(537e) Biomass Gasification with Nickel Oxide/Olivine Catalysts in Fluidized Bed Gasifier

Tar removal from biomass gasification gas is a crucial problem in applying syngas from biomass for its downstream applications. Catalytic biomass gasification has given promising results for tar cracking. A few research groups have investigated the use of olivine for tar cracking. The presence of oxides of iron and magnesium in the mineral olivine give it the ability to crack higher hydrocarbons termed as tars. Olivine surely does have sustainable physical properties for the harsh conditions of a fluidized bed gasifier. Untreated olivine was previously compared by us with dolomite in cracking model tar compounds. Modifying the olivine by calcination at high temperatures showed very promising results towards tar cracking. Also tests related to attrition resistance showed that olivine is very capable of being the gasification catalyst as compared to dolomite. Nickel oxide is known in the literature as an effective catalyst for tar cracking and tar reforming. Therefore, the behavior of nickel oxide on olivine catalyst under reducing conditions with respect to tar cracking is studied.

The purpose of this study is to determine the conversion of a tar (naphthalene) using the nickel on olivine catalyst in a fluidized bed biomass gasifier and moreover to study the effect of olivine calcination on the conversion of tars.

In-situ removal of tar during biomass gasification is being performed in a bubbling fluidized bed biomass gasifier. Different forms of NiO/Olivine catalysts are used. These are: (i) nickel oxide on olivine, (ii) nickel oxide on calcined olivine, (iii) the calcination of catalyst mentioned under (i), and (iv) the calcination of catalyst mentioned under (ii).

The gasifying agent is air. The biomass feed rate is 1 kg/h. The temperature in the gasifier is maintained at 800 ºC. Sand is used as the bed material along with the catalyst.

During the catalyst preparation the hardness of the nickel oxide on olivine catalyst was noticeable and it can be related to the attrition resistant property of olivine. The catalyst is characterized by means of XPS, XRD, SEM and EDX. XPS analysis has revealed that nickel is present at the olivine surface as Ni2+. Presence of iron oxide on the surface of the catalyst after impregnation of nickel and calcination of the catalyst is also seen.

The results of the activity for tar cracking using the catalysts, and the stability of the gasifier with respect to time are also discussed.