Patent Publication Number: US-2022226889-A1

Title: Fluid heating furnace and heating method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-007847 filed on Jan. 21, 2021, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a fluid heating furnace and a heating method. 
     2. Description of Related Art 
     Japanese Unexamined Patent Application Publication No. 2013-146741 (JP 2013-146741 A) describes such a technology that sand (hereinafter referred to as “core sand”) used for a core used in casting is collected so that the core sand is reused by removing impurities and a binder attached to the core sand. More specifically, JP 2013-146741 A describes the following technology. That is, a casting product cast by use of a metal die including a core is subjected to a heat treatment at 500° C. so as to roast an organic binder covering the surface of the core, so that the core is broken. Hereby, core sand from which the organic binder is removed to some extent is collected. 
     SUMMARY 
     In recent years, in order to prevent nicotine, soot, a bad smell (gas), or the like that occurs when an organic binder used for a core is heated in a casting process, a core formed by use of an inorganic binder such as water glass has been used. In a case where core sand is recycled from the core formed by use of the inorganic binder, the inorganic binder is also removed from the core sand by heating. In order to prevent the inorganic binder from solidifying again in a heating furnace, a fluid tank in which the core sand is heated by flowing gas while the core sand is caused to flow by the flowing gas is required. A heating furnace configured such that heating is performed in such a fluid tank is referred to as a fluid heating furnace. A high-temperature discharge gas is caused in the fluid heating furnace, and therefore, the fluid heating furnace has such a problem that its heat efficiency is low. 
     The present disclosure is accomplished in order to solve such a problem, and an object of the present disclosure is to provide a fluid heating furnace and a heating method each of which is improved in heat efficiency. 
     A fluid heating furnace according to the present disclosure is a fluid heating furnace for recycling core sand used for a core. The fluid heating furnace includes a fluid tank and a gas discharge passage. In the fluid tank, the core sand is heated by flowing gas while the core sand is caused to flow by the flowing gas. The gas discharge passage communicates with the fluid tank such that the flowing gas is discharged through the gas discharge passage. The gas discharge passage includes an inlet portion via which the core sand is put into the fluid tank through the gas discharge passage. 
     A heating method according to the present disclosure is a heating method for heating core sand used for a core by use of a fluid heating furnace including a fluid tank in which the core sand is heated by flowing gas while the core sand is caused to flow by the flowing gas. The fluid heating furnace further includes a gas discharge passage communicating with the fluid tank such that the flowing gas is discharged through the gas discharge passage. The gas discharge passage includes an inlet portion via which the core sand is put into the fluid tank through the gas discharge passage. The heating method includes: heating, in the gas discharge passage, the core sand put into the gas discharge passage from the inlet portion by the flowing gas discharged through the gas discharge passage; and further heating, in the fluid tank, the core sand heated in the gas discharge passage. 
     In the fluid heating furnace and the heating method according to the present disclosure, the core sand from the inlet portion of the gas discharge passage is put into the fluid tank through the gas discharge passage. Accordingly, the core sand is heated by the flowing gas discharged through the gas discharge passage before the core sand reaches the fluid tank. Since heat is transmitted from the fluid gas to the core sand, the heat efficiency of the fluid heating furnace is improved by just that much. Accordingly, it is possible to provide the fluid heating furnace and the heating method each of which is improved in heat efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG. 1  is a view schematically illustrating a section of a fluid heating furnace according to Embodiment 1 when the fluid heating furnace is viewed from its lateral side; 
         FIG. 2  is a perspective view illustrating the inside of a gas discharge passage of the fluid heating furnace according to Embodiment 1; 
         FIG. 3  is a view illustrating one example of a dispersion plate in the gas discharge passage according to Embodiment 1; and 
         FIG. 4  is a graph illustrating a sand temperature and a discharge gas temperature in Example 1. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     With reference to drawings, the following describes Embodiment 1 of the present disclosure. However, the present disclosure is not limited to Embodiment 1. Further, the following description and drawings are simplified appropriately for clarification of the description. 
       FIG. 1  is a view schematically illustrating a section of a fluid heating furnace  100  according to Embodiment 1 when the fluid heating furnace  100  is viewed from its lateral side. In order to recycle core sand  200  used for a core used in casting, the fluid heating furnace  100  heats the core sand  200 . For example, the core used in casting is crushed, so that the core sand  200  is obtained. The fluid heating furnace  100  heats the core sand  200  so as to remove an inorganic binder from the core sand  200 , so that the core sand  200  is recycled. As illustrated in  FIG. 1 , the fluid heating furnace  100  includes a fluid tank  101  and a gas discharge passage  102 . The gas discharge passage  102  is provided above the fluid tank  101 . 
     The fluid tank  101  is a heating tank in which the core sand  200  is heated by flowing gas while the core sand  200  is caused to flow by the flowing gas. Here, the flowing gas is gas flowing inside the fluid heating furnace  100 . Along with the flowing of the gas, the core sand  200  inside the fluid tank  101  also flows. More specifically, the flowing gas is supplied into the fluid tank  101  from the lower side of the fluid tank  101 . The flowing gas rises when the flowing gas is heated in the fluid tank  101 , and the flowing gas is discharged outside through the gas discharge passage  102 . As illustrated in  FIG. 1 , the fluid tank  101  includes heaters  101 A, an air chamber  101 B, a sintered wire mesh  101 C, division plates  101 D, an outlet portion  101 E, and so on. 
     The heaters  101 A are provided on side faces and a bottom face of the fluid tank  101 , for example, and heat the core sand  200  inside the fluid tank  101 . Further, the heaters  101 A heat the flowing gas supplied into the air chamber  101 B provided in the lower side of the fluid tank  101 . Further, the flowing gas causing the core sand  200  to flow is also heated by the heaters  101 A together with the core sand  200  inside the fluid tank  101 . 
     The air chamber  101 B is provided on a bottom portion side of the fluid tank  101 , and a predetermined gas is supplied from a predetermined gas source (not illustrated) into the air chamber  101 B. Further, the upper side of the air chamber  101 B communicates with the inside of the fluid tank  101  via the sintered wire mesh  101 C. On this account, the gas supplied into the air chamber  101 B passes through the sintered wire mesh  101 C and moves into the fluid tank  101 . 
     The sintered wire mesh  101 C is a metal mesh configured to prevent the core sand  200  from passing from the inside of the fluid tank  101  to the air chamber  101 B, the metal mesh having a plurality of hole portions with a size that allows the gas to pass therethrough from the air chamber  101 B into the fluid tank  101 . 
     The division plates  101 D are plate-shaped members provided in a standing manner inside the fluid tank  101 . Further, the division plates  101 D are separated from at least one inner wall of the fluid tank  101 . The core sand  200  put into the fluid tank  101  is directed toward the outlet portion  101 E through a passage of the fluid tank  101 , the passage being formed by the division plates  101 D. 
     The outlet portion  101 E is a passage from which the core sand  200  is discharged, the passage being provided at a predetermined height in the fluid tank  101 , for example. In the example illustrated in  FIG. 1 , the outlet portion  101 E is provided on the upper side of the fluid tank  101 . 
     The gas discharge passage  102  is a passage communicating with the fluid tank  101  and configured such that the flowing gas is discharged from the fluid tank  101  through the passage. The gas discharge passage  102  is provided above the fluid tank  101 . The flowing gas turning into an updraft by being heated in the fluid tank  101  is discharged outside the fluid heating furnace  100  through the gas discharge passage  102 . As illustrated in  FIG. 1 , the gas discharge passage  102  includes a tubular main body portion  102 B, an inlet portion  102 A, a dust collecting device  102 C, and so on. 
     The inlet portion  102 A is a container in which a predetermined amount of the core sand  200  can be accommodated and is provided on the upper side of the main body portion  102 B. At least part of a bottom portion of the inlet portion  102 A is opened, so that the inlet portion  102 A communicates with the main body portion  102 B. Hereby, the core sand  200  can be put into the fluid tank  101  from the inlet portion  102 A through the main body portion  102 B. 
     In the gas discharge passage  102  according to Embodiment 1, the flowing gas discharged through the gas discharge passage  102  heats the core sand  200  put into the gas discharge passage  102  from the inlet portion  102 A. Further, in the fluid tank  101 , the core sand  200  heated in the gas discharge passage  102  is further heated. 
     The main body portion  102 B is provided in a standing manner above the fluid tank  101  so that the inside of the fluid tank  101  communicates with the inside of the main body portion  102 B.  FIG. 2  illustrates an example of the inside of the main body portion  102 B of the gas discharge passage  102 . As illustrated in  FIG. 2 , the main body portion  102 B is an angular pipe having a rectangular section. 
     Further, one or more dispersion plates  102 D are disposed in a bridged manner inside the main body portion  102 B in an inclined manner. A plurality of hole portions  102 G through which the core sand  200  can pass is formed in the dispersion plates  102 D. For example, one or more dispersion plates  102 D are disposed in a bridged manner inside the main body portion  102 B such that the dispersion plates  102 D are inclined at a predetermined angle from an inner wall on a first side toward an inner wall on a second side in the main body portion  102 B. Since the core sand  200  put in from the inlet portion  102 A is dispersed by the dispersion plates  102 D, the contact area of the core sand  200  with the flowing gas passing through the main body portion  102 B increases, so that efficiency of heat exchange between the core sand  200  and the flowing gas improves. 
     More specifically, as illustrated in  FIG. 1 , the flowing gas flowing from the fluid tank  101  into the main body portion  102 B rises inside the main body portion  102 B along the dispersion plates  102 D. In the meantime, the core sand  200  put into the main body portion  102 B from the inlet portion  102 A falls along the dispersion plates  102 D and falls on the dispersion plate  102 D on the lower side through the hole portions  102 G provided in the dispersion plates  102 D. As such, due to the dispersion plates  102 D, the core sand  200  falling down in a dispersed manner makes contact with the flowing gas rising along the dispersion plates  102 D, so that heat exchange is performed between the flowing gas and the core sand  200 . 
     Further, the dispersion plates  102 D are inclined in different directions. For example, as illustrated in  FIG. 2 , the dispersion plates  102 D include first dispersion plates  102 E inclined downward from the inner wall on the first side to the inner wall on the second side in the main body portion  102 B, and second dispersion plates  102 F inclined upward from the inner wall on the first side to the inner wall on the second side in the main body portion  102 B. 
     Further, the dispersion plates  102 D inclined in different directions are disposed in a bridged manner inside the main body portion  102 B. For example, the first dispersion plates  102 E and the second dispersion plates  102 F are alternately disposed in a bridged manner over the inner walls of the main body portion  102 B. 
     When the dispersion plates  102 D are placed as such, the core sand  200  is further dispersed, so that efficiency of heat exchange between the core sand  200  and the flowing gas further improves. 
     Further, it is preferable that the dispersion plates  102 D be disposed in a bridged manner over the inner walls of the main body portion  102 B at an angle (an angle at which the dispersion plates  102 D are inclined) equal to or more than an angle of rest of the core sand  200 . Hereby, it is possible to prevent the core sand  200  from staying on the dispersion plates  102 D. 
     Note that the shape of the main body portion  102 B and how to dispose the dispersion plates  102 D in a bridged manner are not limited to the above. For example, in a case where the main body portion  102 B has a cylindrical shape, the dispersion plates  102 D may be provided in a spiral manner along the inner wall of the cylindrical shape. 
     The dust collecting device  102 C removes foreign matter included in the flowing gas, e.g., the core sand  200  or the like, from the flowing gas passing through the main body portion  102 B and then discharges the flowing gas to outside the fluid heating furnace  100 . 
     With reference to  FIG. 3 , the hole portions  102 G provided in the dispersion plate  102 D will be described. In the example illustrated in  FIG. 3 , the dispersion plate  102 D is a punching metal provided with the hole portions  102 G in a zigzag manner. More specifically, the dispersion plate  102 D is provided with the hole portions  102 G formed at predetermined pitches P along a first direction D 1 . Further, the hole portions  102 G each have a circular shape with a predetermined radius ϕ. Further, three hole portions  102 G adjacent to each other are placed at positions of vertexes of a triangular shape. More specifically, two hole portions  102 G adjacent to each other along the first direction D 1  and one hole portion  102 G adjacent to the two hole portions  102 G are placed at the positions of the vertexes of the triangular shape. Here, the angle of the corner, of the triangular shape, at which the one hole portion  102 G adjacent to the two hole portions  102 G adjacent to each other along the first direction D 1  is referred to as θ. The triangular shape may be an isosceles triangle, or when θ is 60 degrees, the triangular shape is an equilateral triangle. 
     Note that the dispersion plate  102 D may be a wire mesh having a plurality of hole portions with a predetermined magnitude. 
     Next will be described a heating method for heating the core sand  200  in the fluid heating furnace  100  according to Embodiment 1. 
     First, the core sand  200  is put into the main body portion  102 B of the gas discharge passage  102  from the inlet portion  102 A. 
     Subsequently, in the gas discharge passage  102 , the flowing gas discharged through the gas discharge passage  102  heats the core sand  200  put into the gas discharge passage  102  from the inlet portion  102 A. More specifically, inside the main body portion  102 B, the flowing gas makes contact with the core sand  200 , so that the flowing gas directly heats the core sand  200 . Further, the core sand  200  is indirectly heated such that the core sand  200  makes contact with a wall portion of the main body portion  102 B heated by the flowing gas or the dispersion plates  102 D heated by the flowing gas. 
     Further, in the fluid tank  101 , the core sand  200  heated in the gas discharge passage  102  is further heated. 
     Example 1 
     Next will be described Example 1 of the present disclosure. As Example 1, heat exchange efficiency between the flowing gas and the core sand  200  in the main body portion  102 B provided with the dispersion plates  102 D was examined. Each of the dispersion plates  102 D according to Example 1 was a punching metal provided with the hole portions  102 G each having a radius ϕ of 5 mm, a pitch P of 8 mm, and an angle θ of 60° as illustrated in  FIG. 3 . Further, the number of the dispersion plates  102 D provided inside the main body portion  102 B of the gas discharge passage  102  was eight, the inclination angles of the dispersion plates  102 D were 30 degrees on the basis of the horizontal direction, and the size of the gas discharge passage  102  was 30 cm in width, 21 cm in depth, and 150 cm in height. Further, as illustrated in  FIG. 2 , the eight dispersion plates  102 D were disposed in a bridged manner inside the main body portion  102 B at regular intervals such that the eight dispersion plates  102 D were alternately inclined in different directions. Further, in Example 1, as the core sand  200 , new sand and recycled sand of AC alumina sand (made by Hisagoya) and new sand and recycled sand of artificial spherical sand of green beads (made by KINSEI MATEC CO., LTD.) were used. Further, the temperature of the flowing gas to be supplied into the main body portion  102 B from the lower side of the main body portion  102 B was 340° C., and the flow rate of the flowing gas was 0.45 liters/m. Further, the temperature of the core sand  200  to be put into the main body portion  102 B from the upper side of the main body portion  102 B was 25° C., and the input amount of the core sand  200  was 165 kg/h. Further, in Example 1, the heat exchange efficiency was calculated based on Formula (1) as follows. 
       Heat Exchange Efficiency=((Sand Temperature after Heating−Sand Temperature before Heating)×Specific Heat of Sand)/Heat Input Amount×100  (1)
 
       FIG. 4  illustrates temperatures of the flowing gas at various positions (positions P 1  to P 5  illustrated in  FIG. 1 ) in the main body portion  102 B and a temperature of the core sand  200  after the core sand  200  passed through the main body portion  102 B (at a position P 5  illustrated in  FIG. 1 ) in Example 1. More specifically, the vertical axis in  FIG. 4  indicates temperature (° C.), and the horizontal axis indicates time (second). Further, a symbol (I) described in the explanatory note in  FIG. 4  indicates a temperature of the flowing gas discharged from the upper side of the main body portion  102 B (the position P 1  illustrated in  FIG. 1 ), symbols (II) to (IV) indicate temperatures of the flowing gas at the positions P 2  to P 4  inside the main body portion  102 B illustrated in  FIG. 1 , respectively, a symbol (V) indicates a temperature of the core sand  200  at the position P 5  illustrated in  FIG. 1 , and a symbol (VI) indicates a temperature of the flowing gas (at the position P 5  in  FIG. 1 ) before entering of the flowing gas into the main body portion  102 B from the upper side of the fluid tank  101 . Note that data illustrated in  FIG. 4  is data of the new sand of the green beads. 
     As illustrated in  FIG. 4 , the temperature (the symbol (VI)) of the flowing gas before entering of the flowing gas into the main body portion  102 B from the upper side of the fluid tank  101  was around 340° C. Due to heat exchange between the flowing gas and the core sand  200  in the main body portion  102 B, the temperature (the symbol (I)) of the flowing gas discharged from the main body portion  102 B decreased to around 35° C. In the meantime, the temperature of the core sand  200  to be put into the main body portion  102 B from the upper side of the main body portion  102 B was 25° C. as described above, and the temperature (the symbol (V)) of the core sand  200  to be put into the fluid tank  101  through the main body portion  102 B increased to around 150° C. It is found that the heat exchange efficiency between the flowing gas and the core sand  200  in the main body portion  102 B was around 94% that is high efficiency. 
     In the fluid heating furnace  100  and the heating method according to Embodiment 1 described above, the core sand  200  from the inlet portion  102 A of the gas discharge passage  102  is put into the fluid tank  101  through the gas discharge passage  102 . Accordingly, the core sand  200  is heated by the flowing gas discharged through the gas discharge passage  102  before the core sand  200  reaches the fluid tank  101 . Since heat is transmitted from the fluid gas to the core sand  200 , the heat efficiency of the fluid heating furnace  100  is improved by just that much. Accordingly, it is possible to provide the fluid heating furnace  100  and the heating method each of which is improved in heat efficiency. 
     Further, the core sand  200  put in from the inlet portion  102 A is dispersed by the plate-shaped dispersion plates  102 D disposed in a bridged manner inside the main body portion  102 B of the gas discharge passage  102  such that the dispersion plates  102 D are inclined, the dispersion plates  102 D having the hole portions  102 G through which the core sand  200  can pass. On this account, the contact area of the core sand  200  with the flowing gas passing through the main body portion  102 B increases, so that efficiency of heat exchange between the core sand  200  and the flowing gas improves. 
     Further, since the dispersion plates  102 D are disposed in a bridged manner inside the main body portion  102 B of the gas discharge passage  102 , the core sand  200  is further dispersed, so that efficiency of heat exchange between the core sand  200  and the flowing gas further improves. 
     Further, the dispersion plates  102 E,  102 F inclined in different directions are provided inside the main body portion  102 B. Hereby, the core sand  200  is further dispersed, so that efficiency of heat exchange between the core sand  200  and the flowing gas further improves. 
     Further, the dispersion plates  102 E,  102 F inclined in different directions are alternately disposed in a bridged manner over the inner walls of the main body portion  102 B. Hereby, the core sand  200  is further dispersed, so that efficiency of heat exchange between the core sand  200  and the flowing gas further improves. 
     Further, the dispersion plates  102 D are disposed in a bridged manner over the inner walls of the main body portion  102 B at angles equal to or more than the angle of rest of the core sand  200 . Hereby, it is possible to prevent the core sand  200  from staying on the dispersion plates  102 D. 
     Note that the present disclosure is not limited to the above embodiment, and various modifications can be made appropriately within a range that does not deviate from the gist of the disclosure. For example, the dispersion plates  102 D may be disposed in a bridged manner over the inner walls of the main body portion  102 B at different angles in accordance with respective positions of the dispersion plates  102 D inside the main body portion  102 B. When the dispersion plates  102 D are inclined at different angles, it is possible to change the time for the core sand  200  to pass on the dispersion plates  102 D. For example, when the inclination angles of the dispersion plates  102 D are set to become smaller from the lower side toward the upper side in the main body portion  102 B, the time for the core sand  200  to make contact with the flowing gas the temperature of which is decreased is made longer in the upper side of the main body portion  102 B, thereby making it possible to improve the heat exchange efficiency.