132

THE COLLIERY GUARDIAN.

January 21, 1916.

ventilating splits 1, 4, 5, and 6; 4in. w.g. necessary to
pass this quantity through the main intake and return
alone.

If for any reason the outerop fans at A X C have
to be abandoned, and the total mine ventilation, 150,000
cu. ft., has to pass through the main intake and return,
then the w.g. required to pass this. quantity through
the main airways alone would be 9 in. The ventilating
unit at the mine entrance would have to be increased
in power by 2J times. Two 60 in. diameter open
running fans of the Ventura type,'’placed at A and C
could each pass 25,000 cu. ft. of air with -J- in. w.g. This
w.g. would be ample for such a split in a 7 ft. seam.
The horse-power ventilating the mine, as suggested on
plan, would equal 66-97. The horse-power-in the air,
passing the whole ventilation to a fan at mine entrance,
would equal 212-92.

The difference in favour of the outcrop fans = 145-75
horse-power in air. With a 60 per cent, efficient unit
this would be equal to 243 indicated horse-power.
Taking 2 lb. of coal per indicated horse-power per hour,
this represents a saving of 2,128-6 tons of coal per year.
It is thus evident that large economies can be effected
by the use of auxiliary fans.

FUEL VALUES*

By Dr. J. H. Paterson.

The financial value to 'the consumer of a fuel must be
measured by the amount of heat which can be obtained
from that fuel by the expenditure of a definite amount
of money. This value is totally distinct from, and is not
affected by, the quantity of the available heat which is
utilised in any given process. In this paper, therefore,
no cognisance is taken of the methods and appliances
used to obtain the most efficient utilisation of the heat
generated, but only the amounts of heat actually avail-
able from the fuel used.

In dealing with fuels of different classes, some diffi-
culty has been met with in finding a common unit of
value for their comparison, and it has been considered
best, for the purposes of this paper, to make this unit
the number of heat units (British thermal units) obtain-
able for one penny, after all the costs of handling the
fuel and causing it to burn have been added to the price
per ton. This number will be referred to hereafter as
the absolute heat value of the fuel in question.

As the cost of fuels varies very considerably in
different parts of the country, the comparison of their
values is impossible unless the prices of all the different
classes considered are those ruling in the same locality.
For the purpose of this paper, therefore, the prices given
are an average of those ruling in the north-east coast
industrial centres. As the present cost of fuels is in all
cases abnormally high, and in some cases (foundry coke
and oil fuel) out of all proportion to the usual value,
pre-war prices and values are shown in the most impor-
tant cases, as well as the present prices and values.

Coal.

It is very generally recognised that the less money one
pays for coal, the more incombustible matter (water
and ash) it is liable to contain, but it is by no means so
generally realised that the absolute heat value increases
rapidly as the price decreases. The following table
(Table I.), which is compiled from the average analyses
of a few selected coals of types in common use, shows
this clearly. In this table the calorific values shown
are the net values, that is, the calorimeter value as
determined on the dried coal, less the amount of heat
carried away as latent heat during combustion, by the
steam produced. The price of the coal as quoted
includes the cost of delivery into the works, this cost
averaging about 2s. per ton.

Table I.

Brice Net jncomb. B.T.U. a it v

Class of coal. per cal. matter. forld A.H.V.
ton. value,
s. d. B.T.U. P.c.

1.	Best screened loco.

coal ............... 23 0...14,280... 5’6 ...115,000... 98,700

2.	Screened steam coal 18 3...13,120...13’35...134,200...110,700

3.	Screened steam coal 18 0...13,260...10’65...137,500...113,300

4.	Smith’s small coal.. 18 6 13,600...10’32...137,000...115,500

5.	Unscreened steam

coal .............. 17 6...13,135...12’25,..140,000...114,400

6.	Washed small coal 15 0...12,780...12’50...153,500...126,100

7.	Heap coal............ 8 0...10,040...29’3 ...222,000...136,200

In fig. 1, the heat units per ton for a large number
of coals have been plotted against the price per ton.
As will be seen, the resulting curve shows remarkable
regularity. It is evident from it that, for prices between
14s. 6d. and 18s. per ton, the heat value paid for falls
away from the regular curve represented by the dotted
line, or, in other words, if coals were sold on a regular
calorific scale, instead of following the laws of supply
and demand, we should expect to pay less than the
present market value between these limits of price. The
coals in this area of price include unscreened steam
coals, washed slacks, and small nuts, all of which are
among the most commonly used classes in large works.

Fig. 2 shows a similar curve constructed at the end of
1913, and reproduced from an article by the author in
The Shipbuilder (vol. x., No. 41). In this case, the
falling off in value occurs between the prices 8s. 9d.
and 11s. 9d.

Tables II. and III. show how the absolute heat values
of coals Nos. 2 and 7 in Table I. are arrived at. The
figures given are those obtained when these coals are
used to heat a frame-bending furnace, and are very
similar for a hand-fired boiler.

* Paper read before the Society of Chemical Industry,
Newcastle Section.

Table II.

Coal No. 2.

One ton of coal has net cal. value of 29,344,000 B.T.U.

Pence.

Coal at 18s. 3d........................ 219

Firing labour .......................... 36

Moving coals and clinker ................ 8

Repairs to grates ....................... 2

265

A.H.V. = 110,700. ’

Table III.

. Coal No. 7.

One ton of coal has net cal. value of 22,489,000 B.T.U.

Pence.

Coal at 8s............................. 96

Firing labour .......'................. 38

Moving coal and clinker ............... 20

Repairs to grates ....................  4-5

Steam for blowing ..................... 6-5

165-0

A.H.V. = 136,200.

Coke.

Coke of all classes requires a blast of air to keep it
burning at a high temperature, so that in determining
its absolute heat value, the cost of this blast must be
included.. Foundry coke has recently reached so
abnormal a price, that its heat value, as shown below,
is misinforming. Its value in 1913, as-shown in Table
VIII., gives a better idea as to its true relative position.
Coke breeze (coke refuse from the gas works) is not
always appreciated at its true value. This breeze,
when screened through a screen of Jin. mesh, loses 40
per cent, by weight of fine dust, and leaves a residue of
coke nuts, which is an excellent fuel for many purposes.
Previous to the war, it paid to throw away the 40 per
cent, of dust, but now that its price has risen, it
becomes worth while to briquette it, . and mix the
briquettes with the screened breeze, the cost of
briquetting being about 5s. per ton of screenings,
including labour and tar binder, and also interest on
capital. Tables IV., V., and VI. show how the abso-
lute heat values of the foundry coke, screened breeze,

x

o

30

23

2,9

26

3i

26

25

24

27

A

Pio. 1. Pence per ton, 1915.

90	110	>30 ISO 170 I9O 210	230	250	270

and the mixture of screened breeze and briquettes are
obtained. In Table V., the screenings from the breeze
are assumed to be worthless, and thrown away.

Table IV.

Foundry coke.

One ton of coke has net cal. value of 30,350,000 B.T.U.

Pence.

Coke at 32s.......................... 384

Firing labour ........................ 36

Moving coke and clinker .............. 9

Repairs to grates ................... 2-5

Blowing .............................. 3-5

A.H.V. = 70,000.

435-0

Table V.

Coke breeze (screened).

One ton of breeze has net cal. value of 29,120,000 B.T.U.

Pence.

Breeze at 10s........................ 120

Cost of screening .................... 13

Moving coal and clinker ............... 9

Firing labour ........................ 36

Repairs to grates ..................... 3

Blowing ............................... 4

185
A.H.V. = 157,400.

Table VI.

Coke breeze (briquetted).

One ton of breeze has net cal. value of 29,120,000,B.T.U.
Pence.

One ton breeze at 6s................... 72

Briquetting 40 per cent................ 24

Firing labour ......................... 36

Moving coal and clinker ................ 9

Repairs to grates ...................... 3

Blowing ................................ 3

147
A.H.V. =200,000.

Producer Gas.

The absolute heat value of producer gas will depend
mainly on the first cost of the coal and on the efficiency
of the type of producer used. The results recorded
below are obtained from a battery of water-sealed pro-
ducers of the Duff type, each producer being capable of
gasifying 10 tons of coal per 24 hours. The coal used in
them is the small coal No. 6 in Table I.

One cubic foot of the cold producer gas has a net
calorific value of 170 British thermal units, and 65 cu. ft.
of cold gas is produced per lb. of coal, or 145,000 cu. ft.
per ton. One ton of coal, therefore, gives cold gas
equivalent to 24,750,000 British thermal units. When,
however, the gas is used hot, as from the above pro-
ducer, the sensible heat of the gas raises this quantity
to 27,000,000 British thermal units. As the original

I 51

32

X 3o

J
o
£ 291
<v

P 76-

<20	150	140	150	160 I7O »6O

Pence per ton, 1913.

80	90 ioo no

Fig. 2.

heat value of the coal was 28,627,000 British thermal
units, this shows a loss in the producer of 5 per cent, of
the available heat. The absolute heat value is arrived
at as shown in Table VII. It may be argued that a
somewhat expensive coal has been chosen when calcu-
lating this absolute heat value, and that if a cheaper
coal were burned in the producer the values shown
would be greater. Experience shows, however, that
this is not the case, as with the stationary type of pro-
ducer, there is a limit to the ash content of the coal,
beyond which good results are impossible. As an
example, in the same producers a small dusty coal was
tried, with the following results :—The cost of the coal
was 11s. per ton, and its heat value 26,150,000 British
thermal units net per ton. The loss in the producer
was 12 per cent., and the heat value of cold gas per ton
of coal 23,000,000 British thermal units net. The cost
of working the producer, supplying steam, and repairs
to plant, amounted to 112-5d. The absolute heat value
of the cold gas was 98,500, and of the hot gas 108,500.
The heat value is therefore 2 per cent, less than with
the dearer coal, and the dissatisfaction among the fire-
men being taken into account, it will be seen that the
cheap coal does not by any means produce cheap gas.
Mechanical producers do away with the labour and
other troubles enumerated above, but owing to their
comparatively short life, increased first cost, and
increased upkeep, their advantages are not very obvious,
in this district, at any rate.

Table VII.

Producer gas.

One ton of coal produces gas with net cal. value of
24,750,000 B.T.U.

Pence.

Coal at 15s.......................... 180

Labour ............................... 37

Steam ................................ 13

Moving coal and	clinker ............... 8

Repair and upkeep ..................... 2

Int. on capital ....................... 6

246
A.H.V. of cold gas = 100,600.

A.H.V. of hot gas = 110,660, or 10 per cent. more.

Oil Fuel.

Within the last 12 months the cost of fuel oil of
moderately good grade has increased by nearly 100 per-
cent. This therefore puts an always expensive fuel
almost out of consideration. Good Texas oil of about
.1,000 secs, viscosity has a net calorific value of about
17,300 British thermal units per lb., or 38,750,000 per-
ton. This oil now costs 105s. per ton. Before it can
be burned in a furnace, it must be first atomised either
by compressed air or steam, or else blown through a
special nozzle at high pressure into a forced draught
furnace. The cost of vaporising oil by compressed air is
10s. per ton of oil, and by steam or by high pressure
feed 6s. per ton.

The absolute heat value is therefore obtained as
follows :—One ton of oil at 105s., l,260d.; steam, 72d.;
handling oil, 8d.; interest on capital, l-5d.; total,
l,341-5d. Thus the absolute heat value is 29,000.

Coal Gas.

Ordinary town gas averages about 510 British thermal
units net per cu. ft. It may be obtained at about Is. 7d.
per 1,000 cu. ft. in most large centres. As there is no
labour or upkeep of plant to consider, unless compressed
air is used, the absolute heat value works out at 27,000.

Powdered Coal.

^Within recent years a method of burning coal by
grinding it to a fine powder and blowing this powder into
the combustion chamber by means of a stream of hot
air, has received considerable attention. In the cement