Mercury Instruments has specially designed the Mercury Stack Gas Monitor SM-4 for precise and reliable measurement of very low Hg concentrations in stack gases with a complex matrix containing SO2, NOx, HCl and others.
Typical fields of applications include:
The heated sampling probe is mounted at the stack. A maintenance-free ejector pump continuously draws sample gas into a dilution unit and past a heated particle filter. A critical orifice stabilizes the sample flow, thus making it independent of the pressure in the stack. The suction vacuum is continuously monitored by a pressure sensor to make operation reliable. A partial flow of the diluted sample is passed through a catalyst where the different forms of mercury contained in the sample are converted to the elemental state. This treated sample is then transported to the mercury detector through slightly heated PFA tubing , which may be tens or even some hundreds of feet away from the sampling probe. The detector (a Mercury Ultratracer UT-3000), one of the most sensitive and selective mercury detection devices in the market, uses a pre-concentration technique featuring the unique Mercury Instruments GoldTrap.
A speciation function to determine the different proportions of elementary and ionic mercury is available as an option)
The mercury present in stack gases is often elemental, but ionic and bound mercury also occurs . To measure total mercury, all these different speciations must be successfully detected. To this end the SM-4 uses a thermocatalytic method to convert all mercury to its elemental form. The reactor works without wet chemistry at low temperature (little above 200 °C) and therefore assures high reliability with low demand for maintenance.
All surfaces in contact with sample gas are heated to temperatures >200 °C to avoid adsorption of mercury.
The sample line consist of Perfluoralkoxy (PFA), a material that stands out for its extremely low interaction with mercury vapor.
The reduction of Hg-compounds takes place at temperatures well above the dew-point. Therefore no condensate occurs which would lead to an increased background signal noise and nonspecific peaks.
The SM-4 uses a highly sensitive detector based on the atomic absorption principle and features an amalgamation unit (GoldTrap) connected upstream. The ultrapure gold surface captures the mercury which is then abruptly released when the gold trap is rapidly heated to approximately 700° C.
Purified air is used as a carrier and there is no need for special carrier gases. The use of air has a self-cleaning effect on the GoldTrap, extending its lifespan.
The sampling probe plays a key role: to extract a representative sample of gas and supply it to the sample conditioning system. All parts that come into contact with the sample are made of special material, guaranteeing a minimum memory effect. All parts are heated so no mercury is retained in the probe. An automatically backflushed filter keeps particles away from the analytical pathway of the sample. Calibration gas is introduced upstream of the sample filter. Both the dilution unit and the catalyst are integral to the sampling probe, thus ensuring minimum length for their connecting lines.
SO2, NOx, HCl, and VOCs all interfere with standard mercury measurement techniques (AAS; AFS).
Modern mercury CEMs try to minimize this negative effect either with preconcentration by amalgamation or by sample dilution. Amalgamation alone, however, reaches its limit when the gold surface is affected by matrix constituents, whereas sample dilution alone may not reduce interference to tolerable levels.
That is why the SM-4 uses both sample dilution and gold trap amalgamation to completely eliminate interference.
The SM-4 can be equipped with an automatic calibrator (IAS HovaCAL for ionic Hg or Mercury Instruments MC-3000 for Hg°). It can perform an automatomatic baseline check as well as automatic calibration at predefined time intervals.
To meet the latest demands for quality assurance QAL3 (European Regulation EN 14181) can be performed automatically by using the integrated HovaCAL calibrator.
Total mercury (oxidised and elemental speciation as option)
Dilution probe with thermocatalytic converter at stack,
Amalgamation (MI GoldTrap),
Cold Vapor Atom Absorption Spectrometry (CVAAS),
Wavelength = 253,7 nm
Low temperature type (200 °C);
directly at stack
0,05 μg/m³ - 500 μg/m³ Hg
(up to 1000 µg/m³ as an option)
0,0001 μg/m³ (Detector);
< 0,01 μg/m³ (System)
180 – 360 sec t
Max. Sample gas temperature:
Ambient temperature range allowed:
-5°C to 40°C
Sample line length:
up to 30 m (100 feet);
up to 100 m (300 feet) option
3 x pairs of relay contacts (dry contacts)
Modem and SM-4 communication software (option)
230 V / 50 Hz;
(110 V / 60 Hz option)
Electrical power consumption:
Analyzer cabinet: 450 VA;
Probe-Converter: 1000 VA;
heated sample line: 30 VA / meter
Analyzer cabinet: 161 x 80 x 60 cm
(63.6”x 31.5”x 23.6”) H x W x D
Probe: 36 x 36 x 66 cm
(14.2”x 14.2”x 26”) H x W x D
Probe controller: 48 x 44 x 27 cm
(19”x 17” x 11”) H x W x D
Analyzer (including automatic calibrator):
130 kg (285 lbs)
14 kg (30 lbs)
28 kg (62 lbs)
6 bar (85 PSI); 16 l/min approx.
Conforms to US EPA 40CFR60 PS-12A Mercury CEMS;
conforms to EN 15267 (European regulation);
Approved and certified by TÜV Rheinland Energie und Umwelt GmbH, Köln,
Report-Nr.: 936/21213740/A of March 26, 2012
As a leading supplier of high precision analytical equipment, we strive at all times to offer top quality solutions. Our quality management system is certified according to ISO 9001.
Funded by the Ministry for Economics and Technology on grounds of a resolution by the German Bundestag
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