GB714434A - Improvements in and relating to methods and apparatus for reactivating bone char - Google Patents

Abstract

In a method of reactivating bone-char which consists in drying the wet spent char before rabbling and burning it in a kiln, and effecting this drying by means of air heated by direct or indirect contact with the hot char to cool the latter subsequent to its burning in the kiln, this heated air is brought into contact with the wet spent char by directing it through curtains of falling char passing to the kiln between pairs of louvres or other means to subdivide the char into separate curtains. Spent moist char is fed from conveyer 22 into drying chamber 23 and is directed by baffles into radial spaces formed by pairs of slotted louvres 24 (Fig. 6) arranged around central hot air inlet 26. Hot air passes from inlet 26 through apertures 26a into alternate spaces between louvres 24, and, after passage through the louvre slots, into and through at least two of the spaces between the louvres through which the spent char is falling as a curtain, is withdrawn through apertures 27a in each other alternate space between louvres 24, to annular chamber 27 having outlet 27b. The louvres 24 may be removable for cleaning. The curtains of spent char after drying collect in hopper 28 from which the char is discharged in controlled manner by reciprocating slotted plates 29. The dry char collects in funnel 30 and is fed at A into a Herreschoff kiln 12 having a plurality of hearths 13 with alternate peripheral and central openings 13a, 13b and rabbling arms 15 with teeth 15a mounted on central rotatable shaft 14 driven by gearing 16 so that the char is rabbled over each hearth and falls to the next lower hearth. Gases withdrawn from the kiln at points 17, 18 preceding the burning zone, may be recycled with combustion air and other gases to the combustion chamber 19 fed with oil fuel or town gas at 20 and returned to the kiln. The heated and burned char from lowermost hearth 13 passes into one of a plurality of coolers 21 having spaced vertical tubes 32 (Fig. 3) with fins 32a over their whole length. Air is delivered under pressure through a screened intake 33 and passes in a zig-zag path round baffles 35 round tubes 32 to ensure rapid cooling. Hot air withdrawn from coolers at 34 passes through conduits and valves 36 to central inlet of drier 23, and branch conduits and valves 37 are provided for venting, if necessary. The reactivated char from tubes 32 falls on to a gate mechanism formed of slotted plates 38, 39 (Fig. 4) which may be brought into register by limited reciprocation of plate 39 by thrustors 43, 44 for controlled discharge of char on to moving table 41 from which it is scraped on to conveyer 42 for transfer to store. The gate mechanism is operated once per <PICT:0714434/III/1> <PICT:0714434/III/2> <PICT:0714434/III/3> <PICT:0714434/III/4> revolution of the central shaft 14 by energizing thrustors 43, 44 by contact 45, controlled by electronic timer 46, so that the rate of discharge of char varies directly with the speed of rotation of the shaft. In a preferred embodiment (Fig. 2 not shown) the air from the coolers is passed through the central hollow shaft of the kiln 12 and thence to the central inlet of the drier 23, and the reciprocation of the slotted plates 29 of the hopper 28 is also effected by the central shaft 14, so that discharge of the char from the drier 23 and from the coolers 21 is related to the speed of rotation of the shaft 14, and the throughput of the various sections can be varied and balanced by altering the speed of the shaft.