Biomass

Biomass is the term for living and recently dead biological matter used for fuel. Most often this is plant matter, like straw, grown to generate electricity or create biofuel. Biomass also includes biodegradable wastes that can be burned as fuel. The ultimate goal of biomass is to offset the use of fossil fuels without impacting the value of our food sources.

Sustainability in action

While innovation is leading to advancements in converting biomass into fuel more economically and efficiently, plant biomass is a promising source of renewable energy and is a growing energy source around the world. According to the Biomass Conversion Research Laboratory at Michigan State University, biomass is abundant and inexpensive enough to provide a plausible alternative to raw petroleum. Annually, plant biomass captures an energy equivalent to about eight times the total energy found in forms like oil, coal and natural gas, meaning it contains enough stored solar energy to meet much of our total energy needs.

ACCIONA's commitment

While ACCIONA is actively exploring the potential of biomass development in North America, we are giving a boost to the biomass business in Spain. We are currently building two biomass plants totalling 32 MW which will enter into operation in 2010. Meanwhile, the largest plant already operating is a 25 MW cereal straw-fired plant in Navarre, Spain. It consumes over 176 tons of cereal straw annually and, in return, produces enough electricity to power 50,000 homes.

In case you’re curious, ACCIONA’s 25 MW cereal straw-fired plant works like this: the straw is transported to the plant in bales that are stored in a warehouse. These bales are then transported to a boiler on a conveyor belt. A cutting system chops up the straw before it falls on one end of a grille located in the boiler, where it is burned. The combustion heats the water in the walls of the boiler until it turns into steam.

From that moment on, a triple process takes place in sequence: after passing through a super-heater, the steam drives a turbine connected to a generator, which produces electricity. The water vapor that has passed through the turbine (now at a lower pressure and temperature) is taken to a condenser, where the steam again turns to water. The water is transported through a closed circuit to the walls of the boiler, and the process starts again. The combustion of the straw produces residue and ash that are used to produce fertilizers.