Physicochemical characteristics and thermal degradation behavior of dry and wet torrefied orange peel obtained by dry/wet torrefaction

Thermal pretreatment or torrefaction of biomass under an inert atmosphere can produce an energy dense and consistent quality solid biomass fuel for combustion and co-firing applications. The present study investigates the properties of orange peel (OP) after dry torrefaction (DT) or wet torrefaction (WT) at different temperatures. Dry and wet torrefactions were executed in a fixed bed reactor under these parameters: temperature (220, 250, and 280 degrees C), residence time (30 min), and pressure (<2.5 MPa). Findings are obtained in a lab-scale batch reactor. Thermal degradation performance of the torrefied biomass was thermo-gravimetrically studied in nitrogen. Proximate, ultimate analysis, and different characterization techniques such as XRD, XRF, FTIR, SEM, and TGA were applied to study the physicochemical characteristics of raw OP and torrefied OP. The results of proximate and elemental analysis showed positive influence of torrefaction on the samples, and it was found that both dry and wet torrefactions processes have upgraded the fuel properties of OP. Results show that the HHV for raw OP was 21.09 +/- 05 MJ kg(-1), whereas it was higher for WT-280 (24.26 +/- 07) and DT-280 (24.23 +/- 17 MJ kg(-1)) at a temperature of 280 degrees C. Torrefaction at 280 degrees C transforms OP from low-value residue to high-quality energy carrier by increasing their energy content and reducing the H/C ratio up to 55.12, 58.11% and O/C ratio up to 54.38, and 55.71% for DT-280 and WT-280, respectively. Results of XRD, FTIR, and SEM confirmed relatively a higher crystallinity, richer surface functional groups, and presence of organic layers with complete lignin structure, in WT samples. A differential equation-based model depicted an improved ignition behavior of both torrefaction treatments. Changes observed by thermo-gravimetric analysis indicated significant changes in thermal behavior with efficient burnout temperature ranges. Findings pertaining to improved fuel properties of orange peel draw conclusion that our model for torrefaction temperature application is highly sensitive to various combustion peaks especially for dry torrefied OP which has added advantage over wet-torrefied samples. Torrefaction treatment clearly revealed improved fuel characteristics and grinding properties closer to coal.

Automated summary

This study investigates the properties of orange peel after dry and wet torrefaction at different temperatures, demonstrating that torrefaction processes significantly improve the fuel properties of orange peel. Both dry and wet torrefaction treatments are found to enhance the energy content of orange peel and transform it into a high-quality energy carrier, with dry torrefaction exhibiting additional advantages. Various characterization techniques show changes in the physicochemical characteristics of torrefied orange peel, indicating improved fuel characteristics and grinding properties closer to coal.