MODELLING AND OPTIMIZATION OF HEAT TRANSFER FOR A STIRLING ENGINE IMMERSED IN A FLUIDIZED BED COMBUSTOR

This work investigates the advantages of placing the hot side heat exchanger of a Stirling engine (SE) immersed in a Fluidized Bed Combustor (FBC). The general objective is to obtain both heat and electric energy using biomass as primary source [1]. This choice is primarily suggested by the more efficient heat transfer between the multiphase fluidized bed medium and the heat exchanger, as compared with immersion in the flue gases [2]. Moreover, the mechanical action of the solid particles reduces fouling of the heat exchange surfaces, a typ- ical problem that arises with biomass combustion. In this paper we explore the possibility of achieving maximum mechanical power, useful to produce electric energy, by exploring the beneficial effects of the heat transfer conditions on the Stirling engine performances if a proper design of the absorber is devised. To this aim, key parameters of the heat exchanger are studied in order to profit of the much enhanced heat exchange coefficients attainable with immersion in the fluidized bed. Indeed, the possibility of reducing the global surface area of the heat exchanger can have a positive impact on the efficiency of the SE due to the corresponding reduction of the dead space.