13 Properties of Coal Coal Classification Coal is classified into three major

13 properties of coal coal classification coal is

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1.3 Properties of Coal Coal Classification Coal is classified into three major types namely anthracite, bituminous, and lignite. However there is no clear demarcation between them and coal is also further classified as semi- anthracite, semi-bituminous, and sub-bituminous. Anthracite is the oldest coal from geological perspective. It is a hard coal composed mainly of carbon with little volatile content and practi- cally no moisture. Lignite is the youngest coal from geological perspective. It is a soft coal composed mainly of volatile matter and moisture content with low fixed carbon. Fixed carbon refers to carbon in its free state, not combined with other elements. Volatile matter refers to those combustible constituents of coal that vaporize when coal is heated. The common coals used in Indian industry are bituminous and sub-bituminous coal. The gradation of Indian coal based on its calorific value is as follows: Grade Calorific Value Range ( in kCal/Kg) A Exceeding 6200 B 5600 – 6200 C 4940 – 5600 D 4200 – 4940 E 3360 – 4200 F 2400 – 3360 G 1300 – 2400 Normally D, E and F coal grades are available to Indian Industry. The chemical composition of coal has a strong influence on its combustibility. The properties of coal are broadly classified as 1. Physical properties 2. Chemical properties 1. Fuels and Combustion 6 Bureau of Energy Efficiency
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Physical Properties Heating Value: The heating value of coal varies from coal field to coal field. The typical GCVs for various coals are given in the Table 1.4. Analysis of Coal There are two methods: ultimate analysis and proximate analysis. The ultimate analysis determines all coal component elements, solid or gaseous and the proximate analysis deter- mines only the fixed carbon, volatile matter, moisture and ash percentages. The ultimate analysis is determined in a properly equipped laboratory by a skilled chemist, while proxi- mate analysis can be determined with a simple apparatus. It may be noted that proximate has no connection with the word “approximate”. Measurement of Moisture Determination of moisture is carried out by placing a sample of powdered raw coal of size 200- micron size in an uncovered crucible and it is placed in the oven kept at 108±2°C along with the lid. Then the sample is cooled to room temperature and weighed again. The loss in weight represents moisture. Measurement of Volatile Matter Fresh sample of crushed coal is weighed, placed in a covered crucible, and heated in a furnace at 900 ± 15°C. For the methodologies including that for carbon and ash, refer to IS 1350 part I:1984, part III, IV. The sample is cooled and weighed. Loss of weight represents moisture and volatile matter. The remainder is coke (fixed carbon and ash). Measurement of Carbon and Ash The cover from the crucible used in the last test is removed and the crucible is heated over the Bunsen burner until all the carbon is burned. The residue is weighed, which is the incombustible ash. The difference in weight from the previous weighing is the fixed carbon. In actual prac-
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