Process for recycling waste mineral material

Abstract

There is provided a delivery system for supplying waste mineral material to a furnace. The system comprises a passage and conveyor arranged in use to move material along the passage to an outlet; and an airlock connected to the passage and through which material is able to pass in use. The airlock is arranged in use to maintain a pressure differential across the airlock. A process for preparing a mineral melt and a cupola furnace are also provided.

Description

[0001] PROCESS FOR RECYCLING WASTE MINERAL MATERIAL

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a process for preparing a mineral melt in a cupola furnace using a plasma torch to heat mineral material and waste or recycled mineral material to form the melt and delivery of the waste or recycled material to the furnace. Typically, the waste or recycled mineral material is introduced into the furnace through a waste inlet located in the side wall of the furnace hot zone.

[0004] BACKGROUND

[0005] Methods of preparing a mineral melt for the production of man-made mineral fibres (MMVF), such as glass fibre or stone fibre, are known to be carried out in shaft furnaces, such as cupola furnaces. These methods involve heating mineral material to form the mineral melt. The heating may be provided by any means, but it is traditionally carried out in the presence of coke and an oxygen-containing gas, or by passing an electrical current between two or more electrodes, e.g. graphite or molybdenum electrodes. The mineral material may also be melted using a plasma torch.

[0006] Spinning processes used to form MMVF inevitably produce various by-products that form waste mineral material. This waste mineral material may be in the form of fine powder-like materials, such as that formed when MMVF is cut, or it may be fibrous in nature. In addition, MMVF products that have served their useful lifetime, such as MMVF insulation removed during building renovation, are also considered waste mineral material. Waste mineral material may comprise binder that was used during the MMVF manufacturing process. The waste may also be in a cured or non-cured state.

[0007] As an alternative to its disposal in landfill sites, waste mineral material may be recycled by combining it with other (conventional) mineral material and heating it to form a mineral melt. That mineral melt may then be spun into new MMVF products. Despite the benefits of recycling waste mineral material, it cannot simply be combined with conventional mineral material and added to the furnace in the usual way. Direct introduction of waste mineral material into a shaft furnace, such as placing it on the top of the mineral stack, is unacceptable. Due to the various geometries of waste mineral material, e.g. fine powders and fibrous material, and its insulating properties it may choke or suffocate the furnace by preventing offgas from travelling up through the mineral stack, by restricting the flow of oxygen through tuyeres and oxygen injection ports of the furnace, or restricting the flow of plasma from a plasma torch into the furnace. This greatly decreases the efficiency of a furnace and may also cause the melting process to fail.

[0008] Waste mineral material may be processed to form briquettes that may be added to a shaft furnace together with conventional mineral material. However, the briquetting process requires the addition of binder to the waste mineral melt, which exacerbates the environmental problems. The use of these briquettes is also unattractive as it increases the complexity and cost of the recycling process and is therefore unattractive on an industrial scale.

[0009] Further, the pressure inside a cupola furnace is typically higher than ambient pressure. This means pressure generally needs to be applied to introduce the waste mineral material or other material into the furnace. To maintain this pressure and avoid gases leaving the furnace a sealed environment is provided. However, providing waste mineral material into the furnace breaks this seal.

[0010] There is therefore a need for an improved method of forming a melt suitable for use in the formation of mineral fibre that uses waste mineral material.

[0011] SUMMARY OF INVENTION

[0012] According to a first aspect there is provided a delivery system for (i.e. suitable for) supplying waste mineral material to a furnace, the system comprising: a passage and conveyor arranged in use to move material along the passage to an outlet; an airlock connected to the passage and through which material is able to pass in use, the airlock being arranged in use to maintain a pressure differential across the airlock.

[0013] This allows a raised pressure (such as above standard atmospheric pressure of about 101 kiloPascals (kPa)) to be maintained on one side of the airlock while allowing material, such as waste mineral material to be provided to a destination, such as a furnace. This avoids backflow of gas or other material from the destination while allowing transition of material from a lower to a higher pressure region and environment. Ultimately, this helps maintain component lifetime by maintaining the condition of an environment on either side of the airlock.

[0014] It is intended that passage is defined by a duct or pipe, but may be provided by any suitable container capable of holding and allowing passage of gas and solid material.

[0015] The passage and conveyor may be arranged horizontally or orientated upward. Typically, however, at least a downstream portion of the passage and conveyor may be arranged at an angle relative to a horizontal axis with a downstream end of the passage and conveyor being a lowest point. This assists with movement of material along the passage and conveyor and reduces the chances of a blockage forming since gravity assists with movement of the material.

[0016] The whole of the passage and conveyor may be arranged in this manner. Typically though, there is a bend in the passage between an upstream portion and the downstream portion. The airlock may be located upstream of the bend and / or the conveyor may be located downstream of the bend.

[0017] As well as being defined as the airlock being “connected to” the passage, since the passage may be provided on either side of the airlock in some examples, or the airlock is provided within the passage, the airlock can be considered to form part of the passage. This is intended to be consistent with the “connected to” language.

[0018] The furnace is intended to be a cupola furnace. The airlock may be a chamber between airtight openings or barriers. The airtight openings or barriers may inhibit air and gas transmission across the airlock. The inhibition of air and gas transmission may be within predetermined tolerances, such as manufacture tolerances.

[0019] The airlock typically may provide a separation between different environments or areas, such as by isolating different areas from each other, and / or may provide an intermediate or transitional space between different areas. This may be achieved by use of the airtight openings or barriers. While the areas may simply be isolated from each other, and the same conditions may be in each area, typically, the airlock provides isolation of areas of different conditions from each other. This may be by providing isolation of areas of typically different pressure and / or temperature, but may include areas of different gas or fluid mix, gas movement amounts or type, solid material content and / or heating conditions.

[0020] The airlock may have one or more compartments. The one or more compartments may define the chamber or be in place of the chamber. The airlock may be a single stage, such as by providing (only) one compartment, area or transition space that regulates pressure change across it. Typically, however, the airlock is a multi-stage airlock arranged in use to maintain the pressure differential across the airlock stages. This allows for manufacturing tolerances in (stages of) the airlock and unavoidable or inadvertent leakage while still maintaining pressure differential overall. The multi-stage airlock is intended to provide a plurality of barriers separated from each other, and each maintaining a different pressure differential across the respective barrier. Each barrier may be in the form of a compartment, area or transition space or may be in the form of a block or other stoppage through which or via which material is able to pass.

[0021] The multi-stage airlock is intended to be an airlock with a plurality of stages instead of an airlock with a single stage (only). In some arrangements, a single-stage airlock could be implemented, however.

[0022] The passage may include a supply pipe arranged in use to hold material. When implementing a multi-stage airlock, material in the supply pipe may provide an airlock stage. While there are circumstances in which material in the supply pipe would not provide an airlock stage, the material providing the airlock stage means the system is able to maintain pressure itself using material passing through it. This reduces need for further components, thus decreasing maintenance requirements and limiting component count. By limiting component count, there is a reduction in component failure and events that may compromise pressure maintenance in the system.

[0023] The supply pipe may be provided at the inlet of the passage, such as by providing the most upstream part of the passage. The supply pipe may be separated from the passage inlet. Should this be the case, the supply pipe may still be upstream of other components, such as (other) components of the airlock and / or conveyor.

[0024] The airlock may include a drive arranged in use to engage material and push engaged material from a low pressure side of the airlock to a high pressure side of the airlock. This provides a mechanism able to transport material across the airlock in an active manner.

[0025] The drive may include one or more vanes against which material rests on engagement with the drive, each vane being moveable from the low pressure side of the airlock to the high pressure side of the airlock. The one or more vanes provide a surface to engage material in order to move it through the airlock.

[0026] The one or more vanes may form part of a rotary feeder, the rotary feeder being arranged in use to provide the airlock with a rotary airlock. This provides a capability of moving material and maintaining material flow while providing a seal or preventing / limiting gas flow from a higher pressure area to a lower pressure area.

[0027] The rotary feeder may be a self-cleaning rotary feeder. This increases throughput and reduces wear or damage caused by material being left behind since there is a reduction in material left in the rotary feeder after cleaning compared to if there was no self-cleaning. To achieve self-cleaning, the rotary feeder may include a scraper arranged in use to pass over each vane thereby removing material. This provides active removal, which may enhance the benefit or help in case there is material stuck or adhered to a surface being cleaned.

[0028] The conveyor may form part of the airlock, or may be within the airlock. In some circumstances, the conveyor may be upstream of the airlock. Typically, however, the conveyor may be downstream of the airlock (upstream and downstream may be defined relative to the direction in which material is passed to the furnace). In other words, the airlock and the conveyor may be arranged sequentially, such as with the conveyor being after the airlock, in (or relative to) the direction in which material is passed to the furnace.

[0029] Irrespective of whether the conveyor is upstream of, downstream of, or sequentially with the airlock, in those arrangements, and others, the airlock and conveyor may be separate features and / or components from each other. For instance, typically, the conveyor and airlock may be independent of each other. This may be while still forming part of the delivery system, such as by being adjacent to each other, following on from each other and / or forming part of the path along which material is supplied to the furnace. By “independent” we intend to mean that the airlock and conveyor are not part of the same component or feature but may still be in contact or connected to each other. This may be achieved by the airlock and conveyor being located at different, separate, and / or non-overlapping parts of a path along which waste material is supplied to the furnace, such as by the delivery system.

[0030] Considered in another way, in use, the airlock may be arranged to move, such as to supply, material to the conveyor. This may be achieved through one or more components of the airlock, such as one of the one or more vanes pushing material towards the conveyor. This allows for material to be moved along the delivery system between the stages or components of the path along with the material is supplied. As demonstrated by various of the options above, and consistent with the detail set out above regarding the intention of the airlock as being defined as “connected to” the passage, the airlock may provide a part of the structure through which the material passes. This is instead of the airlock being provided only when material is present in the delivery system. In this manner, the airlock is capable of functioning and providing a block separating the inside of the furnace from the surrounding environment without material being present in the delivery system. This limits outflow from the furnace when the delivery system is not in use.

[0031] In other words, the airlock may define a portion of a path along which the material passes. This may be achieved by the airlock providing a conduit through which the material is able to pass in use, such as by having one or more walls forming or defining the conduit or the shape of the conduit. The material may be able to pass along the conduit under the influence of gravity and / or by being moved by one or more components of the airlock, such as by the one or more vanes.

[0032] The delivery system may further comprise a continuously open outlet to the furnace. This outlet is intended to be the outlet to which the passage and conveyor are arranged in use to move material along the passage to. While an outlet at the furnace could be closable, having a persistently open outlet allows for material to be provided when it is available and also reduces the likelihood of failure of any closure mechanism that would be in a difficult location to service.

[0033] When the continuously open outlet is provided, the airlock may be separated from the outlet, thereby maintaining the pressure differential away from the outlet. This provides distance between the airlock and outlet into the furnace making servicing of the airlock easier and reducing the airlock’s exposure to heat when the furnace is in use.

[0034] The delivery system outlet may provide an inlet in the furnace.

[0035] The conveyor may be located with an end at the opening.

[0036] The separation of the airlock from the outlet may be achieved by having the conveyor between the outlet and the airlock. The delivery system may further comprise a pressurisation device arranged in use to maintain the pressure between the outlet and the airlock at least at a threshold pressure. This provides an ability to top-up or increase pressure and to maintain pressure if the airlock allows passage of material through it or if there is a leak.

[0037] The pressurisation device may include a gas inlet connected to a gas source and to the passage downstream of the airlock. This provides a simple mechanism that requires no moving parts, and so limits wear on components.

[0038] The conveyor may include an auger conveyor arranged in use to transport material along the auger. This provides a mechanism capable of moving material while providing mechanical support for the material able to counteract pressure exerted on the material in the direction opposite to the direction of (intended) travel of the material.

[0039] The delivery system may further comprise a store connected to an inlet of the passage and arranged in use to hold material. The store may include a conveyor arranged in use to provide material to the inlet of the passage.

[0040] The store may include a transporter arranged in use to transfer material to the inlet, and may include a sensor arranged in use to monitor quantity of material transferred to the inlet. The rate of transfer by the transporter may be based on the monitored quantity. The sensor may be one or more load cells arranged to measure a mass or weight on the transporter or in the store and / or a change in mass or weight on the transporter or in the store. The transporter may be a conveyor, such as a belt conveyor or a plate conveyor. Using the arrangement of the transporter and sensor allows the amount of material passing through the system to be adjusted based on the amount of material provided to the inlet instead of being based on capacity of the downstream components to pass material through the passage. This reduces the chances of a blockage occurring. Further, providing the material, such as waste material, allows that material to make up a portion of the total material added to the furnace for forming the melt, reducing the quantity of previously unused material needed. According to a second aspect, there is provided a process for preparing a mineral melt in a cupola furnace, wherein the mineral melt is for the formation of mineral wool, the cupola furnace comprises: a hot zone at the base of the furnace; a melt outlet in the hot zone; at least one plasma torch that provides plasma heating to the hot zone, by way of a plasma jet that defines a cavity that is substantially void of solid material within the hot zone; a waste inlet located in the side wall of the furnace hot zone; and a delivery system according to any combination of features of the first aspect, the outlet being connected to the waste inlet and configured to deliver waste mineral material to the cavity defined by the plasma jet through the waste inlet, wherein mineral material and the waste mineral material supplied to the furnace is melted to form the mineral melt. An advantage of having the waste inlet located in the side wall is that the waste mineral material may easily move towards the cavity defined by the plasma jet due to gravity. This may be achievable due to the location in the side wall at which this material is provided, such as above or at the height of the cavity defined by the plasma jet.

[0041] Typically, the amount of waste mineral material used may be from 1 to 70%, such as 5 to 65%, or 35 to 65% or 55% to 60%, of the total weight of waste mineral material and mineral material. Formation of a mineral melt in a cupola furnace is usually a continuous process and therefore the ratio of waste mineral material to the combination of waste mineral material and mineral material may be measured over a certain time period. This is because the waste mineral material and / or mineral material may be added portion-wise to the cupola furnace.

[0042] The waste inlet may be located in the wall of the furnace above the point at which the plasma jet enters the furnace; and / or may have an area of from 3 centimetres squared (cm2) to 320 cm2, from 20 cm2to 180 cm2, or from 50 cm2to 115 cm2.

[0043] The distance between the edge of the orifice through which the plasma jet enters the furnace to the edge of the waste inlet is intended to be sufficient (such as sufficiently small) to ensure that the waste mineral material may be melted and incorporated into the mineral melt. This distance may be from 1 cm to 30 cm, from 5 cm to 20 cm, or from 7 cm to 12 cm. Often this distance is defined by the dimensions of water-cooling jackets of both the waste inlet and the plasma jet. The waste mineral material may be fed through the waste inlet by an auger conveyor; or a pneumatic tube transport. If using a pneumatic tube transport, this may use recycled off-gas from the cupola furnace of nitrogen gas (N2) or any other non-oxygen containing gas.

[0044] The cupola furnace may comprise two to five plasma torches, such as three or four plasma torches, located substantially in the horizontal plane around a perimeter of the furnace and substantially equidistant from each other, wherein the plasma jet from each plasma torch may extend towards the centre of the cupola furnace, with each plasma torch having an associated waste inlet. This allows the plasma jet from each plasma torch to extend towards the centre of the cupola furnace. To maximise the rate at which waste mineral material may be added to the furnace, each plasma torch may have an associated waste inlet.

[0045] The waste mineral material may be milled, such as by a rod mill. Any milling may occur prior to being introduced into the cupola furnace through the waste inlet.

[0046] If the waste mineral material is milled, the waste mineral material may be milled to a density of from 500 kilograms per cubic metre (kg / m3or kgm-3) to 1500 kg / m3, such as from 700 kg / m3to 1250 kg / m3, for instance from 800 kg / m3 to 1000 kg / m3. Milling the waste material to these densities means that it may more easily be added to the cupola furnace using the conveyor.

[0047] The furnace may be equipped with at least one tuyere and / or oxygen injection port providing a source of oxygen in the oxidation zone of the cupola furnace.

[0048] The process of the second aspect may be suitable in combination with the process set out in WO 2022 / 106592, the contents of which is incorporated herein by reference. That process is for the production of a mineral melt suitable for use in the formation of man-made vitreous (MMV) fibres, such as glass fibre or stone fibre, which process minimises an amount of NOXand H2produced in the off-gas of a cupola furnace even when a plasma torch is used. This advantage may be achieved when providing greater than 50% of the furnace heating energy may be provided by the at least one plasma torch. Greater than 60%, greater than 70%, greater than 80%, greater than 90% or all of the cupola furnace heating energy may be provided by the at least one plasma torch. Heating may be provided in the hot zone solely by the at least one plasma torch.

[0049] The above advantage may be further assisted by in examples where the at least one plasma torch may use as carrier gas nitrogen (N2), carbon monoxide (CO), carbon dioxide (CO2), or a mixture thereof. The carrier gas enthalpy may be from 2.0 to 6.0 kWh / Nm3, such as from 3.0 to 5.0 kWh / Nm3.

[0050] This advantage may be additionally supported in circumstances where water may be (substantially) excluded from any zone of the furnace where the temperature is above 750 °C.

[0051] The temperature in the oxidation zone may be below 1 ,400 degrees centigrade (°C). This allows NOXto be significantly reduced when oxygen is excluded from zones of a cupola furnace that comprise nitrogen.

[0052] To help minimise the production of NOX, the carrier gas, at most, should comprise only a trace amount of oxygen. This means that the carrier gas may comprise less than 5 weight% of oxygen, such as less than 2 weight%, preferably less than 0.8 weight%, based upon the total weight of the carrier gas. Typically, the carrier gas is devoid of oxygen. This means that there are, at most, only trace amounts of oxygen present.

[0053] The temperature in the hot zone may be greater than the temperature in the oxidation zone.

[0054] The temperature in the oxidation zone may be from 600 °C to 1 ,400 °C, from 600 °C to 1 ,300 °C, from 600 °C to 1 ,200 °C, from 600 °C to 1 , 100 °C, from 600 °C to 1 ,000 °C, from 600 °C to 900 °C, or from 600 °C to below 850 °C; and / or the temperature in the hot zone may be above 800 °C, above 900 °C, above 1 ,000 °C, above 1 ,100 °C, above 1 ,200 °C, above 1 ,300 °C, or above 1 ,400 °C. Operating within these temperature ranges limits formation of NOXsince NOXmay be derived from nitrogen and oxygen under high temperature. The mineral melt may have the following composition expressed as oxides, by weight%: SiO2, 35 - 50, 38-48, or 33-44; AI2O3, 12-30, 15-28, or 16-24; TiO2, up to 2; Fe2O3, 2-12; CaO, 5-30, or 8-20; MgO, 0-15, or 1-12; Na2O, 0-15; K2O, 0-15; P2O5, 0-3; MnO, 0-3; B2O3, 0-3.

[0055] The proportion of Fe(2+) in the mineral melt may be greater than 80% based on total Fe, at least 90%, at least 95% or at least 97% based on total Fe.

[0056] Further details of these example mineral melts may be found in WO 2012 / 140173, which is incorporated herein by reference.

[0057] As is conventional in the art, reference herein to Fe2O3in a mineral melt or fibre composition is intended to refer to the total amount of iron (calculated in terms of Fe2O3) in the melt or composition irrespective of the amount of each oxidation state of the iron present in the composition.

[0058] The carrier gas may comprise, or consist of, at least one component of off-gas produced by the furnace. The at least one component of the off-gas may undergo off-gas cleaning prior to its use as carrier gas. The off-gas cleaning may be to remove particles and / or water.

[0059] According to a third aspect, there may be provided a process for manufacturing man-made vitreous fibres (MMVF) comprising: forming a mineral melt using a process as defined in the second aspect; fiberising the mineral melt by means of a spinning process, such as internal or external spinning process, for example using a cascade spinner; and collecting the formed fibres.

[0060] According to a fourth aspect, there is provided a cupola furnace for preparation of a mineral melt according to a process of the second aspect.

[0061] In line with this, typically, the cupola furnace comprises: a hot zone at the base of the furnace; a melt outlet in the hot zone; at least one plasma torch that provides plasma heating to the hot zone in use, by way of a plasma jet that defines a cavity that is substantially void of solid material within the hot zone; a waste inlet located in the side wall of the furnace hot zone; and a delivery system according to any one of the preceding claims, the outlet being connected to the waste inlet and configured to deliver waste mineral material to the cavity defined by the plasma jet through the waste inlet, the furnace being arranged in use to receive mineral material and the waste mineral material, the mineral material and the waste mineral material being melted to form the mineral melt (such as by being received at the hot zone), the mineral melt being for the formation of mineral wool.

[0062] BRIEF DESCRIPTION OF DRAWINGS

[0063] Example delivery systems and processes are described below in relation to the accompanying figures, in which:

[0064] Figure 1 shows a schematic representation of a section of a cupola furnace configuration according to a first example;

[0065] Figure 2 shows a schematic arrangement of a cupola furnace configuration;

[0066] Figure 3 shows a second schematic arrangement of a cupola furnace configuration; and

[0067] Figure 4 shows a third schematic arrangement of a cupola furnace configuration.

[0068] DETAILED DESCRIPTION

[0069] We have, unexpectedly, found that a waste inlet located in the wall of the hot zone of a cupola furnace allows efficient and effective delivery of waste mineral material into a plasma jet. This is then melted to form a mineral melt, without the various disadvantages.

[0070] Cupola furnaces that are heated using plasma typically comprise a hot zone at the lower portion of the furnace, also referred to as the base of the furnace. One or more plasma torches provide heating to the hot zone at a level sufficient to melt mineral material (a mineral charge). The mineral melt thus forms a pool at the base of the hot zone, in the spaces between the structure supporting the stack of mineral material (usually the mineral material itself or coke is used in the process). Once a certain volume of mineral melt is produced, it is typically removed from the furnace through some form of melt outlet, such as a siphon. Once removed from the furnace, the mineral melt may be used to form man-made vitreous fibre (MMVF) by any suitable method, typically involving a spinning method.

[0071] Plasma torches generate thermal plasma using direct current (DC), alternating current (AC), radiofrequency (RF) and other discharges. Thermal plasmas provide heat, which in DC plasma torches is produced by sending an electric arc between two electrodes, through which arc a carrier gas is passed within a constricted opening. This elevates the temperature of the gas to the point that it enters a fourth state of matter, i.e. plasma. Plasma torches may be transferred or non-transferred. In non-transferred DC plasma torches, the electrodes are inside the housing of the torch. Whereas in a transferred plasma torch one electrode is located outside the housing of the torch (with the other inside the housing of the torch), allowing the arc to form outside of the plasma torch and over a greater distance. In some examples, the plasma torch is a non-transferred plasma torch. In various of those examples, the plasma torch is a direct current non-transferred plasma torch.

[0072] Plasma torches typically use a variety of carrier gases, such as oxygen, nitrogen, argon, helium, air, hydrogen, water steam, or mixtures thereof.

[0073] The one or more plasma torches are typically mounted on an external side of the furnace such that the thermal plasma generated, commonly referred to as a plasma jet, penetrates the hot zone of the furnace. The plasma jet may reach temperatures up to 7000°C, which is sufficient to melt the mineral material in its vicinity.

[0074] As the solid mineral material is melted (and subsequently removed from the furnace via the melt outlet), the stack of mineral material moves down through the furnace to replace it. It has been found that, in practice, the plasma jet defines a cavity (a three-dimensional shape) within the furnace that is substantially void of solid material, e.g. mineral material, waste mineral material, and coke. The temperature and environment within the plasma jet is such that the mineral material in the furnace will typically melt prior to entering the defined cavity, however, that cavity may comprise some solid material. For instance, a section of the stack of mineral material can become detached from the bulk material and fall into the plasma jet. Alternatively, due to the melting process the stack may suddenly and partially collapse leading to solid mineral material entering the plasma jet. That solid material also includes waste mineral material from the waste inlet as discussed below. In any case, any solid material within the cavity would be transient as it would be quickly melted by the plasma jet.

[0075] In various examples, the plasma jet defines a cavity that is void of solid material within the hot zone. That is, no mineral material or waste mineral material enters that cavity.

[0076] The term “waste mineral material” is as mentioned above and includes various byproducts of the MMVF-forming process, which are generally called mineral wool waste. These by-products can include a fine powder-like material that is formed in connection with the cutting, e.g. edge cutting, of mineral wool mats so as to form mineral wool slabs having desired dimensions. It is also able to include recycled mineral material, such as MMVF insulation removed from buildings during renovation, which may otherwise end up in landfill. Waste mineral material may comprise additives, such as binders and hydrophilic or hydrophobic compounds, that were added during the manufacturing process; shot produced during a fiberisation process, such as a cascade spinner fiberising process; slag or previously unmelted or partially melted charge material (i.e. material provided to form a mineral melt at a furnace); and / or other wool, such as coarse wool.

[0077] In some examples, the cupola furnace includes a waste inlet located in the side wall of the furnace hot zone. The waste inlet is typically an opening in the furnace wall. It is configured to deliver waste mineral material to the cavity defined by the plasma jet. In essence, the waste inlet is able to supply waste mineral wool directly into the plasma jet. It will be appreciated that, due to the environment surrounding the plasma jet, the waste mineral material may melt prior to it entering the plasma jet. This may be dependent upon the amount or rate at which the waste mineral material is introduced into the furnace via the waste inlet. Once melted, it will form part of the mineral melt at the base of the hot zone and may be removed via the melt outlet. Various of the above details are set out in PCT / EP2023 / 074057, the contents of which is incorporated herein by reference.

[0078] A delivery system for delivering material, such as waste material, is generally illustrated at 100 in Figure 1. Figure 1 also includes a representation of a section of a cupola furnace configuration with which the delivery system is used in various examples.

[0079] In the example shown in Figure 1 , there is a plasma torch 1. This comprises two separate tubular electrodes 2 and 3 to which direct current is fed through conductors 4 and 5 from a voltage regulating unit, such as a rectifier and a thyristor 6 or a rectifier and an IGBT (Insulated Gate Bipolar T ransistor). Current is fed to the thyristor through a conductor 7 which comprises a transformer 8.

[0080] In some examples, as shown in Figure 1 , the tubular electrodes 2 and 3 are provided with cooling jackets and cooling water is introduced into the cooling jackets by means of a pump 9 and is recycled through a heat exchanger 10. A cooling medium is introduced into the heat exchanger 10 through a feed pipe 11 and is discharged through an outlet pipe 12.

[0081] The plasma torch 1 in the example shown in Figure 1 also comprises a pipe 13 for introducing carrier gas into a distributing chamber 14. The carrier gas flows from this distribution chamber into the space between the electrodes 2 and 3.

[0082] In the example shown in Figure 1 , the plasma torch 1 is connected to the side wall of a cupola furnace 16 through a connecting pipe 15. The end of connecting pipe 15 is inserted in a hole in the wall of the shaft furnace. In use, the plasma jet 17, generated by the plasma torch, extends towards the centre of the cupola furnace and defines a cavity (represented in Figure 1 by dotted line 18). This cavity is substantially void of solid material within the hot zone. Plasma jet 17 provides plasma heating to the hot zone.

[0083] In various examples, the cupola furnace 16 also comprises a waste inlet 19 of the delivery system 100. The waste inlet is located in the side wall of the furnace hot zone. In the example shown in Figure 1 the waste inlet is shown above the orifice through which the plasma jet 17 enters the cupola furnace. Various arrangements of the waste inlet location relative to the plasma jet are possible. Further examples are disclosed in Figures 2 to 4, for example.

[0084] In use, waste mineral material 110 may be delivered through the waste inlet 19 to the cavity 18 defined by the plasma jet. In various examples, this is achieved via an auger conveyor 20 which is mounted rotatably in a feed pipe 21 extending through the waste inlet 19, as shown in figure 1.

[0085] Plasma jet 17 melts waste mineral material 110 and mineral material in the hot zone of the furnace, and the resulting mineral melt pools at the base of the cupola furnace. The mineral melt is then able to be removed from the furnace in the usual way.

[0086] Considering the delivery system 100 in more detail, in the example shown in Figure 1 , this includes three general portions. These are a passage, a conveyor and an airlock. In some examples, there may be one or more further general portions, such as the portion that provides the supply of material, which is described in more detail below.

[0087] The passage extends from the waste inlet 19, which, in some examples, acts as the outlet of the delivery system 100, at a downstream end to an opposing upstream end provided by a supply pipe 112, which has a material inlet at its upstream end. The feed pipe 21 is provided between the waste inlet and supply Pipe-

[0088] While only a single delivery system 100 is shown in Figure 1 , in some examples there are multiple delivery systems or at least multiple waste inlets 19 are provided. In various examples this is in conjunction with multiple plasma jets 17, with which the waste inlets are positioned in complementary manner. In a number of examples, this would equally dispense material to the cavity 18 generated by each plasma jet, such as up to 20% of the material being provided to each cavity.

[0089] The arrangement of the passage in Figure 1 shows the supply pipe 112 and feed pipe 21 connected to each other at an angle providing an elbow in the passage. In other examples, the arrangement of these pipes takes other forms, such as straight or a more acute or less acute angle.

[0090] In various examples, the passage provides a gas seal. The passage is defined in the example shown in Figure 1 by walls. To provide the gas seal, in this example, the walls prevent the passage of gas through the walls.

[0091] The airlock provides an ability to limit the amount of gas that can pass along the passage and to provide a transition between a low pressure environment (for example upstream of the airlock) and a high pressure environment (for example downstream of the airlock). This is achieved by providing barriers between an upstream end and downstream end of the airlock to limit gas transmission between the two ends, such as within the limits of mechanical and manufacturing tolerances. This isolates environments on either side of the airlock from each other.

[0092] In general, the airlock or at least part of the airlock provides a conduit through which material is able to pass. This takes the form of a mechanical or physical structure. For instance, in the example shown in Figure 1 , the airlock includes a rotary valve 114. In some examples, this is provided by a rotary feeder.

[0093] In various examples, the rotary valve 114 includes a central drum with radially extending vanes 116. The vanes are arranged circumferentially around the central drum. In this manner, adjacent vanes define a receptacle capable of holding material.

[0094] In use, the central drum is rotatable. This causes the vanes 116 to rotate, causing the receptacles defined by the vanes to rotate. The central drum and vanes, in the example shown in Figure 1 , are held within an outer drum. The vanes extend between the central drum and the outer drum. While there will naturally be mechanical and manufacturing tolerances to take into account, it is this arrangement of the vanes that provides a major element of the ability of the rotary valve 114 to limit passage of gas. Other components, in various examples, also contribute to this ability by being gas-tight or being configured to limit or restrict passage of gas across or around them.

[0095] In some examples, such as the example shown in Figure 1 , the rotary valve 114 is a self-cleaning rotary valve. In various examples, the self-cleaning ability is provided by a scraper 118. In the example shown in Figure 1 , the scraper is a rotary scraper. In use, this rotates synchronously with the central drum and vanes 116 and is shaped to pass over the vanes and through the receptacles defined by the vanes to remove material located therein that has not left the receptacle by other means.

[0096] In a number of examples, the rotary valve 114 is arranged with a downstream, output, end arranged gravitationally below an upstream, input end. In this manner, material placed into the rotary valve at an input end falls out of the receptacles when moved to the output end when loose. Should material remain in the receptacle, for example, due to becoming adhered to a vane or due to compaction, the scraper 118, when present, assists in loosening and, potentially, removing the material.

[0097] While the airlock, or at least this part of the airlock, is able to be provided by other mechanisms or devices in other examples, the rotary valve provides a means of controlling speed at which material is passed along the passage. The rotary valve also provides a mechanical means for maintaining a higher pressure at an output end compared to (lower) pressure at the input end due to the ability to limit gas passage past the vanes and central drum. This is as well as providing a drive to move material between the lower and higher pressure sides of the rotary valve.

[0098] An example rotary valve is the PAM A / S drop through self-cleaning rotary feeder. However, as noted above, the rotary valve, or this portion of the airlock, is able to be provided by another device.

[0099] In some examples, the rotary valve may have a capability of maintaining a pressure differential of about 250 kPa. While this provides a means of counteracting the back pressure along the passage caused by the raised pressure in the cupola during operation, there will still be some gas loss in an upstream direction through the rotary valve. This may be due to mechanical tolerances as noted above or may be due to gas passing through the rotary valve in the receptacles as these rotate from the output end to the input end. In view of this, in various examples, the airlock has a further stage in use. This makes the airlock a multi-stage airlock.

[0100] The further stage of the airlock is, in some examples, a further mechanical stage or stage provided by a device or apparatus. In other examples, however, another means provides the further stage of the airlock. For instance, in some examples, such as the example shown in Figure 1 , this further stage of the airlock is provided, in use, by the material 110 itself located in the supply pipe 112.

[0101] The material 110, in various examples, has a density between 800 kg / m3and 1 ,000 kg / m3. In combination with the form of the material, this provides a sufficient pack of material to restrict gas passage through the material.

[0102] The form of the material 110 provided in the supply pipe 112 is a milled form. In various examples, this is due to the material being rod milled before being supplied to the delivery system 100.

[0103] The multi-stage airlock provided by the rotary valve 114 and material 110 in the supply pipe provides a suitable restriction on passage of gas in an upstream direction. However, as with most systems, there is still likely to be at least a small amount of gas able to pass in an upstream direction. In view of this, and to assist in providing positive downstream pressure in the passage, in some examples, a gas supply inlet 120 is provided in the passage. In use, this is arranged to provide gas from a source (not shown) into the passage. In the example in Figure 1 , the gas supply inlet is provided downstream of the rotary valve.

[0104] As set out above, in some examples, there is an auger conveyor 20. In the example shown in Figure 1 , this provides the conveyor of the delivery system 100. In other examples, the conveyor is provided by another mechanism, such as a pneumatic system. In the example shown in Figure 1 , the auger conveyor operates as set out above. To allow the auger conveyor to rotate, in some examples, has a drive gear 122. This is arranged in use to rotate the screw of the auger conveyor.

[0105] To limit blockages, in some examples, the auger conveyor 20 and feed pipe 21 are arranged at an angle instead of being, for example, horizontal. In various examples, this arrangement of a downstream end of the conveyor and feed pipe being angled results in a downstream end of the passage and the conveyor being the lowest point of the delivery system 100. This assists movement of the material since the material moves under the influence of gravity as well as due to the movement provided by the auger conveyor.

[0106] The conveyor of the delivery system 100 may have other parts that are arranged to transport the material along the passage. In various examples, this is provided by one or more further auger conveyors and / or other mechanisms, such as belt conveyors, chain conveyors, or pneumatic transport systems. As noted above, however, in some examples, the passage is arranged with a supply pipe 112 orientated to allow material to pass through it under the influence of gravity. The elbow is then provided at the point where the upstream end of the auger conveyor 20 is provided.

[0107] To provide material into the supply pipe 112, in some examples, the system further includes a material store. In various examples, this is provided by a box feeder 124. To transport the material between the box feeder and the supply pipe, the box feeder includes a feeder conveyor 126 in a number of examples. While the feeder conveyor is able to be a variety of conveyors, this is, for example, a belt conveyor or a plate conveyor. In some examples, the box feeder 124, and optionally the other components of the delivery system 100 are provided in an airtight environment or an air barrier (not shown) is provided between this / these and the wider environment.

[0108] In use, material, which is typically waste mineral material, is placed in the box feeder 124. This can be provided by a conveyor system or by some other means. This is then transported to the supply pipe 112 by the feeder conveyor 126. In some examples, the rate at which material is supplied to the supply pipe is controlled based on the speed of the feeder conveyor. In turn, the feeder conveyor speed is set based on weight loss measured using one or more load cells, of which an illustrative example is provided at 128 in Figure 1 against the feeder conveyor. In some examples, the speed is based on the weight addition requirements to the supply pipe 112, rotary valve 114, airlock and / or furnace 16, and the speed determines the weight loss from the box feeder.

[0109] The one or more load cells 128 allow weight loss in the box feeder 124 to be identified. From this, in certain examples, the rate at which material is provided to the supply pipe 112 is calculated. In other examples, the rate at which material is passed to the supply pipe or through the delivery system 100 is controlled based on the rotation rate of the rotary valve 114.

[0110] Turning to the positioning of the waste inlet 19 relative to the cavity 18 provided by the plasma jet 17, examples of this are shown in Figures 2, 3 and 4.

[0111] Figure 2 shows a plan view of an illustrative example arrangement of the cupola 16, plasma torch 1 , feed pipe 21 and waste inlet 19. In this example, it can be seen in Figure 2 that the waste inlet is arranged at an angle relative to the plasma torch. In other words, the plasma torch and waste inlet are not parallel to each other, but have longitudinal axes that intersect, such as intersecting inside the furnace. This intersection, in some examples, is a short distance in front of each of the plasma torch and waste inlet.

[0112] A similar arrangement is shown in the example of Figure 3. The arrangement shown in Figure 3 is able to be implemented at the same time as the arrangement shown in Figure 2 is implemented or is able to be implemented independently (i.e. when the example shown in Figure 2 is not used).

[0113] Figure 3 shows a side view of an illustrative example arranged of the cupola 16, plasma torch 1 , feed pipe 21 and waste inlet 19. In this example, the drive gear 122 is also shown. While this is not shown in Figure 2 or Figure 4, as with other components of the plasma torch and delivery system 100, those components are still present, but are just not shown in the examples shown in these Figures.

[0114] In Figure 3, the waste inlet 19 is arranged above the plasma torch 1 and at an angle relative to the plasma torch. In other words, the plasma torch and waste inlet are (again) not parallel to each other, but have longitudinal axes that intersect , such as intersecting inside the furnace. This intersection, in various examples, is a short distance in front of each of the plasma torch and waste inlet.

[0115] A combination of the arrangements shown in Figure 2 and Figure 3 is shown in the example shown in Figure 4. Similar to Figure 2 and Figure 3, Figure 4 shows an isometric view of an illustrative example arranged of the cupola 16, plasma torch 1 , feed pipe 21 and waste inlet 19. This example shows the waste inlet at an angled arrangement relative to the plasma torch both in a horizontal axis and a vertical axis, with the feed pipe arranged above the plasma torch and being orientated down and towards a point in front of the plasma torch inside the cupola. In Figure 4, the front end of the plasma torch 1 (where the plasma jet is emitted) and the waste inlet 19 are depicted in dotted lines. This is intended to be illustrative of these parts being inside the cupola 16.

[0116] As can be seen from Figure 1 , the waste inlet 19 is open providing a persistently open outlet from the delivery system 100 into the cupola 16. This assists with the ability to provide material into the cupola in a continuous manner when needed.

[0117] In general, some examples provide a delivery system for supplying waste mineral material to a furnace, the system comprising: a passage with an outlet and an inlet; a conveyor arranged in use to move material along the passage to the outlet; an airlock connected to the passage, the airlock including a transfer mechanism arranged in use to move material between a low pressure side and a high pressure side of the airlock; and, potentially, a pressurisation device arranged in use to maintain the pressure between the outlet and the airlock at least at a threshold pressure, such as a pressure that equals or exceeds a pressure in a cupola to which the delivery system is connected. A number of the examples demonstrate this. The process of providing material into the cupola 16 and providing the plasma jet 17, is able to be used in the formation of fibres. Those fibres can be shown to be soluble in physiological saline. Suitable high aluminium, biologically soluble fibres that can advantageously be made using the process described herein are described in WO 96 / 14454 and WO 96 / 14274, and others are described in WO 97 / 29057, DE-U-2970027 and WO 97 / 30002, which are incorporated herein by reference.

[0118] Such fibres commonly have an adequate solubility in lung fluids as shown in vivo tests or in vitro tests, typically conducted in physiological saline buffered to about pH 4.5. Suitable solubilities are described in WO 96 / 14454. Usually the rate of dissolution is at least 10 or 20 nm per day in that saline. The fibres preferably have sintering temperature above 800 °C, more preferably above 1 ,000 °C. The melt preferably has a viscosity at fibre forming temperature of 5 to 100 poise, preferably 10 to 70 poise at 1 ,400°C. Additional examples of this may be found in WO 99 / 28252, which is incorporated herein by reference.

[0119] The MMVF may be formed as a bonded web comprising the MMVF as described above, or MMVF made according to the process described above, and a cured binder composition.

[0120] In some examples, the mineral melt has a viscosity in the range 10 to 30 poises at 1400 °C, such as in the range 20 to 25 poises. An advantage of choosing these viscosities is that the resulting MMVF have a smaller diameter than if the viscosity of the melt were higher. Further, it is possible to use the melt at a lower temperature in order to achieve the required operating viscosities. This saves energy, as it is possible to use the melt at a lower temperature. It also reduces the wear on rotors used to produce fibres, as a lower temperature melt causes less wear. Further details of this example mineral melt may be found in WO 2015 / 055758, which is incorporated herein by reference. The viscosity of the melt may be determined in accordance with ASTM C 965-96.

[0121] The raw materials (mineral material) may be in the form of briquettes. Briquettes are made in a known manner by moulding a mix of the desired particulate materials and a binder into the desired briquette shape and curing the binder. The binder may be a hydraulic binder, i.e. one that is activated by water, for instance Portland cement. Other hydraulic binders can be used as partial or complete replacement for the cement and examples include lime, blastfurnace slag powder, and certain other slags, and even cement kiln dust and ground MMVF shot (JP- A-51075711 , US 4,662,941 and US 4,724,295, each of which is incorporated herein by reference). Alternative binders include clay. The briquettes may also be formed with an organic binder such as molasses, for instance as described in WO 95 / 34514, which is incorporated herein by reference. Such briquettes may be described as formstones.

[0122] The mineral melt prepared via the process described herein, is some examples is suitable for the production of mineral wool, or MMVF, such as glass fibres or stone fibres. In various examples that the mineral melt formed is suitable for use to form MMVF. Therefore, in a number of examples there is provided a process for manufacturing MMVF comprising the steps of forming a melt, for example using a process as described herein; fiberising the melt by means of an internal or external spinning process; such as using a cascade spinner; and collecting the formed fibres.

[0123] The fibres, including MMVF, may be made from the mineral melt in a conventional manner. Generally, they are made by a centrifugal fibre-forming process. For instance, the fibres may be formed by a spinning cup process in which they are thrown outwardly through perforations in a spinning cup, or mineral melt may be thrown off a rotating disc and fibre formation may be promoted by blasting jets of gas through the mineral melt. Fibre formation may be conducted by pouring the mineral melt onto the first rotor in a cascade spinner. In this case, it is typical that the mineral melt is poured onto the first of a set of two, three, four or even more rotors, each of which rotates about a substantially horizontal axis whereby mineral 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 mineral melt on the second rotor is thrown off as fibres although some may be thrown towards the third (lower) rotor, and so forth. In general, that the spinning process often uses a cascade spinner.

[0124] The properties required of a mineral melt to be used in each spinning method are known to those in the art, and the composition of the mineral melt may be tuned to provide those properties. For instance, those skilled in the art are able to select mineral materials to be added to the cupola furnace to produce a specific mineral melt composition, to be spun by a particular spinning process.

[0125] During the fiberizing process, the melt is formed into a cloud of fibres entrained in air and the fibres are collected as a web on a conveyor and carried away from the fiberizing apparatus. The web of fibres is then consolidated, which can involve cross-lapping and / or longitudinal compression and / or vertical compression and / or winding around a mandrel to produce a cylindrical product for pipe insulation. Other consolidation processes may also be performed.

[0126] A binder composition is conventionally applied to the fibres, typically when they are a cloud entrained in air. Alternatively, it can be applied after collection on the conveyor, but this is less preferred. Conventional types of binder for use with mineral wool fibres may be used.

[0127] After consolidation, the web of fibres is passed into a curing device to cure the binder. The curing may be carried out at temperatures from 100 to 300 °C, such as 170 to 270 °C, such as 180 to 250 °C, such as 190 to 230 °C.

[0128] In some examples, that the curing takes place in a conventional curing oven for mineral wool production wherein hot air is blown through the consolidated web, preferably operating at a temperature of from 150 to 300 °C, such as 170 to 270 °C, such as 180 to 250 °C, such as 190 to 230 °C. The curing may take place for a time of 30 seconds to 20 minutes, such as 1 to 15 minutes, such as 2 to 10 minutes. Typically, the curing takes place at a temperature of 150 to 250 °C for a time of 30 seconds to 20 minutes.

[0129] The curing process may commence immediately after application of the binder to the fibres. The curing is defined as a process whereby the binder composition undergoes a physical and / or chemical reaction which in case of a chemical reaction usually increases the molecular weight of the compounds in the binder composition and thereby increases the viscosity of the binder composition, usually until the binder composition reaches a solid state. The cured binder composition binds the fibres to form a structurally coherent matrix of fibres.

[0130] The curing of the binder in contact with the mineral fibres may alternatively take place in a heat press. The curing of a binder in contact with the mineral fibres in a heat press has the particular advantage that it enables the production of high- density products.

Claims

CLAIMS1 . A delivery system for supplying waste mineral material to a furnace, the system comprising: a passage and conveyor arranged in use to move material along the passage to an outlet; an airlock connected to the passage and through which material is able to pass in use, the airlock being arranged in use to maintain a pressure differential across the airlock.

2. The delivery system according to claim 1 , wherein the conveyor is downstream of the airlock.

3. The delivery system according to claim 1 or claim 2, wherein the conveyor and airlock are independent of each other.

4. The delivery system according to any one of claims 1 to 3, wherein the airlock provides a conduit through which the material is able to pass in use.

5. The delivery system according to any one of the preceding claims, wherein the airlock is further arranged in use to move material to the conveyor.

6. The delivery system according to any one of the preceding claims, further comprising a continuously open outlet to the furnace to which the passage and conveyor arranged in use to move material along the passage to.

7. The delivery system according to claim 6, wherein the airlock is separated from the outlet, thereby maintaining the pressure differential away from the outlet.

8. The delivery system according to any one of the preceding claims, wherein at least a downstream portion of the passage and conveyor are arranged at an angle relative to a horizontal axis with a downstream end of the passage and conveyor being a lowest point.

9. The delivery system according to any one of the preceding claims, wherein the airlock is a multi-stage airlock arranged in use to maintain the pressure differential across the airlock stages.

10. The delivery system according to claim 9, wherein the passage includes a supply pipe arranged in use to hold material, and wherein material in the supply pipe provides an airlock stage.

11. The delivery system according to any one of the preceding claims, wherein the airlock including a drive arranged in use to engage material and push engaged material from a low pressure side of the airlock to a high pressure side of the airlock.

12. The delivery system according to claim 11 , wherein the drive includes one or more vanes against which material rests on engagement with the drive, each vane being moveable from the low pressure side of the airlock to the high pressure side of the airlock.

13. The delivery system according to claim 12, wherein the one or more vanes form part of a rotary feeder, the rotary feeder being arranged in use to provide the airlock with a rotary airlock.

14. The delivery system according to claim 13, wherein the rotary feeder is a self-cleaning rotary feeder.

15. The delivery system according to claim 14, wherein the rotary feeder includes a scraper arranged in use to pass over each vane thereby removing material.

16. The delivery system according to any one of the preceding claims, further comprising a pressurisation device arranged in use to maintain the pressure between the outlet and the airlock at least at a threshold pressure.

17. The delivery system according to claim 16, wherein the pressurisation device includes a gas inlet connected to a gas source and to the passage downstream of the airlock.

18. The delivery system according to any one of the preceding claims, wherein the conveyor includes an auger conveyor arranged in use to transport material along the auger.

19. The delivery system according to claim any one of the preceding claims, further comprising a store arranged in use to provide material to an inlet of the passage and arranged in use to hold material.

20. The delivery system according to claim 19, wherein the store includes a transporter arranged in use to transfer material to the inlet, and includes a sensor arranged in use to monitor quantity of material transferred to the inlet, the rate of transfer by the transporter being based on the monitored quantity.

21. A process for preparing a mineral melt in a cupola furnace, wherein the mineral melt is for the formation of mineral wool, the cupola furnace comprises: a hot zone at the base of the furnace; a melt outlet in the hot zone; at least one plasma torch that provides plasma heating to the hot zone, by way of a plasma jet that defines a cavity that is substantially void of solid material within the hot zone; a waste inlet located in the side wall of the furnace hot zone; and a delivery system according to any one of the preceding claims, the outlet being connected to the waste inlet and configured to deliver waste mineral material to the cavity defined by the plasma jet through the waste inlet, wherein mineral material and the waste mineral material supplied to the furnace is melted to form the mineral melt.

22. A cupola furnace for preparation of a mineral melt according to a process defined in claim 21.

Images