Research Article Cold Flow Model Study on a Dual Circulating Fluidized Bed System for Chemical Looping Processes A cold flow model was built and operated in order to study the fluid dynamics of a 120-kW chemical looping pilot rig for gaseous fuels. The system consists of two interconnected circulating fluidized bed reactors with globally circulating bed material (dual circulating fluidized bed – DCFB). Gas mixing between the two re- actors is prevented by moderately fluidized loop seals. In the cold model, both re- actors are fluidized with air at two stages to control the solids circulation. The data presented focus on the solids circulation rates and on pressure profiles of both reactors, depending on selected operating parameters like fluidization gas flow rate, level of gas introduction, loop seal fluidization, and solids inventory. The results show high solids circulations in the global loop between the two reac- tors for the scaled base case operation conditions already at low bed inventories. Keywords: Chemical looping combustion, Circulating fluidized beds, Cold flow model, Dual fluidized bed systems, Fluid dynamics Received: October 13, 2008; revised: November 28, 2008; accepted: December 02, 2008 DOI: 10.1002/ceat.200800521 1 Introduction Chemical looping combustion (CLC) is a typical dual fluidized bed application where reactive particles circulate between two fluidized bed reactors with different gas atmospheres. In the so-called fuel reactor (FR), a hydrocarbon fuel is oxidized by oxygen released from metal oxide particles. In the so-called air reactor (AR), the oxygen carrier particles are re-oxidized typi- cally by air. Such systems often feature loop seals to keep the gas phases separated, typically fluidized with a gas that is toler- able in both reactors. In CLC, the crucial reaction steps from a chemical kinetics point of view are located in the FR. There- fore, the systems proposed and used by different research groups consist of a circulating fluidized bed (CFB) with a larg- er bubbling bed in the return leg of the solids, representing the FR (Fig. 1). The CFB riser is operated as the AR [1, 2]. In the design phase of a 120-kW (fuel power) pilot rig for CLC, it has turned out that the cross section of the bubbling fluidized bed in the FR must be rather large if the necessary gas-solid contact for quantitative gas conversion is to be achieved. The problem with bubbling bed systems for FRs is the potential slip of unconverted fuel in the bubble phase, which can be expected to be increased by high fluidization numbers and small particle sizes. Especially for full-scale power plant applications, tremendous FR dimensions would occur. Therefore, it has been decided to switch to a different type of fluidized bed reactor system for the 120-kW unit, com- bining two CFB reactors in an advantageous way for CLC ap- © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.cet-journal.com Tobias Pröll 1 Karl Rupanovits 1 Philipp Kolbitsch 1 Johannes Bolhàr- Nordenkampf 1 Hermann Hofbauer 1 1 Vienna University of Technology, Institute of Chemical Engineering, Vienna, Austria. – Correspondence: Dr. Tobias Pröll (tobias.proell@tuwien.ac.at), Vienna University of Technology, Institute of Chemical Engineering, A-1060 Vienna, Austria. Figure 1. Dual fluidized bed arrangement with the AR as CFB ri- ser and the FR as a bubbling fluidized bed in the return leg of the solids (LS...loop seal). 418 Chem. Eng. Technol. 2009, 32, No. 3, 418–424