A comparative experimental study on the impact of standard and torrefied wood pellets on the drive parameters of a stratified batch gasifier

In these last years gasification studies have mainly involved raw biomasses. Recently, torrefied lignocellulosic materials have become particularly attractive but the majority of the investigations regarding this thermal treatment have been limited to the characterization of the feedstocks submitted to a wide range of working conditions. Only a limited and well documented number of works specifically dedicated to gasification of torrefied biomasses have been till now published. Most of these works, indeed, report results refer to industrial or pilot plants working within limited range conditions. As a consequence, extended investigations of the impact of the guide parameters of this process on a wide working conditions spectrum are not so easy to found. This work presents the results of an extended experimental campaign carried out on a specific small gasifier designed for a batch configuration and using air as gasification agent. The peculiarity of this experimental study consists in an on line monitoring of the biomass loss during the gasification process and in a direct experimental determination of the main parameters of the process as: the productivity of the syngas, its heating value, the amount of the remaining char, the power of the gasifier and the cold efficiency of the process. In particular the role of the air flow rate as critical parameter and its impact on the cited quantities is highlighted. For this investigation the results obtained for gasification tests of both commercial pellet (CP) and torrefied pellet (TP) characterized by a Mass Yield close to 80% are presented. The adopted experimental device allows to select several air flow rate ranging from 15 to 30 Nl·min-1. The L.H.V. of the syngas reaches values in the range 3.51 \u3c L.H.V. \u3c 3.85 and 4.14 \u3c L.H.V. \u3c 4.31 for CP and TP respectively. The maximum power values set at 2.73 kW for CP and 3.53 kW for TP. Interesting results can be deduced by reporting the trend of the cited quantities Vs. the air flow rate. As general result, the use of torrefied material confirms a significant improvement of the performances of the gasification process compared to those involving conventional biomasses. Please click Additional Files below to see the full abstract

Integrating anaerobic digestion and pyrolysis for treating digestates derived from sewage sludge and fat wastes

P. 32603-32614The coupling of biological and thermal technologies allows for the complete conversion of wastes into energy and biochar eliminating the problem of sludge disposal. The valorisation of fatty residues as co-substrate in a mesophilic digester of a wastewater treatment plant was studied considering an integrated approach of co-digestion and pyrolysis. Four digested samples obtained from co-digestion of sewage sludge and butcher’s fat waste were studied by thermogravimetric analysis. The activation energy corresponding to the sludge pyrolysis was calculated by a non-isothermal kinetic. Arrhenius activation energy was lower for the pyrolysis of a digested grease sample (92 kJ mol−1 obtained by OFW and 86 kJ mol−1 obtained by Vyazovkin) than for the pyrolysis of sewage sludge and its blends (164–190 kJ mol−1 obtained by OFW and 162–190 kJ mol−1 obtained by Vyazovkin). The analysis of the integrated approach of anaerobic co-digestion and pyrolysis of digestates demonstrated that the addition of 3% (w/v) of fat to the feeding sludge results in a 25% increase in the electricity obtained from biogas (if a combined heat and power unit is considered for biogas valorisation) and increasing the fat content to 15% allows for covering all thermal needs for drying of digestate and more than doubles (2.4 times) the electricity production when the scenario of digestion and pyrolysis is contemplated.S