This project builds upon the technology proposed by the Zero Emission Coal Alliance (ZECA) that involves hyrdogasification of coal, production of hydrogen, and carbonation of lime with CO₂ as means of utilizing coal as an energy source without polluting the environment (fig. 1). Hydrogen is then used to produce electricity via high-temperature fuel cells and lime is regenerated to produce a pure concentrated stream of carbon dioxide for sequestration. The focus of the present research is on calcium oxide as an in situ acceptor of carbon dioxide. The presence of CaO in the reforming stage of the power plant does not only allow for CO₂ capture for the purpose of carbon management but also influences the chemical equilibrium to increase hydrogen production yield (fig. 2).

Figure 1. ZECA power plant.

Figure 2. Molar production of H2 as a function of temperature and presence of CO₂ acceptor.

The advantageous nature of the CaO presence during reforming processes is well understood; however, the physical properties of CaO and the kinetics of the carbonation reaction limit the implementation of the concept. First, the physical stability of CaO/CaCO₃ over a long-term application is unsatisfactory due to sintering. Second, after the initial rapid chemically controlled stage, the reaction kinetics is prohibitively slow due to the impermeability of the carbonate layer formed on the surface of CaO.

The present work proposes to apply CaO as a thin layer on a very high surface-area material, such as γ-Al₂O₃, thus providing a sufficient number of reactive sites while overcoming both physical and kinetic limitations. Preliminary results indicate the CaO on γ-Al₂O₃ exhibits a constant conversion profile over eight carbonation-calcinations cycles (fig. 3). Pure CaO, exposed to the same conditions, exhibited a significant decrease in reactivity (fig. 3).

Figure 3. Carbonation/Calcination Cycles in 10% CO₂.

Presently, the research is focused on optimizing the calcium loading on γ-Al2O3-support and understanding the mechanisms behind CO₂ surface adsorption and the resulting reactions. Experimental results are obtained using the thermo-gravimetric analysis techniques, which allow monitoring of weight changes due to reactions taking place as function of temperature. Once the understanding behind reaction mechanisms and kinetics is established, a lab scale flow-through reactor is to be built to integrate the reforming of methane with the CO₂ capture.

Researchers

Anuta Belova, Ph.D. Candidate, Earth and Environmental Engineering, ab2011@columbia.edu
Tuncel Yegulalp, Professor of Mining Engineering, Earth and Environmental Engineering, yegulalp@columbia.edu
Marco Castaldi, Assistant Professor, Earth and Environmental Engineering, mc2352@columbia.edu

Publications

Belova, A., and T. Yegulalp (2006), Thermodynamic optimization of hydrogen production for a coal based power plant with zero emissions, in SME Annual Meeting Transactions 320 (in press).

Yegulalp, T. M., K. M. Lackner, and P. F. Duby (2003), Clean energy from coal—emission-free power generation with option for CO₂ sequestration, in Proceedings of the 19th World Mining Congress, edited by A. K. Ghose and L. K. Bose, 955–996, New Delhi, India.