Furnace comprising cooled shield

Abstract

The present invention relates to a furnace (1) for melting a matrix of raw materials into a molten state. The furnace (1) features at least one furnace wall (5) with a melt outlet aperture defining the melt level and a burner aperture (19) above the melt level. Additionally, the invention includes a shield (2) with a coolant inlet (11), a coolant outlet (12), and a collar (7) extending radially from the burner aperture (19) across part of the furnace wall (5). The collar (7) contains at least one coolant passage (10) fluidly connecting the inlet (11) and outlet (12) through part of the collar (7).

Description

[0001] Furnace comprising cooled shield

[0002] Field of the invention

[0003] The invention relates to a furnace for producing a mineral melt. Such furnaces are well suited for use in the production of man-made vitreous fibres (MMVF) such as stone wool and glass wool.

[0004] Background

[0005] Furnaces for producing melt from raw material matrixes are well known from for instance WO 2022 / 106592 A1. This document describes a cupola furnace comprising at its lower end a furnace bottom and an outlet located above the bottom. A number of plasma torches are positioned through the furnace wall some distance above the level of the melt outlet. The cupola furnace has an inner lining which is made from bricks. The lining covers the furnace bottom and lower parts of the inner furnace wall.

[0006] Summary of the invention

[0007] Using plasma torches for melting raw materials in furnaces allows an efficient use of electricity in furnaces and gives an alternative to using gas, oxy-fuel burners or even coke or coal in the furnaces. We have observed that heat reflection from plasma torches burning at 5,000 to 7,000 °C (degrees Celsius) can damage the inner lining and the furnace wall in the vicinity of the plasma torches. Such damage to the furnace wall is expensive and time-consuming to repair and can ultimately lead to dangerous situations if water leaks directly into the melt in the furnace which may cause an explosion. The damage to the furnace wall was observed as leakages of cooling water through the furnace wall. These leakages were observed when using plasma torches while the furnace wall in the vicinity of the burners was not covered by a shield. The damage was also observed by inspecting the furnace wall after the furnace had been emptied. The inspection revealed that the furnace wallThe shield (2) is preferably positioned within the furnace in such a way that it surrounds the burner aperture (19) in order to protect the furnace wall (5) surrounding the burner aperture (19) from heat reflected off the matrix of solid materials which are used to produce the mineral melt.

[0008] Because the shield (2) comprises its own cooling circuit even cooling is ensured across the shield (2) without gaps where hot spots can form. This also allows cooling of each shield to be controlled individually by supplying as much coolant through the coolant passage in the collar as needed.

[0009] Melt produced in front of the shield and melt rising up to the collar of the shield may be cooled to produce a protective cover of solidified melt covering the whole or parts of the shield. Any part of the shield covered in solidified melt will also lower the amount of heat the shield itself is exposed to because the covered parts are no longer in direct contact with the melt, the hot gasses within the furnace (1) or the gasses and / or plasma reflected back towards the shield (2).

[0010] Should the shield suffer damage either from the reflected heat, the melt within the furnace or from the weight of the matrix of raw materials within the furnace each shield can be replaced more easily than repairing the furnace wall.

[0011] According to a preferred embodiment the invention the furnace (1) is a cupola furnace.

[0012] The furnace is similar in both form and function to the furnaces described in WO 2022 / 106592 A1, US 2018 / 0319692 A1 , US 2009 / 0314035 A1 and EP 3789355 A1. These documents describe cupola furnaces with a base, a top and sides stretching between the base and top. Apertures are positioned in the sides of the furnaces.

[0013] Energy may be added to the lower half of the furnace either through plasma entering the furnace from one or more plasma torches or by combustion of gas mixtureswhich also enters the furnace through torches. Energy may additionally come from burning coke which is part of the matrix by allowing oxygen to enter the furnace from one or more tuyeres. Once the raw material matrix begins to melt, the melt will flow down through the unmelted matrix and into the bottom part of the furnace. Here it will collect and form a pool of melt. Coke in the matrix of raw materials also serves the purpose of holding up the matrix at the bottom of the cupola furnace. Because coke does not melt at the temperatures within the furnace once the lumps of coke reach the bottom of the furnace they will only bum slowly e.g. as they react with and reduces iron to Fe(ll) or Fe in the melt. These furnaces comprise outlets or siphons located above the bottom of the furnace and below the torches or tuyeres to allow melt to leave the furnace while maintaining the pool of melt in the bottom of the furnace. Similar constructions with outlets for melt or slag are shown in US 2018 / 0319692 A1, US 2009 / 0314035 A1 and EP 3789355 A1 with similar positions for either burners and / or tuyeres.

[0014] The furnace typically comprise a range of temperature zones, including (from highest temperatures to lowest) a hot zone, a heating zone and a preheating zone in use.

[0015] In use a matrix of raw materials comprising blocks, briquettes and possibly coke is positioned in the furnace. This matrix is resting on the bottom of the furnace and as the blocks and briquettes are melting and the coke bums and melt is removed from the furnace the raw materials move from the top toward the bottom of the furnace. The raw materials are in the form of blocks and briquettes to allow the passage of hot gasses up through the matrix.

[0016] The bottom of the furnace constitutes the hot zone. The hot zone comprises the melt formed in the furnace, which mineral melt is located in the space between pieces of unmelted matrix which are resting on the bottom of the furnace, and which support the material above. In typical furnaces for making mineral melt the melt temperaturein the hot zone is in the range of 1450 °C (degrees Celsius) to 1550 °C (degrees Celsius). Further, the distance between the top and bottom of the hot zone is relatively large. This is needed to ensure that the correct heating zone temperature is maintained in the furnace.

[0017] The heating zone is located above the hot zone. The lower portion of the heating zone is usually provided with gas inlet nozzles, such as plasma or gas torches or tuyeres through which plasma and / or gas is introduced into the furnace. Heating either comes from the temperature of the gas or plasma directly, when using plasma torches or from combustion of the gas, when using gas torches. The combustion of coke also produces hot gasses such as CO2 or CO. The heating of the matrix takes place by movement of the gasses up through the heating zone. Thereby causing raw material that moves down through the heating zone, by gravity to be heated to its melting point. This melted material flows down into the hot zone at the bottom of the furnace.

[0018] The preheating zone is located above the heating zone and stretches all the way to an exhaust outlet of the furnace. The preheating zone comprises the matrix of raw materials and is heated by the gasses passing up through the furnace from the heating zone.

[0019] The furnace is a generally upright shaft furnace or cupola furnace with a base and a top and sides stretching between the base and top. The generally round furnace has a vertical axis passing through the center of the top and the center of the base. One or more burner apertures are positioned in the sides of the furnace each with their own aperture axis passing through the center of each burner aperture. Each aperture axis intersects with a vertical axis of the furnace at the centre of the furnace, although this is not essential. Generally, the aperture axes have a downward angle from the horizontal of 1 to 10 degrees, preferably 4 to 8 degrees such as 2, 3, 4, 5, 6, 7, 8 or 9 degrees preferably 6 degrees. One or more of these burner aperturesare provided with shields (2) on the inside of the furnace wall surrounding the burner aperture. Burners such as plasma torches can be positioned through the furnace wall. A melt outlet is positioned at the base of the furnace which allows melted material to leave the furnace once the melt reaches a sufficient level within the furnace. The melt outlet therefore determines the height at which the melt is standing in the furnace when the furnace is in use. The burner apertures are placed at a height higher than the melt outlet relative to the base of the furnace.

[0020] The walls of the furnaces in the hot zone and the heating zone are usually layered in ceramic bricks and surrounded by a cooling mantle. The cooling of these parts of the furnace allows a layer of solidified melt to form on the furnace wall which preserves it from the high temperatures produced in the furnace. Tuyeres and torches are also cooled in order to preserve them from the high temperatures in the furnace.

[0021] When hot gasses or plasma from a burner such as a plasma torch, gas burner or oxy-fuel burner are blown into the furnace they may hit parts of the matrix of raw materials which will not readily absorb the energy from the gas and / or plasma. Therefore, the gasses and / or plasma is reflected toward the furnace wall surrounding the burner. The gases may at this point be so hot that they can bum through the protective layer of solidified melt, the ceramic lining and even the cooled furnace wall allowing cooling water to enter the furnace. This is especially an issue when using plasma torches because of the high temperatures produced by these. One example of raw materials with this problem is coke which does not melt, and which only bums slowly.

[0022] According to another preferred embodiment of the invention, the matrix comprises raw materials for making a mineral melt and in an even more preferred embodiment the raw materials comprise stone.The raw materials may comprise, stone, specifically volcanic rock, olivine or dolomite. They may also comprise recycled materials and blast furnace slag, sand, recycled glass, limestone, soda ash and other chemical additives.

[0023] The raw materials are preferably for production of a melt which can be turned into man-made vitreous wool. Man-made vitreous wool is silica based, i.e. it contains SiO4 units as network formers along with various amounts of oxides of boron, aluminum, alkaline earths, alkalis, iron and zirconium, which are added to enhance the manufacturing process or the product performance.

[0024] According to another preferred embodiment the invention the furnace (1) further comprises at least one burner (6) positioned in the burner aperture (19) the burner (6) configured to supply heated gas or plasma through the burner aperture (19).

[0025] The burner can be of various types both providing gas for combustion in the furnace or providing gasses of temperatures high enough to melt the raw materials such as plasma of various types. Specifically, the burner may be a gas burner, oxy-fuel burner or a plasma torch.

[0026] According to another more preferred embodiment of the invention, the burner has a burner outlet (3) and according to an even more preferred embodiment this burner outlet (3) has a radius which is smaller than the radius of the burner aperture (19) such as 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 or 0.2 times the radius of the burner aperture (19). Preferably the burner outlet radius is 0.9 to 0.2 times the radius of the burner aperture and even more preferably the burner outlet radius is 0.6 to 0.4 times the radius of the burner aperture. Herein, radii or other lateral dimensions of the shield are measured relative to a shield center axis extending through the centre of the collar and / or relative to an aperture axis (centerline) of the burner aperture.The burners used in the present invention can be of various types and therefore with various shapes and sizes. The dimensions of the burner aperture and the shield may be selected to correspond to the external dimensions of the burner.

[0027] According to another more preferred embodiment of the invention the burner is at least one plasma torch, specifically at least one arc plasma torch and more specifically at least one non-transferred arc plasma torch.

[0028] The plasma torches used in this invention could be those described in WO 2022 / 106592 A1. Plasma torches generate thermal plasma using direct current (DC), alternating current (AC), radio-frequency (RF) and / or other discharges. Thermal plasmas provide heat, which in DC plasma torches is produced by creating an electric arc between two electrodes. A carrier gas is passed through the arc and subsequently through a constricted opening. This elevates the temperature of the carrier gas to the point where it becomes plasma.

[0029] Specifically, when using plasma torches, the temperature of the plasma may damage parts of the furnace if the plasma is reflected towards the walls of the furnace before its heat can be absorbed by the raw materials within the furnace.

[0030] The output, such as mineral melt output of a cupola furnace is proportional to the cross sectional area of the furnace at the tuyere level. The energy needed to heat the output to a certain temperature and melt the raw materials within the furnace is proportional to the output of the furnace. Therefore when some or all of the energy delivered to the furnace comes from plasma or gas torches the effect needed from each plasma or gas torch may be proportional to and may be scaled with the output of the furnace. Therefore the effect needed from each plasma or gas torch may be proportional to the cross sectional area of the furnace.

[0031] The size of the shield can be proportional to the volume of the torch plume. The volume of the torch plume is proportional to the effect of the torch. Therefore thesize of the shield can be proportional to the cross sectional area of the furnace while fitting within its circular circumference. In order to avoid that the collar of such a shield projects too far into the interior of a furnace the collar of the shield may be shaped to fit the curve of the inner furnace wall, such as by angling parts of the collar.

[0032] In a preferred embodiment of the invention the collar of the shield has a peripheral radius which is at least 15% of the inner radius of the cupola furnace at the tuyere level, preferably the peripheral radius of the collar is at least 25% of the inner radius of the cupola furnace at the tuyere level.

[0033] A preferable embodiment of the invention relates to the furnace according to the preceding embodiments, where the furnace comprises two or more burners, each with a shield surrounding each burner aperture and each shield comprises a separate cooling circuit.

[0034] According to another more preferred embodiment of the invention a part of the burner (6) projects into the furnace through the burner aperture (19).

[0035] The burner (6) comprises a burner outlet (3) from which a stream of gas and / or plasma is ejected. Positioning the burner outlet (3) within the furnace ensures that the hot gasses and / or plasma from the gas or plasma plume does not come into direct contact with the furnace wall.

[0036] A specific embodiment of the invention relates to the furnace (1) according to any one of the previous embodiments wherein the collar (7) has an inner radius which is the same or larger than the radius of the burner aperture (19)

[0037] The collar (7) of the shield (2) allows the flow of gas and / or plasma to pass therethrough into the interior of the furnace. The collar (7) does not cover the burner aperture otherwise it would be possible for the hot gasses and / or plasma exiting the burner to hit the collar directly. The collar preferably abuts the furnace wall.Advantageously this prevents gasses, plasma or mineral melt from coming into direct contact with the part of the furnace wall which the collar (7) covers.

[0038] According to a more specific embodiment of the invention, the collar (7) has a peripheral radius which is at least 1.5 times the inner radius of the collar (7), such as 2 to 5 times the inner radius of the collar (7). Specifically the peripheral radius of the collar (7) can be 2, 3, 4 or 5 times the inner radius of the collar (7).

[0039] According to another more specific embodiment of the invention, the collar (7) has a peripheral radius which is at least 2.5 times the radius of the burner outlet (3). Such as 2.5 to 15 times the radius of the burner outlet (3). Specifically, the peripheral radius of the collar (7) can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 times the radius of the burner outlet (3).

[0040] The peripheral radius of the collar (7) is large enough that the furnace wall surrounding the burner aperture is covered and therefore protected from reflected gasses and / or plasma. The shape, size and curvature of the furnace wall may limit how large the collar of the shield can be practically.

[0041] According to a preferred embodiment of the invention, the shield (2) further comprises a lip (17), extending from the collar towards the interior of the furnace (1 ).

[0042] According to a more preferred embodiment of the invention the lip (17) comprises at least one lip inlet fluidly connected to at least one coolant passage of the collar (7);

[0043] at least one lip outlet fluidly connected to at least one coolant passage of the collar (7) and

[0044] at least one lip coolant passage (13) fluidly connecting the lip inlet and the lip outlet through at least part of the lip (17).According to another more preferred embodiment of the invention, the lip (17) has an outer radius which is smaller than the peripheral radius of the collar (7).

[0045] The outer radius of the lip as described here is the outer radius of the lip where it is connected to the collar of the shield. The lip can also have an outer radius at the point where it projects furthest into the furnace which is different from the outer radius where it is connected to collar. Specifically, the outer radius of the lip can be 1.5 to 3 times smaller than the peripheral radius of the collar such as 2 or 2.5 times smaller.

[0046] According to another more preferred embodiment of the invention the lip (17) has an inner radius which is smaller than the radius of the burner aperture (19).

[0047] Preferably the lip (17) is position at the edge of the collar (7) nearest the burner aperture (19) away from the furnace wall and the lip (17) covers this edge.

[0048] The inner radius of the lip as described here is the inner radius of the lip closest to the furnace wall. The lip can also have an inner radius at the point where it projects furthest into the furnace which is different from the inner radius closest to the furnace wall.

[0049] The inner radius of the lip is preferably 80 to 50% of the radius of the burner aperture (19), more preferably 70 to 60%.

[0050] The lip (7) of the shield (2) serves both to cover and thereby protect part of the burner (6) from gasses and / or plasma reflected by the raw material matrix and to guide the plume of hot gasses or plasma from the burner (6). It achieves this by being narrower than the burner aperture (19) thereby covering at least a part of the burner (6) when a burner (6) is positioned behind the shield (2). It also restricts the width and spread of the stream of plasma and / or gas in use. It comprises at leastone coolant passage for the same reasons that the collar (7) comprises at least one coolant passage and these coolant passages can be connected.

[0051] The combination of shapes and sizes of the collar and lip of the shield allows the shield to protect both the wall of the furnace and the burner itself from the reflected gasses and / or plasma within the furnace while maintaining a reasonable distance from the gas or plasma plume supplied by the burner and the raw materials being melted within the furnace to avoid heat loss within the furnace.

[0052] Specifically the inner radius of the lip is preferably larger than the burner outlet radius such that no obstruction or constriction of the burner outlet is presented by any part of the shield.

[0053] According to another preferred embodiment the invention is the furnace (1) according to any one of the preceding embodiments wherein the shield (2) comprises:

[0054] a back plate (8) with the inlet (11) and the outlet (12) attached to the back of the back plate (8);

[0055] a face plate (9) comprising at least one inlet coolant passage and at least one outlet coolant passage;

[0056] a projecting plate (14) comprising at least one projecting plate inlet, at least one projecting plate outlet and at least one projecting plate passage (13) connecting the projecting plate inlet and the projecting plate outlet; and, a cap (15).

[0057] According to a more preferred embodiment the invention is the furnace according to the previous embodiment wherein the back plate (8), inlet (11) and outlet (12) are made from steel. However, in further examples the back plate, inlet and outlet could be formed by other metals such as titanium, copper or copper alloys.According to a more preferred embodiment the invention is the furnace according to the previous embodiments wherein the face plate (9), projecting plate (14) and cap (15) are made from copper or a copper alloy. Specifically, the copper or copper alloy is oxygen free such as oxygen-free copper (OFC).

[0058] According to a more preferred embodiment the invention is the furnace according to the previous embodiments wherein the back plate (8), face plate (9), projecting plate (14) and cap (15) are assembled by soldering or welding.

[0059] According to a more preferred embodiment the invention is the furnace according to the previous embodiments wherein the inlet coolant passage, the outlet coolant passages and / or the projecting plate passage are provided by milling.

[0060] According to a more preferred embodiment the invention is the furnace according to the previous embodiments wherein the back plate (8) and the face plate (9) make up the collar (7) of the shield (2) and the projecting plate and the cap make of the lip (17) of the shield (2).

[0061] Construction of the shield can be done by assembling the collar from a back plate and a face plate where passages are milled into the face plate and the lip from a projecting plate where a passage is milled into and a cap. This allows the use of appropriate materials for the different parts such as steel for the parts not in contact with the hot gasses and / or plasma or melt in the furnace and copper or a copper alloy for the parts which are in contact with the hot gasses, plasma and melt within the furnace. These parts may then be welded or soldered to seal the parts together in such a way that coolant does not leak into the furnace. The coolant passages in the face plate of the collar are fluidly connected to the projecting plate passage in the projecting plate. This allows coolant to pass through the inlet (11) into one or more of the inlet coolant passages in the face plate of the collar, into the projecting plate passage in the lip and out to the outlet coolant passages in the face plate of the collar and to the outlet (12).The use of copper or copper alloys free of oxygen is done to make the shield more resistant to reducing environments within the furnace. Specifically when producing melts comprising iron or ferrous oxide (FeO) a reducing environment is necessary, under these conditions copper or copper alloys free of oxygen prolongs the lifespan of the shield.

[0062] According to another preferred embodiment the invention is the furnace according to previous embodiments wherein the coolant passages and / or lip coolant passages are provided along chord lines of the collar or lip respectively.

[0063] A different way of constructing the shield is to drill the coolant passages and / or lip coolant passages into the collar or lip respectively and then sealing the ends of these passages in such a way that coolant is not leaked into the furnace. This allows the shield to be made from a reduced number of pieces including the coolant inlet (11) and coolant outlet (12) which may be then assembled by welding or soldering.

[0064] According to a preferred embodiment the invention is the furnace according to any one of the previous embodiments wherein the collar (7) comprises at least four coolant passages (10).

[0065] According to an even more preferred embodiment the invention is the furnace according to the previous embodiment wherein each coolant passage (10) covers at least an angular quarter of the collar (7) of the shield (2) in a meandering path.

[0066] Whether the coolant passages are provided by milling or drilling, the passages should cover the shield as evenly as possible. This can be achieved by adding more passages fed from the same common conduit. When the passages are provided by milling, they can be made as meandering paths across the whole face of the collar. When the passages are provided by drilling, they can be made as straight lines fed from a common conduit. A wide variety of path layouts are possible. For instance that the passages cave have rotational symmetry of at least order 2 around a shieldcentre axis or the passages can have reflective symmetry across at least one plane arranged parallel to the shield centre axis. Preferably each coolant passage defines a “Labyrinthine” path and more preferably each coolant passage comprises a plurality of turns with angles of at least 90 degrees.

[0067] According to a preferred embodiment the invention is the furnace according to any one of the previous embodiments wherein the furnace (1 ) further comprises a flange (18) attached to the furnace wall (5) where the flange (18) surrounds the collar (7) of the shield (2).

[0068] Attaching a flange to the furnace wall surrounding the collar of the shield protects the shield from the matrix of raw materials. During use the raw materials are placed in a stack which slowly moves towards the bottom of the furnace as the materials are melted. The flange surrounding the shield can take part of the pressure from these raw materials off the shield and direct these forces towards the wall of the furnace which is dimensioned to withstand such pressures.

[0069] According to a preferred embodiment the invention is the furnace according to any one of the previous embodiments wherein the furnace (1) comprises at least 2 shields such as 3, 4, 5 or 6 shields.

[0070] The furnace preferably at least as many shields as the number of burners positioned through the furnace wall through burner apertures (19). Having more shields than active burners, allows operators to switch burners during operation, or change the amount of energy provided to the furnace by switching on or off a number of burners.

[0071] According to a preferred embodiment the invention is the furnace according to previous embodiments wherein the burner is positioned at an angle downward from horizontal of 0 to 10 degrees such as 1, 2, 3, 4, 5, 6, 7, 8 or 9 degrees, preferably 4 to 8 degrees and more preferably 6 degrees.The burners are angled downwards in the furnace such that the hot gas or plasma plumes produced by the burners are directed towards the melt within the furnace in operation. This allows the plumes to be longer before they reach the other side of the furnace and directs the heat provided by the burners towards the melt in the furnace. The downward angle of the burners also directs most of the reflected hot gasses and / or plasma towards the bottom of the furnace which is more able to withstand the heat from this gas and / or plasma.

[0072] According to an embodiment, the invention is a method for melting a matrix of raw materials in a furnace (1) as described above, the method comprising the step of passing a heated gas and / or plasma through the burner aperture (19) into the furnace (1) to heat the matrix of raw materials until it melts.

[0073] In order to melt the matrix of raw materials within the furnace, heated gas or plasma is passed through the burner aperture heating the raw materials until they melt. Different sources of heated gas or plasma can be used and other sources of heat such as burning of coke can be present in the furnace.

[0074] According to a preferred embodiment the invention is the method according to the previous embodiment further comprising the step of passing a coolant through the coolant passages (10, 13) in the shield (2).

[0075] Passing a coolant through the passages in the shield allows it to actively remove heat from the region of the wall which it covers and to build up a cover of solidified melt where it comes into contact with melted materials. This solidified melt protects the shield, and the underlying furnace wall from the heat within the furnace. The type and amount of coolant can be adjusted according to the needs of the melting process. The coolant is fluid, preferably liquid. More preferably the coolant is water although other coolant fluids may be used.According to a preferred embodiment the invention is the method according to the previous embodiments wherein the matrix comprises raw materials for production of a mineral melt.

[0076] According to an even more preferred embodiment, the invention is a method according to the previous embodiment wherein the mineral melt is a stone or glass melt for production of man made vitreous fibres (MMVF).

[0077] The melting process is for the production of a mineral melt which can be further processed into mineral fibres such as glass or stone wool. Therefore, the raw materials placed within the furnace are those useful in producing such mineral melts. These raw materials can be volcanic rock, olivine or dolomite. They may also comprise recycled materials and blastfurnace slag, sand, recycled glass, limestone, soda ash and other chemical additives.

[0078] Brief description of the drawings

[0079] Figure 1 shows a cut-away perspective view of a furnace according to the invention.

[0080] Figure 2 shows a cut-away perspective of the shield, furnace wall and burner according to the invention.

[0081] Figure 3 shows a perspective of the shield according to the invention viewed from the back plate.

[0082] Figure 4 shows a cross section of the collar according to one embodiment of the invention.

[0083] Figure 5 shows a cross section of the lip according to one embodiment of the invention.

[0084] Detailed description of the drawingsFigures 1 and 2 show cutaway perspective views of a cupola furnace (1) which comprises a shield (2) arranged to protect its furnace wall (5). Figure 2 shows an enlarged view of the portion of the furnace wall with the shield (2). Figure 3 shows a perspective view of the shield (2). Figure 1 shows the inside of a furnace (1) with a shield (2) positioned in such a way that it surrounds a burner outlet (3). The furnace also comprises several tuyeres (4), positioned at the same height of the furnace (1) as the burner outlet (3). The tuyeres are used to draw additional air into the furnace and they are as such optional. The burner outlet (3) is a position inside the furnace (1) where a hot or burning gas or plasma enters the furnace (1) from a burner (6) such as an oxy-fuel burner, gas burner or plasma torch. The furnace (1) comprises a furnace wall (5) comprising a cooling mantle. The cooling mantle protects the furnace wall from the general temperatures within the furnace by circulating coolant in the mantle. Figure 2 shows a cross section of the shield (2) and furnace wall (5) with a plasma torch (6) inserted in position behind the shield (2) for delivering plasma to the furnace (1). The furnace wall comprises a burner aperture (19) defining an aperture axis at the centra of the burner aperture (19). The burner(6), in this case a plasma torch is positioned in the burner aperture (19). The same shield (2) is shown in figure 3 without the furnace (1) or the plasma torch (6).

[0085] The shield (2) comprises a collar (7) comprising a back plate (8) and a face plate (9). The collar (7) extends radially from the aperture without covering the burner aperture (19). Coolant passages (10) are provided in the face plate (9). The shield (2) further comprises a coolant inlet (11) and a coolant outlet (12) which allow coolant to pass through the furnace wall (5) and into the collar (7) of the shield (2). The coolant passages (10) fluidly connecting the coolant inlet (11) and the coolant outlet (12) through at least part of the collar (7). The shield (2) also comprises a lip (17) comprising a lip coolant passage (13) which is connected to the coolant passage in the collar (7) of the shield (2). Coolant may flow from a supply of coolant into the coolant inlet (11) through one or more coolant passages in the collar (7). From the coolant passages in the collar (7) the coolant may flow into the lip coolantpassage (13) and out of the lip through one or more coolant passages in the collar (7) and out of the coolant outlet (12). During this movement coolant absorbs heat from the shield (2) and transfers it away from the shield (2). Optionally heated coolant from the coolant outlet (12) is returned to the supply of coolant for recycling. The lip comprises a projecting plate (14) and a cap (15). The collar (7) of the shield may be surrounded by a flange (18). This flange (18) protects the shield (2) from the weight and movement of the matrix of raw material as it moves towards the bottom of the furnace (1).

[0086] Figure 3 shows the shield (2) as viewed from behind the back plate (8). The inner diameter of the collar (7) of the shield (2) corresponds to the diameter of a burner aperture (19) in the furnace wall (5), while the inner diameter of the lip (17) of the shield (2) is smaller which means that the lip (17) of the shield (2) covers part of the burner aperture (19). This allows the lip (17) of the shield (2) to protect the front of the plasma torch (6) when the furnace (1) is in use.

[0087] The collar (7) can have a peripheral radius of 250 mm and an inner radius of 90 mm and can have a thickness as measured from where it abuts the furnace wall (5) to the furthest it projects into the furnace (1) of 32 mm. The base plate (8) can have a thickness of 8 mm while the face plate (9) can have a thickness of 24 mm. The lip (17) can have an outer radius at the point where it is connected to the collar (7) of 125 mm and an inner radius closest to the furnace wall (5) of 60 mm. These dimensions are the same for the projecting plate (14). The projecting plate (14) can also have an outer radius where is projects furthest into the furnace (1) of 110 mm and an inner radius where it projects furthers into the furnace (1) of 70 mm. These dimensions are the same as for the cap (15) which is attached to the projecting plate (14) to form the lip (17). The lip (17) can have a thickness as measured from where it is attached to the collar (7) to the furthest it projects into the furnace of 48 mm while the projecting plate (14) can have a thickness of 40 mm and the cap (15) can have a thickness of 8 mm.The shield (2) as shown in figures 1-3 is constructed as described before by assembling the collar from the back plate (8) and face plate (9) where passages are milled into the face plate (9) and the lip (17) from a projecting plate (14) where a passage is milled into and a cap (15). The assembled pieces are then welded together to form the shield (2)

[0088] The dimensions given above for the different parts of the shield are suitable for a wide range of furnaces, burners, melts and raw materials. The dimensions can be changed according to needs and have variations of at least 10 % such as 20 %.

[0089] Various alternative approaches for manufacturing shields are possible. For example, Figures 4 and 5 respectively show cross sections through a collar and lip of a shield which are machined from a single solid piece of material. The coolant passages are provided by drilling straight passages into the piece rather than milled as they are in the construction shown in figures 2 and 3. Similarly the lip can be made from a single piece in the same manner which is shown in figure 5. Subsequently the ends of the holes drilled into the collar (7) and lip (17) are plugged to seal the passages in the shield (2). The plugging is done by welding or soldering. The passages are thereby provided along chord lines in the collar (7) or lip (17). Chord lines are defined here as straight lines passing through the collar (7) or lip (17) from one position on the periphery of the collar (7) or lip (17) to another position on the periphery of the collar (7) or lip (17).

[0090] Similar to the construction of the shield (2) shown in figures 2 and 3 the construction of the shield (2) shown in figure 4 and 5 coolant passages in the collar of the shield (2) are connected to the coolant passages (13) in the lip (17) in such a way that coolant can be passed from the inlet (11) of the shield into a coolant passage (10) of the collar (7) and from the coolant passage (10) in the collar (7) into the lip coolant passage (13) and from the lip coolant passage (13) back through a coolant passage (10) of the collar (7) and to the outlet (12) of the shield (2).The dimensions of the shield when constructed in this other way are similar and with similar variations as described for the first way of constructing the shield.

[0091] In use the furnace (1) is filled with a matrix of raw materials which rests on the base of the furnace (1) and fills its interior to the top of the furnace (1). The raw materials may comprise, stone, specifically volcanic rock, olivine or dolomite. They may also comprise recycled materials and blastfurnace slag, sand, recycled glass, limestone, soda ash and other chemical additives. In cupola or shaft furnaces these raw materials need to be of a certain size in order for the hot gasses to be able to move up through the furnace. Therefore, some of the raw materials may be shaped into briquettes with concrete or other binders in order for them have the correct size. Hot nitrogen gas or plasma with a temperature of 7000 °C (degrees Celsius) is provided through one or more plasma torches which are positioned at the lower half of the furnace (1). Coolant such as water is pumped through the shields (2) covering and surrounding the one or more plasma torches. The heat from the hot gas and / or plasma is absorbed by the matrix over time while some of the hot gas and / or plasma is reflected towards the shield (2). The heat which hits the shield (2) directly is absorbed by the cooling of the shield (2). As the matrix absorbs, the heat from the hot gas and / or plasma it begins to melt and flow down to the base of the furnace (1 ) filling the free space between non-melted parts of the matrix. As the melt rises in the furnace (1) creating a pool of melt, the melt may come into contact with the shield (2). The shield (2) cools the surrounding melt creating a protective layer of solidified melt covering the parts of the shield (2) which come into contact with the melt. When the level of melt has risen to above the height of the melt outlet it flows out of the furnace (1) and is sent through a gutter to a spinner for production of mineral wool.

[0092] In the drawings the shield and collar have been shown with a circular form. It will be appreciated that this is not essential and the shield may take a different shape.The temperature of different types of mineral melt can vary depending on which type of mineral melt is produced.

[0093] For glass, the temperature of the melt can be 900 to 1200 °C (degrees Celsius).

[0094] For stone or rock the temperature of the melt can be 1100 to 1700 °C (degrees Celsius).

[0095] The furnace is a generally upright shaft furnace or cupola furnace with a base and a top and sides stretching between the base and top. The furnace has a vertical axis passing through the center of the top and the base. Burner apertures are positioned in the sides of the furnace each with their own aperture axis passing through the center of each burner aperture. The aperture axes meet in the middle of the furnace at the vertical axis of the furnace. Generally, the aperture axes have a downward angle from the horizontal of 1 to 10 degrees such as 2, 3, 4, 5, 6, 7, 8 or 9 degrees preferably 6 degrees. One or more of these burner apertures are provided with shields (2) on the inside of the furnace wall surrounding the burner aperture. Burners such as plasma torches can be positioned through the furnace wall. A melt outlet is positioned at the base of the furnace which allows melted material to leave the furnace once the melt reaches a sufficient level within the furnace. The melt outlet therefore determines the height at which the melt is standing in the furnace when the furnace is in use. The burner apertures are placed at a height higher than the melt outlet.

[0096] Examples

[0097] One example of a shield according to the invention has the following measurements:

[0098] Collar peripheral radius: 250 mm

[0099] Collar inner radius: 90 mm

[0100] Lip outer radius: 124 mmLip inner radius: 60 mm

[0101] Such a shield is sized to fit a cupola furnace with an internal diameter of 1500 mm, a cross sectional area of about 1.8 square meters (m2) and a burner aperture diameter of about 180 mm. A plasma torch mounted in such a furnace can have an effect of about 2.3 MW.

[0102] Another example of a shield according to the invention has the following measurements:

[0103] Collar peripheral radius: 350 mm

[0104] Collar inner radius: 90 mm

[0105] Lip outer radius: 124 mm

[0106] Lip inner radius: 60 mm

[0107] Such a shield is sized to fit a cupola furnace with an internal diameter of 2250 mm, a cross sectional area of 3.97 square meters (m2) and a burner aperture diameter of about 180 mm. A plasma torch mounted in such a furnace can have an effect of about 6 MW.Figure references

[0108] Furnace (1)

[0109] Shield (2)

[0110] Burner outlet (3)

[0111] Tuyere (4)

[0112] Furnace wall (5)

[0113] Burner (6)

[0114] Collar (7)

[0115] Back plate (8)

[0116] Face plate (9)

[0117] Coolant passage (10)

[0118] Inlet (11)

[0119] Outlet (12)

[0120] Lip coolant passage (13)

[0121] Projecting plate (14)

[0122] Cap (15)

[0123] Lip (17)

[0124] Flange (18)

[0125] Burner aperture (19)

[0126] Items

[0127] 1. A furnace (1) for melting a matrix into a melt, the furnace (1) comprising

[0128] at least one furnace wall (5) comprising a melt outlet defining a melt level within the furnace and a burner aperture (19) above the melt level, the melt outlet and burner aperture extending through the furnace wall and a shield (2) comprising;a coolant inlet (11);

[0129] a coolant outlet (12); and,

[0130] a collar (7) extending radially from the burner aperture (19) across at least a part of an interior surface of the furnace wall (5), the collar comprising at least one coolant passage (10) fluidly connecting the coolant inlet (11) and the coolant outlet (12) through at least part of the collar (7).

[0131] 2. The furnace (1) according to item 1 wherein the furnace (1) is a cupola furnace.

[0132] 3. The furnace (1) according to any one of the preceding items, wherein the matrix comprises raw materials for making a mineral melt.

[0133] 4. The furnace (1) according to any one of the preceding items, wherein the raw material comprises stone.

[0134] 5. The furnace (1) according to any one of the preceding items further comprising at least one burner (6) positioned in the burner aperture (19).

[0135] 6. The furnace according to item 5 wherein the burner (6) comprises a burner outlet (3).

[0136] 7. The furnace according to item 6 wherein the burner outlet (3) has a radius which is smaller than the radius of the burner aperture (19).

[0137] 8. The furnace according to item 7 wherein the burner outlet (3) has a radius which is 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 or 0.2 times the radius of the burner aperture (19).

[0138] 9. The furnace (1) according to any one of items 5 to 8 wherein the at least one burner (6) is at least one plasma torch.10. The furnace (1) according to any one of items 5 to 9 wherein the at least one burner (6) is at least one arc plasma torch.

[0139] 11. The furnace (1) according to any one of items 5 to 10 wherein the at least one burner (6) is at least one non-transferred arc plasma torch.

[0140] 12. The furnace (1) according to any one of items 5 to 11 wherein part of the burner (6) projects into the furnace through the burner aperture (19).

[0141] 13. The furnace (1) according to any one of the preceding items wherein the collar (7) has an inner radius which is the same or larger than the radius of the burner aperture (19).

[0142] 14. The furnace (1) according to item 13 wherein the collar (7) has a peripheral radius which is at least 1.5 times the inner radius of the collar (7), such as 2, 3, 4 or 5 times the inner radius of the collar (7).

[0143] 15. The furnace according to any one of items 6 to 8 wherein the collar (7) has a peripheral radius which is at least 2.5 times the radius of the burner outlet (3).

[0144] 16. The furnace (1) according to any one of the preceding items the collar of the shield has a peripheral radius which is at least 15% of the inner radius of the cupola furnace at the tuyere level, preferably the peripheral radius of the collar is at least 25% of the inner radius of the cupola furnace at the tuyere level.

[0145] 17. The furnace (1) according to any one of the preceding items wherein the shield (2) further comprises a lip (17), extending from the collar towards the interior of the furnace (1).

[0146] 18. The furnace (1) according to item 17 wherein the lip (17) comprises:at least one lip inlet fluidly connected to at least one coolant passage of the collar;

[0147] at least one lip outlet fluidly connected to at least one coolant passage of the collar; and,

[0148] at least one lip coolant passage (13) connecting the lip inlet and the lip outlet.

[0149] 19. The furnace (1) according to any one of items 17 and 18 wherein the lip (17) has an outer radius which is smaller than the peripheral radius of the collar (7).

[0150] 20. The furnace (1) according to any one of items 17 to 19 wherein the lip (17) has an inner radius which is smaller than the radius of the burner aperture (19).

[0151] 21. The furnace (1) according to any one of the preceding items wherein the shield (2) comprises:

[0152] a back plate (8) with the coolant inlet (11) and the coolant outlet (12) extending through the back of the back plate (8);

[0153] a face plate (9) comprising at least one inlet coolant passage and at least one outlet coolant passage;

[0154] a projecting plate (14) comprising at least one projecting plate inlet, at least one projecting plate outlet and at least one projecting plate passage (13) connecting the projecting plate inlet and the projecting plate outlet; and, a cap (15).

[0155] 22. The furnace (1) according to item 21 wherein the back plate (8), inlet (11) and outlet (12) are made from steel.

[0156] 23. The furnace (1) according to any one of items 21 and 22 wherein the face plate (9), projecting plate (14) and cap (15) are made from copper or a copper alloy.24. The furnace (1) according to item 23, wherein the copper or copper alloy is oxygen free.

[0157] 25. The furnace (1) according to any one of items 21 to 24, wherein the back plate (8), face plate (9), projecting plate (14) and cap (15) are assembled by soldering or welding.

[0158] 26. The furnace (1) according to any one of items 21 to 25, wherein the inlet coolant passage, the outlet coolant passages and / or the projecting plate passage are provided by milling.

[0159] 27. The furnace (1) according to any one of items 21 to 26, wherein the back plate (8) and the face plate (9) make up the collar (7) of the shield (2) and the projecting plate and the cap make of the lip (17) of the shield (2).

[0160] 28. The furnace (1) according to any one of the preceding claims, wherein the coolant passages and / or lip coolant passages are provided along chord lines.

[0161] 29. The furnace (1) according to any one of the preceding items, wherein the collar (7) comprises at least four coolant passages (10).

[0162] 30. The furnace (1) according to any one of the preceding items wherein each coolant passage (10) covers at least an angular quarter of the collar (7) of the shield (2) in a meandering path.

[0163] 31. The furnace (1) according to any one of the preceding items wherein the furnace (1) further comprises a flange (18) attached to the furnace wall (5) where the flange (18) surrounds the collar (7) of the shield (2).

[0164] 32. The furnace (1) according to any one of the preceding items wherein the furnace (1) comprises at least 2 shields such as 3, 4, 5 or 6 shields.33. The furnace (1) according to any one of the preceding items wherein the burner (6) is positioned at an angle downward from horizontal of 0 to 10° such as 1 , 2, 3, 4, 5, 6, 7, 8 or 9°

[0165] 34. A method for melting a matrix of raw materials in a furnace (1) according any one of the preceding items comprising the step of passing a heated gas or plasma through the burner aperture (19) into the furnace (1) to heat the matrix of raw materials until it melts.

[0166] 35. The method for melting a charge of materials according to item 34 further comprising the step of passing a coolant through the coolant passages (10, 13) in the shield (2).

[0167] 36. The method according to any one of items 34 and 35 wherein the matrix comprises raw materials for production of a mineral melt.

[0168] 37. The method according to item 36 wherein the mineral melt is a stone or glass melt for production of mineral fibres.

Claims

Claims1. A cupola furnace for melting a matrix into a melt, the furnace comprisingat least one furnace wall comprising a melt outlet defining a melt level within the furnace and a burner aperture above the melt level, the melt outlet and burner aperture extending through the furnace wall anda shield comprising:a coolant inlet;a coolant outlet; and,a collar extending radially from the burner aperture across at least a part of an interior surface of the furnace wall, the collar comprising at least one coolant passage fluidly connecting the coolant inlet and the coolant outlet through at least part of the collar.

2. The furnace according to any one of the preceding claims wherein the shield further comprises a lip extending from the collar towards the interior of the furnace.

3. The furnace according to claim 2 wherein the lip comprises:at least one lip inlet fluidly connected to at least one coolant passage of the collar;at least one lip outlet fluidly connected to at least one coolant passage of the collar; and,at least one lip coolant passage fluidly connecting the lip inlet and the lip outlet through at least part of the lip.

4. The furnace according to any one of claims 2 and 3 wherein the lip has an outer radius which is smaller than the peripheral radius of the collar.

5. The furnace according to any one of claims 2 to 4 wherein the lip has an inner radius which is smaller than the radius of the burner aperture.

6. The furnace according to any one of the preceding claims further comprising at least one burner positioned in a burner aperture the burner configured to supply heated gas or plasma through the burner aperture.

7. The furnace according to claim 6 wherein the burner has a burner outlet, the burner outlet has a radius which is smaller than the radius of the burner aperture, preferably the burner outlet radius is 0.9 to 0.2 times the radius of the burner aperture and even more preferably the burner outlet radius is 0.6 to 0.4 times the radius of the burner aperture.

8. The furnace according to any one of claims claim 6 or 7 wherein the at least one burner is at least one plasma torch, preferably an arc plasma torch and more preferably a non-transferred arc plasma torch.

9. The furnace according to any one of claims 6 to 8 wherein part of the burner projects into the furnace through the burner aperture.

10. The furnace according to any one of claims 6 to 9wherein the burner is positioned at an angle downward from horizontal of 0 to 10 degrees such as 4 to 8 degrees.

11. The furnace according to any one of the preceding claims wherein the collar has an inner radius which is the same or larger than the radius of the burner aperture and a peripheral radius which is at least 1.5 times the inner radius of the collar, preferably 2 to 5 times the inner radius of the collar.

12. The furnace according to any one of the preceding claims wherein the shield comprises:a back plate with the inlet and the outlet attached to the back of the back plate;a face plate comprising at least one inlet coolant passage and at least one outlet coolant passage;a projecting plate comprising at least one projecting plate inlet, at least one projecting plate outlet and at least one projecting plate passage connecting the projecting plate inlet and the projecting plate outlet; and,a cap.

13. The furnace according to claim 12 wherein the back plate, inlet and outlet are made from steel and the face plate, projecting plate and cap are made from copper or a copper alloy, preferably the copper or copper alloy is oxygen free.

14. The furnace according to any one of the preceding claims wherein the furnace further comprises a flange attached to the furnace wall where the flange surrounds the collar of the shield.

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