| Summary: | 博士 === 國立臺灣大學 === 環境工程與科學系 === 86 === The objective of this research is to evaluate the evaporation characteristics of heavy metals including Pb, Cd, and Cu, under various operating conditions, as plastic and cypress were incinerated. In addition, comparisons between the experimental observations and the field study conducted in the municipal waste incineration plant were also made.
The plastic material chosen contained 33% chloride and stabilizers. During combustion, pollution to the environment will result if the treatment operation is inadequate. In order to have a better understanding of the evaporation characteristics of Pb, Cd, and Cu, the effects of the operating parameters, such as combustion temperature, combustion time, humidity, the nitrogen-oxygen ratio and the addition of calcium hydroxide, were evaluated. At a combustion temperature of 600℃ and 5 min of combustion time, the evaporation efficiency of lead was 17.9%; while at 25 min, it was 44.1%. When the temperature was increased to 800℃ and 900℃, with 5 min and 25mm combustion times, the evaporation efficiencies were 61.5% and 94.8%, respectively. Multiple regression analysis was also, applied to determine the dominant factor influencing the evaporation characteristics of heavy metals.
Regarding cypress, we investigated the effects of the addition of lead nitrate and lead chloride, temperature, and combustion time. Results showed that the combustion time and temperature have significant influences on the evaporation of heavy metals. Multiple regression analyses were performed to quantify the influences of operating conditions. Additionally, manganese acetate and calcium nitrate were added to realize their inhibition effect. It was found that manganese acetate has a better inhibition effect on the heavy metals.
The mass balance of heavy metals was examined and the distribution of heavy metals in the waste gas, bottom ash, wastewater, or sludge was also analyzed. The effect of combustion temperature was investigated to simulate the normal combustion temperature, elevated temperature (as the furnace started the operation), and lowered temperature (as the furnace stopped the operation) conditions. At the elevated temperature, the evaporation rate of Pb and Cd in the flying ash increased with the increase of temperature; whereas the variation of evaporation rates was limited under normal combustion temperature. Regarding the distribution ratio of heavy metals in the bottom and flying ash, it was 85% and 15% for Pb, 35% and 61% for Cd, and 92.4% and 6.2% for Cu. It showed that Cd is more volatile than Pd and Cu. On the other hand, the bottom and flying ashes were used for the adsorption experiments and their applicability was discussed.
The major contribution of tins research was to get a better understanding about the evaporation characteristics and the distribution of heavy metals in the bottom and flying ashes. It is also recommended to reduce the use of plastics, in order to preventing the evaporation of heavy metals.
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