US3850616A

US3850616A - Inert gas seal for product discharge from a shaft furnace

Info

Publication number: US3850616A
Application number: US00410876A
Authority: US
Inventors: C Cruse
Original assignee: Armco Inc
Current assignee: Armco Inc
Priority date: 1973-10-29
Filing date: 1973-10-29
Publication date: 1974-11-26
Anticipated expiration: 1991-11-26

Abstract

Method and apparatus for the gaseous treatment of particulate material in a gravity feed shaft furnace having a preheating zone, a heated reaction zone, a cooling zone and a product discharge zone. Heated reactive gas is introduced into the reaction zone and cold reactive gas is introduced into the cooling zone. A cold inert gas is introduced intermediate the cooling and product discharge zones at a pressure equal to that of the cold reactive gas, thereby establishing an isobaric zone. The product discharge zone is maintained at atmospheric pressure so that by withdrawing inert gas as seal gas from the discharge zone, discharge of combustible and/or noxious gas with the product and loss of heat from the furnace are eliminated.

Description

United States Patent 1 Cruse, Jr.

[ Nov. 26, 1974 [22] Filed:

[ INERT GAS SEAL FOR PRODUCT DISCHARGE FROM A SHAFT FURNACE Clyde L. Cruse, Jr., Middletown, Ohio [73] Assignee: Armco Steel Corporation,

Middletown, Ohio Oct. 29, 1973 [21] App]. N0.: 410,876

[75] Inventor:

[52] US. Cl 75/34, 75/91, 266/20 [51] Int. Cl C21b 13/02 [58] Field of Search 75/26, 34, 35, 91; 266/20,

MATERIAL FEE D Primary Examiner-L. Dewayne Rutledge Assistant Examiner-M. J. Andrews Attorney, Agent, or Firm-Melvi1le, Strasser, Foster & Hoffman [57] ABSTRACT Method and apparatus for the gaseous treatment of particulate material in a gravity feed shaft furnace having a preheating zone, a heated reaction zone, a cooling zone and a product discharge zone. Heated reactive gas is introduced into the reaction zone and cold reactive gas is introduced into the cooling zone. A cold inert gas is introduced intermediate the cooling and product discharge zones at a pressure equal to that of the cold reactive gas, thereby establishing an isobaric zone. The product discharge zone is maintained at atmospheric pressure so that by withdrawing inert gas as sea] gas from the discharge zone, discharge of combustible and/or noxious gas with the product and loss of heat from the furnace are eliminated.

11 Claims, 1 Drawing Figure uor REACTIVE sAe COLD REACTIVE GAS INERT 6EAL (9A5 PRODUCT PATENTELNBVZSIQM cow REAQTIVE GAS HOT REACTIVE 6A9:

34 \NERT E-ZAL. eAs

MATERKAL FEED PROD UCT INERT GAS SEAL FOR PRODUCT DISCHARGE FROM A SHAFT FURNACE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and apparatus for the treatment of material in pelletized or particulate form in a gravity feed shaft furnace into the top of which the material is introduced for treatment by a reactive gas in an intermediate reaction zone, and more particularly to improvements relating to pressure control in a product discharge zone at the bottom of the furnace which eliminates discharge of reactive gas into the atmosphere and loss of heat from the furnace. Although not so limited, the invention has particular utility in the gaseous reduction of iron ores at elevated temperatures by reducing gas atmospheres. Iron ores in pelletized form or sized ore particles ranging, e.g. between about one-fourth inch and about 1% inch in diameter, can be treated in the method and apparatus of the invention. For convenience, the term sized ores will be used hereinafter to designate either beneficiated and pelletized iron ores or ores which have been comminuted and subjected to a screening operation for separation of particles within the above size range.

The invention is equally applicable to the reduction of ores in a system wherein the spent reducing gas is regenerated or reformed and reintroduced into the re- 7 duction zone of a shaft furnace as disclosed in US. Pat.

' has generally been cooled in a region above the discharge zone either by a cold. reactive gas introduced into a cooling zone in a stream which split and flowed both upwardly and downwardly within the furnace so that a part of the stream has been utilized as seal gas, or by an inert cold gas, all or part of which has been extracted at a seal gas discharge point. While the use of an inert gas is advantageous from the standpoint of preventing discharge to atmosphere of reactive gas, which may be combustible and/or toxic, the use of an inert gas has the disadvantages of removing heat from the furnace if all the gas is extracted at the seal gas discharge point, or of diluting the reactive gas if a portion of the inert gas stream flows upwardly in the furnace to recuperate the heat in the product.

The use of a cold reactive gas for cooling in the product discharge zone of a shaft furnace is disclosed, inter alia, in US. Pat. No. 3,369,888, issued Feb. 20, 1968 to Clyde L. Cruse, Jr. and U.S-. Pat. No. 3,749,386, is-

' sued July 31, 1973 to Donald Beggs et al. The use of an inert cooling gas is disclosed in US. Pat. No. 2,051,029, issued to Curtis and US. Pat. No. 3,601,381, issued to Donald Beggs.

In the above-mentioned US. Pat. No. 3,369,888 an isobaric zone is provided in an intermediate section of a shaft furnace between a first cooling zone and a reducing zone. The purpose of the isobaric zone is to prevent the mixing of air and gas entering the upper cooling zone with heated reducing gases employed in the reducing zone.

In the above-mentioned US. Pat. No. 3,749,386 provision is made to match substantially the flow of cooled spent reducing gas into the bottom of a cooling zone and the flow of this cooling gas withdrawn from the top of the cooling zone, in order to avoid interchange of gases between the reduction zone and the cooling zone of a shaft furnace. In the above-mentioned US. Pat. No. 3,601,381 an inertcooling gas flows upwardly from the bottom of the cooling zone at a pressure apparently substantially above atmospheric pressure since the pressure at the top of the cooling zone is the same as the pressure of reactive gases introduced into tuyeres in the reducing zone, which are ordinarily introduced at superatmospheric pressure. Accordingly, all the cooling gas is withdrawn through a discharge tube provided therefor under substantial pressure and in large volumes, thereby extracting substantial heat which is dissipated to atmosphere.

It is therefore apparent that the prior art has not suggested a product discharge system wherein the discharge of combustible and/or toxic gases to atmosphere, the loss of heat from the system and dilution of the reactive gas are avoided. Moreover, even where the use of an inert cooling gas has been suggested, large volumes of such gas are required, which result in removing heat from the shaft furnace and/or diluting the reactive gas in the reaction zone of the furnace.

SUMMARY It is a principal object of the present invention to provide a method and apparatus for use in a gravity feed shaft furnace wherein a relatively small flow of inert gas is exhausted from a discharge plenum as seal gas and wherein heat removed from the product in a cooling zone is retained and utilized within the furnace. Discharge of combustible and/or toxic gases, discharge of large volumes of gas of any type and loss of heat from the furnace are all eliminated in the method and apparatus of the present invention. In its broadest form the method comprises introducing a cold reactive gas into a cooling zone of a shaft furnace, introducing a cold inert gas intermediate the cooling zone and the product discharge zone, maintaining an isobaric zone in the furnace between the point of introduction of the cold reactive gas and the point of introduction of the cold inert gas, maintaining the product discharge zone below the point of introduction of the cold inert gas at a lower pressure than that of the isobaric zone, and withdrawing only cold inert gas through a product discharge plenum.

As applied to the gaseous reduction of sized iron ores in a gravity feed shaft furnace having in succession a top portion, a preheat zone, a reducing zone into which a hot reducing gas atmosphere is introduced, a cooling zone and a product discharge zone, the present invention comprises the combination of means for introducing a cold reducing gas into the cooling zone, means for introducing a cold inert gas intermediate the cooling zone and the product discharge zone, means for maintaining an isobaric zone intermediate the plane of introduction of the cold reducing gas and the plane of introduction of the cold inert gas, and means for withdrawing gas from the product discharge zone beneath the isobaric zone at a pressure lower than that of the isobaric zone.

BRIEF DESCRIPTION OF THE DRAWING Reference is made to the sole FIGURE which is a sectional diagrammatic view of a gravity feed shaft furnace embodying the apparatus of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawing, an enclosed gravity feed shaft furnace indicated generally at and having side walls 11 is provided with a conveyor or other conventional means 12 for feeding sized material to be treated through the enclosed top into a top portion 13. A column of material is established which descends by gravity progressively through a preheat zone indicated at 14, a reaction zone indicated at 15, a cooling zone indicated at 16 and a product discharge zone indicated at 17.

A heated reactive gas is introduced into the bottom of the reaction zone through an inlet 18 which may be tuyeres of conventional type. The hot reactive gas ordinarily will be introduced at super-atmospheric pressure.

A cold reactive gas is introduced into the cooling zone 16 through inlet 20, which may also be in the form of tuyeres of conventional type. product After passage through the cooling zone and product discharge zone 17 the treated material is removed by a conveyor belt or other conventional means 21 positioned beneath the discharge plenum 22, which communicates with the present discharge zone of the shaft furnace.

As indicated in the drawing the shaft furnace preferably tapers inwardly in the region of the cooling zone 16 to form a product discharge tube of relatively restricted cross-sectional area supporting the column of material.

Intermediate the cooling zone and the product discharge zone an inlet 25 is provided through which cold inert gas is introduced into the shaft furnace. Although not so indicated in the drawing, the cold inert gas can also be introduced through tuyeres or other conventional means.

As described hereinafter in detail, the pressure in the plane of introduction of the cold inert gas is maintained at the same value as the pressure in the plane of introduction of the cold reactive gas, thereby establishing an isobaric zone indicated at 26 between the horizontal lines A, B in the drawing.

The isobaric zone prevents intermixing of the cold reactive gas introduced through inlet with the cold inert gas introduced through inlet 25. Therefore, the cold reactive gas passes upwardly through the cooling zone, and heat exchange between the material and the gas occurs. The initially cold reactive gas will thus reach substantially the same temperature as that of the reaction zone by the time it passes upwardly into the reaction zone, and it therefore becomes hot reactive gas and is utilized in the treatment of the material.

In the discharge plenum 22 a zone 27 not occupied by the cooled product is maintained at atmospheric pressure, thereby insuring that the cold inert gas introduced through inlet is withdrawn through a seal gas discharge, indicated at 28. Accordingly, no pressure control, valve, or the like is required in the product discharge even though the isobaric zone 26 is maintained atssuper-atmospheric pressure in the preferred practice. The inert seal gas in thus merely vented to atmosphere or recycled to the cold inert gas inlet 25.

Since the product discharge tube 17 is of relatively small volume, it will be apparent that the flow of cold inert gas into the shaft furnace can be relatively small, and the consequent volume of inert seal gas vented through outlet 28 is relatively small. Moreover, since the cold reactive gas introduced through inlet 20 is utilized to effect all, or a great preponderance of, the cooling of the treated product, a large volume of cold inert gas is not needed for cooling purposes. In effect, the cold inert gas can thus be introduced in volumes sufficient only to maintain *the pressure at the point or plane of introduction the same as that at the point or plane of introduction of cold reactive gas, and to function as a seal gas in the discharge plenum.

The means for maintaining the isobaric zone 26 do not constitute a limitation on the invention, and any conventional means for controlling the pressure and/or flow rates of the cold reactive gas and/or cold inert gas may be used. By way of an exemplary showing, means for establishing an isobaric zone of the same type as those disclosed in the above-mentioned US. Pat. No. 3,369,888 are illustrated in the drawing. A differential pressure measurement means is indicated at 30, which is connected to and communicates with the interior of the shaft furnace by

tubes

31 and 32. Tube 31 communicates with the furnace in the plane of introduction of cold reactive gas while tube 32 connects with the furnace in the plane of introduction of cold inert gas. A pressure differential within

tubes

31 and 32 creates a signal in the differential pressure measurement means 30, which is communicated by means indicated at 33 to a valve operating device 34 having lever arms 34a operatively connected to a valve 35 in the cold inert gas inlet line 25. Thus, the flow rate of cold inert gas can be varied in response to a differential pressure measurement so as to increase or decrease the pressure at the bottom of the isobaric zone in accordance with variations in pressure at the top of the isobaric zone. If the cold inert gas is supplied from a compressed gas source, it will of course be recognized that a pressure regulator could be substituted in place of valve 35, ie the pressure of the gas introduced through inlet 25 could be varied without substantial variation in volume of gas introduced.

Although not necessary for proper operation, it is desirable as a precautionary measure to provide pressure control means at the gas seal outlet 28. Since this is maintained at atmospheric pressure a vacuum pump or ejector (not shown), a valve and pressure controller of the same type as elements 30-35 described above, may be provided in communication with outlet 28.

In a preferred embodiment of the method of the invention wherein sized iron ores are subjected to gaseous reduction in a gravity feed furnace having in succession a top portion, a preheat zone, a reducing zone, a cooling zone and a product discharge section, the ores are introduced into the top portion to establish a column descending downwardly by gravity. I-Iot reducing gas, comprising hydrogen and carbon monoxide, is introduced into the reducing zone at a temperature of about 700 to about 980 C- for passage upwardly through the ore column in the reducing and preheat zones. The spent reducing gas is withdrawn from the top portion of the furnace through discharge conduit 19, and the reduced ores which will have attained a temperature of about 650 to about 900 C in the reduction zone move gradually downwardly into the cooling zone. A cold reactive gas is introduced into the cooling zone through conduit at ambient temperature in a volume sufficient to cool the reduced ores to a temperature below the air reoxidation temperature. In so doing the cold reactive gas passes upwardly through the cooling zone and is heated to a temperature substantially the same as that of the ores in the reducing zone. It therefore becomes a hot reducing gas and aids in'the reaction in the reduction zone. The cooled reduced ores move gradually downwardly through the isobaric zone and into the product discharge zone. Cold inert gas is introduced at a rate and- /or pressure sufficient to maintain the isobaric zone intermediate the point of introduction of the cold reducing gas and the point of introduction of the cold inert gas. The cold inert gas passes downwardly through the column in the product discharge zone through the tube 17 to the discharge plenum 22, by reason of the lower pressure existing in the region 27, where it acts as a seal gas and is vented to atmosphere or recycled to cold inert gas inlet 25. No substantial heat transfer occurs, so that the temperature of the seal gas when vented or recycled is not excessive. The cooled product is removed from the bottom of the discharge plenum in conventional manner.

Modifications may be made without departing from the scope of the invention. Thus, although the above described embodiment provides means for controlling the pressure and/or flow rate of the cold inert gas in response to differential pressure measurement means, it will of course be recognized that means for controlling the pressure and/or flow rate of the cold reactive gas may be provided in place of or in addition to the control means for the cold inert gas.

From what has been said above, it will be apparent that the pressure of the isobaric zone will be maintained at a somewhat higher value than the pressure in the reduction and preheat zones in order to insure that the cold reactive gas passes upwardly through the column of material in the reduction and preheat zones. However, under certain conditions of operation it may be desirable at least temporarily to control the pressures at the cold reactive gas inlet and cold inert gas inlet in such manner as to cause a controlled flow at a relatively small rate in either direction through the isobaric zone. The term isobaric zone as used in the appended claims is therefore to be interpreted as including a controlled flow at a relatively small rate in either direction through the so-called isobaric zone.

If desired, the volume of cold reactive gas introduced into the furnace can be controlled so as to leave some heat in the product which would be removed by the cold inert gas.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for the gaseous treatment of sized material in a gravity feed shaft furnace having in succession a top portion, a preheat zone, a reaction zone, a cooling zone and a product discharge portion, said method including the steps of introducing material into said top portion to establish a downwardly descending column of material being treated, introducing hot reactive gas into said reaction zone for passsage upwardly through said column in said reaction and preheat zones, withdrawing spent reactive gas'from said top portion, introducing a cold reactive gas into said cooling zone, and withdrawing cooled treated material from said product discharge portion, the improvement which comprises introducing a cold inert gas intermediate said cooling zone and said product discharge portion, maintaining substantially the same pressure in said furnace at the point of introduction of said cold reactive gas and at the point of introduction of said cold inert gas whereby to create an isobaric zone therebetween, maintaining said product discharge portion below said point of introduction of said cold inert gas at a lower pressure than that of said isobaric zone, and withdrawing only cold inert gas from the lower pressure product discharge portion.

2. The method claimed in claim 1, wherein said isobaric zone is maintained at super-atmospheric pressure, and wherein said lower pressure product discharge portion is maintained at substantially atmospheric pressure.

3. The method claimed in claim 1, wherein the pressure in said isobaric zone is maintained at a higher value than that in said cooling, reaction and preheat zones, whereby to insure that said cold reactive gas passes upwardly through said column.

4. The method claimed in claim 3, wherein said cold reactive gas is heated by said material being treated in said cooling zone and passes upwardly into said reaction zone-at a temperature substantially the same as that of said reactive zone.

5. The method claimed in claim 1, wherein said cold reactive gas cools said material to substantially the same temperature as said cold inert gas.

6. The method claimed in claim 1, wherein said cold I cluding the steps of introducing the ores into said top portion to establish a columndescending downwardly by gravity, introducing hot reducing gas into said reducing zone for passage upwardly through the ore column in said reducing and preheat zones, withdrawing spent reducing gas from said furnace in said top portion, introducing a cold reducing gas into said cooling zone, and withdrawing reduced ore from said product discharge portion at a temperature below the air reoxidation temperature, the improvement which comprises introducing a cold inert gas intermediate said cooling zone and said product discharge portion, maintaining substantially the same pressure in said furnace at the point of introduction of said cold reducing gas and at the point of introduction of said cold inert gas whereby to create an isobaric zone therebetween, maintaining the product discharge portion below said point of introduction of said cold inert gas at a lower pressure than that of said isobaric zone, and withdrawing only cold inert gas from the lower pressure discharge portion.

8. The method claimed in claim 7, wherein said isobaric zone is maintained at super-atmospheric pressure, and wherein said lower pressure product discharge portion is maintained at substantially atmospheric pressure.

9. The method claimed in claim 7, wherein the pressure in said isobaric zone is maintained at a higher value than that in said cooling, reduction and preheat zones, whereby to insure that said cold reducing gas passes upwardly through said column.

reducing gas cools said reduced ore to a temperature below air reoxidation temperature, and wherein negligible volumes of said cold inert gas are withdrawn from said discharge portion.

Claims

1. IN A METHOD FOR THE GASEOUS TREATMENT OF SIZED MATERIAL IN A GRAVITY FEED SHAFT FURNACE HAVING IN SUCCESSION A TOP PORTION, A PREHEAT ZONE, A REACTION ZONE, A COOLING ZONE AND A PRODUCT DISCHARGE PORTION, SAID METHOD INCLUDING THE STEPS OF INTRODUCING MATERIAL INTO SAID TOP PORTION TO ESTABLISH A DOWNWARDLY DESCENDING COLUMN OF MATERIAL BEING TREATED, INTRODUCING HOT REACTIVE GAS INTO SAID REACTION ZONE FOR PASSAGE UPWARDLY THROUGH SAID COLUMN IN SAID REACTION AND PREHEAT ZONES, WITHDRAWING SPENT REACTIVE GAS FROM SAID TOP PORTION, INTRODUCING A COLD REACTIVE GAS INTO SAID COOLING ZONE, AND WITHDRAWING COOLED TREATED MATERIAL FROM SAID PRODUCT DISCHARGE PORTION, THE IMPROVEMENT WHICH COMPRISES INTRODUCING A COLD INERT GAS INTERMEDIATE SAID COOLING ZONE AND SAID PRODUCT DISCHARGE PORTION, MAINTAINING SUBSTANTIALLY THE SAME PRESSURE IN SAID FURNACE AT THE POINT OF INTRODUCTION OF SAID COLD REACTIVE GAS AND AT THE POINT OF INTRODUCTION OF SAID COLD INERT GAS WHEREBY TO CREATE AN ISOBARIC ZONE THERE BETWEEN, MAINTAINING SAID PRODUCT DISCHARGE PORTION BELOW SAID

4. The method claimed in claim 3, wherein said cold reactive gas is heated by said material being treated in said cooling zone and passes upwardly into said reaction zone at a temperature substantially the same as that of said reaction zone.

6. The method claimed in claim 1, wherein said cold inert gas further cools said material.

7. In a method for the gaseous reduction of sized iron ores in a shaft-type furnace having in succession a top portion, a preheat zone, a reducing zone, a cooling zone and a product discharge portion, said method including the steps of introducing the ores into said top portion to establish a column descending downwardly by gravity, introducing hot reducing gas into said reducing zone for passage upwardly through the ore column in said reducing and preheat zones, withdrawing spent reducing gas from said furnace in said top portion, introducing a cold reducing gas into said cooling zone, and withdrawing reduced ore from said product discharge portion at a temperature below the air reoxidation temperature, the improvement which comprises introducing a cold inert gas intermediate said cooling zone and said product discharge portion, maintaining substantially the same pressure in said furnace at the point of introduction of said cold reducing gas and at the point of introduction of said cold inert gas whereby to create an isobaric zone therebetween, maintaining the product discharge portion below said point of introduction of said cold inert gas at a lower pressure than that of said isobaric zone, and withdrawing only cold inert gas from the lower pressure discharge portion.

10. The method claimed in claim 9, wherein said cold reducing gas is heated by said ores in said cooling zone and passes upwardly into said reduction zone at a temperature substantially the same as that of said reduction zone.

11. The method claimed in claim 7, wherein said cold reducing gas cools said reduced ore to a temperature below air reoxidation temperature, and wherein negligible volumes of said cold inert gas are withdrawn from said discharge portion.