PRIME MOVERS AND POWER PLANT MACHINERY.
divided by 33.479 equals 195.6 b. hp. With a boiler efficiency of
65 per cent this would be 127.14 effective b. hp.
An average natural gas yields 22,200 B. t. u. to the pound.
About 22.2 cubic feet of natural gas weighs 1 pound, and 1,000 cubic
feet weighs about 45 pounds; therefore 1,000 cubic feet of natural
gas will produce 45 times 22,200 or 999,000 B. t. u.; 999,000 divided
by 33.479 equals 29.8 b. hp. With a boiler efficiency of 65 per cent
this would be 19.4 effective b. hp.
From the data given above, 1 ton of average coal is evidently
equivalent to 4.1 barrels of fuel oil or 27,000 feet of natural gas, and
1 barrel of fuel oil is equivalent to about 6,450 feet of natural
gas. From the same data, coal fed into the boiler at $5 a ton, in-
cluding all labor, is equivalent to oil delivered to the boiler at $1.22
a barrel, and gas delivered to the boiler at 18.5 cents a thousand feet.
Such comparisons, based solely upon the relative calorific values of
coal, oil, and natural gas, do not consider the greater efficiency of
oil as compared with coal, and of natural gas as compared with oil.
When the fuel value of barrels of fuel oil is compared with that of
tons of coal and feet of natural gas, the gravity of the oil should al-
ways be considered. Fuel oils produce practically the same B. t. u. per
pound, irrespective of their gravities; but the weight per barrel va-
ries with the gravity. For instance, a barrel of oil of 26 B. weighs
21.4 pounds less than one of 16 B.
One pound of average coal requires 11.6 pounds or 143 cubic feet
of air for combustion; 1 pound of fuel oil requires 14.9 pounds or
185 cubic feet; 1 pound of natural gas requires 17 pounds or 211
cubic feet; and 1 cubic foot of natural gas requires 9.4 cubic feet.
CAUSES AND EFFECTS OF HEAT LOSSES.
Boiler efficiency is the ratio of the heat in the steam delivered by
the boiler to the heat in the fuel. Furnace efficiency is the ratio of
the heat delivered to the boiler to the heat in the fuel.
With all types of fuel heat is lost and furnace efficiency reduced
by the burning of the carbon in the fuel to monoxide instead of di-
oxide, the escape of unburned hydrocarbons up the stack because of
insufficient air supply or combustion space, and the admission of too
much air which absorbs heat that would otherwise be absorbed by
the water or steam in the boiler.
Heat losses due to inefficiency of boiler heating surface include
those caused by boiler scale, which insulates the boiler tubes and
plates, retards heat absorption by the water and steam, and thus
makes the temperature of the flue gases too high; and losses due
George, H. C. Surface Machinery and Methods for Oil-Well Pumping. Washington D.C.. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc12407/. Accessed December 21, 2013.