The COURSE50 project aims at developing technologies to reduce CO2 emissions from steel works by approximately 30% in Japan. In order to supply the energy required to separate CO2, a technology for recovering sensible heat from steelmaking slag is being developed as one theme of COURSE50. A twin roll type continuous slag solidification process to obtain a shape suitable for sensible heat recovery was investigated.Sheet-like slag was shaped to a thickness of about 7 mm in a twin roll pilot-scale experiment. The slag thickness depended on the adhesion of the molten slag rather than the thickness of the solidified slag on the roll. The slag condition suitable for the twin roll method was identified as a liquid phase ratio of 60% or more. Based on a laboratory-scale experiment and heat transfer calculations, a combination process using the twin roll method and a countercurrent flow packed bed is expected to achieve a heat recovery ratio of 30% or more from sheet-like slag.

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A continuous solidification process of blast furnace slag was developed to promote the use of air-cooled slag coarse aggregate for concrete. In this process, the molten slag can solidify in only 120 s and the slag thickness is about 25 mm. This process suppresses gas generation and greatly reduces water absorption. Most of the slag is crystalline, and part of the slag has a glass layer on its surface. Slag with a glass layer is brittle because it contains several cracks. Therefore, microscopic observation and thermal stress analysis of the solidified slag were carried out to clarify the mechanism of crack generation in the plate-like slag. In the microscopic observation, several cracks with a length of about 8 mm were found in the slag with the glass layer. From the analysis, in the cooling pattern of the slag on the piled slag a temperature difference of about 200 K exists between the center and the mold side in the slag pit, and keeping this difference results in tensile stress of more than 50 MPa. However, in the cooling pattern of the crystalline slag in the piled slag, the temperature gradient in the slag in the slag pit was very small because the slag was retained in the piled slag, and as a result, the thermal stress was almost 0 MPa.