|Low Cost Charcoal Gasifiers for Rural Energy Supply (GTZ, 1994, 49 p.)|
Gasification is not a new technology. Germany is a country with extensive historical knowledge in practical operation of gasifier powered vehicles, and a lot of literature is available from that time, which is not so long ago: It was during the Second World War, when about 350000 vehicles in Germany were running on gas. But is was not a free decision of the vehicle owners to fix a gasifier on the back of his lorry, tractor, or private car: It was ordered by the military administration in order to save fuel for the war machinery. Virtually every detail of the application of gasifiers on vehicles was regulated by the Special Department for Gas Generators (Zentralstelle fur Generatoren): The type of gasifier, the type of fuel, the fuel supply per month. Great efforts were made to concentrate gasifier manufacturing on a few, standardized types, designed for the available types of fuel (wood, charcoal, anthracite, brown coal, hard coal and peat).
Remarkable is the way of fuel standardisation: Narrow specifications were introduced to standardize particle size, content of ash, sulphur, moisture, tar and volatile components, calorific value and specific weight. Of course, the high requirements of standardization could not be met by small scale fuel production. The preparation of solid fuels was under the responsibility of a special industrial branch, directly under the command of the Central Department for Gas Generators. So, an extremely detailed, centrally organized administrative structure was necessary to realize a substantial conversion (in the order of 25 %) from liquid fuel to solid fuels.
The German experience with gasifiers was definitely not a decentralized, environmentally appropriate technology. It was an emergency technology, which disappeared a few years after the war, when liquid fuels were available again.
The renaissance of gasifiers began in the late seventies. It was the first "oil crisis" which triggered research and development in gasification, especially in those developing countries depending on oil imports. Facing the abundance of agricultural and forestry wastes in these countries, it was a logical attitude to focus on gasification of these low-value resources. But here begins the trouble: Theoretically-but only theoretically-all these plant residues can be gasified. But the extensive experience with gasifiers from World War II was acquired with wood- and coal gasifiers, and this is something completely different. The underestimation of the technical problems which arise when matter like rice husks, straw, saw dust, coconut husks, cotton stalks and so on are to be gasified, resulted in a number of insufficient design proposals and finally in a disappointment of promotors and users.
The fact that the oil prizes did not rise in the anticipated way, but to the contrary remained at low level for nearly a decade, gave the rest to gasifier enthusiasts. The job was just too tricky and not worth the effort.
Meanwhile, the interest in gasification has re-adjusted. It is not seen as a universally applicable option for energy supply, but as a component within the range of available "regenerative energies". It is a valuable supplement to photovoltaic systems, solar collectors, small hydropower systems, wind energy converters, and biogas plants. According to site specific conditions it has to be decided if an energy supply based on renewable energies is technically and economically viable or not, and whether this might be gasification or anything else. An advantage of gasifier systems is it that standard internal combustion engines (Diesel and Otto cycle) for a wide power range (1-100 kW shaft power) can be used for gas operation, and that the investment costs and life cycle costs for a gasifier are much lower than the respective costs for all other regenerative energy converters in the kW-range. A disadvantage is the necessary effort for fuel preparation and the resulting operational costs, which can vary considerably and do in fact define the economic viability of a gasifier-engine-systems.