Biswanath N. Nandi

Inert coal macerals in combustion

Abstract Pilot-scale pulverized-coal combustion experiments with two western Canadian coals have shown that the combustion efficiencies of the coals were inversely related to the inert contents of the coals, i.e. semi-fusinite, fusinite and oxidized vitrinite. These macerals were found to persist through the flame in a partially reacted form. The burn-out of a coal with an inert maceral content over 50% was unaffected by normal changes in combustion conditions; the same changes were successful in improving the burn-out of a coal containing less than 40% inert macerals. Coals with high inert maceral contents produce fly-ash with high levels of unburnt carbon and will require a combination of higher temperatures and higher excess-air levels and longer residence times to achieve combustion efficiencies similar to those of coals with higher reactive-maceral contents. The association of resinitic and bituminous materials with the mineral matter in the Canadian sub-bituminous coal indicated that macerals which contribute significantly to ignition and flame stability are discarded as a washery reject.

Oxidation studies on coking coal related to weathering. 4. Oxygen linkages influencing the dilatometric properties and the effect of cleavage of ether linkages

Abstract Samples of a vitrinite concentrate of Balmer 10, medium-volatile bituminous coal (433) and high-volatile Moss 3 coal (535) were oxidized in air at 85°C for four days to partially destroy the swelling characteristics as measured by the Ruhr dilatometer. Similar samples were oxidized at 100°C for three days to completely destroy the swelling properties. These artificially weathered coals were then treated with reagents to remove peroxides, keto and aldehyde groups. The hydroxyl groups were also blocked to prevent condensation reactions. The result of the removal of these functional groups and the blocking of the hydroxyl groups had little influence in restoring the swelling properties. This suggested that the swelling properties were largely destroyed by ether-type cross-links which form at low temperature. The cleavage of these ether linkages in the Balmer coal using potassium in tetrahydrofuran resulted in the lowering of the melting point and a large increase in dilatation. The values of these properties after cleavage were essentially the same for the fresh and oxidized coal indicating that no significant amount of polymerization through carbon-carbon bond formation occurred during the low-temperatureoxidation step. Indications were obtained that the large increase in dilatation after cleavage was due to steam formation resulting from condensation reactions occurring at the temperature of the dilatation measurements. After the cleavage of the ether linkages, the dilatation could be reduced by blocking the hydroxyl groups or removing water by heat treatment under vacuum.

Nature and thermal behaviour of semi-fusinite in Cretaceous coal from western Canada

Abstract Some western Canadian coals have a petrographic composition which is rich in semifusinite, as compared with Appalachian Carboniferous coal which tends to be rich in vitrinite. It is difficult to explain why a coal rich in semi-fusinite and possessing poor swelling and fluidity can produce coke having a satisfactory stability factor. In an attempt to understand this anomalous behaviour pure macerals of vitrinite, semi-fusinite and fusinite were heated on a Leitz heating-stage microscope to determine their melting character quantitatively. Conclusions from these studies are: 1. (1) high-reflectance semi-fusinite in Cretaceous coal is completely inert; 2. (2) the melting point of the low-reflectance semifusinite is lower than that of the corresponding vitrinite and this maceral is partially reactive.

Effect of oxidation on the chemical nature and distribution of low-temperature pyrolysis products from bituminous coal

Abstract Two bituminous coals, a high volatile Eastern Canadian and a medium volatile Western Canadian, were used to investigate the effect of oxidation on yields and chemical composition of gases, liquids and chars produced during coal pyrolysis. Pyrolysis experiments were performed at 500 °C using the Fischer assay method. Mild oxidation of coals resulted in a decrease of liquid hydrocarbon yields. Further coal oxidation increased the proportion of aromatic carbon in liquid products as determined by n.m.r., and also increased the content of oxygen in liquid products. The content of oxygen in chars was markedly lower than in corresponding coals. An attempt is made to explain reactions occurring during oxidation and subsequent pyrolysis of coal on the basis of differences in chemical composition of gases, liquids and chars.

Conversion of non-coking coals to coking coals by thermal hydrogenation

Abstract Coking properties are observed in four non-coking coals, a lignite, a subbituminous coal, a semianthracite and an oxidized bituminous coal which had been treated by partial thermal hydrogenation. The effects of temperature, reaction time and hydrogen pressure on liquid and solid product yields are examined. Microscopic examination of the hydrogenated solid residues shows that they all contain structures somewhat spherical in shape which are associated with mesophase development. The dilatation, plastic character and free swelling index of the hydrogenated solid products were considerably better than those of the original coals. Dilatation residues produced from hydrogenated solids exhibited anisotropic structures.

Chemical structure of coal macerals in Balmer 10 coal and fusinite from Illinois coal as indicated by reductive alkylation

Abstract A Canadian Cretaceous coking coal from the Balmer 10 seam, Fernie, British Columbia, was separated by sink-and-float methods into vitrinite and a semifusinite-rich fraction. A portion of the vitrinite fraction was oxidized in air at 100 °C for 72 h to destroy the coking properties. The fresh vitrinite, oxidized vitrinite, and semifusinite of the Balmer coal, and the fusinite from Illinois coal, were each subjected to the reductive alkylation procedure of Sternberg, to cleave the ether linkages and octylate the products. The oxygen functional groups before and after ether cleavage were determined, as were the extractabilities by benzene of the octylated products. Thus the molecular weights of the benzenesoluble fractions of the octylated cleavage products were: fresh vitrinite 1930, oxidized vitrinite 1830, and fusinite 1490. The molecular-weight distribution of the octylated cleavage products was estimated by volatility analysis, which demonstrated the presence of much lower-molecular-weight material. Dilatation analysis of fresh and oxidized vitrinite showed that after cleavage of the ether linkages with potassium in tetrahydrofuran, the two could be brought to the same state. The dilatation behaviour of semifusinite after cleavage of the ether links and octylation showed only contraction, whereas the oxidized vitrinite treated in a similar manner exhibited a large dilatation.

Microscopic studies of semi-coke from different macerals after treatment of the coal in K/THF/naphthalene

Abstract The effect of K/THF/ N (potassium in tetrahydrofuran plus naphthalene) on coke structure is illustrated.

On the interaction between pyridine and coal as studied by solCPMAS15N n.m.r.

The interaction between pyridine-15N and both fresh and oxidized coal was studied by means of CPMAS15N n.m.r. In fresh bituminous coal, pyridine interacts only weakly through physical adsorption and hydrogen-bonded complex formation. On the other hand, in oxidized bituminous coal and fresh subbituminous coal the presence of both pyridinium ions and physically sorbed pyridine was observed. The occurrence of proton transfer to pyridine suggests that strongly acidic functions are generated during coal oxidation.

Formation of coke during thermal hydrocracking of Athabasca bitumen

Abstract The formation of two structurally different cokes during thermal hydrocracking of Athabasca bitumen is attributed to differences in coking properties of the asphaltenes and the deasphalted heavy oils. The grain-mosaic coke structure formed from the asphaltenes may be ascribed to the presence of crosslinkage groups derived from the phenolic character of this fraction of the bitumen. Carbonization of the deasphalted heavy oils of the bitumen results in a flow-type coke structure. These two cokes appear to form independently of each other and can therefore be readily identified in samples collected from the reactor.

1H n.m.r. relaxation in bituminous coal and semicoke

Abstract Temperature and frequency-dependent proton relaxation measurements, in conjunction with spin concentrations determined by e.s.r., have shown that for fresh and oxidized coal the relaxation mechanism involves spin-diffusion to paramagnetic centres and to rotating methyl groups on alkyl chains. 1 H relaxation in semicokes is more complex; probably both direct relaxation to paramagnetic centres as well as spin-diffusion contribute.