Combustion Control Technology
Burners can be considered as the interface to carry out the thermal process. So it is mandatory that they are optimized according to several criteria (combustion chamber size, fuel type, operating conditions of the furnace, etc) in order to achieve the best thermal performance of the furnace as far it concerns product quality, low fuel consumption and low Nox emissions.
So, having the best burners available as those of Tenova is necessary but not sufficient.
The overall result is achieved by means of the combined actions of the burners and of the combustion system responsible of actuating the control of the combustion process.
The combustion system is designed to provide sufficient heat input to maintain the design production levels with a skid insulation loss minimum. Each of the temperature control zone's fuel and combustion air headers is equipped with a metering device coupled to a transmitter and with a flow control valve, adequately sized for the design flow conditions. Combustion airflow metering as well as gas metering is by orifice plate, the flow control valves are butterfly type.
The primary variable in the combustion air-fuel flow control systems is each zone temperature, the secondary variable is the fuel-air ratio.
The flow control system is double cross limited such that the combustion airflow and fuel flow are within a prefixed gap controlled in any operating condition. Also, the control system automatically limits the fuel supply to the available air, at the selected ratio. The combustion air can be preheated up to 650°C by a recuperator.
The control of the furnace combustion process is performed by means of the supervisor programme running in the PCs which constitute the Human Machine Interfaces in the control room. The supervisor program, following the control sequences shown in the P&ID drawings, controls the combustion loops. It can control the furnace processes under different operational modes.
In the Automatic Mode, the set point of the respective controller is determined and fixed by the operator via the HMI. The controller derives its output from the PID algorithm.
In the Manual Mode, the operator sets the output of the selected controller via the HMI. The remaining controllers maintain their status unless control or safety logic is violated. At all times it is possible to pass from the Automatic Mode to the Manual Mode.
In every mode at all times interlocks and internal conditions are respected. Furthermore the HMI display of each zone's display screen indicates the current functioning of the controllers.
Bumpless switching from Manual to Automatic mode is also foreseen. The Manual set output of the PID algorithm must always be tracked to match the automatic output when in automatic mode.
The temperature controller of each zone operates in a cascade on the set points of the air fuel flow controllers. The temperature controller output provides set values in parallel for the fuel and air flow controllers, which are controlled by the 'Double Cross Limit Method' (DCL). The high-low selection obtained from the DCL values and the feed back values from air and fuel flow provides an upper and lower limit to variations in air and fuel flows. These operate according to the safety sequence followed by the master controller, on demand (when there is a load request from the temperature master controller) the air leads the rise, on release (when there is a request for a decrease by the temperature master controller) the fuel will lead the decrease. This safety sequence will thus provide dominance of air to avoid the presence of un-burnt gas in the furnace during any transient situation.
Value for Money
- Optimized combustion control means having a strong energy saving mainly in the transient state of the combustion process
- Full integration with Level 2
- Engineering services for upgrades of existing equipment
- Turnkey solutions and installations of integrated systems
- Complete modularity for spare parts supply
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