Thermal recovery from landfill biogas after energy exploitation

Biogas generated in a Municipal Solid Wastes landfill is collected and, when economically advantageous, it is exploited in internal combustion engines to produce electric energy, also taking into account that at present, excellent transformation efficiencies are achievable, precisely 38-40 % of the biogas thermal content. The flue gas deriving from combustion is at about 500 °C, in other terms it has still a valuable enthalpic content. In addition, the engines need lubrification and refrigeration loops, and intercooler devices to cool down the compressed gas mixture before entering the engines themselves. In this frame, thermal recovery is possible by modular heat exchangers: they produce hot water, cooling down respectively oil, water and gas. Moreover, the flue gas can be cooled from 500 °C to 180 °C. In this paper, the Municipal landfill of Torino, Northern Italy, has been considered for a study on thermal recovery from biogas after its energy exploitation. The considered recovery operations are: - district heating - absorption chilling - sludge drying - superheated steam production. Different scenarios are possible, according seasonability, thermal level and quantities of recovery.