KR900005199B1 - Vacuum refining of glassy materials with controlled foaming - Google Patents

Abstract

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Description

Method for Purifying Glass Material

1 is a vertical cross-sectional view of a three stage melting operation consisting of a liquefaction step, a dissolution step and a vacuum purification step according to a preferred embodiment of the present invention.

2 is a schematic representation of a reduced vacuum system with steam condensing means.

* Explanation of symbols for main parts of the drawings

10: liquefaction step 11: dissolution step

12: purification step 15: drum

16: ring 17: support wheel

18: careful wheel 20: lid structure

21: surrounding frame 22: burner

24: chute 25: lining

26: liquefied layer 27: ceramic refractory bushing

28: liquefied material 30: refractory crucible

31: fireproof roof 32: electrode

33: skimming member 35: plunger

36: discharge pipe 37: shaft

40: fireproof lining 41: jacket

42,43: Cooler 44: Orifice

50: foam layer 56: fireproof floor section

57: water cooler 58: throttle member

59: stem 60: melt flow

61 gas conduit 62 heat exchanger

63: water trap chamber 64: vacuum pump

65: equalization column 66: collection container

67: water jacket

This field name relates to the use of subatmospheric pressure to promote the refining action of molten glass and the like, and particularly relates to a practical arrangement for controlling the amount of foam in refining technology and the like.

When the glass is melted, a significant amount of gas is produced as a result of the decomposition of the batch material. Other gases are entrained in the batch material to follow or enter the molten glass from the combustion heat source. Most of the gas leaves the initial stage of melting, but some are incorporated into the melt. Any of the entrained gases will dissolve in the glass. The other forms discontinuous gaseous inclusions known as "bubbles" that will become teeing jade if they remain too high concentrated in the finished product. The gas content rises to the surface and will exit the melt if given enough time in the melting operation stage, known as "purification" or "clarification". Higher temperatures are typically provided to the refining zone to promote the rise and escape of gaseous inclusions by lowering the viscosity of the melt and increasing the bubble diameter. The energy required for the high temperatures used in the refining step and the large melters required to provide sufficient residence time for the gaseous content to escape the melt are the most cost of the glassmaking operation. Therefore, it is desirable to assist the refining operation to reduce this cost. The depressurization action can help the purification process by reducing the partial pressure of the gas stream contained in it and increasing the volume of the surface to speed up the flotation to the surface. It would be impractical to provide a gas-sealed container on a conventional tablet scale to evacuate the interior to US Pat. No. 1,564,235; 2,781,411; 2,877,280; 3,338,694; And the use of vacuum tablets up to relatively small batch operations, such as those disclosed in and 3,442,622.

Continuous vacuum purification processes have been proposed, but have been found to be unacceptable for large scale manufacturing due to several drawbacks of continuous glass manufacturing. United States Patent 805,139; 1,598,308; The main drawback in the continuous vacuum arrangement shown in 3,519,412 is the requirement that the vertical passage into and out of the vacuum region must be relatively narrow due to the pressure differential. These passages complicate the structure of such vessels, particularly in view of the need for gas-sealing walls, increase the exposure of the emissions to contaminating refractory contacts, and impose significant viscous drag on the discharge flow. It can be seen that the substantial height of the glass is necessary to balance the degree of control of the vacuum evenly. Changing the output of such a system is also a problem, especially in terms of viscous drag factor. Variability is important for continuous commercial operations because it is a changing factor in the economic factors that affect the product being manufactured and the desired output.

In each of the three patents, the driving force to increase the flow rate through the passage, which is the vacuum section, is provided only by increasing the depth of the upstream melt in the vacuum section as compared to the depth of the downstream melt from the vacuum section. The magnitude of this height difference is compounded by the viscous drag inherent in these systems. Since the corrosion of the sidewalls is accelerated when the surface of the melt is elevated, a significant change in height further exacerbates the corrosion which subsequently impairs the quality of the product glass.

A simpler structure is disclosed in US Pat. No. 3,429,684, where the batch material is fed through a vacuum lock and melted on top of a vertically elongated vacuum chamber. Changing the emissions in that arrangement seems to require changing the degree of vacuum applied to the chamber, which will adversely alter the degree of purification achieved. Melting the raw material in the vacuum chamber is another disadvantage of the arrangement for three reasons. First, the initial decomposition of the raw material under vacuum will generate a large amount of foam, which will require a large container to hold the foam sufficiently. Secondly, there is a risk that the raw material will follow a short circulation path up to the outlet flow and will not be properly melted and purified. Third, enormous heat needs to be supplied to the melt in the vessel in order to carry out the melting and heating initial stage of the melt to the purification temperature in the vacuum melter. When so much heat enters the vessel, it essentially causes convective flows in the melt that add to the corrosion of the walls and contaminate the purified product flow.

U.S. Patent 4,195,982 discloses first melting the glass at elevated temperatures and then purifying the glass at a lower pressure in the separation chamber. Both chambers are heated.

U.S. Patent 4,110,098 discloses a process of carefully foaming a glass to aid in purification, which is induced by severe heat and chemical blowing agents at atmospheric pressure.

The problem encountered to some extent during vacuum purification in a continuous or batch mode is the large amount of foam that frequently occurs at patented low pressures. A large space must be provided above the liquid container to receive the foam. Since this headspace must also maintain gas-sealing, drying can be a particularly serious economic obstacle in large scale processes. As a result, the foam acts as a factor that limits the degree of vacuum that can be used. It is desirable to alleviate these constraints in the vacuum purification process without incurring much financial loss.

U.S. Patent 3,350,185 discloses a technique for breaking bubbles in a glass melting process at atmospheric pressure, where a sudden change in the oxidation or reduction state of combustion destroys the foam.

The present invention proposes a method of passing molten material into an upper portion of a vertically elongated chamber in vacuum. One advantage is that by imposing almost all the heat energy required to purify upstream from the vacuum chamber, there is little need to heat it in the vacuum chamber and the thermal component of the incoming material maintains itself almost sufficiently at the desired temperature in the vacuum chamber. Burners have been disclosed in the apparatus to maintain combustion in the headspace above the vacuum chamber.

According to the present invention, it has been found advantageous to provide an auxiliary heating device in the head space above the vacuum chamber in order to promote the breakdown of bubbles. It is believed that the foam layer that collects on top of the chamber tends to block the headspace from the heat of the underlying melt. Also, the flowing material will stay in the headspace for a short time and hardly heat the headspace. Therefore, it is believed that the headspace will tend to be relatively cooled, with the result that the foam layer portion is also relatively cooled, resulting in a high viscosity of the foam portion and delayed breakage of that portion. The accelerated breakdown of bubbles caused by heating the headspace is said to be due to the increase in temperature and the low viscosity of the bubbles. If a combustion heat source is used to heat the headspace, the combustion gas may hit the bubble membrane of the foam and mechanically increase the foam breakdown rate.

Part of the present invention finds that the combustion heat source can be operated under reduced pressure in a vacuum refinery chamber at a rate sufficient to achieve the objects of the present invention without seriously affecting the performance of maintaining the desired subpopulation in the chamber. have. It will also be appreciated that the flame can be easily maintained at reduced pressure.

In one mode of operation, other benefits can be obtained by using a heat source that does not produce as much combustion by-products as the gases removed from the melt by the refining process. In other words, it is advantageous to keep the partial pressure as low as possible in any kind of headspace to be purified from the melt. For glass, the removal of nitrogen and carbon dioxide is the main purpose of the purification process. Therefore, it is advantageous to use oxygen enriched combustion products (possibly pure oxygen) to ignite the burner to heat the headspace of the vacuum chamber in order to reduce or eliminate the introduction of nitrogen into the chamber. In addition, the use of some or all of the oxygen instead of air to aid combustion significantly reduces the exhaust gas volume, reducing the load on the vacuum system. To avoid the addition of carbon dioxide around the headspace, burners may use low carbon or non-carbon fuels such as hydrogen. Burning hydrogen with oxygen is particularly advantageous because the combustion product is only water vapor. Since water vapor dissolves relatively high in glass, it is generally not a requirement to remove water for glass purification processes. In addition, the ability to condense the water vapor in the vacuum system virtually eliminates any additional burden on the vacuum pump caused by the headspace burner. On the other hand, a plasma torch is used to heat the headspace. Plasma torches can produce high calories with a relatively small amount of carrier gas. The carrier gas may also be selected from a wide range of gases including inert gases such as steam, hydrogen, oxygen, or helium.

While the detailed description will be developed in conjunction with methods and apparatuses that are particularly suitable for melting glass and similar glassy materials, it should be understood that the present invention may be applied to the processing of other materials.

Although the present invention is not limited thereto, it is usefully used with the vacuum purification system disclosed in the aforementioned US Patent No. 815,494 dated January 1, 1986. In a preferred embodiment of such a system, a subatmospheric space is allowed in the molten material to produce bubbles that eventually break up. A significant increase in the surface area of the foam promotes the removal of gas from the material while under reduced pressure. Returning to atmospheric pressure, the concentrated gases dissolved in the material become low saturated and do not nucleate into bubbles. It is advantageous to increase production because of the active foaming action contained in such a method that promotes the destruction of foam.

In a preferred embodiment, the batch material is first liquefied in a step particularly suited to that step in the process, and the liquefied material can be raised to a temperature suitable for the dissolution of the solid particles essentially and the temperature of the material to be purified. It is transferred in two stages. The molten material is then transferred to a vacuum chamber. As a result, most of the gaseous melt by-products are removed before the material enters the vacuum chamber, and the maximum gas release zone is separated from the refining zone, so that the material in the initial stage of melting cannot mix with the melt portion in the refining. Excessive convection in the refining zone can be avoided because most of the molten heat conditions are satisfied before the material enters the vacuum refining step and thus substantially avoids heating of the refining step. As a result, vessel corrosion is reduced and the probability of incomplete refinement and refinement portion mixing in the melt is reduced. In a preferred embodiment, the input to the purification step is at a temperature suitable for purification, and therefore there is no need to provide little or no heat to the purification vessel. However, in order to substantially maintain the temperature of the material at least at the inlet of the refining step, the vacuum chamber headspace heating means in the present invention may also serve to compensate for heat loss through the walls of the vessel, in particular the top.

In a preferred vacuum purification arrangement, the liquefied material is metered in through the valve means into the upper end of the vacuum chamber and the purified melt exits from the lower end of the vacuum chamber through another valve arrangement. The height of the liquid held in the vacuum chamber is preferably at least slightly greater than the height necessary to balance the vacuum. Thus, the production rate can be controlled by the valve without changing the vacuum pressure of the vacuum chamber and without changing the liquid height. In other words, the range of vacuum pressures can be adopted without changing the production rate. Without the valve, the system would have a relatively low resistance to the flow of molten material.

Preferred conditions for vacuum refineries are vertically elongated containers, particularly conveniently upright cylinders. The liquefied material is drawn into the headspace above the molten material contained within the vessel. When the headspace is depressurized, at least a substantial portion of the material foam appears in the material due to the release of gas dissolved in the material and the expansion of the bubbles. As bubbles form, the surface area exposed to reduced pressure increases significantly, which helps to remove gas flow from the liquid phase. Foaming over the molten pool contained in the container, rather than from the molten pool, is advantageous to break the foam and aid in the release of gas. It has also been found that placing new bubbles on top of the foam layer promotes foam breakdown. Another advantage of the vertically elongated shape is that foaming from above and the product exiting below can cause the total mass transfer to be far from the foaming area so that the foam can be purified so that it is not included in the product flow at all. Since the gas was removed from the melt under reduced pressure, the concentration of the gas dissolved in the melt is reduced below the saturation point at atmospheric pressure. As the molten material proceeds downwards towards the bottom outlet, any increase in pressure due to the depth of the melt in the vessel causes the residual gas to dissolve and remain as small as possible. In addition, the dissolution of the gas may be assisted by the temperature drop as the material proceeds to the outlet.

Typically, when melting glass, raw materials of sodium sulphate, calcium sulphate or other sulfur are included in the batch material to aid the melting and refining process. The presence of sulfur compounds in the melt has been known to be a problem when vacuuming, because it causes a lot of foam and invades the ceramic fireproof walls of the vacuum refining vessel. To date, however, there has been difficulty in melting and purifying glass effectively without sulfur compounds. However, another advantage is that the glass can be melted and purified to a high level of quality with little or no sulfur, which is a preferred vacuum clarification arrangement. This is possible in the present invention because the melting and purification steps are carried out in discontinuous steps, whereby each step is carried out by a process suitable for using minimal or no sulfur.

According to FIG. 1, the whole melting process of the present field name is preferably composed of three steps: a liquefaction step 10, a dissolution step 11 and a vacuum purification step 12. Although several arrangements may be employed to start melting in the liquefaction step 10, an arrangement that is very effective for isolating this process and performing it economically is disclosed in US Pat. No. 4,381,934, which refers to the details of the preferred liquefaction step embodiment. This is embodied here. The basic structure of the liquefaction vessel is a drum 15 which may be made of steel and have a generally cylindrical sidewall portion, a generally open top, and a closed bottom portion except the outlet. The drum 15 is approximately supported by, for example, a circumferential support ring 16 rotatably supported by a plurality of support wheels 17 and held in place by a plurality of guard wheels 18. It is mounted to rotate about the vertical axis. Substantial closure cavities are formed within the drum 15, for example by a lid structure 20 which is fixedly supported by the peripheral frame 21. The lid 20 may be dried from a refractory ceramic material or may take various forms known to those skilled in the drying technique. The arrangement depicted in the figures is an upward helped, inelastic arch structure made of a number of refractory bricks. It should be noted that integral or flat suspension designs may also be employed as lids.

Heat to liquefy the batch material may be provided by one or more burners 22 penetrating the lid 20.

Several burners are preferably arranged around the lid in order to direct the burner's flame to a wide range of materials in the drum. The burners are preferably cooled with water to protect the burners in the harsh environment in the container. The exhaust gases can exit from inside the liquefaction vessel through the lidded opening 23. Waste heat in the exhaust gases can be advantageously used to preheat the batch material in a preheating step (not shown) as disclosed in US Pat. No. 4,519,814.

The batch material, which is preferably in powder form, is supplied to the cavity of the liquefaction vessel by means of the chute 24, which in this embodiment passes through the exhaust opening 23. Details of the supply chutes can be found in US Pat. No. 4,529,428. The batch chute 24 ends right next to the side wall of the drum 10 so that the batch material sinks over the inner wall portion of the drum. The layer of batch material 25 is supported on the inner wall of the drum 10 with the aid of the rotation of the drum and serves as an insulating lining. Since the placement material on the surface of the lining 25 is exposed to the heat of the cavity, it forms a liquefaction layer 26 that flows down the inclined lining up to the central outlet opening at the bottom of the container. The outlet may be equipped with a ceramic refractory bushing 27. The horn of the liquefied material 28 free-falls through the opening 29 leading from the liquefied vessel to the second stage 11.

The second step may be referred to as the dissolution step, because one of its functions is to completely dissolve even the smallest amount of unmelted batch material remaining in the liquefaction stream 28 leaving the liquefaction vessel 10. The liquefied material there is typically only partially molten and substantially gaseous, including unmelted sand grains.

In a typical soda-lime-silica melting process using sulphate as a carbonate batch material and a purification promoter, the gas phase consists mainly of carbon oxides and sulfur oxides. Nitrogen may also come from entrained air.

The dissolution vessel 11 functions to completely dissolve the unmelted particles in the liquefied material coming from the first stage by remaining in a position separated from the downstream purification stage. Soda-lime-silica glass is typically liquefied at about 2100 ° F. (1150 ° C.)-2200 ° F. (1200 ° C.) and enters the dissolution vessel at about 2100 ° F. (1200 ° C.)-2400 ° F. (1320 ° C.) at that temperature. Residual non-melting particles generally dissolve given sufficient residence time. The illustrated dissolution vessel 11 is in the form of a horizontal elongated refractory crucible 30 having an inlet and an outlet at both ends and a refractory roof 31 in order to ensure an appropriate residence time. The depth of the molten material in the melting vessel is relatively shallow to prevent material recycling.

There is no need to add substantially more thermal energy to perform the dissolution step, but the heating action may facilitate the process to reduce the size of the dissolution vessel 11. More importantly, however, it is desirable to heat the material in the dissolution vessel to raise the temperature in preparation for the next purification step. Maximizing the purification temperature is advantageous for reducing the glass viscosity and increasing the vapor pressure of the gas contained. Typically, a temperature of about 2800 ° F. (1540 ° C.) is deemed suitable for refining soda-lime-silica glass, but if vacuum is used to aid purification, a lower peak refining temperature may be used. It can be used without sacrificing quality. The amount by which the temperature can be reduced depends on the degree of vacuum. Therefore, if the purification is carried out in a vacuum according to the invention, only 2700 ° F. (1480 ° C.), preferably only 2600 ° F. (1430 ° C.) and suitably only 2500 ° F., before the glass temperature is purified. It needs to be raised to (1370 ° C.). Reducing the peak temperatures in this order not only significantly extends the life of the refractory vessel but also saves energy. The liquefied material entering the melting vessel only needs to be adequately heated to prepare the molten material for purification. A combustion heat source may be used for the dissolution vessel 11, but this step provides itself as a cavity for electrical heating, so that a plurality of electrodes 32 extending horizontally through the sidewalls as shown in the figure can be provided. Heat is generated due to the resistance of the melt itself to the current passing between the electrodes, which is a technique commonly used in electrically molten glass. Electrode 32 may be in the form of carbon or molybdenum, well known to those skilled in the art. A skimming member 33 can be provided in the dissolution vessel to prevent any suspended material from reaching the outlet end.

The valve for controlling the flow of material from the dissolution step 11 to the purification step 12 consists of a plunger 35 axially aligned with the discharge tube 36. The shaft 37 of the plunger penetrates the roof 31 of the melting vessel to control the flow rate of the material into the purification stage by controlling over the gap between the plunger 35 and the tube 36. The valve tube 36 may be made of refractory metal such as platinum and is sealed into the orifice 44 at the top of the tablet vessel. Although the valve arrangement is preferred, other means may be provided to control the flow rate of the molten material to the purification vessel, as is known in the art. In one example, heating and / or cooling means associated with the discharge line can be used to control the flow rate by adjusting the viscosity of the molten material passing therethrough.

The refining stage 12 preferably consists of a straight cylindrical vessel which is generally cylindrical and has an inner ceramic refractory lining 40 which is protected by a gas-sealed water cooled casing. The refractory material may be alumina-zircon oxide-silica, which is well known in the art. The casing may consist of a double wall, cylindrical sidewall jacket 41 having an annular channel and circular end coolers 42, 43. Any suitable cooling arrangement can be used. An insulating layer (not shown) may be provided between the lining 40 and the jacket 41.

As the molten material passes through the tube 36 and is depressurized in the refining vessel, the gas contained in the melt creates a foam layer 50 which expands in volume and overlies the body of the liquid 51. The foam breaks and mixes with the liquid body 51. The upper portion of the vessel may create subatmospheric pressure in the purification vessel through the vacuum conduit 52 through which the vessel is directed.

If further foaming is needed, conduit 54 may extend into the upper portion of the tablet vessel to add foam breaker into the container. Preferred foam blockers are water which can be brought over the foam continuously or intermittently.

The purified molten material is discharged from the bottom of the refining vessel 12 via an outlet tube 55 made of refractory metal such as platinum. The discharge pipe 55 preferably protrudes above the surface of the built-in refractory bottom section 56 so that no debris enters the output flow. By reducing the insulation effect on the tube 55, the thickness of the bottom section 56 adjacent to the tube 55 can be reduced so that the temperature of the tube is elevated and the material inside the tube does not freeze. The water cooler 57 under the bottom section 56 prevents leakage around the pipe 55. The melt flow rate from the discharge pipe 55 is controlled by a conical throttle member 58 located at the distal end of the stem 59. The stem 59 is associated with a mechanical means (not shown) that adjusts the synergism of the throttle member 58 to control the gap therebetween in order to control the flow rate between the throttle member 58 and the tube 55. have. The melt flow 60 of the refined material flows freely from the bottom of the tablet vessel to a forming step (not shown) which can be molded into the desired product. For example, the refined glass may flow to a floating glass forming chamber in which molten glass floats in molten metal pools to make plate glass.

The tablet vessel 12 may be in various shapes, but a cylindrical shape is preferable. The cylindrical shape is advantageous for making gas-sealed paper. The ratio of medial side contact area to volume is also minimized in the circular cross section. Compared to conventional open-loop recirculation purifiers, the cylindrical vacuum purifier of the present invention only needs a small refractory contact area.

The height of the molten material 51 remaining in the refiner 12 depends on the degree of vacuum imposed in the chamber. In order for the material to be freed from the vessel, the pressure head due to the height of the liquid must be sufficient to set a pressure greater than or equal to the atmospheric pressure at the outlet. The height depends on the specific weight of the molten material, the specific weight of the soda-lime-silica glass is about 2.3 at that temperature. In order to allow for the fluctuation of the vacuum and to ensure the stability of the flow through the outlet, it is desirable to consider the fluctuation of the atmospheric pressure to a height higher than the minimum necessary to offset the vacuum state.

In a preferred embodiment of the present invention, substantially excess height is provided such that the output flow is not determined by vacuum pressure but rather by mechanical valve means. Such an arrangement allows the output and vacuum pressure to change independently of each other. Alternatively, the outlet pressure may be below atmospheric if the pump means is provided to overcome the pressure differential at the outlet. An example pump for use in molten glass is disclosed in US Pat. No. 4,083,711, which is incorporated herein by reference.

The benefits of vacuum in the purification process are achieved gradually. The lower the pressure, the greater the benefit. A slight decrease in pressure below atmospheric pressure can lead to some improvement, but it is desirable to use a substantially reduced pressure to justify the vacuum chamber economically. Therefore, only 1/2 atmosphere or less is desirable to bring proper refinement to soda-lime-silica plate glass. Better results are obtained at less than 1/3 atmospheric pressure. The standard clear soda-lime-silica plate glass compound produced at 100 torr absolute pressure and produced a product with 1 bubble per 100 cm ³ , which is an acceptable level of quality for many glass products. For example, in order to produce commercial tubular glass of about 1 bubble quality per 1,000-10,000 m ³ , a purification pressure of 20-50 torr or less of 100 torr is suitable. Bubbles less than 1mm in diameter are considered invisible and are not included in the bubble count.

As shown in FIG. 1, the head space heating means of the present invention may take the form of a burner 53 which extends into the tablet vessel 12 through the top cooler 42. The burner is preferably equipped with a water-cooled jacket to extend its level. Although the exact mechanism for foam breakdown is not fully understood, the heat from the burner is said to reduce the viscosity of the foam and increase the volume of the foam, both of which cause the bubbles to burst.

When agitated at a sufficiently high flame rate, the bubbles can burst if the flame hits the foam. When the discharge pipe 36 is made of platinum, it is preferable to use an oxide flame so as not to damage the platinum. If platinum is not present in the headspace of the vacuum vessel, it is desirable to reduce the flames to increase the tendency to break bubbles.

The burner 53 is preferably ignited with oxygen so that nitrogen does not enter the system from the combustion air. Nitrogen that can enter the glass has a relatively high defect potential in the glass because of the relatively low solubility in the molten glass. If you want to avoid another cause CO ₂ bubbles in the glass, it is also possible to use hydrogen as a fuel.

Water, a combustion byproduct of hydrogen and oxygen, has a relatively high degree of solubility in molten glass. It is also desirable to avoid CO ₂ because lowering the CO ₂ concentration of the melt is one of the general purposes of the purification step and therefore it is desirable to keep the partial pressure of CO ₂ in the head space of the purification vessel as low as possible. On the other hand, removing water from the melt is generally not critical. Similarly, a plasma torch can be used in place of burner 53, along with a carrier gas that is relatively soluble in glass, such as steam or helium. Oxygen and / or hydrogen may also be used as the plasma carrier gas. One example of plasma torches known in the art is disclosed in US Pat. No. 4,545,798, which is incorporated herein by reference.

In order to reduce the gas volume that must be adjusted by the vacuum pump which in turn makes it easier to obtain a lower pressure, the concentrated combustion by-product from the burner 53 can be removed from the gas exiting the conduit 52 through the conduit 52 from the vacuum chamber. Can be. The substantial part of the exhaust gas consists of water vapor, so that when the burner 53 uses hydrogen and oxygen, the condensation of water vapor is particularly useful because the gas volume remaining after condensation can be quite small. Conventional condensation trap arrangements can be used, one example of which is schematically illustrated in FIG. The exhaust conduit 52 is provided with a water jacket 67 to protect the conduit 61 from hot gas passing through the gas conduit 61. Conventional bush heat exchanger 62 is used to cool the exhaust gas. In the arrangement shown, coolant is passed through a shell to cool the gas flowing through the tube. To condense water vapor from the gas, the gases are cooled down to the dew point of the water at the pressure present in the vacuum system. The condensed water and the remaining residual gas flow to the water trap chamber 63, where the gas is directed to the vacuum pump 64 and the water is drained to the collecting vessel 66, i.e. the equalizing column 65 extending vertically to the drain. . If the solids settle to a significant extent on the surface of the heat exchanger, it is advantageous to let the gas flow upward through the heat exchanger so that the condensed water flowing down drains the precipitate from the heat exchange inlet end.

Melting and clarification aids, such as sulfur or fluorine compounds, are included in the rough glass batch but produce substantially undesirable emissions to the exhaust gas from the glass melting furnace. Although it is desirable to remove them, it has been recognized that in order to obtain the highest level of quality, the use of acid is necessary, especially on the basis of panes. In particular, sulfur raw materials (such as sodium sulfate and calcium sulfate) have been found to produce excessive foaming under vacuum.

Typically, the flat glass batch contains a proportion of 5-15 parts by weight sodium sulfate relative to 1000 parts by weight of silica raw material (sand), of which 10 parts are considered to be suitable for proper purification. However, when working in accordance with the present invention, it has been found that it is desirable to limit sodium sulfate to 2 parts by weight in order to keep the foam at a manageable level, but it has been found that refining is not severely affected. Most preferably, 1 part by weight of sodium sulfate per 1 000 parts by weight of sand is used, with 1/2 being particularly advantageous. This weight ratio is given for sodium sulfate, but can be normalized to other layer feedstocks in molecular weight ratio. However careful the omission of the addition of the sulfur raw material, sulfur can generally enter the melt due to traces of sulfur compounds which are sometimes present in conventional inorganic batch materials.

Claims (17)

A method of refining a material for glass making where a volume of material in the molten state remains in a closed container, a foam layer is on the molten material, and a subatmospheric pressure is applied to the container to assist in the purification of the material. Heating the region in the vessel over the molten material to promote destruction of the metal. The method of claim 1 wherein the heating is performed by combustion in the vessel. The method of claim 2 wherein the combustion action comprises a flame directed towards the foam. 3. The method of claim 2, wherein the combustion action is maintained by an oxidizing gas rich in oxygen content above the oxygen content in the air. The method of claim 4, wherein the oxidizing gas consists essentially of oxygen. The method according to any one of claims 2 to 5, wherein the combustion operation consists of at least some carbon-free raw materials. 6. The method of claim 2, wherein the fuel consists essentially of hydrogen. 7. 6. The method of claim 2, wherein the combustion action produces a combustion product that is substantially CO ₂ free. 7. 6. The method of claim 2, wherein the combustion action produces a combustion product that is substantially nitrogen free. 7. The method of claim 2, wherein the combustion action produces a combustion product comprising water, the water being discharged from the vessel and condensed under subatmospheric pressure. The method of claim 1 wherein the heating is performed by a plasma torch. The method of claim 11, wherein the plasma uses vapor, hydrogen, oxygen, helium, or mixtures thereof as carrier gas. The method according to any one of claims 1 to 5, wherein the subatmospheric pressure is 1/2 or less of atmospheric pressure. The method of claim 1, wherein the additional melt enters the vessel above the height of the remaining melt volume in the vessel. The method of claim 14 wherein the additional molten material is foamed as it enters the vessel. The method of claim 14, wherein the material is removed from the vessel at the outlet at the bottom of the vessel. 6. The glass preparation material according to any one of claims 1 to 5, wherein the glass preparation material is used as a purification aid in an amount of no greater than 2 parts by weight of sodium sulfate relative to 1000 parts by weight of the silica raw material contained in the glass production material. Method containing sulfur compound.

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