Method and apparatus for obtaining and securing optimum thrust of blast fluid flowing into a metallurgical furnace

In a blast furnace tuyere, operating at subsonic velocity, an inner cylindrical air conduit is reduced to a frusto-conical conduit near the tuyere nose. A water cooled, pear-shaped, hollow body within the tuyere is held suspended by a bracket, in a centered position, where it exerts minimum interference with the pressurized fluid flowing partly through it and partly around it, having a cylindrical smaller conduit in such body and an annulus between the outer perimeter of such body and the inner wall of the cylindrical or conical conduit of the tuyere. The bracket slides parallel to the tuyere axis in guides, which are integral parts of the tuyere proper, thereby securing a centered position whenever the bracket is approaching to or retreating from the tuyere nose. The area of the annulus is uniformly decreasing when the body on the bracket is moving toward the tuyere's nose; consequently, the air jet velocity through the tuyere is increased but, by virtue of the diverging-converging inverse annular nozzle between the frusto-conical conduit and the pear-shaped suspended body, a near parallel air current with optimum thrust can be maintained at any position of the body. A driving mechanism serves to actuate the movement of the bracket and body; the driving mechanism being externally mounted at an accessible location.

BACKGROUND OF THE INVENTION 
One metallurgical furnace wherein blast air is used is a blast furnace. A 
blast furnace is kept in operation by blowing preheated air into it 
through a number of tuyeres. The air may be enriched with oxygen; also 
liquid or gaseous hydrocarbons, or pulverized coal may be added to the 
blast air as desired. 
An elongated bubble-shaped space, called a raceway, exists in front of the 
nose of each tuyere. These raceways are diagramatically depicted in FIGS. 
3 and 5 of United Kingdom Pat. No. 400,793. However, those skilled in the 
art will recognize that the raceways in a given furnace are not 
necessarily equal to each other in depth of penetration into the furnace 
nor in peripheral scope. 
Combustion takes place in the raceways where the coke of the burden, and 
the additives, if used, which are introduced through the top of the 
furnace, burn to CO.sub.2 and H.sub.2 O, which, in turn, are further 
reduced to CO and H.sub.2. The CO and H.sub.2 are then utilized as 
reducing agents to reduce the metallic materials of the burden. 
It is generally recognized by those skilled in the art that the size of the 
raceways and their shape depend on the volume, pressure and temperature of 
the blast, as well as the cross-sectional size of the tuyere mouth. The 
degree of penetration of the blast into the burden in the furnace, namely, 
the length of the raceway from the tuyere mouth toward the center of the 
furnace, depends on three factors: 
(1) the mass of the fluid passing through the tuyere; 
(2) the flow velocity of the fluid jet leaving the tuyere mouth; and 
(3) the magnitude of the thrust of the jet which is greatest whenever 
parallel flow of the fluid current is insured. 
Blast fluid velocities also significantly affect the temperature 
distribution within the raceways. With increasing jet velocities, the 
region of highest temperature moves away from the tuyere nose and the 
temperature at the periphery of the raceways falls. The opposite effect 
can be observed when natural gas is used as an additive to the blast 
fluid. A result of unevenly distributed temperature in the raceways are 
erratic currents within the blast furnace which cause the burden to 
descend unevenly, thus disturbing stable furnace operations. This tendency 
toward uneven distribution of burden descent is enhanced by uneven or 
disproportionate tuyere operation, in relation to the other tuyeres within 
the blast furnace, which increases the incidence of erratic and 
undesirable currents. 
Recent reports on blast fluid distribution among the tuyeres of large blast 
furnaces indicate that those tuyeres farthest from the blast fluid 
entrance into the manifold bustle pipe receive more mass of fluid than 
those nearer to the hot blast main entrance to the bustle pipe. The total 
blast is unevenly distributed among the tuyeres of equal mouth size 
cross-sectionally, resulting in the furnace working one-sidedly causing 
impaired production of pig iron. 
Those skilled in the art will recognize that there are certain general 
steps that can be taken to obtain optimum production in large blast 
furnaces. First of all, good burden size is needed. Secondly, the top 
pressure can be increased to obtain additional production. Thirdly, oxygen 
enrichment can be added to further increase production. Fourthly, tuyere 
jet velocities should be maintained within narrow ranges relative to each 
other and they must be corrected for any change in blast conditions. 
Finally, deep penetration of the blast fluid jet into the burden should be 
insured. 
Various means have heretofore been proposed to control the fluid flow both 
within the tuyere and as it leaves the tuyere mouth. It was suggested to 
employ transversally movable plates, cooperating with damper plates, for 
varying the inlet and outlet area of the tuyere. An outlet control similar 
to that suggested is disclosed in U.S. Pat. No. 296,225 wherein a water 
cooled gate is movable to block the flow of blast fluid to varying degrees 
depending on the position of the gate in relation to the tuyere mouth. 
Inserts have been suggested for placement inside the tuyere nose to reduce 
the cross-sectional area of the tuyere mouth, the insert being knocked out 
by a rod inserted through the peephole when it is desired to increase that 
area. Such a system is disclosed in U.S. Pat. No. 2,087,842. It has been 
proposed to provide an apparatus comprising a water-cooled ring disposed 
within and coaxially of a conical tuyere, the outside diameter of the ring 
being equal to the smallest internal diameter of the conical nozzle, the 
tuyere mouth. Such an apparatus is disclosed by U.S. Pat. No. 636,239. As 
mentioned, it has also been proposed to control the blast flow velocity as 
it leaves the tuyere mouth. Specifically, such a method is accomplished by 
deflection means extending beyond the tuyere mouth into the blast furnace 
hearth. Apparatus to effect this method is disclosed in United Kingdom 
Pat. No. 400,793. And, there is a "streamlined" body mentioned in the 
French Patent Letter No. 1,009,336, which body is a rigidly mounted 
vaporizer employed to add atomized water droplets to the blast fluid 
current; it is positioned inside of a tuyere, but it is not used for 
varying blast jet velocities. 
U.S. Pat. No. 296,225 discloses various means of externally controlling a 
sliding stopper. The stopper functions by sliding transversally across the 
tuyere mouth similar to the operation of a gate valve. All of the external 
means for operating the stopper produce a transverse motion of the stopper 
which is opposed to the axis of the tuyere. The tuyere disclosed is of a 
special design, radically different from the tuyeres normally used in 
blast furnaces. This novel tuyere has an upper section which is out of the 
direct flow of the hot blast fluid, providing a convenient arrangement 
within and through which means to operate the stopper can be placed. 
However, this upper section provides an ideal means to create undesirable 
turbulance and unbalanced gas flow. There is no way disclosed or described 
by which the external operation means could be utilized in a cylindrical 
cross-section tuyere where no additional space is provided within the 
tuyere for the movement of the disclosed external operating means. 
U.S. Pat. No. 636,239 discloses a hollow ring adapted to be displaced 
substantially axially within a tuyere until it fills the tuyere mouth and 
leaves only the central opening of the ring for the passage of the blast; 
then, by pulling the ring back, a varying amount of free space is left 
between the ring and the nozzle. As indicated by phantom outline in FIG. 1 
of this patent, the ring drops below the longitudinal axis of the tuyere 
when withdrawn from the tuyere nose, resulting in an unbalanced gas flow. 
United Kingdom Pat. No. 400,793 discloses, in item 6 of FIG. 6, a 
symetrical cylindrical body with a uniform wall thickness, the outer 
surface being coaxial with the bore. The walls are hollow, providing a 
coolant passageway. The specification of this patent states that the 
cylindrical body also takes the shape of a blast tuyere. The indication is 
that, in the shape of a blast tuyere, the cylindrical body would more 
closely resemble the preferred embodiment of the invention shown as item 1 
in FIG. 1 therein; the positioning would be such that the smaller end of 
the blast tuyere shape would be directed away from the center of the blast 
furnace to enable the required deflection of the blast fluid in a manner 
similar to that shown in FIG. 4. 
The manner in which the cylindrical body function is disclosed in United 
Kingdom Pat. No. 400,793 at page 2, lines 40 to 52 as follows: 
". . . there is arranged in the tuyere of the shaft furnace, instead of the 
deflecting body, a perforated body which preferably has the shape of a 
smaller tuyere, in such manner that it may be wholly or partially inserted 
in the axial direction of the main tuyere, into the interior of the 
hearth. With such a shifting of the hollow insert body, a blast inlet 
position in the hearth and consequently the oxidation zone, is shifted 
during the working of the shaft furnace to any desired degree." 
The specification further details the operation of the hollow insert at 
page 3, lines 3 to 11: 
". . . the insert hollow body 6 is moved out of the tuyere 2 into the 
interior of the hearth by as much as the oxidation zones are to be moved 
forward. If the body 6 is fully drawn back into the tuyere 2, then the 
oxidation zone in front of the tuyere again receives that position which 
is given by the position of the tuyere itself." 
United Kingdom Pat. No. 400,793 also teaches a most significant point at 
page 2, lines 90 to 94: 
"That the deflecting body should always be centrally arranged in the tuyere 
2 is important as otherwise a tuyere current is produced which cannot be 
exactly controlled." 
This language points out a critical deficiency found in the apparatus 
disclosed in U.S. Pat. No. 636,239. 
Those skilled in the art are aware that modern tuyere arrangement design 
includes a horizontal blowpipe which carries the hot blast from the tuyere 
stock to the tuyere proper. The blowpipe has spherically machined ends 
that fit tightly into the machined end of the tuyere proper and the tuyere 
stock to give the arrangement a tight fit, even though the tuyere proper 
and the tuyere stock may be misaligned. The blowpipe is held in place by 
pressure from the tuyere stock which, in turn, is held tightly against one 
end of the blowpipe by a heavy spring and rod device called the bridle. 
The bridle is attached to the hearth jacket, through which the tuyere 
extends, and allows limited motion between and misalignment of the central 
axis of the tuyere stock, blowpipe and tuyere proper caused by inexact 
construction and by thermal movement of the furnace shell. The movement 
and misalignment so caused eliminates the ability to centrally position 
and arrange an insert within a tuyere proper, which insert is supported 
from means extending from the peep sight position on the tuyere stock as 
disclosed in both U.S. Pat. No. 636,239 and United Kingdom Pat. No. 
400,793. Both of these patents include means disposed inside of and 
extending through the blowpipe to actuate the longitudinal travel of 
inserted bodies. Such arrangements interfere with the smooth supply of 
additives through the blowpipes; also, the need for replacement of the 
blowpipes and/or the tuyere causes difficulties in realignment. 
The present invention employs actuators disposed fully outside the blowpipe 
and not extending therethrough, and the brackets holding the independent 
inserts are guided parallel to the tuyere's axis within the tuyere proper, 
securing thereby always a central position of the movable inserts. The 
principal objective of the present invention is to provide means for 
obtaining and securing optimum thrust for any given blast condition by 
achieving an exactly controllable concentric blast flow pattern 
simultaneously for a set of individual tuyeres. The principal objective 
being realized, it is possible to correct unstable working of the furnace, 
to equalize the uneven blast distribution, and to compensate for the 
changing blast conditions by enabling the furnace operator to set the 
tuyere jet velocities individually during furnace operation. 
SUMMARY OF THE INVENTION 
A tuyere, designed for operation at subsonic fluid velocity, has a 
cylindrical inner conduit that is reduced to a frusto-conical conduit near 
the tuyere nose. The inner conduit cooperates with an axially movable 
hollow pear-shaped body in such a way that the total flow area is 
uniformly diminishing when the body is moved toward the tuyere nose. The 
body is symmetrically positioned about the central axis of the tuyere, and 
it is held by a bracket means that is guided within the tuyere proper, 
parallel to the axis of the tuyere, to maintain the symmetry of the 
central axis of the tuyere with that of the body when the body is either 
moving or standing still regardless of misalignment and movement among the 
tuyere stock, blowpipe and tuyere proper. The body may be of a solid 
section and made of heat and corrosion resistant material, or it may be of 
hollow section and water cooled. Means are included to actuate the travel 
of the body inside, but not beyond the tuyere mouth, the bracket means 
being easily accessible from outside of the tuyere independent from the 
blowpipe. A cross section of the pear-shaped hollow body reveals an 
airfoil shape, similar to that of an airplane wing. This shape enhances 
parallel smooth flow of hot blast fluid through the hollow center and 
around the periphery of the body such that eddy currents are eliminated 
and, thus, erratic and uncontrollable turbulance, in the flow of hot blast 
fluids through the tuyere, are eliminated. 
For a further understanding of the invention and for features and 
advantages thereof, reference may be made to the following description and 
drawings which illustrate a preferred embodiment of equipment, in 
accordance with the invention, which is suitable for practicing the method 
of the invention.

DETAILED DESCRIPTION 
Referring to FIG. 1, the shell 11 of a metallurgical furnace 13 is lined 
with refractory material 15 in a conventional manner and there are 
provided, around the periphery of the furnace, a number of openings 
exemplified by a tuyere holder 17 through both the shell 11, usually made 
of steel, and the refractory material 15. 
Referring to the drawings, FIGS. 1-3 illustrate the preferred embodiment of 
the present invention. In FIG. 1, a cylindrical blowpipe 19 is lined with 
suitable refractory material, as at 21, and has a convex, spherically 
tapering, generally frusto-conical end portion 23 ending in a convex 
spherical nose 24 that coacts with a concave spherical surface 25 of a 
tuyere 27. The blowpipe 19, in the embodiment of the invention shown in 
FIG. 1, is disposed horizontally. Between the steel blowpipe 19 and the 
refractory lining 21 therein, there is a layer of a suitable insulating 
material 20. The frusto-conical end portion 23 is also lined with the same 
suitable refractory material 21 which is shaped about as shown. 
As will be noted in FIGS. 1 and 2, the tuyere 27 is disposed in a 
downwardly direction from the horizontal blowpipe 19 at an angle W. The 
tuyere 27 is provided with internal water channels 29 for cooling the 
tuyere body 27. The internal conduit 31 through the tuyere 27 is 
cylindrical shaped 30 part way, and then becomes frusto-conical, as at 33, 
near the tuyere mouth 32. Both the cylindrical shaped part 30 of the 
conduit 31 and the frusto-conical part 33 may be lined, respectively, with 
suitable refractory material 21. Alternately, the tuyere may be unlined to 
suit operating conditions. 
Disposed movably within the frusto-conical passageway 33 is a generally 
frusto-conical tubular body 40. The frusto-conical tubular body 40 has a 
cylindrical axial central passage 42, and is provided with internal 
cooling water passages 44. The tubular body 40 is secured fixedly to 
brackets 43, as shown in FIGS. 1-3, and has a pear-shaped outer form. The 
tubular body 40 also may be considered as a body developed by revolving an 
airfoil-like area 38, similar to the cross-sectional shape of an airplane 
wing, about the common longitudinal axis of the tubular body 40 and the 
tuyere 27. 
A pair of cooling fluid conduits 45, 47 are connected to the frusto-conical 
tubular body 40 in order to carry cooling water into and out of the 
cooling water passages 44. The exterior of these conduits 45, 47, as well 
as the brackets 43, are smooth and aerodynamically shaped to promote 
smooth blast fluid flow. It will be noted that the cooling fluid conduits 
45, 47 are entirely independent of the blowpipe 19. 
The cooling fluid conduits 45, 47 are movable in a linear direction, 
parallel to the axis of the internal conduit 31, inside the tuyere 27, and 
are guided by sleeves 49, 51 within the tuyere housing 27. A suitable 
gasket 53 and an O-ring 55 seal the conduits 45, 47 for preventing blast 
air leakage. 
The frusto-conical body 40 is movable axially with respect to the tuyere 27 
be means of a handwheel 57 and a threaded rod 59 which, when turned, moves 
the conduits 45, 47 as well as the body 40. The handwheel 57 and the 
threaded rod 59 are supported in a suitable stand 61 secured by means of 
suitable fasteners 63 to a supporting surface 65 mounted to the furnace 
shell 11. 
It will be apparent to those skilled in the art that the handwheel 57 is 
shown only to illustrate one mechanism for moving the frusto-conical 
member 40. In any application of the invention, another suitable 
apparatus, located remotely from the furnace shell, may be employed. 
However, in any case, the other apparatus or the handwheel 57 and threaded 
rod 59 must be self-locking, which means that whenever the frusto-conical 
member is moved axially to a new position, it remains locked in such new 
position until the handwheel, or whatever other remote operating device is 
used, is actuated to move the frusto-conical member to a new position. 
It will be noted from scrutiny of FIG. 2 that the frusto-conical body 40 is 
shown in a position toward the right of the view, toward the position of 
the tuyere mouth 32. This position of the frusto-conical body 40 is the 
furthest extent of its position toward the tuyere mouth. It will also be 
noted that, at the position depicted in FIG. 2, there is a gap or annulus 
67 between the frusto-conical part 33 of the conduit 31 and the outer 
periphery of the frusto-conical body 40, the frusto-conical body 40 never 
coming into contact with the frusto-conical part 33 adjacent the tuyere 
mouth 30. This annulus 67 provides a peripheral channel which tends to 
guide the periphery of the blast fluid, hereinafter referred to as the 
peripheral portion, in a converging manner upon exit from the tuyere 
mouth. The balance of the hot blast fluid, hereinafter referred to as the 
central portion, is constricted through the central passage 42 of the 
frusto-conical body 40. Both the velocity of the peripheral portion of the 
blast fluid and that of the central portion of blast fluid, constricted 
through the central passage 42 of the frusto-conical body 40, are 
increased in proportion to the decrease in the cross-sectional area of the 
annulus 67. As the central portion meets the converging peripheral portion 
on exit from the tuyere mouth 32, the central portion tends to abate the 
convergence of the peripheral portion while the peripheral portion tends 
to abate divergence of the central portion. The result is a smooth 
parallel flow of balanced velocity hot blast fluid directed toward the 
center of the blast furnace hearth. 
As the frusto-conical body 40 is moved away from the tuyere mouth 32 toward 
the left, as depicted in FIG. 2, shown in phantom, the effective 
cross-sectional area of the tuyere 27 is increased and the velocity of the 
hot blast fluid exiting from the tuyere mouth decreases. 
When the frusto-conical body 40 is moved to a limiting position toward the 
left, the cross-sectional area of the annulus 67 is greatest. Likewise, 
when the frusto-conical body 40 is moved to a limiting position toward the 
right, toward the tuyere mouth 32, the cross-sectional area of the annulus 
67 is least. 
The hot blast fluid flow velocity is always subsonic and least in passage 
42 and annulus 67 when the frusto-conical body 40 is at the limiting 
left-hand position, as viewed in phantom in FIG. 2. When the 
frusto-conical body 40 is at the limiting right-hand position, the hot 
blast fluid flow velocity in the annulus 67 and in passage 42 is greatest. 
Thus, as the frusto-conical body 40 moves from left to right, the total 
flow area of hot blast fluid gradually decreases, consequently the hot 
blast fluid jet velocity increases but remains subsonic. 
Thus, in operating a metallurgical furnace equipped with tuyeres in 
accordance with the present invention, the velocity, as well as the degree 
of projection, of the hot blast fluid into the hearth of the furnace can 
be adjusted within desirable limits; the tuyeres have design 
characteristics that permit variation of the blast fluid velocity within 
preselected limits while maintaining an essentially parallel and smooth 
flow pattern for optimum thrust of the fluid jet by virtue of the integral 
guidance built into the tuyere proper, parallel to the tuyere axis. 
From the foregoing description of the preferred embodiment of the 
invention, those skilled in the art should recognize important features 
and advantages therein, among which the following are particularly 
significant: 
That the total flow of blast fluid through a tuyere in accordance with the 
present invention is variable due to the presence in the tuyere of a 
movable, axially positionable, frusto-conical member having a central 
cylindrical passage and a pear-shaped outer periphery which insures a deep 
penetration of the blast into the burden at any position of the moving 
body, even when blowpipe and tuyere axes are misaligned. 
That the tendency for the blast fluid mass to vary with the distance the 
tuyere is from the entrance of the bustle pipe can be obviated since the 
velocity of the blast fluid in each tuyere of the present invention is 
adjustable and uniformity of the blast fluid mass flowing through all 
tuyeres is readily obtainable. 
Those skilled in the art will recognize that the invention can be applied 
not only to blast furnace construction, but also to any process equipment 
that uses gaseous blast fluids in such quantities that a plurality of 
tuyeres are required and exact control of the blast jet velocities is 
desirable. 
Although the invention has been described herein with a certain degree of 
particularity it is understood that the present disclosure has been made 
only as an example and that the scope of the invention is defined by what 
is hereinafter claimed.