xt754746qd93 https://exploreuk.uky.edu/dips/xt754746qd93/data/mets.xml Moore, Philip North, b. 1849. 1880  books b96-13-34924469 English Stereotyped for the Survey by Major, Johnston & Barrett, Yeoman Press, : Frankfort, Ky. : Contact the Special Collections Research Center for information regarding rights and use of this collection. Coal washing. Report on coal washing for the separation of coal from its impurities  / by P.N. Moore. text Report on coal washing for the separation of coal from its impurities  / by P.N. Moore. 1880 2002 true xt754746qd93 section xt754746qd93 

         N. S. SHALER, DIRECTOR.






         BY P. N. MOORE.


URVY BY MAjORa J ...To . B ,  I -  -A- -,  
                         251 & 252

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  Kentucky, fortunate in her great coal fields, possesses vast
stores of excellent coal which is so pure that it can be used
for iron making without further preparation; but, in comparison
with the whole coal field, the deposits of this class are limited.
The State furnishes no exception to the general rule, that
where there is much that is good there is more that is indif-
ferent or poor, and she possesses still greater quantities of
coal which is unfit for use in iron making, and ranks low for
general purposes.
  It is useless to deny this fact, for it is well known, and the
markets of the State acknowledge it in the prices at which
many of the coals above referred to are sold.  It is wise,
therefore, frankly to acknowledge the unpleasant truth, and to
strive, by superior skill in the manipulation and preparation
of these coals, so to improve them that the disadvantage of
quality may be overcome. It is only through such efforts that
mining of many of the coals even now accessible to trans-
portation can be made profitable, and it cannot be expected
that new fields will be opened while those already open are
not worked at a profit.
  The eastern coal field, while possessing the best iron mak-
ing fuel in the State, a coal of most excellent qualityand as
widely as it is favorably known, and while, in its undeveloped
portions, holding many coals which promise equally well, still
has extensive deposits of coal of good thickness, and favor-
ably located to transportation, which cannot now be utilized on
account of the impurities of the coal, but which, could these
be removed, would become available and a source of great
  The western coal field, unfortunately for itself, in conformity
with the general law of the coal fields of the United States,


that the coals, as a rule, grow inferior to the westward, holds
a greater proportion of these inferior coals. This is so far
true, that the poor coals are the rule, and those of moderate
purity the exception. Thus far, unfortunately, all attempts at
the utilization of the western coals in any branch of iron mak-
ing have been unsuccessful. No coal pure enough and of
suitable structure to use in the furnace without coking has
been found, and the great stores of iron ore of the Cumber-
land River Ore District, which lie so close to the western
border of the coal field, a situation the most favorable for the
building up of a great iron industry, have only been utilized
to a very small extent with charcoal, while the establishment
of the industry which these fuels and ores are so capable of
supporting, and which is destined to enrich this end of the
State, awaits the introduction of new processes, or apparatus
by which the coals can be made available. The only solution
possible to this question seems to lie in the washing and sub-
sequent coking of these coals, by which a fuel should be pro-
duced pure enough for iron making.
  There is no question of more importance, none with a more
vital bearing upon the future manufacturing prosperity of Ken-
tucky, than that of the utilization of these coals, and the es-
tablishment of a permanent iron industry in the western part
of the State; and no further explanation should be needed for
introducing a subject so strictly technical into the Reports of
the Geological Survey.
  Under the stimulus of the severe competition resulting
from the immense development of the manufacturing indus-
tries of the world during the past decade, and the succeeding,
long continued financial and business depression, it has be-
come necessary, in all establishments, to practice the utmost
possible economy. To this end,manufacturers are constantly
endeavoring to lessen the cost by improving the quality, or
decreasing the quantity of their fuels; and the question of the
utilization of poor coals. heretofore considered unsuitable, is
receiving some attention in this country and much more in





Europe, where coals of excellent quality are not found over
so widely extended an area as here.
  Such efforts have taken two directions: one, the invention
and construction of furnaces peculiarly adapted to the con-
sumption of the coals as they are, without further treatment;
the other, the purification of the coal from its objectionable
ingredients, which are, generally, pyrites, slate, and clay.
  Efforts in the first direction have resulted in the introduc-
tion of regenerative or gas furnaces, which are very successful,
and for many purposes all that can be desired. By them, fuel
of almost any character can be used for the production of very
high temperatures, and less fuel for a given result is required
than in any other style of furnaces; but the first cost of these
furnaces is often so large that it prevents their introduction,
and there are also many purposes for which they are not well
  It is, therefore, to the efforts in the second of these direc-
tions or processes for the purification of coals that this paper
will be devoted, and some description of a few of the most
recent processes and apparatus in use in this country and
Europe, for this purpose, will be given.
  The most common impurities of coal are iron pyrites and
slate or shale. In some cases sulphate and carbonate of lime
occur, and also a considerable amount of clay, apparently
washed into the seams of the coal from above. The pyrites
and sulphate of lime furnish sulphur, while the effect of all is
to add greatly to the amount of ash. Where these are pres-
ent, therefore, in considerable percentages, it is evident that
the coal cannot be used raw in the furnace for the manufacture
of iron, neither can it be coked, even if it be a fat or caking
coal; for while the operation of coking expels a large part of
the sulphur by its removal of the volatile matters, it concen-
trates and increases the percentage of ash, so that the coke
will contain, on an average, at least fifty per cent. more ash
than the raw coal from which it is made.
  For general manufacturiiig purposes, such as the production
of steam, while it is not impossible to use impure coals,




they are still very objectionable, as the heating power of such
coals is low, and the quantity of ash and clinket' troublesome
and expensive to remove.   To the manufacturer or iron
maker, every additional pound of ash which his coal contains
is a source of expense-small, it may be, but yet in the aggre-
gate great, and of importance in times like the present, when
the most rigid economy is demanded in every branch of busi-
  The task of separating the slate, pyrites, and other impuri-
ties from coal, has as yet only been successfully accomplished
by washing. The separation is due to the difference in spe-
cific gravity between the coal and its impurities, and the differ-
ent rates at which particles of the same, or approximately the
same, size, but of different specific gravity, settle in currents of
water moving vertically or horizontally.
  The processes all involve the one objectionable feature, that
they require the reduction of the coal to a comparatively small
size, the fineness depending upon the intimacy of the admix-
ture of the impurities with the coal. This is a serious but
unavoidable disadvantage of all the methods; for in no other
way can the desired result be effectually accomplished, since
the intermixture is usually quite intimate; where it is other-
wise, a careful hand-sorting is generally all that is required.
The importance and trifling cost of even hand-sorting does
not seem to be properly appreciated by the managers of Ken-
tucky mines.
  With properly constructed screens and tables, and the use
of boy labor, hand-sorting costs but a trifle, and it adds greatly
to the value of the coal. It is safe to say that much of the
prejudice which prevails in the Louisville markets against
Western Kentucky coals would never have existed, had the
colliery managers attended properly to the screening and sort-
ing of the coal before it went to the cars.
  The necessity for reducing the coal to a small size is no
objection, but rather an advantage, where the coal is suitable
for coking, and is used for that purpose, for it is better pulver.
ized. But this process has, heretofore, with us, confined the



use of washed bituminous coal to that purpose. In the an-
thracite regions of Pennsylvania, however, washing machinery
is coming more and more into use for the removal of slate,
and it is superseding, to a considerable extent, the old meth-
ods of hand-picking, as it is found that the smaller sizes of
coal, which have been washed, are freer from slate than the
larger sizes which are only hand-sorted.
  In Germany, however, at many mines of bituminous coal,
where the coal contains much slate, the washed fine coal of
various sizes, except the very finest, is sold for manufacturing
purposes, and brings a price which fully repays the opera-
tion of washing. There, however, the fine coal, as it comes
from the mine, contains as much as from 20 to 25 per cent.
ash, and the coal seam is so disturbed and crushed that a large
amount of fine coal is obtained in mining, often as much as 6o
to 70 per cent. of the total output. In this case, it becomes a
matter of the most vital necessity to utilize the fine coal or
slack, otherwise so large a proportion of the product would be
lost that the mines could not be profitably carried on.
  It is probable that at many of our western mines, such of
them, at least, as are large producers, even where the coal is
too dry for coking, it will be found profitable to wash the slack,
which is now either thrown away or sold for a trifling price for
steam firing. 'The slack is usually more impure than the lump
coal, as the slate and clay from the roof anUl floor become
mixed with it in the handling it undergoes. The additional
price which can be obtained for it, if it were washed so as to
reduce the ash to 4 or 5 per cent., will probably more than
pay for the washing, and it will have a more ready sale.
  Where the coals are dry or non-coking, the above uses will
probably, for the present, limit the introduction of washing
machinery; but where they are fat or coking coals, its use will
probably become almost universal; for the washed coal will
make far better coke than the unwashed, and the demand for
coke is becoming almost as extensive as for coal itself.




  Without doubt, the use of coke as a metallurgical fuel is
increasing, and destined to a yet greater growth. Its advan-
tages over the best raw coal are so great, that attention is
being more and more turned to its production. and attempts,
with more or less success, are made to produce a coke from
the dry coals of the Mississippi Valley. It is probable that
success will yet reward these efforts; and in that case,the use
of washing machinery will be still further extended, and we
shall see, as in some of the European coal fields to-day, every
colliery equipped with its washing machinery and coke ovens.
Increasing competition will doubtless compel this; for, by such
complete equipments only, every portion of the mine output
can be disposed of to the very best advantage. With such an
outfit, the colliery can produce, on demand, the cleanest lump
coal, washed nut and slack, as well as coke. The separation
into different sizes, as in the anthracite coals, though doubtless
not carried to anything like such an extent, will probably also
follow, and all of the smaller sizes will be sold as washed coal;
while the lump and the sizes of nut coal too large for wash-
ing, will be subjected to a careful hand-sorting by the use of
traveling tables, upon which the coal falls from the screens
and is carried along past boys, who sit upon either side, and
pick out the pieces of impure coal, slate, and pyrites.
   No matter what its reputation, what its nominal purity,
there is almost no coal used for coking which will not pro-
duce a better coke if it is previously washed. The common
expression, '-free from slate and sulphur," is founded on en-
thusiasm rather than fact. There is no coal which does not
contain an appreciable, and usually a considerable, percent-
age of these injurious ingredients, and which cannot be freed
from them, to a large extent, by properly conducted washing.
  The colliery proprietor, who contemplates the erection of
washing machinery, will find the cost of the operation, for a
given quantity of coal treated, distributed under the three fol-
lowing heads:
  (a). Sinking fund and interest upon capital invested in the
machinery, &c.




  (b). Operating expenses, including labor, superintendence,
repairs, &c.
  (c). Waste or loss of coal in washing.
  This loss increases with the original impurity of the coal
and the unskillfulness of the operation.  If properly con-
ducted, little should be wasted with the slate and pyrites
washed out; but,of course,the product of washed coal is less
by the amount of impurities removed.
  Where the coal is purchased for washing, or where the
miner is paid for the fine coal, or, in other words, where the
coal to be treated is anything but a waste material for wlhich
nothing is paid, this item must be as carefully estimated as
any other.
  These items are all subject to great variation with the pe-
culiar circumstances of each colliery; but, given the details in
each case, they are susceptible of close and accurate calcula-
tion by any competent engineer.
  Upon the credit side of the operation is but the single item
of increased price for an improved product of less quantity
than the raw material. Into this item all the advantages of
improved quality, wider sale, increased availability of coals
otherwise unmarketable, &c., heretofore cited, resolve them-
selves. From the nature of the case, this is not always so
susceptible of exact calculation as the estimates of cost; for
the most experienced cannot always tell what will be the future
course of a market for any product. It belongs, partly,among
those subjects which the trained judgment of the keen busi-
ness man must often decide, without being able to give the
detailed steps by which the decision is reached. Neverthe-
less. when the character of the coal is well known, the amount
of daily product, the usual market, and all the local circum-
stances of the colliery, it can be estimated with sufficient accu-
  As a rule, the introduction of washing machinery is only
advisable, when it has been shown, by the most careful investi-
gation in each particular case, that the profit will more than
equal the various items of cost; but there may be circum-




stances where it would be advisable to construct such ma-
chinery though the increased price of the product be barely
equal to the cost, when, by so doing, a colliery can command a
better sale for portions of its output, which otherwise would be
troublesome to dispose of, or not involve actual loss, or when it
is enabled to occupy or retain a market that would otherwise be
lost. Such a case, of course, is really profitable to the col-
liery; for, although there may be no gain on the washed coal
sold, the indirect advantages are very great. It is probable
that such conditions will be more and more prevalent in the
  The above reasoning is based upon the supposition that the
washed coal is sold to coke works or other market. In reality,
however, in a large proportion of cases, the colliery, coke
works, and furnaces which consume the coke, will all belong
to the same owners, and washing apparatus will be introduced
rather for the improvement of the coke and the consequent
less consumption of fuel and improved working of furnace and
quality of iron made, than for direct profit to the colliery. In
reality, however, it amounts to the same thing, and the profit
of the operation can be calculated back to the basis of the
coal washed.
  It has been shown above that the cost of removing the im-
purities from coal, by washing. varies with any one of three
elements, since it is the sumn of the three. It is, of course,
the endeavor of the proprietor or manager to reduce this cost
to the lowest possible limit. It is for him to consider, there-
fore, in the selection of a system of coal washing at any given
place, that he has three directions, in each or any one of which
he can economize, and that saving in the total may often be
effected by a reduction in one or two of them, and an increase
in the third. There can be given no general rules for such
cases. Each locality must be a law unto itself, and the local
circumstances, such as cost and quality of coal, market, pro-
duct most in demand, supply of capital, cost of labor, etc.,
must decide what system is, for that place, the most econom-
ical. For instance, where coal is plenty and cheap, capital



scarce, and interest high, and the product of coal to be washed
limited and irregular, that system of apparatus or machinery is
most economical which requires the least investment of capital,
even if it does involve the waste of a considerable amount of
coal in the endeavor to obtain a clean product. Such a system
may be an imperfect one, but it is not necessarily an expensive
  On the other hand, where capital is plenty and interest low,
while coal commands a good price, and the colliery furnishes
regularly a large amount of coal to the wash apparatus, the
most perfect machinery which wastes a minimum of coal, and
washes with the greatest efficiency, is the most economical,
even if its first cost be large.
   Having seen something of the necessity and use of coal
washing machinery, and having discussed the circumstances
under which it would or would not be advisable to introduce
such machinery, we come now to the subject of the various
systems and apparatus for the removal of the impurities from
coal. As before stated, these all accomplish the result through
the agency of water acting in a great variety of ways. As
yet. though it has been proposed. the substitution of air for
water,as a concentrating medium in coal cleaning,has not been
successfully tried, and it is doubtful if it ever will be success-
ful. It certainly can only be used, if at all, for the fine or dust
coal, and this fact will forbid its use except in very isolated
  The number of systems, and the variety of machines which
have been used in coal washing, is very great, and it is far
beyond the limits of this paper to attempt a description of
even one half of them; nor in a practical discussion of the
subject would it be of any service, for the great majority of
them are old-fashioned, and have been superseded by im-
proved apparatus, and descriptions of them would possess no
practical interest. It is true that many of these are still in
service, but it is only at the older establishments, where they
were built before the improved machinery was introduced. It
would, therefore, possess only an historical interest to describe





machinery which no one would think of erecting at the pres-
ent time.
  The scientific principles of ore dressing, which have been
so elaborately developed through mathematical reasoning and
careful experiment by foreign writers upon the subject, are, of
course, the same which govern coal washing, and the same
laws of classification hold; but, in practice, there is a difference;
for, in ore dressing, it is the heavier product which is usually
the valuable one, while the lighter is the waste, and all the appa-
ratus, therefore, is calculated for saving the heavier portion of
the ore and the rejection, with the least trouble, of the lighter.
In coal cleaning. on the contrary, we have the objects of the
same operation directly reversed, and the heavier slate and
pyrites are the waste, while the lighter material, the cleaned
coal, is the valuable product.  The operation, of course, in
both cases, is the same-that is, the separation of a heavier
material from a lighter; but the different object renders nec-
essary some changes in the construction of the apparatus.
  Discarding, for the present, a variety of systems which be-
long to the past, although locally still in use, and others which
are still too untried to determine the place they will fill in the
future, we have worthy of description, as having proved, by
actual trial, their success, and as being now in most extensive
use at home and abroad, the following systems of coal wash-
ing, classified according to the nanler in which the water acts:
  1. Where the material to be washed is subjected to a hor-
izontal, or nearly horizontal, constant current of water, the
material being submerged in the water, carried along by it,
classified, and deposited at the bottom of the stream in ac-
cordance with the size and specific gravity of the different
particles. This class embraces all the trough or sluice wash-
ers, which will be described more in detail further along.
  11. Where the material to be separated, resting upon a
sieve or screen, is subjected to the action of upward, inter-
mittent,quick currents of water, the water coming from below,
lifting the whole material and then allowing it to settle and
separate in the interval between the strokes. This class em-




braces all the great variety of machines called jigs, in which
the motion to the water is given by a movable plunger, while
the sieve upon which the ore to be separated is placed remains
fixed. The number of jigs which have been invented is very
great, and constantly increasing; they differ widely in detail,
and are of greater or less excellence; but they have the above
principle, which is characteristic of the modern power jig, in
  The above classes comprise, probably, more than nine tenths
of the apparatus for coal cleaning at present in operation;
but there are other systems, which have been used only to a
limited extent, which promise well for the future. There are,
therefore, perhaps, worthy of description, the following addi-
tional systems:
  111. Where the separation is effected by a constant upward
current of water acting against the falling particles of the
material to be separated, the current being so regulated that
the heavier material falls through it, while the lighter is carried
over by the stream of water to a proper receptacle. To this
class belong the so-called syphon washers, in which the upward
current is maintained at a constant velocity by a head of water,
and the Day washing machine, in which the upward current is
produced by two propellers, rotating in opposite directions.
  IV. Where the material is separated by falling into still
water, and by subsequent upward, intermittent currents of
water, induced by a pressure of steam in another part of the
  The only apparatus of this class is known as the Evrard
coal washer.
  In all of the systems above referred to, the completeness of
the separation depends largely upon the proper sizing or clas-
sification of the coal before it goes to the washing apparatus.
As a rule, the more careful the sizing, the more complete the
subsequent separation; and, for the most satisfactory work, only
one size will be submitted to any given piece of apparatus at
one time. It is possible, however, to effect a separation of
coal from its impurities without this careful sizing, but it is



done at the expense of a somewhat greater waste of coal, or a
larger percentage of impurities remaining in the washed pro-
duct. IThis sizing or classification is done by screening, and,
of course, every additional screen necessitates other machin-
ery, and thus adds materially to the cost of separation.
  Here, again, therefore, as in the decision as to the apparatus
to be employed, there must be a choice between the alterna-
tives of a more perfect operation with larger outlay and greater
saving of coal, or a less outlay and greater waste of coal.
  Coming now to the description of the apparatus of the dif-
ferent classes in most general use, we have:

  This style of apparatus is,at once,the simplest, the oldest,
and the cheapest of all forms. It consists of a wooden trough,
furnished at proper intervals with movable riffle bars to inter-
rupt the force of the stream, inclined at an angle sufficient to
produce the proper force of current to carry the coal along,
while the heavier slate and pyrites are deposited in the bottom
of the trough above the riffle bars. The accompanying figures,
Plate I, of the double trough washer, in most common use in
the Lancaster and Durham coal fields, England, will sufficiently
illustrate its operation. The fine coal or slack comes from
the screens directly to the feeding hopper h, whence it falls
into the head of the trough, meeting the stream of water,
which is often the waste water from the mine pumps, intro-
duced by the pipe b. The impurities being heavier, sink to
the bottom of the stream and are interrupted by the riffle bars
r r, while the coal is washed along to the end of the trough,
over a drying screen, into a proper receptacle. The larger
lumps of coal, of course, tend to lodge with the impurities, and
to prevent this, they are stirred with a rake, by the attendant,
from time to time. When the space above the bars becomes
filled with slate so that they no longer interrupt the current,
the hinged gate c is thrown to the opposite side, and the cur-
rent turned into the other channel. Then, by means of the
lever 1, the riffle bars and the trap a in the bottom of the trough




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are raised, and the slate is washed out through the opening
into the car placed to receive it. By this reciprocating action
the washing goes on uninterruptedly. An apparatus of the
size figured, 2 feet 6 inches wide and 40 to 50 feet long,
requires to attend it two men, and will wash from 175 to 200
tons of coal in io hours. This does not, of course, include the
labor of removing the washed coal and the slate. By using a
rake, or stirrer moved by machinery where the washer is
located near available power, the labor of one man can be
dispensed with. The total labor, under the most unfavorable
circumstances, should not exceed six or seven men for 200
tons of coal per day. Estimating these at 1 25 per day,
the maximum cost per ton, for labor,will be 4.37 cents. The
other expenses for washing by this system are not great.
  At the Tursdale Colliery, Durham, England, belonging to
Messrs. Bell Brothers, this system is in use, washing about
400 tons per day. The writer was informed that the coal,
as it came to the wash, contained from 12 to 15 per cent. of
ash, which was reduced to 4 or 5. The cost of washing was
given at 6 pence to the ton of coke produced, or about 3
pence (about 7 cents) per ton of coal, the yield of coke being
5 7 per cent.
  This system of washing has great advantages, in that the
cost of the apparatus is very little; that it is exceedingly
simple; that the expense of repairs is almost nothing; that it
is always in order and ready for operation; that it requires no
machinery except a pump to supply the water-in some cases
a separate pump is not even needed, and that it uses compara-
tively little labor.
  It is open to the objection that it requires a largn amount
of water; that, as there is no previous sizing of the coal, the
washing is either imperfectly done, and all the impurities are
not removed from the coal, or else, if the coal be thoroughly
cleaned, much will be wasted with the slate, and that the oper-
ation is peculiarly dependent upon the care and watchfulness
of the workmen at every step, so that the slightest negligence

1 5



on their part will show itself, at once,in the higher percentage
of ash in the washed coal.
  It is also probable that,in some parts of our country,it would
give trouble by freezing in the winter time.
  This style of apparatus is that in most general use for coal
washing in the Lancashire and Durham coal fields of England;
but the great majority of the collieries in those fields have, as
yet, adopted none at all.
  After the above summary of the advantages and disadvan-
tages of the apparatus, it is necessary to say little more con-
cerning it. It cannot be called a perfect apparatus, and does
not give the finished results of the more elaborately designed
and complicated systems; but it is very efficient, and can be
erected at so trifling a cost that it is to be recommended for all
those collieries where there is an ample supply of water and a
scarcity of capital. It is advisable, also, as an experimental
washer, where it is uncertain what will be the sum of the
advantages to be gained by purifying the coal. With it the
experiment can be tried, and afterwards, if desirable, more
complete and perfect machinery erected.
  It is to be noted, too, that it is capable of doing better work,
if the material were to be previously sized, as in other systems;
but the addition of screens would increase the cost very ma-
terially, and thereby lessen the advantages which it possesses
over others.
  The efficiency of the sluice washer decreases rapidly with
the increasing impurity of the coal to be operated upon; so
that, with very impure coals, it will no longer be an economical
apparatus, for the necessary waste of coal will be excessively
great. It is best adapted to coals with not exceeding I5 per
cent. of ash.
  In using this apparatus, the length and inclination of the
trough and the number and size of the cross bars, is to be
determined by the character of the coal. Where the impu-
rities readily separate, the pitch may be made steep and the
trough short; where they are slow of separation, the inclina-
tion must be more gentle and the trough longer. A very




common slope is one inch to the foot. The height of the riffle
bars must depend upon the depth of the stream of water which
flows over them. While they must be high enough to thor-
oughly check the current of water, they must not be so high
as to prevent the coal from being carried over. Three inches
is an average height, with an interval of from six to ten feet
between them.
                        CLASS II. JIGS.
  We come now to the apparatus of the second class, where
the material is subjected to the action of upward,intermittent
currents of water, which currents are produced by the action
of a wooden or metal piston, or plunger moving up and down
in a closed compartment. Machines of this class are called
jigs. They are the best known and most universally appli-
cable of all machines for the separation of ore or coal. The
method of operation is identical in all of them; but there are
many, very many, modifications of details, and each jig, with
some peculiar modification, is known by the name of the in-
ventor. In all of them  the material to be treated rests upon
a screen or sieve, and the plunger f