Distributing chute for a furnace

A distributing chute for installation in a furnace, particularly suitable for use in a bell-less charging system of a blast furnace, comprises heat-resistant ceramic tiles on its underside. These ceramic tiles are inserted between, and secured by, hollow sections which are attached to the chute body and through which a cooling medium is passed. The ceramic tiles preferably include lateral grooves; the hollow sections being fitted in the lateral grooves for securing the ceramic tiles.

BACKGROUND OF THE INVENTION 
This invention relates generally to a distributing chute for a furnace. 
More particularly, this invention relates to a distributing chute which is 
particularly well suited suited for use in a bell-less charging system of 
a blast furnace. 
A bell-less charging system for a blast furnace is, for example, known from 
U.S. Pat. No. 3,880,302, all of the contents of which are incorporated 
herein by reference. It comprises a distributing chute which is mounted in 
the top of the blast furnace in a rotatable, pivotable manner. The 
underside of the distributing chute is subjected to the full heat 
radiation from the surface of the charge in the blast furnace. 
Whereas it was possible until recently to do without a means of heat 
insulation on the underside of the distributing chute, this is no longer 
the case where contemporary blast furnace operating practice is concerned. 
For example, due to the injection of increasingly large quantities of 
pulverized coal into the blast furnace, the temperature at the surface of 
the charge may exceed 1000.degree. C. The underside of the chute is thus 
subjected to more and more intense heat radiation. Above a certain 
temperature, however, the high-temperature resistant steels of the chute 
body lose their heat-resistant quality and corrosion appears. 
Various heat insulating devices for the underside of the distributing chute 
have been proposed to correct this problem. A double-walled distributing 
chute which is cooled by means of an inert gas is known from 
GB-A-1,487,527, all of the contents of which are incorprated herein by 
reference. However, the effectiveness of this cooling is ensured only if 
very high gas throughputs are employed. However, feeding of large gas 
throughputs into a rotatable, pivotable chute is problematic and difficult 
to achieve. 
An improved means of heat insulation for the underside of the distributing 
chute is known from U.S. Pat. No. 5,252,063, all of the conents of which 
are incorporated herein by reference. The improved heat insulation is 
mainly achieved by means of an improved device for feeding the cooling 
medium into the rotatable, pivotable distributing chute. This proposed 
feeding device enables either a higher gas throughput through the chute 
or, preferably, cooling of the chute with cooling water in a closed 
cooling circuit. For the cooling water, one or two U-shaped cooling ducts 
are longitudinally mounted on the underside of the distributing chute and 
connected to a cooling water distribution system through the suspension 
shafts of the distributing chute. In DE-4216166 it is furthermore proposed 
that the cooling ducts be provided with cooling fins or gills in order to 
achieve more uniform cooling of the underside and/or that the cooling 
ducts be embedded in a refractory material (e.g. a heat-insulating 
concrete). 
Practical experience has shown in the meantime that embedding of the 
cooling ducts in a refractory material is emphatically recommended in 
order to protect the cooling ducts themselves as well as the underside of 
the distributing chute more effectively from the heat radiation (and from 
the generally hostile and severe conditions which prevail above the 
surface of the charge). Without the additional heat insulation of the 
refractory material, the throughput of the cooling medium would have to be 
increased substantially and the cooling ducts would have to be laid very 
close together on the chute body, both of which are not easily feasible. 
Unfortunately it has also been discovered in the meantime that the 
refractory material in which the cooling ducts are embedded develops 
cracks relatively quickly in the furnace and crumbles away from or drops 
off the underside of the chute in relatively large, slab-like pieces. 
SUMMARY OF THE INVENTION 
The above-discussed and other problems and deficiencies of the prior art 
are overcome or alleviated by the distributing chute for a furnace device 
(e.g., shaft furnace) of the present invention. In accordance with the 
present invention, a distributing chute is provided for which the 
underside is more durably protected from the heat radiation in the 
furnace. This is achieved by providing heat resistant ceramic tiles 
affixed to the underside of the distributing chute. The heat-resistant 
ceramic tiles are inserted between, and secured by, hollow sections. These 
hollow sections are fixed to the chute body and connected to a 
distribution circuit for a cooling fluid. The cooling fluid may be a 
liquid, a gas or a vapor. 
In the context of the present invention, it was initially necessary to 
solve the problem of whether ceramic tiles could be mounted on the 
underside of a rotatable, pivotable distributing chute at all and how such 
tiles should be attached to the chute body. 
It is conventional practice to fix refractory ceramic tiles on to static 
furnace walls by means of heat-resistant bolts and cramps. For this, there 
must be adequate axial and radial play between the ceramic tile and the 
mounting, so that the ceramic tiles do not crack when the mountings cool 
down or heat up. In the course of developing the present invention, this 
conventional fixing practice was considered for fixing refractory ceramic 
tiles to the underside of the distributing chute. It was however 
discovered that even if the axial and radial play between the ceramic tile 
and the mounting is adequately dimensioned to absorb the thermal 
deformation of the mountings, cracks formed in the ceramic tiles in the 
area of the mountings. These cracks could be explained by the fact that in 
addition to the thermal stress, the distributing chute is subjected to 
dynamic stress, that is, vibration, jarring and shocks. Excessive play of 
the ceramic tiles in their mountings, especially at right angles to the 
underside of the chute, therefore significantly accelerates the cracking 
of the ceramic tiles. 
By the cooling of the hollow sections, which in the case of the chute in 
accordance with the present invention serve as mountings for the tiles, 
the typical thermal deformation of the mountings was greatly reduced. The 
play of the ceramic tiles in the cooled hollow sections, especially at 
right angles to the underside of the chute, was thereby reduced. As a 
result, the ceramic tiles were in turn subjected to less dynamic stress 
from vibration, jarring and shocks. Furthermore, as a side affect, the 
durability of the mountings was increased by their cooling. 
The ceramic tiles gave far better protection of the underside of the chute 
against heat radiation than a heat-insulating concrete. As a result, the 
required cooling capacity of the cooling medium may be reduced. A reduced 
cooling capacity has a favorable effect on the dimensioning of the 
connections for the cooling medium and in principle permits the use of a 
gaseous cooling medium. 
The ceramic tiles generally have better mechanical properties than a 
castable heat-insulating material. In this context, it should also be 
noted that the size of the ceramic tiles predetermines the maximum size of 
fragments in the event of cracking. These fragments are generally smaller 
than the large, slab-like pieces crumbling away from the underside of the 
chute in the case of the heat-insulating concrete used on the known prior 
art chutes. The maximum crack propagation in the tiles is fixed by the 
individual size of each tile, the crack propagation being halted at the 
tile edges at the maximum. Continuous cracks over the entire length or 
width of the chute, which have been observed where heat-insulating 
concrete is used, are thus effectively prevented. 
To secure the ceramic tiles in the cooled hollow sections, the hollow 
sections might, for example, be provided with a groove in which the 
ceramic tiles may be engaged. However, it is more advantageous if, to 
secure the ceramic tiles, the cooled hollow sections can be engaged in a 
lateral groove in the ceramic tiles in such a way that the hollow sections 
are largely covered by the ceramic tiles. In this embodiment the hollow 
sections are shielded from direct heat radiation by the ceramic tiles, 
which has a beneficial effect on their lifespan. 
With regard to the choice of cross-section for the hollow sections, there 
are of course innumerable possibilities. In the case of hollow sections 
with a circular cross-section, the cross-section of the groove in the 
ceramic tiles roughly corresponds to one half of this circular cross 
section. Hollow sections with a circular cross-section are manufactured as 
standard products in various high-temperature, high-strength steels. Due 
to the cylindrical contact surface between the hollow sections and the 
ceramic tiles, no substantial stress concentrations arise in the ceramic 
tiles, whether due to thermal deformation or due to dynamic forces. 
Furthermore, a circular inside cross-section means reduced pressure drops 
for the cooling medium. 
Similar benefits are achieved by hollow sections with an oval 
cross-section. With an oval cross-section, the contact surface between the 
hollow section and the ceramic tile is larger than with a circular 
cross-section. This reduces the likelihood of pieces breaking off the 
groove in the ceramic tile. Trouble-free guidance of the ceramic tiles in 
the hollow sections is still ensured if the distance between two adjacent 
hollow sections increases. 
For the fitting of the ceramic tiles it is advantageous if the hollow 
sections can be fixed to the chute body first and the ceramic tiles can 
then each be inserted between two of the hollow sections which are fixed 
to the chute body at a certain distance apart. With this embodiment it is 
possible to replace damaged ceramic tiles without having to dismantle all 
the hollow sections. 
Practical experience has shown that the distance between two hollow 
sections should not exceed 200 mm. The length of the ceramic tiles is 
preferably less than 300 mm. If these maximum tile dimensions are adhered 
to, the susceptibility of the ceramic tiles to cracking can be greatly 
reduced. 
To enable insertion of the ceramic tiles, hollow sections arranged parallel 
to each other are joined together at their ends with cross-pieces in a 
serpentine configuration. The ceramic tiles may then each be inserted 
between two adjacent hollow sections. Connections for the cooling medium 
are advantageously located in the area of the cross-pieces, so as not to 
impede insertion of the ceramic tiles. 
The hollow sections may run parallel to the longitudinal axis of the chute 
as straight lengths of tube, which facilitates the insertion of the 
ceramic tiles and permits longer tiles to be used. However, the hollow 
sections may also run perpendicular to the longitudinal axis of the chute 
and take the form of arch-shaped tube segments. The arch-shaped tube 
segment arrangement has advantages with regard to the distribution of the 
cooling medium and reduced consequences of thermally induced deformation 
of the chute cross-section. 
The hollow sections are preferably not welded to the chute body but are 
supported on the underside of the distributing chute by means of a base 
surface and mechanical fixing means so that they may expand axially. 
Welding the hollow sections on the underside of the distributing chute 
would cause the latter to be subjected to thermal stresses when the chute 
body heats up or cools down. The relatively poor heat transmission between 
the freely supported hollow sections and the chute body can be compensated 
for, at least in part, by making the heat transmission area as large as 
possible (i.e. by using the largest possible base surface). 
An advantageous embodiment of the present invention features a T-section 
axially welded by its web to a straight length of tube and the flange of 
the T-section attached to the underside of the chute, parallel to the 
centerline of the chute, so that it may expand axially. 
Another advantageous embodiment of the present invention provides several 
supporting sections movably attached to the underside of the chute, 
parallel to the centerline of the chute, and arch-shaped tube segments 
transversely welded to these supporting sections. 
A cavity is preferably formed between the chute body and the ceramic tiles. 
This cavity may either be filled with an insulating material (e.g. ceramic 
wool) or a cooling gas may be passed through it. 
The above-discussed and other features and advantages of the present 
invention will be appreciated and understood by those of ordinary skill in 
the art from the following detailed discussion and drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring first to FIGS. 1A, 1B and 1C, the distributing chute for a 
furnace device of the present invention is shown generally at 10. Device 
10 has a chute body 12 with a semicircular cross-section. The chute 
cross-section could of course also be oval, trapezoidal or triangular. The 
chute could also be bounded by a lateral surface on only one side or on 
neither side. 
At one end, its top end, the chute body 12 has a suspension device 14 for 
suspending the distributing chute 10 in a driving device which is not 
shown. This driving device is located above the surface of the charge in a 
furnace (for example, in the top of a blast furnace). It causes the chute 
10 to pivot about a horizontal axis in order to adjust the angle of 
inclination of the chute, and to rotate about a vertical axis in order to 
distribute the bulk material circularly onto the surface of the charge. 
The chute 10 has a top side 16 and an underside 18. A chute channel 20 is 
formed at the top side 16 of the distributing chute. Although this top 
side 16 is subject in the chute channel 20 to severe abrasive stress on 
account of the bulk material, it is not directly subjected to the very 
intense heat radiation from the surface of the charge in the furnace. The 
underside 18, on the other hand, is subjected to the full heat radiation 
in the furnace, especially when the chute 10 is in a near-horizontal 
position. 
In the embodiments shown in FIGS. 1A, 1B, 1C and 2A, 2B, and 2C, the 
underside 18 of the distributing chute 10 is provided with a tube coil 22, 
22' which is connected by connecting means (the connections 24, 26 and, 
respectively, 24', 26') to the feed line and, respectively, the return 
line of a cooling fluid distribution circuit which is not shown. This 
connection is accomplished, for example, as described in aforementioned 
DE-4216166, by ducts which run axially through the suspension shafts of 
the chute and are connected via rotary connections to a ring-shaped 
intermediate tank for a cooling liquid (e.g. cooling water) which turns 
with the chute 10. 
In FIGS. 1A, 1B and 1C the tube coil 22 comprises several parallel straight 
lengths of tube 28 which run parallel to the longitudinal axis of the 
chute 10 and are joined to each other at their ends by elbows 30 in a 
serpentine configuration. The axial distance between the straight lengths 
of tube 28 is, for example, approximately 20 cm. Refractory ceramic tiles 
32 are fitted between every two adjacent straight lengths of tube 28. In 
FIG. 4 it is seen that the ceramic tiles 32 have a groove 34 of 
semicircular cross-section on each of two opposing long sides. A straight 
length of tube 28 with a circular cross-section engages positively with 
this groove 34 in such a way that the groove 34 of the first ceramic tile 
receives the first half of the tube cross-section and the groove 34' of 
the adjacent second ceramic tile 32 receives the second half of the tube 
cross-section. The straight lengths of tube 28 are thus completely covered 
externally by the ceramic tiles 32. It should be emphasized that due to 
the cooling of the straight lengths of tube 28, their cross-section does 
not undergo any significant thermal deformation. As a result, the fit 
between the groove 34 and the groove 34' and the outside cross-section of 
the lengths of tube 28 can be designed with relatively little play, which 
results in substantially less mechanical stress on the ceramic elements 32 
due to vibration, jarring, shocks, etc. 
When installing the heat insulation of the chute 10, it is preferable first 
to fix the tube coil 22 to the underside 18 of the chute. An advantageous 
method of fixing the tube coil 22 to the chute body 12 is shown in FIG. 4. 
T-sections 36 are welded on to the straight lengths of tube 28 with their 
webs parallel to the centerline of the tube. The flange of the T-section 
36 forms a support surface 38 for the corresponding length of tube 28 on 
the underside 18 of the chute 10. The larger the area of this support 
surface 38, the better is the heat transmission between the chute body 12 
and the tube coil 22 and thus the cooling of the chute body 12. These 
T-sections 36 are fixed on to the chute body 12 in such a way that an 
axial freedom of movement is preserved between the chute body 12 and the 
T-sections 36. This allows the chute body 12 and the straight lengths of 
tube 22 to expand thermally independently of each other. To achieve this, 
for example, the flange of the T-section 36 is fixed to the underside 18 
of the chute with cramps 40, as indicated in FIG. 4. However, the flange 
of the T-section 36 could also have oblong holes for bolts. The fixing 
method described above makes the tube coil 22 largely independent of 
longitudinal thermal deformations of the chute body 12. The tube coil 22 
is thus subject only to smaller deformations caused mainly by thermal 
deformation of the cross-section of the chute body 12. The tube coil 22 
could of course also form a self-supporting cage suspended from the chute 
body 12 in such a way that it is largely independent of thermally induced 
deformations in the longitudinal and cross sections of the chute body 12. 
The ceramic tiles 32 are insertable between the tubes of the tube coil 22 
fixed to the chute body 12. This insertion of the ceramic tiles 32, which 
are about 30 cm in length, takes place between two adjacent elbows 30 in 
the direction of the elbow 30 which joins the two straight lengths of tube 
28 serving as guides for the inserted ceramic tile 32 (see the arrow 42 in 
FIGS. 1A, 1B and 1C). The elbows 30 which ultimately remain exposed may 
subsequently be cast into an insulating material (e.g. a heat-insulating 
concrete). 
The unions between the connections 24, 26 for the liquid cooling medium and 
the tube coil 22 are advantageously made at the top end of the chute 10 in 
the area of the elbows 30. In this way the previously described insertion 
of the ceramic tiles 32 is not impeded. In FIGS. 1A, 1B and 1C, the elbows 
30 are, for example, alternately connected to the supply pipe 24 and the 
supply pipe 26. As a result, the hydraulic length of the tube coil 22 is 
equal to the length of two lengths of tube 28. To protect the supply pipes 
24, 26 at the top end of the chute from heat radiation, they may be 
embedded in an insulating material (e.g. a heat-insulating concrete). 
The distributing chute 10' shown in FIGS. 2A, 2B and 2C has, in place of 
the tube coil 22 with straight lengths of tube 28 shown in FIGS. 1A, 1B 
and 1C, a tube coil 22' with arch-shaped tube segments 44. The arch shaped 
tube segments 44 are arranged parallel to each other and at right angles 
to the centerline of the chute and are axially spaced approximately 20 cm 
apart. These arch-shaped tube segments 44 are connected at their ends by 
elbows 30' in a serpentine configuration. The connecting pipes 24', 26' 
are connected to the elbows 30' by two collectors 46, 48 which are 
arranged laterally on the chute body 12. The hydraulic length of the tube 
coil 22' is therefore substantially shorter than the hydraulic length of 
the tube coil 22, as a result of which the pressure drop in the tube coil 
22' is substantially smaller. This may be important, as the effective head 
of the cooling liquid is often very small. 
FIG. 5 shows a preferred method of fixing of the arch-shaped tube segments 
44. Flat bars or sections 50 are fixed to the underside 18 of the chute 
10' parallel to its longitudinal axis in such a way that an axial freedom 
of movement is preserved between the chute body 12 and the flat bars or 
sections 50. This permits the chute body 12 and the flat bars or sections 
50 to expand thermally independently of each other. This is achieved, for 
example, in that the flat bars or sections 50 are provided with oblong 
holes 52 and are fastened to the chute body when cold with bolts or rivets 
54. However, the flat bars or sections 50 may instead be fixed with 
clamps. The arch-shaped tube segments 44 are preferably welded on to these 
flat bars or sections 50 in such a way that good heat transmission between 
the tube segments 44 and the flat bars or sections 50 is achieved as far 
as possible. By good heat transmission, it is meant that good cooling of 
the flat bars or sections 50 is achieved, with the result that the latter 
are subject to relatively small thermally induced changes in length. Due 
to the previously described method of fixing of the tube coil 22', the 
tube coil 22' undergoes hardly any deformation due to thermally induced 
longitudinal deformations of the chute body 12. Thermally induced 
deformations of the cross-section of the chute body 12 have, in the case 
of the design of the tube coil 22', practically no influence on the 
lateral play of the ceramic tiles 32 in their curved tube guides. 
FIGS. 3A, 3B and 3C shows an alternative preferred embodiment for a gaseous 
cooling fluid. Instead of a tube coil 22, 22', the chute 10" has several 
parallel straight lengths of tube 56 which are joined at the top end of 
the distributing chute 10" to appropriate cooling gas connections 24", 26" 
via an arch-shaped cooling gas collector 58. At their opposite ends, on 
the other hand, the parallel tubes 56 are open, allowing the cooling gas 
to flow freely into the furnace. 
FIGS. 6 to 9 each show alternative embodiments of the invention with 
various hollow sections. FIG. 6 shows hollow sections 60 with an oval 
cross-section. These have essentially similar advantages to hollow 
sections with a circular cross-section, but have two parallel guide 
surfaces for the ceramic elements 32 at right angles to the underside of 
the chute. Even if the axial distance between two oval hollow sections 
greatly increases due to thermal deformation of the chute, it is ensured 
that the ceramic tiles 32 are still properly secured and guided. As the 
hollow sections 60 do not undergo any substantial deformation, the play 
between the groove and the hollow sections 60 at right angles to the 
underside of the chute may be made relatively small. 
FIG. 7 shows hollow sections 62 with a square cross section. This design is 
much more prone to crack formation in the ceramic tiles 32 than the 
designs in which the hollow sections have a circular or oval 
cross-section. 
FIG. 8 shows an alternative embodiment in which the supporting section 64 
has two solid flanges 66 and 68 and a cooled hollow web 70. The cooled web 
is subject to smaller thermal deformations than a non-cooled web, with the 
result that good guidance of the ceramic tiles between the two flanges 66 
and 68 is ensured even if the chute 10 is heated to a high temperature. 
The flange 68 is not covered by the ceramic tiles 32 and is thus directly 
subjected to the heat radiation. However, it may be additionally protected 
from heat radiation in the furnace by means of an insulating material 72 
(e.g. a heat-insulating concrete) applied on top, as indicated in FIG. 8. 
It will be appreciated that a cavity 74 (see FIG. 4) is advantageously 
formed between the ceramic tiles 32 and the underside 18 of the chute; 
thus the ceramic tiles do not lie directly on the underside 18 of the 
chute. This cavity 74 is preferably filled with a soft insulating material 
(e.g. ceramic wool); this insulating material both improves the thermal 
insulation of the underside 18 of the chute and dampens vibrations of the 
ceramic tiles 32 in the hollow sections at right angles to the underside 
18 of the chute. In the case of a gas-cooled distributing chute 10", the 
gaseous cooling medium may also be passed through this cavity 74. 
In FIGS. 3A, 3B and 3C the gaseous cooling medium is fed into the cavity 74 
through, for example, radial drilled holes in the straight tube lengths 
56. 
While preferred embodiments have been shown and described, various 
modifications and substitutions may be made thereto without department 
from the spirit and scope of the invention accordingly, it is to be 
understood that the present invention has been described by way of 
illustrations and not limitation.