WO2000053818A1

WO2000053818A1 - Combined separation device of rotary drum cooler and stationary magnetic separator

Info

Publication number: WO2000053818A1
Application number: PCT/US2000/005114
Authority: WO
Inventors: David W. Rierson; Philip H. Straub
Original assignee: Svedala Industries, Inc.
Priority date: 1999-03-08
Filing date: 2000-02-29
Publication date: 2000-09-14
Also published as: AU3384000A

Abstract

A combined cooling device and magnetic separator for cooling a heated product stream and removing a magnetic material from the product stream is useful in the production of direct reduced iron (DRI). The combined cooling device and magnetic cooling device and magnetic separators includes a rotating, inclined separating drum (32) that receives the heated product stream at a temperature above the Curie temperature for the magnetic material contained within the product stream. A coolant distribution system (28) cools the product stream to a temperature below the Curie temperature for the magnetic material. A magnetic yoke (58) extends around a portion of the rotating separating drum and removes the magnetic material from the product stream. The magnetic material is collected in a collecting device (66) that directs the magnetic material away from the non-magnetic material contained in the product stream.

Description

WO 00/53818 PCTtUSOO/05114

COMBINED SEPARATION DEVICE OF ROTARY DRUM COOLER AND STATIONARY MAGNETIC SEPARATOR

The present invention relates to the conversion of iron-ore pellets or lumps into metallic iron suitable as feed material for making steel. More specifically, the present invention relates to a combined cooling device and magnetic separator useful in the production of direct reduced iron (DRI).

Direct reduction of iron from iron-ore involves heating the ore to elevated temperatures substantially exceeding the Curie temperature of iron, which is approximately between 700° C and 800°C. At such elevated temperatures, and under the influence of a reducing atmosphere, the ferrous component of the ore is reduced into high-grade metallic iron pellets or lumps that are suitable as feed material for electric furnaces for making steel.

In the scheme of producing DRI, there is often a desire to hot briquette the DRI for the purposes of shipping, storage and handling. Additionally, it is oftentimes desirable to supply the heated DRI to a downstream electric arc furnace for downstream steel making for reasons of energy conservation. Hot briquetting is a proven technology and is a system that is used in combination with the direct reduction process. Typically, hot briquetting is used only with natural gas-based direct reduction processes, and not with direct reduction processes using lump coal as a fuel for reduction and heating. Gas-based direct reduction processes produce a DRI product that does not include any discrete pieces of gangue or undesirable solids in the product stream. The product of gas-based direct reduction processes is, therefore, well-suited for hot briquetting at elevated temperatures (600°C to 700°C) since the gas-based procedure does not simultaneously encapsulate the undesirable gangue materials inside the briquette along with the DRI.

In a DRI process utilizing lump coal as the reductant, the iron-ore is typically reduced in a rotary kiln and a portion of the coal-based direct reduction process product stream includes unbumed carbon and ash from the virgin coal feed. All of the carbon from the coal feed and its attendant ash is not entirely consumed in the coal-based direct reduction process. The unbumed coal, or char, dilutes the quality of the DRI unless the char is removed from the product stream. If it is desired to hot briquette the product produced by coal-based direct reduction or if it is desired to hot charge the DRI directly into an electric arc furnace for downstream steel making, the char should be removed from the product stream prior to subsequent processing.

One method for removing the char from the product stream is to use a magnetic separator to remove the magnetic DRI from the non-magnetic char in the product stream. However, in most kiln-based direct reduction processes that reduce iron-ore with lump coal, the kiln's solid discharge is at a temperature above 1000°C. Therefore, the product stream must be substantially cooled by an industrial cooler to a temperature that allows the product stream to be handled with standard rubber conveyor belting and/or other types of material handling means. Typically, the DRI product stream is cooled by the cooler to a temperature in the range of 100°C to

200°C. After the product stream has been cooled, dry magnetic separation is used to separate the DRI (magnetic) from the char (non-magnetic).

In typical coal-based direct reduction systems, separate coolers and magnetic separators must be positioned downstream from the rotary kiln in which the iron-ore is reduced. Additionally, since the temperature of the product stream must be greatly reduced prior to the magnetic separation, large amounts of heat are required to re-elevate the temperature of the separated DRI when the DRI is fed into a downstream electric arc furnace for making steel.

Therefore, it is an object of the present invention to provide a combined cooling device and magnetic separator that can be used to separate reduced iron from char or other non-magnetic contaminants. It is a further object of the invention to provide an apparatus that cools the direct reduced iron and magnetically separates the iron while the iron is within the cooler. It is a further object of the invention to provide a method of processing pellet or lump ore and magnetically removing the reduced iron.

SUMMARY OF THE INVENTION The present invention is a combined cooling device and magnetic separator for cooling a product stream and removing a desired magnetic metal material from the product stream. The combined cooling device and magnetic separator of the invention includes a rotating separating drum that extends between an infeed end and a discharge end. The separating drum is generally defined by a cylindrical shell. A heated product stream is received at the infeed end of the separating drum and proceeds through the separating drum to the discharge end. The temperature of the product stream at the infeed end of the separating drum is above the Curie temperature for the metallic material contained in the product stream, such that the metallic material in the product stream is non-magnetic at the infeed end.

A coolant distribution system is positioned to indirectly cool the product stream as the product stream travels downstream through the separating drum. The coolant distribution system distributes a supply of coolant over the shell of the separating drum. The shell of the separating drum conducts heat from the product stream to the coolant, such that the coolant can remove heat from the product stream. As the product stream moves downstream through the separating drum, the coolant reduces the temperature of the product stream below the Curie temperature of the metallic material to be removed, such that the metallic material in the product stream becomes magnetic.

A magnetic member is positioned in a spaced relationship to the outer shell near the discharge end of the separating drum such that the magnetic member can pull the metallic material from the product stream. Preferably, the magnetic member is a magnetic yoke having an arcuate shape that extends around at least a portion of the circumference of the separating drum. As the separating drum rotates, the magnetic yoke pulls the magnetic material from the product stream into contact with the inner circumferential surface of the shell. When the magnetic metallic material rotates past the first end of the magnetic yoke, the magnetic material leaves the influence of the magnetic yoke and falls into a collecting device.

The collecting device is positioned below the first end of the magnetic yoke such that the magnetic material falls into the collecting device. Preferably, the collecting device is an inclined collection bin that directs the collected magnetic material out of the separating drum for downstream processing. The portion of the product stream containing non-magnetic material leaves the discharge end of the separating drum and is processed downstream accordingly.

Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the best mode presently contemplated of carrying out the invention.

In the drawings: Fig. 1 is a schematic illustration of an iron-ore direct reduction processing system including a combined cooling device and magnetic separator of the present invention;

Fig. 2 is a perspective view of the combined cooling device and magnetic separator of the present invention;

Fig. 3 is a partial section view taken along line 3-3 of Fig. 2 illustrating the magnetic separation of direct reduced iron; and

Fig. 4 is a section view taken along line 4-4 of Fig. 3 illustrating the magnetic separation of direct reduced iron in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 illustrates a direct reduction system 10 used to process a wide variety of lump ores or pellets to produce a uniform, direct reduced iron (DRI), or sponge iron. The direct reduction system 10 generally receives a supply of ore from a traveling grate 12. The iron-containing ore is combined with a supply of coal 13 as it enters into a rotary kiln 16. The iron-ore and coal are continuously fed into upstream end 18 of the rotary kiln 16 and are conveyed through the rotary kiln 16 while the ore is thermochemically reduced. A combination air fan 17 and start-up burner 19 starts a cold reduction system. Once the system reaches the processing temperature, the use of the burner 19 is discontinued. The rotary kiln 16 includes an air supply means 20 that supplies overbed air into the rotary kiln 16 to further support combustion within the kiln, and maintain the desired processing temperature.

After passing through the rotary kiln 16, a product stream of metalized iron and coal ash, or char, exits downstream end 22 of the rotary kiln 16 and enters into a discharge housing 24. The product stream leaving the rotary kiln 16 is discharged into the discharge housing 24 at a temperature typically greater than 1000°C. At this temperature, the DRI contained in the product stream is nonmagnetic, since the temperature of the product stream is above the Curie temperature for the directly reduced iron.

In accordance with the present invention, a combined cooling device and magnetic separator 26 receives the heated product stream from the discharge housing 24. The combined cooling device and magnetic separator 26 includes a coolant distribution system 28 that cools the product stream within the cooling device and magnetic separator 26 to a temperature below the Curie temperature of the DRI. Preferably, the product stream is cooled to between approximately 700°C and 800°C. At this temperature, the DRI within the product stream becomes magnetic. A magnetic member 30 separates the DRI from the non-magnetic material within the product stream. The separated hot DRI can then be processed downstream as required, while the non-magnetic material can be discarded or further processed as required.

Fig. 2 further illustrates the combined cooling device and magnetic separator 26 of the present invention. The combined cooling device and magnetic separator 26 generally includes a separating drum 32 extending along a slightly inclined longitudinal axis 33 (Fig. 3) between an infeed end 34 and a discharge end 36. The separating drum 32 is defined by a generally cylindrical shell 38 that defines a hollow, open interior 40, as shown in Figs. 3 and 4. In the preferred embodiment of the invention, the cylindrical shell 38 is formed from unlined steel and has a length and a diameter designed to accommodate a specific throughput and achieving the appropriate amount of product cooling. As best seen in Fig. 1 , the separating drum 32 slopes downwardly from the infeed end 34 to the discharge end 36. Thus, the force of gravity urges the product stream received at the infeed end 34 from the discharge housing 24 to flow through the separating drum 32 from the infeed end 34 to the discharge end 36. In addition to being sloped, the separating drum 32 rotates (shown counter-clockwise) about its longitudinal axis 33, as illustrated by arrows 42 in Figs. 2 and 4. The combination of the slope of the separating drum 32 and the rotation of the separating drum 32 urges the product stream to move from the infeed end 34 to the discharge end 36.

As previously discussed, the product stream entering the separating drum 32 at the infeed end 34 is at an elevated temperature above the Curie temperature for DRI. For example, in a contemplated embodiment of the invention, the product stream entering through the infeed end 34 is typically at a temperature of greater than 1000°C. As the product stream including the DRI flows through the separating drum 32, the coolant distribution system 28 operates to cool the product stream below the Curie temperature.

The coolant distribution system 28 generally includes a supply tube 44 connected to a supply of coolant. Coolant, such as water, passes from the supply tube 44 into a distribution tube 46 that generally extends axially above the separating drum 32. The distribution tube 46 includes a plurality of openings 48 spaced along the length of the distribution tube 46 that allows the coolant to be distributed onto exterior surface 50 of shell 38. In this manner, the coolant wets the outer surface of shell 38 of the separating drum 32. As the product stream passes through the separating drum 32, the product stream is cooled by conduction of heat through shell 38 of the separating drum 32. In the preferred embodiment of the invention, the shell 38 is formed from unlined steel such that heat can easily be conducted through the shell 38. As the separating drum 32 rotates, the hot solids contained in the product stream contact the inner surface of shell 38 and heat is transmitted through shell 38 to the coolant. After the coolant from the coolant distribution system 28 passes over the shell 38 and absorbs heat from the product stream, the coolant is collected in a series of collection troughs 52. Each collection trough 52 includes a sloped inner surface 53 and a drainpipe 54 that directs the coolant to a cooling tower or heat exchanger in which the heat can be removed from the coolant. After the heat has been removed from the coolant, the coolant is again recirculated through the supply tube 44 and distribution tube 46 and applied to shell 38.

As the product stream proceeds downstream from the infeed end 34 to the discharge end 36 of the separating drum 32, the temperature of the product stream when it reaches the discharge end 36 can be controlled by the flow rate of the coolant through the distribution tube 46 and the rotational speed of the separating drum 32. For example, increasing the rotational speed of the separating drum 32 decreases the amount of time the product stream is within the separating drum 32, thus increasing the temperature at the discharge end 36. Likewise, increasing the flow rate of the coolant increases the amount of heat removed from the product stream, thus decreasing the temperature at the discharge end 36. In the preferred embodiment of the invention, the combined cooling device and magnetic separator 26 functions to reduce the temperature of the product stream to a temperature below the Curie temperature of DRI (approximately 700°C to 800°C) when the product stream nears the discharge end 36. Referring now to Figs. 2-4, the magnetic member 30 positioned near the discharge end 36 of the separating drum 32 functions to separate the magnetic DRI 54 from the non-magnetic materials contained within product stream 56. In the preferred embodiment of the invention, the magnetic member 30 is a stationary magnetic yoke 58 having a generally arcuate shape. The magnetic yoke 58 includes an arcuate inner surface 59 spaced from shell 38 of the rotating separating drum 32. The arcuate inner surface 59 of the magnetic yoke 58 is spaced such that the strength of the magnetic field has an influence on the magnetic material contained in the separating drum 32. This distance may vary depending on the strength of the magnetic yoke 58. In the preferred embodiment of the invention, the magnetic yoke 58 is formed from a permanent magnet, although an electromagnet is contemplated as being an alternate embodiment of the invention. As can be seen in Fig. 4, the magnetic yoke 58 has an arcuate shape extending between a first end 60 and a second end 62. The magnetic yoke 58 extends around less than half of the outer circumference of shell 38. Specifically, the first end 60 of the magnetic yoke 58 is spaced in a clockwise direction (in the example illustrated) from the a vertical plane 63 that extends through the longitudinal axis of rotation 33 for the separating drum 32. In the preferred embodiment of the invention, the first end 60 of the magnetic yoke 58 is spaced between 10 and 25 degrees from the vertical plane 63. It should be understood that if the separating drum 32 rotates in the opposite, clockwise direction, the first end 60 would then be spaced from the vertical plane 63 in the counterclockwise direction.

As the separating drum 32 rotates, as indicated by arrow 42, the product stream 56 rotates past the second end 62 of the magnetic yoke 58. The magnetic yoke 58 pulls any magnetic material 54 in the product stream 56 into contact with the inner circumferential surface 64 of shell 38. Since the temperature of the product stream 56 near the discharge end 36 of the separating drum 32 has been cooled below the Curie temperature of DRI, the DRI 54 becomes magnetic and is attracted by the magnetic yoke 58. As the separating drum 32 continues to rotate, the magnetic yoke 58 holds the DRI 54 in contact with the inner circumferential surface 64, while the non-magnetic material remains in the bottom of the separating drum 32. In this manner, the combination of the rotating separating drum 32 and magnetic yoke 58 lift the DRI 54 out of the product stream 56.

As the separating drum 32 continues to rotate, the DRI 54 reaches the first end 60 of the stationary magnetic yoke 58. Since the magnetic yoke 58 terminates at the first end 60, the magnetic influence of the magnetic yoke 58 is terminated when the DRI 54 rotates past the first end 60. After rotating past the first end 60, the DRI 54 drops from the inner circumferential surface 64 into a collecting device 66. As can best be seen in Fig. 3, the collecting device 66 is a collection bin 68 having a back wall 70 spaced axially inward from the magnetic yoke 58. The collection bin 68 includes an inclined bottom wall 72 that is connected to a discharge chute 74. The discharge chute 74 directs the collected DRI 54 out of the separating drum 32 for downstream processing, as required. As seen in Fig. 4, the outer wall 75 of the collection bin 68 extends past the vertical plane 63 to insure that the separated DRI is collected, since the rotational inertia of the DRI 54 may carry the DRI 54 past the vertical plane 63. Typically, the heavy DRI 54 falls almost immediately from the inner circumferential surface 64 after passing the first end 60 or the magnetic yoke 58. The non-magnetic materials remaining in the product stream 56 after the

DRI 54 has been removed by the magnetic member 30 discharge out of the end of the separating drum 32 into a separate handling system for subsequent disposition.

By using the combined cooling device and magnetic separator 26 of the present invention, DRI can be removed from the product . After the DRI has been removed from the product stream, the DRI can be processed downstream. Since the temperature of the DRI as it is removed from the product stream is at a relatively high temperature, downstream processing can take place without injecting substantial additional heat into the DRI.

Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.

Claims

CLAIMS We claim:

1. A combined cooling device and magnetic separator for removing a magnetic material from a heated product stream also including non-magnetic materials, the device comprising: a separating drum having a generally cylindrical shell extending between an infeed end and a discharge end, the infeed end receiving the heated product stream; a coolant distribution system operable to indirectly cool the heated product stream as the product stream passes from the infeed end to the discharge end of the separating drum; a magnetic member spaced from the shell near the discharge end of the separating drum, the magnetic member separating the magnetic material from the product stream; and a collection device positioned within the separating drum near the discharge end, the collection device receiving the magnetic material separated by the magnetic member.

2. The device of claim 1 wherein the separating drum is axially inclined and axially rotatable, such that product stream is directed from the infeed end to the discharge end.

3. The device of claim 2 wherein the magnetic member is stationary relative to the rotatable separating drum.

4. The device of claim 3 wherein the magnetic member is a permanent magnet.

5. The device of claim 4 wherein the magnetic member is an arcuate magnetic yoke extending around and spaced from a portion of the shell of the separating drum.

6. The device of claim 5 wherein the magnetic yoke terminates at a first end, the first end of the magnetic yoke being positioned above the collection device.

7. The device of claim 6 wherein the first end of the magnetic yoke is circumferentially spaced from a vertical plane passing through a longitudinal axis for the separating drum.

8. The device of claim 5 wherein the magnetic yoke is radially spaced from the shell of the separating drum a distance such that the magnetic yoke holds the magnetic material in contact with the shell against the force of gravity as the separating drum rotates.

9. The device of claim 1 wherein the coolant distribution system distributes a supply of coolant into contact with the shell of the separating drum such that the supply of coolant removes heat from the product stream.

10. The device of claim 9 wherein the coolant distribution system cools the product stream to a temperature below the Curie temperature of the magnetic material.

11. The device of claim 1 wherein the collection device is an inclined bin that directs the collected magnetic material out of the separating drum.

12. A combined cooling device and magnetic separator for removing a magnetic material from a heated product stream also including non-magnetic materials, the device comprising: a rotating separating drum extending between an infeed end and a discharge end, the separating drum having a generally cylindrical shell, the infeed end receiving the heated product stream at a temperature above the Curie temperature for the magnetic material; a coolant distribution system operable to indirectly cool the product stream to below the Curie temperature for the magnetic material as the product stream passes from the infeed end to the discharge end of the separating drum; a stationary magnetic yoke extending between a first end and a second end, the magnetic yoke positioned to surround at least a portion of the outer shell near the discharge end of the separating drum, wherein the magnetic yoke is spaced from the shell and pulls the magnetic material from the product stream into contact with the rotating shell of the separating drum; and a collection device positioned within the separating drum at the discharge end, the collecting device receiving the magnetic material separated by the magnetic yoke.

13. The device of claim 12 wherein the magnetic yoke is formed from a permanent magnet.

14. The device of claim 13 wherein the magnetic material is iron and the product stream is cooled by the coolant distribution system to a temperature between 700°C and 800°C.

15. The device of claim 12 wherein the collecting device is positioned below the first end of the magnetic yoke.

16. The device of claim 12 wherein the magnetic yoke extends around less than 180° of the shell.

17. A method of separating a magnetic material from a heated product stream including both the magnetic material and non-magnetic materials, the method comprising the steps of: receiving the heated product stream at an infeed end of an inclined separating drum having a generally cylindrical shell; moving the product stream from the infeed end to a discharge end of the separating drum; cooling the product stream as the product stream moves between the infeed end and the discharge end of the separating drum; magnetically separating the magnetic material from the product stream near the discharge end of the separating drum; and WO 00/53818 PCTVUSOO/05114

collecting the separated magnetic material and discharging the magnetic material from the separating drum.

18. The method of claim 17 wherein the step of cooling the product stream includes distributing a supply of coolant into contact with the shell of the separating drum.

19. The method of claim 17 wherein the step of magnetically separating the magnetic material from the product stream includes the steps of: rotating the separating drum; and positioning an arcuate magnetic yoke around a portion of the shell near the discharge end of the separating drum, wherein the magnetic material is pulled into contact with the shell by the magnetic yoke.

20. The method of claim 19 wherein the step of collecting the magnetic material includes positioning a collection bin below a first end of the magnetic yoke, such that the separated magnetic material falls into the collection bin after rotating passed the first end of the magnetic yoke.

21. The method of claim 17 wherein the product stream received at the infeed end of the separating drum is above the Curie temperature for the magnetic material contained in the product stream and the step of cooling the product stream comprises cooling the product stream below the Curie temperature for the magnetic material prior to the magnetic separation.

22. The method of claim 21 wherein the magnetic material is iron and the product stream is cooled to a temperature between 700°C and 800°C prior to the magnetic separation.

23. The method of claim 21 further comprising the steps of: positioning an arcuate magnetic yoke around a portion of the shell near the discharge end of the separating drum; magnetically attracting the magnetic material out of the product stream and into contact with the shell; and rotating the magnetic material past a first end of the magnetic yoke to terminate the magnetic attraction between the magnetic yoke and the magnetic material, thereby causing the magnetic material to fall into a collection bin.