April 12, 1918.

THE COLLIERY GUARDIAN

745

holes. The fifth hole, shown in the illustration,
serves to carry off the volatile products of the
distillation. The coal is levelled after charging by
an auxiliary ram on the coke pusher, space being
left between the top of the coal and the top of the
oven for the outgoing gases to reach the point of
discharge.

Upon completion of the coking process the doors
are raised, and the coke is pushed out by an elec-
trically operated ram. The doors are then lowered
and sealed and the oven is ready for another charge.
Many attempts have been made to develop a
mechanically sealed door, but the conditions of opera-
tion make this a difficult problem, and nearly all
plants still use the mud joint. Careful designing of
the door and its seat make this mudding a much
less serious matter than might be supposed.

Use of Silica Brick.

As stated above, silica brick is largely used in
modern by-product oven construction. There seemed
at first many obstacles to its successful use for such
construction, the principal objections being the large
amount of expansion of the brick when heated, and
the tendency to spall, due to sudden changes in
temperature. When silica brick was first used in
the crowns of beehive ovens it was thought that it
would be an absolute failure, but it was unexpectedly
successful. It was first employed in by-product ovens
at the plant of the Cambria Steel Company, and was
soon after generally adopted.

It has been found that, since most of the expansion
takes place below a red heat, the variations in
temperature during operation do not give any trouble,
and the superior resistance of silica brick to high
temperatures and its satisfactory conductivity under
operating heats make it a superior material. Not-
withstanding its success in American practice, it has
not been employed to any extent in Europe, and only
a few years ago some prominent English brick makers
stated that they did not believe it could be employed,
notwithstanding statements that came from America.

Size and Width of Ovens.

The cubic capacity of American by-product ovens
has increased nearly four-fold since their first intro-
duction. The larger capacity has the advantage of

Fig. 3.



reducing the cost of operation per unit of product,
and the smaller number of units also reduces cost
of construction and repairs. Increases in length and
height of the oven chamber have no effect on the
product and are limited only by structural and heating
conditions. The width of the oven, however, is a
more important factor.

In the early days of the by-product oven in Europe
it was thought that the lean coals of Belgium, running
as low as 15 per cent, volatile, required a very narrow
oven, perhaps not over 14 in. wide, while for high-
volatile coals a width of 20 in. was not infrequent.
American practice has not demonstrated any such
simple rule as this, and perhaps the reason may be
found partly in the fact that oven plants are generally
located at the point of consumption of the coke,
making it easier to obtain mixtures of coals, and for
this reason most plants operate on about the same
average percentage of volatile matter. It has not
been definitely shown in American practice that a
particular width of oven is best suited to coal of a
certain composition. Narrower ovens have certain
advantages: —Firstly, a faster coking time per inch
of width with a given flue temperature; secondly, a
somewhat higher yield of by-products; and thirdly,
a somewhat more uniform cell structure as between
the portion of the coke nearest the wall and that
nearest the centre of the oven.

On the other hand, the larger number of
operations of the oven crew when handling the
narrower ovens increase the labour cost and the
repairs. It has yet to be developed what is the best
oven width to average these conditions. The widest
ovens operating in the United States have an average
width of 21 in., and the narrowest 12 in.

It will probably take much further investigation to
determine where between these limits can be obtained
the best equalising of conditions, and whether the
mixture of coals naturally available for a given plant
will be a factor in determining the best average
width. Some coals require higher temperatures than
others to produce the best coke, but it is not clear
that this fact will lead to the selection of wider
ovens for such coals, or that we can yet say that
any width is definitely the best for a given set of
conditions.

Quality of Coke.

The physical structure of coke is quite as important
as its chemical composition. It is the physical
structure which gives coke its advantage for metal-

lurgical work over other forms of solid fuel, and it
is important that the structure should be adapted to
the conditions under which the coke is to be used.

The blast furnace is the great coke consumer. In
the days of the beehive oven one kind of coal gave
a coke with a certain physical structure, and another
coal gave another structure. Furnaces either adapted
their practice to the coke, or changed their coke
supply. Coke was recognised as hard or soft, porous
or dense, and that was about all that was known
regarding physical structure.

Mr. Brassert says in his paper on “ Modern
American Blast Furnace Practice,” read in 1914, that
“ the early coke produced in our by-product ovens,”
even from the same coals as were successful in the
beehive oven, burned too slowly and made our furnace
operations exceedingly difficult, by preventing rapid
and continuous movement of the stock. The lack of
knowledge and experience along these lines was
responsible for the slow progress attending the intro-
duction of by-product ovens in this country.” The
economy of the by-product oven practically forced its
adoption by the furnace operators, and for several
years, as Mr. Brassert states, “at a number of
American plants by-product coke has been made which
rivals in quality our best beehive product.”

The by-product oven, with its variable mixtures of
coals, variable heats, coking time, width of oven,
fineness of coal charged, and other controlling factors,
permits a control of coke structure formerly
impossible. The problem is to determine first, what
is the structure best adapted to standard furnace
practice, while recognising that special practice
requires modifications of structure; second, what
conditions are necessary to produce it.

Notwithstanding the general acceptance of Gruner’s
theory of ideal combustion in the furnace, the produc-
tion of a high thermal heat at the tuyeres is of the
first importance, and the best coke is that which
reaches the tuyeres in proper condition to produce the
highest temperatures in the tuyere area, and in just
sufficient quantity to do the amount of work required
there under the conditions produced at this maximum
temperature.

The ideal coke is one which will descend through
a furnace shaft to the combustion zone in front of

the tuyeres with the least loss from attrition and
oxidation, and when it arrives there will burn at the
highest possible rate. Of course, these are paradoxical
qualities. However, Mr. Walther Mathesius points
out in his paper on “ Chemical Reactions of Iron
Smelting,” that “modern American coke oven
practice has made enormous strides toward approach-
ing this apparently paradoxical ideal.” He stated
that this is accomplished by producing coke with an
open-cell structure, in which the cell walls themselves
are amply strong and well protected by a graphitic
coating.

The time of contact of the blast with the coke in
the tuyere area can be only a few seconds, and the
speed of any chemical reaction decreases as the relative
quantities of reacting and resulting substances
approach equilibrium. Therefore, the farther these
relative quantities remain from the status of equi-
librium, the higher the rate of resultant combustion.
In seeking to produce the best blast-furnace coke,
the aim should be to produce an open-cell structure,
with cell walls strong and hard. Later experience
may, however, show that there are other requirements
that are still unknown. It is not necessarily true
that the open-cell structure is the same thing as a
high percentage of cell space. The advantage of an
open-cell structure is that it gives the oxygen of the
air easy access to the carbon. It is possible that a
coke of very fine cell structure, having, say, 50 per
cent, of cell space, might offer less surface for prompt
combustion under practical conditions than another
coke containing larger cells, but having the same per-
centage of total cell space.

The composition of the cell wall, which it is agreed
should be hard, thin and strong, and, according to
Mr. Mathesius, covered with a graphitic coating that
is smooth and bright, is a much more complicated
matter. What are the conditions of coal mixture
and coking which produce this kind of wall? We have
not yet found the answer to this question, although
we know some of the conditions that are favourable
to this result. The coal mixture, the degree of fine-
ness of grinding, the coking time, and the heats, are
probably all factors.

Our search for the best coke structure to meet a
given set of furnace conditions is not an easy one,
but we know better which path to start on than we
did even a few years ago. Agreement exists on the
following points at least:—(1) The coke must be hard ;
(2) it must have an open-cell structure; that is, cells

of good size, and approximately 50 per cent, of cell
space; and (3) it must have a high rate of combus-
tibility.

Can we add anything more to this list? Some
investigators have concentrated their comparisons on
the rate of combustibility, but the author cannot
believe that this test alone is sufficient to determine
the best coke structure, because it ignores one of
the sides of the paradox. Whilst the best coke must
burn rapidly at the tuyeres, it must also resist
attrition and oxidation during its descent in the
furnace. Good-sized cells and a good percentage of
cell space, coupled with a hard structure, would seem
to give a coke corresponding to Mr. Mathesius’ defini-
tion. Testing the rate of combustion has been a help
and it is hoped that a test may be found for hardness
of structure better than the crushing of the 1 in.
cube specimens, over which so much time used to be
spent in the days when John Fulton wrote his book
on “ Coke.”

(To be continued.)

CONTRACT PRICES DURING
DtWlOBlLlSAHON.

At a meeting of the Manchester Local Section of the
Institution oi Electrical Engineers on Tuesday last,
Capt. W. P. Digby read a paper on “Contract Prices
Uuring Demobilisation/’ tie said that if we were
not to imperil the opening phases of our competition
for foodstuffs and raw materials by blundering, and
by hasty and inefficient improvisation born of unpre-
paredness, some consideration should be given to the
ractors governing the contract prices for home and
roreign markets for electrical, and, indeed, all
engineering, manufactures, and some machinery pro-
vided to assist in the regulation of these. For tne
purposes of the paper, he regarded tne period of
demooilisation as not only embracing the time occupied
in military demobilisation but also tne period—possioly
longer—required for the complete demobilisation of
industry. It would, of course, have been possible to
use tne expression 1 ‘ period of reconstruction ’ ’ or
“ period of re-establishment/’ The one suggested tne
rebuilding of what was shattered, which was not the
problem before them, and the other implied a re-
instatement of much that could be done without. If
the problems were truly understood and wisely handled,
the period of demobilisation might be the infant stage
of a period of social and industrial renaissance, as tne
Augustine Age in Rome, our own Elizabeth period, or
the artistic renaissance of the latter part of the Middle
Ages. To-day some thousands of works and factories
were classed as controlled establishments. Actually
there was no concern in the country which was not
affected to a greater or less degree by restrictions of
import and export and by priority references. While
it was true that the cessation of hostilities would imply
a cessation of the demand for khaki cloth, for high
explosives, for guns, and the many thousand incidental
accessories of warfare, other demands would be in their
way quite as insistent. One had only to mention the
need for merchant shipping to convey food and raw
materials and to replenish depleted stores of general
commodities all the world over, the renewal of rolling
stock and permanent way on our railway systems, the
arrested demands for similar materials for Indian,
Colonial, and South American railways, mining plant
all the world over, to say nothing of the industrial
reconstruction of Northern France, Belgium, and
Poland (a reconstruction in which large scale electric
power distribution might be the key to the most rapid
achievement of the end in view). In the aggregate
these and other demands—some perhaps already
granted the hall mark of no immediate value in the
shape of a Class C priority certificate—were so complex
and so numerous that great concern must be felt at
the prospect of a too prompt return to conditions of
free trading. The expression “ free trading ” had not,
in this connection, its fiscal or pre-war significance,
but referred rather to a system of import and export
licences or priority certificates. It had been stated
that, for perhaps two years after the war, food control,
either voluntary or with the enforcement of a rationing
system, would be necessary in several countries. It
was not, therefore, difficult to conceive that the preven-
tion of industrial confusion in Great Britain would
require a central authority, allocating part or all the
imports of raw materials to specific purposes, and that
in place of the present system of priority reference
issued by the Priority Branch of the Ministry of Muni-
tions we should be governed in those respects by a
Priority Branch of a Ministry of Commerce. Before
discussing the effects of such control on the engineering
manufacturing industries and its adaptations to meet
the needs of oversea trade, aimed at to secure a large
share of the trade for this country, it was necessary
to consider some statistics of three separate periods.
The first period calling for consideration was that of
the Franco-Prussian War. Judged from the mass of
data available to-day, our records of four or five
decades ago were scanty. We did not know that in
this country the period from 1872 to 1875 was marked
by all the features of a boom period, rising rates of
wages, and cost of food stuffs, together with an
artificial inflation of prices. In quoting a few of the
available figures for that period, the author pointed
out that as war was declared in the late summer of
1870 and peace signed at Versailles in the spring of
1871, the period from 1870 to 1879 should be taken for
the purposes of illustration. So far as the United
Kingdom was concerned, the figures were generally
mean prices and not the weighted figures of the Board
of Trade index numbers, which were only available
from 1871. Of course the high prices of 1873 must
not be claimed as solely due to the effects of the Franco-
Prussian War. Distinction had to be made between
fluctuations due to normal and abnormal causes; the
coincidence of both the normal and the abnormal must
be acknowledged. Under the many contributory causes