KR890001420B1 - Electric furnace construction - Google Patents

Abstract

A furnace for melting thermoplastic material comprises; a refractory vessel having sidewall portions; a discharge opening formed in a lower portion of a vessel; a metallic liner positioned within the refractory vessel in close proximity with the sidewall portions but spaced apart therefrom so as to form a relatively narrow annular space between the liner and the sidewall portions; the refractory vessel having an open upper portion for receiving batch material to be melted; electrode means for melting batch materials delivered to the furnace; and upper edge of matallic liner positioned below the melting line formed by the batch material to be melted and the molten material.

Description

Electric furnaces and how they work

1 is a front view of the furnace of the present invention with no crossover lines to clarify the city;

2 is a diagram of a preferred electrode arrangement with superimposed vectors.

3 is a sectional view of the lined furnace in the start-up mode.

4 and 5 are side and plan views of the electrode arrangement.

6 is a bottom view of the furnace of FIG. 3 showing the electrical insulation of the bottom plate and the electrode.

7 is a cross-sectional view of another embodiment of the present invention.

8 is a plan view of an electrode arrangement suitable for the furnace shown in FIG.

9 is a partial cross-sectional view of a large furnace having a plurality of placement electrodes and a bottom and a support therefor.

10 is a diagram of the electrode arrangement of the furnace of FIG.

* Explanation of symbols for main parts of the drawings

12: outer cell 14: side wall

16: floor wall 24: fireproof container

30 liner 43 thermoplastic material

50: placed electrode

The present invention relates to a relatively high temperature furnace for melting thermoplastics. In particular the furnace is for melting glass, wherein the vessel of the furnace is particularly suitable for resisting the corrosive effect of the glass at temperatures in excess of 1800 ° C. Herein, a means for improving the thermal efficiency at start-up and protecting the furnace is described. And other details are set forth in the specification below.

Refractory lined furnaces have been used for many years to melt glass. However, many standard refractory materials tend to be slowly dissolved or corroded by the glass until the furnace begins to leak. This amount of corrosion increases rapidly as the temperature and glass flow rate increase.

Repairs can be made, but they are not easy to repair, costly and usually shorten their lifespan. The refractory can also be cooled to the outside surface to slow down this corrosion, which increases energy losses.

In general, the most severe corrosion occurs at the side walls near the top of the glass batch. In conventional furnaces, the glass is hottest near the top, and the melting and refining temperatures are limited to 1600 ° C. or less by fire resistance. As the refractory material melts into the glass, many corrosion products are absorbed into the melt batch. The dissolved refractory material becomes part of the glass composition and in some cases adversely affects the quality of the glass. Heavy corrosion products sink to the bottom of the furnace and form a slightly loose protective layer on the bottom wall.

Another area where the refractory is severely corroded is the exit or throat of the furnace. Often this outlet area is covered with a metal protective layer. Sprimulley's U.S. Patent No. 4,029,887 used molybdenum tubes as highly corrosion resistant conduits from furnaces to the front furnace channel. Platinum was also used for the exit liner. In fact, the entire furnace can be lined with platinum, but it is very expensive.

An example of a vertical electromelting furnace is described in US Pat. No. 3,524,206, wherein the top of the melt batch is covered with a cold batch blanket. Corrosion in this type of furnace is most severe around electrodes entering through an upright side wall or sidewall, typically near the so-called melting line. The present invention provides a means for substantially reducing this corrosion and also for minimizing the corrosion effect.

In a conventional vertical electric melting furnace having a cold batch blanket, there is a tendency for bubbles to be contained in the glass since it does not have a free surface capable of quickly eliminating bubbles contained in the glass. Therefore, the time that glass is present in the furnace should be adjusted to allow for sufficient refining. Purely molten glass tends to move quickly through the outlet before it is refined, so the rapidly moving glass starts unwanted reflux which contributes to the breakage of the furnace. Therefore, measures must be taken to control reflux to increase the time that glass is present in the furnace. One method for this is described in US Pat. No. 4,143,232, wherein the controlled reflux is controlled by a deeply submerged electrode operated in the selected heater. Another advantage with the latter configuration is that the generated heat is concentrated at a point far from the wall, thus reducing corrosion around the electrode holes. The improved electrode structure in the present invention is suitable for providing centralized heating and hot spot refining of the glass.

Molybdenum, platinum, platinum alloys, some steel alloys, and iron have long been recognized as materials having higher resistance than conventional refractory materials and are believed to be useful in the construction of glass melting furnaces. Molybdenum, for example, has been used as a liner for electrode materials and stirrer vessels where more severe corrosion occurs at high glass velocities. As noted above, the furnace outlet is often lined with platinum, sometimes molybdenum.

Platinum is very expensive and its use is often only used to melt special glasses such as glasses. As described in British Patent 601,851, iron may be used, but it has a relatively low melting point and most of the glass may be contaminated with colorants. For some purposes, however, iron may be tolerated as furnace liner material.

Molybdenum has been recognized as a metal having high temperature strength, relatively inexpensive, and capable of being chemically combined with many glasses. A distinct disadvantage of molybdenum is that it oxidizes above 550 ° C. In the past it was difficult to manufacture, but now molybdenum can be formed into flat plates, curved plates and pipes, making it an increasingly interesting material. One of the most particular advantages of molybdenum, which melts at 2600 ° C, is its high temperature strength, which makes it possible to use up to about 2200 ° C. For example, platinum, which has been used almost absolutely in high temperature operation, melts at 1700 ° C and can only be used up to about 1600 ° C. Molybdenum is therefore a very useful material because it is substantially cheaper than platinum and has a much higher melting point.

United States Patent No. 3,109,045, issued to Silverman, suggests the use of molybdenum as the container material for glass melting furnaces. The molybdenum crucible portion is immersed in the outer arrangement of the thermoplastic material to protect its outer portion from oxidation. The inner part of the crucible is filled with molten thermoplastic and thus the molybdenum will be protected from the ambient atmosphere and will not oxidize. Even though the outside of the molybdenum crucible is protected by glass, a fireproof tank or an external batching vessel, the located molybdenum crucible is larger than the latter. Thus, the molten glass surrounding the container will freely reflux and ultimately destroy the fire resistant container.

Silverman's devices are size and structure suitable for special melting and are so large that they are not suitable for practical use. In addition, it requires a gas exhaust device to remove air from the batch material in operation to protect the top of the molybdenum container from oxidation. In addition, most glass batches will contain oxidants such as CO ₂ , SO ₂ , H ₂ O, so the batch is not allowed to contact molybdenum. On the other hand, if the glass level is kept above molybdenum, it will soon contact the refractory ring situated on top of the molybdenum and corrode the refractory material soon.

Batch material will be difficult to carry out in molybdenum furnace without adversely affecting gas heating. Because the heat and oxygen in the flame are highest on the glass surface, precisely where protection against corrosion and oxidation is needed. Thus, without paying attention to the following proposal by the present invention, the molybdenum liner will be oxidized since it is exposed to the combustion gas.

Joule heating is preferred as a method of melting glass in furnaces of the type described herein, in particular in molybdenum liner furnaces. However, because molybdenum is conductive rapidly, it is necessary to provide suitable circuitry to place the electrode in the selected location and to optimize the flow of current in the glass. While it is normally desirable to avoid short circuits to the liner, it may be desirable for some materials to place the electrodes and provide a network to flow into the liner to provide uniform power consumption. Furthermore, it is also possible to heat directly to the liner if necessary. Batch electrodes are suitable for this purpose and several such devices are described in US Pat. Nos. 2,215,982, 2,978,526 and 4,159,392. In the preferred device of the present invention, the use of a movable arrangement electrode is contemplated. Although the patent of 2,978,526 described above illustrates such a concept, the device is limited in flexibility and will greatly hinder proper charging of the furnace.

U.S. Patent Application Nos. 244,001 and U.S. Patent Nos. 4,351,664 and 4,352,687, filed on the same date assigned to the assignee of the present application, describe glass useful apparatus and inspection systems useful with the present invention as described in detail.

Methods and apparatus for melting thermoplastics may use a container having a bottom wall and an upstanding side wall. A protective liner for a container formed of a corrosion resistant material is provided. The furnace may include a hot spot that aligns the conductive bottom channel with the bottom electrode through the arrangement.

The proposed method for operating the furnace described herein uses an apparatus that sends symmetrical batch heat dissipation for fast melting. The starter burner is operated with reduced heating to protect the liner made of oxidizable refractory metal.

The furnace 10 of the present invention has an outer cell 12 that has upright and generally cylindrical, circular, polyhedral, rectangular or square sidewalls 14 and bottom walls 16. The bottom wall 16 is divided into sections to allow thermal expansion, which sections are electrically insulated from each other. The outer cell 12 forming the support structure for the furnace 10 must be electrically insulated from the bottom wall 16 by the insulation core 13 without leaking air and is made of steel sheet. Shim 13 also allows for thermal expansion. The furnace 10 is supported from the bottom by a "I" shaped beam 18, which is electrically insulated from the ground by an insulation core 25. A compressible insulating layer 20A, such as a fiber flag made of silicon carbide, is installed directly inside the outer cell 12 and its upper lip from the bottom wall 16. 22). The compressible insulating layer 20A allows for relative movement of the structure during thermal cycling of the furnace.

The annular rigid insulating layer 20B is provided adjacent to the compressible insulating layer 20A.

The fire resistant container 24 comprising the upstanding side wall 26 and the fire resistant bottom wall 28 is installed in the outer cell 12 spaced apart from the rigid insulating layer 20B. The ramming mix 21 is positioned between the rigid insulating layer and the fire resistant container 24 to form a glassy rigid seal therebetween. The ramming mix, sometimes referred to later as temp 21, is a granular refractory material that can be filled or plugged in place or burned or sintered at the start of the furnace. The refractory container 24 is preferably made of a known refractory material that resists glassy corrosion. A liner 30 formed of a high corrosion resistant refractory material is installed coaxially in the refractory container 24.

Tantalum, rhenium, niobium and tungsten may be used, but molybdenum is useful as a suitable material for the liner 30. New metals (eg platinum, rhodium, etc.) may be suitable in some situations, especially where glass is highly oxidized. The latter material is relatively weak at high temperatures and therefore requires an unshown post or inner sleeve and provides extra support to the liner 30. In this situation, a heavily oxidized cathode or direct current bias may be imposed on the liner in conjunction with the consuming positive electrode. This arrangement will be less expensive than using a new metal. It should be mentioned that steel and nickel alloys may be used for relatively low melting points, such as glass, below about 1100 ° C. The electrodes described below for electrically heating the furnace 10 may be made from the above materials but will be as good as molybdenum. Other matters which have been pointed out as useful are not emphasized, because they are quite expensive unless there is any particular reason for their use.

In a preferred embodiment, the liner 30 is made of a molybdenum plate that is firmly riveted together along the overlapping seam, so that no other reinforcement is needed. In addition, the plate of material may be used as a shield for the container if it is firmly spaced apart.

The upstanding wall 26 and the liner 30 of the fireproof container 24 are approximately approximate, leaving a relatively narrow annular spacing 32 between them, which is inherently slightly as large as 2.54 cm (about 1 inch) from intimate contact. Extends to a wider desired space. The gap 32 will be filled with a non-corrosive, high viscosity glassy collet, batch or other layer of refractory lamps (see reference numeral 23) for reasons to be described below.

It is important to understand the function of the liner 30. The liner 30 protects the refractory vessel 24 from corrosion engraved by the thermoplastic (glass) 43 refluxing in the furnace 10. The liner 30 makes it possible to increase the amount of melt and improve the glass quality. The former will be achieved as a result of the high temperatures at which the furnace 10 can be operated. Higher glassy results from the fact that molybdenum causes less contamination of the glass than refractory materials. Refractory materials are used to contact the glass in conventional melt tanks. However, it will eventually corrode and contaminate the glass. Moreover, fire resistant blocks, especially larger ones, will split due to heat shock. The gaps and cracks between the paths of the refractory blocks will act to inhale air into the refractory material and introduce the reactants into the glass.

Loss of refractory material due to the intense heat of the glass furnace will inject contaminants into the glass. The quality of the glass is a measure of the presence of binders and contaminants (eg cords, bubbles, nuclei, etc.) and is affected by all of the above factors prevalent in conventional melt tanks. Thus, the liner 30 protects the refractory vessel from corrosion and enables melting of the glass against the permeable vessel wall as described above, thereby preventing contaminants from entering the glass.

The highest corrosion resistant liner material currently available for economical high temperature operation is molybdenum, so it is desirable to select it. Molybdenum is rapidly oxidized at temperatures above about 550 ° C and must be shielded from oxygen. In a preferred embodiment of the present invention, the liner 30 maintains the glass level above its upper edge 31 and is positioned below the glass level to protect the inner surface of the liner. Tightly filled material in space 32 and trap 29 shields the outer surface of the liner from oxygen contamination.

The bottom wall 28 of the furnace 10 will be aged with several materials, including a refractory material or including the same material that forms the wall of the liner 30. However, for the sake of explanation, a furnace with a fire resistant bottom will be described and others will be described below with reference to FIGS. 7 to 10.

Also a mixture of tightly packed sand, ramming mixes and high adhesion (i.e. hard) glass cullets may be used in place of the refractory vessels 24, insulation layers 20A and 20B and temps 21 to 23 described above. have. Thus, the liner 30 with or without the bottom wall will be placed in a granular shape surrounded by the outer cell 12 and the off cell block 27 (described below). In this arrangement the sand, color and temp will not be highly insulated but will provide protection for the liner 30. This is because when heated, these materials will form a highly viscous glass composite and will melt or half melt the material that shields the liner 30 from oxygen. The loss of heat transfer due to the reflux of the externally flowing liner will be greatly reduced since the molten or semi-melted sand is highly viscous. Examples of useful materials are sand, silica or zirconia and Ramming Mix-Corhart # A893 or # 251420.

If the bottom or bottom electrode 40, which will be described below, is incorporated into the furnace, the bottom wall 28 must be lined with a coherent # 1350 zircon and a high resistance fire resistant material having an electrical resistivity of at least 100 ohm-inch at 1800 ° C. do. Although not shown in FIG. 1, in particular, the liner 30 may be provided to extend across the bottom wall 28 when the melt application is for tempered glass at high temperatures. This configuration will rule out practical use of the bottom electrode because of the resistance of the material of the liner 30.

Only one bottom electrode is shown in FIG. 1 to simplify the drawing. It will be angularly positioned in the hole 42 in the bottom wall 28 and extend into the interior space 46 of the furnace. Although not shown, each bottom electrode 40 is excited by a connection at its end 47. Heating takes place primarily from the tip 44 towards the molten thermoplastic 43 in the space 46. The bottom electrode 40 may move so that the tip 44 is axially adjusted in the direction of arrow a ₁ .

A plurality of placement electrodes 50 may also be used to melt the thermoplastic material 43. Likewise only one electrode is shown for simplicity of the drawings. Each electrode is installed around the furnace 10 and has various degrees of freedom. The placement electrode 50 includes an external electrode or ceramic sleeve portion 51 and an inner electrode 52 of concentric refractory metal. It is powered by an electrical connection (not shown) at its end 53 and its tip 54 is located in the space 46. The electrode 52 can be adjusted well along the axes A ₁ and a ₂ . The placement electrode 50 is horizontally supported by an arm 56 supported by the sleeve 58. The support structure 60 attached to the outer cell 12 holds the sleeve 58 via a shaft 62 sleeved at the support 64.

In operation, the support structure 60 remains fixed relative to the outer cell 12, but the sleeve 62, which is sleeved in the support 6, moves axially in the direction of the _two- way arrow a ₂ . can do. The horizontal sleeve 58 is rotatably mounted to the upper end 66 of the shaft 62, which is shown by arrow a ₃ . The support arm 56 carried in the sleeve 58 thus rotates about the vertical axis A ₁ of the axis 62, as shown by arrow a ₃ . The horizontal support arm 56 rotates around the horizontal axis A ₂ as shown by arrow a ₄ and also moves along it in the direction shown by arrow a ₅ . The placement electrode 50 need not be vertical as shown. This can be inclined by modifying the bracket 57 which holds the electrode 50 in the arm 56.

The placement electrode 50 carried by the support structure 60 or the like can move up and down radially with respect to the centerline C of the furnace 10, with respect to the vertical plane, and with an arch shape with respect to the horizontal plane. . Thus, each electrode 50 has a degree of freedom and is thus adjustable to oppose any one of a selected series of coordinate systems in space 46 in operation.

The center disposed electrode 80 is vertically opposed along the center line C of the furnace 10, and likewise powered from its end 82 by an electrical connection (not shown). It is mated to the horizontal support 86, which is mounted to the support structure 92 fixed to the horizontal sleeve 88, the vertical axis 90 and the outer cell 12 by ceres. The center arrangement electrode 80 is employed to move vertically in the direction of the double arrow a ₆ to adjust the position of its tip 96. It may be arranged to be supported from the same arm (eg 56) as the placement electrode to save space on the furnace 10. For example, in FIGS. 4 and 5 the center electrode 80 and the placement electrode 50 are connected by the same support 60 ', ie the same support 60' on the other along the axis A ₁ . Can be supported. Such an arrangement with the other electrodes positioned 120 ° away exposes most of the top surface of the furnace 10 for easy filling.

In another embodiment of the present invention, the bottom electrode is stationary and an additional placement electrode (not shown) is replaced with it at a position approximately peripherally interlaced with respect to the placement electrode 50. Such an arrangement of six beach electrodes about 60 ° away from the center line C results in a symmetrical electrode arrangement that will be heated near the top of the furnace where the most efficient melting takes place.

It has been known that if the tips 54, 44 of each electrode 50, 40 are located approximately between the centerline C of the furnace and the wall of the liner 30, the melting process will be improved. In the case of a relatively small furnace 10, i.e. a furnace of about 4 to 6 feet in diameter, the electrode 50 is about half of the distance from the centerline C to the liner 30, which is It should be installed symmetrically around. Of course, other arrangements are possible, as will be described below.

The arrangement electrode 50 and the bottom electrode 40 are very useful because they both function slightly differently. The bottom electrode 40 is particularly suitable for starting before insertion of the batch electrode 50. It can also be used during full operation for floor adjustment and fine control. The batch electrode 50 is mainly used for high ratio full time melting, which can be used alone. The central arrangement electrode 80 is mainly used to melt glass. Moreover, the furnaces can be used in a variety of ways, as the electrodes 50, 40, 80 are operated alone or in combination. Although not described in detail herein, it is to be understood that the electrodes 50, 40, 80 can be cooled with water by providing an external jacket for carrying cooling water. Such an arrangement extends the electrode life.

The outlet tube 100 having the central hole 101 is preferably arranged in the hole 102 in the refractory bottom 28 and made of the same material as the liner 30, that is, molybdenum. An electrical connection, not shown, is coupled to the hole 102 at or near the end. The outlet tube 100 may be powered through its molten thermoplastic material 43 to its tip 103 which heats the tip 96 of the central electrode 80. As the tube 100 is corroded by electric heating and the central electrode 80, which can be replaced more easily, can be electrically biased with a direct current voltage, it becomes a consuming electrode.

Upon powering up the centrally disposed electrode 80 and the outlet tube 100, the hot spots 106 pass through a large current therebetween to form in the bath of the thermoplastic material 43. The tip 96 of the center electrode 80 and the corresponding tip 103 of the outlet tube 100 may be a large surface area disc capable of sending high current. The energy lost in the hot spot 106 aligns the material 43 just before it leaves the furnace through the aperture 101 of the outlet tube 100. The alignment temperature rises significantly and is concentrated near the center of the furnace circumference to reduce breakage of the furnace walls.

In order to further reduce the furnace wall temperature, the refractory vessel 24 has a vertical upright wall 26 near the upper edge 31 of the liner 30. The fire resistant block 27 is offset as shown in FIG. 1 or 9 or recessed as shown in FIG. 3 to provide a step to the side wall 26. The upstanding fire-resistant sidewall 26 is thus radially recessed above the liner 30 so that the temperature of the material near the block 27 is determined by the thermoplastic material 43 (ie glass) and the placement electrode ( Corrosion by 110) is reduced to a point where it can be ignored.

A channel or trap 29 is formed between the liner 30 and the recessed or offset block 27. In one embodiment, the trap 20 is filled with non-corrosive glass that melts at startup and flows slowly into the space 32. The horizontal flange 33 of the liner 30 extends radially outwardly to cover the top surface 35 of the fire resistant sidewall 26. At start-up, the flange 33 prevents the rapid flow of molten material 43 installed in the trap 29 into the space 32, because the outer edge 37 of the flange 33 27) because it is the coldest near, and the glass at this location is the most viscous. In addition, the corrosion of the block 27 is reduced because it is too far from the high heat in the center of the furnace 10.

At the bottom end 36 of the liner 30, a slot 39 is formed between the bottom wall 28 of the fireproof container 24 and the liner 30. The slot 39 collects and collects the molten thermoplastic mixture 41 "and the refractory oxidation product. The molten material at the bottom of the slot 39 is cooler than the other parts of the furnace 10. 41 ") tends to be highly viscous or opaque. By this means, there is a sealing action between the molten material 43 in the interior space 46 and the material in the lining space 2.

Likewise, the space 32 between the liner 30 and the upstanding fire resistant sidewall is narrow. The reflux generated by the heat in the furnace 10 is thus reduced or sufficiently reduced in such space by substantially reducing the refractory reflux. The space 32 serves to solidify the mixture 45 of corrosive product and thermoplastic material. Corrosion of the refractory is prevented because the corrosive products adjacent to the space 32 do not continuously sweep away.

Although passive cooling is done in the sealed space 32 and prevents circulation of the material held therein, one or more of the cooling tubes 112 delivers cooling gas near the middle or middle portion of the space 32. Can be provided. The extra cooling that is synthesized ensures sealing as the efficacy of the hardened glass adjacent to the interruption of the liner space 32.

Many of the methods mentioned above allow for the use of narrow areas that impede sliding in sensitive areas of the furnace as devices to protect the refractory from corrosion. By way of example, it includes an extension of the flange 33 into the offset block 27 and a connection of the bottom end 26 of the liner 30 into the sidewall 26. All of the above are designed to be mounted to the inner surface of the liner 30 and to the relatively cold portion of the refractory container 24 to prevent movement of the glass. In addition, if a non-oxidizing liner is used, the upper margin 31 can extend to the end of the thermoplastic 43 and no provision for the offset block 27 is required.

It has been mentioned that the bottom wall 28 of the fireproof container 24 can be lined with molybdenum. This feature is described in Figures 9 and 10 below. Also refractory temp, chromium oxide refractory can be used as the bottom wall material. The latter choice is inevitably undesirable because they are materialized and mixed with the glass, while they are a viable and useful choice for some types of glass. Electrically conductive chromium oxide will be impractical for use as a bottom electrode.

The absence of molybdenum bottoms for the liner 30 is generally good except when melting corrosive or viscous glass that requires high temperatures. This is because it allows the flexibility of the bottom electrode. This reduces the manufacturing cost of the furnace. Moreover, since most of the bottom wall 28 is protected by placing corrosion products, provision of a bottom liner would not be necessary unless extreme high temperatures are required. On the contrary, the present invention will be further described in the specification because the bottom lined furnace has or does not have a protector substantially matched to the bottom for the liner 30.

Referring to other features of the present invention, the batch material forming batch blanket 110 will continue to apply thermoplastic 43 to furnace 10. The furnace is operated in such a way that the dissolution line 111 separating the batch blanket 110 and the molten material 43 extends across the furnace 10 above the level of the flange 33 of the liner 30. It is important. By always maintaining a layer of molten material on the flange 33, the liner 30 is protected from oxygen and gas products contained within the batch blanket 110. The upper margin 31 of the liner 30 will oxidize because it pushes out the batch material and is not covered with molten glass. However, the trap 29 formed by the upper margin 31 and the clock 27 is mainly used for starting purposes. And the oxidation of the upper margin 31 does not create a detrimental effect.

It is necessary to understand the startup sequence to further explain the important features of the present invention. Conventional furnaces with liners that can be oxidized remove inert gas at startup. After that the furnace is activated. In special glass, small scale devices for special glass can be operated in vacuum. Such devices are difficult to scale up, especially where thermal efficiency and economic factors create a vacuum and where exhaust gases are not required.

In the present invention, the starting of the furnace 10 is the same as starting a normal vertical melting furnace. 3, the cover 11 is placed on top of a furnace 10 of a type similar to that used in conventional vertical melting furnaces. The burner 9 is located through the cover 11 and the fuel is supplied through the processing supply pipe 15 and the combustion air is supplied through the air supply pipe 17 from any source not shown. At start-up the furnace is partially filled from dotted line 3 to dotted line B, represented by an angle (typically 45 °) placed in the cullet with crushed glass or cullet. The upper margin 31 of the liner 30 is preferably covered. The cullet is added through the outlet 19 as the filled material melts. The bottom electrode 40 is powered after the batch has at least partially melted. Once the furnace 10 is filled with a molten thermoplastic material (see glass line G), the liner 30 is prevented from oxidation.

During start-up, the purge gas P is pressurized by the input to the furnace 10 through the inlet pipe 63. The inlet pipe 63 is hermetically welded to the outlet 65 at the bottom wall 16 of the shell 14 so that the purge gas P is used to fill the space in the shell 12 to protect the equipment from oxidation. . Purification gas P is used to fill the space in the shell 12 to protect the equipment from oxidation. Since the shell is sufficiently sealed, purge gas (P) will be retained in the furnace (10) and ensure a safe and efficient startup of the furnace (10). Once the furnace is filled with molten glass, the purge gas will be shut off. .

In the present invention, in order to protect the liner 30 from oxygen, the burner 9 operates in such a way that the combustion product does not contain excess coral and is made under an atmospheric condition where the melt contact of the initial cullet B is reduced or intermediate. do. In some glass, it is not considered desirable to significantly reduce combustion since carbon contamination of the liner 30 is believed to harm the glass.

Once the material has fully melted the burner 9 will be stopped and the bottom electrode 40 will be powered to maintain the temperature of the furnace. The cover 11 is then removed and the placement electrodes 50, 80 are inserted at each position (see FIGS. 1, 2, 4 and 5). The batch blanket 110 will then be continuously imposed on the furnace 10 as the dissolved material 43 is removed from the bottom through the outlet tube.

Although not shown, charging control means are used, in particular, to hold the placement blanket 110 in a predetermined orientation in the region of the trap 29. The preferred method of operation is to have control filling and the ability to control the hydrostatic head of the glass. The dissolution line 111 can then be controlled by charging, a combination of heads and vertical adjustment of the electrodes 50, 80.

2 illustrates one possible electrode arrangement of the present invention. The bottom electrode 40 is shown as a circle, the arrangement electrode 50 is shown as a cross, and the center arrangement electrode 80 and the outlet tube 100 electrodes are shown as green circles around the cross mark, respectively. Since the bottom electrode 40 is heated to a closed delta type, the next adjacent electrode is heated as shown by the vector arrow 40 'between each electrode 40. Likewise, the placement electrode 50 may be heated in turn in a closed delta form superimposed over the first mentioned heating pattern in the same direction or in the opposite direction of the bottom electrode 40, as shown by the vector arrow 50 '. will be. The electrodes 40, 50 are preferably arranged away from the wall of the liner 30 to concentrate heat near the center of the furnace. In the arrangement shown, the outer circumferences of the two electrodes 40, 50 are interlaced, or they are electrically symmetrical due to double delta heating and physical symmetry. The same heating pattern and symmetry will occur when three parts have been replaced by the bottom electrode 40.

The symmetry mentioned above is important for melt efficiency and uniformity. Furthermore, by heating the electrodes 40, 50 symmetrically high, the liner will necessarily operate at medium or ground potential. Thus, the risk of breaking current from the liner 30 and into the cell 40 operating at the ground potential is minimized and suctioning the glass into the cell through the insulating layers 20A-B may be acceptable.

In a typical vertical furnace, the outer wall of the refractory vessel is cooled slowly to slow the corrosion of the vessel itself. However, the present invention utilizes the insulating layer 20 to protect heat in the furnace 10 while the liner 30 resists high temperature corrosion. The insulation of the furnace 10 allows for greater energy efficiency and operation at higher temperatures, thereby significantly improving the melt ratio. Since the refractory material of the furnace 10 is protected by the liner 30, it can withstand higher operating temperatures that enable the use of the insulating layer 20. Although the glass contact refractory material at the wall 26 is softened by the top temperature of the furnace, the intermediate layer of the tamp 21 will delay the leakage of the glass into the insulating layer 20. Several layers of protective material continuously limit the destructive impact of corrosion on the furnace 10. Moreover, in places where reflux seems to cause breakage of the furnace 10, reflux should be prohibited or restricted. For example, general reflux induction of the material in the seal space 40 is inhibited by the liner 30 from the wall 26 of the refractory vessel 24 and between the liner 30 and the outer shell 12. The space 32 is limited so that any movement of material therein is prohibited. This is especially the case when the viscous material is located in the space 32.

As mentioned above, the same result will occur if the fireproof container 24, the tamper 21 and the insulating layers 20A, 20B are replaced with sand, cullet, tamper or a mixture thereof. Although the heat loss is increased, the electrical loss will be approximately the same since the liner operating at ground potential is not a current source.

Another feature of the invention as shown in FIG. 1 is that the side wall 14 of the outer shell 12 will be directly coupled to and monitored at ground or medium potential. This provides important stability. Ground strap 49 couples sidewall 14 to ground 6 as a safety feature. The current detector 48 senses the current flowing from the side wall 14 to ground (G). If a flow of current occurs in the strip 49, the side wall is no longer insulated. When this occurs, the driver must cut off the ground strip 49 to prevent leakage to ground and build a barrier wall (not shown) around the furnace to protect people. An additional safety measure of operation is to install the electrode to ground so that the liner 30 is not grounded and the bottom 16 of the outer shell 12, which is characteristically inoperable in conventional furnaces, is not grounded and normally has any voltage ( V) flows out. The insulation core 13 isolates the bottom 16 from the side wall 14 and the similar insulation core 25 from the "I" beam and associated support structure from the flow voltage carried on the floor 16.

As shown in FIG. 6, the bottom wall 16 of the outer shell 12 is divided into a plurality of sections 16A ... 16n (only three are shown). If bottom electrode 40 is used, it is sleeved through bottom wall 16 through hole 42. Each non-conductive sleeve 59, which is an electrode 40, is insulated from the bottom wall 16. Each section 16A-16n of the bottom wall 16 is insulated from each other by an insulating core 69. Thus, if a short circuit occurs between the electrodes in the section 16A of the bottom wall 16, the current will not conduct to the adjacent electrode. In addition, if one or more electrodes are shorted to each bottom wall section 16A-16n, a destructive short will occur for each electrode. If a short circuit normally occurs from the bottom wall 16, it occurs near the hole 42 to be filled with hot glass. Therefore, the divided bottom wall 16 is a prudent measure considering this. Once the glass has penetrated the room, the operation will continue despite the increase in heat and electrical losses. Since the shell parts are separated, destructive failures can be avoided. Likewise, the glass flowing to the bottom wall of the shell will prevent destructive currents from flowing to ground because the “I” beam 18 is insulated therefrom. Although not shown, the division of the bottom wall 16 includes sections that do not have electrode positions therethrough.

It is believed that the furnace of the present invention will operate at a maximum temperature of 1700 ° C to 2000 ° C. In general, the molten amount of the glass furnace is discharged whenever the temperature increases by 100 ° C. Thus, the furnace described herein has a performance that is two to five times greater than a conventional electric heating device. Conversely, the conventional electric heating furnace similar to the furnace of the present invention has only half its glass output. For example, a typical electric furnace of 12 feet (363 cm) in diameter can be replaced with a furnace of the type described herein having a diameter of between 181 and 273 cm (about 6 to 9 feet). Moreover, the height of this furnace will be considerably lower than that of a conventional vertical furnace. Low height furnaces are easy to manufacture and require less structural material for the low head of glass contained therein.

Moreover, due to the higher temperatures practically attainable, very hard glass can be melted in large quantities. It is also possible to try entirely new and only theoretical constructions.

An embodiment of the furnace 10 described herein is a relatively compact polyhedral melting furnace having a diameter of 120 cm (about 4 feet) and a length of 90 cm (about 3 feet). The furnace is capable of melting silicate glass at a rate of 1.5 cubic meters per tonne of Corning Cod 7073 beams. This figure is considerably large compared to the melting volume of conventional furnaces ranging from 6 to 12 cubic feet per tonne for gas-fired regeneration and 3.0 cubic feet per tonne for vertical ignition glass melting units.

The device can economically melt a melt amount of soda lime glass at 0.75 cubic feet per tonne and possibly 0.5 cubic feet per tonne. As a result, relatively high performance furnaces of the type described herein are theoretically useful for so-called float glass processes and thus obviate the need for conventional float blast furnaces.

Fully lined furnaces of the type described herein should not produce any fire resistant codes, which only require about 2.25 × 10 ⁶ BTU / ton, while a typical gas regeneration float furnace is about 5.7 × 10 ⁶ BTU / This will require a ton and will result in a reduction in query quality in the generation of the code. In addition, although the efficiency decreases gradually as the conventional furnace wears down due to use, in the system considered here, the furnace maintains high efficiency for substantially the entire useful life due to its excellent wear characteristics.

It should be understood that the furnace 10 and inner liner 30 will be one of many conceivable formations, from circular to polyhedral, planarly square or rectangular. The sidewalls are also tilted to form a conical structure to control reflux and move the upper margin of the furnace away from the center, while maintaining a hot central area with a smaller glass concentrator. However, the features of the present invention for protecting the liner and fireproof vessel are essentially inherent. The furnace 10A as shown in FIG. 7 is an outer outlet tube without an upright outlet electrode portion 103 above the bottom 28. And a conical liner 30A coupled directly to 100. (See Figure 1). Hot spots 106A may be obtained by means of placement electrodes 50A arranged closely and deeply submerged. Placement electrode 50 as described in FIG. 1 is installed over electrode 50A and intersected between electrodes 50A (see FIG. 9), low electrode 50 is also less deeply submerged and furnace 10A. Radially spaced from the center (C) of the).

In another embodiment of the invention shown in FIGS. 9 and 10, the outer shell 12, the insulating layer 20, the fireproof container 24 and the narrow space 32 are separated from the fireproof container 24. The furnace 10D including the liner 30B is shown. The fireproof container 24 includes an upstanding side wall 26 and a bottom 28. The liner 30B includes a side wall 72 and a bottom 74 as well as the upper upright outer flange 33 described above.

The refractory vessel bottom 28 is slightly inclined downward toward the outlet tube 100 as shown and is separated from the liner bottom 74 by a relatively narrow space 76. In order to maintain the space 76, several supports will be provided. The outer peripheral edge of the bottom 74 is supported by the flange portion 84 extending in one direction protruding from the side wall 72. It should be noted that the bottom 74 may be welded or abutted to the sidewall 72 of the liner 30B or simply laid on the flange 84 as shown. An intermediate support or shim 94 is implemented in the recess 95 in the vessel bottom 20. The annular tubular central support 98 has a radially extending flange 99 that supports the inboard portion 97 of the liner bottom 74. The central support 98 lies in the inboard recess 946 of the floor 28. Flange 84, shim 94 and central support 98 may be made of any suitable material, including certain refractory materials and molybdenum. The space 76 is normally filled with thermoplastic to protect the liner. Several supports for the bottom 74 are retained in the space 76 and prevent the escape of the protective material.

The connector 93 extends through the bottom wall 16 of the outer shell 12 and the bottom 28 of the fireproof container 24 and is coupled to the liner floor 74. The spaced end of the connector 93 is connected to a power source to charge the liner bottom 74. The outer portion of the liner 30B may be electrically connected with an extra connector 93 (not shown) to ensure good electrical symmetry. The electric heater 105 includes the spaces 32 and 76 between the liner 30B and the fireproof container 24 and the slots 36 in the floor 28 of the fireproof container 24 and the outlet pipe 100 for starting and furnace control. It is installed in various positions including the surrounding annular space 96.

The pair of placement electrodes 50 supported by the arm 87 are installed on the furnace 10 and extend through the placement blanket 110 to the melting zone below the melting line 111. In a preferred embodiment several pairs of placement electrodes 50B are provided at 30 ° or 60 ° intervals around the furnace (see FIG. 10). Although the placement electrodes 50B are shown in pairs, other arrangements, such as single and triple combinations, may be used. A suitable arrangement is to install one or more electrodes in a set 50-50B along a radial line to symmetrically enclose the furnace protrusion. 10 shows a relatively close electrical spacing resulting from several sets of electrodes 50-50B. This arrangement makes it possible to heat the electrodes 50-50B to each other and create a current between them that are tightly coupled. If the electrode spacing is symmetrical and the electrical ignition is balanced to produce a relatively uniform temperature across the furnace, a relatively small reflux roll will occur.

9 shows the symmetry that occurs around the radial position of the electrode. The different radius electrodes 50 are powered to maintain somewhat the same temperature in their respective radial portions. The perimeter of each electrode 50 will be hotter than the glass surrounding it, and the glass movement below each electrode 50 will be directed vertically upward. {Circular arrows (0 and 1) indicating external and internal reflux stones Reference}. There will be a descending glass between the electrodes 50.

If the temperature remains the same around the electrode from the center of the furnace 10B to the liner 30B, each electrode 50 will have its own reflux roll that will not be overpowered by the larger, dominant reflux roll. Will produce. Many small reflux rolls move larger reflux at lower speeds due to greater shear forces between them. Therefore, the time for the glass to reside in the melting furnace is increased. The penetration depth of the roll is a function of the glass viscosity at the melting temperature. It is usually desirable to keep the roll small. However, in view of the fact that a centrally placed electrode (shown in FIG. 1) may be used for refining, deep penetration of reflux does not affect the electrodes of the glass used for the quality of the glass.

1 and 7, each of the placement electrodes 50 and 50 is relatively close to the top of the furnace melting line 111. By concentrating the heat high here, in the furnaces 10, 10A and 10B, the molten glass here does not tend to be highly refluxed and is close to the required high ie batch blanket 110. This is particularly helpful in the case of glass (eg, alumino-silicate glass) having a resistance that changes rapidly with temperature. Much energy may be consumed just below batch blanket 110 to effect more efficient melting.

The electrode configuration of the electrodes 50, 50A, 50B should be symmetrical. This should be particularly symmetrical, for example in large furnaces such as furnace 10B shown in FIGS. 9 and 10. Here, the electrodes 50-50B are installed every 30 or 60, but may be differently set to different heating patterns, for example, a transverse heating pattern, an ambient heating pattern, and the like. Other combinations and configurations are possible up to an interlocking interval of 15 ° C. but the device shown is now good.

Symmetrical heating of electrodes placed close to the batch blanket has the advantage of maintaining vertical and horizontal temperature stability to produce products of good quality for more effective use of energy. Normally, purely heated glass in a glass melting furnace tends to rise due to a decrease in its density with increasing temperature. Similarly, more dense cooling glass tends to move downward. In this way a rolling movement of the reflux roll or molten glass is done and the difference in glass density is maintained in the melt as it creates the driving force that results in such a rolling movement. In the present invention, if the heat is raised high in the furnace, i.e., just below the melting line 111, the heated glass tends to remain near the top of the furnace. Of course, some cooling will take place and the glass will be refluxed downward. Will flow. However, since the glass is heated near the top of the furnace, its initial motion is limited and thus the potential of other nearby glass is reduced. The tendency to leave freshly heated glass near the top of the furnace is enhanced because it is closest to equilibrium and is in a position that is quickly displaced and not cooled.

The uniformity of the horizontal temperature distribution is there even in the suppression of one major reflux roll from the hot side to the cold side of the furnace. By balancing the heat input horizontally, the tendency to produce excessive heating or cooling of the glass that inspires reflux is lowered.

The present invention also includes a liner bottomless system with a bottom electrode as in FIG. However, the liner bottoms with the bottoms are arranged in pairs along the radial line, as shown by the arrangement in FIG. 10.

Many furnace sizes are possible from the relatively small device of FIG. 1 (10 cm (4 inches in diameter)) to the larger device shown in FIG. 9 (300 to 900 cm (10 to 30 feet) in diameter). Larger sizes are also possible and the number of electrodes will increase as the diameter increases, it will be necessary to import a series of interdigitated multiple electrodes.

The features of each embodiment described herein may be merged with each other and interchanged with one another. For example, the layers of the refractory ramming mix 21 shown in FIGS. 1 and 3 may also be incorporated in other embodiments. Because of the many interchangeable features, the foregoing is merely illustrative and is not limited thereto.

Therefore, while the preferred embodiments of the present invention have been described, various changes and modifications may be made without departing from the spirit and scope of the present invention, which will be apparent to those skilled in the art, and also in the appended claims. It is intended to include all such changes and modifications that fall within the true spirit and scope.

Claims (21)

In the electric furnace for melting the thermoplastic material, a fireproof container 24 having sidewalls 26, a discharge hole 102 formed in the lower portion of the fireproof container, and a liner and sidewalls have a relatively folded annular space 23 therebetween. A fire resistant container having a metal liner 30, 30A, 30B installed in the fire container which is in close proximity to the side wall but spaced from each other to form a side wall) and an open top for receiving the batch material 110 to be melted. Under the melting line 111 formed by 24, means for dissolving the batch material conveyed in the furnace, the means 40, 50, 80, and the batch impurities to be melted and the molten material 43 thereunder. And an upper edge of the liner in the furnace. 2. The tram area 29 according to claim 1, wherein the side wall 26 is radially outwardly adjacent the top of the liner and the flange portion 33 of the liner is always offset and the tram area 29 between the top of the liner. An electrical furnace in contact with said offset sidewall to form a wall. 3. The electric furnace of claim 1 or 2, wherein a narrow annular space (32) between the liner (30) and the adjacent surface of the sidewall (26) is in communication with the interior of the liner. 2. The electric furnace of claim 1, wherein a fluid delivery outer cell (12) is provided adjacent the outer peripheral portion of the liner to cool the thermoplastic material in the vicinity thereof. The upright outlet pipe (100) according to claim 1, wherein the upright outlet pipe (100) is located through a hole in the bottom wall (28) of the fireproof container (24) and the upright outlet pipe (100) is located at a selected level on the bottom wall of the furnace. An outlet end 104 having an inlet at its free standing end 103, the inlet being positioned to receive the molten thermoplastic material from the level and the thermoplastic being located away from the inlet of the outlet tube And an electrode (80) means for heating said reserve outlet tube so that energy is concentrated relatively high in said hot spot (10b) near said inlet opening of said upright outlet tube. 6. Electric furnace according to claim 5, characterized in that the electrode (80) means is straight biased with respect to the discharge pipe so as to be a consuming electrode. 2. The electrode means according to claim 1, wherein the electrode means is interposed therebetween through a set of electrodes 40 or 50 arranged through one of the upper open ends of the furnace and a hole in the bottom wall 28 and a thermoplastic material therebetween. An electric furnace comprising means for exciting an electrode at all times for heating with an electric energy heating current. 8. Electric furnace according to claim 7, characterized in that the electrodes (40, 50) means are spaced away from the upstanding side walls of the liner (30). 8. A method according to claim 7, wherein at least one set of electrode (50) means is positioned through the batch blanket (110) into a relatively constant molten material (43) at the bottom of the batch to concentrate electrical heating flow in the molten material adjacent to the batch. An electric furnace characterized in that it is located with their spaced ends. 2. The electric furnace of claim 1, wherein the liner (30) comprises a portion of a bottom wall (36) that engages a lower portion of the side wall (26). The electric furnace of claim 1, further comprising an electrical connector (33) connected to the liner (30B) for electrically exciting. 2. The annular space 32 between the liner 30 and the side wall 26 is relatively narrow compared to the space 46 in the center of the liner and is employed to retain material therein. An electric furnace, characterized in that it provides a limited space to prevent movement of the material. The electric furnace of claim 1, wherein the liner (30) consists of molybdenum, tungsten, tantalum columbium and alloys thereof. 2. The annular space (32) according to claim 1, characterized in that the annular space (32) is at least partly filled with a ramming mix, sand, granular refractory material or a relatively high viscosity glass that is relatively difficult to introduce reflux and selected at a relatively high temperature. Electric furnace. The bottom margin of the liner (30) and the bottom wall (28) of the furnace (10) according to claim 1, wherein the slot (39) forms an effective seal against the flow of thermoplastic material between the outer part and the backing part of the liner. An electric furnace, characterized in that formed between). 2. The electric furnace of claim 1, wherein an insulating layer (20) surrounds an upright sidewall (26) of the fireproof container (24). 17. The compressible insulating layer 20B according to claim 16, wherein the insulating layer 20 comprises at least one rigid insulating layer 20A and a compressible insulating layer 20B adjacent the upstanding sidewalls employed to accommodate its relative movement during the thermal cycle of the furnace. An electric furnace, characterized in that provided. 2. The electric furnace of claim 1, wherein an electric heater (104) is located in the space between the liner (30B) and the fireproof vessel (24). A method of operating an electric furnace having an oxidizable protective liner in which a batch material containing a toxic gas composition in its gap trapped can be dissolved into a large amount of molten thermoplastic material in the furnace. Stacking, heating the furnace with a mixture of fossil fuel and air, and oxidizing the liner to protect the oxidizable liner from oxidation due to gaseous material trapped between the gaps of combustion air and the batch material. Adjusting the air to the fuel mixture in a sub metrological condition to ignite under an intermediate condition. A method of operating an electric furnace according to claim 1, further comprising the steps of: maintaining the level of molten glass in the furnace during normal operation of the furnace at a level above the upper extreme of the metal liner; And wherein the entire surface of the metal liner is brought into contact only with molten glass. A method for melting a thermoplastic material in a fireproof container according to claim 1, comprising the steps of: supplying a non-melting material to be melted in the metal-lined fireproof container, supplying electrical energy to melt the batch material, and Supplying a molten batch material into a metal lined inner container, feeding a thermoplastic material to the annular space and causing the material to become a half melted viscous body, a molten batch material and the half melted Surrounding and oxidizing all of the oxidizable metal liner by said supply of viscous material, and discharging the molten internal material from the metal lined vessel. Method for Melting Plastic Material.

Images