Abstract:
An arrangement for the dosed introduction of fine-particulate material into a reactor vessel comprises a fluidized bed sluice, into which a material supply means enters from above and into which a gas duct feeding a fluidization gas runs in the lower end region thereof and which includes an overflow tube for conveying on the fine-particulate material. In order to introduce the fine-particulate material into the reactor vessel at specific zones, a plurality of independently connectable fluidized bed sluices are provided outside of the reactor vessel, the fluidized bed sluices having overflow tubes which project into the interior of the reactor vessel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an arrangement for the dosed introduction of fine-particulate material into a reactor vessel, comprising a fluidized bed sluice, into which a material supply means enters from above and into which a gas duct feeding a fluidization gas runs in the lower end region thereof and which includes an overflow tube for conveying on the fine-particulate material, as well as to a plant including an arrangement of this type and a method of operating this arrangement. 
     2. Description of the Related Art 
     An arrangement of the aforementioned type is known from U.S. Pat. No. 4,277,205. This arrangement features a central tube, from which a plurality of overflow tubes lead to charging points distributed over the cross section of the reactor vessel. The central tube, together with the overflow tubes, is arranged inside the reactor vessel in a way that it can be turned in order to ensure a uniform distribution of the fine-particulate material in the reactor vessel. The arrangement inside the reactor vessel is required for turning the overflow tubes but causes heavy wearing-out of the turning mechanism and of the seals, particularly if the reactor vessel is used for reactions taking place at higher temperatures and if violent gas flows occur. 
     The known arrangement has the disadvantage that the fine-particulate material can be fed into the reactor vessel only uniformly distributed over the cross section but not specifically to certain charging points or charging zones. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to avoid these disadvantages and difficulties and to create an arrangement of the aforementioned type and a method of operating this arrangement, which allow a dosed introduction of fine-particulate material into the reactor vessel. In particular, the time-dependent feeding of fine-particulate material at specific points in various zones of the reactor vessel has to be made possible, wherein the arrangement, however, may be of rigid and fixed design so as to avoid wear problems and to minimize investment and maintenance expenses. 
     Another object of the invention is to create an arrangement for the introduction of fine-particulate reduction product from charging substances comprised of ore, in particular, iron ore and fluxes and at least partially having a portion of fines at an arrangement for the production of metal melts, in particular pig iron, wherein the reduction product forms highly gas-permeable zones, which, however, are connected with one another three-dimensionally, thus ensuring good accessibility for the reducing gas. 
     According to the invention, this problem is solved in an arrangement of the aforementioned type by a plurality of fluidized bed sluices which provided outside of the reactor vessel and which can be connected and disconnected independently of one another, whose overflow tubes project into the interior of the reactor vessel. 
     A preferred embodiment is characterized in that the arrangement is provided with a central tube forming a fluidized bed sluice and that at least two overflow tubes, each running into a further fluidized bed sluice, depart from the central tube, wherein each further fluidized bed sluice is formed by a receptacle, into which a gas duct feeding a fluidization gas runs in the lower region thereof and from which at least one overflow tube departs, running into the reactor vessel, and wherein the fluidization gas ducts each are equipped with valves for the locally dosed introduction of the fine-particulate material. 
     By means of the valves, individual or several of the further fluidized bed sluices enclosing the central tube can be activated or deactivated. The fine-particulate material first accumulates in the central tube and, when the central tube is being charged with a fluidization gas, also fills the further fluidized bed sluices. Depending on whether a fluidization gas is fed to one of the further fluidized bed sluices, this fluidized bed sluice becomes clear and the fine-particulate material can enter the reactor vessel from this fluidized bed sluice via the overflow tube. By alternately connecting the fluidization gas, the material flow and, thus, also the charging point or charging zone in the reactor vessel can be varied. Furthermore, the fine-particulate material can be dosed via the gas volume, therefore the valves are expediently designed as flow control valves. 
     It has been proved that a dosed introduction is expediently accomplished by means of at least two, yet eight at the most, and preferably three or four fluidized bed sluices. 
     In order to prevent the fine-particulate material entering the reactor vessel through an overflow tube in the form of a strand from fanning, the ends of the overflow tubes running into the reactor vessel are advantageously provided with a gas feeding means for forming a gas jacket developing on the lower end of the overflow tube, wherein the overflow tube expediently comprises a double jacket defining an annular gap cavity and the gas feeding means runs into the annular gap cavity. 
     For the formation of a gas jacket, the lower end of the overflow tube is preferably provided with an annular gap opening or several openings for the exit of a gas flowing through the annular gap cavity. 
     To allow charging of fine-particulate material to the entire cross section of the reactor gas, the fluidized bed sluices are expediently provided at a distance from the central tube and preferably in a radially symmetric arrangement. 
     An arrangement for the production of metal melts, in particular, pig iron, from charging substances comprised of ore, in particular, iron ore and fluxes and at least partially having a portion of fines, is characterized by at least two fluidized bed reactors consecutively connected in series, wherein the ore is conducted from one fluidized bed reactor to another fluidized bed reactor via conveying ducts in one direction and the reducing gas is conducted from one fluidized bed reactor to another fluidized bed reactor via reducing-gas connection ducts in the opposite direction, and by a melter gasifier, into which a supply duct conducting the reduction product from the fluidized bed reactor arranged last in the flow direction of the ore runs via an arrangement for the dosed introduction of the fine-particulate reduction product, as well as a duct supplying carbon and another duct supplying oxygen, a reducing-gas conveying duct departing from the melter gasifier and running into the fluidized bed reactor arranged last in the flow direction of the ore. 
     The gas ducts for feeding the fluidization gas advantageously depart from a reducing-gas conveying duct. 
     In order to form a highly gas-permeable bed from the fine-particulate material in the reactor vessel, the fluidized bed sluices, which are preferably arranged beside the central tube, are alternately activated. 
     According to a preferred embodiment, the fluidized bed sluices are activated on grounds of process measurements of a process occurring in the reactor vessel, by means of which the position of a charging point or charging zone for fine-particulate material is determined in the reactor vessel, whereupon the fine-particulate material is distributed by specifically switching off and on the fluidized bed sluices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention is explained in greater detail by the embodiments shown in the drawing. 
     FIG. 1 schematically represents the example of an overall arrangement for the production of metal melts, in which the arrangement according to the invention is advantageously used. 
     FIG. 2 illustrates a detail of FIG. 1 on enlarged scale. 
     FIG. 3 represents a plan view of FIG.  2 . 
     FIG. 4 shows a detail of an end of the overflow tube on enlarged scale according to a modification embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The arrangement according to FIG. 1 comprises three fluidized bed reactors  1  to  3  consecutively connected in series, wherein a fine-particulate material containing iron oxide, such as fine ore, is conducted to first fluidized reactor  1 , where the fine ore is preheated and possibly prereduced in preheating stage  5 , via ore conveying duct  4  and subsequently from fluidized bed reactor  1  to fluidized bed reactors  2 ,  3  via conveying ducts  6 . In fluidized bed reactor  2 , prereduction takes place in prereduction stage  7 , and in fluidized bed reactor  3 , the fine ore is finally or finish-reduced to sponge iron in final reduction stage  8 . 
     The reduced fine-particulate reduction material, i.e. sponge iron, is conducted to melter gasifier  10  via conveying duct  9  in a specific way as described later. In melter gasifier  10 , a reducing gas containing CO and H 2 , which is formed from carbon carriers such as coal, and oxygenous gas in melter gasifier zone  11  formed by a fluidized bed. This reducing gas is introduced into fluidized bed reactor  3  via gas discharge duct  12 , which serves as reducing-gas conveying duct  12  for fluidized bed reactor  3 , which is arranged last in the flow direction of the fine ore. 
     The reducing gas is discharged from melter gasifier  10  via several gas outlet sockets of radially symmetric arrangement. 
     The reducing gas is conveyed from fluidized bed reactor  3  to fluidized bed reactors  2  to  1  in counterflow to the ore flow via connection ducts  13 , discharged from fluidized bed reactor  1  as top gas via top gas discharge duct  14  and subsequently cooled and scrubbed in wet scrubber  15 . 
     Melter gasifier  10  comprises a supply duct  16  for solid carbon carriers, supply duct  17  for oxygenous gases and possibly supply ducts for carbon carriers which are liquid or gaseous at ambient temperature, such as hydrocarbons, and for burnt fluxes. In melter gasifier  10 , molten pig iron or molten steel input material and molten slag accumulate beneath melter gasifier zone  11 , which are tapped via taphole  18 . 
     In reducing-gas conveying duct  12 , which departs from melter gasifier  10  and runs into fluidized bed reactor  3 , dust-collecting means  19 , such as a hot gas cyclone, is provided, wherein the dust particles separated in this cyclone are fed to melter gasifier  10  via return duct  20  with nitrogen as conveying means and via burner  21  under oxygen injection. 
     The reducing gas temperature can be adjusted by the preferably provided gas return duct  25 , which departs from reducing-gas conveying duct  12  and returns part of the reducing gas into the reducing-gas conveying duct  12  via scrubber  26  and compressor  27 , upstream of the arrangement of hot gas cyclone  19 . 
     To adjust the preheating temperature of fine ore, an oxygenous gas, such as air or oxygen, can be fed to preheating stage  5 , i.e. fluidized reactor  1 , via duct  28 , which results in partial combustion of the converted reducing gas fed to preheating stage  5 . 
     According to the invention, the fine-particulate sponge iron is charged via charging means  29 , which is located at dome  30 , which closes melter gasifier  10  towards the top, and represented on enlarged scale in FIG.  2 . 
     Charging means  29  is formed by central tube  31  representing the fluidized bed sluice, into which conveying duct  9  runs from above. The lower region of central tube  31  has a gas-permeable bottom  32  for forming a fluidized bed sluice, to which fluidization gas is fed via gas duct  33  feeding fluidization gas. Gas duct  33  is a branch duct of gas return duct  25 . 
     From central tube  31 , overflow tubes  34 —three according to the represented embodiment—depart at a distance from the gas-permeable bottom, which lead radially symmetrically downwards at an angle from central tube  31  located centrally above melter gasifier  10 . These overflow tubes  34  run into further fluidized bed sluices  35 , which are formed by receptacle  36  and which, analogously to the central tube, are provided with gas-permeable bottom  32  in the lower region, with a junction of a gas duct  33  feeding a fluidization gas, and with overflow duct  37  departing in the upper region. The overflow ducts are arranged radially outwards and project through dome  30  of melter gasifier  10  into the interior of the latter. 
     All gas ducts  33  which run into one of fluidized bed sluices  31 ,  35  are provided with valves  38  so as to allow the permeability to and conveyance of or stoppage of conveyance of the fine-particulate reduction material by activating and deactivating each of fluidized bed sluices  31 ,  35 , without requiring a mechanical actuation of parts coming into contact with the fine-particulate hot reduction material. By alternately activating various of the further fluidized bed sluices  35  and, thus, conveying via various overflow tubes  37 , a more concentrated material flow can be achieved than by continuously conveying material via all overflow tubes. As a result, the discharge of fine-particulate material from melter gasifier  10  with reducing gas  12  existing melter gasifier  10  can be minimized because strands  39  entering the melter gasifier through overflow tubes  37  are denser and more compact. 
     The alternate activation and deactivation of overflow tubes  37  can also be used to counteract any nonuniformity in distribution of circumferential temperature in melter gasifier  10  or of the gas flow rates through gas outlets. In this case, process measurements are used to activate or deactivate a specific overflow tube out of overflow tubes  37  via a process computer in order to achieve a higher degree of equidistribution. 
     The temporary activation and deactivation of overflow tubes  37  can also be used to form lenses of particulate direct reduction material in melter gasifier  10 , which are enclosed by degassed coal particles (char particles) and, thus, by optimally gas-permeable zones on all sides. The reducing gas can diffuse well into the lenses formed by fine-particulate direct reduction material from all sides. 
     Moreover, the use of fluidized bed sluices  31 ,  35  allows charging against a higher pressure in melter gasifier  10  as the pressure difference between fluidized bed reactors  31 ,  35  and melter gasifier  10  can be eliminated in fluidized bed sluices  31 ,  35 . Furthermore, the material to be fed into the melter gasifier can be easily dosed by controlling the flow rate of the fluidization gas. 
     According to an embodiment represented in FIG. 4, end regions  40  of overflow tubes  37 , which project into the interior of melter gasifier  10 , are designed as double jacket tubes  41 . Outer jacket  42  and inner jacket  43  of double jacket tube  41  define annular gap cavity  44 , whose end  45 , which is located outside of melter gasifier  10 , is connected to closed-circuit supply duct  46  for cooling gas. Cooled reducing gas branched off from gas return duct  25  via branch duct  47  preferably with a further compressor not represented in greater detail is used as cooling gas. At end  48  of double jacket tube  41 , which projects into the interior of melter gasifier  10 , either annular gap opening  49  or several adjacent holes, with center lines located approximately in parallel with longitudinal center line  50  of double jacket tube  41 , are provided, through which the cooling gas flows into the interior of melter gasifier  10 . 
     The sponge iron, which forms a freely falling strand  39  at lower end  48  of double jacket tube  41 , flows through central interior  51  of double jacket tube  41 . Lower end  48  of double jacket tube  41  is located at a vertical distance from dome  30  at a point where the reducing gas has not yet reached its maximum flow velocity. This strand  39  is enclosed by the cooling gas also exiting at lower end  48  of double jacket tube  41  and forming gas jacket  52  at this point and is prevented from expanding. This gas jacket  52  thus forms a protective covering for at least part of the height of free fall of sponge iron—analogously to double jacket tube  41 , so the fine particles of the sponge iron are not entrained by the reducing gas ascending at a relatively high velocity. 
     At level  53 , where strand  39  expands as the supporting effect of the gas jacket weakens, the velocity of the reducing gas is considerably lower, so the fine particles are not prevented from falling or descending into the fluid bed of melter gasifier zone  11 . 
     The cooling gas velocity at the point of exit from double jacket tube  41 , i.e. its lower end  48 , is at least 10 times and preferably 50 to 100 times higher than the maximum velocity of the reducing gas. 
     Thus, the gas jacket may be relatively thin-walled, so the volume of the reducing gas returned into melter gasifier  10  is relatively small. 
     As cavity  44  of double jacket tube  41  is flown by cooling gas, which subsequently exits at lower opening  49  of double jacket tube  41 , a cooling effect is achieved in accordance with the mechanical load on double jacket tube  41 . 
     The largest cooling effect of the cooling gas is achieved at the point of maximum load on double jacket tube  41  by its dead weight, i.e. in the zone where double jacket tube  41  passes through dome  30  of melter gasifier  10 . While the cooling gas is flowing on through cavity  44  of double jacket tube  41 , the cooling gas heats up, which results in an increase in cooling gas velocity. Therefore, relatively short double jacket tubes  41 , whose mechanical and thermal loading is accordingly lower than in the case of very long downpipes reaching up until shortly above the fluid bed, will suffice. As a result, the design according to the invention features a very high stability. 
     Owing to the cooling effect, very expensive special materials on special ceramic basis or super alloys on Fe basis are not required. On the contrary, it will suffice to manufacture double jacket tube  41  of elevated-temperature steel.