GB942620A - Improvements in or relating to a method of sintering fly ash into lightweight aggregate - Google Patents

Abstract

<PICT:0942620/C1/1> Fly ash residue of varying carbon content is sintered to form a lightweight concrete aggregate, by depositing pellets of fly ash, formed by binding with water, in a layer upon the upper surface of a moving grate, igniting and heating the top of the layer by combustion with fuel and air from above, drawing air downwardly through the layer and the grate while under the region of ignition and heating in order to heat the pellets to a temperature at which they sinter, and also in a region thereafter in order to cool the sinter, discharging and crushing the sinter from the moving grate to form a lightweight aggregate component, sensing and determining the increase and decrease in change of temperature of the pellets in the region of ignition and when the temperature increases and decreases from a predetermined constant temperature, adjusting the supply of fuel and air to the ignition zone to maintain the constant temperature. In Fig. 2, fly arm is fed from silo 10 along belt conveyer 11 to a huge bin 12 from which the fly ash is fed by a vibrating screw feeder 13 <PICT:0942620/C1/2> into a pelletizing drum 14, from which the pellets pass, via an oscillating conveyer 15, on to the upper strand 16 of a continuous sintering machine with wind boxes 17. The air for combustion and cooling of the sintered fly ash is drawn downwardly through the sinter bed into wind boxes 17 under the action of suction 18 through a waste gas duct 19, which discharges through a waste heat stack 20. The pellets are discharged through shoot 21 to hammer mill crusher 22, which discharges the crushed sinter as lightweight aggregate. For igniting and controlling the heating of the fly arm pellets, a downwardly open radiant heat ignition furnace chamber 25 is mounted thereover, close to feeder 13. The chamber (see Fig. 3) has an enclosed flat surface roof 26 extending downwardly from a tall front wall 27 to a shorter rear wall 28, and is provided with a burner nozzle 29, for fuel gas and air, disposed in the upper half of the tall front wall and set therein to direct the burning fuel along lines to directly impinge first on the short rear wall 28 at a level above the base of the short wall, and then above the top surface of the bed of pellets. The fuel is fed through line 31 and air through line 32. The rate of flow of fuel and air is governed by valves 35 and 36, these valves being interconnected for use in unison by linkage 38. To maintain the constant temperature, means 39 for sensing temperature changes is connected to means 40 via wiring 41 and mechanisms 42, which adjusts fuel and air valves 35 and 36. Means 39 is preferably a thermocouple or optical pyrometer. 44 is an electric motor-operated valve positioner. 60% of the pellets should pass through 200 mesh sieve (U.S. Standard). The sintered fly ash is crushed to 3/8 inch. An example is given wherein the temperature of ignition is 2200-2400 DEG F.