Compatibility
The production of energy by thermal solutions must be carefully verified in account of its potential environmental impact, and more in general taking into account its sustainability, as concerns modification of natural environment, exhaustion of resources, consumption of materials or chemicals during the production of considered fuels.
It is necessary first of all to consider the origin of the required raw material that is used for thermal production (biomass, solid conventional fuels, liquid fuels, organics to be converted in biogas, combustible residuals, and so on): the territorial modification that are required for production, the water and chemicals consumption, the eventual modification in the use of soil, the energy employed in production, pretreatment, transport and preparation of fuel, generation and disposal of solid or liquid residuals must be carefully considered.
Many considerations have been done about this aspect, and a procedure of LCA is well consolidated as a support to these determinations, but the specific territorial data and the potential interactions or synergies with other parallel, agricultural or technological activities that are operating in the same territory must be considered.
A very important aspect of compatibility is connected with the atmospheric emissions coming from energetic production : in this connection first of all the emission of greenhouse gases must be taken into account, together with considerations about the renewability of emitted carbon; the specific ratio between energetic production and use and connected emission of GHG is a very important parameter of compatibility for thermal energy production.
From the other side, with reference to the local acceptability of thermal plants, or in general of thermal apparatus, the emission of atmospheric pollutants (dust, nitrogen oxide, but also micro-pollutants) must be verified, and the technological possibilities, deriving from the Best Available Techniques, must be adopted in order to limit the foot-print of a plant on the air quality of the surrounding area. Also the problem of the water requirement for plant operation, reject of used wastewater, production and disposal of sludges and solid residuals must be considered, with specific reference to the aspects of technological possibilities for reuse or the more or less problematic identification of areas for final disposal.
In order to move in direction of the best solution from the point of view of environmental compatibility, different tools must be employed from the different operators of the system of energetic production : best choice of fuel, suitable technology for energy production and emission limitation, integral utilization of the produced energy (in this sense the co-generation, combined heat and power, CHP, is a very important possibility), territorial planning of the distribution of operating plants are the principal arguments that must be considered for the more acceptable solutions.
It is important to note that in many cases the best solution for energy production is not univocal in considerations of different aspects : social and political aspects connected with biomass production are in many cases counter-acting in comparison with problems of atmospheric impact, the limitation in GHG emission is operating on a global scale and very often doesn’t correspond to an acceptable solution on a local scale, the distribution of energy plants on the metropolitan areas is very often counter-balanced by considerations about energy consumption and local atmospheric impact from automotive transport, and so on.
In general, it must be taken into account that the choice of the best technology is a necessary but not always sufficient condition in order to obtain a condition of acceptability, and this choice is in general subsequent to considerations concerning use of soil, evaluation of alternative fuels, distribution of energy plants, public policies for thermal vectors utilization, and so on.
Bio-energy production
In account of the large territorial distribution of different biomass feedstocks, that leads to a traditional utilization of the material, and from the other side by considering the aspects of renewability and carbon neutrality, the production of energy by using different materials of biological origin is very largely diffused, and it can be evaluated a large margin of further positive development.
The aspects that must be considered in this direction are:
Type of feedstocks, sustainability in original production, needs for pre-treatment
Technological solutions (thermal, chemical, biological) used to produce energy or to obtain liquid fuels
Limitation of impact during feedstocks transformation and utilization
Generation and final disposal of residuals
Overall carbon foot-print of the energetic system, and life Cycle Assessment
Economic and social aspects of biological feedstocks production and energetic valorization
The forest and agricultural production of original biomass, and the exploitation of animal wastes or organic residuals coming from food production activities must be carefully defined, in account of original and natural possibility to use natural resources, potential competitivities in use of soil, social and employment aspects connected with agricultural or food – production sectors, geographical distribution of potential feedstocks, needs of disposal of organic residuals suitable to be energetically destinated.
The technologies to produce directly electrical or thermal energy, or liquid or gaseous fuels from biomass are very different, and can be considered from the point of view of scale of application, needs of pretreatment of the original material, complexity of energetic transformation operations, secondary environmental impact, maturity of the proposed technology. The operating schemes can vary from direct thermal valorization (direct combustion) solution, to biological transformations able to produce biogas or bio-methane, to chemical treatments useful to produce liquid fuels, or also base or intermediate chemicals : many reviews dealing with these different solutions can be found both in specialized textbooks or in illustrative flow-sheets of plant producers.
Fig. 3 – Schemes for biomass energetic valorization
It is very important to consider the global flow sheet of energetic biomass exploitation with the methodology of LCA, by considering all the contributions in terms of energy consumption and production, chemicals utilization in the different steps, from biomass obtention by natural sources, to pretreatment, valorization, disposal of residuals; the carbon footprint and the Global Warming Potential corresponding to these schemes, in comparison with different paths to produce energy, can be usefully considered in the evaluation of the meaning of bio-energy in the general framework of energy production.
Fig. 4 – General scheme for LCA of a bio-energy path
Together with the consideration of the meaning of bio-energy as a system to positively operating to limit climate change, also the aspect of local acceptability, and of the economic sustainability must be taken carefully in account.
From the first point of view, it is fundamental to consider the effect of bio-energy in use of soil, potential competition with food production, water consumption, use of chemicals for growth and their potential dispersion, local atmospheric impact coming from thermal valorization, effect of residuals on the quality of the receiving environment; also the aspect of global energy utilization, with co-generation and district heating hypothesis, is very important for the right evaluation of planning distribution and local acceptability.
The economic meaning and sustainability of bio-energy is also absolutely important : in this direction it is required to take into account from one side the original price and eventual incentivation of agricultural products (or potentially the synergic cost effects of organic wastes energetic disposal), from the other side the policies, the tariffs and the support measures for energy coming from renewable sources: a global budget, considering both direct, industrial costs, but also political and financial decisions about this energy branch, leads to an important aspect of sustainability.