Economical Analysis of Alternative Uses of Biogas Produced by an Anaerobic Digestion Plant

In the frame of the Italian market and regulations, some alternative uses of biogas produced by an anaerobic digestion plant fuelled by zootechnical effluents, integrated with corn silage, are investigated. In particular, on the basis of an existing plant, the following alternatives to the use of the generated biogas are analyzed and compared under the economical point of view: use of a cogeneration plant to produce electric energy (self-consumption and sale of the surplus to the power supply network operator) and thermal energy (digester and post-digester heating, and feeding of a cereal dryer); use of a trigeneration plant to produce electric energy (self-consumption and sale of the surplus to the power supply network operator) and thermal/refrigeration energy (heating of the digester and post-digester, and air conditioning of the company’s warehouses); use of a regenerative water-based scrubbing plant for up-grading the quality of the produced biogas, obtaining biomethane for direct sale to the network operator. This comparison is carried out considering the technical differences between the three alternatives, as well as the related investment and operative costs. A sensitivity analysis on the main parameters influencing the payback time of the three alternatives has been also carried out, showing that the most important parameter to consider is the cost of energy (as either electric or biomethane vector). On these grounds, using the Net Present Value approach, an assessment of the most convenient option in terms of shortest payback time and highest returns is made.