|
Matching Livestock Systems with Available Resources |
MEKARN Regional Conference 2007 |
There has been, and continues to be, a heated debate about the wisdom underlying the policies being promoted in rich countries to replace imported petroleum products with bio-fuels derived from forms of biomass that are also the primary source of food for humans and feed for animals. Ethanol is promoted as the replacement for gasoline, and is derived mainly maize and sugar cane,. Hundreds of ethanol distilleries are in operation and under construction. Distilleries that will use wheat and cassava are also in the pipeline. The main source of bio-fuel that can be used in diesel engines is the oil from the African oil palm, oilseed rape, soybeans and other oilseeds.
Indicative of the concern being felt in many quarters concerning development of fuel from crops that are the staple of the human diet, was the decision made recently by the President of Mexico when he vetoed the growing of maize and sugar cane for conversion into biofuels.
One of the most vehement critics of the ethanol program is Professor Tad W. Patzek of the Department of Civil and Environmental Engineering, University of California. His conclusions at the recent (September 2007) OECD Round Table on Sustainable Development of Biofuels, in Paris, were: “to decrease all automotive fuel use …. by up to 6 percent per year ….., while switching to rechargeable hybrid and all-electric cars”.
Professor Patzek recommended that the electricity should be generated from direct use of solar energy in photovoltaic panels. However, this technology is still extremely expensive with a 5KWe power supply requiring an investment of over USD 30,000 or USD 6,000 per KWe. A related issue is that such systems offer few opportunities of employment.
The alternative approach, that is the subject of this presentation, is the generation of electricity as a by-product , or associated product, of food/feed production. The concept underlying this approach is the "fractionation of the biomass". Most plant material consists of cell walls and cell contents, the former acting as physical support structures for the plant while the latter are composed of compounds that are mostly edible by humans and or animals. Inedible cell wall biomass is easily converted to an inflammable gas by the process of gasification, the gas in turn being the source of fuel for internal combustion engines driving electrical generators. The cell contents and related structures, such as tree leaves, are used as animal feed.
The model being implemented in Colombia is based around sugar cane and forage trees. Sugar cane is separated into soluble sugars (for animal feed or human food) and residual fibrous biomass (feedstock for gasification), by passing the cane stalks through a crushing machine. In the case of the forage trees, the crushing machine is replaced by goats which are naturally adapted to consume the most nutritious parts of the tree (the leaves and bark) leaving as residue the highly lignified stems and branches which, like the sugar cane bagasse, serve as feed stock for gasification. This model is highly appropriate for decentralized, small-scale production of electricity in rural areas. Long distance transport of biomass (as to a conventional distillery or power plant) is avoided, rural employment opportunities are promoted for growing the biomass, and availability of low-cost sources of electricity will facilitate development of rural industry, including access points for charging the batteries of electric vehicles..
It is estimated that the investment in a 5 KW gasifier-motor-generator, linked to a “UPS” (Uninterruptible Power Supply) and backup batteries will be of the order of USD 7,500 (USD 1,500/KWe), less than 25% of the cost of a comparable solar-voltaic system.