Whole coals

The KDF filter was first tested in prototype on a coal mine in northern Germany. It was installed in parallel with existing vacuum filters and it produced filter cakes consistendy lower in moisture content by 5 to 7% than the vacuum filters. Two production models have been installed and operated on a coal mine in Belgium. The filter is controlled by a specially developed computer system this consists of two computers, one monitoring the function of the filter and all of the detection devices installed, and the other controlling the filtration process. The system allows optimization of the performance, automatic start-up or shut-down, and can be integrated into the control system of the whole coal washing plant. 

Studies initiated by the author in CSIRO (13) seek to throw light on the role of the various macerals by studying the conversion, under catalytic hydrogenation conditions, in Tetralin as vehicle, of maceral concentrates from a high volatile bituminous coal. Some preliminary results, given in Fig. 3, show conversions as almost complete for the hand picked vitrain (>90% vitrinite) from a high volatile bituminous coal (Liddell seam N.S.W., 83.6% carbon and 43% volatile matter both expressed on a dry ash-free basis). However, it is evident that the conversion of the whole coal increases rapidly with increase in hydrogen pressure (under otherwise similar conditions - batch autoclave, 4h. 400°C). 

In the work now reported coal fractions derived from a solubilised coal were reacted individually with Tetralin, without any additions of catalyst or gaseous hydrogen, and the reaction products studied to determine the effect that chemical type had on the reaction. The untreated whole coal was also reacted to test whether phenol, present in the coal fractions as a result of the fractionation procedure, was having any significant effect on the reaction with the fractions. 

Approximately 3g samples of the coal fractions and of the whole coal were then reacted separately with 25 - 30 ml of tetra-lin at 450°C in a type 316 stainless steel, sealed reactor, 13 cm high by 2 cm diameter. The reactor was heated by plunging it into a preheated fluidised sand bath after 4 hours it was removed and quenched rapidly. 

Proton nmr spectra of fractions A, B and C and all bottoms products were recorded on a Varian HA lOOnmr spectrometer using a solution of the sample dissolved in pyridine-d5. Spectra were run at room temperature with tetra methyl silane (TMS) as an internal standard, with a sweep width of 0 to 1000 cps from TMS. Fraction D and the whole coal were only partly soluble in pyridine and it was therefore not possible to get representative spectra from them. 

The amount of residue recovered from the other two fractions is almost the same as that recovered from the whole-coal reaction, suggesting that the combined phenol and residual solvent end up... 

As expected, both the bottoms products and the residues, where formed, have substantially higher carbon and lower oxygen contents than the original fractions, but whereas in the bottoms products the hydrogen contents have increased, in the residues they are reduced. The bottoms products, including that from the whole coal, are remarkably similar in composition to each other. Lkkewise the residues are similar in composition to each other. 

Aliphatic material still remains in the residue from the whole coal, but is virtually eliminated in the residue from fraction C. The absorption at 1170 cm-1 -jn the spectra of both residues may be due to benzofuran type structures (8), but it is felt that the strong absorption in the region 1000 - 1200 cm-1 may have been enhanced by the presence of silica, a major component of the ash content in this coal. 

The nmr analyses of the bottoms products given in Table IV show the material to have a large aliphatic content. The aromatic/aliphatic ratios of the fractions are higher than for the whole coal because of the presence of combined phenol reaction with Tetralin reduces these ratios considerably, presumably by transfer of much of this material to the solvent-range product, but some of it must remain in the bottoms as the aromatic/aliphatic ratio of the composite bottoms product from the fractions is higher than that from the whole coal. It was not possible to calculate the contribution that the diluents, excess solvent and combined phenol, made to the aromatic H, but the large monoaromatic content of the bottoms product must be due, in part, to these. 

Distribution of protons by type and overall aromatic/aliphatic proton ratios for the original fractions and bottoms products, as determined by proton nmr. Proton distribution for fraction D and the whole coal are not included as these materials were only partly soluble and the resultant spectra were not representative of the whole material. 

Although the usual nomenclature in calling this solid a "residue" has been followed, such nomenclature is misleading in terms of reaction mechanism. Some of the "residue" formed in the reaction of the whole coal is genuine unreacted residue and some is a reaction product with the evidence suggesting that condensation reactions may be involved in its formation (10). 

Because llptlnltes comprise only a small fraction of most Australian bituminous coals, the M2J pyrograms for typical whole coals (Figure 2(E) and (F)) closely reflect the thermal behaviour of the aromatlc-rlch macerals. 

Simultaneously with the efforts to determine the origin of mineral matter in coal, systematic efforts were underway to estimate the quantitative distribution of trace and minor elements in American coals. The early analyses were performed on high-temperature ashes, and as a consequence, the investigators had to be content with determining the nonvolatile metallic oxides. However, with the advent of the low temperature asher and improvisations and advances in wet chemical, radiochemical, and instrumental analytical techniques, we not only can analyze nondecomposed mineral matter but also can study the composition of whole coal. 

Silica (Quartz). Quartz is ubiquitous in all coals. Rao and Gluskoter (I) reported that, on the average, 15% of the mineral matter in coals from the Illinois Basin was quartz. O Gorman and Walker (2) found 1-20% quartz in 16 whole coal samples from various parts of the United States. 

The total iron concentrations in the whole coal samples were determined by x-ray fluorescence spectrometry, and the concentrations of iron oxide in the corresponding ash samples were calculated. 

Table VII shows the analytical wavelengths chosen, the concentration ranges calculated to the whole coal, average relative standard deviations, and detection limits in ash determined by the spectrographic method.

Very little data have been reported on the analysis of elements in whole coal and mine dusts in particular. Kessler, Sharkey, and Friedel analyzed trace elements in coal from mines in 10 coal seams located in Pennsylvania, West Virginia, Virginia, Colorado, and Utah (5). Sixty-four elements ranging in concentration from 0.01 to 41,000 ppm wt were determined. Several surveys published previously have provided data on the concentration of minor elements in ashes from coals rather than a direct determination on the whole coals or mine dusts. Previous investigations include studies by Headlee and Hunter (6), Nunn, Lovell, and Wright (7), Abernethy, Peterson, and Gibson (8), and others (9, 10, 11,12). 

TJecent interest in the trace element content of coal has increased the need for rapid and accurate analytical methods for their determination. Because x-ray fluorescence analysis has demonstrated its usefulness in determining major, minor, and trace elements in numerous other types of materials, it was felt that this method could be extended to trace element determinations in whole coal. In the past, such analyses were seriously hampered by the lack of standard samples. However, research being conducted in our laboratories under the sponsorship of the U. S. Environmental Protection Agency produced a large number of coal samples for which trace elements had been determined by two or more independent analytical procedures, for example, optical emission, neutron activation, atomic absorption, and wet chemical methods. These coals were used as standards to develop an x-ray fluorescence method that would determine many trace and minor elements in pressed whole coal samples. 

Preliminary Investigation of Major and Minor Elements in Whole Coal and Coal Ash... 

Two different types of materials, coal ash and whole coal, were analyzed, and sample preparation was varied accordingly. 

Whole coal was ground with a binder (10 wt % ) and pressed into a disk, which was used as the analytical sample. The binder was a commercial product, Somar Mix, and the sample was ground in a No. 6 Wig-L-Bug for 3 min. Pellets 1% in. in diameter were then formed at 40,000 psi in a die designed for that purpose. Sample preparation techniques are given in detail in a previous publication (1). 

Because of these encouraging results and previous work on brown coals by Sweatman et al. (4) and Kiss (5), which indicated that major and minor elements could be determined in whole coal, a series of 25 coals was prepared for x-ray fluorescence analysis. For each coal, a low-temperature ash, a high-temperature ash, and the whole coal itself... 

Trace element determinations on whole coal have been severely handicapped by the lack of analyzed standards. Because of this it was necessary to prepare calibration curves from samples analyzed in our laboratories by independent methods. The accuracy of the x-ray fluorescence method is, therefore, dependent on the accuracy of the methods used to analyze the calibrating standards. It was too difficult to prepare standards by uniformly adding known quantities of trace elements to ground whole coal. 

The light coal matrix of carbon, hydrogen, and oxygen and the relatively slight variation of heavier trace elements permit their determination with minimum interferences. The same whole coal procedures previously... 

The accuracy of the x-ray fluorescence method was evaluated by calculating, from the 50 whole coals analyzed, the mean variation of each element from its mean concentration, determined by the other independent methods previously mentioned and listed in Table III. Detection... 

Table III. Comparative Accuracy for Whole Coal and Limits of Detection Based on 5 0 Samples...

The relative errors for all elements determined are given in Table IV. For completeness, data on minor elements in whole coal also are included in the trace element tables. These data indicate the precision obtained for the x-ray fluorescence analysis on replicates of 15 samples of whole coal ground to —325 mesh. 

Table IV. Deviation on — 3 2 5 Mesh on 15 Samples of Whole Coal...

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