Effect of pyrolysis conditions on the char gasification with mixtures of CO2 and H2O

Desorption kinetics of CO in char oxidation and gasification in O2, CO2 and H2O

“…Hecht et al [20] assumed that the CO desorbed instantaneously after adsorption of O 2 , CO 2 or H 2 O for coal chars at temperatures above 1700 K. With such an assumption, the surface sites are, however, never occupied and the global reaction orders with respect to O 2 , CO 2 and H 2 O are one. This may be the case under some conditions [21][22][23], although generally low reaction orders have been reported for O 2 [e.g., [23][24][25] as well as for CO 2 and H 2 O [e.g., [26][27][28][29][30]. In R1-R7, the reaction order with respect to a gaseous reactant is one for the adsorption step and zero for the desorption step.…”

Influence of temperature and particle size on the single and mixed atmosphere gasification of biomass char with H 2 O and CO 2

“…Pyrolysis conditions Mixed atmosphere mechanism [3] Wood char (4 cm) Same activation energy and dependance on the sum of partial pressure [4] Birch wood char (45-63 μm) Slow pyrolysis Competition 24°C/min [5] Pine wood char (5.5 mm) Medium rate pyrolysis in a screw reactor at 60°C/s Synergy [7] Various biomasses Slow pyrolysis 10°C/min Synergy [9] Dried sewage sludge char (1.2 mm) Fast pyrolysis in FBR Additivity [10] Olive tree pruning char (1.9 mm) Fast pyrolysis in FBR Additivity [11] Beech wood char ( More recently, Chen et al [16] investigated the effect of the pyrolysis conditions on the gasification reactivity of lignite chars in mixtures of H 2 O + CO 2 . Two kinds of char were prepared from a lignite by fast py rolysis using a drop tube furnace and by slow pyrolysis using a fixed bed furnace at a temperature of 1273 K. Char gasification reactions with CO 2 , H 2 O and their mixtures were performed in a thermogravimetric analyser (TGA) system.…”

Gasification under CO2–Steam Mixture: Kinetic Model Study Based on Shared Active Sites

“…Li et al [17] also pointed out that the reaction mechanism of lignite char gasification was in accordance with the separate reactive site reaction mechanism under lower gasification pressures, whereas it was superior to the common reactive site reaction mechanism when gasification pressures further increased. On the other hand, Chen et al [18] found that the overall gasification rate is not equal to the sum of the char-CO 2 reaction rate and char-steam reaction rate, but there was no evidence proving that the two gasifying agents competed for active sites. An L-H model with two dimensionless parameters was proposed by Umemoto et al [19] to evaluate the rate of char-CO 2 -steam gasification, and could estimate interactions more accurately than other models.…”

“…Recently, some researchers [14][15][16][17][18] came to investigate interactions in the char-CO 2 -steam reaction using the Langmuir-Hinshelwood (L-H) model based on the theory of absorption and desorption. Roberts and Harris [14] found that char-CO 2 and char-steam reactions occur at the common active sites and indicated that steam and CO 2 competed for active sites of chars.…”