Production of Metallurgical Coke Utilizing Low-Rank Coals Upgraded by Mild Solvent Treatment

Abstract

Steel industries need to increase the use of low-rank coals in coke making since coking coals have been depleting and the price of coking coal has been increasing. In this study we propose to pretreat low-rank coals in non-polar solvent such as 1-methylnaphthalene below 400°C for converting them to a substitute for coking coals. The proposed method was found to be effective in deoxygenating low-rank coals significantly while suppressing cross-linking or polymerization reactions which often accompany deoxygenation reactions. The amount of low-molecular-weight compounds formed in the solvent-treated coals was comparable to that existing in coking coals. Coking tests utilizing the solvent-treated coals suggested that the solvent-treated coals can be substitutes for slightly-coking coals in coke making process.

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

“…The recovered binder was then physically mixed with 1-MN insoluble coal fraction (left over on the filter paper) using a mortar and pestle to get solvent treated coal also called chemical upgraded coal. 20,[23][24][25]29,32) The particle size of upgraded coal sample was < 150 micron. The solvent treated/refined coal was carbonized to produce coke.…”

“…Another approach is to chemical upgrade the coal by increasing its H/C ratio by solvent treatment. [3][4][5][6][7][8][9][10][11][20][21][22][23][24][25] Takanohashi et al treated different coals with 1-MN and obtained 1-MN soluble fractions. 7,32) This 1-MN soluble coal fraction was called coal-derived binder.…”

“…3,5,[6][7][8][9]27,29,31) They investigated the interactions between caking and slightly caking or non-caking coals using NMR analysis and H/C ratio and concluded that the binders (HPC) enhance the thermo-plasticity of the coal blend due to their high thermo-plasticity and overlapping thermoplastic temperature range with that of coals. 3,[19][20][21][23][24][25][26][27] Sakimoto et al introduced carbon matrix connectivity index to estimate the coke drum index which directly correlates with the coke strength. 3,29) They concluded that the addition of binders (HPC) increase the carbon matrix connectivity of the coke leading to increased coke strength.…”

“…The coke strength is strongly dependent on the pore structure and the carbon matrix which are affected by both the coking coal characteristics and the carbonization conditions. 12,13,[20][21][22][23][24][25][26] Development of the pore and the carbon structure during the carbonization process depends on the softening, melting and re-solidification characteristics of the coal. It also depends on the heating rate, heating pattern of carbonization and the maximum coking temperature.…”

Reforming of Low-rank Coal by Chemical Upgrading

“…The H/C and O/C ratio of the solvent upgraded coal showed significantly low values, 0.66 and 0.10, respectively, similar level to that of caking coals. 21) Additionally, the aromaticity f a of the upgraded coal became 0.77 from 0.62 for the original L coal, suggesting that during the MN treatment, some kinds of aromatization reactions might occur. Thus, the chemical upgraded coal originated from a low-rank coal was successfully produced in high yield.…”