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신미수(Mi-Soo Shin),장동순(Dongsoon Jang),이용국(Yongguk Lee) 대한환경공학회 2016 대한환경공학회지 Vol.38 No.12
분리막의 제조에 있어서 높은 분리도와 투과도가 요구되지만 투과도와 분리도는 반비례하는 경향이 있으므로 현실적으로 가능하지 않다. CO₂ 포집의 비용절감 측면에서 살펴보면 분리막의 재질 자체보다는 투과도와 분리도가 분리막의 모듈이나 시스템의 성능이 미치는 영향이 더 중요하다고 할 수 있다. 예로 들어 CO₂ 13%와 N₂ 87%인 혼합기체를 분리도를 5로 고정시킨 후 유량의 10%가 분리막을 통하여 투과된다고 가정하면 투과한 10% 중에 CO₂ 4.28%, N₂가 5.72%로서 투과한 기체중 이산화탄소의 농도가 42.8%가 된다. 이 경우 이산화탄소의 순도는 42.8%이며 첫 번째 투과에 의해 얻은 이산화탄소의 회수량은 4.28/13 = 32.9%가 된다. 만일 투과도와 분리도를 두배로 증가시킬 경우 이산화탄소의 순도는 64.5%, 이산화탄소 회수량은 12.9/13 = 99.2%로 나타났다. 이 경우 대부분의 CO₂가 회수되었으며 이것이 의미하는 바는 주입된 이산화탄소가 투과되지 않고 그대로 통과하여 빠져나가는 양은 거의 제로에 가까운 경우로서 이산화탄소 분리에는 이상적인 설계나 운전조건이라 할 수 있다. 일정한 주입농도에서 주어진 투과도에 대하여 이산화탄소를 100% 회수하는 임계 분리도가 존재함을 알 수 있으며, 임계 분리도 이상 높아질 경우 이산화탄소 회수되는 양이나 순도 향상에 별다른 영향이 없음을 시사하고 있다. 이상의 결과에서 주어진 이산화탄소의 농도에 대해서 분리막을 이용한 분리에서 이산화탄소를 100% 투과시키는 임계 투과도와 분리도가 설계와 운전조건의 최적화를 위하여 절대적으로 중요함을 알 수 있다. Manufacturing membrane materials with high selectivity and permeability is quite desirable but practically not possible, since the permeability and selectivity are usually inversely proportional. From the viewpoint of reducing the cost of CO₂ capture, module performance is even more important than the performance of membrane materials itself, which is affected by the permeance of the membrane (P, stagecut) and selectivity (S). As a typical example, when the mixture with a composition of 13% CO₂ and 87% of N₂ is fed into the module with 10% stage cut and selectivity 5, in the 10 parts of the permeate, CO₂ represents 4.28 parts and N₂ represents 5.72 parts. In this case, the CO₂ concentration in the permeate is 42.8% and the recovery rate of CO₂ in this first separation appears as 4.28/13 = 32.9%. When permeance and selectivity are doubled, however, from 10% to 20% and from 5 to 10, respectively, the CO₂ concentration in the permeant becomes 64.5% and the recovery rate is 12.9/13 = 99.2%. Since in this case, most of the CO₂ is separated, this may be the ideal condition. For a given feed concentration, the CO₂ concentration in the separated gas decreases if permeance is larger than the threshold value for complete recovery at a given selectivity. Conversely, for a given permeance, increasing the selectivity over the threshold value does not improve the process further. For a given initial feed gas concentration, if permeance or selectivity is larger than that required for the complete separation of CO₂, the process becomes less efficient. From all these considerations, we can see that there exists an optimum design for a given set of conditions.
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CO<sub>2</sub> 저감을 위한 미분탄과 산소/수소 당량 혼합기체 혼소에 대한 수치 해석적 연구
신미수 ( Misoo Shin ),김용주 ( Yongju Kim ),이용국 ( Yongguk Lee ),장동순 ( Dongsoon Jang ) 한국폐기물자원순환학회 2016 한국폐기물자원순환학회지 Vol.33 No.1
These days, the development of various pre- and post-combustion techniques has been pursued in order to reduce the emission of CO<sub>2</sub> in the fleet of coal-fired power plants, since it is of great importance to each country`s energy production while also being the single largest emitter of CO<sub>2</sub>. As part of this kind of research efforts, in this study, a novel burning method is tried by the co-burning of the pulverized coal with the stoichiometric mixture of the hydrogen and oxygen (H<sub>2</sub>+1/2O<sub>2</sub>) called as HHO. For the investigation of this idea, the commercial computational code (STAR-CCM+) was used to perform a series of calculation for the IFRF (International Flame Research Foundation) coal-fired boiler (Michel and Payne, 1980). In order to verify the code performance, first of all, the experimental data of IFRF has been successfully compared with the calculation data. Further, the calculated data employed with pure coal are compared with the co-burning case for the evaluation of the substituted HHO performance. The reduced amount of coal feeding was fixed to be 30% and the added amount of HHO to produce a similar flame temperature with pure coal combustion was considered as 100% case of HHO addition. This value varies from 100 to 90, 80, 60, 50, 0% in order to see the effect of HHO amount on the performance of pulverized coal-fired combustion with the 30% reduced coal feeding. One of the most important thing found in this study is that the 100% addition of HHO amount shows approximately the same flame shape and temperature with the case of 100% coal combustion, even if the magnitude of the flow velocity differs significantly due to the reduced amount of air oxidizer. This suggests the high possibility of the replacement of the coal fuel with HHO in order to reduce the CO<sub>2</sub> emission in pulverized coal-fired power plant. However, an extensive parametric study will be needed in near future, in terms of the reduction amount of coal and HHO addition in order to evaluate the possibility of the HHO replacement for coal in pulverized coal-fired combustion.
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CF<sub>4</sub>의 소각 특성에 대한 전산 연구
김용주 ( Yongju Kim ),박민정 ( Minjung Park ),신미수 ( Misoo Shin ),이용국 ( Yongguk Lee ),장동순 ( Dongsoon Jang ) 한국폐기물자원순환학회 2016 한국폐기물자원순환학회지 Vol.33 No.5
A parametric study has been made numerically on the thermal incineration of CF<sub>4</sub>, one of the perfluorocarbons (PFCs) emerging recently as issues of public concern in a practical CDM incinerator developed for the thermal destruction of HFC-23. In doing this, a turbulent combustion model of the fast combustion approximation is reasonably assumed using the typical auxiliary fuel, CH<sub>4</sub>, for the supply of the heat, and the necessary species of hydrogen and oxygen atom. In addition, the performance of the stoichiometric gas mixture of hydrogen and oxygen (H<sub>2</sub>+ 1/2 O<sub>2</sub>) was examined as a special auxiliary fuel not only in order to enhance the thermal destruction efficiency but also the reduction of the CO<sub>2</sub> emission by the elimination or the reduction of the auxiliary fuel CH<sub>4</sub> in this incineration process. The calculation results showed that the thermal destruction efficiency of CF<sub>4</sub> using methane as an auxiliary fuel increases with the amount of methane. However, the thermal destruction efficiency did not reach a satisfactory level (i.e., < 95%), even with the application of a CH<sub>4</sub> amount more than four times of the stoichiometric value. This is explained by the improper turbulent mixing effect between CH<sub>4</sub>, CF<sub>4</sub> and air especially in a large scale practical incinerator employed for the destruction of HFC-23. For the case of H2+ 1/2 O<sub>2</sub> as the auxiliary fuel, however, the thermal destruction efficiency, surprisingly, reached almost 100%, which shows the high potential of the thermal destruction of CF<sub>4</sub> by the use of HHO gas. Further, a detailed evaluation for the effect of the turbulent mixing on the thermal destruction of CF<sub>4</sub> will be quite necessary, considering operating conditions together with the type of auxiliary fuels.
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