(45b) Hydrodynamic Characteristics of High Pressure High Temperature Counter-Current Moving Bed Chemical Looping System Circulated with Geldart Group D Oxygen Carrier Particles
The chemical looping combustion processes developed at the Ohio State University (OSU), which uses Fe-based oxygen carrier and a counter-current moving bed reducer design, have the capability of achieving nearly 100% carbon capture and the flexibility of co-generating high purity hydrogen and electricity. To accommodate the moving bed operation, the oxygen carriers are classified as Geldart Group D particles with an average particle diameter of 1.5 mm and a density of 2500 kg/m3. The system consists of a reducer operated as counter-current moving bed reactor, and a combustor operated as a fluidized bed reactor, to perform reductionâoxidation reaction cycles for converting fuels carbon dioxide (CO2). An oxidizer can also be integrated into the system, between the reducer and combustor reactors, to produce a nearly pure stream of hydrogen (H2). The oxidizer is operated in the counter-current moving bed mode similar to the reducer reactor. An L-valve is used in the chemical looping systems to transport the solids between the moving bed reactors and the fluidized bed combustor where the aeration gas flow rate is directly correlated to the global solid circulation rate. An iso-kinetic device is installed on the standpipe of the moving bed side to measure the solids circulation rate of the system. Thousands of hours of operations with different solids circulation rates and gas processing capacities have been performed on sub-pilot and pilot scales of the systems under high operating pressures (>10 atm) and temperatures (>1,000 °C). The hydrodynamic characteristics of oxygen carrier particles operated in the systems, such as pressure drops and fluidization regimes, under different operational conditions are obtained. The operational ranges of gas flow rates for the reducer and the combustor under different pressures and temperatures are obtained. The characteristic relationship between solids circulation rate and aeration gas of L-valve under different temperatures is investigated. The gas demands for fluidizing the combustor and transporting solids through the riser under varing operating temperatures and pressures are also investigated. Fluidization regimes of the combustors are identified. The slugging behavior of the combustor with high height-to-diameter ratio under elevated temperature conditions is also investigated with the aid of ECVT measurement.