coal trade bulletin - Clpdigital.org

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Sulphur in coke is almost wholly present as sulphide
of iron (FeS) or, perhaps more properly
speaking, magnetic sulphide of iron (Fe,S,,) and
as such, readily dissolves in the iron during the
smelting process, unless it is carried into the slag
by the use of suitable fluxes. In blast furnace
practice this is commonly done by the use of limestone
with the charge of ore and coke in addition
to the other functions that the flux stone performs.
It is generally believed that the sulphur, in whatsoever
form it is introduced into the furnace, is
transformed to calcium sulphide (CaS) at high
temperatures and by virtue of its lighter specific
gravity, floats off with the slag instead of dissolving
in the metal, from which is deduced the
well known axiom of the furnaceman: "A hot
furnace makes low sulphur and high silicon iron,
and a cold furnace, high sulphur and low silicon,"
which is true, unless it is run hot and limy when
both the sulphur and silicon will be low.
THE COAL TRADE BULLETIN. 43
BASIC COKE*
By 1 R. Campbell. Chief Chemist H. C. -rick Coke Company
In passing it may be remarked that the chief
source of sulphur in blast furnace operation, is
the coke, hence it is easy to understand why the
furnaceman always has his "weather eye" open
for the sulphur content of the coke, especially if
it runs over 1 per cent. The average coke operator
knows what it means to try to pacify an irate
furnaceman if he has been so unfortunate as to
ship out a few cars of coke above the prescribed
limit in sulphur. Of course, up in the Connellsville
region we would not like to be accused, nay
even suspected, of such a breach of metallurgical
etiquette, where by repute we have the finest
coking coal in the world.
This brings us to the question, "Why does the
furnaceman object to more than 1 per cent, sulphur
in the coke?" Too often the coke operator
is apt to think that the ills of the furnaceman are
largely imaginary, and that he is seeking to excuse
himself by venting his spleen on the coke,
but there is a reason, and a valid one, why the
sulphur in coke ought not to exceed 1 per cent.
greatly, to
MAKE GOOD IROX.
In round numbers, a ton of coke makes a ton of
pig iron and usually about one-half ton of slag
is produced, from which it is easily deduced that
with a properly working furnace, the one-half ton
of slag must carry all the sulphur in the ton of
coke, i. e., the slag must carry double the sulphur
found in the coke. Thus, if a 1 per cent, sulphur
coke is used, the slag will have to carry about 2
*Paper read before the Coal Mining Institute of America.
Pittsburgh, Pa., December 4 and 5. 1913.
per cent, to remove it completely from the iron.
Now the practical limit of solubility of the sulphur
in the slag is usually considered to be from
2 per cent, to 2V4 Per cent.; in other words, unless
the furnace is run very limy, which is detrimental
to the lining, mere or less, we do not expect the
slag to hold more than 2 per cent, or 2>4 per cent.
sulphur. There are rare instances where the slag
has carried 2\'-2 per cent, or even higher, sulphur
for a considerable length of time.
This, then is the main reason why the furnaceman
does not like his coke to exceed 1 per cent.
sulphur greatly. Coke much above IVi per cent.
sulphur has but little metallurgical value for the
economical manufacture of low sulphur iron.
BASIC COKE.
In view of the foregoing, many attempts have
been made to improve the chemical quality of coke
from the sulphur standpoint during its manufacture.
This paper concerns itself only with the
addition of crushed limestone to the charge of
coal, or the formation of basic coke. The idea
is old. Fulton tried it a number of years ago.
1 believe he mentions it in his book on "Coke."
Lately the scheme has been revived, both here and
abroad, the claim being made that the cause for
past failure lay in the fact that the mixtures were
not scientifically made.
According to the claims of these latest investigators,
the limestone must be added in proportion
to the ash of the coal to form a slag consisting
of a mono-silicate of lime. In other words, the
limestone addition is calculated much after the
manner of burdening a furnace. To illustrate,
the following analyses are shown:
Coal Analysis.
Volatile matter 39.05%
Fixed carbon 52.34
Ash 8.61
Sulphur 2.09
Composition of Ash.
Silica 47.85%
Iron oxide 15.84
Alumina 23.98
Lime 4.41
Magnesia 1.66
Sulphur 1.11
From the above, we calculate that 12 i_ per cent.
of limestone, of good quality, is needed to flux the
ash. It is the hope also that the sulphur in the
coal will pass into the slag during the coking
process. Both the coal and limestone must be
crushed very fine. The coal should all practically
pass a %-inch screen, and the limestone, a
20-mesh screen. The mixture must be intimate
and thorough.