CO₂ Gasification of Chars Prepared from Wood and Forest Residue: A Kinetic Study

Abstract

The CO 2 gasification of chars prepared from Norway spruce and its forest residue was investigated in a thermogravimetric analyzer (TGA) at slow heating rates. The volatile content of the samples was negligible; hence the gasification reaction step could be studied alone, without the disturbance of the devolatilization reactions. Six TGA experiments were carried out for each sample with three different temperature programs in 60 and 100% CO 2 . Linear, modulated, and constant-reaction rate (CRR) temperature programs were employed to increase the information content available for the modeling. The temperatures at half of the mass loss were lower in the CRR experiments than in the other experiments by around 120 °C. A relatively simple, well-known reaction kinetic equation described the experiments. The dependence on the reacted fraction as well as the dependence on the CO 2 concentration were described by power functions (n-order reactions). The evaluations were also carried out by assuming a function of the reacted fraction that can mimic the various random pore/random capillary models. These attempts, however, did not result in an improved fit quality. Nearly identical activation energy values were obtained for the chars made from wood and forest residues (221 and 218 kJ/mol, respectively). Nevertheless, the forest residue char was more reactive; the temperatures at half of the mass loss showed 20−34 °C differences between the two chars at 10 °C/min heating rates. The assumption of a common activation energy, E, and a common reaction order, ν, on the CO 2 concentration for the two chars had only a negligible effect on the fit quality.

CO 2 gasification of charcoals produced at various pressures

“…Indeed, the reaction order obtained in the present study is in good agreement with the literature [47]. Kinetic studies of non-isothermal gasification was carried out by Wang et al [10,53] and the results revealed reaction orders of 0.44 and 0.58 for wood char and forest residue char, respectively, and between 0.36 and 0.42 for torrefied biomass. From another work reported by Vamvuka et al [54], which investigated the gasification of different chars from municipal solid waste, paper sludge and sewage sludge, reaction orders between 0.4 and 0.6 were also obtained.…”

“…This is also consistent with the fact that the amount of low reactivity secondary charcoal obtained from the condensation of tarry vapor is significantly reduced for pyrolysis of biomass under low pressure [9]. Recently, an attempt to study non-isothermal CO2 gasification kinetic of charcoals prepared at atmospheric pressure and low heating rate carbonization of Norwegian wood and forest residue was carried out by Wang et al [10]. It was found that the CO2 gasification activation energies were nearly identical for chars produced from wood and forest residues, about 221 and 218 kJ/mol, respectively.…”

Modeling and Experimental Study of Ore-Carbon Briquette Reduction under CO–CO2 Atmosphere

“…The internal gas diffusion resistance of R 1 was not considered because the transformation of Fe 2 O 3 to Fe 3 O 4 (Equation (1)) proceeds very quickly in the initial stage of the briquette reduction. The reaction rate of the reaction given in Equation (4) is Equation (20) [36].…”

Towards a meaningful non-isothermal kinetics for biomass materials and other complex organic samples

“…Still this approach is not yet popular. In the field of biomass research we found the simultaneous LSQ evaluation of modulated, CRR and other type of experiments together only in works in which we participated [14][15][16][17][18][19].…”

“…We followed the latter approach in our recent works: the cellulose component was described by Eq. (1) with the same type of f() function which was used in our combustion and gasification studies [9,[13][14][16][17][18][19].…”