Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B14/00—Crucible or pot furnaces
  • F27B14/06—Crucible or pot furnaces heated electrically, e.g. induction crucible furnaces with or without any other source of heat
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B14/00—Crucible or pot furnaces
  • F27B14/06—Crucible or pot furnaces heated electrically, e.g. induction crucible furnaces with or without any other source of heat
  • F27B14/061—Induction furnaces
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B14/00—Crucible or pot furnaces
  • F27B14/08—Details specially adapted for crucible or pot furnaces
  • F27B2014/0843—Lining or casing

Definitions

• the subject of this invention is a crucible and a hearth of an induction furnace for the incineration and vitrification of organic matter, the vitrification of radioactive or non-radioactive waste, the vitrification of hazardous waste and the fusion of refractory bodies.
• the structure of such ovens essentially comprises a refractory concrete hearth comprising cooling water circuits on which is installed a side wall called the crucible, surrounded by an inductive coil where an electric current flows at frequencies above 100 kHz which is the source of the power produced inside the crucible to melt the material present therein.
• These ovens are mainly used for the incineration and vitrification of organic matter, the vitrification of radioactive or non-radioactive waste and the fusion of refractory bodies.
• the side wall of the crucible is normally made of metallic material permeable to magnetic fields. It contains a cooling circuit so that, firstly, the wall withstands the very high temperatures reached to melt refractory materials such as glass and, secondly, to compensate for the electrical power dissipated by joule effect in the structure.
• a crucible is called a "cold crucible”.
• it is normally divided into vertical sectors, joined by their transverse faces by interposing an electrical insulating material, to limit the currents induced in the wall which would produce thermal losses and an electromagnetic coupling between the inductor and the contents of the crucible.
• the vertical sectors are arranged like a barrel stave.
• the cooling circuit • is usually composed of vertical pipes drilled in each of the sectors.
• a first means consists in surrounding the crucible with a circular bandage made of cement or glass fabric impregnated with elastomer or epoxy resin. Another means which offers greater cohesion is to weld the sectors to each other on a circular flange above the inductor where the intensity of the magnetic field is lower.
• a last type of mounting which is preferred for the invention consists in assembling the vertical sectors making up the shell by screws on a circular flange above the inductor. To facilitate assembly, the sectors are provided with assembly tabs on the part mounted outside the shell.
• the sole supporting the ferrule is made up of metal boxes crossed by a cooling circuit placed in refractory concrete or made up of metal tubes of various sections (round, square, rectangular, and) mounted in parallel or in rafters and placed in refractory concrete.
• the boxes or tubes are spaced from each other by a width of refractory concrete.
• One of the faces is positioned so as to be perfectly vis-à-vis with the molten contents of the oven.
• the shape of the boxes can be diverse: rectangular, triangular, etc.
• the known crucibles and soles suffer from insufficiency which can be detailed as follows. To be applicable to the combustion-vitrification of organic materials on molten glass baths, or the fusion of refractory bodies in an induction furnace, much higher frequencies and heats than in other applications are necessary. Risks of electric short circuits can appear between the metallic elements constituting the cold crucible (the sectors, the flanges), constituting the hearth support of the crucible (cooled metal cans) and between the elements of the crucible and the hearth. These short circuits appear even when the electrical insulators between the crucible sectors and the bottom boxes are wide.
• the solution adopted consists in coating the metal sectors constituting the crucible and the metal boxes of the hearth on one or all of their faces with a layer of electrical ceramic insulation: at least on the internal and lateral faces of the sectors facing each other to eliminate electric arcs, or, depending on chemical and electrical attack, on all faces including the head, the foot and the face facing the outside of the oven.
• These ceramic coatings are in addition to the electrical insulators positioned between the crucible sectors and the bottom boxes and they allow perfect electrical protection between the various metallic elements of the furnace and even between the metallic elements and the molten coating.
• Refractory ceramic coatings which are perfectly electrically insulating, are produced for example with an acetylene flame or with a plasma torch. The materials more frequently screened are based on alumina, nullity, cordierite, zircon, zirconia, zirconate and silicon carbide, with different dopants compatible with electrical stresses.
• the metal boxes are placed in the floor by interposing an electrical insulator such as refractory concrete.
• the crucible sectors once coated on one or all of the faces of ceramic electrical insulators, they can be mounted and screwed onto the cooled flange which can also be coated with electrical insulator.
• a mounting of the crucibles will be detailed by screws because it makes it possible to limit the mechanical assembly (local compressions) and thermal (if there are welds) constraints, but the invention applies perfectly to the other mounting types detailed in the state of the art.
• the sharp edges oriented on the internal face of the oven are machined with rounded radius of curvature.
• the removal of any sharp edges by machining in the radius of curvature concerns the edges facing the interior of the induction furnace.
• the presence of chamfers on the other edges, outside the crucible, may suffice without being an obligation.
• the dimensioning of these radii of curvature achieves the following functionalities:
• the radius of curvature should not be small (less than 1 mm) for example to avoid trapping material in the free air gap between the sectors when varying the height of the glass bath, as in some configurations described in the state of the art, it is possible to keep an electrical insulator such as mica in one intersector (mica thickness between 0.1 and 4 mm) or to mount the joined elements without additional electrical insulators than the deposition ceramic.
• the radius of curvature must be small (less than 5 mm) to be sure that the cooled metal sectors are close enough to prevent molten glass from coming into contact with the electrical insulation placed in the intervals, at the risk of damaging it and to make the material flee from the interior of the crucible towards the exterior.
• the invention differs in the specific case of incineration and vitrification applications of organic materials, vitrification of waste and fusion of refractory bodies by the low values of the heat fluxes exchanged between the material to be vitrified and the walls of the furnace.
• these fluxes are weaker by an order of magnitude than in cold metal melting crucibles by the creation against the wall of the furnace of a self-crucible of glass, solid and refractory.
• the electrical protection ceramic materials are perfectly cooled, preventing their degradation, their flaking and above all preventing pollution of the vitrified material.
• FIG. 1 represents a crucible welded in accordance with the prior art
• FIGS. 2 and 3 illustrate an embodiment of a crucible of the invention
• FIGS. 4 and 5 illustrate the method of manufacturing the crucible
• a crucible comprises a refractory concrete hearth which bears the reference 1, a side wall bearing the reference 2, its stainless steel sectors bearing the reference 3, intermediate layers of electrical insulators the reference 4, and turns of the inductor the reference 5.
• the details of construction and arrangement of these elements are in accordance with the preceding description.
• the side part 2 is only partially shown, but it is clear that it extends over a circle or a complete revolution, as for any other crucible including those of the invention.
• Each of the sectors 3 is hollowed out with a cooling circuit 6 extending over almost its entire height and composed here of a pair of vertical parallel conduits and joining at the bottom of the sectors 3 (only one of these conduits being visible in the sectional representation).
• the coolant inlet and outlet holes 7 and 8 communicate the conduits outside sectors 3 and they open into superimposed collectors 9 and 10 belonging to the same flange 11 to which the sectors 3 are welded by a circular bead 12 at their upper outer edge. Even with this weld, it is possible to add an external bandage 13 to the structure under the flange 11 to improve the cohesion of the side wall 2 and ensure gas tightness.
• the drawbacks mentioned previously of the two methods of assembling the side wall 2 do not however disappear if these methods are combined.
• the sole 1 is cooled by a circulation of water in metal cans which have not been shown here.
• the sectors of the side wall are marked with the reference 20. They have the same external shape and are also traversed by a pair of conduits of a cooling circuit 21, the ends of which open to the outside by tubes 23a and 23b (FIG. 3).
• the sectors 20 of the invention are not bare but covered with a ceramic coating 22 which can be chosen from compositions based on alumina, mullite, cordierite, zircons, zirconia, or zirconate, different additives that can be added according to the thermal, chemical and electrical constraints that the crucible will have to face.
• a single sector 20 is shown with the coating 22 in Figure 2, but all are actually provided.
• the coating 22 is present on the sector 20 of FIG. 3, but has not been shown for the sake of lightening the drawing. It is recommended to cover at least the internal face 24 of the sectors 20 and their lateral faces 25 and 26, which are the faces subjected to corrosion and to the appearance of electric arcs; however, it is not bad to also cover the outer face 27, which is shown here or even the upper and lower faces.
• the coating 22 extends to the top of the sectors 20. Its thickness is between 50 ⁇ m and 500 ⁇ m depending on the applications.
• An additional provision to reduce the probability of electric arcs, while allowing better adhesion of the coating 22, is to remove the sharp edges between the faces 24 to 27 of the sectors 20: here, the edges 28 and 29 internal to the oven (between the internal face 24 and the lateral faces 25 and 26) have been rounded to a radius of curvature which may be from one to five millimeters, and the other edges, such as 30 and 31 (between the external face 27 and the other lateral 25 and 26) were simply chamfered; this latter arrangement is only necessary to facilitate adhesion of the coating 22 at the junction of two coated faces.
• the horizontal edges of the sectors 20, at the top and at the bottom, can also be rounded or chamfered if electric arcs are to be feared with neighboring elements.
• the sectors 20 comprise an upper tab 32, also in a sector of a circle which overhangs the external face 27. It comprises a notch 33 ′ opening to the outside.
• a flat flange 34 of circular shape is placed on all the legs 32 and includes threads 35. Screws 36 are engaged in the threads 35 through the notches 33 and support below the lugs 32, which they hold against the flat flange 34.
• the sectors 20 are held in place and form a single assembly.
• An external bandage 37 can be added to seal the crucible in air and make the assembly even firmer, without however being essential; it can be made of solid glass fabric impregnated with elastomer or epoxy resin. Finally, layers of electrical insulator 38, made of mica for example, can be introduced between the lateral faces 25 and 26 of neighboring sectors 20.
• a ceramic coating 57 can also be placed on the flange 34, and above all on its lower face 58 which touches the tabs 32 of the sectors 20. Here also it is useful to chamfer the edges joining two ceramic coated faces.
• the sectors 20 after being machined to a precision sufficient in the necessary places (in particular on the lower face, placed on the concrete floor 1, on the upper face of the legs 32 and on the lateral faces 25 and 26) and coated with ceramic by plasma deposition and abrasive polishing , are roughly placed on the flat flange after being turned over, a conical centering wedge 42 is placed on them, and clamps 43 are engaged around them and tightened to approach them until they all touch the conical flank of the corner 42.
• the layers of electrical insulation 38 have already been inserted.
• the diameter of the side wall and its preload can be adjusted.
• the screws 36 are then tightened to join the tabs 32 to the flat flange 34 located under them.
• the bandage 37 can be formed first by windings 371 situated between the cable ties 43, then by the complementary windings when the cable ties 43 have been removed. This laying of the bandage in two stages makes it possible not to loosen the preload of the side wall by prematurely loosening the collars 43.
• FIGs 6 and 7 illustrate the sole 46 of the embodiment of the invention. It comprises a main plate 47 provided with a central concavity which occupies the cooling boxes 48. Each box 48 comprises a supply pipe 49 and a water outlet pipe 50. In a similar manner to the sectors 20 of the crucible, care is taken to protect the boxes 48 metallic chemical and thermal aggressions and to guard against the opposition of electric arcs arising from them. They too are coated with ceramic, at least on the upper face (overlooking the molten bath) 51; the coating has the reference 52.
• edges 53 delimiting this upper face 51 are rounded, also at a radius of curvature of one to five millimeters; the other edges 56 (vertical and delimiting the lower face 55) can also be rounded or at least chamfered, especially if the lateral faces 54 and lower 55 which they delimit are also coated with ceramic.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Crucibles And Fluidized-Bed Furnaces (AREA)
• Furnace Housings, Linings, Walls, And Ceilings (AREA)
• Furnace Details (AREA)
• Vertical, Hearth, Or Arc Furnaces (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Magnetic Heads (AREA)
• General Induction Heating (AREA)
• Table Devices Or Equipment (AREA)
• Cookers (AREA)

Applications Claiming Priority (3)

Publications (2)

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• 2002
  • 2002-02-04 FR FR0201276A patent/FR2835601B1/fr not_active Expired - Lifetime
• 2003
  • 2003-01-31 DE DE60300941T patent/DE60300941T2/de not_active Expired - Lifetime
  • 2003-01-31 AT AT03709913T patent/ATE298873T1/de not_active IP Right Cessation
  • 2003-01-31 EP EP03709913A patent/EP1485664B1/de not_active Expired - Lifetime
  • 2003-01-31 JP JP2003566474A patent/JP4287281B2/ja not_active Expired - Lifetime
  • 2003-01-31 AU AU2003214344A patent/AU2003214344A1/en not_active Abandoned
  • 2003-01-31 RU RU2004126690/02A patent/RU2301949C2/ru active
  • 2003-01-31 WO PCT/FR2003/000299 patent/WO2003067166A2/fr not_active Ceased
  • 2003-01-31 KR KR1020047011996A patent/KR101006751B1/ko not_active Expired - Fee Related
  • 2003-01-31 ES ES03709913T patent/ES2243892T3/es not_active Expired - Lifetime
  • 2003-01-31 CN CNB038032449A patent/CN100402962C/zh not_active Expired - Lifetime
  • 2003-01-31 US US10/501,919 patent/US6996153B2/en not_active Expired - Lifetime

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