August 6, 1915.

THE COLLIERY GUARDIAN

271

The Coking of Coal at Low Temperatures, with Special Reference
to the Properties and Composition of the Products.*

By S. W. PARR and H. L. OLIN.

produce polymerisation with the formation of more
complex substances of higher molecular weight, and
that comparatively valueless products such as naphtha-
lene and heavy pitch are produced in increasing quan-
tities. In other words, the lighter and more valuable
hydrocarbons are being destroyed in favour of the
heavier ones which find little industrial use.

This report covers a series of studies made during the
period from 1911 to 1913 on the coking properties of
Illinois coal. It is a continuation of the work described
in Bulletin No. 60 of the University of Illinois
Engineering Experiment Station.^ Its distinctive
feature has been the use of an apparatus which would
yield the main products of coke, gas, and tar in quantities
sufficient for a detailed study of these products, and, to
a certain extent, quantities sufficient for a determination
of their values by practical tests on a commercial scale.

For the present investigation an apparatus was
designed to utilise about 100 lb. of coal. The coking
process was studied, and the mixture for producing the
best product determined. It was found that a smokeless
fuel may be produced especially well adapted to domestic
purposes, including its use in open grates. Its freedom
from tar or condensable hydrocarbons makes it easily
adapted to generating producer gas, thus affording a
good substitute for anthracite coal in suction gas
producer practice. In the study of the composition and
properties of the tar, this material was found to have
a very low content of free carbon, a relatively high
percentage of light boiling distillate, and an unusually
high content of tar acids or phenols. The apparatus
used in the experiments is an elaboration of that
employed in 1910, and is capable of producing material
in greater quantities than was possible with the older
type. As shown in the detailed diagram fig. 1, it
consists of a boiler plate shell A, lined with asbestos to
prevent excessive radiation of heat; within this, forming
the coking chamber, is a shell B of the same material
containing a cone of light sheet iron C, perforated
with T36 in. holes, designed to confine the coal charge
and to allow a free circulation of gases. To obtain the
non-oxidising atmosphere such as was used with the old
apparatus, steam was admitted from the high pressure
main at E, passed through the coil F, where it was
superheated by the hot currents ascending from the gas
burner, and then conducted into the coking chamber.
The heat was supplied by a blast-ring burner D,
connected with the gas and air mains, and no difficulty
was experienced in producing the desired temperatures.
The charge of crushed coal was fed into the hopper Gl-
and admitted to the retort through a large gate valve.
The coked residue was removed, after cooling the
apparatus, through the bottom at H. Gases of com-
bustion escaped through the opening J, which was
connected with a flue, while the distillates were
conducted through an outlet pipe to a condenser
consisting of several 4 ft. lengths of inch pipe connected
by return elbows. Cold water was allowed to drip over
this gridiron-like contrivance. The tars were passed
through a water-sealed exit at the bottom, while the
gases, fairly clean, were collected in a gasometer.

To study further the coking qualities of Illinois coals
at temperatures ranging from 400 degs. Cent, to 500 degs.
Cent, and to obtain a quantity of the coke residue
sufficient in amount for practical tests in order to
determine its commercial value, a series of runs was
made using the apparatus described. In this report,
products from representative types only are illustrated
and described, since the results of tests of different coals
of a given field showed little variation. Of particular
interest during the process of distillation was the
behaviour of the coals from the northern districts,
especially those from Vermilion County. As the heating
progressed, a black pitchy substance dripped from the
joints of the containing ovens but it hardened imme-
diately on cooling, forming a brittle mass much
resembling asphalt. This was undoubtedly the cementing
principle which is instrumental in forming coke.
According to Lewes, it consists of substances derived from
the resins of the original coal sources, which melt at
about 300 degs. Cent, and decompose at slightly higher
temperatures, yielding on the one hand liquid products
which distil out as tar vapours and hydrocarbon gases,
and, on the other, a pitch residuum, which at 500 degs.
Cent, forms a mass of coke. His general theory that
these resinic- substances are readily oxidisable, and in
their oxidised condition have much to do with coke
formation, is borne out in these experiments by the fact
that no weathered coal of any type produced the gummy
exudation mentioned, although there was no apparent
diminution in the amount of gases given off. Compared
with the bituminous coals of the Eastern States, those
of Illinois are exceedingly rich in this resinous binding
material. Strangely enough the abundance of the
coking material which the western types possess is the
cause of their inferiority in the matter of making dense,
hard coke; for with the decomposition of the resinic
bodies and the deposition of cementing carbon there
occurs at the same time an evolution of large quantities
of gases which inflate the pasty mass and make the
resulting coke more or less light and spongy. Indeed,
certain Vermilion County coals, after being heated
under conditions which allow free expansion, present
the appearance of hardened froth, because of the
excessive development of cell structure in the coke.

As has been shown in the previous work, the porosity
of the product may be appreciably reduced by subjecting
the contents of the oven during the heating period to a
considerable pressure. Another means to the same end
which was recognised in the first experiments and which

* From Bulletin No. 79, University of Illinois Engineering
Experiment Station.

f “ The Coking of Coal at Low Temperatures/’ by
S. W. Parr and H. L. Olin.

has been applied in the latter series is the addition of
inert coke dust to the raw coal as fed into the retort.
This material, acting in the capacity of a “ blotter,”
reduces the plasticity of the softened mass and allows
the gases to escape freely without producing a blowing
effect. The diluting medium in the case of the
specimens shown here was a mixture of various semi-
cokes which had accumulated in the course of the work.
The material was crushed and ground to a fineness of
40 or 50 mesh and thoroughly mixed with the rest of
the charge in ball mills. An analysis of a composite
sample of this semi-coke breeze gave the following
results :—

Composition of Inert Coke Mixture.

Moisture				Actual.  1’85 ...	Dry.
Ash 	'		11-90 ...	12-15
Volatile matter 		19-85 ...	20’22
Sulphur 		2’62 ...	2’67
Fixed carbon 		66-40 ...	67’65
Calorific value (B.T.U.)...	11,243 ...	11,454

The effect of the addition of this foreign substance is
exceedingly interesting. Certain types of coal, as, for
instance, those from Ver-

Fig. 1.

milion County, produce
hard firm coke when
mixed with as much as
100 per cent, of their
own weight of the coke
dust; those from the
southern districts with
higher fixed carbon do
not need so great a
dilution. Not only is
the texture made firmer
by this treatment but
the density is increased.

The following is a
summary of the results
obtained:—

1. Coke of good density
and hardness may be
made by mixtures of
semi-coke and raw coal
if both are finely divided
and evenly mixed. A
variation is noticeable in
the quantity of such non-
coking material which
may be incorporated with
different coals. For ex-
ample, fresh coal from
Vermilion County will
carry such an addition
of 100 per cent, of its

weight to advantage.
Coals from Saline and Williamson counties give coke of
the highest density when mixed in the proportion of
50 per cent, of their weight with semi-coke.

2. The coke resulting from the low temperature
process has from 18 to 22 per cent, of volatile matter
remaining, but since it has been heated above 400 degs.
there should be none oi the tar constituents remaining.
The most convincing test on this point, as also the best
method of arriving at a conclusion as to its adapta-
bility for such work, was to try out the material in a
suction gas producer. The results indicated that no
clogging effect whatever results, thus showing the
absence of tar bodies. The physical operation of the
producer as well as the grade of the gas produced was
fully equal, if not superior, to the performance of the
outfit when anthracite was used.

3.	The semi-coke has such an amount of volatile
matter remaining together with the right degree of
coherence as to make it especially well adapted to house-
hold use. It is clean to handle, free from dust, and
burns without smoke or the formation of soot. Especially
to be noted in this connection is its ability to retain a
fire without undue attention as to draughts, etc.

4.	The average specific gravity of the tar is 1,069. It
is rich in low boiling distillate passing over at 210 degs.
This product averages 18 per cent, of the total. The
pitch residue amounts to approximately 30 per cent,
and is remarkably free from precipitated carbon.

5.	The adaptability of the tar for wood preservation
processes seems to be indicated by the high percentage
of tar acids. These constituents make up from 28 to 30
per cent, of the crude material. The larger part, about
22 per cent., is found in the second distillate (210 degs.-
325 degs.), only about 7 per cent, coming over below
210 degs.

6.	Approximately 10 per cent, of the crude tar is
found to be low boiling distillate free from the tar acids
and suitable for use in internal combustion engines.

7.	Naphthalene is absent. The free carbon in the
crude tar is less than 2 per cent., and the residual
product after the light distillate and heavy oils are
removed would be classed as hard pitch.

8.	A principal feature results from this study of these
various substances—namely, that all three of the
general divisions of coke, tar and gas have specific
properties of an especially valuable sort which would
indicate that the process of coking at low temperatures
could be established successfully on a commercial basis.

There is sufficient unanimity among the authorities to
establish the fact, fully confirmed by the worker in
organic chemistry, that rise of temperatures tend to

RETAIL COAL PRICES.

We continue in this and following issues a digest of
the evidence given by witnesses heard before the Com-
mittee appointed by the Board of Trade to enquire into
the causes of the present rise in the retail price of coal
sold for domestic use.

Evidence from West Yorkshire.

Mr. Roslyn Holiday, who also gave evidence on
March 12, said he was general manager of the Ackton Hall
Colliery Company, with an output of about 600,000 tons a
year, of which about 50,000 came to London. The output
of their district would be somewhere about 13,800,000 tons,
and 60 per cent, of it would be industrial. In their case
much is industrial coal. The effect of the war had been to
reduce the output, because in the first place a number of
men had left, a large number having enlisted. The total
number of men who had left was 250, out of about 1,500.
Their output normally was about 16,000 tons a week, now
it was 11,000 tons. Their production fluctuated a good deal,
depending on shipping. If boats turn up they were able to
work the pit better and send more coal away. The output
had fluctuated during the war. In the West Yorkshire
district as a whole, it was only the very best quality of
house coal that came by rail, as that would stand the
freights; and also the very best quality of coal was so much
damaged by shipping—being tipped—that people who
wanted large lumps of coal were prepared to pay the higher
cost of freight by rail. Owing to the war and the risks to
shipping, customers were asking that coal should be sent by
rail; that had happened very considerably in West Yorkshire,
and the result had been that owing to the great congestion
on the railways delay had been caused which would not
have happened in normal times. At present coal from their
collieries was being sent by sea. It was all contracted for
at 12s. 6d. per ton f.o.b., leaving it to the customer to
charter the ship. They supplied several large London
factors. Of course, one of the principal causes of their
reduction was absentees. Taking their pit with about 1,500
men, including compensation men in normal times and men
ill, there would be perhaps about 80 to 100 men away from
work; but the number had increased so rapidly, that now
it was 290 to 300 or 340 men who were away. One explana-
tion was that wages were higher. Witness thought it was
quite possible that with the restriction of hours of the
licensed houses it meant the men did not waste their money
in the way they did, and therefore they had enough money
to afford a holiday.

Witness said that as far as possible they fixed up some-
where about 75 per cent, of their output in order to insure
regular working to cover the standing charges. The whole
of the coal coming up to London was at a fixed price. There
was a sliding scale at certain collieries. There were a few
remaining in West Yorkshire which had a sliding scale based
on the prices fixed by certain big factors in London of
kitchen coal. They themselves did that for many years, but
they had not worked under a sliding scale now for six or
seven years, because it always worked against them. A
good number of other collieries had also abandoned it. At
one time prices of kitchen coal were fixed by a number of
firms of merchants, and when kitchen coal was quoted at
a certain price in London, either rise or fall, the contract
price rose or fell. But a number of firms dropped out, the
matter got into the hands of two or three people who seemed
to arrange it, so the collieries gave it up and had a fixed
price now. Some had an addition for winter, but witness’s
firm had a fixed price over the whole period. The objection
to the sliding scale was that if they fixed up a large quantity
on a sliding scale, anticipating a rise, and then they found,
due to the cause just mentioned, that there was no rise
and they had kept more for the open market, they could
have sold at a better price, they were losing. Witness said
that up to the present they had been able to execute all
their contracts. They had contracts for coal going to
Germany and Belgium, which, of course, not being taken,
had allowed them to keep up their contract quantities in this
country. The price of their contracts last summer was
12s. 6d. free on board at Goole, giving an equivalent at
the pit head of 10s. 9d. The 10s. 9d. coal had risen to
13s. 6d., but the amount of free coal was so small that it was
hardly worth considering. Their 25 per cent, margin had
practically gone. Witness said he had only heard of one
case in West Yorkshire in which notice had been given
that they were unable to fulfil their contract quantities.
He might preface that by saying there was a clause in
some contracts that in case of strikes, or some restriction of
output over which the colliery proprietor had no control, a
proportionate reduction in the quantity supplied should be
made. He had heard of no case in which a colliery had
cut down the percentage of its contract deliveries and had
utilised the percentages so cut down by putting it on the
market as free coal.

Asked if there were any local associations in the district
that discussed pit-head prices with a view to determining
them, witness said there was only the West Yorkshire Coal
Owners’ Association, but they as an association had no
authority to deal with prices. The prices were discussed
by them not as an association, because their articles of
association did not allow them to deal as an association
with them. At the time before the contracts were going to
be fixed it was likely they would meet together and exchange
views. Some of the local contracts were fixed and based
on the price arranged by the West Yorkshire Colliery
Owners; that is, some contracts were fixed with a sliding
scale as they were in London. Supposing the West
Yorkshire coal owners met and decided on an advance of
prices or a reduction, the contracts were subject to the same
rise or fall. That at one time was very prevalent, and a
large number of contracts in Yorkshire were regulated in
that way, but it had fallen a great deal into disuse. The
natural tendency of West Yorkshire collieries was to look
for and execute orders in the immediate neighbourhood rather
than to search for them in London. There was a certain
number of seams of coal which were not of first-class quality,
but they were a class of coal that was bought on the
Continent a good deal. But when there were the good coals