CORA - the constant ratio control system for mixture heating
The CORA system is a specially designed supply station to pre-mix gas and combustion air in a constant ratio for firing inside distributors and forehearths. The major advantage of this combustion system is its near to 100% stable COnstant RAtio of gas and air over the entire control range under different operating conditions.
The CORA system meets all requirements for distributors and forehearths, e.g. wide and constant control range, low maintenance and optimum combustion.
Gas/air ratio control
The natural gas is supplied by the main gas skids for the distributor and forehearths. The gas now enters the individual Cora stations as well as the combustion air which is supplied by frequency controlled combustion air fans. The combustion air flows through a differential pressure orifice plate before it flows into the mixing pipe. The air differential pressure is transferred to a gas controller which supplies the gas pressure proportional to the determined volume of air on the output side. An absolutely stable gas/air ratio along the entire control range is achieved due to the ratio control, which works according to volume, as opposed to Venturi or injector mixers which work according to pressure.
The required mixing of gas and combustion air takes place in a specially developed mixing pipe. The special design ensures that a turbulent current can be maintained even with very small gas and air volumes. In this way a favourable gas/air mixture is ensured. The size of the gas/air mixers used depends upon the heating levels required in the zones to be heated and can be changed easily. The gas/air mixture is then channeled through a gas mixture line to the special HORN HGGB gas mixture burners which are installed along the distributor and forehearths.
Fuel output control
The burner output in the respective control section is controlled via the combustion air volume. The volume of the combustion air can be adjusted by the motor control valve which receives the command from the measured temperature in the respective section inside the distributor or forehearth. The required volume of natural gas is then automatically supplied by the ratio controller as described in the section “Gas/air ratio control“.
The CORA system is equipped with the following safety devices:
- Gas safety shut-off valve in the main gas line
- Gas safety shut-off valve in each control section
- Gas pressure switch for min./max. gas pressure monitoring
- Air pressure switch for min. air pressure monitoring
- Gas pressure switch for min. mixture pressure monitoring