THE COLLIERY GUARDIAN

AND

JOURNAL OF THE COAL AND IRON TRADES.

Vol. CXIII.	FRIDAY, JANUARY 26, 1917.	No. 2926.

Dry Preparation of Bituminous Coal in Illinois.*

II.—IMPURITIES AND BREAKAGE.

By E. A.

Removad of impurities and avoidance of breakage
are the two standards by which coal preparation is
measured. The object of coal mining is not only to
produce the greatest possible tonnage at the least cost,
but to produce the greatest possible percentage of clean
lump coal. Perfect mining would mean not only the
extraction of all the coal, but the winning of it in a
perfectly clean condition, with 100 per cent. lump.
Were this possible, subsequent mechanical breakage
could easily and cheaply produce finer sizes, as needed,
in as pure a condition as the original lump.

On the whole, Illinois has pure coal compared with
many sections, and it is possible to clean lump coal by
hand in the railroad car. If the market calls for a
steam coal, very little preparation is necessary. If the
market requires domestic, one must screen and pick,
and even re-screen. The biggest problem is to toad
without breakage.

No seam of Illinois coal is free from at least small
amounts of impurities. Since mines situated in widely
separated districts over an area of approximately 36,800
square miles are worked in five different seams, great
variations are possible locally in th© nature and in the
extent of the impurities in an individual seam, and in
the physical characteristics of the coal itself.

The most persistent impurity in Illinois coal is the
famous “ blue band ” or shale band in seam No. 6,
which averages 1 to 2 in. in thickness, and is situated
about 20 in. above the bAtom of the seam. It extends
with considerable regularity over an area of at least
5,000 square miles. Impurities such as pyrites
(“ sulphur ”) and shale bands are of frequent local
occurrence in all the seams. Whilst it cannot be said
that any one district in Illinois has an advantage over
others in this respect, considerable variance occurs
among mines in the same district, not only in the impuri-
ties in the coal, but also in the care displayed in
removing the same before the coal is shipped to market.

Friability means the tendency to produce fines under,
like conditions. The Illinois coals are not so friable as
the coking bituminous coals of the Appalachian region,
and in freedom from the breakage which occurs during
mining, preparation, and shipment, they are perhaps
not excelled by coal from any other section of the
bituminous fields of America. Taken as a whole, the
different seams in Illinois show considerable uniformity
as regards friability, although sometimes the same seam
in different districts or even in the same district will
vary, depending probably on the thickness of the cover
and the regularity of the bed. A seam buried under
several hundred feet of cover is likely to be firm; a seam
which has been tilted or folded is likely to be somewhat
friable. At only two places in the State where mining
is undertaken have the beds undergone any extensive
regional faulting and tilting, all being practically hori-
zontal. This has tended to keep the beds regular in
general phys;cal structure over large areas. Since
Illinois coal is relatively firm, the preparation of sized
coals intended for competition with the domestic sizes
of anthracite has recently become a noticeable feature.

Removing Impurities.

Removal of Impurities Underground. — Most of the
larger pieces of separable impurities which have been
mined with the coal may be removed underground by
hand sorting during loading, but the time spent in
doing this reduces a miner’s daily output of loaded cars;
consequently, there is an inclination to minimise this
work.

The claim has often been made that the most efficient
place for inspection of coal for impurities is underground
during loading. However, a,s the miners usually work
in pairs only, and in separate rooms, continual under-
ground inspection in the dim light is impossible. At
several mines in which persistent bands of impurities
occur, the assistant mine manager makes regular trips
through the mine, and by noting the size of the waste or
rejected pile, or the character of the coal in a partly-
loaded car, he is able to estimate rather closely the per-
centage of rejected impurities. If he detects careless-
ness, word is sent to the regular coal inspector at the
surface plant to watch closely for the cam of the miner
in question. It is probable, however, owing to the
multiple duties of the assistant mine manager, and to
the limited number of these officials allowable under
the agreement between the operators and miners, that
underground inspection is casual rather than systematic.

Once in the mine oar, further inspection is impos-
sible until the coal is dumped or spread out on the

♦ University of Illinois Bulletin No. 88.

HOLBROOK.

screen in the tipple. One mine only was visited in
which inspection was attempted in the loaded cars at
the shaft bottom before hoisting. Since the natural
tendency is to put clean coal on the top of the car, it is
difficult to see how such inspection could be effective.
At the particular mine noted, condemned ears were not
hoisted into the tipple, but were set off at the surface
landing, and kept there for the inspection of the
interested parties, and in full view of all men entering
or leaving the cage. It was explained that the effect of
this was noteworthy.

It is necessary to emphasise how closely all the impuri-
ties loaded with the coal are within the control of the
miner at the face. If he takes pride in his trade, is
careful, undercuts with skill, uses powder with judg-
ment, and loads with care, a considerable part of pre-
paration has been accomplished, and he has done his
part towards making a good name in the markets for the
mine in which he works.

Removal of Impurities in the Tipple.—At practically
all mines in Illinois an attempt is made to remove the
bulk of impurities loaded underground 'at one or more of
the following places in the surface plant :—(a) In the

Yr

i Sri

Fig. 1.—Operation of a Picking Table.

tipple during screening; (b) on picking bands or belts
after screening: (c) during the loading of the railroad
cars underneath the tipple.

At. one of these places a coal inspector, dock boss, or
rock man is stationed, who not only watches for
impurities, and penalises the miner according to the
joint agreement, but often has general charge over the
men picking and loading the coal. Some companies
place an inspector at each tipple, others employ a single
inspector, who covers two or more of their neighbouring
surface plants. Large companies frequently have one
chief inspector, who superintends dock bosses at the
individual tipples. In all cases, close inspection was
reported beneficial in lowering the percentage of ash in
the coal. Frequently the buyer is notified if a railroad
car which has been loaded contains defective coal. An
economy of 0'6 per cent, will pay for inspection at the
mines.

At a few tipples in the State the dock boss “ rides ”
the screen; that is, he is seated on a stationary support
just above the shaking screen, from which, with perhaps
one or two assistants, he can bend down and remove the
impurities from time to time. If the screen is narrow
(7 ft. or less), the dock boss and his assistants may
stand at the sides and remove impurities; in either ease
throwing the rejected material into chutes which lead to
a refuse ear or pile below. Such inspection is not very
efficient in the dusty surroundings if a considerable
amount of impurities is present, if la large tonnage
(perhaps 2,000 tons or more) passes over the screens, or
if wide screens (7 to 10 ft.) are used. Another factor
hindering the detection of impurities is 'the mixture of
sizes from nut to the largest lumps, which must be
examined at the same time. In such a mixture of sizes,
Ipmps are bound to hide the impurities of nut size. This
difficulty is overcome at several tipples by the use of a
patented combined screen and picking table. The screen

is horizontal, and of sufficient length and movement to
separate efficiently the sizes, and allow picking on the
screen under favourable conditions. This screen will
be described later.

Within the last few years, the demand for cleaner
coal has forced Illinois operators, especially at the large
mines, in which from 2,500 to 5,000 tons per day were
handled in the tipple, to adopt these picking tables or
belts as a method of removing the refuse. The picking
tables (fig. 1) are from 3 to 5 ft. wide, often 30 ft. long,
30 in. above the floor, and are endless belts either of
rubber or of steel links covered with small over-lapping
sections of steel plate. The tonnage handled is up to
1,000 tons per day per belt. These belts catch the coal
as it falls through or leaves the screen, and convey it
horizontally at right angles to the screen. Each size
of coal may have an individual belt or picking table.
Thus the coal, spread out on the belt, and travelling at
a speed of from 30 to 60 ft. per minute, passes before
men or boy pickers, who can easily pick out the refuse.
Dirty coals, of course, require low speed and additional
pickers. Speed depends also on the size, on the colour,
and on the shape of the impurities; that is, the ease
with which they can be distinguished.

In general, picking tables, bands, or belts have the
following advantages -(1) Thorough inspection, nil coal
being spread out in fixed sizes and moving at a fixed
rate; (2) decreased length of chutes and height neces-
sary to feed certain tracks; (3) loading of coal in a con-
stant stream with minimum velocity and breakage; (4)
safetv and effectiveness of pickers—they are no longer
exposed to the dust on the screens or to
danger in the loading ears; (5) combined
with a movable loading boom they
further reduce the breakage, and allow
easy loading on cars of different heights.
The only disadvantages are first cost and
maintenance.

At one mine in which pyrites refuse is
saved from the tables, six rock pickers,
three on lump and three on egg, pick out
50 tons of pyrites per day, or about eight
tons per man per day. On account of
the high percentage of refuse, stationary
ploughs are fixed on the tables close
above the belt, so that the moving coal
may be turned over, and thus expose to
view any hidden impurity.

At other mines, including some of the
largest, inspection and picking are
carried on only when the railroad cans
are being loaded with the screened coal.
The stream of coal filling the car is
closely watched by one or two men, who
throw overboard from time to time the
noticeable pieces of impurities. They
often use large rakes to pull the
impurities from under the falling
stream of coal. In such eases,
picking is for appearance only, the
actual amount of impurities removed
being usually under 1 per cent, of the size loaded. At
some mines only the lump sizes are picked. At other
mines the egg and nut sizes, as well as lump sizes, are
picked. At these mines the dock boss usually watches
the railroad cars and not the screens for impurities.
Fig. 2 illustrates car picking on egg coal.

Car picking is sufficient if the amount of refuse is
small or consists of only occasional and accidental pieces
—possibly one or two tons per 1,000 tons loaded. In
these cases it is possible to remove all noticeable impuri-
ties from the top of the car before shipping. Car pick-
ing is not sufficient to clean systematically a dirty coal.
A piece of impurity even if detected cannot always be
removed from a stream of lump coal falling and rolling
into a car without exposing the workman to danger of
injury from the large lumps. Consequently such
imparities are buried rather than removed. _ The danger
of being injured by the small egg and nut sizes is not so
great. In one case as much as 1 per cent, of the egg
size is thrown out of the car during loading; however,
the percentage is usually much smaller. The removal
in this way, as refuse, of a noticeable percentage of the
coal would probably be commercially impossible.

The chief difficulty with hand-picking in any form is
that of securing 'conscientious labour to do the work.
Another feature is the amount of good coal going to
waste with the shale and sulphur. For instance, if an
impure band | in. thick is noted in perhaps an 8 in.
lump of coal, the whole is likely to be discarded. Exami-
nation of some of the refuse heaps to which the rejected
lumps are hauled has revealed many tons of good coal.
At a few mines these lumps are pulled from the picking
belt, the impure band split off, and the good coal
returned to the belt. This operation is called
“ skinning ” the coal.

Sizing should take place before the picking is begun.
If picking is attempted on 1{ in. lump coal, the eye of