OPTIMIZATION OF DESIGN PARAMETERS OF A STIRLING GENERATOR FOR USE WITH A FLUIDIZED BED COMBUSTOR

Abstract

This work investigates the possibility to place the head of a Stirling engine, more specifically the elements of the hot side heat exchanger, in direct contact with the sand of a Fluidized Bed Combustor. This choice is primarily suggested by the heat exchange coefficients between the multiphase fluidized bed medium and the surface of the heat exchanger, much larger than those attained when the heat exchanger is located in the stream of hot flue gases. Moreover, the mechanical action exerted by the fluidized solid particles substantially reduces the fouling usually caused by impurities in exhaust gases of a biomass combustion process. A mathematical model, which covers the fluidized bed and the Stirling engine, is developed and used to optimize design and operating conditions with specific attention to the Stirling hot side heat exchanger. It is shown that the choice to place the heat exchange in direct contact of the fluidized bed can lead to an improvement of performance in terms of efficiency and shaft power output.