Electricity Production from Renewables Energies

5.4. Cogeneration by biomass

Traditionally, wood and agriculture waste can be burnt to generate heat. When this heat is in the form of steam at high temperature, it is possible to simultaneously generate heat (or cold) and electricity. This is the principle of cogeneration by biomass. Cogeneration enables the optimization of installation costs and energy efficiencies [LEV96]. This will be the subject of the following sections.

5.4.1. Origin of biomass – energy interests

By definition, biomass designates all organic matter of plant, animal or fungus origin able to become sources of (renewable) energy by combustion, possibly after anaerobic digestion or chemical transformations [HOO 04]. The biomass concerned for electricity generation is mainly that of the first category. We can find lots of materials coming from different origins [SAB 09]:

– wood;

– wood by-products, waste resulting from the wood industry;

– traditional agriculture products;

– organic waste.

The CO₂ equivalent balance of a complete cycle of electricity generation by biomass is not always easy to determine. The combustion of biomass emits CO₂, whereas CO₂ is sequestered during the growth phase of the plantations. Moreover, depending on the resource used as biomass, CO₂ is also emitted by the growth process of the biomass (plantation, fertilizer, crop and transport) and must be attributed to the entire CO₂ balance. We thus distinguish two types of biomass resources:

– resources coming from waste or by-products;