Modelling and experimental investigation of small-scale gasification CHP units for enhancing the use of local biowaste

Small-scale gasification Combined Heat and Power systems, fed by biowaste resources, have the potential to enhance local renewable energy production, reduce carbon emissions and address the challenges of waste disposal. However, there is a lack of understanding on the influence of challenging feedstocks, such as, for example, digestate, poultry litter and municipal solid waste, on the syngas quality and the incidence of the drying stage in the overall process. This paper addresses this gap by analysing and comparing 40 samples of the most common biowaste feedstocks. We developed a stoichiometric-thermodynamic one stage equilibrium model that was experimentally validated and calibrated by laboratory results, with a maximum error of 15% between real and predicted values. Simulation results show that the low heating value of the syngas produced from biowaste resources analysed ranges from 3.1 to 5.4 MJ/Nm³ on a dry basis. Working at the optimal equivalence ratio increases the electricity and thermal output by up to 20%. To achieve a feedstock moisture content of 10%, the drying process may require up to 60% of the heat produced. Furthermore, results show that downdraft gasification based combined heat and power, is a feasible and interesting option to deal with biowaste resources which can potentially avoid the cost, risk and externalities of landfilling while it contributes to the increase of local electricity and heat production from renewable energy sources, both for grid and off-grid applications.