BAGASSE AS FUEL 457 



Similarly, the temperature of combustion of bagasse with associated 

 water and with various quantities of excess air can be calculated. Certain 

 examples are tabulated below, referring to the typical dry bagasse with 

 45, 50, 55 per cent, of associated water. The specific heat of oxygen is taken 

 as 0-22. 



EXCESS AIR. 

 Water per cent. None. 50 per cent. 75 per cent. 100 per cent. 



bagasse. ^ Rise in temperature F. x^ 



45 3320 2430 2160 1940 



50 3020 2310 2000 1850 



55 2770 2140 1900 1720 



These calculations do not take into consideration unburnt fuel or losses 

 due to radiation. 



The temperature of combustion is a most important point in the economics 

 of bagasse firing. If caused either by an excess of air, by an insufficient 

 supply of air, or by an excess of water (inefficient mill work), the temperature 

 falls below a certain limit, products of distillation are formed which pass 

 through the furnace unburnt, and lower the quantity of heat which would 

 otherwise be afforded by the bagasse. Hence, the effect of sending to the 

 furnaces material containing only a little more than the normal quantity 

 of water may have an effect on the steam production quite out of all pro- 

 portion to a computation based on the heat required to evaporate the ad- 

 ditional quantity of associated water. Bolk 7 believes that the point at which 

 unburnt products distil over is where the bagasse contains 52 per cent, 

 or more of water. 



Steam Available from Bagasse. The subjoined table is calculated on the 

 following basis : each pound of water present in the flue gases, whether 

 associated water .or water formed on combustion, abstracts 1,250 B.T.U. : 

 each pound of gases, whether carbon dioxide, oxygen, or nitrogen, abstracts 

 100 B.T.U. 



These data correspond to external air at about 80 F. and to a flue gas 

 temperature of a little over 500 F. No allowance is made for radiation loss 

 or for unburnt fuel. The calculation is made for bagasse with 45, 50, 55 

 per cent, water, the dry matter being taken as having a heat of combustion 

 of 8,350 B.T.U. per Ib. The last column in the table gives the computed 

 Ibs. steam per ton of cane containing 10 per cent, fibre, and can be easily 

 converted to conform with any other fibre content. It is not to be overlooked 

 that when the bagasse contains 55 per cent, water there is only 40 per cent, 

 fibre, and hence 500 Ibs. bagasse per ton of cane. When the bagasse contains 

 45 per cent, water, there is 50 per cent, fibre, and only 400 Ibs. bagasse per 

 ton of cane. Accordingly, the quantities in the penultimate column ex- 

 pressing the computed Ibs. of steam per Ib. of bagasse are not directly pro- 

 portional to the steam available per ton of cane. The quantity of dry fuel 

 available remains the same, the heat afforded is the same, but more goes 

 away as steam in the flue gases in one case than in another. As has been 

 already remarked, however, with the higher percentages of water, there is 

 reason to believe that the combustion becomes more and more imperfect, 

 so that differences much greater than those indicated by the calculation 

 actually do occur. 



