Sensor-based identification of elemental carbon and metal in spent refractory bricks

Recycling of spent refractories offers an opportunity to lower the dependency on raw material imports. The main challenges in recycling of refractories are the separation of different refractory types and the removal of impurities. Thus, this study focuses on the sensor-based detection of elemental carbon and metal impurities in spent refractory bricks. The fundamentals of refractories as well as the current situation in recycling of refractories are described. This study focuses on eight different types of refractories, which cover the vast majority of refractories applied in the steel industry. All tests described were conducted with four different types of samples whose preparation is described too. Subsequently, various physical properties were measured in order to find a suitable feature for identifying elemental carbon and metal impurities. Based on the results of the evaluation of physical properties, two features were identified and further evaluated, induction and microwave heating behavior. For both features, a brief theoretical background, the test setup, and the results are described. It showed that, with some limitations, microwave heating can be used to identify elemental carbon. Induction can only be used for presorted fractions. Based on these results, a new process was proposed, containing the already applied LIBS-technology, supplemented by microwave heating and induction. The technologies currently applied for recycling of spent refractories need improvement in order to meet the strict quality requirements for refractories and increase the quantity of recycled refractories. Investigations have shown the possibility to improve the sorting of spent refractories by applying inductive sensors and microwave heating.