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Biomass

The use of biomass as a source of energy has been helping humankind since the beginning of our era, when people discovered how to use fire for their benefit . It consists on the use of matter coming from vegetal photosynthesis, that unleashes the biological chain. Plants, that contain chlorophyll, transform carbon dioxide and water into organic material with high energetic value through photosynthesis. This material can be transformed afterwards into thermal power, electricity or bio fuels. According to its origin, biomass can be divided into animal and vegetal, being the last one the one that has more uses nowadays.

The most relevant sources of biomass are the following:

• Forest waste: waste coming from intervention of humans on forests (pruning, grazing off, clearings, cuttings)

• Agricultural waste: they can be surplus of cereal straws, feedings, rests of vineyard pruning. One of the most used is the stone of olives.

• Farm waste: they are basically the excrement of farm animals.

• Industrial waste: rests of industrial processes, they can be very diverse, from wooden structures, sawdust or fish backbones.

• Waste water: In water purification plants there are big amounts of mud and biogas that can be used for other processes.

• Solid urban waste: In the province of A Coruña we have two examples of how to use this fuel, one of them is in the SOGAMA facilities in Cerceda and another is in the SUW plant of Nostián, in A Coruña.

• Energy crops: They are plants cultivated in order to be used as biomass to be transformed into bio fuel. The most used are sugar cane, some cereals (oats, barley, wheat, corn), thistle, beet sugar, sunflower, etc.

In other latitudes there is research going on about the use of palm trees or fruits such as the jojoba.

Once biomass is obtained it can be transformed into energy trough several methods. The most common ones are the following:

• Thermo chemical methods: Depending on the origin of biomass, it can be done through combustions, as it is done in traditional heating systems that work with wood, or in biomass facilities such as the one in Allariz (Ourense).

• Gasification/pyrolisis: high temperatures are used with low amounts of oxygen. In the process they free monoxide and carbon dioxide, hydrogen and methane. It can also be obtained as a result of the process, vegetable coal.

• Biologic or chemical methods: they are based on using micro organisms that contribute to the process of biomass degradation, and they produce products with high energy contents. The most common ones are the following:

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    Alcoholic fermentation: This process has different fermentation phases. Carbon accumulated in plants is transformed into alcohol according to the type of biomass. These processes have an energetic consumption that may not match renewable parameters. This way bio fuels such as bio ethanol or bio diesel are obtained.
  • Methane fermentation or anaerobic digestion: In this process there work certain microbes that in the absence of oxygen generate gases such as methane and carbon dioxide. This process is used in biodigestion of urban waste plants, in waste water purifying plants and in the fermentation of farm waste.

The fuels obtained by these processes have many environmental advantages, the emission of sulphur to the atmosphere by combustion is scarce, they don’t free particles, ash production is reduced and they can be reused as compost or fertilizer.