Torrefaction subsequent to pelletization: Characterization and analysis of furfural residue and sawdust pellets

Use of neural network and multivariate statistics in the assessment of pellets produced from the exploitation of agro-industrial residues

The production of pellets from residual biomass generated monocropping by Brazilian agribusiness is an environmentally and economically interesting alternative in view of the growing demand for clean, low-cost, and efficient energy. In this way, pellets were produced with sugarcane bagasse and coffee processing residues, in different proportions with charcoal fines, aiming to improve the energy properties and add value to the residual biomass. The pellets had their properties compared to the commercial quality standard. Artificial neural networks and multivariate statistical models were used to validate the best treatments for biofuel production. The obtained pellets presented the minimum characteristics required by DIN EN 14961-6. However, the sugarcane bagasse biomass distinguished itself for use in energy pellets, more specifically, the treatment with 20% of fine charcoal because of its higher net calorific value (17.85 MJ·kg^-1) and energy density (13.30 GJ·m^-3), achieving the characteristics required for type A pellets in commercial standards. The statistical techniques were efficient and grouped the treatments with similar properties, as well as validated the sugarcane biomass mixed with charcoal fines for pellet production. Thus, these results demonstrate that waste charcoal fines mixed with agro-industrial biomass have great potential to integrate the production chain for energy generation.

Effect of in-situ torrefaction and densification on the properties of pellets from rice husk and rice straw

The research on preparing high-quality pellets by combining torrefaction and densification of biomass has received widespread attention. This paper investigated the influence of torrefaction temperature on biomass and evaluated the quality of three kinds of pellets (raw pellets, ex-situ torrefied densified pellets and in-situ torrefied densified pellets). When the torrefaction temperature was raised to 300 °C, the energy yield of rice straw (RS) and rice husk (RH) quickly decreased to 71.08% and 77.62%, and the cellulose was decomposed significantly. The results proved that 250 °C was an optimum temperature for RS and RH torrefaction. The densities of RS and RH in-situ torrefied densified pellets were 1236.84 kg/m³ and 1277.50 kg/m³ under 150 MPa, respectively. The density, Meyer hardness, hydrophobicity, and mechanical specific energy consumption of the pellet increased with the increase of molding pressure. The in-situ pellets had higher Meyer hardness, hydrophobicity, and lower mechanical specific energy consumption under the same molding pressure than raw pellets and ex-situ torrefied densified pellets. In addition, the bonding mechanism was studied by using scanning electron microscopy and ultraviolet auto-fluorescence. In-situ torrefaction and densification facilitated the formation of self-locking and the migration of lignin between particles. Compared with RH pellets, RS pellets had higher quality due to the higher hemicellulose content, which was necessary for forming stable hydrogen bonds.

Effect and Optimization of Process Conditions during Solvolysis and Torrefaction of Pine Sawdust Using the Desirability Function and Genetic Algorithm

Understanding optimal process conditions is an essential step in providing high-quality fuel for energy production, efficient energy generation, and plant development. Thus, the effect of process conditions such as the temperature, time, nitrogen-to-solid ratio (NSR), and liquid-to-solid ratio (LSR) on pretreated waste pine sawdust (PSD) via torrefaction and solvolysis is presented. The desirability function approach and genetic algorithm (GA) were used to optimize the processes. The response surface methodology (RSM) based on Box-Behnken design (BBD) was used to determine the effect of the process conditions mentioned above on the higher heating value (HHV), mass yield (MY), and energy enhancement factor (EEF) of biochar/hydrochar obtained from waste PSD. Seventeen experiments were designed each for torrefaction and solvolysis processes. The benchmarked process conditions were as follows: temperature, 200-300 °C; time, 30-120 min; NSR/LSR, 4-5. In this study, the operating temperature was the most influential variable that affected the pretreated fuel's properties, with the NSR and LSR having the least effect. The oxygen-to-carbon content ratio and the HHV of the pretreated fuel sample were compared between the two pretreatment methods investigated. Solvolysis pretreatment showed a higher reduction in the oxygen-to-carbon content ratio of 47%, while 44% reduction was accounted for the torrefaction process. A higher mass loss and energy content were also obtained from solvolysis than the torrefaction process. From the optimization process results, the accuracy of the optimal process conditions was higher for GA (299 °C, 30.07 min, and 4.12 NSR for torrefaction and 295.10 °C, 50.85 min, and 4.55 LSR for solvolysis) than that of the desirability function based on RSM. The models developed were reliable for evaluating the operating process conditions of the methods studied.

Improving the Conversion of Biomass in Catalytic Pyrolysis via Intensification of Biomass—Catalyst Contact by Co-Pressing

Biomass pyrolysis is a promising technology for fuel and chemical production from an abundant renewable source. It takes place usually in two stages; non-catalytic pyrolysis with further catalytic upgrading of the formed pyrolysis oil. The direct catalytic pyrolysis of biomass reduces the pyrolysis temperature, increase the yield to target products and improves their quality. However, in such one-stage process the contact between biomass and solid catalyst particles is poor leading to an excessively high degree of pure thermal pyrolysis reactions. The aim of this study was to enhance the catalyst-biomass contact via co-pressing of biomass and catalyst particles as a pre-treatment method. Catalytic pyrolysis of biomass components with HY and USY zeolites was studied using thermogravimetric analysis (TGA), as well as experiments in a pyrolysis reactor. The liquid and coke yields were characterized using gas chromatography, and TGA respectively. The TGA results showed that the degradation of the co-pressed cellulose occurred at lower temperatures compared to the pure thermal degradation, as well as catalytic degradation of non-pretreated cellulose. All biomass components produced better results using the co-pressing method, where the liquid yields increased while coke/char yields decreased. Bio-oil from catalytic pyrolysis of cellulose with HY catalyst mainly produced heavier fractions, while in the presence of USY catalyst medium fraction was mainly produced within the gasoline range. For hemicellulose catalytic pyrolysis, the catalysts had similar effects in enhancing the lighter fraction, but specifically, HY showed higher selectivity to middle fraction while USY has produced higher percentage of lighter fraction. Using with both catalysts, co-pressing had the best effect of eliminating the heavier fraction and improving the gasoline range fraction. Spent catalyst from co-pressed sample had lower concentrations of coke/char components due to the shorter residence times of volatiles, which suppresses the occurrence of secondary reactions leading to coke/char formations.

Torrefaction behavior of hot-pressed pellets prepared from leucaena wood

In this study, torrefaction behavior of hot-pressed wood pellet prepared at 250 °C and compression pressure of 70 MPa was examined at temperature 260-300 °C. It was found that the torrefaction behavior of hot-pressed pellet (HP) was significantly different from that of Raw and cold-pressed pellet (CP). The mass yield and energy yield for torrefaction at 300 °C and 30 min holding time for HP were 54.5% and 84.4%, respectively. Whereas the mass yield and energy yield for torrefaction at 300 °C and 30 min for Raw were 41.5% and 58.1%, respectively. From the gas formation analysis, it was found that the dehydration and deoxygenation reactions were accelerated to produce a large amount of H₂O and CO₂ during the torrefaction of HP. It was judged that torrefaction of hot-pressed pellet was very effective to prepare high quality black pellet.