Steam:
Its Generation and Use

___________________________ _____________ _________ _________________________________ _____________________________ __________ ____________ ever, where the engine is used for so short a time in each year, that the saving may not be sufficient to pay the interest on the additional cost, and a cheaper engine, even if comparatively wasteful, may be better economy. Compound engines, when high pressures can be obtained, have an advantage in economy over single cylinders, and even “triple” and “quad- ruple” expansion engines under some conditions show a saving oversimple ‘ ‘compound. ’ ’ But they require a pressure of from 100 to 200 lbs. and a comparatively steady load to develope their ad- vantages to a great degree. Such pressures can be safely carried on Babcock & Wilcox boilers. A large boiler is generally an advantage, but it is not economy to use a large engine to develop a small power. Sufficient steam to fill the cylin- der at the terminal pressure — each stroke — has to be furnished whether the engine is doing more or less work, and this frequently amounts to far more than the steam used to do the work. 1 hus, a 24 X 48 engine, making 60 revolutions per minute, without “cut-off,” uses 30 horse-power of steam in displacing the atmosphere, without exerting any available power. For the same reason back pressure greatly increases the cost of the power. “Most of the abuses connected with steam en- gineering have arisen from two causes — avarice and ignorance ; avarice on the part of men who are imbued with the idea that cheap boilers and engines are economical, and that these can be operated by a class of men who are willing to work for the lowest wages; ignorance on the part of those who claim to be engineers, butXvho at the best are mere starters and stoppers.”— J. H. Vail, Gen. Supt. Edison E.L. Co.,New York. Efficiency of Pumping Machines. Many engines, from the small “ donkey ” feed pump to the great water-works engine, are used exclusively for pumping water, and it is usual to reckon their “duty” by the water pumped, ex- pressed in millions of foot pounds for each 100 lbs. coal burned ; each million of duty represent- ing about 0.13 of one per cent, of the thermal value of the steam. The following table is based on one given by Chas. E. Emery, Ph. D., in the “ Report and Awards, Group XX, U. S. Cen- tennial Exposition OF PUMPING MACHINES. chimney draft, showed an average excess of air equal to 48 per cent, of the whole quantity. A series of 12 tests made by same with arti- ficial blast, gave an average excess of only 22 per cent, of the whole quantity, and in a few cases none at all, with only traces of carbonic oxide, showing perfect combustion. In a summary of experiments made in England, published in Bourne’s late large work, “Steam, Air and Gas Engines,” it is stated that: “A moderately thick and hot fire with rapid draft uniformly gave the best results.” “Combustion of black smoke by additional air was a loss.” “ In all experiments the highest result was always obtained when all the air was introduced through the fire bars.” “ Difference in mode of firing only, may pro- duce a difference of 13 per cent.” (in economy). Different fuels require different furnaces, and no one furnace or grate-bar is equally good for all fuels. The Babcock & Wilcox Co. provide with their boilers, a special furnace, adapted to the particular kind of fuel to be used. Efficiency of the Engine. A first-class boiler will deliver to the engine 75 per cent, of all the energy in the combustible, or say 10,875 out °f a total I4>5°° heat units, or, allowing about 8 per cent, for ashes, 10,000 heat units for each pound of coal burned. This rep- resents 7,720,000 foot pounds of energy, which, if all utilized by the engine, would give 3.90 horse- power for one hour, or at the rate of 0.26 lbs. coal for each hourly horse-power. But, by the greatest refinement in engines yet accomplished, the cost of a horse-power has not been brought below lbs. coal per hour, or 17 per cent, of the energy delivered by the boiler, while the average engine uses 3^ lbs. coal per horse- power, and discharges, unutilized, 93 per cent, of the energy delivered to it! I he greater p.u t of this loss is in the latent heat of the steam, which is exhausted into the atmosphere, or con- denser, and is unavoidable so far as now known. Still, the fact remains that many an ordinary en- gine uses four times as much steam for the same power as is required by the best engines. It is economy, therefore, in most cases, to use a high-class engine. There are instances, how- TABLE OF EFFICIENCY . __________________________ __________________________ _________________________________________________________ ______ _________________________________________ Description. Duty in Million Foot Pounds per no lbs. Coal. Per Centage of Ther- mal Value of Steam Used. Equivalent in Coal per Hourly Horse- power. 30 to IIO 15 to 3° 8 to 15 3 to IO 2 to 5 3.89 co 13.25 1.94 “ 3-Sg 1.04 “ 1.94 0-39 “ Mo 0.26 “ 0.65 6.68 to 1.95 13.4 “ 6.68 25.00 “ 13.40 66.6 “ 25.00 100 “ 66.60 ___________ ________ Pumping Engines.________________■. • • • • • • • v Steam pumps, large size, proportioned for work Steam pumps, small size, for ordinary uses______ Vacuum pumps___________.................................. Injectors, lifting water only...................