INTERACTIVE PROCESSES IN GASIFICATION AND COMBUSTION .3. COAL CHAR PARTICLE ARRAYS, STREAMS AND CLOUDS/

A comprehensive review is presented on the interactive transport proce sses in the gasification and combustion of a cloud of drops and solid particles. The review is divided into three parts. Part I is concerned with the interactive processes for arrays, streams and clouds of drop s, Part II presents a review of isolated coal, carbon and porous char particles pertaining to interactive processes, and finally Part III de als with the interactive processes for solid particle arrays, streams and clouds. Isolated particle gasification (pyrolysis and heterogeneou s) and combustion were briefly reviewed in Part II. Because of strong analogy of the group ignition and combustion, to porous char ignition and combustion, the literature on porous char combustion was also incl uded in Part II and new results were presented on the internal ignitio n of porous char particle using Frank-Kamanetsky type of analysis. Par t III presents an integrated approach starting from arrays to clouds a nd gasification to combustion. The interactions occur through processe s ranging from pure diffusive to convective transport processes. Appro ximate criteria for interactive processes are given. As opposed to liq uid drop arrays and clouds, there is no systematic study for arrays of char or coal particles. Due to the similarity between droplet evapora tion and char combustion, new results are presented for the combustion of char arrays in quiescent atmosphere. Convective effects are also b riefly discussed. Expanding the Frank-Kamenetsky analysis to ignition of clouds, simple solutions are presented for cloud ignition temperatu res. A comparison of results between different techniques and between theory and experiment is given. Interesting results for the ignition c haracteristics of coal dispersions are obtained in that the particles with relatively small or low volatile matter which ignite heterogeneou sly when isolated are found to ignite homogeneously under cloud condit ions. The minimum ignition temperature is found to increase with decre ase in size under isolated mode while the opposite is true under inter actions. The problems of the gasification, ignition, and combustion of clouds in confined and unconfined volumes are reviewed. Experiments c onducted with streams (laminar flow reactors, LFR) and clouds (TGA, he ated grids, shock tubes, batch of particles in LFR, Hertzberg Ignition apparatus) are reviewed. Following the drop literature, the relation between array and group combustion is presented. Finally, the relevanc e of the reviewed literature to pollutants' formation and destruction and spray combustion modeling is briefly discussed.