642

THE COLLIERY GUARDIAN

March 28, 1918.

CHEMISTS IN COKE OVEN PRACTICE.

The necessity for the employment of skilled chemists
in coke oven practice was convincingly urged before a
meeting of the members of the Northern Section of the
Coke Oven Managers’ Association, held at Darlington
on Saturday last, by Dr. J. T. Dunn, F.I.C., public
analyst for Newcastle-upon-Tyne, Northumberland,
Gateshead, South Shields, Tynemouth, Berwick, and
Sunderland. Mr. W. Diamond presided over a large
audience.

Dr. Dunn said he wished to enquire into what a
chemist had to do on a coke oven plant, what business
he had there, if any, and then to see what kind of
training would be good for him. A few years ago, if
one had suggested to a colliery proprietor in Durham
who coked his coal in beehive ovens and sold his coke,
that he was really a chemical manufacturer and that he
ought to have a chemist to conduct his work, one would
have been laughed at. The coal owner at that time built
his oven, put his coal into it, set fire to it, had his
workmen to regulate the fire, and produced and sold his
coke; that was all he thought or cared about. It never
occurred to him that there was anything else connected
with the business. Nowadays, although the coke was
and must be the principal product, it was not the only
product of the coke oven. They had learnt that, in
former times, they threw away valuable products which
they now had to collect and make the most of. We
produced tar, ammonia and gas. From both the gas
and the tar we got benzene and toluene and other
substances which at all times had a great value, but
which, owing to present circumstances, had an altogether
artificial and tremendous value. The necessity for
controlling all these processes, for making the most out
of each branch of them, was very much more
prominently before us at present. It was recognised
that a chemist was required in such a set of operations
for, at any rate, what he might call the routine control
of the work. The object of the coke maker was, of
course, from a given quantity of a certain coal to
produce as good a coke and as much of it as he could,
and, at the same time, to produce as many of those
by-products in as large quantity as possible. He
required for that purpose to know something about
his materials, and also something about the treatment
through which he was going to put these materials. It
was quite clear that, in order to do that, he required, at
any rate, chemical analyses. He must know something
about the analyses of his coal and coke and, if he was
making sulphate of ammonia, he had to have methods
of determining the strength of his ammonia liquor and
of his finished sulphate. He might even have to make
routine tests of pyrites and of materials for sulphuric
acid making; or, if he was buying acid, he must be able
to test the strength and purity of his deliveries.
He had also to have methods of determining the value
of his benzol when produced. For all these purposes
there was no difficulty in persuading people that a
chemist was necessary if the works were to go on satis-
factorily. It was possible to have a man trained to do
that routine work, who might do it very well so long as
things were going satisfactorily, but who, nevertheless,
might have no very wide or extended or scientific know-
ledge of chemistry. If the object of the coke maker
was to do his best with the materials, he needed some-
thing more than such a man. We had made very great
progress in the way of coking coal since the days of
the old beehive oven, but no one would say, he took it,
that now we had reached that end, and that no further
improvement was possible in the coking process. We
had always got to be on the look-out for possible ways
of doing things better, and we required for that purpose
a certain amount of knowledge. If they thought of
the materials that were used and the scientific knowledge
that we actually possessed at the present time about
coal and coke, they would agree that that knowledge
was extraordinarily little. We knew, as a matter of fact,
that there were very great differences and varieties of
coal, particularly in regard to coking, and that some
coals yielded a very good coke, whilst others yielded no
coke at all—merely an incoherent powder—and that
between these extremes there were numerous varieties
and differences. Until a very few years ago, nothing at
all was known as to the nature of coal, and although a
great deal of work had been done during the last 20 years
in research of that kind, we still knew really very little.
He believed it was Prof. Bedson who started the work,
which had now been done in a variety of quarters, as to
the action of solvents, pyridine, etc., on coal. They
had attempted to get in that way an idea of what the
coal contained, but the extent of the knowledge so
gleaned was very soon summed up. It appeared that
there were two constituents in most coals—one
soluble in pyridine and similar solvents, and the other,
which was insoluble. The former was more or less
of a resinous character, and corresponded to and
had been derived from the resinous constituents of the
original vegetable substances from which the coal itself
was formed. The other wa.s a humus-like constituent,
a derivative of a degraded cellulose, and appeared to be
derived from the woody tissue of the original plants.
The former constituent had to do with the coking of the
coal; when carbonised, it swelled and coked, whereas
the other constituent did not. That was about the
extent of the knowledge we had so far got in that direc-
tion as to the nature of coal. We knew, also, in an
empirical sort of way, that the coals containing a very
little hydrogen or oxygen—coals approaching anthracite
in their composition—did not coke, and that coals which
contained a very great deal of oxygen and very often a
great deal of hydrogen as well, also did not coke, whilst
the coking coals contained intermediate quantities of
oxygen and hydrogen. Coking coal exposed to the
weather, and so becoming partially oxidised, tended to
lose its coking properties. We soon reached the end of
our knowledge. The experiments that had been done as
to the action of solvents on coal had been done by a
comparatively small number of investigators, each of
whom had examined a small number of coals, so that we

could not be said to know very much, even in that one
line of investigation, as to the greater number of the
varieties of coal that existed.

Nature of the Coking Process.

The nature of the coking process, also, was a thing
of which we knew very little. They were all familiar
with the way in which coal coked, and. there appeared to
be little doubt that coking was due to what was known
as the cracking of hydrocarbons. Many of the hydro-
carbons low in hydrogen were less volatile than those
which contained more hydrogen, and their deposition
upon the solid residue from the coking formed the binding
material which made the difference between a coke and
an incoherent residue. Beyond a general statement like
that, however, he thought there was very little definitely
known as to how that coke was formed at all. We knew,
too, that in regard to coals that did coke, the nature or
physical properties of the cokes differed very con-
siderably. If one took certain coals—coking ‘coals,
par excellence—they did not have a very high amount
of volatile matter, and they formed, when coked, a very
hard and very dense coke. If one took what one might
call a gas coal, similar in its general properties to coking
coal but containing a larger proportion of volatile
matter, such coal was apt to swell up considerably when
it coked, and formed a lighter and less dense coke than
the coking coal proper. Such a coal, if it were mixed
with a coal that coked very badly or not at all, appeared
to have a sufficiency of coking power to bind the other
non-coking coal and to form a coke which, perhaps, was
even better in quality than the coke from the original
gassy coking coal, inasmuch as, whilst equally hard, it
was very much denser. So, on the Continent particularly,
'where coking coal was not as common as it was in this
country, a very great deal of coke was the product of
mixtures of coal in that way. What the reason was—
what was the property of the one coal that enabled it
to behave in that particular way whilst the other behaved
in the other way—were matters about which we were
quite in the clouds as yet. It was known that when a
coal was coked the tendency was, in the first place, for
hydrocarbons to come off as the temperature rose, and
that the gases which came away Inter on contained
smaller quantities of hydrocarbons and more hydrogen.
A certain number of experiments and observations had
been made on the evolution of gases at different periods
in the coking process. In all these cases it was seen
that, in the earlier stages, there were considerable
quantities of ethylene hydrocarbons and methane, but
comparatively little hydrogen; in the later stages the
former had almost disappeared, the second was reduced
in proportion and the hydrogen was increased. So far
as he knew, in none of these cases had the investigation
been pushed to the simultaneous examination of the tar
which came away at the corresponding periods. If one
spoke of the gases that came away from a coke oven,
one was in the habit of thinking of the uncondensed
gases which came away after the tar had been separated,
but in order to get to ascertain what was taking place
inside the oven—the gases including what was after-
wards condensed in the form of tar—a complete exami-
nation must include not only changes in composition
of the uncondensed gases, but also the changes
in composition of the tar. So far as he knew,
very little work had been done in that direc-
tion. Then there was the point as to the com-
position of the gases under similar conditions coming
away from different classes of coal altogether. For
example, there "were, in Northumberland, many coals,
chiefly used as steam coals, some of them containing
very considerable proportions of volatile matter. When
carbonised, they formed only an inferior coke, if any at
all. Some of them left practically a powdery residue
with no cohesion whatever. Yet they differed from
anthracites, inasmuch as they contained very consider-
able proportions of volatile matters. In investigating
the difference between a coking and a non-coking coal,
it would be all-important to know what was the compo-
sition of the gases which came away from such coals as
those Northumberland coals, and whethei- the gases
were similar to or quite different from those from an
ordinary coking coal. He thought that the former was
probable. Some information might be got in that way
as to the actual process going on.

Low Temperature Distillation.

Of late years, low-temperature distillation had been
in a good deal of very needless controversy as to its
merits and demerits as distinguished from high tempera-
ture carbonisation. Each of the two processes appeared
to him to be useful in its place. It was quite obvious
that one could not and never would be able to use a
low-temperature distillation process for the production
of blastfurnace coke or large quantities of low
calorific power gas such as was produced in a gasworks.
Therefore, it was absurd to speak of low-temperature
distillation as being preferable, or not preferable, to
high-temperature distillation. There was also the fact
that, when one distilled coal at a low temperature, the
different class of products indicated that these products
themselves might fill a space in our industrial economy
not occupied by any products of high-temperature
distillation. There were very marked differences
between the products of the two distillations of the
same coal. One got a larger yield of coke in a low-
temperature process than at a high-temperature, but
that coke—although, when made from a good coal,
forming a most admirable domestic fuel or a fuel for any
purpose where a smokeless fuel was wanted and where
hardness or density of the fuel was not important—would
be of no use whatever for many purposes for which coke
was used, because it was soft and readily crushed.
It still contained a considerable amount of volatile
matter, and was no substitute whatever for hard or blast
furnace coke. Again, the gas obtained in these
circumstances was very much smaller in amount than
that from high temperature distillation in a gas works, and
was correspondingly richer in heavy hydrocarbons. If it
were scrubbed, one found that, although it yielded light
liquid hydrocarbons similar in character to the benzol
obtained by scrubbing coke oven gas, these hydro-
carbons were not benzol at all, and were of no use

whatever for the production of benzol derivatives such
as were made from benzene or its homologues obtained
from coal tar in ordinary high temperature working.
Distillation at low temperature resulted in a very much
greater quantity of oils than distillation at high tempera-
ture, but these oils, although useful for fuel purposes,
and although they might be found to contain particular
products useful for special purposes, were paraffins or
cyclic paraffin hydrocarbons almost entirely, and the tar
contained no hydrocarbons, or very little hydrocarbon
of the benzene series. An interesting point in connec-
tion with the low-temperature distillation was that some
French investigators had extracted from coal, by means
of solvents, some of the same hydrocarbons of the tar
or the oils which were furnished by low-temperature
distillation, indicating that, while most of the products
of low-temperature distillation were due to destructive
distillation, some of them were existent in the coal
itself, and at a low temperature were simply distilled
without changing their composition.

He mentioned these points to emphasise how little
we really knew about the ultimate nature of coal; how
little, therefore, we could be said to know at all about the
coking process’, and what an enormous amount of room
there was for investigation which might lead to improve-
ment and a better control of the process of coking.
The more definite scientific knowledge we could acquire
as to the nature of coal and the coking process, the
better we should be able to control that process, and
produce at will cokes having particular desirable
characteristics. If one took the other products of the
coke oven, one found very much the same state of things.
A good deal was known about coal tar as to its com-
position. Possibly, the composition of coal tar did not
so very much affect the coke-oven manager or chemist,
inasmuch as, in the great majority of cases, he did not
deal with it himself but turned it over to someone else.
Still, he had to know something about the composition
of the tar and about the products of its distillation and
the various subjects that could be isolated from it.
Similarly with ammonia—in the great majority of cases
the amount of ammonia was dependent chiefly upon the
temperature. One of the differences between low-
temperature and high-temperature distillation was that
one got very much less ammonia from a given coal at
the low temperature than at the high. A coal which
would yield about 25 lb. of sulphate to the ton in
ordinary gasworks practice would possibly not yield
more than 10 or 12 pounds if distilled at a low tempera-
ture. In the low-temperature distillation, the tempera-
ture at which ammonia was formed was hardly reached.
On the other hand, if ammonia were exposed for any
considerable length of time to a high temperature, it
was very readily decomposed. Moreover, neither process
yielded, in the form of ammonia, more than just a
fraction of the total nitrogen in the coal. That was a
matter in which there was room for investigation. In
the great majority of cases the ammonia was collected
as sulphate, but, of late, a great deal of work had been
done in the production of ammonia liquor, of concen-
trated ammonia. Proposals had been made that it
should be converted into nitrate, instead of sulphate,
for use as a manure. It had been suggested that coke
ovens might take their nitric acid from the atmosphere
by the electrical utilisation of some of their superfluous
power and make their ammonia into nitrate. That was
another direction in which the operations of the chemist
would be required.

Composition of Coke Oven Gases.

He supposed that the coke-oven manager did not •
study the composition of his gases very much. He was
not compelled to produce a gas of a certain quality, as
were gasworks people, although, of course, the com-
position of the gas was an index, at any time, of what
was going on in the ovens. He looked upon the gas as
something from which he was going to extract as much
benzene and toluene as he could. It was a question
whether they should use scrubbing or solution methods,
whether they should use freezing methods—the possi-
bility had never gone out of the speaker’s mind of using
a method of freezing by expansion, as was done in the
preparation of liquid oxygen or liquid air. That was a
question of physical chemistry and of cost.

Coke Oven Refractories.

Then, again, they had to consider not only the
materials with which they were working, but also the
apparatus in which they dealt with these materials.
The materials for the construction of ovens were very
complex and a considerable amount of chemical and
physical knowledge was required in connection with
them. If they were heating a substance in a chamber
by heat applied from outside, it was desirable that the
material of the chamber should be as good a conductor
of heat as possible; on the other hand, if they con-
sidered the external walls of that chamber, the walls
between the flue and the chamber, they wanted the
outside to be as bad a conductor of heat as possible. If
the chamber was all made of the same material, it was
very difficult to ensure that they could, have both these
inconsistent qualities at the same time, and they were
reduced then simply to questions of dimensions of
material and to constructing their apparatus so that
they would favour the conduction of heat to the inside
of the material and retard conduction outwards. Also,
they required a substance which would stand very rapid
changes of temperature without fracture or disintegra-
tion. The question of the materials of which the coke
oven bricks were to be formed was very important from
that point of view. The differences between fireclay,
which tended constantly to shrink when heated and
re-heated, and silica, which had the opposite tendency,
were questions of much importance and still required
much investigation. It had been found that the
expansion which took place when silica was heated was
due to a transformation of the quartz into tridymite—
by no means an instantaneous operation. If, however,
they could complete the conversion of the quartz into
tridymite during the process of burning these bricks, it
completed at the same time the total possible expansion
and avoided further trouble. That was one of the
many questions of refractory materials which required
consideration.