Biomass, energy production and the bio-refinery concept.(RENEWABLE ENERGY)

The use of biomass as a source of renewable energy promises to provide another alternative to fossil fuels, and is furthermore a positive factor in any assessment of the longer-term prospects for fertilizer consumption. However, biomass tends to be a low density and bulky material, for which the handling, storage and transportation are major cost items. Ken Gilbert assesses the merits of biomass in the production of energy and he furthermore examines the concept of bio-refining, whereby a crop could be converted into a range of food, feed, fuel and other chemical products.

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Biomass has been defined as "the total mass of living matter within a given unit of area." Biomass is a sustainable resource that is constantly being formed by living entities by the intervention of air (oxygen), carbon dioxide, water, soil and sunlight. Light is particularly important as the potential limit on biomass yield is set by the amount of light available, its efficiency of interception and the efficiency with which intercepted light is converted to biomass. If biomass is not used as food, feed, chemical raw material or as an energy source, it is degraded in situ by micro-organisms to give its elementary constituent parts--water, carbon dioxide and energy in the form of heat. Carbon dioxide used in its formation is balanced with carbon dioxide released in its degradation, i.e. it is carbon neutral. However, in converting biomass to useful energy products, the amount of fuel used for growing, harvesting, drying, transporting and processing has to be taken into account. The balance between energy in and energy out is crucial. This is where conflict arises between different parties, as was mentioned in the article, Are Biofuels Really An Economical Alter native? (Fertilizer International, No. 409, November/December 2005.)

It has been said that the continuous growth of plants on our planet exceeds our primary energy requirements many times over. It has been calculated that the amount of radiation energy received from the sun that is captured by plants amounts to about 50 billion t/a of crude oil equivalent units (toe). Current annual consumption of primary energy is about 9.7 billion toe. The amount of biomass that would be available for energy use is only a small part of the total but it is a huge tonnage nevertheless. For example, it has been calculated that if half the straw ploughed back into the soil in Germany were converted into fuel, it could replace 14% of the country's diesel consumption. Furthermore, if the area left fallow in Germany (about 10% of agricultural land) were used to produce biomass for fuel, the replacement of petroleum diesel could be doubled to 28%. Prof. Scheffer at the University of Kassel/Witzenhausen has said that the total bioenergy potential in Germany is the equivalent of 56 million toe. This is sufficient to meet 50% of total transportation fuel requirements without any effect on food production. Prof. Kaltschmitt at the Institute for Energetics and the Environment in Leipzig has calculated that there is enough biomass in the EU-25 to produce up to 115 million t/a of synthetic automotive fuels. With regard to the United States, the Secretary of Energy Samuel W. Bodman, when opening a workshop on biorefineries, referred to the April 2005 report by his department, A Billion- Ton Feedstock Supply for a Bioenergy and Bioproducts Industry, which he felt dismissed the concerns of those who question the ability of biomass to supply enough energy to meaningfully displace a significant proportion of current petroleum consumption. The study found that biomass production potential in the United States exceeds 1.3 billion dry tons per year, which is enough to meet over one-third of the current demand for transportation fuels.

In basic terms, biomass consists of 38-50% …