Document G5ROX6N8rM9Gp2BK1LQGoggx

320 CHAPTER 14 1953 Guide a heat balance when required in testing of heating devices. Typical ulti mate analyses of the various kinds of coal are shown in Table 1.' Other important qualities of coals are the screen sizes, ash fusion tem perature, friability, caking tendency, and the qualities of the volatile matter. In considering these factors the following points are of interest. The volatile products given off by coals when they are heated differ mate rially in the ratios by weight of the gases to the oils and tars. No heavy oils or tars are given off by anthracite, and very small quantities are given off by semi-anthracite. As the volatile matter in the coal increases to as much as 40 percent.of ash and moisture-free coal, increasing amounts of oils and tars are released. For coals of higher volatile content, the relative quantity of oils and tars decreases and is therefore low in the sub-bituminous Table 1. Typical Ultimate Analyses fob Coals Btu per Lb CoNBirruKNTB, Pm Cent Rank Moist, Minenilmatter- free* Moist, as Received Oxygen drogen Carbon Nitrogen Sulfur' Ash OH- y- Anthracite___ ______ .. 14,600 12,910 5.0 2.9 80.0 0.9 0.7 10.5 87.9 Semi-Anthracite._______ 15,200 13,770 5.0 3.9 80.4 1.1 1.1 8.5 89.3 Low-Volatile Bituminous___ ___ 15,350 14,340 5.0 4.7 81.7 1.4 1.2 6.0 91.4 Medium-Volatile Bituminous_________ 15,200 13,840 5.0 , 5.0 79.0 1.4 1.5 8.1 89.0 High-Volatile Bituminous A_______ 14,500 13,090 9.2 5.3 73.2 1.5 2.0 -8.8 87.7 High-Volatile : Bituminous B..______ 13,500 12,130 13.8 5.5 68.0 1.4 2.1 9.2 87.3 High-Volatile Bituminous' C_______ 12,000 10,750 21.0 5.8 60.6 1.1 2.1 9.4 87.4 `Sub Bituminous B___ 10,250 9,150 29.5 6.2 52.5 1.0 1.0 9.8 88.2 Sub Bituminous C.____ 9,000 8,940 35.8 6.5 46.7 0.8 0.6 9.6 89.0 Lignite--........................... 7,500 6,900 44.0 6.9 40.1 0.7 1.0 7.3 91.0 (Btu as received) X 100 -i- (100 -- 1.1 Ash) coals and in lignite. The percentage of ash and its fusion temperature do not indicate the composition or distribution of its constituents. Classification of Coals A classification of coals is given in Table 2, and a brief description of the kinds of fuel is given in the following paragraphs, but it should be recog nized that there are no distinct lines of demarcation between the kinds, and that they graduate into each other. Anthracite is a clean, dense, hard coal which creates little dust in handling. It is comparatively hard to ignite, but it burns freely when well started. It is non-caking, it bums uniformly and smokelessly with a short flame, and it requires no attention to the fuel bed between firings. It is capable of giving a high efficiency in the common types of hand-fired furnaces. A tabulation of the quality of the various anthracite sizes will be found in a Bureau of Mines Report.3 Standard anthracite sizing specifi cations are shown in Table 3. Semi-anthracite has a higher volatile content than anthracite. It is not so hard, and ignites somewhat more easily. Otherwise their properties are similar. Semi-bituminous coal is soft and friable, and fines and dust are cheated by handling it. It ignites somewhat slowly and burns with a medium length of flame. Its caking properties increase as the volatile matter increases, but the coke formed is relatively weak. Having only half the volatile matter content of the bituminous coals, it can be burned with less production of smoke, and is sometimes called a smokeless coal. Fuels and Combustion 321 - The term'bituminous coal covers a large range of coals and includes many types bavin" distinctly different composition, properties, and burning characteristics. This coals range from the high-grade bituminous coals of the East to the poorer coals of the West. Their caking`properties range from coals which melt completely, to those from which the volatiles and tars are distilled without change of form, so that they are classed as non-caking or free-burning. Most bituminous coals are strong Table 2. Classification of Coals by Rank" Legend: F.C. = Filed Carbon. V.M. = Volatile Matter. Btu = British thermal units. Class Group Limits of Fixed Carbon or Btu Minebal-Matter- Free Basis Requisite Phtbical Properties I. Anthracite. II. Bituminous**. III Sub-bitumi nous IV. Lignitic....... 1. Meta-anthracite Dry F.C., 98 per cent or more (Dry V.M., 2 per cent or less) 2. Anthracite Dry F.C., 92 per cent or more and less than 98 \ per cent (Dry V.M., 8 per cent or less and more than 2 per cent) 3. Semi-anthracite........ Dry F.C., 86 per cent or more and less than 92 per cent (Dry V.M., 14 per cent or less and more than 8 per cent) 1. Low volatile bituminous ooal... Dry F.C., 78 per cent or more and less than 86 per cent (Dry V.M., 22 per ' cent or less and more than 14 per cent) 2. Medium volatile bituminous Dry F.C., 69 per cent or coal more and less than 78 per cent (Dry V.M., 31 per cent or less and more than 22 per cent) 3. High volatile A bituminous corn 4. High volatile B bituminous coal 5. High . volatile C bituminous Goal 1. Sub-bituminous A coal............. 2. Sub-bituminous B coal.............. Dry F.C., less than 69 per cent (Dry V.M , more than 31 per cent); and .moist* Btu, 14,000* or more Moist* Btu, 13,000 or more . and less than 14,000* Moist Btu, 11,000 or more and less than 13,000* Moist Btu, 11,000 or more and less than 13,000* Moist Btu, 9500 or more and less than 11,000* 3. Sub-bituminous C ooal. 1. Lignite......................... 2. Brown coal................... Moist Btu, 8300 or more and less than 9500* Moist Btu less than 8300 Moist Btu less than 8300 Non-agglomerating Either agglomerat ing or nonweathering^ Both weathering and non-agglomerat ing* Consolidated Unconsolidated This classification does not include a few coals which have unusual physical and chemical properties and which come within the limits of fixed carbon or Btu of the high-volatile bituminous and sub-bituminous ranks. All of these either contain less than 48 percent dry, mineral-matter-free fixed carbon, or have more than 15,500 moist, mineral-matter-free Btu. If agglomerating, classify in low-volatile group of the bituminous class. _ Moist Btu refers to coal containing its natural bed moisture but not including visible water oh the surface of the coal. d It is recognized that there may be non-caking varieties in each group o f the bituminous class. * Coals having 69 percent or more fixed carbon on the dry, mineral-matter-free basis shall be classified according to fixed carbon, regardless of Btu. There are three varieties of coal in the high-volatile C bituminous coalgroup, namely. Variety 1, agglom erating and non-weathering; Variety 2. agglomerating and weathering; Variety 3, non-agglomexating and non-weathering, Adapted from AJ3.T.M. Standards, 1937, Supplement, p. 145, American Society for Testing Materials. and non-friable enough to permit the screened sizes being delivered free from fines. In general, they ignite easily and burn freely; the length of flame varies with different coals, but it is long. Much smoke and soot are possible, if improperly fired, especially at low rates of burning. Sub-bituminous coals occur in the western states; they are high in moisture when mined and tend to break up as they dry or when exposed to the weather; they are la?v spontaneously when piled or stored. They ignite easily and quickly, and have a medium length flame; are non-caking and free-burning; the lumps tend to break into small pieces if poked; very little smoke and soot are formed. Lignite is of woody structure, very high in moisture as mined, and of low heating