796

THE COLLIERY GUARDIAN.

April 19, 1918.

daily output necessary to make it a paying concern.
It had struck him most forcibly that perhaps the people
most interested did not carefully calculate beforehand
the daily output and other possibilities of the new
field. To his mind, it was absolutely outrageous that
at some collieries there should have been an expensive
fitting put up that was quite out of the question when
regard was paid to the possible output. Proceeding,
Mr. McLaren said that there were many points in
connection with the seams that ought to be taken into
account. They ought to pay due consideration to the
number and thickness of the seams, and so arrange
matters that sufficient men were apportioned to the
seams to guarantee a steady daily output. He depre-
cated sinking a pit in a virgin field on the evidence
disclosed by a solitary bore. There ought always to
be more than the evidence of one bore to justify pit
sinking operations. There were cases that he knew
of in Scotland where pits had been sunk on such
insufficient evidence, with disastrous results, and he
did not wonder at it at all. It ought to be insisted
upon that, in any field where the minerals had been
unproved or were unknown, more than one bore should
be put down.

Mr. John Gibson (Kilmarnock) said that he was not
without hope that in course of time there would be
instituted in every university or college a chair of
industrial economics, and that the subject would be
made compulsory on every student of technical science.
The question of pipes and power presented a most
interesting problem. The first point to be considered
was what was the profit that a coal mining venture
might reasonably aspire to get. The money invested
in the production of coal ought to have a much larger
return than money invested in almost any of the other
great industries. A shaft or a mine represented so
much capital sunk irrecoverably, whereas, in the case
of a factory, the capital was sunk largely in machinery
and plant; and if the venture failed the building might
be utilised for some kindred industry, and consider-
able assets might be realised from the plant. Mining,
therefore, ought to earn higher profits than manufac-
ture. Now, manufacture was rather riskier than
Government stock, and he submitted that manufac-
turers should look for twice the amount of interest
that was derived by stockholders. Following the same
process of reasoning, a coal company ought to receive
four times the amount of interest on invested capital
that a Government stockholder did. A little considera-
tion of the practical work of mining would bear out
this contention.

Mr. James Black (Shettleston) said there was only
one point to which he desired to draw attention,
namely, the monetary value of the frictional losses
capitalised. If the author explained how he arrived
at the value of £60 it would be instructive.

Mr. C. C. Reid (Cowdenbeath) said the impression
left on his mind was that the author was proposing
a policy which was at least a very near relation to
pai simony. The author advocated the need for greater
productivity so as to make the industry more profit-
able, and said that if the mines became unprofitable
their operations would cease. He (Mr. Reid) did not
understand what was exactly meant by that. If it
meant that because a greater part of the mining opera-
tions of the country were unprofitable these would
cease, he would ask the question What about the need
for the product? Then in dealing with the sinking
and fit-up of shafts, Mr. Mowat said that if a fit-up
largely outlived the life of the colliery it became a
monument to the creator’s want of judgment. On
that point he would merely say that if the author
could produce one pit that was a monument to its
creator s want of judgment in that way, he himself
could produce 20 where there had been failure to
equip the pits with plant sufficient in any degree to
exhaust the field.

Mr. James Leckie said that if this question of the
monetary value of frictional losses could be emphasised
it would be a great benefit to the members of the
institute.

Mr. Wm. Riddell (Bothkennar) said that the ques-
tion raised by Mr. Mowat was undoubtedly very impor-
tant. Holding the balance between first cost and
maintenance charges was an ever-present problem
with the colliery management, although it was perhaps
often handled in a somew’hat indifferent manner in the
daily routine of work. The two sides of the question
were not weighed in the balance with sufficient care.
The subject presented a large number of problems that
were difficult to decide. Even although a change was
made to convert a current expense into a capital
charge, or vice versa, it must remain a matter of doubt
whether the change was a wise one. Indeed, very
often such a change would take the form of a specula-
tion. As an example, a longwall face 200 yards in
length was undercut by one coal cutter. In the middle
of the run there was a fault, the ripping, at which to
allow the coal cutter to pass through, costs the wages
of one man per day, or, roughly, £150 annually, and
was equal to fd. per ton on the output from this face.
Supposing that this continued for four years, the sum
paid in wages, with compound interest at 5 per cent.,
would amount to about £630, or practically the cost of
a second-hand coal cutter, with interest at 5 per cent,
for four years on the capital so expended. What
would be the correct thing to do in such a case? The
majority of managers would continue incurring the
expense of ripping the fault and cutting the run with
one machine. Who would contend that to do so was
bad management, and that a second coal cutter should
be provided at once—one to cut on each side of the
fault? The author had said that if the shaft and
fittings much outlived the economic life of the mineral
field they became a monument to their creator’s want
of judgment; but he (Mr. Riddell) could not agree
with that conclusion, and he thought it was only neces-
sary to refer to the recent naper read by Mr. Henry
Rowan (Cowdenbeath) on “ Stripping and Relining
a Shaft” to prove that the author’s conclusion would
not, as a rule, be the correct one. The same might be
said of much of the other constructional work about a

colliery. It was clearly a matter of the choice of
material and of the method adopted, and instead of
indicating a lack of judgment it would, in many
instances, be rather a proof of good management.
What appeared to be a short-sighted policy in colliery
management and one which added enormously both
to capital charges and current expenses, was that of
supplying inferior and inefficient plant and material
because its first cost was low. The root of the matter
would appear to depend on two main factors—judicious
management coupled with a correct system of
allocating the different charges or expenses.

The discussion was adjourned till next meeting.

THE BY-PRODUCT COKE OVEN IN THE
UNITED STATES *

By W. H. Blauvelt.

(Continued from page 745.)

Foundry and Domestic Coke.

In addition to the iron blast furnace, foundry
cupolas afford a steady market for coke, and in recent
years the domestic market has grown to importance.
Foundry coke is usually made on a somewhat slower
coking time than furnace coke, as cupola practice
calls for larger and tougher pieces.

The production of domestic coke is now a greatly
different industry from what it wras in earlier days,
when most of the domestic coke was produced in gas
works. At that time it was often regarded as some-
thing to be got rid of with the least trouble, rather
than as a regular and important source of income to
the works. Great care is now taken in the sizing and
preparation of domestic coke and the complete
removal of breeze and dirt. The following table
shows approximately the usual sizes produced: —

Size of square Opening of screen
through.	over.

In.	In.

Egg coke........ 3’5	....... 1’5

Nut coke........ 1’5	....... 1’0

Pea coke........ 1'0	  0’5

Breeze.......... 0'5	..... —

These screens are varied locally to meet market
requirements. It would be desirable to have a
standard for each domestic size throughout the
country, but where the demand for one size is large
relative to another, it is natural for the operator to
modify his screen openings accordingly.

In American practice, where domestic coke competes
mainly with anthracite, a hard structure is generally
regarded as desirable. This is contrary to English
practice, where familiarity with bituminous coal as
a domestic fuel makes quick inflammability a
desirable quality, so that coke containing a consider-
able amount of volatile matter is often sold success-
fully. Even the partially coked coal, produced by
low-temperature distillation, is preferred to the hard
clean coke which is becoming familiar to the American
consumer.

Preparation of Coal.

The practice of locating American ovens at the point
of consumption of the coke has made it easy to bring
together several coals of different qualities, and this
has in many cases permitted the production of a better
coke by admixture than could be made from any one
of the coals used alone. For example, a coal of excel-
lent coking qualities but high in ash can be mixed
with a low-ash coal of poorer cokability, or an excess
or deficiency in the coking quality of the main coal
supply can be corrected by mixture with another coal.

Except in cases where the source of coal supply is
fixed, it seems desirable to arrange the plant for
the preparation and mixing of as many as three of
four kinds of coal. Means permitting the accurate
proportioning of the different coals are, of course,
essential in such a plant. The mixture of coals
generally calls for their being ground quite finely,
in order to bring the particles of the different qualities
of coal closer together. The general practice is to
grind so that from 70 to 80 per cent., or more, will
pass through a | in. screen. This fine grinding is also
often advantageous where there are many pieces of
slate of considerable size in the coal, since each large
piece of slate in the coke is usually a centre of cracks
that tend to shatter the structure.

Various degrees of fineness in grinding are often
adopted to improve the structure of the coke, but in
some cases, especially where only one coal is used,
a better structure is produced from considerably
coarser coal. Fine grinding reduces the weight of
the coal mass per cubic foot, and consequently the
capacity of the oven. With ordinary coals the weight
of charge is generally computed on the basis of 40
to 43 cu. ft. per net ton, depending somewhat on the
coals, and largely on the degree of fineness.

Use of Coals Formerly Considered Unsuitable.

The by-product oven, with its control of heats,
coking time, mixture of coals, and fineness in grind-
ing, has permitted the use of many coals for making
metallurgical coke which would not have been suit-
able with the beehive oven. As the best coals are
being progressively exhausted, this point becomes more
important. Owing to the extraordinary conditions
caused by the war, some coals hitherto considered
entirely unsuitable for making metallurgical coke
have been successfully used: for example, the
unwashed coals of southern Illinois.

To use such coals successfully it is necessary to
make a careful study of the coking qualities of each
one in order that any deficiencies it possesses may be
supplied by the proper selection of the coals forming
the mixture. Very satisfactory furnace results have
been gotten when using important percentages of
coals heretofore considered unsuitable, and these
results are encouraging on account of the progressive
disappearance of the best of the coking coals now
available.

* From a paper read before the American Institute of
Mining Engineers.

Recovery of By-Products.

The distillation or coking of coal in closed retorts,
now generally known as by-product ovens, was first
introduced for the purpose of saving the several
valuable products contained in the volatile matter of
the coal, which were all destroyed in the beehive
process. The advantages in the production of coke
outlined above were not then realised, but fortunately
it has developed that the best oven conditions for the
production of coke are, in general, the best for the
production of by-products also.

Attempts have been made to obtain higher yields
of ammonia by blowing steam into the coke, somewhat
after the manner followed with the Mond producer,
which recovers from three to four times as much
ammonia, but none of these processes has been
developed commercially. Higher coking heats tend
to break down the combinations to their ultimate
elements. For example, the gas produced from high-
temperature coking will contain more hydrogen and
less marsh gas, and a larger volume will be produced
of lower calorific value. When coking at very low
temperatures, as in the production of “coalite,”
practically no benzols are produced, and the hydro-
carbons recovered are of the aliphatic series. A
small quantity of very rich gas is obtained, and the
ammonia yield is low. At high coking temperatures
the tendency is for the toluol, the more complex
hydrocarbon, to break down into benzol, and at very
high temperatures the yields of both are reduced.
The temperature conditions to which any particular
particle of hydrocarbon is submitted in its travel from
the original piece of coal up to the hydraulic main are
so complicated and so varied that a theoretical discus-
sion of these reactions is of little value.

Cooling the Gas.

Much improvement has been effected in the efficiency
of the condensing apparatus since the early days of
the tubular cooler, in which the gas circulated around
the tubes of an apparatus similar to a vertical boiler,
while the cooliifg water flowed through the tubes on
the counter-current principle. The author has in mind
one single-stage condensing apparatus 10 ft. in
diameter and 45 ft. in height of effective cooling
surface, in which 12,000,000 cu. ft. of gas per day
are cooled on the average from 80 degs. to 20 degs.
Cent., in which the cooling liquor enters the apparatus
5 degs. below the exit temperature of the gas, and
leaves it at not more than 10 degs. below the enter-
ing gas temperature. In such an apparatus very little
condensate separates from the gas at a low
temperature, and as a result the benzols remain in
the gas and the separation of tarry matter from the
ammonia liquor is sharp and easily effected.

Removal of Tar.

An efficient system of removing the light tars in a
high-tension electric field has been developed by F. W.
Steere, the plan adopted being similar to that used
in the well-known Cottrell system, except that the
special conditions permit the use of an alternating
current of the necessary high voltage, since the
problem is merely the agglomeration of the minute
globules of tar to permit their effective removal by
tar extractors of the usual type. This process has
been worked out commercially and is simple and
effective.

Tar as Fuel.

One of the interesting developments in the operation
of by-product ovens in connection with steel plants
is the growing use of tar as a fuel for metallurgical
furnaces. At one plant, producing over 20,000,000
gals, of tar per year, the entire amount has for years
been utilised as fuel in open-hearth and heating
furnaces, where its value as fuel is much, higher than
its value in the ordinary tar market. Generally
speaking, the tar used in steel furnaces is handled
in the same manner as ordinary petroleum fuel oil,
having about the same viscosity, and its use presents
no difficulties after the details of its application have
been worked out. It has a higher fuel value per
gallon than ordinary petroleum fuel oil.

Recovery of Ammonia.

The so-called direct and semi-direct processes for the
manufacture of ammonium sulphate have been very
generally applied to oven plants in recent years. The
direct process requires only the removal of the tar
from the gas without any more cooling than is neces-
sary for this purpose, after which the gas is passed
through a bath of sulphuric acid and the sulphate
is recovered. The direct process has been applied to
a considerable extent in Europe, where the percentage
of chlorides in the coal is quite small, but where the
amount of chlorides is relatively large it is necessary
to remove them before the acid bath is reached.

This introduces the “ semi-direct” process, in which
the gas is cooled to remove the chlorides and then
reheated and passed into the acid. The fixed ammonia
condensed out in the cooling process is distilled and
generally the ammonia from the stills is returned to
the gas before it reaches the acid bath. The per-
centage of ammonia that has to be distilled in the
’’semi-direct” process depends upon the amount of
fixed ammonia in the gas and varies from 15 to 40
per cent, of the total ammonia.

In recent years, by refinements in the distillation
process, it has been made possible to produce pure
ammonia direct from the crude weak liquor, and this
product is quite equal in quality to that produced
from ammonium sulphate. These processes have the
advantage of avoiding the waste of sulphuric acid
inherent in the ammonium-sulphate process.

'	Coke-Oven Gas.

In America, coke-oven gas has long been used for
domestic purposes, over 40 important cities and towns
being wholly or partly supplied with oven gas, and
a number of years ago the daily sales for domestic
purposes had reached 50,000,000 cu. ft. Europe has
lagged far behind America in this respect.

During the last few years the whole subject of using-
oven gas in open-hearth furnaces has been success-
fully worked out, and it is now in regular operation