Furnace for melting granular material

Abstract

To provide a furnace for melting granular material.SOLUTION: The present application discloses a furnace for melting particulate material comprising a furnace chamber (12), a feed hopper (14), a snout (18) and at least one burner (16). The particulate material falls along the projections into the melting vessel 13 and the flue gases 19 produced by the burners flow upwards, thereby preheating the particulate material. This process of preheating particulate material utilizing flue gas begins with the flue gas in the high temperature section. The efficiency of the preheating of the particulate material by the flue gases is significantly improved and the heat losses are reduced.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to the field of melting and to a melting device for melting materials, more particularly to a furnace for melting granular materials. [Background technology]

[0002] Rock wool (mineral wool or stone wool) is a fibrous material formed by spinning or stretching molten minerals or rocks. Rock wool can be used for thermal insulation, filtration, and soundproofing. Traditionally, the conventional method for producing rock fiber or slag fiber melts uses a shaft furnace. A free-standing stack of granular material is heated by burning fuel in the shaft furnace. This stack gradually melts while being replenished from the top, and the molten material flows down the stack and is discharged from the bottom. A common furnace used for this purpose is a hot metal furnace. The granular material can be coarse crushed rock, crushed stone, crushed slag, or briquettes made from fine granular material. Dry granular material has low thermal conductivity and emissivity, making it a poor conductor of heat. Therefore, accumulated granular material degrades the heat energy transferred from the burner. Even though the surface of the stack softens due to melting, the interior of the stack remains unevenly heated.

[0003] The invention patent with publication number (Patent Document 1) discloses an exemplary apparatus for producing rock wool using a hot metal furnace. In the hot metal furnace, for example, basalt, blast furnace slag, and coke are melted to produce rock wool and cast iron. The slag and cast iron, primarily containing metal, are separated and then combined in a final process to obtain rock wool. This type of hot-air combustion-assisted melting technology uses hot air obtained by heat exchange between the hot metal furnace exhaust gas and cold air as the combustion-assisted gas. However, this method results in a slow furnace heating rate due to the low oxygen content of air. Insufficient fuel combustion results in high levels of CO and other gases remaining in the furnace. The resulting rock wool fibers are short and thick, with poor flexibility and elasticity.

[0004] The Chinese invention patent (Patent Document 2) discloses a furnace apparatus for producing glass, basalt fiber, or rock wool. A schematic diagram of the furnace apparatus is shown in Figure 1. The inner surface of the rear section of the bottom wall 304 of the furnace body 30 is generally raised upward to form the bottom of the pre-melting tank 34. The bottom of the pre-melting tank generally protrudes upward to form a tab 35 near the discharge side. A flue gas port 31 is provided at the top of the rear side wall 302, and the flue gas port 31 is located higher than the tab 35. A pair of first combustion lances 50 is symmetrically arranged above the pre-melting area near the discharge side of the pre-melting tank. Two first combustion lances 50 are inserted into the furnace chamber from the left and right side walls of the furnace body, with nozzles facing each other and both pointed toward the raw material pile. Four pairs of second combustion lances 60 are inserted into the furnace chamber from the left and right side walls of the furnace body. A silo is provided at the rear upper part of the furnace. The disadvantages of this type of furnace are high investment costs and very low waste heat recovery efficiency. The contact time between the flue gas and the material is very short. The dead zone of solidification formed by the natural accumulation of material is excessive, which results in a large amount of waste that cannot be melted.

[0005] One or more burner nozzles positioned below the melt surface allow the burner flame and / or combustion products to pass through the melt. This configuration is called a submerged burner. U.S. Patent Publication No. 2003 / 0109998 discloses a method and apparatus for melting solid raw materials using submerged burners. A melting chamber is equipped with at least five submerged burners, each with a central axis protruding from the outlet. The submerged burners are arranged in a substantially annular combustion area. At the bottom of the melting chamber, adjacent burners are spaced apart from each other and controlled so that computational fluid dynamics simulations show the generation of a substantially annular melt flow in the melt. The burners are positioned at an appropriate distance of approximately 250 to 750 mm from the sidewall of the combustion chamber. This is to prevent the layer of solidified material on the wall from becoming excessively thick. Excessive distance from the burners can result in undesirable melt flow and blind spots in the center of the furnace where the melt is not mixed sufficiently, resulting in reduced melt uniformity.

[0006] The drawbacks of the above-mentioned prior art are also very obvious. Flue gas from the furnace can reach temperatures of up to 1350°C or higher, and this portion of the flue gas absorbs approximately 17-21% of its energy. In the prior art, a waste heat boiler or heat exchanger is added to the low-temperature section of the flue. The flue gas in the high-temperature section is not fully utilized, resulting in low flue gas heat recovery efficiency. Furthermore, materials such as rock wool soften at high temperatures, making the high-temperature section prone to clogging. While electric furnaces can sometimes be used to increase the melting area, they are prone to damage, have a short lifespan, and high maintenance costs. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US11254599B2 specification [Patent Document 2] CN110922028B specification [Patent Document 3] US10336640B2 specification Summary of the Invention [Problem to be solved by the invention]

[0008] A general object of the present disclosure is to provide a furnace for melting granular material, which furnace has a significantly high flue gas heat recovery rate. [Means for solving the problem]

[0009] A first aspect of the present application provides a furnace for melting granular material, the furnace comprising: a furnace chamber including a melting tank having a side wall, a bottom wall, and a melt surface; a feed hopper configured to supply particulate material to the furnace chamber, the feed hopper including a feed opening; a protrusion positioned between the feed opening and the melting tank and protruding upward from the bottom wall of the furnace chamber so that the particulate material descends along the stack surface toward the melting tank; at least one burner configured to heat the granular material in the melting tank to form a melt and generate flue gases; The device is configured to include:

[0010] According to an exemplary embodiment of the present invention, flue gas flows upward along the stack surface, thereby preheating the granular material.

[0011] According to an exemplary embodiment of the present invention, the dead zone and fluidized layer are formed continuously from the stack surface to the sidewall of the furnace chamber.

[0012] According to an exemplary embodiment of the present invention, the protrusions are shaped as a multi-gradation stepped configuration, stairs, rectangular blocks, trapezoidal blocks or conical blocks.

[0013] According to an exemplary embodiment of the present invention, the top of the protrusion is located below the feed opening and above the melt surface.

[0014] According to an exemplary embodiment of the present invention, the protrusion is adjacent to a side wall of the furnace chamber.

[0015] According to an exemplary embodiment of the present invention, the protrusion and the melt outlet of the furnace are located on opposite sides of the furnace.

[0016] According to an exemplary embodiment of the present invention, at least one burner is adjacent to the bottom wall of the furnace chamber.

[0017] According to an exemplary embodiment of the present invention, at least one burner is a submerged burner.

[0018] The at least one submerged burner comprises three or more submerged burners, the three or more submerged burners sharing a common cooling system and / or fuel and oxidant supply system.

[0019] According to an exemplary embodiment of the present invention, the submerged burner comprises a fuel passage and an oxidizer passage, which are constructed to discharge the fuel and oxidizer, respectively, outside the submerged burner, allowing the fuel and oxidizer to mix outside.

[0020] According to an exemplary embodiment of the present invention, the melting tank is a rectangular space bounded by a bottom wall and four side walls.

[0021] According to an exemplary embodiment of the present invention, the height of the vertical protrusion is 1.3 to 6 times, preferably 1.5 to 5 times, more preferably 2.5 to 4.5 times the set value of the melt depth in the melting tank.

[0022] According to an exemplary embodiment of the present invention, the outermost point of the protrusion projected onto a horizontal plane downstream along the melt flow direction is marked as X, and the horizontal distance L1 between X and the central axis of the nearest burner is greater than 200 mm, preferably in the range of 200 mm to 500 mm.

[0023] According to an exemplary embodiment of the present invention, downstream along the melt flow direction, a line connecting M and X, which are the end points of the top surface of the protrusion, forms an angle (F) with the horizontal plane in the range of 25° to 80°, preferably 35° to 75°, and more preferably 50° to 70°.

[0024] According to an exemplary embodiment of the present invention, downstream along the melt flow direction, a line connecting endpoints M and X of the top surface of the protrusion forms an angle (F) with the horizontal plane at an angle greater than the static angle of repose of the granular material.

[0025] According to an exemplary embodiment of the present invention, downstream along the melt flow direction, the outermost point of the feed opening projected onto a horizontal plane is marked as Y, and the horizontal distance L2 between X and Y is in the range of 200 mm to 1000 mm.

[0026] According to an exemplary embodiment of the present invention, the granular material has a particle size in the range of 20-80 mm, preferably 50-80 mm.

[0027] According to an exemplary embodiment of the present invention, the melting tank is an annular space bounded by a bottom wall of the furnace and a peripheral side wall of the furnace, and the protrusion is positioned within the annular furnace.

[0028] According to an exemplary embodiment of the present invention, the protrusions are circumferentially arranged and together with the bottom wall of the furnace and the side wall of the furnace define a melting tank.

[0029] In accordance with an exemplary embodiment of the present invention, the feed openings are equally spaced circumferentially.

[0030] A second aspect of the present application provides a method of melting granular material, said method comprising melting granular material in a melting bath of a furnace in accordance with the foregoing.

[0031] A third aspect of the present application is a method for preheating granular material using flue gas produced from a furnace, comprising: providing a furnace, the furnace comprising a furnace chamber, the granular material being fed into the furnace chamber (12) via a feed hopper; one or more burners disposed on the furnace configured to combust a fuel and an oxidant, thereby generating flue gas; providing a protrusion positioned between the feed opening and the melter bath, the protrusion defining a stack surface along which the granular material enters the melter bath in a direction opposite to the flow of flue gas, whereby the granular material is preheated, at least partially melted, and falls onto the melt surface; The present invention provides a method comprising:

[0032] Compared with the prior art, the technical solution provided in this application has the following advantages: 1. The entire furnace protrusion lifts the pile formed by the continuously falling granular material, thus increasing the contact time between the granular material and the flue gas. 2. The protrusion and the melt outlet are located on opposite sides of the furnace, which greatly increases the efficiency of the flue gas preheating the granular material and the heat recovery efficiency of the flue gas. 3. The process of preheating granular material with flue gas starts with hot flue gas, and there is no need to cool the flue gas, thereby reducing heat loss. 4. The granular material softens and melts during the preheating stage and enters the melt bath, thereby accelerating the formation of the melt. 5. The flame and combustion products of the submerged burner are in direct contact with the medium to be heated, and the heat transfer time is long and the heat exchange is complete, thereby improving energy efficiency and reducing CO2 and NO X emissions will decrease. 6. Submerged burner combination allows flexibility to meet various power range requirements, reduces costs and saves space by creating a more compact structure.

[0033] The advantages and spirit of the present application will be further understood from the following detailed description of the invention and the drawings. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 is a schematic diagram of the furnace disclosed in the '661 patent. [Figure 2] FIG. 2 is a schematic diagram of the furnace structure of the first embodiment provided in the present application. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is a schematic diagram of the furnace structure of the first embodiment provided in the present application, which is equipped with an exhaust gas passage. [Figure 5] FIG. 5 is a schematic diagram of the furnace structure of the second embodiment provided in the present application. [Figure 6] FIG. 6 is a cross-sectional view taken along line BB in FIG. [Figure 7] FIG. 7 is a schematic diagram of the furnace structure of the third embodiment provided in the present application. DETAILED DESCRIPTION OF THE INVENTION

[0035] In the figure, 11 indicates the furnace, 121 indicates the bottom wall (of the furnace), 122 indicates the side wall (of the furnace), 12 indicates the furnace chamber, 13 indicates the melting tank, 14 indicates the feed hopper, 15 indicates the feed opening, 151 indicates the screw feeder, 16 indicates the (submerged) burner, 17 indicates the melt surface, 18 indicates the protrusion, 19 indicates the flue gas, 20 indicates the stack surface, 21 indicates the dead zone, 22 indicates the fluidized bed, 23 indicates the exhaust gas passage, 24 indicates the silo, 25 indicates the temperature control device, and 26 indicates the melt outlet.

[0036] Specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, it should be understood that the present application is not limited to the embodiments described below, and the technical ideas of the present application can be implemented in combination with other known technologies or other technologies that function similarly to these known technologies.

[0037] In the following description of specific embodiments, many directional terms are used to clearly indicate the structure and operation of the embodiments. However, it should be understood that terms such as "front," "rear," "left," "right," "outside," "inside," "outward," "inward," "axial," and "radial" are not limiting terms but are terms of convenience.

[0038] In the following description of specific embodiments, terms such as "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inside," and "outside" are used to indicate orientations or positional relationships based on those shown in the drawings and are intended only to facilitate a simplified description. They are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be configured, or operate in a particular manner, and therefore should not be construed as limiting the present application. Furthermore, when a first structure is described as being positioned "above" or "below" a second structure, this should be understood to mean that the first structure is positioned further or closer to a horizontal plane. In the present application, the plane on which the bottom wall of the furnace is located is defined as the horizontal plane.

[0039] Additionally, the terms "first" and "second" are used for descriptive purposes only, without limiting chronological order, quantity, or importance, and should not be interpreted as indicating or implying relative importance or as implicitly specifying the number of technical features depicted. Rather, they should be interpreted merely as a means to distinguish one technical feature from another in the technical solution. Consequently, a feature defined as "first" or "second" may explicitly or implicitly include one or more such features. In the description of this application, "plurality" ("multiple") means two or more unless otherwise specified. Similarly, modifiers such as "a" ("one") appearing in this specification are not intended to be quantitative, but rather to describe a technical feature not appearing in the preceding sentence. Similarly, unless modified by a specific word expressing quantity, nouns in this specification should be considered to include both the singular and the plural, i.e., a technical solution may include a single related technical feature, but may also include multiple technical features. Similarly, modifiers such as "approximately" or "about" that appear before a number in this specification generally include that number (actual number), and the specific meaning thereof should be understood within the context.

[0040] In this application, "at least one" should be understood to mean one or more, and "plurality" means two or more. The term "and / or" is used to express a relationship between related objects and indicates that three relationships may exist. For example, "A and / or B" may refer to three situations: only A is present, only B is present, or both A and B are present, where A and B may be singular or plural. The symbol " / " generally indicates an "or" relationship between the related objects before and after it. "At least one of the following items" or similar expressions refers to any combination of these items, including any combination of single items or multiple items. For example, at least one of a, b, or c may refer to a, b, c, "a and b," "a and c," "b and c," or "a, b, and c," where a, b, and c may be singular or plural.

[0041] For purposes of this application, unless expressly provided and limited, terms such as “attached,” “connected,” “joined,” “fixed,” etc. shall be broadly interpreted, e.g., there may be a fixed connection, a detachable connection, or an integral connection; there may be a mechanical connection or an electrical connection; there may be a direct connection or an indirect connection via an intermediary; there may be a connectivity within two elements or an interactive relationship between two elements. For those skilled in the art, the specific meaning of the above terms in this application may be understood on a case-by-case basis. “Fixed coupling” or “fixed connection” or “inert coupling” shall be understood to mean that the connection between two or more structural members is not configured to provide relative movement. Examples of fixed connections are welded or bolted connections, and in some cases, welded and threaded connections. “Moveable connection” or “movable” or “movable connection” shall be understood to refer to a connection between two or more structural members that allows relative horizontal and / or vertical movement between the members under extreme dynamic loads. Such connections typically do not allow movement under static or general dynamic loads (e.g., as imposed by light / weak winds).

[0042] The terms "unit," "piece," "thing," and "module" used in this specification refer to a unit for processing at least one function or operation, and may be implemented by hardware components or software components or a combination thereof.

[0043] The terms "upstream" and "downstream" as used herein are defined with respect to the expected flow of a fluid (e.g., melt in a furnace). The upstream end corresponds to the end closest to the inlet where the fluid enters the furnace. The downstream end corresponds to the outlet or nozzle end where the fluid exits the furnace. Furthermore, positions or areas away from the protrusion are downstream in the direction of melt flow, and positions or areas closer to the protrusion are upstream in the direction of melt flow.

[0044] Unless expressly indicated to the contrary, each aspect or embodiment defined herein may be combined with any other aspect or embodiment. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

[0045] term A furnace is a kiln suitable for and / or configured to melt granular materials. Granular materials may refer to any material suitable for fiber production, including, but not limited to, glass fiber, mineral fiber, rock fiber, or slag fiber. The raw material for producing rock wool or basalt fiber is block rock. Melting block rock in a furnace is a process in which the rock absorbs heat from a low-temperature solid state to soften and melt. The melting temperature of block rock typically exceeds 1000°C, making furnaces particularly energy-intensive. Rock wool is a mineral made from natural ores such as basalt (or gabbro) and is processed into products such as rock wool panels, rock wool felt, and rock wool pipe casing, depending on the application. The particle size of the granular material used in this application ranges from 0.05 mm to 80 mm, preferably from 20 mm to 80 mm.

[0046] For stacked granular material systems, the angle of repose is one of the most important parameters that describes the fundamental properties of particles related to friction. The angle of repose refers to the finite angle at which a particle stack can remain at rest relative to a horizontal surface. In practice, the angle of repose can take on a range of values ​​before the stacked pile loses stability, i.e., there is a maximum stable angle before collapse occurs. A large amount of granular material is dumped on a horizontal surface and piles up in a cone shape. The included angle between the surface of the pile and the horizontal surface is the angle of repose. The angle of repose is related to particle density, particle surface area, particle shape, and the coefficient of friction.

[0047] The angle between the inclined plane of the free pile and the stationary horizontal plane is the static angle of repose. When measuring the static angle of repose, due to the presence of fine particles in the loose granular material, once it has piled up to a certain level, some of the loose pile will be prone to collapse under the action of gravity or impact forces. The air trapped between the particles of the loose pile will change the fluidity, so the actual angle of repose is often lower than the theoretical static angle of repose. When there are many large-sized loose piles, few small-sized materials, and a lot of air in the loose pile, the angle between the hypotenuse of the collapse of the loose pile and the bottom edge will often not be equal to the theoretical static angle of repose.

[0048] Those skilled in the art are familiar with various methods for measuring the static angle of repose, such as powder physical property testers. The discharge angle method, pour angle method, sliding angle method, and shear box method are common methods for testing the angle of repose of powders.

[0049] As used herein, the term "fuel" refers to gaseous, liquid, or solid fuels, which may be used interchangeably or in combination. If at least partially gaseous, it may be introduced directly into the burner. If liquid or solid, it is introduced near the burner. Gaseous fuels may be natural gas (primarily methane), propane, hydrogen, syngas, biomass gas, or any other hydrocarbon and / or sulfur-containing and / or nitrogen-containing compounds. Solid or liquid fuels may be any compound primarily in carbon and / or hydrocarbon and / or sulfur-containing form. Those skilled in the art can determine the method of introducing gaseous, liquid, or solid fuels as desired, and the present invention does not intend to impose any limitations.

[0050] As used herein, the term "nozzle" refers to the component located at the end of the burner that ejects fuel and oxidant to cause their combustion, and may be a standalone component or a component integrated with other components.

[0051] As used herein, the terms "melting" and "dissolving" include the act of heating a heated medium from a substantially solid state to a substantially liquid state. The composition of the heated medium can exist in any state between a substantially solid state and a substantially liquid state, including a substantially solid state and a substantially liquid state, such states being between a solid particulate material and a melt with any range of partial melting.

[0052] As used herein, the term "melt" or "molten material" refers to a substance obtained by melting, which may contain inorganic components, metals, or organic components, etc., and may be molten rock wool, molten glass, molten metal, molten resin, molten waste, etc.

[0053] As used herein, the term "preheating" refers to heating of particulate material prior to introduction into the melting bath.

[0054] As used herein, refractory materials are defined as materials and products (not excluding materials containing metallic components) that have a heat resistance equivalent to at least 1500°C. This definition means that the heat-resistant material can withstand at least 1500°C without softening or collapsing under its own weight according to heat resistance test standards. The surface in contact with the molten material or melt may be a water jacket assembly or a combination of refractory materials. The water-cooled jacket assembly may be a piping network structure that allows the passage of a cooling fluid, such as water. The protrusion may include a water-cooled jacket assembly or refractory materials.

[0055] Hereinafter, specific embodiments of the present application will be described in detail in conjunction with the drawings. The embodiments can be seen through multiple perspective drawings. The same reference numerals in the embodiments generally indicate the same or corresponding components. Therefore, the descriptions of the embodiments are incorporated into each other, and the description of the subject matter common to each embodiment will generally not be repeated in this specification.

[0056] Embodiment 1 2 shows a structural schematic diagram of an exemplary furnace of the present invention. The furnace 11 has a furnace chamber 12 for melting granular material. The furnace chamber 12 is configured with a melting tank 13, i.e., a space for melting, surrounded by at least a bottom wall 121 and side walls 122. The body of the furnace 11 is made of a refractory material. The melting tank 13 is, for example, a substantially rectangular space surrounded by the bottom wall 121 and four side walls 122.

[0057] The feed openings 15 of one or more feed hoppers 14 face the bottom wall 121 of the furnace. The granular material falls through the feed openings 15. At this point, the feed openings 15 and the furnace's melt outlet 26 are located on opposite sides of the furnace. A feed system such as a feed hopper known to those skilled in the art is used. In this embodiment, basalt ore and dolomite ore with particle sizes ranging from 20 to 80 mm (preferably 50 to 80 mm) are selected as examples. The centers of blocks with larger particle sizes are very difficult to heat. If the granular material also includes powdery granular material with particle sizes ranging from 0.05 to 2 mm, a screw feeder 151 can be used in conjunction with the feed system. The screw feeder 151 can be mounted horizontally on one side of the feed openings 15, and this portion of the powdery material is fed to the granular material falling through the feed openings 15, where it is mixed and moves downstream together.

[0058] At least one submerged burner 16 located in the bottom wall 121 provides thermal energy. The thermal energy is transferred from the submerged burner flame to the melt surface 17. The submerged burners 16 extend upward from the bottom wall 121 into the melt. Fuel and oxidizer introduced through nozzles at the ends of the submerged burners 16 are combusted to produce flue gases 19. The submerged burners preferably discharge combustion products at high pressure into the melt. The flue gases 19 rise through the melting vessel 13, and the particulate material enters the melting vessel 13 in a direction opposite to the escaping flue gases 19. The particulate material is thus preheated and at least partially melted. For a given submerged burner design, one skilled in the art must adjust the distances between the burners and between the burners and the walls. Adjacent burners at the bottom of the furnace are spaced and controlled. Multiple submerged burners 16 may share a cooling system and / or a fuel and oxidizer supply system. The submerged burner 16 may include a fuel passage and an oxidizer passage (not shown). The fuel passage and the oxidizer passage are configured to discharge fuel and oxidizer, respectively, to cause the fuel and oxidizer to mix. The flame direction of the submerged burner attached to the bottom wall 121 of the furnace is upward. Exemplarily, the angle between the flame direction and the vertical extension is between 0 and 10 degrees.

[0059] Advantageously, the submerged burner can use hydrogen as fuel. Hydrogen has many advantages as a clean energy source. Because submerged combustion performs heat transfer by direct contact and heat convection, the heat of the hydrogen flame is completely transferred to the heated material, thus enabling better utilization of the thermal energy of hydrogen combustion. Hydrogen as fuel for the submerged burner also has the following advantages: water is the only product of its oxidative combustion, thus reducing carbon dioxide emissions from this combustion process; when hydrogen is used as fuel, the partial pressure of the gaseous water produced is different from that of other gases present in the glass, which makes it easier for these gas bubbles to absorb and coalesce to form large bubbles that are then expelled; furthermore, the large amount of OH ions produced by hydrogen combustion can reduce the surface tension of the abundant bubbles of various sizes in the glass liquid, facilitating the escape of the gas in the bubbles from the melt. The above advantages of hydrogen make it suitable for use as a fuel for submerged burners in material melting.

[0060] Considering the particle size, composition, moisture content, and other factors of the basalt particles in this embodiment, the theoretical static angle of repose is 35°. The protrusion 18 is specifically provided to improve the heat exchange efficiency between the pile formed by the particles and the flue gas. The protrusion 18 is located near one of the side walls of the furnace chamber, between the feed opening 15 and the melting tank 13. Preferably, the protrusion 18 and the furnace melt outlet 26 are located on opposite sides of the furnace. The protrusion 18 can lift the pile formed by the continuously falling granular material, thereby increasing the heat exchange area between the granular material and the flue gas 19 and increasing the effective heat transfer from the flue gas to the granular material. The existence of a conventional dead zone makes heat exchange between the flue gas and the granular material particularly difficult. Therefore, it is a further objective of the present application to utilize the temperature of the flue gas to preheat more granular material, allowing this granular material to melt and soften before finally falling into the melting tank, thereby facilitating the formation of a melt in the melting tank. The protrusions 18 can withstand the pressure of the granular material continuously descending over them, thereby extending the contact time between the granular material and the flue gas 19. The protrusions 18 define a stack surface 20 that contacts the granular material. The area from the stack surface 20 to the side wall of the furnace chamber is successively formed with a dead zone 21 and a fluidized layer 22. The dead zone 21 is a holding layer of granular material, where the granular material is mostly in an unmelted solid state. The fluidized layer 22 is a mobile layer of granular material, where the granular material, after some softening, is in a transition state that includes both a solid and a liquid state. Another objective is to minimize the risk of clogging the feed stream or blocking the flue gas due to overheating, melting, or rapid softening of the granular material.

[0061] This embodiment is not intended to limit the particular shape of the protrusions 18, which may be, for example, a multi-gradation stepped configuration or staircase, rectangular blocks, trapezoidal blocks, conical blocks, or other pile-like structures. The tops of the protrusions 18 are positioned below the feed opening 15 and above the melt surface 17.

[0062] The height of the vertical protrusion 18 is 1.3 to 6 times, preferably 1.5 to 5 times, and more preferably 2.5 to 4.5 times the set melt depth in the melting tank. The set melt depth is considered to be the target melt height after stable operation of the furnace, i.e., the height from the melt surface 17 to the bottom wall 121 of the furnace.

[0063] The melt can be removed continuously or in batches. A melt outlet 26 is located near the bottom wall of one of the short side walls of the rectangular melting tank. When loading the granular material near the side wall of the furnace, the melt outlet is preferably located opposite the feed opening. In the case of discontinuous melt discharge, the opening and closing of the melt outlet can be controlled, for example, by a ceramic piston. As the granular material continues to melt, the melt forms a melt surface 17 within the melting tank, which may be the upper surface of the melt. The flow direction of the formed melt is generally shown in FIG. 2 as being from right to left. Therefore, a location or area to the left near the melt outlet 26 in FIG. 2 is downstream in the melt flow direction, while a location or area to the right away from the melt outlet 26 is upstream in the melt flow direction.

[0064] As shown in Figure 2, the leftmost end point of the protrusion 18 downstream along the melt flow direction is marked as X. The horizontal distance L1 between X and the central axis of the nearest submerged burner 16 is greater than 200 mm, preferably 200-500 mm. If L1 is too short, the bubbles formed by the submerged burner 16 will collide with the granular material descending along the protrusion and wash the walls of the protrusion, affecting the effective melting of the granular material and the furnace life. If L1 is too long, the heat exchange efficiency between the flue gas 19 and the granular material will decrease, and the dead zone area will become larger.

[0065] The trapezoidal cross-section of the protrusion shown in FIG. 2 is an example. Downstream along the melt flow direction, a line connecting the leftmost end point M of the top surface of the protrusion with X forms an arc angle (F) with the horizontal plane that exceeds the static angle of repose of the granular material, e.g., in the range of 25° to 80°, preferably 35° to 75°, and more preferably 50° to 70°. Y is the projected end point of the feed opening 15 along the more downstream (i.e., leftmost) side, and the horizontal distance L2 between X and Y is in the range of 200 to 1,000 mm. The distance between X and Y ensures that the descending granular material is more tilted to descend along the surface of the protrusion, reducing the likelihood of accumulation on the already softened granular material.

[0066] The technical solution of this embodiment is to preheat the granular material by using the flue gases produced by combustion in the submerged burners of the furnace. The temperature of the flue gases leaving the melt is related to the depth of the melt in the furnace, the flame characteristics of the submerged burners, the type of fuel and oxidant, and the physical properties of the melt.

[0067] As an example, the furnace in this embodiment has a vertical height of approximately 1,300 mm from the top of the furnace to the bottom wall of the furnace. The bottom wall of the furnace is equipped with eight multi-nozzle (12-nozzle) submerged burners, each with an output of 80 kW or less. Take a production line where the furnace has a discharge capacity of 120 tons / day as an example. After the furnace stabilizes, the melt depth reaches a set value of 650 mm, at which point the melt surface in the furnace stabilizes. The vertical distance from the feed opening 15 to the melt surface is approximately 4 meters. The maximum height of the vertical protrusion is 3.25 meters.

[0068] Figure 3 shows a cross-sectional view taken along line AA in Figure 2. The cross-sectional width of the feed opening 15 is approximately 70% to 100% of the width L3 of the side wall at the charging end of the furnace.

[0069] Figure 4 further shows a schematic diagram of the rectangular furnace of Figure 2 equipped with an exhaust gas channel. The flue gas exhaust leaving the furnace continues into the exhaust gas passage 23. Granular material conveyed by a silo 24 connected to the feed hopper first exchanges heat with this part of the flue gas exhaust, improving the utilization of the flue gas.

[0070] Flue gas 19 generated from the submerged burner 16 escapes from the melt at 1500°C and reaches a temperature of approximately 1350°C to 1200°C above the melt surface 17. In this embodiment, the flue gas can be classified into high-temperature flue gas (temperature above 800°C), medium-temperature flue gas (500 to 800°C), and low-temperature flue gas (less than 500°C, preferably less than 300°C, more preferably less than 150°C). In this embodiment, the flue gas that contacts the granular material descending through the protrusion 18 in the melting tank 13 is primarily high-temperature flue gas. Furthermore, the flue gas that rises to the vicinity of the feed opening 15 is primarily medium-temperature flue gas. The flue gas discharged from the exhaust gas passage 23 is primarily low-temperature flue gas. The low-temperature flue gas directly heats the granular material from the silo 24, the belt conveyor that transports the granular material, and the like. Devices for regulating the flow of flue gases, such as exhaust fans, are well known to those skilled in the art for controlling the residence time of the flue gases in the furnace and will not be discussed here. On one side of the feed opening 15, a temperature control device 25 is provided to control the temperature at which the flue gases enter the exhaust gas passage 23 to prevent overheating of the feed hopper 14.

[0071] Compared to melting the same granular material in a furnace with direct submerged burners, heat losses can be reduced from approximately 21% to 5%-13% if the temperature of the final escaping flue gas exhaust is reduced to below 150°C.

[0072] Embodiment 2 Figure 5 shows a schematic diagram of another type of furnace of the present application. Figure 6 shows a cross-sectional view along line BB in Figure 5. The furnace chamber comprises a melting tank 13 as known to those skilled in the art. The melting tank 13 is an annular space surrounded by a bottom wall 121 and a side wall 122, where at least one feed opening 15 is located in the center of the furnace.

[0073] The protrusions 18 may be positioned within the tubular furnace, preferably at the center thereof. Flue gases generated by at least one submerged burner 16 attached to the bottom wall 121 of the furnace flow upward and circumferentially, counter-contacting the falling particulate material. The submerged burners 16 may be disposed within a substantially circular combustion area. Furthermore, each submerged burner 16 may be disposed at equal intervals around the circumference of the furnace.

[0074] Embodiment 3 FIG. 7 shows a schematic diagram of yet another furnace of the present application. The protrusions 18 are distributed along a circle and, together with the bottom wall 121, define a melting tank 13. The melting tank is positioned at the center of the furnace and is provided with multiple submerged burners 16. Flue gases 19 flow upward and generally along the circumference. At least one feed opening 15 may be equally spaced around the circumference of the annular space. Particulate material enters the melting tank 13 downward and in all directions through each feed opening 15.

[0075] The present invention improves upon a melting device for granular materials with a specific particle size range, thereby further eliminating the problem of particles becoming stuck and unable to continue falling due to melting, softening, and stickiness of the material. The protrusion design elevates the material pile, increasing the contact area between the granular material and flue gas in the hot section and significantly reducing heat loss. The nozzles of the submerged burners are immersed in the medium to be heated. Flexible combinations of submerged burners allow for a wide range of power outputs. This furnace fully meets one or more of the aforementioned objectives.

[0076] What is described in this specification is merely a more specific embodiment of the present application, and the above embodiment is only used to illustrate the technical solutions of the present application, rather than to limit the present application. Any technical solutions that can be obtained by those skilled in the art according to the concept of the present application through logical analysis, reasoning, or limited experiments shall fall within the scope of the present application. [Explanation of symbols]

[0077] 11 Furnace 12 Furnace room 13 Melting tank 14 Feed hopper 15 Feed opening 16 Submerged burner 17 Melt surface 18 Protrusion 19 Flue gas 20 Stack Surface 21 Dead Zone 22 Fluidized Bed 23 Exhaust gas passage 24 Silo 25 Temperature control device 26 Melt outlet 121 Bottom wall 122 Side wall 151 Screw feeder

Claims

1. A furnace for melting granular material, said furnace (11) comprising: a furnace chamber (12) comprising a melting tank (13) having a side wall (122), a bottom wall (121), and a melt surface (17); a feed hopper (14) configured to feed granular material into the furnace chamber (12), the feed hopper having a feed opening (15); a protrusion (18) positioned between the feed opening (15) and the melting tank (13) and protruding upward from the bottom wall (121) of the furnace chamber (12) so that the granular material descends along a stack surface (20) into the melting tank (13); at least one burner (16) configured to heat the granular material in the melting tank (13) to form a melt and generate flue gases (19); A furnace comprising:

2. 2. A furnace for melting granular material according to claim 1, characterized in that the flue gases (19) flow upward along the stack surface (20), thereby preheating the granular material.

3. 3. A furnace for melting granular material according to claim 1 or 2, characterized in that the dead zone (21) and the fluidized bed (22) are formed continuously from the stack surface (20) to the side wall (122) of the furnace chamber.

4. 3. A furnace for melting granular materials according to claim 1 or 2, characterized in that the protrusions (18) are shaped as multi-gradation stepped configurations, staircases, rectangular blocks, trapezoidal blocks or conical blocks.

5. 3. A furnace for melting granular material according to claim 1 or 2, characterized in that the top of the protrusion (18) is located below the feed opening (15) and above the melt surface (17).

6. 3. A furnace for melting granular material according to claim 1 or 2, characterized in that said at least one burner (16) is adjacent to said bottom wall (121) of said furnace chamber (12).

7. A furnace for melting granular material according to claim 7, characterized in that said at least one burner (16) is a submerged burner.

8. 3. A furnace for melting granular material according to claim 1 or 2, characterized in that the height of the protrusion (18) in the vertical direction is 1.3 to 6 times the set value of the melt depth in the melting tank (13).

9. 3. A furnace for melting granular material according to claim 1 or 2, characterized in that the outermost point of the protrusion (18) projected onto a horizontal plane downstream along the melt flow direction is marked as X, and the horizontal distance L1 between X and the central axis of the nearest burner (16) is more than 200 mm.

10. 3. A furnace for melting granular material according to claim 1 or 2, characterized in that, on the downstream side along the melt flow direction, a line connecting end points M and X of the top surface of the protrusion (18) forms an angle (F) with the horizontal plane in the range of 25° to 80°.

11. 3. A furnace for melting granular material according to claim 1 or 2, wherein the outermost point of the feed opening (15) projected onto the horizontal plane at the downstream side along the melt flow direction is marked as Y, and the horizontal distance L2 between X and Y is in the range of 200 mm to 1000 mm.

12. 3. A furnace for melting granular material according to claim 1 or 2, characterized in that the melting tank (13) is an annular space surrounded by the bottom wall (121) of the furnace and the peripheral side wall (122) of the furnace, and a protrusion (18) is positioned within the furnace.

13. 2. A furnace for melting granular material according to claim 1, characterized in that the protrusions (18) are arranged circumferentially and together with the bottom wall (121) of the furnace and the side wall (122) of the furnace define a melting tank (13).

14. A method of melting granular material, comprising melting the granular material in a melting tank of a furnace according to any one of claims 1 to 13.

15. 1. A method for preheating particulate material using flue gas produced from a furnace, comprising: providing a furnace (11), said furnace comprising a furnace chamber (12), and wherein granular material is fed into said furnace chamber (12) via a feed hopper (14); one or more burners (16) disposed on the furnace (11) configured to combust a fuel and an oxidant, thereby producing flue gases (19); providing a protrusion (18) positioned between the feed opening (15) and the melting tank (13), the protrusion (18) defining a stack surface (20) along which the granular material enters the melting tank (13) in a direction opposite to the flow of the flue gas (19), whereby the granular material is preheated, at least partially melted, and falls onto the melt surface (17); A method comprising:

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