IMPROVEMENTS IN THE MANU- FACTURE OF IRON IN BLAST FURNACES
Year: 1882

page_text: LETTERS PATENT to Charles Cochrane of The Grange Stourbridge in the
County of Worcester for an Invention of IMPROVEMENTS IN THE MANU-
FACTURE OF IRON IN BLAST FURNACES
PROVISIONAL SPECIFICATION left by the said Charles Cochrane at the
Office of the Commissioners of Patents on the 19th October 1882.
CHARLES COCHRANE of the Grange Stourbridge in the County of Worcester
"IMPROVEMENTS IN THE MANUFACTURE OF IRON IN BLAST FURNACES
17
It has been found that the principal cause of the loss of fuel in blast furnaces
of ordinary construction is due to the carbonic acid evolved both from the lime-
stone aud from the ore in being reduced at the red hot zone of the furnace, which
carbonic acid takes up carbon from the incandescent fuel to form carbonic oxide
gas which passes away. Now, according to my present invention, I more or less
prevent the production of carbonic acid at the red hot zone, firstly by constructing
the furnace of such a large size and by charging the ore in lumps of such moderate
size that the reduction thereof shall be practically completed before it reaches the
red hot zone; and secondly, I employ in combination with such construction of
furnace and mode of charging the ore, lime in place of limestone so that no carbonic
acid gas is evolved therefrom.

page_text: '
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Charles Cochrane in the Great Seal Patent Office on the
25th January 1883.
CHARLES COCHRANE of The Grange Sourbridge in the County of Worcester
"IMPROVEMENTS IN THE MANUFACTURE OF IRON IN BLAST FURNACES
"
It has been found that the principal cause of the loss of fuel in blast furnaces
of ordinary construction is due to the carbonic acid evolved both from the lime-
stone and from the ore in being reduced at the red hot zone of the furnace, which
carbonic acid takes up carbon from the incandescent fuel to form carbonic oxide
gas which passes away. Now according to my present invention, I more or less
prevent the production of carbonic acid from the above substances at the red hot
zone, firstly by constructing the furnace of such a large size relatively to the size
of the lumps of ore treated, or by breaking up the ore into lumps of such
moderate size that the reduction of the ore shall be practically completed before
it reaches the red hot zone; and secondly, I employ in combination with such
construction of furnace and inode of charging the ore, caustic, lime in place of
limestone so that practically no carbonic acid gas is evolved therefrom.
In carrying my invention into practice, the limestone should be thoroughly
burnt in suitable kilns of any known construction, and the resulting caustic lime
should be drawn from the kiln whilst still warm, and be protected from exposure
to rain or weather by being loaded into barrows or trucks suitably enclosed, and
by preference arranged so that they will open of themselves when the barrow is
to be emptied. By this means the caustic lime will be prevented from absorbing
any sensible proportion of carbonic acid or water from the atmosphere.
In furtherance of this protection the caustic line should be charged in its.
suitable proportion for smelting purposes directly on to the charging bell of the
blast furnace, or into the furnace itself and as quickly as possiblo be covered up
either with coke or ironstone; by this means, when the charge is lowered into
the furnace, as the lime is below the other materials of the charge, it will not be
liable to absorb the aqueous vapour rising from the moist coke or moist ironstone,>
which it would do if placed above these. Also, the interval of time between the
introduction of the consecutive charges will be utilised in enabling the moisture
contained in the coke and ironstone of the previous charge (which may be con-
siderable, especially in the coke in wet weather) to be driven off before the fresh
charge of lime falls on to them. The object of the above precautions is to prevent
as far as possible the formation of hydrate of lime, commonly known as slaked
lime, which would be as detrimental to the economic working of the furnace, if not
more so, than the limestone with its contained carbonic acid.
As before stated, in order to effect the successful working of blast furnaces
according to my invention, it is also necessary that the size of the blast furnace,
shall be so proportioned relatively to the size of the lumps of ironstone charged,
that the whole of this shall become reduced or converted into sponge of iron before
it reaches the red hot zone. If this precaution be not taken, that is to say, if the
lumps of ore are of such a size that they will descend through the upper part of
the furnace and reach the red hot zone before the whole of their mass could be
properly acted upon by the carbonic oxide, carbonic acid will be evolved from
the process of reduction in tho presence of the red hot coke, and this will be partly
taken up by the caustic lime, which, will thus become reconverted into carbonate
of lime to be again reduced in a still lower region entailing a corresponding
absorption of fuel in the process.

page_text: Thus, to avoid this occurrence, if large lumps of ironstone, or even a mixture
of large and small lumps, be used, the furnace should be of very large dimensions,
and I have found for instance that a height of about thirty ft. above the red hot
zone is advisable for this purpose, when lumps of about fourteen inches in size or
average diameter are used, but 1 in no way limit myself to these proportions, nor
is it possible to give any precise rules as to the size of the furnace, beyond the
general rule above stated, because the fulfilment of the required conditions may
depend not only upon the size of the ironstone lumps but also upon the nature
of the ore, which may in some varieties be acted upon more readily by the
carbonic oxide than in others. If the ore be reduced to a comparatively sinall
size, existing blast furnaces may in many cases be found available, and experiments
will soon shew to what size the ore should be reduced for use in blast furnaces
of existing dimensions, to insure complete reduction before reaching the red hot
zone.
In all cases it is important to insure the greatest possible dryness of both
ironstone and coke to obtain the fullest possible benefit from my above described
Invention.
Having thus described the nature of my invention and in what manner the
same is to be performed I wish it to be understood that I do not claim generally
the use of caustic lime in blast furnaces, as I am well aware that this has been
already tried, but under conditions and for purposes different from those of my
before described invention, but I claim.:-
The herein described method of working a blast furnace so as to diminish the
amount of carbonic acid gas evolved at the red hot zone, by employing a furnace
of such large dimension relatively to the size of ore treated as to effect the
reduction of the ore before it reaches the red hot zone and by using in com-
bination with such furnace caustic lime as a flux instead of limestone.
In witness whereof I the said Charles Cochrane have hereunto set my hand
and seal this sixth day of January in the year of our Lord One thousand
eight hundred and eighty three.
CHARLES COCHRANE. (L.S.)