Effect of Carbonization Heating Rate on the Tensile Strength of Cokes Prepared from Chemically Upgraded Low Rank Coals

摘要

In this study, effect of carbonization heating rate and solvent removal method on the tensile strength of cokes prepared from chemical upgraded coal samples was investigated. A low rank coal, L coal, was solvent treated at 420℃, 2 h with 1-methylnapthlene (1-MN) solvent. Upgraded coal samples were obtained by removing 1-MN from the solvent treated samples. Two different approaches were applied to remove 1-MN from the treated samples; washing with tetrahydrofuran (THF) and that with n-hexahe (HEX). All upgraded samples were first pelletized under a mechanical pressure and time of 40 MPa and 10 min, respectively, and then carbonized at heating rate of 3, 10 or 25℃/min. Carbonized coke samples strength was measured as tensile strength (MPa). It was found that lower heating rate gave higher tensile strength irrespective of solvent removal method. This may be due to that lower heating rates allowed the coal upon heating to undergo softening, melting and re-solidification for longer time. n-HEX-washed upgraded samples showed higher strength than THF-washed ones when the same heating rates were applied. Surfaces of coke samples were observed by scanning electron microscopy (SEM) and it was found that pore development structures of cokes n-HEX-washed samples and those from THF-washed samples were different from each other. This difference may be responsible for that in the strength.