Brown coal deposition

The most significant Tertiary coals are represented by the vast brown coal deposits in Victoria, particularly in the Latrobe Valley. These brown coals with 68-70% carbon, occur in very thick seams (up to 200 meters) under shallow cover (<30 meters). These coals differ from the Tertiary brown coals of North America in that they have a much lower ash yield and significant amounts of the ash-forming inorganic constituents are present as cations on the carboxylic acid groups which are a characteristic of low rank coals ... 

Under the given conditions of the Rhenish brown coal deposit, an opencast mining operation, a high output and the large feed quantities required for future refining plants brown coal petrography is one out of many tesserae for quality assessment. The development of appropriate modes of determining the quality characteristics of raw brown coal is a task indispensable for the future. 

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. 

Hard coal, representing over 50% of the fossil raw materials, is the carbonaceous material with by far the greatest availability. Confirmed world resources of hard coal are around 6,900 billion t of these, some 550 billion t can be recovered by current mining techniques. Brown coal deposits total some 6,500 billion t, of which 430 billion t are recoverable. In comparison with coal reserves, economically recoverable oil reserves are only 95 billion t, and natural gas deposits 90,000 billion m (around 72 billion t). 

Large reserves of brown coals occur in Victoria with smaller deposits in New South Wales and South Australia. 

Bitumen describes a black or dark brown masticlike material that is thermoplastic in nature and softens upon heating. The sources of bitumen are petroleum or coal deposits. The natural product is commonly called gilsonite or pitch, a mineral formed by an old weathered petroleum flow at the surface of the earth that has left behind the larger molecules from the petroleum. A principal source in the past has been Lake Trinidad, a 445,000 m2 deposit on the island of Trinidad. Bitumen from petroleum or crude oil is called asphalt (qv). It is the material left behind after all the valuable compounds, eg, gasolines, have been distilled out of the cmde oil. The amount and quality of asphalt is dependent on the source of the crude oil used in the refining process. Some cmde oils have a higher content of asphaltic bitumen left after the distillation process. Bitumen from coal is coal-tar pitch. It remains after the valuable coal oils and tars have been distilled out of the coal tars produced by distractive distillation. Most industrial applications for bitumen products use asphalt or coal-tar pitch because the supply is more uniform and plentiful. 

Lignite was deposited relatively recently ica 2.5-60 x ldh yr ago), mainly during the Tertiary era. L. S. deposiis include those in the Dakotas. Alaska. Montana, and Wyoming. The Miocene period provided the brown coal deposiis that are up to 500 m thick in the Latrobe Valley of Victory in Ausiralia. 

Extensive deposits of soft brown coal exist in Tertiary age sediments in a number of areas in Victoria and the largest single deposit occurs in the Latrobe Valley, about 150 kilometers east of Melbourne. In this region the coal seams often exceed 150 metres in thickness, with an overburden to coal ratio usually better than 1 2 making the coal ideally suited for large-scale open-cut mining. 

In this Brown Coal Evaluation Programme a sampling philosophy was adopted that would highlight the natural variability of the coal and indicate the range of coal qualities which may be encountered during mining and utilization of the deposits. 

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. 

Catty acids are widely distributed in nature and have been studied extensively in petroleum (1, 2) and sediments (1, 3, 4, 5), as well as in living organisms (6, 7, 8). Fatty acids are major components in most living organisms, and since they are geochemically quite stable (9), they are important components in most depositional environments. The presence of fatty acids in coals has been recorded (10, 11, 12), but there appears to be little published information available on their distribution, particularly in brown coals, except in montan wax deposits (13, 14). In contrast, the distribution of n-alkanes in coals has been widely studied, and the maxima of the distributions have been shown to range from C29... 

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. 

The slagging and fouling tendencies of coals largely differ according to the deposit but also differ within the deposit because of widely varying coal composition. Ash properties are so complex that evaluation of coal performance is extremely difficult. The performance of coals in furnaces are further complicated by the processes which control deposition on heat transfer surfaces in boilers. Based on these complications, we must neither deceive ourselves as to the possibility of reliable estimates nor deny the possibility of making a useful estimate of the performance of brown coal in boilers. 

Schneider (9 ) with brown coals of different origin in a drop tube furnace similar to that used by Field clearly showed the influence of different mineral substances on ash deposition. Sand particles (Figure 2) maintained their former shape in combustion or showed changes only at their edges while other ash constituents fused together into dark brown or glassy-clear spheres. 

Use of the Field tube for determining the performance of coals is limited by the short residence time of 0.3 seconds (2.1 m) and the inability to use particles larger than 0.14 mm. This limits the extent of particle size changes and the structure of the mineral substance relative to pulverized fuels or coarse-crushed brown coals used in utility boilers. This difference probably has an effect on the formation of deposits. 

The rate of the oxidation process is determined by the reactivity of the starting carbon and oxidizer. The greater the reactivity of the substrates the lower the temperature of the process in which uniform formation of the pores in the granules is observed. In the case of carbonaceous materials the cokes of brown coals show the greatest reactivity, and the cokes of hard coals the smallest activity. The cokes of pit coals show an intermediate reactivity. This is connected with the earlier mentioned ordering of the crystallographic structure of carbon, which is of significant importance in the case of modification of carbon deposits contained in the carbon-mineral adsorbents in which the carbonaceous compound may be characterized by a differentiated chemical and physical structure. Thus the surface properties of hydrothermally modified complex adsorbents are defined by the course of three processes ... 

Major coal deposits coincided with periods following regression, which is consistent with the most suitable conditions for deposition—a steady increase in accommodation space—being predominantly found in lowland coastal swamps (Section 3.4.2a). Two main episodes of coal formation can be distinguished the first during the Carboniferous—Permian and a second smaller episode spanning the Jurassic to early Tertiary. The majority of coals formed in the earlier episode are now bituminous coals or anthracites, whereas those from the Tertiary are mainly brown coals. 

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