Following its enormous success with packaged applications such as electrode breakage detection for the glass industry and automation of the sterilization process for hospitals, Eurotherm’s Visual Supervisor has now demonstrated its potential in the steel industry with it’s recent integration in a gas flare control system for a blast furnace.
The system consists of a flare tip located on top of a stack and is equipped with six circumferentially mounted natural gas pilot burners each monitored by one thermocouple. The main flame being itself monitored by four thermocouples or infrared sensors.
During normal flaring operations, the blast furnace gas pressure is controlled. Any increase is relieved by flaring the excess gas.
The application includes a pressure loop and a flow loop sharing one unique analogue output. The functionality is such that when the system is under pressure control, the flow loop output tracks the active control loop output. When flow control is selected, the pressure loop enters Track mode.
Under normal conditions, the operator has a choice of controlling either the gas pressure or the gas flow. Interlocking sequence permitting, the above is carried out by using the appropriate soft-key button on the Visual Supervisor mimic. An automatic switchover dictated by various furnace conditions is also built-in.
Pilot burner monitoring
There are six pilot burners on the stack, continuously lit during operation. All six are provided with a thermocouple to monitor their status. Any failure (temperature reading below 100°C – adjustable) produces an alarm and should any four from six fail, then the flaring system is automatically shut down. Flaring is restarted once three or more pilot burners are operational.
Main flame detection
The main flame status is monitored by four thermocouples. Any failure produces an alarm. If none of the thermocouples succeed in detecting a temperature higher than a preset value, within an adjustable ignition time from asking for flaring, the control valve is automatically closed.
If the blast furnace gas pressure is still higher than the setpoint, the control valve is released again for automatic control. The main flame detection is attempted a certain number of times and following a total failure, the controller is then locked out for 20 minutes (adjustable) with the control valve held at 0%. Flaring is now inhibited.
Coupled with features such as trending, logging, reporting, messaging, batch handling and barcode reading, the Visual Supervisor is proving itself as one of Eurotherm’s strongest unit solutions.