Location and long-term capacity planning of agricultural biogas plants

Anaerobic digestion of animal manures and energy crops is gaining importance as a means to provide »a sustainable energy supply« (Weiland, 2010). Indeed, versatility is a main advantage of biogas, as it can be used for heat and power generation and also as a vehicle fuel. However, the profitability of available technologies for biogas exploitation mainly depends on local conditions (e.g. agricultural practices, climate) and particularly on regional or national subvention schemes, which promote different end uses: for instance, power generation – particularly in small plants - and depuration for injection in existing methane distribution grids are supported in Germany, vehicle gas and heating gas are widespread in Sweden, while power generation is especially fostered in Italy (Soldano, 2009). Once technologies and end uses are defined, subsidies also affect decisions on facilities design, especially as to the interdependent issues of location and long-term capacity planning. As to power generation from biogas, two main trends can be derived from industrial practice in several countries (e.g. AlSeadi, 2009), i.e. larger centralized plants vs. small scale decentralized plants, typically at farm level. Small plants are usually simpler, more socially acceptable and require less transport, but hardly exploit residual heat from biogas combustion and may have difficulties in slurries and digestate management concerning nutrient distribution to farm soils. Centralized plants usually exploit residual heat more efficiently and may reap economies of scale in facilities construction and management, but are associated to larger flows, especially as to transportation of biomass and of residual slurries. Optimization models can support capacity and location decisions, e.g. to resolve centralization-decentralization dilemmas, and above all, assuming a rational economic behaviour of markets, they allow to simulate the development of local energy and logistics systems and to evaluate local regulation and subvention frameworks when the installation of new facilities depends on private initiative. However, a literature review shows that, while a number of optimization models are devoted to supply chains centred on solid biomass combustion (e.g. Chinese and Meneghetti, 2009, Rentizelas and Tatsiopoulos 2010), very few contributions (Delzeit et al., 2009) are concerned with biogas supply chains. In this paper, specific issues concerning biogas as compared with other bioenergy supply chains are analyzed. An optimization model based on mixed integer linear programming is then elaborated for the Friuli Region, using available data for the provinces of Udine and Pordenone (APE, 2008). Various scenarios are discussed to show the implications of regulation frameworks for local bioenergy supply chains. Economic supply distances are assessed and transnational repercussions are discussed given the current situation of biogas development in bordering countries (Jan, Grmek, 2008).