16

THE COLLIERY GUARDIAN

July 2, 1915.

tion of the benzol. The lower portion forms a reser-
voir for the circulating benzol wash oil, and the upper
portion is filled with wooden grids. Benzol wash oil is
constantly circulated over these grids, the gas passing
through them. By this means the gas is brought into
very intimate contact with the oil, with the resulting
absorption of the benzol. From these scrubbers, the gas
now being freed of tar, ammonia, miosture, naphthalene
and benzol, passes through a return main to the ovens.
It is here distributed under each oven wall into 15 parts,
which supply the Bunsen burners for heating the
vertical flues with gas.

Crude Benzol Plant.

The benzol plant is designed to produce 65 per cent,
light oil (crude naphtha), and consists of a large C.I.
light oil still, which is surmounted by a vertical oil
warmer or heat exchanger, and two oil pre-heaters, one
of which is spare. There is also a benzol condenser,
having two condensing coils, the lower portion of the
vessel being built as a decanting chamber. All of the
condensed products from the coils flow into this
decanting chamber, and are there separated, the water
running to waste and the light oil (crude naphtha) being
led into the crude naphtha storage tanks. The hot
debenzolised oil leaving the still passes through a wash
oil cooling plant, consisting of several units of the
“ Otto ” type counter-current wash oil coolers, on to
the pumps, which pump the wash oil to the scrubbers
again. It will thus be seen that the entire plant—
benzol scrubbers and crude still—'are in constant opera-
tion, the oil flowing continuously through the scrubbers,
then through the warmer and heater, through the still,
and then through the wash oil cooling plant on to the
scrubbers again. The installation includes a 30-ton
wash oil storage tank and two 50-cu. m. crude naphtha
storage tanks. The entire benzol plant is so arranged
that it may be supervised by the attendant in the
exhauster house, as only very occasional inspection is
necessary.

Exhaust Steam Turbine Plant.

The generating plant consists of two Parsons turbo-
alternators, the capacity of one being 500 kw., whilst
that of the other, recently installed, is 600 kw. The
turbines are of the mixed-pressure type, and are capable
of developing their full output with exhaust steam at a
pressure of 1| lb. above that of the atmosphere, or with
boilers at a gauge-pressure of 70 lb. per sq. in. The
regulation of the high- and low-pressure steams is abso-
lutely automatic, and, so long as there is sufficient
exhaust steam for the required load, no high-pressure
steam is used, but, so soon as the exhaust steam is
found to be insufficient, the high-pressure steam is
admitted, and continues to be used until a further
supply of exhaust steam is available. The exhaust
steam is obtained from several reciprocating engines at
the West Wylam Colliery, and is taken to the exhaust
steam receivers. The duty of these receivers is to
equalise the pressure of the exhaust steam of the recip-
rocating engines, and to cleanse the steam to a certain
degree from water and oil. The turbines exhaust into
a surface condenser, which is capable of maintaining a
vacuum of 28-5, with a barometric pressure of 30 in.,
when working at full load, or, in other words, 95 per
cent, of the possible vacuum obtainable. The circu-
lating water used for condensing the steam is pumped
from the pit, and it falls by gravity through the con-
denser, and the use of a circulating pump is therefore
rendered unnecessary. The volume of water used for
condensing the steam is about 2,000 gals, per minute.
The air pump is of the ordinary three-throw type, as
manufactured by Messrs. C. A. Parsons and Company
Limited, and it requires only from 8 to 10-brake horse
power for driving. The air-pump discharge water is
returned to the hot well for boiler feed purposes. The
steam consumption, when working with exhaust steam,
is 31 lb. per kw. hour, and, when working with live
steam, -it is 21-5 lb. per kw. hour. Both of the turbines
are capable of 25 per cent, overload for two hours, and
50 per cent, overload for short periods. The 'alternators
are of the three-phase type, 550 volts, 50 periods,
running at 3,000 revolutions per minute, and they are
designed to give their full output with a power factor
of 80 per cent. They are of the revolving field type,
and are fitted with Parsons’ patent leakage path voltage
regulator. The exciter is coupled direct to the alter-
nator, and is fitted with carbon brushes, which have
proved quite satisfactory at a speed of 3,000 revolutions
per minute. The current is taken from the alternators
to the switchboard, manufactured by Messrs. J. H.
Holmes and Company, of Newcastle-on-Tyne, which is
of the remote control type. There are no switches,
fuses, or any metal-carrying current on the face of the
board, so that the risk to the operator when carrying out
switch arrangements is reduced to a minimum. The
distribution system is, for the most part, overhead,
with bare conductors, protected by lightning arresters
both on poles and at the switchboard. The power is
taken to the Mickley Company’s group of collieries,
and is used for pumping water out of the West Wylam
Pit, where the regular feeder is 3,500 gals, per minute,
for the haulages and electrical coal-cutters, and also at
the various parts of the new coke-oven plant. The
500-kw. set was put down some few years ago for the
purpose of unwatering some old workings, and for prac-
tically two years this set ran continuously, and the
volume of water dealt with was 4,000 gals, per minute.
This will afford an idea of the economies which were
effected by the utilisation of the exhaust steam, which
was sufficient to run the plant, except at the week-ends,
when the exhaust steam was not available.

For permission to inspect these works whilst under
construction and since completion, and to publish the
foregoing particulars and accompanying drawings and
photographs, the writer acknowledges his indebtedness
to Mr. Sidney Bates, the agent of the Mickley Coal
Company Limited.

The Winding Drums of Practice and of Theory.

WITH NOTES ON FACTORS OF SAFETY AND ECONOMY OF WINDING ROPES.*

By H. W. G. HALBAUM.t

(Continued from, page 1324, vol. cix.)

Balancing the Load.

A further objection is that the load against the engine
cannot be made anything like uniform where a parallel
drum is used. Certainly, the dead load may be made
uniform by placing a tail rope under the cages; but the
live loads are scarcely affected, unless the tail ropes are
much heavier than the winding ropes. There are two
difficulties attaching to the latter method. First, the
specially designed tail rope would greatly increase the
cost of the rope, since the ordinary tail rope may consist
of a disused winding rope; and, secondly, it would add
to the inertia of the mass that has to be put into
motion. This inertia, even in the ordinary case, absorbs
a surprising amount of power — whether the parallel
drum be used in connection with the “ orthodox ”
system, or in connection with the endless rope system
of winding.

It is submitted, therefore, that the parallel drum,
wide or otherwise, and with or without tail ropes in
the shaft, is a drum which severely stresses the engine
by obliging it to do nearly all the work of the wind
during the period of acceleration only.

„(«)	(b) (c)r

<U i

UJ 5 -J

Fig. 2.—Showing Drum Surface Normal
to Radii Vectores of Ropes Centring
at Mid-wind.

There are thus four distinct faults in connection with
the plain wide parallel drum : (1) The tendency of the rope
to slip along the surface; (2) the spreading of the rope,
as at (a) and (c) in fig. 1; (3) the lateral friction, as
illustrated at F in the same sketch; and (4) the bad
balancing of the live loads against the engine. These
items may be taken one by one.

(1)	Why does the rope slip? Simply because the
surface of the drum is not normal (that is, perpen-
dicular) to the line of pressure contained in the rope.
This line of pressure, due to the gravity of the load in
the shaft, becomes, practically, and so far as the resist-
ance of the drum is concerned, the line of gravity itself.
The centre of gravity (again so far as the pull on the
drum is concerned) is at the pulley. A normal line on
any winding drum, therefore, corresponding to the line
of dead “ level,” is, for each rope having lateral travel,
the arc of a circle, the centre of which is at the pulley,
and the successive radii vectors of which are contained
in the rope as it takes up its successive positions along
the drum. The winding drum of theory, therefore, has
a surface inclined to the axis and curvilinear, for exactly
the same reason that every horizontal plane on the
earth is spherical. The “ pulls ” in each case radiate
from a common centre, which, in the case of the earth,
is situated at the centre of terrestial gravity, and, in
the case of the winding drum, is found at the pulley.

If, therefore, the ropes centre at mid-wind (as shown
in fig. 1), the theoretical drum surface for each rope
assumes a barrel shape, as shown in fig. 2, in which,
however, the curvature is sharper than that which would
be required in most cases. This merely defines the
theoretical drum required to prevent actual slip of the
ropes at (a) and (c). But since, with centres at middle
wind, slipping at (b) is prevented by lateral friction at
F, the drum may be made parallel at (b), and thereafter
slope down gently to (a) and (c), still centring the ropes at
middle wind. This theoretical form may be called the
“ barrel drum ”; it is only efficient to prevent the rope
from actually slipping, and it effects that purpose quite
naturally, because its surface is everywhere normal to
the pressure exerted along the radius vector of the ropes.

(2)	But, whilst preventing slip, it does nothing to
prevent spread. The rope still will strike diagonally

* From a paper read before the North of England Institute
of Mining and Mechanical Engineers.

t Greenwell Medallist.

across the drum, and finally coil diagonally. Never-
theless, the surface having already been “ levelled,” in
order to remove the risk of slip in one direction, it
becomes evident that it is possible so to incline the sur-
face of the drum that the rope will slip gently in the
opposite direction, and thus continually take up the
position desired. That this is quite feasible should be
evident from the plain conical drum which was in many
cases discarded because the rope slipped too much.

When, however, the idea of fully counter-balancing
the weight of the rope by such means alone, and under
all conditions, however grotesque, is once given up as
impracticable, it is reasonable to ask whether one cannot
accomplish the far less formidable task of counter-
balancing the angle of the rope by some such means.
The failure of the plain conical drum was often due
entirely to the fact that those in charge so centred their
ropes that the rope angle and the drum inclination both
pulled in the same direction. But there is really no
reason why the angle of the rope, exerting force in one
direction, should not be easily and accurately compen-
sated by an angle on the drum exerting force in the
opposite direction. In that event, the rope would still
strike diagonally across the top of the drum, but would
certainly refuse to climb the back of the drum, pro-
vided that the angle of inclination were at least equal
to the angle of repose. The angled rope would con-
tinually settle into its proper position at the back of the
drum, simply because that is now the lowest position,
which, relatively to the line of pressure, the loaded rope
can possibly occupy. It cannot spread, because that
would mean climbing up its angle of repose, neither can
it mount the coil immediately below, since that would
be climbing a still steeper angle, and an angle, more-
over, the negotiation of which by the rope is absolutely
opposed by the entire line of pressure contained in the
rope.

With regard to the measurement of the angle of
repose, it must be noted that the datum line lies in the
surface of the theoretical barrel drum. This line is
always normal to the line of pressure; and, like the level
line of nature, is a curved line in which all points are
equidistant from the centre of gravity. To illustrate
this, it may be imagined that in fig. 3, the circle A-B-C
represents a level line produced through a complete
circumference in the earth’s crust. The inner black
line a b c may be imagined as a tunnel, started from
the point a, and continued half-way round the earth at
a uniform dip of about 1 in 4. Both lines are curved
lines. Similarly, the actual inclination of the drum,
relatively to the curved surface of the theoretical barrel,
may be plotted in like manner. In most cases, how-
ever, there will be no occasion to split very fine hairs
over the matter. As the arcs are very small compared
with the radius, they differ little from straight lines,
and may often be taken as straight lines, the inclina-
tions of which are determined by the arcs. Moreover,

Fig. 3.—Showing that a “ Level Line ” is
Really a Circular Arc and a “ Uniform
Gradient” Really a Spiral.

the angle of inclination need not be very precise; it
must be large enough to satisfy the angle of repose,
although not so large as to overbalance the live loads to
an undesirable degree; but it may have almost any
magnitude lying between those two limits. Of course,
in some instances, these limits may approximate very
closely, especially if the drums be comparatively small;
but the difficulties herein discussed are found princi-
pally in connection with the larger plants.

Now, it may be admitted that all this will lead one
back, step by step, to the plain ^pgrooved tapered drum
which appears to have come into almost general dis-
favour. Yet, in some instances, this very type of drum
is still employed with excellent results. The object of
now groping one’s tedious way through the elementary
theory of the subject is to discover, if possible, the
mechanical reason why such good results have been
obtained in some cases and not in others.

Let the ropes centre at meetings, then the angle of
maximum obliquity need not exceed, say, 2degs. If
the ropes be lubricated, the angle of repose should never
exceed, say, 12 degs. Therefore, the slope of the drum,
relatively to its axis, need not exceed 12 + 2 = 14 degs.
at the commencement, nor 12 degs. at the middle of wind.