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Lignocellulosic biomass has low energy content and is high in oxygen content. The proximate and ultimate composition of lignocellulosic biomass is inferior compared to coal. The grinding properties of biomass are completely different compared to coal. Biomass is fibrous, whereas coal is brittle. One way to make biomass look like coal is through torrefaction. The biomass is roasted in an oxygen-free environment at temperatures of 200–300°C for different residence times. During torrefaction, the biomass loses the low energy content of volatiles and produces a solid product that is high in energy content. The solid fraction rich in carbon is torrefied biomass or ‘biocoal’. Biocoal represents a renewable energy commodity that can substitute coal. The torrefied biomass has superior biomass in terms of proximate and ultimate composition and physical properties such as grinding and particle size, but the challenge is low in bulk density. The low bulk density is primarily due to the loss of low energy content volatiles during the torrefaction process. One way to increase the density of the torrefied biomass is through densification. The densification systems commonly used today are pellet mills and briquette presses. Densification helps improve the transportation and handling of low-density torrefied biomass. The challenge is in making a durable pellet using torrefied biomass as the biomass loses its binding ability. Typically, binders are used for making torrefied and densified biomass. The challenge of adding binders is introducing foreign material to the biomass and changing the composition. In addition, adding binders can change the torrefied material properties, such as hydrophobicity. The other option to overcome this limitation is to torrefy the densified biomass. This chapter looks at the production of torrefied and densified biomass and its physical properties.

Quality properties of microwave-torrefied oat hull pellets were determined as a result of pelleting trials at different pellet die temperatures, sample particle sizes, and binder formulations. Microwave-torrefied ground biomass samples were compressed at two levels of pellet die temperatures (95°C and 145°C), two particle sizes (fine and coarse), and two levels of binders at different wt% (sodium lignosulfonate and sawdust). Quality of pellets was examined based on relaxed pellet density, pellet tensile strength, moisture absorption, moisture content, ash content, and higher heating value. Results showed that pellets made from fine particle size at high die temperature (145°C) have improved density and tensile strength. The best binder for density and tensile strength improvement was 10 wt% sodium lignosulfonate. However, since raw sawdust is abundantly available and cheaper than lignosulfonate, it is best recommended as a low-cost effective binder for densifying torrefied oat hull into pellets. Overall, all the densified pellets had a moisture content of 4–5% wet basis. Moisture absorption decreased when increasing torrefaction temperature, and pellets formulated with lignosulfonate presented higher moisture absorption and lower calorific value. Moreover, the addition of lignosulfonate significantly increased the pellet ash content, while sawdust significantly decreased the ash content of microwave torrefaction oat hull pellets.

This study aims to identify the feasibility to use food waste as fuel by torrefaction of food waste and comparing the influence upon the characteristics of torrefied products and temperature, heat carrier. According to the experiment result with reaction temperature 180℃~270℃ in nitrogen gas heat carrier and oil media heat carrier, the lower is the reaction temperature, water reduction was more effective by oil media heat carrier. But it was confirmed that, as the temperature is heightened, the difference was minimal. The caloric value rose from initial 660kcal/kg to 6,800Kcal/kg. As reaction temperature is heightened, Van krevelen Diagram moved to the range of Lignite range. It was confirmed that food waste can be converted to solid fuel through torrefaction reaction, and the higher is the reaction temperature, the closer to the low grade coal.