Characterization of Residual Particulates from Biomass Entrained Flow Gasification

Abstract

Biomass gasification experiments were carried out in a bench scale entrained flow reactor, and the produced solid particles were collected by a cyclone and a metal filter for subsequent characterization. During wood gasification, the major part of the solid material collected in the filter is soot. Scanning electron microscopy (SEM) images coupled with energy dispersive spectroscopy (EDS) show agglomerated nanosize spherical soot particles (<100 nm) that are very rich in carbon. In comparison to wood gasification, the soot content in the filter sample from straw gasification is quite low, while the contents of KCl and K2SO4 in the filter sample are high. SEM images of the straw filter samples show that with steam addition during gasification, where the soot yield is lower, the filter sample becomes richer in KCl and K2SO4 and appears as irregular crystals, and the typical particle size increases from below 100 nm to above 100 nm. During gasification of dried lignin, the filter sample mainly consists of soot and nonvolatilizable inorganic matter. SEM images of the parent wood particles and the derived char samples show that they have similar structure, size, and shape but the derived char particle surface looks smoother indicating some degree of melting. The reactivity of the organic fraction of the samples was determined by thermogravimetry, and it was found that char was more reactive than soot with respect to both oxidation and CO2 gasification. The activation energy for the soot conversion is higher than for the char conversion. These results support the observation from gasification experiments that char is more easily converted than soot. Surprisingly, the soot produced at a higher temperature is more reactive than the soot produced at a lower temperature.

Characterization of char and soot from millimetric wood particles pyrolysis in a drop tube reactor between 800°C and 1400°C

“…This can explain the higher reactivity of char from 1400°C experiments compared to that from 1200°C, and also the higher reactivity of soot sample collected after 2 s of residence time compared to that of sample collected after 4 s of residence time for experiments at 1200°C. The same correlation between the increase of reactivity and mineral content with temperature, for soot from biomass pyrolysis, was also observed by Qin et al [18].…”

“…The present study is an attempt to fill in the lack of information about char and soot in the context of biomass gasification in an en trained flow reactor. Only one recent work has been found in liter ature about this subject [18]. Characterization experiments were then performed on char and soot coming from wood particles pyrolysis in a drop tube reactor (DTR), a well adapted reactor to study biomass conversion in the conditions of an entrained flow reactor at lab scale.…”

Comparison of high temperature chars of wheat straw and rice husk with respect to chemistry, morphology and reactivity

“…A plot of ln(Àln(1ÀX) T À2 ) versus T À1 gives a straight line whose slope and intercept determine the values of the activation energy (E a ) and pre-exponential factor (A). The results of Qin et al [35] showed that a first order reaction model in both char mass and gasification agent can describe the experimental results well. The reactivities of wheat straw and rice husk chars were compared using reaction rates calculated for the derived kinetic parameters (A and E a ) at a fixed oxidation temperature of 400 C.…”

Influence of H 2 O, CO 2 and O 2 addition on biomass gasification in entrained flow reactor conditions: Experiments and modelling

“…Indeed, soot gasification experiments have shown that soot gasification by steam was 2-20 times slower than char gasification between 750°C and 950°C [27]. Soot gasification by CO 2 is 2-30 times slower than char gasification at 1100°C [28].…”