In this study, investigations were made to understand the mechanism of increase in coke strength on binder addition by analyzing physical and chemical characteristics of coal-binder interface. Three binders, oil derived Asphalt pitch (ASP), coal derived HyperCoal (HPC) and Coal tar pitch (CTP) were used to understand the effect of binder. A new method to observe the coal-binder interface boundary at microscopic level by Scanning Electron Microscope (SEM) was developed. When base coal was a non-caking coal, coal-binder interface boundary was clearly observed by SEM for the first time. From observed images, it was found that ASP and HPC bound differently on the coal surface. When base coal is a caking coal, the interface could not be distinguished but sulfur mapping confirmed the presence of interface. Preliminary Laser Raman analysis suggests there may be some interactive effect of coal and binder on each other's carbon structure development. Contribution of fraction of coal surface coated with binder towards coke strength is considered.
A subbituminous coal was treated with a wash oil or 1-methyl naphthalene (MN), for 1 hr or 2 hr at 673 K or 693 K under nitrogen, in order to chemically upgrade the low-rank coal. In case of wash oil as the treated solvent, the extraction yield at 673 K reached 66 mass%, daf after recovering the solvent, however, some of wash oil remained in the extract because the wash oil contained polar compounds of 8.5 masst%. The extraction yield with MN at 673 K was 41.2 mass%, daf and it decreased with an increase in the severity of the extraction condition; it was 36.3 mass%, daf at 693 K for 2 hr. The more polar solvent which contained polar compounds of 21.7 mass%, called the Super-Solvent (SS), was successfully produced by separation of the wash oil with methanol/water (3:1 by weight) mixture. The extract obtained from the extraction with SS showed similar degree of the H/C and O/C atomic ratios as bituminous coals, indicating that chemically upgrading reactions might occurred by the solvent treatment. After the solvent treatment with MN at 693 K for 2 hr, hexane was used as the washing solvent, resulting that the ratio of hexane soluble fraction was a few. Thus, the solvent upgraded coal originated from a low-rank coal was successfully produced in high yield. The H/C and O/C ratios of the solvent upgraded coal became the similar level as those of caking coals. Decarboxylation and aromatization reactions might occur during the solvent treatment.
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°C, 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-hexane (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°C/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.
Synopsis :In order to obtain highly reactive cokes, a Ca-ion exchanged brown coal (Loy-Yang coal) was added to a caking coal (Goonyella coal) with different blending ratios and cokes were then prepared from these blended coal samples. With the addition of Ca-loaded coals, the CO 2 -gasification reactivity of the resulting cokes was significantly increased. Their initial reactivity was particularly enhanced, at a maximum, being thirty times as high as the reactivity of a coke prepared from a single Goonyella coal. This is because the reactive part derived from the brown coal in each coke was initially gasified with the other part from the caking coal almost intact. Since, as coke texture, the former part (from the brown coal) is included in a matrix of the latter part (from the caking coal), the mechanical strength was not lowered so much, even though the cokes were gasified up to a conversion of 10%. In conclusion, this study demonstrates that some addition of a Ca-ion exchanged brown coal to a caking coal is quite promising for the production of highly reactive and high strength cokes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.