METHOD AND MELTING FURNACE FOR MANUFACTURING GLASS

Abstract: A melting furnace for glass manufacture which is provided at its one end (1) with an infeed opening (7) for batch material (6), and which has at its other end molten-glass outfeed means (12). The furnace includes at least one furnace burner (10, 11) which together with molten material (8) present in the furnace heats and melts the batch material charged to the furnace and present in the form of a layer on the melt, during movement of the batch material towards the other end (2) of the furnace, so that the batch material mixes with the melt. The furnace also includes at least one further burner (13) of the so-called oxygen-fuel-type at the infeed-end (1) of the furnace, so as to achieve additional, intensive heating of batch material (6) charged to the furnace, in combination with at least one further burner (14) of the so-called oxygen-fuel-type provided to achieve additional, intensive heating of the molten material (8) essentially in the hottest zone (9) of the melt. The invention also relates to a method for use when manufacturing glass in a melting furnace.

Description: METHOD AND MELTING FURNACE FOR MANUFACTURING GLASS The present invention relates to a method for manufac¬ turing glass in a melting furnace, in which glass batch material is charged to the furnace at one end thereof and forms a blanket layer on molten bath material present in the furnace and is heated by said molten material and by the flame of at least one furnace burner, such as to melt during its passage to the other end of the furnace and mix with said molten bath mater¬ ial, and in which molten glass is taken-out at said other end of the furnace. The invention also relates to a melting furnace for use when manufacturing glass in accordance with this method. In order to obtain a high quality glass in glass manu¬ facturing processes according to the aforegoing, it is necessary to ensure that the glass mixture is highly homogenous, which presumes that the incoming, succes- sively melting glass batch material is well mixed with the molten glass already present in the furnace. For reasons of economy, on the other hand, it is de¬ sired to reduce the residence time of the molten glass mass in the furnace, so as to increase the amount of molten glass produced for each unit of energy applied for heating and melting the glass material. It is also desirable to enable the capacity of existing furnace systems to be increased. Thus, in order to achieve optimum results, it is neces¬ sary to adapt the through-flow rate to correspond to the melting energy that can be utilized and the admix¬ ture that can be achieved. The amount of energy which can be supplied to the furnace is limited, inter alia. by the fact that the resultant furnace temperature must not be excessively high. Normally, it is the furnace arch or furnace vault temperature at the hottest point in the furnace which is determinative in this respect. Mixing efficiency is dependent on temperature gradients in the molten bath, since admixture of the glass melt is totally dependent on the flows that can be achieved in the bath. Convective flows are highly significant to admixture and homogenization of the glass mass in con- ventional melters, although other factors, such as the introduction of batch material into the furnace and the removal of molten glass therefrom also influence the movements occurring in the glass mass. In the conventional operation of melters equipped with side-mounted furnace burners, attempts are made to maintain two major flows in the glass mass, namely one in a molten zone which extends from the infeed end to the hottest zone in the furnace, which normally lies at a distance in the order to 2/3rdε to 3/4ths of the fur¬ nace length from said infeed end, and a flow in a fining zone extending between the hottest zone of the furnace and the removal end thereof. These flows occur because molten glass will always tend to flow in a direction towards a point of lower tem¬ perature. Hot glass which rises to the surface in the hottest zone of the melt will thus flow towards the colder input end in and beneath the surface layer of the molten bath and the batch material floating thereon which is dissolved successively in the melt. As the glass cools, when approaching the infeed end, the density of the glass becomes higher, therewith result¬ ing in a downward flow which then returns to the hot- test zone, along the bottom of the furnace. Another flow in the upper layer of the melt is directed from the hottest zone towards the removal end of the furnace, which is colder and where the flow is directed downwards. That part of the melt which is not be removed from the furnace returns to the hottest zone, along the furnace bottom. The position of the hottest zone is controlled with this type of furnace by means of the furnace burners. As those skilled in this art are aware, desired flows are achieved correspondingly in the glass mass in a melter in which the furnace burner is located at the inlet end of the furnace. With the intention of improving the productivity of a melter equipped with side-mounted furnace burners, it has been proposed, see WO82/04246, to provide the furnace with a pair of mutually opposing, highly- intensive burners of the so-called oxi-fuel type, these burners being directed onto the free liquid surface of the melt in order to reinforce and supply additional heat to the hottest zone of the furnace. Only a limited degree of additional heating can be achieved with this technique, since the temperature of the brick lining located above the surface of the glass in this zone is normally already quite close to the critical tempera¬ ture of the lining material. Furthermore, booster energy is supplied relatively late in the process, which reduces the usefulness of this energy. The earlier booster energy can be supplied, the easier it is to increase production rate, since this will result, inter alia, in more rapid melting and improved fining of the melt, i.e. more complete degasification of the melt. The European Patent Specification 0 127 513 describes a glass melting method in which the glass batch material is heated intensively at the infeed end of the furnace with the aid of an oxygen-fuel-burner. This enables a large amount of booster energy to be supplied to the furnace, without placing limitations on the furnace arch. When large quantities of thermal energy are supplied at the inlet end of the furnace, however, the desired temperature profile in the furnace is changed in an undesirable manner, and consequently those tem¬ perature gradients required in the melt for producing the convection currents needed for mixing, homogenizing and fining the molten glass are not obtained. In the case of high production rates, there is consequently a risk that glass batch material will pass through the hottest zone without melting sufficiently and without being homogenized with the remainder of the melt, therewith resulting in glass of low quality and also a glass which will contain a greater number of bubbles. A main object of the present invention is to provide a glass manufacturing method which will enable additional thermal energy to be supplied so as to increased pro¬ duction yield without detriment to the quality of the molten glass taken from the furnace. The present invention is based on the realization that considerable additional thermal energy, or booster energy, can be supplied to the glass batch material at the infeed end of the furnace, inter alia, with the intention of accelerating melting of the glass batch material, provided that additional thermal energy is also supplied to the melt at its hottest point at the same time, thereby maintaining in the melt the tem- perature gradients required to achieve the desired convection currents therein. Another object of the invention is to provide a melting furnace for the manufacture of glass which operates in accordance with the method. A method according to the invention and of the kind defined in the introductory paragraph of the descrip¬ tion is particularly characterized by combining addi¬ tional, intensive heating of the batch material at the infeed end of the furnace with the aid of at least one so-called oxygen-fuel-burner, with additional, inten¬ sive heating of the molten material in the furnace substantially in the hottest zone with the aid of at least one further so-called oxygen-fuel-burner. This method thus enables heating of the glass batch material and the molten glass mass to be intensified, so as to increase production yield while maintaining quality as a result of maintaining in the melt the convection currents necessary for mixing and homo¬ genizing the glass mass. Remaining characteristic features of the inventive method and of an inventive melting furnace operating in accordanpe with the method are set forth in the following claims. The invention will now be described in more detail with reference to exemplifying embodiments thereof and with reference to the accompanying drawings. Figure 1 is a longitudinal-sectional " View of an inventive melting furnace. Figure 2 is a cross-sectional view of the furnace illustrated in Figure 1. Figure 3 is a view of the furnace of Figure 1 from above and partly in section and illustrates the burner positions. Figure 4 is a view corresponding to Figure 3 with respect to a furnace equipped with end-mounted furnace burners. The melter illustrated in Figures 1-3 is of the kind equipped with side-mounted furnace burners. The furnace includes a rear end-wall 1 and a front end- and parti¬ tion wall 2, a bottom 3, an arched roof 4 and two side- walls 5. The glass batch material 6, from which the glass is manufactured and which may possibly contain crushed glass, and desired minerals, is charged through an infeed opening 7 in the rear end-wall 1. The batch material charged to the furnace will therewith float on the relatively highly-viscous bath 8 of molten glass present in the furnace. As the batch material 6 moves forwards in the furnace while being heated by both the flames of the burners and the underlying hot glass bath 8, the batch material will melt and mix with the molten glass. All of the batch material will have melted into the underlying molten glass, when reaching the hottest zone of the bath 8, this zone being referenced 9. The side-mounted burners comprise fuel-supply nozzles 10, which fuel may be either gas or oil, and relatively large openings 11 for the passage of combustion air and waste gases. The same number of burners is provided on both side-walls and the air openings 11 preferably communicate with regenerators 15 arranged along the sides of the furnace, these regenerators being shown schematically in Figures 2 and 3. When the furnace is in operation, the burners on one side-wall of the furnace are used alternately with the burners on the other side-wall, the hot combustion gases passing out through the openings 11 in the side-wall whose burners are at that moment inactive. The combustion gases function to heat the regenerators, the heat of which is subsequently used to pre-heat the combustion air when the burners on this side-wall of the furnace are activated. The burners are controlled so that the hottest zone 9 in the glass bath 8 will be located at the position desired, normally at a distance from the inlet end 1 corresponding to 2/3rds to 3/4ths of the length of the furnace. It is endeavoured therewith to produce flows in the molten bath caused by temperature gradients in said mass, along the paths illustrated by the arrows A and B respectively. Molten glass, which in both paths returns to the hottest zone 9 along the bottom 3 of the furnace, rises towards the surface of the bath at said point and is divided into two flows which are directed towards the colder regions at the rear end-wall and the front end-wall of the furnace respectively, where the glass sinks to the bottom and then returns to the hot¬ test zone. No account has been taken of lateral flows, among other things, in this somewhat simplified ex¬ planation. The flows discussed above, however, repre- sent the main flows desired in the majority of melters. The region extending from the infeed opening 7 to the hottest zone 9 represents a melting zone in which glass batch material 6 charged to the furnace is melted down in the molten glass 8. The region extending between the hottest zone 9 and the front end-wall 2 of the furnace forms a fining zone, in which final homogenization of the glass 8 takes place and gas bubbles are permitted to leave the glass bath. The final, homogenized glass is removed through an outfeed opening 12 and supplied to subsequent glass-manufacturing machines. For the purpose of accelerating and rendering more effective the processes of melting batch material 6 charged to the furnace and homogenization of the molten glass 8, in accordance with the invention, there is provided at the infeed end of the furnace at least one, and in the illustrated embodiment two, highly- effective booster burners 13 of the oxygen-fuel-type. The flames of these burners are directed onto the still solid batch material, so as to accelerate heating of said material. The burners are fed with a mixture of fuel and oxygen, so that the flame temperatures will be very high, and consequently non-combustible consti- tuentε of atmospheric air need not be heated in the burners. This results in more effective combustion. However, if this additional thermal energy were only to be supplied at the infeed end of the furnace, the temperature gradients in the mass, and therewith the flow conditions, would be changed and result in im¬ paired homogenization and when removal of the glass mass is increased, there is a risk that non-molten batch material will pass through the melting zone and into the fining zone. The time for.obtaining complete degasifying in the fining zone can therewith also be excessively short. For the purpose of solving these problems in accordance with the invention, the booster burners 13 are combined with at least one further burner, in the illustrated embodiment two mutually opposing burners 14 of the so- called oxygen-fuel-type mounted on the side-walls 5 of the furnace. The flames of these burners are preferably directed obliquely down onto the surface of the bath at the position corresponding to the hottest zone 9 in said bath. The temperature in the hottest zone is increased with the aid of these burners, therewith enabling the temperature profile of the furnace and the temperature gradients in the bath to be optimized essentially in a manner commensurate with that in a furnace which is not provided with booster burners. It will be seen from Figure 2 that the booster burners 14 are directed slightly downwards onto the bath sur¬ face, suitable angles of inclination may be 0-30 * , preferably 10-20 * . The burners may also be directed slightly obliquely to the inlet end of the furnace. As shown in Figure 3, the booster burners 13 mounted at the infeed end of the furnace are directed obliquely forwards and inwards in relation to the feed direction of the batch material 6. The precise positioning and alignment of both the burners 13 and the burners 14 may, however, be determined in dependence on the type of furnace used and on prevailing operating conditions. The number of burners may also be varied as desired, although the hub of the invention is that additional thermal energy, or booster energy, is supplied to the furnace at both the infeed-end thereof and in essen¬ tially the hottest zone of the furnace. The described oxygen-fuel-type burners used to boost thermal energy may also be used to replace one or more conventional furnace burners. When the furnace is in operation, all booster burners can be activated simultaneously or, alternatively, only those booster burners which are located on the same side as those typical furnace burners which are active at that time. The oxygen-fuel-burners used may have any desired configuration and may, for instance, comprise burners of the kind sold by AGA AB under the designation "Oxy- fuel-burners". A suitable power range is from 0.1-4 MW per burner. The combustible gas used is preferably natural gas, although other gases may, of course, also be used. Figure 4 is a schematic illustration of the invention as applied in a melter of the kind in which the conven¬ tional furnace flame 16 has a horseshoe configuration and departs from a burner 17 and 18 respectively on one side of the rear end-wall 21 of the furnace, the waste gases being sucked out through an opening 19 and 20 provided in the opposite side of said end-wall. The air openings 19, 20 also communicate with a respective regenerator 22 and 23, and consequently the combustion air can be pre-heated by alternating between the two burners^ such as to reverse the flow of air through said openings. The numeral 24 identifies an inlet opening through which batch material is charged to the furnace, and the ultimate glass mass is removed through the outfeed opening 25. In the case of the illustrated embodiment, additional, intensive heating of the batch material is achieved with the aid of a highly-intensive burner 26 of the so- called oxygen-fuel-type located between the air open- ings 19, 20. In order to maintain a desired temperature profile in the furnace, the furnace is provided, in accordance with the invention, with two additional booster burners 27, 28 of the so-called oxygen-fuel- type, the flames of which additionally heat the molten glass in the hottest zone of the furnace, in a manner similar to that described with reference to the earlier embodiment. Depending on requirements or operating conditions, it is possible, also in this case, to either activate one or both of the mutually opposing booster burners 27, 28. The single burner 26 on the rear end-wall 21 of the furnace can be supplemented with an additional booster burner optionally located for achieving desired heating of batch material charged to the furnace. Thus, when applying the present invention, it is pos¬ sible to supply more energy so as to melt the batch material more rapidly without exceeding the critical arch temperature of the furnace, since a major part of this additional or booster energy can be supplied at the beginning of the melting zone where arch tempera¬ ture is relatively low. Trials have shown that this also results in a higher yield, i.e. a larger quantity of molten glass can be taken from the furnace for each unit of energy supplied, while maintaining high quality. This is achieved, inter alia, because the batch material is melted at an early stage in the furnace and because the temperature gradients required to achieve effective mixture and homogenization of the glass melts are maintained at the same time as the glass temperature in both the melting zone and the fining zone are increased. This elevated temperature in the fining zone enables, inter alia, gas bubbles to leave the nolten bath more readily.

Claims: 1. A method for manufacturing glass in a melting furnace, in which batch material is charged to the furnace at one end thereof, this material forming a blanket layer on molten material present in the furnace and being heated by said molten material and by the flame from at least one furnace burner, so that the batch material will melt and admix with said molten material during its movement towards the other end of the furnace, and in which molten glass is taken out at said other end of the furnace, and in which method additional, intensive heating of the material in the furnace is effected with the aid of at least one so- called oxygen-fuel-burner, partly at the infeed-end of the furnace and partly downstream of said infeed-end, c h a r a c t e r i z e d by achieving through said oxygen-fuel-burner located downstream of the infeed-end of the furnace additional, intensive heating of the molten material in said furnace substantially in the hottest zone therein. 2. A method according to Claim 1, c h a r a c ¬ t e r i z e d by achieving said additional, intensive heating of the molten material in the furnace in said hottest zone with the aid of two mutually opposing so- called oxygen-fuel-burners, which are directed obli¬ quely downwards onto the surface of the molten bath. 3. A method according to Claim 1 or 2, c h a r a c - t e r i z e d by achieving the additional, intensive heating of the batch material at the infeed-end of the furnace with the aid of two so-called oxygen-fuel- burners which are directed from the sides of the fur¬ nace obliquely inwards and forwards onto a longitudinal centre line of the furnace. 4. A method according to Claim 2 or 3, c h a r a c ¬ t e r i z e d by activating the oxygen-fuel-burnerε mounted on one side of the furnace alternately with the oxygen-fuel-burners mounted along the other side of the furnace. 5. A method according to any one of Claims 1-4, when applied in a furnace having two typical furnace burners mounted on the rear end-wall of said furnace, c h a r a c t e r i z e d by achieving said additional, intensive heating of the batch material at the infeed- end of the furnace with the aid of a so-called oxygen- fuel-burner mounted between the two existing typical furnace burners. 6. A melting furnace for glass manufacture, said furnace having provided at one end (1) thereof an infeed opening (7) through which batch material (6) is charged, and which includes at least one furnace burner (10, 11), the flame of which are operative, together with molten glass (8) present in the furnace, to heat and melt the batch material charged to the furnace and present in the form of a layer on said molten glass during the passage of said batch material towards the other end (2) of the furnace, such that said batch material is mixed with said molten glass, and which furnace has molten glass outfeed means (12) provided at its other end, and which furnace further includes one burner (13) of the so-called oxygen-fuel-type at the infeed-end (1) of the furnace in combination with at least one further burner (14) of the so-called oxygen- fuel-type downstream of said infeed-end, c h a r a c - t e r i z e d in that the oxygen-fuel-burner (14) mounted downstream of the infeed-end of the furnace is operative to achieve additional, intensive heating of the molten material (8) in the furnace, essentially in the hottest zone (9) thereof. 7. A melting furnace according to Claim 6, c h a r - a c t e r i z e d in that it includes two mutually opposing so-called oxygen-fuel-burners (14) at the position of the hottest zone (9) in the furnace. 8. A melting furnace according to Claim 6 or 7, c h a r a c t e r i z e d in that the furnace includes at its infeed-end (1) two so-called oxygen-fuel-burners (13), each of which is mounted on a respective side of a longitudinal centre line of the furnace and which are directed obliquely inwards and forwards to said centre line. 9. A melting furnace according to Claim 6, of the kind provided with two typical furnace burners (17, 18) in the rear end-wall (21) thereof, c h a r a c t e r i z e d in that the furnace further includes a burner (26) of the so-called oxygen-fuel-type mounted between the two typical furnace burners (17, 18). 10. A melting furnace according to any one of Claims 6-9, c h a r a c t e r i z e d in that the oxygen-fuel- burners (13, 14; 26, 27, 28) form an angle of 0-30", preferably 10-20 * to the horizontal plane.

Inventors: ANGEL RICHARD, ANGEL, RICHARD
Applicants: AGA AB
Application year: 1990
Main classification: C03B5
IPC codes: C03B5