Steam pretreatment of Salix to upgrade biomass fuel for wood pellet production Amit Kumar Biswas ⁎, Weihong Yang, Wlodzimierz Blasiak Division of Energy and Furnace, Department of Materials Science and Engineering, Royal Institute of Technology (KTH), Brinellvagen 23, SE-100 44 Stockholm, Sweden abstract article info Article history: Received 2 January 2011 Received in revised form 12 March 2011 Accepted 11 April 2011 Available online 30 April 2011 Keywords: Steam explosion Pretreatment Pellet Combustion Pyrolysis Upgraded biomass fuel Steam explosion (SE) pretreatment is served to separate the main components of woody biomass. In general there is a noticeable gap in literature in terms of application of steam explosion process to upgrade biomass fuel for wood pellet production. In order to study the influence of steam explosion pretreatment on biomass fuel, Salix wood chips was used as raw material. Four different SE experiments were performed by varying two key process factors; time and temperature. Elementary quality and ash properties of the pretreated residue were investigated. Moreover, physical and thermochemical properties of the pellet, produced from the residue, were also investigated. Reduction in ash content especially in alkali metals was observed in steam treated residue. Pretreatment of biomass also enhanced carbon content and reduced oxygen amount in the fuel which enhanced the heating value of the fuel. Moreover, pretreatment enhanced pellet density, impact resistance, and abrasive resistance of pellet. However, small degradation in ash fusion characteristics and char reactivity was also observed as the severity of the process increased. © 2011 Elsevier B.V. All rights reserved. 1. Introduction During recent years, worldwide wood pellet industry has experienced dramatic changes. Global wood pellet production increased from 8 million ton/year to 13 million ton/year between years 2007 to 2009. Among that 13 million ton, 8 million ton was consumed by European countries in 2009. It is predicted by European Biomass Association that the consumption of 50 million ton will be reached in European countries by 2020 [1,2].Therefore, wood pellet is going to play an important role in energy market of Europe. However, conventional wood pellet holds some inferior characteristics both as fuel and pellet. As a fuel, use of biomass in combustion and gasification process involves technical difficulties such as low ash sintering temperature and low heating value [3,4].Moreover, due to low bulk density and high moisture content in the fresh biomass, the handling cost is considered to be crucial. Kumar and co-workers identified that transportation cost is the second highest cost after the capital cost for direct biomass fired power plant [5]. Although densification ease the problem associated with bulk biomass but conventional wood pellets still hold some demerits along with previously mentioned problems of biomass. The problems are lower hardness, lower specific weight, and high sensitivity to moisture. At the same time, wood should be screened to smaller particle size to have better pellet quality which imposes additional cost to the pellet producers [6]. Hence, improvement of wood pellet both in terms of fuel and pellet quality is indispensable. Currently, different approaches have been considered to improve the quality of wood pellet, for example, torrefaction. Another promising technology is Steam explosion (SE) pretreatment process. Previously, application of biomass steam explosion process was devoted to ethanol, and binderless panel production [7–11]. Recently this concept has been brought into attention for improvement of wood pellet. Steam explosion process involves separation of main components of woody biomass (lignin, cellulose and hemicelluloses) by both chemical degradation and mechanical deformation. The process involves adiabatic expansion of water inside the pore of wood tissue and auto hydrolysis of cell components [7]. Considering SE process for wood pellet production, it is important to focus on its fuel characteristics due to end use application. Despite a number of impressive studies on thermochemical behavior of steam pretreated residue had been conducted, most of them were performed on the residue which had gone through simultaneous saccharification and fermentation (SSF) [12–14]. As a result, ligno- celluloses structure was further modified due to SSF. Although those studies were performed on SE residue with SSF, many striking facts were brought into attention. Öhman et al.,[12]. has compared non- hydrolyzed residue with some reference biomass samples. They concluded that non-hydrolyzed residue has low slagging tendency, very low emission of particulate and similar gaseous emission as other biomass. Eriksson et al. [13] pointed that combustion of non- hydrolyzed residue did not involve instability. In fact, it reveals that SE pretreatment can improve the quality of biomass as a fuel for thermal application. However, application of steam explosion process in improvement of wood pellet is not often addressed. The objective of this paper is to investigate the effect of steam explosion pretreatment on biomass as a fuel for thermal application as Fuel Processing Technology 92 (2011) 1711–1717 ⁎ Corresponding author. Tel.: + 46 8790 8459; fax: + 46 8207 681. E-mail address: akbiswas84@gmail.com (A.K. Biswas). 0378-3820/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2011.04.017 Contents lists available at ScienceDirect Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc