Encapsulites, and the suppression of internal gas pressure in industrial metallurgical coke blends

Abstract

Isolated, encapsulated coke microstructures in industrial coke blends, (referred to here as encapsulites), contain textural evidence of growth in high pressure conditions revealed by collapsed, stretched, and pulled-apart thin pore walls, with crushed porosity. This texture is not rare in blends, but is more commonly seen in single-source test oven cokes that have generated very high internal gas pressures. In addition, reflectances of encapsulite microstructures are quite different from the enveloping coke, leading to identification of two varieties, (1): isotropic, low-bireflectance coke derived from soft coking coal, surrounded by a low anisotropy coke envelope, and, (2): highly-anisotropic fused-inertinite or fused-vitrinite, contained within an envelope of a lower rank coke.Time, temperature and fluidity play critical roles in the order and magnitude of development of encapsulites, where entrapment by a fluid plastic layer of earliest melting vitrinites isolates not-yet-melted coal particles. Subsequently, with rising plastic layer temperatures, the encapsulated material also melts, but it is now enclosed within an impermeable, gas-proof semicoke that acts as a pressure suppressor. The encapsulite may develop a thickened outer wall, but internal thin-cell-wall porosity implodes, causing localized structural collapse. The development of encapsulites is a/the mechanism that suppresses and dampens the internal gas pressure exerted by strongly expanding coals used as components in some industrial blends. Encapsulite volumes of 2.23–22.4% are described.Encapsulites contribute to mechanical strength. Thick walls of isotropic material protect against CO2 reactivity attack, adding strength to coke. On fused inertinite kernels of highly anisotropic encapsulites, measured anisotropy quotients (AQ’s) of >8.3, are of similar magnitude to pyrolytic carbon, which too increase CSR quality.