Oil Engines vs. Steam for Small Water Works
Efficiency of the Oil Engine as a Means of Motive Power for the Plant of Lesser Size—Some Instances of Waste—
Comparative Figures in Plants Using Steam and Oil
ECONOMY of operation is one of the important results aimed at by the superintendent of a water works plant, whether it be large or small, municipally operated or privately owned. This problem is of especial importance to the plant supplying a small city, whose funds are apt to be more restricted and the income of whose water works will be comparatively smaller. Any plan of operation, therefore, which will tend to assist the superintendent of such a system to save expense will be welcome. The suggestions which Mr. Prince makes in the following paper should be well studied by those who still cling to the use of steam as motive power for such small plants.
The primary object in presenting the subject of this paper is to arouse a discussion which ought to be helpful in determining the respective merits of fuel oil engines and steam engines when applied to small plants. It. might be contended that if steam is not as economical as oil as a heat agent in a combined electric and water plant, it certainly would become less economical when used only for pumping water. It is assumed that a considerable number of water works superintendents have to do with combined electric and water plants and are interested in the subject as to whether in operating small combined electric and water plants, fuel oil engines or steam engines should be chosen. By small plants, let us mean plants that supply electric current and pump water for communities less than 10,000 population.
The writer has been more and more impressed with the fact that many villages and small cities using steam power plants are not able to meet maintenance and operating expenses. In numbers of instances coming under our notice the town is not able to pay the coal bill, to say nothing of fixed charges and labor. Relief from this deplorable condition is in many instances being obtained through purchase of current for municipal purposes from transmission lines. To the writer it would seem decidedly advisable, under present conditions, that towns of less than 10,000 population should not install steam driven power plants.
Comparative Efficiency of Steam and Oil Drive
As a first step, let us consider simply the thermo dynamics of the question. These small power plants will use from seven to eight pounds of coal per KWH. If we assume a thermal value of coal as 10,000 thermal units, seven pounds will represent 70,000 heat units. One KWH is equal to 3393 heat units. It is therefore apparent that we would obtain a thermal efficiency represented by the expression 3393/70000 = .048. Compare this result with that obtained from oil drive. We will assume 8/10 pound of oil per KWH and 20,000 heat, units per pound of oil, we then have 3393/16000—.212 thermal efficiency, or over four times the steam efficiency. The latent heat, of steam is largely responsible for this great loss; in large plants, some of this latent energy is recovered, but in small plants, such as we have under consideration, very little of this 80 per cent, loss, represented by this latent, heat is recovered.
Use Coal Because Their Fathers Did
Like the fellow that votes the Democratic ticket because his grandfather voted for Andrew Jackson, so we continue to use water, which is one of the poorest heat agents, because Watt happened to utilize it. Our reason for this is doubtless owing to the fact that it is so generally distributed over the earth’s surface and hence generally available, though undoubtedly it will later be discarded altogether for a more scientific and efficient medium.
“The writer has been more and more impressed with the fact that many villages and small cities using steam power plants are not able to meet maintenance and operating expenses. In numbers of instances coming under our notice the town is not able to pay the coal bill, to say nothing of fixed charges and labor. To the writer it would seem decidedly advisable, under present conditions, that towns of less than 10,000 population should not install steam driven power plants.”
Americans are proverbially wasteful as compared with other peoples. About thirty years ago the writer was engaged in the employ of an Eastern firm in designing and installing gas producers in many large industrial plants such as Bethlehem, Pcncoyd, Cambria. Homestead, etc.
Some Instances of Waste
When travelling in connection with this business we often passed through the coke producing district of Pennsylvania and noticed the deplorable waste of monoxide gases that were emitted from their coke ovens. Years after, measures were adopted to utilize these gases and this criminal waste was largely eliminated along lines that had been in use in Germany for many years. The writer used to try to have parties in the Pittsburgh district shut off the natural gas wells that were allowed to waste the gas when not in use. Many Pennsylvania towns never turned off the gas lights from one year end to the other. In no other nation in the world would such prodigal waste be allowed.
As an instance of unwarranted waste at the present day that is permitted in this country, reference is made to an article in the issue of October 28, 1922, of the Literary Digest, based upon statements made by George Granger Brow n of the Chemical Engineering Department of the University of Michigan. It appears that the average performance of five million Ford cars in this country is estimated at 17 1/2 miles per gallon of gasoline. Tests made in New Jersey demonstrated that by improving the carburetor the performance of the machine can be increased 14 1/2 per cent. Professor Brown states that if this were done on all Ford machines, there would result a yearly saving of 400,000,000) gallons of gasoline, an amount exceeding one-fourth the total output of the country. In Europe, where gasoline is more expensive, machines are made to run ,35 to 60 miles on a gallon. Probably the cars there are considerably lighter than the Ford touring car, but this fact is broad enough to bear out the statement that America is wasteful of its natural resources.
As another instance of waste, in which America is not alone, is the continued use of the locomotive engine, which is one of the most inefficient machines in industrial life. The future will see this loss stopped, but until that times comes, the waste will go on.
A Case of Economy by the Use of Oil
In the same way st.eam engines have been installed in municipal power plants, which years ago were justified when coal was less than one-third of its present cost; today, in the opinion of the writer, it would be far better to discard the small steam plants which have been rendered obsolete by the high prices of coal and economy made possible by the development of fuel oil engines, which, as shown above, are four times more efficient than the steam engine using seven pounds of coal per KWH.
We have recently received a report from the engineer of a water works plant in a western city of 25,000 population. This plant was operated by steam prior to 1915, but in that year was changed over to a full Diesel plant. This letter states that when steamoperated, the plant consumed from 3400 to 4000 pounds of coal per million gallons of water pumped, and current was purchased at 3 1/2c per KWH.
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Oil Engines vs. Steam for Small Plants
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The engineer gives the operating expense as follows :
3804 pounds of coal at present prices in bin,
($9.35 per ton) ………………………. $17.78
Estimated cost of lubricating oil ……….. .50
Cost of 260 KWH at 3.5c……………… 9.10
Total cost per 1,000.000 gallons …….$27.38
Present cost, using fuel oil …………… 6.93
Saving, $20.45, equal to over 73 per cent.
We quote the following front the engineer’s report: “These oil engines have been in continuous use except during periods of overhauling since they were installed, and we consider them practically as good as new.” Since 1915 the above city installed two 520 h.p. oil engines for electrical purposes.
Some Other Cities That Found Oil Economical
A city in Texas having a population of approximately 3500 has in service a Diesel engine installed in 1915. During 1921 this engine operated 8629 hours (98.47 per cent) at an average cost for
Fuel per KWH of ………………….. $0.0059
Supplies, maintenance and lubrication…….0039
Total average cost per KWH for 680,193
KWH generated average output, 10.08
KWH, per gallon of fuel oil……….0146
The above figures of cost do not include interest and depreciation.
An Iowa town of 1248 population has two Diesel engines which were installed in 1917 and 1920. Operating costs per KWH for 1921 were as fol-
Fuel oil ……. 0060
Lubricating oil ……………………….0007
Total average cost per KWH for 563,685
KWH generated ………………….0155
The above figures do not include interest and depreciation.
A Kansas town of about 3500 population has three Diesel engines in service which were installed in 1915, 1917 and 1920. All expenses including interest, taxes and depreciation per KWH for 1921 amounted to $.0272, the fuel oil cost alone being $.0044.
A particularly interesting case is that of a Kansas town which formerly operated a steam plant. About eleven years ago steam was replaced by oil drive, coal at that time costing $1.95 in the bin. Later the city secured contracts with coal mines adjacent to the city limits for furnishing electric power for operating coal mining machinery, and additional oil engines were installed. At that time the cost of coal in the bin was $3.05 and the cost of oil was .04 1/4 Per gallon in tank lots.
We submit that it is a very significant fact that oil drive is used with which to mine coal. If coal operators find it cheaper to buy electric current generated by oil engines, it is difficult to understand how towns located at a distance can logically use steam power, having regard to the fact that the average small steam engine develops but five per cent, thermal efficiency and fuel oil engines from 21 to 33 per cent., dependent upon the load and type of engine employed.
Two More Comparative Cases
The writer recently reported on a water works property which is used to supply water to a city of 4,000 population. The water is first pumped from wells to a filter plant under a head of about 65 feet and then repumped into the city under a head of 200 feet. The average cost of coal during 1921 was $6.67 per ton and the cost for the year was $2,811. The yearly pumpage was 113,400,000 gallons, which indicates a fuel cost of 2 1/2c per 1000 gallons. In this instance water could have been pumped at a fuel cost of 1.2c per 1000 gallons.
“A Kansas town of about 3,500 population has three Diesel engines in service which were installed in 1915, 1917 and 1920. All expenses including interest, taxes and depreciation per KWH for 1921 amounted to $.0272, the fuel oil cost alone being $.0044.”
In a Western town in which the firm with which the writer is connected, installed a semi-Diesel pumping plant; water was pumped against a head of 250 feet at a fuel cost of lc per 1000 gallons, equal to 8/10c per KWH.
Many more instances could be cited where oil drive has repaced steam. Numbers of cases have come to the writer’s attention in which financial failure of power plants have been turned into paying investments by substituting oil engines in place of steam engines.
How an Iowa Plant Saved Money
We will add one more case which has come to our attention and this in a way of a quotation taken from a letter received from a city manager of an Iowa town.
“The municipal water plant was installed in 1883 and has been steam operated from that date until September 1, 1921, and using as the principal prime mover for the past twenty years a Laidlaw-Dunn Gordon Cross Compound, Condensing Pumping Engine of 1.5 million gallons capacity per 24 hours, using as an auxiliary a Worthington Tandem Compound, Non-Condensing Pump of the same capacity. These units are in good condition and the duty performance is, I believe, all that could be expected of (his type of equipment.
“On September 1. 1921, we installed a three stage, centrifugal pump of 800 GPM., direct connected to a 75 HP. 2300 volt, G. E. Induction motor, the steam equipment now being used as an auxiliary. We have not had occasion to use the steam equipment since the installation of the motor driven unit which will indicate the reliability of the present equipment.
“The municipal electric plant which was put in operation April 1, 1920, furnishes the current needed to pump the city water supply, is housed in the same building and the same attendants operate both plants. This arrangement has resulted in such a marked saving in pumping costs that viewed from a comparative basis of former operating conditions it might be said that the pumping now costs us nothing; the idea I mean to convey is: that with no greater fuel expenditure than was formerly necessary to pump the water supply by steam power, by the use of the Diesel engine and the installation of electrical equipment we are now pumping the water, furnishing current for the Boulevard Lighting System and selling service to the amount of nearly $1500 per month.
“This installation consists of one 250 BHP Diesel engine direct connected to a 225 KVA. generator and has furnished continuous 24 hour service since May 1, 1920, the only shut downs being for periods of about two hours each Sunday afternoon for the purpose of valve changing and general inspection. No expenditures have been made for repairs and no parts have been renewed by reason of breakage or wear. No adjustments of main bearings has been made, the alignment is practically undisturbed, but one adjustment of connecting rod bearings has been made. No trouble has been experienced from faulty lubrication, air injection or water cooling. Cooling jackets are practically free from scale. Fuel consumption has not exceeded the maker’s guaranty. Fuel used is 32/36 gravity gas oil, average cost during period of operation, 6 cents per gallon in the storage tanks at the station. No trouble has been experienced in obtaining an adequate supply of fuel oil. Fluctuation in price has not been sufficient to cause an unbalanced revenue return.”
Good Work by Wyoming Plant
In addition to the above, it might be well to refer to the pumping station at Casper, Wyoming, which is a city of about 20,000 population. One semi-Diesel engine of 200 HP. capacity supplied that, city with water without stand-by service for a period of over four years and during that time operated 135 days continuously, 24 hours per day without shutdown.
“Like the fellow that votes the Democratic ticket because his grandfather voted for Andrew Jackson, so we continue to use water, which is one of the poorest heat agents, because Watt happened to utilize it. Our reason for this is doubtless owing to the fact that it is so generally distributed over the earth’s surface and hence generally available, though undoubtedly it will later be discarded altogether for a more scientific and efficient medium.”
At the end of that time the engine was stopped for a period of a few hours in order to grind a valve and was again put in service and run for one hundred days at 24 hours per day.
At the end of four years this machine was supplemented by a second machine of the same type and capacity. The cost of renewing the first machine so that it was practically as good as new amounted to $150.
From the writer’s observation, it would appear that the fuel oil engine of today is a dependable machine as well as economical in service.
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Oil Engines vs. Steam for Small Plants
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Tabulated Data of Economical Results
We are adding some tabulated data ot economical results that can be obtained by the use of oil and steam_ engines. We have assumed towns of 1000. 2500, 5000 and 10,000 population being supplied with power for furnishing electric lighting and power, also pumping required water supply.
For 1,000 population we assume ………… 550
For 2,500 population we assume ………… 1800
For 5,000 population we assume ………… 3600
For 10,000 population we assume ………… 7500
These assumptions may be at considerable variance with special cases hut they are based upon our own observation and upon information from various sources. It is believed that unit costs will fairly represent average results.
In closing, the writer desires to state that he is not interested in oil engines other than from the stand-point of an engineer desiring to obtain the most economical results in the interest of his clients. Having been in charge of steam plants for over thirty years and in charge of two of the largest privately owned water plants in the country, viz: Omaha and Denver, we fully appreciate all advantages attached to steam power plants but we are bound to recognize the benefits accruing through improvements in the art of generating power and we affirm that it is our belief as before stated, that oil engines in their present state of development are far more economical in furnishing electrical power and pumping water for plants that serve communities of 10,000 people or less.
Tabulation showing approximate cost of power plants for towns of various sizes and operating expenses for steam and oil power plants.
The above Maintenance and Operating Expenses include labor, fuel and lubricating oil. repairs, 6 per cent, interest on investment, depreciation based on 4 per cent, sinking fund; life of oil engines assumed as 15 years, all other propert.y 25 years.
Price of coal $8 per ton for 1,000 and 2,500 population; hand firing. Evaporation, 6-1.
Price of coal $7.50 for 5,000 population; mechanical stokers. Evaporation, 8-1.
Price of coal $7 for 10,000 population, mechanical stokers.
Price of fuel oil, 6c. per gallon.
Price of lubricating oil, 60c. per gallon.
Excerpts from paper read before the annual convention of the Iowa Section of the American Water Works Association.
It is expected that a new election for the installation of a water works system will be held in Berne, Ind., within the next few weeks. A year ago the town voted for the water works by a substantial majority, but the attorney for the village discovered that the election was not legal in all respects and the bonds could not be issued unless another election was held. One reason for this was that there had not been proper legal advertising for the bond issue. The date for the election has not yet been determined.