CA1219026A - Electric melting of solidified glass in melting units - Google Patents

Abstract

ELECTRIC MELTING OF SOLIDIFIED
GLASS IN MELTING UNITS

ABSTRACT OF THE DISCLOSURE
A method and apparatus for electrically melting solidified glass in difficult to reach regions of a glass melting furnace (15) are not readily accessible with fossil fuel heating means and, more particularly, to an electrode (35a-35e) arrangement for electrically heating solidified glass in difficult to melt regions such as a submerged outlet throat (15) between a furnace melter section (11) and the riser (16) through which the glass is supplied in production.

Description

~21aO26 ^ 1 -D E S C R I P T I O N
ELECTRIC MELTING OF SOLIDIFIED
GLASS lN MELTING UNITS

TECHNICAL FIELD
This invention is a method and electrode arrangement for electrically melting solidified glass in 15 difficult to reach regions of a glass melting furnace not readily accessible with fossil fuel heating means and more particularly to electrical heating of solidified glass in regions such as a submerged outlet throat between a furnace melter section and the ri;er through which the glass i5 20 supplied in production.
During periods of curtailment of furnace operations in the production of glass, the practice has been to maintain the upper region of the melter section and the outlet throat at a low temperature by supplying a low 25 level of heat thereto. Upon decision to restart the furnace, the start-up time can thus be minimized as well as the thermal shock and mechanical stress of startup of the furnace.
The cost of energy for maintaining furnaces in a 30 heated condition over such an extended period, for example, in the order o~ months, hDwever, is an extre~ely costly non-productive burden. To eliminate such high cost, two alternate approaches are possible, one being to drain the furnace co~pletely upon shut-down, and the second is to 35 allow the glass to completely solidify in the furnace.
When a glass melting furnace is completely drained during down times, restart procedures correspond -~$

~2~9Q26

- 2-1 much to those of start-up of a new furnace. Restart of a completely drained furnace, however, has the disadvantage that spalling of refractory and cracking under thermal stress can result in areas of previous wear of the furnace.
Restart of a furnace with solidified glass of the previous melt therein is often found more desirable in that it reduces the thermal shock difficulties. Where a submerged throat exists in the outlet end of the furnace, however, remelting of the solid glass in the thr~at is lO extremely difficùlt to accomplish because of its inaccessability to external sources of heat in addition to remoteness of heat of the melt.
Accordingly, it is a general object of the present invention to provide a method and means for melting 15 solidified glass in the difficult to reach regions of a glass melting furnace.
More particularly, it is an object of the present invention to provide a method and means for electrically melting solidified glass in a submerged throat between the 0 melter and the riser sections of a glass melting furnace.
BACKGROUND ART
During periods of curtailment or reduction of usage of glass melting furnaces, it has been the practice to maintain the glass in a submerged throat in a molten 25 state by use of electrodes as disclosed in Maddux, U.S.
Patent 3,997,710. This becomes extremely uneconomical as the length of out-of-service time increases. Methods have been developed to remelt glass in a melter section by combustion heating means as disclosed in Froberg et al, 30 U.S. Patent 3,842,180. This method, relying on combustion heating, will not work in areas which are inaccessible to fossil fuel combustion such as a submerged throat. Similar methods of remelting glass in a forehearth by means of combustion gas has been disclosed by Nuzum, 1n U.S. Patent

3,1g8,619. Again, combustion gases cannot be used in the present invention. The only other non-combustion gas means for melting glass in an inaccessible region is through 12190Z~

1 Radio Frequency heating such as disclosed by Ferguson, U.S.
Patent 2,186,718. The ph~sical size of the submerged throat makes this method impractical. The present invention using Joule effect heating elements and 5 sequencing the power between selected pairs of electrodes overcomes the problems associated with the prior art.
DISCLOSURE nF THE INVENTION
Solidified glass in a submerged throat of a glass melting furnace is melted according to the invention by the 10 step by step thawing or melting of glass between each adjacent pair of a series of electrodes spaced apart from each other in a path extending from a position just before the entry to the throat to a position at the riser. The spacing of the electrodes in the series is such that when 15 power is applied between any two adjacent electrodes when molten material exists about one of the electrodes, a Ooule effect conductive path is provided to the next adjacent electrode. Under such condition, glass between the two electrodes can be melted by supply of electric energy 20 between the two adjacent electrodes. Molten glass is then, in turn, provided about the second electrode to permit Joule effect heating of glass between it and the next succeeding electrode of th~ series as well as between such next electrode and the first electrode. Thus, solidified 25 glass between each succes;ive adjacent pair of electrodes can be melted step-by-step to provide a continuous molten path through the throat to the riser whereupon the glass can be supplied for production and conventional heating of the glass can be relied upon.
A feature of the invention is that it allows curtailment of glass production by complete shutdown of a furnace without requiring full drainage of the glass or requiring that it be main~ained hot during the shutdown period.
Another feature of the invention is that it maximizes production for the energy input regardless of fluctuating demands for output.

~219026 ~R I EF DESCR I PTI ON OF T~IE ~RAW I NGS
FIGURE 1 is a broken away plan view illustrating an electric glass melting furnace with a submerged throat and riser in its exit end leading to a forehearth from 5 which molten glass is supplied for production of products such as glass fibers.
FIGURE 2 is a cross sectional view taken on line 2^2 of the throat portion of the electric furnace represented in FIGURE 1.
FIG~RE 3 illustrates in perspective the submerged throat represented in cross section in FIGURE 2 showing the electrodes inserted in the submerqed channel for melting solidified glass therein.
BEST MnDE F~R CARRYING OUT THE I_VENTION
Referring to the drawings in greater detail, FIGURE 1 illustrates a plan view of an electric furnace lU
having a melting region 11 heated by electric power supplied by way of electrodes 20 located in the four corners of the furnace. The furnace here illustrated is of 20 the cold top type in which the batch is supplied to the top of the molten mass within the furnace, such batch being melted at its interface with the underlying molten pool of glass. As the molten glass is heated by the power supplied at the electrodes 20, it is withdrawn for use in production 25 of products through a recessed channel or slot 12 located at the mid-region of one wall of the furnace. Thus glass is flowed through an outlèt throat 15 to a riser 16 connected to the furnace forehearth 17 for the supply of glass to units for production of products such as glass fibers.
In supplying glass from the furnace through a submerged throat, as illustrated, it is conventional to provide supplementary heat by way of electrodes 30 and 40 located in the slot 12 leading to the throat 15 and at the 35 exit from the throat in the region of the riser 16, respectively. Thus, the glass flowing from the melting region can be controlled in temperature by supply of the ~2~go26 1 supplementary heat before its introduction into the forehearth. This arrangement is quite advantageous in assuriny proper and stable temperature of the glàss output from the melting region upon its introduction into the S forehearth for use in production.
As hereinabove described, production at times is required to be curtailed, usually for economic reasons, and the downtime can continue for extended periods such as d matter of weeks or even months. Whereas it has been a lO practice to maintain such furnaces in a heated condition under low power supplied from electrodes 2~, because of the high cost of drainage and restart of an empty furnace, it is more desirable to shut down the furnace with a full load of glass contained therein. Such shutdown of the furnace, 15 however, has a disadvantage in that certain regions of the furnace, such as the submerged throat, when loaded with solidified glass is extremely difficult Dr practically impossible to melt by conventional means for reinitiation of the flow of glass output.
According to the present invention, one or more auxiliary or supplementary electrodes are specially inserted or permanently provided in the difficult to reach regions, such as the submerged throat 15. In the arrangement illustrated, a series of electrodes 35a, 35b, 35c, 3sd and 35e are pro~ided in spaced relation within the throat 15 between the main power supply electrodes 30 and 40 located at the entry and exit ends of the throat respectively. In normal operation of the furnace, glass flows from the melting region 11 into the recessed channel 30 or slot 12 and upon passage through the throat 15 to the riser 16 and forehearth 17, it is controlled in temperature by supply of additional heat by ~oule effect current flow between the electrodes 3~ and 40. The power of electrodes 30 and 40 is supplied frc,m transformer 50 which has a 35 primary 51 and d secondary 52 connected to the electrodes 30 and 4U. However, when the furnace is shut down and the glass is allowed to solicify in the melting region 11 and ~Z~90Z6 l the throat 15 these electrodes are ineffective to melt the solidified glass because of the non-conductivity of the glass in its solidified condition.
When glass in a furnace is allowed to solidify or 5 otherwise approach solidity in an area such as the melting region, it can ordinarily be remelted such as with a combustion burner to melt the desired solidified regions.
In the case of an electrit furnace 10, the glass surface in the regions of the electrodes can be selectively melted to 10 establish a conductive path between electrodes 20 of opposite potential and, thereafter, melting can continue by application of power to the electrodes to promote the flow of Joule effect current and thus progressively reestablish a molten pool.
Solidified glass in the throat 15 of the furnace, however, cannot be so reathed with a combustion burner and, accordingly, reestablishment of flow through the throat by such means is usually practically impossiblP. Although the glass about the electrode 3û might be melted, no conductive 20 path is provided through the throat because of the non-conductive solidified glass therein between the electrodes 30 and 40. Thus, where electrodes 35a to 35e are not permanently in place, a series of such electrodes can be installed by drilling through the refractory 25 underlying the throat 15 for insertion of as many electrodes 35 as are necessary for progressive melting of the glass between the electrode 30 to the electrode 40.
Ilore specifically, molten glass of the melting region is present about the electrode 30 after conventional 30 heating of the glass in the melting region 11. The molten glass about the electrode 30 then allows establishment of an electrically conductive path between it and the adjacent electrode 35a. Thus, when the power output of the transformer 50 is applied between electrode 30 and 35a, 35 glass can be melted between these two electrodes. In addition, glass can be melted in the region about the electrode 35a in sufficient amount to perm~t establishment lZ19(!26 1 of a conductive path between electrodes 35a and 35b. The secondary lead 56 of the transformer ~0 can then be removed from the electrode 35a and connected in turn to `electrode 35b to establish a Joule effect conductive path between the 5 electrodes 30 and 35b. The glass about the electrode 35b can thereupon be melted to permit subsequent flow of current between 35b and 35c by connection of the transforrn~r lead 56 to electrode 35c. The solidified glass in the throat 15 can thus be progressively melted by 10 successive connection of the transformer secondary lead 56 to each of the electrodes 35a to 35e, one at a time until a complete conductive path of molten glass is established between electrodes 30 and 40, whereupon conventional heating of the throat glass can be resorted to by steady 15 supply of power thereto.
As a variation of this procedure, a voltage can be established between electrodes 30 and 40 to maintain a potential difference thereb2tween during the sequential application of voltage in advancing relation from electrode 20 3~ to 35a, 35b, 35c, etc., by moving the jumper 56 of secondary 52 of the transformer 50 to each succeeding electrode as the melt is advanced through the throat.
Thus, the voltage between electrodes 30 and 40 will take over as soon as the mass of glass in the throat is 25 sufficiently conductive to effect a generation of heat.
As still another variation of the described arrangeménts, the electrodes 35a to 3~e can be permanently installed with a sequencing circuit designed to both provide heat when necessary during operation of the furnace 30 and to automatically advance application of power to the melt in the throat from a cold start without need for manually connecting jumpers from one electrode to another as the glass is melted therein. In addition, electrodes in the throat may be grouped and sequenced or might be aligned 35 with different spacing in staggered relation through the throat.

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Thus, while certain arrangments of the present invention have been described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and 5 scope of the invention as claimed.
INDUSTRIAL APPLIC~BILITY
The present inv~ntion pertains to glass melting furnaces~ This invention overcomes the problem of having to completely drain a glass melting furnace prior to shutdown 10 conditions.

Claims (9)

C L A I M S

1. A method of melting solidified glass in a submerged throat of a glass melting furnace comprising providing at least a first electrode in the melter chamber supply slot, providing a second electrode in the covered submerged throat, heating glass about said first electrode to a conductive condition around said first electrode and supplying electric energy between said first electrode and said second electrode to establish a Joule effect conductive path therebetween to more fully melt the glass therebetween, subsequent electrodes adjacent said second electrode along the length of the covered submerged throat, sequentially supplying electric energy between said first electrode and subsequent electrodes along said submerged throat to sequentially thaw the solidified glass by conduction of heat from the region between the first electrode and second electrode until the glass around the subsequent electrodes become conductive and electric power for Joule effect heating can be applied to subsequent electrodes in the submerged throat until all of the glass in the submerged throat is molten.

2. The method of claim 1 wherein adequate electric energy is supplied to said first electrode and said second electrode to melt the glass about said second electrode and between said second electrode and said subsequent electrodes.

3. The method of claim 2 wherein the subsequent electrode is a third electrode in said submerged throat which is within electrically conductive reach of said second electrode and supplying electrical energy between said first and said third electrode to melt glass in said submerged throat beyond said second electrode.

4. The method of claim 2 wherein the subsequent electrodes are a series of electrodes in spaced relation extending along the submerged throat including said second electrode and said series of electrodes are energized in sequence beginning with said first electrode as an entry electrode to the region located in the channel of the melter section and the last electrode of the series as an exit electrode outside the submerged throat in the riser section to progressively melt glass about each such electrode thereby to progressively advance the conductive path between adjacent electrodes in the series until a conductive path is established between said entry or first electrode and exit or last electrodes for establishment of a glass flow path through said submerged throat.

5. An electrode arrangement for melting solidified glass in a submerged outlet throat of a glass melting furnace comprising a series of spaced apart electrodes including a first electrode at the entry to the throat and a last electrode at the exit of the throat, at least one additional electrode in said throat between said first and said last electrode, means for melting glass around said first electrode to provide molten glass between said first electrode and said additional electrode electric energy means for establishing a Joule effect current therebetween for melting glass about said additional electrode to provide molten glass for establishment of a conductive path between said additional electrode and its next adjacent electrode, sequentially applying electric energy means between said first electrode and said next adjacent electrode until a molten glass conductive path is completed through the submerged throat between said first electrode and said last electrode.

6. A glass melting furnace electrode arrangement as defined in claim 5 wherein said electric energy means includes a means to sequentially supply the said electric energy means between said first electrode and subsequent electrodes along said submerged throat as the solidified glass becomes electrically conductive along said submerged throat.

7. A glass melting furnace electrode arrangement as defined in claim 6 wherein said electric energy means is connected in such a manner to supply electric energy between said first electrode and each said additional electrode sequentially until said electric energy means supplies electric power between said first electrode and said last electrode.

8. A glass melting furnace electrode arrangement as defined in claim 6 wherein at least two additional electrodes exist in a series adjacent relationship between said first electrode and said last electrode, and each such additional electrode is energized by electric energy means in sequence to melt glass thereabout.

9. A glass melting furnace electrode arrangement as defined in claim 5 wherein a sequencing means is provided for energizing said additional electrodes in sequence to melt glass about each additional electrode in turn until a molten conductive path is provided between said first electrode and said last electrode.