HIGH SHEAR MIXER AND GLASS MELTING APPARATUS AND METHOD

nia, OH 43560 (US). (74) Agent: HEINL, Kevin, J.; Brooks & Kushman, 1000 Town Center, Twentv-Second-Floor, Southfield, Ml 48075 (US). (81) Designated States: AT, AT (European patent), AU. BB, BE (European patent), BF (OAP1 patent), BG, BJ (OAPI patent), BR, CA. CF (OAPI patent), CG (OAPI patent), CH, CH (European patent), CI (OAPI patent), CM (OAPI patent). DE, DE (European patent), DK. DK (European paient), ES, ES (European patent), FI, FR (European patent), GA (OAPI patent), GB, GB (Euro¬ pean patent), GN (OAPI patent), GR (European pa¬ tent), HU, IT (European patent), JP, KP, KR, LK, LU, LU (European patent), MC (European patent), MG, ML (OAPI patent), MR (OAPI patent), MW, NL, NL (Euro¬ pean patent), NO, RO, RU, SD, SE, SE (European pa¬ tent), SN (OAPI patent), TD (OAPI patent), TG (OAPI patent). Published Wiih international search report. (54)Title: HIGH SHEAR MIXER AND GLASS MELTING APPARATUS AND METHOD RAW MATERIAL TREATMENT FACILITY '53 (57) Abstract A glass melter (30) having a mixing impeller (34) for converting a feed stream (38) supplied to a vessel (32) into a vitrified glass melt (50). Heating means such as electrodes (36) or a gas burner (58) are used to heat the glass melt (50). Electrode (36) ar¬ rangements are proposed for minimizing current flow through the impeller (34). Current flow through a special continuous circu¬ lar impeller or conical pump (70) is disclosed. A cylindrical vessel (98), triangular vessel (94), square vessel (32), and hexagonal vessel (96) are disclosed. Methods of processing particular waste streams are disclosed including coated mineral Fibers, fly ash, radioactive material, chemical waste and the like. HIGH SHEAR MIXER AND GLASS MELTING APPARATUS AND METHOD TECHNICAL FIELD The present invention relates to glass melting methods and apparatus and more particularly relates to glass melting apparatus having a highly stirred portion of the melt volume. BACKGROUND OF INVENTION Vitrification holds promise as an approach to disposing of hazardous wastes and recycling glass manufacturing scrap. In the manufacture of glass, vitrifiable material is heated to its melting point and then cooled to form glass. Conventional glass-making furnaces are large refractory lined tanks using direct heat from gas burned in the furnace above the upper surface of a pool of molten glass. Electric glass furnaces have also been developed which heat vitrifiable material by application of electrical energy through the material which is commonly referred to as Joule effect heating. Fluid flow in such furnace is primarily convective flow. In either gas fired or electrically heated glass-making furnaces, only limited agitation, if any, of the glass bath is permitted so as to minimize formation of bubbles in the glass. Bubbles are generally undesirable in finished glass products. In the early 1970's, Owens-Illinois developed a three step rapid melting refining system described in U.S. Patent Nos. 3,850,606; 3,554,885; 3,988,138 and 3,819,350. This rapid melting refining system project is summarized in an article entitled "Rapid Melting and Refining System", Ray S. Richards, Ceramic Bulletin, Volume 67, Number 11, 1988 Page 1806. In the rapid TT \J 7*' l*J*J>Jém melting refining system, the glass-making process was divided into three separate steps. Special machinery was designed for heating glass to melt batch material in a first step, homogenizing glass to remove sand grains and seeds in a second step and refining the glass mix by the removal of seeds and bubbles by centrifuging in a third step. The Owens-Illinois system was directed to the manufacture of glass used in making containers and the like. The rapid melting system achieves an equivalent melting capacity of a conventional cold top electric melter with only ten to fifteen per cent of the melt area required by the conventional melter. The smaller melter size and lower temperatures reduce volitization and heat losses. In addition, the size and cost of air pollution control equipment may be reduced. Lower average temperatures for maintaining a glass melt in molten condition of 100 to 200°F are achieved because a uniform integral glass temperature is maintained. These advantages of the rapid melting process for recycling or vitrification were not recognized by the trade prior to this invention. The 1988 Richards article presented the results of the earlier work and proposed adaptation of the Owens-Illinois process for vitrification of hazardous waste material including low-level radioactive waste, municipal incinerator waste and asbestos waste material. However, an apparatus and method for implementing that proposed process had not been attempted and was not disclosed or suggested in the 1988 Richards article. The Owens-Illinois system employed the impeller of the mixing device as a primary electrode for Joule-effect heating. Current concentration at the tips of the impeller and the use of single phase power limited scale up of the Owens-Illinois melter. The problems related to converting the melting and refining system proposed by Owens-Illinois to vitrification of hazardous waste material and recycling are addressed by the present invention. The present invention also addresses some of the unsolved problems which were encountered by the rapid melting and refining system referred to above. The primary problems associated with conventional gas and Joule heated melters is their large size and cost, expensive air pollution control equipment, energy costs, their need for continuous uninterrupted production and their inability to change production rates significantly without quality upsets. Another kind of problem encountered in conventional glass-making or vitrification processes can be categorized in part by reference to the feed stream supplied to the glass melting furnace. The conventional feed stream for the glass-making process includes "raw batch" and may also include cullet such as recycled bottles, glass beads, specialty glasses, window glass or glass foam. "Raw batch" may also include mixtures of silica, alkali and stabilizing ingredients such as lime, alumina, lead and barium. A primary problem associated with processing such feed streams is segregation and subsequent homogeneity control. Another problem with prior art systems is that pre-blended batch can only be pre-heated to a limited extent without it adhering to and blocking equipment. It would be desirable to recycle scrap from mineral wool production. Fiberglass scrap may have up to fifteen per cent organic binder. When this scrap is added to conventional melters, carbon residue from organic binders in the scrap is trapped in the melt and creates an unacceptable black glass. Scrap mineral fibers are light-weight and tend to float on the surface of the glass melt where they obstruct heat transfer. Light-weight feed streams also can be carried out of the furnace in the exhaust gas stream. Fly ash and bottom ash from incinerators generally referred to as ash, may include highly toxic material which can be made resistant to leaching by vitrification in a glass melting furnace. Fly ash presents problems which are in some respects similar to problems faced in recycling scrap mineral fibers, in that a light-weight, low density feed stream must be introduced into the glass melt. An additional problem relating to the vitrification of ash is that ash changes composition depending upon the source of ash and the constituents of the waste incinerated. For example, in the fall of the year a large volume of organic waste from leaf disposal is processed in municipal waste incinerators. This change in composition of the ash may require modification of the chemical constituents supplied to the glass melt in addition to the ash. Fly ash also presents special problems due to its toxicity which creates handling problems. Radioactive wastes may be in the form of a liquid slurry or dry waste. Radioactive waste can further be divided into high-level, intermediate and low-level radioactive waste. Another radioactive waste stream is contaminated earth. A problem associated with vitrification of radioactive waste is handling radioactive material in a safe manner. Some radioactive waste streams include absorbent pads used to absorb minor spills of contaminated material at radioactive sites. One problem associated with the disposal of absorbent pads is the large volume of organic material used to absorb a small amount of radioactive material which exacerbates waste disposal problems. Industrial waste feed streams including those from plating, painting and other industrial waste present special waste disposal problems which can be addressed by vitrification. Toxic inorganic substances found in chemical and industrial waste streams may be disposed of with excellent leach resistance when vitrified. Problems relating to chemical industry waste include disposal of incinerator bottom and fly ash. Bottom ash may include a considerable volume of metal which can interfere with Joule effect heating. It is anticipated that other feed streams, including but not limited to asbestos and refractory fibers, may be processed by vitrification and problems associated therewith may be solved by applicant's invention as summarized below. DISCLOSURE OF INVENTION According to the present invention there is provided an apparatus for melting material comprising: a vessel having an opening for receiving feed material which is converted into molten mineral material in said vessel and an outlet port for removing molten mineral material from the vessel; an impeller means disposed in said vessel for mixing feed mat erial and molten mineral material in said vessel; a plurality of electrodes disposed in said vessel for passing electrical energy from one electrode to another through said molten mineral material in said vessel; and power circuit means for electrically heating feed material and molten mineral material in said vessel, said power circuit means being electrically connected to said electrodes, said impeller means being electrically isolated from said power circuit means; characterized in that the outlet port has a teapot spout including a throat portion opening into said vessel below the surface of said molten mineral material in 5a said vessel, the teapot spout also including a riser extending upwardly from said throat portion to an opening through which said molten mineral material is poured from said vessel when said molten mineral material in said vessel exceeds the height of said spout, and the throat portion and the riser of the teapot spout including a plurality of electrodes for heating the molten material in this throat portion and riser. The impeller functions to mix the molten vitreous material and feed material. The impeller may also mix the feed material and molten vitreous material with the atmosphere above the molten vitreous material. Variables relating to the impeller function relate to the type of impeller selected whether radial, axial, conical, etc. The number of blades provided on the impeller, the pitch of the blades, size and angle of the conical impeller and the depth at which the impeller is rotated in the molten material all affect impeller function. Speed of rotation of the impeller and impeller shaft angulation also affect operation. The atmosphere above the molten bath is preferably of a controlled oxidation state. For instance, if it desirable to oxidize feed material constituents, an oxidizing atmosphere may be maintained in the vessel. A slightly negative gas pressure may be maintained in the vessel to draw off gases from the feed material and molten vitreous material as they are mixed. Hazardous gases also may be controlled by providing negative pressure in the vessel. Gas pressure, significantly below atmospheric, can be used to remove gases from the melt. A reducing atmosphere or inert atmosphere may be maintained in the vessel to inhibit oxidization of the impeller or other component parts of the apparatus, to produce reduced melts or to control glass chemistry. The mixing mode of the impeller co-operates with the composition of the atmosphere in the apparatus to process molten vitreous material. The rate of interaction with the atmosphere in the vessel can be modified by the mixing mode. The impeller can also be used to draw feed material down into the molten vitreous material at a controlled rate to facilitate oxidization or other reactions on the surface of the bath, or at a rapid rate to maximize feed rate. The impeller can be used to lift molten vitreous material over feed material to submerge feed material in the vessel. Light-weight feed material may be submerged by the mixing action of the impeller wherein vitreous material is caused to engulf feed material as it is added. Two or more impellers :.iay be used to improve mixing rates or draw down of feed material. In one embodiment, the impeller can be a cone shaped centrifugal element which is rotated to pump molten vitreous material upward into the atmosphere in a manner similar to a sprinkler. This mixing mode maximizes surface contact with the atmosphere in the vessel and also allows for swamping of feed material. A conventional impeller disposed partially submerged in the molten vitreous material can turbulently mix molten vitreous material with feed material and may also function in a sprinkler fashion. The height can also be changed to cause the impeller to spray glass above the surface of the melt or clear sludge accumulations from the bottom of a vessel. The height of the impeller in the molten vitreous material can be adjusted upwardly and downwardly to alter the density of the glass output. Impeller composition is matched to the atmosphere in the vessel. For instance, a molybdenum impeller may be selected for operation in a submerged melt of many glasses regardless of the oxidation state of the atmosphere. If a molybdenum impeller is used in a melter with an oxidizing atmosphere, the molybdenum will oxidize if the impeller becomes exposed to the atmosphere through either the drawing down of atmosphere into the bath or by operating the impeller in a partially submerged mode. Consequently, it is preferable to operate a molybdenum impeller in a reducing or inert atmosphere if contact with the molybdenum impeller is made by the atmosphere. The impeller may also include cooling/circulation means to prevent oxidation of the impeller. A cooling medium may be circulated partially or fully through the impeller shaft and impeller blades depending upon the requirements of an application. In a preferred mode of the invention a three phase electrical current is provided to the vessel through a multiple of three electrodes wherein the number of blades corresponds to the number of multiples of three electrodes provided. For example, a system having a large two bladed impeller would have six electrodes arrayed so that when the impeller rotates, the two blades of the impeller are aligned with electrode pairs of identical phase. Similarly, a vessel having nine electrodes and a three bladed impeller may be provided wherein sets of three electrodes of identical phase are aligned with the three blades of the impeller simultaneously. If it is desirable to use single phase electrical current, four electrodes may be provided with an impeller having two or three blades. Two blades provide the best electrical performance, however, three blades are better for mixing and are better than four blades electrically. A three bladed impeller can be used with four electrodes which are arrayed so that the three blades of the impeller are not aligned with any two electrodes at any time. A single-phase electrical current can be provided to two electrodes with an impeller having three blades when the two electrodes are arrayed so that two of the three blades are not aligned with any two electrodes at any time. These and other objects and advantages of the present invention will be better understood in view of the attached drawings and detailed description of various embodiments and methods by which the present invention is practiced. BRIEF DESCRIPTION OF DRAWINGS FIGURE 1 is a perspective view of a mixer glass melter made according to the present invention. FIGURE 2 is a fragmentary plan view of a mixer/melter shown in FIGURE 1. FIGURE 3 is a cross-sectional view taken along line 3-3 in FIGURE 2. FIGURE 4 is a cross-sectional view of an alternative embodiment of a mixer/melter. FIGURE 5 is an alternative embodiment of the mixer/melter of the present invention. FIGURE 6 is a cross-sectional view of an alternative embodiment of the mixer/melter of the present invention. FIGURE 7 is a perspective view of an alternative embodiment of an impeller. FIGURE 8 is a schematic plan view of an alternative embodiment of a mixer/melter. FIGURE 9 is a schematic plan view of an alternative embodiment of the mixer/melter. FIGURE 10 is a schematic plan view of an alternative embodiment of the mixer/melter. FIGURE 11 is a schematic plan view of an alternative embodiment of the mixer/melter. FIGURE 12 is a schematic plan view of an alternative embodiment of the mixer/melter. FIGURE 13 is a schematic plan view of an alternative embodiment of the mixer/melter. FIGURE 14 is a schematic plan view of an alternative embodiment of the mixer/melter. FIGURE 15 is a schematic plan view of an alternative embodiment of the mixer/melter. FIGURE 16 is a cross-sectional view of an alternative embodiment of the mixer/melter of the present invention. FIGURE 17 is a fragmentary cross-sectional view of an alternative embodiment of the mixer/melter. FIGURE 18 is a fragmentary cross-sectional view of an alternative embodiment of the mixer/melter. FIGURE 19 is a cross-sectional view of an alternative embodiment of the mixer/melter of the present invention. FIGURE 20 is a fragmentary cross-sectional view of an alternative embodiment of the mixer/melter of the present invention. FIGURE 21 is a prospective view of a second stage molten glass spinner. FIGURE 22 is a cross-sectional view of an alternative embodiment of a second stage molten glass spinner cup. FIGURE 23 is a fragmentary cross-sectional view of an alternative embodiment of the mixer/melter of the present invention. FIGURE 24 is a cross-sectional view of an alternative embodiment of the mixer/melter of the present invention. BEST MODE FOR CARRYING OUT INVENTION Referring now to FIGURES 1 and 2, one form of the melter apparatus 30 of the present invention is shown as a substantially complete system. A generally cube-shaped vessel 32 shown with an impeller 34 and electrodes 36 contained therein. Feed material 38 is provided to the melter apparatus 30 via a hopper 40. Feed material 38 is moved from the hopper 40 to the vessel 32 by means of a screw conveyor 42. The screw conveyor 42 extends through an opening 44 in the vessel 32. The opening 44 is in the head space above the melt in the vessel. The impeller 34 is connected by a shaft 46 to a drive motor 48. Referring more particularly to FIGURE 2, the vessel 32 is used to contain a glass melt while it is being heated by electrodes 36 which are preferably arrayed in the vessel 32 about the impeller 34. As feed material 38 is dispensed from the hopper via the screw conveyor 42 it is added to the vessel through an opening 44 in the head space in the vessel 32 above the glass melt 50. Referring to FIGURE 1, an outlet port 52 is provided in vessel 32 to discharge a portion of the glass melt 50. An off-gas stack 54 removes gases through the outlet port 52 to a treatment facility 58 shown diagrammatically in FIGURE 1. An auxiliary gas burner 59 may be provided in vessel 32 above the glass melt. The auxiliary gas burner 59 provides supplemental heat for pre-heating feed material as it falls into the vessel and provides additional heat to the upper surface of the glass melt 50. If oxidation of the feed material 38 is desired an excess air burner may be used as the gas burner 59. The hopper 40 may include a rotary feeder (60) to facilitate providing a continuous flow of feed material 38 through hopper 40. The glass melt 50 is generally removed from the vessel 32 through outlet port 52, however, a drain (not shown) is provided in the bottom of the vessel 32 so that the vessel 32 may be completely emptied for servicing or for a shut-down as will be described more fully below. Referring now to FIGURE 3, melter apparatus is shown in a "sprinkler" mode wherein the impeller 34 is rotated rapidly above or adjacent to the top surface of the glass melt 50 so that drops 64 of the glass melt are propelled outwardly above and along the surface of the melt. The drops 64 of the glass melt 50 are sprayed substantially tangentially outwardly toward the walls 66 of the vessel 32. Drops 64 contacting the wall 66 will run down wall 66 and return to the melt 50. Operation in the "sprinkler" mode offers several potential advantages including rapid incorporation of feed material 38 into the melt. Light-weight material such as fiberglass scrap or fly ash tends to float on the surface of the glass melt 50. By operating in the "sprinkler" mode, light-weight feed material 38 can be swamped or engulfed by the drops 6 4 as they are sprayed outwardly from the impeller 34. As shown in FIGURE 3, the blade 68 of the impeller 34 is preferably of no pitch or reverse pitch to raise or lift the drops 64 out of the glass melt so that they become airborne. Another potential advantage of operating in a "sprinkler" mode, is that a controlled atmosphere maintained above the glass melt for reacting chemically with the glass melt 50 can be encouraged to react by the increased surface area presented by the drops 64 of glass melt as they spread outwardly. For example, if an oxidizing atmosphere is maintained and carbon particles are found in the drops 64, the carbon will tend to oxidize from the drops 64 as they are exposed to the atmosphere above the glass melt 50. Alternatively, by maintaining a partial vacuum above the glass melt 50 vacuum de-gassing of the drops 64 may occur as they are propelled outwardly by the impeller 34. Referring now to FIGURE 4, an alternative embodiment is shown wherein a conical pump 70 is provided in place of the impeller 34. The conical pump 70 includes a f rustoconical wall 72 having a lower opening 74 which is aligned with an axis of rotation and below an upper opening 76 which is also aligned with the axis of rotation of the conical pump 70. The frustoconical wall 72 is connected by spokes 78 to the shaft 46 to operate the conical pump 70 in a "sprinkler" mode, the smaller opening 74 is placed below the surface of the glass melt 50 with the upper opening 76 extending above the upper surface of the glass melt 50. As the conical pump 70 is rotated rapidly about the axis of rotation, glass entering the lower opening 74 tends to move, by centrifugal force, outwardly and upwardly along the frustoconical wall 72 until it exists the conical pump 70 at the upper opening 76. Upon exiting, filaments or drops 64 of the glass melt 50 are sprayed radially outwardly toward the wall 66. The conical pump 7 0 is expected to provide all the advantages of the impeller embodiment shown in FIGURE 3 and may provide additional operational advantages. A drain 80 is provided in the bottom of the vessel 32. The drain 80 may be fitted with a thermocouple 88 to provide temperature control. Referring now to FIGURE 5, the conical pump 7 0 is shown operating as a centrifugal pump to draw the glass melt 50 downwardly through the conical pump 70. An upper opening 76' of the conical pump 70 is preferably located somewhat below the surface of the glass melt 50. The conical pump 70 includes a frustoconical wall 72 which forms a lower opening 74' and is located coaxially with and below the upper opening 76'. The lower opening 74' is larger than upper opening 76". When the glass melt 50 enters the upper opening 76' it is driven downwardly and outwardly by centrifugal force toward and through the lower opening 74' . The conical pump 70, when oriented in this manner, forms a void in the upper surface of the glass melt which is generally centered about the shaft 46. Any feed material 38 deposited on the surface of the glass melt 50 tends to be drawn down into the glass melt through the void. Referring to FIGURE 6, a melter 30 is shown having a gas supply pipe 86 opening into a vessel 32. Oxygen, a reducing atmosphere, or inert gases may be supplied via the pipe 86 to maintain a controlled oxidation state in the head space 87 of the vessel 32. If the impeller is formed of a metal (such as molybdenum) which may react with a gas (such as oxygen) contained in the head space 87 of the vessel 32, the vortex drawn by the impeller should not extend to the impeller. By limiting the depth of the vortex, degradation of the impeller by oxidation can be avoided. At temperatures in excess of 1,2000F, molybdenum degrades rapidly in the presence of oxidizers. Under these conditions, the glass melt functions as shield to prevent corrosion of the impeller. Referring now to FIGURE 7, an alternative embodiment of the impeller is shown which shall be referred to as a "shrouded impeller" 90. Shrouded impeller 90 has a plurality of blades 68' which are bounded on their upper and lower edges by upper and lower cone sections 91 and 92, respectively. The primary advantage of the shrouded impeller 90 is that it reduces the power current density at the tips of the blades 68'. If the blade is included as an electrode in the power circuit or even if the impeller extends close to the electrodes, a situation is presented in which the shrouded electrode 90 may offer an attractive alternative. The continuous outer edge of the cone sections reduces current fluctuations caused by movement of the blades relative to the electrodes. The cone sections 91 and 92 also reinforce the blades structurally which improves durability. Referring now to FIGURE 8, an alternative embodiment of a vessel 32 wherein a triangular vessel 94 is shown. A triangular vessel may include three electrodes 36 located in the region of the three corners of the triangular vessel 94. If a three electrode 36 array is provided, a preferred impeller 34 would include two blades 68. By providing two or four blades and three electrodes 36, a three phase power supply can be provided since the two blades 68 of the impeller 34 never align with any two electrodes 36. Referring now to FIGURE 9, a hexagonal vessel 96 is shown wherein six electrodes 36 are arrayed about the impeller 34. The electrodes are spaced equidistant from the axis X of the shaft 46 on which the impeller 34 is mounted. The impeller 34 preferably includes two blades. The electrical circuit used is preferably a three phase circuit in which diametrically opposed electrodes are of the same phase so that when the two blades of the impeller align with any two electrodes, there is diminimus relative voltage potential difference between them. In this way, the impeller is effectively eliminated from the electrical circuit. The impeller 34 is electrically isolated and should not be grounded. Referring now to FIGURE 10, a cylindrical vessel 98 is shown. The cylindrical vessel is preferably connected in a single phase electrical circuit. The cylindrical vessel 98 preferably has a metal liner 100 which is surrounded by a layer of insulation 102. The electrical circuit is preferably a single phase electrical circuit with the impeller acting as one electrode and the metal liner 100 being connected to ground so that Joule-effect heating occurs between the impeller 34 and the liner 100. The impeller shown in FIGURE 10 is a shrouded impeller such as one shown in FIGURE 7 above. Referring now to FIGURE 11, a truncated equilateral triangle shaped vessel 104 is shown. The vessel includes a refractory liner 106 and a metal shell 108. The truncated equilateral shaped vessel 104 lends itself to use in a three phase circuit wherein one or more electrodes of the same phase are positioned in the region of the truncated corners 110 of the vessel 104. As shown in FIGURE 11, three electrodes of the same phase are located in each of the corners 110. The purpose of providing multiple electrodes in each corner is to increase the surface area of electrodes available thereby minimizing the charge concentration. Referring to FIGURE 12, an alternative embodiment is a truncated equilateral triangle shaped vessel 104 is shown wherein three phase power is provided to the vessel with an electrode for each phase being located in the region of each truncated corner 110. This arrangement lends itself to applications where high resistance glass is melted. A hot spot is created adjacent to each corner 110 between the electrodes 36- The impeller circulates molten glass in the vessel to distribute heat within the vessel 104. In FIGURE 12, a three bladed impeller may be used even though the electrodes 36 are arranged in three groups since the impeller in this configuration is essentially out of the circuit due to the high concentration of flux between the electrodes in each corner. A three bladed impeller is advantageous because a three bladed impeller is more mechanically stable than a two bladed impeller. Referring now to FIGURE 13, another embodiment showing the use of a truncated equilateral vessel 104 is shown wherein six electrodes are provided with two electrodes being located in each of the truncated corners 110. This arrangement lends itself to use in a three phase circuit or in a single phase circuit. If three phase power is provided, electrodes 36 in each truncated corner 110 would preferably be of different phase. If single phase power is provided opposite polarity electrodes would be provided in each truncated corner 110. In either embodiment, hot spots are created in each corner. The impeller 34 has two blades 68 to minimize transmission of current through the impeller to the other truncated corners. Referring now to FIGURE 14, another alternative embodiment is shown wherein a square vessel 32 such as that shown in FIGURE 1 is provided. Nine electrodes are shown arrayed in a generally circular arrangement about the axis of rotation X of the shaft 46. The nine electrodes are connected to a three phase power circuit with the three phases being alternated sequentially about the circumference of the circle on which the electrodes 36 are placed. A three bladed impeller 34 is provided which offers good fluid flow and stability. The unique advantage of this arrangement is that when the blades 68 of the impeller 34 pass an electrode, the tips of the blades point towards electrodes of the same phase. In this way the impeller 34 is effectively removed from the circuit as the impeller is not connected to ground or the electric circuit. Heating takes place around the electrodes in a generally circular pattern and the impeller mixes the glass melt 50 to distribute heat throughout the glass melt 50. Referring now to FIGURE 15, the vessel 32 is provided with six electrodes and includes an impeller 34 having two blades 68. Three phase power is provided to the electrodes which are again arrayed about the axis X of rotation of the shaft 46 with the phases of diametrically opposed electrodes being identical. The impeller is effectively removed from the circuit and there is little tendency for current to be conducted through the impeller which is not grounded and is isolated from the electrical circuit. In FIGURES 14 and 15, the vessel 32 preferably has a refractory lining and a metal shell as previously described. Referring now to FIGURE 16, a top down electrode vessel 116 is shown. Electrodes 118 extend through and are mounted in the cover 120 of the vessel 122. The top down melter 116 can be used to process a glass melt in which metal precipitates tend to accumulate in the bottom of the vessel 116. If electrodes extend from the bottom of a vessel 32 and metallic residue accumulates adjacent to the bases of the electrodes a conduction path will be created between electrodes through the accumulated metal residue 124. Water cooled electrode holders 126 may be provided to shield the electrodes from the atmosphere in the head space 128 of the vessel above the level of the melt 130 and below the cover 120. If molybdenum electrodes 118 are used exposure to oxidizers in the head space 128 would result in unacceptable erosion of the electrodes 118. The water cooled electrode holders 126 shield the molybdenum from erosion and extend slightly into the glass melt. The glass melt 130 shields the electrodes 118 below the surface of the glass melt 130. An impeller 132 is provided in the center of the melter 116. The impeller 132 shown in FIGURE 16 is a three bladed impeller which mixes the glass melt 130 as it is heated by the electrodes 118. The glass melt is removed from the vessel through a "teapot spout" 134. The teapot spout includes a throat portion 136 which extends horizontally from a lower portion of the vessel 122. A riser 138 extends vertically from the throat 136 to the spout opening 140. As the level of the glass melt 130 in the vessel 122 exceeds the level of the opening 140, the glass melt 130 overflows from the spout. A plurality of electrodes 142 are provided in the throat 136 and riser 138 to keep the glass melt 130 from blocking the teapot spout 134 which would occur if the glass melt is permitted to cool. A water cooled shield 144 is provided above the throat 136 to protect the vessel 122 in the region above the throat 136. A drain plug 146 is shown in a tab hole 148 adjacent to the base 150 of the vessel 122. Accumulated metal residues of various waste streams may be accumulated at the base of the vessel 122 and periodically poured off through the tap hole 148 by removal of the drain plug 146. By this technique heavy phases, some of which may be valuable, may be removed from the melter 116. A gas burner 152 is preferably provided at the opening 140 to keep the glass freely flowing as it enters the opening 140. Referring now to FIGURE 17, another alternative vessel 154 is shown wherein electrodes 156 extend through side walls 158 of the vessel. A drain plug 160 is placed in a tap hole 162 adjacent to the bottom 164 of the vessel 154. The impeller 166 is shown aligned in height with the electrodes 156. It is anticipated that the impeller may be raised or lowered relative to the level of the electrodes 166. The tap hole 164 is provided to allow draining of heavy phases which may accumulate in the bottom 164 of the vessel 154. The impeller 166 mixes the glass melt 168 to circulate the glass melt in the vessel 154 and thereby distribute the heated portion of the glass melt. Referring now to FIGURE 18, another alternative is shown wherein a vessel 170 having horizontally extending electrodes 172 extending from a side wall 174 close to an adjacent side wall 176 of the vessel 170. The horizontal electrodes 172 allow for accumulation of metals in the bottom of the vessel 170 and present increased surface area as compared to the side wall electrode embodiment of FIGURE 17. The impeller 178 is a shrouded impeller having a cylindrical wall. The shrouded impeller minimizes voltage differential fluctuations caused by rotation of the impeller 178. Referring now to FIGURE 19, an oxidation reaction melter 180 is shown wherein a vessel 182 is provided in which a glass melt 184 is mixed by an impeller 186. The glass melt 184 is heated by side wall electrodes. The electrodes shown are tin oxide electrodes, or similar material, which is formed as block shaped electrodes protruding only slightly from the side walls 190 of the vessel 182. Also shown in FIGURE 19 are oxidizer injector tubes 192. Oxygen, air, steam or other oxidizers may be supplied to the glass melt below the surface of the glass melt 184. Oxygen added below the surface of the glass melt 184 will react with constituents of the glass melt 184 which are able to be oxidized. A water cooled or oxidation resistant impeller 186 mixes the glass melt 184. In addition, oxidizer injected below the surface of the glass melt 184 also causes vigorous mixing of the glass melt 184. In some situations the impeller 186 may be eliminated from the vessel 182 and mixing can be caused solely by injection of the oxidizers or other gases through the oxidizer injectors 192. A drain opening 194 is shown in the base 196 of the vessel 182. The opening 194 would be capped by a drain plug (not shown) as previously described. The oxidation reaction melter 180 could be used as a primary glass melter or it could be used as a second stage in series with a mixer/melter as previously described. The vessel 182 includes an inlet 196 through which molten glass is received from a prior mixer/melter operation. Alternatively, the inlet 196 could be used to receive glass constituents, waste material for vitrification or other feed stocks in a dry, slurry, or other form. Referring now to FIGURE 20, an alternative oxidation reaction vessel 198 is shown. The oxidation reaction vessel 198 features an oxidizer injector 199 which is mounted in a base 200. The oxidizer injector 199 could be used in combination with an impeller or various electrode combinations as previously described. Alternatively, the oxidizer injector 199 could be used in a conventional gas burner heated melter tank as a second stage to a mixer/melter as described herein. Referring now to FIGURE 21, a spinning disk 201 is shown which may be used in a second stage reactor to direct a molten glass stream supplied to a second stage reactor outwardly as glass filaments 202. For example, carbon contaminants can be oxidized if an oxidizing atmosphere is maintained above the glass melt in the second stage reactor. The spinning disk 201 preferably has a plurality of ribs 203 to drive the molten glass stream radially. As shown in FIGURE 22, a rotating cup 204 can be used to form glass filaments 205 in a second stage vessel by pouring molten glass from a first vessel into the rapidly rotating cup 204. In FIGURE 23, an alternative embodiment is shown which features a plurality of liquid metal electrodes 206 located in the base 208 of the vessel 210. The vessel has an impeller 212 which stirs the glass melt 216 while current is supplied to the liquid metal electrodes 206 to heat the melt 216 above and between the electrodes 206 by Joule effect heating. Referring now to FIGURE 24, an alternative glass melter 218 is shown wherein a plasma 220 directed by heaters 221 at the surface of the glass melt 222. Alternatively, the heaters 221 can be plasma, arc or oxygen fuel burners which provide an intense energy source. Intense heating of the glass melt, occurs at the point where the plasma 220 impinges on the glass melt 222. This intensely heated portion of the glass melt 222 is intermixed with the remainder of the glass melt by means of the impeller 226. The impeller 226 is a shrouded impeller having upper and lower frustoconical sections 228 and 230 flanking impeller blades 232. Glass melt adjacent to the smaller opening of the frustoconical sections 228 and 230 is driven by centrifugal force towards the blades 232. The blades 232 expel the glass melt radially outwardly to create a mixing flow in the melter 218. The preceding embodiments of the present invention are provided by way of example. The scope of the present invention should be measured by reference to the following claims.