• Energy Research

Abstract This study investigated the synergistic effect of co-torrefaction with intermediate waste epoxy resins and fir in a batch-type reactor towards biochar improvement. The synergistic effect ratio was used to judge the interaction between the two materials assisted by statistical tools. The main interaction between the feedstocks was the catalytic reaction and blocking effect. Sodium presented in the intermediate waste had a pronounced catalytic effect on the liquid products during torrefaction. It successfully enhanced the volatile matter emissions and exhibited an antagonistic effect on the solid yield. Different from the catalytic reaction that occurred during short retention time, the blocking effect was more noticeable with a longer duration, showing a synergistic effect on the solid yield. Alternatively, a significantly antagonistic effect was exerted on oxygen content, while the carbon content displayed a converse trend. This gave rise to a major antagonistic effect on the O/C ratio which was closer to coal for pure materials torrefaction. The other spotlight in this study was to reuse the tar as a heating value additive. After coating it onto the biochar, the higher heating value could be increased by up to 5.4%. Although tar is considered as an unwanted byproduct of torrefaction treatment, the presented data show its high potential to be recycled into useful calorific value enhancer. It also fulfills the scope of waste-to-energy in this study.

To investigate the efficacy of torrefaction in a vacuum environment, wood sawdust was torrefied at various temperatures (200–300 °C) in different atmospheres (nitrogen and vacuum) with different residence times (30 and 60 min). It was found that the amount of biochar reduced at the same rate—regardless of atmosphere type—throughout the torrefaction process. In terms of energy density, the vacuum system produced biochar with better higher heating value (HHV, MJ/kg) than the nitrogen system below 250 °C. This was the case because the moisture and the high volatility compounds such as aldehydes diffused more easily in a vacuum. Over 250 °C, however, a greater amount of low volatility compounds evaded from the vacuum system, resulting in lower higher heating value in the biochar. Despite the mixed results with the solid products, the vacuum system increased the higher heating value of its liquid products more significantly than did the nitrogen system regardless of torrefaction temperature. It was found that 23% of the total energy output came from the liquid products in the vacuum system; the corresponding ratio was 19% in the nitrogen system. With liquid products contributing to a larger share of the total energy output, the vacuum system outperformed the nitrogen system in terms of energy density.

Renewable biomass sources are organic materials, in which solar energy is stored in bio-chemical bonds, and which commonly contain carbon, hydrogen, oxygen, and nitrogen constituents, along with traces of sulfur.

Abstract Agro-industrial residue is widely considered as a rich source of energy, with varying characteristics depending on the geographical region or origin from where it is collected. Rice husk, bagasse, corncob, wheat straw and wood chips do not find many applications in Pakistan. As they are available in large quantities and at lower cost, therefore it makes them a favorable candidate for bioenergy. In this study, five agro-industrial residues, of Pakistani origin, were thermally degraded in the absence of air and at a constant heating rate of 5 °C min−1. Kinetics of the pyrolysis process was performed using Coats-Redfern method at five reaction mechanisms. Corncob was found to degrade at lower temperature with fastest rate as compared to all the other wastes. The kinetic parameters obtained from Coats-Redfern method were used to evaluate the thermodynamic behavior of these wastes and afterwards a comparison was drawn. Based on the ascending order of the activation energy, the residues can be classified in terms of preference as corncob > rice husk > wood chips > wheat straw > bagasse.

Abstract The experimental results of microalgae pyrolysis kinetics are beneficial to the reactor design in the biomass-to-energy process. To understand the complex pyrolysis process of microalgae, pyrolysis kinetics of microalgae components pretreated by wet torrefaction was evaluated using the independent parallel reaction model. Four and five reaction models were implemented to analyze the pyrolysis kinetics of microalgae Chlorella vulgaris ESP-31 (high-carbohydrate) and FSP-E (high-protein), respectively. Five pseudo-components were required to investigate the microalga FSP-E due to the extra carbonaceous material at temperatures higher than 600 °C. In the pyrolysis TGA curves, the first peak of microalga ESP-31 was diminished whereas only a slight decrease in the first peak of microalga FSP-E for the pretreated microalgae in water and H2SO4 solutions. From the results, pyrolysis kinetics with a fit quality of at least 97% was predicted for both species of microalgae. The activation energy of carbohydrates for microalga ESP-31 was decreased from 221.33 to 64.59 kJ mol−1 after pretreated in H2SO4. In contrast, the activation energies of proteins and lipids were increased for the pretreated microalgae ESP-31. Small changes in the activation energy range of carbohydrates, lipids, and other components were observed for microalga FSP-E compared to microalga ESP-31. On top of that, the thermal degradation temperatures and activation energies of carbohydrates and proteins for the pretreated microalgae ESP-31 and FSP-E displayed the opposite trend. In short, kinetic parameters of microalga ESP-31 could be effectively affected by low-temperature wet torrefaction compared to microalga FSP-E.

Abstract Microalgae have received increasing attentions due to its capacity of carbon fixation and serving as feedstock for producing biofuels and other value-added products. Microalgae can be used to remediate wastewater for simultaneously nutrient removal and biomass production, thereby significantly lowering the costs of microalgal feedstock. Recently, converting microalgal biomass biochar is of particular interest since biochar has numerous opportunities in application. In this review, innovative methods developed for microalgae-based wastewater treatment are described. Conventional and novel technologies used for producing biochar from microalgal biomass, such as pyrolysis and hydrothermal approaches, are presented. Future challenges and potential applications of the biochar derived from microalgal biomass collected from wastewater treatment system (e.g., soil amendment or adsorbent) are also discussed.