Università di Pisa, Italy
Roberto Gabbrielli has a PhD in Energy Power Systems and is assistant professor in Industrial Plants at the Department of Civil and Industrial Engineering of the University of Pisa (Italy). His research activity concerns the development and experimentation of renewable combined heat and power plants, such as small scale biomass gasification systems and concentrated solar power plants.
The development of numerical simulation models is an important tool in order to provide more accurate qualitative and quantitative information on biomass gasification. The modelling of the gasification process can be generally executed adopting one of the following approach: steady state models (equilibrium models), transient state models (kinetic models) and models based on the computational fluid dynamics. This paper shows a comparison between an equilibrium model and a kinetic one, built within the study and applied to a full-scale woody biomass gasification plant with fixed-bed downdraft gasifier using Aspen Plus. The models include the technical characteristics of all the plant components (gasifier, cyclone, exchangers, piping, etc.) and works following the main control logics of the real plant, that have been implemented in it. The simulation results have been validated using those obtained during an extensive experimental activity. The kinetic model assures a reliable estimation of the hydrogen and methane concentration in the syngas, that are not properly evaluated with the equilibrium model. After the model validation, the influence of operating parameters as equivalent ratio, biomass moisture content and gasifying air temperature on syngas composition, lower heating value and cold gas efficiency have been analyzed in order to assess the operative behavior and energy performance of the experimental plant. Recovering the sensible heat of the syngas at the outlet of the gasifier, it is possible to obtain high values of the gasifying air temperature and an improvement of the overall gasification performances