Coal, maximum fluidity

Plastic properties are sensitive to the oxidation or weathering of coals. Maximum fluidity is lessened, and extensive oxidation may destroy the fluidity of coal completely. Samples should be tested as soon as possible after they are collected and should be stored under water or in a nonoxidizing atmosphere if there is to be a delay before they are tested. Proper packing around the stirrer in the plastometer is an important step in the measurement of plastic properties. Some coals may not pack easily due to their weathered condition or to the size consist of the sample. An excess of very fine coal makes the test sample hard to pack. 

Liquefaction of fusible coal at high temperature. The liquefaction of Itmann coal, of which softening point and maximum fluidity temperature are 417° and 465°C, respectively, was carried out at several temperatures using decacyclene as a liquefaction solvent. 

Figure 1. Liquefaction yields vs. maximum fluidities in the fused state of coal (%), solvent (SRC pitch benzene soluble) (O), pyrene ((B), no solvent. Coal.sol-vent ratio = 1 3 reaction temperature = 390°C(8).

Figure 2 illustrates the relationship between the coke strength (DI30/15) and the maximum fluidity (MF) of blended coals in the coke oven battery at Nippon Kokan s Fukuyama Works with the reflectance (Ro) of blended coals as the parameter. 

Coal ground to <4.75 mm was placed in the plastometer equilibrated at 300 C. The coal was then heated at a standard rate of 3 C/min to the desired temperature without stirring and allowed to cool. Heat-treatment temperatures ranged in 25 increments between 300 and 550 C for the Pittsburgh No. 8 coal, between 300 and 500 C for the Illinois No. 6 coal, and between 400 and 550 C for the Lower Kittanning coal Other samples of these coals were subjected to the standard Bethlehem plastometer test to measure the temperatures of onset of fluidity, maximum fluidity, and resolidification. 

Spectra of semicokes made from Pittsburgh No 8 coal at various temperatures are shown in Figure 7 Increasing the heat-treatment temperature from 300 C causes little change in a given spectrum until 400 C At this temperature, corresponding to the onset of fluidity, the peaks become sharper At 450 C, corresponding to maximum fluidity, the peaks become their sharpest. Beyond the resolidification temperature of 470 C, spectral definition is lost, and by 525 C the spectrum is essentially featureless ... 

Spectra of semicokes from the Lower Kittanning coal are shown in Figure 9 The spectrum with the most distinct peaks in this series is the 500 C semicoke However, as in the case of the Illinois No 6 series, there is not the marked improvement in spectral quality at the temperature of maximum fluidity that we observed in the Pittsburgh Seam series There is also evidence of carbonyl groups at 1740 cm in this series of semicokes — possibly corresponding to esters ... 

At the temperature of maximum fluidity the vibration at 860 cm reaches Its maximum. This peak, which arises from highly substituted aromatic rings. Is consistent with a model of liquid crystals composed of layered aromatic sheets with lone hydrogen atoms only on the edges. The 860 cm peak becomes significant In each coal at only one temperature. In another Pittsburgh No. 8 samplj, whose fluidity was severely reduced by oxidation, the 860 cm peak did not become significant at any temperature. Hence, fluidity and mesophase are evidently related. 

The Gieseler test is the only one that attempts to measure the actual extent of the plasticity of fluidity attained. The Gieseler test is used to characterize coals with regard to thermoplastic behavior and is sometimes an important tool used for coal blending for commercial coke manufacture. The maximum fluidity determined by the Gieseler is very sensitive to weathering (oxidation) of the coal. 

Plastic properties of coal, as determined by the Gieseler plastometer, appear to be sensitive to oxidation, which can have a maiked effect in decreasing the maximum fluidity. In fact, prolonged oxidation may completely destroy the fluidity of a coal. To reduce oxidation, samples should be tested soon after collection or, if delay is unavoidable, storage under water or in a nonoxidizing atmosphere such as nitrogen is advisable. 

F ure 2.24. The variation of maximum fluidity (logddpm) of a rank range of coals with carbon content (wt% (dmmf)) of the coals. 

Coals are not homogeneous but are made up with macerals, these being recognizable components (by optical microscopy) within the coal derived from specific plant components. Coals may possess different quantities of macerals so accounting for small differences in rank. The exinite group of macerals exhibit maximum fluidity, the vitrinites have an intermediate position and the fusinites (like a wood charcoal) are non-fusible. 

Three bituminous coals, of decreasing rank, with volatile matter content 17.8 to 32.2 wt.% were used. The most important characteristics of the parent coals are given in Table 1 and indicate that the Turon coal has the maximum fluidity. The three coals were ground to <1 mm. The ground coals were placed in trays and oxidised in an oven, in air, at 140 C up to 24 h (Gregory 8 h). To carbonize the coals, 400 g of fresh and oxidised coal was placed in stainless steel cylinders (11.5 cm high, 9 cm internal diameter) within an electrical furnace and heated at 5 K min to a final heat treatment temperature of 1000°C. Strength and reactivity data of resultant cokes are published (ref. 14). 

Mochida and co-workers have also shown that the degree of solubilization of coals in polyaromatic solvents relates directly to their fluidity (18). We did not obtain fluidity measurements directly on this series of coals but data developed by Honda (19) indicate that a maximum in fluidity occurs at 85% Cmaf (see Figure 11). This is in the same region of carbon content in which we observed a maximum in conversion at short time (see Figure 6). 

Extents of coalification (coal rank) are usually measured in terms of carbon and volatile contents as well as reflectance measurements, the latter being a direct indicator of extents of aromaticity in the coal (Table 2.1). Coalification (rank) has proceeded continuously without discontinuities in terms of analytical data. Some physical properties, however, have not developed continuously. Fluidity (plasticity), an important industrial property, rises and falls with increasing coal rank. On heating coals in an inert atmosphere, fluidity increases from zero at 81 wt% carbon, reaching a maximum at about 87 wt% carbon, falling to zero at about 91 wt% carbon (Figure 2.24). 

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