Compaction and cementing of char particles with a tar-derived binder

Abstract

A theoretical picture of the briquetting of char with binder and the conversion to formed coke has been developed from first principles. Sequential fracture of links in a load-resisting network of particles and fragments of char spreads the essentially passive binder over many fracture surfaces by successive microextrusion from the narrowing interstices between the fragments. During the later stages of compaction the binder may become partially 'trapped' within a relatively large interconnected region of filled interstices, leading to significant hydrostatic pressures and micro-intrusion into fine cracks and so to an additional contribution to the spread of binder. The final load is supported by a compact of elastically strained fragments of char, which are frequently interconnected by binder bridges. Release of the strains as the load is removed expands the compact and stretches the binder bridges, reducing the surface area interconnected by bridges and possibly breaking some bridges, leading to a new distribution of binder. By curing and carbonization, the remaining binder bridges are transformed in situ into permanent links, which cement the char fragments together to produce the required strength. The associated shrinkage of these links, especially those that had been considerably stretched, should greatly affect the shrinkage of the whole briquette. © 1988.