High-rank bituminous coal

Yun, Y., and Suuberg, E. M. (1992). Structural changes in high-rank bituminous coals caused by solvent swelling and heat. Division of Fuel Chemistry, American Chemical Society Preprints of Papers 37(2), 856-865. 

The mode of formation of hypersaline brines has been discussed by the osmotic filtration through clay and shale deposits. The salinity of the brine ground waters increases with depth and when they are in contact with fuel bearing strata, correspondingly more chloride is taken up by the fuel. However, according to Skipsey (13) the high rank bituminous coals because of their low porosity are unable to take up large amounts of the chloride and associated cations, and the chlorine content rarely exceeds 0.2 per cent. The... 

High ranked bituminous coals like those of the Pittsburgh seam contain a distribution of discrete mineral matter particles in the size range from 50 to 1 pm which can be released and physically separated from the coal by normal fracture mechanisms experienced in wet ball milling. Separation of the product coal from the mineral matter dispersed in water was achieved by agglomeration methods. 

Under a specific set of process parameters, anthracite can be classed as unreactive while the high-rank bituminous coals require more severe conditions than the lower-rank coals. Thus, the lower-rank subbituminous coals and lignites produce overall lower yields and lower ratios of liquid/ gases than the bituminous coals. Obviously, these rules are mere generalities and caution should be exercised in applying such rules on a universal basis. 

Figure 5. Adsorption hysteresis of methane measured on a Hungarian hazardous high rank (bituminous) coal at 25°C [13]. o adsorption desorption.

Hard coals (high-rank bituminous coals) are the preferred precursor in many countries, because they can be used both for production of inexpensive activated carbons, and also for the more expensive granular, hard carbons with well-developed porous structures. As-received coals have some porosity (which decreases with increasing rank of coal), and consequently further treatments are needed to increase the porosity. Low rank coals (peat, lignite, brown coal), which do not fuse on carbonization, are used to produce activated carbons with a wide pore-size distribution. The yield of activated carbons from coal is generally larger than for lignocellulosic materials, above 30 wt%. 

The Australian Permian coals vary widely in rank (maturity) and type (vitrinite content) from the Oaklands (N.S.W.) coal at 72% (dry ash-free basis) carbon, a hard brown coal (6), containing 17% vitrinite, at one extreme - through high volatile bituminous coals such as Galilee (Queensland) coal at 77% carbon, 16% vitrinite Blair Athol (Queensland) coal at 82% carbon, 28% vitrinite, Liddell (N.S.W.) coal at 82% carbon, and >70% vitrinite - to low volatile bituminous such as Peak Downs (Queensland) at 89% carbon, 71% vitrinite, and Bulli seam (N.S.W.) 89% carbon, 45% vitrinite. 

Formation of asphaltenes during solubilization of low-rank bituminous coals has been attributed to cleavage of open ether-bridges (6). But while the presence of such configurations in high- and medium-rank bituminous coals is well established (7), their existence in less mature coals remains to be demonstrated. From reactions of low-rank bituminous coals with sodium in liquid ammonia or potassium in tetrahydrofuran, it has, in fact, been concluded that open ether-bonds are absent (8) or only present in negligible concentrations (9). 

The results for a low rank bituminous coal show a high diversity of molecular weights for such compounds, from 80 to 800 Daltons most abundant compounds are in the range from 230 to 430 Daltons ... 

With respect to partial conversion by flash pyrolysis, the principal consideration in a choice between otherwise equivalent coals is the fact that liquid yields tend to increase with rank up to high volatile bituminous coals and thereafter to fall off sharply. 

Most of the analyses of Antarctic coal were based on blocks of transportable size taken from surface outcrops. In earlier work, sections of purer coal were cut from the blocks and submitted for analysis. In later work, selected blocks were crushed, and a float fraction of purer coal was submitted to provide analytic data from each deposit. These samples, while not useful for determining coal grade, may be adequate for indicating rank. Practically all of the Antarctic coal, with the exception of that at Amery (which may represent high volatile bituminous coal), corresponds to medium volatile bituminous or higher rank. The high apparent rank Antarctic coal may be classified according to conventional ASTM standards of rank based on proximate analysis, but it seems clear that these results serve only as a first approximation. 

Aliphatic structures are still of major importance in the second group of resinites, those of the bituminous coals, but aromatic structures are present in significant amounts. The spectra of these resinites display the type of absorption pattern that has come to be associated with other coal macerals, particularly the sporinites and to a large extent the vitrinites. This pattern is established in the resinites of the high volatile bituminous coals. Furthermore, resinites of this group are reactive during carbonization and oxidation processes in which their behavior parallels that of similarly affected vitrinites of equivalent rank. 

Inherent or equilibrium moisture is used for calculating moist, mineral-matter-free calorific values for the rank classification of high-volatile bituminous coals. It is also used for estimating free or surface moisture, since total moisture is equal to the sum of the inherent moisture and the free moisture and is considered the inherent moisture of the coal as it occurs in the unexposed seam, where the relative humidity is probably near 100%. However, due to physical limitations, equilibrium moisture determinations are made at 96 to 97% relative humidity and used as inherent moisture values. 

The preliminary results of studies now underway suggest that the spectral peak (A max) of some macerals, is more sensitive to variation in coal rank than previously believed. In the high volatile bituminous coals studied, an increase of 3 V-types (0.45 -0.75% reflectance) resulted in about a 50 nm increase of A max. 

The H-Coal process produces approximately 3-3.5 barrels of liquid product for each ton of coal.42 Tests showed that the process is best suited for high-volatile bituminous coal the use of low-rank coals significantly reduced throughput and distillate yields. The successful performance of the ebullated bed reactor in the H-Coal process led to its later use in two-stage liquefaction systems. 

The changes in fatty acid distributions and levels with lithotype might well be different from the changes observed with varying coal rank. In order to compare coals of significantly different rank, we also examined the monocarboxylic acids from a highly volatile bituminous coal. 

Sample Selection and Preparation. Samples were selected from two high-volatile bituminous coals, namely, Illinois No. 6 bright coal and an eastern Kentucky splint coal from Perry County. The choice of these coals was based on the desire to contrast the fine structure of coals of equal rank but of different lithotypes. For both coals the samples were obtained from limited regions of their respective coal seams. Detailed coal petrography was performed on these samples, and TEM specimens were subsequently selected from representative polished blocks. 

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