 |
| ||||||||||||||||||||||||||||||
For an assessment of the part which gasifier technology can play in the energy scenario of the near future, the potential of an increased energetic use of biomass has to be seen in a broader context.
Agriculture and forestry, especially that of the so-called developing countries, will increasingly be confronted with the following problems:
- On the one hand only a small amount of harvested plant material is really being used.
A far larger part of biomass remains as waste (wood cuttings, shavings, saw dust, straw, cotton stalks, coffee pulp, bagasse, rice husks and so on), and thus poses a local disposal problem, which most of the time is "solved" by burning.- On the other hand primary manufacturing processes need energy, which is usually provided by consuming fossil fuels. For countries with a weak economy this means an additional strain on their balance on foreign exchange payments by importing mineral oil, respectively a loss of income by fewer exports. In addition the consumption of fossil fuels always implies a strain on the atmosphere by increasing the CO2 content (introducing carbon stored in fossils into the atmosphere).
- Furthermore, developing countries have an enormous demand for biomass, needed for domestic firing processes as well as for drying processes in industry or crafts. This demand is usually covered by firing wood and charcoal from forest stands. The devastating consequences for the natural resources are well-known.
Facing these problems the tasks of agriculture and forestry have to be reconsidered. In addition to the classic demand for a sustainability of production-which is not at all realized at all times - the protection of environment and resources has to be increasingly taken into account. This requires
- protecting the still existing forest stands
- securing the sustainability of forestry by afforestation
- growing energy plantations appropriate to the according site
- efficient use of biomass by integration of waste and residues of agriculture and forestry as a source of energy and for substitution of firewood.
By making energetic use of residues and waste material the ruthless exploitation of resources could be limited and a rational, environmentally adequate use of energy could be promoted. In this context the following technical procedures are of special interest:
(1) Gasification of residual biomass materials for generation of heat and power
(2) Substitution of firewood by other plant material
(3) Production of biocoal briquettes for use as cooking fuel and/or gasifier fuel.
In this report, a low cost charcoal gasifier for power applications in the range of 2 - 10 kW is presented and discussed. This gasifier seems to be appropriate for applications in rural areas of developing countries. But, this does not mean that gasification technology is already available to an extent that could contribute significantly to solve the problems listed above. The fact that, at the given state of the art, only charcoal can be recommended as fuel for small gasifiers (and, as well, that the use of charcoal cannot be recommended for large gasifier units!) indicates the actual limits of this technology. Charcoal production is bound (or should be bound) to forest management, and charcoal gasifiers should be used within close reach of forest areas. Even within this limitation, there is enough room for a substantial number of sites for gasifier units.
With respect to the regional energy consumption patterns however, the impact of small gasifier-engine-systems is rather marginal. If charcoal production is established, the major part of it will be consumed as cooking fuel. The additional demand for gasifier fuel is limited by site-specific considerations (is a gasifier suitable for a certain application), by economic considerations (is it significantly cheaper than competing energy supply systems) and by the still important aspect of acceptance of a reduced operational comfort.
Considering all these limits, an uncontrollable dissemination of small gasifier plants to an extent that results in an additional stress on natural resources appears not to be realistic.
An aspect which is not yet sufficiently studied is the use of commercially low-value charcoal for gasification: Observations in Argentina as well as in Malaysia have shown that a certain percentage of the charcoal, produced in local kilns, is of a physical dimension (particle size 1-2 cm) which is not desired by domestic consumers but well suited for gasifier application. A classification of kiln charcoal into "cooking fuel" and "gasifier fuel" may result in an increased efficiency of charcoal use without much additional demand for wood to be carbonized.
But certainly, the gasification of unused biomass residues, especially from agriculture, for the purpose of gaining mechanical and electrical energy in rural areas could considerably enlarge the contribution of biomass energy within a national energy scenario. Using uncharred biomass in gasifiers is easier when the biomass fuel is already available in a shape and size which demand no further treatment. This is for instance the case with nutshells, corn cobs, rice husks, saw dust and wood shavings.
Especially rice husks and saw dust/wood shavings are raw materials which are widely spread but hardly used. Gasifiers for rice husks have been intensively investigated in South East Asia and India for many years. Gasifiers for sawdust are practically nonexistent at the moment, even though the technology was still being employed in Germany a few years ago. In many countries of the Third World, however, there is a high demand in mechanical and electrical power for small saw-mills (10-20 kW power output), which could be met by stationary gasifiers (application for driving machines as well as power supply for small settlements). But, all existing gasifiers for agricultural and forstry residues share the basic disadvantage of producing a tar loaden gas, which has to be cleaned in a special gas cleaning train before entering the engine. This process is not always effective and, in most cases, results in condensates which require a final treatment before being released to a drainage system. This final treatment is neglected in practice. The design of gasifiers for uncharred biomass, producing a ,,tar free gas" (at least in defined quality) within the thermochemical process (and not by a cleaning process) is a demand which is not yet solved.
Gasifiers for heat applications are technically much less sophisticated, as tar loaden gases can be burnt with excess air in the burner. Obtaining process heat for industrial drying plants by means of gasification systems could contribute considerably to the protection of natural resources. The efficiency of gas producers is about twice as high as that of a simple furnace. The potential savings in firewood have to be estimated to be rather high (e.g. for large tea-drying plants: several thousand tons of wood per year and plant).
Co-generation of heat and power, based on biomass fuels, is a technology of increasing importance for industrial applications.
Fuel for gasifiers and fuel for domestic cooking will always compete to a certain extent. The search for alternative cooking fuels will play an important part in the future, and a basically available technology is the production of briquetted fuel from residues/ wastes in agriculture and forestry. An alternative to traditional charcoal production could be the production of big-coke briquettes from especially common agricultural waste, using methods of an "intermediate technology". A classification of biomass or big-coke briquettes with respect to their suitability to domestic firing, but also to gas production by means of gasifiers is needed to form a basis for further decisions.
The problems are not so much in the technical as rather in the economical and political field. Fuel prices, for example the price of biocoal briquettes, have to be seen as political prices. If a relevant substitution of fossil fuels and fire wood by briquettes is acknowledged as an important goal, a subsidized price for briquettes may be worth thinking about.
A risk of the increased offer of commercial fuels, derived from a variety of biomass residues, is possibly a reduced availability of "free" fuel for the poorest of the poor.
Information policy
Not every detail of the gasifier technology has yet been solved, and the rather convincing approach of the ferrocement gasifier as a cheap and reliable equipment in the power range of around 1 0 kW is just a first step. But, if the advantages of big-energy in a future energy supply scenario are taken seriously, it just depends on the decision to do it.
This decision has to be based on a broad public support. Gasification technologies are rather unknown, compared to other renewable energies like photovoltaics, wind energy, and even biogas plants. Quite a lot of prejudices and misinterpretations appear when people are confronted with a technology which is based on biomass consumption- that is, at least in industrialized countries closely connected with overexploitation of forest reserves, which is definitely not the meaning of "sustainable biomass manage meet". A correct and comprehensive information about the meaning of "energetic use of biomass" in the context of a sustainable biomass management is necessary to create a general acceptance.
Governmental backstopping
A new technology - and for the user, a gasifier is a new technology - needs some support to be integrated in a commercially oriented economy. Even under the improved starting conditions which an economically viable ferrocement gasifier may have compared to its more expensive predecessors, this technology will have to compete with more familiar and established equipment and even face an unfair competition with subsidized prices for liquid fuels.
Any dissemination of gasifier technology must therefore be based on an energy policy which encourages the use of new and renewable energies. India and Thailand belong to the few countries which already go in this direction:
"The Thai government has adopted a policy of utilizing locally available energy sources in order to reduce the amounts of imported energy. (...) For biomass this policy calls for a more efficient utilization of wood and charcoal and using more crop residues such as rice husk and bagasse"[7].
The Thai government encourages the adoption of nonconventional energy technologies through soft loans and tax exemptions for manufacturers of technically reliable gasification systems. An important demand is seen in rural electrification: 6% of the 50000 villages of Thailand are not connected to the grid, but is is estimated that 20 % of the rural population needs decentralized energy supply due to the fact that even existing electric grids can not supply all households and the numerous demands in the fields (e.g. irrigation pumps). Furthermore, mechanical energy is needed for rice milling, paddy threshing, milling of corn, cutting of wood in sawmills, crushing and squeezing of sugar cane [7].
The most important power demand is seen in the range of 5-10 kW.
According to Jain [6], the situation in India is very similar: "Changes in international oil scenario and increased import budgets for petroleum products etc. resulted in specific commitment being made to renewable sources at the national policy making level. This has been reflected through establishment of a separate department (Department of Nonconventional Energy Sources - DNES) within the Ministry of Energy at the Government of India level and establishment of state nodal agencies to propagate increased use of renewable sources in almost all states".
In the context of an overall national strategy aimed at reducing dependence on imports of petroleum products, power generation by gasifier systems is seen as a major focus. A need is defined for mechanical shaft power applications with major emphasis on irrigation systems, on electricity generation for rural industries, farms and institutions, and in direct heat applications for rural industries as well as for institutional cooking. The relevant power range, especially for millions (!) of irrigation water pumps, is 3.5-7.5 kW. For rural electrification and thermal applications, 10 kW electrical output respectively 50 kW thermal output is the adequate size.
Jain gives an interesting assessment of the quantitative impact of a large scale application of gasifier units for irrigation pumping in India:
- 1% of the current national firewood consumption can be adequate for producer gas based operation of 240000 pump sets (3.5 kW each) or for electrification of 60 000 villages.- A farmer could just use 3 to 4 % of his land for fast growing tree species to support his entire irrigation needs perennially. Alternatively, he could use up to 25% of the residues produced and meet his irrigation needs through small scale producer gas systems.
- Typical energy plantation yields can be anywhere between 10 tons and 60 tons (wet weight) per hectare and year and the country has a minimum of 62 million hectar of wasteland, a significant fraction of which could be used for energy plantations."
According to Jain, even hundreds of thousands of small scale gasifier systems would only have a marginal impact on the environmental balance. Nevertheless, it is desirable to focus dissemination programmes on biomass surplus areas and to ensure the sustainable production of feedstock, either in terms of residues or through fast growing tree species.
It must be seen, however, that despite all governmental support the dissemination of gasifier technologies in Thailand and India has not yet been as successful as expected. Obviously, the gasifier technology is still not as attractive to the potential user, compared to the conventional diesel or gasoline system.
Stimulating large scale applications of gasifier systems
The next steps should be the integration of demonstrative plants in project activities which present a convincing model for"biomass management". Having in mind that gasifier technology can contribute to environmental protection, especially with respect to the global concern about CO2 emissions, some isolated demonstration projects are definitively not enough. A large scale application however will depend on politic decisions and economic considerations and will require the following steps to be taken:
(1) Effective use of biomass resources for energetic purposes has to be recognized as part of a policy of increased use of regenerative energies with the aim to reduce expenses for petroleum products, to reduce CO2 emissions and to increase the living standard in underprivileged areas. Biomass energy has to be considered as an important contribution to the efficient and sustainable management of biomass resources.(2) Local manufacturing of gasifier systems should be encouraged by investment subsidies and tax exemptions.
(3) The energy demand and the respective demand and offer of biomass fuels has to be balanced. This will require careful selection of sites for installation in the early phase of a dissemination programme. In the long run, a commercialization of gasifier fuels by fabrication of biocoal briquettes from agricultural residues is one of the most important requirements for large scale introduction.
(4) With respect to application, two different strategies should be pursued:
a) Commercial application for irrigation water pumping, mechanical and electric power generation for cottage industries, gas generation for institutional cooking. A financial package of soft loans, tax reduction etc. may be necessary to compensate competitive advantages of traditional energy supply systems.b) For underprivileged areas and communities, fully subsidized electricity supply can be seen as a part of a policy of compensation of social deficits. The involvement of gasification technology offers a step to rural autonomy and creation of additional jobs on the countryside. A continuous technical assistance will be necessary until the technological knowledge and experience has settled. Energy provision alone, however, will not be sufficient for any progress.
(5) The aspect of fuel supply for gasifiers should be seen in a context with the fuel supply for cooking purposes. In the long run, firewood and charcoal from forest reserves should, to a large extent be replaced by fuels derived from agricultural and forestry residues. The cultivation of fast growing energy plants on areas, not needed for agriculture, may be a necessary contribution to the energy potential.
 |
 |
