Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman Direct and two-step gasification behaviour of Victorian brown coals in an entrained flow reactor Tao Xu ⁎ , Sankar Bhattacharya Department of Chemical Engineering, Monash University, VIC 3800, Australia ARTICLE INFO Keywords: Gasification Entrained flow Two-step gasification Pyrolysis Direct gasification Brown coal ABSTRACT This study assesses the gasification behaviour of three Victorian brown coals in CO 2 using a bench – scale entrained flow reactor in terms of gas quality and carbon conversion. Two gasification processes were in- vestigated: a) gasification of coal in a single step, b) pyrolysis of coal followed by gasification of the char in two steps. The effect of temperature (1000–1400 °C) and input CO 2 (10–40 vol%) concentration on two gasification process was investigated. It was found that higher temperature and input CO 2 concentration increased CO concentration and carbon conversion. The gasification process (direct and two-step gasification) had little effect on the overall carbon conversion but had a significant effect on the gas composition of the product gases. During two-step gasification, coal pyrolysis contributed to around 65% carbon conversion, almost all H 2 and 22–30% CO. Char gasification contributed to around 35% carbon conversion and 70–78% CO. By contrast, direct gasi- fication generated little H 2 and more CO in the product gases than two-step gasification. It was estimated that the CO was generated from coal pyrolysis (18.8–24.2%), Boudouard reaction (55.1–66.5%), and the reverse water- gas shift reaction (13.1–19.3%). Regardless of direct or two-step gasification, it was found that entrained flow gasification achieved very high carbon conversion (∼98%) for Victorian brown coals at 1200 °C with around 7 s residence time for the particle size of 90–106 μm. 1. Introduction In Australia, Victorian brown coals represent a significant, low cost energy resource with reserves of 430 billion tonnes. These brown coals are the primary energy source in the state of Victoria, supplying ap- proximately 85% of the state’s electricity [1]. However, brown coal utilisation is limited to mine-mouth power generation using conven- tional pulverised coal-fired combustion units at relatively low efficiency and high greenhouse gas emission [2,3]. Therefore, beyond its direct combustion, great effort is being made by the industry and academia to develop low-emission coal technologies, to utilise such vast resources for higher value products with low emission [4]. As one clean coal technology, gasification is a thermochemical conversion method where fuel reacts with reactants like steam and carbon dioxide to produce syngas (CO/H 2 ) which can be used for generation of power and a variety of chemicals and liquid fuels [5–7]. Among three major gasifier types – fixed bed, fluidized bed, and entrained flow gasifiers – the en- trained flow gasifiers dominate the world gasification market for syngas production, and is potentially the only gasification process for reliable co-production of power and chemicals using brown coals [8–10]. En- trained flow gasifiers achieve a high conversion (98–99.5%) by operating at high temperatures (1250–1600 °C) and short residence time (a few seconds) with small feed size (< 200 μm) [11]. Given the high operating temperatures, the syngas cooler fouling and blockage [12,13], corrosion and erosion of refractory [14,15] and slag mobility [16–18] are important issues in practice to ensure a good availability, reliability and maintainability performance of entrained flow gasifiers. Moreover, the fundamental understanding of the process and in- formation on the gaseous products of entrained flow gasification using brown coals is limited. Relatively few experimental studies on entrained flow gasification of low-rank coals have been reported in the literature. Tremel et al. investigated pyrolysis and gasification behaviour of a German lignite in an entrained flow reactor [19]. They found that with the increase of temperature and residence time, the carbon conversion increased. Harris et al. examined entrained flow gasification behaviour of Aus- tralian sub-bituminous coals at high temperature and pressure [20], and assessed the effect of temperature and coal types on coal conver- sion. Cristina et al. [21] and Guo et al. [22] found that high CO 2 con- centration improved carbon conversion of sub-bituminous and bitu- minous coal in an entrained flow reactor. However, since the quality and composition of coal vary considerably from one coal to another, the https://doi.org/10.1016/j.enconman.2019.05.092 Received 14 March 2019; Received in revised form 6 May 2019; Accepted 26 May 2019 ⁎ Corresponding author. E-mail address: Charlie.Tao.Xu@gmail.com (T. Xu). Energy Conversion and Management 195 (2019) 1044–1055 0196-8904/ © 2019 Published by Elsevier Ltd. T