Composition and Calorific Value of Bagasse —The proportion of fiber contained in the cane and density of the juice are important factors in the relation the bagasse fuel will have to the total fuel necessary to generate the steam required in a mill’s operation. A cane rich in wood fiber produces more bagasse than a poor one and a thicker juice is subject to a higher degree of dilution than one not so rich.
Besides the percentage of bagasse in the cane, its physical condition has a bearing on its calorific value. The factors here entering are the age at which the cane must be cut, the locality in which it is grown, etc. From the analysis of any sample of bagasse its approximate calorific value may be calculated from the formula,
| B. t. u. per pound bagasse | = |
| ( 22 ) |
Where F = per cent of fiber in cane, S = per cent sucrose, G = per cent glucose, W = per cent water.
This formula gives the total available heat per pound of bagasse, that is, the heat generated per pound less the heat required to evaporate its moisture and superheat the steam thus formed to the temperature of the stack gases.
Three samples of bagasse in which the ash is assumed to be 3 per cent give from the formula:
| F = 50 | S and G = 4.5 | W = 42.5 | B. t. u. = 4183 | |||
| F = 40 | S and G = 6.0 | W = 51.0 | B. t. u. = 3351 | |||
| F = 33.3 | S and G = 7.0 | W = 56.7 | B. t. u. = 2797 |
A sample of Java bagasse having F = 46.5, S = 4.50, G = 0.5, W = 47.5 gives B. t. u. 3868.
These figures show that the dryer the bagasse is crushed, the higher the calorific value, though this is accompanied by a decrease in sucrose. The explanation lies in the fact that the presence of sucrose in an analysis is accompanied by a definite amount of water, and that the residual juice contains sufficient organic substance to evaporate the water present when a fuel is burned in a furnace. For example, assume the residual juice (100 per cent) to contain 12 per cent organic matter. From the constant in formula,