Air/Gas Ratio is the fundamental parameter in flame treatment process
The fundamental parameter that rules the flame treatment process in the plants designed and manufactured by EsseCI is the air/gas ratio.
Where the mixture flow represents the amount of energy supplied to the burner, the air/gas ratio is the quality of such energy. Compared to all other parameters of the treatment and, in particular, the mixture flow (being the amount of energy), if the air/gas ratio is not optimised, a significantly lower value of surface wettability is obtained on the treated surface, with a reduction in the effectiveness of the treatment itself.
Hence, the crucial importance of proper and careful control of this process parameter.
Air-gas ratio control: Jonoflame (JCS, Jonoflame Control System)
For the air/gas ratio control, EsseCI traditionally uses a calorimetric control system called Jonoflame (JCS, Jonoflame Control System).
This system requires a small quantity of the mixture intended for the burner to be released and burned in the Jonoflame. The temperature of this pilot flame is detected by a thermocouple, which sends the value to an air/gas ratio controller.
Depending on the current temperature value read and in line with the set-point for this temperature (resulting from the wettability tests), the controller acts on the motorised gas valve, opening or closing it in order to adjust the process value of the variable to that of the set-point.
This device is sensitive to the variation of the supply pressure of the mixture and to the thermocouple position. Any maintenance and calibration operations should only be performed by experienced operators
LCS (Lambda Control System) analyzer
With the aim of rendering control of the air/gas ratio even easier, EsseCI technicians have studied and developed a solution using the latest generation of oxygen lambda sensors for the air-gas ratio control, thus creating a control system based on the lambda sensor functioning principle (LCS, Lambda Control System).
Zirconium dioxide lambda sensor
The introduction of the lambda sensor has modified the control data acquired, moving it from the air/gas ratio to the percentage of oxygen. It no longer being necessary to read the temperature of the pilot flame, it was possible to eliminate the thermocouple and the problems relating to calibrations. Numerous tests have confirmed that the data acquired by the lambda sensor provides correct information, just like the oxygen analyser, and it is thus possible to use as an air/gas ratio control for the mixture to be analysed.
These lambda sensors are comprised of a solid electrolyte based on zirconium dioxide. This material conducts oxygen ions from a temperature of 300° C.
The element of the sensor with zirconium dioxide is hollow. The inner side is in contact with the ambient air (for reference), whilst the outer side is in contact with the exhaust.
Both sides of the probe are covered by a thin porous layer of platinum that acts as an electrode. Under operating conditions, due to different concentrations, oxygen ions move within the element. The “migration” takes place from the area in contact with the outside air in the direction of that in contact with the exhaust gases.
Migration generates an electric voltage (V) on the platinum electrodes. This tension is processed by the new EsseCI control system.
Advantages of the LCS – Lambda Control System
The main advantages of the LCS system can be summarised as:
- Correct operation over a wide range of supply pressure of the mixture;
- Independence from environment-relative humidity values;
- Readiness to respond to modification requests;
- For the control of the ratio air/gas and thus the control of optimum treatment, the LCS flame provides an absolute value as output, such as that of the LAMBDA (λ) and not related temperature flame value, as measured by thermocouple in the calorimetric Jonoflame system.