Cement, Energy and Environment

t • Table-2 Chemical composition of flyash CaO Si02 AI203 Fe203 Cl Na20eq Pb(mg/kg) Zn(mg/kg) Dioxin ~ ~ ~ ~ ~ ~ ~ TEQ/g) Average Maximum Minimum Flyash 37.6 42.7 31 .0 10.0 15.0 5.2 6.1 8.4 2.9 Ash shown in Table 2, the flyash of the stoker-type incinerator consists of 50 - 60 per cent components, 20 per cent of chlorine, some heavy materials and around 4 ng of dioxins. In order to use this flyash as a cement raw material it is necessary to manage these impurities so as not to cause any deterioration in quality or process problems. The chlorine needs to be eliminated before use and dioxins to be decomposed in the high temperature zone (above 800 1.0 1.6 0.5 17.4 23.0 9.7 7.5 10.5 5.1 'C) of the preheater tower or the rotary kiln. HybriDesalter™ As a result of receiving increased requests to utilize high chlorine ash, Taiheiyo Cement Corporation was prompted to develop an ash desalting process suitable for cement plants. The first generation process was developed in association with an engineering company, but it was soon recognized that it was necessary to develop a new process more suitable for cement plant processes and circumstances. Table-3 Properties of desalinated filter cake 2210 5800 550 7050 14 000 2700 3.8 11 .0 0.9 Taiheiyo Cement Corporation developed an ash desalting process, the "HybriDesalter™", optimized for the desalination of chlorine containing ashes, such as incinerator flyash and K– Powder product by the chlorine bypass system. "The Kumagaya cement plant, which produces 2.1 million tpa, uses around 60 000 tpa of incinerator ash (45 000 t of bottom ash and 15 000 t of f/yash)." Former Process HybriDesaltern.' Chloride content of flyash (wt %)* 16.0 16.0 Water/ash dissolution ration 5.0 4.0 (water demand) Residual chlorine content in desalinated cake (wt %)* <0.5 <0.5 Moisture (wt%) 55.0 35.0 *Dry weight basis Table-4 Chemical composition of process water Filtrate Final processed Pb mg/1 Cu mg/1 Zn mg/1 Raw saline After carbonation 299 0.90 13.2 105 0. 16 5.0 saline N.D N.D N.D 5