DETERMINATION OF THE MOST ECONOMICAL FUEL In every power plant the fuel bill is perhaps the largest single item of expense confronting the manager or superintendent.
In selecting a fuel which will be the most economical for any particular service, there are a number of points to be considered other than the comparative price per ton of coal, per barrel of oil or per i,000 cubic feet of gas, as the case may be. Some of the most important of these points are: Reliability of Supply.
Is the plant operation liable to suffer on account of a scarcity of fuel due to strikes, lack of cars, increased demand, cold weather, etc.? Will the supply of fuel be uniform in quality? Is it advisable to provide a large storage space and carry a supply of coal sufficient to tide over any possible scarcity, and, if so, what is the loss due to exposure? Is the company from which fuel is purchased in a position to carry out its contract? Operation.
Will the same careful attention to the fires be obtained with one fuel as with another, under all conditions of weather? What will be the comparative labor cost of handling each fuel? Is the elimination of smoke, dirt and storage space an item to be considered at this plant? Will a reduction in boiler stresses and a uniform steam pressure be productive of more economy of operation and maintenance? What fuel will most readily adapt itself to sudden demands for power? 'Money Value.
Giving due consideration to the existing equip ment and the peculiar requirements of the plant, what is the comparative money value of the several available fuels ? Barrels of Oil Equivalent to a Ton of Coal.
This is almost invariably the first question the prospective user of oil asks when contemplating a change from coal to oil, and it is a question often difficult to answer.
Coal varies in quality over a wide range, from the high priced anthracite and bituminous coals of the East to the low grade lignites of the Middle West, while the quality and heating value of the oil varies within narrow limits. Thus it would seem that the only fair comparison would be in actual test for a particular installation and coal.
This comparison of fuels under test conditions brings in another factor often overlooked but which will be self-evident to the engineer. When burning coal in the furnace of a boiler, the economical use of that fuel is dependent in a great measure on hard work, skill, and close attention to firing, on the part of the fireman. A lazy fireman, in order to save physi
cal exertion, can easily and does waste by improper firing, io to 20 per cent. of the coal fired, and when the conditions existing in the average boiler room (where coal is used as fuel) are considered, the desire to sidestep physical exertion cannot perhaps be wondered at.
When a boiler efficiency test is being run, however, how different things are; the very best firemen avail able are pressed into service, and are kept on the jump doing their utmost to keep the efficiency at a high and unnatural mark. When the test is over and the report on "the excellent work our boilers are doing" has been made, things fall back into the same old operating routine, and boiler efficiency becomes normally low again.
Compare the foregoing with the conditions existing in boiler rooms where oil fuel is used. No physical exertion is required, as in the case of firing coal, and the fireman becomes a boiler operator, with ample time to make oil burner and feed water adjustments and to watch closely the operation of the boiler plant, instead of being a coal and ash shoveler, with little or no time nor disposition to do anything more.
oil under boilers requires no exertion, physi cal or mental, on the part of the boiler operator, and as a result he can and will maintain his boiler efficiency at the same high mark month after month just as though he were running a continuous efficiency test.
In burning oil, test conditions are every-day con ditions. This cannot be said of coal. Hence the comparative test results are often misleading.
Knowing the average daily evaporation per pound of coal, and per pound of oil, as fired, which means as purchased, the comparison is readily obtained, as far as actual combustion is concerned. This does not take into account the many advantages of the liquid fuel outlined on page io.
Assume the average evaporation from and at 2 1 F. per pound of coal as fired to be 7 lbs., and for oil 15 lbs. (these figures will cover the average case) ; then the ratio of evaporation is as 7 is to 15 and the pounds of oil equivalent to 2000 lbs. of coal will be 7:15:: x or x = 933 lbs. ; which, divided by 314 lbs. per barrel equals 2.97 bbls. oil equivalent to one ton of coal.