MEGASS AS FUEL. 



This matter is one of great importance in furnace design, as a ratio of 

 grate area to heating surface which gives excellent results with the megass 

 from one variety of cane may be quite insufficient when the megass from 

 another variety is being stoked, although the total heat units available per ton 

 of cane may be identical in both instances. 



It must, however, not be overlooked that the quantity of fuel varies with 

 the percentage of fibre in the cane, and that this cause will often explain a 

 shortage of fuel ; the results summarized immediately above tend to explain 

 the state of an abundance of fuel and insufficiency of steam which most people 

 connected with a sugar factory must have experienced. 



Effect of Moisture on Thermal Value. The difference in the 

 thermal value of the same megass when the moisture varies from 48 per cent, 

 to 52 per cent, is not very great, but Bolk 6 has shown that at about the higher 

 limit the temperature of combustion is so lowered that decomposition 

 products distil over incompletely burnt, and with this incomplete combustion 

 very great heat losses occur. 



Heat Available from Megass. This calculation can best be 

 shown by worked out examples. 



Let the megass burnt contain 45 per cent, water and 55 per cent, dry 

 matter ; let the flue gases leave the boiler at a temperature of 550 F., the 

 temperature of the atmosphere being 84 F. ; let the air entering the furnace 

 be twice the theoretical amount necessary for combustion ; let the megass 

 contain 46-5 per cent, carbon, and 6 -5 per cent, hydrogen, calculated on dry 

 weight, or 25 '6 per cent, and 3'6 per cent, respectively, on actual weight. 



To raise 1 Ib. of water from 84 F. to 212 F. requires 128 B.T.TJ. ; to 

 convert this water into steam at 212 F. requires 966 B.T.U., and to heat this 

 steam at constant pressure to 550 F. requires (550 212) -48 = 162 B.T TL, 

 the specific heat of steam at constant pressure being '48. 



Each pound of water vapour in the flue gases then carries away 

 128 4- 966 4- 162 = 1256 B.T.TJ. The specific heats of carbon dioxide^ oxygen 

 and nitrogen are '22, -22, and -24, respectively, so that each pound of carbon 

 dioxide in the flue gases will carry away '22 (550 84) B.T.U., and similarly 

 for the oxygen and nitrogen. 



On combustion each pound of carbon gives 3*67 Ibs. of carbon dioxide, 

 and each pound of hydrogen 9 Ibs. of water. 



Per pound of megass the products of combustion are then 



Carbon dioxide -256 X 3'67 = '939 Ibs. 



Oxygen in excess air .. .. -256x2-67= '683 ,, 



Nitrogen -256 X 2 X 9-36 = 4-792 ,, 



Associated water '45 ,, 



Combined water -036 X 9 = -324 ,, 



413 



