CHAPTEE XX. 



MEGASS AS FUEL. 



The battery of boilers and its connections form one of the most important 

 parts of any factory, and are of peculiar interest in a sugar works, in view of 

 the evaporation produced by the steam here generated, in addition to that 

 required to supply motive power for the engines ; efforts to economize steam 

 within the factory are in great part useless unless economy is also practised in 

 the combustion of the fuel. The subject of boilers, as such, is a special one 

 of its own, and its discussion is quite outside the limits of a work such as the 

 present ; only a few points of special interest in the sugar factory are here 

 mentioned. 



Boilers. In general boilers may be divided into a number of classes, 

 such as external and internal fired boilers ; the Lancashire, Cornish and 

 marine boilers fall into the latter class, and these are quite unsuited for use 

 with megass and other low grade fuels. All boilers used with such fuels are 

 externally fired, and are (in comparison with coal and fuel oil fired boilers) 

 provided with large external combustion chambers. 



The boilers in use in sugar factories are almost entirely of the multi- 

 tubular class, and these are divided into the smoke tube type, where the 

 heated gases circulate within the tubes, and the water tube where they pass 

 externally to the tubes. 



The Smoke Tube Multitubular. The smoke tube multitubular 

 boiler consists of a cylindrical shell of length usually not less than twice the 

 diameter; sizes 14ft. x 7ft., or 12ft. X 6ft are frequently met with. The 

 boilers erected at the Puunene Mill of the Hawaiian Commercial and Sugar 

 ompany are 20 ft. X 7 ft., and this size is commonly used in the Hawaiian 

 Islands ; so great a length is objected to by some engineers on the ground that 

 the part of the boiler remote from the furnace is very ineffective, but the 

 results in fuel economy in the Hawaiian Islands .are such as to leave no doubt 

 in the writer's opinion that such objections are ill-founded. 



In the end plates of the shell are drilled a number of holes into which 

 are expanded tubes, generally about four inches in diameter ; these tubes form 

 the greater part of the heating surface. A boiler seven feet in diameter will 

 have about 120 such tubes, and if fourteen feet long will have approximately 

 1,800 square feet of heating surface ; increasing the length to 20 feet will 

 give a heating surface of 2,600 square feet. 



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