Kuipers, J.A.M.

Noorman, S.

Sint Annaland, M. van

English

Sint Annaland, van, M.

Pure OAI Repository

Novel reactor technology for chemical-looping combustion

NARCIS 

van Sint Annaland, M.

University of Twente Research Information

NOVEL REACTOR TECHNOLOGY FOR CHEMICAL-LOOPING COMBUSTION  S. Noorman, M. van Sint Annaland, J.A.M. Kuipers  Fundamentals of Chemical Reaction Engineering,                                                       University of Twente, Enschede, the Netherlands   Chemical-looping combustion (CLC) is emerging as an interesting alternative technology for power production. The main advantage of CLC over conventional processes is that direct contact between fuel and air is circumvented, so that carbon dioxide is obtained without nitrogen dilution and intrinsically expensive CO2 sequestration or anthropogenic emissions are avoided. In CLC fuel and oxygen are contacted via an intermediate oxygen carrier, a metal/metal oxide that can alternately be oxidized and reduced. The oxidation of this material is strongly exothermic, which is used to heat the air stream to very high temperatures (1200 °C) and drive a (gas) turbine. During the (often endothermic) regeneration with methane, carbon dioxide without nitrogen dilution is formed. In the literature an interconnected fluidized bed system has been proposed for CLC, schematically depicted in Fig. 1a, where the particles are transported between an air reactor (typically a riser) and a regeneration unit (fluidized bed). With this reactor system the continuous production of hot air was achieved and the main problems associated with air/methane slip were solved.   air CH4N2/O2CO2/H2O air CH4N2/O2 CO2/H2O Figure 1: Possible reactor configurations for CLC:  a) interconnected fluidized bed system; b) periodically operated packed bed system  The main drawbacks of this reactor concept are related to the transport of the oxygen carrier. Not only additional energy input is required to transport the particles, also a cyclone is required to separate the particles from the hot air stream. The particle separation is particularly difficult, because even fines (formed due to inevitable particle attrition) need to be removed in view of the downstream gas turbine, and expensive because of the extremely high operating temperatures. In this paper a novel reactor concept for CLC is proposed and studied. In this reactor concept the particles are not transported, but kept inside a packed bed reactor and are alternately exposed to oxidizing and reducing conditions by periodic switching of the gas feed streams (Fig. 1b). The main advantages of this reactor concept are that the use of an expensive cyclone can be avoided and that it allows for a better utilization of the oxygen carrier (i.e. a larger difference between the oxidized and reduced state). A packed bed reactor model for CLC has been developed to study the dynamic reactor behaviour using a very efficient finite difference technique with higher order temporal and spatial discretisation with local grid and time step adaptation. With this model, supported with analytical approximations, it is demonstrated that also with packed bed reactor technology, a constant high temperature air stream can be produced (Fig. 2).  6007008009001000110012000 1000 2000 3000 4000Time [s]Temperature [oC] Figure 2: Temperature profile of product gas stream during multiple cycles (dotted lines indicate when the fluidization step takes place)  It was found that the amount of active material in the bed can be used to control the air temperature. Moreover, it will be shown that for optimal operation over multiple cycles a short fluidization step is required before switching from reducing to oxidizing conditions and vice versa in order to level off temperature and concentration profiles. Preliminary calculations have demonstrated that very high energy efficiencies (>80%) can be realized.      

Novel Reactor Technology for Chemical-Looping Combustion

http://purl.utwente.nl/publications/68778

Novel reactor technology for chemical-looping combustion

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NARCIS

Pure OAI Repository

NARCIS

University of Twente Research Information

NARCIS

University of Twente Research Information