Abstract
A lab-scale downdraft fixed bed reactor was used for the study of sewage sludge, a non-lignocellulosic biomass, torrefaction to enhance the thermochemical properties of sewage sludge. The torrefaction was carried out for a temperature range of 200–350 °C and a residence time of 0–50 min. Degree of torrefaction, torrefaction index, chemical exergy, gas analysis, and molar ratios were taken into account to analyze the torrefied product with respect to torrefaction temperature. The effect of torrefaction temperature was very pronounced and the temperature range of 250–300 °C was considered to be the optimum torrefaction temperature range for sewage sludge. Chemical exergy, calorific value and torrefaction index were significantly influenced by the change in the relative carbon content resulting in decrease of the O/C and H/C molar ratios.
Highlights
Biomass as a renewable energy source is recognized globally and is available in a generous amount on the earth, which can be transformed into biofuels or energy, utilizing various thermal, physical, or biological processes
Pyrolysis reaction may have occurred at a higher torrefaction temperature, resulting in the decrease in the degree of torrefaction at 350 ◦ C with an increase in torrefaction residence time
An increase in the degree of torrefaction was seen at higher torrefaction temperature and residence time
Summary
Biomass as a renewable energy source is recognized globally and is available in a generous amount on the earth, which can be transformed into biofuels or energy, utilizing various thermal, physical, or biological processes. Utilizing biomass or waste can lessen the environmental issues due to high carbon dioxide emissions, which are produced by fossil fuels. Clean and renewable energy sources are in high demand [3] and sewage sludge is acknowledged as a low-cost material for biomass combustion [4] yet, these wastes are disposed into landfills or the ocean due to economic reasons. Utilizing sewage sludge to generate heat through incineration and combustion can be a good alternative but the emission of heavy metals has led to various disagreements [5]. Due to low hemicellulose and cellulose, and a high ash content of sewage sludge, the combustion behavior is entirely different from that of lignocellulosic biomass [6]
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