326

THE COLLIERY GUARDIAN.

February 18, 1916.

CURRENT SCIENCE

The Effect of Aeration and “ Watering Out ” on the Sulphur
Content of Coke.

Mr. J. R. Campbell (Transactions of the American
Institute of Mining Engineers) discusses this subject
after touching briefly on the forms in which sulphur is
supposed to exist in Coking coal to be carbonised in bee-
hive or by-product ovens. This element exists in coal
as sulphides, sulphates, and the so-called organic
sulphur (in combination with the carbon, hydrogen, and
oxygen of the coal). For most coking coals, it can be
safely assumed that the preponderance of sulphur is in
the form of pyrite (FeS2). When exposed to compara-
tively low temperatures during the coking process, it
loses six out of the 14 atoms of its sulphur (or 42-8 per
cent.) expelled or volatilised. Fe7S8 remains in the coke
as pyrrhotite, or magnetic sulphide of iron; this accounts
fo.r the highly magnetic properties of the powdered coke.
In the beehive methods of coke making, the sulphur is
oxidised along with the other volatile products : first,
into sulphur dioxide (SO2); secondly into sulphuric
anhydride (S03); and, finally, into stilphuric acid, as it
comes into contact with the air and moisture. In a
properly regulated draught on a beehive oven, there is
never complete combustion of the gases. In other
words, the coking process should be carried on in a
reducing atmosphere, and a low-grade producer gas kept
issuing from the trunnel head. For coals of about 30
per cent, volatile matter, the ratio of air to gas is
34 to 1. In complete combustion, the ratio is 6 to 1,
producing an extremely high temperature in the crown
of the oven (3,500 degs. Fahr.) more than enough to
cause fusion of the refractories used. A good coking
temperature is 2,500 degs. Fahr, in the crown of the
oven.

It follows, then, that the sulphur remaining in the
coking mass as iron sulphide cannot in any way be
affected by the aeration or draught on the oven. Among
beehive coke oven operators there used to be a saying,
“ the hotter the oven, the more sulphur burned out.”
This probably never was true unless the aeration was
carried to complete combustion of the fixed carbon
itself, in which case the iron sulphide (FeS) would, of
course, be oxidised to Fe2O3, and the sulphur liberated,
as usual. This condition would not be productive of
good results, as the percentage of coke yield would be
abnormally Iotv and the “ ashes,” or “ braize,” corre-
spondingly high. This is evidence that, so far as the
pyritic sulphur is concerned, any sulphur that is volatile
at all is so at comparatively low temperatures through
the agencies of distillation, and no practical method of
super-aeration will help in the least in the further elimi-
nation of sulphur.

On the other hand, overheating promotes certain
chemical reactions in which sulphur compounds with
other bodies on which heat has no effect. If the coking
process proceeds too quickly, or if the heat is irregular,
the de-sulphurisation of the coke is apt to be less
complete.

In the by-product oven, which1 is essentially a true
distillation process, the sulphur is distilled from the
pyrites as atomic sulphur, but, apparently, it afterwards
combines with the hydrogen of the coal gas, forming
sulphuretted hydrogen.

Here, again, appears the fallacy of super-aerating bee-
hive ovens to eliminate sulphur, for in by-product ovens
in which no air is admitted there is just as much de-sul-
phurisation of the coke as in the beehive process; in
fact, there is more de-sulphurisation when the matter of
increased yield is considered. For example : Given a
yield of 70 per cent, coke by the beehive process and 75
per cent, by the by-product process from coal carrying 1
per cent, sulphur, the practical volatilisation of sulphur
from the beehive process is only 18-3 per cent., while in
the by-product it is 23-7 per cent.

Of the forms of sulphur that may be present in addi-
tion to pyrites, organic sulphur will remain, for the
most part, in the coke, being unaffected by aeration
except in the event of total destruction of the carbon
itself, with which the organic sulphur is supposed to be
combined. Any sulphates present, such as CaSO4,
would also be unaffected by aeration or super-aeration
in the beehive process; no amount of “ airing ” would
help to eliminate the sulphur. Cases are known in
which the sulphur in the resultant coke was as high, or
even higher, as in the coal, sc that much of the sulphur
must have been present as sulphate, or as “ organic ”
sulphur; or else the ash of the coal was rich in iron,
lime, and magnesia.

Theoretically, it would seem possible to remove con-
siderable sulphur by the quenching process. The action
of the water on the iron sulphide formed in the coking
process is as follows : FeS + H2O ~ FeO + H2S.' The
odour of sulphuretted hydrogen is easily detected, and
the colour of the coke, wherein rust spots appear, shows
the presence of iron oxide. The practical coke burner is
always suspicious of what he terms “ rusty coke,” as it
invariably is an indication of a high sulphur content. In
beehive practice, too, sulphuretted hydrogen is evolved,
but, at the same time, the water as steam is decom-
posed by the carbon H2O + C = CO + H2, which fact
probably accounts for a part of the large percentage of
carbon monoxide and hydrogen gas found in the gas
from trunnels of beehive ovens, the water being formed
from the combustion of the gases during the coking pro-
cesses, which is virtually a low-grade producer gas of
the following percentage composition (by volume) :—
CO2, 3-0; CO, 9-0; H2, 110; CH4, 0-3; N?, 76-7. The
desulphurisation of coke by water cannot be complete.
The coke mass cools too quickly, and its very structure
prevents the rapid penetration of the water thrown on
it, especially in the denser varieties. As the tempera-
ture is lowered, the reaction becomes too slow to be of
practical benefit. Data as to the exact amount of

AND TECHNOLOGY.

sulphur eliminated in this way are rather scarce, but
experience, based on the general laws of volatilisation
set forth elsewhere, leads to the conclusion that only an
infinitesimal percentage of sulphur is thrown off during
the quenching process. Laboratory and practical tests,
in which the coke has been allowed to cool naturally,
show but little difference in the sulphur content from
those in which the coke has been quenched with water.
Certainly there could be only a few hundredths of 1 per
cent, in favour of the water-quenched coke, at the most,
in a coke averaging 1 per cent, sulphur.

The prime object' of the use of water is to lower the
temperature of the coke for handling, not for de-sulphuri-
sation, and the quenching process should be so regarded.
However, it is concluded that quenching by the by-pro-
duct practice will eliminate more sulphur than by the
beehive method, which may partially explain the greater
total volatilisation of sulphur in the former, elsewhere
intimated.

The addition of hydrochloric acid to the water greatly
facilitates the removal of sulphur during the quenching
process. The action of this acid on iron sulphide is
positive at all temperatures, thus, FeS + 2HC1 = FeCl2
+ H2S. At one time the cost prohibited the use of this
method, but with the depletion of low sulphur coking
coals, this may, in the near future, be a factor in the
elimination of sulphur.

Tar Dehydration.

In a paper read before the Southern District Associa-
tion of Gas Engineers and Managers, Mr. R. Wardle
described the Hird continuous process for dehydrating
tar, as installed at Tottenham. The plant proper con-
sists of five vessels : the still, heat inter-changer, con-
denser, and two sight seal boxes; and is capable of
dealing with 20 tons of tar per day. There are storage
tanks for receiving the distillate and dehydrated tar
respectively, together with feed pump, or overhead tank,
according as the tar is forced into the still or is allowed
to flow by gravity through the plant.

The still is of mild steel plates, is rectangular in shape,
lift, long by 5ft. wide by 3ft. bin. deep, and fitted
with one horizontal row of five Gin. steel tubes, running
longitudinally about 3 in. from the bottom of the still.
Vertical baffle plates, 21 in. deep, are fixed between the
tubes in such a manner that the tar is made to travel
from end to end of the still four times on its way from
the inlet to the outlet pipe—a total distance of approxi-
mately 40 ft.

The heat interchanger is composed of two steel tubes
placed horizontally, one inside the other. The outer
tube is 11 ft. long by 2 ft. diameter, and the inner 11 ft.
long by 1ft. diameter; and they are secured together by
two end plates. The crude tar passes through the inner
tube in one direction, and the dehydrated tar along the
annular space in the opposite direction. A run-off cock
is provided at the bottom to empty the still when
required. The condenser is 4 ft. diameter by 7 ft. deep,
and is fitted with a 3 in. cast iron coil, through which
the vapours from the still pass. The sight seal boxes
are provided with a mid-feather, and on the top there
is a take-off pipe for sulphuretted hydrogen; and also
a lid through which samples can be readily taken. A
furnace suitable for burning coke breeze is placed under
the still at one end, and is supplied with forced draught.
The furnace gases pass through the heating tubes away
to the chimney.

The crude tar is pumped direct from the wells, slowly
and continuously, into the condenser, where it serves as
the cooling agent for condensing the vapours from the
still, and is itself, at the same time, appreciably raised
in temperature. The tar leaves the condenser through
an inverted U pipe, and passes into the heat inter-
changer. Here a considerable amount of heat is
imparted to it by the outgoing tar, and it enters the
still at about 160 degs. Fahr. It then slowly travels
along the four channels formed by the baffle plates,
giving off the light and middle oils on its way to the
outlet pipe. From there it flows into the annular space
of the heat interchanger, and then through the overflow
pipe into the sight box, and away to the storage tank.

The vapours pass along the still head into the con-
denser, and the condensate flows, by gravity, through
the second sight box into the receiving tank. The
ammoniacal liquor is run off from the bottom of the
vessel into the wells. Any sulphuretted hydrogen gas is
trapped at the seal box, and travels along the take-off
pipe to a small oxide purifier.

Coke as a Boiler Fuel.

Mr. E. W. L. Nicol, A.I.E.E. (Electrical Review)
describes a method of adapting a chain grate to burn
coke, as used in this country under boilers of 20,0001b.
per hour capacity, without materially reducing the capa-
city or efficiency. An auxiliary hopper for coke is fixed
below the usual hopper, and the coke is fed upon the
grate with a thin layer of coal on the top of it to ensure
its ignition. The ignition arch has been retained.
With this method, air leakage into the furnace is elimi-
nated, and normal capacity and efficiency are obtained.
To break and grade coal to suitable size, for either
coking- or sprinkler-type stokers, an ordinary coke
cutter, absorbing about 4 or 5 horse-power, will deal
effectivelv with 30 tons per hour at a verv insignificant
cost.

In considering the question of substituting coke for
coal fuel in a power station handicapped by being laid
out and equipped to use a uniform class of coal only,
the problems of storage and capacity of machine stokers
and boilers naturally arise. The reserve stocks of coal
usually carried by gas authorities are necessarily con-
siderable, and, to a coke user buying under contract,
would, of course, be available. This consideration
should to some extent offset the disadvantage of the rela-

tively greater bulk of coke. At normal rates of com-
bustion, and with equal draught, the steaming capacity
of a hand-fired boiler will be reduced by afiout 15 per
cent, to 20 per cent, by substituting coke for coal of
similar calorific value.

MINERS’ FEDERATION’S VISIT TO
GOVERNMENT RESEARCH STATION.

The executive committee of the Miners’ Federation
of Great Britain has, by the invitation of the Home
Office, visited the Government station at Eskmeals for
experimental research into the cause and the prevention
of explosions in coal mines. The miners’ representa-
tives were received by Mr. William Brace, M.P., Under-
secretary of the Home Office, Sir Richard Redmayne,
Chief Inspector of Mines, Dr. Wheeler, and other
members of his staff.

Mr. Brace expressed the pleasure which he felt in
welcoming them on the occasion of their visit. They
would be -able, after seeing the experiments which Dr.
Wheeler would show them, to tell the men that the
Government was losing no opportunity by way of
research and experiment to making mining life more safe
than it was at present.

Sir Richard Redmayne added a few words of welcome.
He assured the miners’ representatives that the Home
Office was equally concerned with them in securing
safety for the workmen in the mines. They wanted all
to be pulling at the same end of the rope.

The party, under the guidance of Dr. Wheeler and
members of his staff, then witnessed experiments in the
prevention of explosions from coal dust by means of an
admixture of an equal quantity of stone dust.

The experiments were completely successful, but the
miners’ representatives, through Aid. W. House, vice-
president of the Federation, gave expression to the
nervousness of the miners as to the effect of stone dust
on the lungs of the workers, and asked Sir Richard
Redmayne if the Home Office would delay the issue of
regulations for a short time, to enable the miners to
consider the matter.

Sir Richard Redmayne promised to lay their wishes
before the Home Secretary, but he assured the represen-
tatives that the most careful experiments were being
made so as to protect the health of the miners from any
possible danger. Experiments had been made on
guinea-pigs so as to obtain a stone dust which will be
as 'innoxious as ordinary coal dust.

Mr. Brace, M.P., Under-Secretary at the Home Office,
presided at the luncheon.

Aid. W. House, vice-president of the Federation,
proposed the health of Mr. Brace, Sir Richard
Redmayne, and Dr. Wheeler. Fie remarked that they
especially thanked the Home Office Secretary, Sir
Richard Redmanye, and Mr. Wm. Brace. They
were delighted that the Home Office responded so
readily to their request to see these experiments. They
also thanked Dr. Wheeler and his colleagues, who
seemed to be doing everything in their power to reduce
the dangers of mining life.

Mr. W. Abraham, M.P. (“ Mabon ”), in supporting
the vote of thanks, said they were there to see what
science was doing to endeavour to save life.

Mr. W. Brace, M.P., in replying, said that the Home
Office had as one of its principal purposes the protection
of the lives and limbs of the coal miners of the country.
Since he had been at the Home Office he had found on
its staff some of the most capable and self-sacrificing
men to be found in this country. He had found in Sir
Richard Redmayne a colleague who was in distinct
sympathy with the higher aspirations of the miners, as
expressed through the Miners’ Federation of Great
Britain. He wanted them to look upon the Flome Office
as being entirely at their disposal, and having only one
thought, and that was to give the people who produce so
much of the wealth of the country a fighting chance for
their lives in the production of coal.

Sir Richard Redmayne remarked that there must be
something right in the old country yet, when they found
a Government Department, and the leaders of the
Miners’ Federation, endeavouring to work hand in hand
in order to secure a common end, and that the better-
ment of conditions in the mines. Nothing would cheer
Dr. Wheeler and his staff more than this recognition of
his work there. It was a long long road to the securing of
the safety of miners, and it was only step by step that
they could approach to it. Grateful as the miners might
be, the Home Office were equally grateful to Dr. Wheeler
for the arduous self-sacrificing work he had been
carrying out there.

Dr. Wheeler said' the Home Office experimental
station existed only for one purpose, and that was to
find out the truth. It had no object whatever except to
find out what were the causes of dangers down the mine
and the means of preventing those dangers. It had so
far only tackled the question of explosions from coal
dust, but there were the questions of spontaneous com-
bustion, and numerous others. He thought they had
reached a stage when they would be able to say that it
would be impossible to have explosions in a pit. Fires
might be more difficult to deal with. The chief cause of
accidents in mines was falls of roof, and that was a
matter which would require a good deal of considera-
tion. It seemed to him that while the Government
experimental station existed, efforts should be made to
deal with all the causes of accidents and deaths in pits.
He thought it was proved that the Senghenydd disaster
was caused by a bare electric wire used in signalling.
He wanted to say that a bare wire could be used without
danger in a pit, and that bare wire signalling w’as not
dangerous, but that the danger existed in the type of
signalling instrument used.