Thermo-economic analysis of a micro-cogeneration system based on a rotary steam engine (RSE)

A rotary steam engine (RSE) is a simple, small, quiet and lubricant-free option for micro-cogeneration. It is capable of exploiting versatile thermal sources and steam temperatures of 150–180 °C, which allow operational pressures less than 10 bar for electrical power ranges of 1–20 kWe. An RSE can be easily integrated in commercially available biomass-fired household boilers. In this paper, we characterize the boiler-integrated RSE micro-cogeneration system and specify a two-control-volume thermodynamic model to conduct performance analyses in residential applications. Our computational analysis suggests that an RSE integrated with a 17 kWth pellet-fueled boiler can obtain an electrical output of 1.925 kWe, in the design temperature of 150 °C, the electrical efficiency being 9% (based on the lower heating value of the fuel, LHV) and the thermal efficiency 77% (LHV). In a single-family house in Finland, the above system would operate up to 1274 h/y, meeting 31% of the house's electrical demand. The amount of electricity delivered into the grid is 989 kW h/y. An economic analysis suggests that incremental costs not exceeding € 1500 are justifiable at payback periods less than five years, when compared to standard boilers.

► We characterize and model a micro-cogeneration system based on a rotary steam engine.
► We assess the performance of the above system in a residential building in Finland.
► The above system is capable of meeting 31% of the building's annual electrical demand.
► The above system may cost at most € 1500 more than a standard boiler system.