Cement, Energy and Environment

: ~~~~~~~~~-~~~~~0~-. To Loin t11tt Foil• or the bag filter. The discharge ratio is 80 per cent and 20 per cent respectively. Properties of the ash Bottom ash The chemical analysis of the bottom ash, shown in Table 1, indicates that it is Figure 2. Flow diagram of HybriDesalter™ for chlorine-containing ashes. similar in composition to cement, with Furthermore, bottom ash includes various foreign objects and f/yash includes some heavy metal components. In the response to such requests, Taiheiyo Cement Corporation focussed on the removal of foreign objects from bottom ash and the desalination of flyash to remove harmful components. After 10 years of operation, the company has optimized the management process for flyash in order to improve the profitability and this business to increase the total utilization rate of waste materials. Ash from the stoker-type incinerator Bottom ash and flyash In Japan, 50 million t of household wastes are discharged annually, of which 71 per cent are processed in incinerators, resulting in the production of 5 million t of ash. The normal disposal route for this ash is burial in landfill sites. Figure 1 illustrates a stoker– type incinerator and ash discharge system. The bottom ash is discharged from the incinerator end and submerged into water to cool it. The flyash is collected at the cooling tower Table-1 Chemical composition of bottom ash CaO, Si02, AI20 a and Fe 2 0 3 in the region of 70 - 80 per cent. Most of the ash is therefore usable as alternative raw materials for cement manufacture, but up to 7 per cent foreign objects, such as metals and blocks of sintered ash, are rejected by a magnetic separator or specially designed sieves to ensure their proper removal. This sorted bottom ash still contains 30 per cent water, so transportation facilities had to be design to avoid adhesion to the wall or conveyers. As the chlorine content is around 1 per cent, it can only be used as a raw material if a chlorine bypass system is installed. CaO Si02 AI203 Fe203 Cl Na20eq Pb(mg/kg) Zn(mg/kg) Dioxin . (%) (%) (%) (%) (%) (%) (ng- TEQ/g) Average 21 .8 29.9 15.3 8.0 1.1 4.6 1170 3300 0.100 Maximum 26.0 36.8 20.2 12.0 1.7 5.3 3900 8100 0.560 Minimum 19.1 25.0 12.0 2.8 0.7 4.1 120 940 0.000 Moisture: 27.3% (max 35 .0%, min 19.0%} Foreign objects: 6.7% (max 9.8%, min 2.6%) 4