Shaft furnace

The invention relates to a shaft furnace (1), particularly to a direct-reduction shaft furnace, with a bed (2) of lumpy material, particularly lumpy material containing iron oxide and/or sponge iron, with discharge devices (4) for lumpy material which are located above the bottom area (3) of the shaft furnace (1), as well as with inlet ports (6) for a reduction gas which are arranged above the discharge devices (4). Arrangements (7) for moving the material in the shaft furnace (1) are located between the area formed by the inlet ports (6) and that formed by the discharge devices (4).

BACKGROUND OF THE INVENTION
 The invention relates to a shaft furnace, particularly to a
 direct-reduction shaft furnace, with a bed of lumpy material, particularly
 lumpy material containing iron oxide and/or sponge iron, wherein discharge
 openings for lumpy material are located above the bottom area of the shaft
 furnace and inlet ports for reduction gas above the discharge openings.
 Many shaft furnaces, particularly reduction shaft furnaces of the
 aforementioned type, are known from prior art. Such a shaft furnace, which
 is essentially designed as a cylindrical hollow body, generally contains a
 bed of lumpy material containing iron oxide and/or sponge iron, with the
 lumpy material containing iron oxide being charged into the upper part of
 the shaft furnace. Reduction gas coming, for example, from a melter
 gasifier is injected into the shaft furnace and thus into the solid bed
 through several inlet ports arranged along the circumference of the shaft
 furnace in the area of the lower third of the shaft furnace. The hot,
 dust-laden reduction gas ascends through the solid bed, completely or
 partially reducing the iron oxide of the bed to sponge iron.
 The completely or partly reduced iron oxide is extracted from the shaft
 furnace by means of discharge devices located between the bottom area of
 the shaft furnace and the area of the gas inlet ports. These discharge
 devices are usually designed as radially (related to the shaft furnace)
 arranged discharge screws.
 The zone located in the area of the shaft bottom in which the discharge
 devices are arranged must have a maximum active discharge area in order to
 allow the bulk material to subside as uniformly as possible and to ensure
 continuous movement and mixing of the material in the reaction zone.
 However, the small number of discharge devices and the involved space
 conditions have the disadvantage that part of the bulk material located in
 the plane of the discharge devices cannot be covered by these discharge
 devices so that nonmovable zones with very steep inner angles of repose
 are formed above these nonactive areas.
 These zones, which are referred to as "dead man", have the disadvantage
 that a portion of the reaction space volume becomes partly inactive,
 active volume meaning the region of a shaft furnace where the desired
 gas-solid reactions occur.
 As a result, cakings and agglomerates may form in these regions owing to
 the long dwelling times of ores and of already reduced ores, which impair
 the material flow and consequently reduce the material reaction and, thus,
 also the productivity.
 The prior-art arrangement essentially features two zones above which "dead
 man" forms, that is, the central region not covered by the radially
 arranged discharge devices and another zone formed by two wedge-shaped
 regions located between two discharge devices each, wherein the bulk
 pyramids building up in these dead zones impede the solid flow and build
 up to a level where the reduction gas inlet ports are concealed by the
 bulk material that is building up and the dust freight of the reduction
 gas forms a bed that is relatively impermeable to gas. As a result, the
 required homogeneous gas distribution in the shaft furnace does not take
 place.
 EP-B-0 116 679 describes screws for moving solid particles in a shaft
 furnace and for discharging such particles. These radially arranged and
 overhung screws are of identical length and have a cylindrical cross
 section. Although the dead corners between the screws are minimized by the
 installation of wedge-shaped baffles, "dead men" cannot be prevented from
 building up.
 EP-B-0 085 290 reveals arrangements of short conical screws supported in a
 tapered baffle located in the center, which also serves as angle of
 repose, as well as along the circumference of the shaft furnace. Although
 the formation of a central "dead man" can be minimized through the
 wedge-shaped baffle located in the center, there are still inactive zones
 between adjacent discharge devices, which lead to the formation of
 undesirable bulk pyramids as already mentioned.
 None of the arrangements of discharge devices and/or baffles known from
 prior art is capable of preventing the formation of bulk pyramids referred
 to as "dead man" between two adjacent discharge devices each at the inner
 edge of the shaft furnace.
 Accordingly, the object of this invention is to avoid the formation of bulk
 pyramids between two adjacent discharge devices each at the inner edge of
 the shaft furnace or to reduce such formation to an extent that the tips
 of the bulk pyramids are located considerably below the area of the
 reduction gas inlet ports and the latter are no longer concealed by
 nonmovable bulk material.
 SUMMARY OF THE INVENTION
 The invention is characterized in that devices for moving the material in
 the shaft furnace are located between the area of the gas inlet ports and
 that of the discharge devices.
 The moving devices, arranged according to the invention, effectively
 prevent the build-up of bulk pyramids in and above the area of the gas
 inlet ports. Owing to this arrangement, the reaction material is
 extensively mixed and lowered particularly in the upper part of the shaft,
 i.e. the area of the reaction space where reduction processes take place.
 The number of devices for moving the material in the shaft furnace is
 preferably double the amount of discharge devices for lumpy material. The
 large number of moving devices ensure a homogeneous discharge of the
 reaction material.
 According to a specially preferred design, two moving devices each are
 allocated in pairs to one discharge device each so that either of the two
 moving devices is located above as well as beside the discharge device,
 one on the left and the other one on the right. Owing to this special
 arrangement of moving devices according to the invention, removal of bulk
 pyramids starts from their edges. As a result, the height of the bulk
 pyramid is considerably reduced and therefore can no longer cover the gas
 inlet ports located along the circumference of the shaft furnace, which
 ultimately leads to a homogeneous gas distribution in the shaft furnace.
 Moreover, the active volume of the reaction space is increased thereby.
 According to a preferred embodiment, the moving devices are designed as
 screw conveyors whose helicoids have an infinitely high pitch, if
 necessary, at least over a partial area of one screw conveyor each.
 According to a feature of the invention, the helicoids of the screw
 conveyors are comprised of exchangeable paddles and/or paddles fixed to
 the shafts of the screw conveyors. Previous experience has shown that such
 paddles are exposed to high mechanical and abrasive stresses while
 material containing iron oxide and/or sponge iron is being moved. When
 maintenance work is to be carried out at the screw conveyors, it is very
 advantageous not to have to replace the entire screw but only the damaged
 paddles.
 According to another feature of the invention, the shafts of the screw
 conveyors are overhung, i.e. cantilevered, and cooled, if necessary.
 Although the shafts have an essentially cylindrical shape, they can be
 designed with a constant and/or inconstant inward pitch, i.e. tapered
 towards the center of the shaft furnace, at least over a partial area of
 their length.
 According to another feature of the invention, the envelope of the
 helicoids of one screw conveyor each is essentially cylindrical but can be
 designed with a constant and/or inconstant inward pitch, if necessary, at
 least over a partial area.
 The flexible design of shafts and/or helicoids allows adjusting the
 conveying behavior of the screw conveyors to the fluid dynamics of the
 material to be conveyed.
 According to another feature of the invention, the helicoid of each screw
 conveyor is designed in a way that each screw conveyor conveys towards or
 from the center of the shaft furnace or radially to the screw conveyor.
 According to another feature of the invention, the screw conveyors are
 axially movable for temporary service. This embodiment has the advantage
 that each screw conveyor is easily accessible for the purpose of
 maintenance work and that it is not necessary to permanently operate each
 screw conveyor but that they can be temporarily used for removing the bulk
 pyramids.
 According to another feature of the invention, the direction of rotation of
 each individual screw conveyor is continuous or discontinuous, clockwise
 or anticlockwise, or oscillating.
 Owing to the flexible motion and direction of rotation, the relevant
 geometrical conditions of the bulk pyramids can be taken into account.
 Moreover, the reaction material is homogeneously mixed.
 According to a preferred embodiment of the invention, the oscillation or
 rotation of two screw conveyors each allocated in pairs to one discharge
 device is oppositely directed. According to this preferred embodiment, the
 conveying direction is essentially radial but may also have a minor axial
 component, if necessary.
 According to another embodiment of the invention, the head of each screw
 conveyor is designed as drill bit in a manner known in general, which
 allows boring into a bulk pyramid caked together in temporary service.
 According to another embodiment of the invention, motors are provided to
 drive the shafts of the screw conveyor. Driving the shafts by means of
 motors allows flexible adjustment of the screw conveyors to the process
 and facilitates installation and dismantling because the drive is mounted
 on the traveling device anyway.
 According to an embodiment of the invention, sensors are provided to
 identify the boring behavior of the screws. An undesirable boring behavior
 of a screw, for example, means that the screw head deviates from the
 desired direction during boring into a bed that may have partially caked.
 Boring is a sensitive process that may cause expensive repair work in case
 of maloperation by the personnel. Hence, sensors form an essential part of
 process control.
 According to another feature of the invention, the speeds and/or the boring
 behavior of the individual shafts of the screw conveyors are controlled
 according to the conveying characteristics and/or the boring behavior, so
 the motion characteristics of the screw and of the boring head can be
 adjusted to the relevant process requirements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1 represents the problem to be solved: The interior of shaft furnace 1
 contains solid bed 2 which is discharged from shaft furnace 1 through
 discharge devices 4 radially arranged above bottom 3 of shaft furnace 1.
 Between radially arranged discharge devices 4 (designed as screw
 conveyors; not represented), high bulk pyramids 5 have built up which
 project over part of gas inlet ports 6 and conceal the latter. The active
 volume of shaft furnace 1 is reduced by the volume of bulk pyramids 5, and
 the gas permeability of the solid bed is not uniform.
 FIG. 2 displays shaft furnace 1 with moving devices 7 arranged according to
 the invention. To each discharge device 4, two moving devices 7 are
 allocated which are located both above and beside discharge device 4, one
 on the left and the other one on the right.
 FIG. 3 displays shaft furnace 1 with moving devices 7 arranged according to
 the invention as well as bulk pyramids 5 reduced because of the use of
 moving devices 7 arranged according to the invention. Gas inlet ports 6
 are no longer concealed by bulk pyramids 5. Solid bed 2 features uniform
 gas permeability, and the active volume of shaft furnace 1 is increased.
 FIG. 4 displays a top view of the plane of moving devices 7 with discharge
 devices 4 located underneath. Two moving devices 7 are allocated to each
 discharge device 4, so wedge-shaped region 8 between two discharge devices
 4 above which bulk pyramids build up is reduced.
 Since the angle of repose is a constant variable depending on the material,
 the height of the bulk pyramid is reduced as its base decreases.
 FIG. 5 displays a detail view of discharge device 4 with two moving devices
 7 located above which are designed as screw conveyors in this case. Arrows
 8 indicate the directions of rotation of moving devices 7, which are
 opposed to each other so that material is conveyed from the bulk pyramids
 (not represented here) to the discharge area of discharge devices 4.
 FIG. 6 displays a schematic view of a conveyor 7. The conveyor includes a
 shaft having a cylindrical portion 9 and a tapered portion 10, on which
 are mounted paddles 11 and drill bits 12, serving as the points of the
 conveyor.