Bagasse is the fibrous portion of the sugar-cane left after the juice has been extracted. In the modern process of sugar manufacture, the cane is pressed so tightly that it is ready for fuel without further treating. Under favorable conditions it forms an excellent fuel. The pressed cane is a by-product which must in some way be got rid of.
It is usually fed into the furnace through an automatic hopper; or it may be dumped in the fire-room and fed into the furnace by hand. The furnace is constructed of brick, independent of the boilers; and when bagasse is consumed at a high temperature, the oxygen contained in it is nearly sufficient to satisfy the carbon and hydrogen, so that little air from the outside is required. Such material, of course, cannot be fed into an ordinary furnace.
Liquid Fuels. These consist of petroleum and its products, and their use has become quite extensive in the last few years. The field would undoubtedly be wider were there less difficulty in obtaining a regular and constant supply. The greatest quantities of petroleum oil are produced in the United States and Russia. Large quantities are found on the Pacific Coast, especially in Southern California; and in that section of the country, oil is used as fuel to a greater extent than in the East, being largely used on tugboats, ferryboats, and locomotives.
The following, approximately, is the composition of petroleum: Carbon 82 to 87 per cent.
Hydrogen 11 to 15 per cent.
Oxygen 6/10 to 6 per cent.
The theoretical heating power of petroleum is approximately 20,000 B. T. U. per pound, which is nearly half as much again as that of good coal. Oil has a further advantage over coal, in that no unburned fuel necessarily passes through the furnace, and there is no ash—an important item in marine work.
The composition and specific gravity of petroleums vary considerably, many of the lower grades being unsafe on account of their low flash-point.
The fuel is fed into the furnace through an atomizer operated either by steam or by compressed air. Several types of such devices are shown in Fig. 72. The use of the oil as a fuel can be readily controlled by the simple manipulation of a valve; and if the fire is once regulated to produce the required heat, it can be kept at that point with very little care.
The fire can be started with slight trouble, and can be extinguished instantly. The vaporizing efficiency of oil is much greater than that of coal; and on the Pacific Coast, where oil can be readily obtained, it is a much more economical fuel.
If burned properly, without too heavy an air-blast, there should be no production of smoke. A considerable saving may be effected in the fire-room force, one man being able to operate several burners. There is, of course, danger from explosion, on account of vapor which rises from the fuel; but if the fuel tank is thoroughly ventilated, there is little danger from this source.
Oil fuel may be used to advantage in what is called mixed firing; that is, the oil may be sprayed onto the bed of burning coal. This has been condemned by many engineers, but it has nevertheless gained considerable headway, and, under proper conditions, has given satisfactory results. It is beyond the scope of this work to go minutely into the subject of oil fuel; but for further information the student is referred to the reports of the Oil Fuel Boards of the U. S. Navy and of the British Admiralty.
Gas.Gas has many advantages over any other kind of fuel. There are four different varieties—natural gas, coal gas, water gas, and producer gas. Natural gas is used largely in the vicinity of Pittsburg, Buffalo, and some parts of Indiana, both for illuminating and for steam purposes. Where natural gas is plentiful, it is by far the cheapest fuel that can be used.
Coal gas, made by the distillation of coal, and water gas, obtained by the decomposition of steam by incandescent carbon, have been used both for lighting and for fuel; but in most cases these gases may be used to greater economy directly in the cylinder of a gas engine than as fuel under a steam boiler. The same may be said of producer gas, which is made by blowing steam and air through incandescent coal.
The relative values of these gases for evaporation, are shown in the following table: Evaporative Power of Gases