Biogas

Biogas consists of approximately two thirds methane and one third carbon dioxide. Its production has a significant advantage over starch crop based and cellulosic biomass: it does not compete with human food demands for grain or starch. It is produced by fermenting such organic substances as solid waste or sewage, as well as agro-industrial wastewater. It can also be collected from landfill sites and marshes where it occurs naturally. Biogas is deployed either to generate heat and electricity or as a motor fuel. When serving the transport sector, it is applied to natural gas engines. In order to be appropriate for vehicles, it has to be purified by removing or separating carbon dioxide, moisture, hydrogen sulphide and other corrosive components. The purified gas is then compressed to a pressure of 200-250 bars in order to be applicable for vehicles. Since biogas burns well, it is used for direct combustion to provide energy in the form of heat or electricity. Although the main component of biogas is methane, which is a common greenhouse gas, when burnt as fuel it releases only half as much carbon dioxide for a given fuel value than most other fuels and does not give off poisonous carbon monoxide, so biogas is considered environmentally friendly.

Syngas

Syngas, the result of pyrolytic gasification, refers to a mixture of carbon monoxide, carbon dioxide, hydrocarbons and hydrogen. It is generated from a variety of feedstock, including coal, petroleum, gas and other materials of biomass origin, e.g. manure or agricultural waste. It can be chemically converted into fuels like methanol, being an intermediate for alternative liquid fuel technologies; in addition it can provide feedstock for a number of chemicals, mainly hydrocarbons. It is also a raw material for higher alcohols to be used in detergents and for ammonia in fertilisers. Syngas has similar properties to natural gas. It burns clean, so it can be combusted to generate heat or electricity. It also plays a role as a potential source of hydrogen production for fuel cells.

Producer gas

Producer gas is generated when wood, municipal wastes, charcoal or coal is converted into a gasoline like product through gasification. It consists of some 40 per cent combustible gases, mainly carbon monoxide, hydrogen and some methane. The rest is non-combustible, mainly nitrogen, carbon dioxide and water vapour. Although producer gas has a rather low calorific value due to its high nitrogen content, it is widely used in industry as a supplementary source for power or electricity generation. Producer gas used in internal combustion engines that were designed to run on diesel or gasoline affects engine performance, as its properties differ from that of the conventional fuels.

Biodiesel

Biodiesel can be made from vegetable oil plants like rape, sunflower, soybean, the fruits of oil palms, as well as from animal fats, algae and recycled cooking greases. It is more and more common to use biodiesel as an additive to conventional diesel fuels, so as to reduce the noxious gases emitted by internal combustion. With some engine modifications, it can also fuel a vehicle in its pure form. However, when applied in its pure form, biodiesel has a higher flash point than that of fossil-based diesels. Its viscosity results in a more intense pulverization, which is just another disadvantage. Nevertheless, if properly treated, these shortfalls can be abated. Moreover the advantages of biodiesel greatly surmount its disadvantages. Just to mention a few, it is non-hazardous, non-toxic, and biodegradable, it reduces air pollutants such as particulates, carbon monoxide, hydrocarbons, and air toxics. It burns more efficiently than petroleum diesel; its higher lubricity can reduce engine wear, prolonging its lifetime.