Brown coal volatiles

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. 

Figure 6. Dependence of maximum tar yields and corresponding total volatile matter yields during flash pyrolysis on atomic hydrogen-to-carbon ratio for some Australian and V.S.A. coals (O, 9), black coals (X), brown coals (A), Pittsburgh No. 8 (USA.) ( ), Montana lignite (USA).

The first part of this paper has shown that Australian black and brown coals differ significantly in a number of respects from coals of similar ranks from North America and elsewhere in the northern hemisphere. The rest of the paper than proceeded to indicate the progress being made to determine how the characteristics of Australian coals influence their conversion to volatile and liquid products during pyrolysis and hydrogenation. 

Figure 5. Relationship between conversion and volatile matter percent in coal (9), with catalyst (O), no catalyst (A), Morwell brown coal.

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. 

Lignite brownish-black woody-structured coal, lower in fixed carbon and higher in volatile matter and oxygen than either anthracite or bituminous coal similar to the brown coal of Europe and Australia. See also Rank. 

Figure 1. Variation in conversion with volatile matter content for Victorian brown coals.

Rhenish brown coal has an average ash content of about 4 % (mf), a volatile matter of about 52 % (maf) and a lower heating value of 25.6 MJ/Kg of coal (maf). The final analysis of the coal under maf conditions shows the following average composition ... 

Various standardized analyses have been developed to determine the chemical composition of coals. Among them are the proximate analyses, which quantify the volatile and non-volatile components, and the ultimate analyses, which determine the elemental composition. These, and examples of other types of analyses, are listed in Table 4.5. Data are often recorded on a dry and ash-free (daf) basis, because of the variable amount of unbound water (particularly in brown coals) and inorganic minerals that may be present. A mineral-matter-free (mmf) rather than simple ash-free basis is often used for elemental composition in order to take account of the oxides, sulphides etc., and also the water of crystallization in inorganic minerals, when calculating the composition of the organic matter. 

Partially hydrogasified coal, upon further reaction in the high temperature second stage, gave rate constants quite similar to those obtained with Disco char (14) and residual Australian brown coal (I), both containing little volatile matter. 

The volatile matter increases from less than 8% in antracite to more than 27 wt% in lignite. In addition, the content of water may vary from less than 5 wt% in antracite to about 60% in German brown coal. Nitrogen (0.5-2%) will be converted into ammonia. The sulphur content may typically vary from 0.5-5 wt%. Sulphur will be converted to COS and H2S. Sulphur will poison downstream synthesis catalysts and must be removed. Chlorine is normally below 1 wt%. Chlorine may cause corrosion problems in downstream equipment. Chlorine will react with ammonia from the nitrogen and deposition of ammonia chloride may foul waste heat boilers and limit their operating temperature [230]. 

The principles and precautions applicable to coal grinding and drying are even more stringently applicable to lignite (brown coal), which is especially hazardous on account of its higher content of volatile matter. 

Table 3.5 shows typical samples according to the ASTM classification mosdy displaying American coals. A typical Indian high-ash mediiun volatile bituminous coal as well as a German brown coal (lignite B) are added for comparison. Again the dilemma of coal classification becomes evident, as none of the analyzed parameters changes steadily with rank alteration. 

Li, X., Hayashi, J., Li, C. Z. Volatilization and catalytic effects of atkah and alkaline earth metallic species during the pyrolysis and gasification of Victorian brown coal. Part Vll. Raman spectroscopic study on the changes in char structure during the catalytic gasification in air. Fuel 2006, 85, 1509-1517. 

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