Biomass is an energy source derived from organisms which are living, or were recently alive. These can be animals, or other small creatures, such as algae, but are usually plants or plant-derived. These take two forms: materials such as sugarcane and corn starch which are distilled to form bioethanol for fuel cells, or plant material which is burned directly to produce energy (lignocellulosic biomass).
When biomass is burned, carbon is released into the atmosphere in the form of carbon dioxide, or sometimes methane, both of which are greenhouse gases and contribute to global warming. However, in a managed biomass environment, this is reabsorbed by trees and other plants grown to replace those burned. In practice, biomass is intended to be a fully sustainable fuel, with the raw materials constantly replenished by means of forestry management and replanting.
When we burn fossil fuels (coal, natural gas, and oil), we release carbon into the environment that was previously stable, trapped within those fuels for millions of years. Biomass burning releases carbon that would reach the atmosphere anyway, since plants will eventually die and release their carbon content through their natural decay processes as part of the carbon cycle.
In fact, rotting plant matter is more likely to produce methane, which is a more potent greenhouse gas than carbon dioxide. As long as we replace the woodlands, we can create a closed carbon cycle, where the carbon released is balanced out by the carbon absorbed. The carbon released by burning fossil fuels can therefore be regarded as more environmentally damaging than the equivalent volume produced by burning biomass.
The main attraction of biomass is its sustainability. While virgin wood and energy crops such as miscanthus are often burned, energy can also be extracted from waste products. Examples include agricultural residues such as straw, food waste, and industrial waste such as residues and sludge from paper mills. In the UK, with our large poultry industry, there is potential for the use of poultry sludge and litter to provide some of our energy requirements.
Our environment can benefit in other ways from the use of biomass fuel. Harvesting of timber and energy crops gives greater incentive to manage our woodlands. With more managed planting and coppicing, our wildlife can benefit from maintenance of its natural habitats, and this will encourage biodiversity.
UK power production
Drax power station, which is situated in North Yorkshire, is the largest in the UK. Biomass burning was first tested here in 2004 using locally-sourced willow. Drax also uses wood pellets, along with other fuels such as olive and sunflower pellets, the husks from peanuts, and the by-products of rape oil production.
Although much of the fuel Drax currently burns is brought in from overseas, it is intended in the future to source biomass directly from farmers and other suppliers, either in the form of waste products, or plant matter grown specifically for burning. Farmers would be able to sell their waste products for fuel, rather than arranging for their disposal. Local networks of production and usage become possible, thus reducing costs and benefiting the local economy. Biomass also offers opportunities for new businesses to emerge in support of this growing technology.
There are other uses of biomass than being burned in power stations. Methane gas, although damaging if allowed into the environment, can be used as fuel if extracted and contained. Landfill sites, and human and agricultural waste, all produce usable methane gas, also known as biogas. Waste vegetable oils or animal fats can produce biodiesel, which can be used in standard diesel engines.
Does biomass have a future?
Looking to the future, research is progressing on the biomass to liquids process. This uses the whole plant, and so reduces the carbon dioxide produced and increases yield. In this method the plant is reduced to gaseous form, and then processed to produce syngas (hydrogen and carbon monoxide). This syngas is then polymerised, or built back up, into hydrocarbons like biodiesel.
Along similar lines, research on cellulosic ethanol is attempting to use the inedible parts of plants along with grasses and trees to produce biofuel in a process that reduces greenhouse emissions by 85% over conventional gasoline. Algal biomass, which grows at a much faster rate than trees and even grasses, may also be able to be used to produce biofuels in a similar process to those just outlined.
In conclusion, biomass energy is a field that is currently helping produce greener energy, and also offers exciting opportunities for the future.