Research on Carbonization Properties of Coking Coals

Abstract

코크스는 고로 조업에서 열원 및 통기유지제로 사용되는 매우 중요한 원료이지만 점결성이 우수한 고급 강점탄의 가격 상승으로 철강제품 가격에서 연원료의 비용이 지속적으로 상승하고 있다. 이에 저가의 저품위 비야금용 석탄 배합비율 증대를 통해 제선 연원료의 원가경쟁력 제고의 필요성이 지속 제기되고 있지만 저품위 비야금용 석탄의 배합비 증대시 Coke 품위의 저하가 예상된다. 이에 본 연구에서는 Coke의 품질을 예측할 수 있는 차별화된 모델 개발을 최종목표로 총 3단계의 연구를 진행 중에 있다. 첫 단계로 석탄의 종류 및 혼합, 탄화조건에 따른 석탄의 열분해 거동 및 발생 가스 성분을 측정하여 석탄 등급별로 경향성을 분석하였고, 탄화 중 발생하는 Char, Gas 및 Tar의 물질수지를 석탄 등급별로 구분하였다. 또한 석탄의 탄화 후 잔류하는 Char에 대해 FT-IR 및 XRD 장비 활용하여 석탄 종류 및 탄화 조건에 따라 탄화과정 중 화학적 조직의 변화를 분석하였다. 그 결과 석탄 등급에 따라 탄화과정 중 발생되는 Char, Gas, Tar에 일정한 경향성을 확인하였으며, 화학적 구조의 변화도 일정한 경향성이 있음을 확인하였다. 그리고 본 연구에서 확인한 내용들을 Data Base화 하여 2,3단계 연구의 기초 Data로 사용하고자 한다.

This research was conducted to investigate the carbonization behavior of coking coals at various temperatures (300, 400, 500, 600, 800 and 1000 °C) to gather valuable data for establishing a carbonization model of the coking coals. First of all, behaviors of releasing gas during carbonization were measured by using Quadruple Mass Spectrometry (QMS) and the relationship between coal rank and the amount of releasing gas was investigated at the various temperatures. It was confirmed that as the coal rank decreased, the amount of releasing gas was increased and the initial temperature of releasing gas moved to the lower temperature. Secondly, the mass balance among carbonization products such as gas, tar and char was evaluated during the carbonization. As the coal rank decreased, the yields of the gas and the tar were increased while the yield of the char was decreased at all temperature regions. It means that lower rank coals decomposed faster than higher rank coals. Thirdly, the change in aromatic CH (3030 ~ 2950 cm-1) and aliphatic CH (2920 ~ 2850-1) of raw coals and the char in the thermoplastic region (300 ~ 500 °C) was measured by Fourier Transform Infrared Spectroscopy (FT-IR). The peak area ratio of aromatic CH to aliphatic CH (AaroCH/AaliCH) had close relationship with mean reflectance and aromaticity of raw coals. As the coal rank decreased the peak area ratio (AaroCH/AaliCH) was decreased. It means that lower rank coals have lower aromaticity. Lastly, graphitization degree of the char was calculated by X-ray diffraction (XRD) analysis. Interlayer spacing (d002) and crystal height (Lc) of (002) carbon band represent the graphitization degree of the char. As the coal rank decreased, the interlayer spacing (d002) was increased while crystal height (Lc) was decreased. It means that the higher rank coals were easily transferred to graphite structure.