Charles George Warnford Lock.

Economic mining: a practical handbook for the miner, the metallurgist and ... online

. (page 22 of 76)
Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 22 of 76)
Font size
QR-code for this ebook


Heating Valne.


1

1 Percentaae of Fixed


Heating Vatoe.










Carbon in Coal, Dry




British


! Carbon in Coal, Dry




Brftbh


and Free from Aah.


Galoriea.


Thermal
Units.


1 and Free from Ash.


Calorifli.


TbenDal

Units.


97


8,200


14,760


63


8,400


15,120


94


8.400


15,120


60


8,100


14,580


90


8,600


15,480


57


7.800


14,040


87


8,700


15,660


54 ■


7,400


13,520


80


8,800


15,840


51


7.000


12,600


72


8,700


15,660


50


6,800


12,240


68


8,600


15,480









But below 50 per cent, of fixed carbon the law does not hold, f(
some tests of lignites depart considerably from the average curve, i
do also cannel coal and turf. In the case of cannel coal t^is may 1
accounted for by the relatively hich percentage of hydrogen and 1<>
percentage of oxygen, but it is difficult to account for the high vai^
shown by turf. i

Comparison of the industrial or steaming power by Johnson*s ai
Gruner's tests with the heating value as determined by a calorimet
strongly emphasises the fact that in the burning of highly bituminon
<k>als under ordinary steam-boilers a ^eater percentage of heat is k
than in the burning of anthracite and semi-bituminous coals. Th«
is but little difference in the calorimetric heating power of ooi
containing respectively 70 and 85 per cent, of fixed carbon, but
industrial practice the latter give 15 to 20 per cent higher resnil
This is simply due to the great difficulty in ordinary boiler fumao
of burning the excess of volatile combustible matter, which oo
sequently passes out of the chimney in smoke and unbumed gasea^

While a consumer who estimates the value of a coal by



Digitized by



Google



NON'METALLIFEROUS MINERALS, 193

dementary oomposition has a good chanoe of finding a figure
roffioiently near to the trath, except in the case of extra-hydrogenous
soals (0) of the nature of cannel coal, still it is difficult to determine
trith precision the hydrogen and the carbon contained in a coal, and
It is more simple to have recourse to a calorimeter, which permits us
to appraise the value of all the combustibles without exception, and
inth precision.

An excellent form of calorimeter is described in detail in
inmaJkt de Physique et de Chimie, 1861 and 1885. The bomb consists
)f a shell of forged Siemens Martin steel, 654 c.c. capacity, weighing
ibont 8} Dxj and with walls 8 mm. thick, nickel-plated outside, ana
internally ooated with a white enamel to protect it from the corrosive
fcction of the gases of combustion. This coating is very thin, and
iffers no appreciable resistance to the transmission of heat.

The combustible whose calorific power is to be determined is
placed in a platinum capsule suspended in the interior of the shell,
uul the shell is immersed in water in a calorimeter made of thin
iheet brass, which is surrounded by a non-conducting envelope. The
miform weight of 2*2 kilo, of water is used, and the quemtity of
sombustible used is generally 1 grm. I'he shell is filled with oxygen
{KB under a pressure of 20 to 25 atmospheres, the stopper is tightly
closed, and the combustible is ignited by passing an electric current
through a fine iron wire placed in the combustible. The combustion
■liich takes place is complete and almost instantaneous. The heat
lisengaged is transmitted, without any loss, to the water in the
lalorimeter, where its quantity is measured by a delicate thermo-
Deter, the water being thoroughly stirred by a spiral agitator. On
looount of the rapidity of the experiment the greater part of the
ftnrections nsually necessary in calorimetric work are negligible ; for
ntample, those due to the evaporation of water and to the variations
in temperature of the room. The correction for the " water equiva-
ient " of the apparatus itself was determined by experiment to be
181 grm., which is to be added to the weight of water used in the
lalorimeter, or 2200 grm. The correctness of this figure was further
proved by experiments on the combustion of naphthaline, the calorific

Ewer of which had been determined by a great number of trials to
9692 calories per kilo. Three experiments with the bomb gave
>• 6855, 9 • 6855, and 9 • 6935 calories, a mean of 9 • 688 calories per grm.
In conducting an experiment, the observer notes the temperature
bom minute to minute for 4 or 5 minutes before the ignition, while
Bonstantly stirring the water; then having made the ignition, the
temperature is noted ^ minute and 1 minute afterwar<^ and- then
* om minute to minute until the temperature is reached from which
begins to decrease regularly. This temperature is the maximum.
^ observation is continued about 5 minutes longer to determine
law followed by the thermometer after the maximum, and the
pODse^iient correction to be applied for cooling of the calorimeter by
IBidiatioiL. After opening the bomb its interior is washed with dis-
Bled water so as to collect the liquid nitric acid which may be
tonoed during the explosion. The amount of this acid is determined
vc^ometrically by titrating with a solution of potash. All the data



Digitized by



Google



194



ECONOMIC MINING.



heiog thus obtained, the calculation for calorific power Q of the com-
bustible is made as follows : —

Let D be the difference of temperature observed ;

a, the correction for cooling ;

P, the weight of water in the calorimeter ;

P', the equivalent in water of the shell and its accessories ;

|>, the weight of nitric acid (NjOcH^O) ;

p', the weight of the spiral of iron wire ;
• 23 cal. is the heat of formation of 1 grm. of nitric acid ; and'
1 ' 6 cal. is the heat of combustion of 1 grm. of iron.

We have

Q = (D + a) (P + F) - (0-23p + 1-6|>').

In an industrial determination of the heating power of a sample of
the well-known Nixon's Navigation Coal from South Wales, analysis
gave :—

Fixed carbon, without ash 86*30

Volatile matter, without water 10*15

Uygroscopio water 1*85

Aflb, by cfJoination : 1*70

10000





Preliminary Period.




Combustion.




min.


o


min.





min.


o





15*20


84 .


16*60


7


1832


1


15-20


4 .


17*92


8


18-80


2


15-20


5 .


18*82


9


18*30


3


15*20


6 .


18*34


10


18-30








maximum


11


18*26



Pressure of oxygen, 26 atmospheres.
18° -34 - 18*' -26



a =



'_^"- = 0^-016 per minute.



Differeuce of temperature observed 3*140

Correction 4-5, 5-6; 0*016 x 2 = 0*032

Correction 4-8} 0-005



Difference corrected



3177; 8ay318



We have then, for the quantity of heat disengaged, (2200 -f 481)
grm. X 3° -18 = 8-5256 calories; less weight of iron wire, -025 grm.
X 1*6 = 0-040 calories; nitric acid found, 0-16 grm. x 0-23 =
0-0345— total, 8*4511, or for 1 kilo, of the coal, 8451 calories.

The tendency to spontaneous ignition in coal has been suppoeei
to increase with the quantity of pjrrites present in it, but experimei^
shows that it is the tendency or power of the cual to absorb oxygiett
which must be taken as the true index of danger, and this may
be roughly gauged by the amount of moisture which the ooal lu4>



Digitized by



Google



NON-METALLIFEROUS MINERALS.



1 95



abaorbed from the air. If muoh moisture be found in an air-dried
sample of ooal, it at onoe stamps it as a highly absorbent form, whioh
most on that acoount be stored with special precautions ; if but little
moifiture be present, it is probably unable to take up enough oxygen
to lead to serious mischief.

This is shown in the annexed table, which ako makes it clear
how little pyrites has to do with ignition : —



I LiaUUty to SpontaiwouB
Combnstton.



Very slight



Medium



Great



Pyrites per cent.



113

IDl to 3-04

1-51

1-20
1-08
115

112
0-83
0-84
100



MoUtore
percent.



2 54
2-75
3-90



5(y
55
75

85
30
52



901



When once coal has taken up oxygen, and the early stages of
heating are passed, and the temperature has again fallen, all danger
of ignition is over, and it may be stored in any quantity with perfect
safety, so that if it were practicable to keep newly won coal for a
month in moderate-sized heaps, and then to avoid much breakage in
afterwards loading it, spontaneous ignition would be almost unknown.

An idea of the enormous scale on which coal mining is conducted
may be gained from the subjoined statistics of the output of the
principal producing countries in 1890 : —

MiUkm Tons.

Great Britain 184}

Germany 70

France 26

Belgium .. .. 20

Austria 9

United States 141}

The cost of production per ton, taking total outputs right
in 1890, was as follows :—

t, d.

Canada 4 4}

Great Britain 4 2|

United States 3 0}

Continental Europe 2 9|



Of these Bums, the labour cost was : —

«. d.

United States 2 8}

Canada 3 6

Great Britain .. .. 3 8

Continental Europe 1 lOi



Percent,
of the ToUl.
89i
801
77*
67}



Digitized by



o 2

Google



196 ECONOMIC MINING.

The average output per miner per week is approximately as
follows: —

TOQS.

Oontinental Europe 27f

Canada 24i

United Statee 23}

Great Britain 18|

These calculations refer entirely to hand-mined coal as it comes
from the miner, without being screened or otherwise treated. Hand-
mined generally costs a good deal more than machine-mined coal, the
difference being occasionally as much as 50 per cent. The cheapest-
mined bituminous coal is now mined by hand and loaded on the rail-
road cars— every expense, improvements, d^c, included — in some parts
of the United States for about 1«. lOjd. per ton of 2000 lb.

Machine mining is steadily being extended in America, and not
only is compressed air being used more and more each year, but
electricity as well is gaining ground. Some of the best coal-cutters
are now driven by the current, and electrical underground haulage
(and lighting) is recommending itself for rapidity, easy control, and
cheapness.

The various methods of mining for coal and the operations
incidental thereto, have been described in a previous chapter (see
pp. 99-102 so far as regards matters of general application.

Cutting, — Something remains to be said here about coal-cutting
machines as compared -^th hand labour. The table on p. 197, by
Blake Walker, deals with the question on the basis of English rat^
of wages. It is so far open to comment in that insufficient stress is
laid upon the risks of delays and extra costs incidental to breakdowna
with cutting-machines, and a certain proportion of cases will oocm
where a machine cannot be used at all.

Another point which cannot be disregarded is the necessity foi
having intelligent and skilled men in charge of the coal-cutter. Thesf
are not always easily obtained. In any event, the advantages of 1
machine will greatly depend upon the local labour market, and w<
may therefore expect machine cutting to make most headway -when
wages are high. It is therefore all uie more interesting to note th<
following remarks by Scott in drawing a comparison between han<
and machine cutting in Pennsylvania. He tinds that in machin
mining the stalls can be made much wider, because of the grea
rapidity of mining, so that the roof will stand a shorter time wit
fewer pillars. The immediate effect of the introduction of coa
cutting machineiy is to reduce the cost of undercutting from 2Qd. \
5(2. per ton of Ij^in. coal in the Pennsylvanian district. Taking ini
account the other expenses, there is a saving of 25 per cent. Anoth<
advantage of machine mining is that perfect pillars are left and oa
be recovered, as there is no temptation to rob them. The reductic
of the number of stalls for the same output, due to machin ery, all
causes a great saving in the timber, the number of roads and the trar
ways that have to he kept up. The saving of coal due to tiie intr
duction of machinery, is also very great ; this arises from the sma
amount of slack and the larger coal produced by the smaller heig]



Digitized by



Google



ROUS MINERALS.



197



i




II


S-o


s


S


•^•"i




»


s


IS


1


CO


^

i


to


04

S "


ja





•0^






•9*-^


^


09




4J ©1


Cl










i


1




















«>


•9»H


CO





^


id


•at-






•X3^




»


IH


"" lA


g


^


•^


CO


»o ^


i

a


^


1


••00


s


S


•9'^




09


li




•^00


09


rH


CO


iS




















Oi


•oO


CO





fH


u


•X3CO


s


^


^i^




<o


s


is


i


CO


00




09


to ©9

iH






5*


•ieo






«^


-^


01




4J


^
































•oO


00





i-t


1


.


"OO






•^'^









"> eA


g


U)


10


•O


«o








10


10






iH





bSS


09


•ao>


t«.


^


to




i> j


••CO


«o


M


•9 ^


to


pH


t^


5S


«r










It




















GO


«o


09





IH iH












HN








•0
01


00


CO





to 04


It

a • ^


1




g


S3


'O'CO

•9'^







Fi^


2


li


'Oi,


-4*


4*


m


\\




















•oO


©9





iH


,










HN











00


00


09


to t»


J.


1^


«04


s


S









fH


S


11


»H


•<»•*


09


m


iH

fH


1


iu




-


-^








=




•90


09





iH












g


CO


CD


"■^


-^






>33


'««








•oco


-^


00





S|2


g


-'^t.





«


iH ^


•«




•bCQ


to


c^


•9<^





I^


b-


^^






p-i






^


a




















•9*0


IH.





iM iH


e


^























^


iH


a>


0)


s

p


^
sq


i


•00




s


•9-^




CO


s


11


S


t3«


09


CO


S «'


1




















IH


•oO


fH





IH


/.





















QO


QO


09


09


2




1^


•^s


10





•X30


^


CO


?


li


10


'tt'w


<o


n


iH ©9






5-


•a 1-4


'^





••^


to


fH




t*








fH






Ut


















§


•0*0


IH





iH



























CO


00


t^


t^


^




ti




!8


s




to




IH


g







•oi


<D


pH


S »


5


?

1




















1H


••0


IH





fH










OJ













09


09


00


00 CO


S


i


1




s


s




10




IH




is


1






C4




00 fH

fH




- 5


i








©a













fH


pH


oa


00 r*


,


Si


ti<o








•xit-


-^





s


ss





•»•«


W


09


00 IH




>j^




^


04








52














,«• <


■B ^4






•0<44


10


IH
















u.


















©1


•9O


fH










, - ^






/— '^— N


,_^^«^


^«,-^_^




» ^— *— N


>— ^^~<


» .— ^— V


,— ^— s










j


1


11 •


^1
1.1




1.=


1








? !
I ■








1:


1

•s

t

1


1




•s


4^ S

£.3


Hi


.a

1


H


1:
1:



Is


I:

a


1 !

ll
II



Digitized by



Google



igS ECONOMIC MINING.

and greater depth of undercutting, and also from the pillars not being
orushed. An estimate is given of the saving in expense by using a
plant of 7 machines, run 10 hours a day, and cutting 233 tons. The
cost is 29/. 11«. 3d., made up as follows: fuel, 9^. Id. ; wages, 22. lOs. ;
deterioration of boiler, engine, electrical apparatus and wire, 12. 6<. :
cost of repairs, 1/. 0«. Sd,; cost of working, 4/. 17«. ; loading and
blasting, 19Z. 8«. The indirect saving is estimated at 21. 19«. The
cost of hand mining is 382. 6«. 8ri Worked out per ton, the saving
would seem to be 9(2. directly and 3c2. indirectly.

A number of coal-cutting machines will be found described in the
author's ' Mining and Ore-dressing Machinery ' ; but two or three of
the most modem forms deserve description here.

The Jefi&ey pneumatic coal-cutting machine, introduced into this
country by John Davis & Son, of Derby, consists of a bed frame
occupying a space 2 ft. wide by 7 ft. 6 in. long, composed of two steel
channel h«irs firmly braced, the top plates on each forming racks ^with
their teeth downward, in which the feed-wheels of the diding frame
engage. Mounted upon and engaging with this bed frame is a sliding
frame, similarly braced, consisting maiidy of two steel bars, upon
which are mounted, at the rear ends, one double 5 by b\ in. engine,
from which power is transmitted through straight gear and iwt>nn
wheel to the rack, by means of which the sliding frame is fed forward.
Upon the front end of this sliding frame is mounted the cutter-bar,
held firmly by two solid steel shoes, with suitable brass boxes. The
cutter-bar contains steel bits, made of tool steel, held in place by set-
screws. When the cutter-bar is revolved these cutters or bits cover
its entire face. The cutter-bar is revolved by an endless curved link
steel chain from the driving shaft, and as it is revolved, is advanced
by the above mechanism into the (K)al, or other material, to be under-
cut to the desired depth.

The present cutter- bar is a great improvement over those formerly
used, as instead of being weakened at the sprocket by being squared,
to admit of the former straight link chain, it is now made round and
increased in diameter at this point. The bar is driven as before by a
curved link chain, thus not only permitting it to be strengthened at
this point, but greatly increasing the leverage of the chain by
throwing it farther out upon the sprockets^ and greatly lessening the
power required to revolve the bar in the coal, as well as reducing the
friction and wear upon the chains. The feed is thrown on and oSL
by means of a lever. The cut under the coal, 6 to 6 ft. by 3 fL 6 in.,
is made, and the cutter-bar is withdrawn in 4 to 6 minutes.

In the Jeffrey electric cutter, the engine is replaced by an electric
motor and the frame is 8^ ft. long. The motor occupies a space 20 in.
square. The current required is 30 to 50 amperes at a pressure ol
220 volts. Each motor is wound to develop 15 h.p., but often onl^
requires 7^. The armature is run at 1000 rev. a minute and tlM
cutter-bar at 200.

The Sergeant coal-miner, made by the Ingersoll-Sergeant Drill C(k
possesses several distinctive features. The valve is operated bj i
very simple device, consisting of two valves in the same chesty aaMJ
entirely independent of the action of the main piston. The vml'vi



Digitized by



Google



NON-METALLIFEROUS MINERALS. 199

motion is reliable and positive. Having no dead centres, it always
iitarta on turning on the air, and has no outside hand wheels or
moying parts. By means of this duplex slide-valve system the
itioke is made variable both in length and strength, and the force
of blow and length of stroke are tinder instant and thorough control
of the operator.

The r^alator is very simple, and can be adjusted instantly to
giTe a long heavy blow for " blocking out," or a quick light blow for
** backing out," or finishing the cut.

An improved air cushion has been substituted for the device
formerly used, consisting of a heavy sewn leather washer, held in
place by the air pressure in a reservoir, which is connected by a small
pwsage with the main air supply. This leather is protected from the
blow of the piston by a steel washer, and both the washer and leather
are free to move against the elastic air. Both the outside and inside
circumferences of the air cushion are kept tight by an improved
form of leather packing ring. The device is very durable, and is
mexpeusive to replace when worn out. There is no waste of air,
la none of the air contained in the reservoir is exhausted or passed
through the valve. This makes a most elastic and durable cushion.

The picks are of forged steel, with shanks made square and of full
size where they enter the socket, and, unlike the old style of turned
thanks, never break. They are readily kept in order by any common
blacksmith, and require no special took for sharpening.

Balancing for any duty is readily effected by loosening one nut
md slipping the hub backward or forward in a slot cast in the side
►f the cylinder. This obviates the necessity for hanging on cumber-
ome weights.

The piston is made of special forged steel, and is corrugated to
irevent rooking or twisting, and unlike the square piston sometimes
laed, does not bind or cut. It is held in place by a composition
oetal sleeve which is bolted into the front head.

The wheels are provided with large hub bearings — 4 in. diam. —
hich eases the effect of the blow on the operator, and obviates lost
lotion. The movement backwards and forwards on the board while
Mining at fall speed — 190-250 double strokes per minute — is about
m. ; no rachet, pawls, or similar device is required to prevent recoil.
Wheels can be furnished of any size, thus adapting the machine for
rearing, entry driving or any desired duty.

Having but three moving parts, the machine is exceedin^y
mple, durable^ and economical; the makers guarantee it to mine
ttJ at less expense for fuel, labour, and repairs than any other
achine.

Its small size, great strength, and extreme simplicity adapt it for
!ar]y all kinds of bituminous coal mining. It has no gears, chains,
itter-bars, levers, pulleys or other complicated attachments revolving
tder the coal to produce friction or consume power, and requires no
yc\% or jacks to hold it in place. It is worked from an inclined
ard of convenient size, while making an open channel under the
d of 4 or 5 ft. of face and 3-5 ft. undercut, as desired. The cut can
made of any desired vertical height, 8-18 in. high on the face



Digitized by



Google



200 ECONOMIC MINING.

and tapering to 2 in. at the back, the same as done by skilled manTuJ
labour. But one man is required to operate the machine, with the
assistance of a common labourer to shovel away the cuttings, and
keepan extra board set in advance as the work progresses.

The operator can swins the machine and direct the blow with
one hand and can work either right or left handed. The machme
requires but little space and can be used successfully in narrow vdna
around and between props, and wherever a miner can swing a pick.

Less air is required to run these machines than any other, and
they will cut with an air pressure of 40-50 lb., 76-150 lineal ft of
£stce, 4-5 ft. xuidercut, the amount of work done depending on the
character of the coal and the skill of the operator.

Following is an estimate of the machinery necessary to run
5 Sergeant coal-cutters by compressed air : —

£ «. d. £ «. d
1 IngeraoU-Sergeant standard class " A " straight line aii-
oompreesor, of piston inlet cold air pattern, st^un cylinder
16 in. diam., air 16} in., stroke 18 in. ; complete, with im-
proved water circnlating jacketed cylinder and heads, and
automatic and adjustable regulator with unloading device
for air and steam ; capacity sufficient to run 5 coal-mining

machines 531

1 steel aur receiver, 42 in. diam. ; height 120 in. ; furnished

complete with gauges, safety valve and fittings 35 10

1 70-h.p. (actual) horizontal tubular boiler, of arch front
pattern, with stack, frrates, gauges, rollers, brackets, and
fittings, including injector, complete ready to fire, except

brickwork 175 10

Estimated cost of pipes, valves, and fittings, to oonnect boiler
with air-ocnnpressor, and air<»mpressor with receiver .. 20

Total net cost of compressor outfit 762

„ weight „ 28,8001b.

5 Ingersoll-Sergeant standard ooal-mining maohinea, at
76/. each 375

80 picks for same at 8Z. 8s. per doz. 21

5 50-ft. lengths of 1-in. air hose, wire-wound, with patent
couplings attached, at 6Z. If. each 30 5

Total net cost of coal mining outfit 426 5 \

„ weight „ .... 41101b.



Total net cost of complete outfit 1,188 S

M weight „ .. 32,9101b.



Cleaning. — With the increasing scarcity of good coal, it has
necessary for colliery owners and managers to pay more attention
improvements in and labour-saving appliances for the treatment of ^i
coal when above ground, in order to enable them to profitably
seams of dirty coal, avoiding at the same time all waste. On 1
other hand the question of having as clean a coal as possible far ^
production of coke, and clean small coal, such as nuts, for steam p
poses, demands no small attention, as buyers pay a higher prios



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 22 of 76)