On the integration between fluidized bed and Stirling engine for micro-generation

The present article deals with the integration of a fluidized bed combustor and a Stirling engine for cogeneration purposes. An experimental study was carried out, proving the ability of the bed to exchange heat at high rate with an immersed coil that realistically emulates the heat exchanger of a small Stirling engine. The heat transfer coefficient attains values up to 280 W m−2 K−1. No dirtying of the immersed surface occurred during a combustion test of biomass.The paper also reports on a newly developed mathematical model of a fluidized bed combustor coupled with a Stirling engine for co-generation purposes. It consists of four fundamental blocks describing i) the heat transfer, ii) the fluidized bed combustion, iii) the heat recovery, and iv) the Stirling engine. The model produces as relevant outputs the bed temperature, the mechanical power and the efficiency of the Stirling engine, at changing the operating conditions and geometrical parameters of the system. A slow dynamic response is predicted, that it is significantly improved by adopting an efficient control strategy. On the whole, the model results indicate that the proposed “integrated system” is of interest for micro-scale cogeneration from biomass fuels.

► High heat-exchange rate in fluidised bed is appealing for coupling a Stirling engine.
► A mathematical model of a coupled system newly developed.
►  The “integrated system” is of interest for micro-scale co-generation (1 kW) from renewable fuels.
► A PID control strategy largely enhances the system performances.