Kinetic models comparison for steam gasification of different nature fuel chars

Abstract

The reactivity in steam of five different types of solid fuels (two coals, two types of biomass and a petcoke) has been studied. The fuel chars were obtained by pyrolysis in a fixed-bed reactor at a temperature of 1373 K for 30 min. The gasification tests were carried out by thermogravimetric analysis (TGA) at different temperatures and steam concentrations. The reactivity study was conducted in the kinetically controlled regime and three representative gas-solid models, volumetric model (VM), grain model (GM) and random pore model (RPM), were applied in order to describe the reactive behaviour of the chars during steam gasification.The kinetic parameters of these models were derived and the ability of the models to predict conversion and char reactivity during gasification was assessed. The best model for describing the behaviour of the samples was the RPM. The effect of the partial pressure of steam in gasification was studied, and the reaction order with respect to steam was determined. The reactivity of the chars was compared by means of a reactivity index. Biomass exhibited a higher reactivity than coals and petcoke. However, significant differences in reactivity were observed between the two types of biomass used, which could be due to catalytic effects.

Kinetic models comparison for non-isothermal steam gasification of coal–biomass blend chars

“…The values of k 0 e -E/RT were calculated and plotted on an Arrhenius diagram using the kinetic parameters in Table 3 ( Fig. 4) and then compared with those obtained in the isothermal experiments [46]. A good agreement can be observed between the k 0 e -E/RT values estimated by both methods, indicating that the TPR technique provides reliable kinetics parameters when data from the three heating rates are used, in agreement with Miura and Silveston [13].…”

“…In a previous study [46], a kinetic analysis of the steam gasification of the PT, CH and OS char samples was carried out at constant temperature. The results obtained using the TPR technique were then compared with those obtained from experiments performed at constant temperature.…”

The kinetics of gasification of char derived from sewage sludge

“…The values of pre-exponential factors and activation energy are in the expected range determined for different biomass char The kinetics of gasification of char derived from sewage sludge 697 gasification reactions (e.g. Di Blasi [4], Fermoso et al [7], Klose and Woelki [25]). However, the activation energy for carbon dioxide (223 kJ/mol) is slightly lower than the value of 260 kJ/mol given by Scott et al [26] for char derived from sewage sludge containing similar amount of ash.…”

“…On the other side, type and composition of fuel used for char preparation strongly affect the rate of gasification [6,7]. Gasification is usually carried out with air, oxygen and steam mixtures.…”

“…Gasification is usually carried out with air, oxygen and steam mixtures. The gasification process is very often performed with steam as the gasifying agent; the advantage of using steam is that this process yields higher amounts of hydrogen [7]. However, nowadays when there is a worldwide discussion about utilization of carbon dioxide, the so-called dry gasification by means of CO 2 is also of great importance [8,9].…”