11 September 2018 - 16:00
Nothing goes to waste
Biomass transformation in energy production: generation of sustainable value
Renewable energies (RES) are already well on track to hitting the target of 20% of all energy sources in Europe by 2020, although their growth rate has slowed down slightly over the last two years, following the strong impulse between 2005 and 2015. What is clear is that almost 86% of the new capacity installed in Europe in 2016, with nearly equal proportions over the last nine years, was from renewable energy sources.
These figures are contained in the latest 2017 European Environment Agency report, which includes the comforting news that, in addition to a drop in the consumption of traditional fossil fuels, the use of renewable energy sources in 2016 released 11% less CO2 into the atmosphere than in 2015, which in turn was 9% down on the previous year. Specifically, there are 10 distinct subcategories of RES (renewable energy sources): hydroelectric, onshore wind, solid biomass, photovoltaic, biogas, offshore wind, geothermal, solar concentration, bioliquids, and tidal energy. To date, in this very wide panorama the first four account for more than 85% of the total.
If the European target is to produce over 104,000 ktoe (kilotons of oil equivalent) from RES by 2020, the most interesting figures concern the expected average growth rates which, without changing the relative weights of the various sources mentioned, would still see a very big average annual growth in both on-shore and off-shore wind power and solid biomass - an annual average of around 7%. This compares to a 4% reduction in photovoltaics after the enormous growth recorded between 2010 and 2015. The development of renewable sources naturally involves material constraints of a physical nature - of course tidal energy cannot be used by countries whose sea doesn’t have much of a tide - and policies of economic incentives and administrative simplification for new installations.
Looking at the solid biomass sector, which is the specific subject of this article, we should remember that the strong relative growth in their contribution to the total energy produced over the last decade derives from the development of cogeneration technologies and the process of conversion of coal-fired power plants. We now need to specify exactly what we mean by solid biomass and to explain the operation of a power station fuelled by this energy source in order to understand, in addition to its benefits, its negative aspects which the EU has taken into account in drawing up its energy policy development plans.
By solid biomass we mean a wide range of products of organic and mainly vegetable origin, which largely come from wood, forest, and agricultural or agro-industrial residues. Wood and forest residues also include all those products that can be considered waste from wood processing such as debarking, dead branches and sawdust, used in the form of wood chips or pellets, while agricultural residues come from pruning and agro-industrial shells and pomace and to all that we should also add, for example, waste from paper processing.
All this material is a solid fuel that can be burned in a cogeneration plant to produce electricity and heat. Generally, in fact, only 40% of the energy released by combustion is transformed into electricity, while the remaining part is turned into thermal energy which, if not recovered, is dispersed uselessly into the environment. A biomass power plant thus generates electricity from the steam produced by the combustion of the listed materials, which drives a turbine connected to an alternator. The biomasses burn in a combustion chamber, producing the heat necessary to transform the water into steam in the boiler, which is sent under pressure to the turbine.
The steam rotates the turbine, which in turn rotates an alternator rotor that produces alternating electric current. At the turbine outlet, the steam is cooled in a condenser and returns to its liquid state, and then water is returned to the boiler. Through cogeneration some of the steam leaving the turbine can be recovered and used for heating. High efficiency cogeneration plants are therefore able to exploit more than 90% of the energy produced with undoubted economic and ecological advantages, reducing the emission of CO2 and other pollutants and solving the problem of the disposal of production waste.
Thanks to the impressive land reclamation work by Genagricola, one of Generali Group’s companies, Ca’ Corniani is today an efficient biomass plant at the forefront of innovation in modern and key areas such as food production, environmental sustainability and in the search for alternative energy sources.