Large-scale Municipal Solid Waste Research Articles

Removal of carbon dioxide by a spray dryer

With the global warming due to greenhouse effects becoming serious, many efforts are carried out to decrease the emissions of CO 2 from the combustion of carbonaceous materials. In Taiwan, there are 19 large-scale municipal solid waste incinerators running and their total emission of CO 2 is about 16 950 kton y −1. Spray dryer is the most prevailing air pollution control devise for removing acid gas in waste incineration; however, the performance of spray dryer on the removal of CO 2 is seldom studied. This study employs a laboratory-scale spray dryer to investigate the removal efficiency of CO 2 under different operating conditions. The evaluated parameters include different absorbents mixed with Ca(OH) 2, operating temperature, the concentration of absorbent, and the inlet concentration of CO 2. Experimental results show that the best removal efficiency of CO 2 by a spray dryer is 48% as the absorbent is 10%NaOH + 5%Ca(OH) 2 and the operating temperature is 150 °C. Comparing this result with previous study shows that the performance of spray dryer is better than traditional NaOH wet scrubber. For NaOH + Ca(OH) 2 spray dryer, the removal efficiency of CO 2 is decreased with the inlet concentration of CO 2 increased and the optimum operating temperature is 150 °C. Except NaOH + Ca(OH) 2, absorbents DEA + Ca(OH) 2, TEA + Ca(OH) 2, and single Ca(OH) 2 are not effective in removing CO 2 by a spray dryer.

Evaluation on speciation and removal efficiencies of mercury from municipal solid waste incinerators in Taiwan

Two large-scale municipal solid waste incinerators (MWIs) located in Taiwan were selected for conducting flue gas sampling to determine the chemical speciation of mercury by both USEPA Method 29 and Ontario Hydro Method (OHM). In addition, the emission characteristics and removal efficiencies of mercury were evaluated via isokinetic sampling of flue gas upstream and downstream of APCDs. Results indicated that the average removal efficiencies of Hg for MWI-A and MWI-B were 29.56 and 44.70%, respectively. In terms of mercury speciation by USEPA Method 29 and Ontario Hydro Method (OHM), oxidized mercury (Hg 2+), in the flue gas was predominant at the inlet of APCD for both incinerators. Less than 30% of mercury in the flue gas existed in the elemental form (Hg 0) at APCD inlet. Mercury emitted from the stack also predominated as a form of Hg 2+ in MWI-A. Approximately 90% of total mercury emission from the stack existed in the form of Hg 2+ for MWI-A. Due to the higher removal efficiency of soluble mercury (Hg 2+) in wet scrubber, less total Hg was actually emitted from MWI-B than MWI-A. Regarding the removal efficiency of Hg 0 in the flue gas, the APCDs of MWI-A (DSI+FF) had a higher removal efficiency than that of MWI-B (ESP+WS) possibly due to the reduction of Hg 2+ which occurred in the wet scrubber.