The Tekran® Model 1130 Mercury Speciation Unit gives the Model 2537A Mercury Vapor Analyzer the ability to simultaneously monitor both elemental and reactive gaseous mercury (RGM) species in ambient air. Although the majority of atmospheric mercury is present in elemental form, differentiation is important due to the greater local impact of reactive (ionic) forms. (Reactive mercury has much higher wet and dry deposition rates than does elemental.) Speciation is of particular interest close to industrial sources such as waste incinerators which may discharge the majority of their mercury emissions in ionic form, in particular mercuric chloride (HgCl2).
The system is capable of operating in conjunction with the Model 1135 Particulate Mercury Unit. This module mounts directly above the Model 1130 and provides the additional ability to measure fine fraction (< 2.5 micron) particulate bound mercury simultaneously with the elemental and reactive forms.
Principles of Operation
A specially coated annular denuder captures reactive mercury while allowing elemental mercury to pass through. During the sampling (adsorption) phase, the Model 2537A provides real time measurement of elemental mercury. During the analysis (desorption) phase, the denuder is flooded with zero air and heated. This causes the captured reactive mercury to be released and reduced to elemental form. The Model 2537A detects this eluted mercury, providing a measurement of total reactive mercury captured during the previous sampling period. After cooling, the denuder is ready for another cycle. All timing parameters on the Model 1130 are programmable, allowing automatic RGM readings to be taken at user specified intervals. (From 30 minutes to 6 hours)
The denuder module islocated out of doors, eliminating the problems inherent in transporting reactive mercury. The module is insulated and temperature controlled to allow stable year round operation.
A heated line is used to minimize losses while carrying sample air and zero air between the various system components.
The pump module generates the additional flow required to increase loadings on the denuder. A closed loop controller using a pump and mass flow meter guarantees accurate flow rates. The same pump and MFM combination is used during the analysis phase to generate the zero air required for desorption. The pump module also provides the zero air required by the instrument during CLEAN and CALIBRATION cycles, thereby eliminating the need for a separate pressurized zero air cylinder and regulator.
The control unit allows timed and event driven control of the various instrument functions required for the Model 1130. It is fully synchronized with the operations of the Model 2537A analyzer. All Model 1130 sample and desorb cycle timings are fully programmable. Model 2537A routine calibrations are initiated by this unit to ensure that calibrations do not disrupt desorption operations. The control module is also capable of managing the analysis sequence of the Model 1135 particulate unit.
The regenerable annular denuder can be periodically recoated, as required. Field replacement of the denuder is simple and does not require tools. The denuder can be rinsed using deionized water and recoated in the field. Alternatively, a second denuder may be supplied with the sampler to allow exchange in the field with subsequent recoating in your lab.
During sampling, the total flow rate through the denuder consists of two components. The Model 2537A typically draws 1 lpm and the Pump Module typically draws 9 lpm. Both flows are set using precision mass flow monitors with closed loop pump controllers.
Tekran provides a Windows® based application, Combine with every Model 2537A. This free program provides proper time alignment for any set of data readings, leaving appropriate gaps during periods of no data and combining results from several capture files. Combine also separates data based on the status of the Model 1130. Readings for RGM and Hg0 can thus be placed into separate columns, making subsequent processing by spreadsheet or database programs straightforward.