Patent GB-1454278-A (GB)
Title: Descending bed of sub-divided solid material
IPC: C04B2/12
Filed: 1973-11-12
Abstract: 1454278 Cooling and heat-treating granular material ASSOCIATED PORTLAND CEMENT MFRS Ltd 5 Dec 1974 [12 Nov 1973] 52385/73 Heading F4B A method of treating granular &c. material with a contraflow stream of gas comprises passing the gas upwardly through a descending bed of the solid material located in an annular chamber defined by the opposed surfaces, differing in radius by a width a, of vertical outer and inner substantially coaxial cylindrical walls surmounting an annular flow the upper surface of which, except for a peripheral flat region, slopes down to the central aperture therein for discharge of solid material, the bottom edge of the outer wall being in gas tight sliding relationship to the peripheral flat region of the floor and the bottom of the inner wall being higher than the bottom of the outer wall by a distance h, the inner wall and outer wall being independently free to rotate about their vertical axis and the floor being driven about its vertical axis which is offset from said axis of the walls, characterized in that the bed is maintained in a stable critical mode defined as the condition wherein the height h is not substantially less than, and not substantially more than 10% in excess of the value satisfying the relationship tan #=h/a where # is the operative angle of repose of said solid material at the bottom of the bed. The method is shown applied to a cement raw materials preheater having a rotary hearth 1 driven by a motor M about an axis 0<SP>1</SP> and coaxial cylindrical walls 2, 2<SP>1</SP> defining a treatment chamber 24 and surmounted by an annular cover 40 with flanges 41 depending into water troughs 31, 32 and independently rotatable about an axis 0 offset from axis 0<SP>1</SP>, the hearth having a central discharge opening 5. The hearth has a track 9<SP>1</SP> rotatably supported on rolls 9 and engaged by lateral rollers 8 and is driven through reduction gearing 9 and a pinion 33 engaging a rim gear 34. The outer wall 2 has a tyre 15 rotatably supported by rollers 16, 16<SP>1</SP> and by lateral rollers 17. The inner wall 2<SP>1</SP> and the cover 40 are mounted on a framework 26 suspended by a king pin 27 and spindle 37 from a central bearing 38. Thrust rollers 44 mounted in brackets 47 from a superstructure 39 engage a rail 45 on said framework 26. A roof lining 25<SP>1</SP> has a sloping portion 28 leading to a check point 29, Fig. 1 or C, Fig. 3, and a valve device 105 feeds the chamber 24. In order to provide for adjustments in operation, devices such as screws should be provided for adjusting the height of the roof 25 and for altering the offset distance between the axes 0 and 0<SP>1</SP>, preferably associated with means for determining the level of material. The angle # of the hearth should be about 5-7¢ degrees and not more than about 20 degrees. Hot gases from a kiln pass upwardly through the opening 5 in countercurrent to the material. With the apparatus operating as indicated the movement of the charge material will be substantially gravitational, i.e. it is not subject to crushing pressure from the walls 2, 2 which will rotate with it. The charge material will thus descend vertically through the annular chamber 24, change direction smoothly through 90 degrees and progress across the hearth in incremental orderly manner. Using the diameter AA<SP>1</SP> Fig. 2, as a datum line and 0<SP>1</SP> as the reference point for the rotational position of the apparatus, during the first half of a revolution of a point in the hearth, the change of effective radius of the hearth exposed to the annular bed will permit access of charge material to the hearth below said bed. The rate of descent will increase in proportion to sin γ to the 90 degree position and increase again to zero at the 180 degree position. With the passage of the point from γ=180 degrees to γ=360 degrees it will recede from the axis 0<SP>1</SP> by a distance equal to twice the offset distance and material will discharge from the hearth aperture at a rate increasing to γ=270 degrees and decreasing to zero at γ=360 degrees. Other parameters of the treated solid material vary in a predetermined manner with # and may be used with control of the height h to produce the critical mode. These parameters include the bulk density of the charge material, the relation between given particle sizes, the circumferential lag of the outer wall behind the hearth, the minimum power requirement, and the pressure drop through a given bed height. Another parameter is that the discharge rate be linearly proportional to the distance between axes 0 and 0<SP>1</SP> or another that the point of maximum solids discharge on the perimeter of the discharge orifice is on a line perpendicular to the line joining 0 and 0<SP>1</SP>. The apparatus may be also used for cooling materials and for indurating and/or partially reducing ore pellets, line burning, bloating of clays or shale, and drying or carbonizing coal. Specifications 1,059,149, 950,576, 934,230, 828,888 and 828,886. U.S. Specifications 3,403,895, 3,331,595, 2,945,683, 2,861,788, 2,842,350 and 1,429,925 are referred to.