Dipl. Ing. Matthias Mayerhofer Technische Universität München ...
Dipl. Ing. Matthias Mayerhofer Technische Universität München ...
Dipl. Ing. Matthias Mayerhofer Technische Universität München ...
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18 Biomass Gasification<br />
Figure 9: Langmuir-Hinshelwo and Eley-Riedeal mechanism<br />
The Mars-Van Krevelen Mechanism<br />
This mechanism is used to describe the kinetics of reactions such as selective oxidation of hydrocarbons<br />
and it is more applied for the hydrodesulfurization and NOx removal.<br />
Because steam reforming is a highly endothermic reaction the maximum conversion is achieved<br />
with high temperature and low pressure and high steam-to-hydrocarbon ratio. Their basic advantage<br />
is that their use does not reduce the heating value of the gas. The Mars-van Krevelen<br />
mechanism is based on the idea that adsorption of one molecule occurs on top of another molecule<br />
which had previously been adsorbed (Ross, 2012).<br />
The tar decomposition is significantly affected by the presence of methane due to the catalytic reforming<br />
reactions (Hepola,1997b). The basic processes in which they are used are hydrogenation<br />
reactions, steam reforming (production of H2 or syngas), and methanation (Sehested,2006).<br />
2.4.4.3 State of the art<br />
The basic criteria that a catalyst should fulfill to commercially feasible are listed below (Sutton,2001),<br />
(Courson,2000), (Hepola,1997b):<br />
1. Effectiveness in the removal of tars<br />
2. Capability of reforming methane<br />
3. Should provide a suitable syngas ratio depending on the desired application<br />
4. Resistance to deactivation due to carbon deposition, sintering and sulfur poisoning<br />
5. Easily regenerated<br />
6. Resistance to mechanical stresses<br />
7. Inexpensive<br />
8. Compatible with the continuous oxidation and reduction cycles<br />
9. The catalyst life time is also a basic factor that can control the viability of the whole process