The efficient use of fuel : a text book on fuels and their efficient utilization for the use of students and technical men in industry.

  • Great Britain. Ministry of Power.
Date:
1958
Catalogue details

Licence: Public Domain Mark

Credit: The efficient use of fuel : a text book on fuels and their efficient utilization for the use of students and technical men in industry. Source: Wellcome Collection.

    23/910 (page 9)
    from which air is excluded (see Chapter 30). Although moisture also is volatile and is expelled at the same time, the percentage of moisture is always recorded separately; volatile matter does not, therefore, include moisture. The volatile matter expelled consists of: (a2) water not originally present as either free or inherent moisture, but derived from the chemical decomposition of the coal and the shaly matter. (0) a complex mixture of combustible gases including hydrogen, methane, ethane, benzene, etc.; (c) tar, a complex mixture of hydrocarbons and other organic compounds, some of the latter, especially phenols, containing oxvgen in their chemical composition. Practically none of the volatile matter expelled from coal when heated existed as such in the original coal ; the substances composing it are chemi- cally formed as a result of disruption of the coal substance. The percentage of volatile matter expressed as a fraction of the dry, ash-free coal, or preferably expressed as a fraction of the dry, mineral-matter-free coal, is a valuable guide to the character of the coal and its probable suitability for use in industry. Calculation of Volatile Matter to dry mineral-matter-free basis Owing to the evolution, during the volatile matter test, of volatile con- stituents of some of the inorganic mineral matter in coal, the amount of volatile matter actually expelled during the test is usually greater than the amount of (organic) volatile matter derived from the coal substance. Accord- ingly the following corrections are applicable as deductions from the volatile matter figure of the proximate analysis, all constituents being expressed as percentages of the air-dried coal: (a) in cases where both pyritic sulphur and chlorine have been determined, 0-13 A+ 0-2 S,,,+0-7 CO,+0-6 Cl—0-20; (>) in cases where chlorine but not pyritic sulphur has been determined: 0-13 A+0-2 Sita +0°7 CO.+0-6 Cl—0-32; (c) in cases where neither pyritic sulphur nor chlorine has been determined, 0-13 A+0-2 Sita +0°7 CO,—0-13. The net amount of volatile matter, recalculated to the dry, mineral-matter- free basis is, of course, calculated by first applying the appropriate correction to the figure for V.M. on the air-dried basis and then es the corrected value thus obtained by 100/(100—moisture—M.M.), 1. VM __ (V.M.—correction) x 100. aeman-t —_ 100—moisture—M.M. PROXIMATE ANALYSIS Three ‘constituents’ of coal, namely moisture, volatile matter and ash, have been discussed. There remains for consideration a fourth term used in coal technology, fixed carbon. The procedure of determining the percentages of moisture in the coal sample, volatile matter, fixed carbon and ash is termed “proximate analysis’. The percentage of fixed carbon is not a figure determined by analysis in the laboratory; it is obtained by deducting from 100 the per- centages of moisture, volatile matter and ash obtained by analysis. The term fixed carbon is, therefore, virtually a hypothetical concept, derived purely arithmetically. Its use does not imply the existence of uncombined carbon in coal, nor does it bear any direct relationship to the total carbon in coal as. determined by an Ultimate Analysis (the procedure for which is discussed. below). There is probably, in fact, no free carbon in coal. In this context. therefore, fixed carbon cannot be considered as a precise constituent of coal.