Air/Gas Ratio is the fundamental parameter in flame treatment process
The fundamental parameter that rule the flame treatment process of the plants designed and manufactured by esseCI is the air/gas ratio
If mixture flow represents the amount of energy supplied to the burner, the air/gas ratio is the quality of such energy: compared to all the other parameters of the treatment and, in particular mixture flow (ie the amount of energy), if the air/gas ratio is not optimized, is obtained, on the treated surface, a significantly lower value of surface wettability, with a reduction in the effectiveness of the treatment.
Hence the crucial importance of proper and careful control of this process parameter.
air-gas ratio control: Jonoflame (JCS, Jonoflame Control System)
esseCI, for air-gas ratio control, traditionally uses a calorimetric control system called Jonoflame (JCS, Jonoflame Control System)
According with this system a little quantity of the mixture intended for the burner is spilled 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 according to the set-point for this temperature (resulting from the wettability tests), the controller act on the motorized gas valve, opening or closing it, in order to adjust the variable’s value process to that of the set-point itself.
This device is sensitive to the variation of the supply pressure of the mixture and to the thermocouple position; maintenance and calibration should be performed by experienced operators.
LCS (Lambda Control System) analyzer
With the aim of making even easier the air/gas ratio control esseCI technicians have studied and developed a solution using, for the air-gas ratio control, the latest generation of oxygen lambda sensors creating so a control system based over 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.
Beeing not more necessary the reading of the temperature of the pilot flame it has been 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 as oxygen analyzer and is therefore possible use as air/gas ratio control for the mixture to be analyzed.
These lambda sensor are constituted by a solid electrolyte based on zirconium dioxide. This material conducts oxygen ions from a temperature of 300 ° C.
The element of the sensor with the zirconium dioxide is hollow. The inner side is in contact with the room air (reference), while the outer side is in contact with the exhausted.
Both sides of the probe are covered by a thin porous layer of platinum that acts as electrode. In operating conditions, due to different concentration, oxygen ions move within the element. The “migration” takes place from the area in contact with the outside air to 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 summarized as:
- Correct operation over a wide range of supply pressure of the mixture.
- Independence from environment relative humidity values.
- Readiness of response to requests for changes.
- For the control of the ratio air/gas and thus for the control of optimum treatment to the LCS flame provides as output an absolute value as the value LAMBDA (λ) and not related temperature flame value as measured by thermocouple in the calorimetric Jonoflame system.
Lambda Control System description
The LCS analyzer is composed of a nozzle burner that burns the mixture to be analyzed into a combustion chamber. The air-gas mixture that arrives to the combustion chamber passes through a filter, and is controlled in pressure.
The ignition of the mixture takes place by means of the ignition electrode fed by special transformer.
Inside the combustion chamber the exhausted products are analyzed by an oxygen sensor which transmits its signal to a PLC. LCS is able to control, in real time, the composition of the mixture used in terms Lambda according to the following criterion:
Lambda> 1,000; Mixture with excess air
Lambda = 1.000; Stoichiometric mixture
Lambda <1.000; Mixture with excess gas
The Lambda value is read on the Touch Panel Display of the mixture generator.
New LCS mixture analyzers
The EsseCI has finished the testing phase of the flame treatment plants with the new LCS mixture analyzers.
They are already in operation in various parts of the world, systems that work using the LCS technology, others who work with LCS in parallel to the traditional jonoflame calorimeter.
Is possible its use in three main sectors of the market:
– Polyolefin films
– 3D objects in polymeric material.
The company “EsseCI flame treaters” continues with the development of technology and the evolution of their treatment plants in order to make them more reliable, managed by remote control, but at the same time simple to use.