the American Institute of Electrical Engineers, New Yorh, March 21, 1893, President Sprague in the Chair. THE COST OF STEAM POWER PRODUCED WITH ENGINES OF DIFFERENT TYPES UNDER PRACTICAL CONDITIONS; WITH SUPPLEMENT RELATING TO WATER POWER. BY CHAS. E. EMERY, PH. D. 1. The paper of the writer on "The Cost of Steam Power," published in vol. xii, Trans. Am. Soc. C. E., November, 1883, seemed to supply information desired on the general subject by many engineers not practicing in that branch of the profession, and the writer has often been urged to modify the paper to suit more recent conditions. On investigation it appears that the original paper is still substantially correct for the particular purposes to which it was originally applied. It was designed to show the capitalized or present value of steam power in different units maintained forever. The cost of the power in pounds of coal was for the larger engines based on testimony taken relative to large sized condensing engines operating regularly at Fall River, Mass. This was distributed by judgment to the amount of water evaporated in the boilers per pound of coal and required by the engines per horse power, but such distribution evidently did not affect the final results. The prices of engines and boilers employed were higher than the ruling prices to-day, but these form a small percentage of the total capitalized values. The price of coal employed was also higher than the ruling prices in many localities at present, which directly affects the results, but it is evidently impossible to assume any price for coal which will apply to all locations. For these reasons it is believed that the table can still be employed with advantage by any one sufficiently familiar with the subject to make the necessary corrections for different conditions. 2. It has been decided at the present time, instead of revising the former tables, to compare the cost of developing a given amount of power with several of the different kinds of steam engines now in general use. A unit of 500 net horse-power has been selected for the purpose, though some of the comparisons are on the basis that several such plants are in the same station. In order to make the comparison at the same speed, it is assumed in all cases that the power is delivered at a speed of 250 to 350 revolutions per minute, corresponding to the jack-shaft speed of slow engines and the actual speed of high speed engines. 3. It will be attempted in this presentation to examine all the principal causes which affect the cost of steam power in engines of different types operated under practical conditions, but the substantial equalization of the cost of the power developed with engines of different types and different degrees of economy, when expenses independent of the coal consumed are considered, will necessarily form a prominent feature of the discussion, for the reason that such expenses have frequently been neglected or inadequately discussed, so that their very important bearing on the results is not generally understood. It will be shown that such additional expenses are fairly constant, independent of the type of engine, and that without considering interest or dividends they will in some cases equal the cost of coal. It will be seen, therefore, in comparing two engines both of which are good, so that one, for instance, will only effect a saving of coal compared to the other of, say, 124%, making the relative costs of fuel as 8 to 7, that, if additional costs equal to the former be added to both, the relative economies will be as 16 to 15, and the saving reduced to 61% simply by the summation of costs. If then we assume that all expenditures should pay 10% interest or dividends on capital invested, and 10% of the difference in first cost of the engines equals an amount which represents a saving of 61% of fuel, then the cost to the owner of the steam plant will be exactly the same in the two cases, since in one case he will pay in additional interest or dividends on the capital invested the same sum as he will pay for additional fuel if he uses the cheaper engine. 4. In general it will be found as in the above illustration that the mere cumulation of costs, other than for fuel or interest, has the greatest effect in reducing the percentage of saving due to a more economical consumption of fuel, and that a consideration of interest and dividends may simply neutralize or reverse percentages that were already made very small from the first named cause. 5. The original cost of the plant is evidently of great importance, where on one hand money is dear, or on the other coal is cheap or the work irregular. When the interest or dividend charges and others akin thereto are duly considered, it will readily be seen that the number of hours an engine operates in a year has a very important influence on the question of first cost, as such charges for a given steam machinery will be exactly the same whether the latter be operated one hour per day during part of the year, or 24 hours per day for the entire year, and the interest will also be the same whether the coal used cost $1.00 or $10.00 per ton. The saving in the total cost of coal consumed, either during the short hours or at the low price per ton, will evidently not be such as to warrant the adoption of high priced steam machinery. 6. It should be observed that various conditions in addition to those previously named operate to equalize the total cost of different kinds of steam machinery. For instance, with more economical engines smaller boilers are required, so the saving in the cost of the boilers partly compensates for the higher cost of the engines. Again, coal is at the present time cheap compared with former prices, and this is true also of steam engines of ordinary construction, which facts tend to maintain former conditions. On the contrary, steam machinery designed to secure economy, though lower than formerly, is still relatively high. It will be found that a consideration of all the facts available imposes very important conditions in relation to the selection of particular types of steam machinery for a particular duty and location. 7. Principally to obtain uniformity of expression we may preliminarily state, on a somewhat elementary basis, that steam engines at the present time may be divided into two general classes, distinguished as high speed and low speed engines, and though most low speed engines are operated at higher speeds than were employed years ago, there is still a definite distinction, although in many cases the gradations not only appear to reach, but perhaps cross each other. The high speed engines are best distinguished by the fact that they are of comparatively short stroke, and develop approximately the same piston speed as long stroke engines by an increased number of revolutions. 8. We have also simple, compound and triple compound engines of both the high and low speed types, and either of them may be horizontal or vertical. Most low speed engines of the power proposed are of the Corliss type, or at least have much the same general proportions, and some means of automatically cutting off the steam by the action of the governor to produce regulation of speed. There have been so many high speed engines brought out during late years of both the simple and compound type, and triple compound engines are being developed by so many builders, that it will be invidious to mention one name rather than another, though doubtless some engines possess advantages which others do not. In most high speed engines the steam is both distributed and cut off by a lap valve operated by a governor revolving with the main shaft, which acts to move the center of the eccentric in a line transverse to the crank at a distance from the center of the shaft equal to the lead. The effect is to modify the cut-off, substantially as with a link motion, by reducing the throw so that the angular motion required to move the valve through its double lap forms a greater or less proportion of the whole motion and therefore varies the angle of steam admission while the lead is maintained substantially uniform.1 9. Either of the above engines may also be operated with the steam escaping into the atmosphere or to a condenser, and in the latter case an air-pump may or may not be used. The first class of engines can no longer be distinguished as "high pressure engines." They are referred to herein as "non-condensing engines." Those of the second class are called "high pressure condensing, without vacuum," while the term "condensing engines" is a general one applied to those in which the steam is condensed and a vacuum formed. 10. Table I, submitted herewith, shows in detail the cost of one horse-power per year developed in engines of different kinds 1. While it is true that small high speed engines have been known for a long time, it is believed, and in relation to one of the principal forms it is known, that the present revival started with a discussion of the subject by the writer for a circular of the Novelty Iron Works about 1868, which, notwithstanding the closing of the works, was preserved to the profession by the late lamented Prof. W. P. Trowbridge, then Vice-President of the Company. See tables and Formula Relating to Non-Condensing Engines," W. P. Trowbridge. N. Y, 1870. The present general adoption of the fly wheel governor revolving with the main shaft is undoubtedly due largely to the late lamented J. C. Hoadley, when at Lawrence, Mass. His successors were Messrs. Armington & Sims. See p. 152, Report Judges Group XX., Cent. Exh. 1876. when operated for 10 hours per day for 308 days in the year and for 20 hours per day for every day in the year, with columns showing the results in each case for coal costing $2, $3, $4 and $5 per ton. The results are at first presented on the basis that the power required is comparatively steady so that no surplus machinery is required. A second presentation shows the results for electric light and other plants in case 50% surplus machinery be provided to supply the maximum power during certain portions of the day, and the power for the remainder of the day is sufficiently low to maintain the average. 11. In column b of Table I will be found the designation of the several types of engines compared, arranged by the amount of fuel required to produce one horse-power. Distinguishing letters are provided at the left in column a for convenience of reference. In general the kind of engine employed will be understood from the names at a glance. There are presented on different lines of the table, simple high and low speed engines, both condensing and non-condensing, compound high and low speed engines, both condensing and non-condensing, high speed triple compound engines, condensing and non-condensing. There are also three lines devoted to low speed condensing triple compound engines. Of these, line J shows the probable results with machinery designed to secure economy in construction rather than the highest economy of fuel. Line K refers to a low speed triple compound engine more expensively constructed, for which the economy is assumed lower than in the other case and for which the results are believed to be the best that can be secured under ordinary average practice even with the best machinery. There has, however, for comparison, been added another line, L, assumed to be operated at still lower economy by the use of boilers of unusual economy and careful attention to the details of operation, for which purpose $1 per day is added to the labor account. The results shown in this line are believed to be the maximum which can be obtained under the conditions of unusually good practice with the best care available. 12. It is assumed that the details and proportions of the different types of engines are of a kind which have proved reliable in practice, so that no large allowances are necessary for breakdowns or important repairs. 13. Column e shows the indicated horse-power required to produce 500 net horse-power. As previously stated the net power |