KENNETH ALLEN, M. Am. Soc. C. E.--The speaker would like to know whether
anything has been done in the United States toward utilizing marsh mud
for fuel.
In an address by Mr. Edward Atkinson, before the New England Water Works
Association, in 1904, on the subject of “Bog Fuel,” he referred to its
extensive use in Sweden and elsewhere, and intimated that there was a
wide field for its use in America.
The percentage of combustible material in the mud of ordinary marsh
lands is very considerable, and there are enormous deposits readily
available; but it is hardly probable that its calorific value is
sufficiently high to render its general use at this time profitable.
As an example of the amount of organic matter which may remain stored in
these muds for many years, the speaker would mention a sample taken from
the bottom of a trench, which he had analyzed a few years ago. Although
taken from a depth of about 15 ft., much of the vegetable fiber remained
intact. The material proved to be 70¾% volatile.
Possibly before the existing available coal deposits are exhausted, the
exploitation of meadow muds for fuel may become profitable.
HENRY KREISINGER, Esq.[29] (by letter).--Mr. Wilson gives a brief
description of a long furnace and an outline of the research work which
is being done in it. It may be well to discuss somewhat more fully the
proposed investigations and point out the practical value of the
findings to which they may lead.
In general, the object is to study the process of combustion of coal.
When soft coal is burned in any furnace, part of the combustible is
driven off shortly after charging, and has to be burned in the space
between the fuel bed and the exit of the gases, which is called the
combustion space. There is enough evidence to show that, with a constant
air supply, the completeness of the combustion of the volatile
combustible depends on the length of time the latter stays within the
combustion space; but, with a constant rate of charging the coal, this
length of time depends directly on the extent of the combustion space.
Thus, if the volume of the volatile combustible evolved per second and
the admixed air is 40 cu. ft., and the extent of the combustion space is
80 cu. ft., the average time the gas will stay within the latter is 2
sec.; if the combustion space is 20 cu. ft., the average time the
mixture can stay in this space is only ½ sec., and its combustion will
be less complete than in the first case. Thus it is seen that the extent
of the combustion space of a furnace is an important factor in the
economic combustion of volatile coals. The specific object of the
investigations, thus far planned, is to determine the extent of the
combustion space required to attain practically complete combustion when
a given quantity of a given coal is burned under definite conditions.
With this object in view, the furnace has been provided with a
combustion space large enough for the highest volatile coals and for the
highest customary rate of combustion. To illustrate the application of
the data which will be obtained by these experiments, the following
queries are given:
Suppose it is required to design a furnace which will burn coal from a
certain Illinois mine at the rate of 1,000 lb. per hour, with a
resulting temperature of not less than 2,800° Fahr. How large a
combustion space is required to burn, with practical completeness, the
volatile combustible? What completeness of combustion can be attained,
if the combustion space is only three-fourths of the required extent? In
the present state of the knowledge of the process of combustion of coal,
these queries cannot be answered definitely. In the literature on
combustion one may find statements that the gases must be completely
burned before leaving the furnace or before they strike the cooling
surfaces of the boiler; but there is no definite information available
as to how long the gases must be kept in the furnace or how large the
combustion space must be in order to obtain practically complete
combustion. It is strange that so little is known of such an old art as
the combustion of coal.
The research work under consideration is fundamentally a problem in
physical chemistry, and, for that reason, has been assigned to a
committee consisting of the writer as Engineer, Dr. J. C. W. Frazer,
Chemist, and Dr. J. K. Clement, Physicist. The outcome of the
investigation may prove of extreme interest to mechanical and fuel
engineers, and to all who have anything to do with the burning of coal
or the construction of furnaces. In the experiments thus far planned the
following factors will be considered:
_Effect of the Nature of Coal on the Extent of Combustion Space
Required._--The steaming coals mined in different localities evolve
different volumes of volatile combustible, even when burned at the same
rate. The coal which analyzes 45% of volatile matter evolves a much
greater volume of gases and tar vapors than that analyzing only 15 per
cent. These evolved gases and tar vapors must be burned in the space.
Consequently, a furnace burning high volatile coal must have a much
larger combustion space than that burning coal low in volatile
combustible.
There is enough evidence to show that the extent of combustion space
required to burn the volatile combustible depends, not only on the
volume of the combustible mixture, but also on the chemical composition
of the volatile combustible. Thus the volatile combustible of low
volatile coal, when mixed with an equal volume of air, may require 1
sec. in the combustion space to burn practically to completeness, while
it may require 2 sec. to burn the same volume of the volatile
combustible of high volatile coal with the same completeness; so that
the extent of the combustion space required to burn various kinds of
coal may not be directly proportional to the volatile matter of the
coal.
_Effect of the Rate of Combustion on the Extent of Combustion Space
Required._--With the same coal, the volume of the volatile combustible
distilled from the fuel bed per unit of time varies as the rate of
combustion. Thus, when this rate is double that of the standard, the
volume of gases and tar vapors driven from the fuel is about doubled. To
this increased volume of volatile combustible, about double the volume
of air must be added, and, if the mixture is to be kept the same length
of time within the combustion space, the latter should be about twice as
large as for the standard rate of combustion. Thus the combustion space
required for complete combustion varies, not only with the nature of the
coal, but also with the rate of firing the fuel, which, of course, is
self-evident.
_Effect of Air Supply on the Extent of Combustion Space
Required._--Another factor which influences the extent of the combustion
space is the quantity of air mixed with the volatile combustible.
Perhaps, within certain limits, the combustion space may be decreased
when the supply of air is increased. However, any statement at present
is only speculation; the facts must be determined experimentally. One
fact is known, namely, that, in order to obtain higher temperatures of
the products of combustion, the air supply must be decreased.
_Effect of Rate of Heating of Coal on the Extent of Combustion Space
Required._--There is still another factor, a very important one, which,
with a given coal and any given air supply, will influence the extent of
the combustion space. This factor is the rate of heating of the coal
when feeding it into the furnace. The so-called “proximate” analysis of
coal is indeed only very approximate. When the analysis shows, say, 40%
of volatile matter and 45% of fixed carbon, it does not mean that the
coal is actually composed of so much volatile matter and so much fixed
carbon; it simply means that, under a certain rate of heating attained
by certain standard laboratory conditions, 40% of the coal has been
driven off as “volatile matter.” If the rate or method of heating were
different, the amount of volatile matter driven off would also be
different. Chemists state that it is difficult to obtain accurate checks
on “proximate” analysis. To illustrate this factor, further reference
may be made to the operation of the up-draft bituminous gas producers.
In the generator of such producers the tar vapors leave the freshly
fired fuel, pass through the wet scrubber, and are finally separated by
the tar extractor as a black, pasty substance in a semi-liquid state. If
this tar is subjected to the standard proximate analysis, it will be
shown that from 40 to 50% of it is fixed carbon, although it left the
gas generator as volatile matter. It is desired to emphasize the fact
that different rates of heating of high volatile coals will not only
drive off different percentages of volatile matter, but that the latter
itself varies greatly in chemical composition and physical properties as
regards inflammability and rapidity of combustion. Thus it may be said
that the extent of the combustion space required for the complete
oxidation of the volatile combustible depends on the method of charging
the fuel, that is, on how rapidly the fresh fuel is heated. If this
factor is given proper consideration, it may be possible to reduce very
materially the necessary space required for complete combustion.
_The Effect of the Rate of Mixing the Volatile Combustible and Air on
the Extent of the Combustion Space._--When studying the effects
discussed in the preceding paragraphs, the rate of mixing the volatile
combustible with the supply of air must be as constant as practicable.
At first, tests will be made with no special mixing devices, the mixing
will be accomplished entirely by the streams of air entering the furnace
at the stoker, and by natural diffusion. Although there appears to be
violent stirring of the gases above the fuel bed, the mixture of the
gases does not become homogeneous until they are about 10 or 15 ft. from
the stoker. The mixing caused by the air currents forced into the
furnace at the stoker is very distinct, and can be readily observed
through the peep-hole in the side wall of the Heine boiler, opposite the
long combustion chamber. This mixing is shown in Fig. 20. _A_ is a
current of air forced from the ash-pit directly upward through the fuel
bed; _B_ and _B_ are streams of air forced above the fuel bed through
numerous small openings at the furnace side of each hopper. Those
currents cause the gases to flow out of the furnace in two spirals, as
shown in Fig. 20. The velocity of rotation on the outside of the two
spirals appears to be about 10 ft. per sec., when the rate of combustion
is about 750 lb. of coal per hour. It is reasonable to expect that when
the rate of mixing is increased by building piers and other mixing
structures immediately back of the grate, the completeness of the
combustion will be effected in less time, and a smaller combustion space
will be required. Thus, the mixing structures may be an important factor
in the extent of the required combustion space.
To sum up, it can be said that the extent of the space required to
obtain a combustion which can be considered complete for all practical
purposes, depends on the following factors:
(_a_).--Nature of coal,
(_b_).--Rate of combustion,
(_c_).--Supply of air,
(_d_).--Rate of heating fuel,
(_e_).--Rate of mixing volatile combustible and air.
Just how much the extent of the combustion space required will be
influenced by these factors is the object of the experiments under
discussion.
_The Scope of the Experiments._--With this object in view, as explained
in the preceding paragraphs, the following series of experiments are
planned:
[Illustration: Fig. 20.
SECTION THROUGH STOKER SHOWING MIXING OF GASES
CAUSED BY CURRENTS OF AIR]
Six or eight typical coals are to be selected, each representing a
certain group of nearly the same chemical composition. Each series will
consist of several sets of tests, each set being run with all the
conditions constant except the one, the effect of which on the size of
the combustion space is to be investigated. Thus a set of four or five
tests will be made, varying in rate of combustion from 20 to 80 lb. of
coal per square foot of grate per hour, keeping the supply of air per
pound of combustible and the rate of heating constant. This set will
show the effect of the rate of combustion of the coal on the extent of
space required to obtain combustion which is practically complete. Other
variables, such as composition of coal, supply of air, and rate of
heating, remain constant.
Another set of four or five tests will be made with the same coal and at
the same rate of combustion, but the air supply will be different for
each test. This set of tests will be repeated for two or three different
rates of combustion. Thus each of these sets will give the effect of the
air supply on the extent of combustion space when the coal and rate of
combustion remain constant.
Still another set of tests should be made in which the time of heating
the coal when feeding it into the furnace will vary from 3 to 30 min. In
each of the tests of this set, the rate of combustion and the air supply
will be kept constant, and the set will be repeated for two or three
rates of combustion and two or three supplies of air. Each of these sets
of tests will give the effect of the rate of heating of fresh fuel on
the extent of combustion space required to burn the distilled volatile
combustible. These sets of experiments will require a modification in
the stoker mechanism, and, on that account, may be put off until all the
other tests on the other selected typical coals are completed. As the
investigation proceeds, enough may be learned so that the number of
tests in each series may be gradually reduced. After all the desirable
tests are made with the furnace as it stands, several kinds of mixing
structures will be built successively back of the stoker and tried, one
kind at a time, with a set of representative tests. Thus the
effectiveness of such mixing structures will be determined.
_Determining the Completeness of Combustion._--The completeness of
combustion in the successive cross-sections of the stream of gases is
determined mainly by the chemical analysis of samples of gases collected
through the openings at these respective cross-sections. The first of
these cross-sections at which gas samples are collected, passes through
the middle of the bridge wall; the others are placed at intervals of 5
ft. through the entire length of the furnace. Measurements of the
temperature of the gases, and direct observations of the length and
color of the flames and of any visible smoke will be also made through
the side peep-holes. These direct observations, together with the gas
analysis, will furnish enough data to determine the length of travel of
the combustible mixture to reach practically complete combustion.
In other words, these observations will determine the extent of the
combustion space for various kinds of coal when burned under certain
given conditions. Direct observations and the analysis of gases at
sections nearer the stoker than that at which the combustion is
practically complete, will show how the process of combustion approaches
its completion. This information will be of extreme value in determining
the effect of shortening the combustion space on the loss of heat due to
incomplete combustion.
_Method of Collecting Gas Samples._--The collection of gas samples is a
difficult problem in itself, when one considers that the temperature of
the gases, as they are in the furnace, ranges from 2,400° to 3,200°
Fahr.; consequently, the samples must be collected with water-cooled
tubes. Thus far, about 25 preliminary tests have been made. These tests
show that the composition of the gases at the cross-sections near the
stoker is not uniform, and that more than one sample must be taken from
each cross-section. It was decided to take 9 samples from the
cross-section immediately back of the stoker, and reduce the number in
the sections following, according to the uniformity of the gas
composition. Thus, about 35 simultaneous gas samples must be taken for
each test. The samples will be subjected, not only to the usual
determination of CO_{2}, O_{2} and CO, but to a complete analysis. It is
also realized that some of the carbon-hydrogen compounds which, at the
furnace temperature, exist as heavy gases, are condensed to liquids and
solids when cooled in the sampling tubes, where they settle and tend to
clog it. To neglect the presence of this form of the combustible would
introduce considerable error in the determination of the completeness of
combustion at any of the cross-sections. Therefore, special water-cooled
sampling tubes are constructed and equipped with filters which separate
the liquid and solid combustible from the gases. The contents of these
filters are then also subjected to complete analysis. To obtain
quantitative data, a measured quantity of gases must be drawn through
these filtering sampling tubes.
_The Measuring of Temperatures._--At present the only possible known
method of measuring the temperature of the furnace gases is by optical
and radiation pyrometers. Platinum thermo-couples are soon destroyed by
the corrosive action of the hot gases. The pyrometers used at present
are the Wanner optical pyrometer and the Fery radiation pyrometer.
_The Flow of Heat Through Furnace Walls._--An interesting side
investigation has developed, in the study of the loss of heat through
the furnace walls. In the description of this experimental furnace it
has been said that the side walls contained a 2-in. air space, which, in
the roof, was replaced with a 1-in. layer of asbestos. To determine the
relative resistance to heat flow of the air space and the asbestos
layer, 20 thermo-couples were embedded, in groups of four, to different
depths at three places in the side wall and at two places in the roof.
In the side wall, one of the thermo-couples of each group was placed in
the inner wall near the furnace surface; the second thermo-couple was
placed in the same wall, but near the surface facing the air space; the
third thermo-couple was placed in the outer wall near the inner surface;
and the fourth was placed near the outer surface in the outer wall. In
the roof the second and third thermo-couples were placed in the brick
near the surface on each side of the asbestos layer. These
thermo-couples have shown that the temperature drop across the 2-in. air
space was much less than that across the 1-in. layer of asbestos; in
fact, that it was considerably less than the temperature drop through
the same thickness of the brick wall.
The results obtained prove that, as far as heat insulation is concerned,
air spaces in furnace walls are undesirable. The heat is not conducted
through the air, but leaps across the space by radiation. In furnace
construction a solid wall is a better heat insulator than one of the
same total thickness containing an air space. If it is necessary to
build a furnace wall in two parts on account of unequal expansion, the
space between the two walls should be filled with some solid, cheap,
non-conducting materials, such as ash, sand, or crushed brick. A more
detailed account of these experiments may be found in a Bulletin of the
U.S. Geological Survey entitled “The Flow of Heat Through Furnace
Walls.”
WALTER O. SNELLING, Esq.[30] (by letter).--The work of the United States
Testing Station at Pittsburg has been set forth so fully by Mr. Wilson
that a further statement as to the results achieved may seem like
repetition. It would be most unlikely, however, that studies of such
variety should possess no other value than along the direct lines being
investigated. In the case of the Mine Accidents Division, at least, it
is certain that the indirect benefits of some of the studies have been
far-reaching, and are now proving of value in lines far removed from
those which were the primary object of the investigation. They are
developing facts which will be of great value to all engineers or
contractors engaged in tunneling or quarrying. As the writer’s
experience has been solely in connection with the chemical examination
of explosives, he will confine his discussion to this phase.
In studying the properties of various explosives, and in testing work to
separate those in which the danger of igniting explosive mixtures of
coal dust and air, or of fire-damp and air, is greatest, from those in
which this danger is least, much information has been collected. Mr.
Wilson has described many of the tests, and it can be readily seen that
in carrying out these and other tests on each of the explosives
submitted, a great many facts relating to the properties of explosive
compounds have been obtained, which were soon found to be of decided
value in directions other than the simple differentiation of explosives
which are safe from those which are unsafe in the presence of explosive
mixtures of fire-damp or coal dust.
The factors which determine the suitability of an explosive for work in
material of any particular physical characteristics depend on the
relationship of such properties as percussive force (or the initial blow
produced by the products of the decomposition of the explosive at the
moment of explosion), and the heaving force (or the continued pressure
produced by the products of the decomposition, after the initial blow at
the instant of detonation). Where an explosive has been used in coal or
rock of a certain degree of brittleness, and where the work of the
explosive with that particular coal is not thoroughly satisfactory, it
becomes evident that through the systematic use of the information
available at the Testing Station (and now in course of publication in
the form of bulletins), in regard to the relationship between percussive
and heaving forces in different explosives, as shown by the tests with
small lead blocks, the Trauzl test, and the ballistic pendulum, that
explosives can be selected which, possessing in modified form the
properties of the explosive not entirely satisfactory in that type of
coal or rock, would combine all the favorable properties of the first
explosive, together with such additional advantages as would come from
its added adaptation to the material in which it is to be used.
For example, if the explosive in use were found to have too great a
shattering effect on the coal, an examination of the small lead-block
test of this explosive, and a comparison of this with lead-block tests
of other explosives having practically the same strength, as shown by
the ballistic pendulum, will enable the mine manager to select from
those already on the Permissible List (and therefore vouched for in
regard to safety in the presence of gas and coal dust, when used in a
proper way), some explosive which will have the same strength, and yet
which, because of lessened percussive force or shattering effect, will
produce coal in the manner desired. If one takes the other extreme, and
considers a mine in which the product is used exclusively for the
preparation of coke (and therefore where shattering of the coal is in no
way a disadvantage), the mine superintendent’s interest will be
primarily to select an explosive which, as indicated by suitable
lead-block, Trauzl, and ballistic pendulum tests, will produce the
greatest amount of coal at the least cost.
As the cost of the explosive does not form any part of the tables
prepared by the Testing Station, the relative cost must be computed from
the manufacturer’s prices, but the results tabulated by the Station will
contain all the other data necessary to give the mine superintendent
(who cares to take the small amount of trouble necessary to familiarize
himself with the tables) all the information which is required to
compare the action of one explosive with that of any other explosive
tested.
In this way it is seen that, aside from the primary consideration of
safety in the presence of explosive mixtures of fire-damp and coal dust
(a condition alike fulfilled by all explosives admitted to the
Permissible List), the data prepared by the Testing Station also give
the information necessary to enable the discriminating mine manager to
select an explosive adapted to the particular physical qualities of the
coal at his mine, or to decide intelligently between two explosives of
the same cost on the basis of their actual energy content in the
particular form of the heaving or percussive force required in his work.
Up to the present time the investigations have been confined to
explosives used in coal mining, because the Act of Congress establishing
the Testing Station has thus limited its work. Accordingly, it is not
possible to compare, on the systematic basis just mentioned, the
explosives generally used in rock work. It is probable that, if the Bill
now before Congress in regard to the establishment of a Bureau of Mines
is passed, work of this character will be undertaken, and the tables of
explosives now prepared will be extended to cover all those intended for
general mining and quarrying use. Data of such character are
unobtainable to-day, and, as a result, a considerable percentage of
explosives now used in all mining operations is wasted, because of their
lack of adaptation to the materials being blasted. It is well known, for
example, that when an explosive of high percussive force is used in
excavating in a soft or easily compressed medium, a considerable
percentage of its force is wasted as heat energy, performing no other
function than the distortion and compression of the material in which it
is fired, without exerting either an appreciable cracking or fissuring
effect, or a heaving or throwing of the material.
Owing to lack of information in regard to the exact relationship between
the percussive and the heaving force in particular explosives, this
waste, as compared with the quantity required for the work with a
properly balanced material, will continue; but it is to be hoped that it
will soon be possible to give the mining and quarrying industries
suitable information in regard to the properties of the various
explosives, so that the railroad contractor and the metal miner may have
the same simple and exact means of discrimination between suitable and
unsuitable explosives that is now being provided for the benefit of the
coal miner.
Another of the important but indirect benefits of this work has been the
production of uniformity of strength and composition in explosives. An
example of this helpful influence is the standardization of detonating
caps and electric detonators. In the early days of the explosive
industry, it was apparently advantageous for each manufacturer to have a
separate system of trade nomenclature by which to designate the
strengths of the different detonators manufactured by him. The necessity
and even the advantage of such methods have long been outgrown, and yet,
until the past year, the explosive industry has had to labor under
conditions which made it almost impossible for the user of explosives to
compare, in cost or strength, detonators of different manufacturers; or
to select intelligently the detonator best suited to the explosive to be
used. After conference with the manufacturers of detonating caps and
electric detonators, a standard system of naming the strengths of these
products has been selected by the Testing Station, and has met with a
most hearty response. It is encouraging to note that, in recent trade
catalogues, detonators are named in such a way as to enable the user to
determine directly the strength of the contained charge, which is a
decided advantage to every user of explosives and also to manufacturers.
The uniformity of composition of explosives (and many difficulties in
mining work and many accidents have been rightly or wrongly attributed
to lack of uniformity) may be considered as settled in regard to all
those on the Permissible List. One of the conditions required of every
explosive on that list is that its composition must continue
substantially the same as the samples submitted originally for official
test. Up to the present, all explosives admitted to the Permissible List
have maintained their original composition, as determined by subsequent
analyses of samples selected from mines in which the explosive was in
use, and comparison with the original samples.
The data assembled by the Testing Station in regard to particular
explosives have also been of great benefit to the manufacturers. When
the explosives tests were commenced, comparatively few explosives were
being made in the United States for which it was even claimed by the
manufacturers that they were at all safe in the presence of explosive
mixtures of gas or coal dust. It was evident that, without systematic
tests, very little knowledge of the safety or lack of safety of any
particular explosive could ever be gained, and, consequently, the user
of explosives was apt to regard with incredulity any claim by the
manufacturer in regard to the qualities of safety. Owing to lack of
proof, this was most natural; and it was also evident that the very slow
process of testing, which was offered by a study of mine explosions
during past years, was sufficient only to prove the danger of black
powder, and not in any way to indicate the safety of any of the brands
of mining powder for which this property was claimed. Indeed, one of the
few explosives to which the name, “safety,” was attached, at the time
the Government experiments were first undertaken, was found to be
anything but safe when tested in the gallery, although there is no
reason to believe that the makers of this and other explosives claiming
“safety” for their product, did not have the fullest confidence in their
safety.
The Testing Station offered the first opportunity in the United States
to obtain facts in regard to the danger of any particular explosive in
the presence of explosive mixtures of gas or coal dust. With most
commendable energy, the manufacturers of explosives, noting the early
failures of their powders in the testing gallery, began at once to
modify them in such ways as suggested by the behavior of the explosives
when under test, and, in a short time, returned to the Testing Station
with improved products, able to stand the severe tests required. In this
way the Testing Station has been a most active agent in increasing the
general safety of explosives, and the manufacturers have shown clearly
that it never was their desire to offer inferior explosives to the
public, but that their failures in the past were due solely to lack of
information in regard to the action of explosives under the conditions
which exist before a mine disaster. The chance being offered to
duplicate, at the Testing Station, the conditions represented in a mine
in the presence of gas, they showed an eagerness to modify and improve
their explosives so as to enable them to answer severe mining
conditions, which is most commendable to American industry.
In regard to the unfavorable conditions existing in mines in the past,
the same arguments may be used. In spite of the frequency of mine
accidents in the United States, and in spite of the high death rate in
coal mining as compared with that in other countries, it must be said in
fairness that this has been the result of ignorance of the actual
conditions which produce mine explosions, rather than any willful
disregard of the known laws of safety by mine owners. Conditions in
American mines are far different from those obtaining in mines abroad,
and, as a result, the rules which years of experience had taught to
foreign colliery managers were not quickly applied to conditions
existing in American mines; but, as soon as the work at the Pittsburg
Station had demonstrated the explosibility of the coal dust from
adjoining mines, and had shown the very great safety of some explosives
as compared with others, there was at once a readiness on the part of
mine owners throughout the country to improve conditions in their mines,
and to take advantage of all the studies made by the Government, thus
showing clearly that the disasters of the past had been due to lack of
sufficient information rather that to any willful disregard of the value
of human lives.
Another of the indirect benefits of the work of the Station has resulted
from its examination of explosives for the Panama Canal. For several
years the Isthmian Canal Commission has been one of the largest users of
explosives in the world, and, in the purchase of the enormous quantities
required, it was found necessary to establish a system of careful
examination and inspection. This was done in order to insure the safety
of the explosives delivered on the Isthmus, and also to make certain
that the standards named in the contract were being maintained at all
times. With its established corps of chemists and engineers, it was
natural that this important work should be taken up by the Technologic
Branch of the United States Geological Survey, and, during the past
three years, many millions of pounds of dynamite have been inspected and
samples analyzed by the chemists connected with the Pittsburg Testing
Station, thus insuring the high standard of these materials.
One of the many ways in which this work for the Canal Commission has
proved of advantage is shown by the fact that, as a result of studies at
the Testing Station, electric detonators are being made to-day which, in
water-proof qualities, are greatly superior to any similar product. As
the improvements of these detonators were made by a member of the
testing staff, all the pecuniary advantages arising from them have gone
directly to the Government, which to-day is obtaining superior electric
detonators, and at a cost of about one-third of the price of the former
materials.
All the work of the Technologic Branch is being carried out along
eminently practical lines, and is far removed from such work as can be
taken up advantageously by private or by State agencies. The work of the
Mine Accidents Division was taken up primarily to reduce the number of
mine accidents, and to increase the general conditions of safety in
mining. As the work of this Division has progressed, it has been found
to be of great advantage to the miner and the mine owner, while the
ultimate results of the studies will be of still greater value to every
consumer of coal, as they will insure a continued supply of this
valuable product, and at a lower cost than if the present methods,
wasteful alike in lives and in coal, had been allowed to continue for
another decade.
A. BARTOCCINI, Assoc. M. Am. Soc. C. E. (by letter).--The writer made a
personal investigation of the mine disaster of Cherry, Ill. He
interviewed the men who escaped on the day of the accident, and also
several of those who were rescued one week later. He also interrogated
the superintendent and the engineer of the mine, and obtained all the
information asked for and also the plans of the mine showing the
progress of the work.
After a careful investigation the writer found that the following
conditions existed at the mine at the time of the disaster:
_First._--There were no means for extinguishing fires in the mine.
_Second._--There were no signal systems of any kind. Had the mine been
provided with electric signals and telephones, like some of the most
modern mines in the United States, the majority of the men could have
been saved, by getting into communication with the outside and working
in conjunction with the rescuers.
_Third._--The miners had never received instructions of how to behave
in case of fire.
_Fourth._--The main entries and stables were lighted with open
torches.
_Fifth._--The organization of the mine was defective in some way, for
at the time of the disaster orders came from every direction.
_Sixth._--The air shaft was used also as a hoisting shaft.
_Seventh._--The main shaft practically reached only to the second
vein; its extension to the third and deepest vein was not used.
_Eighth._--Plans of the workings of the second and third veins were
not up to date. The last survey recorded on them was that of June,
1909. This would have made rescue work almost impossible to men not
familiar with the mine.
_Ninth._--The inside survey of the mine was not connected with the
outside survey.
Would it not be possible for the United States Geological Survey to
enforce rules which would prevent the existence of conditions such as
those mentioned? The Survey is doing wonderful work, as shown by the
rescue of twenty miners at Cherry one week after the conflagration; but
there is no doubt that perhaps all the men could have been saved if
telephone communications with the outside had been established.
Telephone lines to resist any kind of a fire, can easily be installed,
and the expense is small, almost negligible when one considers the
enormous losses suffered by the mine owners and by the families of the
victims.
H. G. STOTT, M. Am. Soc. C. E.--The curves shown by Mr. Wilson give a
clear general idea of the relative efficiencies of steam and gas engines
when treated from a purely theoretical thermodynamic point of view. This
point of view, however, is only justified when small units having a
maximum brake horse-power not exceeding 1,000 are considered.
The steam engine or turbine operating under a gauge pressure of 200 lb.
per sq. in., and with 150° superheat, has a maximum temperature of 538°
Fahr. in its cylinder, while that of the gas engine varies between
2,000° and 3,000° Fahr.
The lubrication of a surface continually subjected to the latter
temperature would be impossible, so that water jackets on the cylinders
and, in the larger units, in the pistons become absolutely necessary. As
the cylinders increase in diameter, it is necessary, of course, to
increase their strength in proportion to their area, which, in turn, is
proportional to the square of the diameter. The cooling surface,
however, is only proportional to the circumference, or a single function
of the diameter. Increasing the strength in proportion to the square of
the diameter soon leads to difficulties, because of the fact that the
flow of heat through a metal is a comparatively slow process; the thick
walls of the cylinders on large engines cannot conduct the heat away
fast enough, and all sorts of strains are set up in the metal, due to
the enormous difference in temperature between the inside and the jacket
lining of the cylinder.
These conditions produce cut and cracked cylinders, with a natural
resultant of high maintenance and depreciation costs. These costs, in
some cases, have been so great, not only in the United States, but in
Europe and Africa, as to cause the complete abandonment of large gas
engine plants after a few years of attempted operation.
The first consideration in any power plant is that it shall be
thoroughly reliable in operation, and the second is that it shall be
economical, not only in operation, but in maintenance and depreciation.
Therefore, in using the comparative efficiency curves shown in Mr.
Wilson’s paper it should be kept in mind that the cost of power is not
only the fuel cost, but the fuel plus the maintenance and depreciation
charges, and that the latter items should not be taken from the first
year’s account, but as an average of at least five years.
The small gas engine is a very satisfactory apparatus when supplied with
good, clean gas, and when given proper attention, but great caution
should be used before investing in large units, until further
developments in the art take place, as conservation of capital is just
as important as conservation of coal.
B. W. DUNN, Esq.[31] (by letter.)--The growing importance of
investigations of explosives, with a view to increasing the consumer’s
knowledge of proper methods for handling and using them, is evident when
it is noted that the total production of explosives in the United States
has grown from less than 9,000,000 lb. in 1840 to about 215,000,000 lb.
in 1905. Table 5 has been compiled by the Bureau of Explosives of the
American Railway Association.
TABLE 5.--Manufacture of Explosives in the United States, 1909.
---------------------+-------------+------------------------------
Kind of explosives. | Number of | Maximum Capacity, in Pounds.
| factories. +--------------+---------------
| | Daily. | Annual.
---------------------+-------------+--------------+---------------
Black powder | 49 | 1,220,150 | 366,135,000
High explosives | 37 | 1,203,935 | 361,180,500
Smokeless powders | 5 | 75,686 | 22,705,800
---------------------+-------------+--------------+---------------
The first problem presented by this phenomenal increase relates to the
safe transportation of this material from the factories to points of
consumption. A package of explosives may make many journeys through
densely populated centers, and rest temporarily in many widely separated
storehouses before it reaches its final destination. A comprehensive
view of the entire railway mileage of the United States would show at
any instant about 5,000 cars partially or completely loaded with
explosives. More than 1,200 storage magazines are listed by the Bureau
of Explosives as sources of shipments of explosives by rail.
The increase in the demand for explosives has not been due entirely to
the increase in mining operations. The civil engineer has been expanding
his use of them until now carloads of dynamite, used on the Isthmus of
Panama in a single blast, bring to the steam shovels as much as 75,000
cu. yd. of material, the dislodgment of which by manual labor would have
required days of time and hundreds of men. Without the assistance of
explosives, the construction of subways and the driving of tunnels would
be impracticable. Even the farmer has awakened to the value of this
concentrated source of power, and he uses it for the cheap and effective
uprooting of large stumps over extended areas in Oregon, while an entire
acre of subsoil in South Carolina, too refractory for the plow, is
broken up and made available for successful cultivation by one explosion
of a series of well-placed charges of dynamite. It has also been found
by experience that a few cents’ worth of explosive will be as effective
as a dollar’s worth of manual labor in preparing holes for transplanting
trees.
The use of explosives in war and in preparation for war is now almost a
negligible quantity when compared with the general demand from peaceful
industries. With the completion of the Panama Canal, it is estimated
that the Government will have used in that work alone more explosives
than have been expended in all the battles of history.
Until a few years ago little interest was manifested by the public in
safeguarding the manufacture, transportation, storage, and use of
explosives. Anyone possessing the necessary degree of ignorance, or
rashness, was free to engage in their manufacture with incomplete
equipment; they were transported by many railroads without any special
precautions; the location of magazines in the immediate vicinity of
dwellings, railways, and public highways, was criticized only after some
disastrous explosion; and the often inexperienced consumer was without
access to a competent and disinterested source of information such as he
now has in the testing plant at Pittsburg so well described by Mr.
Wilson.
The first general move to improve these conditions is believed to have
been made by the American Railway Association in April, 1905. It
resulted in the organization of a Bureau of Explosives which, through
its inspectors, now exercises supervision over the transportation of all
kinds of dangerous articles on 223,630 of the 245,000 miles of railways
in the United States and Canada. A general idea of the kind and volume
of inspection work is shown by the following extracts from the Annual
Report of the Chief Inspector, dated February, 1910:
1909. 1908.
“Total number of railway lines members of
Bureau December 31st 172 158
Total mileage of Bureau lines December 31st 209,984 202,186
Total number of inspections of stations for
explosives 6,953 5,603
Number of stations receiving two or more
inspections for explosives 1,839 1,309
Total number of inspections of stations
for inflammables 6,950 1,098
Number of stations receiving two or more
inspections for inflammables 1,886 ....
Total number of inspections of factories 278 270
Number of factories receiving two or more
inspections 75 69
Total number of inspections of magazines 1,293 1,540
Number of magazines receiving two or more
inspections 349 361
Total number of boxes of high explosives
condemned as unsafe for transportation 10,029 4,852
Total number of kegs of black powder
condemned as unsafe for transportation 1,468 531
Total number of cars in transit containing
explosives inspected 475 448
Total number of cars in transit showing serious
violations of the regulations 168 197
Total number of inspections of steamship
companies’ piers
(inflammable, 75; explosive, 63) 138 ....
Total number of inspections made by Bureau 16,087 8,959
Total number of lectures to railway officials
and employes and meetings addressed on the
subject of safe transportation of explosives
and other dangerous articles 215 171
1909. 1908. 1907.
“Total number of accidents resulting
in explosions or fires in
transportation of explosives by rail 12 22 79
Total known property loss account
explosions or accidents in
transporting explosives by rail $2,673 $114,629 $496,820
Total number of persons injured by
explosions in transit 7 53 80
Total number of persons killed by
explosions in transit 6 26 52
“During the same period reports have been rendered to the Chief
Inspector by the Chemical Laboratory of the Bureau on 734 samples,
as follows:
Explosives 211
Fireworks 186
Inflammables 304
Paper for lining high explosive boxes 31
Ammunition 2
----
Total 734
“As a means of ensuring the uniform enforcement of the regulations, by
a well grounded appreciation of their significance and application,
the lectures delivered by representatives of the Bureau have proved
most successful. The promulgation of the regulations is not of itself
sufficient to ensure uniformity or efficiency in their observance, and
so these lectures form a valuable supplement to the inspection
service. They have been successfully continued throughout the year,
and the requests for the delivery of them by the managements of so
many of the membership lines, is a convincing testimonial of the high
esteem in which they are held.
“While the lectures are primarily intended for the instruction and
information of the officials and employes of the railway companies,
and especially of those whose duties bring them into immediate contact
with the dangerous articles handled in transportation, the
manufacturers and shippers are invited, and they have attended them in
considerable numbers. Many of this class have voluntarily expressed
their commendation of the lectures as a medium of education, and
signified their approval of them in flattering terms.
“The scope of these lectures embraces elementary instruction in the
characteristics of explosives and inflammables and the hazards
encountered in their transportation and in what respects the
regulations afford protection against them. The requirements of the
law, and the attendant penalties for violation, are fully described.
Methods of preparation, packing, marking, receiving, handling and
delivering, are explained by stereopticon lantern slides. These are
interesting of themselves, and are the best means of stamping the
impression they are intended to convey upon the minds of the
audiences, and are always an acceptable feature of the lectures. The
reception generally given to the lectures by those who have attended
them, often at the voluntary surrender of time intended for rest while
off duty, may be stated as an indication that the subject matter is
one in which they are interested.
“The facilities of the Young Men’s Christian Association, in halls,
lanterns and skilled lantern operators, have been generously accorded
and made use of to great advantage, in connection with the lectures at
many places. The co-operation of this Association affords a convenient
and economical method of securing the above facilities, and the
Association has expressed its satisfaction with the arrangement as in
line with the educational features which they provide for their
members.
“During the year 1909, 215 lectures were delivered at various points
throughout the United States.”
The Bureau of Explosives, of the American Railway Association, and the
Bureau of Mines, of the United States Geological Survey, were
independent products of a general agitation due to the appreciation by a
limited number of public-spirited citizens of the gravity of the
“explosive” problem. It is the plain duty of the average citizen to
become familiar with work of this kind prosecuted in his behalf. He may
be able to help the work by assisting to overcome misguided opposition
to it. Evidences of this opposition may be noted in the efforts of some
shippers to avoid the expense of providing suitable shipping containers
for explosives and inflammable articles, and in the threats of miners’
labor unions to strike rather than use permissible explosives instead of
black powder in mining coal in gaseous or dusty mines.
Too much credit cannot be given Messrs. Holmes and Wilson, and other
officials of the Technologic Branch of the United States Geological
Survey, for the investigations described in this paper. They are
establishing reasonable standards for many structural materials; they
are teaching the manufacturer what he can and should produce, and the
consumer what he has a right to demand; with scientific accuracy they
are pointing the way to a conservation of our natural resources and to a
saving of life which will repay the nation many times for the cost of
their work.
When these facts become thoroughly appreciated and digested by the
average citizen, these gentlemen and their able assistants will have no
further cause to fear the withdrawal of financial or moral support for
their work.
HERBERT M. WILSON, M. Am. Soc. C. E. (by letter).--The Fuel Division of
the United States Geological Survey has given considerable attention to
the use of peat as a fuel for combustion under boiler furnaces, in gas
producers, and for other purposes. It is doubtless to this material that
Mr. Allen refers in speaking of utilizing “marsh mud for fuel,” since he
refers to an address by Mr. Edward Atkinson on the subject of “Bog Fuel”
in which he characterized peat by the more popular term “marsh mud.”
In Europe, where fuel is expensive, 10,000,000 tons of peat are used
annually for fuel purposes. A preliminary and incomplete examination,
made by Mr. C. A. Davis, of the Fuel Division of the Geological Survey,
indicates that the peat beds of the United States extend throughout an
area of more than 11,000 sq. miles. The larger part of this is in New
England, New York, Minnesota, Wisconsin, New Jersey, Virginia, and other
Coastal States which contain little or no coal. It has been estimated
that this area will produce 13,000,000,000 tons of air-dried peat.
At present peat production is in its infancy in the United States,
though there are in operation several commercial plants which find a
ready market for their product and are being operated at a profit. A
test was made at the Pittsburg plant on North Carolina peat operated in
a gas producer--the resulting producer gas being used to run a gas
engine of 150 h.p.--the load on which was measured on a switch-board.
Peat containing nearly 30% of ash and 15% of water gave 1 commercial
horse-power-hour for each 4 lb. of peat fired in the producer. Had the
peat cost $2 per ton to dig and prepare for the producer, each
horse-power-hour developed would have cost 0.4 of a cent. The fuel cost
of running an electric plant properly equipped for using peat fuel, of
even this low grade, in the gas producer would be about $4 per 100 h.p.
developed per 10-hour day.
Equally good results were procured in tests of Florida and Michigan peat
operated in the gas producer. The investigations of peat under Mr. Davis
include studies of simple commercial methods of drying, the chemical and
fuel value, analyses of the peat, studies of the mechanical methods of
digging and disintegrating the peat, and physical tests to determine the
strength of air-dried peat to support a load.
The calorific value of peat, as shown by numerous analyses made by the
United States Geological Survey, runs from about 7,500 to nearly 11,000
B.t.u., moisture free, including the ash, which varies from less than 2%
to 20%, the latter being considered in Europe the limit of commercial
use for fuel. Analyses of 25 samples of peat from Florida, within these
limits as to ash, show a range of from 8,269 to 10,865 B.t.u., only four
of the series being below 9,000 B.t.u., and four exceeding 10,500
B.t.u., moisture free. Such fuel in Florida is likely to be utilized
soon, since it only needs to be dug and dried in order to render it fit
for the furnace or gas producer. Many bituminous coals now used
commercially have fuel value as low as 11,000 B.t.u., moisture free, and
with maximum ash content of 20%; buckwheat anthracite averages near the
same figures, often running as high as 24% ash.
One bulletin concerning the peats of Maine has been published, and
another, concerning the peat industries of the United States, is in
course of publication.
Mr. Bartoccini asks whether it would not be possible for the United
States Geological Survey to enforce rules which would prevent the
existence of conditions such as occurred at the mine disaster of Cherry,
Ill.
The United States Government has no police power within the States, and
it is not within its province to enact or enforce rules or laws, or even
to make police inspection regarding the methods of operating mining
properties. The province of the mine accidents investigations and that
of its successor, the Bureau of Mines, is, within the States, like that
of other and similar Government bureaus in the Interior Department, the
Department of Agriculture, and other Federal departments, merely to
investigate and disseminate information. It remains for the States to
enact laws and rules applying the remedies which may be indicated as a
result of Federal investigation.
Investigations are now in progress and tests are being conducted with a
view to issuing circulars concerning the methods of fighting mine fires,
the installation of telephones and other means of signaling, and other
subjects of the kind to which Mr. Bartoccini refers.
Much as the writer appreciates the kindly and sympathetic spirit of the
discussion of Messrs. Allen and Bartoccini, he appreciates even more
that of Colonel Dunn and Mr. Stott, who are recognized authorities
regarding the subjects they discuss, and of Messrs. Kreisinger and
Snelling, who have added materially to the details presented in the
paper relative to the particular investigations of which they have
charge in Pittsburg.
Mr. Snelling’s reference to the use of explosives in blasting operations
should be of interest to all civil engineers, as well as to mining
engineers, as should Colonel Dunn’s discussion concerning the means
adopted to safeguard the transportation of explosives.
Since the presentation of the paper, Congress has enacted a law
establishing, in the Department of the Interior, a United States Bureau
of Mines. To this Bureau have been transferred from the Geological
Survey the fuel-testing and the mine accidents investigations described
in this paper. To the writer it seems a matter for deep regret that the
investigations of the structural materials belonging to and for the use
of the United States, were not also transferred to the same Bureau. On
the last day of the session of Congress, a conference report transferred
these from the Geological Survey to the Bureau of Standards. It is
doubtful whether the continuation of these investigations in that
Bureau, presided over as it is by physicists and chemists of high
scientific attainments, will be of as immediate value to engineers and
to those engaged in building and engineering construction as they would
in the Bureau of Mines, charged as it is with the investigations
pertinent to the mining and quarrying industries, and having in its
employ mining, mechanical, and civil engineers.