Document k6eV0LMjQq0oGmn7O4oK5Qn8O

American Society of Heating and Ventilating Engineers Guide, 1932 of Mines and the lower curves show the averages of the pounds of water evaporated per pound of coal under similar and normally good operating conditions. A brief description of the kinds of fuels is given in the following para graphs, 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 burns freely when well started.. It is non-caking, bums with a short flame, creates very little smoke, burns uniformly and the fuel beds , 250 Chapter 16--Fuels require little attention between firings. It is capable of giving a high efficiency in the common types of hand-fired furnaces. Semi-anthracite has a higher volatile content than anthracite, is not as hard and ignites somewhat more easily; otherwise its properties are similar to those of anthracite. Semi-bituminous coal is soft and friable, and fines and dust are created by handling. It ignites somewhat slowly and burns with a medium length of flame. Its caking prop erties increase' as the volatile matter increases, but the coke formed is relatively weak. Having only half the volatile matter-content of the more abundant bituminous coals it can be burned with less production of smoke, and is sometimes called smokeless coal. The term bituminous coal covers a large range of coals, and includes many types having distinctly different composition, properties and burning characteristics. The 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 completely melt, to those from which the volatile and tars are distilled without change of shape, so that they are classed as non caking or free-burning. Most bituminous coals are strong and non-friable enough to permit of the screens sizes being delivered free from fines. In general, they ignite easily, burn freely; the length of flame varies with different coals, but it is long. Much smoke and soot are possible and are difficult to reduce to reasonable amounts 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 liable to ignite 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 value; it is clean to handle. It has a greater tendency than the sub-bituminous coals to disintegrate as it dries, and also is more liable to spontaneous ignition. Freshly mined lignite, because of its high moisture, ignites slowly. It is non-caking. The char left after the moisture and volatile matter are driven off burns very easily, like charcoal. The lumps tend to break up in the fuel bed and pieces of char falling into the ash pit continue to burn. Very little smoke or soot is formed. Coke Coke is produced by the distillation of the volatile matter from coal. The type of coke depends on the coal, or mixture of coals used, the tem peratures and time of distillation and, to some extent, on the type of retort or oven; coke is also produced as a residue from the destructive distillation of oil. High-temperature cokes. Coke as usually available is of the high-temperature type, and contains between 1 and 2 per cent volatile matter. High-temperature cokes are sub divided into beehive coke of which comparatively little is now sold for domestic use, by product coke, which covers the greater part of the coke sold, and gas-house coke. The differences between these three cokes are relatively small; their denseness and hardness decrease and friability increases in the order named. In general, the lighter and more friable cokes ignite and burn the more easily. Low-temperature cokes are produced at lower coking temperatures, and only a portion of the volatile matter is distilled off. Cokes as made by various processes under develop ment have contained from 10 to 15 per cent volatile matter. In general, these cokes ignite and burn more readily than high-temperature cokes. The properties of various low-temperature cokes may differ more than various high-temperature cokes because of the differences in the quantities of volatile matter and because some may be light and others are briquetted. The sale of petroleum coke for domestic furnaces has been small and is generally confined to the Middle West. They vary in the amount of volatile matter they contain, but all have the common property of a very low ash content, which necessitates the use of refractory pieces to protect the grates from being burned. Air Required for Burning Solid Fuels In order to obtain perfect combustion a definite amount of air is re-quired for each pound of fuel fired. A deficiency of air supply will result 251