Experimental Results and Design of Chemical-Looping Combustion of Methane in a Fixed Bed Reactor with Nickel Based Oxygen Carrier

Experimental Results and Design of Chemical-Looping Combustion of Methane in a Fixed Bed Reactor with Nickel Based Oxygen Carrier

Ari F. Fischer, Zhiquan Zhou, Lu Han, and George M. Bollas

Department of Chemical, Materials & Biomolecular Engineering,
University of Connecticut, Storrs, CT 06269 USA

Abstract:

            Increasing concerns with carbon emission and the future of energy production has made research into cleaner fuel production an important field of study.  Chemical-Looping Combustion (CLC) is a novel combustion process that has a great potential to reduce carbon emissions from the burning of fossil fuels.  CLC utilizes a metal catalyst such as nickel oxide to supply oxygen to burn fuel such as methane.  CLC is a two-part cycle, where in a reduction phase fuel is flown through the reactor and combusts with the oxygen, and in oxidation step air is flown through to oxidize the metal.  This process is beneficial because fuel can be burned with an indirect air source, and produces concentrated carbon dioxide and water, providing an output that can be sequestered easily.

	Figure 1: Reduction and oxidation cycles performed in a CLC process

At the Center for Clean Energy Engineering at the University of Connecticut, a bench scale fixed bed reactor has been designed to test CLC at varying parameters.  The reactor has a 9.8 mm diameter and is placed inside a furnace that runs at 800° C.  This design allows for a detailed study of how varying operating parameters affect the overall CLC efficiency based on output gas composition and combustion time.  The operating temperature, flow rates, and pressure can all be adjusted. Paired with modeling efforts by UConn students, optimal reactor parameters such as flow rates, temperature, pressure, reactor length, and so on, are hoped to be determined and validated with experimental results.  Measuring the concentrations of carbon monoxide, carbon dioxide, and methane in the outlet gas provides an analysis of the reactor's effectiveness at combusting the fuel and forming the desired products.  This presentation will focus on the fixed bed design for CLC, and operating conditions and experimental set up, and discussion of results.  This research hopes to further the understanding of CLC technology and determine its efficiency and effectiveness as a tool for energy production. 

            The cycle includes four steps.  During the first step (reduction), methane diluted in argon is flown through the reactor at a constant flow rate regulated by the mass flow controllers.  Next, an argon purge is initiated to remove any methane from the bed and purge the IR cell.  Following the purge, the carrier is oxidized by flowing air through the reactor.  Finally, the system is purged again with argon to clean the bed and purge the IR cell.  This cycle is repeated until the desired results are collected.  The data is processed in the FT-IR Gas Analyzer, which produces real time mole fractions of the outlet gas.

            The oxygen carrier is located in the center of the reactor and is held in place between two quartz wool barriers.  NiO-Al₂O₃ is used as the oxygen carrier, and is prepared with dry impregnation with Al₂O₃ as the support.  A nickel nitrate solution is added to the powder, and is stirred at room temperature, then dried at 120 °C for 12 hours.  It is then calcined at 850 °C in air for 5 hours.  The solids are sieved to a particle diameter of 140 µm.  The effects of multiple cycles on the strength of the carrier will be studied. 

            In conclusion, preliminary results are promising and show consistency and repeatability. High methane conversion and carbon dioxide production is measured throughout multiple cycles.

Figure 2: Schematic of reactor design

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