US3625500A

US3625500A - Metallurgical furnace fume exhausting

Info

Publication number: US3625500A
Application number: US877197A
Authority: US
Inventors: James D Bell
Original assignee: National Steel Corp
Current assignee: National Steel Corp
Priority date: 1969-11-17
Filing date: 1969-11-17
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07
Also published as: CA919907A

Abstract

Metallurgical furnace fume exhaust structure has membrane walls assembled from finned, watercooled, metal tubes. Studs are mounted on the walls in a pattern for retaining and supporting a layer of slag which is splashed from the furnace, deposited on the walls, and solidified by the cooling fluid. The slag is accumulated to form a continuous protective layer covering the portions of the walls which are subject to most severe deterioration by action of the exhaust fumes. A coating of corrosion-resistant metal protects the tubes from attack by the slag.

Description

United States Patent 72] Inventor James 0. Bell Weirton, W. Va. [21] Appl. No. 877,197 [22] Filed Nov. 17, 1969 [45] Patented Dec. 7, 1971 [73] Assignee National Steel Corporation [54] METALLURGICAL FURNACE FUME EXHAUSTING 24 Claims, 4 Drawing Figs.

[52] [1.8. CI 266/35, 266/43 5| 1 Int. Cl. C2lc 5/42 [50] Field of Search 266/31, 34

[56] References Cited UNITED STATES PATENTS 3,138,648 6/1964 McFe aters.. 5 266/35 3,323,495 6/1967 Blaskowski 266/31 3,379,427 4/1968 Zherebin et al.. 266/43 3,380,728 4/1968 Baillie 266/35 3,396,958 8/1968 Maehara et al. 266/31 Primary ExaminerGerald A. Dost v Attorney-Shanley and O'Neil ABSTRACT: Metallurgical furnace fume exhaust structure has membrane walls. assembled from finned,- watercooled, metal tubes. Studs are mounted on the walls in a pattern for retaining and supporting a layer of slag which is splashed from the furnace. deposited on the walls. and solidified by the cooling fluid. The slag is accumulated to form a continuous protective layer covering the portions of the walls which are subject to most severe deterioration by action of the exhaust fumes. A coating of corrosion-resistant metal protects the tubes from attack by the slag.

PATENTEUBEII m1: 3.625500 FIGS.

Y m'vamon mas o. BELL H64 momms METALLURGICAL FURNACE FUME EXHAUSTING BACKGROUND OF THE INVENTION This invention relates to metallurgical furnace exhaust structures and more particularly to fume exhaust hoods for basic oxygen process (BOP) steelmaking converters.

Fume exhaust hoods for BOP converters are conventionally of the membrane-wall type, i.e., have thin metal walls through which cooling water is circulated. In normal service, the walls are exposed to the highlycorrosive action of the exhaust fumes. The fumes cause rapid erosion of the metal of the walls, particularly in the lower regions of the exhaust hood. Such deterioration reduces the strength capability of the walls to contain the high-pressure water flowing through the walls and creates necessity for frequent, expensive repairs and costly downtime on the BOP converter. Further, bursting failure of a hood wall during converter operation releases explosive forces and creates dangerous conditions. The draft through the hood is destroyed and flames, fumes, high-pressure water, and steam spill out into the shop.

In attempts to overcome this problem, it has been proposed to provide the hood with a protective lining, and a number of metallic and nonmetallic lining materials have been suggested. Various metallic coatings have been tried without success, it having beenfound that the coatings spalled off quite rapidly. Also, ceramic linings have been used and, in addition to failing to provide the solution to the problem, suflered from the further disadvantage of retarding heat interchange between the hot exhaust fumes and the watercooled hood walls so that gas temperatures increased throughout the gas collection unit.

Accordingly, main objects of the invention are the provision of improved metallurgical furnace fume exhaust structures which overcome the disadvantages of the prior art, which effectively resist the corrosive action of the exhaust fumes, and which have extended service lives.

Other objects of the invention will appear from the following detailed description which, in connection with the accompanying drawings, discloses a preferred embodiment of the invention for purposes of illustration only and not for determination of the limits of the invention. For defining the scope of the invention, reference will be made to the appended claims. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side view of a BOP converter installation including a fume exhaust hood embodying principles of the invention;

FIG. 2 is an enlarged view of details of the fume exhaust hood of FIG. I;

FIG. 3 is an enlarged cross-sectional view on line 33 of FIG. 2; and

FIG. 4 is a cross-sectional view on line 4-4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. I, a fume exhaust hood 10 is shown in operative position over a BOP converter or furnace l2. Hood I is hollow and generally annular in cross section, and has continuous sidewalls 13. The walls of the hood direct hot exhaust fumes away from converter 12 to a conventional gas cleaning system, not shown.

Hood includes a fume-entry portion 14, and fumes pass from entry portion 14 to an offset portion 16 which conducts the fumes to a stock portion 18. Fumes pass upwardly through stack portion 18 to the gas cleaning system.

Offset portion 16 of hood 10 includes an opening 20 through which an oxygen lance 22 is lowered and raised in a conventional manner to carry out a conventional top-blown oxygen steel refining process in converter 12. A slag hopper l9 communicates with the interior of offset portion I6 for entrapment, collection and removal of splashed slag and other matter spewn and carried by the effluent gases from the open mouth of converter 12.

Hood I0 is of the nonsealed type, entry portion 14 being spaced slightly above converter 12 for entry of a limited quantity of ambient air into the hood along with the exhaust fumes. Combustible gases contained in the fumes combine with the oxygen in the air and burn within the hood, for recovery of the heating value of the combustible gases through heat interchange with water passed through hood walls 13.

Hood walls 13 are of the membrane type in that a plurality of finned tubular members 24 (FIGS. 2,3) is employed in their construction. Tubes 24 are arranged in side-by-side relationship and extend upwardly from an annular water supply header 26 (FIG. I) at the bottom of hood 10 to a discharge header (not shown) at the top of the hood. The tubes conduct cooling water upwardly from the supply header to the discharge header through fluid passages 26 (FIG. 3) defined by the open internal cross sections of the tubes.

Each tube 24 includes a generally cylindrical body portion 28 and a pair of

fin members

30, 32 which project from body portion 28 radially outwardly in opposite directions. Tubes 24 are arranged with the fins of contiguous tubes abutting one another in gastight sealed relationship to define a continuous wall for confining the fumes.

The interior or fume-directing surfaces of the walls of hood entry portion 14 and offset portion 16 are covered by a very thin coating 34 of a corrosion-resistant metal, for a purpose to be described. The thickness of coating 34 is greatly exaggerated in the drawings, for clarity in illustration.

Body portion 28 of each tube 24 includes an apex portion 35. A plurality of spaced-apart studs 36 is welded to the apex portions of the tubes. Studs 36 project from the surface of the walls into the hood interior. Each stud has a generally cylindrical configuration, and the studs are covered by corrosion-resistant coating 34. The studs are distributed over the walls of hood entry portion 14 (FIG. I) and over the walls of offset portion 16.

Studs 36 are arranged in a diamond-shaped pattern, as indicated at 38, for retaining and supporting a continuous slag layer 40 (FIGS. 2, 3, 4) which is formed on the walls by slag splashed from converter 12, deposited on the walls, and cooled and solidified by the cooling fluid circulating through the walls. The layer is formed progressively by accumulation of splashed solidified slag and covers those portions of the membrane walls, including the fins of tubes 24, which are subjected to contact with splashing slag. The slag has a large shrinkage coefficient and, upon solidification, contracts and firmly grips the projecting studs 36. The studs being at the apex portions of the tubes, slag held by the studs locks in place the slag in the depressions between the tube apex portions, for continuity in the slag layer. Slag layer 40 protects the metal of the membrane walls from corrosive and erosive conditions prevailing inside the hood. The slag layer thus formed has a thickness'which for the most part approximates the length of the studs. This condition is illustrated in FIG. 3, which depicts a portion of the hood walls in the lower reaches of the offset portion of the hood. However, at some locations along the fume exhaust path, the slag thickness may be somewhat greater or less than the length of the studs. The slag layer tends to form in thicknesses which are greater at the lower end portion of the hood, where splashing activity is greater, and are less in the upper regions where the splashing activity diminishes. The slag layer appears to be self-liquidating, in

that normally the slag does not accumulate beyond an equilibrium thickness which varies with proximity to the converter along the fume exhaust path. In any event, the slag layer accumulates to form a continuous cover over lower portions of the hood walls, extending upwardly to the vicinity of the upper end portion of offset portion 16. The slag layer protects the tubes, including the fins, from the corrosive and erosive action of the exhaust fumes in the regions where heretofore wall deterioration as a result of fume action had been particularly severe. In FIG. 2, a portion of slag layer 40 is removed for purposes of illustration.

BOP steclmaking slag typically includes the following constituents in varying proportions: FeO, F6 0,, MgO, CaO, 5,0 M 0 P 0 and MnO. The slag would corrosively attack tubes 24, which are conventionally made of plain carbon, boiler-tube steel containing 0.06-0.35 percent carbon,

0.27-0.80 percent manganese, up to 0.05 percent phosphorus, up to 0.06 percent sulfur, and the balance essentially iron. The purpose of metal coating 34 on tube 24 is to prevent the slag from chemically attacking the ferrous metal of the tubes, and any metal resistant to corrosion or attack by the slag can be employed. Aluminum and aluminum-base alloys are economical and well suited for this purpose, but other metals can be used. Aluminum coatings from about 0.010 inch to about 0.025 inch thick are adequate.

in making an exhaust hood structure according to one exemplary application of the principles of the invention, the membrane walls forming hood are assembled in a conventional manner from tubes having an outside diameter of about 4 inches and having fins about three-fourths inches wide. Steel stud bolts three-eighths inch in diameter and 1 inch long are welded to the tubes in a diamond-shaped pattern. The studs are spaced along the tubes so that the distance between centerlines of stud members across diagonal 42 of diamondshaped pattern 38 is about 2 inches. The walls are then cleaned by abrasive blasting. A coating of aluminum about 0.02 inch thick is applied in molten form to the walls, including the studs, by conventional flame spraying techniques.

A flow of cooling water is passed through the walls, and operations in converter 12 are initiated. Converter 12 is charged with raw materials in the usual way and lance 22 is lowered through hood opening 20 to perform the steel refining process. The process proceeds with violent chemical and physical reactions which cause splashing of slag from the converter. The slag strikes the walls of the hood, and is cooled and solidified by action of the cooling water circulating through the hood walls. The slag shrinks as it solidifies, securely gripping studs 36, and progressively accumulates to form a continuous protective layer over the hood walls by the time about eight heats of steel are blown in converter 12.

If desired, tubes 24 can be precoated with a bonding layer of an alloy containing 80 percent nickel and 20 percent aluminum, to improve adherence of aluminum coating 34 to the tubes. Such a bonding coat can be extremely thin, e.g., from about 0.003 inch to about 0.007 inch (preferably about 0.005 inch) in thickness, and can be applied by the same technique employed for the aluminum coating. As indicated above, the aluminum coating can be applied by flame-spray metallizing, but other conventional techniques can be employed.

BOP vessel exhaust hoods according to the invention are highly advantageous. Prior to the present invention, hood life was limited to approximately six converter campaigns, but hoods built in accordance with the invention appear to have indefinite service lives. The protective slag layers are selfrepairing in that, should a portion of the blanket spall away, it is quickly built up again by newly deposited slag. Surprisingly, the combination of the slag layer and embedded studs does not significantly retard heat interchange between the fumes and the walls of the hood. Construction of hoods according to the invention is inexpensive both with respect to materials employed and to the amount of labor required, and construction is facilitated by the fact that the slag layer is formed in situ.

lclaim:

l. Metallurgical furnace exhaust structure, comprising wall means having a surface for directing exhaust fumes away from a metallurgical furnace, which surface is subject to attack by effluent from the furnace,

the wall means including fluid passage means for conducting cooling fluid through the wall means, and

a plurality of spaced slag-anchoring stud members projecting from said surface of the wall means,

the stud members being positioned in a predetermined pattern for retaining and supporting a continuous accumulated protective layer of slag splashed from the furnace, solidified on said surface of the wall means by the cooling fluid, and covering said surface of the wall means.

2. The structure of claim I,

said surface of the wall means being corrosion-resistant.

3. The structure of claim 1,

the wall means including a ferrous metal base portion and a corrosion-resistant metal coating,

the corrosion-resistant metal coating having an exposed surface defining said surface of the wall means.

4. The structure of claim 3,

the corrosion-resistant metal being selected from the group consisting of aluminum and aluminum-base alloys.

5. The structure of claim 3,

the corrosion-resistant metal coating being aluminum and being from about 0.010 inch to about 0.025 inch in thickness.

6. The structure of claim 3,

the ferrous metal being steel. 4

7. The structure of claim 3,

the corrosion-resistant metal coating covering the stud members.

8. The structure of claim 1,

the wall means including a plurality of tubular members,

each tubular member having an apex portion,

the stud members being carried by the apex portions of at least some of the tubular members.

9. The structure of claim 8,

the tubular members being generally parallel to one another,

each tubular member including a pair of oppositely directed, outwardly projecting fin members,

each fin member being in gastight sealed relationship with a fin member on a contiguous tubular member.

10. The structure of claim 1,

each stud member having a generally cylindrical configuration.

11. The structure of claim I,

the predetermined pattern having a generally diamondshaped configuration.

12. The structure of claim ll,

the stud members having centerlines spaced from one another a distance of about 2 inches across a diagonal of the diamond-shaped pattern.

13. Metallurgical furnace exhaust structure, comprising wall means having a surface for directing exhaust fumes away from a metallurgical furnace, which surface is subject to attack by effluent from the furnace,

the wall means including a base portion and a corrosion-resistant metal coating.

the corrosion-resistant metal coating having an exposed surface defining said surface of the wall means,

slag-anchoring means projecting from said surface of the wall means,

the slag-anchoring means being positioned in a predetermined pattern for retaining and supporting a continuous accumulated protective layer of slag splashed from the furnace, solidified on said surface of the wall means by the cooling fluid, and covering said surface of the wall means.

14. The structure of claim 13,

the corrosion-resistant metal coating covering the slaganchoring means.

15. The structure of claim 13,

the slag-anchoring means including a plurality of stud members.

l6. Metallurgical furnace exhaust structure, comprising wall means having a surface for directing exhaust fumes away from a metallurgical furnace, which surface is subject to attack by effluent from the furnace,

the wall means including fluid passage means for conducting cooling fluid through the wall means,

a plurality of spaced slag-anchoring stud members projecting from said surface of the wall means, and

a continuous protective layer of slag covering said surface of the wall means,

the stud members being positioned in a predetermined pattern for retaining and supporting the layer of slag.

17. The structure ofclaim 16,

the wall means including a plurality of tubular members,

each tubular member including a plurality of outwardly projecting fin members,

each fin member being in gastight sealed relationship with a fin member on a contiguous tubular member,

the slag layer covering the fin members.

18. Converter exhaust hood structure, comprising wall means having a surface for directing exhaust fumes away from a converter, which surface is subject to attack by effluent from the converter,

the wall means including a base portion and a corrosion-resistant metal coating,

the wall means including a plurality of tubular members,

each tubular member including fluid passage means for conducting cooling fluid through the tubular member,

the corrosion-resistant metal coating covering the stud members,

the stud members being positioned in a predetermined pattern for retaining and supporting a continuous accumulated protective layer of slag splashed from the converter, solidified on said surface of the wall means by the cooling fluid, and covering said surface of the wall means.

19. The structure of claim 18,

the tubular members being generally parallel to one another,

each tubular member including an apex portion,

the stud members being carried by the apex portions of at least some of the tubular members,

20. The structure of claim 19,

the predetermined pattern having a generally diamondshaped configuration. t

21. The structure of claim 20,

the base portion being steel and the corrosion-resistant metal coating being selected from the group consisting of aluminum and aluminum-base alloys.

22. The structure of claim 21, including a bond coating consisting of about percent nickel and about 20 percent aluminum interposed between the corrosion-resistant metal coating and the base portion of the wall means.

23. Method of making a metallurgical furnace exhaust structure comprising the steps of providing wall means having a surface for directing exhaust fumes away from a metallurgical furnace, which surface is subject to attack by effluent from the furnace,

mounting a plurality of slag-anchoring stud members on the wall means in a predetermined pattern for retaining and supporting a layer of slag covering the wall means,

coating said surface of the wall means and the stud members with a corrosion-resistant metal,

charging the furnace with metal to be refined,

treating the charged metal with a gaseous refining agent, thereby establishing a violent refining reaction causing splashing of slag from the furnace,

passing cooling fluid through the wall means, thereby solidifying slag splashed from the furnace on said surface of the wall means, and

accumulating solidified slag to form a continuous protective layer of slag covering said surface of the wall means.

24. The method of claim 23,

the wall means being steel and the corrosion-resistant metal being selected from the group consisting of aluminum and aluminum-base alloys.

Claims

1. Metallurgical furnace exhaust structure, comprising wall means having a surface for directing exhaust fumes away from a metallurgical furnace, which surface is subject to attack by effluent from the furnace, the wall means including fluid passage means for conducting cooling fluid through the wall means, and a plurality of spaced slag-anchoring stud members projecting from said surface of the wall means, the stud members being positioned in a predetermined pattern for retaining and supporting a continuous accumulated protective layer of slag splashed from the furnace, solidified on said surface of the wall means by the cooling fluid, and covering said surface of the wall means.

2. The structure of claim 1, said surface of the wall means being corrosion-resistant.

3. The structure of claim 1, the wall means including a ferrous metal base portion and a corrosion-resistant metal coating, the corrosion-resistant metal coating having an exposed surface defining said surface of the wall means.

4. The structure of claim 3, the corrosion-resistant metal being selected from the group consisting of aluminum and aluminum-base alloys.

5. The structure of claim 3, the corrosion-resistant metal coating being aluminum and being from about 0.010 inch to about 0.025 inch in thickness.

6. The structure of claim 3, the ferrous metal being steel.

7. The structure of claim 3, the corrosion-resistant metal coating covering the stud members.

8. The structure of claim 1, the wall means including a plurality of tubular members, each tubular member having an apex portion, the stud members being carried by the apex portions of at least some of the tubular members.

9. The structure of claim 8, the tubular members being generally parallel to one another, each tubular member including a pair of oppositely directed, outwardly projecting fin members, each fin member being in gastight sealed relationship with a fin member on a contiguous tubular member.

10. The structure of claim 1, each stud member having a generally cylindrical configuration.

11. The structure of claim 1, the predetermined pattern having a generally diamond-shaped configuration.

12. The structure of claim 11, the stud members having centerlines spaced from one another a distance of about 2 inches across a diagonal of the diamond-shaped pattern.

13. Metallurgical furnace exhaust structure, comprising wall means having a surface for directing exhaust fumes away from a metallurgical furnace, which surface is subject to attack by effluent from the furnace, the wall means including a base portion and a corrosion-resistant metal coating. the corrosion-resistant metal coating having an exposed surface defining said surface of the wall means, the wall means including fluid passage means for conducting cooling fluid through the wall means, and slag-anchoring means projecting from said surface of the wall means, the slag-anchoring means being positioned in A predetermined pattern for retaining and supporting a continuous accumulated protective layer of slag splashed from the furnace, solidified on said surface of the wall means by the cooling fluid, and covering said surface of the wall means.

14. The structure of claim 13, the corrosion-resistant metal coating covering the slag-anchoring means.

15. The structure of claim 13, the slag-anchoring means including a plurality of stud members.

16. Metallurgical furnace exhaust structure, comprising wall means having a surface for directing exhaust fumes away from a metallurgical furnace, which surface is subject to attack by effluent from the furnace, the wall means including fluid passage means for conducting cooling fluid through the wall means, a plurality of spaced slag-anchoring stud members projecting from said surface of the wall means, and a continuous protective layer of slag covering said surface of the wall means, the stud members being positioned in a predetermined pattern for retaining and supporting the layer of slag.

17. The structure of claim 16, the wall means including a plurality of tubular members, each tubular member including a plurality of outwardly projecting fin members, each fin member being in gastight sealed relationship with a fin member on a contiguous tubular member, the slag layer covering the fin members.

18. Converter exhaust hood structure, comprising wall means having a surface for directing exhaust fumes away from a converter, which surface is subject to attack by effluent from the converter, the wall means including a base portion and a corrosion-resistant metal coating, the corrosion-resistant metal coating having an exposed surface defining said surface of the wall means, the wall means including a plurality of tubular members, each tubular member including fluid passage means for conducting cooling fluid through the tubular member, a plurality of spaced slag-anchoring stud members projecting from said surface of the wall means, the corrosion-resistant metal coating covering the stud members, the stud members being positioned in a predetermined pattern for retaining and supporting a continuous accumulated protective layer of slag splashed from the converter, solidified on said surface of the wall means by the cooling fluid, and covering said surface of the wall means.

19. The structure of claim 18, the tubular members being generally parallel to one another, each tubular member including an apex portion, the stud members being carried by the apex portions of at least some of the tubular members, each tubular member including a pair of oppositely directed, outwardly projecting fin members, each fin member being in gastight sealed relationship with a fin member on a contiguous tubular member.

20. The structure of claim 19, the predetermined pattern having a generally diamond-shaped configuration.

21. The structure of claim 20, the base portion being steel and the corrosion-resistant metal coating being selected from the group consisting of aluminum and aluminum-base alloys.

22. The structure of claim 21, including a bond coating consisting of about 80 percent nickel and about 20 percent aluminum interposed between the corrosion-resistant metal coating and the base portion of the wall means.

23. Method of making a metallurgical furnace exhaust structure, comprising the steps of providing wall means having a surface for directing exhaust fumes away from a metallurgical furnace, which surface is subject to attack by effluent from the furnace, the wall means including fluid passage means for conducting cooling fluid through the wall means, mounting a plurality of slag-anchoring stud members on the wall means in a predetermined pattern for retaining and supporting a layer of slag covering the wall means, coating said surface of the wall means and thE stud members with a corrosion-resistant metal, charging the furnace with metal to be refined, treating the charged metal with a gaseous refining agent, thereby establishing a violent refining reaction causing splashing of slag from the furnace, passing cooling fluid through the wall means, thereby solidifying slag splashed from the furnace on said surface of the wall means, and accumulating solidified slag to form a continuous protective layer of slag covering said surface of the wall means.

24. The method of claim 23, the wall means being steel and the corrosion-resistant metal being selected from the group consisting of aluminum and aluminum-base alloys.