The revision of the present energetic model has as natural outcome the gradual giving up of fossil fuels (exhaustible and polluting) in favour of renewable sources.
Energies from renewable sources
The main characteristic of renewable sources lies in the availability and in a regenerative capacity that exceeds their consumption. Qualities that make them potentially inexhaustible.
The European regulation (directive 2001/77/CE) recognizes as renewable energy sources the following non-fossil sources: wind, solar, geothermic, wave-motion, tide-motion, hydraulic, biomass, dumping gases, residual gases from depuration processes, biogases.
Gruppo Bioenergie, through its controlled companies, has been successfully operating for years in the sector of biomasses and has undertaken some projects for the production of renewable energy in the wind, solar and biogas field.
Biomasses are renewable sources in all respects as they have null impact on the overall CO2 cycle– in fact the CO2 fixed in the plant during its growth is the same released during the various phases of energy conversion. In addition, biomasses involve various advantages that can be summarized as follows:
A biomass power plant, besides producing clean energy, contributes towards the development of the territory, strengthening the economic pre-existing activities and creating new employment prospects, as the inhabitants of the Communes where the power plant is established are involved both in the manufacturing and the management phase of the power plant.Besides, all direct and indirect sectors connected with the biomass power plant are developed.Also unused and abandoned territories for the alimentary production find new life. As a matter of fact, the requirements of wood to be used as fuel in power plants stimulates the development of local agro-energetic production chains and exploits those already existing, such as the exploitation of wood coming from the programmed cutting down or from the cleaning of woods, orchards etc.
The energy contained in biomasses and used by men and animals through the digestion can be directly used as thermal energy in the combustion process (traditional and prevailing use), for the production of electrical energy (coupled with thermal energy) or concentrated in a variety of solid, liquid or gaseous fuels that make the transport and the final useeasier.In short, the process of biomass conversion into energy can be grouped in two big categories:
Thermochemical processes are based on the heat action that enables the necessary chemical reactions to change the material into energy and can be used for products and residues whose C/N ratio has values exceeding 30 and the humidity content does not overcome 30%.
The most suitable biomasses for undergoing thermochemical conversion processes are the firewoodand all its by-products (sawdust, shavings, etc.), the most common cultivation by-products of lignocellulosic kind (cereal straw, pruning residues of vines and orchards etc.) and some machining wastes (shells, stones etc.).
Combustion is a chemical oxidation reaction of a fuel with a comburent (air or Oxygen) that occurs at high speed and with strong development of thermal energy. From the thermodynamic point of view it is a conversion process of the chemical fuel energy into heat.
The attained temperature value depends on the calorific power of the fuel, on the type of comburent used and on the fuel/comburent ratio. To obtain a complete combustion, and then the total exploitation of the available chemical energy, you operate with an excess of comburent; the excessive increase is not opportune because it causes a decrease of the maximum attainable temperature.
Combustion, at present, remains the most reliable solution.
The most diffused technologies for the combustion of solid biomasses, at present used in medium-big size plants, are the following:
All cycles foresee then the production of vapour that is expanded into turbines connected with generators for the production of electricity. The fume treatment systems for biomasses are typically:
Besides, it is foreseen a monitoring in continuous of: fume temperature, O2, CO, COT, SO2, HCl, NOx, dusts.
The combustion ashes of virgin biomasses are rich in mineral elements that are absorbed during the plant growth phase and come from the substratum where the plant grows. In particular, according to the zone where biomasses are cultivated, combustion ashes contain relevant quantities of alkaline substances such as oxides of potassium, of sodium, of calcium, of Magnesium and carbonates.The ashes produced by biomass plants are subdivided into heavy ashes, that’s to say deriving from the real combustion bed and constituting the predominant part, and light ashes, finer fraction obtained through the purification of combustion fumes by means of filters.Typically, thanks to their chemical-physical characteristics, their recycling is possible both as element constituting the charge for the production of cements and as amending substance in the formulation offertilizing composites.
In various European nations, some time ago they have already foreseen a direct reuse of ashes from combustion biomasses directly in agricultural fields.
The production cycle of electricity of a biomass power plant is based on the Rankine cyclewith the vapour production at high temperatures and pressures which is expanded into a turbine that feeds an electricity generator.For the vapour condensation from the gaseous to the liquid state, for its reuse in the cycle, it is foreseen a condensation systemwhere some low temperature warmth is yielded through a condenser to a closed water cycle.The project of the thermal cycle, optimized to produce electrical energy in efficient way, implies that even if the involved warmth quantity is high, the temperature at which the warmth is available is low (about 35-40 °C) and this makes it scarcely interesting for civil thermal uses.
The cogeneration of heat is anyway possible if it is taken into account since the design phase, optimizing the overall thermal cycle.
The biomass used by Bioenergie plants is constituted, by order of importance, by:
The plants of Biomasse Italia mainly use biomass coming from selective interventions of forest maintenance of the Calabria basin and additional quantities of peanut shells coming from the machining of oils and olive residues that derive from the production process of olive oil.
The San Marco Bioenergie power plant at Bando d’Argenta receives almost 80% of biomass coming from dedicated productions of decennial poplar groves cultivated in the Padana Plain basin and the remaining part derives from selective interventions of forest maintenance of the Apennine territory. Marginally are used biomasses coming from saw mills or from collections of explants of orchardscultivated in the Ferrara area.
Fast growing biomasses are wood cultivations with short cutting down cycle (2 – 3 years) characterized by fast growth and large productionof biomass. The plantation site must be chosen in the outskirts of the road net and of the Power Plant, to reduce transport costs.The need of producing wood implies notable induced employmentin the primary sector, which differentiates biomass power plants from traditional fuel ones.Bioenergie promotes the signature of contracts with the producers of fast growing biomasses conforming to acceptability plant requisites also over long periods.
San Marco Bioenergie, according to the contracts signed in 2008, has purchased almost 20,000 tons of fast growing poplar from the suppliers of Veneto, Emilia Romagna and Lombardy.
The companies of Gruppo Bioenergie have acquired an integrated policyfor the protection of the environment, of workers’ health and safety, the pursue of continuous improvement, the personnel’s training and the integration with the territories that house the power plants.To this end all operational companies are provided with environmental management systemscertified in compliance with ISO 14001 standards.From the technical point of view, the plants of the group are designed and manufactured applying theBest Available Techniques in force at the design time.
Finally, the policies of Bioenergie promote the saving of natural resources employing high-efficiency productive cycles, the reuse of the treated water resources, the recovery of wastes produced selecting their suppliers among those able to avoid the conveyance to dumps.