Proximate analysis coal moisture

Each of these is reported in the proximate analysis. Coal analyses can be reported on several bases as-received, moisture-free (or dry), and mineral-matter-free (or ash-free). 

Analysis. The proximate analysis is based on determinations of volatile matter, moisture, and ash for a coal sample. Fixed carbon is then calculated by difference. Volatile matter is determined empirically by measuring the weight loss when coal is heated in a covered cmcible at either 950°C (ASTM D3175 or D5142) or 900°C (BS). 

Fixed carbon, the residue left after the volatile matter is driven off, is calculated by subtrac ting from 100 the percentages of moisture, volatile matter, and ash of the proximate analysis. In addition to carbon, it may contain several tenths of a percent of hydrogen and oxygen, 0.4 to 1.0 percent nitrogen, and about half of the sulfur that was in the coal. 

The composition of coal is conveyed by representing its proximate and ultimate analysis. The former implies determination of contents of moisture, volatile matter, fixed carbon, and ash, while the latter implies total carbon, hydrogen, oxygen, nitrogen, sulfur and ash. Here, an account will be provided of the constituents of coal, moisture, volatile matter, ash, fixed carbon, and some miscellaneous components. 

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. 

Coal, Analytical Procedures. The most frequently made analysis of coal is the proximate analysis. This includes detns of moisture, volatile matter, fixed carbon and ash. Sometimes it is combined with detn of sulfur and phosphorus, which really belongs to the ultimate analysis, and includes also detn of carbon, hydrogen, nitrogen and sulfur. In most cases, the heating value of coal expressed in BTU/lb is also detd,... 

Many of the test methods applied to coal analysis are empirical in nature, and strict adherence to the procedural guidelines is necessary to obtain repeatable and reproducible results. The type of analysis normally requested by the coal industry may be a proximate analysis (moisture, ash, volatile matter, and fixed carbon) or an ultimate analysis (carbon, hydrogen, sulfur, nitrogen, oxygen, and ash). 

Total moisture of coal Ultimate analysis of coal Ultimate analysis of coke Chlorine in coal and coke Phosphorus in coal and coke Arsenic in coal and coke Analysis of coal ash and coke ash Determination of moisture-holding capacity of hard coal General introduction and methods for reporting results Determination of total moisture of coke Proximate analysis, determination of moisture content of the general analysis test sample... 

Thus, to classify coal, the calorific value and a proximate analysis (moisture, ash, volatile matter, and fixed carbon by difference) are needed. For lower-rank coals, the equilibrium moisture must also be determined. To calculate these values to a mineral-matter-free basis, the Parr formulas are used (ASTM D-388). 

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. 

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. 

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... 

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. 

The chemical composition of a coal usually is expressed by either an ultimate or proximate analysis or by both. Ultimate analysis refers to an analysis routine that includes moisture, combined water, carbon, hydrogen, sulfur, nitrogen, and ash. 

The proximate analysis indicates the moisture, ash, and volatiles content of a fuel. The volatile yield is sensitive to heating rate and peak temperature. The yield experienced during the relatively slow and cool proximate analysis is lower than that experienced by coal in mai combustors by about 30%. However, the relative volatile yields of many coals are appioxiniately indicated by the proximate analysis. 

European and American researchers in the nineteenth and early twentieth centuries proposed several coal classification systems. The earliest, published in Paris in 1837 by Henri-Victor Regnault (1810-1878), classified coal types according to their proximate analysis (determination of component substances, by percentage), that is, by their percentages of moisture, combustible matter, fixed carbon, and ash. This system is still favored, in modified form, by many American coal scientists (Speight, 2005). 

The proximate analysis of coal was developed as a convenient and effective means for determining the distribution of products obtained by heating coal under a set of standard conditions. This particular group of tests has been used widely as the basis for coal characterization in connection with coal utilization. The proximate analysis (ASTM, 20111) of coal may also be considered as the determination of the general properties of coal and is, in reality, the determination of moisture content, volatile matter content, ash yield, and (by difference) fixed carbon yield in contrast to the ultimate analysis of coal which provides the elemental composition (Figure 8.5). 

Thus, the objective of the proximate analysis is to determine the amount moisture, volatile matter yield, ash yield, and fixed carbon from the coal sample. Mineral matter is not directly measured but may be obtained by one of a number of empirical formula either from the yield of mineral ash or from data derived from the ultimate analysis. 

The analyses of the air-dried equilibrated sample for moisture, ash, and volatile matter are collectively termed the proximate analysis. Fixed carbon is, by definition, the difference between 100 and the sum of the analytes (moisture, ash, volatile matter). The proximate analysis gives information on the classification of coal by measuring the relative percentage of volatile and nonvolatile organic matter as those of moisture and noncombustible mineral matter. 

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. 

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. 

Figure 3. TG curve (A) illustrating a programmed-temper-ature method for the proximate analysis of coal, where the line B defines the temperature program a) Moisture b) Volatiles c) Fixed carbon d) Ash e) Point at which the atmosphere was changed to air...

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