OIL FUEL IN SUGAR MILLS The sugar mill engineer's first and last thought is reliability. Every minute lost during the grinding season has a dollar sign prefixed to it. He spends eight to nine months each year getting ready for the three or four months' day and night period of rush. To be perfectly sure of his fuel supply, to know that, when needed, he can develop with his equipment his full rated boiler horse power and more; to see his fuel supply in storage before the season begins and to know that it will remain unchanged in quality, ready to use at a moment's notice; all this means more to him than any comparative evaporative figures, even more in some cases than comparative prices.
Every sugar mill engineer knows that to success fully burn his bagasse, it is necessary that it be cut up fine and well dried by a hot air blast; and even then, if fed too fast, the result is apt to be a partial failure, as it should be burned at a high rate of com bustion. The installation of a single oil burner in the bagasse furnace will enable this inferior fuel to be completely and rapidly burned, no special design of furnace being necessary to enable oil to be used with bagasse.
Sugar mills are often located in out of the way places, and it is difficult to deliver solid fuel, either due to excessive freight rates or on account of the general condition of the country. Oil fuel lends itself readily to these conditions as the delivery may be at points four or five miles from the mill, where an oil barge will fill up the storage tanks, which are con nected to the mill by pipe line.
When coal is used in sugar refineries, it is necessary to use the very best grade, since inferior grades of coal slack badly when stored; and, moreover, the freight is just as much for inferior coal as for the better grades. Hence the price per ton is usually high.
Another point which appeals to the sugar mill operator is the labor charge. He knows that good firemen are hard to obtain, especially when he can use them but three months in the year and cannot afford to retain them during the idle period. He is consequently forced to obtain new help for each season's grinding.
When using oil fuel, one man does the work of a dozen firemen, ash-handlers, unloaders, etc., and, moreover, he can usually arrange to keep this man the year around.
The ratio of oil used to tons of cane ground and manufactured into sugar depends upon the quality of the cane and the ability to run full load. In the Louisiana sugar district, where the cane has about 1o% fibre, they obtain about three pounds of juice to one pound of bagasse (with 75% extraction). As one pound of bagasse contains about 4,20o B.T.U., and as a boiler and grate efficiency of 55% is all that is obtainable, there will be available in the form of steam only about 2,300 B.T.U., which is not enough to work up the three pounds of juice.
A fair average for Louisiana sugar mills is about six to eight gallons of oil fuel per ton of cane ground and manufactured into sugar, when the entire amount of bagasse available is also burned.
In a well equipped and up-to-date Louisiana sugar house, the green bagasse, direct from crushing plant to the furnaces, furnishes in the neighborhood of two-thirds of the necessary fuel.
The internally fired boiler seems to give the best satisfaction and when set with a Dutch oven in front will develop on the average about 24 boiler horse power hours from the bagasse of one ton of cane at 75% mill extraction. The theoretical results which are given below are considerably higher.
One ton of Louisiana cane at 75 % mill extraction yields I5oo pounds of juice and 5oo pounds of bagasse. The latter contains about 420o B.T.U. per pound, of which 55 % is transmitted to the boiler water.
(4200 x 55%) x 500 = about 34 boiler horse power hours.
970.4 x34.5 or nearly boiler horse power per day of 24 hours.
While the above results have been obtained under exceptionally favorable conditions, they should not be given undue consideration, and are of value only in showing what has been accomplished. Like all other power installations, sugar mills are subject to many varying conditions, such as quality of the cane, weather, interrupted service, sudden demands for power, etc., all of which affect the economical opera tion of the plant as a whole.