Analysis of biomass chars thermal decomposition: Experimental tests and modelling in N2 and CO2 atmosphere

Char is a by-product of biomass gasification; nonetheless, it can be valorized in several ways, for wastewater treatment, for instance, or as bio-fertilizer. Char has also been observed to have a high potential for catalytic tar reduction. With a view to designing a char-based gas filtering system for tar cracking applications, it is of key importance to study the behavior of char in terms of mass degradation. For this purpose, the process of char thermal decomposition under different operating conditions has been addressed in the present work. Char samples collected from a local small-scale gasification plant have been studied both under inert (nitrogen) and under reactive (carbon dioxide) atmosphere. Thermogravimetric tests and thermal degradation tests in a lab-scale fixed-bed reactor have been performed. In carbon dioxide, the char mass loss resulted to be much more conspicuous, since many and complex reactions are involved in the kinetics of CO2 gasification. As regards the thermal decomposition of char in inert atmosphere, it has then been modelled by means of a first-order kinetic model coupled with a fluid-dynamic model, thus reproducing the temperature distribution and the mass loss occurring inside the fixed-bed reactor. The developed model predicted the char degradation in a satisfactory way.