Kinetic modeling of tar steam reforming in biomass gasification
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School of Chemical Engineering |
Master's thesis
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Date
2013
Department
Major/Subject
Teknillinen kemia
Mcode
Kem-40
Degree programme
Language
en
Pages
xii + 81 + [17]
Series
Abstract
The aim of this study was to model the kinetic parameters for tar steam reforming using benzene as a tar model compound. In the literature part, the activity of various types of catalysts, effect of S/C and temperature and kinetic parameters obtained by several researchers were reviewed. Catalytic activity of each catalyst on steam reforming was determined in decreasing order as: NiMo/Y-Al<sub>2</sub>O<sub>3</sub> > calcined dolomite [CaMg(O)<sub>2</sub>] > Dolomite [MgO]> Quicklime [CaO]. The Ni catalyst was concluded to be the most widely used catalyst in benzene steam reforming and catalytic performance of it is improved even more in the presence of support material such as Al<sub>2</sub>O<sub>3</sub>. The researchers came up with different results in a considerable interval for kinetic parameters (e.g., in the range of 56-326 kj/mol for the activation energy). The discrepancy between kinetic parameters occurs due to the chosen type of tar compound, catalyst as well as operating conditions. Some researchers have studied real tar while some studied more stable tar model compounds such as benzene, toluene, and naphthalene. Operating conditions such as presence or absence of gasifying gas agents in feed also play important role in decomposition rate of tar. The experiments were carried out over NiO/Al<sub>2</sub>O<sub>3</sub> catalyst at 750-900°C and under atmospheric pressure by using atmospheric plug flow reactor (APFR). The effects of product gases were also tested by feeding CO and H<sub>2</sub> into steam reforming reactor. Kinetic rate equations were derived based on Langmuir-Hinshelwood model and power law model with different assumptions. After kinetic parameters were estimated, thermodynamic consistency, confidence interval of estimated parameters and correlation between them were checked to evaluate the reliability of the model. Activation energy and pre-exponential factor were estimated as 238 kj/mol and 1.4 x 10<sup>13</sup> m<sup>3</sup> / (kg<sub>cat</sub>.h) respectively for benzene steam reforming based on single site adsorption of benzene on NiO/Al<sub>2</sub>O<sub>3</sub> catalyst. It was also concluded that CO enhanced the decomposition of benzene whereas H<sub>2</sub> had an inhibiting effect on the reaction.Description
Supervisor
Lehtonen, JuhaThesis advisor
Kaisalo, NooraKeywords
steam reforming, kinetics, Langmuir Hinshelwood