Development of high effciency & low-cost desulfurization flux for hot metal by utilizing waste red mud

Abstract

고품질 철강 제품에 대한 수요가 증가함에 따라 제품의 황을 낮추기 위한 요소 기술이 요구되고 있고, 고로에서 생산되는 용선 내 황 농도는 저품위 원료, 특히 저품위 코크스의 사용으로 인해 점차 상승 중임. 그럼에도 불구하고 API, 후판제품, 자동차강판 등 황의 농도가 낮은 제품에 대한 수요는 지속적으로 증가하고 있어, 고율적-친환경-저비용의 경쟁력이 있는 탈황 기술의 개발이 필요함. 탈황에는 형석을 함유한 CaO계 Flux가 주로 사용되어 왔지만 유해하기 때문에, 무형석 플럭스의 개발에 대해 많은 연구가 진행되어 옴. 본 연구에서는 알루미나 생산 공정의 부산물인 Red mud를 CaO계 탈황 플럭스와 혼합하여 최적의 탈황 조건을 검토하였음. 탈황 효율(탈황율, 최종 황의 농도)은 Red Mud의 배합비, 환원여부, 기계적 교반 등의 다양항 조건하에서 연구를 진행하였으며, 현재 상업적으로 활용되고 있는 탈황 Flux와의 탈황 효율에 대해서도 비교하였음. 본 연구에서 검토된 Flux는 탈황 효율 면에서 경쟁력 있는 결과를 나타냄을 확인할 수 있었음. 본 연구조건에서는 Red Mud를 환원 후 20% 배합 시 5분 시점의 탈황 속도가 가장 빠르게 나타남. 추가로, 탈황 효율을 정량적으로 평가하기 위해 Index를 검토하였으며, Index는 평형론적 측면에서 최종 탈황 수준을 고려하고, 속도론적 측면에서 10분 시점까지의 속도 상수, 탈황 Flux내 CaO 량을 고려하여 도출하였음. 이렇게 검토된 Index를 기반으로 비교 시에도, 상업적으로 사용중인 Flux 대비 동등 수준의 효율을 확인할 수 있음. 경제적인 측면에서 Red Mud는 부산물로써 원가경쟁력을 가지고 있어, . 탈황 비용을 낮출 수 있을 것으로 예상되며, 실 조업에 적용 가능성에 대해서도 추가적인 검토가 필요할 것으로 판단됨.

Demand for high-quality steel products is increasing, and accordingly, refining technology is required to reduce the sulfur content in products. The concentration of sulfur in hot metal produced from the blast furnace increases gradually due to the use of low-grade raw materials. This makes producing low sulfur hot metal after desulfurization difficult. Nevertheless demands for low S products such as API, thick plate products, and automotive steel products keep increasing. Therefore, it is necessary to develop efficient, environmental-friendly, and cost-competitive desulfurization technology. CaO-based flux containing fluorspar has been mainly used for the desulfurization, but it is harmful to human body and environment. Therefore, many studies have been conducted on the development of flux without fluorspar. In the present study, red mud which is a by-product of alumina production process was blended with a CaO-based desulfurization flux to investigate the optimal conditions for the desulfurization. The red med mud was used as a fluxing agent in order to effectively melt the burnt lime. The desulfurization efficiency (removal rate of S and final content of S) was examined by changing conditions, such as mixing ratio of the red mud, pretreatment of the red mud, and mechanical stirring. Desulfurization efficiency obtained in two cases, one with the currently used desulfurization flux in POSCO (Pohang and Gwangyang steelworks) and the other with the desulfurization flux blended with red mud in the present study were compared by a series of experiments on a lab scale. It was found that the flux blended in the present study showed very competitive results in terms of the desulfurization efficiency. A desulfurization index was introduced in order to quantitatively evaluate the desulfurization efficiency: when the pre-reduced red mud was blended with the burnt lime 20% by mass, it showed almost the same level of desulfurization efficiency with the flux used in Gwangyang steelworks, POSCO. In terms of an economical aspect, since the red mud is a by-product or a waste, its use is considered to be free at the moment, thereby giving a cost-competitiveness. It is expected that the cost for desulfurization could be lowered. It has been confirmed in the present study that the same level of desulfurization efficiency was obtained using the red mud mixed flux, when it is compared to the currently used flux in the steelworks. It is expected that this new flux can be used in practical operations in near future.