FI79828B - FOERFARANDE FOER SMAELTNING AV GLAS. - Google Patents

Abstract

Batch material for glass or ceramic is mixed with solid or liq. fuel which is combusted in pre-heating zone; ash and unmelted batch are passed to 2nd stage to melt batch, melting is then completed under oxidising conditions. Powdered material is heated so that source of O2 is supplied to combustion zone; gas and solid flows are co-current. Constituents not melting below 900 deg.C are mixed with fuel which is combusted to give 900 deg.C; mixt. of batch and ash is passed to 2nd zone and mixed with lower melting components and melting then completed. Batch for 1st zone includes alkaline earth carbonates which become calcined.

Description

1 79828

This invention relates to the use of solid carbon fuels, such as coal, as a fuel source in a glass manufacturing process or similar melting process, and to the use of mixtures of solid or liquid fuels with raw materials. More specifically, the invention relates to a method according to the preamble of appended claim 1.

10 It is well known that in areas where coal is available, it is usually the cheapest energy source compared to other traditional energy sources such as natural gas, fuel oil and electricity. Therefore, it has been proposed to use coal as a fuel source in glass melting, etc. Examples of such proposals can be seen in U.S. Patent Nos. 3,969,068 and 4,006,003. However, the use of coal as a fuel in direct burning furnaces has been found to have certain disadvantages that have reduced its widespread use. The biggest drawback is the ash content of coal-20. When coal is burned by an incinerator in an open furnace-type furnace conventionally used to melt glass, substantial amounts of ash pass through the exhaust gas stream, which can cause clogging of the regenerators and necessitate removal of the ash from the exhaust gas before it can be discharged into the atmosphere. Some of the ash settles on the walls of the melting chamber, where it melts into a liquid slag that runs down the walls of the vessel into the melt. The flow of molten slag has a detrimental effect on the refractory parts of the furnace 30, and the molten slag entering the melt introduces undesired compositional variations and inhomogeneities into the product material. Slag often has a high iron content relative to glass and running slag into the melt can cause unwanted color streaks. These problems 35 have hampered the use of coal as a direct fuel for the smelting of products, for which uniformity of composition 2 79828 is an important factor. This is especially the case for flat glass, where compositional variations cause optical distortion in the glass product.

A disadvantage of using coal or other coal fuel in admixture with raw materials, especially when smelting clear glass, is that coal has, in quantities sufficient to provide significant energy to the smelting process, a reducing effect on the melt and the iron and sulfur present in the reduced glass. brown coloring. In addition, coal itself promotes the passage of iron and sulfur into the smelter. Small amounts of powdered coal (typically less than 0.1% by weight) have been added to the clear glass charge to aid in the melting process, but such amounts are not significant energy sources and larger amounts were considered harmful. Even in the manufacture of amber glass, the amount of carbon used would not be considered a significant fuel addition.

U.S. Patent No. 3,294,505 discloses the melting of glass in a layer of batch briquettes and coke. The process is limited by a relatively narrow group of low viscosity glass combinations for low quality applications. In addition, it would be desirable to avoid the cost of agglomeration of the charge.

U.S. Patent Application Serial No. 624,879, filed June 27, 1984, discloses a method for wetting glass with fuel oil. Only a small part of the energy requirement of the smelting process is filled with fuel oil.

Another problem with the use of coal and some other coal fuels is that such fuels contain relatively volatile hydrocarbon fractions that are driven off and escaped with the exhaust gas if heated prior to ignition. This is a problem especially if it is desirable to preheat the raw; 35 ka substances as a mixture with carbon fuel. The supply of carbon fuels in non-atomized form to the combustion zone also causes a flue gas loaded with smoke, which is undesirable from an environmental point of view. Post-combustion or other treatment of the exhaust gas or pre-carbonation of the fuel in the pre-operation are expensive options that are preferably avoided.

In one aspect of the present invention, a fuel having an ash content (e.g., coal) is used as an essential source of energy for the smelting process while avoiding the problems typically associated with ash. The method according to the invention is mainly characterized by what is mentioned in the characterizing part of the appended claim 1. Preferably, the charge material and fuel are fed in the preheating step as a mixture with each other to cause the ash to be distributed throughout the charge and to make direct contact with the charge and fuel during combustion. Combustion is maintained by supplying an oxidant (preferably substantially pure oxygen) to the combustion zone during the preheating step. The material can be mixed in the preheating step to improve contact between the charge and the fuel and to mix the ash into the charge. The heated batch and ash mixture, preferably still in powder form, is transported to the next stage where the mixture is liquefied.

A significant portion of the total energy required to melt can be generated by an economical fuel, such as coal, by preheating the charge material to a temperature just below the temperature at which significant melting occurs. By feeding a nearly homogeneous mixture of charge and ash to the liquefaction step, the melt that then forms can be substantially uniform in composition even if substantial amounts of ash are added. Therefore, one of the problems associated with the use of ash-producing fuel, such as coal, is substantially alleviated.

35 Combustion of fuel when in contact with the charge material and thus avoiding the removal of ash 4 79328 to the formation of exhaust gas and slag on the inner surfaces of the vessel avoids environmental problems and damage to the furnace, which is desirable for any smelting process. But preventing the slag from running into the melt makes the present invention particularly attractive for melting glass, etc. when compositional homogeneity is important. Even relatively viscous, difficult-to-homogenize glass, such as soda-lime-silica flat glass, which has very high optical quality standards, can be selected by this invention. Another advantage is that batch agglomeration is not required.

In yet another aspect of the invention, the oxygen distribution and temperature in the preheating step can be controlled to produce substantial amounts of carbon monoxide as a fuel combustion product. The carbon monoxide is transported to the next stage, such as the liquefaction stage, where it acts at least in part as fuel for the combustion of this stage. In another alternative, the combustion of the first stage may be incomplete, in which case some part of the fuel 20 may be left unburned so that it can be transported with the charge to the second stage, where it operates at least as part of the fuel.

To allow higher temperatures in the preheating step and to increase the amount of carbon monoxide produced at relatively low temperatures, the glass components that melt can be omitted from the first step and introduced into the second step or the next step. With the exception of the sodium source (e.g., calcined soda), the soda-limestone-silica glass charge in the first step allows the use of temperatures high enough to calcine carbonate source materials, such as the production of limestone and dolomite and carbon monoxide. The treatment of the silica source material (sand) alone in the first stage allows the first 35 stages to be operated at very high temperatures, whereby large amounts of carbon monoxide can be obtained as exhaust gas.

After the liquefaction step, a third lie can be included in which the melting process can proceed further. When the fuel is mixed into the charge, there may be incomplete contact between the fuel and the oxidant-5 in the liquefaction stage or excess fuel may be present and thus the liquefied material may leave the second stage in the reduced state. In that case, the third step may also include means for re-oxidizing the melt by re-immersed combustion, an oxygen-containing flame and / or by passing oxidizing agent (preferably oxygen) bubbles through the melt. Reoxidation is particularly useful to avoid discoloration of clear glass. Unwanted discoloration of the clear glass caused by iron and sulfide ions can be avoided by re-oxidizing the melt in the third step.

The chemical constituents of coal ash are generally compatible with most glass constituents and therefore the glasses may have some ash with little or no adverse effects on the glass product, provided that the ash can be thoroughly homogenized in the melt. However, when coal is the main fuel source, it is difficult to sufficiently homogenize the amount of ash produced in a conventional smelting process for some types of glass for which optical requirements are critical. Therefore, it is an advantage of the present invention that coal is used as a fuel in a separate step in the smelting process so that the batch mixing of the ash is performed prior to liquefaction. In a separate preheating-30 stage, less than the total energy requirement is also required, so that less coal is needed and less ash is produced. In addition, the overall efficiency of the phased melting process has been found to reduce the overall energy requirements for melting the glass, further reducing the fuel requirements. As a result, coal can provide most or all of the energy source up to the preheating of the flat glass 6 79828 charge up to the melting temperature. In some operating models, coal may be the primary or entire source of energy for the entire liquefaction operation.

The novel fuel arrangements of this invention may form the entire fuel source or may supplement conventional heat sources. The share of the total thermal energy requirement of the preheating phase promoted by the new arrangements is substantial; i. greater than that previously achieved in the art when carbonaceous material was added as a melting aid, colorant, or binder. It is believed that up to 5% energy improvement is unnatural to these prior art uses of carbonaceous material in the melter. For economic reasons, it is preferred that the new fuel use 15 of the present invention be maximized so that it accounts for the majority of the energy in the preheating phase and optimally all of the energy.

Another feature of the preferred embodiments of this invention is the reduction of exhaust emissions from incomplete combustion products, for example, smoke, soot, or volatiles from the fuel. As the charge material in contact with the solid or liquid fuel is transported toward the heating zone, the temperature of the fuel gradually increases and the fuel begins to release volatiles and smoke before it ignites completely. The resulting undesired emissions are substantially eliminated due to this aspect of the invention when the gas flow in the preheating step is maintained substantially parallel to the flow of the charge-fuel mixture through the preheating step. This downstream flow-30 model transports emissions from the early heating stages to the combustion zone where the combustible emissions are ignited. Not only are harmful emissions eliminated, but their combustion also contributes to the heating of the charge material. The exhaust gas from the preheating stage can be further combusted by conveying it to the next combustion zone, such as the liquefaction stage.

The invention also results in other environmental benefits.

7 79828

The stepwise process allows the use of oxygen to support combustion instead of air. Elimination or reduction of the amount of nitrogen in the combustion gases reduces the amount of nitrogen oxides (NOx) formed. The volumes of the exhaust gases are substantially reduced when oxygen combustion is used and thus the gas velocity is reduced, which in turn results in less removal of the particulate charge material. The absence of nitrogen also causes a higher flame temperature. The use of substantially pure oxygen and the exclusion of all air maximizes these benefits, but the benefits can be partially realized by the amount by which the oxygen concentration exceeds the air concentration.

Another environmental benefit is that some of the sulfur emissions associated with the combustion of normally sulfur-containing fuels, such as coal, can be reduced. Contact between the combustion gases and the charge material (especially a glass print containing limestone, etc.) can remove sulfur oxides from the gas stream.

In an alternative mode of transmission for the broader aspects of this invention, fuel that may have ash content is burned at a stage in the smelting process for initially liquefying the charge so that the slag from the ash content of the fuel integrates with the liquefaction material. Since the slag is introduced into the product stream at an early stage of the smelting process, it can be homogenized at that stage and in the subsequent stages of the smelting stage.

Preferred embodiments of the liquefaction step comprise inclined melting surfaces surrounding the central stretch, with a large portion of the inner surface of the vessel forming a melting material on which the ash or slag can be trapped. The charge is fed to the sloping surface as the liquefied material flows down the sloping surface into the drain pipe. In the next step, the smelting process can be continued.

35 The relatively small amount of refractory material exposed to slag during the liquefaction step reduces the possibility of erosion in the vessel and the concentrated 8 79328 run of slag into the melt.

The charge material and coal, or other solid or liquid fuel, are preferably in contact with each other when the fuel is burned in the liquefaction step. The fuel and charge can be fed separately, but it is preferred to mix the fuel into the charge before feeding. When the liquefaction zone is heated to the flash point of the fuel, the combustion of the fuel is continued by feeding an oxidizing agent, preferably substantially pure oxygen, to the combustion zone.

In an alternative embodiment, a burner of a known type for burning solid, pulverized fuels, such as coal, may be used in the liquefaction step. The ash carried by the gas is collected on the surrounding smelting surfaces and is combined with the liquefied charge material.

The invention can be more fully understood from the drawings and the accompanying description.

Figure 1 shows a preferred embodiment of the present invention having a rotary kiln preheating step shown partially broken, a second stage rotary liquefaction chamber, and a third stage processing chamber.

Figure 2 is an enlarged vertical cross-section of the second and third stages, with the third stage embedded in the incinerator.

A detailed description of the present invention will be made with reference to an example of a glass melting operation in which the present invention has been found to be particularly useful. The invention is useful with all types of glasses, including flat glass, container glass, fiberglass, and sodium silicate glass.

It should be understood, however, that the invention is useful for melting other, similar material, and in particular for converting mineral-type materials 35 to the molten state. Other examples include: smelting glass and ceramic materials, smelting frit, and smelting ores.

9 79828

The first stage may be various gas and solid contact devices, but the preferred embodiment is a rotary kiln, as shown in Figure 1. Alternative devices include a fluidized bed and a cyclone separator / 5 contactor known in the art. The rolling furnace comprises a cylindrical shell 2 rotatably supported by rollers 3 at a slight angle to the horizontal. The single-walled metal shell shown in the figure may be sufficient or better thermal performance may be achieved by a refractory lining or a double-walled metal shell with insulation between the shells.

The stationary inlet shell 4 closes the inlet end of the rolling furnace. The feed tube 5 extends through the wall of the shell to align the powdered charge material from the feed furnace-15 from the feed rate monitor 6. The charge B may be mixed with the fuel before being fed to the winch furnace or the fuel and the charge may be fed separately to the winch where they mix. The oxidizing gas (e.g. air, but preferably oxygen) can be fed to the wort 20 through a duct 7 extending through the wall of the inlet shell 4. The duct 7 may extend into the winch at a sufficient distance to form a combustion zone some distance downstream of the charge feed area. Batch materials containing oxygen-containing compounds, such as carbonates, can form part of the oxygen to maintain combustion. This is advantageous because the carbon dioxide is removed before the charge is liquefied. After liquefaction, the release of carbon dioxide would have formed bubbles in the melt and are difficult to remove. In the preferred embodiment, the combustion products flow downstream of the charge through the wort furnace to the second stage liquefaction device 10 through an outlet cover connecting the two stages.

Ignition can be initiated in the combustion zone by auxiliary heating means, such as a burner temporarily placed in the furnace. Once ignition of the fuel in contact with the charge has been achieved, the combustion zone can be maintained in a substantially fixed area of the blast furnace by balancing the rate of oxygen supply and the rate at which the charge and fuel are conveyed along the blast furnace. The latter speed is substantially controlled by the speed at which the 5 tilted ovens are rotated. The solid materials and gas streams move in parallel through the blast furnace so that the volatile materials originally withdrawn from the fuel travel to the combustion zone where they are combusted.

Although not advantageous, the gas and charge could flow countercurrent to each other in a guest furnace or other preheater. In that case, it may be necessary to provide means for making the exhaust gas environmentally acceptable, such as a bag collector for particulate matter. Some of the exhaust gas can be recycled to the combustion zone in either the preheating or liquefaction stages to eliminate combustible materials. Another technique for treating the exhaust gas and recovering the waste is to transport the exhaust gas into contact with the charge material 20 in the preceding preheating additional step. A charge material containing carbonates (e.g., limestone) is also useful for removing sulfur oxides from the exhaust gas.

A specific preferred embodiment of the second step is shown in Figure 2 and is in accordance with the teachings of U.S. Patent No. 4,381,934 to Kunkle et al. and U.S. Patent Application Serial No. 661,267, issued October 16, 1984, also to Kunkle et al. which are incorporated herein by reference. The second step is to arrange the charge of the charge and is characterized by a sloping melting surface for receiving the charge material, which melts in a thin layer on the sloping surface and flows away rapidly after liquefaction. The liquefaction step presented herein is described by Kunkle et al. a preferred embodiment of the teachings in which the inclined surface substantially surrounds the central recess 35 and the vessel rotates about a substantially vertical axis. The circular order offers particular advantages to the present invention and to the efficiency of the melting process in general, but it should be understood that this invention in its broader aspects is not limited to a circular liquefaction arrangement.

5 By separating the liquefaction stage from the rest of the smelting process, energy is used more efficiently at each stage of the process by optimizing the conditions at each stage to meet certain needs of the stage. Additional efficiency is achieved by surrounding the heated zone with charge material and using an insulating layer of charge material or compatible material to thermally insulate the liquefaction zone. Due to the overall energy efficiency of the stepwise process and since only a part of the total energy required for smelting is consumed in the liquefaction zone, it has been found that the amount of energy consumed in the liquefaction step is relatively low and various heat sources can be used efficiently. Combustion of fuel, especially by oxygen injection, is preferred and electrical sources such as an arc furnace or plasma lamp may be used. Coal-20 li or other solid fuel may form part or all of the fuel in the second stage and part of it may be non-combustible fuel from the first stage. When carbon monoxide is formed in the first stage, the flue gas from the first stage can be transported to the second stage, where it can generate a substantial amount of its energy needs.

Referring to Figure 2, the liquefaction step 10 generally includes a cylindrical vessel 12, which may consist of a steel drum. The container 12 is supported on an annular frame 30 14, which in turn is positioned for rotation generally vertically about an axis corresponding to the centerline or axis of symmetry of the container, a plurality of support rollers 16 and alignment rollers 18. The base portion 20 of the container holds an axially aligned annular sleeve 22 which defines a downcomer 24 in the center 35. The sleeve 22 may consist of a plurality of ceramic 12 79328 pieces and the base portion 20 may be removably attached to the remainder of the container 12 to facilitate replacement of the sleeve 22.

The refractory cover 26, preferably in the form of an upwardly dome 5, is provided with a stationary support, a surrounding frame part 28. The cover 26 may include at least one opening through which at least one cooled gas distribution pipe 30 may pass. The distribution pipe 30 may comprise a burner or to dispense an oxidizing agent to support the combustion of the fuel, which fuel is introduced into the liquefaction chamber. If fuel is introduced from the first stage, line 30 can be used to introduce oxygen or the like into the vessel when the ignition temperature is reached. Optionally, part of the heat for the liquefaction stage may be generated by a conventional burner or other heat source in addition to the energy obtained from the fuel from the first stage. Line 30 may be centrally located or may be angled or eccentrically positioned to direct oxygen and / or fuel 20 to the melt bed.

An opening 32 through the lid 26 may be provided for feeding the charge to the liquefaction stage and, as shown in Figure 2, the outlet jacket 36 at the end of the wort 1 may be provided with a chute portion adapted to guide the material 25 to the liquefaction stage. An adjustable flap 38 may be located at the end of the chute to direct the flow of charge to the side walls of the vessel 12.

Preferably, a stable layer of powdered material 40 lines the inside of the container 12. This layer acts as an insulating liner 30 to protect the container 12 from heat inside the container. In those applications where it is desirable to avoid contamination of the product material, the layer 40 is preferably substantially the same composition as the batch material. Before the melting process is initiated, a stable liner 40 is placed in the melter by feeding loose powdery material, such as batch material, into vessel 12 as the vessel is rotated. The loose material generally assumes a parabolic shape, as shown in Figure 2. The powdery material may be wetted, for example, with water during the initial stage of forming a stable liner to promote cohesion to the layer along the sidewalls. When the liner 40 consists of a cartridge material, it need not contain a fuel component that can be mixed into the cartridge during the operation. Other small differences between the liner material and the through-material may be acceptable, depending on the requirements of that process.

During the melting process, the continuous feed of the charge to the liquefaction step 20 results in a descending charge flow distributed on the surface of the stable liner 40 and liquefied in the transfer liner 42 passing to the bottom of the vessel and passing through the open drops from the first step 10 to the second step 11 for further processing. In this way, the initial step of liquefying the charge can be performed efficiently because after liquefaction, the material is immediately removed from the vicinity of the heat source and continuously replenished with fresh feed material, thus maintaining a large temperature difference and therefore a high heat exchange rate in the liquefaction vessel. Continuous replacement with a relatively cool, fresh feed material in cooperation with the insulating layer maintains the structural integrity of the liquefaction vessel when forced cooling of the vessel is not used.

The liner material 40 forms a thermal insulator and preferably also acts as a non-contaminating surface for the melt transfer layer 42, and most preferably the stable liner contains one or more components of the feed material. Because of the thermal conductivity of the liner material 35, it is desirable that it be relatively low so that practical layer thicknesses can be used while avoiding the need for forced cooling of the outer surface of the container. In general, the raw materials of a granular or powdery mineral source provide good thermal insulation, but in some cases it may be possible to use the intermediate or the product of the smelting process as a non-contaminating stable layer. For example, the glass manufacturing process ground glass crumb (waste glass) could form a stable layer, although a thicker layer may be required due to the higher thermal conductivity of the glass compared to the glass mass. 10 In metallurgical processes, on the other hand, the use of a metallic product as a stable layer would result in unreasonably large thicknesses to provide thermal protection to the vessel, but some ore materials may be satisfactory as insulating layers.

The preferred embodiment of the liquefaction step described above involves rotating the liner around the central orifice, but it should be understood that the present invention is applicable to embodiments in which the liner surrounds the heated orifice but does not rotate. In addition, the invention is applicable to embodiments where the liner is an inclined surface but does not surround the heat source (e.g., melting occurs on an inclined surface). Examples of such variations are described in the previously mentioned Kunklen et al. patent and patent application.

Air could be used as an oxidant, but it is preferable to use oxygen (i.e., a higher oxygen content than air) to reduce the volume of pass-through gas. As a result, both the first and second stage devices can be made compact because the exhaust gas flow is relatively low in volume and high in temperature. Elimination of nitrogen from the system also increases flame emission and therefore increases heat transfer. The strong combustion heat supported by the oxygen combustion is compatible with the preferred embodiments of the second stage due to the thermal protection and efficient heat transfer provided by the surrounding liner.

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The temperature reached in the preconditioning phase depends on the amount of fuel, which in turn depends on the amount of fuel and oxygen used. Even a small amount of combustion is beneficial because of the heat it transfers to the input-5 rials. Preferably, the amount of heat generated by combustion in the first stage is sufficient to produce the maximum temperature increase of the charge without melting the components of the charge to such an extent that the charge no longer flows freely. For example, a typical flat glass batch mixture containing substantial amounts of soda ash would be limited to temperatures below the melting point of soda ash (851 ° C), preferably lower, to prevent clogging of the blast furnace. Alternatively, the components that melt at the relatively low temperature of the charge may be omitted from the charge fed to the first stage, but may be fed directly to the second stage and thus allow higher temperatures to be achieved in the first stage. Preferably at temperatures above about 870 ° C, calcium carbonate and magnesium carbonate, typical glass mass components, are calcined, i. they decompose and release carbon dioxide. Elimination of carbon dioxide while the materials are still in a solid state is advantageous because it avoids the formation of carbon dioxide bubbles in the melt. Even higher temperatures 25 may be allowed in the preheater if the material to be heated at this stage is limited to the parts of the charges that melt at the highest temperature and the rest of the ingredients are fed directly to a later stage. For example, only heating the sand in a blast furnace would allow preheating temperatures above 1,000 ° C to be achieved. Separate preheaters can be equipped with any materials that bypass the first stage. Some of the ingredients in the molten glass mass, such as soda ash or sodium hydroxide, can be fed to the second stage in molten form. It may also be advantageous to feed the cullet directly to the second stage when the first stage is operated at relatively high temperatures, i.e. in which case the cullet can be preheated by contacting it with the exhaust gas.

At most operating temperatures, the combustion of the first stage can produce some carbon monoxide if there is insufficient oxygen for complete combustion of the fuel. Thus, the exhaust gas from the first stage can be transported to the second stage, where the carbon monoxide content acts as part or all of the fuel for the second stage-10, which burns with additional oxygen. The proportion of carbon monoxide in combustion products increases and the proportion of carbon dioxide decreases at higher temperatures. Therefore, in order to produce the prevailing amounts of carbon monoxide as a second stage fuel, it is preferred that the first stage be operated at a maximum temperature above about 15,900 ° C. When sufficient fuel and too little oxygen are supplied, the total Stage II fuel requirement can be met by Stage 1 carbon monoxide. Combustion of fuel to carbon monoxide releases about a third of the fuel from the heat-20 reservoir and the rest is released when carbon monoxide burns to carbon dioxide. Therefore, the relative energy requirements of the first and second stages should be taken into account when selecting the amount of carbon monoxide to be generated in the first stage. For example, a glass cartridge is capable of using twice as much energy in the preheating stage as in the liquefaction stage, so that the production of carbon dioxide alone in the first stage is not the most efficient use of energy. When preheating a complete flat glass charge mixture, a favorable distribution of the heat content of the fuel can be achieved when the first stage exhaust gas contains about 50% carbon monoxide and 50% carbon dioxide (on a molar basis).

The ability to use coal is an advantage of the present invention because some areas are rich and low cost coal. But other solid or liquid carbonaceous fuels can also be advantageously used in this invention, for example, fuel oil, crushed coke, petroleum coke, peat and lignite, oil shale, sawdust, bagasse and waste paper. Liquid petroleum products, such as fuel oil, also have the advantage of wetting the charge to suppress dust formation and transport it in the exhaust gas stream.

For economic reasons, coal is a preferred fuel, especially bituminous coal. Typical Pennsylvania bituminous coal typically has a calorific value between 25.5 and 34.8 million. joules / kg (11,000 to 15,000 BTU / pound) and an ash content of about 3-9% by weight depending on the source. Melting the glass in a conventional, efficiently operated off-site regenerator furnace burning natural gas or fuel oil is considered to require at least 7-8 million joules / kg of glass produced. Taking, for example, a typical Pennsylvania coal with a calorific value of about 32 million. joules / kg and an ash content of about 7% by weight, the combustion of such coal in a conventional glass melting furnace so as to obtain the total energy required for melting would give an exceptionally large amount of ash. The liquefaction process described above has been found to consume about 2.3 to 3.5 million. joules / kg throughput. At this level of energy consumption, much less coal is required to meet energy needs and therefore ash imported from coal into the melt is at acceptable levels even in the manufacture of the high quality glass required for flat glass.

The amount of coal used depends on the temperature reached in the preheating step and the heat content of the coal in question, which in turn is a function of its own carbon content. Since combustion cannot be complete because oxygen cannot reach all parts of the coal, it may be advantageous to add a little more coal than is theoretically required. For example, about 2-3% of the Pennsylvania coal described above, mixed with a flat glass charge mixture, has been found to preheat the charge to a temperature of about 550-650 ° C when burned with excess oxygen. In this case, the amount of carbon monoxide produced is small. In another example, ie 79828, a flat glass cartridge with a soda source (e.g., soda ash) omitted from the first stage (thus comprising mainly sand, limestone, and dolomite) and mixed with about 6-10% by weight of coal-5 is preheated to about 1,100 -1 300 ° C when fired. A substantial amount of limestone and dolomite is calcined, and if a limited amount of oxygen is used in the combustion zone, there is more carbon monoxide than carbon dioxide in the combustion product stream. Other carbonaceous fuels 10 may replace coal in amounts determined by their respective heat contents.

It should be understood that while the fuel in contact with the charge preferably provides at least most and preferably all of the energy required for the preheating step, the advantages of the present invention can be achieved with smaller amounts of fuel fed to the charge. In that case, some energy can be obtained with conventional burners by heating the preheating phase. In implementations where the gas flow goes in the opposite direction to the charge flow in the preheater, the exhaust gas from the liquefaction step to the preheating may provide some energy for the preheating.

Solid fuels, such as coal, which must be mixed into the charge, are preferably finely divided.

For example, coal is preferably up to 60 mesh (US standard screen size) and 200 mesh coal has been found to be particularly satisfactory. The flash point of coal varies somewhat, but the oxidation of typical bituminous coal can begin at about 170 ° C and continue to burn spontaneously at temperatures above 250 ° C when pure oxygen is used.

The following is a typical ash content of 25 parts by weight of coal

SiO 2 2, 2 parts by weight 35 a12 ° 3 0.6

Fe 2 O 3 0.27 19 79328

CaO 0.1 part by weight

Na and K 0.5

It can be seen that these ash ingredients are compatible with the soda-lime-silica flat glass composition, which composition may be as follows:

SiO2 72-74 wt% Al 2 O 3 0-2

Na 2 O 12-15 K 2 O 0-1 10 MgO 3-5

CaO 8-10

Fe 2 O 3 0-0.2 SO 3 0-0.5

Soda-lime-silica-lasil-15a of the above type usually has a viscosity of at least 100 poise at 1,425 ° C.

The temperature at which the batch liquefies in the second stage depends on the batch materials in question, in particular the amount of ingredients that melt at its lowest temperature and the melting temperature. The most common low-melting ingredient in glass mass is soda ash, which melts at 851 ° C. In practice, it has been found that commercial flat glass formulations liquefy at a slightly higher temperature, about 1,090 to 1,150 ° C. The heat of the liquefaction step can raise the temperature of the liquefied material slightly higher before it leaves the step, and thus the temperature of the liquefied glass batch flowing from the liquefaction step can typically be in the order of 1,260 ° C, but usually not more than 1,320 ° C. Such a temperature and short residence time in the nes-30 bottling vessel are seldom sufficient to complete the complex chemical and physical reactions associated with the smelting process. Accordingly, the liquefied material is transferred to a third or "processing" step 11, where the melting process is continued.

35 For glass, treatment in the processing zone typically involves raising the liquefied temperature to promote the melting of the remaining sand grains and to remove gaseous inclusions from the melt. A peak temperature of about 1,370 to about 1,510 ° C is considered desirable for flat glass processing. Another desirable operation that can be performed at this stage is to homogenize the molten material by mixing. Also, when the batch is liquefied under reducing conditions, resulting in a molten material that reaches the refining stage in the reduced state, re-oxidation of the melt may be required for some end uses. Therefore, the function of the refining step in this invention may be to introduce an oxidizing agent into the melt. All these objects are achieved by the preferred embodiment shown in Figure 2. The highly mixed refining step is well suited not only for controlling the oxidation state of the melt, but also for adding dyes, cullet or combination modifiers that melt relatively easily. Thus, great flexibility is provided for the production of very different products.

The preferred embodiment of the refining step shown in Figure 2 uses immersed combustion in two chambers. The single-chamber processing step may be sufficient for some applications, but for flat glass, the preferred embodiment comprises two submerged combustion chambers 50 and 52, each having a pool 53 and 54, respectively, for molten material 25. The chambers may be provided with oxygen bubble tubes 55 and 56 and water-cooled burners 57 and 58 below the surface of the molten material. The immersed drain 59 allows material to flow from chamber 50 to chamber 52. An opening 60 in the roof of chamber 50 allows molten material 44 to fall from liquefaction step 10 into chamber 50. Exhaust gas from liquefier 10 and first stage 1 may enter the refiner through orifice 60. An exhaust port (not shown) may be at the top of the chamber 50. The chamber 52 has an opening 62 at its top for removing exhaust gases.

A fuel such as natural gas and an oxidant, preferably oxygen, is fed to burners 57 and 58 and 2i 79328 combustion occurs when the gas streams reach the melt basins 53 and 54. Another fuel that can be advantageously used in immersed bulbs is hydrogen because its combustion product is water that is highly soluble in molten la-5. The use of oxygen as an oxidant is advantageous because it avoids the introduction of air into the melt without a high nitrogen content having poor solubility in the molten glass. The use of undiluted oxygen also improves the contact between the oxygen and the reduced portions in the melt. An additional 10 oxidants may be introduced into the burners in addition to the amount required to burn the fuel to correct the reduced state of the liquefied material entering the refining step. Alternatively, if the liquefied material entering the refining step has sufficient non-combustible carbon or if the melt temperature does not need to be increased, the oxidant can be injected alone into the melt tanks 53 and 54 to provide only reoxidation. The oxidant can be introduced separately from the immersed burners, such as through bubble tubes 55 and 56. It has been found advantageous to use 20 bubble tubes in conjunction with immersed combustion. The bubble tubes can be adapted to inject a stream of small oxidant bubbles into the melt, which increases the contact area between the melt and the oxidizing gas, and the immersed combustion provides vigorous mixing to mix the oxidant bubbles throughout the melt mass. Submerged combustion thus gives the melt a very efficient homogenization.

The amount of excess oxidant introduced into the refining step will vary depending on the conditions involved and the degree of reduction of the material entering the stage and the desired oxidation state of the final product. The amount of agitation, the size and shape of the vessel, the efficiency of the gas-liquid contact, and the residence time in the processing step are factors in achieving reoxidation. In order to achieve homogeneous reoxidation to meet flat glass standards, it has been found advantageous to perform reoxidation in two successive chambers, as shown in Figure 22 7 9 3 2 8, and thus to ensure that each portion of the permeable material is subjected to oxidation conditions for a sufficient dwell time. gives a brown glass because sulfur is present in the sulfide state and iron is also present. If clear glass is desired, reoxidation is performed to increase the oxidation state of the coloring ions + 3 +2 sufficiently, typically expressed by the term Fe / Fe ratio. For a normal commercial grade bright plane + 3 +2 it has a Fe / Fe ratio between about 1.5 and 3.0 and a transmit-10 dance of at least 70% (preferably at least 80%) for light with a wavelength of 380 nanometers, 6 mm with a thickness of. Clear flat glass can sometimes also be characterized by a transmittance of at least 60% at 1 000 nanometers +3 +2 (6 mm thick). Fe / Fe ratios significantly higher than those mentioned above have been achieved by introducing oxygen bubbles into the molten glass, which was originally dark brown. The change in color from brown to bright during oxidation is easily observed and thus the appropriate degree of oxidation can be easily assessed by visual observation.

20 Although coal can bring excess iron into the melt, clear glass can be obtained by reoxidation. But the exact fitting of a normal flat glass to the spectrum may require a reduction in the amount of iron that is normally deliberately included in the input (usually in red) for distortion.

Downstream of the reoxidation chambers there may be a smoothing chamber 64, as shown in the drawing, in which additional residence time may be used to remove gas inclusions from the melt and to cool the melt to a temperature suitable for further processing. The molten material may enter the leveling chamber 64 through the shrinkable drain 66. In the arrangement shown, the residence time in the chamber 64 is extended by a recessed barrier 67 and a surface barrier 68, which form a tortuous path to the melt flow. The treated Su-35a material can be removed from the processing step 11 through the channel 70, which can lead to a molding process or the like, which in the case of 23 79828 glass can be formed into glass sheets, fibers, bottles or the like by known means.

In an alternative embodiment, the ash-containing fuel is burned during the liquefaction step. The preheating phase 5 does not have to be in this embodiment. Separating the liquefaction step from the remainder of the smelting process provides an environment in which a large portion (substantially all) of the ash content of the fuel can be introduced into the product material without adversely affecting the homogeneity of the product. The rapid flow of liquefied material from the liquefaction step has a substantial mixing effect and the processing in subsequent steps preferably subjects the liquefied charge and slag to further homogenization. Further, since the melting takes place in a relatively thin layer, the fuel mixed with the charge material has a good oxygenation so that the combustion is relatively complete. As in other embodiments, the fuel may be fed to the combustion zone separately from the charge, but it is preferred to feed the mixture of fuel and charge to the liquefaction step. The use of oxygen-enriched combustion is also preferred. Incomplete combustion of the fuel in the liquefaction step results in molten material entering the refining step in a reduced state that may need to be repaired. Therefore, the function of the refining step in this embodiment 25 is to introduce an oxidant into the melt.

The amount of coal used in the liquefaction step depends, of course, on the heat content of that coal, which in turn is a function of its solid carbon content. In the case of the Pennsylvania coal described above, adding about 30 to 6% by weight of the weight of the charge to the coal would theoretically provide the total energy required to liquefy the flat glass charge. But since combustion is not complete because oxygen does not reach all parts of the coal, it is advantageous to add slightly more coal than is theoretically required if the coal constitutes the entire energy requirement of the liquefaction stage. Therefore, for example, it is preferred to add 24,79,828 coal to about 10% of the weight of the charge. Carbonaceous fuels other than coal may be added in amounts determined by their relative heat contents. The invention also encompasses filling the energy consumption of less than 5 to 5 k of the liquefaction stage with the carbon content of the charge. In such a case, part of the energy may be introduced by the carbon of the charge and the remainder may be introduced by a conventional burner or other means of heating in the liquefaction chamber.

In a specific example of an alternative embodiment, using the arrangement shown in Figure 2 without preheating, a standard commercial glass mass (but excluding sulfur-containing melting aids such as glauber's salt cake or gypsum) f was mixed with 5-6% by weight of coal and melted at a rate of about 6.8 kg per hour. Coal was the only fuel source in the liquefaction stage and the liquefied charge was brown and foamy when it entered the refining stage. Each reoxidation chamber had one immersed burner and one bubble tube-20 ki. Each immersed burner was fed at 7 standard cubic meters per hour with hydrogen and 3.6 standard cubic meters per hour with oxygen. Each bubble tube was fed 0.56 standard cubic meters per hour with oxygen. The volume of molten material ranged from 0.28 to 0.56 cubic to 25 meters, and the average residence time of melt growth as it passed both chambers was estimated to be about 30 minutes. The temperature of the first chamber was about 1,290 ° C and the temperature of the second chamber was about 1,370 ° C. An auxiliary burner (not shown) was in the upper space of chamber 64 to facilitate lowering of the foam.

30 The glass leaving the refining stage was clear, almost bubble-free, and more oxidized than commercial flat glass. The batch mixture used would normally give glass with an iron content (expressed as FejO 2) of about 0.11% by weight. Due to the iron introduced by the coal, the glass of the example was found to contain 0.16% by weight of iron. Sulfur in coal was found to form glass with 0.063 wt% SO 2 without reoxidation and less than 0.01% SO 2 with reoxidation.

Claims (17)

A process for melting an ice cream batch or the like, in which the process of combustion of ash-containing fuel is used as a heat source for the process, characterized in that liquid or solid ash-containing fuel is mixed in direct contact with the ice-cream material, said fuel. is incinerated so that the batch is heated, the amount of fuel in the mixture being sufficient to heat the batch to a temperature just below its melting temperature before a final melting step, or wherein said amount of fuel is sufficient to provide the majority of the heat required. in the smelting step after the batch has reached a temperature just below its melting temperature, whereby ash from the combusted fuel may remain in the final glass product. 2. A process according to claim 1, characterized in that the ash-containing fuel is mixed with the batch material before it is measured in a preheating stage, the combustion of the fuel takes place in the preheating stage, where the batch material is heated at a temperature just below its melting temperature and the batch is measured in a melting step, the batch material being transferred in liquid form. 3. A process as claimed in claim 2, characterized in that the ash-containing fuel is substantially all of the energy needed in the preheating stage. 30 A method according to claim 2 or 3, characterized in that the preheating step comprises stirring the batch material in a rotating vessel, where the batch material is brought from one end of the rotating vessel to its other end. 35 5. A process as claimed in claims 2 to 4, characterized in that an oxygen source, whose oxygen concentration is greater than that of the air, is measured in the preheat stage to support combustion. 6. A method as claimed in claims 2 to 4, characterized in that the charge material is brought through the pre-heating step from an input end to an output end and combustion gas flow in the pre-heating stage is generally poured in the output end direction. 7. A process according to claim 6, characterized in that combustion products from the preheating stage are brought into the melting stage. 8. A process according to claim 7, characterized in that the combustion products contain carbon monoxide which is combusted in the melting step. 15 9. A process according to claim 1, characterized in that the batch material is transferred in liquid form in the smelting step and the combustion of the ash-containing fuel in the smelting stage constitutes most of the energy required for the smelting of the batch material. 20 10. A process according to claim 9, characterized in that the molten material is removed from the melting step in a reduced state and brought downstream to a zone where it is subjected to re-oxidizing conditions. 25 11. A process according to claim 10, characterized in that the oxidizing conditions of the downstream zone are later achieved by injecting gaseous oxygen into the mass of the molten material. Method according to claim 11, characterized in that the stirring of the material in the downstream zone is carried out by injecting burning gases into the mass of the molten material. 13. A process according to which as claimed in claims 9-12, characterized in that the fuel 35 which is in contact with the batch material is essentially the entire source of energy for the batch melting. 30 79828 14. A method according to claim 1, characterized in that the fuel is mixed in the batch before it is measured in the zone where the combustion takes place. 5 15. A process according to which as claimed in the preceding claims, characterized in that the batch is a soda-limestone-silica glass batch. 16. A process according to which, according to the preceding claims, characterized in that the fuel contains coal. 17. A process according to which, according to the preceding claims, characterized in that the fuel contains a liquid crude oil product.