Upgrading Refuse-Derived Fuel Properties From Reclaimed Landfill Using Torrefaction

Landfill resource reclamation or landfill mining offers an attractive option to harvest the primary materials remaining behind in landfills or open dump sites. After reclamation, the major fractions left after removing soil-like material are paper and plastic fractions, which can be used transformed to refuse-derived fuel (RDF) as a fuel. However, the variation of constituents in RDF causes to low-quality fuel derived from the reclaimed landfill. The torrefaction process is proposed here to upgrade the fuel properties in terms of heating value, energy density ratio, and hydrophobicity. A torrefaction oven was used to torrefy RDF from reclaimed landfill at a controlled temperature of 250, 300, and 300 °C and a residence time of approximately 30 min in an inert environment using Nitrogen gas. The experiment results showed an optimum torrefaction temperature of 250 °C, which resulted in the improved heating value of RDF by up to 14.12%, an increased energy yield of 107.78%, and an energy density ratio of 1.14. These results demonstrated greater energy yield from the torrefied RDF compared with raw RDF. The hydrophobic property of torrefied RDF was also improved with the torrefaction process due to low water adsorption capability of torrefied RDF that was evaluated to be only one-half of that of raw RDF. The fuel upgrading of RDF from reclaimed landfill achieved via the torrefaction process improved the fuel properties that offers its direct use or, in conjunction with other coal fuels, for power generation.

Characteristics of Miscanthus Fuel by Wet Torrefaction on Fuel Upgrading and Gas Emission Behavior

Biomass is a solid fuel that can be used instead of coal to address the issue of greenhouse gases. Currently, biomass is used directly in combustion or via co-combustion in coal-fired power plants. However, its use is limited due to calorific value and ash problems. In this study, wet torrefaction (WT) was carried out at various temperatures (160 °C, 180 °C, and 200 °C) and the properties of the product were evaluated. In comparison to dry torrefaction, the ash contained in biomass was extracted by an acidic solution (i.e., acetic acid) from the overreaction of the biomass. From examining the ash content of the treated WT, it was confirmed that K2O of basic ash was mainly extracted. In particular, in the case of K2O, since the main cause of combustion problems are issues such as fouling and slagging, the removed WT can be stably combusted in the boiler. Finally, the combustion and emission behaviors were evaluated by TGA-DTG and TGA-FTIR. As the fuel-N was decreased in the WT proess, the NOx in the emission gas after combustion was lower than that of raw miscanthus, and SO2 showed a similar value. As a result, it was confirmed that the WT sample is an advanced fuel in terms of fuel upgrading, alkali minerals, and NOx emission compared to raw miscanthus.

Supercritical Carbon Dioxide Extraction of Lignocellulosic Bio-Oils: The Potential of Fuel Upgrading and Chemical Recovery

Bio-oils derived from the thermochemical processing of lignocellulosic biomass are recognized as a promising platform for sustainable biofuels and chemicals. While significant advances have been achieved with regard to the production of bio-oils by hydrothermal liquefaction and pyrolysis, the need for improving their physicochemical properties (fuel upgrading) or for recovering valuable chemicals is currently shifting the research focus towards downstream separation and chemical upgrading. The separation of lignocellulosic bio-oils using supercritical carbon dioxide (sCO2) as a solvent is a promising environmentally benign process that can play a key role in the design of innovative processes for their valorization. In the last decade, fundamental research has provided knowledge on supercritical extraction of bio-oils. This review provides an update on the progress of the research in sCO2 separation of lignocellulosic bio-oils, together with a critical interpretation of the observed effects of the extraction conditions on the process yields and the quality of the obtained products. The review also covers high-pressure phase equilibria data reported in the literature for systems comprising sCO2 and key bio-oil components, which are fundamental for process design. The perspective of the supercritical process for the fractionation of lignocellulosic bio-oils is discussed and the knowledge gaps for future research are highlighted.

A Temperature Model for Synchronized Ultrasonic Torrefaction and Pelleting of Biomass for Bioenergy Production

Low-energy and volumetric density of biomass has been a major challenge, hindering its large-scale utilization as a bioenergy resource. Torrefaction is a thermochemical pretreatment process that can significantly enhance the properties of biomass as a fuel by increasing the heating value and thermal stability of biomass materials. Densification of biomass by pelleting can greatly increase the volumetric density of biomass to improve its handling efficiency. Currently, torrefaction and pelleting are processed separately. So far, there has been little success in dovetailing torrefaction and pelleting, which only requires a single material loading to produce torrefied pellets. Synchronized ultrasonic torrefaction and pelleting has been developed to address this challenge. Synchronized ultrasonic torrefaction and pelleting can produce pellets of high energy and volumetric density in a single step, which tremendously reduces the time and energy consumption compared to that required by the prevailing multistep method. This novel fuel upgrading process can increase the biomass temperature to 473–573 K within tens of seconds to create torrefaction. Studying the temperature distribution is crucial to understand the fuel upgrading mechanism since pellet energy density, thermal stability, volumetric density, and durability are all highly related to temperature. A rheological model was established to instantiate biomass behaviors when undergoing various ultrasonic vibration conditions. Process parameters including ultrasonic amplitude, ultrasonic frequency, and pelleting time were studied to show their effects on temperature at different locations in a pellet. Results indicated that the volumetric heat generation rate was greatly affected by both ultrasonic amplitude and frequency. This model can help to understand the fuel upgrading mechanism in synchronized ultrasonic torrefaction and pelleting and also to give guidelines for process optimization to produce high-quality fuel pellets.