US3802872A - Counter-current reaction method - Google Patents

Abstract

A counter-current reaction between two fluids of different specific gravities is produced in a rotating drum having an inwardly directed flange at its top with a central opening therein and having discharge passages opening into the interior through the bottom adjacent the wall of the drum. The drum rotates about a vertical axis. A heavier fluid such as molten iron containing sulphur is introduced into the drum close to the top thereof but below such flange, and a material of lower specific gravity such as a desulphurizing agent is introduced into the drum near the bottom. The two flow in counter-current to each other the length of the drum. The treated iron is discharged through an outlet passage in the bottom end and the slag spills over the edge of the opening in the flange at the top.

Description

I United States Patent 1 [111 3,802,872 Ostberg Apr. 9, 1974 COUNTER-CURRENT REACTION METHOD Primary E \'aminerCharles N. Lovell [76] Inventor: Jan Erik ostberg, Torps sated Assistant E.\'ammerPeter D. Rosenberg Bettna, Sweden [22] Filed: May 10, 1972 [57] ABSTRACT [21] Appl. No.: 252,087 A counter-current reaction between two fluids of different specific gravities is produced in a rotating drum Related Apphcauon Data having an inwardly directed flange at its top with a Continuation-mp3" of 797,124 6, central opening therein and having discharge passages I969- abmdoned' 7 opening into the interior through the bottom adjacent w the wall of the drum. The drum rotates about a verti' [52] L33. (1|. 75/93, 75/53, 75/61 Cal axis A heavier f d h as molten iron Contaim [51] II". C] C22!) 9/00, C216 7/02 m Sulphur is introduced into the drum close to the [58] Field 0' Search 75/53, 61, 93, 58 p thereof but below such flange and a material of lower specific gravity such as a desulphurizing agent is [56] Re'erences C'ted introduced into the drum near the bottom. The two UNITED STAT S P TE S flow in counter-current to each other the length of the 2,622,977 12/1952 Kalling 75/6l rum. The treated iron is discharged through an outlet 3,653,879 4/1972 Wienert 75/93 passage in the bottom end and the slag spills over the 3,715,202 2/1973 Kosmider.. 75/58 edge of the opening in the flange at the top. 3,592,629 7/l97l Ando 75/58 3 Claims, 3 Drawing Figures COUNTER-CURRENT REACTION METHOD RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 797,124, filed Feb. 6, 1969, and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for carrying out metallurgical processes with counter-current flow of the reactants.

2. The Prior Art A chemical or metallurgical reaction means a change in chemical composition of the participating phases, starting from a state of nonequilibrium. The inherent tendency of reestablishing equilibrium brings about a transport of material within the bulk of the phases to the interfaces between the phases where the respective elements are transferred. It is selfevident that the procedure would be promoted if it were possible to maintain as much nonequilibrium to the end of the process as possible. The natural means of doing this is to arrange a continuous flow of the participating phases in counter-current.

This is a well-known fact. In processes where a gas is the main reactant such a counter-current flow has also been put into effect. An example of this is the blast furnace process and other processes for the reduction or ore in shaft furnaces. In classical metallurgical methods a flow during the actual procedure is a rare thing. It is true that methods have been invented for pouring one phase into another or for stirring molten phases, or to bring a phase into some predescribed pattern of flow.

All these things contribute to improved final results but even in the best of these set-ups the continuous rearrangement of the chemical equilibrium which distinguishes the process with counter-current flow of the reactants can be obtained only to a small degree.

When it comes to systems where even non-gaseous phases play a major role in the process, the call for counter-current processes has been simultaneous with the trend towards continuous processes. A more or less steady flow is a distinguishing feature of continuous operations and it becomes natural to investigate in this connection whether a counter-current flow could be arranged.

In a number of proposals for such processes a metallic phase is brought to flow in channels which are slightly inclined. The reactants, which form a lighter phase may be brought to flow substantially in the opposite direction if they are charged in the end where the metallic phase is discharged and forced to flow in the opposite direction by means of barriers of some sort.

Another approach is to bring the metallic phase into an uphill flow because of the forces from electromagnetic fields and to charge the non-metallic reactants in the top end, where the metallic phase is discharged. The non-metallic reactants, which are not influenced by the electromagnetic field, because of the force of gravity flow counter to the current of the metallic phase.

A closer look at systems of this type will reveal shortcomings. One such is that the flow is rather slow, whereas it is well known that transferral particularly in the boundary layers is very much favored by rapid flow. In addition to that, the slow flow will cause a need for more space of the apparatus. Another disadvantage is that the depth of the liquid layers in systems such as these is bound to be large, which increases the distance over which material has to be transported and also diminishes the relative interfaces.

It is in fact not very easy to arrange an exact countercurrent. It is impossible to make the flows sufficiently uniform. There will be regions of a flow backward within the phases and so forth.

SUMMARY OF THE INVENTION The object of the present invention is to overcome or to improve upon the shortcomings of the processes for counter-current flow of reactants so far proposed or used. The method according to this invention utilizes as the driving force for the flow the field of force created by the centrifugal force and to some degree the force of gravity.

The method is most easily carried out in a vessel, which rotates about a vertical axis. When two or more fluid phases either liquid or fluid because of small grain size are brought into rotation within such a vessel, separate layers of each phase are formed, whereby the heaviest phase is closest to the periphery of the vessel and the lightest phase is innermost. A pressure is created in the liquid layers. This pressure is a function of the speed of rotation amd may at a high number of rotations be as high as wanted. Although the force of gravity may be utilized in order to control parts of the flow, flow may also take part in a direction opposite to the direction of the force of gravity when the centrifugal force because of the rotation exceeds that force. This means that it is possible to choose the direction of flow by means of proper location of charging and discharging means.

Now, if one phase, for example the heavy phase, is charged in at the top of the vessel and discharged in at the bottom of the vessel and the lighter phase or phases are created by material charged in at the bottom of the vessel and discharged at the top of the vessel, the phases pass by each other in counter-current. The control of the flow is performed by means of control of the rate of charging and discharging. The velocity of the flow may thus be at will very high, the thickness of the layers may be extremely low, if that is desired. It is true that two layers may not make exactly the same travel in opposite directions but there will be no backward flow in any of the layers. The heavy phase travelling upwards and the light downwards would also give a counter-current picture.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 shows in cross-section an apparatus for carrying out the invention;

FIG. 2 is a detail of a modification of a part of FIG. 1; and

FIG. 3 shows a modification of another part of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method will now be described in closer detail with reference to the apparatus schematically represented in FIG. 1.

A bottom part 1 l is fixed to a cylindrical rotating part 12. A charging apparatus 13 extends through the middle of the roof 14 of the drum. The roof is fixed to the furnace chamber and rotates along with it at the same speed. The charging device consequently also rotates with the furnace chamber. The furnace chamber proper is cut off by an inwardly extending flange 15. This flange prevents the liquid metal from being thrown out upwards. The shell is surrounded by a rigid ring 16 supported by three or more driving wheels 17. The chamber is shown cylindrical. However, where the material from the charging device hits the side-walls at a great speed, it may be desirable to expand the furnace diameter somewhat, partly because it may be helpful to increase by this means the hydrodynamic pressure and partly because the flow pattern in the liquid here may be regulated with greater ease in this way. It may also be advantageous to make the drum conical, for instance with an inner diameter which diminishes downwards. This change in horizontal section of the chamber may be gradual and uniform or may be concentrated in limited areas. The normal form of the horizontal section is circular.

The charging device 23 is preferably made of ceramic material. Thisis normal though by no means necessary. The ceramic refractory material is reinforced by pipes 19 through which air or some other medium is blown for cooling. The cooling medium is transferred from a non-rotating casing 20, which communicates with a carefully machined protecting shell 21 around the charging device with which pipe 19 communicates. When the heat stresses are not excessive, the charging device may merely be just a cooled steel structure with perhaps a protective coating of ceramic material.

The liquid to be treated is charged from for instance trough 22 into the funnel 23 in the top of the charging devicev That funnel is the end part of a large central pipe 24. This pipe 24 ends at the bottom in a pumping device, which throws the liquid out substantially horizontally. The passages 25 which constitute this centrifugal pump may also be directed somewhat upwards or downwards, which is an efficient means of regulating the flow pattern in this mixing and reaction area.

The pipe 26 indicates a pneumatic device for charging fluidised solid material such as fine ore or for the addition of reactants or additives. The pipe 26 may substitute pipe 24 and passages 25 in reduction processes. The pressure casing. 27 is used for this purpose. According to FIG. 1, this pipe opens into one of the channels 25 forming the centrifugal pump. The openings from this device may however also end at a lower level or even higher (see passage 27' in FIG. 2). The use of different heights for different charging passages or jets, the inclinations and number of the channels can be varied to provide a great number of regulating factors for the control of the mixing and reaction zone.

In one particular case blast furnace hot metal is treated in the drum in order to reduce its sulphur conat its lower end in a pumping device, which brings the iron out substantially horizontally.

At its lower end of the drum a pipe passes through the central hole 31 in the bottom. The bottom wall 32 extends inwardly towards the hole 31 further than the point at which the pipe 32 discharges into the bottom of the drum. Likewise, hole 31 is of less diameter than the opening in flange 15. This pipe is the means for introducing pneumatically transported sodium, which in this particular case is the desulphurizing agent. Because of the pressure of the transporting air the effect of the discharging jets and the effect of the carbon dioxide released from the sodium, a vigorous stirring takes place in front of the jets. The sodium is rapidly melted and ready for reaction with the iron.

The iron forms a molten layer next to the side wall of the drum and upon this layer a layer of sodium slag is carried. The iron travels downwards where it is discharged from the drum through the outlet channels 29. Each channel has an opening 29a into the drum adjacent to the side wall of the drum or even projecting somewhat into the wall. The outlet channels may directed to give a turbine effect. The outlet may of course be arranged in other and simpler ways but there are several advantages from this arrangement. Because of the centrifugal force acting upon the liquid in the radial part of each outlet channel, the flow rate in the outlet channels is retarded and a great part (and in many cases the greatest part) of the pressure created because of the rotation is counteracted. This makes it possible to use larger and more practical cross-sections for the channels 29. Again, the centrifugal effect generates energy and for that reason a large portion of the energy necessary for rotation is regained. The liquid iron in this case issuing from the channels 29 is caught in an annular trough 30' The arrangement of the channels 29 makes for a metal trap, which controls the thickness of the layer of molten iron. It is prevented from proceeding upwards by the flange 15. Inside this layer of molten iron a layer of molten sodium slag is formed. The iron layer prevents it from escaping downwards but as soon as the layer has reached a thickness such that it reaches the rim of the flange 15 it will proceed further upwards and be discharged radially outwards by centrifugal force. The flange 15 may be substituted by a number of holes in an otherwise closed roof of the drum. These holes may be located at various radial distances and when the proper one is closed a means is created for controlling the thickness of the slag layer. The discharge of this layer may of course also be through a liquid trap as is shown for the iron layer at the bottom.

When the sulphur rich iron is charged, it meets a slag, which has during its passing upwards gradually taken up sulphur. The iron having as charged a sulphur 0.120 percent content meets a slag having more than 16 percent ofsulphur mainly in the form of sodium sulphide. However, because of the high content of sulphur in the iron it is still possible for the slag to take up some more sulphur from it. At the discharge end where the iron on its way downwards has been gradually desulphurized its sulphur content has dropped to below 0010 percent. At this low level it meets a freshly molten sodium slag completely free from sulphur and some additional desulphurization is still possible. To reach this result an amount of some 6 kgs. of sodium per ton of iron treated is needed in this particular example.

The sodium slag is very aggressive towards almost any type of refractory material. However in the drum proper the inside wall is protected by a continuous skin of iron and the erosive slag has no change to get to the lining. Above the flange 15 this is not so however. In order to reduce the attack in this area some addition may be called for in order to cool down the sodium slag or to influence its fluidity. These additions are for instance made together with the iron or otherwise in the device for charging the iron such as the separate pipe 26 for pneumatic transport from the pressure line 27 to openings 27' (FIG. 2). The passages for these additions may discharge into the mixing zone in front of the charging device or even over or below this area.

The desulphurization of hot metal is just one example among very many, which lend themselves to a treatment of this kind. Prerefining of other types, the total processing of hot molten iron to steel, finishing operations in steelmaking as well as some types of vacuumtreatment are other examples. In the manufacture of alloys, for example aluminum-based alloys or copperbased alloys, brass and the like, numerous processes can be performed in fundamentally a corresponding way. The apparatus is also applicable for the manufacture of iron directly from fine iron ore.

Good means for control of the flow through the apparatus is called for. One such means is the control of the cross-sectional area of the outlet channels. In order to close the channels at the start of the operation, plugs of some material which is burnt away or melted away may be introduced into the channels, for example plugs of wood or aluminum. As a means for control during operation, a normal stopper and nozzle device may be used, and in some cases electric induction control has advantages. Again, a slide gate nozzle may be applied to the outlet channels.

For a good performance of the process, close control of the flow rate through the drum and of the quantity of liquid, which is retained in the drum are called for.

The handling capacity of the drum has to be adjusted to the greatest quantity, which can be transferred to the drum without risk of overloading and the control is produced by reduction from this maximum rate of charging. It is also necessary to be able to adjust the relative quantities of heavy and light phases. All these necessary changes may be performed in many ways. It is particularly valuable in this type of a counter-current process that so many ways of control are possible. Some examples will be mentioned here not in order to list all the possibilities, but in order to show the great adjustability of this procedure. One such possibility is to control the speed of revolution of the drum. Both the quantity of liquid charged by the charging means and the rate of discharge through the outlet channels or openings are functions of the speed of revolution of the drum. The characteristics vof these functions are not identical, however, and a formula can be established for each apparatus, which can be used as a basis for control. Further, in all the cases where the charging has a long feed pipe, this can be filled to a preset height, which is also a control of the quantity of material which enters into the drum. Again, as previously mentioned. the flow rate through the drum may be controlled by varying the cross-section area of the outlet openings.

As shown in FIG. 3, the last part 29a of the tubular channel 29a may also be formed so that the stream leaves the apparatus as an inclined jet. By so doing the gutter may be located further from the center of the apparatus and space is thus provided for other purposes.

The term fluid as used herein includes both liquids or molten solids and solid material in powder or granular form and capable therefore of flowing.

I claim:

1. Method of carrying out a reaction between fluids of different specific gravities, in a drum rotating about a vertical axis having a first outlet opening at one end adjacent the inner wall of the drum and having at least one second opening at the other end spaced inwardly a substantial distance from such inner wall, which comprises introducing the fluid of greater specific gravity into the drum adjacent said second end and introducing the fluid of lower specific gravity into the drum adjacent said first end, thereby causing said fluids to travel in counter-current to each other longitudinally of the drum, withdrawing the fluid of greater specific gravity through said first outlet opening, and removing the treated material of less specific gravity through the second opening.

2. Process as claimed in claim 1, in which said fluid of greater specific gravity is molten iron containing sulphur and said fluid of less specific gravity is a desulphurizing agent.

3. Process as claimed in claim 1, in which said first opening is at the. bottom of the drum and said second opening is at the top of the drum.

Claims (2)

1. 2. Process as claimed in claim 1, in which said fluid of greater specific gravity is molten iron containing sulphur and said fluid of less specific gravity is a desulphurizing agent.
2. 3. Process as claimed in claim 1, in which said first opening is at the bottom of the drum and said second opening is at the top of the drum.

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