Structure and reactivity of rice husk chars under different bulk densities

Abstract

The effects of bulk density on the structure and combustion characteristics of rice husk (RH) char were studied under isothermal conditions. The char from each reaction stage was obtained through pyrolysis of RH/Al2O3. Thermogravimetric-Fourier transform infrared analysis was used to study the release of gaseous products during the fine particle pyrolysis of RH/Al2O3. The results showed that the bulk density of the particles seriously affected the release rate and product distribution of gaseous products during pyrolysis, especially in the release phase of volatiles. In comparison, biomass pellets had a faster pyrolysis reaction rate at low bulk densities, which resulted in lower contents of O and H in the char obtained at this stage, and the aromatic structure content slowly increased. In the carbonization stage, the low bulk density promoted the increase in surface area and pore volume expansion of char. The degree of aromatization in char was higher, but the carbon content decreased. The addition of Al2O3 limited the growth of aromatic crystallites, while the char obtained at high bulk density tended to be graphitized. The char reactivity at the two bulk densities first decreased and then slightly increased, but the char obtained at high bulk density had better combustion reactivity.

Combustion and flue gas evolution characteristics of rice husk in various mixtures and layers with Al2O3 particles and char prepared with different pyrolysis parameters

“…Numerous experiments were undertaken to monitor the mass reduction of char during heating and combustion in air, ultimately ascertaining that the duration of the ceramic tray's residence in the furnace was 2 min, 3 min, 4 min, 5 min, and 6 min. The charecterictics of char samples were reported in our previous works (Liu et al 2019(Liu et al , 2023. The blending mode was defined as low stacked density, and the covering mode was defined as high stacked density.…”

Evolution of pyrolysis characteristics and gas components of biochar prepared by either mixing or layering rice husk with inert aluminum oxide

“…After some reaction time, it was placed in a desiccator with nitrogen for complete cooling, weighing, recording, and then stored in a sample bag. Through several experiments to observe the weight loss of char during pyrolysis, the residence time of porcelain boat was determined at 2, 3, 4, 5, and 6 min (Liu et al 2019). According to the experimental data of char and relative density among biochar, the mixing (or "blending") mode was labeled as RH-B-t; the covering mode was labeled as RH-C-t, where t stands for residence time.…”

“…Based on the condition, two kinds of packing arrangements were compared in this work for pyrolysis. One set of specimens was prepared by mixing biomass and Al2O3 (Azuara et al 2015;Liu et al 2019). Chattopadhyay et al (2009) studied the Cu/Al2O3 catalyzed pyrolysis of biomass by thermogravimetric experiment, in which Al2O3 was used as the catalyst carrier.…”

“…It was found that the char prepared at low bulk density contains less O and H functional groups, and the char has good specific surface area and pore structure. High bulk density promotes the degree of aromatization of char, and char has good combustion reactivity; none of chars prepared at the target density reached a significant degree of graphitization (Liu et al 2019). The mass transfer resistance will aggravate the secondary cracking reaction.…”

Biochar Synthesis from Mineral- and Ash-Rich Waste Biomass, Part 1: Investigation of Thermal Decomposition Mechanism during Slow Pyrolysis

“…An increase in exothermicity (as seen in DSC) and the presence of non-condensable gases corroborate this observation. Lower bulk density increases HeSTR [127] as it hinders the release of tar vapors and improves aromatization [128]. This is because at lower bulk densities, the height of the substrate increases (diameter of crucible being a constant), which increases the residence time of tar in the matrix [129].…”