Elsevier

Energy

Volume 96, 1 February 2016, Pages 127-141
Energy

High fidelity model of the oxygen flux across ion transport membrane reactor: Mechanism characterization using experimental data

https://doi.org/10.1016/j.energy.2015.12.055Get rights and content

Highlights

  • We developed a model for the simulation of an oxygen membrane reactor.

  • We started from the experimental data for the model validation.

  • We develop a model in ACM which enable a simple integration in more complex systems.

  • The model permit to investigate also different reactor design.

  • High fidelity on the results of the optimization process.

Abstract

As a consequence of growing energy demand and expanded use of fossil fuels, CO2 level in the atmosphere has risen in the last couple of centuries. The principal effect of these anthropologic emissions of greenhouse gases is global warming. In the last years, there has been much effort on finding a long term solution to this problem, mostly based on clean power technologies. In order to reduce green-house gas emissions different technologies to capture CO2 are under investigation. One of the most promising technologies is oxy-combustion using ITM (ion transport membranes) used in air separation units or integrated directly in reactors. This work presents a model for the integration of dense oxygen membrane modules in air separation units. An axially resolved model for the distribution of oxygen concentration is developed, incorporating a model of the oxygen flux across membrane surface and its dependency on the local conditions, which satisfies the conservation equations of mass and energy. The oxygen flux model is based on accurate experimental measurements and incorporates the effects of chemistry at the surface and diffusion in the bulk material, as well as heat and mass transport on the feed and sweep side.

Section snippets

Membrane technology

The integration of gas separation membranes in energy systems has been actively investigated in recent years [1], [2], [3], [4], thanks to the possibility of providing novel plant configurations and achieving higher performances at lower cost [5]. One of the most important application for membranes is in the reduction of greenhouse gas emissions. Extensive use of fossil fuels has been responsible of the emission of huge quantities of CO2 and different technologies are under investigation,

ITM structure

In this work, attention is focused on a particular class of oxygen separation membranes, namely the high temperature mixed-conducting ceramic membranes. Dense perovskite ion transport membranes (ITM) produce a flux of pure oxygen, based on the difference between partial pressures of oxygen on the two sides which can be used for several applications [27]. This type of dense membranes, at high temperature, allows oxygen ion to pass through the crystal lattice. Oxygen permeation through a dense

Geometry structure

First step in the development of the membrane module is the definition of the reactor geometry, which affects the ITM performance. The surface area to volume ratio (s/v) is defined by the structural characteristic of the reactor, and affects both the thermal and the fluid-dynamic problem. A low value of s/v corresponds to higher pressure drop and bigger reactor. As has been shown previously [26], both the pressure drop and the temperature profile affect the oxygen flux, so geometry optimization

Methodology

The membrane model is written in Aspen Custom Modeler®, which is an Aspen Product. ACM allows the creation of rigorous model for process equipment, using an easy language. The model can be also exported to Aspen Plus® or simply linked with Excel. In this way, it is possible to integrate the reactor model with other components. Most membrane models are implemented in Matlab®. Using Matlab® is not possible for modeling the entire system, in which the membrane is integrated, unless a Matlab® model

Experimental data and flux model

In this part, the validation and assessment of the membrane model are conducted. As already presented in Ref. [26], the MIT-RGD group has characterized the behavior of LCF membranes. Using an experimental apparatus, they measure the oxygen flux of LCF oxygen permeable membranes under different thermodynamic conditions. Given that the main objective behind developing a reactor model is estimating its thermodynamic performances, and finding the optimal conditions under which the component should

Conclusions

This paper focuses on the characterization of the membrane reactor. The physical and chemical mechanism of the permeation across a dense membrane has been described. The high fidelity model provides an accurate simulation for the integration of the membrane reactor with the energy plant. The paper extends previous works using detailed analysis and an experimental validation. The application of the model will be presented in the future work, where for example the integration of this membrane

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