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ABSTRACT

Full Name:Muflih Arisa Adnan

Thesis Title:TAR ELIMINATION IN BIOMASS GASIFICATION -- DEVELOPMENT OF Fe2O3/SiO2-Al2O3FLUIDIZABLE CATALYSTS AND THERMODYNAMIC MODELING

Major Field:Chemical Engineering

Date of Degree:January 2017



This research deals with the removal of tars from biomass gasification processes. In the regard, both experimental and thermodynamic modeling approach have been considered. In experimental study, iron oxide on SiO2-Al2O3 catalysts are synthesized, characterized and evaluated in a fluidized bed using toluene as a tar model compound.  Under the studied reaction conditions, Fe2O3/SiO2-Al2O3 yield high toluene conversions (76%). The composition of the gases produced (H(12%), CO (44%), CO2 (18%) and CH4 (1%)) are close to their corresponding equilibrium values. The Fe2O3/SiO2-Al2O3 catalyst also display stable activities over repeated reaction and re-generation cycles. The presence of Si enhances the stability of the γ-Al2Osupport at high temperatures as revealed by TGA, XRD and BET surface area analysis. NH3-TPD showed that the addition of Fe2O3increase the catalyst acidity, which contributed to the higher tar conversion. Thus, the relatively cheap and unharmful Fe2O3/SiO2-Al2O3 catalyst has great potential for industrial applications in tar elimination from biomass gasification processes.  

 

The performance of a gasification process for different biomass is evaluated by developing a thermodynamic model using Aspen Plus. The parametric study is evaluated by varying the gasification temperature, the reformer temperature, the oxygen equivalence ratio, and the steam to carbon ratio. It is found that at same gasification temperature and with no gasifying agent, the increase of H2/CO ratio of producer gas is proportional to the H/O ratio in the feed biomass. The gasification of algae with oxygen exhibits the highest H2/CO ratio (0.94).  The highest cold gas efficiency is found during gasification of algae with oxygen (0.93) or steam (1.60), while the highest gas system efficiency is obtained for rice husk using the same gasification agents (1.11 or 0.89 with oxygen or steam, respectively).

 

The thermodynamic model is further developed to take into account of presence of tar in the gasification process. The model shows higher accuracy as compared to the conventional model in term of the composition of producer gas. The parametric study is conducted by varying O2 equivalence ratio, steam to carbon (S/C) ratio, and split ratio of the gasifying agents through different zones (e.g., combustion zone, counter-current reduction zone, or co-current reduction zone). Introducing the gasifying agents through counter-current reduction zone has positive effect on the gasification performances in term of cold gas efficiency (CGE), gasification system efficiency (GSE), and H2and CO concentrations. Gasification with steam exhibits higher H2 concentration (0.44 at S/C ratio=1) when compared to gasification with oxygen (0.28). In the gasification with oxygen, high CGE (0.79) and GSE (0.94) are observed when ER = 0.3.

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