The effect of char properties on gasification reactivity

Abstract

In this study, CO 2 gasification of raw and acid-washed chars obtained from various types of lignocellulosic biomasses (woody and agricultural waste biomasses) was studied under isothermal conditions (850°C) using thermal gravimetric analysis. The effect of surface area and alkali/earth alkali metals on the reactivity of the chars was investigated. The different kinetic models were used to fit with the reactivity data by using least square method. The gasification of chars with higher surface area was found to be faster than that of chars having lower surface area. The acid treatment decreased the overall gasification rate for each raw chars. However, although the AI (alkali index) values of chars obtained from agricultural biomasses had equal or higher than that of woody biomass chars, their initial rates were considerably lower. It was concluded that indigenous alkali metals of chars have a remarkable influence of gasification reactivity but an adequate surface area should be provided to react with CO 2 .

Analysis of Porous Structure Parameters of Biomass Chars Versus Bituminous Coal and Lignite Carbonized at High Pressure and Temperature—A Chemometric Study

“…These parameters have also been reported to influence the swelling behavior and fluidity of a fuel [3,[7][8][9][10] as well as reactivity of the resulting chars [4,9,[11][12][13]. In some studies, the properties of the porous structure of chars, reflected in the total pore volume, pore area, and pore size distribution, were studied, since the shape and interconnections between pores significantly influence the physical properties of a material, such as its density, mechanical strength, and sorption capacity as well as thermal conductivity and mass flow in thermochemical processing [14,15]. The influence of pyrolysis temperature and heating rate [5,[16][17][18][19][20][21][22], fuel particle size [17,22,23], as well as physical or chemical pre-treatment of carbonaceous materials [24][25][26][27] on the porous structure of chars has also been reported.…”

Steam Gasification of Sawdust Biochar Influenced by Chemical Speciation of Alkali and Alkaline Earth Metallic Species

“…While the gasification of biochar took place everywhere but slowly in the HCl-biochar in order to consume the small ring systems selectively, the reaction in the AAEM-containing biochar was more focused on/around the AAEM sites and took place much more rapidly [53]. As shown in Figure 7, comparing the results of steam-gasified origin biochar and H2O-biochar samples, there is a significant decrease of 0.65 × 10 6 , showing that the increase of surface O-containing functional groups during gasification …”

“…Usually, gasification can be divided into two steps, namely biomass devolatilization (first stage, relatively fast) and biochar gasification (second stage, relatively slow). According to previous studies [3][4][5][6][7], the gasification of pyrolysis biochar is the rate-limiting step for the overall gasification reaction, which is usually the focus of research on biomass gasification reactions. Besides, among the various gasifying agents (air, oxygen, CO 2 and steam) for biomass/biochar gasification [8,9], steam is preferred for increasing the heating value of syngas and producing a gaseous fuel with relatively higher H 2 for application in the fuel cells and hydrogen engines [10].…”

A review on conversion of biomass to biofuel by nanocatalysts

“…Depends on using steam, oxygen or CO2 as gasification agent, conversion of the residual chars can be presented sequentially as follows (Duman et al, 2014)(Eq. 8-10):…”