Document 9JNMdwjdQEzM7pG2rZX1B75wV

HEATING VENTILATING AIR CONDITIONING GUIDE 1940 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 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 pound of coal, in the handling and storing properties, and in the burning characteristics. A description of the relationship between the qualities of coals and these characteristics requires considerable space; a treatment applicable to heating boilers is given in Bureau of Mines Bulletin No. 276. The classification of coals by rank involves several of the items indicated in a proximate analysis of the coal. This analysis determines the content of volatile matter, fixed carbon, ash and moisture. The calorific value and sulphur content are often reported with the proximate analysis. Volatile 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 traneous water in the fuel. Other important qualities of coals are the screen sizes, ash softening temperature, 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 materially 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 per cent of ash and moisture-free coal, in creasing amounts of oils and tars are released. For coals of higher volatile content, the relative quantity of oils and tars decreases, so it 166 3SfX!5(&tf't''"'' ' CHAPTER 9. COMBUSTION AND FUELS is low in the sub-bituminous coals and in lignite. The percentage of ash and its fusion temperature do not indicate how the ash is distributed or how much of it is less fusible lumps of slate of shale. ' 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 recognized 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 very little dust in handling. It is comparatively hard to ignite but it burns freely when well started. It is non-caking, it burns uniformly and smokelessly with a short flame, and it requires little 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 Bureau of Mines Report of Investigations No. 3283. Semi-anthracite has a higher volatile content than anthracite, it is not as hard and ignites somewhat more easily; otherwise its properties are similar to those of anthracite. Table 5. Classification of Coals by Rank* Legend: F.C. = Fixed Carbon. V.M. = Volatile Matter. Btu = British thermal units. Class Group Limits or Fixed Carbon or Btu Mineral-Matter-Fees Rabtb Requisite Physical Properties 1. Meta-anthracite 2. Anthracite 1. 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] Dry F.C., 86 per Cent or more and iees than 92 per cent (Dry V.M., 14 per cent or less and more than 8 per cent] Non-agglomerating6 II. Bituminous*^__ 1. Low volatile bituminous ___ 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 coal Dry F.C., 69 per cent or more and less than 78 per cent (Dry V.M., 31 per cent or less and more than 22 Der cent) 3. High volatile A bituminous Dry F.C., less than 69 per oent (Dry V.M., more than 31 per cent); and moist6 Btu, 14,000* or more 4. High volatile B bituminous <***1 Moist* Btu, 13,000 or more and law than 14,000* 5. High volatile C bituminous coal- Moist Btu, 11,000 or more and than 13,000* Esther agglomerating* or non-weathering/ III, 8ub-bituminous- 2. Sub-hitmninnnn R twl 3. Riib-hitnminrmfl C. vl Moist Btu, 11,000 or more and law than 13,000* Moist Btu, 9500 or more and I*** Both weathering and than 11,000* non-agglomerating* Moist Btu, 8300 or more and Ibbh than 9500* Moist Btu less than 8300 Moist Btu less than 8300 ,, ..... rSkT TJHiTSm?11*8 . i carl?n f,,Btu of the high-volatile bituminous and sub-bituminous EM ll.fc'Lt Staeml-SrleffeethBtu48 ^'"nt ^ "d""h"****" " >" *If agglomerating, classify in low-volatile group of the bituminous class, eurfa^of theUco!ierS t0 ^ containing its natural bed moisture but not including visible water on the *It is recognized that there may be non-caking varieties in each group of the bituminous class, according to " the dry' "^`-matter-free basis shall be classified three varieties of coal in the High-volatile C bituminous coal group, namely. Variety 1 aS non-WKtheringn'Wea hennB; Vanety 2- Sglomerating and weathering; Variety 3. non-agglomerating Phikddpto.fr0m A-S TM- Standar<is. 1937. Supplement, p. 145. American Society for Testing Materials. 167