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The problem of energy recovery from biomass by means of a combustion process, while assuming more and more importance, accordingly with the Kyoto Protocol, is requiring as well processes able to optimize efficiencies. Such optimization should not only be related to possible plant solutions, but should also take into relevant consideration the characteristics of biomasses used, which cause, through the combustion process, different problems mainly of the environmental kind and not of easy solution. The present paper analyzes such problems by keeping in due account the different factors capable of influencing at the end the adopted solution. Particularly, the possibility to employ complex cycles is discussed with reference to both the kind of fuel employed and the plant size. It is also emphasized how the possible energy costs can condition the optimum choice, mainly if influenced by binding rules.

A thermodynamic analysis is presented for a reciprocating engine operating under heat exchange instead of through a combustion process, with the purpose to evaluate if such solution can be justified in the light of the obtainable performances. As far as the cycle is concerned, the engine operates identically to a conventional one, but the system configuration departs unavoidably from conventional solutions for reasons mainly related to heat exchange processes (exchanged thermal power, problems related to wall temperature, etc.). Taking into account real cycles effects, both attainable efficiencies and specific powers are determined, with reference to the system characteristics. Attainable efficiencies present quite satisfactory results, while specific powers, related to exchanged thermal powers, on the contrary, show much lower values than those normally encountered for conventional engines.

The design of recovery steam generators for incineration plants encounters certain specific problems, related to the nature of the exhausted gases, which, if not properly faced, can strongly condition the conduction of the whole system. Two problems, namely, demand for particular attention: the corrosion at high temperature and the formation of organochlorine compounds, in presence of ashes and/or deposits for definite temperature intervals. These phenomena can be controlled and minimized, whenever possible, by limiting to the greatest extent the regions where the temperatures of the metallic walls and of the ashes and/or deposits are within the critical interval.