KR930001960B1 - Method and apparatus for melting materials - Google Patents

Abstract

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Description

Melting method and heating device

1 is a vertical cross-sectional view of a preferred embodiment of the induction heating apparatus according to the present invention,

2 is a horizontal cross sectional view along line 2-2 of FIG. 1,

3 is a partially enlarged cross-sectional view of the bottom portion of the container of FIG.

4 is a sectional view along line 4-4 of FIG. 3,

5 is an electric circuit diagram included in the induction heating apparatus of the present invention,

6 is an enlarged view of the coil terminal portion of FIG.

7 is a vertical sectional view of a radiant heating vessel used in a preferred embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

10: guide coil 11, 12: cylinder half

13: cooling tube 14: non-conductive inlet tube

15: discharge pipe 20: inner fireproof block

21: Outer fire block 26: Lower wall part

27: binding band 30: upper layer

31: second layer 32: water cooler

33: fireproof paper layer 34: copper plate

40: discharge pipe 41: central portion of the fire resistance

42, 43: cooler 50: flow control element

51: arm 52: positioning means

60: inverter 61: transformer

62: capacitor 70, 71: bridge

72, 73, 81, 82: flange 74, 75: terminal

76: coolant hose 77: electrical insulation shim

80: conductive shim 90: bubbler tube

The present invention relates to a method and apparatus for melting a material such as glass by induction. The invention can be applied to the melting of current-inducing materials, in particular to the melting of glass or similar materials.

It is known that when a material is placed in a coil through which an alternating current flows, the material can be heated by an induced current. One advantage of this type of heating is that the material to be heated is not in contact with the electrical source, ie there is no need to immerse the electrode in the melt.

The general concept of induction heating glass is disclosed in many prior patents, such as US Pat. Nos. 1,830,481, 1,906,594, 3,205,292 and 3,244,495. Many of the prior art is limited to small devices, and large scale glass melting by induction heating has not received much commercial acceptance. That is, due to the economics of induction heating, it was not advantageous to use induction heating to melt glass and similar materials on a large scale.

In general, the thermal energy obtained by burning fuel was more economical than electrical energy for melting the glass. Moreover, induction heating has been thought to be low in efficiency of converting power into thermal energy. In addition, some people in the art have believed that a huge induction coil will be required for large scale induction heating of the glass.

The main drawback associated with induction melting is to prepare a container suitable for the melt. As such, the vast majority of prior art is limited to small apparatus, and large scale melting of the glass by induction heating has not received much commercial acceptance. Since the vessel is placed in the electric field of the induction coil, the vessel itself can be heated under induction current. This is generally undesirable, because power is wasted in the vessel rather than in the material to be heated, and also heating of the vessel can accelerate the corrosion of the vessel, which can thermally damage the vessel and contaminate the product. Because.

Non-metallic vessels can be cooled from the outside to maintain their temperature below a temperature that is significantly sensitive to induced currents, but such cooling can deprive a significant amount of thermal energy in the melting process. In addition, cooling the exterior of the ceramic vessel can create a temperature gradient that can impose a thermal stress large enough to damage the vessel. On the other hand, the use of multi-piece ceramic containers assembled from a number of pieces poses a problem of water solubility of the molten material, especially in large scale operations. It is undesirable to use steel or such metal struts to maintain the structural safety of multi-piece ceramic vessels, since stray currents induced in the struts may not be able to Because it is taken away. Metal vessels, on the other hand, are very sensitive to induced currents, so a lot of power loss occurs even when the vessel is cooled. Moreover, cooling the metal container causes a great deal of heat loss due to the high thermal conductivity of the metal. An example of a cooled metal induction heating vessel is shown in US Pat. No. 3,461,215.

According to the present invention, the powdered material is supplied to a first container in which the material is liquefied mainly by radiant heat transfer, and the liquefied material is discharged from the first container to the second container, in which the liquefaction is carried out. A method of melting a material is provided that includes increasing the temperature of the liquefied material by imparting an alternating electromagnetic field to the liquefied material in the second vessel to induce a current to the liquefied material to bring the molten material into a molten state.

The present invention also provides a method of induction heating of a molten material (eg, glass) with gaseous inclusions, which method, in an active heating zone of a vessel surrounded by an induction coil, causes the current to flow through the material. Impart an alternating electromagnetic field to the material to induce it to heat the material; Passing the heated material through the inert area in the vessel under the induction coil; Retaining the material in an inert zone an average of one hour prior to release from the vessel. The present invention also provides an apparatus for performing each of the above-described methods.

Liquefaction of batch materials can be performed more economically in an ablating type melter of the type shown in US Pat. No. 4,381,934 than in an induction heater. In order to effectively transfer heat, combustion heating is carried out using a large temperature difference between the material being heated and the heat source. Liquefaction of the batch material in the first place provides a large temperature difference, and thus helps combustion heating itself. The aforementioned U.S. patent technique reinforces this advantage by enhancing the outflow of hot liquefied material and by keeping the cold batch exposed to radiation to maintain large temperature differences.

The liquid leaving the liquefaction zone is not a fully molten glass, but an opaque fluid in the form of foam that contains unmelted sand grains and the like.

However, the additional energy required to complete the melting and purification of such effluent liquids constitutes only a small fraction of the total energy required to melt the glass in conventional tank melters.

However, in order to complete the melting of the liquefied material, the temperature of the already hot material must be raised, and thus no large temperature difference is provided. Induction heating, on the other hand, does not require a temperature difference to transfer energy to the material. Thus, induction heating is ideally suited for the second stage of the melting process.

Compared to a total energy consumption of about 6 million BTUs per tonne for melting soda-lime-silica flat glass in large-scale continuous furnaces, only about 50,000 BTUs per tonne (28.6 kcal / kg) is required to carry out the purification. It is required to supply the glass in the heater. In the present invention, most of the energy is consumed in a more economical liquefaction stage, and the size of the induction heater and the amount of electrical energy consumed can be minimized by using induction heating in the second stage of the melting process, ie the "purifier". .

There are other advantages to feeding the material to the induction heater while already liquefied. In such a continuous process, it is preferable to stably circulate the molten material in the induction heating vessel. However, supplying cold material to the top of the container may be superimposed with naturally rising thermal convection, thus causing instability. However, providing molten material to the top of the vessel is consistent with the purpose of removing bubbles from the melt.

In the present invention, a single turning induction coil is used with a multi-piece ceramic refractory vessel for induction heating of molten material such as glass. The single pivot induction coil takes the form of a divided metal cylinder which acts as a joining means for maintaining the structural integrity of the fire container it surrounds. The metal wall of the cylinder acts as a continuous barrier to prevent any leakage that can occur through the junction of the ceramic vessel. The rigidity of the metal cylinder can be maintained by the cooling means associated with the cylinder.

In a preferred embodiment, the ceramic container consists of two or more separate layers. The inner layer is mainly chosen depending on whether it is suitable for contact with the molten material being heated, and the outer layer is mainly chosen according to its thermal insulation. The thickness of the inner layer is chosen to provide a thermal gradient such that the temperature at its outer surface is approximately equal to the solidification temperature of the molten material (or the opacity of the glass). The outer insulating layer of the ceramic is selected to provide additional thermal gradients to reduce heat loss to a minimum consistent with maintaining the inner surface of the insulating layer at a temperature just below the opacity of the molten component. This composite container structure minimizes the thickness of the container wall, thereby minimizing power loss in the container wall, maximizing the inductive coupling effect and maintaining structural integrity without excessive heat loss.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

7 is a vertical sectional view of a preferred embodiment using a radiant heating vessel according to US Pat. No. 4,381,934, in which a drum rotating about a vertical axis of rotation supplies the liquefied material to the induction heating apparatus. To provide a batch surface (which is a rotating parabolic plane about the heat source).

The principles of the present invention may be applied to induction heating of a wide variety of molten materials, but the description of the present invention will primarily relate to embodiments specifically designed for melting glass. In addition, certain embodiments to be described are suitable for relatively high speed continuous processing. The present invention is particularly advantageous under such conditions but is not limited thereto.

With particular reference to FIGS. 1 and 2, in the illustrated embodiment, the single pivot induction coil 10 consists of two cylindrical halves 11, 12 surrounding a portion of a cylindrical ceramic vessel. . Copper is the preferred material for such induction coils because of its high electrical conductivity.

The thickness of the cylindrical halves 11, 12 depends on the strength required for the particular application, but in the particular embodiment described, a thickness of 0.25 inch (0.635 cm) has been found to be suitable. A plurality of cooling tubes 13 are welded to the outer surfaces of the cylindrical halves 11 and 12. Water or other coolant may be supplied to the cooling tube 13 through the non-conductive inlet tube 14.

The coolant passes through the semi-circular passage along one side of the cylindrical body to reach the discharge pipe 15, and the coolant is discharged by the discharge pipe, or another cooling tube 13 on the same side of the cylindrical body to return along the other semi-circular passage. You can enter Depending on the size of the vessel and the degree of cooling required, the coolant may pass through additional tubes before being discharged.

In the induction heating zone, the vessel comprises an inner cylinder formed of a plurality of fire blocks 20. Cylindrical forms are most effective and preferred, but other forms may also be used. The inner cylinder can be formed by arranging a plurality of fire blocks 20 in circumferentially and longitudinally arranged layers, and in each circumferential arrangement, each fire block is wedge shaped, when they are placed Form a circle or polygon.

For example, in the specific embodiment shown in FIGS. 1 and 2, the fire resistant block 20 is arranged in three layers in the longitudinal direction of the cylinder, ie the container, in which ten blocks are circumferential. Arranged in a direction, each block having two shaved surfaces on each of the inner and outer sides, so that when the blocks are arranged in the circumferential direction, they can form a pentagon. The refractory block 20 is a refractory material selected for the molten material to be treated. In the case of melting the glass, suitable refractory materials are alumina-zirconia-silica refractory materials. This type of refractory material is suitable for contact with molten glass, but the thermal insulation is relatively poor compared to other types of refractory ceramic materials.

Accordingly, the radial thickness of the refractory block 20 may be such that any molten material that can escape through the connections or gaps may harden or at least become viscous before reaching the outer surface of the refractory block. It is chosen enough to provide a temperature gradient between the surfaces. In the case of glass, a suitable temperature gradient provides the outer surface of the refractory block 20 with a temperature not higher than the devitrification temperature of the particular glass to be melted. In typical commercial soda-petrified-silica flat glass compositions, such temperatures are about 1800 ^° F. (about 980 ° C.). Good acceptance of the melt in the vessel can be achieved when the temperature of its outer surface is close to the softening point of the glass (about 1400 ^° F. (750 ° C.)).

In addition, the refractory block 20 should have a relatively high electrical resistance at high temperatures so as not to be sensitive to induced current. For example, satisfactory results can be obtained in refractory materials having an electrical resistance of about 5-10 times the electrical resistance of the molten material to be treated.

While not essential to the principles of the present invention, another desirable feature is that the refractory is of a type that can be repeatedly cycled between room temperature and operating temperature.

On the outer surface of the inner fire resistant cylinder formed of the fire block 20, an outer fire resistant cylinder composed of a plurality of fire blocks 21 is disposed. This refractory block 21 is made of a refractory ceramic material selected in consideration of thermal insulation, i.e., having a relatively low thermal conductivity. The outer refractory block 21 has a lower thermal conductivity than the inner refractory block 20 and usually has a thermal conductivity of 1/2 or less, preferably about 1/5 or less of the inner refractory block. Since the inner refractory block 20 is separated from the molten material in the container by the thickness of the inner refractory block 20, the outer refractory block 21 does not have to consider contact with the molten material, but it is considered to have some degree of suitability at relatively low temperatures. It is preferable. Examples of suitable materials for the outer refractory block are porous (low density) clay refractory materials. Because of its low thermal conductivity, the outer fire block provides an additional thermal gradient that can allow contact with metal induction coils on its outer surface, while at the same time achieving the object of providing a minimum additional thickness to the vessel wall. have.

Minimizing the overall wall thickness is desirable to maximize power efficiency by placing the induction coil as close as possible to the material being treated and minimizing the amount of material in the coil from which stray currents can be induced. The temperature of the induction coil should be kept low enough to prevent significant oxidation of the metal, to minimize the electrical resistance of the copper and to prevent excessive loss of strength.

The cooling tube 13 helps to keep the coil temperature low, and the heat gradient provided by the outer refractory block 21 should be sufficient to maintain the required degree of cooling and heat loss at an appropriate level. When the coolant is water, the cooling temperature and the outer surface of the outer refractory block 21 are preferably maintained at 100 ° C or lower.

The structure of the vessel portion above the induction coil is not as important as that in the induction coil, but for convenience, the same structure may continue to the portion above the vessel shown in FIG. A fire resistant lid member 22 having a supply hole 23 may be installed at the upper end of the container. The raw material may be supplied through the feed hole 23, but at least in the case of glass, the raw material is preferably liquefied in the preceding step of the melting process. In the melting process of the present invention, liquefaction is mainly carried out by radiant heat transfer in a conventional vessel according to the liquefaction process described in US Pat. No. 4,381,934.

A suitable surge hopper 24 or the like may be installed to hold the material to be supplied to the induction heating vessel.

The thickness of the lower wall portion 26 of the vessel of the induction coil mill is not critical, but it is important to ensure that it is in contact with the molten material without contamination. Thus, the lower wall portion 26 is preferably made of a refractory material suitable for contact with the molten material (alumina-zirconia-silica type refractory material in the case of glass) and formed to provide the required insulation at any wall thickness. Do. As in other parts of the container, the lower wall portion 26 may consist of a plurality of wedge-shaped fire walls. Binding strip 27 (preferably made of stainless steel to minimize ferromagneticity) or the like may be used to hold the block in place without excessive loss of power due to stray currents induced in the binding band. It can be installed around the lower part. The power loss in the tie strip 27 can be further reduced by minimizing the cross-sectional area of the metal and placing it as far as possible under the induction coil and separating each strip into a plurality of electrically insulated pieces along its length.

The bottom of the vessel is also made of refractory material suitable for contact with the molten material. Details of the floor structure can be seen in the enlarged view of FIG. The top layer 30 of the bottom structure is preferably made of a refractory material suitable for contact with the molten material (such as alumina-zirconia-silica type refractory material in the case of glass melting).

Underneath the top layer 30, a second layer 31 of a material (such as a low density clay refractory material) may be provided which takes into account thermal properties. Cooling is done outside the bottom structure to ensure the receipt of molten material in the vessel. In the illustrated embodiment, the annular water cooler 32 forms the base for the vessel. The refractory paper layer 33 and the copper plate 34 may be disposed between the water cooler 32 and the second layer 31. The copper plate acts to shield the water cooler 32 from stray induction current, especially when the water cooler is made of mild steel.

While various devices for discharging molten glass or similar materials from the vessel are well known in the art and may be used in the present invention, a particularly advantageous discharge device is described with reference to FIG.

The discharge device comprises a refractory metal (eg platinum-rhodium alloy) discharge pipe 40 installed in the center of the bottom of the container. The discharge pipe 40 extends through the refractory center portion 41, which is preferably made of a refractory material suitable for contact with the molten material. Discharge pipe 40 extends above the bottom surface of the container to prevent any debris from the bottom of the container from entering the discharge stream. The fire resistant central portion 41 is inclined toward the discharge pipe 40, thereby thinning the refractory thickness and thus reducing the thermal insulation near the discharge pipe, thereby maintaining a relatively high temperature in the discharge pipe and thus preventing freezing of the molten material in the discharge pipe. Additional coolers 42, 43 are provided below the fire resistant central portion 41 and around the discharge conduit 40 to ensure receipt of the molten material in the container.

Various means of controlling the flow of molten material, such as glass, through the gravity discharge tube are well known in the art. Many such devices involve controlling the viscosity of a material by variably heating or cooling the outlet tube. Connecting the discharge line and the induction coil is a typical example. In some cases, this can be used satisfactorily with the present invention. However, there are some drawbacks to large-scale glass melting. The amount of heat in the fast flowing flow of glass (for example, at a rate of hundreds or thousands of kilograms per hour) is so great that it becomes difficult to significantly influence the viscosity of the flow by heat transfer through the wall of the discharge pipe. On the other hand, if proper heat exchange is provided to perform the adjustment of the flow rate, the sensitivity of the glass viscosity to temperature makes it difficult to finely control the flow rate.

Physical flow restrictors ("plungers") for regulating the flow of molten glass are known in the art. Typical plunger structures include structural elements disposed within the melting vessel to interact with the top of the discharge orifice. Such a structure is not suitable for induction heating vessels as in the present invention. Thus, the preferred structure for controlling the flow of molten glass in the present invention includes external flow blocking means for interacting with the lower end of the discharge pipe.

A particularly advantageous structure is shown in the figure, in which a streamlined "teardrop" type flow control element 50 is supported directly below the discharge tube 40 to form an annular hole through which the flow of molten glass passes. . By changing the vertical position of the flow regulating element 50, the size of the annular hole can be changed, and thus the flow rate of the molten glass is adjusted. The flow regulating element 50 is supported by an arm 51 extending horizontally, which arm is provided in the positioning means 52. The positioning means 52 may be a technician's milling table or the like and preferably has three-dimensional adjustability. In order to maintain a coherent flow of glass, the flow regulator is in the form of encouraging a concentrated flow pattern.

The molten glass flowing around the flow control element 50 recombines in a single flow by flowing along the concentrated surface of the lower end of the element.

In addition, the portion of the arm 51 in the flow of molten glass may have an inverted teardrop shape as shown in FIG. 4, and is inclined downward along its length to prevent the molten glass from remaining on the arm. have. This shape causes the device to generate minimal disruption to the glass flow. The device is capable of active flow control over a wide range from the top active shutoff position to the wide open position lowered to a few centimeters below the discharge pipe. The term "teardrop" as used herein is not limited to the exact definition of the term, but may include various streamlined forms that taper toward the end.

For ease of manufacture, the teardrop form may be preferably formed by coupling the cone to the hemisphere. Other variations may include non-circular horizontal sections or non-spherical upper portions. For contact with the molten glass, the flow control element 50 and the arm 51 are preferably made of molybdenum coated with a platinum-rhodium alloy. The core can be made of a metal that is less precious than molybdenum, or a refractory ceramic material, covered with a noble metal, and cooled internally if necessary.

An electrical system for an induction heater is shown schematically in FIG. A typical industrial power source, three phase 60 Hz alternating current, is connected to an inverter 60 which sends a high frequency single phase output to a transformer 61. The transformer 61 preferably has a number of taps in its secondary coil so that the voltage to the induction coil 10 can be changed if necessary. Induction coil 10 is connected to a secondary coil of transformer 61 in parallel with capacitor 62.

The capacitor 62 and the induction coil 10 form a resonant circuit having high frequency and high amperage therebetween, thereby enabling the use of a small number (for example, one) of induction coil turns. The high amperage generates high magnetic flux in spite of a small number of guide coil turns, thus providing a large guide line performance to the guide coil. Alternatively, the magnetic flux can be increased by increasing the number of induction coil turns, but a high voltage is required, which undesirably limits the type of inverter that can be used.

At frequencies up to about 10 kHz, solid state inverters with relatively high efficiency and low cost can be used. Typically, multiple capacitors can be used in parallel to each other to provide the required layer capacitance.

The frequency and capacitance of the resonant circuit can be represented by the following equation.

Other design calculations for induction heating coils are described in the American Institute of Electrioal Engineers Transactions (1957), Part 2, pages 31-40 of R. Am. Baker.

6 shows one form of a capacitor 62. In this case, a water-cooled capacitor is installed across the legs of the induction coil 10. In this structure, the capacitor 62 is one of several that can be installed vertically arranged vertically across the spacing of the induction coils. On each side of the gap of the flow coil 10, radially extending legs 70, 71 are provided, which legs have flanges 72, 73 at their outer ends, respectively, which flanges. The capacitor 62 is installed in the.

Screwed terminals 74 on one side of each capacitor 62 are associated with one pole of the capacitor and connected to flange 72 on one side of the induction coil. Terminals 75 on the other side of the capacitor 62 are associated with the opposite pole of the capacitor and are connected to the flange 73 on the other side of the induction coil. The terminals 74, 75 are tubular and are connected to coolant hoses 76 which supply coolant to the internal cooling means of each capacitor 62. Induction coil legs 70 and 71 are electrically insulated from each other by electrical insulation fittings 77. Since the cylindrical guide coil 10 also acts as a binding means for the fireproof container, the guide coil is held taut by a bolt 78 that pushes the legs 70, 71 toward each other. Non-conductive bushings 79 may be installed around the bolt 78 to maintain electrical insulation of the legs.

Similarly, on the other side of the induction coil 10, two cylindrical halves 11, 12 are bolted together with a conductive shim 80 between the radially extending flanges 81, 82. (See Figure 2). Initially, the empty container is blocked by the induction coil and heated using an auxiliary heater. As the refractory parts of the container expand as they heat up, the binding tension of the cylindrical induction coil 10 gradually increases by rotating the bolt to enlarge the spacing between the cylindrical halves at one or both of the connections between the cylindrical halves. Relaxes.

Initially, the legs 70 and 71 and the flanges 81 and 82 are in contact with each other and can be inserted after the shims 77 and 80 preheat the vessel to the operating temperature. Thereafter, a current can be supplied to the induction coil.

The typical resistivity of the molten glass is about 6-14 ohm-cm, depending on the temperature, which is higher than the material in which induction heating is more commonly performed. This provides some advantages in designing induction heating systems for melting the glass.

The current penetration depth in the material being heated is an important factor in the design of the induction heating system. Typically, it is recommended that the diameter of the material being heated is about three times the current penetration depth (see, eg, British Patent No. 1,430,382), but in molten glass, the diameter of the glass melt should be less than or equal to the current penetration depth. It has been found that when induction heating can be performed effectively. The current penetration depth into the glass can be calculated by the following equation.

Until now, it has been believed that induction heating of glass requires huge induction coils or very high frequencies. However, at present, the low ratio between the melt diameter and the current depth suggests that the glass receiving vessel can deliver power to the glass efficiently while being relatively simple and that relatively low frequencies (eg 10 kHz or less) can be used. If the size of the container increases, the frequency can be even lower.

Some theories of induction heating applied to melting glass have been presented in "Glass Technology" (October 1973), Vol. 14, No. 5, pages 115-124 by "B-Slots" and "Hach Roshon".

A common consideration in induction coil design is that the length of the induction coil must be greater than or equal to its diameter, which is applicable to the present invention. An effective transfer of power to the melt is obtained when the length of the coil is equal to its diameter, but more effective power transfer may be possible when the coil length is longer. The internal diameter of the refractory vessel is determined by the expected production rate and the required residence time. The composite container wall structure described herein provides a dense containment of the melt and provides the outer diameter of the container, such as the diameter of the induction coil. Minimizing the difference between the inner diameter of the vessel and the coil diameter results in the advantage that the magnetic flux is more useful for inducing current in the melt, enabling the use of a practical current and a single induction coil. For a given volume, it is desirable to minimize the height of the vessel to minimize the heat loss area through the wall. The height of the vessel is generally about the same coil length as to place the material to be heated in the maximum magnetic flux region.

It is desirable for the melt to have additional depth slightly above or below the coil. When melting the glass, it has been found to be particularly advantageous to provide additional depth below the coil to set the residence time for the molten glass after passing the maximum temperature in the coil area and before exiting the vessel. This additional residence time is beneficial for removing bubbles from the melt and in some cases for cooling the glass to a temperature that more closely matches the requirements of the molding process performed on the molten glass. It has been found that a residence time of approximately one hour under the coil is advantageous. Structurally expressed, the inner depth of the vessel below the coil may be at least half the diameter of the coil.

Glass is an important inductor of induced currents only at high temperatures. For example, soda-lime-silica glass is at least 2200 ^o F (1200%) and becomes a sensitizer at a suitable voltage. Thus, the induction heating process begins by heating the glass melt by means of auxiliary heating means.

Once the glass is sensitive (preferably at a resistance of about 14 ohm-om or less), the unheated raw glass batch material can be fed to the induction heater and melting can be carried out therein.

However, it is desirable to liquefy the glass batch in a separate step and to supply the liquefied material to the induction heater at a temperature at which the material can be sensitive to the induced current. In this case, the induction heater acts to raise the temperature of the glass to carry out the melting process and in particular to purify the glass, ie to remove gaseous inclusions from the melt.

In flat glass quality soda-lime-silica glass, tablets usually require a temperature of at least about 2600 ^° F (1425 ° C.). While other materials may be liquefied at different temperatures, soda-seok-silica glass is typically liquefied at temperatures between about 2200 ^o F (1200 ° C.) and about 2400 ^o F (1315 ° C.), the temperature at which the material responds to induced currents. And may be supplied to an induction heater.

Sulfur compounds, usually sodium sulfate ("manganese"), have typically been included in glass batches to aid melting and purification. Since the decomposition products of sulfur compounds are very volatile, sulfur compounds were added to the glass batch in amounts significantly greater than the amount theoretically required for some of the sulfur to remain in the initial melting stage and to be present in the melt for assistance during the purification stage.

Since sulfur compounds decompose into gaseous products, they are the main cause of undesirable emissions from glass melting processes. Therefore, efforts have recently been made to minimize the amount of sulfur used in glass making.

The advantage is that the glass can be melted and purified by the present invention without adding sulfur to the glass batch. However, the presence of some sulfur is believed to be beneficial during the purification process. The present invention, when carried out in a two step liquefaction and purification process, maintains a high proportion of sulfur content in the melt so that it can be present in the purification step. This is believed to be due to the rate at which the glass batch is liquefied in a special liquefaction step so that much of the sulfur is transported into the refining vessel with little loss of sulfur through volatilization. Therefore, adding only a small amount of sulfur to the glass batch can take advantage of the purification in the presence of sulfur. It has been found that 3 parts by weight or less per 1 part by weight of 1000 parts by weight of sand in the glass batch can provide a large amount of sulfur in the induction heating refining zone of the present invention.

On the other hand, it has been found that the amount of at least 3 parts by weight per 1000 parts by weight of sand can generate excessive foam in an induction heating vessel. 2 parts by weight of candles per 1000 parts by weight of sand are preferred.

A bubbler, such as a water cooled bubbler tube 90 shown in FIG. 1, may optionally be installed at the bottom of the induction heating vessel. Such a bubbler may be used if it is necessary to circulate the hot melt into the cold lower region to prevent excessive cooling of the lower region, which may unduly reduce emissions through the discharge pipe 40.

EXAMPLE

In the vessel as shown in the figure, 10 tons / day (9,000 kg / day) of soda-lime-silica glass was successfully processed. The diameter and height of the induction coil was 60 inches (1.5m) and the bottom of the coil was located 40 inches (lm) above the bottom of the fire resistant container. The level of molten material in the vessel was maintained at about 4 inches (10 cm) above the induction coil. The refractory of the inner layer was a Citeron AZS refractory commercially available from "Combustion Engineering Company" and its thickness was 10 inches (25 cm). The refractory material of the outer layer was a low density clay under the trademark Finsulation, available from "Findley Repositories Company" and its thickness was 2 inches (5 cm). The thermal conductivity of the outer refractory layer under operating conditions was estimated to be about 1/10 of that of the internal refractory layer.

The induction coil was 0.25 inch (6 mm) thick copper. The glass batch was pre-liquefied and then fed to an induction heating vessel at a temperature of about 2300 ^° F (1260 ° C.) and a maximum temperature of about 2800 ^° F (1540 ° C.) was obtained within the area of the induction coil. In the area under the induction coil, the glass temperature dropped to about 2600 ^° F (1425 ° C.) before exiting the vessel. When the work was stabilized, about 110 kw current was supplied to the induction coil at a frequency of 650 volts RMS, 9.6 kHz.

FIG. 7 shows a chamber as a first stage liquefaction vessel in which a glass batch is arranged to surround a central heat source and rotates about a vertical axis. The rotary melter 83 includes a housing consisting of a cylindrical body 84 made of steel and a bottom 85 made of steel. This housing is vertically supported by a number of rollers 86 installed in the frame 87.

Multiple side rollers 88 maintain alignment of the housing. The housing can be rotated, for example, by driving one of the rollers 86 or 88 by means of a motor (not shown). In the central hole in the bottom 85, a refractory ceramic bushing 89 suitable for the contact of the molten glass and having the central hole 90 is provided. Any suitable structure may be installed to support the frame 87, but for the purpose described below it is desirable to make the entire structure of the melter 83 relatively mobile. Thus, the ceiling hoist means can be coupled to the attachment means 91 attached to the top of the frame 87. The upper end of the container may be closed by a fire resistant lid 93 which can be supported by the frame without moving. The lid 93 is provided with a central hole 94 into which a burner 95 or other radiant heating means can be inserted. Alternatively, multiple heat sources may be used. The lid is also provided with a feed hole 96 so that a glass batch can be fed into the vessel from the screw feeder 97 or the like. Before the vessel is heated, a stable batch layer 98 is provided in the vessel by feeding the glass batch while rotating the housing.

The batch layer is generally contoured to a parabolic surface as shown in FIG. During heating, when batch is continuously supplied to the vessel of FIG. 7, the falling batch flow 99 is distributed over the surface of the stable batch layer 98 and liquefied by the action of heat. The liquefied layer 100 flows to the bottom of the container and passes through the central hole 90 of the bushing. Liquefied batches fall from the exit holes in the form of small droplets 101 and can be collected in the poo1 102 in the vessel 103 to flow directly into the hopper 24. Exhaust gas in the liquefaction vessel produced by the combustion may pass through the central hole 90 and may be discharged through the flue 104. Alternatively, an exhaust port may be provided in the lid 93.

Claims (11)

A method of melting a material, such as glass, by introducing a partially molten material into a vessel and imparting an alternating electromagnetic field to the partially molten substance in the vessel by flowing a current around the vessel through a single turning induction coil. The method of claim 1, comprising continuously discharging the material from the container. The method of claim 1, wherein a majority of the thermal energy for melting the material is imparted to the material prior to being introduced into the container. The method of melting any one of claims 1 to 3, wherein the current is an alternating current having a frequency of about 10 kHz. The method of claim 1, wherein the partially melted material is introduced into the vessel at a temperature of 1200-1320 ° C. (2200-2400 ^° F). The method of claim 5, wherein the temperature of the material in the vessel is raised to 1420-1540 ° C. (2600-2800 ^° F.). (1) a fire resistant container made up of a plurality of nonmetallic blocks to form a cavity for containing the molten material; (2) metal cylinders 11 and 12 surrounding most of the vessel to form an electrical circuit around the vessel and to provide a barrier to prevent leakage from the vessel; (3) means (80, 81, 82) for applying a compressive force to the container by the cylindrical body; And (4) means for supplying the cylindrical body with an alternating current sufficient to induce a current in the material to heat the molten material in the vessel. 8. Apparatus according to claim 7, wherein the cylindrical body (11, 12) consists of halves divided along its length. 9. The container according to claim 7 or 8, wherein the container comprises an inner layer (20) of a refractory material that can be in contact with the molten material and an outer layer (21) having a different composition and lower thermal conductivity than the inner layer. Consisting of a heater of a substance. 10. The apparatus of claim 9, wherein the thermal conductivity of the outer layer (21) is less than half the thermal conductivity of the inner layer (20). 10. The apparatus of claim 9, wherein the thickness of the inner layer (20) is twice the thickness of the outer layer (21).

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