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Material characteristics affecting formcoke Gill, Wayne William


The influence of aggregate and binder phase characteristics on formcoke products has been studied. This involved investigating the compaction kinetics of the system and determining the mechanical strength of the briquettes produced. The char phase was characterized in terms of density, hardness, porosity and residual volatile matter content and the rheological properties of the binder phases used were established elsewhere. The strength and wetting behaviour of the aggregate-binder interface were studied using model materials (an SRC pitch binder and a graphite rod aggregate) as well as those produced in this work. Analysis of compaction curves was carried out using the CCWL Hot Compaction Model for Char-Binder Coal systems which was found to adequately describe the observed compaction behaviour. Briquette strength was characterized by ultimate compressive strength and comparisons were made for a constant briquette bulk porosity of 35% (by volume). Results indicate that binder phase fluidity affects compaction viscosity during the particle flow stage of compaction and that char porosity influences final briquette bulk density by affecting the amount of total compaction required to obtain a given bulk density. In general, increased total compaction was shown to result in higher product bulk density and high bulk density was found to yield higher gross composite strength. The latter relationship was seen to be approximately linear over the range of bulk porosity encountered in this study. A higher briquette strength was found for systems with aggregates carbonized at lower temperatures. This was attributed to a combination of higher porosity and stronger char-binder interfacial strength, although the former effect was considered to predominate in the systems considered here. Binder phase fluidity was also seen to affect briquette strength, higher fluidity resulting in higher strength. It was concluded that this was due to increased binder penetration of the aggregate phase. With no significant pore structure in the aggregate, as found with high temperature char, briquette strength was seen to become approximately constant for the three binder coals used. It was concluded that a good formcoke product was aided by a highly fluid binder and a char pore structure accessible to the binder phase.

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