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The meeting was called to order at ten o'clock on Thursday morning by President Williams, who said:
To encourage the fullest possible discussion, the executive. committee intended to have comparatively few papers this year, but looking over the programme you will find few if any papers or subjects that could well have been omitted. By common consent, each speaker will be limited to three minutes, unless in any instance a longer time be desirable.
We shall now listen to the paper entitled Gas Engines and Producers for Central Stations, by Mr. Robert T. Lozier, of New York. The paper will be illustrated by stereopticon.
GAS ENGINES AND PRODUCERS FOR
In presenting this subject I should like to consider it under two heads:
First-The fundamental principles upon which the gas engine and producer work.
Second-The application of this apparatus to central stations. The economy in fuel consumption is the main feature that recommends the gas engine for adoption.
The first reason why an internal-combustion engine is more economical than a steam prime mover is because, as its name implies, the carbon in the fuel is burned directly in the cylinder of the engine instead of in the fire-box of the boiler. Secondary reasons for the increased economy of gas-engine and producer plants lie in the facts that the stack losses are eliminated; the producer operating as a furnace is more economical than a steamboiler fire-box; the losses in the auxiliaries for cooling and cleaning the gas are very much less than exist in the auxiliaries of a steam plant; there are no losses in transmitting the gas, which is conveyed at atmospheric pressure and temperature, as against the radiation, condensation and leakage found in steam-transmission lines, and the stand-by losses of the producer when shut down are remarkably small.
At the risk of going over ground familiar to all, I might state that gas engines are, properly speaking, heat engines, just as much as are steam engines, in that they depend upon the first law of thermodynamics, namely, "Heat by expanding bodies is a source of mechanical energy." It is because we are able to introduce in the gas-engine cylinder a gas at atmospheric temperature and pressure, which upon ignition develops a so much higher temperature than is possible to transmit over a steam-pipe line, that we are able to develop such a large horse-power within such a small radiating surface. This is worked out by the application of the following formula:
in which T equals the total temperature range of the power medium, gas or steam, when acting upon the engine's piston taken from absolute zero, which is 460 degrees below Fahrenheit zero, and ranges up to the highest temperature developed by this medium in the heat engine cylinder. T, is the temperature at which this power medium exhausts.
So that if the gas mixture burns at 2500 degrees Fahrenheit, to which we add 460 degrees to get the total temperature range to absolute zero, we have a total absolute temperature developed by the power medium (gas) of 2960° = T. If this gas after burning exhausts at a temperature of 800 degrees Fahrenheit and this is added to 460 degrees, then the total absolute temperature of the exhaust will be 1260° T1; substituting these values for the above formula, we have
= 57.5 per cent thermal efficiency for the gas
Now for the steam engine. If we admit steam at 367 degrees (153 pounds gauge pressure) and add 460 degrees we obtain 827 degrees, the total absolute temperature developed in the steam-engine cylinder, equals T; and if we credit the engine with the lowest temperature of exhaust that is possible in practice, which we will assume to be 100 degrees Fahrenheit, this, plus 460 degrees, gives us 560 degrees as the absolute temperature of the exhaust. The steam-engine equation, therefore, would be
= 32.3 per cent thermal efficiency for the steam
From the foregoing it will be seen that the steam engine has inherently and under the best theoretical conditions but 56 per cent of the thermal efficiency of the gas engine-and in speaking of steam engines in this paper I include steam turbines as well. These efficiencies are theoretical and, besides, do not include the operating plant (boilers and producers), auxiliaries, and piping losses. Perhaps I may be pardoned if I stop to quote some authorities on best practices here and abroad to show what is actually being accomplished with both types of plants in centralstation operation.
H. G. Stott* gives an over-all thermal efficiency of 9.7 per cent for one of the best American central stations.
* American Institute of Electrical Engineers, Vol. XXV, No. 1.
H. M. Hobart* gives the logs of a large number of representative central stations in England developing between eighteen and forty-five million kilowatt-hours per year, from which an average of 7.2 per cent thermal efficiency is obtained. For the Continent of Europe, the average proves to be 8.3 per cent.
We have Paul Windsor's report on two 300-kw gas-engine units, running on a 70 per cent load-factor at Boston. In this report he charges the plant with all coal deliveries and credits it with the kilowatts output at the switchboard, so that he includes standby losses, charging losses, wastage, and so forth. For a long series of tests he gets an over-all thermal efficiency of something slightly in excess of 15 per cent.
James Atkinson,‡ of England, gives a thermal efficiency of 22.75 per cent for units of about 150 horse-power. The writer's experience in a careful test, including standby losses, on an 800-hp suction gas plant gave an over-all thermal efficiency of about 18 per cent. I think that this last is the correct over-all thermal efficiency to assume.
Two thousand, five hundred and sixty-four B. t. u. constitute the theoretical horse-power. Dividing that quantity by the various thermal efficiencies above cited, we get the total B. t. u. required to develop a horse-power. Dividing this total by the number of B. t. u. in a pound of coal, we get the number of pounds of coal required by each plant respectively to develop an electrical horse-power, so that we have:
Based on one pound of coal containing 13,000 B. t. u.
To bring the subject down more closely, I have assumed the following figures (see page 407) as the basis for a comparison that would apply to most central stations in this country.
*Electrical World, November 25, 1905.
Interurban Railway Association at Columbus, September, 1906.
The foregoing is based on coal of 13,000 B. t. u. per pound.
So much for the relative efficiency of the producer-gas engine with respect to other forms of heat engines.
If the economy of the engine is conceded, the question next arises as to the engine's reliability as concerns not only the stability of the mechanical parts but also the continued and uninterrupted service so far as the operation of the gas is concerned. A sufficient number of gas engines of both large and small size have been in operation to determine their reliable and continuous performance under the most trying conditions of service and running twenty-four hours a day without shut-down.
The United States Steel Corporation installed an experimental 500-hp plant at the Edgar Thompson Steel Works eighteen months ago and as a result of the performance of this engine finally decided to equip the entire plant with gas engines at Gary, Ind., having a total capacity of 56,000 horse-power. This same 500-hp experimental engine was afterward purchased by the Winchester Repeating Arms Company, whose large works are located at New Haven, Conn. It is one of four gas engines of a similar size and type that will be installed at that plant in connection with six smaller engines of the vertical type. After experimenting with gas engines operating on producer gas for a period of over seven years, this concern has become entirely convinced of their economy, reliability and stability, and when the plant is complete will abandon its steam engines entirely.
It is the general impression that the repairs on gas engines are greater than on steam engines. This in practice does not seem to be the case. I do not care to say that the repairs will