For all real-world applications, such as fluidized-bed and packed-bed combustion, it is essential to understand the combustion characteristics of an individual solid biomass particle. Under a variety of operating circumstances, investigations on the combustion and mass loss of single pellets of sugarcane (SC) and guava leaves (GL) were conducted. A visualization technique was used to capture the combustion processes of volatile and char. Both homogeneous ignition and hetero–homogeneous simultaneous ignition of both volatiles and char were found. When compared to the material composition and particle-size distribution of the pellet, the brightness of the pellet changed differently with increasing air mass flow rate and hot air temperature. By increasing the hot air temperature and air mass flow rate, the volatile flame of biomass pellets was made shorter and brighter, which lowered the volatile burnout duration. The majority of the entire conversion time is spent on char burning. Compared to other angles, the pellet orientation angle of 30° has a shorter ignition time, a lower surface temperature, and a lower burnout temperature.

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This study aims to investigate the combustion characteristics and mass loss behaviors of rice straw and wheat straw biomass pellets experimentally in a laboratory fixed bed combustor under various operating conditions. High-speed photography was used to record images of the combustion process, and a sensitive balance was utilized for recording the particle mass history during the combustion process in addition to K-type thermocouples for temperature measurements. For both materials, the single pellet was exposed to various air temperatures and different flow rates of air. The orientation of the biomass pellet was positioned at various angles from 0 (horizontal), 30°, 45°, 60° (inclined), and 90° (parallel) to the hot air stream at different flow rates. Both glowing reactions and flameless ignition have been noticed in all experiments at all pellet orientations. All pellets experienced low and high luminosity volatiles without flames, followed by a bright radish color and short-lived combustion of the chars. Although the volatile contents of the two materials are identical, the volatile combustion duration of wheat straw (17–258 s) is less than that of rice straw (20–300 s), which could be due to differences in particle sizes, shapes, and structural compositions. The results also show that increased air temperatures lessen the time it takes for volatile and char to ignite and burn off. It also raises the temperature of surface ignition. Starting from the horizontal position and increasing the orientation angle of the pellet, the volatile and char ignition times increase up to 30° and then drop up to 90°, with angle 45° giving the lowest value. The same pattern was also noticed for volatile and char burnout times. The pellet horizontal position (0°) exhibits reduced combustion and mass loss (%) time intervals. The order of increasing the maximum temperature at the pellet surface was 30° > 60° > 90° angles. Increasing the air temperature reduces the times of char combustion, devolatilization, volatile burnout, and char burnout. As the air flow rate increases, the effect on the combustion parameters alternates between increasing and decreasing values.

The plant residue of sesame and broad bean stalks and the capsule were thermally decomposed using thermogravimetric analysis under N 2 at different heating rates. Two zones of devolatilization characterized the thermal decomposition process. The primary zone evolved about 90% of the released volatile matters and the reactivity of biomasses is very affected by the change of heating rate. Three kinetics approaches were used to analyze the devolatilization kinetics. The Coats and Redfern method was the best approach to estimate the kinetic parameters for these materials. The mass loss rate and conversion versus temperature were used to investigate the weakness of the DAEM and model-free methods for modeling the pyrolysis behavior under the severe changes among the different heating rates.

Mixing and segregation characteristics of biomass particles are of practical importance because the in-bed combustion efficiency of volatile matter affects the vertical location of biomass in bubbling fluidized bed combustor. Sesame and broad bean stalk biomass materials mixed with sand used in this study. The superficial gas velocity, biomass chip length, sand particle size and mass fraction of biomass varied as experimental variables. The mixing and segregation behavior of mixtures were analyzed in terms of mixing index. It was found that the variability in the chip-shape made the sesame chips is quantitatively and qualitatively higher homogeneity and mixedness than the broad bean chips. The optimum overall mixing index for the sesame and the broad bean is around 0.96 and 0.84 at dimensionless superficial gas velocity (U/Umf) of 2.0 (1.40 m/sec) and 2.1 (1.25 m/sec), respectively. It was found that as the mean diameter increased and the sphericity decreased, the mixing quality decreased. The average sand particle size of 371 µm can keep good mixing with biomass chips of both materials, compared with average particle sizes of sand 550 and 700 µm. Increasing the initial biomass mass fraction yields a poor mixing of the investigated biomass stalks.