Steam gasification of biomass in a conical spouted bed reactor with olivine and γ-alumina as primary catalysts Aitziber Erkiaga, Gartzen Lopez, Maider Amutio, Javier Bilbao, Martin Olazar ⁎ Department of Chemical Engineering, University of the Basque Country UPV/EHU, P.O. Box 644-E48080 Bilbao, Spain abstract article info Article history: Received 25 April 2013 Received in revised form 28 June 2013 Accepted 17 July 2013 Available online 22 August 2013 Keywords: Steam gasification Tar cracking Biomass Spouted bed Olivine γ-alumina Olivine and γ-alumina have been used as primary catalysts for tar elimination in the continuous steam gasifica- tion of pine wood sawdust in a bench-scale plant provided with a conical spouted bed reactor. A comparison of the performance of each catalyst with that observed for a bed made up of inert silica sand shows that both cata- lysts have a significant activity for tar cracking/reforming, given that the amount of tar obtained by operating with beds of inert sand is reduced by 79% and 84% when olivine and γ-alumina are used, respectively. The tar cracking reduces selectively the content of light and heavy PAHs, giving way to an increase in the concentration of light aromatics. Furthermore, both catalysts cause a positive effect on the gas composition by slightly enhanc- ing the water–gas shift and reforming reactions. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The valorization of lignocellulosic biomass (available and wide- spread renewable source) by means of thermochemical and catalytic processes is one of the most promising alternative to fossil fuels, given that it does not contribute to a net rise in the level of CO 2 in the atmo- sphere [1]. The biomass gasification process takes place at high tempera- tures (generally in the 600–900 °C range or even higher) in the presence of a gasifying agent (air, oxygen, steam, CO 2 , or mixtures of these compo- nents) and allows obtaining a gaseous stream composed mainly of per- manent gases (CO, H 2 , CO 2 , CH 4 ,H 2 O and N 2 when air is used as an oxidizing agent). This gas can be used as fuel (contains 70–80% of the original biomass energy) and/or feedstock for the production of liquid fuels and raw materials by means of catalytic processes of increasing in- dustrial implementation such as Fischer Tropsch and DME synthesis [2–4]. In the DME synthesis the interest is centered on the incorporation of CO 2 in the feed with the biomass derived syngas [5–7]. However, a fraction of the biomass (around 10 wt.%, depending on gasification conditions and biomass type) remains as carbonaceous solid residue (char) or is transformed (mainly during the devolatilization process prior to gasification) into a complex mixture of volatile organic compounds (tar), which include aromatic and heterocyclic species as well polycyclic aromatic compounds (PAHs) [8]. Furthermore, ashes (derived from char gasification) and N, S and Cl containing compounds (such as NH 3 , HCN, H 2 S and Cl) are also formed. Consequently, the gas requires complex purification steps (accounting for 50% to 75% of the overall cost) in order to meet specifications. These specifications be- come particularly restrictive for applications involving the catalytic con- version of syngas into fuels [9] and for highly efficient solid fuel cells (SOFCs) [10]. The main challenge for the valorization of syngas lies in its tar content, which condenses or polymerizes below 300 °C, leading to the fouling, corrosion and blocking of pipes, heat exchangers and par- ticle filters, thus causing a reduction in the process efficiency. Moreover, tars are dangerous due to their carcinogenic nature and contain a signif- icant amount of energy that may be transferred to the syngas. Measures to avoid tar formation are essential and, accordingly, several reviews deal with the strategies for the production of a tar free syngas [11–16]. These strategies can be gathered into two groups: i) primary, by reducing or limiting the tar formation in the gasifier; ii) secondary, by cleaning the gaseous product at the outlet of the gasifier, which may involve physical (wet scrubbing, filtration, electrostatic precipitation), thermal and/or catalytic processes. The main advantages of using steam as gasifying agent lie in the pro- duction of a syngas with a high hydrogen concentration, nitrogen free and high heating value (N 10 MJ m -3 ). Different reactor configurations are commonly used for the steam gasification of biomass, which according to their hydrodynamic behaviour can be classified as follows: fixed bed, fluidized bed, moving/downdraft and updraft [17,18]. Fluid- ized beds are the most commonly used [19–26], with their main advan- tages being: i) isothermal bed with a suitable temperature control (generally below 900 °C) and vigorous particle movement that avoids bed agglomeration due to ash melting; ii) high heat transfer rate (crucial for this endothermal process) enhanced in dual fluidized beds with heat recovery by external combustion of the char [21]; iii) suitable for scaling up the process and co-feeding the biomass with other materials (coal, Fuel Processing Technology 116 (2013) 292–299 ⁎ Corresponding author. Tel.: +34 946012527; fax: +34 946 013 500. E-mail address: martin.olazar@ehu.es (M. Olazar). 0378-3820/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fuproc.2013.07.008 Contents lists available at ScienceDirect Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc