Chemical Looping Combustion (CLC) technologies utilize commonly metals/metal oxides as oxygen carrier, circulating between an air reactor and a fuel reactor. The oxygen carrier transfers oxygen from the air reactor to the fuel reactor to oxidize the fuel. After reduced by the fuel, the oxygen carrier is transferred to the air reactor to be oxidized to its original state under the effect of air. Therefore, the connection of the fuel reactor and air reactor makes up the CLC process for CO2 capture.
In the case of solid fuels, such as coal or biomass, the reaction pattern is more complex. In the fuel reactor the char should be firstly gasified by gasification agents such as steam or carbon dioxide, and then the gasification products react with the oxygen carriers. The presence of oxygen carrier particles in the fuel reactor could accelerate char gasification rate, since the gasification products surrounding the oxygen carrier particles are consumed. However, this enhancing effect is not sufficient, especially for coal with a low reactivity. In order to minimize the char elutriation and loss to the air reactor, to accelerate char gasification rate in the fuel reactor is a significant issue.
Objectives of the research
The basic objectives of this proposed research is to obtain high coal conversion, high gas conversion and high CO2 capture during the CLC process of coal with the functional iron-based oxygen carrier particles. In this research, the cheap materials will be used to develop some novel oxygen carrier particles with high reactivity. A commercial strategy for the functional iron-based oxygen carrier particles with catalytic reactivity to accelerate coal gasification will be developed. The catalytic mechanism will be investigated. Further, the pilot scale CLC facility of Hamburg University of Technology of Germany will be used to carry out the investigation during the continuous coal-fueled CLC experiments.
Step 1: Oxygen carrier production by spray drying and fluidized bed granulation.
Step 2: Oxygen carrier test and catalytic mechanism investigation. The mechanical strength of the particles and the residence ability to attrition of the particles will be. The reaction performances of the selected oxygen carrier particles will be investigated in a small fluidized bed reactor with coal as solid fuel. The reacted particles will be characterized by XRD, BET, SEM, XPS and cross-cut EDS to detect the chemical compositions, the pore structure, the morphology changes and the element migration, respectively. Based on these experiments, the detailed catalytic mechanism will be revealed.
Step 3: Operation and optimization of the pilot scale CLC facility. Based on the pilot scale CLC facility, various coal conversion performances with the developed oxygen carrier will be investigated. The effect of temperature, coal particle size and oxygen carrier circulation on coal conversion and combustion efficiency will be assessed. Coal gasification and combustion of both gasification products and volatile matter will be evaluated.
T. Song, J. Wu, H. Zhang, L. Shen (2012): Characterization of an Australia hematite oxygen carrier in chemical looping combustion with coal. In: International Journal of Greenhouse Gas Control 11.
T. Song gratefully acknowledges the Research Fellowship for postdoctoral Researcher awarded by Alexander von Humboldt Foundation.