CO₂ Gasification Kinetics of Biomass Char Derived from High-Temperature Rapid Pyrolysis

Abstract

The char of three typical biomasses, rice straw char (RS char), chinar leaves char (CL char), and pine sawdust char (PS char), was prepared in a high-frequency furnace, which could efficiently reduce secondary reactions under rapid pyrolysis conditions at 800−1200 °C. The rapid pyrolysis char produced was isothermally gasified in a thermogravimetric analyzer (TGA) under a CO2 atmosphere. Effects of biomass type and pyrolysis temperature on intrinsic carbon structures and morphologic structures of char and further on gasification characteristics of char were investigated using a Raman spectrum analyzer, scanning electron microscopy (SEM), and a surface area and pore size distribution analyzer. Gasification kinetic models were also contrastively discussed under different conditions. Results show that gasification rates decrease with the increasing pyrolysis temperature. Under the morphologic characteristic reserved conditions, morphologic structures present obvious effects on gasification rates. Gasification reactivity of the three biomass chars is in the order of CL char > RS char > PS char. Melting and shrinkage happen during rapid pyrolysis of PS, and the disappearance of the pore and decrease of the specific surface area of PS char lead to the low specific surface area and gasification rates of PS char. Unobvious melting happens to RS char and CL char, and the initial physical structures can be almost reserved, while CL char presents larger porosity and specific surface area, which make its gasification rates higher than those of RS char. In most conditions, the random pore model (RPM) performs well to describe gasification rates of biomass char studied in this work. However, for gasification of PS char at high temperatures, during which high gasification rates can be maintained in high conversion ranges, the modified random pore model (M-RPM) performs better. For gasification of RS char and CL char at low temperatures, during which gasification rates present a sharp decrease and trailing in medium−high conversion ranges, the shifted M-RPM performs better.

The CO2 Gasification Kinetic Study of WEEE Plastic Char Derived from Medium Temperature pyrolysis

“…On the other hand, the existence of the char would be a potential problem for the recycling of further metal screening and refinement. The gasification behaviors of coal char and biomass char have already been widely studied (Zhang, Ashizawa, Kajitani & Miura, 2008;Yuan, Chen, Li & Wang, 2011;. For instance, Zhang et al (2008) have investigated the steam gasification of 14 kinds of biomass chars and found that the extended random pore model could predict the gasification rates of all 14 kinds of biomass chars very well.…”

“…studied the CO 2 gasification behaviors of various coal chars and concluded that the CO 2 gasification behaviors had a close relationship with their physicochemical Properties, especially with the CO 2 chemisorbed volumes of chars. With regard to biomass and coal chars, the intrinsic alkali (K and Na), alkaline (Ca and Mg) and transition (Fe) metal contents also play important roles on the char gasification rates (Zhang, et al 2008;Yuan et al, 2011;Lahijania, Zainala, & Mohamedb, 2012). In addition, the Si and Al metal contents generally exert severe inhibition effect on the gasification reaction (Zhang, et al, 2008;Zhang, et al, 2010;Yuan, et al, 2011).…”

“…With regard to biomass and coal chars, the intrinsic alkali (K and Na), alkaline (Ca and Mg) and transition (Fe) metal contents also play important roles on the char gasification rates (Zhang, et al 2008;Yuan et al, 2011;Lahijania, Zainala, & Mohamedb, 2012). In addition, the Si and Al metal contents generally exert severe inhibition effect on the gasification reaction (Zhang, et al, 2008;Zhang, et al, 2010;Yuan, et al, 2011). Consequently, for different biomass and coals char containing various amount of alkali and alkaline metal contents, their gasification performance are totally different.…”

“…The gasification reactivity and kinetic parameters are essential for the efficient and reliable design of the gasification system. Thermogravimetric analysis (TGA) is an ideal instrument for investigating the gasification characteristics of carbonaceous materials because of its high accuracy, simplicity of design and ease of operation (Yuan et al, 2011). By means of TGA, different models can be applied to evaluate the kinetic parameters and the activation energy.…”

Effect of Carbonaceous Deposit on Bed Particles During Rapid Pyrolysis on Gasification Rate of Biomass Char in Fluidized Bed

“…However the produced char was generally taken out after the char is cooled and then it is again heated up and gasified. Furthermore, in most of the biomass gasification experiments, the number of biomass species are limited (Yuan et al, 2011).…”