Agglomeration kinetics of coking coal particles during the softening phase

Agglomeration kinetics under thermal conditions describe the structure and formation of larger bodies, termed agglomerates from coal particles, as a preliminary phase of semi-coke formation. Knowledge on particle adhesion characteristics are of particular importance for determining the strength as well as the structure of the agglomerates. Several adhesive forces acting during the adhesion mechanism may be roughly subdivided into bonding with and bonding without material bridges. The purpose of the present work was to investigate the adhesion mechanism; the formation and growth in time of the bonding neck between two particles, as well as the change of functional correlation with other parameters, i.e. temperature and coal quality. Experimental investigation of the kinetics of agglomeration was carried out using apparatus in which a coal layer was heated by radiation in an atmosphere of flowing nitrogen. Camera recordings allowed quantitative assessment of the growth of the bonding neck with time, and additionally the dependence of the parameters on temperature and coal quality could be determined. The evaluation of the tests yielded clear indications supporting the assumption that increased adhesion of two viscous spheres under the effect of surface tension can be used as a physico-chemical model for the agglomeration of two coal particles under thermal conditions.