Developments Toward an Intelligent Electric Arc Furnace at - Tenova

MODEL INPUTS AND OUTPUTS
Initial work towards a dynamic control system for the EAF has focused on building a mathematical model for calculating a dynamic
mass and energy balance applied to the gas-phase of the EAF. The idea of calculating a mass/energy balance of the gas-phase of the
EAF is not new. What differentiates the current approach from that of others is that here the balance is calculated dynamically using
actual measurements of off-gas composition and temperature. Figure 15 shows the general structure of the modeling effort:
AIR
INLEAKAGE
Water
Inleakage
OFFGAS
O2, CH4, C
Figure 15: EAF gas-phase mass and energy balance.
Temperature
Static Pressure
Composition
In the past, measurement of furnace off-gas temperature has been attempted with traditional sheathed thermo-couples. Although
thermocouples have been able to provide temperature measurements for brief periods of time, they have been found to be un-reliable
long-term in the harsh EAF environment. TGTI has identified an infra-red (IR) gas-phase pyrometric technology based on the
emissivity of carbon dioxide and is working towards adopting the technology to the EAF environment. Initial trials at CMC Texas
have shown promise.
The model takes as its inputs the instantaneous rate of flow of methane, oxygen and injected carbon into the EAF freeboard. In
addition to process parameters, real-time values of off-gas composition and temperature are provided by the EFSOP ® system. An
additional piece of information that is required to close the mass balance is an estimate of the rate of off-gas leaving the EAF. From a
modeling point of view, this value scales the model and forms the basis of the calculation. The initial approach is to relate the off-gas
rate to a measure of static pressure at the fourth hole. The empirical relationship can be tuned to an overall carbon balance. To this
end, TGTI has developed a static pressure probe that is loosely based on the same design of the EFSOP ® extractive probe for off-gas
analysis. Simply, it is a water-cooled probe, fitted with a pressure transducer and positioned in the elbow of the EAF.
Given these inputs, the model uses elemental (carbon, hydrogen, oxygen and nitrogen) and energy balances to calculate:
a) Carbon entering the gas-phase (as CO gas) through decarburization and combustion of carbon – from carbon balance
b) Hydrogen entering the gas-phase (as H2O) from water-cooling, leaks, wet scrap, etc. – from hydrogen balance
c) Oxygen leaving the gas-phase due to oxidation (carbon, iron, silicon, etc.) – from oxygen balance.
d) Air in-leakage entering the gas-phase – from nitrogen balance.
e) Heat losses from the gas phase – enthalpy balance given composition and temperature.