Proximate Analysis of Coal and Coke

In quality control, the proximate analysis of coal and coke is of importance. Thermogravimetry provides a convenient method for performing a proximate analysis, usually in 10-20 min. Proximate analysis covers the determination of moisture, volatile matter, fixed carbon and ash in coals and cokes and is used to establish the rank of coals, to determine the ratio of combustible to incombustible constituents, or to provide the basis for commercial trading and otherwise evaluating coal for various purposes. Hence it is important to both the suppliers and users of coal to have a rapid, accurate and reliable procedure for proximate analysis. 

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The standard test method for proximate analysis (ASTM D-3172) covers the methods of analysis associated with the proximate analysis of coal and coke and is, in fact, a combination of the determination of each of three of the properties and calculation of a fourth. Moisture, volatile matter, and ash are all determined by subjecting the coal to prescribed temperature levels for prescribed time intervals. The losses of weight are, by stipulation, due to loss of moisture and, at the higher temperature, loss of volatile matter. The residue remaining after ignition at the final temperature is called ash. Fixed carbon is the difference of these three values summed and subtracted from 100. In low-volatile materials such as coke and anthracite coal, the fixed-carbon value equates approximately to the elemental carbon content of the sample. 

ASTM D-3172. Standard Practice for Proximate Analysis of Coal and Coke. 

ASTM. 20111. Practice for Proximate Analysis of Coal and Coke (ASTM D3172). Annual Book of ASTM Standards, Section 05.05. American Society for Testing and Materials, West Conshohocken, PA. 

Proximate analysis, determination of moisture content of the general analysis sample of coke Proximate analysis, determination of volatile matter content Proximate analysis, determination of ash content Determination of gross calorific value Ultimate analysis of coal and coke, determination of carbon and hydrogen content, high temperature combustion method Liebig method... 

Although in many laboratories the methods described above remain the methods of choice for determining the proximate analysis of coal, there is also a test method for the proximate analysis of coal by instrumental procedures, assuming that calibration is an integral part of the procedure (ASTM D-5142). This method covers the determination of moisture, volatile matter, and ash and the calculation of fixed carbon in the analysis of coal and coke samples prepared in accordance with standard protocols (ASTM D-2013). The results may require a correction for bias or be corrected for instrument calibration using samples of known proximate... 

ASTM D-5142. Standard Test Methods for Proximate Analysis of the Analysis Sample of Coal and Coke by Instrumental Procedures. 

For example, all of the carbon in coal is determined by ultimate analysis and it is not an indication (or determination) of the carbon-forming propensity (i.e., the coke-producing ability) of the coal as is the case with the test for the volatile matter content of coal. Thus, just as there has been the need to develop standard methods for the proximate analysis of coal, there has also been the necessity to develop standard methods for the ultimate analysis of coal. 

Proximate Analysis. This includes (he determination of total moisture, volatile matter, and ash and the calculation of fixed carbon for coals and cokes. The term Proximate" should not be confused with Ihe word approximate." since all Proximate Analysis tests are performed according lo rigid specifications and tolerances. Proximate Analysis results may be used lo establish the rank of coals to show the ratio of combuslible lo incombustible constituents, lo provide the basis for buying and selling coal, and to evaluate for beneliciation, or other purposes. 

As an extension of the proximate analysis or coal assay, it is worthy of note that new methods continued to be developed. For example, thermogravimetric analysis has been extended to cover determinations of volatile matter (as well as determination of moisture and ash) in coal and coke. These constituents can be measured by pyrolyzing the samples in oxygen and air, and the weight loss at prescribed temperatures was measured by using a thermobalance. 

The chemistry and physics of coal can be expressed in terms of composition, which is defined as ultimate (elemental) analysis, and behavior, which is described in empirical terms by a prescribed method (also defined as proximate analysis) (Chapters 8 and 9). Therefore, it is just as important that coke be defined in terms of analytical data that suits the utility and meets the objective for which the coke was produced (Marsh and Smith, 1978 Patrick and Wilkinson, 1978). 

As in the case of coal, all determinations included in proximate analysis (moisture, ash, and volatile matter contents) are the subject of national and international standards (ISO 579 for the determination of total moisture content ISO 687 and ASTM D3173 for the determination of moisture in the analysis sample ISO 1171 and ASTM D3174 for the determination of ash ISO 562 and ASTM D3175 for the determination of volatile matter content). Table 6 summarizes typical coke chemical properties for some operating blast furnaces in Europe. 

The elemental analysis of coal, i.e., its C, H, O, N, S, and ash residue, may be important to a chemist who wishes to use coal as a chemical or source of carbon, but to an engineer who wants to bum the coal in a heat- or power-generating plant or a coking oven, other parameters are more important— most notably its heat of combustion, moisture level, volatile matter, carbon and sulfur content, as well as the ash. This is called the proximate analysis and it is determined as follows ... 

Table II. Proximate Analysis of Coke and Three Kinds of Lump Coal/%...

The coke residue is the result of the hydrogen-deficient stoichiometry of the process. With a proximate analysis (determination of the compounds, moisture, ash, etc., present) of carbon 80%, volatiles 10%, sulfur 6%, and ash 4%, the coke has a fuel value near that of high rank coals. It is burned in the site power plants to provide steam and electrical power for oil sands processing. However, the high sulfur content detracts from its wider utility as a fuel. Any coke in excess of the current fuel requirement is finely powdered and incorporated into the dyke walls to help trap any hydrocarbons present in water seepage through the wall. 

Where MVY is maximum volatile yield (percent), and VMpj is volatile matter measured in a standard proximate analysis. The r for this equation is 0.945, over a suite of 10 fuels ranging from fresh sawdust to petroleum coke and including lignite, PRB, western bituminous, Illinois basin, and Pittsburgh seam coals. Using this equation the maximum... 

All the materials used including sinter, pellet, coke and three kinds of lump coal are from a certain ironworks. The composition of sinter and pellet are given in Table I. Proximate analysis and ultimate analysis of coke and three kinds of lump coal are... 

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