Two Advanced Models for the Kinetics of the Variation of the Tar Composition in Its Catalytic Elimination in Biomass Gasification

Abstract

Biomass gasification in fluidized beds generates tar that can be effectively eliminated with catalysts located downstream from the biomass gasifier. Some previously obtained results from such catalytic tar elimination were hard to be understood because the tar was considered as only one or two lumps. For this reason, in this work, tar is considered in two ways: (i) as being composed of six different lumps and (ii) as a continuous mixture. For these studies, tar was sampled before and after two catalytic beds located in a slip-flow downstream from a fluidized-bed gasifier (pilot scale). Such tar samples were then completely characterized, and the tar composition was thus determined before and after the catalytic bed. The conversion of each of the species present in tar, and thus of the lumps, was calculated at different temperatures and space-times in the catalytic reactor. The two most advanced reaction networks and their corresponding kinetic models are presented here. The first one provides the evolution with gas residence time of the mean molecular weight of the tar and of the variance of the tar molecular weight distribution. The second kinetic model is based on a set of six kinetic equations and eleven kinetic constants, which are calculated here. This second model allows the species present in tar to be ranked according to their reactivity or resistance to being destroyed. Predictions from these models are consistent with all existing data on this matter.

Steam reforming of phenol over Ni-based catalysts – A comparative study

“…8) indicated that coke was accumulated on both supports in significant amounts, strongly suggesting that deactivation was essentially caused by the carbonaceous species formed during decomposition of phenol on the metal oxides. In the case of the catalytic steam reforming of phenathrene [20], opening of the aromatic rings has been proposed as the first step in the formation of ring radicals which further react or condense to lead to coke on the catalyst surface. This aromatic ring-opening mechanism could also be applied in our phenol steam reforming case.…”

Kinetic modeling of a combined tar removal and methanation reactor for biogenous synthesis gas at medium temperature conditions

“…Another method is to consider tar as a single lump component of the type C x H y O z or with an unspecified formula. To improve the single lump model, Corella [26] proposed two advanced kinetic models for catalytic tar removal in õbiomass gasification processes, considering tar composed of six different lumps and as a continuous mixture. Tables of kinetic constants of different literature sources are presented in [27,28,10,9].…”

“…Since kinetic constants for one-or two lump models are specific for a given gasifier, feedstock and process [26], the kinetic values have to be adapted to the experimental conditions. A comparison of literature values, considering data determined under experimental conditions similar to the setup described in Section 2, indicates comparable values for the Activation energy E app in different literature sources.…”

Integrated Biomass Gasification with Catalytic Partial Oxidation for Selective Tar Conversion

“…In their work, a simple kinetic model is used to describe the overall tar elimination network. Corella et al 23,24 conducted extensive studies on tar elimination reactions and kinetics. Figure 36 is a summary of E app values found by several authors with different catalysts.…”