Preheater for lime kiln

Abstract

A preheater for particulate material comprising a cylindrical refractory lined vessel with top feed and exhaust offtake. The preheater diameter is enlarged below the offtake so that the sloping material forms an area surrounded by ports which receive hot gases from the kiln. The lower portion of the preheater is conical, leading toward a small central discharge point. This portion constitutes a soaking zone in which heat is allowed to penetrate the material.

I claim: 
     
       1. In a preheater for particulate materials such as limestone, a refractory lined vessel having an upper material intake section, an exhaust offtake concentrically mounted in said section, means for feeding material into said section, a gas intake section below said material intake section, a plurality of circumferentially arranged ports around said gas intake section, means feeding hot gases to said ports, whereby the gases will flow radially inwardly through said material, a material holding section extending downwardly from said gas intake section, said material holding section being entirely below said ports and being sufficiently deep to permit heat to be absorbed by the interiors of the particles of material, .[., and a material discharge port at the bottom of said material holding section.]. .Iadd.the depth of said material holding section relative to the height of said gas intake section being so great that substantially the entire material holding section is remote from the path of gases flowing into said gas intake section, said material holding section being so constructed that little gas flow will take place in said holding section, a material discharge port at the bottom of said material holding section, and feeding means connected to said material discharge port and controlling the retention time of material in said holding section so as to cause the high surface temperatures developed on each particle to be diffused substantially into its entire volume.Iaddend.. 
     
     
       2. The combination according to claim 1, said material intake section being cylindrical, said exhaust offtake being circular, said material feeding means being so arranged that the level of material is maintained above said offtake. 
     
     
       3. The combination according to claim 1, said gas intake section being of larger diameter than said material intake section and so shaped that the angle of repose of descending material will form an inclined frustoconical surface around its periphery. 
     
     
       4. The combination according to claim 3, said gas feeding means comprising an annular distribution duct around said ports, the ports being located adjacent the top of said enlarged section. 
     
     
       5. The combination according to claim 1, said material holding section being conical, said material discharge port being centrally located and of relatively small area. 
     
     
       6. .[.The combination according to claim 5, further provided with.]. .Iadd.In a preheater for particulate materials such as limestone, a refractory lined vessel having an upper material intake section, an exhaust offtake concentrically mounted in said section, means for feeding material into said section, a gas intake section below said material intake section, a plurality of circumferentially arranged ports around said gas intake section, means feeding hot gases to said ports, whereby the gases will flow radially inwardly through said material, a conical material holding section extending downwardly from said gas intake section, said material holding section being entirely below said ports and being sufficiently deep to permit heat to be absorbed by the interiors of the particles of material, a material discharge port of relatively small area centrally located at the bottom of said material holding section, and .Iaddend.a conical lower baffle concentric with and spaced inwardly from said conical holding member, whereby the entire cross-sectional area of said holding zone will be coupled to said discharge port. 
     
     
       7. In a preheater for particulate materials such as limestone, a refractory lined vessel having a cylindrical section, a circular exhaust offtake concentrically mounted in said section, means for feeding material into the top of said vessel so that the level of material is maintained above said offtake, a section of larger diameter than said cylindrical vessel section below the offtake and so shaped that the angle of repose of descending material will form an outwardly and downwardly inclined frustoconical surface around its periphery, a plurality of circumferentially arranged ports adjacent the top of said enlarged section, means feeding hot gases to an annular distribution duct around said ports, a conical material holding section extending downwardly from said enlarged section, said material holding section being entirely below said ports and being sufficiently deep to permit heat to be absorbed by the interiors of the particles of material, .[., and a single centrally located material discharge port of relatively small area at the bottom of said holding section.]. .Iadd.the depth of said material holding section being so great relative to the height of said enlarged section that substantially the entire material holding section is remote from the path of gases flowing onto said frustoconical material surface, said material holding section being so constructed that little gas flow will take place in said holding section, a single centrally located material discharge port of relatively small area at the bottom of said holding section, and feeding means connected to said material discharge port and controlling the retention time of material in said holding section so as to cause the high surface temperatures developed on each particle to be diffused substantially into its entire volume. .Iaddend. 
     
     
       8. .[.The combination according to claim 7, further provided with.]. .Iadd.In a preheater for particulate materials such as limestone, a refractory lined vessel having a cylindrical section, a circular exhaust offtake concentrically mounted in said section, means for feeding material into the top of said vessel so that the level of material is maintained above said offtake, a section of larger diameter than said cylindrical vessel section below the offtake and so shaped that the angle of repose of descending material will form an outwardly and downwardly inclined frustoconical surface around its periphery, a plurality of circumferentially arranged ports adjacent the top of said enlarged section, means feeding hot gases to an annular distribution duct around said ports, a conical material holding section extending downwardly from said enlarged section, said material holding section being entirely below said ports and being sufficiently deep to permit heat to be absorbed by the interiors of the particles of material, a single centrally located material discharge port of relatively small area at the bottom of said holding section, and .Iaddend.a conical lower baffle concentric with and spaced inwardly from said conical holding chamber, whereby the entire cross-sectional area of said holding zone will be coupled to said discharge port. 
     
     
       9. The combination according to claim 8, said offtake comprising a downwardly open frustoconical member connected to a horizontal duct passing through said cylindrical vessel section. 
     
     
       10. In a preheater for particulate materials such as limestone, a refractory lined vessel having a cylindrical section, a circular exhaust offtake concentrically mounted in said section, means for feeding material into the top of said vessel so that the level of material is maintained above said offtake, a section of larger diameter than said cylindrical vessel section below the offtake and so shaped that the angle of repose of descending material will form an inclined frustoconical surface around its periphery, a plurality of circumferentially arranged ports adjacent the top of said enlarged section, means feeding hot gases to an annular distribution duct around said ports, said annular distribution duct being so formed as to allow settling of dust entrained in said gases, drains for said dust in the bottom of said duct, a conical material holding section extending downwardly from said enlarged section, and a single centrally located material discharge port of relatively small area at the bottom of said holding section. 
     
     
       11. In a preheater for particulate materials such as limestone, a refractory lined vessel having an upper material intake section, an exhaust offtake in said section, means for feeding material into said section, a gas intake section, means feeding hot gases to said gas intake section, a material holding section extending downwardly from said gas intake section, .[.and.]. a material discharge port at the bottom of said material holding section, said gas intake section being located a substantial distance above said discharge port whereby the hot gases will flow across stone having a relatively low surface temperature, said material holding section being entirely below said gas intake section and of sufficient dimensions to allow time for substantial inward diffusion of the surface heat on particles descending therethrough, .Iadd.the depth of said material holding section being so great relative to the height of said gas intake section that substantially the entire material holding section is remote from the path of gases flowing into said gas intake section, said material holding section being so constructed that little gas flow will take place in said holding section, and feeding means connected to said material discharge port and controlling the retention time of material in said holding section so as to cause the high surface temperatures developed on each particle to be diffused substantially into its entire volume. .Iaddend. 
     
     
       12. The combination according to claim 11, said material intake section being cylindrical, said material holding section being conical. 
     
     
       13. The combination according to claim 12, said gas intake section being disposed between said material intake and holding sections and having an annular gas distribution duct.