970

THE COLLIERY GUARDIAN.

November 8, 1918.

labour. Where such is the case, how many boiler houses
one can go into and find the firemen making two moves
when one would do; and where a careful study of the
situation, a litrle ingenuity displayed and a motion
study of the firemen made by the man in charge, would
cut the actual work of the firemen down to half.

The principal efficiency obtained in any boiler room
is naturally the way in which the fires are handled to
suit the particular coal that has been decided upon as
the most commercially economical to use, or that
location has made necessary. With the high costand
insufficient supply of labour, hand firing is becoming
obsolete, and rightly so, except in the case of single
boiler plants under certain conditions.

Hand Firing*.

There are two ways of hand firing, the spreading
method and the coking method. The writer’s experience
is that the spreading method gives the better efficiency
in the long run. The coking method, however, if care-
fully carried out, gives the least smoke; but there is
real difficulty in getting it done right, and for that
reason alone the spreading method is more efficient.

The spreading method consists of opening the doors
alternately and spreading the fuel from the front to the
back wall evenly over the surface of the fire ; it means
that alternately one side of the.fire is bright while the
other is blanketed with green coal.

The coking method consists of placing considerable
coal on the front quarter of the giate and on the dead
plates, and after it cokes pushing it gradually back and
tilling up the front again.

Mechanical Firing*.

However, by far the most efficient practice is the
installation of modern stokers, which can be divided
into three types—overfeed, underfeed and chain grates.

The overfeed and chain grates are practically a
mechanical application of hand firing. The underfeed
type works on a different principle, and is the most
economical and greatest capacity generating stoker.

Briefly, the principle of the underfeed stoker is this.
There is always a hot fire on the top of the fuel bed,
and the green coal is fed underneath; the volatile gases
are given off, and, passing through an incandescent bed
of fuel, are thoroughly consumed, thus making the
boiler absolutely smokeless, except when fires are first
started or being cleaned.

With the underfeed stoker, full benefit of the heat
radiated from the surface of the fire is secured, as well
as the heat carried to the boiler surface by the hot gases
of combustion; and the heat radiated from the bottom
of the fire is constantly heating up the coal and
distilling its gases, whereas, in the overfeed type stoker,
there is present a covering of green coal for some time,
which prevents the heat of radiation reaching the top
of the fire, while the radiation from the bottom of the
fire is lost.

A closed air chamber is used, and air is forced
through the tuyeres into the retort—the steam pressure
controlling the whole operation, which is absolutely
automatic. If the steam goes up, the blower slows
down, reducing the volume of pressure of air going
through the tuyeres, and at the same time cutting
down the supply of coal to the retort, making an ideal
condition.

The underfeed stoker is very successful on widely
fluctuating loads, as it will automatically take care of
loads varying from zero to 200 per cent, within periods
of three or four minutes, and do it efficiently.

All stokers, however, require some intelligence in
their operation—different kinds of coal requiring
different methods of handling, and no fixed rule for
firing, air pressure, etc., can be set down for any
particular coal. Coals that by approximate analysis
may appear to be the same may have to be handled
quite differently to get the best results caused by the
different composition of the ash.

As a general rule low volatile, high carbon coking
coals require a fairly heavy fire and high blast pressure
to cut the coke, whereas high volatile coals require a
lighter fire and a volume of air at less pressure.
Lignites are most successfully burned on a stoker by
running a very light fire at a rapid rate with a large
volume of air at a low pressure, and by burning them
as newly mined as possible before they dry out.

High CO2 and absence of CO. results in high initial
furnace temperature, and high furnace temperature
means greater efficiency. It is bad practice to run five
boilers at a low furnace temperature, and low efficiency
when four boilers at high furnace temperature and
greater efficiency will do the same work. With a CO2
recording machine, the man in charge can check
efficiency as he goes along, and if the CO2 is averaging
less than 10 per cent., he should investigate each boiler
individually, study the draught gauges, take the tem-
perature of the escaping gases, and examine the fires to
see that there are no holes in them.

Every boiler room of large capacity should have a
technically trained engineer in charge with full autho-
rity, whose only duty should be obtaining results in the
boiler house.

In the smaller boilei’ house the chief engineer of the
plant, who usually is responsible, should realise that
the efficiency of his plant depends to a very large extent
on the operation of his boiler room.

Having found out by careful tests the best way to
burn the coal to the best efficiency, the engineer should
see that the firemen carry out instructions, keep a
record of the results secured by each fireman, and
where possible pay him a bonus on his individual
efforts, and not on the results of the whole. A fireman
is not a machine but a human being, and a little
encouragement and a pecuniary interest go a long way
toward increasing ultimate boiler room efficiency.

In conclusion, the value of the use of instruments,
the buying of coal by analysis, etc., is very largely lost
if careful records are not kept of the daily results, and
comparisons made weekly and monthly. Forms should
be made out on which should be recorded daily the
amount of coal used, water evaporated, temperature
of feed water, pressure of steam, CO2 record and

draught pressures, analysis of the coal, and the amount
of ash wheeled out. From the daily reports, weekly
and monthly summaries should be entered on forms and
forwarded to the main office.

STEEL CANTILEVER SUPPORT FOR
HEADFRAME.

Supporting the headframe over a mine shaft by
cantilever trusses was the expedient resorted to at the
“ A ” shaft of the Pioneer mine of the Oliver Iron
Mining Company, at Ely, Minn., because of unstable
ground.

This shaft was sunk in the early ’90s, and was then
equipped with a timber-frame shaft-house. It had been
impossible to explore the ground in advance to such an
extent as to determine thoroughly the nature of the
underlying rock, but no change of alignment was
experienced until 1900, when a slip in the formation was
noticed about 135 ft. below the collar of the shaft. The
depth at that time was 1,110 ft. The alignment was
maintained without difficulty, however, by trimming
the timbers and occasionally replacing a shaft set.

A steel headframe was built in 1909, up to which
time the settlement at the surface had not been serious.
In this structure the rear columns were placed 70 ft.
from the shaft, and were supported on independent
concrete piers, founded in good solid ground. The
front columns and ore-pocket columns were supported
on a concrete base, 50 ft. by 65 ft. and 3 ft. thick, rein-
forced at top and bottom with steel rods, so that when
settlement occurred the entire front portion would
move uniformly, thus causing no undue stress in the
steel members.

The bases of the rear columns were provided with a
hinged joint. The bases of the front columns and ore-
pocket columns were fitted with brackets, so that jack-
screws could be placed under these to raise the columns
and thus take up any settlement of the ground. From
1909 to 1912 the settlement due to the slip in the shaft
amounted to 9 in., which was taken up by jacking the
front columns of the shaft at different times and putting
blocking under the bases.

ADOPTED PLAN

ore\

■"ORE.

COAL TRESTLE

Concrete
«-• Waffs

1 e

Stock
Pile
nr-

' ALTERNATIVE FLANS

A A, Concrete Waffs

B Bj Steel Girders andStruts

% L
’ $

/

-Shafi

/

$ I
A

# . I

Headframe is Hung from a Giant Bracket.

Movement of the ground became much more serious
in 1912, and it was apparently unsafe to continue mining
operations near the shaft without making provision to
support the shaft house. Consideration was given to
three different methods for supporting the shaft house
and pockets.

The first plan was to excavate the entire portion
between the line of slip and the shaft, and construct a
vertical concrete wall with two wings, all founded on
solid rock. This would extend from the first level in the
shaft, 135 ft. below the collar to the under side of the
reinforced concrete base supporting the front portion
of the shaft-house, as shown by dotted lines A—A in the
drawing. The wall would carry the entire load of the
foundations, tracks, cars, front portion of shaft-house
and ore in shipping pockets, and would support the
rear portion of the main shaft from first level to
surface.

The second plan was to excavate beneath the rein-
forced concrete base and place two horizontal steel
girders under it, as shown by dotted lines B—B. The
rear ends of the girders would be anchored on good
ground back of the slip, and the ends over the shaft
would be supported by structural steel struts or
columns placed at an angle of 45 degs. and seated on
solid rock.

The third plan, which was adopted, was to construct a
steel cantilever support, having its footings on perma-
nent ground on back of the slip. This carries the
portion of the shaft-house above the stockpile trestle,
which consists of skip dumps and headsheaves. All
main columns of the shaft-house were disconnected at
splices at the stockpile floor elevation, except the rear
batter-brace columns, which have a firm footing. The
cantilever support thus maintains the headsheaves and
skip dumps in permanent position, and the front part of
the shaft-house, including the stockpile floor and
shipping pockets, now cut loose from the upper portion,
will be kept in position by jacking up and blocking the
column bases as may be required by ground settlement.

Adoption of this plan was based upon the fact that
its first cost was the lowest, and that this structure was

above ground, where it could be erected readily and
inspected easily. As the rear columns of the cantilever
support are on solid rock and have an uplift, the pier
excavation was made in the shape of a prismoid and the
concrete was poured without the use of forms. The
concrete pier was made large enough for its weight
to balance the uplift due to the weight of the shaft-house
portion; the bond of the prismoid in the solid rock is an
additional safety factor.

As toe mine shaft is constructed of timber sets and is
considerably larger than the skips and cages, there is
sufficient room for lining the timber guides without re-
timbering or enlarging the shaft. The cantilever
support has now been in service for practically five
years, and has kept the upper part of the shafthouse in
accurate alignment. The lower portion has settled twro
feet, which has been taken care of by jacking up and
blocking the front column.—Engineering News-Record.

IGNITION OF EXPLOSIVE MACHINES BY
ELECTRIC SPARKS.

By M. J. Meunier.

The various workers who have investigated the
subject of the ignition of explosive mixtures by electric
sparks have not all arrived at concordant results,
because the majority neglected to take into considera-
tion one of the principal causes of irregularity—namely,
that ignition does not depend solely on sparks and on
their temperature, but also on the manner in which the
combustion of the mixtures may proceed.

In practice, sparks often occur on the breaking of
a conductor by fusion or through short-circuiting.
Before breaking, the metal attains a high temperature,
often much over 600 degs. Cent., which is accepted as the
ignition point of firedamp.* If, under these circum-
stances, the firedamp does not ignite, it is evidently
because it has undergone the special form of com-
bustion termed “convergent” (see Colliery Guardian,
January 10, 1913, p. 70) ; such as occurs in
incandescent gas lamps, gas mantles, etc. When
the spark is produced at the moment of rupture,
it is surrounded by a kind of sheath composed
of burned gases; and in order to produce ignition it
will be necessary for the heat to be transmitted through
the sheath to the point where the composition of the
gaseous mixture has not been modified by the products of
the convergent combustion. The phenomenon is of the
catalytic order, and, in fact, one may consider that all
solid^ bodies, in the form of wire, act as catalysts,
though in different degrees, according to their nature.
Electric light filaments behave in this way; and the
experiments of Messrs. Watteyne and Stassart, as well
as those of the writer and M. Couriot, find a simple
explanation by this hypothesis.

* Sparks given off at 1,200 degs. Cent., the fusion
temperature of iron, or at 1,350 degs. Cent., the fusion
temperature of platinum, failed to ignite mixtures of air
and methane of maximum explosibility.— (H. Couriot and
J. Meunier.)

THE AMERICAN COAL TRADE.

The bituminous mines during the week ended Octo-
ber 5 shipped 12,585,000 net tons of coal (according to
the Coal Age, October 17). Though this output is a
decrease of 462,000 net tons as compared with pro-
duction the week preceding, the total not only exceeds
the weekly requirements of the country by 4 per cent.,
but helps to make up 3*2 per cent, of the existing soft
coal shortage. Anthracite production during the same
week totalled 2,052,000 net tons, a decrease of 19,000
net tons as compared with output the week ended
September 28.

Labour shortage and poor car supply are again
noticeably to the fore in the bituminous regions. In
the anthracite region production is being seriously
curtailed by the influenza epidemic.

The most carping critic must now admit that the
Fuel Administratien has amply justified itself. A
number of other important industrial centres report
ample reserve stocks of fuel. Coal is now relatively
easy to obtain.

Only the premature closing of the Lake season by
severe weather will prevent the north-west from
receiving its allotment of 28,000,000 net tons of bitu-
minous coal by way of the Great Lakes.

Actual assignment of production quotas has been
begun by the Director of Production for the Fuel
Administration, Eventually each mine in the United
States will be required to maintain a specified rate of
output.

American manufacturers have been invited by the
Port and Harbour Facilities Commission to make a
careful study of the entire port situation to the end
that possible new and ingenious methods of handling
cargo and coal may be developed in conjunction with
the best arrangement of piers, warehouses and other
terminal facilities.

It is understood that shipments must now begin to
increase very fast to meet urgent needs in France,
Italy and other Allied countries, but not until lately
was it thought prudent to deprive New England of the
coal such a move would mean. Several large modern
colliers were withdrawn recently from the coastwise
trade in order to carry cargoes overseas. Despatch has
improved at Hampton Roads.

Chemical Industry and Coal.—The address delivered by
Prof. P. Phillips Bedson, of the Chair of Chemistry,
Armstrong College, Newcastle, as newly elected chairman
of the Newcastle-upon-Tyne section of the Society of
Chemical Industry, at the section's annual meeting last
week, was largely in the nature of a review of the Tyne-
side chemical trade’s development since 1886. He referred
to the establishment in the locality of processes for the
manufacture of compressed gases, instancing those at the
various colliery rescue stations at which the liquefaction
of air and the separation of its constituents were practised.
He mentioned also the manner in which, since the out-
break of war, the coal tar colour industry had been used as
an illustration to bring home the importance of research.