Abstract
Tar in the product gas of biomass gasifiers reduces the efficiency of gasification processes and causes fouling of system components and pipework. Therefore, an efficient tar conversion in the product gas is a key step of effective and reliable syngas production. One of the most promising approaches is the catalytic decomposition of the tar species combined with hot syngas cleaning. The catalyst must be able to convert tar components in the synthesis gas at temperatures of around 700 °C downstream of the gasifier without preheating. A Ni-based doped catalyst with high activity in tar conversion was developed and characterized in detail. An appropriate composition of transition metals was applied to minimize catalyst coking. Precious metals (Pt, Pd, Rh, or a combination of two of them) were added to the catalyst in small quantities. Depending on the hot gas cleaning system used, both transition metals and precious metals were co-impregnated on pellets or on a ceramic filter material. In the case of a pelletized-type catalyst, the hot gas cleaning system revealed a conversion above 80% for 70 and 110 h. The catalyst composed of Ni, Fe, and Cr oxides, promoted with Pt and impregnated on a ceramic fiber filter composed of Al2O3(44%)/SiO2(56%), was the most active catalyst for a compact cleaning system. This catalyst was catalytically active with a naphthalene conversion of around 93% over 95 h without catalyst deactivation.
Highlights
In the gasification of biomass, a gas mixture that essentially consists of the components CO, CO2, H2, H2O and higher hydrocarbons, as well as aromatic compounds, is produced
One of the most promising approaches is the catalytic decomposition of the tar species combined with hot syngas cleaning
Depending on the hot gas cleaning system used, both transition metals and precious metals were co-impregnated on pellets or on a ceramic filter material
Summary
In the gasification of biomass, a gas mixture that essentially consists of the components CO, CO2, H2, H2O and higher hydrocarbons, as well as aromatic compounds (condensable tar), is produced. One of the most promising methods to overcome this problem is the catalytic decomposition of tar species, where the energy content of the tar can be converted into fuel gas. Among the most promising Ni-supported metal oxide catalysts for catalytic performance in steam reforming and resistance to coke deposition was 15 wt% Ni/CeO2 (75%) ZrO2 (25%) [14]. In the last two decades, catalytic materials have been investigated in tar conversion and more compact systems with catalytic filters. The switch from standard ceramic filter elements to catalytic filter elements leads to a highly integrated hot gas cleaning system with significantly reduced investment costs (see Figure 2). To ensure that the catalysts are effective at lower temperatures, small amounts of Pt, Pd, Rh, or Ru and in some samples, a combination of two of these noble metals were used
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