Modelling and characterisation of the pyrolysis of secondary refuse fuel briquettes and biomass materials

Abstract

This research was established due to an increase of interest in renewable energy sources and utilisation of various wastes and biomass. Gasification is currently one of the most promising thermal-chemical conversion techniques for recovering energy from waste, and the pyrolytic behaviour of secondary refuse fuel (SRF) briquettes and biomass-derived fuels is the starting point for the process. The purpose of this study was to evaluate the pyrolytic characteristics of SRF briquettes and biomass materials, suggest a kinetic model for simulating the pyrolytic process and obtaining the kinetic parameters, and then predict the yield of volatile products in pyrolysis. Knowledge of the chemical composition, the thermal behaviour and the reactivity of SRF briquettes and their blends with other materials, such as biomass and plastic during pyrolysis is very important for the effective design operation of gasification units. The kinetics of the pyrolysis of simulated SRF briquettes, SRF briquettes and pulverised biomass samples was successfully modelled by a scheme consisting of two independent general order parallel reactions of the main components which were hemicellulose, cellulose, lignin and plastic. The kinetic parameters estimated through the model were comparable with those reported in the literature. In this research, activation energy values varied between 30 – 70 kJ/mol for lignin pyrolysis, 96 – 137 kJ/mol for hemicellulose and cellulose pyrolysis, and about 260 kJ/mol for plastic pyrolysis. Biomass has a very high volatile content. Adding biomass into SRF briquettes could increase the volatile yield. Increasing the plastic content of SRF briquettes could increase the volatile yield, the derivative thermogravimetric (DTG) peak height and the repeatability of pyrolysis. Inorganic component could shift the cellulose pyrolysis to a lower temperature and cause the hemicellulose pyrolysis and the cellulose pyrolysis highly overlapped, but it could have a positive effect by acting as catalysts and lower the activation energy in the pyrolysis of hemicellulose and cellulose. Molasses used as a binder could improve the DTG peak height and restrain the curve shifting effect of inorganic component on the hemicellulose and cellulose pyrolysis, but couldn’t restrain the lignin pyrolysis at low temperatures during the hemicellulose and cellulose pyrolysis. Molasses could restrain the effect of the lignin pyrolysis at high temperatures on the plastic pyrolysis. Mechanical biological treatment (MBT) process could highly improve the volatile yield and improve the DTG peak height of SRF briquettes.

This research was established due to an increase of interest in renewable energy sources and utilisation of various wastes and biomass. Gasification is currently one of the most promising thermal-chemical conversion techniques for recovering energy from waste, and the pyrolytic behaviour of secondary refuse fuel (SRF) briquettes and biomass-derived fuels is the starting point for the process. The purpose of this study was to evaluate the pyrolytic characteristics of SRF briquettes and biomass materials, suggest a kinetic model for simulating the pyrolytic process and obtaining the kinetic parameters, and then predict the yield of volatile products in pyrolysis. Knowledge of the chemical composition, the thermal behaviour and the reactivity of SRF briquettes and their blends with other materials, such as biomass and plastic during pyrolysis is very important for the effective design operation of gasification units. The kinetics of the pyrolysis of simulated SRF briquettes, SRF briquettes and pulverised biomass samples was successfully modelled by a scheme consisting of two independent general order parallel reactions of the main components which were hemicellulose, cellulose, lignin and plastic. The kinetic parameters estimated through the model were comparable with those reported in the literature. In this research, activation energy values varied between 30 – 70 kJ/mol for lignin pyrolysis, 96 – 137 kJ/mol for hemicellulose and cellulose pyrolysis, and about 260 kJ/mol for plastic pyrolysis. Biomass has a very high volatile content. Adding biomass into SRF briquettes could increase the volatile yield. Increasing the plastic content of SRF briquettes could increase the volatile yield, the derivative thermogravimetric (DTG) peak height and the repeatability of pyrolysis. Inorganic component could shift the cellulose pyrolysis to a lower temperature and cause the hemicellulose pyrolysis and the cellulose pyrolysis highly overlapped, but it could have a positive effect by acting as catalysts and lower the activation energy in the pyrolysis of hemicellulose and cellulose. Molasses used as a binder could improve the DTG peak height and restrain the curve shifting effect of inorganic component on the hemicellulose and cellulose pyrolysis, but couldn’t restrain the lignin pyrolysis at low temperatures during the hemicellulose and cellulose pyrolysis. Molasses could restrain the effect of the lignin pyrolysis at high temperatures on the plastic pyrolysis. Mechanical biological treatment (MBT) process could highly improve the volatile yield and improve the DTG peak height of SRF briquettes.