Coolant coils for a smelting furnace roof

A roof structure for an electric arc smelting furnace includes a spider frame for supporting a plurality of independent removable coolant coil sections. An inner coil section is generally annular in shape and includes a coolant pipe which spirals completely around a central opening in the roof structure. An intermediate coil section is also generally annular in shape, but includes a coolant pipe which extends around the circumference of the inner section, reverses itself around the circumference of the first pipe of the intermediate section, and then reverses itself once again around the circumference of the second coolant pipe of the intermediate section, to form a generally serpentine pattern. A plurality of semi-annular outer coil sections are supported radially outwardly from the intermediate coil section. Each outer section includes a first pipe located generally centrally within the semi-annular section and extending from end to end. A second pipe reverses the coolant flow and is located radially outwardly from the first pipe. A third coolant pipe is connected to the second coolant pipe and is located radially inwardly of the first coolant pipe within the outer section.

TECHNICAL FIELD 
The present invention relates generally to electric arc smelting furnaces, 
and more particularly to an improved furnace roof structure with removable 
coolant coils. 
BACKGROUND OF THE INVENTION 
Electric arc furnaces are utilized in the production of steel from scrap 
and the like. Smelting furnaces typically are designed as welded steel 
structures with water cooled walls and roof panels to protect the 
structure against the high temperatures of the furnace. 
Currently, furnace roofs are provided with a plurality of generally 
pie-shaped cooling coil panels made from pipes which are removably mounted 
to a spider frame on the roof. In this way, failure of weld joints or the 
pipe may be repaired by removing and replacing one of the removable coil 
panels. 
However, current cooling coil panels suffer several drawbacks. Each prior 
art panel is typically formed from lengths of pipe connected in a 
serpentine shape with gradually increasing lengths of pipe between end 
caps. Thus, in forming a "pie-shaped" panel, the point of the panel has a 
very short length of pipe between a pair of generally U-shaped end caps to 
return the pipe in the opposite direction. It can be seen that in such a 
design, many turns in the pipe are necessary to create the desired shape. 
Each such turn requires welded joints, which are the main areas of failure 
in such coolant coils. Each turn in the pipe also forms a restriction to 
water flow through the pipe, thereby reducing the velocity of water flow 
and increasing the pressure within the pipe. 
Another problem with prior art pie-shaped designs for cooling coil panels 
lies in the fact that higher stresses and greater failure rates occur near 
the center of the roof section as compared to the outer peripheral region 
of the roof section. Thus, a pie-shaped panel is more likely to have only 
a small portion of the coil damaged by heat and stress near the point of 
the pie-shaped section. The replacement of such a panel thereby throws out 
a large portion of cooling coil which has not been damaged, thereby 
increasing maintenance costs and wasting materials. 
Finally, the pie-shaped design of prior art coil panels utilizes a 
serpentine arrangement of pipe with the adjacent pipe lengths welded 
together and connected by caps with a tight 180.degree. turn. Such a 
serpentine design restricts expansion, and builds greater stresses on each 
weld because of the number of tight caps which are utilized. 
It is therefore a general object of the present invention to provide an 
improved electric arc furnace roof with removable cooling coils. 
Another object of the present invention is to provide a furnace roof with 
cooling coils which have fewer turns than conventional serpentine designs 
of pie-shaped panels. 
Yet another object is to provide a furnace roof with a plurality of cooling 
coils designed to permit replacement of coils in high stress areas 
independently of coils in lower stress areas of the roof. 
These and other objects will be apparent to those skilled in the art. 
SUMMARY OF THE INVENTION 
The roof structure for an electric arc smelting furnace of the present 
invention includes a spider frame for supporting a plurality of 
independent removable coolant coil sections. An inner coil section is 
generally annular in shape and includes a coolant pipe which spirals 
completely around a central opening in the roof structure. An intermediate 
coil section is also generally annular in shape, but includes a coolant 
pipe which extends around the circumference of the inner section, reverses 
itself around the circumference of the first pipe of the intermediate 
section, and then reverses itself one again around the circumference of 
the second coolant pipe of the intermediate section, to form a generally 
serpentine pattern A plurality of semi-annular outer coil sections are 
supported radially outwardly from the intermediate coil section. Each 
outer section includes a first pipe located generally centrally within the 
semi-annular section and extending from end to end. A second pipe reverses 
the coolant flow and is located radially outwardly from the first pipe. A 
third coolant pipe is connected to the second coolant pipe and is located 
radially inwardly of the first coolant pipe within the outer section.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, in which similar or corresponding parts are 
identified with the same reference numeral, and more particularly to FIG. 
1, an electric arc smelting furnace is designated generally at 10 and 
includes a generally cylindrical container 12 and a circular roof 14. 
Three electrodes 16 project upwardly through a central opening 18 in roof 
14, which heat the interior of container 12. 
Referring now to FIG. 2, the cooling coil panels of the present invention 
are designated generally at 20 and are suspended from a spider frame 22. 
Frame 22 includes an outer pipe extending around the circumference of 
frame 22 to form an outer ring 24. A plurality of spokes 26 are formed 
from pipes extending radially inwardly from outer ring 24 to an inner ring 
28. Cooling coil panels 20 are then suspended from spokes 26, as shown in 
FIG. 3. 
FIG. 4 is a schematic view of all of the coolant coil panels 20 utilized in 
conjunction with the furnace roof 14 of FIG. 1. For purposes of clarity, 
cooling coil panels 20 have been separately identified in three main 
categories: (1) inner loop section 30; (2) intermediate loop section 32; 
and (3) outer loop sections 34, 36, 38, 40, 42, 44, 46 and 48. Each 
coolant coil loop section 30-48 is removable, to permit easy repair or 
replacement. Inner loop section 30 and intermediate loop section 32 each 
extend substantially 360.degree. around central opening 18, to form 
generally annular shapes, with intermediate loop section 32 concentric 
with and extending radially outwardly from inner loop section 30. Outer 
loop sections 34-48 are shaped like a semi-annulus extending substantially 
180.degree. around central opening 18 and the next adjacent loop section. 
Thus, outer loop sections 34 and 36 are substantially identical and are 
mounted to form a substantially 360.degree. ring radially exterior of 
intermediate loop section 32. Similarly, outer loop sections 38 and 40 are 
substantially the same and are located radially exterior of outer loop 
sections 34 and 36 respectively. Outer loop sections 42 and 44 correspond 
with one another in the same fashion, and outer loop sections 46 and 48 
form the outer most ring of the cooling coil panels 20. It can be seen 
that this arrangement of cooling coil loop sections extending generally 
circumferentially around central opening 18 permits simple replacement of 
an inner section of the cooling coils without requiring the replacement of 
portions of the outer ring coils. Since the temperatures and stresses on 
the inner loop sections are typically greater than those on the outer 
sections, there is less waste involved in replacing only those coils which 
are damaged or are in need of repair. 
The inner loop section 30 is shown in more detail in FIG. 5. Inner loop 30 
begins at inlet 50 and extends in an expanding spiral around central 
opening 18, the spiral having an increasing diameter so as to 
circumnavigate opening 18 three times to form three coils 52, 54 and 56. 
Coil 56 reverses direction at a three-quarter circle 58 and a fourth coil 
60 extends in a reverse direction around third coil 56 until again 
reaching three-quarter circle 58, wherein the circuit of inner loop 
section 30 is exhausted at outlet 62. 
Referring now to FIG. 6, intermediate loop section 32 is shown in greater 
detail. From inlet 64, a first coil 66 extends around the perimeter of the 
inner loop section (not shown in FIG. 6) to a location immediately 
adjacent the location of three-quarter circle 58 (see FIG. 5). A 
180.degree. elbow 68 reverses the direction of fluid flow to form a second 
coil 70 which extends adjacent first coil 66 around the perimeter of the 
first coil and past inlet 64 to a location adjacent three-quarter circle 
58. A cap 72 again reverses the fluid flow to form a third coil 74 which 
extends completely around the second coil and beyond cap 72 to form a 
fourth coil 76 extending to an outlet 78. 
A smoke hole 80 is formed in roof 14, as shown in FIGS. 2 and 4, and 
cooling coil panels 20 extend into contact therewith. Referring now to 
FIG. 7, outer loop section 38 is shown in more detail. It should be noted 
that outer loop sections 36, 40, 42, 44, 46 and 48 are substantially the 
same as outer loop section 38, and therefore the other outer loop sections 
will not be detailed beyond that already described hereinabove. Outer loop 
section 38 is generally semi-annular in shape and includes a left end 38A 
and a right end 38B. An inlet 82 is located at left end 38A of loop 
section 38 and the first coil 84 extends from inlet 82 along the 
longitudinal center line of loop section 38, to the opposite end 38B. A 
cap 86 reverses the fluid flow in first coil 84 and initiates the second 
coil 88. Second coil 88 is located radially outwardly from first coil 86 
and extends there along to the left end 38A of loop section 38. A 
180.degree. elbow 90 redirects fluid from second coil 88 to a third coil 
92 located radially inwardly of first coil 84. Third coil 92 extends to 
right end 38B of section 38 where it is connected to a pair of elbows 
forming a U-shaped joint 94. U-shaped joint 94 directs fluid flow to a 
fourth coil 96 located radially outwardly of second coil 88, and extends 
to left end 38A. Another U-shaped joint 98 connects fourth coil 96 to the 
fifth coil 100 which is located radially interiorally of third coil 92 and 
extends to the right end 38B of section 38 to outlet 102. 
Referring now to FIG. 8, a typical joint between a pair of loop sections is 
shown. For ease of description, a typical joint between inner loop section 
30 and intermediate loop section 32 is shown. A flat strap 104 is mounted 
along the outer most coil 60 of inner loop section 30, on the upper 
surface thereof. A similar strap 106 is mounted on the upper surface of 
intermediate loop section 32 inner most coil 66 (which is positioned 
immediately adjacent coil 60 of inter loop section 30). Straps 104 and 106 
are bolted or skip welded to diametric sides of expansion pipe 108. A 
longitudinal split 110 is formed in expansion pipe 108 intermediate the 
connection of straps 104 and 106 thereto, to permit expansion between 
sections 30 and 32. Expansion pipe 108 is mounted to frame 22 to support 
the sections. Additional flat straps 112 may be located between adjacent 
pipe coils in order to close any gaps between the various coils. 
Slag anchors 114 are mounted on the interior surfaces of the various coils 
as shown in FIGS. 8 and 9. Anchors 114 preferably are formed from short 
lengths of square cross section shaft mounted in staggered formation on 
the various coils, and serve to retain slag which splatters during the 
smelting process and sticks to the cooled surface of the coils. Once the 
splatter slag solidifies it forms an insulated layer along the inter 
surface of the coils. 
Referring now to FIG. 10, the smoke hole 80 is shown in cross sectional 
view. A cooling loop section 116 is provided partially upwardly along the 
smoke hole. Preferably, loop section 116 includes a pipe 118 which extends 
in a spiral helix pattern upwardly along the smoke hole. 
Whereas the invention has been shown and described in connection with the 
preferred embodiment thereof, it will be understood that many 
modifications, substitutes and additions may be made which are within the 
intended broad scope of the appended claims. There is therefore been shown 
and described a roof structure for an electric arc smelting furnace which 
accomplishes at least all of the above stated objects.