IMPROVEMENTS IN BLAST FURNACES."
Year: 1878

page_text: PROVISIONAL SPECIFICATION left by Charles Denton Abel at the Office of
the Commissioners of Patents on the 10th January 1878. A communication
from abroad by John F. Bennett, of Pittsburg, Pennsylvania, in the United
States of America.
25
CHARLES DENTON ABEL, of Southampton Buildings, in the County of Middlesex.
IMPROVEMENTS IN BLAST FURNACES." [A communication from abroad by John
F. Bennett, of Pittsburg, Pennsylvania, in the United States of America.]
Blast furnaces as heretofore constructed consist in their main divisions of,―
First. The well, which is to contain the molten metal, and is usually of com-
paratively small area in cross section.
Second. The boshes, which usually are made of the form of an inverted truncated
cone, with the sides diverging widely toward the top, to form what is commonly
known as the belly of the furnace, which has an area in cross section largely in
excess of the well below, and usually also of the throat above.
And, Third. The stack or shaft of the furnace, which extends upward from the
boshes any desired distance, according to the inclination of the builder. This upper
shaft usually converges toward the top or throat, so as to give an opening somewhat
smaller in area than the belly of the furnace, but still considerably in excess of the
well, or of the point of junction between the well and boshes.
Tuyers through which the blast is forced into the furnace have been inserted
through the walls of the well, their nozzles terminating nearly even with the inner
face of the wall. As the inner walls or lining wore away, these tuyeres were moved
back, so as still to keep their nozzles nearly even with the wearing face. While
furnaces in use differ from each other more or less in detail, yet they as a rule have
substantially the parts and proportions given.
The difficulties which attend this form and construction, and which are effec-
tually overcome by the present improved construction of furnace are,―
First. It is necessary to place the tnyeres pretty low down in order to produce
sufficient heat in the lower part of the well to keep the metal and slags therein
in a molten condition, and the well being comparatively small in cross section, such
[Price 4d1

page_text: lowering of the tuyeres results in lowering and contracting the zone or belt of fusion,
and reduces the efficiency of the furnace. Again, by placing the tuyeres with their
nozzles even or nearly even with the inner face of the furnace wall; the upward
currents of the blast are brought near to the furnace wall or lining, which is thus
subjected to intense heat. Such heat renders the material of the linings more or
less plastic, so that it is easily worn away by the abrasion or attrition of the
descending charge. In time this wearing away of the furnace wall necessitates the
pulling down and rebuilding of the same.
Another difficulty attending this arrangement of the tuyers is, that the ascending
gases being brought thereby close to the side walls, tend to follow such walls in
making their escape from the furnace as the lumps and irregular pieces lying against
the wall do not pack as densely as in the centre of the furnace, and thereby offer
an easier passage for such gases; but in so doing they do not act equally upon all
parts of the charge, and their full effect is not realized, which results in lessening
the production and increasing expense. To overcome this difficulty the boshes of
the furnace have been widely expanded toward the belly; but such construction
of the boshes interferes seriously with the uniform descent of the charge along the
same, which is a very important consideration; and again, the belly of the furnace
being made so much larger than the throat, it is very difficult to get an even and
proper distribution of the materials when they reach the belly of the furnace in
their descent.
According to the present improved construction of furnace the inner walls
constitute substantially two frustrums of cones, placed base to base, the lower one
resting its smaller end upon the foundation or hearth, and extending upward one-
third the height of the furnace, or to the point of greatest area in cross section, the
upper cone beginning with its largest end at such point of greatest area, and
extending upward two-thirds of the height of the furnace.
The inner diameter of the furnace at the base or hearth is, by preference, two-
fifteenths of the whole height of the furnace, and the area in cross section at the
belly or point of greatest diameter is not less than twice, nor greater than three
times the area at the base. The area of the throat is, by preference, the same
as of the base, but may be increased by one-half when desired, as when the relative
area at the point of greatest diameter is increased.
The area of the charging opening in the throat, which is closed by a bell as usual,
is made about one-half the area of the throat.
The tuyeres are inserted through the walls of the furnace at a height above the
base equal to one-half the diameter of the base, or one-fifteenth the height of the
furnace. This position of the tuyeres is given as affording the best results with
a blast of about five pounds to the square inch, and of a temperature of about
1000° Fahr. If the blast be weaker, say, one pound, giving a blast of four pound
to the square inch, then the tuyeres should be lowered a little, depending upon the
capacity of the furnace, so as to keep the molten metal below sufficiently heated.
The higher the tuyeres are placed, and at the same time a sufficient heat be
maintained below, the more productive will be the furnace, for the zone or belt
of fusion will thereby be increased.
The dimensions given to the base of the furnace provide for a much larger plane
chamber or zone in which fusion takes place, and the heat from the same is
correspondingly increased. This of itself enables the tuyeres to be placed higher
in the furnace than could be done in the old form, as such increased heat above
assists in keeping the metal below properly heated.
Instead of placing the nozzles of these tuyeres even with the inner face of the
wall, as has heretofore been done, they are, according to the present Invention, made
to project into the interior of the furnace, by preference, until their nozzles reach
an imaginary circle, which will divide the area at that cross section into two equal
parts, or in any case they project to such distance that the reflex currents made
by the mutual action of the several jets shall not return or strike back against the
walls of the furnace, or until they shall have been converted into carbonic oxide

page_text: gas or carbonic acid gas, in which condition they will not act destructively on the
lining. By this arrangement the walls are subjected in a much less degree to the
destructive action of the heat and gases of the furnace, and in consequence of the
diminished activity thus secured about the walls, particles of free or nearly free
carbon settle upon and become attached to the walls. This accumulating carbon
forms in course of time a coat of lining, closely resembling in its nature black lead
or plumbago, and making substantially the lower part of the furnace a black lead
crucible, which practically never wears out, for it continually renews itself by the
action of the furnace as worn away by the attrition of the descending charge or
stock. And it is partly with a view to the formation of this coat or lining that the
furnace is constructed with so great area in cross section at the base, as room is
thus provided for the same between the face of the wall and nozzles of the tuyeres,
and also provide for free passage of the molten metal and slags through the space
between the nozzles, which is always kept clear by the action of the blast.
An additional advantage is also secured by the enlarged size of this part of the
furnace, as the area of the zone of fusion above the tuyeres is thereby materially
increased, and other things being equal, the productiveness of a furnace of given
capacity depends upon the area of this zone; and furthermore, the walls of the
furnace being further removed the ascending gases, which are generated near the
centre, do not as readily take to the walls for passage, but rather ascend up through
the body of the charge and permeate the whole mass. This last result is also in
a measure secured by the even distribution of the charge secured as before described
by the reduced charging hole.
By making the lower part of the furnace of a continuous conical form, not only
is the area of the zone of fusion increased as already described, but also the angle
formerly made at the top of the well or at the junction of boshes and well is
avoided, thus securing a freer action of the furnace.