Proximate analysis of coal

Table III. Proximate Analysis of Coal Consumed During Test Period ...

The proximate analysis of coal is presented as a group of test methods (ASTM D-3172 ASTM D-3173 ASTM D-3174 ASTM D-3175 ASTM D-5142 ISO 1171) that has been used widely as the basis for coal characterization in connection with coal utilization. These analyses are in contrast to the ultimate analysis of coal, which provides information about the elemental composition. 

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. 

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

A typical proximate analysis of coal by microcomputer-controlled thermogravimetry. 

The proximate analysis of coal samples has also been described by Fyans (122), Sadek and Harrell (123), Earnest and Fyans (124), Hassel (125), and others. Using TG, Serageldin and Pan (126) described the reaction kinetics of the thermal decomposition of coal. 

Compositional analysis of coal, polymers and rubbers deals with the determination of volatile materials under an inert gas atmosphere and then combustibles under an oxidising atmosphere. The procedure is described in ASTM E 1131 (1998). The thermobalance must be capable of rapid heating rates and the system must allow gas switching to be performed quickly and completely. The quality of the inert atmosphere is most important and must not permit any significant oxidation during the determination of the volatiles. The proximate analysis of coal is shown in Figure 10. Using classical analytical methods, these determinations would take several hours. 

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. 

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. 

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. 

A TG method has also been devised for the proximate analysis of coal, permitting four samples per hour to be analyzed with results of the same precision and accuracy as BS and ASTM methods [10]. A typical curve is shown in Figure 3. The approach taken here can be generalized to the compositional analysis of many materials [1IJ. 

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...

Thermal analytic questions connected with coal (see also below) are by far too numerous to be treated here. But as coal is intimately coupled to wood just one example of coal combustion shall be given in this chapter. TG proved to be a convenient and quick means for a proximate analysis of coal to determine the moisture content, the volatiles, fixed carbon and the amount of ash. Figure 2 shows the burning profile of different coal samples heated slowly from 50 to 800°C in an oxidative atmosphere. Steps in the TG curve are due to a small loss... 

Figure 7 Schematic thermogram with the different steps during the determination of the proximate analysis of coal or lignite [95].

---