Abstract:
A charging device for a shaft furnace, which includes at least one charging hopper having a discharge orifice arranged in a position off-centre with respect to the central axis of the shaft furnace, and a material distribution device arranged below this hopper. The material distribution device includes a feed channel coaxial with the central axis of the furnace and a rotatable, pivotable chute, which is arranged below the feed channel for distributing a charge in the shaft furnace. The charging device also includes a connecting box in the shape of a funnel, arranged between the material distribution device and the charging hopper. The connecting box possesses a lower central outlet communicating with the charging hopper and at least one upper inlet which is arranged off-centre with respect to the central axis of the furnace and communicates with the discharge orifice of the hopper. According to the invention, the charging device includes at least one spreader situated upstream of the distribution device, on the trajectory of the material discharged from the discharge orifice. The spreader enables a flow of material to be dispersed to both sides of the feed channel.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention concerns a device for charging a shaft furnace, especially a blast furnace, comprising at least one and in general several charging hoppers which normally act as airlock reservoirs and are connected by a connecting box to a material distribution device with a rotatable, pivotable chute for distributing the charge inside the shaft furnace. 
     BRIEF DISCUSSION OF RELATED ART 
     There is a considerable number of charging devices of this type that equip blast furnaces around the world. For a blast furnace, charging normally takes place as follows: when a first hopper is being charged under atmospheric pressure, a second hopper, which is then under blast furnace pressure, discharges its load through the connecting box into a central feed channel of the material distribution device. Fed by this central channel, the rotatable, pivotable chute distributes the charge over the charging surface of the furnace. When the second hopper is empty, it is isolated from the furnace and reduced to atmospheric pressure for refilling. The first hopper or, as the case may be, a third hopper, which has been previously filled, is then put under blast furnace pressure ready to feed the material distribution device. 
     With these charging devices, the flow of material leaving the hoppers normally follows a trajectory off-centre with respect to the central axis of the furnace, due to the eccentric position of the hoppers. It follows that the zone of impact on the rotatable, pivotable chute is variable and asymmetrical, and when the chute is in its withdrawn, inactive position, the impact on the charging surface of the furnace will not be central. On the one hand, asymmetrical, variable impact on the chute complicates the distribution procedure, because the distance over which the material slides along the chute varies with the angular position of the chute and depends on the hopper that is used. On the other hand, the eccentric trajectory from the chute poses a problem, especially when it is desired to improve the performance of a blast furnace by forming a coke chimney in the furnace charge around the central axis of the blast furnace. Using the charging devices described above, it is barely possible to form such a chimney of coke, as the devices are incapable of directing their loads accurately towards the centre of the furnace. Various solutions to this problem have been proposed, for example in the Luxembourg patents LU 85879, LU 86336 and LU 86340 of the applicant. In classical charging installations, the material being charged flows along the inclined wall of the connecting box before it reaches the rotatable, pivotable chute. The solutions mentioned above consist essentially in providing an additional conical funnel inside the connecting box. The output from this funnel is controlled by a metering unit in order to form a retainment of material in the funnel. In this way, the asymmetrical outflow into the chute is reduced or eliminated. However, these solutions require the installation of an elaborate control procedure as well as substantial and complex modifications to the classical charging device. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention proposes a charging device for a shaft furnace that allows, by simple means, centring the trajectory of the charge on the central axis of the furnace. 
     The invention provides a shaft furnace charging device comprising at least one charging hopper with a discharge orifice arranged offset with respect to the central axis of the shaft furnace, and a material distribution device arranged below this hopper. The material distribution device comprises a feed channel coaxial with the central axis of the furnace and a rotatable, pivotable chute arranged below the feed channel designed for distributing a charge into the shaft furnace. The charging device also comprises a funnel-shaped connecting box arranged between the material distribution device and the charging hopper. This connecting box possesses a lower central outlet communicating with the feed channel and at least one upper inlet arranged offset, i.e. off-centre with respect to the central axis of the furnace and communicating with the discharge orifice of the hopper. According to an important aspect of the invention, the charging device comprises at least one dispersion means—a spreader—situated upstream of the above-mentioned distribution device and on the trajectory of material discharged from the discharge orifice, that allows dispersing a flow of material to both sides of the above-mentioned feed channel. 
     It is known that, due to the funnel shape of the box, horizontal components of velocity will inevitably be communicated to each flow of matter entering off-centre and passing through the box. Consequently, the flow leaving the feed channel becomes eccentric. On the rotatable, pivotable chute, when the latter rotates, such an eccentric flow travels variable sliding distances. In fact, the zone of impact on the chute depends on the relative rotational position of the chute when the incident flow is not coaxial. The sliding distance travelled on the chute governs the degree of deceleration of the material. The result is that the speed of the material leaving the chute also depends on the rotational position of the chute. Thus it is not easy to achieve a desired charge profile of concentric circular zones, and the profile obtained often tends to be rather elliptical. Furthermore, the formation of a coke chimney, if this is desired, is also hampered. 
     The spreader according to the invention makes it possible to divide a flow of material discharged from the hopper and to disperse it, in the form of at least two separate flows, on to opposite sides of the inclined surfaces of the connecting box, that is to say to both sides of the feed channel. When the flows thus previously separated by the spreader come together again, the collision between them is sufficient to reduce or eliminate their horizontal components of velocity, thus creating a flow which is essentially centred, that is to say, essentially coaxial with the central axis of the furnace. Considering such a spreader, it will be appreciated that it is mechanically simple and hence reliable, that it can easily be arranged inside the connecting box and that its installation requires only few modifications to known charging devices. 
     According to a simple embodiment, the spreader comprises a spreader plate arranged inside the connecting box. According to a first variant of the invention, this spreader plate is a fixed horizontal plate. According to a second variant of the invention, this spreader plate is a pivotable plate that can be pivoted between an operating position and a non-operating position. In operating position, the plate is generally positioned horizontally so as to constitute an obstacle transverse to the direction of flow. In non-operating position, the plate is withdrawn, for example along the vertical direction, so as not to impede the flow of material. 
     In the case of a pivotable plate, the spreader plate advantageously has a geometry enabling it to at least partially cover the feed channel when in operating position. A pivotable plate can be greater in area than a fixed plate. The fact that it can at least partially cover the feed channel when in operating position makes it possible to optimize the spreading of material across the whole channel. 
     In an advantageous embodiment, the spreader also comprises a retaining edge by means of which an accumulation of material can be retained on the spreader. Such an accumulation can, in particular, reduce the effects of abrasive wear of the spreader. For efficient division and diversion of the flow of material, the spreader preferably comprises two opposite sides arranged contiguous with the walls of the connecting box. 
     In an advantageous embodiment, the feed channel comprises a first upper tubular section and a second lower tubular section, the horizontal cross-section of the first and/or the second tubular section tapering along the direction of material flow. This enables further improvement of the degree of centring of the flow of material at the outlet of the feed channel. 
     It is evident that the invention lends itself particularly well to a charging device employing several hoppers and to use in blast furnaces. It will also be appreciated that the spreader as described can easily be incorporated into an existing charging device as an improvement. In a preferred embodiment, the charging device comprises three charging hoppers, each having a discharge orifice offset with respect to the central axis of the furnace and comprising three spreaders, each discharge orifice having its respective spreader associated with it. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and characteristics of the invention will become apparent in the detailed description of two advantageous forms of embodiment presented below, with reference to the attached drawings, in which: 
         FIG. 1  is a vertical cross-section, along the axis I-I in  FIG. 2 , showing a charging device for a shaft furnace according to a first embodiment; 
         FIG. 2  is a horizontal cross-section of the device according to  FIG. 1 , showing the spreaders; 
         FIG. 3  is a vertical cross-section along the axis III-III in  FIG. 4 , showing a charging device for a shaft furnace according to a second embodiment; 
         FIG. 4  is a vertical cross-section through the device according to  FIG. 3 , showing other spreaders. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A charging device, generally identified by reference number  10 , is shown as an example in  FIGS. 1 and 3 . This charging device  10  equips a blast furnace throat  12 , which is not shown in its entirety in the drawings. Reference  15  identifies the central axis of this blast furnace. 
     The charging device  10  comprises, in known manner, a first hopper  16 , a second hopper  18  and a third hopper  20 , which act as airlock reservoirs for the material to be charged. Only the lower parts  22 ,  24  of the first and second hoppers  16 ,  18  are shown in the drawings. Although the third hopper  20  and its lower part  25  are present, they are not visible in the cross-sections. In  FIGS. 1 and 3 , it can be seen that the hoppers  16 ,  18  are arranged side by side, off-centre with respect to the central axis  15  of the blast furnace. The same applies to the third hopper  20 . In fact, the three hoppers  16 ,  18 ,  20  are arranged symmetrically with respect to the central axis  15 . 
     The reference number  26  generally identifies a material distribution device arranged below the hoppers  16 ,  18 ,  20 . This material distribution device  26  comprises, in known manner, a feed channel  28  coaxial with the central axis  15  of the blast furnace and a rotatable, pivotable chute  30 . The latter is arranged below the feed channel  28  and can turn round the central axis  15  and pivot about an essentially horizontal axis of suspension, so as to be able to distribute the charge through the throat  12  on to the charging surface of the blast furnace (not shown). 
     A connecting box  32  is arranged vertically between the material distribution device  26  and the hoppers  16 ,  18 ,  20 . The connecting box  32  is essentially funnel-shaped. It comprises, in known manner, a lower discharge outlet  34  which communicates with the feed channel  28  of the material distribution device  26 , and three upper inputs  36 ,  38 ,  40  arranged symmetrically with respect to the central axis  15  and connected to the lower parts  22 ,  24 ,  25  of the hoppers  16 ,  18 ,  20 . Only the inputs  36  and  38  of the first and second hoppers  16  and  18  are shown in  FIGS. 1 and 3 . The lower parts  22 ,  24 ,  25  of the hoppers  16 ,  18 ,  20  are provided with respective discharge orifices  42 ,  44 ,  46 , of which only the discharge orifices  42  and  44  are shown. Due to the positioning of the hoppers  16 ,  18 ,  20 , it follows that the discharge orifices  42 ,  44 ,  46  are also off-centre with respect to the central axis  15  of the blast furnace. 
     In known manner, for each of the hoppers  16 ,  18 ,  20 , a material gate valve  48 ,  50 ,  52  respectively serves to interrupt and control the flow to be discharged alternatively via one of the discharge orifices  42 ,  44 ,  46 . A lower sealing valve  56 ,  58 ,  60  is associated with each of the material gate valves  48 ,  50 ,  52  and serves to seal the hopper  16 ,  18 ,  20  with respect to the blast furnace. It should also be noted, that respective upper sealing valves, mounted at the upper end of the hopper  16 ,  18 ,  20  and serving to seal the latter with respect to the outer atmosphere, is not shown in the figures. 
       FIG. 1  shows a flow  62  of charge material being discharged from the second hopper  18  to be distributed by the rotating, pivoting chute  30 . Also shown in  FIG. 1  are a first spreader  66  and a second spreader  68 . A third spreader  70  associated with the third hopper  20  is shown in  FIG. 2 . Each of these spreaders  66 ,  68 ,  70  is situated on the natural trajectory of the flow of material discharged by the respective hopper  16 ,  18 ,  20 , that is to say vertically below the discharge orifices  36 ,  38 ,  40  from which the material flows out. 
     In charging phase, the spreaders  66 ,  68 ,  70  serve to spread the material flow and thus to divide it and divert it towards different sides of the inclined walls of the connecting box  32 . In particular, as can be seen in  FIGS. 1 and 3  for the spreader  68  and the flow  62 , the spreaders  66 ,  68 ,  70  serve to divide the material flow,  62  for example, essentially into two separate partial flows, as indicated by the references  62 ′ and  62 ″. Because they are spread in this way, these flows  62 ′ and  62 ″ are directed to both sides of the feed channel  28 , on to opposite parts of the inclined inner walls of the connecting box  32 . These partial flows  62 ′ and  62 ″ are thus distributed both sides of a plane passing through the central axis  15  and perpendicular to the plane of  FIGS. 1 and 3 . The mass flow rates of the partial flows  62 ′ and  62 ″ are similar. It will thus be appreciated that a collision between the partial flows  62 ′ and  62 ″ in the region of the lower discharge outlet  34  of the connecting box  32  will result from their deflection along the two free sides of the spreaders  66 ,  68 ,  70 . This collision creates a single flow which is essentially coaxial with the central axis  15 . It will also be appreciated that the dispersion into two partial flows  62 ′ and  62 ″ and their collision will substantially reduce or even eliminate horizontal velocity components. Irrespective of which of the hoppers  16 ,  18 ,  20  it originates from, each recombined flow presents the same impact zone on the rotatable, pivotable chute  30 . Since this impact zone is centred on the central axis  15 , by virtue of the corresponding spreader  66 ,  68 ,  70 , it will be appreciated that the velocity of the material issuing from the chute  30  is independent of the rotational position of the chute  30 . Furthermore, each recombined flow has the advantage of impacting centrally on the charging surface of the blast furnace when the chute is withdrawn (i.e. out of the way) and inactive, as shown in  FIG. 1 . An example of a such a recombined material flow is indicated by the reference  62 ′″ in  FIGS. 1 and 3  for a discharge issuing from the second hopper  18 . 
       FIG. 2  shows the three spreaders  66 ,  68 ,  70  and their position inside the connecting box  32 . The spreaders  66 ,  68 ,  70  are arranged symmetrically with respect to the central axis  15 . Each of the three spreaders  66 ,  68 ,  70  shown in  FIG. 2  comprises a spreader plate  66 ′,  68 ′,  70 ′ of rectangular shape with a retaining edge  66 ″,  68 ″,  70 ″. As is clearly visible in  FIG. 1 , the retaining edges  66 ″,  68 ″,  70 ″ serve to retain an accumulation  66 ″′,  68 ″′,  70 ″′ of material, conical in shape, on the spreader plates  66 ′,  68 ′,  70 ′. This accumulation  66 ″′,  68 ′″,  70 ″′ of material serves to reduce the abrasion on the plate  66 ′,  68 ′,  70 ′ resulting from the considerable quantities of material charged into the blast furnace. The spreader plates  66 ′,  68 ′,  70 ′ and the retaining edges  66 ″,  68 ″,  70 ″ are made from a material of high mechanical strength, such as wear-resistant steel or steel clad with an appropriate ceramic material. 
     In the embodiment according to  FIGS. 1 and 2 , the spreader plates  66 ′,  68 ′,  70 ′ are fixed immovably in a horizontal position inside the connecting box  32 . The spreader plates  66 ′,  68 ′,  70 ′ are separated from the inclined wall of the connecting box  32  by a vertical distance enabling the trajectories of the flows on both sides of the feed channel  28  to be obtained. This vertical distance also permits the passage of a partial flow  62 ″ below the respective spreader plate  66 ′,  68 ′,  70 ′. The dimensions of the fixed spreader plates  66 ′,  68 ′,  70 ′, especially their surface areas, are chosen so as to leave a passage on the side of the feed channel  28  and on the side opposite to the latter. Each spreader plate  66 ′,  68 ′,  70 ′ is arranged essentially beneath the discharge orifice  36 ,  38 ,  40  to which the plate is allocated. As can be seen in  FIGS. 1 and 2 , the geometrical centre of each of the spreader plates  66 ′,  68 ′,  70 ′ is aligned to a flow  62  of given flow rate. This flow rate, which is defined by the setting of the respective material gate valve  48 ,  50 ,  52 , is generally an intermediate flow rate, less than the maximum rate, as illustrated in  FIGS. 2 and 4 . In fact, the connecting box  32 , due to its funnel-shape, is able to centre the flow of material for high flow rates, though it is incapable of doing this for intermediate or low flow rates. It will be appreciated that the spreaders  66 ,  68 ,  70  provide a solution to this problem. In  FIG. 2 , the partial flows flow  62 ′ and  62 ″ both sides of the feed channel  28  can also be seen. The way in which the material is distributed by the spreader  68  is approximately indicated by the set of arrows visible in  FIG. 2 . It will be appreciated that once the first discharge has been released, each of the spreaders  66 ,  68 ,  70  constitute an assembly formed of a spreader plate  66 ′,  68 ′,  70 ′, a retaining edge  66 ″,  68 ″,  70 ″ and an accumulation of material  66 ″′,  68 ′″,  70 ′″. 
       FIGS. 3 and 4  show another embodiment. In  FIGS. 3 and 4 , identical or similar elements to those shown in  FIGS. 1 and 2  are indicated by the same reference numbers. The embodiment in  FIGS. 3 and 4  is similar in configuration and characteristics, so only the differences are described below. The main differences between this embodiment and the one described above consist in the way in which the spreaders  166 ,  168 ,  170  are mounted inside the connecting box  32  and in the shape of the spreader plates  166 ′,  168 ′,  170 ′ that they comprise.  FIG. 3  also shows the rotatable, pivotable chute  30  in operating position and the impact of the flow  62 ″′, coaxial with the central axis  15 , on to the chute  30 . 
     As can be seen in  FIGS. 3 and 4 , the structure and positioning of the spreaders  166 ,  168  and  170  are essentially similar to the arrangement described above. However, it can be clearly seen that the spreaders  166 ,  168 ,  170 , and especially their spreader plates  166 ′,  168 ′,  170 ′, have a larger surface area. In order to make possible this increased surface area without blocking the passage of the charge material towards the lower discharge outlet  34  of the connecting box  32 , the spreader plates  166 ′,  168 ′,  170 ′ are mounted pivotable on pivot shafts  80 . The pivot shafts  80  rotate in bearings in the wall of the connecting box  32  to form an axis of rotation for each of the spreader plates  166 ′,  168 ′,  170 ′. This enables each of the spreader plates  166 ′,  168 ′,  170 ′ to be pivoted between an essentially vertical parking position, in which it is non-operational and does not obstruct the flow of material, and a horizontal operating position in which the spreader plate  166 ′,  168 ′ or  170 ′ intercepts, divides and diverts the flow of material  62 . In  FIGS. 3 and 4 , the spreader  168  is shown in operating position, while the spreaders  166  and  168  are in non-operating position. The pivoting of these spreaders  166 ,  168 ,  170  can advantageously be coupled to the actuation of the corresponding sealing valve  56 ,  58 ,  60 . It can also be seen in  FIG. 4  that the shape of the spreader plates  166 ′,  168 ′,  170 ′ is pentagonal. Thus, in operating position, part of each spreader plate  166 ′,  168 ′,  170 ′ partially covers the lower discharge outlet  34 , and hence the feed channel  28 , in order to improve the spreading of material to both sides of the latter. 
     Returning to  FIGS. 1 and 3 , two other aspects of the charging device  10  remain to be noted. The feed channel  28  comprises a first upper tubular section  28 ′ and a second lower tubular section  28 ″. The first aspect is that these upper tubular sections  28 ′,  28 ″ are tapered, that is to say that their diameter decreases towards the bottom. This enables better focalization of flows  62 ″′ set at higher rates than that shown in  FIGS. 1 and 3  on to the central axis  15 . For each of the tubular sections  28 ′,  28 ″, this decrease in diameter is adapted to the increase in the velocity of flow according to its output direction, so as to focus the material without hindering its free flow. The second aspect is that the first tubular section protrudes to some extent into the connecting box  32 , as can be seen in  FIGS. 1 and 3 . This has the effect of creating an obstacle in the path of the charge material on the inclined walls of the connecting box  32 . The result is the formation of an accumulation of material in the form of a slope, identified by reference number  90 . This permanent layer of material  90  considerably reduces the wear on the sloping walls of the connecting box  32 .