Document K67JkdX55egRORo4XEqJzrowo

328 CHAPTER 14 1955 G* value; it is clean to handle. It has a greater tendency than the sub-bituminoua coalg : to disintegrate as it dries, and it 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,:]^ charcoal. The lumps tend to break up in the fuel bed, and pieces of char falling inft the ashpit continue to burn. Very little smoke or soot is formed. icr.v Dustless Treatment In order to allay the dust, the more friable coals are sometimes sprayed with various petroleum products, a solution of calcium chloride, or a mii- ture of calcium and magnesium chlorides. * The coal is usually treated at the mine, but sometimes by the local dis tributor just before delivery. The salt solutions are sprayed under high Table 3. Standard Anthracite Specifications* Test Mesh Round Size of Coal Through In. Broken .................... Stove........................ Nut.......................... Pea............................ Buckwheat............ Barley...................... No. 4 .................. No. 5 . .............. 4% 3H to 3 2mMe Me Me Me Me Hs Me Oveb In. 3H to 3 2Me m lMe Me Me Me Hr OVEB8X2E Max- % _ 5 7mH 10 10 10 10 20 30 Undbhsizf Max. % Min. 9 15 1H 15 7M 15 7M 15 15 m m15 7tf 17 20 10 30 10 No limit Maximum Impurities Slateb % Boneb % or Ash* % 11 11 2 11 3 11 4 12 13 13 15 15 14 * Approved and adopted, effective July 28, 1947, by the Anthracite Committee (Manual of Statist!! Information, Anthracite Institute). b When slate content in the sizes from Broken to Nut inclusive is less than above standards, bone content may be increased by one and one-half times the decrease in the slate content under the allowable limits, out slate content specified above shall not be exceeded in any event. c Ash determinations are on a dry basis. . A tolerance of 1 percent is allowed on the maximum percentage of underaize and the maximum percents** of ash content. The maximum percentage of undersize is applicable only to anthracite as it is produced the preparation plant. > Slate is defined as any material which has less than 40 percent of fixed carbon. \ . Bone is defined as any material which ha^ 40 percent or more, but less than 75 percent of fixed carbon. pressure; using from 2 to 4 gal or from 5 to 10 lb of the salt per ton of coal, depending on its friability and size. Oil for-the dustless treatment of coal is also applied under high pressure, in concentrations of 1 to 8 qt per ton of coal, depending upon the characteristics of the coal and oil. Dustless treatments, which are of such a corrosive nature that they may damage coal handling or burning equipment, should not be used. Classification of Cokes Coke is produced by the distillation of the volatile matter from coal. The coke depends on the coal or mixture of coals used, the temperatures and time of di3*" lation and, to some extent, on the type of retort or oven. Coke is also produced as 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 percent volatile matter. High-temperature cok are subdivided into beehive coke of which comparatively little is now sold for dome3 use, by-product coke, which covers the greater part of the coke sold, and gas-house colaj The differences among these three cokes are relatively small: their denseness an hardness decrease and friability increases in the order named. In general, the light6* and more friable cokes ignite and burn more readily. Low-temperature cokes are produced at low coking temperatures, and only a Por*'1,< of the volatile matter is distilled off. Cokes, as made by various processes under yelopinent, have, contained from 10 to 15 percent volatile matter. In general, tu , cokes ignite and burn more readily than high-temperature cokes. The propert'66 various low-temperature cokes may differ more than those of the various high-tc**1 Fuels and Combustion 329 perature cokes because of the differences in the quantities of volatile matter, and because some may be light and others briquetted. Petroleum cokes, which are obtained by coking the residue left from the distillation of petroleum, 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 pieceB to protect the grates from being burned, COMBUSTION OF SOLID FUELS Firing Methods for Anthracite An anthracite fire should never be poked or disturbed, as this serves to bring ash to the surface of the fuel bed, where it may melt into clinker. Egg size is suitable for large fire-pots (grates 24 in. and oyer) if the fuel can be fired at least 16 in. deep. For best results this coal should be fired deeply. Stove is the proper size of anthracite for many boilers and furnaces. It bums well on grates at least 16 in. in diameter, on which it is fired about 12 in. deep. The fuel should be fired deeply and uniformly. Chestnut size coal is in demand for fire-pots up to 20 in. in diameter, and is usually fired to a depth of from 10 to 15 in. Pea size coal is often an economical fuel to bum. When fired carefully, pea coal can be burned on standard grates. Care should be taken to shake the grates only until the first bright coals begin to fall through the grates. The fuel bed, after a new fire has been built, should be increased in thickness by the addition of small charges until it is at least level with the sill of the fire-door. A satisfactory method of firing pea coal consists of drawing the red coals toward the front end, and piling fresh fuel toward the back of the firebox. Pea size coal requires a strong draft, and therefore the best results generally will be obtained by keeping the choke damper open, and regu lating solely by means of the cold air check and the air inlet damper. Buckwheat size coal, for best results, requires more attention than pea aize coal, and in addition the smaller size of the fuel makes it more difficult to bum on ordinary grates. Greater care must be taken in shaking the pates than with the pea coal on account of the danger of having fuel fall the grate. In house heating furnaces, the coal should be fired ar!^ ,more frequently than pea coal. When banking a buckwheat coal fire, it is advisable after coaling to expose a small spot of hot fire by putting a straight poker down through the bed of fresh coal. This will serve to ignite the gas that will be distilled from the fresh coal and prevent th t j "goition which, in some, cases, depending upon the thickness of f fresh coal, is severe enough to blow open the doors and dampers t,he (umace. Where frequent attention can be given and care exercised manipulation of the grates, this fuel can be burned satisfactorily without e aid of any special equipment, except small mesh grates. In general, it will be found more satisfactory with buckwheat coal to amtam a uniform heat output and, consequently, to keep the system jh,,rm,a ^le time, rather than to allow the system to cool off at times and form l a^emPf t burn the fuel at a high rate while wanning up. A uni form `iW ^re w'^ minimize the clinker formation and keep any clinker thro i,lnian easily broken up condition so that it readily can be shaken com/-' &rate. Forced draft and small mesh grates or, for greater venience, domestic stokers are frequently used. uckwheat anthracite No. 2, or rice size, is used principally in stokers