FI78282B - FOERFARANDE FOER SMAELTNING AV ETT MATERIAL, SPECIELLT GLAS. - Google Patents

Description

1 78282

The present invention relates to a method for melting a material, in particular glass.

The use of immersion firing to melt glass has been proposed in several patents, including U.S. Patent Nos. 3,170,781; 3,224,855; 2,237,929; 3,260,587; 3,606,825; 3,627,504; 3,738,792 and 3,764,287. In submerged combustion, combustion gases are fed below the surface of the molten pond 10 and are bubbled upward through the melt. The advantage of this procedure is that the material to be heated is in close contact with the combustion gases and the thermal energy released from them, whereby a very advantageous heat exchange ratio is achieved. A further advantage is that the introduction of the kaas-15 into the melt causes strong mixing, which may be advantageous in some melting processes.

However, a significant disadvantage of immersion combustion is that the blowing of gas in large volumes into the melt is in some cases difficult to reverse. In other words, the melt, especially the glass, can in some cases become foamy and the foam can be difficult to break. This tendency of immersion heating to increase the gas content of the melt has been an obstacle to the acceptance of immersion heating in the glass manufacturing industry because one of the objects of the glass melting process is to remove as many bubbles and other gaseous inclusions as possible from the molten glass. Proposals to use immersion heating to melt glass have generally been limited to their use in the early stages of glass melting to avoid the growth of gaseous inclusions in the later stages of the melting and cleaning process.

In the present invention, immersion heating is used in a glass melting process or the like in a manner that takes advantage of its advantages and avoids the disadvantages of excessive foaming.

This is achieved by the process according to the invention, characterized in that the raw material is liquefied in the first melting vessel in a flowable state, the liquefied melt-containing material is removed from the first melting vessel to the second melting vessel, and the liquefied material is kept in the second melting vessel gas is injected below the liquefied mass in an amount sufficient to heat and mix the liquefied mass and convert the liquefied material to the molten state.

Immersion heating is thus used in the second stage of the glass melting process, which follows the first, liquefaction stage of the glass raw material mixture. The major part of the required heat supply for the glass 15 raw material alloy materials to be converted to molten glass is formed in the first step by methods which are particularly well suited to the liquefaction process (e.g. the methods disclosed in U.S. Patent No. 4,381,934). The liquefied but only partially melted material is then transferred to a second stage where it is heated by immersion combustion heating. In this second step, the heat supply requirement is only to raise the temperature of the material from its liquefaction temperature to a temperature suitable for completing the melting process and cleaning the glass, i. to remove gas-25-like inclusions. When the temperature rise in the first stage is typically of the order of 1093 ° C in the second stage, only a few hundred degree temperature rises are typically used. Due to the modest thermal requirements of the second stage, the immersion heating temperature 30 uses a minimum amount of combustion gases that are injected into the melt, thereby minimizing the foaming effect and yet effectively achieving the process targets of this stage. At the same time, the mixing of the melt by up-combustion heating promotes the overall performance by improving the homogeneity of the glass and promoting the dissolution of the sand grains.

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According to another aspect of the invention, immersion heating is used to melt glass or similar material without having to form an additional gas phase in the melt using hydrogen as the fuel and oxygen as the oxidizing agent. The use of oxygen instead of air avoids the introduction of nitrogen into the melt, which substantially reduces the amount of gas introduced into the melt. Avoiding the introduction of nitrogen into the melt is also advantageous in that the nitrogen is poorly soluble in the molten glass. The use of hydrogen as a fuel instead of hydrocarbons avoids the introduction of carbon dioxide, which is also poorly soluble in molten glass, the melt. On the other hand, the combustion product of oxygen / hydrogen combustion is water vapor, which is very soluble in molten glass. Thus, the present invention reduces the volume of the gas phase formed in the immersion combustion 15, and the gas fed to the melt is easily transferred to the liquid phase. Another advantage is that oxygen / hydrogen combustion generates relatively high temperatures, which improves the rate of heat transfer to the melt. In the drawings 20, Fig. 1 is a vertical cross-section of a glass melting apparatus using immersion heating together with a first stage liquefaction vessel; lines 3-3 of Figure 2.

Figure 1 shows an example of a preferred embodiment of the invention, wherein the immersion combustion chamber 10 is after the liquefaction vessel 11 of the raw material mixture. The type of liquefaction degree shown in the drawing is disclosed in U.S. Patent No. 4,381,934 and U.S. Patent Application Serial No. 481,970, dated April 4, 1983 (both to Kunkle et al.), Which are incorporated herein by reference. This type of liquefaction method is characterized by the transfer of radiant heat to the inclined surface of 4,782,82 glass raw material alloy materials, which causes rapid liquefaction of the liquefied material. The particular embodiment shown therein comprises a drum 12 rotatably mounted about a vertical axis by means of a support ring 13 and rollers 14. The stationary lid 15 is provided with openings for accommodating at least one bulb 16 and for feeding raw materials into the vessel and for removing combustion gases from the vessel through the channel 17. The raw materials fed to the rotating drum 12 form a parabolic-like liner on the inner walls leading to a central outlet (not shown) at the bottom of the drum. This type of liquefaction arrangement has been found to be advantageous for liquefying sodium / lime / silicon glass, but it should be noted that other liquefaction arrangements known in the art are also suitable for the purposes of the present invention. For example, an abbreviated furnace type or electric resistance type glass melting device may be used in the first step. When handling glass types or materials other than ceramic materials, sintered glass materials, or ores, a liquefaction step specifically adapted for this material may be used.

The liquefied glass mixture removed from the first stage liquefaction vessel is typically foamy, which includes the indigestible granules of the glass raw material mixture. In the embodiment shown in Figure 1, the liquefied material falls through a cylindrical collar 20 into a receiving vessel 21 into which a mass 22 of foamy material can accumulate. The liquefied material can be fed directly from the liquefaction vessel 11 to the immersion combustion vessel 10, but it is preferable to use an intermediate vessel for balancing ability and to improve access below the liquefaction vessel 11. The intermediate vessel may be formed of a substantially inclined surface leading to the immersion combustion chamber, as shown in the figure, or may have a significantly larger volume to provide additional residence time for the material and may be provided with means for heating the material or other treatments.

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The immersion combustion chamber 10 is a box of substantially refractory material adapted to store a pool of molten material 25, the depth of which is considerable. In the example shown in Figure 1, the immersion burner-5 toast is provided with two immersion burners 26, but the number of burners may be higher or lower depending on the heating requirements in each application. The burners 26 extended through the bottom of the vessel, but installation in the side wall is also possible. It is also preferred that the mouth-10 nata burners be oblique to the walls of the vessel.

The structure of the burner is not critical to the present invention, but details of an example of a burner structure suitable for use in the present invention can be seen in Figures 2 and 3. The top 15 of the burner is provided with a cover 27 preferably having an aperture arrangement having a central opening 28 surrounds a plurality of openings 29. Typically, oxidizing gas is supplied through the central opening 28 and through the openings 29 surrounding the fuel gas, but the opposite arrangement is also possible. In the preferred method using oxygen / hydrogen combustion, oxygen is fed through orifice 28 and hydrogen through orifices 29. Referring specifically to Figure 3, the supply to the central opening 28 takes place from the tube 30. The larger diameter tube 31 surrounds the central tube 30 so that an annular space is formed between them, through which the opening 29 is fed. Both tubes are surrounded by a cooling jacket 32 which forms an annular space between the tube 31 and the jacket 32 through which a cooling medium such as water can be circulated to maintain the burner 30 at the correct temperature. Preferably, the annular space for the cooling medium is provided with compartments (not shown) to form flow paths for the coolant, the coolant circulating the inlet 33 near the end vault 27 and back to the outlet 34. In some immersion combustion arrangements 35 a burner 6 78282 of the type shown and both fuel and oxidizing gas are injected into the melt and combustion is allowed to take place in the melt. In this case, the energy released during combustion is transferred directly to the molten material. In addition, when using combustion outside the burner 5, the conditions to which the burner is exposed are less stressful, which reduces the durability requirements.

The discharge channel 40 leads the immersion combustion chamber 10 to the glass forming step. Preferably, damp conditions are generally used in the channel 40 to allow bubbles to escape from the melt and to allow the melt to cool to a suitable temperature for molding treatments. In order to prevent any foam on the surface of the melt 25 of the immersion combustion chamber 10 from entering the channel 40, it is preferable to use a surface sealing fence 41 at the inlet of the channel 40.

The pressure of the fuel and oxidant fed to the immersion burner 26 must, of course, be high enough to exceed the hydrostatic pressure of the melt 25. In each case, the required pressure depends on the density of the melt and its depth, but it has been found, for example, that if the depth of the molten soda-lime-silicon glass is 0.6 m, a pressure of 34,500 Pa is required. The amount of fuel fed to the burners depends on the heat requirements of the particular application, the heat content of the fuel used, and the efficiency of heat transfer to the molten material. When heating soda-lime silicon from about 1260 ° C to about 1540 ° C, it has been found that a heat transfer efficiency of about 70% can be achieved. The thermal content of hydrogen is about 10.4 joules / cm or 12.2 joules / cm including the heat of vaporization.

30 For a material, such as flat glass, for which slightly oxidizing conditions are usually desired, excess oxygen is supplied to the bulbs in addition to the amount required for combustion. Furthermore, the thorough mixing and close gas / liquid contact achieved by the immersion combustion chamber makes it very suitable for adjusting the degree of oxidation of the melt or its other chemical property 7,78282. For example, reducing conditions can be used in the liquefaction step and molten glass can be oxidized in the immersion combustion chamber. Conversely, it is also possible to use a small amount of oxygen in the immersion combustion chamber to make the melt-5 sex in a more reduced state. The ability to adjust the oxidation state of molten glass is useful in forming the color and light transmission properties of glass. The arrangement also allows the addition of dyes or other additives to the immersion combustion chamber. The immersion combustion chamber may be a suitable mixing and / or reaction vessel in which several separately liquefied components can be mixed together. In this regard, a plurality of liquefaction vessels 11 may feed into the immersion combustion chamber.

In the present invention, any hydrocarbon fuel can be used in connection with burners, of which natural gas is a particularly suitable example. When oxygen is used instead of air, the volume of oxidizing gas injected into the melt can be reduced to about one-fifth.

The advantages of using hydrogen combustion with 20 oxygen, whereby the combustion product consists mainly of water vapor, can be seen from the following comparison of the solubilities of the gases in the molten glass in the saturation state, as described in the literature:

Gas Solubility (at 1400 ° C) 25 N 2 0.56 x 10 μg / cm 2 CO 2 80 x 10 "6 * 'H 2 O 2700 x 10" 6 "

The solubilities of nitrogen, which is the main constituent of air, and carbon dioxide, 3q, which is the main product in the combustion of hydrocarbons, in molten glass are much lower than in water. Thus, by avoiding the use of air and hydrocarbon fuel, some poorly soluble species can be disregarded in the gas phase in the melt, leaving only a very highly soluble aqueous phase substantially remaining absorbable in the melt. Also when using oxygen instead of air 8 78282

It should be noted that oxygen / hydrogen immersion combustion provides advantages in addition to the recommended two-stage arrangement. Thus, general aspects of the invention include the supply of glass raw material-alloy materials directly to the immersion combustion chamber 10, 5 which is heated by the combustion of hydrogen with oxygen.

Another high temperature source that can be used in the present invention is a plasma torch. In a plasma torch, a carrier gas is used to direct a high temperature plasma formed by an electric arc after the bulb nozzle. The carrier gas may be a combustible gas or it may be unreacted or even inert. For example, the carrier gas may be water vapor, which is preferred due to the relatively high solubility of water in molten glass. Oxygen can also be a suitable carrier gas because its solubility in molten glass is almost equal to that of water. Helium may also be suitable despite its relatively poor solubility because its diffusibility into molten glass is very good.

In summary, the heat source for immersion combustion may be lump heat released from the gas as it burns in the immersion combustion chamber or burns immediately prior to injection into the chamber, or may be thermal energy released from the gas that is electrically activated. These can be collectively referred to as radiant gases. Additional 25 heat sources such as overhead combustion flames or electric resistance heating can be used in the immersion combustion chamber.

The immersion combustion chamber 10 is first heated when it is empty using burners 26. The heated chamber can then be gradually filled with molten material from the liquefaction step 11 or a glass raw material mixture or glass crushed glass. Once the molten pond 25 has been formed, the operation of the immersion burners can be stopped and restarted simply by switching off and restarting the fuel supply. When the burner is not in use, it is advantageous to prevent the melt from entering the burner and cooling can be continued by blowing gas into the burner, for example by means of an oxidizing gas stream.

The detailed description provided herein is directed to certain embodiments to illustrate the preferred embodiment of the invention, but it should be noted that other modifications and variations known to those skilled in the art may be applied without departing from the spirit and scope of the invention as defined in the following claims.

Claims (11)

A method of melting a material, especially glass, characterized in that a liquid material is transferred in liquid form in a first melting vessel (11) to a liquid state, the liquid material which contains indigestible grains is removed from it. the first melting vessel into a second melting vessel (10), and the liquid material is retained in the second melting vessel (10) and radiation gas which is substantially free of nitrogen is injected under the liquid mass into sufficient men to heat and mix. the liquid mass and to transfer the liquid material to a molten state. 15 2. A process according to claim 1, characterized in that the radiation gas consists of the combustion products of a fuel and an oxidizing agent. 3. A method according to claim 2, characterized in that the fuel and the oxidizing agent 20 are injected separately into the liquid mass. 4. A method according to claim 2 or 3, characterized in that the combustion products are injected into the liquid mass from a burner (26) in which the combustion has begun. 25 5. A process according to any one of claims 2-4, characterized in that more of the oxidizing agent is injected into the other melting vessel than is required for the combustion. 6. A method according to claim 1, characterized in that the radiation gases include a plasma flow. Process according to Claim 1 or 6, characterized in that the radiation gas consists mainly of water vapor. 35 8. A method according to claim 1, characterized in that the radiation gas is formed by: