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Page 10
Some little time since a gentleman from a neighboring city called upon
me for information upon the subject of coverings in general and their
comparative values. Being an intelligent man he said frankly at the
outset that he knew very little on the subject. He had, however, in
common with all of us, heard the word "asbestos" used as a shibboleth
for years, but he desired definite knowledge, and after he had digested
the information he should act on his judgment. I devoted sufficient time
to him to put him in possession of the salient points of the subject.
His understanding was acute. He left me to seek elsewhere further light
upon this matter. After some few days he returned and directed that the
magnesia covering be applied to his work. In the course of conversation
he remarked that he had received great diversity of advice from those to
whom he had gone. One man, who had been years in the business of selling
steam plants, told him that the best thing for him to use was hair-felt,
even though the steam-pressure might run up to 125 pounds to the inch.
Now, as a matter-of-fact, the man who gave that advice simply showed
himself an unsafe guide; and from his inability to keep abreast with
modern knowledge, that he had no conception of the fire-hazard which his
advice was to thrust upon the innocent inquirer, and that his advice was
little short of being morally criminal.
The subject of the fire-hazard of organic coverings has been pretty
thoroughly investigated and can be pretty well-known, when there is any
inclination to get out of ruts which long years of travelling in has
deepened. How many fires (cause unknown?) have really originated from
the slow carbonizing of organic material on steam-pipes? It is but
recently that the hair-felt covering on the steam end of a Worthington
pumping-engine, within ten miles of us, not only burnt itself but
destroyed some thousands of dollars worth of walnut lagging. Cases of
the combustion of these organic coverings are numerous and are
well-known.
Few appreciate the great loss of heat from uncovered or imperfectly
covered pipes. Many have an indistinct impression that there may
possibly be some slight loss. But there is in many cases an absence of
knowledge upon this subject where it should be complete. The most
correct data available show that the radiation from uncovered two-inch
steam-pipe, with 60 pounds steam-pressure, is 391.83 kilo. centigrade
heat-units one foot one hour, or 21,739.78 kilos. of coal for 100 feet
per year of 300 days of 10 hours each; one kilo. equals 2,205 pounds.
Properly combining these figures we see that there are 23.97 tons of
coal lost by radiation from that uncovered pipe. If the coal costs $4
per ton, the radiation from this 100 feet of pipe will amount to $95.87.
From the same pipe covered with Wm. Berkefield's fossil meal
composition, 32/100-inch thick, the most powerful inorganic non-heat
conductor used as a covering at the time these investigations were made,
there was radiated 24,109 kilo. cent. heat-units one foot one hour, or
1,337.63 kilos. of coal for the year. This would be 1-474/1000 tons of
coal at $4 per ton, amounting to $5.89. Then $95.87 less $5.89 equals
$89.98, the saving effected by covering this pipe with William
Berkefield's fossil-meal composition 92/106 of an inch thick. Or, in
other words, the saving effected was over 93 per cent of the total
possible radiation, using a thickness of one inch this loss would be
reduced to $5.50.
From the same data we find (page 44) it stated that while the radiation
through 25 m.m. of Wm. Berkefield's fossil meal was 7.7 heat-units,
through 25 m.m. of carb. magnesia it was 6.7 heat-units, therefore the
proportions 7.7: 6.7 = $5.50: $4.80 gives us the coal value of heat lost
by radiation through the magnesia covering. To put this in another form:
From the running-foot of two-inch pipe uncovered the loss is 96 cents,
while, from the same pipe covered with the magnesia, the loss is less
than five cents; or a saving of over 91 cents per year. To accomplish
this saving the cost of the covering should be taken into account. This
was 27 cents. Therefore, the investment in the magnesia covering is paid
back in less than four months. The data which we have used were obtained
by the use of a calorimeter measuring the quantity of heat passing
through covering. The other possible method of arriving at this
knowledge would be to accurately measure the condensation of the steam.
In these experiments, owing to several reasons, it was not deemed
advisable to rely upon the second method. Recently, however, I have seen
in the _American Engineer_ of June 12, a report of the proceedings of
the Michigan Engineering Society containing a paper by Professor Cooley,
of Ann Arbor, Mich., in which he says:
"The benefits of covering steam-pipes to prevent radiation are
strikingly illustrated by the following example: The Thomson-Houston
electric-light plant in Ann Arbor has about 60 feet of seven-inch pipe
connecting the boilers with the engines and two large steam-drums above
the boilers: in March, 1887, the steam at the far end of this pipe was
tested to determine the amount of entrained water, the pipes and drums
at the time being uncovered. An average of nine experiments gave 31.01
per cent moisture. In June of the same year, after the pipes were
covered with magnesia sectional-coverings, the quality of the steam was
again tested, the average of five experiments giving 3.61 per cent
moisture; the tests were made by the same men from the same connections,
and in the same manner. The pipes and steam-drums in March were
subjected to a draught, which, of course, aided the condensation. Enough
water passed into the cylinders to retard the engines, producing a
disagreeable noise. In June the weather was warmer and the pipes and
steam-drums were well protected. The quality of steam at the boilers was
tested in June, and showed about three per cent moisture. Assuming that
100 incandescent horse-power were being developed at the time, and that
each horse-power required 30 pounds of steam; if the steam is assumed to
have 25 per cent entrained water due to condensation in the pipes and
connections, then 4,000 pounds steam will need be produced in the
boilers, or 1,000 pounds more than necessary. To produce this steam will
require about 125 pounds of good coal per hour, or 1,000 pounds per day
of eight hours. One-half ton per day at $3 per ton for 300 days, $450.
The actual cost of the covering put on complete probably did not exceed
$150."
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