Syngas Chemical Looping: Particle Production Scale Up and Kinetics Investigation
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Date
2009-06
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The Ohio State University
Abstract
The syngas chemical looping process (SCL) is a novel method for the conversion of carbonaceous fuels to both electricity and hydrogen while capturing carbon dioxide and other pollutants. Since coal is a pollutant intensive carbon based fuel, conventional coal based energy conversion systems with inadequate pollutant control devices have been criticized for emissions of CO2 and various other pollutants. The SCL process has the potential to transform the conventional coal conversion processes to a clean, zero emissions process. The separation of CO2 and other contaminants is inherent in SCL, hence no dedicated pollutant control device is required. At the heart of the SCL process is an oxygen carrying metal oxide particle. The scale up of particle production was investigated because the total throughput of the process is directly proportional to the amount of particles being recycled. At present, particles are synthesized through pelletization of composite powders. The production rate of the particles was limited since the fine composite powders (2 – 7 microns) were constantly clogging during the feeding step. Through size increase of the composite powders to 425 – 1000 microns via granulation, clogging was significantly reduced. In addition to scale up of the particles, kinetic studies on particle size were also carried out. Results show that particle size is not a significant factor in the determination of the reaction rate. Pressure effects on the oxygen carrier reaction kinetics were also investigated. A high pressure thermogravimetric analyzer was used to study pressure effects by measuring mass changes of the oxygen carrier with time. A previous study stating that iron reactivity decreased with pressure was disproved. Pressure effects were investigated by maintaining the same molar flow rate and mole fraction of hydrogen with the balance of nitrogen. The reaction kinetics increased with pressure and temperature over the pressure range of 1.3 atm to 30 atm and temperatures between 700 to 800 ˚C. There was also evidence of the presence of a boundary layer at higher pressures which caused a mass transfer limitation with regard to reaction rate. The previous claim was found to be attributed to the formation of the reactant gas boundary layer around the particles.
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Keywords
chemical looping, clean coal, hydrogen, carbon sequestration