Particle Size Optimization for Syngas Chemical Looping Process

The syngas chemical looping (SCL) process developed at OSU can efficiently convert coal derived syngas into hydrogen with in-situ CO₂ capture. In this novel process, two moving bed units are used to convert syngas into hydrogen through the assistance of an oxygen carrier particle. A third unit, an entrained bed combustor, is used to convey the oxygen carrier particles to complete the redox (reduction-oxidation) cycle. The reaction kinetics and thermodynamics of the combustor are well understood. Major challenges for the entrained bed design lie in the clear understanding of the hydrodynamics as well as the optimization of the oxygen carrier particle size. A desirable particle should be easy to convey in the third reactor while not being fluidized in the two moving bed units.

In this paper, a systematic approach is adopted to study the entrainment behavior of the oxygen carrier particles. The configurations and operating conditions for all three reactors in the SCL process are considered. A set of particle sizes are first determined based on theoretical estimation and then tested in the sub-pilot scale SCL demonstration reactor constructed at OSU. The hydrodynamics of particles conveying in the entrained bed reactor are studied. The required conveying gas velocities for the particles are then determined using the entrained bed combustor. The optimized particle size range for the operation of all three reactors is then determined. Key information for the SCL reactor demonstration such as particle attrition is also obtained.