| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 106 === The accelerated carbonation system combined with semi-dry rotary kiln was developed and investigated the feasibility of the carbon dioxide capture and non-hazardous treatment of municipal solid waste incineration (MSWI) fly ash and bottom ash. The carbon dioxide capture efficiency, the tested metals leaching characteristics and acid neutralization capacity of MSWI fly ash and bottom ash after accelerated carbonation reaction, , and reduction in cement usage by stabilization were discussed, respectively.
The experimental results showed that pH value of MSWI fly ash and bottom ash could significantly decrease from 12 to 9 and below by accelerated carbonation during 8 hours reaction time. It is implied MSWI fly ash and bottom ash have matched criteria of carbonation reaction. In the case of moisture content effect on carbon dioxide capture efficiency, the carbon dioxide was captured by MSWI fly ash and bottom ash were decreased from 29.66 g/kg and 77.73 g/kg to 27.46 g/kg and 66.37 g/kg with moisture content increasing from 20 % to 30 %, respectively. This is because higher moisture content of ash could tend to block the pores of fly ash resulted in decreasing diffusion of carbon dioxide. On the other hand, due to the filling ratio of MSWI bottom ash in carbonation system was lower than that of fly ash, it can have a higher porosity and good diffusion of carbon dioxide resulted in MSWI bottom ash exhibits good carbon dioxide capture efficiency than that of MSWI fly ash. The presence of sulfur dioxide (SO2) could occur a competitive reaction during accelerated carbonation process. The experimental results indicated carbon dioxide was captured by MSWI fly ash and bottom ash were decreased from 29.66 g/kg and 77.73 g/kg to 23.79 g/kg and 64.17 g/kg with sulfur dioxide concentration increasing from 0 ppm to 30 ppm, respectively. That is, the sulfur dioxide could competitively react and consume the calcium content of fly ash and/or bottom ash resulted in decreasing carbon dioxide capture efficiency.
Based on the analysis results of environmental safety of MSWI fly ash and bottom ash by accelerated carbonation, the all tested heavy metals of carbonated fly ash and bottom ash were in compliance with current Taiwan EPA regulation thresholds. In the case of variation in Pb TCLP concentration of fly ash, it was significantly decreased from 4.12 mg/l to 0.16 mg/l and below after accelerated carbonation reaction. It could conclude that the accelerated carbonation has good potential for enhancing in Pb stabilization of MSWI fly ash. According to the results of compressive strength of stabilization product using fly ash before and after carbonation treatment, it was shown that the cement usage amounts for MSWI fly ash stabilization after carbonation could approximately reduce 20 % under controlled at the similar requirement of compressive strength of stabilization product. In summary, this research has been successfully developed and proven the performances of accelerated carbonation reaction system combined with semi-dry rotary kiln. It could have good potential for carbon dioxide sequestration, but also could reduce the cement usage amounts in MSWI fly ash stabilization. The multiple purposes of resources reduction, harmless of MSWI fly ash, and carbon dioxide sequestration by accelerated carbonation have been conducted in this research.
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