Characterization of hazardous gases evolved from various biomass wastes during biochar production using TGA-MS

Abstract

The utilization of biomass waste by biochar production seems to be an efficient and environmental friendly way of biomass treating. Biochar is produced from biomass by low temperature pyrolysis (torrefaction). In this work, twelve different biomass wastes generated in the Czech Republic has been characterized by thermogravimetric analysis combined with mass spectrometry (TGA-MS). Most of all published works are focused on TGA-MS analysis of evolved hydrocarbon gases or on analysis of condensed liquids. This work is converting focus mainly on inorganic gases produced during pyrolysis, which can be toxic, explosive or corrosive. There is a few or none published works focused on sulfur or chlorine compounds in evolved gas. Some compounds that could be potentially produced with biomass compositions were not detected at all (e.g. H2S). Furthermore, it has been found that temperatures higher than those commonly used in torrefaction (i.e., 400 °C) are needed to produce compounds like H2. From the obtained results it can be also seen that CO2, NH3, NO2, SOx, Cl2 and HCl are mainly produced and their concentration reaches maximum just at this temperature. It has been proved that biomass, which contains sulfur and chlorine, releases SOx and HCl during torrefaction. Sulfur oxides, ammonia and chlorine compounds are strongly corrosive. The real conditions of pyrolysis on industrial scale can thus be adjusted according to the TGA-MS data. These data can be also used for the selection of a biomass, most suitable for pyrolysis, where almost no gases are generated with corrosive effect on the pyrolyser.