Dynamic 2D Heterogeneous Model for Chemical-Looping Combustion in Fixed Bed Reactors

Dynamic 2D heterogeneous model for chemical-looping combustion in fixed bed reactors

Lu Han, Zhiquan Zhou, and George M. Bollas, Department of Chemical, Materials & Biomolecular Engineering, University of Connecticut, Storrs, CT

Abstract:

The objective of this work is to present a dynamic, heterogeneous two-dimensional model for fixed bed chemical-looping reactors. This model can be applied to chemical-looping reforming processes and is suitable for use with large catalyst pellets in industrial-scale applications as well as small catalyst pellets in small-scale units. This model is applied to modeling the reduction step in chemical-looping combustion to examine the dynamic behavior and process sensitivity in the fixed bed reactors.

The reactions involved in the chemical-looping reduction reaction step are:

Non-catalytic gas-solid reactions:
Catalytic gas-solid reactions:
+

The kinetics for all reactions used follows the results by Zhou, et al. who developed a kinetics network capable of modeling various published experimental data.

A mathematical model is developed with the assumptions of an axially dispersed plug flow with negligible mass or heat variations in the radial direction of the reactor, external and internal transport effects to the catalyst particles, and reaction occurring inside the pores of the oxygen carrier. The model equations used (shown below) consider the mass, energy, and momentum balances of the gas along the reactor, and the mass and energy balances inside the catalyst pellet. The gas phase momentum balance is assumed to be in pseudo-steady state in which the Ergun equation is applied.

Bulk phase	Catalyst phase

In this presentation, model predictions will be compared against experimental data from various laboratories utilizing fixed bed reactors for chemical-looping combustion and reforming. Process sensitivities to pressure changes, catalyst characteristics, thermal gradients, and diffusional limitations will be illustrated and discussed.

Acknowledgement: This material is based upon work supported by the National Science Foundation under Grant No. 1054718.

 

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