Steam gasification of biomass coupled with lime-based CO 2 capture in a dual fluidized bed reactor: A modeling study Bijan Hejazi a,⇑ , John R. Grace a , Xiaotao Bi a , Andrés Mahecha-Botero b a Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, BC V6T 1Z3, Canada b NORAM Engineering, 200 Granville Street, Suite 1800, Vancouver, BC V6C 1S4, Canada highlights  Integrated biomass gasification and cyclic CO 2 capture in a DFB reactor is modeled.  Limestone particles constitute all or a fraction of the bed material.  Model predictions are compared against available data from the literature.  The influence of CO 2 capture on steam gasification of biomass is illustrated.  Some design and operating conditions could be identified for the gasifier bed. article info Article history: Received 3 December 2012 Received in revised form 19 July 2013 Accepted 19 July 2013 Available online 8 August 2013 Keywords: Biomass Gasification CO 2 capture Reactor modeling CaO sorbent abstract Steam gasification of biomass integrated with CO 2 capture in a dual fluidized bed with carbon sequestra- tion is among the promising technologies being developed for sustainable production of hydrogen. A sim- ple steady state model which considers two coupled reactors, one calcining limestone particles, while the other steam gasifies biomass and simultaneously carbonates the lime sorbent, is developed in this paper. A stoichiometric equilibrium model is applied for biomass gasification, with enhancement of CO 2 removal by carbonation and incomplete conversion of sorbent particles due to kinetic limitations, mixing of the solids and loss of sorbent reactivity because of sintering. To optimize the overall performance of the pro- cess, sensitivity analyses are preformed over the most important design and operational parameters. Model predictions are compared with available data from the literature, showing the influence of CO 2 capture on gasification. A parametric study reveals the effects of key process variables such as tempera- ture, pressure and solids circulation rate. The model is useful in identifying design and operating condi- tions for integrated gasification and carbon capture. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Emissions of large amounts of Greenhouse Gases (largely CO 2 ) to the atmosphere, mostly as a by-product of burning fossil fuels in man-made processes, are contributing to climate change. The need to move towards a sustainable energy future is motivating a search for new technologies to address the ever-growing world energy demand. Among the options for reducing greenhouse gas emissions is gasification of biomass. Despite its long history, there is renewed interest in gasification, due to its ability to produce H 2 as a clean energy carrier [1]. Steam gasification of biomass coupled with CO 2 capture, is particularly appealing to produce H 2 -rich product gas, with a sorbent to capture CO 2 in situ [2]. Enhanced hydrogen production from renewable resources (e.g. biomass) with simultaneous CO 2 capture, when integrated with CO 2 sequestra- tion, could result in net removal of CO 2 from the atmosphere [3]. Lime (CaO) is able to selectively absorb CO 2 through exothermic gas–solid carbonation and reversibly release the captured CO 2 by endothermic calcination: Carbonation : CaO ðSÞ þ CO 2 $ CaCO 3ðSÞ DH 0 298 ¼178:2 kJ=mol ð1Þ The importance of this reaction lies in its reversibility, facilitat- ing cyclic calcination/carbonation. This process has several advan- tages including: I. Enhanced H 2 production due to a shift in the key equilibrium reactions of gasification. II. Production of a concentrated stream of CO 2 , suitable for stor- age (sequestration). III. The exothermic carbonation reaction can supply most of the heat demand of the endothermic gasification reactions. IV. Limestone particles show some catalytic activity for tar cracking and reforming. 0016-2361/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2013.07.083 ⇑ Corresponding author. Tel.: +1 604 827 3178. E-mail addresses: bhejazi@chbe.ubc.ca, bijanhejazi@gmail.com (B. Hejazi). Fuel 117 (2014) 1256–1266 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel