Combustion and Flame 189 (2018) 240–256 Contents lists available at ScienceDirect Combustion and Flame journal homepage: www.elsevier.com/locate/combustfame Particle formation during pressurized entrained flow gasification of wood powder: Effects of process conditions on chemical composition, nanostructure, and reactivity Henrik Wiinikka a,b,∗ , Pal Toth a,c , Kjell Jansson d , Roger Molinder a , Markus Broström e , Linda Sandström a , JoAnn S Lighty f , Fredrik Weiland a a RISE Energy Technology Center AB, Box 726, SE 941 28 Piteå, Sweden b Energy Engineering, Division of Energy Science, Luleå University of Technology, SE-971 87 Luleå, Sweden c University of Miskolc, Institute of Thermal Energy, B1 404 Miskolc-Egyetemváros, 3515 Miskolc, Hungary d Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden e Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University, SE-901 87 Umeå, Sweden f Department of Chemical Engineering, University of Utah, Salt Lake City, UT, United States a r t i c l e i n f o Article history: Received 9 June 2017 Revised 31 August 2017 Accepted 23 October 2017 Keywords: Gasification Biomass Soot Nanostructure HRTEM a b s t r a c t The influence of operating condition on particle formation during pressurized, oxygen blown gasifica- tion of wood powder with an ash content of 0.4 wt% was investigated. The investigation was performed with a pilot scale gasifier operated at 7 bar(a). Two loads, 400 and 600 kW were tested, with the oxygen equivalence ratio (λ) varied between 0.25 and 0.50. Particle concentration and mass size distribution was analyzed with a low pressure cascade impactor and the collected particles were characterized for mor- phology, elemental composition, nanostructure, and reactivity using scanning electron microscopy/high resolution transmission electron microscopy/energy dispersive spectroscopy, and thermogravimetric anal- ysis. In order to quantify the nanostructure of the particles and identify prevalent sub-structures, a novel image analysis framework was used. It was found that the process temperature, affected both by λ and the load of the gasifier, had a significant influence on the particle formation processes. At low tempera- ture (1060 °C), the formed soot particles seemed to be resistant to the oxidation process; however, when the oxidation process started at 1119 °C, the internal burning of the more reactive particle core began. A further increase in temperature ( > 1313 °C) lead to the oxidation of the less reactive particle shell. When the shell finally collapsed due to severe oxidation, the original soot particle shape and nanostructure also disappeared and the resulting particle could not be considered as a soot anymore. Instead, the particle shape and nanostructure at the highest temperatures ( > 1430 °C) were a function of the inorganic con- tent and of the inorganic elements the individual particle consisted of. All of these effects together lead to the soot particles in the real gasifier environment having less and less ordered nanostructure and higher and higher reactivity as the temperature increased; i.e., they followed the opposite trend of what is ob- served during laboratory-scale studies with fuels not containing any ash-forming elements and where the temperature was not controlled by λ. © 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved. 1. Introduction Under directive 2009/28/EC, the European Union member states have taken on binding national targets for raising their share of re- newable energy in all forms of transport to 10% by 2020 [1]. Pres- surized entrained flow gasification has been used since the 1950s to produce fossil motor fuels from coal and have proven to be a ∗ Corresponding author at: RISE Energy Technology Center AB, Box 726, SE 941 28 Piteå, Sweden. E-mail address: henrik@etcpitea.se (H. Wiinikka). promising technology for the production of renewable motor fu- els from biomass as well [2]. Gasification involves the production of raw syngas which is first upgraded to clean syngas through the removal of particles and tars before being converted to a liquid in downstream catalytic processes. Cleaning raw syngas is essential in avoiding fouling and clogging as well as catalyst poisoning in the downstream synthesis plant [3,4]. In order to demonstrate that it is possible to produce syngas from pulverized biomass powder, a 1 MW pilot scale pressurized entrained flow biomass gasifier (PEBG) was commissioned in 2011 in Piteå, Sweden [5]. Initial work focused on the gaseous com- https://doi.org/10.1016/j.combustflame.2017.10.025 0010-2180/© 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.