OPTIMUM CONDITIONS OF CARBONATION OF MUNICIPAL SOLID WASTE INCINERATION BOTTOM ASH FOR DECHLORINATION

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  • 一般廃棄物焼却灰の脱塩における炭酸化処理の最適条件
  • イッパン ハイキブツ ショウキャクバイ ノ ダツエン ニ オケル タンサンカ ショリ ノ サイテキ ジョウケン

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 According to the report in 2015, around 44 million ton of municipal waste was generated every year in Japan. Out of which 80% was incinerated generating around 3.3 million ton of incineration ash which ended in the landfills. Recycling of the incineration ash to cement material has been performed or planned in some local municipalities where the capacity of landfill site was insufficient to meet future demand of ash disposal.<br> The permissible chloride content in ordinary portland cement (OPC) is 0.035 %wt, however incineration ash contains higher chloride concentration (0.2-5 %wt). Soluble chloride can be removed by washing with water, but insoluble chloride cannot be washed out because it exists in ash as a stable mineral: Friedel's salt 3CaO·Al2O3·CaCl2·10H2O. Friedel's salt can be decomposed by many methods like thermal, sulfation and carbonation to remove chloride.<br> In this study, the author examined effective method to remove insoluble chloride from ash by carbonation method using wet-CO2 gas in a column-type reactor. The effects of L/S ratios, gas flow rates and treatment times were studied. It was found that the optimum conditions for effective carbonation were: L/S ratio = 0.3, flow rate = 1000 mL / min, and treatment time = 2 - 3 hours. Using these optimum conditions before rinsing with pure water, the total chlorine content of the incinerated ash after washing was reduced to about 0.5%wt from 1.39 %wt (untreated sample) and the insoluble chlorine content is reduced to about 0.2%wt. Since the insoluble chloride content was reduced to < 0.3%, the ash can be used as one of the component in OPC mixture.

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