Abstract
The present work aims at investigating the valorization of biomass forestry residues by means of experimental analysis on a small-scale open top gasifier. In order to evaluate the effect of high bark content, experimental test have been performed in an open-top gasifier with increasing shares of bark and woodchips and different levels of secondary air supply, used as adjustable parameter for the optimization of the conversion process. Samples have been characterized using standard methodologies for assessing the moisture and ash content, the elemental composition and the calorific value. Moreover, the bark content in the standard woodchips has been quantified to be 8 % in mass. High content bark samples (30 % and 80 % in mass of total bark) have been then prepared mixing the standard woodchips with barks. Using the prepared mixtures, gasification tests were performed with an open-top gasifier installed at the Free University of Bolzano. This specific pilot-scale gasification plant is a downdraft system, where both gas and feedstock move downward as the reactions proceed. The core of the gasification system is a stainless-steel cylindrical reactor. The air required for gasification is partly drawn from the top, and the remaining from the air nozzle at the char combustion zone. The results of the experimental campaign showed that the generally negative impact of bark addition, demonstrated by a reduction – at a set level of secondary air – of the calorific value of the producer gas and of the cold gas efficiency, can be counterbalanced acting on the secondary air and therefore on the equivalence ratio of the process, a parameter that has been demonstrated to allow an optimization of the process as a whole thanks to a linear correlation with the cold gas efficiency.