Earticle

본 연구는 전기로 제강 공정에서 주로 사용되는 경소돌로마이트를 폐 MgO-C계 내화물을 활용하여 Flux로서 재활용하고, 이를 통하여 슬래그 내 철을 환원하는 기초연구를 진행하였다. 연구에 사용된 슬래그는 국내 단조기업에서 EAF(Electric Arc Furnace) Slag를 공급받아 조성분석을 진행하였다. 이후 FeO, SiO2, Al2O3를 혼합하여 base slag를 제조하였고 1600℃에서 Flux를 혼합하여 EAF slag를 제조하였다. 경소돌로마이트, 생석회와 폐 MgO-C 내화재를 추가한 슬래그와 경소돌로마이트, 생석회만을 Flux로 투입한 슬래그의 화학조성 및 상을 비교하기 위하여 XRD와 XRF 분석을 실시하였다. 염기도는 폐 MgO-C 내화물을 넣은 EAF slag가 2~3 범위로 적정 범위였으며, 슬래그로부터 환원된 철립은 분석결과 Fe함량 97.74%로 확인되었다. 경소돌로마이트 사용량 중 일부를 폐 MgO-C 내화물로 대체하여 제강 환원제로 재활용함으로서, 내화물 내의 탄소 성분으로 인하여 산화 슬래그로부터 제선용 철 품위(50% 이상)을 회수하는 것이 가능할 것으로 판단된다.

This study aimed to determine the methods of employing waste MgO-C refractories as a flux to replace light-burned dolomite mainly used in the electric furnace during the steelmaking process. The slag used in this study was supplied by a domestic forging company, and its chemical composition was analyzed. Subsequently, a base slag was prepared by mixing it with FeO, SiO2, and Al2O3. Next, the base slag was manufactured by mixing it with a flux at 1600℃. To compare the slag with added light-burned dolomite, quicklime, and waste MgO-C refractory and the slag containing only light-burned dolomite and quicklime, the analysis of XRD and XRF was performed. The basicity was within the appropriate range of 2 to 3 for the EAF slag containing MgO-C refractory, and metallic iron reduced from slag was found to have an iron content of 97.74 wt.%. By partially replacing light-burned dolomite with waste MgO-C refractory as a steelmaking reduction agent, it was observed that metallic iron recovery of over 50% from the slag was feasible due to the carbon component in the waste refractories.

현재 전기로(EAF) 제강 공정에서는 내화재 보호 및 탈황능 개선을 위해 MgO 함유 Flux인 경소돌로마이트를 사용하고 있으며, 탈산 효과와 동시에 Slag foaming을 통한 전력에너지를 저감시키기 위해 가탄제를 투입하고 있다. 본 연구에서는 상기 효과들을 경제적으로 달성하기 위해 폐 MgO-C계 내화재를 사용하고자 한다. 폐 MgO-C계 내화재는 현재 대부분 재활용되지 못하고 폐기되고 있는 실정이지만 다량의 MgO와 흑연 성분을 함유하고 있어 제강용 Flux로서의 효용가치가 입증되면 대량 재활용이 가능할 것으로 기대된다. 본 실험에서는상용 EAF slag 조성을 토대로 Target 조성 범위를 설정하였다. Target EAF slag가 원만히 형성될 수 있도록 하기 위해 Flux와 함께 투입될Pre-melt base slag를 제조하였다. Pre-melt base slag는 SiO2, Al2O3, FeO를 혼합하여 알루미나 도가니에 장입 후 1450℃에서 1시간 이상가열하여 제조하였다. 이후 제조된 Pre-melt base slag에 혼합 Flux #2(경소돌로마이트+폐 MgO-C계 내화재+석회석)을 가하여 용융반응시험을 수행하고 그 결과를 기존 제강 Flux에 해당하는 혼합 Flux #1(경소돌로마이트+석회석) 경우와 비교 평가하여 그 대체 가능성을 평가하였다. 신뢰성있는 평가를 도출하기 위해 XRD, XRF 및 Slag foam height, Slag basicity, 철 회수 등의 평가를 종합하였다.

In the steelmaking process using an electric arc furnace (EAF), light-burnt dolomite, which is a flux containing MgO, is used to protect refractory materials and improve desulfurization ability. Furthermore, a recarburizing agent is added to reduce energy consumption via slag foaming and to induce the deoxidation effect. Herein, a waste MgO-C based refractory material was used to achieve the aforementioned effects economically. The waste MgO-C refractory materials contain a significant amount of MgO and graphite components; however, most of these materials are currently discarded instead of being recycled. The mass recycling of waste MgO-C refractory materials would be achievable if their applicability as a flux for steelmaking is proven. Therefore, experiments were performed using a target composition range similar to the commercial EAF slag composition. A pre-melted base slag was prepared by mixing SiO2, Al2O3, and FeO in an alumina crucible and heating at 1450°C for 1 h or more. Subsequently, a mixed flux #2 (a mixture of light-burnt dolomite, waste MgO-C based refractory material, and limestone) was added to the prepared pre-melted base slag and a melting reaction test was performed. Injecting the pre-melted base slag with the flux facilitates the formation of the target EAF slag. These results were compared with that of mixed flux #1 (a mixture of light-burnt dolomite and limestone), which is a conventional steelmaking flux, and the possibility of replacement was evaluated. To obtain a reliable evaluation, characterization techniques like X-ray diffraction (XRD) analysis and X-ray fluorescence (XRF) spectrometry were used, and slag foam height, slag basicity, and Fe recovery were calculated.

현재 EAF 전기로 제강공정에서는 슬래그 중의 MgO 함량을 증가시켜 탈황능과 내화재 수명을 개선시키고자 돌로마이트(백운석) 용제(Flux)를 첨가하고 있으며, 또한 에너지효율을 증가시키기 위해 용강 중에 가탄재를 취입하고 있다. 이러한 견지에서 폐 MgO-C계 내화재를 재활용하는 연구를 진행하였다. 폐 MgO-C계 내화재는 MgO(>70%)과 탄소(>10%)를 대량 함유하고 있기 때문이다. 이런 목적으로 제강 슬래그를 대상으로 해서 폐 MgO-C계 내화재를 첨가하는 효과를 실험하였고 그 결과를 경소 돌로마이트를 첨가한 결과와 비교하여 폐 MgO-C계 내화재 재활용 효과를 평가하였다. 폐 MgO-C계 내화재를 사용해서 얻은 결과가 슬래그 염기도 측면에서 경소 돌로마이트를 사용한 결과와 유사하게 나타남으로써 기존 경소 돌로마이트 대체 가능성을 확인하였다. 특히 폐 MgO-C계 내화재를 사용한 경우에는, 폐 내화재에 다량 함유된 흑연 성분에 의한 슬래그 중의 철산화물과의 환원반응으로 CO가스가 발생하여 생긴 크고 작은 기포들이 관찰되었으며 이로써 슬래그 Foaming 효과를 기대할 수 있는 것으로 확인하였다.

In EAF steelmaking industries, MgO content in slag increases due to the addition of dolomite flux to protect refractory lines of furnaces and improve the desulfurization capability of slag. In addition, coal powder is injected in the molten steel bath to increase the energy efficiency of the process. In this regard, the utilization of waste MgO-C refractory material as a flux was examined because it has high amounts of MgO (>70%) and graphite carbon (>10%). A series of experiments were carried out using industrial EAF slag with added light burnt dolomite and waste MgO refractory material from a Korean steel company. The results for the addition of the two fluxes were similar in terms of slag basicity; therefore, it is expected that waste MgO-C refractory material can successfully replace dolomite flux. In addition, when the waste MgO-C refractory material was added as flux, slag foaming phenomenon was demonstrated because of the reaction between the graphite from the refractory material and iron oxides in the slag.

Alinite계 클링커 합성 시 MgO의 영향에 대해 검토하였다. Alinite 조성비 및 Alinite 조성비에 MgO를 3.77% 대체하여 760℃ 및 800℃에서 1,400℃까지 100℃간격으로 3시간 열처리하여 합성 상 및 수화열을 측정하였다. MgO를 첨가하지 않은 경우, 1,300℃에서 alinite, CCA와 함께 -C2S상과 f-CaO가 다량 존재하였으나, MgO를 첨가한 경우, 1,300℃이상에서 alinite 상만이 존재하였으며, 1,300℃에서 가장 높은 형성률을 보였다. 또한, MgO를 첨가한 경우, OPC에 비해 유도기를 거치지 않은 수화거동을 보였다.

The effect of MgO in synthesis of alinite clinker was investigated. Clinker of alinite composition ratio and alintite clinker substituted for MgO of 3.77% were sintered at 760℃ and between 800℃ and 1,400℃ at the interval of 100℃. Synthesized phases and hydration heat of alinite clinker with MgO and without MgO were then investigated. As a result, alinite, CCA, ?-C2S and f-CaO phases are synthesized in alinite clinker without MgO sintered at 1,300℃, while only alinite phase is synthesized in alinite clinker with MgO sintered at 1,300℃ with the highest synthesis rate. Heat evolution of alinite clinker with MgO has no induction period.

본 연구는 건식제련법으로 폐 PCB를 처리하는 공정에서 슬래그 중 Ni의 용해거동에 대한 기초연구로서, CaO-SiO2-Al2O3-MgO계 슬래그와 Cu-5 wt%Ni합금 사이의 Ni 분배거동을 1623 ~ 1823 K의 CO2-CO 분위기 중에서 조사하였다. 평형산소분압이 증가할수록 Ni의 분배비는 선형적으로 증가하였으며, 이 결과로부터 Ni의 슬래그 중 용해반응은 다음과 같이 나타낼 수 있다. 슬래그 중 염기성 산화물(CaO와 MgO)의 농도가 증가할수록 Ni의 분배비는 선형적으로 증가하였다. 그러나 반응 온도가 높을수록 Ni의 분배비는 선형적으로 감소하였다. 이러한 결과로부터 Ni의 분배비에 미치는 실험변수의 영향을 다중 회귀분석하여 다음과같은 경험식을 얻었다.

To obtain the fundamental information on the dissolution of nickel into the slag in the pyrometallurgical processes for treatmentof wasted PCB, the distribution ratios of nickel between CaO-SiO2-Al2O3-MgO slag and copper-5 wt%Ni alloy were measuredat 1623 K to 1823 K under a controlled CO2-CO atmosphere. The distribution ratio of Ni increased linearly with increasingoxygen partial pressure. Therefore, the dissolution reaction of nickel into the slags could be described by the following equation; The distribution ratio of Ni increased linearly with increasing content of basic oxides(CaO and MgO) in slag. However, thedistribution ratio of Ni decreased linearly with increasing temperature. From these results, the empirical equation of distributionratio of Ni was obtained by the following equation from the analysis of experimental conditions by multiple regression.

본 연구에서는 폐 PCB의 주성분인 Cu와 CaO-SiO2-Al2O3-MgO계 슬래그의 평형실험에 의해 Cu의 용해도에 대하여 조사하였다. 1673 K ~ 1825 K 범위에서 일정한 비율로 미리 용융된 4원계 슬래그와 Cu를 흑연 도가니에 각각 20 g 장입한 후, 10시간동안 평형을 유지하였다. 분위기 중의 산소분압은 CO가스와 Ar가스의 비율을 조절하여 10−17.23 ~ 10−15.83 atm 범위로 제어하였다. 평형산소분압과 염기도 및 MgO 농도가 증가할수록 슬래그 중 Cu의 농도는 증가하였다. 그리고 반응 온도가 높을수록 슬래그 중의 Cu의농도는 감소하였다. 슬래그 중으로 용해되는 Cu의 반응은 발열반응이다.

In this study, the solubility of Cu, which is a main metal component of wasted PCB, in CaO-SiO2-Al2O3-MgO slag systemwas investigated. Each 20 grams of Cu chips and the quaternary slag manufactured was placed in an carbon crucible and meltedfor 10 hours in the temperature between 1673 K and 1825 K to confirm the equilibrium state. The oxygen partial pressure wascontrolled by the ratio of CO and Ar gas in the range of 10?17.23 to 10?15.83 atm. The concentration of Cu in the slag increasedwith increasing oxygen partial pressure, slag basicity, and MgO content in the slag. The concentration of Cu in the slag decreasedwith increasing temperature. The Cu dissolution reaction in the slag is an exothermic reaction.

Ti 터닝 스크랩은 스펀지 제조 공정, 가공용 소재 제조 공정, 제품 제조 공정 등 다량으로 발생하고 있으며, 이러한 스크랩의 재활용 공정 중 하나는 Fe-Ti 합금 제조이다. 그러나 Fe-Ti 합금 제조 시 Ti 스크랩의 불순물로 인한 합금내 불순물 증가 및 합금 내 Ti 손실 등의 문제가 발생할 수 있다. 본 연구에서는 1873K 및 Ar 분위기에서 FeO-TiO2-MgO-Al2O3 다원계 슬래그와 Ti 함량 60wt% 이상의 Fe-Ti 합금의 평형 반응을 통해 합금 내 Ti 손실을 줄이며 불순물인 N과 C 제거에 대한 슬래그 조성의 영향을 조사하였다. Fe-Ti 합금의 Ti 농도는 Ti 터닝 스크랩을 장입하여 제어하였다. 또한, 합금 제조시 Al을 추가 장입하여 Ti보다 우선 산화를 통해 생성된 Al2O3가 슬래그에 함유되는조건에서 슬래그내 γTiO 증가하고 합금 내 Ti 손실 감소를 확인하였다. 한편, Al 추가 장입과 관계없이 Fe-Ti 합금내 불순물인 N는 슬래그의 FeO/TiOx비가 감소할수록 약 0.02wt% 이하로 감소하며, C는 0.1wt% 이하로 감소하는 것을 확인하였다. Fe-Ti 합금내 생성된 평형산화물은 TiO 상으로 확인되었다. Fe-Ti 합금 내 Ti 손실을 줄이기 위해서는 Ti보다 우선 산화 반응이 일어나는 첨가물이 필요하다고 판단된다.

A large amount of scrap of Ti turnings is generated from manufacturing processes of sponge and product. One method of recycling of Ti scrap is through the production of ferrotitanium alloys. However, during the production of ferrotitanium alloys, impurities in Ti scrap can lead to an increase in the overall impurities and a loss of Ti from the Fe-Ti alloy. In the present study, the influence of the slag composition on reducing the loss of Ti and the removal of impurities from Fe-Ti alloys was investigated by evaluating the equilibrium between the FeO-TiO2-MgO-Al2O3 multi-component slag and an Fe-Ti melt with a titanium content of over 60 wt% at 1873 K under Ar atmosphere. The Ti content in the Fe-Ti alloy was adjusted by charging with scrap of Ti turnings from industry. When the Fe-Ti alloy was melted with the addition of Al scrap, Ti loss from the Fe-Ti alloy decreased owing to the preferential oxidation of Al over Ti in the Fe-Ti melts and the reduction in the activity coefficient of TiO for the slag containing Al2O3. On the other hand, regardless of Al addition, the contents of N and C in the Fe-Ti alloy decreased to less than 0.02 wt% and 0.1 wt%, respectively, as the FeO/TiOx ratio in the slag decreased. The equilibrium oxide generated in the reactions with a high concentration of Ti was TiO. To reduce Ti loss in the Fe-Ti alloy, elements that are preferentially oxidized over Ti should be added to the Fe-Ti alloy.

The IMO’S 72nd MEPC meeting proposed the goal of reducing greenhouse gas emissions by up to 50% by 2050. Thus, various eco-friendly fuels are proposed as alternatives, but there are also various issues that need to be tackled, such as storage stability and supply system issues in a special environment a ship has. Therefore, in this study, the possibility of reducing greenhouse gases was analyzed by applying MGO as an alternative to boilers operated with HFO, a Bunker-C series. As a result, the exhaust gas temperature decreased by about 11.54% from 316.9℃ to 280.3℃, and the amount of oxygen content increased by about 0.38% from 6.27% to 6.65%. It can be seen that carbon monoxide can be reduced by about 45.28% by simply converting fuel from 45.29 ppm to 24.78 ppm, and carbon dioxide, which is a typical greenhouse gas, can be reduced by about 0.49% from HFO by 11.08% to MGO by 10.59%. This means that some greenhouse gas reduction is possible only by shifting between ship fuels that satisfy ISO-8217, but since there are limitations to achieving strong carbon neutrality proposed by IMO, it will be necessary to actively utilize the use of various alternative fuels in the future.

This study intends to analyze physical and chemical changes using Thermo-Gravimetric Analysis (TGA) of MGO-bioethanol mixed fuel oil. We will analyze the thermal stability and state changes of MGO-Bioethanol mixed fuel oil and conduct and utilize various basic experiments on its applicability as ship fuel oil in the future and eco-friendly alternative fuels. The physical and chemical conditions set through this experiment were set through non-isothermal heating at about 20°C to 933°C, and the heating rate was 100°C/min, the measurement time was 10 minutes, and the amount of samples in each mixed fuel oil was about 18mg-24mg. In the range of pyrolysis temperatures from 235.241°C to 253.320°C, the weight of BE0 was 30.992%, BE10 was 36.199.%, BE20 was 35.879%, and BE30 was 35.725%, indicating that the pyrolysis temperature and weight tended to increase as the bioethanol content increased.

Biodiesel is a traditional energy field that can replace low-quality marine fuels for ships and various studies have been conducted. Since the 2000s, Korea has introduced a mandatory supply system of biodiesel for domestic vehicle diesel, gradually raising the blending ratio from 0.5% to 3.5%, and is expected to raise the mandatory blending ratio to about 8.0% by 2030. Therefore, in this study attempted to blend high-quality samples that meet the biodiesel quality standards manufactured by domestic companies with MGO in ratios ranging from 0 to 60%. We utilized a 1-ton combustion chamber to compare and analyze the exhaust gas emissions characteristics. As a result, in the BD60 condition, which represents the maximum range in this study, the O2 increased by approximately 1.5%p, and CO2 tended to decrease by 1.1%p. NOx decreased by approximately 18.2%p from 34.1 ppm to 27.9 ppm. In the case of SOx, a very low concentration of 0.08 ppm was detected under the BD0 condition, and it was undetectable under all other conditions containing biodiesel. This suggests that MGO itself has excellent low-sulfur oil quality and can implement zero SOx through biodiesel mixing. Furthermore the combustion efficiency decreased by approximately 1.91%, from 72% to 70.2%, and the exhaust gas temperature also decreased by about 4.5%p. However despite the lower calorific value of biodiesel compared to MGO, it demonstrated relatively close thermal output per unit content. This indicates sufficient potential for biodiesel to serve as a viable alternative fuel for ships in the future.

This study intends to use the possibility of an eco-friendly alternative fuel to be applied to ships as a sample manufacturing method for ship MGO and bioethanol mixed fuel oil as basic evidence. The components of the manufactured mixed fuel oil were analyzed using the ISO-8217 standard testing method. As a result of analysis showed that in the lower calorific value decreased to 43030J/g at BE0 fuel and 37010J/g at BE30 fuel. The high calorific value decreased to 46.065MJ/kg at BE0 fuel and 39.460MJ/kg at BE30 fuel. The density decreased to 840.8kg/m3 at BE0 fuel and 837.0kg/m3 at BE30 fuel. In the case of flash point it was 67.5℃ when BE0, and decreased to less than 40.0℃ when BE10 to BE30. Finally the Kinematic Viscosity was 3.011mm2/s at BE0 and decreased to 2.502mm2/s at BE30.

LMO(LaMnO3) buffer layer of superconducting coated conductor was deposited on IBAD-MgO template in the plasma atmosphere at 650 oC which is relatively low compared with conventional deposition temperature of more than 800 oC. Deposition method of LMO was DC sputtering, and target and deposition chamber were connected to the cathode and anode respectively. When DC voltage was applied between target and chamber, plasma was formed on the surface of target. The tape substrate was located with the distance of 10 cm between target and tape substrate . When anode bias was connected to the tape substrate, electrons were attracted from plasma in target surface to the tape substrate, and only tape substrate was heated by electron bombardment without heating any other zone. The effect of electron bombardment on the surface of substrate was investigated by increasing bias voltage to the substrate. We found out that the sample of electron bombardment had the effect of surface heating and had good texturing at low controlling temperature.

This study sought to apply different MgO additions to Zirconia (20wt % Frit) and thereby determine its mechanical properties depending upon variation of temperature, as a part of elementary study. First, in terms of sintering density depending on sintering conditions, it was found that sintering density increased as temperature varied from 1100 to 1300 . As the addition of MgO increased, it was found that sintering density tended to decrease at each temperature. For the maximum sintering density obtained from pellet, it was found that 3wt% MgO addition specimens sintered at 1300 had its maximum sintering density as high as 97.39%. This study measured mechanical properties of these specimens, and it was found that their bending strength tended to decrease as the content of MgO addition increased. And it was found that their bending strength reached up to 162 MPa when 3wt% MgO was added to them for sintering process at 1300°ΔC. It was also found that those specimens had Vickers microhardness up to 4.6 GPa when 5wt% MgO was added to them for sintering process at 1300.

$850{\sim}1000^{\circ}C$ 정도의 저온에서 소성된 MgO 분말을 적정량 치환한 콘크리트는 장기팽창성을 갖는다. 이러한 팽창성은 저온소성한 MgO 분말의 느린 수화반응을 통해 이루어지기 때문에 장기재령까지 수축을 보상하는 특성을 가진다. 최근 수화열 저감, 내구성 향상 등의 이유와 함께 건설 산업의 탄소저감을 위한 방안으로 플라이애시 및 고로슬래그 등과 같은 혼화재의 사용이 증가하고 있다. 따라서 저온소성한 MgO 분말을 팽창재로 사용하기 위해서는 이러한 혼화재와 MgO 분말을 함께 사용한 콘크리트의 특성 규명이 필요하다. 이 연구에서는 플라이애시 콘크리트에 저온소성한 MgO 분말을 치환한 콘크리트의 슬럼프, 공기량, 수화열뿐만 아니라 장기재령 압축강도 및 길이변화 등의 기본 물성을 실험을 통해 조사하였다. 단열온도 상승시험 결과, 5% 수준으로 MgO 분말을 치환한 콘크리트의 단열온도상승속도 및 최종온도가 플라이애시 콘크리트보다 다소 작게 나타났다. 또한 압축 강도 실험결과 물-결합재비에 따라 저온소성한 MgO 분말이 장기재령 압축강도에 미치는 영향이 다르게 나타났으며, 장기적인 길이변화 실험 결과 저온소성한 MgO 분말을 치환한 콘크리트에서 큰 팽창효과를 확인할 수 있었다.

Although the lightly burnt MgO at $850{\sim}1000^{\circ}C$ has expansibility, it does not lead to unsound concrete. The expansion of MgO could compensate for shrinkage of concrete for a long-term, because the hydration of MgO occurs at a slow pace. Recently, the study and application of mineral admixture such as fly ash and blast furnace slag have increased for the hydration heat reduction, durability improvement, and reducing $CO_2$ emission in the construction industry. Thus, it is necessary to research on the concrete that contains both a mineral admixture and MgO as an expansion agent. This study investigates fundamental properties of fly ash concrete with lightly burnt MgO through various experiments. The adiabatic temperature test results showed that the fly ash concrete with MgO of the 5% replacement ratio had the slower pace of the temperature rise and the lower final temperature than the fly ash concrete. The influences of MgO on long-term compressive strength varied depending on water-binder ratio, and the long-term length change test results indicated the expansion effects of the FA concrete containing MgO.