Stack emission sampling
Mercury sampling system compliant with UNI EN 13211 normative
This method is focused on discharged mercury in emission coming from hazardous city waste incinerators. The method is applicable in the concentration range of 0.001 mg/m3 to 0.5 mg/m3.
The system includes a heated probe with glassware set necessary for sampling heavy metals, without any metal part coming into contact with sampling gas. A special bubbler support is located outside the sensor, immediately after the heated container holding the filter holder. This process avoid forming condense in the sampling line with the loss of the speciment.
The norm foresees two different sampling methods, the first one consist of direct gas passage in both supports into the same suction flux, the second one with a derived flux. Even if the mercury is prevalently present in gaseous form, it may also been found in dust or in drops inside blast chilling. Anyway Isokinetic sampling is necessary to accurately collect dust and drops. When the Isokinetic sampling is over, dust, drops and aerosol form must be sampled by the same device. This process is required because of the parting into gaseous/solid/liquid form of the mercury.
The device may be placed directly to the heated probe completed with heated filter holder box (600/SIR1500BB) through a set of glass unions. Sample is absorbed through two sealed and refrigerated bubblers straight to the tank located in the back of the device; in addition to a third empty bubbler. The volume of a sample extracted will be considered compatibly at the instrumental detectability limits, in order with the analytical chosen method. Three kind of filtering membranes may be used: dealing with low concentration sample, membrane must be high quality and free to any binder. The choose is between: fiber glass, quartz fiber or preferably glass fiber covered by PTFE (maximum recommended temperature 300°C)
Isokinetic direct sampling. Sampling device has to be designed to reduce gas time to the minimum between sonde nozzle and bubbling absorbers (less than 5s). Sonde temperature must be checked at least at 120°C and also 20°C over the acid dew gas point. The heating device must be designed to reduce to the minimum the non-heated area next to the filter holder union. The direct line foresees a Isokinetic sampling directly linked to the filter holder.
Derivate sampling.A second suction flow is placed in derivation. Device does not concern isokintetic sampling mode in real time. The filter holder must have a heated tank (withdrawal feeler is the same as the isokintetic option) and linked directly to the bubblers attached at the output, three of them with sintered septum containing a solution adsorption and an empty impinger without septum. Due to lower gas concentrations and environmental limits, sampling time might be extended.
In this method it’s not recommended direct sampling with all adsorbing elements (filter and impinger) because of the high flux and high volume of solution adsorption needed.