(331d) Coal Direct Chemical Looping Process: Geldart Group D Particle Applications
Chemical looping processes have developed into a promising technology for the efficient conversion of carbonaceous fuels to electricity and/or high value energy carriers with minimal carbon emissions. These processes utilize an oxygen carrier solid material to indirectly supply oxygen to the fuel source eliminating the need for costly and energy intensive gas-gas separation techniques. As one of the most advanced chemical looping units developed to date, the Ohio State University (OSU) 25 kWth sub-pilot coal direct chemical looping (CDCL) process for solid fuel conversion has been successfully demonstrated for over 570 hours of operation achieving >99% fuel conversion and nearly 100% CO2 capture efficiency. The OSU CDCL process consists of a packed moving-bed reducer reactor with a counter-current gas-solid contacting pattern and a bubbling/turbulent fluidized-bed combustor reactor. Geldart Group D metal oxide particles are used in this demonstration unit as the oxygen carrier material. The hydrodynamic characteristics of an interconnected moving-bed and fluidized-bed reactor process significantly deviate from conventional circulating fluidized bed (CFB) systems.
In this study, the hydrodynamic gas-solid flow characteristics and reactant conversion of the 25 kWth CDCL process are examined. Particularly, the counter-current gas-solid flow and reactions in the moving bed reducer are investigated in terms of its advantages for full fuel conversion and high purity of CO2 concentration. Further, the interrelationship between the stoichiometric oxygen demand, reaction residence time, and superficial gas velocity requirements that ensure oxygen carrier regeneration in the combustor are analyzed. The application of non-mechanical valves for flow control of oxygen carriers is also studied.