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to do a certain piece of work and each gallon contains 140,000 B.t.u., 3,000,000 B.t.u. in all, it will take 3,000,000 B.t.u. in coal to do the same work, but the coal is cheaper. If oil were 5 cents a gallon, it would take coal at $10 a ton to equal the cost; so the reader will perhaps agree that this is not the proper method of comparing efficiencies, any more than saying that the cost of gasoline per gallon is the operating cost of running an automobile. The true way is to measure the efficiency of the furnace by the comparison of the input and output, and below are given results of some efficiency tests made for a well-known concern contemplating a revision of its furnace practice.
Powdered Coal-(Furnace using preheated air for combustion.)
Furnace cold at 60° F.
Steel and furnace heated to 2200° F.
Rise in temperature, 2140° F.
By test, 6.29 lb. of steel heated per pound of coal burned.
0.117 X 2140 250 B.t.u. per lb. of steel.
Fuel Oil-Same furnace with same rise in temperature and
the same charge of work.
Heated 8.68 lb. of steel per pound of oil.
1 lb. of oil 19,400 B.t.u. input.
Another furnace using fuel oil. (Not using preheated air.)
Charge of wrought iron, 2150 lbs.
Oil required, 22 gal.
2150 lb. X 113 B.t.u. = 242,950 B.t.u. output.
1 gal. oil 140,000 B.t.u.
140,000 B.t.u. X 22 = 3,080,000 B.t.u. input.
In making comparison as to the relative first costs and operating costs, let us assume a plant now using fuel oil with a consumption of 50,000 gallons of oil per month at a cost of 5 cents per gallon, delivered at the shop. (These estimates were made for the company already mentioned.)
(1) Fuel Oil:
Cost of equipment (storage tanks in place, auxiliary pressure
Contractor's profit (15%).
Engineering and contingencies (10%)..
(2) Powdered Coal:
Pulverizing machinery, house, foundations, trestle and track,
Contractor's profit (15%)...
Engineering and contingencies (10%)........
(2A) Fuel Oil for Small Furnaces:
Tank in place, auxiliary tank in place, piping and fittings,
Contractor's profit (15%).
Engineering and contingencies (10%)....
Powdered coal with fuel oil..
FUEL CONSUMPTION OF PLANTS
For the fuel-oil plant, at 50,000 gallons of oil per month and
140,000 B.t.u. per gallon, 7,000,000 B.t.u. are consumed per
If we allow 10 pounds of coal at 14,000 B.t.u., equal to 1 gallon of oil, we have 500,000 pounds or 250 tons of coal used per month, for the powdered-coal plant. In addition, this plant consumes about 8,000 gallons of oil, the difference being compensated for by coal required in drying the main fuel supply."
Powdered Coal Plant (Estimated cost, $97,000):
Fixed charges: Interest (5%)..
Taxes and insurance (1%).
Operation: Coal (250x2.50x12)
Labor (1 operator, 2 assistants)
Electricity for motors
Total yearly charge..
ADVANTAGES AND DISADVANTAGES OF LIQUID FUEL
From the foregoing it becomes evident that there are certain advantages which oil fuel has over coal when burned under boilers. These advantages may be summed up as follows:
(1) It is often found that it is desirable to push boilers far beyond their normal rating for a shorter or longer period of time. Tests that have been made by the United States Navy Department with fuel oil show that the heat absorptive powers of boilers. is very great, and that this pushing can be accomplished with only a small drop in efficiency. In their tests with fuel oil the evaporation per square foot of heat surface has been increased from three pounds of water from and at 212 degrees F. to fifteen pounds of 'water. During this increase in rating, which is 500 per cent of the normal rating, there was a loss in efficiency of only two per cent. Boilers can be pushed twice as rapidly with oil as they can with coal.
(2) The loss of heat up the stack is diminished owing to
the smaller amount of air necessary for the complete combustion of oil over its equivalent in coal.
(3) A more equal heat distribution in the combustion chamber is possible inasmuch as the fire box doors do not have to be open for firing and as a consequence there is higher efficiency.
(4) The cost of handling fuel is reduced because it is done mechanically by pumps when fuel oil is used and the reduction. in the number of firemen is in the proportion of five or six to one. (5) A large increase in steam capacity is possible. The grate area absolutely limits the amount of coal that can be burned efficiently, whereas the amount of oil that can be burned efficiently is not affected by the grate size. The output of boilers can be augmented by 30 to 50 per cent by substituting oil for coal.
(6) Fires can be started and stopped instantly as required, avoiding standby losses, and this required head of steam can be rapidly obtained from a cold boiler and can be maintained with the utmost regularity. No fuel is lost through banking.
(7) The storage tanks for fuel oil can be located where desired, while coal bins must be near the boilers.
(8) The life of the boilers is prolonged because in handfired coal furnaces a combination of stresses on the furnace plates occurs when the furnace doors are frequently opened.
(9) Fuel oil can be burned to smokeless combustion without sparks.
While fuel oil will undoubtedly effect the economies claimed for it, there are several disadvantages attendant on its use. These may be enumerated as follows:
(1) Fire risk is increased and city ordinances, while becoming less stringent, still look with disfavor on its use.
(2) Under certain conditions the vapor from fuel oil forms an explosive mixture with air.
(3) Nearly all fuel oil burners make an objectionable roaring sound.
(4) Auxiliary apparatus is necessary to start an oil fire or to maintain it, or both.
(5) Fuel oil has a tendency to leak through valves and joints in the system.
Mr. Lindon W. Bates, in a paper read before the New York section of the American Society of Mechanical Engineers, has the following to say regarding Colloidal Fuel:
Colloidal Fuel is a combination of liquid hydro-carbons with pulverized carbonaceous substances, the components so combined and so treated as to form a stable fuel capable of being atomized and burned in a furnace. It is made in three forms, a liquid, a gel and a mobile paste. The new composite is intended primarily to be used as fuel. While the designation "Colloidal" is given it because so much of the combination is in the colloidal state, the name is not scientifically adequate, since much of the solid component is not reduced to colloidal dimensions. The title is, however, descriptive because of the important colloid-like characteristics of the composite. It is liquid up to the ratios of oil sixty percent and coal forty percent or thereabouts. It is a mobile paste up to the ratio of oil twenty-five percent and coal seventyfive percent. All kinds of oils and solid carbons may be used The cheap coal breakages and wastes are all available. The liquid is used in the self-same way as oil fuel and with the same apparatus. The coal particles are maintained in a state of suspension in the oil during the time required for the use of the fuel -days, weeks or months. (See fig. 16.)a
It is of interest to read the results of a special study made Jan. 3, 1920, by Messrs. Dow and Smith, Chemical Engineers, of New York City, to confirm certain technical aspects of Colloidal Fuel Grade 15, a typical grade, containing 38% mixed coal and coke, in Mexican Reduced Oil, made in August, 1919, and shipped to the Imperial Japanese Navy in Japan:
"We have examined your sample of colloidal fuel to determine whether electrolites cause a precipitation of any of the suspended particles.
Oil News, Feb. 20, 1920. P. 26.