Patent Publication Number: US-7909556-B2

Title: Charging device and distribution chute for a shaft furnace

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a charging device for a shaft furnace, in particular for a blast furnace. The present invention also relates to a distribution chute for use in such a charging device. 
     BRIEF DESCRIPTION OF RELATED ART 
     In blast furnaces, charging devices of the so-called “bell-less” type have found widespread use over the past decades. These charging devices are arranged at the furnace top and comprise a distribution chute and a drive mechanism to which the chute is mounted. During the charging procedure, charge material is discharged in bulk from a hopper through a central feed channel onto the distribution chute. The drive mechanism rotates the distribution chute about a first essentially vertical axis and pivots the chute about a second essentially horizontal axis. As a result, any desired charge profile, i.e. distribution of bulk material (burden) over the charging surface of the blast furnace, can be achieved. 
     In a particular charge profile, a vertical coke shaft or coke chimney is provided around the central axis of the blast furnace by charging coke centrally. Such a coke chimney serves to improve the operation of the blast furnace by increasing draft. Furthermore, such a coke chimney allows to feed coarse coke to the centre in order to increase permeability of the dead man. In order to create this central coke chimney within the burden, the distribution chute is pivoted into a central charging position. In this position, the chute should ideally not intercept the flow of bulk material which falls vertically from the central feed channel. 
     EP 0 062 769 discloses a charging device for a shaft furnace with a distribution chute that has a tapering tubular shape. Although an integrally funnel shaped type of distribution chute according to EP 0 062 769 allows accurate centre charging, it is not suitable for blast furnaces which require the chute to be pivotable to small inclination angles (close to horizontal) and/or for charging devices which require the pivoting axis of the chute to be offset from the central axis of the chute. 
     With many known charging devices and distribution chutes, it is however often impossible to completely avoid interception of the burden flow during central charging. For example, constructional constraints often make it impossible to pivot the distribution chute into a fully vertical position or a position sufficiently out of the way, such that its outlet portion remains partially within the charge path during central charging. The burden flow is thereby partially deflected, which of course is detrimental to central charging. There is a similar problem in case the distribution chute comprises one or more transverse bars for imparting rigidity to its trough-shaped main part. Such transverse bars typically form an obstruction which intercepts and scatters the burden flow during central charging, even if the main part of the chute itself is positioned sufficiently out of the way. 
     JP 11 001709 discloses a distribution chute with an auxiliary shoot fixed to the downstream end of the trough-shaped main part. The auxiliary shoot comprises tapering side plates for limiting the spread of the burden flow in lateral direction and a reflecting plate for redirecting the burden flow that exits the main part towards the centre of the furnace when the chute is in central charging position. 
     JP 07 179916 discloses a distribution chute comprising a trough-shaped main part and an additional straightening chute that is pivotably supported at the tip end of the main part for redirecting the burden flow vertically. This distribution chute comprises a link rod coupled to the straightening chute and to the support structure of the main part, so as to form a parallelogram linkage mechanism that maintains the straightening chute in vertical orientation. Besides improving burden distribution in radial direction, the distribution chute according to JP 07 179916 may also improve central charging if the straightening chute is funnel shaped. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a charging device for a shaft furnace with a distribution chute of simple construction that improves central charging of bulk material. 
     The invention further provides a charging device for a shaft furnace which comprises a distribution chute for bulk material and a drive mechanism for the distribution chute. The distribution chute has a trough-shaped main part with an open impact section and an outlet section. The main part provides a sliding channel between the impact section and the outlet section. The drive mechanism for the distribution chute is capable of rotating the distribution chute about an essentially vertical axis and pivoting the distribution chute about an essentially horizontal axis so as to allow distribution of bulk material on a charging surface of the shaft furnace. According to the invention, the distribution chute comprises a circumferentially closed funnel portion which tapers in the direction of flow and is arranged downstream of the impact section and with its outlet at the downstream end of the trough-shaped main part. When the distribution chute is in central charging position, this funnel portion insures that the flow of bulk material is centred and guided onto the desired target area of the charging surface, i.e. the centre of the furnace. Undesired deflection and uncontrolled distribution of charge material are thereby avoided. In addition, the funnel portion provides rigidity to the distribution chute. Arranging the outlet of the funnel portion at the downstream end of the trough-shaped main part enables centering of the burden flow at the lowermost end of the distribution chute when the latter is in central charging position. There is no need for significant deviation of the burden flow and hence the exposure of the circumferentially closed funnel portion to the considerable abrasive wear caused by the burden is minimal. Furthermore, since the circumferentially closed funnel portion imparts rigidity to the distribution chute in the outlet section, the need for additional stabilizing transverse bars can be eliminated. As will be appreciated, use of this charging device is beneficial to any kind of charging procedures which involve central charging in general and formation of so-called “coke chimneys” in particular. 
     As opposed to JP 07 179916, with the distribution chute according to the invention, there is no need for associating an additional mechanism that would be exposed to the severe inner atmosphere of the furnace with the distribution chute. In contrast to JP 11 001709, the inside surfaces of the funnel portion are arranged so as to be subject to a minimum of wear caused by the burden during central charging, because the deviation angle of the centred burden flow is relatively small. Furthermore, and also in contrast to JP 11 001709 and JP 07 179916, the total length of the distribution chute is not increased by the funnel portion since its outlet is arranged at the downstream end of the trough-shaped main part. 
     According to a preferred embodiment, the funnel portion has an apex half angle greater than or equal to the angle enclosed between the longitudinal axis of the trough-shaped main part and the vertical when the distribution chute is in central charging position. The apex half angle is to be understood as half of the apex angle of a cone whose surface generates the shape of the funnel portion. It may be noted that this cone may have a general, i.e. not necessarily circular, base and need not be a right cone. 
     In case the charging device comprises a central feed channel arranged above the distribution chute for feeding bulk material onto the distribution chute, it is preferable that the outlet cross section of the funnel portion approximately equals the outlet cross section of this central feed channel. 
     In another preferred embodiment, the funnel portion is limited to 10-50% of the length of the distribution chute starting from the downstream end of the main part. The funnel portion covers the outlet section and/or the sliding channel, but it does not, at least not entirely, cover the impact section. In fact, the latter needs to be accessible for receiving bulk material during the usual (non-central) charging procedure. To this effect, the open impact section advantageously extends over at least 40% of the length of the trough-shaped main part starting from the upstream end of the main part such that bulk material can be fed to the distribution chute over a wide range of inclination angles. 
     From a structural point of view, the funnel portion can be divided into a chute portion of the trough-shaped main part and a cover portion covering the chute portion. In this case, the cover portion may comprise a cover having a shape which is generated by a frustum of a cone. Again, this cone need not be a right circular cone but may have any suitable, generally conical configuration. In another variant, the cover portion comprises an inclined cover plate arranged at an angle with respect to the main part and lateral linking plates for fixing the inclined cover plate to the main part. In yet another variant, the cover portion comprises a first upstream inclined cover plate, a second downstream inclined cover plate, the first and second inclined cover plates being arranged at an angle with respect to the main part, and lateral linking plates for fixing the first and second inclined cover plates to the main part. In both of the latter cases, the angle by which the inclined plate(s) is (are) mounted, is chosen analogous to the aforementioned apex half angle. 
     As will be appreciated, the funnel portion is preferably arranged so as to guide and centre a flow of bulk material on the central axis of the shaft furnace when the distribution chute is in central charging position. 
     Preferably, the distribution chute comprises mounting flanges for mounting the distribution chute to the drive mechanism, the flanges being configured such that the longitudinal central axis of the main part is offset from the essentially horizontal pivoting axis. 
     The invention also proposes a distribution chute for a charging device as described above. According to the invention, the distribution chute comprises a circumferentially closed funnel portion which tapers in the direction of flow and is arranged downstream of the impact section and with its outlet at the downstream end of said trough-shaped main part. 
     As will be appreciated, the distribution chute and the charging device according to the present invention are particularly suitable for use in a metallurgical blast furnace. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The present invention will be more apparent from the following description of not limiting preferred embodiments with reference to the attached drawings. In the drawings, in which identical or similar parts are identified by identical reference numerals throughout, 
         FIG. 1 : is a vertical cross-sectional view of a first embodiment of a charging device with a distribution chute according to the invention; 
         FIG. 2 : is a cross-sectional view along plane II-II of the distribution chute according to  FIG. 1 ; 
         FIG. 3 : is a cross-sectional view along plane III-III of the distribution chute according to  FIG. 1 ; 
         FIG. 4 : is a vertical cross-sectional view of a second embodiment of a charging device with a distribution chute according to the invention; 
         FIG. 5 : is a cross-sectional view along plane V-V of the distribution chute according to  FIG. 4 ; 
         FIG. 6 : is a vertical cross-sectional view of a third embodiment of a charging device with a distribution chute according to the invention; 
         FIG. 7 : is a cross-sectional view along plane VII-VII of the distribution chute according to  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a furnace throat of a blast furnace generally identified by reference numeral  10 . The top closing on the throat of blast furnace  10  comprises a charging device  12  for charging a burden  14  of bulk material such as ore and coke into the blast furnace  10 . The charging device  12  comprises a distribution chute  16  and a drive mechanism  18  to which the distribution chute  16  is mounted. 
     In a manner known per se, the drive mechanism  18  is configured for rotating and pivoting the distribution chute  16 . During the charging procedure, it rotates the distribution chute  16  about the vertical central axis  20  of the blast furnace  10  and pivots the distribution chute  16  about an essentially horizontal axis  22 , i.e. about mounting shafts by which the drive mechanism  18  holds the distribution chute  16 . A detailed description of such a drive mechanism  18  is given e.g. in U.S. Pat. No. 3,880,302 and therefore omitted here. 
     In  FIG. 1 , the distribution chute  16  is shown in central charging position i.e. pivoted down into an almost vertical position. The distribution chute  16  comprises a trough-shaped main part  23 . In this embodiment the main part  23  has the shape of a longitudinal half of a tube, i.e. a semi-cylindrical hollow body, other configurations, e.g. distribution chutes having (semi-)rectangular cross-sections, are however not excluded. In a manner known per se, the main part  23  has an open impact section  24 , which means that the impact section  24  is not circumferentially closed, for receiving bulk material and an outlet section  25  for delivering bulk material onto a given point of the charging surface of the blast furnace  10 . When the distribution chute  16  is less inclined than shown in  FIG. 1 , the main part  23  provides a trough-shaped sliding channel between the open impact section  24  and the outlet section  25 . 
     As will be appreciated, the distribution chute  16  further comprises a circumferentially closed funnel portion  26  which tapers in the direction of flow i.e. from the impact section  24  towards the outlet section  25 . In fact, during central charging as shown in  FIG. 1 , a free falling flow  28  of bulk material is fed vertically via a central feed channel  30  into the central region of the blast furnace  10 . This allows for example to form a central coke chimney within the burden  14  as schematically indicated at  32 . As will be appreciated, the impact section  24  is open on the side opposite to the bottom of the main part  23  i.e. open towards the central feed channel  30  over a substantial portion, preferably at least 40%, of the length of the main part  23  so as to allow receiving bulk material from the central feed channel  30  in any position, i.e. from small inclination (nearly horizontal) angles to high inclination angles (nearly vertical), of the distribution chute  16 . When the distribution chute  16  is in central charging position as shown in  FIG. 1 , the funnel portion  26  insures centring and guiding of the flow  28  of bulk material onto the central axis  20  of the blast furnace  10 . It may be noted that the distribution chute  16  is normally rotated about the central axis  20  during central charging, with the funnel portion  26  this rotation is however not mandatory. As shown in  FIG. 1 , the outlet  33  is arranged at the downstream end of the main part  23 , i.e. the outlet  33  of the funnel portion  26  per se coincides with the outlet of the distribution chute  16 . The funnel portion  26  covers the outlet section  25  and part of the sliding channel in between the open i.e. uncovered impact section  24  and the outlet section  25 . In the embodiment of  FIG. 1 , the funnel portion  26  extends over approximately 42% of the total length of the distribution chute  16  (values from 10%-50% being preferred). As seen in  FIG. 1 , the funnel portion  26  is arranged downstream of the impact section  24 . In other words, funnel portion  26  does not cover the open impact section  24  onto which bulk material is fed during radial and circumferential charging, i.e. when the distribution chute  16  is not in central charging position. 
     As further seen in  FIG. 1 , the funnel shaped portion  26  is designed such that its summit line is at an angle α with the longitudinal central axis  34  of the main part  23 . The angle α corresponds to half of the apex angle of an imaginary cone matching the funnel shaped portion. The angle α is preferably chosen greater than, or at least equal to an angle β, defined by the trough line of the main part  23  and the vertical central axis  20 , when the distribution chute  16  is in central charging position. In fact, the angle β depends on constructional constraints and is generally greater than zero. By choosing the angle α and the minimum clearance between the summit line and the trough line accordingly, it is insured that the flow  28  is entirely collected and centred. 
     As best seen in  FIGS. 2 and 3 , the free passage cross-sectional area of the funnel portion  26  decreases in the direction of flow. At the outlet  33 , the cross-sectional area of the funnel portion  26  shown in  FIG. 3  is chosen so as to be essentially equal to the free passage cross-sectional area at the outlet of the central feed channel  30 . Furthermore, the surface defined by the outlet  33  is approximately perpendicular to the longitudinal central axis  34  of the main part  23 . This insures optimum concentration and centring of the flow  28  while avoiding detrimental congestion of bulk material in the funnel portion  26 . Depending on the type of charge material and on the vertical distance between the outlet of the central feed channel  30  and the outlet  33  during central charging, the cross-sectional area of the outlet  33  may also be configured smaller than cross-sectional area of the outlet of the central feed channel  30 . As a matter of fact, the flow  28  may taper in downward direction due to gravitational acceleration such that a smaller cross-section of the outlet  33  may improve centering without causing congestion. 
     As further seen in  FIGS. 1 to 3 , the slanting funnel portion  26  according to the first embodiment comprises an essentially semi-cylindrical chute portion  36  of the main part  23  and a cover portion  38  connected to the main part  23 . As seen in  FIG. 1 , the cover portion  38  comprises a cover member having the shape of a lateral surface portion of a frustum of a cone. To provide this arrangement, the essentially semi-cylindrical portion  36  and the frusto-conical cover portion  38  can be integrally formed out of a suitably shaped single steel plate which is bent and welded into shape. A similar distribution chute  16  can be obtained by machining an entirely cone-shaped pre-form funnel or alternatively, by fixing together two separate parts having the shape of the portions  36 ,  38 . It may be noted that the latter procedure allows to retrofit existing chutes with a funnel shaped portion  26  and that the former procedure provides a main part which is conical rather than semi-cylindrical. 
       FIGS. 4 and 5  show a second embodiment of the charging device  12  according to the invention. For the sake of conciseness, only those aspects in which the second embodiment differs from the first embodiment are detailed below. 
     In  FIGS. 4 and 5 , the distribution chute  16 ′ comprises a circumferentially closed funnel portion  26 ′ having a reduced length when compared to the first embodiment. The funnel shaped portion  26 ′ of this embodiment is limited to approximately 15% of the length of the distribution chute  26 . The funnel portion  26 ′ is arranged in the outlet section  25  of the main part  23  only. While insuring similar effectiveness in the central charging position as shown, this embodiment allows reducing the total weight as well as material and manufacturing cost of the distribution chute  16 ′. 
     As seen in  FIG. 5 , the funnel portion  26 ′ comprises an essentially semi-cylindrical chute portion  36  of the main part  23 . It furthermore comprises a cover portion  38  having an inclined cover plate  40  arranged at an angle α, with respect to said main part  23  and lateral linking plates  42  for fixing the inclined cover plate  40  to the main part  23 . As will be appreciated, the angle α is chosen according to the same principle and has the same effect as mentioned above. The height of the linking plates  42  is chosen such as to warrant that the free passage cross-sectional area at the outlet of the funnel portion  26  is essentially equal to the free passage cross-sectional area at the outlet of the central feed channel  30 . As mentioned above, it is not excluded to design the distribution chute  16 ,  16 ′ such that the free passage cross-sectional area at the outlet  33  of the funnel portion  26  is smaller than the free passage cross-sectional area at the outlet of the central feed channel  30 . 
       FIGS. 6 and 7  show a third embodiment of the charging device  12  according to the invention. For the sake of conciseness, only those aspects in which the second embodiment differs from the previously described embodiments are detailed below. 
     The distribution chute  16 ″ shown in  FIG. 6  has an overall configuration similar to that of the distribution chute  16 ′ shown in  FIG. 4 . The essential difference resides in the fact that the inclined cover plate  40  of the distribution chute  16 ′ has been replaced by a first upstream inclined cover plate  44  and a second downstream inclined cover plate  46 . The inclined cover plates  44 ,  46  are arranged with an intermediate gap  48  on the linking plates  42  as seen in  FIG. 7 . Surprisingly, it has been found that, provided the cover plates  44 ,  46  have sufficient effective dimension in the flow direction, the presence of the gap  48  has little adverse effect if any on concentration, centering and guiding of the flow  28 . Thus the configuration of the funnel portion  26 ″ shown in  FIGS. 6 and 7  allows further savings in total weight and material cost. 
     It will be appreciated that the funnel shaped portions  26 ,  26 ′,  26 ″ as previously described allow to impart rigidity to the main part  23  and, in particular, to insure that the outlet section  25  is not deformed due to thermal and/or mechanical stress. Compared to known braces or transverse links provided for the same purpose, this effect is achieved by the funnel shaped portions  26 ,  26 ′,  26 ″ without any detrimental influence on central charging. 
     It remains to be noted that, in any of the preceding embodiments, the main part  23  is preferably made of heat resistant steel and may comprise an inward cladding of wear resistant material (not shown) as well as so called stone boxes as described e.g. in EP 0 640 539. Advantageously, the slanting funnel portion  26 ,  26 ,  26 ″, in particular the cover portion  38 , is also provided with an inward cladding of wear resistant material in those regions which are subject to abrasive stress. In general, in the circumferentially closed funnel portion  26 ,  26 ,  26 ″ or at least in the region near the outlet  33 , the inner surface of the distribution chute  16 ;  16 ′;  16 ″ is smooth, e.g. devoid of stone boxes and other protrusions, whereby uniform discharging of charge material is warranted. The distribution chute  16 ;  16 ′;  16 ″ may further comprise a cooling arrangement as described in GB 2 281 610 if required. Furthermore, as seen in  FIGS. 1 ,  4  and  6 , the distribution chute  16 ;  16 ′;  16 ″ has duckbill-shaped mounting flanges for removable mounting of the distribution chute  16 ;  16 ′;  16 ″ to the drive mechanism  18  by means of mounting shafts defining the horizontal pivoting axis  22 . By virtue of the mounting flanges, the longitudinal central axis  34  of the main part  23  is offset from the horizontal pivoting axis  22 .