APPARATUS FOR AND A METHOD OF REMOVING MATERIAL

Abstract: Material in liquid or solid form is removed from a surface by means of an open ended ejector pipe which receives a flow of gas under pressure through one or more injectors located along its lenght. In use of the apparatus, a flow of gas is induced into the open end of the ejector pipe sufficient to draw particles of material through the pipe and to eject these particles at a location remote from the free surface of the material.

Description: Apparatus For and a Method of Removing Material This invention relates to apparatus for and a method of removing material in liquid or solid form from a surface; more especially, the invention relates to apparatus for and a method of removing material in liquid or solid form from the surface of a fluid having a density greater than that of the material to be removed. More particularly, but not exclusively, the invention concerns the removal of slag or similar materials from the surface of a liquid metal, e.g. molten iron or steel. Conventionally, slag is removed from the surface of the liquid metal contained in a vessel such as a ladle by raking manually the liquid surface or by means of a mechanical vacuum suction pump. Manual raking is not satisfactory for reasons of inefficiency in that fluid slag readily flows around the rake edges and complete slag removal is difficult whilst liquid metal can be lost both during raking and ladle tilting. Mechanical vacuum pumps can only be used in suction systems incorporating a complete seal at all joints and involve the use of considerable amounts of cooling water directly injected into the suction pipe to ensure solidification of slag immediately it enters the suction pipe. The presence of cooling water is a potential cause of explosion should it become mixed with the liquid metal and may result in injury to plant operatives. Such equipment is complex and maintenance intensive which reflects in its relative expensive capital and running costs. The present invention sets out to overcome these and other disadvantages. According to the present invention in one aspect, there is provided a method of removing a material in liquid or solid form from a surface by drawing such material upwardly through an ejector pipe connected to receive gas under pressure through injectors located along its length. According to the present invention in another aspect, there is provided apparatus for removing material in liquid or solid form comprising an open ended ejector pipe adapted to receive a flow of gas under pressure through one or more injectors located along the length of the ejector pipe whereby, in use of the apparatus, there is induced into the open end of the ejector pipe which lies immediately above the free surface of the material to be removed a flow of gas sufficient to draw particles of such material through the pipe and to eject such particles through the pipe end remote from the free surface of the material. The ejector pipe is preferably formed from a plurality of tubular sections joined together to define the required flow path of gas and particles passing therethrough. -In one arrangement, each pipe section includes at least one injector connectable to a source of gas under pressure and formed with at least one injection nozzle. The pressure of the gas admitted to the or each injector and its direction of entry into the ejector pipe may vary along the height and circumference of the pipe. The gas under pressure may, for example, be air or other readily available suitable compressed gaseous fluid. The ejector pipe may be supported above the surface of the material to be removed by a verticaly movable frame mounted for pivotal movement in a direction transverse to the material surface. The vertical movement of the frame is preferably determined in such a way that the distance between the surface of the material and the lower edge of ejector remains no more than a pre-set dimension by incorporation of a suitable transducer and control mechanism. The pre-set height may be set to suit the individual ejector pipe assembly and its inlet fluid flow and pressure. One method of measuring the height of the ejector above the liquid surface is a line-of- sight optical system as used for casting machine mould level control. The removal of liquid slag by means of an ejector pipe as described can lead to blockage of the device as liquid slag freezes and adheres to the walls of the device to fill the internal diameter. The ejector pipe can be adapted to include one or more features designed to prevent blockage. One such feature is the manufacture of the bottom tip of the device in a heat resistant material such as refractory. This section may be detachably connected to the lowest pipe section. Another feature may be lining the internal diameter of each pipe section with an insulating material such as refractory. The ejector pipe walls, the primary gas and the induced air flow are the main means by which the slag cools. This cooling can be reduced by, for example, the addition of liquid or gaseous fuel to heat the induced air flow over and above that received from the liquid surface. This can be achieved by adding gaseous or liquid fuel in a controlled manner into the device through the injector nozzles along with the primary gas flow or from external burners suitably located around the outside of the bottom ejector pipe section. ø Blockage of the internal diameter can alternatively be prevented by freezing the liquid slag so that it canot adhere to the walls of the ejector. The ejector pipe can be adapted to include for the addition of a coolant in a controlled manner into the device via the injector nozzles into the ejector pipe along with the primary gas flow. The coolant may be water which in conjunction with the primary gas flow forms a mist giving excellent heat removal characteristics at minimum water flows as well as being fail safe in that if the primary air supply ceases, so would the flow of water. In any of the adaptations outlined previously, it is possible that some slag may adhere to the internal diameter of the device. This slag build-up can be readily removed by vibration or percussive impact of the ejector pipe to shake the slag from the walls. The invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which:- Figure 1 is a longitudinal section taken through apparatus in accordance with the invention; Figure 2 schematicaly illustrates four alternative constructions of ejector pipes in accordance with the invention; Figure 3 is an elevational view partly in section of the apparatus illustrated in Figure 1 and handling apparatus therefore, and Figures 4 and 5 are respectively side elevational and plan views of alternative handling apparatus to that illustrated in Figure 3« The apparatus illustrated in Figure 1 comprises an ejector pipe 1 including a tip and a plurality of connected tubular sections 3 each including an annular injector nozzle 4 formed with an array of discharge orifices 4c and connected to a supply of gas under pressure, e.g. air or inert gas where chemical reaction is to be avoided. As illustrated, the tip 2 of the pipe 1 is positioned a small distance above the surface of a bath of liquid metal 5 contained in a vessel, e.g. a ladle. A slag layer 6 is formed on the surface of the liquid metal which should be removed to improve the efficiency of further processing of the liquid metal. The tip 2 has a shaped entry and is manufactured from a consumable material, preferaly one with a high melting point, e.g.refractory material. The sections 3 may be manufactured from tubular steel and the injector nozzles 4 from any suitable material, these including steel or ceramic. The tip 2 is 20 preferably connected to the adjacent end of the lowermost section 3 by a simple arrangement of pins and clips or is bolted thereto for ease of replacement. The sections 3 may be joined together by any suitable means such as welding. The assembled sections 3 define the path to be taken by the flow of gas through the pipe 1. As illustrated, the sections 3 define an arcuate flow such that ejected material falls clear of the bath of liquid material and its containment vessel. Controlled amounts of a fluid coolant, e.g. water, may be introduced into the ejector pipe 1 through the injector nozzles 4c at locations remote from the tip 2 to aid solidification of particles of liquid slag drawn through the pipe 1. A liquid or gaseous fuel may be combusted to produce heat to maintain the slag in a molten state and prevent it from adhering to the internal walls of the pipe. The fuel may be added through the injector nozzles or alternatively be introduced through burner nozzles mounted on the outside of the ejector pipe to heat the- induced air flow over and aove that received from the surface of the slag layer 6. In operation of the illustrated apparatus the ejector head is suspended from support trunnions secured around the upper end of the pipe to ensure that the ejector pipe is maintained vertically over the free surface of the bath. Compressed gas is introduced into the pipe 1 through the injectors to create an upward flow of compressed gas over the internal surfaces of the sections 3- The flow of gas to each injector nozzle may be controlled to achieve an even or varied flow along the length of the ejector pipe. Similarly, the pattern of discharge nozzles 4c may be selected to provide a given flow pattern. In addition, the direction and angle at which the gas flow is introduced into the ejector pipe may be selected by suitable design of the injector nozzles. Thus, the gas flow may initially be directed parallel to the longitudinal axis of the respective pipe section or inclined thereto. The height of the slag suction device is seleted and the pressure of the gas injected into the pipe 1 through the injectors is maintained at a level sufficient to produce a gas flow capable of lifting particles of the less dense slag and transporting them through the device and over the edge of the contaning vessel, but incapable of lifting particles of the denser liquid metal below the slag layer. The primary pressurised g-as injected into the ejector pipe 1 through the injectors 4 reduces the pressure existing at the shaped entry of the tip 2 to a level below atmospheric or that pertaining above the free surface of the slag to induce a flow of gas into the shaped entry and through the pipe 1. This induced gas flow mixes with the gas injected through the nozzles 4c and is discharged through the open end of the pipe remote from the tip 2. The reduced pressure at the shaped inlet to the head causes a peak 7 of slag to form below the tip entry with the result that the flow of gas drawn into the pipe over the slag peak shears droplets from the slag surface which are drawn into the pipe by the gas flow. As droplets pass upwardly through the pipe they are cooled and further fragmented by the compressed gas introduced through the injectors 4. Solidification of the slag particles may be aided by coolant introduced into the pipe at locations remote from the tip. Alternatively to prevent solidification liquid or gaseous fuel may be introduced continuously or during specific periods during slag removal into the ejector pipe 1 either with compressed gas injected through the injector nozzles 4c or separate therefrom. From the foregoing, it will be appreciated that efficient operation of the ejector pipe depends upon the pressure of gas admitted to the pipe through the injector nozzles 4c and the height of the tip 2 above the surface of the slag layer 6. There is a relationship between the gas flow rate supplied to the ejector pipe and the induced secondary flow which controls the removal of the liquid slag and ensures its passage through the apparatus. In general the ejector design, the flow rate supplied to it, and its distance from the slag surface should be such as to ensure a superficial gas velocity at the entrance to the ejector pipe in the region of at least 40 m/s. The required distance between the tip 2 and the slag surface may be controlled using a closed loop control incorporating an ejector pipe height drive with feedback from position sensors arranged to detect the relative position between the tip 2 and the free surface of the slag layer. A typical method of measuring the height is by optical line-of-sight systems.. Four alternati e constructions of ejector pipe 1 are schematically illustrated in Figure 2. The ejector pipe 1 illustrated in Figure 2a comprises four » tubular sections 3 in place of the th_ree sections illustrated in Figure 1. Full annular injector nozzles 4 are positioned adjacent the entry end of the pipe 1 and intermediate the adjacent sections 3- The ejector pipe illustrated in Figure 2b has three tubular sections _ and includes, in addition to the annular injector nozzles 4c, two part annular injector nozzles 4a positioned along the length of two adjoining sections 3. The ejector pipe illustrated in Figure 2c includes a section 3a closed at one end which is positioned to induce a flow of gas which passes across that admitted to the ejector pipe through its entry. A part annular injector 4a is positioned towards the closed end of the section 3a. The ejector pipe illustrated in Figure 2d is similar to that illustrated in Figure 2c; in this construction however, the part annular injector nozzle 4a is replaced by a central injectbr nozzle 4b. Ladles of liquid metal are normally transported by either an overhead crane or within a track mounted vehicle. Where ladles are handled by crane it is preferable that a device which can manipulate the ejector pipe 1 away from or over the top of the ladle is• incorporated. Typical manipulators for this purpose are shown in Figures 3 to 5. Apparatus for supporting and locating the ejector pipe 1 is illustrated in Figure 3 * The pipe 1 is secured to a fabricated arm 10 movable vertically along a vertical guide track of a column 11 by means of a winch 12 connected to drive a continuous strand 13 which is anchored to the arm 10 and which passes over upper and lower pulleys mounted on the column 11. The column 11 forms part of a swinging support frame 14 supported between bearing pedestals 15 mounted on a support structure 16 fabricated from heavy steel sections and mounted on a turntable 17 comprising a slewing ring 18 and a motor driven gear box. The frame is rotatable about a straight line joining the bearing pedestals by means of a pneumatically or hydraulically operated cylinder 19 carried by the structure 16 which co-operates with a lever arm 20 secured to the frame 14. Gas under pressure is supplied to the injector nozles of the ejector pipe 1 through a flexible pipe 21 connected to a source of pressurised gas. As illustrated, the ejector pipe 1 is located above the free surface of a layer of slag floating on the surface of a bath of molten metal contained in a ladle 22. Movement of the pipe towards and away from the slag surface is effected by operation of the winch 12 and movement of the ejector pipe transverse to the slag surface is achieved by means of the cylinder 19 and by the turntable 17. All of these movements can readily be controlled either manually or through a programmable controller. Solidified slag ejected from the ejector pipe 1 may be collected in a suitably positioned collection vessel. Alternatively, or additionally, fume handling apparatus may be provided to enable transport of ejected material to a collection point without contact with the atmosphere. An alternative manually operable system for supporting and locating the ejector pipe is illustrated in Figures 4 and 5. In this apparatus, the ejector pipe is mounted at one end of a beam 23 by means of brackets 24 which receive trunnion arms 25 secured to the external surface of the pipe 1. The beam 23 is supported in a forked pivot 26 which permits angular and rotational movement of the beam. The beam is retained in the pivot 26 by means of a sleeve 27 which encompasses the beam and which is fitted with a counter balance weight 28 for balancing the beam when carrying the ejector pipe 1. The sleeve 27 includes a clamping device 29 operable to prevent rotational movement of the beam about its longitudinal axis when the ejector pipe is in use. The clamping device can be released by movement of a lever 30 to enable the beam and ejector pipe 1 to be rotated through 90° for purposes of manipulating the arcuate pipe over the lip of a ladle before and after use. As will be seen from Figure 5, the assembly of the beam 23 and pivot 26 is supported on an arm 31 which is, in turn, supported for pivotal movement within pedestal bearings 32 mounted on a fixed support frame 33- Gas under pressure is conveyed to the injector nozzles of the ejector pipe 1 by flexible hose 34. Manual manipulation of the apparatus illustrated in Figures 4 and 5 is achieved by means of controls located at the end of the beam 23 remote from the ejector pipe. Thus, the beam 23 may be rotated about its longitudinal axis when the clamping device 29 is released; the beam can be pivoted about the forked pivot 26 to move the ejector pipe in a vertical sense; and, finally, the beam can be rotated about the pivot formed by the pedestal bearings 32 to enable the pipe 1 to sweep over the free surface of the material to be removed. The ejector pipe 1 is maintained at a predetermined angle, normally vertical by means of a pivoting parallelogram formed by the ejector pipe 1, the beam 23, a tie rod 35 and a lever 36. In an alternative arrangement, vertical movement of the ejector pipe may be accomplished by means of a mechanical jacking system. Whereas the invention has been described above with reference to the removal of a material in liquid or solid form from the surface of a more dense fluid, it is to be understood that the invention may be employed to remove a material, such as a slag, from an otherwise empty vessel. The material may be discharged to a location spaced from the vessel or, particularly in the case of a liquid slag sprayed onto the walls of the vessel for insulation purposes or for protection from erosion or for rebuilding after erosion of refractory linings of metallurgical process vessels.

Claims: CLAIMS : 1. A method of removing a material in liquid or solid form from a surface by drawing such material upwardly through an ejector pipe connected to receive gas under pressure through injectors located along its length. 2. Apparatus for removing material in liquid or solid form from a surface comprising an open ended ejector pipe adapted to receive a flow of gas under pressure through one or more injectors located along the length of the ejector pipe whereby, in use of the apparatus, there is induced into the open end of the ejector pipe which lies immediately above the free surface of the material to be removed a flow of gas sufficient to draw particles of such material through the pipe and to eject such particles through the pipe end remote from the free surface of the material. 3. Apparatus as claimed in Claim-2 in which the ejector pipe is formed from a plurality of tubular sections joined together to define the required flow path of gas and particles passing therethrough. 4. Apparatus as claimed in Claim 3 in which each pipe section includes at least one injector formed with at least one injector nozzle connectable to a source of gas under pressure. 5. Apparatus as claimed in any one of Claims 2 to 4 in which the pressure of the gas admitted to the injectors and its direction of entry into the ejector pipe is varied along the height and circumference of the pipe. 6. Apparatus as claimed in any one of Claims 2 to 5 in which the ejector pipe is supported above the surface of the material to be removed by a verticaly movable frame mounted for pivotal movement in a direction transverse to the material surface. 7. Apparatus as claimed in any one of Claims 2 to 6 in which the section of the ejector pipe which, in use, lies immediately above the surface of the material to be removed is manufactured from a • consumable heat resistant material and is detachably connected to an adjacent pipe section. 8. Apparatus as claimed in any one of Claims 2 to 7 in which heating means are provided to heat the induced gas flow to a temperature in excess of that at which the induced gas is admitted to the ejector pipe. 9. Apparatus as claimed in any one of Claims 2 to 8 in which at least one injector is connectable to a source of a coolant. 10. Apparatus as claimed in any one of claims 2 to 9 in which means are provided to vibrate the ejector pipe. 11. Apparatus for removing material in liquid or solid form from the surface of a fluid substantially as herein described with reference to Figure 1 or Figure 2 or Figure 3 or Figures 4 and 5 of the accompanying drawings. 12. A method of removing a material in liquid or solid form from the surface of a fluid substantially as herein described with reference to Figure 1 or Figure 2 or Figure 3 or Figures 4 and 5 of the accompanying drawings.

Inventors: HAWKINS RICHARD JOHN, PERRY ROBERT MAIDENS, ROBERTSON THOMAS, SABHARWAL ANIL KUMAR, HAWKINS, RICHARD, JOHN, PERRY, ROBERT, MAIDENS, ROBERTSON, THOMAS, SABHARWAL, ANIL, KUMAR
Applicants: BRITISH STEEL CORP, BRITISH STEEL CORPORATION
Application year: 1985
Main classification: C21C7
IPC codes: B22D43, C21C7, C22B7, F27D3