3.            IMPLICATIONS

3.1        Energy Efficiency Implications

Looking at the transport sector we can say that the actual efficiency of an engine varies with design, size and running conditions. The average efficiency of diesel and gasoline engines under good condition is considered to be 30% and 20% respectively.

The efficiency of an engine running on producer gas is normally less because the gas-air mixture has a lower energy density, and there is other power losses associated with mixture induction in engines. Theoretically, gasoline and diesel engines operating on producer gas suffer a power loss of 30% and 20 % respectively. In practice, considering a wide range of producer gas quality, a power drop ranging from 25 % to 60 % can be expected when a diesel or gasoline engine is running on producer gas.

As far as biogas is concerned the part that can be used for energy production is methane. In combined heat and power plants it is converted into electricity and heat with an overall efficiency of about 80-90%. Because the chemical reaction combines the carbon in the organic matter with the hydrogen from water to form methane, it follows that for the optimum gas production the ratios of the raw materials should also be optimum. This is extremely difficult to quantify because the feedstock can be so variable. The electrical efficiency of a gasification-based combined cycle plant is much higher than that of a combustion-based steam cycle plant of the same scale. Thus a 30MWe state-of-the-art combustion plant will give an efficiency of 31% whereas a gasification plant would be capable of 42% efficiency.

3.2        Social Implications

The production of biofuels can provide numerous local, regional, and national economic benefits. The growth and conversion of biomass feedstocks creates jobs for local people in rural, agriculture-based areas. Because the market for transportation fuels is large, the widespread use of biofuels will increase the demand for raw material and will therefore increase the income for farmers. Increased demand for feedstock also helps to reduce the amount of surplus crops and reduces the need for national farming subsidies. Conversion of the raw material into fuels also provides economic benefits through the construction and operation of processing facilities. These facilities provide local employment and development opportunities in the rural areas of both developed and developing countries and can help improve their financial infrastructure.

As far as gaseous fuels are concerned, simple anaerobic digesters are used in rural areas of some developing countries to produce biogas from manure and crop residues at scales ranging from household to village. They provide fuel for cooking and power, by-products in the form of fertiliser and feed for pigs and fish farms, and substantial environmental and human health benefits.

3.3        Environmental Implications

Transportation is a major cause of adverse environmental impacts. Much of this transportation-caused environmental damage can be substantially alleviated by substituting biofuels for fossil fuels or just by using them as fuel additives. Carbon monoxide emission, for example, is a direct result of incomplete combustion, which biofuels can reduce because of the oxygen they contain. Other serious toxins contained in smog, such as PAN and ground-level ozone, are the result of a complex reaction triggered by ultraviolet radiation, but the principal ingredients are carbon monoxide, hydrocarbons, and nitrogen oxides. Again, adding biofuels to gasoline or diesel produces more complete combustion reducing carbon monoxide and unburned tailpipe hydrocarbon emissions. On the other hand, the typical 10% blend of ethanol with gasoline is more volatile than straight gasoline or ethanol (which has very low volatility), so hydrocarbon evaporation from the fuel system may be higher with ethanol blends.

Nitrogen oxide formation increases with combustion temperature, so NOx production actually goes up slightly with oxygenated fuels. The overall impact, however, of biofuels use is to substantially reduce the emission of smog-causing pollutants. The reduction of these unwanted products provides local and regional air quality and environmental benefits, particularly in industrial centres.

In contrast to other biofuels, biogas shares some of the disadvantages of fossil fuels in that it produces pollutants when burned, such as waste gases, some of which are toxic. These can be reduced by chemical processes before releasing the remainder into the atmosphere. The quantities involved are insignificant compared with other sources - although this would be something to consider if the use of biogas is to be increased. Carbon dioxide - the greenhouse gas largely responsible for global warming - is also released. However, this originates from plants which have absorbed it from the atmosphere, so no additional carbon dioxide is involved.