Aspects of Pore-Structure Development During Carbonization of Preoxidized and Preheated Coals

摘要

An investigation was carried out to compare the pore-structure development during carbonization of preoxidized and preheated coals. Coals oxidized in the laboratory at 100 exp 0 C and industrial blends preheated in the Cerchar preheater were carbonized from room temperature in a small oven. The development of the porous structure was monitored by using a microscope to examine sections cut from the center of the carbonized charges after cooling and filling with epoxy resin. The tensile strength of cokes produced from identical charges in a small oven heated from both side-walls was also determined. (1) Oxidation of high volatile coals at 100 exp 0 C leads to cokes with reduced porosity, pore size and pore-wall thickness. Provided the coke was completely fused, discrete linear relationships between the dilatation of the oxidized coal and the porous structure parameters were obtained. (2) A change in the preoxidation time results in little change in the coke's tensile strength if the structure is well fused. The tensile strength diminishes when fusion is incomplete. (3) Cokes from preheated charges of the blends examined had smaller pores, slightly thicker pore walls, lower porosity and higher tensile strength than those of cokes produced under identical conditions from the untreated charges. (4) These differences suggest that treatment of coal in the Cerchar preheater alters the nature of the coal in a way which influences its subsequent carbonization behaviour. (5) The changes in coke pore size and tensile strength resulting from the altered behaviour of the coal after preheating are similar in direction and magnitude to those observed on drying and densifying an untreated coal charge. (6) The differences between the effects of preheating and preoxidation on coke strength and structure are not consistent with the view that oxidation of coal in the preheater plays a dominant role. (ERA citation 05:021568)