석탄을 가스터빈에 직접 사용하여 발전 효율을 높이고자 용매추출법으로 회분이 제거된 청정석탄 제조공정이 개발되고 있다. 용매추출에 의해 생산된 청정석탄에는 미량의 알카리금속이온이 들어있어서 연소시에 터빈 날개의 부식을 일으킬 수 있다. 이 연구에서는 청정석탄 제조공정의 알카리금속이온 제거를 위하여 무기이온교환제인 α, β-인산금속 산화물들(ZP: Zr(HPO4)2, TP: Ti(HPO4)2, ZTP: ZrTi(HPO4)4, Z1TP3: Zr0.25Ti0.75(HPO4)4, Z3T1P: Zr0.75Ti0.25(HPO4)4)과 H-Y 제올라이트를 제조하여 수용액 및 석탄이 용해된 고온의 유기용매(N-methyl-2-pyrrolidone)에서 나트륨 이온 제거 특성을 비교 분석하였다. β 형태의 인산금속산화물들은 모사 수용액(Na+ Conc. 100 ppmw)에서 α 형태에 비해 높은 이온교환용량을 가지고 있으며 H-Y 제올라이트에 비해서도 높은 나트륨 이온 제거용량을 보여주었다. 이온교환매체가 고온의 유기용매(Na+ Conc. 12 ppmw in NMP)일 경우에는 H-Y 제올라이트의 나트륨이온 제거율은 300 ℃까지 90% 이상이었으나, 그 이상의 온도에서는 50% 가량으로 급격히 감소하는 경향을 보여주었다. 그러나 β 형태의 인산 금속산화물들은 여러 온도조건(250~400 ℃)에서 90% 이상의 제거율을 나타내었고 강산용액을 이용한 재생 후에도 최초 실험과 유사한 나트륨 이온 제거율을 보여주었으며 그 중 가장 높은 제거율을 나타낸 Zr0.75Ti0.25(HPO4)2는 알카리 금속이온 제거공정에 가장 적합한 무기이온교환제로 판단된다.

Currently, Ash-free clean coal producing process by solvent extraction is under development. The produced ash-free clean coal can be directly combusted in a gas turbine which results in substantial improvement of power generation efficiency. However, the clean coal produced by the solvent extraction still contain trace amount of alkali metal which may cause corrosion on turbine blades during the direct combustion. In present work α,β-metal (Zr and Ti) phosphates and H-Y zeolite were synthesized and their ion exchange characterizations were investigated for the application on alkali metal removal for clean coal production. Na+ ion removal capacities of the metal phosphates and H-Y zeolite were measured and compared in both aqueous solution (100 ppmw, Na+) and coal dissolved N-methyl-2-pyrrolidone (NMP, 12 ppmw Na+) at elevated temperature. In aqueous solution, the β form metal phosphates showed very high ion exchange capacities compared to α form. β form metal phosphates also showed higher Na+ removal capacities than H-Y zeolite. In ion exchange medium of NMP, all the α form metal phosphates showed over 90% of Na+ ion removal efficiency in the temperature range of 200 to 400 while that of H-Y zeolite decreased as a half when the temperature was over 350. In addition, the regenerated metal phosphates by acid treatment showed no sign of degradation in Na+ removal efficiency. Among the metal phosphates used, Zr0.75Ti0.25 (HPO4)2 showed the best performance in Na+ removal and is expected to be the most suitable inorganic ion exchanger for the alkali metal removal process.

Ash-free Coal Na+ Ion Removal Capacity Metal Phosphate H-Y Zeolite

Wang J, Li C, Sakanishi K, Saito I, Fuel, 84(12/13), 1487 (2005)
Yoshida T, Takanohashi T, Mashimo K, Fuel, 81(11/12), 1463 (2002)
Yoshida T, Li C, Takanohashi T, Matsumura A, Sato S, Saito I, Fuel Process. Technol., 86(1), 61 (2004)
Sakanishi K, Akashi E, Takarada T, Fuel, 83, 739 (2004)
Son WK, Park SG, J. Korean Ind. Eng. Chem., 9(2), 249 (1998)
Clearfield A, Inorganic Ion Exchange Materials, Boca Raton, Florida (1982)
Sahu BB, Parida K, J. Colloid Interface Sci., 248(2), 221 (2002)
Kapoor MP, Inagaki S, Yoshida H, J. Phys. Chem., 109(19), 9231 (2005)
Mayumi I, Shuji O, Takashi A, Tooru Y, Sadayuki S, Hiroyuki Y, J. Nippon Enerugi Gakkai Sekitan Kagaku Kaigi Happyo Ronbunshu, 40, 52 (2003)
Clearfield A, U.S. Patent No. 4,059,679 (1977)
Chang JS, Park SE, Lee YK, J. Korea Inst. Chem. Eng., 27(3), 323 (1989)
Hwang TS, Lee SA, Lee MJ, Polym.(Korea), 26(2), 153 (2002)
Sugano M, Mashimo K, Wainai T, Fuel, 78(8), 945 (1999)