The AMESA system uses the “simplified” cooled probe method which was designed more than 20 years ago. The target was to have an easy handling sampling method in which the organic pollutants (e.g. PCDD / PCDF) of all three physical conditions (gaseous, solid, liquid) are adsorbed in only one adsorption cartridge. Contrary to the other existing methods, this has the big handling advantage that only 1 part (adsorber cartridge) has to be exchanged and to be sent to the dioxin laboratory.
This method, the most practical for long-term sampling of dioxins, combines the advantages of the cooled probe method of EN 1948-1 and the US EPA method 23A.
The other methods described in EN 1948-1 (cooled probe, filter-cooler) produces condensate which has to be collected and analysed.
According US EPA method 23A the collected condensate does not need to be analysed, because it is well known that the amount of dioxins in the condensate is negligible. This was confirmed with AMESA in a lot of measurements in which the condensate was collected and analysed separately.
In the filter-cooler method the sampling probe is heated: this leads to a higher risk of deposits of dioxins in the sampling probe in comparison to the cooled probe method in which the sampling probe is flushed already by the condensate generated in the sampling probe.
The use of the dilution method have also a higher risk of dioxin deposits inside the heated probe. Additionally, there is the risk that dioxins from the dilution air are injected into the system. Therefore a second dioxin adsorber has to be installed always in the dilution air supply.
The operating principle of AMESA sampling system is as follows:
A cooled probe (<50°C) is used to extract a part of the flue gas isokinetically from the stack. Dioxins and furans which are combined in the gas, the dust and the condensate of the flue gas are adsorbed in a specific cartridge filled with XAD-2 and quartz-wool.
An automatic leakage test is performed before and after the sampling cycle to validate the non-contamination of the adsorbing cartridge.
After adsorption, the measured gas is pumped through a flexible tube to the control cabinet, where the gas is cooled down (<5°C) to completely remove the condensate. The isokinetic extraction is controlled continuously as a function of the flue gas velocity, temperature and pressure, by use of a thermal mass flowmeter and a frequency controlled pump.
The dried measured gas flow is determined twice by means of a calibrated gas meter and a thermal mass flowmeter.
AMESA operates fully automatically and all necessary data are stored internally and on a removable SRAM card. Both the XAD-2 cartridge and the SRAM card are to be sent to a specialized laboratory for further analysis of PCDD/PCDF.
The new AMESA can be equipped with 4 sampling units, thus allowing successive automatic sampling of different pollutants (dioxins, heavy metals…) on the same stack, or multiplexing on different stacks (max. 4).