Document rBVOjOa3x1RyKrj8M61m00Vov

Heating Ventilating Air Conditioning Guide 1939 air entering by each of the three intakes is reduced in the same proportion. I If the ashpit door is closed the air admitted through the ashpit is reduced } and increased through the other two intake openings. * Methods of control of draft conditions when burning oil or gas are ] noted in Chapter 11, Automatic Fuel Burning Equipment. ; CLASSIFICATION OF COALS I The complex composition of coal makes it difficult to classify it into \ clear-cut types. Its chemical composition is some indication but coals \ having the same chemical analysis may have distinctly different burning \ characteristics. Users are mainly interested in the available heat per *' Fig. 4. Correct and Incorrect Methods of Draft Regulation in a Hand-Fired Furnace 1 J pound of coal, in the handling and storing properties, and in the burning ; characteristics. A description of the relationship between the qualities f. of coals and these characteristics requires considerable space; a treatment l applicable to heating boilers is given in Bureau of Mines Bulletin 276. i The classification of coals by rank involves several of the items indicated i in a proximate analysis of the coal. This analysis determines tlie content 1 of volatile matter, fixed carbon, ash and moisture. The calorific value and sulphur content are often reported w;ith the proximate analysis. Volatile f matter is the loss of weight when the coal sample is heated to 1732 F for 7 min. Fixed carbon is the difference from 100 per cent of the sum of ; other losses, not including sulphur. Ash is the incombustible impurity in < the coal and has no heating value. . Moisture is the inherent and ex- j traneous water in the fuel. $ A classification of coals is given in Table 5, and a brief description of the | kinds of fuels is given in the following paragraphs, but it should be f recognized that there are no distinct lines of demarcation between the I kinds, and that they graduate into each other. | jjAnthracite is a clean, dense, hard coal which creates very little dust in handling. It is comparatively hard to ignite but it burns freely when well started. It is non-caking, 1 it burns uniformly and smokelessly with a short flame, and it requires little attention to j the fuel bed between firings. It is capable of giving a high efficiency in the common 1 172 1 Chapter Combustion and Fuels of hand-fired furnaces. A tabulation of the quality of the various anthracite t>. rpeVwm;j| be foouunnddlin Bureau oc f Mines Report of Investigations No. 3283. SIZeS ihracite has a higher volatile content than anthracite, it is not as hard and somewhat more easily; otherwise its properties are similar to those of anthracite, ignites ^ js soft ancj friable, and fines and dust are created by handling it. r*?*'* mew|,at slowly and burns with a medium length of flame. Its caking pro- k '^increase as the volatile matter increases, but the coke formed is relatively weak. Table 5. Classification of Coals by Rank5* Legend* FC. = Fixed Carbon. V.M. = Volatile Matter. Btu = British thermal units. Grou? Liuits of Fixed Carbon or Btu Mineral-Matter-Free Baris Requisite Phtbical Properties 1. Meta-anthracite.-------- 2. Anthracite----------------- |. Anthracite-------3. Semi-anthracite-. Dry F.C., 98 per cent or more (Dry V.M., 2 per cent or less) 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) Non-agglomerating* Dry F.C., 86 per cent or more and less than 92 per cent (Dry V.M., 14 per eent or tees and more than 8 per cent) II. Bituminous4-. 1. Low volatile bituminous coal... 2. Medium volatile bituminous coal 3. High volatile A bituminous coal.. 4. High volatile B bituminous coal.. 5. High volatile C bituminous coal.. Dry F.C., 78 per cent or more and Icbb than 86 per cent (Dry V.M,, 22 per cent or less and more than 14 per cent) Dry F.C., 69 per cent or more and less than 78 per cent (Dry V.M., 31 per cent or (ess and more than 22 per cent) Dnr 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* Either agglomerating* or non-weathering/ 1. Sub-bituminous A coal III. Sub-bituminous. 2. Sub-bituminous B coal 3. Sub-bituminous C coal Moist Btu, 11,000 or more and less than 13,000* Moist Btu 9500 or more and less than 11,000* Moist Btu 8300 or more and less than 9500* Both weathering and non-agglomerating* IV. Lignitic__ t. Lignite., 2. Brown coal.- Moist Btu less than 8300 Moist Btu less than 8300 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. AH of these coals either contain less than 48 per cent dry, mineral-matter-free fixed carbon or have more than 15,500 moist, mineral-matter-free Btu. *lf 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 on the surface of the coal. 4It is recognized that there may be non-caking varieties in each group of the bituminous class. Coals having 69 per cent 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 coal group, namely. Variety 1, a^*^mnrweaUierinn0D*Wea^er'nB' Variety 2. agglomerating and weathering; Variety 3, non-agglomerating Philadd^h^ ^rm ^ST.M. Standards, 1937, Supplement, p. 145, American Society for Testing Materials, Having only half the volatile matter content of the more abundant bituminous coals it can be burned with less production of smoke, and it is sometimes called smokeless coal. jj .-^ef^mbituminous coal covers a large range of coals and includes many types having frnfi*!!? udifferent composition, properties, and burning characteristics. The coals range the high-grade bituminous coals of the East to the poorer coals of the West. Their , " PrPerties range from coals which completely melt, to those from which the raHneS a* ^rs a^e distilled without change of form, so that they are classed as non- g or Iree-burning. Most bituminous coals are strong and non-friable enough to 173