Modeling of gas/particle flow in coal conversion with a drop tube reactor using a lumped kinetic model accounting volatiles-char interaction

Coal conversion including reforming of nascent tar over the char surface in a drop tube reactor (DTR) was studied both experimentally and numerically. Victorian brown coal and char prepared from the same coal were co-fed into an atmospheric DTR. The effects of reaction temperature (973-1173 K), solid hold-up (8.31 × 10^{- 6}-2.50 × 10^{- 4}), residence time (0-4.6 s for gas; 0-0.78 s for solid particles), and steam partial pressure (0-0.05 MPa) on the conversion characteristics were investigated. A 4-lump kinetic model consisting of tar, gases, char, and soot with 6 global reactions was developed based on the experimental results. The lumped kinetic model was integrated with a computational fluid dynamics (CFD) simulation using an Eulerian-Eulerian approach for mixed phase flow to simulate the coal conversion experiments in the DTR. The CFD results for product distribution during coal conversion in the DTR showed reasonable agreement with the experimental results. The CFD approach presented is suitable for use in designing and optimizing a pyrolyzer for a triple-bed combined circulating fluidized-bed coal gasifier, consisting of a downer (pyrolyzer), a bubbling fluidized bed (gasifier), and a riser (combustor).