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Zuber C.,Agnion Highterm Research GesmbH | Hochenauer C.,University of Graz | Kienberger T.,Agnion Highterm Research GesmbH
Applied Catalysis B: Environmental | Year: 2014

In order to remove tars from a synthesis-gas produced with an allothermal, pressurized fluidized-bed biomass gasifier, a catalytic gas-cleaning-process is used. The tars are removed by means of catalytic steam reforming on a commercial nickel catalyst at temperatures of around 500°C in a packed bed reactor. The synthesis-gas enters the reforming reactor at 300°C. Due to the strongly exothermic methanation-reaction the catalyst bed heats up to temperatures high enough to achieve sufficient catalyst activity for tar reforming. Ni-catalysts are sensitive for sulfur poisoning, therefore the main sulfur component in the hydrogen-rich synthesis-gas, hydrogen sulfide (H2S), is adsorbed in a packed bed reactor, filled with ZnO, upstream the tar reformer. Beside H2S there are further sulfur compounds in the gas stream which cannot be removed efficiently by means of ZnO. The aim of this work is to investigate whether it is possible to use a commercially available Co-Mo catalyst for hydrodesulfurization (HDS) upstream the ZnO-bed in order to convert organic sulfur compounds into H2S. Hydrodesulfurization processes are state-of-the-art in large-scale petrochemistry. The process-conditions in this common use-case differ from these in the application discussed within this work. To examine the ability of HDS in the process discussed here, specific HDS-tests and overall system tests were carried out with a synthesis-gas from a laboratory gasifier. The used synthesis-gas was produced with an allothermal fluidized bed gasifier with wood pellets as fuel. The HDS-catalyst started to show activity for hydrogenation of thiophene at a temperature of 350°C under atmospheric pressure. The use of hydrodesulfurization showed a positive influence on the catalyst deactivation of the subsequent Ni-catalyst. © 2014 Elsevier B.V. Source


Zuber C.,Agnion Highterm Research GesmbH | Husmann M.,University of Graz | Schroettner H.,University of Graz | Hochenauer C.,University of Graz | Kienberger T.,A+ Network
Fuel | Year: 2015

In the field of allothermal biomass gasification with steam in a fluidized bed, the removal of tar is the critical step in the process chain. In the approach presented in this work, in a catalytic steam reforming process the tar species are converted to permanent gas components by means of a Ni-catalyst at 500°C. The issue with catalysts based on nickel is that these are poisoned by sulfur components in the synthesis gas. This leads to an increased catalyst deactivation and consequently to elevated operating costs of the facility. The main sulfur species in the synthesis gas of an allothermal steam gasifier is hydrogen sulfide (H2S). In order to reduce the sulfur-related deactivation of the Ni-catalyst, zinc oxide (ZnO) can be used as an upstream adsorbent to remove the main sulfur compound H2S. The aim of this work is to investigate the loading process and the regenerability of a commercial ZnO-adsorbent under realistic conditions. The sulfidation of the ZnO was done with a real synthesis gas produced from wood pellets with a steam blown laboratory gasifier. In order to examine the sulfidation process in the packed bed, the permanent gas composition and the H2S-concentration of the synthesis gas were measured at five sampling points in the reactor and at the reactor outlet. The adsorbent was operated at a constant temperature of 300°C. As a second focus, the regeneration of the used zinc oxide was examined. Regeneration cycles were carried out with mixtures of air, nitrogen and steam in different compositions at elevated temperatures between 650°C and 800°C. The sulfided and regenerated adsorbents were analyzed with a scanning electron microscope (SEM) in combination with energy-dispersive X-ray spectroscopy (EDXS). The sulfidation tests showed the development of the sulfidation process in the packed bed during the experiment. In contrast to the related literature, the ZnO-adsorbent used here turned out to be unsuitable for regeneration under the tested conditions. The used adsorbent was a commercially available product and mainly consisted of ZnO. The SEM-EDXS examination showed that the sulfur was still bonded on the adsorbent after different regeneration experiments. © 2015 Elsevier Ltd.All rights reserved. Source


Kienberger T.,Agnion Highterm Research GesmbH | Zuber C.,Agnion Highterm Research GesmbH | Novosel K.,Agnion Highterm Research GesmbH | Baumhakl C.,Friedrich - Alexander - University, Erlangen - Nuremberg | Karl J.,Friedrich - Alexander - University, Erlangen - Nuremberg
Fuel | Year: 2013

For the production of Raw-SNG (Substitute Natural Gas) from synthesis gas of allothermal biomass gasification beside the methanation reactions, also tar-cleaning and desulfurization must be considered. In this work the tar and sulphur containing synthesis gas of an allothermal bench-scale gasifier is used to investigate a process in which the three mentioned steps are done in a simple way, suitable for decentralized application. Therefore, for the step of desulfurization the use of metal-oxides in a simple fixed-bed adsorber is investigated. For the second and third step Nickel is not only used to catalyze the methanation-reaction, it is also used as catalyst for high-temperature hydrocarbon reforming. Both steps are carried out in one apparatus: In a polytropic reactor (reactor just cooled by thermal losses), the exothermic methanation-reaction leads to a temperature-rise in the reactor of up to around 500 °C. It is investigated, whether this rise in temperature is sufficient to achieve an in situ tar conversion. Due to strong chemisorptive bondings of sulphur components, remaining in the gas after the MeO-adsor-ber, as well as a result of the biomass-tar, an increased Ni-catalyst deactivation turns out to be disadvantageous. This work replies to the question whether this catalyst consumption results from remaining sulphur in the synthesis gas, or from carbon-depositions resulting from biomass-tar. Parameter-studies are done with the aim to reduce the mentioned catalyst-deactivation to an economically feasible level. In order to reach a synthesis gas to Raw-SNG-conversion near to the theoretic thermodynamic equilibrium, the overall reaction kinetics must be considered. It is determined which gas residence times are needed in order to reach the expected synthesis gas conversion. © 2013 Elsevier Ltd. All rights reserved. Source

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