PHILIPPINE COALS AS FUEL. 353 



centimeter (105 pounds per square inch) was maintained. The average 

 length of the tests was about seven hours. The plant, the apparatus used 

 and all conditions were preserved as nearly constant as possible. It was 

 my purpose to burn each coal with the maximum economy in this type 

 of furnace. For a Philippine coal a regular and uniform method of 

 firing is essential. It was found that the best method of firing was in 

 small quantities every four or five minutes. A thin fuel bed is also 

 needed and it must not be frequently worked. An entire test of seven 

 hours duration was made without once disturbing the fire. 



Inert matter in a coal is detrimental to its value in that the total 

 number of heat units is proportionally decreased. Moisture further 

 reduces the efficiency directly by the Sf)ecific heat of the water, but the 

 content of ash ordinarily found in Philippine coal has very little if any 

 further effect. It seldom produces clinlvcr and for this reason the 

 presence of sulphur is no detriment. Moreover the percentage of sulphur 

 in Philippine coal is usually extremely small. 



A short fire box, the usual vertical baffling and an ordinary bar grate 

 are not suited successfully to burn Philippine coal. An average of 9-| 

 per cent less of the theoretical heat xmits were absorbed by the boiler 

 when Philippine coal was consumed in the plant of this Bureau than 

 with the Australian coal ordinarily used and for which the plant was 

 selected and installed. The efficiencies recorded in Table II include 

 those of the boiler, fire box and grate. 



There is very little variation in the steam pressure and the amount of 

 water evaporated per hour. When a boiler with a satisfactory rate of 

 water circulation, absorbing surface, etc., has been used the deviation 

 from the maximum efficiency of a plant depends largely on the adapt- 

 ability of the furnace grate and stack. The economy is greatest with 

 those coals which have a high fuel ratio, bum completely and give 

 a high combustion chamber temperature. "With satisfactory absorption 

 the greater the difference between the temperature of the combustion 

 chamber, gases and the boiler, the greater the efficiency and the less the 

 loss to the stack. When Philippine coals are burned in an ordinary 

 furnace they are at a disadvantage as they tend to burn out of the range 

 of the boiler tubes with the result that there is low evaporation and high 

 chimney temperature. A longer fire box or an increased number of 

 baffle walls, or both, and a carefully selected grate would probably greatly 

 increase the efficiency of Philippine coals. If the number of baffle walls 

 is greatly increased, care must be exercised that there is sufficient draft. 



The tendency to burn out of the range of the boiler tubes which coals 

 high in volatile matter show, is aggravated by an excessive draft. The 

 greater the quantity of air drawn through the fuel bed, the more rapid 

 the combustion and the farther in the rear of the combustion chamber 

 it takes place. With a heavy draft the result is high chimney temperature 



