| dc.description.abstract | This research investigated the feasibility of energy conversion of sludge derived from the Science Park wastewater treatment plant by gasification. The experimental conditions were designed to controll gasification temperatures (700~900℃) and add different proportions (5%, 10%, 15%) of dolomite and olivine as mineral catalysts. This research aimed to study the effect on produced gas composition and energy production efficiency and evaluate the trace metals emission characteristics during sludge gasification. Meanwhile, the study was also conducted to assess the reusability of olivine catalysts.
Experimental results indicate that the hydrogen and carbon monoxide compositions increased from 5.27 vol.% and 2.42 vol.% to 11.38 vol.% and 12.58 vol.% with the temperature increasing from 700℃ to 900℃ during the major gas production phase (5~16 minutes), respectively. The average heating value of the produced gas increased significantly from 2.00 MJ/Nm3 to 6.14 MJ/Nm3. This is because higher gasification temperatures facilitate water gas and Boudouard reactions. Examining the effect of dolomite and olivine as mineral catalysts at 900℃,it was observed that the 10% dolomite addition resulted in hydrogen and carbon monoxide compositions of 13.32 vol.% and 11.44 vol.%, corresponding with an average gas heating value of 6.15 MJ/Nm3. Conversely, using 5% olivine yielded 10.73 vol.% for hydrogen and 13.77 vol.% for carbon monoxide, with an average gas heating value of 5.04 MJ/Nm3. In summary, dolomite proved to be a superior catalyst, significantly increasing produced gas yield and heating value compared to high-temperature gasification and the olivine addition. Furthermore, experiments involving the reuse of 5% olivine after three cycles demonstrated improved catalytic effects. The produced gas compositions were 12.48 vol.%~15.43 vol.% for hydrogen and 6.63 vol.%~11.98 vol.% for carbon monoxide, respectively. The average heating value of the produced gas was approximately 5.18 MJ/Nm3, higher than that of fresh olivines. It implied that the reused olivine could provide a superior catalytic performance after the recycling experiment.
According to the results of heavy metal emission characteristics and speciation simulation, the solid-phase partitioning percentage of Zn was increased from 77.25% to 82.10% with the increase in gasification temperature. However, in the case of dolomite and olivine addition, the Zn solid-phase partitioning percentage was increased from 72.30% and 86.27% to 74.70% and 90.27%, respectively. This is because dolomite and olivine containing CaO could adsorb the gas-phase Zn and the crystallization of ZnFe2O4(s) and ZnSiO3(s) facilitated by olivine containing Fe2O3 and SiO2. Regarding the olivine recyclability results, 5% reused olivine as a catalyst could also provide good Zn adsorption performance due to the adsorption and crystallization mechanism. The Zn solid-phase partitioning percentage was increased from 91.49% to 97.90%. Additionally, special heavy metals Mo, In, and Ga derived from sludge emission characteristics showed insignificant variations in solid-phase partitioning percentage with increased gasification temperatures. Except for In, the solid-phase partitioning percentage was decreased from 61.11% to 25.03% with an increase in temperature. It implied that In emissions could be significantly influenced by the gasification temperature.
In conclusion, the gasification of sludge derived from Science park′s wastewater treatment plant is feasible, and this research confirms it. The addition of tested mineral catalysts enhances produced gas yield and heating value, and the tested olivine exhibited promising recyclability. The study also investigates the emission characteristics of various metals during the gasification process, providing valuable insights for Science Park wastewater treatment plants regarding the strategy selection for sludge utilization in energy conversion techniques and controlling metal emissions. | en_US |