Brown coal lithotypes

As stated before, volatile carbon % is considered to be one of the most important parameters of hydroliquefaction. Also a fairly good linear relationship between the volatile carbon % in coal and low temperature tar yield from coal is found in Morwell brown coals, based on the data from the State Electricity Commission of Victoria (SECV) in Australia, as shown in Fig.9 Therefore, the low temperature tar yield is also estimated to be an important parameter. In addition, the color tone of brown coal (lithotypes) is shown in this figure. From this figure, it is observed that both volatile carbon % and low temperature tar yield are in a fairly good relation to the color tone of brown coal. Thus, as proposed by the Australian researchers, the color tone of brown coal is considered to be an important parameter. 

Based on macropetrographical criteria (determination of the lithotypes by visual examination with the naked eye) 15 brown coal lithotypes were selected for the investigations described in the following they represent more than 90 % of the main seam. 

Figure 3 shows these 15 brown coal lithotypes arranged according to stratification (unbanded to banded coal) and texture (plant tissue content). 

Micropetrography evaluates the coal components ascertainable by microscopy. Figure 4 shows an extract of the results obtained from the combined maceral-microlithotype analysis after the International Handbook of Coal Petrography of the 15 brown coal lithotypes. 

Figure 3. Macropetrographical classification of 15 brown coal lithotypes from the Rhenish area. (Reproduced with permission from Ref. 2. Copyright 1981, Schriftleitung Braunkohle.)...

Subsequent to the petrographical coal analysis, both a chemical and a chemo-physical investigation were carried out. Figure 7 shows the chemical and physical properties of the investigated brown coal lithotypes. 

Figure 8. Heating value of the brown coal lithotypes as a...

In order to establish statistically usable data on the briquetting behaviour of Rhenish brown coals, the 15 brown coal lithotypes were briquetted under identical conditions (water content, grain size distribution and mould pressure) with a laboratory press. 

Two gasification processes under development, namely High Temperature Winkler Gasification (HTW) and hydrogasification of lignite (HKV), encouraged to study the gasification behaviour of various brown coal lithotypes (15). 

The lithotype profile was investigated in greater detail with the product composition of the different brown coals being reported in Tables 1 and 2. A distinct decrease in the total concentration of detectable oxidation products occurs with darker lithotypes (Table 1). This result is consistent with increasing aromaticity (Figure 2) and the preferential attack on aromatic structures by the pertrifluoroacetic acid reagent. The total destruction of the tertiary structure within the brown coal lithotypes is evidenced by their low yield of insoluble products (Residue) which is primarily composed of mineral matter. 

Product Composition of Brown Coal Lithotypes Pertrifluoroacetic Acid Oxidation Mixtures... 

This study reports the monocarboxylic fatty acid content of a series of brown coal lithotypes from the Latrobe Valley, Victoria, Australia. We have looked both at the solvent-extractable, or free, fatty acids (which include those extractable as esters or intact lipids) and at those that are released upon hydrolysis (saponification) of the residue after solvent extraction. The latter are presumably bound chemically to the coal matrix (kerogen) and are therefore designated as bound acids. The total acids are taken as the sum of the free and bound acids. 

It should be pointed out that the lithotype classification for brown coal does not conform to that for black coal. To date, the International Committee for Coal Petrology (ICCP) has not finalized a brown coal lithotype classification however, it is generally agreed that a lithotype classification should be based on macroscopic characteristics that can be determined in open cut faces. This principle has been followed in classifying the Latrobe Valley coals according to a system developed and used by the State Electricity Commission of Victoria (SECV) (25). 

Samples. Brown coal lithotype samples were taken from a bore core from the Flynn field in the Loy Yang region of the Latrobe Valley, Victoria, Australia. The brown coal deposits in this area are believed to be Miocene to Eocene in age. All five lithotype samples were taken at depths between 93 and 100.5 m below the surface in a 120-m core and were provided by the SECV. The black coal sample was from the Upper Hunter region (Permian) of New South Wales (Sydney Basin), Australia, and had a carbon content of 81.3%, dry, ash-free basis (DAF). This sample was provided by the Australian Coal Industry Research Laboratories Ltd. (ACIRL). The characteristics of these samples are set out in Table II. 

Acid groups such as triterpenoid acids, dicarboxylic acids, and hydroxy acids also are present in brown coal. Although this paper is restricted to the monofatty acid levels and distributions in brown coal lithotypes, these other acid types also have been observed to vary in level and distribution with lithotype and may, in fact, prove to be useful as indicators of the depositional environments. 

Rhenish brown coal consists of a variety of lithotypes which are already discernible in the coal seam by brightness variations. 

To determine potential raw material impacts on brown coal hydroliquefaction, the 15 lithotypes were converted into liquid products using various techniques (18) ... 

Figure 17 shows the product yields of indirect brown coal hydrogenation with tetralin as a function of stratification and texture (lithotype... 

For the purpose of an assessment with a view to refining, the petrographical, chemical and physical properties of lithotypes of Rhenish brown coal were established and compared with one another. 

Victorian brown coals are thought to be largely amorphous, containing aromatic layers of single substituted benzene rings crosslinked by aliphatic chains to form a three dimensional structure. Their carbon content is quite low, varying from 60 to 70. One would therefore expect its porous system to be somewhat like that of an open structure having micropores which are randomly-oriented. In this preliminary study two samples of Yallourn ream coal were taken from the Yallourn open cut mine in the Latrobe Valley, Victoria, Australia. The samples, a pale and a medium dark lithotype, are representative of the extremes in coal types found in the Yallourn ream. 

Chemical Variation as a Function of Lithotype and Depth in Victorian Brown Coal... 

Victorian brown coal occurs in five major lithotypes distinguishable by color index and petrography. Advantage has been taken of a rare 100 m continuous core to compare and contrast chemical variations occurring as a function of lithotype classification. For many parameters there is a much greater contrast between the different lithotypes than there is across the depth profile of (nearly) identical lithotypes. Molecular parameters, such as the distributions of hydrocarbons, fatty acids, triterpenoids and pertrifluoroacetic acid oxidation products, together with gross structural parameters derived from IR and C-NMR spectroscopic data, Rock-Eval and elemental analyses and the yields of specific extractable fractions are compared. 

The monofatty acids (Ci -C 2) f om five lithotypes of Victorian brown coal and from a Sydney Basin black coal were analyzed by gas-liquid chromatography. The different profiles observed for the various lithotypes have been interpreted in terms of differences in depositional environment, while differences in rank appear to be responsible for the large differences between the brown and black coal samples. The presence of several classes of acids in these coals is reported, but of these the presence of monounsaturated and diunsaturated acids is particularly important in view of their assumed geochemical instability. 

Solvent Extraction. A significant portion of brown coal is solvent-extractable. Figure 1 shows that for the lithotypes examined in this study, between 9.5% and 15% of the coal was solvent-extractable. Indeed, more than 20% of brown coal has been shown to be extractable for particular samples (29). The amount of material solvent-extractable from black coals is substantially less (5.6%) and, from our work on coals ranging from 81% to 89% C [DAF] (29), was observed to decrease with increasing rank. Leythaeuser and Welte (30) observed that their ex-... 

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