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Sorting of MSW incineration bottom ash according to size and density by applying Air Table separator
( Seungki Back ),( Hirofumi Sakanakura ) 한국폐기물자원순환학회(구 한국폐기물학회) 2019 한국폐기물자원순환학회 심포지움 Vol.2019 No.1
Various types of metal could be contained in a municipal solid waste (MSW) incineration bottom ash ranging from a large size of scrap metal to trace of valuable metal in small size particles. Recently, interest in physical separation of metals from MSW incineration bottom ash is growing up in order to move towards a material cycles society. Separation and characterization of MSW incineration bottom ash could derive two effects: recovery of metals as resources and excluding toxic metals before recycling the bottom ash in construction as a secondary raw material. The present research examined the Air table separator as a dry method for physical sorting according to size and density of bottom ash particles. Recycling of scrap metal such as iron and aluminum have been widely carried out in commercial MSW incineration plants. Also, ferrous and non-ferrous metals were separated from incineration bottom ash using conventional magnetic and eddy current separation. However, efficiency for small particles of a commercial eddy current separator is known to be unsatisfactory. A technique for separating small size particle containing metal compounds is needed to be applied in order to more aggressive metal recovery from incineration bottom ash. Air Table is an effective method for sorting mixtures of various particles with different density. Air Table has advantages; low capital and operating costs and less possibility secondary contamination because Air table is a dry type physical separator without chemicals. Particles with different density could be separated by changing of variables: air injection rate, vibration intensity, end slope, and side slope. Introduced target sample could be separated depends on density of particles by controlling the variables of Air Table. In this study, Air Table separation was applied to classification of MSW incineration bottom ash depends on particle density. And, bulk density and dry density of separated bottom ash were measured. MSW incineration bottom ash with 4-8, 2-4, 1-2, and 0.5-1 mm was applied to Air Table to identify particle movement on Air Table by various operating conditions as a performance test. The outlet of Air Table was divided into 4 parts to collect separated bottom ash particles according to its density. Based on data from the performance test, the effect of each variable (air injection rate (1.0-2.9 m/sec), vibration intensity (5.5-8.0 Hz), and end slope (3-14.5˚)) on particle movement was evaluated. Then, the bottom ash with 4 size ranges was classified into 6 bulk density ranges from < 0.7 g/cm3 to >1.1 g/cm3 at intervals of 1 g/cm3. Measuring cylinder and balance were used for the measurement of bulk density of particles. And, the dry density meter (AccuPyc Ⅱ 1340, Micromeritics) was applied to measure the dry density in a series of experiments. The dry density of the separated bottom ash was measured ranging from 2.19 g/cm3 to 3.63 g/cm3. The fractions which contain a high proportion of the specific elements could be separated according to particle size and its density. XRF analysis was conducted to identify the element composition of the separated particles. Heavy metals (Pb, Cu, Zn) of the higher density fractions showed high concentration compared to the lighter density fractions. On the other hand, the concentration of certain elements (Ca, Cl, etc.) showed a negative correlation with the density of the particles. The results of this study could be utilized for the sorting of MSW incineration bottom ash in terms of recycling of metal, and reducing of environmental hazard.
백승기(Seungki Back),이은송(Eun-Song Lee),서용칠(Yong-Chil Seo),이규종(Kyu-Jong Lee) 한국환경에너지공학회 2022 한국열환경공학회 학술대회지 Vol.2022 No.1
수은에 오염된 토양의 정화를 위하여 굴착 후 열적처리 조건을 도출하는 기초 실험을 수행하였다. 국내에서 확인된 오염 토양에서 함량 기준 약 10~2200 mg-Hg/kg의 수은이 검출되었으며, 토양환경보전법 토양오염우려기준 (2 지역, 10 mg-Hg/kg)을 초과하는 수치이다. 연속추출실험 결과 강산에 의해 추출되는 수은화합물이 85% 이상 존재함에 따라 토양의 정화를 위해 토양세정법과 함께 열적처리의 적용이 요구되었다. 토양 시료를 깊이 (0-0.5, 0.5-1 m) 및 입경 (0-0.04, 0.04-0.075 mm) 별로 채취하고 수은화합물의 함량을 분석한 결과, 깊이에 따른 수은 함량의 차이는 적었으며 작은 입경의 토양 내 수은 함량이 높은 것으로 확인되었다. 머플 전기로를 이용하여 300-600℃ 조건에서 입경 별 토양 시료의 열적탈착 실험을 진행한 결과, 450℃ 에서 30분 이상 처리하는 경우 수은의 토양오염우려기준을 만족하였다. 도출한 조건을 열적탈착, 분진제어, 활성탄홉착공정으로 구성된 파일럿 설비 (20 kg/batch) 에 적용하고, 오염 토양의 처리공정에서 수은 물질수지를 산정하였다. 처리 후 토양의 수은 함량 및 배출가스의 수은 농도는 각각 5.1-8.6 mg-Hg/kg 및 2.5-3.3 μg-Hg/Sm3로 확인되었으며, 토양에 서 탈착된 수은의 86-92%가 활성 탄에 흡착되어 제어 되었다. 본 연구를 통해 환경기준치 (수은 항목)를 달성하는 오염 토양의 열적처리 공정 조건을 도출하였고, 활성탄흡착을 통해 배출가스 내 수은을 제어할 수 있음을 확인하였다. 향후 수은오염 토양의 정화를 위한 설비 구축에 본 연구 결과를 활용할 수 있으며, 최적 열적탈착 조건 확립을 위하여 토양 내 수은화합물의 형테를 예측하기 위한 연구가 필요하다.