METHOD OF MAKING MINERAL FIBRES

Abstract

The invention provides a method to form a melt for making man-made vitreous fibres, in which mineral raw material is melted in a gas-fired cyclone furnace and the mineral charge comprises a material that comprises metallic aluminium.

Claims

1. A method of making man-made vitreous fibres (MMVF) which comprise at least 3 wt % iron oxides determined as Fe.sub.2O.sub.3, the method comprising providing a cyclone furnace, providing mineral raw material comprising (a) material that comprises metallic aluminium and (b) other mineral component, providing fuel and combustion gas to the cyclone furnace, melting the mineral raw material in the cyclone furnace to form a mineral melt, and forming MMVF from the melt.

2. A method according to claim 1 wherein the material comprising metallic aluminium is particulate.

3. A method according to claim 1, wherein the material that comprises metallic aluminium is alu-dross.

4. A method according to claim 3 also comprising providing a cyclone preheater system in connection with the cyclone furnace, forming hot exhaust gases in the cyclone furnace, and transporting hot exhaust gases from the cyclone furnace to the cyclone preheater system, wherein the alu-dross enters the cyclone preheater system before being melted in the cyclone furnace such that the alu-dross is pre-heated prior to the melting step.

5. A method according to claim 4, wherein the cyclone preheater system comprises a first cyclone preheater and a second cyclone preheater, wherein the exhaust gases are transported from the cyclone furnace to the first cyclone preheater and from the first cyclone preheater to the second cyclone preheater, and from the second cyclone preheater to an exhaust outlet, wherein the alu-dross is mixed with the other mineral component and the resulting mineral raw material is introduced to the second cyclone preheater, transported from the second cyclone preheater to the first cyclone preheater, and then transported from the first cyclone preheater to the cyclone furnace.

6. A method according to claim 4, wherein the cyclone preheater system comprises a first cyclone preheater and a second cyclone preheater, wherein the exhaust gases are transported from the cyclone furnace to the first cyclone preheater and from the first cyclone preheater to the second cyclone preheater, and from the second cyclone preheater to an exhaust outlet, wherein the other mineral component is introduced to the second cyclone preheater and is transported from the second cyclone preheater to the first cyclone preheater, wherein the alu-dross is introduced to the first cyclone preheater and mixes with the other mineral component in the flow of exhaust gases to form the mineral raw material, and wherein the mineral raw material is transported from the first cyclone preheater to the cyclone furnace.

7. A method according to claim 2, wherein the alu-dross comprises from 0.5 to 10 wt % metallic aluminium and from 50 to 90 wt % aluminium oxide.

8. A method according to claim 1, wherein from 5 to 30 wt % of the mineral raw material is alu-dross.

9. A method according to claim 1 wherein the material that comprises metallic aluminium is a material comprising from 45 to 100 wt % metallic aluminium.

10. A method according to claim 9, wherein the material that comprises metallic aluminium is aluminium granulate.

11. A method according to claim 10 wherein the aluminium granulate is added by direct injection into the cyclone furnace.

12. A method according to claim 1, wherein the mineral raw material comprises from 0.1 to 0.5 wt % metallic aluminium.

13. A method according to claim 1 wherein the fuel is gaseous.

14. A method according to claim 1, wherein the fibres have a ratio of Fe(II):Fe(III) of above 2, such as above 3.

15. A method according to claim 1, further comprising consolidating the MMVF to form a consolidated product comprising the fibres.

16. A method according to claim 1, wherein the MMVF have a content of oxides, as wt. %, as follows: SiO.sub.2 35 to 50 Al.sub.2O.sub.3 12 to 30 TiO.sub.2 up to 2 Fe.sub.2O.sub.3 3 to 12 CaO 5 to 30 MgO up to 15 Na.sub.2O 0 to 15 K.sub.2O 0 to 15 P.sub.2O.sub.5 up to 3 MnO up to 3 B.sub.2O.sub.3 up to 3.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0087] FIG. 1 illustrates an exemplary layout of the cyclone furnace and cyclone preheater system.

DETAILED DESCRIPTION

[0088] FIG. 1 shows a cyclone furnace 1 which comprises a cylindrical top section, a frustoconical bottom section and a cylindrical base section. Preheated mineral material (with or without the component that is the source of metallic aluminium) is introduced into the cyclone furnace via a mixed mineral material conduit 3. The fuel is introduced via conduit 2. The mineral material is introduced together with combustion air via conduit 4 and secondary air which is provided in compressed air supply 5 and is introduced through a lance (not shown) into the cyclone furnace to ensure thorough mixing of the fuel with the combustion air and to sustain the circulating motion of the combustion gases and suspended material in the cyclone furnace 1. A minor amount of combustion gas and fuel are diverted from the main feed which leads to the top section of the cyclone furnace, to the bottom section of the cyclone furnace via routes which are shown in FIG. 1 as 6 and 7 respectively. Secondary fuel, such as natural gas, is also injected through supply 8 into the base section of the cyclone furnace, shown in FIG. 1 as 8.

[0089] The fuel is combusted in the combustion gas, which is preferably pure oxygen or oxygen-enriched air, in the cyclone furnace, thereby melting the mineral charge.

[0090] When alu-dross is used as the source of metallic aluminium, the alu-dross may be mixed with the other mineral component and then supplied to silo 19. From silo 19, the mineral charge, including alu-dross, is supplied to second conduit 14 and undergoes initial preheating in second preheater cyclone 13. The mineral charge is then introduced into first conduit 11 and subsequently passes to the first preheater cyclone 12. This option has the benefit of easily maintaining a stable relation between the metallic aluminium content and the other mineral components of the mineral charge.

[0091] Alternatively when alu-dross is used as the source of metallic aluminium, the alu-dross may be provided at ambient temperature to silo 20 and from silo 20 to the first conduit downstream to the other mineral components of the mineral charge, which is supplied from silo 19 as described above in the first option. The alu-dross mixes with the preheated other mineral component in the airflow. This option is useful when the alu-dross comprises some residual ammonia and there are restrictions on the amount of ammonia in the flue gas.

[0092] Another option is to include alu-dross directly into the cyclone furnace 1 at conduit 3. This option is less thermally efficient, but does ensure complete decomposition of any residual ammonia in the alu-dross due to the high temperature in the cyclone furnace 1.

[0093] When aluminium granulate or aluminium blocks are used as the source of metallic aluminium, the metallic aluminium is added directly to the cyclone furnace 1.

[0094] Metallic aluminium could be provided as aluminium granulate and added at location 8 via an oxy-fuel burner with a central injection lance for the metallic aluminium. The other mineral charge is provided from silo 19 and preheated as described above.

[0095] Alternatively, metallic aluminium could be provided in block form, shaped as a rod, bar, or lump. Block form aluminium is preferably added to the cyclone furnace separately from particulate mineral raw material and may be added directly to the melt pool. Smaller Al blocks may be injected into the furnace via burner ports. Larger Al blocks may be injected into the furnace from an inlet in the top of the furnace. Bulk aluminium may be blown or otherwise injected directly into the melt pool at the base of the furnace; this may be preferable to minimise oxidation of aluminium in the circulating gases within the furnace, thereby maximising the effect of the metallic aluminium interacting with the other mineral components.

[0096] In all all cases, the mineral charge is melted in the cyclone furnace 1 and the resultant mineral melt is collected in the base zone of the cyclone furnace 1 and exits the furnace via outlet 9. The exhaust gases that are generated from combustion of the fuel are fed through flue 10 at the top of the circulating combustion chamber to the first conduit 11 where they are used to heat the mineral materials. The exhaust gases then flow to a first cyclone preheater 12 where they are separated from the mineral charge. The exhaust gases flow from the first cyclone preheater 12 to the second cyclone preheater 13 via a second conduit 14. Following the second cyclone preheater 13 the exhaust gases flow through conduit 15 to a dust cyclone 16 and into a chamber 17 where indirect heat exchange with the combustion gas occurs to preheat the combustion gas. The exhaust gases are then treated to make them safe to pass to the atmosphere such as by filter 18 and, if needed, a DeSOx plant. Filter fines may be collected from filter 18 and recycled into the furnace 1.

[0097] Some of the mineral charge may be carried up with the exhaust gases from the second cyclone preheater 13 through conduit 15. This is separated from the exhaust gases in dust cyclone 16 and recycled back to join the preheated mineral materials via conduit 22.

[0098] The exhaust gases leave the circulating combustion chamber via a flue 10. The exhaust gases enter the first conduit 11 and are quenched from a temperature of between 1500 and 1900° C., usually around 1650° C. to a temperature of between 900 and 1200° C., normally around 1100° C. by quenching air. The provision of hot exhaust gases at temperatures greater than 800° C. is beneficial in particular when there is a need to remove ammonia from alu-dross prior to melting.

[0099] The raw materials used as the other mineral components of the mineral charge can be selected from a variety of sources, as is known. These include basalt, diabase, nepheline syenite, glass cullet, bauxite, quartz sand, limestone, rasorite, sodium tetraborate, dolomite, soda, olivine sand, potash. Waste materials may also be used.

[0100] The MMV fibres may be made from the mineral melt in conventional manner. Generally they are made by a centrifugal fibre-forming process.

[0101] For instance the fibres may be formed by a spinning cup process in which they are thrown outwardly through perforations in a spinning cup. The melt is fiberised by the spinning cup technology (also sometimes described as internal centrifugation). The melt preferably has a temperature at the end of the feeder channel in the range 1260° C.-1300° C. before it is led to the spinning cup. The melt preferably cools down when it is transferred from the feeder channel to the internal part of the spinning cup in such a way that the temperature for the melt when flowing through the perforations of the spinning cup is in the range 1150° C.-1220° C.

[0102] The viscosity of the melt in the spinning cup is in the range of 50 to 400 Pa.Math.s, preferably 100 to 320 Pa s, more preferably 150-270 Pa.Math.s. If the viscosity is too low, fibres of the desired thickness are not formed. If the viscosity is too high, the melt does not flow through the apertures in the spinning cup at the right pull rate, which can lead to blocking of the apertures in the spinning cup.

[0103] The melt is preferably fiberised by the spinning cup method at a temperature between 1160 and 1210° C. The viscosity of the melt is preferably in the range 100-320 Pa.Math.s at the spinning temperature.

[0104] In an alternative fibre-forming method, melt may be thrown off a rotating disc and fibre formation may be promoted by blasting jets of gas through the melt.

[0105] In a preferred method fibre formation is conducted by pouring the melt onto the first rotor in a cascade spinner. Preferably in this case the melt is poured onto the first of a set of two, three or four rotors, each of which rotates about a substantially horizontal axis whereby melt on the first rotor is primarily thrown onto the second (lower) rotor although some may be thrown off the first rotor as fibres, and melt on the second rotor is thrown off as fibres although some may be thrown towards the third (lower) rotor, and so forth.

[0106] The MMVF may be collected and consolidated to form a consolidated product comprising the MMVF. Typically such product may comprise additional ingredients such as binder, with MMVF being the major component. The fibres resulting from the spinning process are preferably collected on a conveyor belt.

[0107] Binder can be applied to the MMVF either during the fiberisation process, or post fiberisation. The binder may be applied by spraying the MMVF. Conventional types of binder for use with stone wool fibres may be used. The binder is then cured to produce a final product. The MMVF with binder is generally cured in a curing oven, usually by means of a hot air stream. The hot air stream may be introduced into the MMVF with binder from below, or above or from alternating directions in distinctive zones in the length direction of the curing oven. After curing, the cured binder composition binds the fibres to form a structurally coherent matrix of fibres.

[0108] The MMVF may be consolidated after collection, for instance by cross-lapping and/or longitudinal compression and/or vertical compression, in known manner. Usually consolidation occurs prior to curing of binder.

[0109] The MMVF produced by the method of the present invention, and the MMVF of the invention, have excellent fire resistance at 1000° C. The MMVF can be made into a product for use in any of the conventional applications for MMVF, such as sound or heat insulation or fire protection. Such products include insulation products such as batts, granulate, boards, rolls, pipe sections, and other products such as ceiling tiles, wall tiles, façade elements, acoustic elements and loose fibres. The product may be used in high temperature environments, such as at least 400° C. up to 1000° C.

[0110] The product may have any of the densities known in the art for the relevant application. For instance it may be in the range 20 to 1200 kg/m.sup.3, preferably 20 to 300 kg/m.sup.3, more preferably 20 to 150 kg/m.sup.3. Shrinkage benefits are seen for all product types, but it is observed that especially good shrinkage reduction is seen when the density of the product is relatively low, for instance not more than 50 kg/m.sup.3.

[0111] Any preferred features disclosed in this application are disclosed in combination with any other preferred feature.

EXAMPLES

Example 1

[0112] Reference samples of consolidated MMVF products were prepared from a mineral melt (reference charge) having the following composition:

TABLE-US-00002 TABLE 2 SiO.sub.2 Al.sub.2O.sub.3 TiO.sub.2 Fe.sub.2O.sub.3 FeO CaO MgO Na.sub.2O K.sub.2O P.sub.2O.sub.5 MnO 42.6 18.5 0.5 6.9 0.0 18.9 9.2 1.9 0.8 0.2 0.5

[0113] The reference consolidated products were manufactured to a density of 30 kg/m.sup.3. The mineral melt was prepared in a cyclone furnace in accordance with FIG. 1.

[0114] Invention samples of consolidated MMVF products were manufactured using MMVF spun from a mineral charge having the composition of Table 2 with the addition of 0.4 wt % Al granulate (equivalent to 0.2 wt % metallic Al). The added Al granulate was in addition to all of the components listed in Table 2. The densities of the example products were also 30 kg/m.sup.3.

[0115] The area shrinkage of the reference products and the example products was measured according to an internal test method consisting of 5 steps:

[0116] 1) cutting, measuring and weighing test specimens from product test unit;

[0117] 2) selecting representative test specimens from test unit;

[0118] 3) removing binder at 590° C.;

[0119] 4) sintering test specimens at 1000° C.+/−20° C. for 30 minutes; and

[0120] 5) Measure area of sintered test specimen.

[0121] The shrinkage is measured as a % reduction in surface area of each product. The major face of each product that is measured for shrinkage is equivalent to the major face that would be apparent in a finished product. For example, the reduction in length and width of a slab, but not its thickness, is measured.

[0122] Relative area shrinkage between raw material charge with and without addition of aluminium granulate

TABLE-US-00003 TABLE 3 aluminium granulate tests Shrinkage of reference Shrinkage of invention Sample Number samples samples 1 87.7 72.7 2 103.6 79.0 3 83.7 75.0 4 117.6 5 107.6 Normalised average 100.0 75.6 shrinkage

Example 2

[0123] Reference samples were prepared in the same way as for Example 1.

[0124] Invention samples were prepared in the same way as the reference samples, but with the addition of alu-dross.

TABLE-US-00004 TABLE 4 alu-dross tests Shrinkage of reference Shrinkage of invention Sample number samples samples 1 100.2 45.6 2 99.8 51.2 3 46.5 4 54.1 Normalised average 100.0 49.4 shrinkage