CA1310184C - Conveying screw for furnace - Google Patents
Conveying screw for furnaceInfo
- Publication number
- CA1310184C CA1310184C CA000518680A CA518680A CA1310184C CA 1310184 C CA1310184 C CA 1310184C CA 000518680 A CA000518680 A CA 000518680A CA 518680 A CA518680 A CA 518680A CA 1310184 C CA1310184 C CA 1310184C
- Authority
- CA
- Canada
- Prior art keywords
- conveying screw
- screw according
- fluid
- chamber
- pipe
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Abstract
CONVEYING SCREW FOR FURNACE
ABSTRACT OF THE DISCLOSURE
A countercurrent fluid cooled conveying screw is disclosed.
Suitable for furnace applications, the screw includes an outer shaft spatially circumscribing an inner tube. A plurality of hollow, fluid cooled flights are affixed to the outer shaft and are in fluid flow communication with coolant coursing through the screw. The coolant is first directed through the flights and then back through the outer shaft before exiting through the inner tube.
ABSTRACT OF THE DISCLOSURE
A countercurrent fluid cooled conveying screw is disclosed.
Suitable for furnace applications, the screw includes an outer shaft spatially circumscribing an inner tube. A plurality of hollow, fluid cooled flights are affixed to the outer shaft and are in fluid flow communication with coolant coursing through the screw. The coolant is first directed through the flights and then back through the outer shaft before exiting through the inner tube.
Description
301$~
~ EYING SCREW FO~ FURNACE
Ths instant invention relates to furnace design in general and more particularly to a countercurrent fluid cooled discharge screw disposed immediately above the hearth in a rotary hearth furnace.
BACKGROUND
Direct reduction o~ iron oxide and other metallic oxides may be conducted in rotary hearth furnaces ("RHF") using pelletized or briquetted ~eed deposited upon the rotating hearth.
Briefly, an RHF i~ continuous reheating ~urnace generally having a aircular inner wall circum~cribed by a spaced circular inner outerwall. The void ~ormed therebet-ween includes a circular rotating hearth. In order to retain the heat generated within the furnace the walls are relatively low so as to enable the roof to be close to the hearth. Burners may be installed in the inner and outer walls and in the roof.
Material is usually loaded (dropped) onto the rotating hearth by a conveyor or chute. After ~he material is carried on the hearth, it is usually removed by a discharge screw. Due to high temperatures (1300-2300 F
[704 - 1260 C]) involved, the screw if frequen~ly water cooled. See U.S. patent 3,443,931. Ga~es are permitted to vent through a flue located in the roof.
A conventional conveying or discharge screw consists o~ a central shaft with a ~olid helical ~light welded thereto. A cooling fluid is passed through a bore disposed within the shaft. Other s~rew designs utilize a plurality of spac~d solid flights disposed about the shaft.
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~ EYING SCREW FO~ FURNACE
Ths instant invention relates to furnace design in general and more particularly to a countercurrent fluid cooled discharge screw disposed immediately above the hearth in a rotary hearth furnace.
BACKGROUND
Direct reduction o~ iron oxide and other metallic oxides may be conducted in rotary hearth furnaces ("RHF") using pelletized or briquetted ~eed deposited upon the rotating hearth.
Briefly, an RHF i~ continuous reheating ~urnace generally having a aircular inner wall circum~cribed by a spaced circular inner outerwall. The void ~ormed therebet-ween includes a circular rotating hearth. In order to retain the heat generated within the furnace the walls are relatively low so as to enable the roof to be close to the hearth. Burners may be installed in the inner and outer walls and in the roof.
Material is usually loaded (dropped) onto the rotating hearth by a conveyor or chute. After ~he material is carried on the hearth, it is usually removed by a discharge screw. Due to high temperatures (1300-2300 F
[704 - 1260 C]) involved, the screw if frequen~ly water cooled. See U.S. patent 3,443,931. Ga~es are permitted to vent through a flue located in the roof.
A conventional conveying or discharge screw consists o~ a central shaft with a ~olid helical ~light welded thereto. A cooling fluid is passed through a bore disposed within the shaft. Other s~rew designs utilize a plurality of spac~d solid flights disposed about the shaft.
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.~
.~
' ' .
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':
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- 2 - I 3 1 0 1 ~4 Due ~o corrosive nature of the gases and materials present within the RHF, coupled with the high temperatures therein, the discharge screw is subject to frequent failure. The flights generally deteriorate.
Corrosion and erosion caused by high temper~tures and bad actors (sodium, sulfides, chlorides, fluorides, potassium lead, zinc, tin, iron, nickel and chromium) within the RHF
oftentimes chew up the screws and render them useless after only about three months. Expensive material~ such as HH
alloy ~20% nickel, 20% chromium, remainder iron) as well as IN 659 were not satisfactory.
In addition, the spaces b~tween the flights accumulate fluffy fines which tend to cake together. The fines act as a sponge which serve to collect and concen-trate the corrosive gases present within the furnace.
As can be imagined, fre~uent screw replacement necessitates frequant downtime, high maintenance and labor costs, and inefficient use of the furnace which in turn lead to higher unit costs. Clearly a ~etter screw design is necessary.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved discharqe screw capable of better withstanding the rigors of an RHF.
The screw includes a central shaft and a plural-ity of helical water cooled flights arranged thereon. The coolant flows through the screw in two stages: once through the flights and then in a countercurrent fashion back through the screw before being reversed for exit.
Moreover, the ~lights may be faced with a corrosion resis-tant overlay.
,.~,.
~ 3 ~ ~ 3 1 0 1 ~4 BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plan view of a rotary hearth furnace.
Figure 2 is a sidelels~ation, of an embodiment of the inventlon.
Figure 3 is a cross sectional view takerl along linP 3-3 in Figure 2.
Figure 4 is a cross sectional view o~ an embodi-ment of the invention.
PR~FERRED MODE FOR CARR~ING OUT T~E INV~TIO~
Referring to Figure 1, there is shown a greatly simplified view of a rotary hearth furnace (RHF? 10. The RHF 10 includes an insulated outer wall 12 and an insulated - inner wall 14. A hearth 16 rotates within the RHF 10 in the direction shown by arrow 18. A plurality of burners 20 are situated about the RHF 10. Curtains 22 divide the RHF
10 into distinct sections. Matsrial is introduced onto the hearth 16 by a feeder 24 mounted in the roof ~not shown~ of the RHF 10.
After material processing is complete; tha~ i5, after almost one complete rotation o~ the hearth 16, the material is remov~d by discharge screw 26 and is deposited into a bin (not shown) for subsequent treatme~t. The discharge screw 26 is driven by motor and mechanical linkage 28. Water is supplied to the screw 26 through coupling 30.
Figures 2 and 3 depict the ~crew 26 in greater detail. Th~ screw 26 includes shaft 32 affixed to two pipes 62 each ha~ing an internal bore 34 for water passage therethrough. A plurality of spac~d hollow helical fligh~s 36 circumscribe the shaft 32. It is preferred to utilize six or seven ~lights 36 si~ce more flights will tend to :`
-, , ~,~
cause particulate matter to cake between the flights 36.
The flights 36 are shown in a clockwise righthand spiral. Accordingly, the screw 26 rotates in direc-tion 38. However, the invention is not limited to thisparticular embodiment.
Water is 7 ntroduced into the screw 26 at water coupled end 40 and exit~ through drive end g2.
The flights 36 are hollow to permit water flow therethrough. Slots 4~, formed in two sections of the shaft 32 (see Figure 4), allow the water to pass from the bore 34 to the flight 36 and vice-versa. A corrosion resistant overlay ~4 may be affixed to the leading edge of the flight 36. ST~LLITE (a trademark) 6 has been utilized as a overlay 44 but it sometimes has craeked after a period of time. The crac~s then propagate into the mild steel flight 36 causing small water leaks. Although the experi-ence with the S~LLITE alloy has been sometimes disapp~int-ing, it is still preferred tQ use an overlay 44.
Figure 4 is a detailed vi~w of the screw 26. The ends 40 and 42 are affixed to appropriate affixing means (not shown) to ensure water-tight integrity and allow for ~he rotation of the screw 26. Wa~er flow is shown by arrows 48. Caps 74 and 76 prevent the water from leaking out of the screw 26.
The shaft 32, by a series of internal baffles, causes the water to flow in a serpentine or countercurrent flow before exiting.
The water flow 48 ~irst courses through the pipe 62 from the water coupling end 40 whereupon it enters chamber 50. The chamber 50 includ~s apertures 52 which cause the water to flow into second chamber 54 and then to I ~
_ 5 _ ~310184 the flights 36 via the slots 46. Although only one 810t 46 is depicted at the water coupled (or proximal) end 40, it should be understood that the number o~ slots 46 match the number of flights 3Ç.
The water ~lows through the entire le~gth o the flights ~6 towards the distal end 42 where it reenters the sha~t 32 through the slot 46 into chamber 72. The water continues to flow through ape.rture 68 formed in bulkhead 66 into annular space 56 fo~med between the sha~t 32 and inner tube 58. Spacers 64 secure the physical relationship between the shaft 32 and the inner tube 58.
The water flows, in a countercurrent fashion, towards bulkhead 60 where it i6 reversed again and forced into tube 58. ~he water, now flowing through tube 58 passes through aperture 70 in the ~ulkhead 66 towards the distal end 42 and then out of the screw 26.
By *orcefully routing the wat~r back toward~ the proximal end 40 in a counter~low ~ashion, three cooling operations are conducted simultaneously. Firstly, water ~lowing through the flights 36 cools the Plights 36 and reduces the possibility of ~light 36 deterioration.
Secondly, the watPr ~lowing back through the annular space 56 cools the shaft 32 area between the flights 36. This area becomes caked with hot material which if not cooled will hasten the demise of the screw 26. ~hirdly, the water ~lowing through the tube 58 and the pipe 62 kseps these components relatively cool.
In experimental tests, the screw 26 has lasted approximately two to three times longer than a c~nventional water cooled solid flight discharge screw. Such screws, on average, lasted only two to three months whereas the instant sarew 26 has lasted from four to nine months~
~oreover, b~y utillzing the instant design, it ie possible ' ' ' - 6 - ~ 3 1 0 1 ~
to fabricate the screw 26 out of mild steel rather than expensive exotic alloys.
The pitch, lead angle, length and number of the flights are, of course, a function of the size of the RHF, the environment and materia:L to treated within the RHF.
Under particula~ conditions, the temperature within the RHF
was about 1800F (982~C) and the flight~ were about 16.25 feet [4.9 meters) long. The outer shaft 32 was about 1.5 1~) feet ~.45 meter) in diameter with the entire shaft 32 about 17.2 feet (5.2 meters) long. The lead angle 68 was about 35 15' and the pitch 70 was about 13.3 inches (33.8 centimetres). See Figure 2. Due to the cooling capability of the screw 26, the water temperature entered the screw 26 at about 90 F (32.2C) and exited the screw 26 at about 120 F (49 C) at a flow rate of about 300 yallons per minute (1136 Jmin.) at about 10-15 pounds per square inch (69-103 KPa).
While in accordance with the provisions of the statute, tnere ls illustrated and de~cribed herein specific embodiments o~ the invention~ Those skilled in the art will understand that changes may be made in the form of the invention covered by the claims and the ~ertain features o~
the invention may sometimes be used to advantage without a corresponding use o~ the other features.
i ~,
Corrosion and erosion caused by high temper~tures and bad actors (sodium, sulfides, chlorides, fluorides, potassium lead, zinc, tin, iron, nickel and chromium) within the RHF
oftentimes chew up the screws and render them useless after only about three months. Expensive material~ such as HH
alloy ~20% nickel, 20% chromium, remainder iron) as well as IN 659 were not satisfactory.
In addition, the spaces b~tween the flights accumulate fluffy fines which tend to cake together. The fines act as a sponge which serve to collect and concen-trate the corrosive gases present within the furnace.
As can be imagined, fre~uent screw replacement necessitates frequant downtime, high maintenance and labor costs, and inefficient use of the furnace which in turn lead to higher unit costs. Clearly a ~etter screw design is necessary.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved discharqe screw capable of better withstanding the rigors of an RHF.
The screw includes a central shaft and a plural-ity of helical water cooled flights arranged thereon. The coolant flows through the screw in two stages: once through the flights and then in a countercurrent fashion back through the screw before being reversed for exit.
Moreover, the ~lights may be faced with a corrosion resis-tant overlay.
,.~,.
~ 3 ~ ~ 3 1 0 1 ~4 BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plan view of a rotary hearth furnace.
Figure 2 is a sidelels~ation, of an embodiment of the inventlon.
Figure 3 is a cross sectional view takerl along linP 3-3 in Figure 2.
Figure 4 is a cross sectional view o~ an embodi-ment of the invention.
PR~FERRED MODE FOR CARR~ING OUT T~E INV~TIO~
Referring to Figure 1, there is shown a greatly simplified view of a rotary hearth furnace (RHF? 10. The RHF 10 includes an insulated outer wall 12 and an insulated - inner wall 14. A hearth 16 rotates within the RHF 10 in the direction shown by arrow 18. A plurality of burners 20 are situated about the RHF 10. Curtains 22 divide the RHF
10 into distinct sections. Matsrial is introduced onto the hearth 16 by a feeder 24 mounted in the roof ~not shown~ of the RHF 10.
After material processing is complete; tha~ i5, after almost one complete rotation o~ the hearth 16, the material is remov~d by discharge screw 26 and is deposited into a bin (not shown) for subsequent treatme~t. The discharge screw 26 is driven by motor and mechanical linkage 28. Water is supplied to the screw 26 through coupling 30.
Figures 2 and 3 depict the ~crew 26 in greater detail. Th~ screw 26 includes shaft 32 affixed to two pipes 62 each ha~ing an internal bore 34 for water passage therethrough. A plurality of spac~d hollow helical fligh~s 36 circumscribe the shaft 32. It is preferred to utilize six or seven ~lights 36 si~ce more flights will tend to :`
-, , ~,~
cause particulate matter to cake between the flights 36.
The flights 36 are shown in a clockwise righthand spiral. Accordingly, the screw 26 rotates in direc-tion 38. However, the invention is not limited to thisparticular embodiment.
Water is 7 ntroduced into the screw 26 at water coupled end 40 and exit~ through drive end g2.
The flights 36 are hollow to permit water flow therethrough. Slots 4~, formed in two sections of the shaft 32 (see Figure 4), allow the water to pass from the bore 34 to the flight 36 and vice-versa. A corrosion resistant overlay ~4 may be affixed to the leading edge of the flight 36. ST~LLITE (a trademark) 6 has been utilized as a overlay 44 but it sometimes has craeked after a period of time. The crac~s then propagate into the mild steel flight 36 causing small water leaks. Although the experi-ence with the S~LLITE alloy has been sometimes disapp~int-ing, it is still preferred tQ use an overlay 44.
Figure 4 is a detailed vi~w of the screw 26. The ends 40 and 42 are affixed to appropriate affixing means (not shown) to ensure water-tight integrity and allow for ~he rotation of the screw 26. Wa~er flow is shown by arrows 48. Caps 74 and 76 prevent the water from leaking out of the screw 26.
The shaft 32, by a series of internal baffles, causes the water to flow in a serpentine or countercurrent flow before exiting.
The water flow 48 ~irst courses through the pipe 62 from the water coupling end 40 whereupon it enters chamber 50. The chamber 50 includ~s apertures 52 which cause the water to flow into second chamber 54 and then to I ~
_ 5 _ ~310184 the flights 36 via the slots 46. Although only one 810t 46 is depicted at the water coupled (or proximal) end 40, it should be understood that the number o~ slots 46 match the number of flights 3Ç.
The water ~lows through the entire le~gth o the flights ~6 towards the distal end 42 where it reenters the sha~t 32 through the slot 46 into chamber 72. The water continues to flow through ape.rture 68 formed in bulkhead 66 into annular space 56 fo~med between the sha~t 32 and inner tube 58. Spacers 64 secure the physical relationship between the shaft 32 and the inner tube 58.
The water flows, in a countercurrent fashion, towards bulkhead 60 where it i6 reversed again and forced into tube 58. ~he water, now flowing through tube 58 passes through aperture 70 in the ~ulkhead 66 towards the distal end 42 and then out of the screw 26.
By *orcefully routing the wat~r back toward~ the proximal end 40 in a counter~low ~ashion, three cooling operations are conducted simultaneously. Firstly, water ~lowing through the flights 36 cools the Plights 36 and reduces the possibility of ~light 36 deterioration.
Secondly, the watPr ~lowing back through the annular space 56 cools the shaft 32 area between the flights 36. This area becomes caked with hot material which if not cooled will hasten the demise of the screw 26. ~hirdly, the water ~lowing through the tube 58 and the pipe 62 kseps these components relatively cool.
In experimental tests, the screw 26 has lasted approximately two to three times longer than a c~nventional water cooled solid flight discharge screw. Such screws, on average, lasted only two to three months whereas the instant sarew 26 has lasted from four to nine months~
~oreover, b~y utillzing the instant design, it ie possible ' ' ' - 6 - ~ 3 1 0 1 ~
to fabricate the screw 26 out of mild steel rather than expensive exotic alloys.
The pitch, lead angle, length and number of the flights are, of course, a function of the size of the RHF, the environment and materia:L to treated within the RHF.
Under particula~ conditions, the temperature within the RHF
was about 1800F (982~C) and the flight~ were about 16.25 feet [4.9 meters) long. The outer shaft 32 was about 1.5 1~) feet ~.45 meter) in diameter with the entire shaft 32 about 17.2 feet (5.2 meters) long. The lead angle 68 was about 35 15' and the pitch 70 was about 13.3 inches (33.8 centimetres). See Figure 2. Due to the cooling capability of the screw 26, the water temperature entered the screw 26 at about 90 F (32.2C) and exited the screw 26 at about 120 F (49 C) at a flow rate of about 300 yallons per minute (1136 Jmin.) at about 10-15 pounds per square inch (69-103 KPa).
While in accordance with the provisions of the statute, tnere ls illustrated and de~cribed herein specific embodiments o~ the invention~ Those skilled in the art will understand that changes may be made in the form of the invention covered by the claims and the ~ertain features o~
the invention may sometimes be used to advantage without a corresponding use o~ the other features.
i ~,
Claims (19)
1. A conveying screw connected to a non-rotational coolant supply means and a non-rotational coolant removal means, the screw comprising a rotationally drivable central shaft and at least one hollow conveyor flight connected thereto, wherein the central shaft is hollow and is formed with a pipe section protruding from each end thereof, a first cap and a second cap disposed at each respective end of the shaft surrounding each respective pipe section whereby to form chambers between each cap and its adjacent pipe section, the pipe section at the first cap having defined therethrough coolant ducts in fluid communication with its adjacent chamber said adjacent chamber being in fluid communication with a first end of said at least one hollow flight, an inner pipe being disposed inside the hollow shaft in concentric arrangement between the chambers and open facing the chamber adjacent the first cap, the inner pipe being in fluid communication with the remote end of said at least one hollow flight through the chamber adjacent said second cap, whereby coolant from said supply means passes from the chamber adjacent the first cap through said at least one hollow flight and through the chamber adjacent the second cap into the hollow shaft.
2. The conveying screw according to claim 1, wherein at least the hollow shaft is made of mild steel.
3. The conveying screw according to claim 2 wherein a first bulkhead spans the interior of the outer tube so as to sealingly separate the fluid distribution chamber from the inner tube.
4. The conveying screw according to claim 1 wherein the inner tube causes the fluid to back flow through the void toward the proximal end of the screw before exiting from the distal end.
5. The conveying screw according to claim 1 wherein the screw is comprised of mild steel.
6. The conveying screw according to claim 1 wherein the flights are overlayed with a corrosion and erosion resistant material.
7. The conveying screw according to claim 1 wherein the flights are helical.
8. The conveying screw according to claim 1 wherein the flights are equidistant from one another.
9. The conveying screw according to claim 1 disposed in a furnace.
10. The conveying screw according to claim 9 disposed in a rotary hearth furnace.
11. The conveying screw according to claim 1 wherein the fluid is in a heat exchange relationship with the flights and outer shaft.
12. The conveying screw according to claim 2 wherein the means for introducing fluid into the screw includes a first pipe affixed the proximal end of the screw, one end of the pipe including a plurality of apertures communicat-ing with the fluid distribution chamber.
13. The conveying screw according to claim 12 wherein the apertured end of the pipe forms a first fluid chamber therein whereas the outer shaft forms a second fluid cham-ber, about the pipe in fluid flow communication with a flight.
14. The conveying screw according to claim 1 wherein the proximal end is registered to a source of fluid.
15. The conveying screw according to claim 1 wherein the conveying screw is registered to means for rotating the conveying screw.
16. The conveying screw according to claim 15 wherein the distal end is registered to the means for rotating the conveying screw.
17. The conveying screw according to claim 1 wherein a second bulkhead spans the interior of the outer shaft, the second bulkhead including a first aperture in fluid flow communication with the void and a second aperture in fluid flow communication with the inner tube.
18. The conveying screw according to claim 17 wherein a third chamber is disposed at the distal end of the screw, the third chamber in fluid flow communication with the apertures.
19. The conveying screw according to claim 18 wherein the means for removing the fluid from the screw includes a second pipe affixed to distal end of the screw, one end of the second pipe registered with the inner tube and the third chamber.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000518680A CA1310184C (en) | 1986-09-19 | 1986-09-19 | Conveying screw for furnace |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000518680A CA1310184C (en) | 1986-09-19 | 1986-09-19 | Conveying screw for furnace |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1310184C true CA1310184C (en) | 1992-11-17 |
Family
ID=4133981
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000518680A Expired - Fee Related CA1310184C (en) | 1986-09-19 | 1986-09-19 | Conveying screw for furnace |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1310184C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2009379A1 (en) * | 2006-04-06 | 2008-12-31 | Nippon Steel Engineering Co., Ltd. | Screw conveyor for discharging reduced iron from rotary hearth reduction furnace |
-
1986
- 1986-09-19 CA CA000518680A patent/CA1310184C/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2009379A1 (en) * | 2006-04-06 | 2008-12-31 | Nippon Steel Engineering Co., Ltd. | Screw conveyor for discharging reduced iron from rotary hearth reduction furnace |
| EP2009379A4 (en) * | 2006-04-06 | 2013-03-06 | Nippon Steel Eng Co Ltd | Screw conveyor for discharging reduced iron from rotary hearth reduction furnace |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |