Semianthracite coals

Methods of coal liquefaction have been available since the beginning of the twentieth century but the cost has initiated searches for more effective new processes. For example, in the Bergius process for direct coal liquefaction, the coal is treated with hydrogen under pressure at 450°C (840°F) in the presence of a solvent and an iron oxide catalyst. The activity of this catalyst is low, however, because the solid iron oxide cannot enter the macromolecular network structure of the insoluble coal. Semianthracite coal, which only contains a small amount of volatile components, cannot be converted by this process. 

Fig. 3. Comparison of burning profiles for coals of different ranks where ( ) represents anthracite (-) semianthracite ( ) LV bituminous (° ) HV...

Fig. 10. Coal fields of the conterminous United States where H represents anthracite and semianthracite low volatile bituminous coal medium and...

Coal Petrography. Of the 36 samples examined microscopically, approximately one-half contained gas vacuoles produced by thermal distillation of the coal. Thus, these coals that might otherwise have been referred to the rank of anthracite can be regarded as natural coke. All the samples, including those with gas vesicles, appeared to be fairly dense, with no macroscopic indication of a coke-structure development. The samples with the most advanced vacuole development appeared to be almost metallic in luster. All the coal entities normally encountered—vitrinoids, micrinoids, semifusinoids, and fusinoids— were present, whereas the exinoids and resinoids, which are difficult to identify with certainty in semianthracite or anthracite, were not positively identified in... 

Semianthracite or anthracite containing recognizable coal entities that do not appear to be altered in this unit, which occurs 1117 feet below the sill... 

Reflectance. The optical properties (reflectance) are not in accord with the chemical properties for these coal samples, and the maximum reflectance of the coals indicates that they are higher in rank than would be concluded from the chemical data alone. These discrepancies are not surprising since these coals are thermally metamorphosed and may not follow the normal coalifica-tion curve (8). For the subject samples, it was decided that chemical data did not suitably indicate rank or the degree of thermal metamorphism, particularly in those instances where the samples contained so much ash that they were not suitable for routine chemical tests. The maximum reflectance in oil of these coals ranges from 2.6% to 11.5% (Table I). The lower reflectance is similar to that encountered in some semianthracites and anthracites, whereas the upper reflectance is more nearly that of graphite or long term, high tern-... 

Hardness. The Antarctic coals have Knoop hardnesses that range from 27 kg./sq. mm. to 188.6 kg./sq. cm. (Table I). Other natural cokes are generally the hardest, and the semianthracites are generally the softest. Hardness increases as the distance from the sill decreases for the coals from the Terrace Ridge area (Figure 11). However, when all the samples are considered, the hardness does not necessarily correlate in a completely regular manner with another single set of test data. 

Semianthracite rank of coal such that on a dry, mineral-matter-free basis, the volatile matter content of the coal is greater than 8% but equal to or less than 14% (or the fixed carbon content is equal to or greater than 86% but less than 92%), and the coal is nonagglomerating. 

Sparking fuels fuels that do not yield a coherent cake as residue in the volatile matter determination but evolve gaseous products at a rate sufficient to carry solid particles mechanically out of the crucible when heated at the standard rate usually, all low-rank noncaking coal and lignite may also include those anthracite, semianthracite, and bituminous coals that lose solid particles as described above particles escaping at the higher temperatures may become incandescent and spark as they are emitted (ASTM D-3175). 

In this paper the combustion reactivities of four flash pyrolysis chars are compared with the results for chars produced from low and high-rank coals under conditions simulating pulverized-coal combustion, for anthracite and semianthracite, and petroleum coke. Reactivity is expressed as the rate of combustion of carbon per unit external surface area of the particle, with due correction being made for the effect of mass transfer of oxygen to the particle. 

A third parameter is chosen to qualify the different classes of coal volatile matter for anthracitic coals dilatation for semianthracite and bituminous coals and calorific value for subbituminous coal and lignite. The scheme is expressed by mean of a code number of four digits, which refers to the rank (first digit), type (second and third digits), and qualification (fourth digit) of coal (Uribe and Perez, 1985). 

Anthracite is the highest rank of coal and has a carbon content of over 87% on a dry ash-free basis. Anthracite coal generally has the highest heating value per ton on a mineral matter-free basis. It is often subdivided into semianthracite, anthracite, and meta-anthracite on the basis of carbon content. Anthracite is often referred to as hard coal but this is a Layman s term and has little to do with the hardness of the coal. 

Semianthracite Term used to identify coal rank specifically refers to coal that possesses a fixed-carbon content of 86 to 92%. 

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