One of the more important aspects for obtaining a highly productive operation in an EAF is related to the amount of Hot Heel or Liquid Heel being present in the main vessel in between individual melts. The Zensor Hot Heel Monitoring Tool allows the operator to assess the amount of hot heel present in the vessel after individual tapping operations.
Relevance of Hot Heel
The presence of a liquid heel in EAF operations can have multiple outcomes, from reducing energy consumption and lowering tap-to-tap times to a longer refractory life (due to lower damage by the scrap), more efficient steel refining (such as Phosphorous removal), improved slag properties, the ability to melt larger pieces of scrap and a higher arc stability (less flicker), thus longer electrode life.
Knowing the amount of hot heel prior to each melt offers the ability to fine-tune process parameters, assess how to dose the slag forming products, (when relevant) amount of carbon to be injected. Determining the amount of liquid heel present in the furnace is quite a challenge. Direct measurements are difficult due to the high temperature inside the furnace, but also the presence of slag, smoke and fumes. Indirect measures require specific equipment and the apparatus suffers from the high-temperature conditions as well, all leading to a high uncertainty and a lower reliability of the equipment
A new approach
When a liquid is in a container, and this container moves (tilts), the liquid starts moving. Once the tilting stops, the liquid keeps on moving for a while. This movement of the liquid is called sloshing.
The same happens in the EAF vessel after tapping of the steel. When the furnace is brought back into the horizontal position, the liquid steel does not immediately stop, but keeps on moving slightly back and fro, until all the kinetic energy has dissipated. This movement of the steel results in a continuous shifting of the center of mass of the furnace, and results in a small, but measurable dynamic movement of the entire structure.
The Hot Heel monitoring tool uses as a basis a set of sensors to continuously measure the movement of the furnace. The sensors are located outside the hot zone, so have a very high survival rate. Moreover they are relatively low cost, so easily replaced should damage occur. The data is analyzed continuously and moments where sloshing occurs are detected automatically. Subsequently the resulting dynamics are transformed into an amount of liquid metal being present at that moment.
In its basic implementation, an assessment can be made relative to the previous melt. When the client agrees to perform a number of calibration runs, liquid heel quantities can be assessed with higher accuracy.