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In this paper, the activity of a cobalt/molybdenum (Co/Mo) industrial catalyst to water gas shift reaction for hydrogen production was investigated in a three fixed bed reactor pilot plant by using a biomass-derived tar-rich synthesis as a feed-stream. A parametric variation study was carried out to assess CO conversion and selectivity for the water gas shift reaction as function of reaction temperature (T) in the range 300-450°C.

Die Katalyse der Wassergasshift-Reaktion (WGSR) stellt eine interessante Technologie bei der Wasserstoffherstellung auf Basis von holzartiger Biomasse dar. In dieser experimentellen Arbeit, wurde die katalytische Aufbereitung von Holzgas aus einer Wirbelschichtdampfvergasung untersucht. Zwei verschiedene kommerzielle Katalysatoren wurden getestet. Katalysator 1 (Co/Mo-basiert) wurde f��r Gasgemische entwickelt, welche betr��chtliche Anteile an Schwefel enthalten. Katalysator 2 (Fe/Cr-basiert) wurde f��r schwefelfreie Gasgemische entwickelt. Beide Katalysatoren wurden an zwei unterschiedlichen Apparaturen getestet. An der Kinetikapparatur der Technischen Universit��t Wien wurden die Katalysatoren im Laborma��stab mit k��nstlichen Gasmischungen beaufschlagt und empirische Kinetikmodelle aufgestellt (Power law rate Modelle). Die verwendeten Gasmischungen wurden dabei an die Zusammensetzung von Holzgas angepasst und ein Schwefelwasserstoffgehalt von 100 vol.ppmdb eingestellt. Au��erdem wurde im Zuge dieser Dissertation eine Versuchsanlage realisiert, um diese Katalysatoren im gr����eren Ma��stab mit realem Holzgas zu beaufschlagen. Diese Anlage wurde am Standort des Biomassevergasungskraftwerks Oberwart aufgebaut, an dem Holzgas durch die Zweibettwirbelschichtdampfvergasung von Holzhackschnitzel hergestellt wird. Ein Teilstrom des dort produzierten Holzgasgemisches wurde entnommen und��ber die Versuchsanlage geleitet, welche mit drei seriell geschalteten Festbettreaktoren ausgestattet war. Die Pilotanlagewurde auf einen trockenen Holzgasvolumenstrom von 2 m3/h ausgelegt. Vor Ort wurden der Einfluss verschiedener Betriebsparameter, die Langzeitstabilit��t der Katalysatoren und die Auswirkung der Katalysatoren auf Schwefel- und Teerverbindungen untersucht. Die Aktivit��t des Co/Mo-basierten Katalysators wurde durch h��here Schwefelgehalte gesteigert. Im Gegensatz dazu, wurde die Aktivit��t des Fe/Cr-basierten Katalysators durch die Zugabe von Schwefelwasserstoff reduziert. In Kombination mit den relativ geringen Schwefelkonzentrationen im Holzgas des Kraftwerks Oberwart, erzielte der Fe/Cr-basierte Katalysator wesentlich bessere Kohlenmonoxid Konversionsraten. In starker Abh��ngigkeit von den Betriebsbedingungen (Temperatur, Raumgeschwindigkeit, Wassergehalt) konnten Konversionsraten von bis zu 95 % erzielt werden. In Kooperation mit anderen Forschungsprojekten, konnte das Gasgemisch im Ausgang der Versuchsanlage zu hochreinem Wasserstoff aufbereitet werden. Die Anwendung dieses Wasserstoffs in einer PEM Brennstoffzelle wurde demonstriert., Catalysis of the water gas shift reaction (WGSR) is an interesting process for the biomass based production of hydrogen. In this predominately experimental work, the catalytic refinement of wood gas derived from biomass steam gasification was investigated. Two different commercial water gas shift catalysts were tested: a Co/Mo-based catalyst which was developed for sour shift applications in gas mixtures containing hydrogen sulfide; and a Fe/Cr-based catalyst which was developed for sweet shift processes downstream sulfur removal. Both catalysts were investigated at two different experimental setups. At the "Test rig for chemical kinetics" at the Vienna University of Technology, experiments were carried out on a laboratory scale using synthetic gas mixtures simulating wood gas composition. Based on these results, empirical power law rate models were established in order to describe the reaction kinetics for both catalysts). Both models were valid for a hydrogen sulfide content of 100 vol.ppmdb. Also, a pilot plant was designed, assembled, commissioned, and optimized within this thesis in order to investigate the catalysis of the WGSR on a bigger scale using real wood gas. This facility ("Pilot plant for catalytic wood gas processing") was processing wood gas generated by means of dual fluidized bed steam gasification of wood chips at the commercial heat and power plant in Oberwart, Austria. About 2 m3/h of dry wood gas were processed over three fixed bed reactors connected in series. At this facility, the influence of various reaction parameters, the long-term stability, and the catalytic side effects were investigated. The activity of the Co/Mo-based catalyst was enhanced with increasing sulfur loads in the feed, whereas the activity of the Fe/Cr-based catalyst was decreased with higher sulfur loads. In combination with the rather low sulfur loads of the present wood gas, the performance of the Fe/Cr-based catalyst was considerably better than the performance of the Co/Mo based catalyst. Strongly depending on the reaction parameters (temperature, gas hourly space velocity, and steam to dry gas ratio) up to 95 % of the present carbon monoxide was converted to hydrogen and carbon dioxide according to the WGSR. In cooperation with other research projects, this shifted gas mixture was further processed to produce pure hydrogen based on wood gasification. Also, the usage of the generated hydrogen in a PEM fuel cell was demonstrated.

In this paper, the activity of a cobalt/molybdenum (Co/Mo) commercial catalyst for the Water Gas Shift Reaction for hydrogen production was investigated in a three fixed-bed reactor pilot plant using a tar-rich synthesis gas from a full-scale biomass gasification plant as feed-stream. A parametric variation study was carried out to assess CO conversion (X CO ) and selectivity for the water gas shift reaction as a function of the operating temperature (T) in the range 300–450 °C. The effects of four dry gas hourly space velocities (GHSV), Case A-Case D, two steam to dry synthesis gas ratios (H 2 O/SG), 56% v/v and 67% v/v, and a H 2 S concentration in the range 100–220 ppm v,db were investigated: the highest CO conversion (∼95%) was observed in the base case (Case A GHSV) at 67% v/v H 2 O/SG, and 450 °C, the lower the operating temperature the lower the CO concentration, the lower the gas hourly space velocity the higher the CO conversion and the higher the H 2 O/SG the higher the CO conversion. The effect of H 2 S variation on CO conversion was also studied, keeping the operating temperature constant (≈365 °C) and using the Case D GHSV: CO conversion increased as the H 2 S concentration increased and X CO ≈ 40%. Selectivity was not influenced by the parameters investigated. Finally, the effect of the catalyst on tar removal was studied and a CO conversion close to 85% was found.