« SebelumnyaLanjutkan »
centre of distribution at the rate of three pounds of coal per kilowatt, while the gas plant will deliver its current at the rate of one and one-half pounds of coal per kilowatt-hour to the same section. As concerns labor, we should run the gas substation for such periods only as when the cost per kilowatt-hour generated by the substation is cheaper than if the current were supplied from the steam station, which must necessarily run for twenty-four hours per day. The cables already installed are amply large to supply the current when the load-factor runs down to a point where it pays to shut off the gas station. Therefore the labor cost per kilowatt-hour on the gas station will not be more than on the main steam station and may be slightly less; however, we will call it the same. It will be seen that with an investment charge the same in either case, the fuel cost about two mills per kilowatt-hour in favor of the gas-engine plant, the labor cost the same, we shall be able to obtain all the advantages of a self-generating substation distribution without increasing the cost to generate a kilowatt-hour. I shall not attempt to
. dwell upon what these advantages are, but I am able to say that such as they are they are available when desirable. This is true because when the gas engine runs it takes less coal per kilowatt-hour than the main steam station does and it can be shut down when the load-factor is low, thus saving the labor charge. The standby losses in the producer are of a negligible quantity, so that in this respect, again, we are able to obtain results not possible with a steam substation.
In order to determine the exact periods at which it is profitable to shut down the gas-engine plant, an application can be made of the graphic comparison that I have devised for comparing the cost of operating various power plants (Figures 5 and 6). By application of this method, or any other method that may prove convenient, the cost per kilowatt-hour for each hour in the day under certain load conditions is obtained, and it is a simple matter to adjust the periods when the gas substation will run to suit. The case that I have cited is purely hypothetical, and undoubtedly the first steps in this direction will be made where the conditions are more extreme; especially will this lie the case where it is desired to reach centres of distribution at such distances from the main station plant as to make conductor
FIG. 5-Daily LOAD CHART-STEAM-ENGINE MAIN AND GAS-ENGINE
Capacity 1000 KW 8700 HOURS
36 Ccod perkhout
200otos - aten
Fig. 6-ANNUAL Cost of LABOR AND COAL, STEAM VERSUS GAS ENGINES
investment and conductor losses governing factors in the equation.
In conclusion, it seems that the conditions best suited to gas-engine operation are those of high load-factor, because it is in this respect that the gas engine is able to make its biggest saving and offset possibly liigh interest and depreciation charges because of its higher first cost. This can, of course, be determined for each instance by working out an equation in which all the elements are included.
DISCUSSION MR. FERGUSON: I should like to ask Mr. Lozier how much space would be occupied by a gas-engine substation of, say, 1000 kilowatts. Mr. Lozier suggests that it would be cheaper to use a gas substation than an electric substation. It has occurred to me, however, that, inasmuch as in our large cities, where the substations are ordinarily used, the substations are located in parts of the city where land and buildings are very expensive, the cost of the space occupied should enter into this discussion. His curves assume that the cost of space is the same whether the substation is gas or electric. As I understand it, the gas substation occupies considerably more space than the electric substation, therefore these costs should be considered. I notice he gives six pounds of coal per kilowatt-hour for the electric substation and one and one-half pounds for gas substation or generating station. In another case he shows three pounds for steam and one and one-half pounds for gas. I would ask him what would be the comparative figures with the cheapest grade of coal, costing somewhere in the neighborhood of $1.25 per ton, instead of high-grade coal at $3.00 per ton. I should like to know the number of pounds of coal per kilowatt-hour used by the gas substation, the coal having 8000 to 9000 B. t. u.
MR. P. O. KEILHOLTZ (Baltimore, Md.): Has Mr. Lozier made an analysis of the angle of variation of gas engines, or if the analysis has not been made, has it been determined? In other words, what is the coefficient of steadiness, in the terms of Professor Rankin, of the gas engine? We know what it is in the case of a steam engine.
MR. DECAMP: I ask if the by-products of producer gas are worth anything at all.
MR. GEORGE W. MARTIN (New York): I think the point made by Mr. Ferguson as to the amount of space occupied by gas engines is very important. In one of the substations being designed by the New York Edison Company eight 2000-kw rotaries are being installed, making 16,000 kilowatts in a station 50 by 100 feet. I doubt if an equivalent capacity of gas-engine units could be placed in the same space.
MR. E. F. McCabe: I ask how water gas compares with the other manufactured gas usually used—coal gas.
MR. HOWARD T. SANDS (Haverhill, Mass.): I ask Mr. Lozier, in the case of the San Francisco plant, where he states the ability of the engine to carry an overload of, I believe, thirtythree and one-third per cent for some hours, what percentage of efficiency of the engine is sacrificed to carry that overload ?
MR. LOZIER: In reply to Mr. Ferguson's inquiry regarding the space occupied by the substation plant, I purposely limited the size to 1000 kilowatts, so as to make it available for localities where real estate might be high. I do not advocate the use of gas engines for all substations, but I thought that possibly this method might prove of value to work out any given case, so as to see whether or not it would pay in such case to use gas engines in the substation. I believe that for this substation a plot of ground 50 by 100 feet would amply take care of 1000 kilowatts. I took the precaution to get the price on a two-mile cable to supply 1000 kilowatts, and found it would cost $80,000 for the cable alone.
The purpose of my paper is to show a method that will permit of all the factors bearing upon the case being put in an equation the result of which will determine whether gas engines are available for the case in hand.
As concerns the question of six pounds of coal for a 500-kw plant and three pounds of coal in the other case: Unless you are putting in a gas engine to take the place of a very inefficient steam plant, due to the low load-factor of a central lighting station, I am frank to confess that you have got to figure out the local conditions before you can state whether or not the gas engine will pay. Many stations are running on six pounds of coal per kilowatt-hour. In the case of the substation referred to I took the limit to which I thought we could safely go, namely,
three pounds of coal, for steam, because that is based on large waterside station of many thousands of kilowatts. As to the case of the station in which you use a low grade of steam coal
MR. FERGUSON: I want to know what the pounds of coal per kilowatt-hour would be in the case of the gas engine if you use the same kind of coal you would use in a large electric generating plant ; that is, the lowest grade of coal in the market.
MR. LOZIER: So far as getting the actual B. t. u. out of the coal is concerned, you can get the B. t. u. out of the coal better with the producer than with the steam boiler. As to the handling of the low-grade coal in the producer, I may refer you to Mr. Bibbins' paper, presented last night, in which he gave the different classes and mixtures of coal successfully used.
MR. FERGUSON : Can you answer more specifically as to what the pounds of coal per kilowatt-hour would be in your producer-gas plant if you used, instead of $3.00 coal, a very low grade of coal, so that we can put it on the same basis as a steam plant?
Mr. Lozier: If I reduced the B. t. u. in my coal from 13,000 to 9000, I should have to increase the coal consumption slightly more than 25 per cent; that is to say, I should run up to about one and three-fourths to two pounds of coal.
Mr. Keilholtz asked about the cyclic variation of gas engines. I shall have to be excused on that point.
Mr. DeCamp asked about the by-products of producer gas. There are no by-products; we eat them all up; everything goes into the gas except the ash.
Mr. McCabe's question was in regard to water gas and illuminating gas. Straight water gas has two functions; for heat work, and, when carbureted, for illuminating purposes. It is one of the best fuel gases known. Mr. Loomis worked out the combined water-gas and producer-gas proposition very nicely, and it is a very interesting case. Water gas is coming more and more into use. Straight water gas can not be used in gas engines, because of the high content of hydrogen.
Mr. Sands asked about the high efficiency of the San Francisco plant running at thirty-three and one-third per cent overload. I should imagine that the maximum efficiency of the