Cement, Energy and Environment

Sample A B Flyash 3 3.7 (ng- Dioxin TEO/g) content Treated 0.002 0.055 filtrate (pg-TEQ/1 Recycling of waste materials or fuels The amount of incineration ash containing chlorine and heavy metals that can be used as cement raw material can be increased using the desalination and chlorine by pass systems. Figure 3 shows the chlorine balance of a plant utilizing incineration ash. The desalination process is also used for K-Powder, which cannot be added to cement due to the limitation on chlorine in the final product. 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 flyash). Without the flyash desalination process, the total chlorine input would increase to 1570 ppm and it would be necessary to install a huge chlorine bypass system to manage it. But as indicated in Figure 3, the chlorine bypass capacity can be reduced by 77 per cent using the desalination process. The flyash chlorine is decreased by 97.5 per cent, from 1200 ppm in the flyash (clinker basis), to 30 ppm in the desalinated cake. chlorine n Table-5 Dioxin analysis results c D E F G H 3.1 3 2.9 3.1 2.6 1.5 0.043 0.012 0.027 0 0.006 0 around 150 ppm (clinker basis} , so it is not desalinated. Instead, the chlorine bypass is increased by 180 ppm of clinker and the resulting 150 ppm in the K– Powder (clinker basis) is managed within the desalination process to maintain control of the chlorine content in the cement. Thus, by using a desalting process and chlorine bypass system simultaneously, Taiheiyo Cement Corporation is able to achieve an environment-friendly recycling system in the cement plant whilst preserving the life of diminishing landfill capacity, especially in urban cities. Dioxins Table 5 shows the dioxin content of incineration flyash -lo'CIUI... ~- 1.~-~ ISO .... "B <\."()~ ~<- ~~- ·I(~ JO~ ~~-·­ .. -.)60~ I J K L M 2.3 4.7 2.9 1.1 4 0 0.001 0.0004 0.004 0.005 and its saline filtrate. It is well known that dioxins are not dissolvable in water, so even in 13 samples of flyash containing around 3 ng of dioxin, the dioxin content of the filtrate can only be detected at a level of hundredths of picograms. This is less than the waste water standards and below the average for river waters in Japan. The dioxin concentration in the kiln exhaust gas was also checked, comparing dioxin levels with and without the charge of incineration ash cake. The dioxin em1ss1on level remained at between a millionth part to a ten thousandth part nano-gram TEO per normal cubic metre of gas. Therefore, the decomposition of dioxins by injecting into the high temperature zone over 800 ·c is confirmed. ..: -:no 0.."""«-250~ t.!~t;•-).50~) The content bottom of the ash is Figure 3. Chlorine balance of a cement plant utilising incineration ashes. 6 1