Biomass is an important primary energy source as well as renewable energy source. As the most promising biomass utilization method, gasification/pyrolysis produces not only useful fuel gases, char and chemicals, but also some byproducts like fly ash, NOx, SO2 and tar. Tar in the product gases will condense at low temperature, and lead to clogged or blockage in fuel lines, filters and engines. Moreover, too much tar in product gases will reduce the utilization efficiency of biomass. Therefore, the reduction or decomposition of tar in biomass derived fuel gases is one of the biggest obstacles in its utilization for power generation. In this paper, we review the literatures pertaining to tar reduction or destruction methods during biomass gasification/pyrolysis. On the basis of their characteristics, the current tar reduction or destruction methods can be broadly divided into five main groups: mechanism methods, self-modification, thermal cracking, catalyst cracking and plasma methods.

The reduction and control technology of tar during biomass gasification/pyrolysis: An overview

The catalytic performance of supported noble metal catalysts for the steam reforming (SR) of ethanol has been investigated in the temperature range of 600–850 °C with respect to the nature of the active metallic phase (Rh, Ru, Pt, Pd), the nature of the support (Al2O3, MgO, TiO2) and the metal loading (0–5 wt.%). It is found that for low-loaded catalysts, Rh is significantly more active and selective toward hydrogen formation compared to Ru, Pt and Pd, which show a similar behavior. The catalytic performance of Rh and, particularly, Ru is significantly improved with increasing metal loading, leading to higher ethanol conversions and hydrogen selectivities at given reaction temperatures. The catalytic activity and selectivity of high-loaded Ru catalysts is comparable to that of Rh and, therefore, ruthenium was further investigated as a less costly alternative. It was found that, under certain reaction conditions, the 5% Ru/Al2O3 catalyst is able to completely convert ethanol with selectivities toward hydrogen above 95%, the only byproduct being methane. Long-term tests conducted under severe conditions showed that the catalyst is acceptably stable and could be a good candidate for the production of hydrogen by steam reforming of ethanol for fuel cell applications.

Production of hydrogen for fuel cells by steam reforming of ethanol over supported noble metal catalysts

Insight into steam reforming of ethanol to produce hydrogen for fuel cells

Reaction network of steam reforming of ethanol over Ni-based catalysts

Biomass gasification is an interesting technology in the future development of a worldwide sustainable energy system, which can help to decrease our current dependence on fossil fuels. Biomass gasification is a thermal process where solid fuel is converted into a useful gas using several gasifying agents such as air, and steam. The producer gas has a great number of applications. The most important is being combustion for power and heat generation as well as raw gas for production of fuels or chemicals. This review mainly presents the recent progresses on tar elimination during the biomass gasification. Then, novel non-catalytic absorption and adsorption methods of tar removal under ambient temperature conducted by our laboratory members were also explained. In our opinion, the tar removal can be conducted by combination of catalytic reforming in the gasifier and oil materials adsorption in the scrubber. Furthermore, the tar catalytic reforming is a most significant step during biomass gasification or pyrolysis. Thus, the development of reasonable catalysts for tar elimination has been faced with a significant challenge in current society.

E.G. Cerrella

Papers

Hydrogen from steam reforming of ethanol. characterization and performance of copper-nickel supported catalysts