PL148248B1 - Method of melting glass furnace charges - 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

The present invention relates to a method of melting glass charge with the use of carbonaceous fuels (such as coal, and the use of mixtures of solid or liquid fuels with raw materials for these processes. In regions where coal is present, it is usually the cheapest source of energy compared to other traditional energy sources). such as natural gas, fuel oil and electricity. Thus, there have been proposals to use coal as a fuel in smelting glass and similar processes. Examples of such proposals are given in US Pat. Nos. 3,969,068 and 4,006,003. However, the use of carbon As a fuel in direct-heating furnaces, it has some drawbacks that have hampered the spread of this method, notably the presence of ash in the coal. There is a significant amount of ash that can clog the regenerators, so ash removal is necessary the flue gas before it is released into the atmosphere. "Part of the ash is deposited on the walls of the smelting chamber and melts and flows with the liquid slag along the walls of the tank to the molten glass. The flow of molten slag adversely affects the refractory lining of the furnace, and he it adheres to the molten glass itself, changing its composition and causing the product to be non-uniform. The slime often contains more iron than the glass, and this running down causes streaked streaks in the glass. These are important obstacles to the use of coal as a direct heating fuel in melting processes where product homogeneity is important. This applies in particular to window glass, where variations in composition cause optical distortions. Another disadvantage of using carbon or other carbon fuels mixed with raw materials, especially when smelting clear glass, is that enough carbon to generate the necessary energy in the melting process it reduces the molten product, and the reduced iron and sulfur color the glass brown. Moreover, some of the iron and sulfur from the carbon goes into the molten glass. Small amounts of powdered carbon (usually less than 0.1% by weight) were included in the clear glass charge to facilitate the smelting, but such amounts were of no importance as an energy source and the addition of larger amounts was considered harmful. Even in the production of brown glass, the amount of carbon used was not of energetic significance. US Pat. No. 3,294,505 was fused with smelting the glass in a bed of briquetted charge and coke. This 3Q process is limited to fine grade glass with low viscosity and low quality. It would also be desirable to avoid the cost of agglomerating the charge. In parallel US patent application W.fftl 879 a technique for wetting the glass melt with fuel oil is described. Oil provides only a small part of the necessary energy. melt. thiiy problem posed by carbon, etc.-. In coal fuels, the relatively volatile hydrocarbon fractions which are heated before firing up escape with the exhaust gases. In particular, the problem arises when it is necessary to "preheat the coal-fuel mixture. Feeding the coal fuels in a non-comminuted form into the combustion zone leads to the emission of smoke which is not desirable for environmental reasons. Afterburning or other persistence of the waste gas or the pre-coking of fuels is also a costly operation. The method according to the invention for melting the glass batch or the like, in which the combustion of the ash-containing fuel is used as a heat source for the process, consists in mixing the liquid or solid fuel containing the ash. in direct contact with the glass charge, the fuel is burned and the charge is heated, while the amount of fuel in the mixture is kept at a level sufficient to pre-heat the charge to a temperature slightly below the fusion temperature before the final stage. liquid, or the amount of fuel remains at a sufficient level in order to provide most of the heat necessary for the liquefaction once the charge has reached a temperature slightly below its fusion temperature and allows ash from the burned fuel to remain in the finished glass product. ash (e.g. coal) is used as the primary energy source for the smelting process, avoiding the problems associated with the presence of ash. The fuel containing ash burns in the batch process of preheating the charge in the smelting process, whereby the ash is combined with the charge , charge and fuel should be fed mixed to the preheating stage to ensure even distribution of ash in the charge and close contact of fuel and charge during combustion. The combustion process in the preheating step is sustained by feeding an oxidant, preferably substantially pure oxygen, to the combustion zone. In this step, the material is optionally mixed to improve contact between the charge and the combustible fuel. in powdered form, it passes to the next stage, where the mixture turns into a liquid state. A large part of the total energy requirement for the smelting process can be satisfied with a low-cost fuel such as coal by heating the charge to a temperature just below the temperature. perature in which fusion takes place. By giving an almost homogeneous mixture of the charge and ash to the melting stage, a liquid substance with a homogeneous composition is obtained despite the introduction of a significant amount of ash. One of the problems associated with the use of an ash-containing fuel such as coal is thus solved. By burning the fuel in contact with the charge, thus avoiding the ash entrainment with the exhaust gas and the formation of a slag on the inner walls of the tank, problems of environmental pollution and furnace failure which are relevant to smelting processes are also avoided. The process of the invention is particularly advantageous for smelting processes and the like, where homogeneity of composition is important, by avoiding slag flow into the molten mixture. Even difficult to homogeneous glasses, such as sodium-calcium-silica window glass meeting high optical quality standards, can be produced by this method. Another advantage is that it is not necessary to agglomerate the charge. In the method of the invention, it is possible to control the inflow and temperature of oxygen in the preheating step in such a way as to produce significant amounts of carbon monoxide as a fuel combustion product. The carbon monoxide is transferred to the next stage, the melting stage, where it constitutes at least part of the fuel burned. Alternatively, the combustion in the first stage may be incomplete whereby some fuel may pass with the feed to the next stage, which is at least part of the fuel needed therein. and to increase the amount of carbon monoxide produced, the fusible components of the charge may be omitted in the first stage and introduced in the second or subsequent stage. By removing the source of sodium (e.g. sodium carbonate) from the charge of soda-lime-silica glass, it may be used in the first stage. use temperatures high enough to calcine carbonates such as limestone and dolomite and to produce carbon monoxide. By treating only the source of silicon (sand) in the first step, it is possible to apply very high temperatures there and obtain great amounts of carbon monoxide. In the solid-to-liquid phase transition, there is a further, third, step in which fusion processes can also take place. When the charge is mixed with the fuel, incomplete contact of the fuel with the oxidant in the melting stage or the presence of excess fuel is possible, whereby the molten material may leave the second stage in a reduced form. In this case, the third step involves the use of melt re-oxidisers, for example, sub-pentacial combustion with an oxygen-rich flame or bubbling the oxidizing agent (preferably oxygen) through the melt. The re-oxidation prevents the tinting of clear glass in particular. The undesirable tinting of the transparent glass 60 with iron and sulfur ions can be avoided by re-oxidizing the molten substance in the third stage. the ash was homogeneously melted in the molten mass. However, in the case of glasses with high optical requirements, it may be difficult to homogeneously distribute the resulting amounts of ash through the glass when carbon is the principal fuel in the conventional melting process. The advantage of the process of the invention in this situation is the use of coal as the fuel in the first, periodic stage of the entire melting process, whereby the charge is mixed with the ash before liquefying. the energy is less than the total requirement, so less coal can be used and less ash will be produced. The overall efficiency of the staged melting process is the secret that the energy requirement of the entire fusion straight line is lower, and thus, again, the carbon consumption is lower. Thus, carbon may be the most important source of energy in the process of heating the glass charge almost to the melting point. In some cases, carbon may be the most important or sole source of energy for the entire melting process. The new method of using fuel according to the invention can either cover the entire amount of fuel or supplement conventional heat sources. Part of the total heat energy requirement in the pre-heating stage is significant, i.e. more than in the previously known methods of adding carbon substances as fluxes, dyes or binders. at most 5% of the energy requirements of the process. For economic reasons, it is desirable for the new method of using the fuel of the invention to provide most of the energy required for the preheating step, preferably all of these energies. Another feature of a preferred embodiment of the invention is to limit the mission of non-com- bustion products such as smoke. , soot or oxidisable substances in fuel. As the charge mixed with liquid or solid fuel moves towards the heated zone, the temperature of the fuel gradually increases and it begins to separate volatile components and smolder before ignition. The released volatile components are eliminated in the process of the invention, because in the preheating step, it flows in the same direction as the feed-fuel mixture moves. In a current flow circuit, the volatile components from the initial heating stages reach the combustion zone, where the combustible parts are incinerated. Not only is the emitted pollutants removed in this way, but their heat of combustion also contributes to the heating of the feedstock. The off-gas from the preheating stage 60 can be further burned by passing it to the next combustion zone, for example in the melting stage. The invention also has other environmental benefits. The staged operation of the process allows the use of oxygen instead of air to support combustion. Eliminating or reducing the amount of nitrogen in the exhaust gas reduces the amount of nitrogen oxides (NOx) produced. When oxygen is used, the exhaust gas volume and hence the velocity is significantly reduced, so that the gas entrains fewer particles of the fragmented charge. The absence of nitrogen causes the flame temperature to be higher. The use of pure oxygen and the complete elimination of air increases these benefits, but they can be achieved in part depending on how much the oxygen concentration exceeds the air concentration. Other environmental benefits are the reduction of sulfur emissions from the combustion of sulfur-containing fuels such as The contact between the flue gas and the charge (especially glass charge containing shafts and the like) can lead to the removal of sulfur oxides from the gaseous stream. Alternatively, in the method of the invention the fuel containing ash is burned in the preliminary charge melting stage * and Thus, any molar resulting from the presence of ash is homogeneously combined with the molten substance. As the molten glass fuses with the product in the initial melting stage, the product may homogenize in this and subsequent melting stages. The preferred methods of carrying out the melting stage require the use of inclined melting surfaces surrounding the cavity, so that a significant part of the inner surface of the vessel is a melting substance that absorbs ashes or slags. As the molten mass flows down the sloped surfaces to the outlet, the charge is applied to these surfaces. In the next step, the melting process is continued. The small area of the refractory lining exposed to the slag during melting reduces the risk of tank erosion and intense drainage of the slag into the molten mass. Coal or other solid or liquid fuel should be in contact with each other during the combustion of the fuel during the melting stage. The fuel and charge may be treated separately, but it is better to mix them before loading. When the fusing zone is heated to the ignition temperature of the fuel, the combustion is sustained by supplying an oxidant, preferably pure oxygen, to the combustion zone. An alternative method of carrying out the method of the invention is to use a burner that fuses powdered solid fuels, such as like coal. The ash entrained with the gases is collected on the surrounding melting surfaces and is combined with the melt. The invention can be understood more fully in the drawings and the following description of the method. Figure 1 shows a preferred device for carrying out the method, according to the invention consisting of a preliminary stage rotary kiln. heating, partially in section, a rotatable second-stage fusion chamber and a third-stage purification chamber, and Fig. 2 shows an enlarged cross-section of the second and third stage devices, and the third stage uses a subsurface burner. The following is a detailed description of the method of the invention with reference to an example of a glass melt for which it is particularly useful. The method of the invention can be used to produce all types of glass, including window glass, bottle glass, fiberglass and water glass. This means that the invention can be used to melt other similar substances, and in particular to melt mineral substances. Other examples include: fusing glazes and ceramics, fusing frit, and smelting metals from ores. In the first step, any device for contacting gases with solids can be used, but preferably the rotary kiln 1 shown in Fig. 1. Alternative devices are fluidized or cyclone distributor / contactor as known in the art. The rotatable 2 ° furnace is a cylindrical shell 2 which is supported to rotate on the rollers 3 and forms a slight angle with the horizontal. A single wall metal cylinder as shown in the figure may be suitable, although better thermal efficiency can be achieved with a flame retardant liner or a double wall metal cylinder and wall-to-wall insulation. The fixed inlet housing 4 closes the inlet. for rotary kiln. A feed pipe 5 passes through the wall of the housing, directing the particulate charge from the dosing device 6 to the rotary kiln. The charge B may be mixed with the fuel prior to filling into the furnace, or the fuel and charge may be separately fed to the rotary kiln, and in this case the mixing will take place in the furnace itself. Oxidizing gas fop. air, preferably oxygen) is supplied to the furnace via a line 7 passing through the wall of the inlet housing 4. The line 7 should extend into the furnace at such a depth that the combustion zone is formed at a distance from the charging point. Oxygen-containing feedstocks, such as carbonaceous materials, can provide some of the oxygen to support combustion. This is advantageous as it removes carbon dioxide prior to melting the charge. After the charge has been melted, the release of carbon dioxide would lead to the formation of bubbles that are difficult to remove in the melt. According to a preferred embodiment, the combustion products are co-current with the charge to the second stage melter 8 by closing the outlet 9 connecting the devices of both stages. The second stage melter 8 consists of a closed vessel 10, a refractory cover 11 which has at least one opening. At least one conduit 12t passes through this opening. take place in it Tafination of the alloy. The ignition of the combustion zone may be initiated by an auxiliary heating device, such as a burner which is periodically inserted into the furnace. Once the fuel in contact with the charge has ignited, the combustion zone may be maintained in a specific region of the rotary kiln by controlling the oxygen flow rate and the speed at which the charge and fuel move along the kiln. The solids and gases move along the furnace in a co-current, whereby the volatile substances withdrawn from the fuel in the initial phase pass into the combustion zone and are incinerated. While this is not preferred, the gas and charge in the rotary kiln or other preheater may flow countercurrently. In this case, it may be necessary to use exhaust gas purifying agents to a degree that meets the requirements of environmental protection, for example, bag dust. Part of the exhaust gas may be returned to the combustion zone or to the preheating stage or to the melting stage to avoid flammable parts from it. Another way to treat the exhaust gases and recover heat is to contact the exhaust gases with the charge in an additional pre-heating stage. heating. A feed mixture containing carbonates (e.g., limestone) is useful for removing sulfur oxides from exhaust gases. A particularly preferred second step is shown in Figure 2 and conforms to the teachings of US Pat. No. 4,381,934. and United States Patent Application No. 661,267. In the second step, the melting of the charge takes place on the inclined fusing surfaces. The charge placed thereon melts and, as a thin film, flows quickly from the inclined surface. The fusing device 8 shown in FIG. 2 is the preferred device for carrying out the method according to the above patents. In apparatus 8, there are inclined surfaces surrounding a central cavity, and the entire reservoir 10 rotates about a vertical axis. The rotating vessel and d "provide some advantages in terms of the method of the invention and the overall efficiency of the fusion processes, but it should be understood that the invention in its broader sense is not limited to the rotary melter. The separation of the melting stage from the rest of the stages. The process stages provide higher energy efficiency at each stage of the process by optimizing the conditions at each stage and adapting them to the specific requirements of each stage. Additional benefits are achieved by surrounding the heating zone with the feed substance and thermal insulation of the fusion zone with an insulating layer of the charge or other suitable substance Due to the energy efficiency of the staged process and the use of only a portion of the energy needed for the fusion process in the fusion stage, the amount of energy used in this stage is relatively small, allowing efficient use of various heat sources. Coal heating is recommended, particularly when using oxygen, you can also take advantage of electrical energy in the form of an electric arc or a plasma torch. The coal or other solid fuel may be all or part of the fuel used in the second stage, and it may be partly unused fuel in the first stage. If the first stage produces carbon monoxide, the first stage exhaust gas transferred to the second stage, where they can cover a significant part of the energy demand. According to Fig. 2, the second stage melter 8 comprises a cylindrical vessel 10, which may be a steel drum. The tank 10 is suspended from a pivoting frame 14, rotated about a vertical axis corresponding to the symmetry axis of the tank on a plurality of support 15 and adjusting rollers 16. The lower part 17 of the tank is an axially mounted ring sleeve 18 which is the main outlet of the molten charge 19. The sleeve 18 consists of a plurality of ceramic pieces, and the lower portion 17 is detachably attached to the remainder of the vessel 10, which facilitates the replacement of the annular sleeve 18. The refractory cover 11, preferably in the form of a dome, is supported by a fixed surrounding frame 20. The cover 11 has at least one opening through which at least one supply conduit 12 passes either the chilled gas or is a burner or may be an oxygen feed conduit or other oxidizing agent supporting combustion of the fuel supplied to the fusing chamber. If fuel is supplied from stage one, line 12 may be used to supply oxygen or a similar gas to the tank after the ignition temperature is reached. In addition to the energy supplied by the fuel from the first stage, some of the heat to the melting stage may pass from a conventional burner or other heat source. The conduit 12 may, as shown, be centrally located to fill the entire reservoir with oxygen, or may be positioned off-center at an angle to direct oxygen and / or fuel to the fused layer. Cover 11 has an opening 21 for feeding the charge to the stage. and as shown in FIG. 2, the end of the rotary kiln 1 may be provided with an outlet closure from a chute for directing the charge to the melting stage. The adjustable deflector 22 at the end of the chute can direct the stream of charge against the side walls of the tank 10. The interior of the tank 10 is covered with a solid layer of ground mass 23 to insulate the tank 10 against the high internal temperature. In those applications where it is necessary to avoid contamination of the product, layer 23 should have the same composition as the stock. Prior to the commencement of the fusing process, layer 23 is placed in an oven by feeding a loose powdery mass, for example a batch material, thereto and rotating the reservoir 10. The powdery material is deposited on a paraboloid surface as shown in FIG. 2. The powdered material may be wetted, for example water in the first step of lining formation, to facilitate adhesion of layer 23 to the walls. When layer 23 is a batch mass, it need not include fuel that is later introduced into the batch. Other slight differences between the input of layer 23 and the batch are acceptable and will depend on the specific process requirements. During the fusing operation, the stream of batch 10 fed to the fusing step 8 is spread over the surface of the permanent liner 23, heated by the heat of combustion in the vessel 10. and melting, forming a transitional layer 24 flowing to the bottom 5 of the tank and flowing through the opening 19 in the sleeve 18. The molten material 25 flows from the second stage melter 8 to the tank 13 for further processing. In this way, it is possible to efficiently carry out the initial stage of melting and melting the charge, because the charge immediately drains away from the vicinity of the heat source and is constantly replenished with fresh charge, thanks to which there is a large temperature difference and a high rate of heat exchange in the 2biomik . Constant topping up with relatively cool, fresh stuff, and the insulating properties of the lining protect the tank against damage and prevent external forced cooling of the tank. The solid layer 23 provides thermal insulation and serves as a non-contaminating contact surface for the transition molten layer 24. Most preferably it should contain one or more batch ingredients. The thermal conductivity of the liner should be relatively low in order to provide a layer of reasonable thickness and not to apply uneconomical forced cooling to the outside of the tank. Typically a granular or powdered feed is a good heat insulator, but in some cases it will be possible to use intermediates or melt products as non-contaminating, permanent layers. For example, in the glass making process, the powdered barge (gaps) may form a permanent layer, although the thickness of the layer 38 will need to be greater due to the higher thermal conductivity of the glass compared to the batch of glass. In metallurgical processes, on the other hand, the use of a metallic product to form a durable layer would require the formation of a thick layer to provide thermal protection to the vessel, but some ores may be well suited for insulating layers. Fusing takes account of the rotations of the liner about the central opening, but it should be understood that the method of the invention also covers applications in which the liner surrounds a rotating, heated opening. The method of the invention further includes applications in which the liner does not rest on sloped walls, but does not surround a heat source. Examples of such processes are disclosed in the above-mentioned patents. Air is used as the oxidant, but preferably oxygen (that is, a gas with a higher oxygen concentration than air) is used, which reduces the gas volume of the process. As a result, the first and second stage equipment can be made more compact since the exhaust gas stream is relatively low in intensity and high temperature. Removal of nitrogen from the system also increases the emissivity of the flame and thus accelerates the heat exchange. The intense flux of combustion heat associated with the use of oxygen is compatible with the preferred method of implementing the second stage in view of thermal protection and efficient heat transfer associated with the surrounding lining. The temperature achieved in the preheating stage depends on the intensity of combustion, which in turn Depends on the amount of fuel and oxygen supplied. Even low-intensity combustion is advantageous in terms of the heat transferred to the charge. Preferably, the amount of heat associated with the combustion in the first stage increases the temperature of the charge almost to the melting point of the feed components when the charge ceases to be free flowing. For example, a typical window glass melt containing significant amounts of sodium carbonate may be heated to a temperature slightly below the melting point of sodium carbonate (851 ° C) and preferably even slightly lower to prevent a furnace flooding. rotary. One possibility is to omit the relatively easily meltable components of the charge fed to the first stage and feed them directly to the second stage, whereby higher temperatures are permissible in the first stage. It is preferred that, at temperatures above 870 ° C., the carbonates of calcium and magnesium, typical components of the glass furnish, calcify, that is, decompose with the release of carbon dioxide. Removal of carbon dioxide while the input materials are still old is advantageous as it prevents the formation of carbon dioxide bubbles in the molten mass. Even higher temperatures can exist in the preheater if the substance to be heated at this stage consists of the most difficult melt components of the charge. and the remaining ingredients are added in the next step. For example, heating the sand alone allows the temperature to exceed 1000.degree. C. during the preheating. Separation preheating devices can be provided for each component not entering stage one. Some of the feed components, for example sodium carbonate and sodium hydroxide, "may be given in the molten form in the second stage. It may also be advisable to feed the cullet directly in the second stage when relatively high temperatures are used in the first stage. preheat the key with the exhaust gases. For most operating temperatures, the first stage combustion produces a certain amount of carbon monoxide, if the oxygen supplied is not sufficient to completely burn the fuel. The exhaust gases from the first stage can therefore be sent to the second stage, where the carbon monoxide present in them, burned with an additional amount of oxygen, constitutes part or all of the fuel needed for this tap. The carbon monoxide content of the combustion products increases and the carbon dioxide content decreases with increasing temperature. for carbon monoxide fuel for the second stage, use temperatures in excess of approximately 9000 ° C in the first stage. in the first stage there is sufficient fuel and insufficient oxygen, the entire fuel requirement in the second stage can be satisfied with carbon monoxide from the first stage. Combusting the fuel to carbon monoxide releases about a third of the heat of combustion, and the rest is released when carbon monoxide is burnt. to the dioxide. Thus, when selecting the amount of carbon monoxide to be produced in the first stage, the relative energy requirements of the first and second stages must be taken into account. For example, the glass batch may consume twice as much energy in the first pre-heating stage as in the melting stage. Thus, producing only carbon dioxide in the first step may not be an energetically advantageous procedure. By heating the complete feed for the production of window glass, a suitable distribution of the thermal efficiency of the fuel can be achieved, producing in the first stage a gas containing about 50 mole% carbon monoxide and 50 mole% carbon dioxide. The possibility of using coal, which is present in some regions in large quantities and at a relatively low price, but other fuels can be advantageously used here, for example heating oil, coke dust, petroleum coke, peat, brown coal, shale oil, sawdust , bagasse and waste paper. Liquid petroleum products such as fuel oil moisten the charge and prevent dusting and entrainment of dust with the exhaust gases. For economic reasons, coal is the best fuel, especially hard coal. The heating value of typical Pennsylvania hard coal ranges from 25.5 to 34.8 MJ / kg with an ash content from 3% to 9% by weight, depending on the source. The efficiently fused glass process, burning natural gas or heating oil in the top burners in a regenerative furnace, consumes at least about 7 to 8 MJ / kg of glass produced. Taking into account the example of Pennsylvania coal with a calorific value of about 32 MJ / kg and an ash content of about 7% by weight, it can be calculated that burning such coal in a conventional glass furnace, in an amount sufficient to meet the energy needs of the output, would create too much the amount of ash. The melting process described above consumes about 2.3 to 3.5 MJ / kg of product. With this level of energy consumption, much less carbon is needed to meet the energy needs, so that the amount of ash introduced into the melt does not exceed the level acceptable even for the production of high-quality window glass. The amount of carbon used depends on the temperature you want to achieve in the the pre-heating stage and the calorific value of a given grade of coal, which in turn depends on its carbon content. Since combustion may be incomplete as some of the coal may not receive oxygen, it is advisable to use a slight excess of carbon compared to theoretically required. For example, from about 26% to about 3% by weight of Pennsylvania coal, described above, when mixed with the batch for producing window glass, it preheats the batch to a temperature of about 550 ° C to about 650 ° C when combusted. 30 35 40 45 50 55 60 148 248 13 with excess oxygen. In this case, little carbon monoxide is formed. Another example is a batch for the production of window glass, in which sodium carbonate was omitted in the first stage (thus mainly composed of sand, limestone and dolomite), and which, when added from about (P / t to about 10% by weight) Coal is preheated on combustion of fuel to a temperature of about 1100 ° C to about 1300 ° C. Much of the limestone and dolomite are calcined and, if a limited amount of oxygen is supplied, the flue gas stream contains more oxide than carbon dioxide. carbon fuels in an amount determined by their calorific value.It should be borne in mind that although the fuel in contact with the charge can provide most, and preferably all of the energy required for the preheating stage, some benefits are also obtained by using smaller amounts of fuel fed In this case, part of the energy can be supplied by a conventional burner in the preheating stage. to the charge under preheating, the exhaust gas from the melt stage may supply some of the energy for preheating. Fuel steels, "such as coal, should be finely divided before being mixed with the charge. The carbon grains should pass through a screen with apertures of 0.250 mm, and preferably through a screen with apertures of 0.074 mm. The ignition temperature of the different types of coal varies somewhat, but the oxidation of typical hard coal can start at about 170 ° C and combustion, when supplied with pure oxygen, is self-contained at temperatures above 250 ° C. The typical composition of ash formed from 25 parts by weight of carbon is as follows: parts by weight SiO * 1.2 A120, 0.6 Fe2Oa 0.27 CaO 0.1 Na K 0.5 It can be seen that the ash components are compatible with the components of the soda-lime-silicon window glass. which may have the following composition: • / weight SiO2 72-74 AlgO, 0-2 Na20 12-15 K20 0-1 MgO 3-5 CaO 8-10 v Fe2Ot 0-0.2 SO, - "0— 0.5 Soda-lime-silicon glass of the above type usually has a viscosity of at least 10 Pa at a temperature of 1425 ° C. The temperature at which the charge melts in the second stage depends on the composition of the charge, in particular the quantity and melting point of the highest easier to melt components In the glass charge the most common easily melted component 14 is sodium carbonate at a temperature of It is known in practice that industrial glassware melts at a slightly higher temperature, about 1090 ° C to about 1150 ° C. The heat of the fusing step 5 may raise the temperature of the melt slightly higher, so that the melt flowing out of the melter has a temperature in the order of 1260 ° C, but typically does not exceed 1320 ° C. This temperature and the short residence time in the melt vessel are seldom sufficient to complete the complex chemical reactions and physical changes of the melting process. Accordingly, the molten substance passes to the third stage, the so-called refining 13, which is a further step in the smelting process. In the case of glass, treatment in the refining zone requires raising the temperature of the molten material to facilitate the degree of residual sand grains and to remove gas inclusions from the molten mass. Refining window glass requires a temperature of about 1370 ° C to about 1510 ° C. Another additional operation that can be carried out at this stage is the mixing of the molten substance to homogenize it. If, moreover, the charge has melted under reducing conditions and goes to the refining stage in a reduced state, then it is sometimes necessary to re-oxidize the molten mass. The function of the refining step of method 80 of the present invention is to introduce into the molten mass of the medium. oxidizing. All these aims are achieved with the preferred method of implementation shown in FIG. 2. Vigorous agitation in the refining step promotes not only the change in the oxidation state of the melt, but also the addition of dyes, contaminants or relatively easily melting modifying additives. A wide variety of products can therefore be produced. The preferred method of carrying out the refining step shown in FIG. 2 employs a subsurface combustion process in both chambers. For some applications single-chamber refining is sufficient, but the window glass manufacturing process must be carried out in two subsurface combustion chambers 26 and 27 with molten tanks 28 and 29. The chambers are provided with oxygen tubing 30 and 31. and water-cooled burners 32 and 33 located below the melt level. Sub-surface hollow opening 34 allows substance to flow from chamber 26 into chamber 27. An opening 35 in the upper portion of chamber 26 allows molten material to flow from the melt step into the mosquito 26. The exhaust gases from the melting step 8 and the first 55 of step 1 may flow through port 35 into the refining stage. There may be an outlet at the top of chamber 26 (not shown in Fig. 2). Chamber 27 has a gas outlet port 36 at its top. 60 Fuel, such as natural gas, and an oxidant, preferably oxygen, are fed in. to burners 32 and 33, and combustion occurs when the gas stream contacts the melt tanks 28 and 29. Another fuel that may be used in subsurface burners 85 is hydrogen, since its combustion product is water. well soluble in molten glass. The use of oxygen as an oxidizing agent is advantageous since it thus avoids the introduction of nitrogen from the air into the melt which is poorly soluble in the molten glass. The use of diluted oxygen also improves the contact between the oxygen and the reduced components of the molten mass. An excess of oxidant, compared to the amount of fuel, may be fed to the burners to improve the degree of oxidation of the molten material entering the refining stage. Alternatively, if the melt entering the refining step contains a sufficient amount of unused carbon, the solder, unless raising the melt temperature is necessary, only oxygen may be pumped into the melt tanks 28 and 29 for the sole purpose of reoxidizing the feed. be fed with the omission of subsurface burners, for example through delivery pipes 30 and 31. It is preferable to use both oxygen bubbler and subsurface combustion at the same time. The burners can be adapted to deliver a stream of oxidant melt bubbles, which increases the surface area of the melt with the oxidant, and vigorous mixing due to subsurface combustion promotes the distribution of the oxidant bubbles in the molten mass. Sub-surface combustion also causes homogenization of the melt. The excess of oxidant supplied to the refining stage depends on the specific conditions, and therefore on the degree of reduction of the substance entering this stage and the required degree of oxidation of the final product. The factors important in the reoxidation process are the intensity of agitation, the size and shape of the vessel, the effectiveness of the gas-liquid contact and the residence time during the refining stage. In order to achieve the homogeneous oxidation required for window glass, it is advisable to re-oxidize in two successive chambers as shown in the figure to ensure that each portion of the melt is oxidized at the appropriate residence time. the reduced state is manifested by a brown color due to the presence of sulfur in the form of sulphides and iron. If a colorless glass is produced, the reoxidation leads to an increase in the degree of oxidation of the colored ions, expressed by the ratio of Fe + a / Fe + 2. For standard commercial grade clear glass, this ratio is from about 1.5 to 3.0 with a transmittance of at least 70% (preferably at least 80%) for a light with a wavelength of 380 nm and a thickness of 6 mm. This circle is sometimes characterized by 60% transmittance for a wavelength of 1000 nm (6th of the thickness). Much higher Fe + 3 / Fe + 2 ratios of oxygen bubbles were achieved in a dark brown colored molten glass. The fading of the color during the oxidation is readily perceptible and thus the degree of oxidation can be easily determined from the observation. Although the carbon may increase the iron content of the melt, the reoxidation produces a colorless glass. However, precise spectroscopic measurements by comparison with standard glass transmittance. may indicate the need to reduce the amount of iron that is usually deliberately added (in the form of polishing rose) to obtain the color. Behind the reoxidation chambers may be a conditioning chamber in which the product remains for a certain time necessary for the escape of gaseous gases. inclusions from the melt M and cooling the melt to a temperature suitable for further processing. The molten substance flows into the conditioning chamber 37 through the sub-sectional opening 38. In the system shown, the residence time in the chamber 37 15 is additionally extended by the subsurface baffle 39 and the upper baffle 40, forcing a complex flow of the melt stream. The processed melt may leave the refining step through a channel 41 leading to a forming step or the like 20, where, in the case of glass, it is rendered in the form of glass panes, fibers, bottles and the like by known methods. It is laid in the fusing stage. A pre-heating step is not needed here. By separating the melt step from the remainder of the smelting process, an environment is created in which most, practically all, of the ash contained in the fuel 30 can be included in the product without compromising the homogeneity of the product. The rapid outflow of the molten substance from the melting stage ensures that it is well mixed, and the processing in the following steps is made to subject the melt and the molten slag to further homogenization. Moreover, since the melting takes place in a relatively thin layer, the fuel mixed with the feed has easy access to oxygen so that the combustion is substantially complete. 40 As with other embodiments, the fuel may be fed to the combustion zone separately. but rather it is desirable to feed a mixture of fuel and charge to the melting stage. The use of an oxygen supply is also desirable. Incomplete combustion of the fuel in the melt stage leads to a portion of the reduced molten substance being fed to the refining stage, which may need to be corrected. Thus, in this method of implementation, the function of the refining step is to introduce an oxidizing agent into the molten mass. The amount of carbon used in the fusion zone depends, of course, on the calorific value of the grade of carbon concerned, which in turn depends on its elemental carbon content. When using the Pennsylvania coal mentioned above, the addition of carbon in an amount of about 0% by weight of the batch theoretically provides all the energy required for the fusing step of the batch to produce the window glass. However, due to the low combustion efficiency resulting from the lack of oxygen access to some of the carbon, it is advisable to use a little more than theoretically required amount of carbon if the carbon is to provide all the energy for the melting step. For example, it is advisable to add carbon in an amount of about 10% 17 148 248 18 by weight based on the feed. Coal fuels other than coal may be added in amounts determined by their calorific value. The method according to the invention also allows the energy requirement of the melting stage by the carbon contained in the feed to be not fully met. In this case, some of the energy is supplied by the coal from the charge and the remainder is provided by a conventional burner or other heating device in the fusing chamber. (excluding sulfur-containing fluxes such as sodium sulfate technical or gypsum) was mixed with 5% to 6% by weight of coal and melted at a yield of about 6.8 kg per hour. entering the refining stage was foamed and had a brown color. Each of the reoxidation chambers was equipped with a single subsurface burner and a discharge tube. Each of the subsurface burners was supplied with 7 m3 / h of hydrogen and 3.6 m3 / h of oxygen. Each of the pressing tubes was supplied with 0.56 m3 of oxygen per hour. The volume of the melt in each of the chambers ranged from 0.28 to 0.56 m3, and the average time of molten mass arrival in the refining stage was estimated to be about 30 minutes. The temperature of the first chamber was about 1290 ° C. and in the second, around 1370 ° C. An additional burner (not shown in Fig. 2) at the top of the chamber 47 was used to extinguish the foam. The glass drained from the refining step was colorless, nearly bubble-free, and more oxidized than commercial glass. The charge used should conventionally yield a glass with an iron content, based on Fe 2 O 3, of about 0.1% by weight. By transferring some iron to the carbon, the glass in the example contained 0.16 wt% carbon. The sulfur of the carbon caused the glass to contain 0.063 wt% SO3 without reoxidation being performed and less than 0.01% SO3 for reoxidation. Patent No. 1 A method of melting a glass charge or the like, in which the combustion of ash-containing fuel is used as the heat source for the process, characterized in that the liquid or solid fuel containing ash is mixed in direct contact with with the glass charge, the fuel is burned and the charge is heated, while the amount of fuel in the mixture is kept at a level sufficient to preheat the charge to a temperature slightly below the fusing temperature before the final liquefaction stage, or the amount of fuel is maintained be at a level ¦ sufficient to supply most of the heat necessary for the liquefaction, after the batch has reached the temperature is not slightly below its fusing point and the ash from the burnt fuel is left in the finished glass product. 2. The method according to p. The method of claim 1, wherein the ash-containing fuel is burned in a preheating step in which the feedstock is heated to a temperature slightly below the fusion temperature, and the feedstock is liquefied in the melting step, with the fuel agitated. mix with the batch before it is sent to the pre-heating stage. 3. The method according to p. The process of claim 2, wherein all the energy required for the preheating step is supplied with the fuel containing ashes. 4. The method according to claim 15 A process as claimed in claim 2 or 3, characterized in that in the preheating step, the feedstock is mixed in a rotary vessel as the feedstock moves from one end of the rotary vessel to the other. 5. The method according to p. The process according to claim 2 or 3, characterized in that a gas having an oxygen concentration higher than that in air is fed to the preheating stage to sustain combustion. 6. The method according to claim The process of claim 5, characterized in that oxygen is used as the source of oxygen. 7. The method according to p. The method of claim 2 or 6, characterized in that part of the oxygen for combustion of the fuel in the preheating step is provided in oxygen-containing feedstock. 8. The method according to p. A process as claimed in claim 2, characterized in that in the preheating step, the feedstock is transported in a co-flow and the flue gas in this step is passed in the opposite direction. 9. The method according to p. The process of claim 8, wherein combustion products from the preheating step are passed to the melting step. 10. The method according to p. The process of claim 8 or 9, wherein the gaseous oxygen source is introduced into the preheating vessel at an intermediate location distant from both the inlet and the outlet. '11. The method according to p. The process of claim 2, wherein the feedstock is fed to the preheating stage in loose and pulverulent form. 12. The method according to p. The process of claim 1, wherein the temperature of the combustion zone in the preheating step 50 is at least '. 900 ° C. 13. The method according to p. A process as claimed in any one of claims 1 to 12, characterized in that a feedstock containing alkaline earth metal carbonates is introduced into the preheating step, and the temperature is maintained in this step at a temperature sufficient to calcine a significant portion of the carbonates. 14. The method according to p. A method according to claim 13, characterized in that a substance which does not contain components which melt at temperatures below the calcination temperature is introduced into the preheating stage, and a feedstock which melts at temperatures below the calcination temperature, such as soda ash, is introduced into the liquefaction stage. . (148 248 19 15. A method according to claim 1, characterized in that the major part of the energy necessary to melt the feed substance is provided by burning the ash containing fuel in the discharge zone. that the molten substance is removed from the second zone in a reduced state and passed to the next zone, where the conditions for reoxidation prevail. The method of claim 17, wherein the material in the next zone is mixed by introducing flue gas into the interior of the molten substance. a zone divided into two chambers, the molten substance moves from one chamber to the other, with subsurface combustion taking place in each chamber. characterized in that the total amount of energy necessary to melt the feed material is provided by burning the ash containing fuel in the liquefaction zone. 21. The method according to p. The method of claim 15 or 20, characterized in that the molten material is discharged from the second zone in a partially unmelted state. 22. The method according to claim The process of claim 21, wherein the fuel is mixed with the feed just prior to feeding the feed to the liquefaction zone. 23. The method according to claim The method of claim 2, characterized in that the feed substances in the fluidization zone fuse on an inclined surface from which it flows freely. 24. The method according to claim 23. The method according to claim 23, characterized in that the feed material entering the leakage zone is deposited on the inclined surface surrounding the central cavity. 25. The method according to claim A method according to claim 24, characterized in that the charge material on the surface rotates around a central cavity. at 26. The process of claim 1, wherein the fuel is coal. 27. The method according to claim The method of claim 1, characterized in that the fuel used is a liquid petroleum product. 148 248 P / K 32 34 31 33 38 39 40 Fig. 2 EN EN EN EN

Claims (27)

1. Claims 1. A method of melting a glass or the like charge, in which the combustion of ash-containing fuel is used as the heat source for the process, characterized in that liquid or solid fuel containing ash is mixed directly before contact with the glass charge, this fuel is burned and the charge is heated, the quantity of fuel contained in the mixture being kept at a level sufficient to pre-heat the charge to a temperature slightly below the fusion temperature before the final liquefaction stage, or the quantity of fuel is maintained at a level sufficient to provide most of the heat necessary for the liquefaction after the charge has reached a temperature slightly below its fusing temperature and the ash from the burned fuel is left in the finished glass product. 2. The method according to p. The method of claim 1, wherein the ash-containing fuel is burned in a preheating step in which the feedstock is heated to a temperature slightly below the fusion temperature, and the feedstock is liquefied in the melting step, with the fuel agitated. mix with the batch before it is sent to the pre-heating stage. 3. The method according to p. The process of claim 2, wherein all the energy required for the preheating step is supplied with the fuel containing ashes. 15 4. The method according to p. A process as claimed in claim 2 or 3, characterized in that in the preheating step, the feedstock is mixed in a rotary vessel as the feedstock moves from one end of the rotary vessel to the other. 5. The method according to p. The process according to claim 2 or 3, characterized in that a gas having an oxygen concentration higher than that in air is fed to the preheating stage to sustain combustion. 25 6. The method according to p. The process of claim 5, characterized in that oxygen is used as the source of oxygen. 7. The method according to p. The method of claim 2 or 6, characterized in that part of the oxygen for combustion of the fuel in the preheating step is provided in oxygen-containing feedstock. 8. The method according to p. A process as claimed in claim 2, characterized in that in the preheating step, the feedstock is transported in a co-flow and the flue gas in this step is passed in the opposite direction. 9. The method according to p. The process of claim 8, wherein combustion products from the preheating step are passed to the melting step. 10. The method according to p. The process of claim 8 or 9, wherein the gaseous oxygen source is introduced into the preheating vessel at an intermediate location distant from both the inlet and the outlet. ' 11. The method according to p. The process of claim 2, wherein the feedstock is fed to the preheating stage in loose and pulverulent form. 12. The method according to p. The process of claim 1, wherein the temperature of the combustion zone in the preheating step 50 is at least '. 900 ° C. 13. The method according to p. A process as claimed in any one of claims 1 to 12, characterized in that a feedstock containing alkaline earth metal carbonates is introduced into the preheating step, and the temperature is maintained in this step at a temperature sufficient to calcine a significant portion of the carbonates. 14. The method according to p. A method according to claim 13, characterized in that a substance which does not contain components which melt at temperatures below the calcination temperature is introduced into the preheating stage, and a feedstock which melts at temperatures below the calcination temperature, such as soda ash, is introduced into the liquefaction stage. . (148 248 19 15. The method according to p. The method of claim 1, wherein the major part of the energy necessary to melt the feedstock is supplied by burning the ash-containing fuel in the liquefaction zone. 16. The method according to p. The method of claim 15, wherein the molten substance is removed from the second zone in a reduced state and passed to the next zone where the conditions for reoxidation prevail. 17. The method according to p. The process of claim 16, wherein the oxidative condition is maintained in the next zone by introducing gaseous oxygen into the interior of the molten substance. 18. The method according to p. A process as claimed in claim 17, characterized in that the material in the next zone is mixed by introducing flue gas into the interior of the molten material. 19. The method according to claim 17. The process of claim 17, wherein in the next zone divided into two chambers the molten substance moves from one chamber to the other, with subsurface combustion taking place in each chamber. 20. The method according to p. The method of claim 15, characterized in that the total amount of energy necessary to melt the feed substance is provided by burning the ash-containing fuel in the liquefaction zone. 21. The method according to p. The method of claim 15 or 20, characterized in that the molten material is discharged from the second zone in a partially unmelted state. 22. The method according to claim The process of claim 21, wherein the fuel is mixed with the feed just prior to feeding the feed to the liquefaction zone. 23. The method according to claim The method of claim 2, characterized in that the feed substances in the fluidization zone fuse on an inclined surface from which it flows freely. 24. The method according to claim 23. The method according to claim 23, characterized in that the feed material entering the leakage zone is deposited on the inclined surface surrounding the central cavity. 25. The method according to claim A method according to claim 24, characterized in that the charge material on the surface rotates around a central cavity. in 26. The method according to claim The process of claim 1, wherein the fuel is coal. 27. The method according to claim The method of claim 1, characterized in that the fuel used is a liquid petroleum product. 148 248 P / K 32 34 31 33 38 39 40 Fig. 2 EN EN EN EN