the wax vapours leaving the wick meet the oxygen in the air surrounding the flame. Wood burns in much the same way as the wax in the candle, with a few specific differences. Most of these differences are due to the fact that candles are made from highly refined wax, and wood is a less pure fuel – but much more available and affordable than wax. Wood and other solid biomass constitute, after all, the oldest cooking fuels. They are even today the most prevalent source of cooking energy on the planet. As in the case of the candle, also the burning of wood and other solid biomass is a sequence of transformations – occurring in close proximity, but separated by small distances in time and space, as shown in Figure 1. Figure 1: Changes in Solid Fuel The solid substances undergo changes determined by the presence of heat and oxygen: 1. as biomass is heated, it evaporates excess moisture and it‘s surface temperature increases, 2. at elevated temperatures, biomass pyrolyses (‗decomposes by fire‘) into combustible vapours and a solid, known as ―char‖, 3. red hot ‖char‖ can be converted to ash if sufficient oxygen is available, 4. mixed with oxygen the vapours and gases generated can be combusted when ignited HERA – GIZ Manual Micro-gasification Version 1.01 January 2011 8
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Micro-gasification: Cooking with gas from biomass - Amper

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