Research Article Hydrodynamics of a Novel Biomass Autothermal Fast Pyrolysis Reactor: Flow Pattern and Pressure Drop A novel biomass, autothermal, fast pyrolysis reactor with a draft tube and an in- ternal dipleg dividing the reactor into two interconnected beds is proposed. This internally interconnected fluidized beds (IIFB) reactor is designed to produce high-quality bio-oil using catalysts. Meanwhile, the pyrolysis by-products, i.e., char, coke and non-condensable gases, are expected to burn in the combustion bed to provide the heat for the pyrolysis. On the other hand, the catalysts can be regenerated simultaneously. In this study, experiments on the hydrodynamics of a cold model IIFB reactor are reported. Geldart group B and D sand particles were used as the bed materials. The effects of spouting and fluidizing gas velocities, particle size, static bed height and the total pressure loss coefficient of the pyroly- sis bed exit, on the flow patterns and pressure drops of the two interconnected beds are studied. Six distinct flow patterns, i.e., fixed bed (F), periodic spouted/ bubbling bed (PS/B), spouted bed with aeration (SA), spout-fluidized bed (SF), spout-fluidized bed with slugging (SFS) and spouted bed with backward jet (SBJ) are identified. The investigations on the pressure drops of the two beds show that both of them are seen to increase at first (mainly in the F flow pattern), then to decrease (mainly in the PS/B and SA flow patterns) and finally to increase again (mainly in the SA and SF flow patterns), with the increase of the spouting gas ve- locity. It is observed that a larger particle size and lower static bed height lead to lower pressure drops of the two beds. Keywords: Autothermal, Fast pyrolysis reactors, Flow pattern, Interconnected fluidized beds (IFB), Internally circulating fluidized bed (ICFB), Pressure drop Received: October 20, 2008; revised: November 17, 2008; accepted: November 18, 2008 DOI: 10.1002/ceat.200800541 1 Introduction Biomass fast pyrolysis (BFP) is the thermal decomposition of biomass in an inert atmosphere using high heating rates and short residence times. It has a great potential for the conver- sion of biomass into energy-dense liquids, i.e., crude bio-oil. Yields of up to 75 % liquid product have been reported at mild operating conditions [1]. Compared to raw biomass, bio-oil has a high energy density, and can be transported easily. To date, many types of pyrolysis reactors, e.g., fluidized beds [2–4], transported and circulating fluidized beds [5, 6], spouted beds [7], ablative and vacuum pyrolysers [8, 9], have been used in BFP technology. The spouted bed type is one of the most promising and advanced reactors [10]. However, the bypassing characteristic of the spouting gas to the annulus re- sults in a long gas residence time and a high maximum spout- ing pressure drop of the bed. In order to reduce the bypass of spouting gas, a spouted bed reactor with a porous draft tube, known as an internally circulating fluidized bed (ICFB), was proposed by Milne et al. in 1992 [11]. In the ICFB reactor, the heating rate in the draft tube can reach 10 5 K/s and the gas res- idence time is below 1 s. BFP with high bio-oil yields can be realized in this reactor. Since the overall reaction is an endothermic reaction pro- cess, heat is required for biomass pyrolysis. The most econom- ical method to provide heat is an autothermal system. To date, many autothermal systems for BFP processes have been report- ed in the literature [12, 13]. These systems are known as twin/ dual fluidized beds or externally interconnected fluidized beds (EIFB). In the EIFB reactor, char and sand are separated from © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.cet-journal.com Huiyan Zhang 1 Rui Xiao 1 Qiwen Pan 1 Qilei Song 1 He Huang 2 1 Thermoenergy Engineering Research Institute, Southeast University, Nanjing, P. R. China. 2 College of Life Science and Pharmacy, Nanjing University of Technology, Nanjing, P. R. China. – Correspondence: Prof. R. Xiao (ruixiao@seu.edu.cn), Thermoenergy Engineering Research Institute, Southeast University, Nanjing 210096, P. R. China. Chem. Eng. Technol. 2009, 32, No. 1, 27–37 27