January 25, 1918’.

THE COLLIERY GUARDIAN

175

ment of the basic open-hearth process, lower silicon
content was the practice, round about 1 per cent.,
while, as the sulphur could be somewhat eliminated in
that process, its maximum limit could be raised beyond
what was demanded for hsematite iron in the acid pro-
cess. The sulphur content, however, must not be
excessive. With iron w’ith 1 per cent, silicon and
below, it was more difficult to keep the sulphur regu-
larly below OTO per cent., and also to control the fur-
nace operations, than when making foundry iron or
iron for the acid steel process. There appeared to be
a wide field for research in the direction of ascertain-
ing the best temperature and rate of gasification for
each class of coal used, as the coals from different
depths had not the same coking power, no less than
coals from different districts.

The physical composition of the coke was as impor-
tant as the chemical. The most important physical
characteristic was the hardness or density, which was a
measure of its resistance to abrasion or crumbling. A
good hard coke would produce more intense heat than
soft, also. The efficiency of heat utilisation in a blast
furnace depended upon the concentration of heat, and
that was best produced by a hard fuel.

Hardness Test.

Mr. Hewson then described a hardness test made
with pieces of an average sample of coke of from J in.
to 1 in. across. These were sifted through a Jin.
mesh, and the portion remaining on the sieve was
taken and dried at 120 degs. Cent., 281b. being
weighed and placed in a drum or rattler, together with
a dozen cast iron balls 1J in. in diameter. The drum
was given 1,000 revolutions in about an hour, and the
coke withdrawn and sifted on a J in. mesh, that
remaining on the sieve being then weighed and calcu-
lated to a percentage of the original weight. That was
given as the hardness number. Thus : remaining on
Jin. sieve, 271b. 2 oz. ; passed through, 14 oz. ; total,

28 lb.;	equalled 96’9 as the hardness.

28

The chemical composition of the coke resolved itself
ultimately into the amount of available carbon which
it contained, i.e., the quantity of carbon present in
the coke in excess of that necessary to melt the slag
formed by the ash and sulphur of the fuel, together
with the limestone used to flux them. That also was
affected by the physical nature of the coke. Accord-
ing to Forsythe,, the ash required double its weight of
limestone, and the sulphur 3J times its weight to form
slag. The slag required 25 per cent, of its weight of
carbon to melt it. That, deducted from the fixed
carbon, was called “ available carbon.”

Mr. Hewson gave a series of analyses and hardness
numbers for 18 beehive cokes, in which the hardness
numbers ranged from 97-5 to 93’7; and for 12 by-pro-
duct cokes, in which the hardness numbers ranged
from 97-5 to 91-7. Cokes below 94 hardness, he stated,
caused serious trouble in working, and resulted in the
furnaces scaffolding or hanging and getting decidedly
cold. Cokes below 85 per cent, available carbon had
caused irregularities if burdened at the same rate as
others, evidently from shortage of heat producing-
carbon. Of a number of samples, the best all-round
cokes were: a beehive coke which had an analysis of
8-14 per cent, of ash, 0-81 per cent, of sulphur, 91 per
cent, of fixed carbon (of which 86-14 per cent, was
“available”), and a hardness number of 95-3; and a
by-product coke with an analysis of 7-87 per cent, of
ash, 0-80 per cent, of sulphur, 91-66 per cent, of fixed
carbon (of which 86-94 per cent, was “ available ”),
and a hardness number of 97-5. The analytical and
physical data, he said, emphasised the desirability of
using one class of coke exclusively upon one furnace
if sufficient supplies were available. Where such a
procedure was adopted, more uniform results in the
working of the furnace and the quality of the iron
had been observed.

Soft Coke.

The bad effect of soft coke was cumulative and pro-
portionate to its softness, from its liability to crumble
during handling between the ovens and the furnace
bell, resulting in a large quantity of breeze and small
coke being charged into the furnace, and from the
crushing of the coke in the furnace. Both these causes
resulted in less available carbon reaching the tuyeres
than in the case of harder material.

The function and behaviour of sulphur in the fur- *
nace had been exhaustively investigated by Wuest and
Wolff in 1903, who concluded that, contrary to the
generally held opinion, the sulphur in the coke does
not reach the level of the tuyeres of the blast furnace
without undergoing alteration, a great portion of it
being previously volatilised by the ascending gases, and
then largely absorbed from the gases by the descend-
ing charge, in which condition it arrives in front of
the tuyeres. Tip to 800 degs. Cent., the sulphur is
principally absorbed by the oxides of iron from the
sulphur-laden gases, whereas from 800 degs. Cent,
upwards, the position is reversed, and the lime
becomes the chief absorbent of the sulphur.

DISCUSSION.

Dr. J. E, Stead (Middlesbrough) wrote that he had
never heard of Forsythe, whom Mr. Hewson quoted as
an authority. He did not think that Forsythe was a
recognised authority. Bell, a long time ago, had
stated all, or nearly all, that Mr. Hewson attributed
to Forsythe. He did not know whether Mr. Hewson
was aware of the fact, but they had had to use the
very densest and hardest retort carbon in order to set
up the highest temperature in their little furnace for
determining the melting point of firebricks, etc. With
cold blast, they got up to a maximum temperature of
1,750 degs. Cent., whereas ordinary coke of the porous
variety would not give anything like that temperature ;
and charcoal—which was still more porous—gave a
still lower result; so that there seemed to be some doubt
that the hard porous coke was best for giving the
highest hearth temperatures.

Dr. G. P. Lishman (Lambton Coke Works) wrote
that he had always understood that a coke suitable for

a blast furnace was one which, though it might
readily break down to the size of a fist, was very hard
and difficult to crush beyond that point. It seemed to
him, therefore, that the hardness test should be taken
on lumps of that size, and not on coke broken down
to inch pieces. Forsythe’s first desirable charac-
teristic was obviously incompatible with a given test
made in either way.

Mr. G. Weyman (chief chemist of the Newcastle and
Gateshead Gas Company) said it was quite an acci-
dent to get from the same colliery anything like the
same type of coal twice in succession. Most collieries
worked several seams of coal, and one never knew what
seam one was going to get. Sometimes a trainload
itself might be a mixture of two or more seams. An
experiment which was carried out recently, in which
samples of each truckload of a train of 15 trucks were
taken, showed that the ash varied from something like
3 per cent, up to 24 per cent. The samples were taken
as w’ell as could be, a good many bucketfuls out of each
truck were crushed down, and particular care was
taken not to exclude the stone, which was part of the
coal so far as the fire was concerned. The variations
were enormous, although the average of the whole
trainload was probably not more than 10 per cent. He
could quite imagine that blast furnace people getting
coal with that variable amount of ash might be much
disgusted.

Phosphorus in Coke.

Mr. E. F. Knott (manager of the Priestman
Collieries’ Coke Ovens) said that, with regard to
density of coke, he thought that, if one got a porous
coke, it was very often apt to be soft and easily broken
down in the furnace. Mr. Hewson did not mention
the question of phosphorus in the coke, a rather impor-
tant point, as, in that part of the world, there was a
premium placed on a low phosphorus content in coke.
The coke represented about three-fourths of a coke
oven’s total products, and, if one did not make a good
saleable product, and could not get rid of it, one would
have to shut down very quickly, and lose all other
by-products. He thought it was rather satisfactory
that Mr. Hewson’s tables showed that the hardest coke
was a patent coke. He noticed that the sulphur in the
cokes did not in any way follow the ash content. The
highest ash was 13, and contained only 0-84 of sulphur,
whereas an ash of only 7 contained even less sulphur
than that. As to the variation in coal, he knew of one
pit in which there was one seam of coal that was not
cokable at all, practically, whilst all the other seams
were all right.

Mr. W. Diamond (manager of the Marley Hill Coke
Ovens of Messrs. John Bowes and Partners, and
chairman of the Northern Section of the Coke Oven
Managers’ Association) observed that a blast furnace
manager could not possibly expect to have the same
quality of coke from Derbyshire or South Yorkshire as
from Durham, for instance. The coke from Derbyshire
was very friable, and had been described as “ pretty
rotten.” South Yorkshire was somewhat better, but
could not be compared with Durham coke. The
density, chemical composition, and mechanical proper-
ties of Durham coke far surpassed those of the cokes
of the other two counties. In the last 12 or 13 years
there had been a considerable improvement in the
design of patent ovens. The old ovens took anything
up to 50 hours for the carbonisation of South Yorkshire
coal, whereas the more modern ones did the work in
about 35 hours, and produced a harder coke. At the
majority of coke oven installations nowadays there were
installed washeries, which, in itself, guaranteed that
the coke would be of uniform quality. There were very
few such places where the ash rose above 10 per cent.

Mr. A. Short (manager of Messrs. Cookson’s Lead
Works, formerly of the Priestman Coke Ovens) said
that, speaking both as a maker and as a user of coke,
the point that struck him was the importance Mr.
Hewson attached to the hardness test. There was an
extremely small variation in the hardness number—
from 98 down to 91. In using coke from a bin, there
was an astonishing difference in appearance between
that coke and the same coke on the bench. The trans-
port made an enormous difference in the appearance
of the coke, and that fact certainly made him, as a
user of coke, more forbearing than he would otherwise
be. He would be very much interested to know what
should be the limit of hardness of a coke suitable for
blast furnace work. As to the testing of coals for
coking, he felt sure that a good deal more should be
done by coal owners, who contemplated putting up their
own ovens, to get an absolutely reliable test of the
coal they were going to treat. For many years a
German firm—he was speaking of 15 years ago—had a
complete battery of small ovens, in which samples of
coals were tested for customers who contemplated
putting up their own ovens. He thought it would be
very advisable to have a coal testing station on a really
big scale—it might have to be a joint concern—in this
country. A great proportion of the cost would be
covered by the coke and by-products obtained from
such a station. There might be ovens of different sizes
which could be heated to different temperatures. He
had no doubt that the early prejudice against patent
coke was very largely due to the fact that the coal was
either badly coked in a good oven, or in some other
way was not right.

Mr. Weyman remarked that gas coke was, of course,
not as good as coke oven coke for blast furnaces, but,
in some cases, it had been used. In one case, it was
rejected because the phosphorus content was too high,
but the phosphorus was in the coal to start with.

Dr. J. H. Paterson (chief chemist to Messrs. Swan.
Hunter and Wigham Richardson Limited) referred to
Dr. Stead’s statement as to the temperature produced
from the combustion of coke. The speaker had had,
within the last few years, a good deal to do with high-
temperature reactions, and it had been necessary to
make investigations of the reasons for the production
of high temperatures with various fuels. Various
types of blast furnace coke, ordinary gas coke, and
retort carbon had been used for that purpose. It was

well known that, if one increased the weight of fuel
per cubic inch per minute, one could increase the
temperature within limits, and it was quite feasible
that, if one could increase the surface of the fuel, one
might increase the temperature. The burning of coke
or any other fuel, when a blast of air was projected on
it, took place at the surface, and the rate at which it
burned depended partly on the surface exposed to the
blast, but very much more on the capacity of the fuel
to absorb oxygen at high temperatures, and to produce
what was commonly known as surface combustion in a
very intense form. He was inclined to say that, if it
were possible to determine—as it had been possible
with other materials—how far from the actual surface
combustion was taking place in the material, one might
get a reason for the production of higher temperatures
with some types of carbon.

Grading Coke.

Mr. C. H. Ridsdale (consulting chemist, Middles-
brough) spoke as a practical blast furnace man, and as
one who had been associated closely with coke ovens
and technically responsible for them for 19 or 20 years.
During part of the time that he had been responsible
for blast furnace practice, and so on, they graded coke
that came into the works, calling the best No. 1, and
grading the rest by quarters down to No. 3, which they
considered to be too bad to use. The Priestman
Collieries’ coke, he mentioned incidentally, always
graded as No. 1 for mechanical condition. Mr.
Hewson’s paper, in a nutshell, was to the effect that
“ bad coke makes bad iron.” That w’as true. Any-
one who ivanted to be patriotic must produce good coke,
for our military success depended upon good iron. As
to porosity, he did not think any coke man need be
afraid of making his coke too dense and too hard. The
densest coke they could produce was quite porous
enough for blast furnace purposes. Of course, a soft
coke was very soluble in carbon dioxide in the upper
part of the furnace. That was one reason why a
manager liked a hard coke. If they got a big coke,
like beehive coke, it helped to keep the furnace very
open, and now, more than ever, the tendency was to
get small ores. If they had small ores and small coke,
they could not drive their furnaces. He could tell
them positively, as a blast furnace man, that, if they
had a ton of coke with 2 cwt. of dead small, it would be
very much better if it w7ere practicable to sieve out
that 2 cwt., and put only the 18 cwt. into the furnaces.
They would get better working, and just as much heat.
Mr. Hewson made a great point of the large effect on
a furnace working with a comparatively small variation
in the condition of the coke. They must consider that
matter in connection with what happened in a blast
furnace. When carbon burned to CO only, it only
gave off 2,473 heat units. In ideal furnace working,
they got those 2,473 heat units, and then the CO passed
up the furnace and took carbon from the ores in the
upper part of the furnace and formed CO2; then they
got the burning of that CO and C02, and got another
5,607 heat units. That was when they were working
on peroxide ores. In practice, nothing but a pure
peroxide ore was reduced in the upper part of the
furnace as it ought to be. That w’as only getting an
efficiency of 2,300 heat units per unit of coke—not a
very abnormal state of things for furnaces on basic
and a good many other classes of iron. In that furnace
the loss of 1,153 heat units, equivalent to J cwt. of
coke, was sufficient to cause a drop in quality of pig
from open grey mottled to ordinary white—the former
a perfectly good iron for steel making, the latter
unsuitable. Secondly, that same J cwt. difference in
coke equivalent was equal to a reduction in quality of
resulting iron equal to 0-8 cwt. in pig, the iron passing
into the slag instead of being reduced, and raising the
iron content to 2-44 per cent. The same effect could
be produced by a variety of causes, such as leakage of
water at the tuyeres, drop in temperature of blast,
badly-calcined stone reaching tuyeres, etc., and,
amongst others, a drop in quality of the coke used, due
to more ash, and hence less carbon, equal to 1’15 per
cent. As to the reason that apparently small causes
had such marked effects on furnace working, particu-
larly w’ith furnaces which, like those on basic, had to
use a lot of refractory materials, he made, in 1900,
some very careful balance-sheets of heat received and
consumed by blast furnaces with coke consumptions
varying from 21 to 30 cwt. The data so obtained had
constantly proved to be reliable in practice. They
showed clearly that, however high the coke consump-
tion, of the whole coke charged, most of the heat
yielded went in doing what might be termed “ dead
ivork,” work the effect of which was not apparent
(effecting the necessary chemical changes, heating the
escaping gases, etc.), and that it was only the small
balance over what was necessary for those purposes,
namely, a very small excess of heat, which, once the
“dead” requirements were satisfied, produced the
effects on the grade of the iron. The effects of small
variations of heat available were thus accentuated
when they occurred in the hearth. Thus, in the case
of a furnace using 27 cwt. of coke, the heat produced
by 21 cwt. was used up for purposes other than the
fusion of slag and pig, and only that from 6 cwt. w’as
used in the hearth for that fusion. Looked at in that
light, one got a very different impression of the effect
of J cwt. of coke or its equivalent, for it equalled 8J
per cent, of all used in the hearth. That explained
why any drop in quality, either chemical or mechani-
cal, abstracting so large a proportion of the heat from
the hearth, told so heavily on the product. As to the
size of the coke, the breaking from large to small
pieces was not so important as the crushing. If they
got “ mush ” that crushed dowm to the small stuff that
blew’ out into the flues, and they got it in the dust
catchers and the flue dust, and then they had trouble.

Friability v. Hardness.

Dr. J. T. Dunn (Public Analyst for Newcastle) said
that, in regard to coke, the question arose as to what
was meant by “ hardness.” One read in the text-
books that coke was used instead of charcoal because it
was harder, and would bear the burden of the furnace
better, but the burden of the furnace could hardly be