Intermediate pyrolysis of hazelnut shell: temperature effect on energy conversion and products characteristics

Abstract

Residual biomass is a renewable and clean energy source that is expected to play a crucial role in the energy transition. Thermochemical valorization of agro-industrial waste represents a promising alternative, which is still requiring further investigation with regard to the economical sustainability. In this study, intermediate pyrolysis of hazelnut shell was performed employing a laboratory scale screw-type reactor, evaluating the impact of temperature on the mass and energy flows of the process. The results show that temperature has a significant impact on the liquid and non-condensable gas yields, whilst biochar yield remains stable in the range of 18-23 w/w %. Pyrolysis condensates spontaneously split into organic and aqueous fractions and have calorific value of 18.1-18.5 MJ/kg and 1.9-3.2 MJ/kg, respectively. GC-MS analysis revealed that aromatic compounds dominate the organic fraction, while acetic acid is very abundant in the water-phase (125-147 g/L), suggesting attracting the potential recovery of chemicals. The carbon conversion efficiency for intermediate pyrolysis is around 90% and the theoretical energy recovery ratio is maximized at 76.6 % at 500 ° C. Moreover, the energy recovery ratio is rather high 72-76 % in the temperature range explored, showing that intermediate pyrolysis may adapt effectively to changes in temperature.