PHILIPPINE COALS AS FUEL. 341 



DISCUSSION". 



The data sustain the conclusions that the value of a coal for producing 

 steam in an ordinary boiler is determined not only by its fuel ratio and 

 by the total number of heat units set free during its complete combus- 

 tion, but it is also dependent largely upon other and variable factors. 



Im'purities in the coal. — The purity of the coal — that is, the admixtu.re 

 of earthy matter, moisture and other foreign material which it contains — 

 is an important consideration. If the percentage of ash and water is 

 small the theoretical heat value of the coal is proportionally increased 

 and from a. commercial standpoint the original cost of freight and han- 

 dling per thermal unit and the expense of removing the ash as well is 

 correspondingly decreased. These items represent a direct saving. More- 

 over, with coals high in moisture the efficiency is lowered directly by 

 the specific heat of the water. 



The color of the ash indicates the iron content and is also usually 

 taken as an indication as to whether or not the coal will clinker. How- 

 ever, iron is but one constituent and other factors enter in just as they 

 influence the fusion point of clay ^- or cement. As comparatively few 

 coals burn without forming clinker, it is interesting to note that in many 

 of the tests of Philippine coal, in particular the tests of the coal from 

 the military reservation, Batan Island, where the percentage of ash is 

 high and it is brick-red, very little clinker was produced. It is probable 

 that the ash bed in this non-coking, highly volatile coal is not heated 

 sufficiently high to form clinker. The distillation of volatile matter is 

 endothermic and therefore the explanation of the lack of clinker is 

 probably partly to be found in the fact that the distillation of this large 

 percentage of volatile matter keeps the temperature of the fuel bed low. 

 Furthermore, in a non-coking coal the lumps are thoroughly disintegi'ated 

 with the expulsion of the volatile matter and the ash kept cool by the 

 air and gases passing through and around its particles. If the same 

 ash were in a coking coal it would be held in the lump and probably be 

 heated hot enough on the grate and in the fuel bed to melt it and produce 

 clinker. 



It is believed that a reasonable amount of ash has little influence on 

 efficiency other than the amount of combustible carried away, except 

 where it interferes mechanically. If a coal clinkers and tends to close 

 the air spaces it greatly increases the labor in connection with its con- 

 sumption and entails a loss of heat through the furnace doors through 

 frequent opening to work the flres. On the other hand, although clinker 



" Cox, A. J. : The occurrence, eompoaition and radioactivity of the clays from 

 Luzon, P. I., This Journal, Sec. A. (1907), 2, 427. 



