It is widely acknowledged that the world has to reduce its dependency on fossil fuels. This means we must obtain more of our energy from renewable sources. Many options are being explored, as it seems inconceivable that any single type of renewable energy will be able to satisfy all the world’s energy needs. In many applications biomass can replace fossil fuels very satisfactorily – but the world needs food as well as fuel, and there are conflicting opinions on the extent to which agricultural land should be used to produce fuel instead of food.
Types of Biomass
Biomass is animal or vegetable material that was recently, or still is, alive. There are two categories of biomass: crops which are grown specifically for use as biofuel, and waste matter. In the first category are virgin wood from managed forestry programmes, and a wide range of energy crops such as sugar beet, wheat, maize, potatoes and rapeseed. Waste matter comes from three main sources: some is agricultural waste, some is food waste, and some is the waste and co-products resulting from manufacturing and industrial processes.
Uses of Biomass
Virgin wood is used mainly for power generation, particularly in Combined Heat and Power plants.
Energy crops have a range of uses. Sugar crops and the starches from grain crops and potatoes can be converted into bioethanol, which is added to petrol; in the EU, petrol can contain up to 5% bioethanol. Rapeseed is one of the crops grown extensively in the UK; rapeseed oil is converted into biodiesel. Vegetable oils are also used to fuel diesel engines. Depending on type, conversion processes may be necessary, although some types of vegetable oil can be used without chemical processing.
Dry biomass from agricultural waste – such as straw and poultry litter – is widely used in power stations as a substitute for fossil fuels, and particularly in Combined Heat and Power plants. However, not all agricultural waste is used as a fuel as it has other potential uses, for example as a fertiliser.
Food waste again includes many different types of organic matter, each of which must be treated differently. Some of it will be dry biomass and some will be oil, which can be treated and used for the same purposes as oil from purpose-grown crops. Wet food waste can be used to produce biogas.
Biomass Versus Fossil Fuels
Bio-energy is classed as renewable because, with properly managed programmes in place, it is sustainable. By planting fresh crops and new trees we can ensure future supplies. But it is not a self-perpetuating, inexhaustible resource in the same way as sunlight, winds and tides. When we convert wind power, water power or solar power into electrical energy, we do so without depleting those sources in any real sense; but in order to obtain energy from biomass we have to burn it. So it is in some ways more comparable with fossil fuels.
To a large extent, the use of biomass parallels the use of fossil fuels. Biodiesel can replace diesel; solid biomass can replace coal; and so on. The substitution is simple because fossil fuels are, essentially, compressed biomass that was created millions of years ago. Biofuels, like fossil fuels, produce carbon dioxide emissions. The important difference is that the growth and subsequent destruction of biomass is part of a continuous process, known as the carbon process.
At any given moment, biomass is being destroyed and returning carbon dioxide to the atmosphere, but at the same time the living material that will in due course become biomass is taking carbon dioxide out of the atmosphere. If the biomass was not burnt but was left to decay naturally, the results would be the same.
Economic Implications of Biomass
The new emphasis on growing biofuel crops has wide-ranging implications. There has already been a significant change in land use, with agricultural land that has traditionally been used for producing food, now being turned over to the production of fuel crops. Market forces dictate that shortages will inevitably lead to higher prices, so if insufficient food crops are grown, everybody will suffer. There are many factors to be taken into account, and governments must ensure that, in trying to avert a potential fuel crisis, we do not instead create a food crisis.