GB743265A - Improvements in or relating to method of producing expanded spherulized, thin-walled unicellular particles and the expanded spherulized thin-walled unicellular particles resulting from said method - Google Patents

Abstract

<PICT:0743265/III/1> <PICT:0743265/III/2> <PICT:0743265/III/3> <PICT:0743265/III/4> <PICT:0743265/III/5> Expanded spherulized thin-walled unicellular particles for use as light weight aggregate are prepared by sub-dividing a clay shale into particles of about 4 mesh size or smaller and passing the particles as a gaseous suspension through a heated zone having a temperature between 2000 DEG and 4000 DEG F. and subjecting the particles to heat in said zone for only such a period of time as to completely fuse the particles and simultaneously effect volatilization of gasifying components in the clay shale thereby inflating the particles to produce unicellular spheroidal particles of larger size than the original clay shale particles and cooling the expanded particles to solidify them before coming to rest, the temperature and time of exposure to said temperature being such that the maximum expansion of the particles is effected without rupture of the enclosing wall of fused clay shale. In Fig. 1 a refractory lined heating zone 50 is proved with a burner and clay injection means. Sub-divided clay is introduced from hopper 25 to be entrained in combustible and/or combustion supporting gas introduced at 24, and passed to a burner 12 inside a housing 10a where it is mixed with combustion supporting and/or combustible gas entering at 21. The particles suspended in the hot gases pass through the chamber 50 to lateral openings 53 to be collected in vessels 55. The burner is shown in detail in Fig. 2 wherein clay shale particles entering from hopper 25 are entrained when they leave a depending pipe 25a by a stream of gas entering at 24. Another stream of gas entering at 21 passes concentrically around the gaseous suspension of clay particles in the inner pipe 22 to enter a chamber 13 and from thence enters the chamber 50 through an orifice formed between plates 16 and 40 and the inner pipe 22. An alternative burner is shown in Fig. 6 where an air suspension of clay is fed through pipe 57 and combustible gas is fed from aperture 63 to flow concentric with the clay suspension through annular channels 64a and 65a. Additional air enters at 68 and flows through channel 69a. The clay may be suitably entrained by the air stream in an apparatus as in Fig. 8, wherein clay shale is fed from a hopper 58 into a rotating star feeder 59, the clay dropping through a channel 61 to be entrained in an air stream flowing through pipes 57 in the direction shown. The preferred heating zone is shown in Fig. 7 wherein a refractory lined cylindrical vessel having walls 81 and 81a is surmounted by two frusto conical sections 77 and 74 the divergence of the section 77 being greater than that of 74. The top cylindrical walled portion 81a may be provided with longitudinally extending grooves to increase the surface area and improve the radiating surface but below this part of the wall, the wall 81a should be smooth and may be air cooled as shown by annular air channels 87 through which cooling air is passed thereby becoming preheated for passage to the burner. The clay shale may be dried at about 105 DEG C. to a 2-3 per cent moisture content before treatment. The clay shale employed should preferably contain from 2-10 per cent by weight Fe2O3, the Fe2O3 acting as a source of gas when it is decomposed to ferrous oxide and oxygen on heating of the shale; the shale should also preferably have a silica to alumina weight ratio from 3 to 1 to about 8 to 1 and preferably the total content of lime plus magnesia in the shale is less than 16 per cent; the fusion point of the shale is preferably between 2000 and 2345 DEG F. The proportion of combustible gas and air are preferably so adjusted that the atmosphere of the furnace is reducing, by the employment of a 60 to 75 per cent of the stoichiometric oxygen requirements. In a typical case the final product is from 50 to 500 microns in diameter, representing an expansion of 5 to 50 diameters with attendant decrease of bulk density to less than 50 lbs. per cubic foot.ALSO:Expanded spherulized thin-walled unicellular particles for use as light-weight aggregate are prepared by sub-dividing a clay shale into particles of about 4 mesh size or smaller and passing the particles as a gaseous suspension through a heated zone having a temperature between 2000 and 4000 DEG F. and subjecting the particles to heat in said zone for only such a period of time as to completely fuse the particles and simultaneously effect volatilization of gasifying components in the clay shale thereby inflating the particles to produce unicellular spheroidal particles of larger size than the original clay shale particles and cooling the expanded particles to solidify them before coming to rest, the temperature and time of exposure to said temperature being such that the maximum expansion of the particles is effected without rupture of the enclosing wall of fused clay shale. The clay shale may be dried at about 105 DEG C. to a 2-3 per cent moisture content before treatment. The clay shale employed should preferably contain from 2-10 per cent by weight Fe2O3, the Fe2O3 acting as a source of gas when it is decomposed to ferrous oxide and oxygen on heating of the shale; the shale should also preferably have a silica to alumina weight ratio from 3 to 1 to about 8 to 1 and preferably the total content of lime plus magnesia in the shale is less than 16 per cent; the fusion point of the shale is preferably between 2000 and 2345 DEG F. The proportion of combustible gas and air are preferably so adjusted that the atmosphere of the furnace is reducing, by the employment of a 60 to 75 per cent of the stoichiometric oxygen requirements. In a typical case the final product is from 50 to 500 microns in diameter, representing an expansion of 5 to 50 diameters with attendant decrease of bulk density to less than 50 lbs. per cubic foot.