Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Fluidisation characteristics and inter-phase heat transfer on product yields in bubbling fuidised bed reactor Joshua Clissold a , Salman Jalalifar a,c , Fatemeh Salehi a,b, ⁎ , Rouzbeh Abbassi a,b , Maryam Ghodrat d a School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, NSW, Australia b Macquarie Sustainable Energy Research Centre (MQ-SERC), Macquarie University, Sydney, NSW, Australia c Australian Maritime College, College of Sciences and Engineering, University of Tasmania, Launceston, Tasmania, Australia d University of New South Wales Canberra, Canberra 2610 ACT, Australia ARTICLE INFO Keywords: CFD Biomass Bubbling fuidised bed Fast pyrolysis process Bio-oil ABSTRACT Fluidisation and mixing of sand and biomass particles have signifcant efects on product yields in bubbling fuidised bed reactors (BFBR). There is a lower limit for the velocity of fuidising media known as minimum fuidisation velocity. Similarly, an upper limit is defned for velocity where the bio-oil production is maximised – known as the maximum efective velocity (MEV). A computational fuid dynamics (CFD) simulation for biomass fast pyrolysis process in a 2-D lab-scale BFBR is developed to analyse the variation of MEV as the sand particle size varies. The model is frst validated using the experimental data. Then, a parametric study is conducted for the carrier gas velocities in a range of 0.3–1.1 m/s where the sand particle sizes vary from 0.4 to 1 mm, and the biomass particles are in a range of 0.2–0.5 mm. Efects of the packing limit are also analysed. For this purpose, the diferent sand particle sizes and their corresponding MEV are tested at the sand packing limits of 45, 55, 65, and 75 mm in which the optimal packing limit is found to be 55 mm. A detailed thermodynamic study is performed with the focus on the sand particle size and packing limit afecting the heat transfer rates between phases. A decrease in required heat transfer rates is directly linked to an increase in bio-oil yield. It is observed that heat transfer between sand-biomass is much more efcient than the heat transfer between nitrogen-biomass, confrming the importance of the sand particles as the heat carriers. 1. Introduction Fossil fuels have drastic consequences on the environment and signifcantly contribute to climate change which is arguably one of the most prominent issues today. On the other hand, there is a limited supply of such fuels that cannot be replenished once they have been extinguished [1]. These reasons have created needs for drastic changes towards more sustainable fuels for the future. Bio-oils are attractive alternatives that signifcantly produce lower toxic pollutants and minimising their environmental impacts. They can be extracted from the biomass-driven fuel systems; however, the process is still expensive. Efcient biomass-driven fuel systems that turn biomass into bio-oil have been a topic of considerable interest with the focus on maximising economic and environmental benefts. Any form of organic matter available on earth can be classifed as biomass. These include wood, agricultural products (as well as their waste by-products), aquatic plants and algae, both terrestrial and aquatic animals, and human waste [2,3]. Carbon neutrality is one of the advantages of organic-based fuel since carbon dioxide recycles in the photosynthesis process and releases back into the environment. Hence, when this type of energy is used, no carbon is added or taken away the same way as fossil fuels [4]. Pyrolysis process is one of the most favourable thermochemical conversion for bio-oil production. In this process, organic materials in an inert atmosphere at moderate temperatures in a few seconds de- composes. The three main products of biomass pyrolysis process are solid biochar, non-condensable gases, and liquid bio-oil. Multiple re- actors have been designed for producing bio-oil using the fast pyrolysis process [3,5–8]. Among them, bubbling fuidised bed reactor (BFBR) is the most popular design due to their straightforward applications, uniform solid mixing, adequate heat and mass transfer between parti- cles (reacting biomass and heat carriers), ability to operate in a con- tinuous state and consequently high production of bio-oil yields. In a typical BFBR, heat carriers that have high heat capacity (i.e. sand particles) are initially packed. The feedstock is injected from the side of the reactor while an inert carrier gas (usually nitrogen) fows from the bottom of the reactor. https://doi.org/10.1016/j.fuel.2020.117791 Received 29 December 2019; Received in revised form 22 February 2020; Accepted 4 April 2020 ⁎ Corresponding author at: School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, NSW, Australia. E-mail address: fatemeh.salehi@mq.edu.au (F. Salehi). Fuel 273 (2020) 117791 0016-2361/ © 2020 Elsevier Ltd. All rights reserved. T