DCCLXIV.* REDUCTION IN COST OF STEAM POWER FROM 1870 TO 1897. BY F. W. DEAN, BOSTON, MASS. In the year 1870 the most economical steam engine in use in mills was the Corliss simple condensing engine, which used nineteen or twenty pounds of steam per horse-power per hour. Previous to that time compound engines had been used in England in mill practice, and simple engines had in many cases been changed to compound. In this country compound pumping engines had been used to a very limited extent, notably the Worthington direct-acting tandem duplex compound, the first one of which was put in at the Charlestown, Mass., water works in 1863, and the installation of the Morris engine at Lowell and the Leavitt engine at Lynn are well-known examples of them in the early part of the period which we are considering. The Lowell engine was of the Simpson type, so named from the Simpsons, of London, who originated the arrangement of two compound cylinders with different lengths of strokes under one end of a beam. It is known as the Morris engine from Henry G. Morris, the builder, but its design is due to the late Robert Briggs, of Philadelphia. The Pawtucket pumping engine, built by George H. Corliss, and started on June 30, 1878, is another important example of economical pumping engines, and probably was the most economical steam engine which had been built up to that time, having used less than 14 pounds of dry steam per indicated horse-power per hour. While these engines are not mill engines, they influenced the practice of builders of mill engines, and can properly be considered with them. Pumping engines have heretofore been the Presented at the New York meeting (December, 1897) of the American Society of Mechanical Engineers, and forming part of Volume XIX. of the Transactions. leaders in economy, but at present the best pumping and mill engines are practically equally economical. Of course, the greatest single step in economy was the introduction of the compound engine. At the present time we may cite the Louisville pumping engine and several mill engines, one or more at Grosvenor Dale, Conn.; Natick, R. I.; West Boylston, Mass.; Berkley, R. I., and Lawrence, Mass., as being about on a par, and representing the best commercial economy. In 1873 the most economical compound engines used about 16 pounds of steam per indicated horse-power per hour, as shown by tests of the Lynn and Lawrence pumping engines, which then established new records for duty. Improvements in methods of using steam were made until it is now as easy to design an engine to use less than 13 pounds of feed water per horse-power per hour as it was to use as little as 16 pounds in 1875. At this date steam jackets were common, and were used in all engines which gave the most economical performances. The steps, however, that lowered the steam consumption of compound engines from 16 pounds to 14 pounds per indicated horsepower per hour were largely the introduction of a cut-off on the low-pressure cylinder and a reheating receiver between the cylinders. Although the reheater was invented by the late E. A. Cowper, of London, in 1862, so far as I know, it was first used in this country by E. D. Leavitt in his engines for the Calumet & Hecla Mining Co., and is regarded by him as one of the most important causes of the economy of his engines. These features appear to have been the principal means of lowering economy to 14 pounds of steam; but to what are we to attribute the step to 13 pounds? Clearance is well known to be an important factor, and its reduction, especially in the last cylinder of a series, is important for economy. It is receiving constant attention from careful designers, and its reduction is a constant source of gain. The 13-pound mark has also been reached by an increase in steam pressure with resulting increase in the number of expansions. In some cases a reduction in the size of the high-pressure cylinder has doubtless contributed toward economy, by means of which smaller surfaces are exposed to the boiler steam than would otherwise be the ease. This carries with it a pro portional reduction of initial condensation in the cylinder which is most prolific in this cause of waste. Still further, the 13-pound mark has, in general, been attained by engines which have a low-pressure cylinder larger for the work to be done than is commonly the case, so that the mean effective pressure referred to the low-pressure cylinder is in the vicinity of 21 pounds. There are occasional exceptions, as in the case of the Louisville engine, which worked with a mean effective pressure referred to the low-pressure cylinder of 25 pounds. Such cases are exceptional, and their economy can be attributed to great perfection of detail. It will in general be observed, however, whatever may be said of other causes, that most of the extreme cases of economy are those in which a good vacuum has been maintained. This leads me to say that the importance of good vacuums is often not appreciated, and that air pumps and condensers are as often too small. There is a strong tendency nowadays to underrate steam jackets, but I believe that in every case where they have been wasteful, or where their economy is indifferent, at all events with ordinary speeds, an examination would show that the jackets are air-bound, water-logged, blowing through traps, or that the jacket piping is bare, and thus steam for heating the building is charged to the engine. Such an arrangement of pipes can furnish but indifferent material for giving up latent heat to the working fluid within the cylinders, and is, in fact, absurd. The effect of reheaters in drying out steam which issues from a preceding cylinder and in superheating it to 60 degrees or 90 degrees, as is often the case, for use in the next cylinder, cannot be otherwise than advantageous, for, as Professor Thurston shows in his paper of 1894 before this Society, heat so added to the working fluid saves much more steam than was condensed to liberate this heat. While these considerations are very general, they are necessarily so, for nobody can attribute to any one of the features named its proper effect. Moreover, their combinations are very varied. Whatever may be said pro and con on this subject, it cannot be denied that the best results have been obtained from engines equipped with jackets and reheaters. Considering economies effected, it is safe to say that, without including triple-expansion engines, steam economy has steadily decreased from 20 pounds to 12 pounds per indicated horsepower between 1870 and 1897. This corresponds to a saving of 20-12 37 per cent. Within this period of twenty-seven years the use of exhaust steam has extended in various mills, such as cotton, woollen, and paper mills, so that in some mills the cost of steam power is next to nothing. Economies of this kind are not confined to the use of the exhaust of non-condensing engines, for since 1895 the writer's firm has had installed at the Washington Mills, Lawrence, Mass., a large surface-condensing vertical compound engine, the rejected heat of which is utilized. In this mill large quantities of warm water are used in the dye-house, which has heretofore been heated by exhaust and direct steam. Now the circulating water of the new engine is sent from the condenser to the dyehouse by the circulating pump at about the temperature required. In this case the rejected heat of the engine is just as effectively used up as it would be if the engine were non-condensing and sending its exhaust to the dye-house. There are advantages, moreover, in the compound surface-condensing engine, for there is less rejected heat to use, with consequent diminished chance for waste, and there is less heat lost by radiation from a pipe full of warm water than from one full of steam. This constitutes one of the latest forms of recent economies. It may be mentioned incidentally that by the surface-condensing engine, oil is kept out of the dye-house and away from the cloth. The air-pump discharge, being small in volume, and containing all of the cylinder oil, can be easily taken care of in any way which appears to be advantageous. What is there to be said concerning boilers within the period that we are considering? of The horizontal return tubular boiler is still the standard the country, and will probably so remain. It is cheap, and, if properly built, it is safe. As its tube-heating surface can be effectively blown with steam with the certainty that the jet will strike every part thereof, and as, furthermore, its tubes can be effectively scraped at any time without taking the boiler out of service, it must necessarily be more economical than any of the *By "standard" is meant the favorite and most commonly employed boiler. numerous water-tube boilers which are now being introduced. The fire surfaces of the latter can only be indifferently blown, and they cannot be scraped at all unless the boiler is cooled down, and in general it cannot then be done with anything approaching thoroughness. There is scarcely any improvement to be noted in the horizontal return tubular boiler during the last twenty-seven years as far as economy is concerned, but I believe that grates have been improved to a measurable extent, resulting in an economy of perhaps 2 per cent. My own experience teaches me that the internally fired boiler, either of the locomotive or vertical type, will save under equal conditions some 7 per cent. of coal compared with the horizontal return tubular boiler, besides causing an important economy in doing away with brickwork. Mr. Bryan Donkin, in a recent paper before the Institution of Civil Engineers, in discussing boiler economies, says: "Generally speaking, internally fired boilers give a higher efficiency than those externally fired. The old and well-known locomotive type, with smoke tubes and induced draught, stands high as a very economical steam generator." Such praise from so careful an investigator as Mr. Donkin should carry great weight. Within twenty-seven years economizers for heating feed water in smoke flues have become common. Although subject to a rather large depreciation, in the general case they will save about 7 or 8 per cent. of coal. There are economies to be obtained from the use of vertical engines. These come from reduction of friction, reduction of repairs to cylinders and pistons, and diminished cylinder oil consumption. It would not surprise me if there were a net saving of 5 per cent. by reduced friction of a vertical compound compared with a horizontal engine. Summing up the various items that have been mentioned, the following may be presented as the economies of the period from 1870 to 1897 : Saving due to compounding, jackets, reheaters, higher |