Project nominated for the Excellence in sustainability Steelie Award 2022
Because hot metal transport vessels have a large surface area and the transport time in these vessels is long, being around 6 hours if the pretreatment process is also included, the heat loss from the surface of the outer steel shell is the largest among all the vessels used in the steelmaking process.
Therefore, JFE attempted to reduce the vessel surface temperature by using high-performance heat-insulating material, thereby suppressing radiant heat transmission. In this process, the upper limit temperature for use of the insulator and demonstrating the required performance over the long term became issues.
These problems were solved by optimising the installation position of the insulator based on thermal transfer calculations, small-scale experiments, etc. The durability and effect of the insulating material were also verified by a commercial plant test conducted over an extended period of time, which showed that the heat loss from the vessel surface could be reduced to 55 to 75% of the conventional level.
There were no effective recycling applications for the refractories used in the hot metal ladle. As reasons for this, in addition to the fact that multiple types of raw materials are used in various special-purpose refractories, the refractories are also contaminated by other materials and impurities such as slag.
JFE solved the problem of multiple raw materials by adopting a policy of using the same type of brick raw materials. For contamination by remaining different materials and impurities in recovered refractories, JFE carried out a detailed investigation of the contamination route and the mechanism by which the contaminants affect refractory properties.
As a result, the company succeeded in substantially reducing the level of impurity contamination by improvement of the refractory dismantling and management methods and adopting a simple particle-size sorting method.
By further combining these methods and a newly-developed raw material management method, we established a “closed-loop refractory recycling technology” that makes it possible to use stable, low-cost recycled refractory raw materials at a blending ratio of 70%, which is the world’s highest level in shaped bricks. With the cooperation of Shinagawa Refractories Co., Ltd., JFE Steel is now conducting long-term stable refractory recycling.