Abstract
The growing search for alternative energy sources is not only due to the present shortage of non-renewable energy sources, but also due to their negative environmental impacts. Therefore, a lot of attention is drawn to the use of biomass as a renewable energy source. However, using biomass in its natural state has not proven to be an efficient technique, giving rise to a wide range of processing treatments that enhance the properties of biomass as an energy source. Torrefaction is a thermal process that enhances the properties of biomass through its thermal decomposition at temperatures between 200 and 300 °C. The torrefaction process is defined by several parameters, which also have impacts on the final quality of the torrefied biomass. The final quality is measured by considering parameters, such as humidity, heating value (HV), and grindability. Studies have focused on maximizing the torrefied biomass’ quality using the best possible combination for the different parameters. The main objective of this article is to present new information regarding the conventional torrefaction process, as well as study the innovative techniques that have been in development for the improvement of the torrefied biomass qualities. With this study, conclusions were made regarding the importance of torrefaction in the energy field, after considering the economic status of this renewable resource. The importance of the torrefaction parameters on the final properties of torrefied biomass was also highly considered, as well as the importance of the reactor scales for the definition of ideal protocols.
Highlights
Fossil fuels, such as oil, natural gas, and coal, represent the primary energy sources existent on the planet
The hydroxyl groups present in wood are partially destroyed by dehydration, which prevents the formation of hydrogen bonds, causing the torrefied biomass to become hydrophobic [25]
The potential of biomass as a replacement to fossil fuels leads to a number of issues, such as the increase in their price and environmental consequences due to their excessive harvesting and plantation
Summary
Fossil fuels, such as oil, natural gas, and coal, represent the primary energy sources existent on the planet. Some of the problems associated with the energy production of biomass in its original form when in comparison with fossil fuels are its lower density, higher moisture content, and hydrophilic nature, which cause its HV to decrease, making it difficult to use biomass for large scale productions [3,22,23] All these parameters influence the logistics of the energy production process using biomass, as well as its energetic efficiency [24]. Laboratory scale reactors are considered the most important due to their price, which is considerably lower than in other scales, allied with the fact that this scale is enough to define the right parameters to use even when applying them to different scales [29] In this article, such studies are summarized and reviewed to study the concept of torrefaction and the current and innovative attempts to improve the outcomes of this process, the quality of torrefied biomass using different techniques and the different sources of raw biomass
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