Model-based Level-2 control of the Electric Arc Furnace comprises the on-line observation of the current process state, and the control of electrical and chemical energy input as well as of the continuous charging of materials like DRI or HBI.

Structure of dynamic mass and energy balance model

The process observation calculates the current status of the heat, i.e. the temperature as well as weight and composition of steel and slag. It starts with the status of the hot heel, which is estimated from the measured tap weight of the preceding heat. The current heat temperature is calculated based on an energy balance. It considers the required meltdown energy of all charged and continuously added materials, energy losses by radiation, waste gas, cooling water and electrical losses, and the energy input by electrical energy, gas burners, and blown oxygen. If required, additionally the energy input by CO post-combustion or scrap preheating,  e.g. in a shaft furnace, is taken into account. Weight and analysis of steel and slag are determined within a mass balance. The effect of all material additions is taken into account based on their composition and yield, considering relevant metallurgical reactions.

 

Result of the energy balance for an example heat

Automatic process control calculates the set-points for energy input and material additions  according to the quality-dependant aim values for tap analysis and temperature of the heat, taking into account restrictions and rules from the practice data. The electrical and the chemical energy input via gas burners is controlled via operating diagrams with set-points for different power steps according to the achieved specific electrical energy input during meltdown.  In case of a thermal overload of the water-cooled wall panels, the electrical power is reduced automatically. The feed rate of continuously added materials like DRI or HBI is calculated dynamically from a specific feed rate and the current power input. Thus the feed rate  reflects fluctuations in the energy supply, which avoids the occurrence of "ice bergs".

 

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Structure of the model-based process control system with engineering data, measured data from the basic automation system and set-points for process control 

Example: on-line observation of the melt temperature

• Alexandria National Steel, Egypt
• Megasteel, Kuala Lumpur, Malaysia
• Marienhütte, Graz, Austria 
• Saarschmiede, Völklingen, Germany 
• Benteler, Lingen, Germany