A METHOD AND AN APPARATUS FOR PRODUCING MINERAL WOOL

Abstract: The present invention relates to a method of producing mineral wool, mineral raw material (2) is introduced into a melting unit (3), preferably a cupola furnace, for heating the mineral raw material in such a manner that molten mineral material (4) is formed on the bottom of the melting unit, whereafter the molten mineral material is discharged from the melting unit, heated further, and introduced along at least one tapping chute (8, 9) into a spinning machine (10) in which the mineral material is converted into fibre form. In order to make the mineral melt homogeneous and to ensure that the high quality of the obtained mineral wool, the method according to the invention is characterized in that said further heating is carried out by heating the molten mineral material (4') by means of electric plasma, the plasma heating being carried out in the tapping chute (9) while the molten mineral material (4') flows in the tapping chute so as to obtain a rapid adjustment of the temperature of the molten mineral material and to introduce the molten mineral material into the spinning machine (10) at an even temperature.

Description: A method and an apparatus for producing mineral wool The present invention relates to a method of producing mineral wool, wherein mineral raw material is introduced into a melting unit, preferably a cupola furnace, for heating the mineral raw material in such a manner that ' molten mineral material is formed on the bottom of the melting unit, whereafter the molten mineral material is discharged from the melting unit, heated further and introduced along at least one tapping chute into a spinning machine in which the mineral material is converted into fibre form. The invention is also concerned with an appar¬ atus for the production of mineral wool, comprising a feeding device, a melting ' unit, preferably a cupola furnace, a transport device comprising a tapping chute, an additional heating device and a spinning machine, the feeding device being intended for the supply of mineral raw material into the melting unit, the melting unit for heating the mineral material into molten mineral material, the transport device for transporting the molten mineral material from the melting unit to the spinning machine, the additional heating device for further heating the molten mineral material from the melting unit prior to its introduc¬ tion into the spinning machine, and the spinning machine being intended for producing mineral material in fibre form. Iή the production of mineral wool it is import- ant that the molten material to be introduced into the spinning machine -is homogeneous, which requires ' hat the melt should have accurately defined temperature and viscosity as well as a composition such that it is formed into fibres of desired length and thickness in the spinning machine. In practice, even and homogene- ous raw materials are used in an attempt to achieve a homogeneous melt, whereby the viscosity of the melt depends on temperature which should kept as even as possible. The cupola furnace, which is the most frequent¬ ly used melting unit in the production of mineral wool, does not, however, melt the raw material even¬ ly, which is partly due to the fact that the melt stays only about two minutes on an average on the fur- nace bottom before it is discharged from the furnace. Therefore it is not possible to obtain a homogeneous melt in the cupola furnace, which, however, is neces¬ sary for carrying out the spinning operation success¬ fully. It is even more difficult to obtain a constant temperature in the melt before its introduction into the furnace since so called iron tappings have to be carried out intermittently during the process and since the molten mineral material cools when it flows in the tapping chute between the cupola furnace and the spinning machine. The cooling affects adversely the fibre formation properties of the molten mineral material. The temperature of the melt from a cupola fur¬ nace normally varies from 1400 to 1500°C with a melt composition of about 60% of AI2O3 + Siθ2- In a normal case, a temperature of about 1460°C is a preferred operating temperature for spinning. It is known that instead of trying to at once obtain the right operating temperature, it is usually easier to first melt the material to a lower tempera¬ ture ranging from 1400 to 1460°C and then raise the temperature to the required operating temperature by supplying additional energy. This is carried out, e.g., by means of an intermediate container provided with an oil or gas burner, whereby the melt is heated by the hot flame primarily through radiation. However, such an intermediate container has to comprise a heat transfer surface of several square metres to be able to raise the temperature of 5 tons of melt by 100°C in one hour. FI Patent Application 2943/68 discloses the use of an intermediate container connected between a spinning machine and a furnace in which the mineral material is to be melted. The intermediate container comprises an electrode furnace and its function is to eliminate variations in the composition of the mineral material. A problem with the intermediate container is that it has to possess a high capacity in order to be able to compensate for variations in the composition of the molten mineral material. High capacity involves large size, which is not only undesirable as such but also results in great heat losses to the surroundings in practice. The intermediate container is therefore expensive to manufacture and maintain. Since the intermediate container is formed by a conventional electrode furnace, the temperature of the molten ma¬ terial cannot be adjusted sufficiently rapidly to be able to introduce mineral melt at an even temperature into the spinning machine, thus ensuring the high quality of the final product. FI Patent Specification 41435 discloses produc¬ tion of mineral wool. This prior art method uses an intermediate container comprising a channel-type in¬ duction furnace with a capacity many times greater than that of the melting furnace. The channel-type conduction furnace is heated by means of an inductor unit which allows the molten material to be mixed. In practice, this prior art method has the same problems as the apparatus of FI Patent Application 2943/68. SE Patent Specification 8504074-9, publication number 451714, describes a burner the function of which is to prevent the solidification and accumula¬ tion of material in the tapping chute between the cupola furnace and the spinning machine. This burner, which heats the material stream, is arranged at the opening of the tapping chute. FI Patent Application 880135 discloses a method of producing mineral wool. The method uses a shaft furnace in which the mineral material is melted by plasma heating. Since the plasma heating is effected within the shaft furnace, high local temperatures in the furnace cause the following problems: First, despite the plasma heating, the temperature of the molten mineral material cannot be adjusted sufficient- ly rapidly if a rapid adjustment is needed due to, e.g., greater variations in the composition and physi¬ cal properties (size and shape) of the fed mineral ma¬ terial. Second, greater amounts of nitrogen oxides are formed, which is undesirable and/or unallowed from the environmental point of view and therefore the method requires an expensive gas purification plant. Third, the method does not allow for efficient recov¬ ery of the iron oxides contained in the mineral raw material. The present invention, which solves the prob¬ lems associated with the production of mineral wool by prior art methods, especially in connection with pro¬ duction carried out by means of a cupola furnace, is concerned with a method and an apparatus for economi- cal production of high-quality mineral wool. The method is mainly characterized in that said further heating is carried out by heating the molten mineral material by means of electric plasma, the plasma heating being carried out in the tapping chute while the molten mineral material flows in the tapping chute so as to obtain a rapid adjustment of the temperature of the molten mineral material and to introduce the molten mineral material into the spinning machine at an even temperature. The apparatus according to the invention, in turn, "is characterized in that the addi¬ tional heating device is formed by a plasma heating device arranged in the tapping chute for heating the molten mineral material while it flows in the tapping chute. The invention is based on the idea that the molten mineral material is heated rapidly by means of electric plasma shortly prior to its introduction into the spinning machine. One major advantage of the method of the inven- tion is that the molten mineral material is made high¬ ly homogeneous that the fibres formed in the spinning machine are of desired shape, that is, they are suffi¬ ciently long and have uniform diameter, which ensures the high quality of the final product. The final prod- uct so obtained has good, uniform thermal and mech¬ anical properties. Furthermore, no local cooled por¬ tions are formed in the molten mineral material, whereby the formation of "pearls" is avoided, which is an advantage in that such pearls are either rejected as waste or they deteriorate or spoil the quality of the final product. The structure of the apparatus according to the invention is particularly advantageous in that it can be effected substantially by means of standard compo- nents. Accordingly, the apparatus can be advantageous¬ ly realized by modifying existing apparatuses. In the following the invention will be de¬ scribed in more detail by means of a preferred embodi¬ ment with reference to the attached drawing, wherein Figure 1 is a schematic view of the production of mineral wool; Figure 2 is an enlarged sectional view of a de¬ tail of the apparatus of Figure 1; and Figure 3 is ' a cross-sectional view of the tapping chute shown in Figure 2 along the line III- III. Figure 1 shows schematically the apparatus of the invention for the production of mineral wool. The apparatus comprises a feeding device 1 for introducing mineral raw material 2 into a cupola furnace 3. The mineral raw material 2 is heated in the cupola furnace 3 by burning coke up to a temperature sufficient to form molten mineral material 4 in the bottom of the cupola furnace 3. Iron melt 5 is positioned undermost in the bottom of the cupola furnace. The bottom of the cupola furnace 3 is provided with a tapping spout 6 through which the molten mineral material is trans¬ ported to a spinning machine generally indicated with the reference numeral 10 via a transport device gen- erally indicated with the reference numeral 7 and com¬ prising two tapping chutes 8 and 9. The transport de¬ vice 7 is connected to an additional heating device 11 which consists of a plasma heating device. This heats further the molten mineral material prior to its introduction into the spinning machine 10. The spinning machine, which comprises a number of rotating wheels, converts the molten mineral material into thin fibres by means of the centrifugal force. In a spinning chamber 12 the thin fibres are sucked against a transport band 13 on which a thick fibre mat 14 is formed. From the spinning chamber 12 the fibre 14 mat is passed into the following process step: the fibre mat is cured, pressed, and cut into sheets of desired shape, whereafter the sheets are piled and packed. When the molten mineral material leaves the cupola furnace 3, its temperature is adjusted to about 1400°C, that is, to a value 50 to 70°C lower that what is desirable at the spinning machine 10. In prac¬ tice, a temperature adjustment to 1400°C involves that the temperature of the molten mineral material varies between about 1450°C and 1300°C. Accordingly, the tem¬ perature of the molten mineral material has to be raised by about 20 to 150°C by means of the plasma de¬ vice. The plasma heating device 11, of the TA (Trans¬ ferred Arch) type, is described in more detail in con¬ nection with Figure 2. The use of the TA type plasma heating device is to be preferred since it is able to supply great amounts of energy " into the molten mineral material within a short time. Temperatures of about 15 000 K can be obtained between the electrodes in this type of device. The device requires that the ma¬ terial to be heated is electrically conductive, which the molten mineral material is. It appears from Figure 2 how the plasma device is connected to the tapping chute 9 of the apparatus. Molten mineral material is fed from the tapping chute 8 to the tapping chute 9. The tapping chute 9 is mostly covered by a cover 15 so as to prevent heat losses from the flowing molten min- eral material into the surroundings. A covered tapping chute is to be preferred also for the reason that it prevents the molten mineral material from splashing off the tapping chute. The molten mineral material in the tappi-ng chute 9 is indicated with 4' and the iron melt separated from the mineral material with 5'. The tapping chute 9 is thereby provided with a space 16 for the separation of iron drops. In addition, the tapping chute 9 is tiltable and provided with a back- wardly directed outlet opening 17 for the discharge of the iron melt 5' so that it will not enter the spinn- ing machine. The plasma heating device 11 is connected to the tapping chute 9 in such a manner that its nega¬ tive plasma electrode 18 is positioned in the cover 15 above the molten material 4', 5' and the positive electrode 19 is positioned under the molten material in such a manner that it is in direct contact with the iron melt 5' . This connection of the plasma elec¬ trodes 18, 19 makes the electrical plasma go through the molten mineral material while this moves, where- fore the transfer of heat from the plasma to the molten mineral material is particularly efficient. The temperature of the molten mineral material can be ad¬ justed rapidly by controlling the capacity between the electrodes 18, 19 by means of a plasma energy supply unit 20. The plasma heating device 11 comprises a thermometer 21, such as an optical pyrometer which measures the temperature of the molten mineral ma¬ terial when it emerges from the cupola furnace. The pyrometer 21 is connected to a ^ regulator 22 which, in turn, is connected, with a suitable delay dependent on the melt flow, to the plasma energy supply unit 20. By means of the electric plasma the molten mineral ma¬ terial is heated up to a temperature such that the viscosity of the molten material is improved before it reaches the spinning machine 10. It is to be seen from Figure 2 that the- spinning machine comprises a number of rotating spinning wheels the direction of ro¬ tation of which is shown with arrows. Thin mineral fibres project from the spinning wheels. These fibres are of even and high quality due to the homogeneity of the molten mineral material obtained by means of the additional plasma heating. Figure 3 shows the tapping chute 9 of Figure 2 as seen along the section III-III. The invention has been described above with reference to a preferred embodiment. It is to be understood that the invention, however, can be realized in many different ways within the scope of the idea of the invention and the attached claims. The geometry of the tapping chute can, of course, vary. It is further to be noted that the plasma heat¬ ing device need not necessarily be of the TA type; a plasma device of the NTA (Non Transferred Arc) type can be used as well. This type of plasma provides arc temperatures of about 3000 to 4000°C, which is noticeably less than with the TA type. It is also typical of the NTA type that the plasma is applied to the surface of the molten material only. This involves that the molten material has to be mixed efficiently in order that the heat of transfer would take place efficiently. An advantage of the NTA type is that it does not otherwise put such high requirements on the process. Inert carrier gas is used on applying electric plasma, preferably nitrogen and argon for ef- ficient transport and transfer of plasma energy to the molten mineral material. Irrespective of the type of plasma device, the number of the electrodes as well as their accurate position can vary. The melting unit used in the embodiment described is a cupola furnace, which is to be preferred in the realization of the in¬ vention; alternatively, the melting unit can be an electric furnace, for instance.

Claims: Claims : 1. A method of producing mineral wool, wherein mineral raw material (2) is introduced into a melting unit (3) , preferably a cupola furnace, for heating the mineral raw material in such a manner that molten min¬ eral material (4) is formed on the bottom of the melting unit, whereafter the molten mineral material is discharged from the melting unit, heated further and introduced along at least one tapping chute (8, 9) into a spinning machine (10) in which the mineral ma¬ terial is converted into fibre form, c h a r a c¬ t e r i z e d in that said further heating is carried out by heating the molten mineral material (4 1 ) by means of electric plasma, the plasma heating being carried out in the tapping chute (9) while the molten mineral material (4 1 ) flows in the tapping chute so as to obtain a rapid adjustment of the temperature of the molten mineral material and to introduce the molten mineral material into the spinning machine (10) at an even temperature. 2. A method according to claim 1, c h a r a c¬ t e r i z e d in that the temperature of the molten mineral material (4 1 ) is raised by means of the plasma heating by about 20 to 150°C. 3. A method according to claim 1, c h a r a c¬ t e r i z e d in that inert carrier gas is used in the plasma heating so as to transfer the plasma energy efficiently into the molten mineral material. 4. A method according to any of the preceding claims, c h a r a c t e r i z e d in that it utilizes a plasma heating device of the TA (Transferred Arc) type. 5. An apparatus for the production of mineral wool, comprising a feeding device (1), a melting unit (3), preferably a cupola furnace, a transport device (7) comprising a tapping chute (8, 9), an additional heating device (11) and a .spinning machine (10), the feeding device being intended for the supply of min- eral raw material .. (2) into the melting unit, the melting unit for heating the mineral material into molten mineral material (4), the transport device for transporting the molten mineral material from the melting unit to the spinning machine, the additional heating device for further heating the molten mineral material (4') from the melting unit prior to its introduction into the spinning machine, and the spinning machine being intended for producing mineral material in fibre form, c h a r a c t e r i z e d in that the additional heating device is formed by a plasma heating device (11) arranged in the tapping chute (9) for heating the molten mineral material (4' ) while it flows in the tapping chute. 6. An apparatus according to claim 5, c h a r- a c t e r i z e d in that the plasma heating device ' (11) comprises a negative plasma electrode (18) ar¬ ranged above the molten mineral material (4' ) in the tapping chute (9), and a positive plasma electrode (19) arranged under the molten mineral material (4 1 ) in the tapping chute in direct contact therewith, a thermometer (21) for measuring the temperature of the molten mineral material immediately before it is introduced into the spinning machine (10), the thermo¬ meter being connected to a plasma energy supply unit (20) which is controlled by a regulator (22) connected between it and the thermometer. 7. An apparatus according to claim 6, c h a r¬ a c t e r i z e d in that the tapping chute (9) is tiltable and its bottom comprises a space (16) for the separation of iron drops, and it is provided with a backwardly directed outlet (17) for the discharge of molten iron (5') .

Inventors: LAUREN HENNING JOHN EMIL, SOLIN PETER ARNOLD HENRIK, LAUREN, HENNING, JOHN, EMIL, SOLIN, PETER, ARNOLD, HENRIK
Applicants: PARTEK AB, OY PARTEK AB
Application year: 1989
Main classification: C03B5
IPC codes: C03B5, C03B37