Continuous Mercury Monitoring system (CMM)

The Gasmet CMM mercury monitoring system can measure the lowest concentrations of total mercury in samples containing high amounts of dust and gases such as SO2, which traditionally have complicated mercury measurement in e.g. installations such as coal-fired power plants stations and power plants co-incinerating refuse derived fuels. Cold Vapor Atomic Fluorescence (CVAF) offers detection of nanograms of Mercury in a cubic meter (ng/Nm3), which allows effective sample dilution. The potentially interfering SO2 absorption is completely avoided by the technique. 

A specially designed sampling system and sample dilution with nitrogen generated in the CMM cabinet ensure short response times and low memory effects for mercury. Conversion of all Mercury species (HgCl2 etc.) into atomic Mercury takes place just before the measuring cell, ensuring that the total mercury concentration is always measured accurately and reliably. The system calibrates itself automatically with nitrogen, mercury vapor and optionally also mercury chloride solution in order to comply with both European and US regulations.

 

SYSTEM PARTS

  1. Dilution probe: The Gasmet™ CMM features a dilution sample probe for the sampling of the stack gas. Also included are instrument air backflush and calibration gas inlet. Controller for the sample probe is fitted inside the analyzer cabinet for easy access. As an option, the sample probe can be fitted with an inertial filter. 

  2. Mercury Analyzer: The analyzer unit is based on the CVAF principle. Fluorescence of atomic mercury in the sample gas is measured at 254 nm (in the ultraviolet region of light). Ionic species of mercury are converted to elemental mercury with a built-in thermal converter. Built-in control panel PC enables fully automatic system control. For more information please refer to CVAF Technology.
  3. Gasmet MAUI software: Possibility to control of the CMM system also remotely.




  4. Calibration unit: The calibration unit prepares both Hgo and HgCl2 test gas. The calibration gas can be introduced to the sample probe before the particle filter, as required by the performance criteria. There is no need to use expensive calibration or dilution gases with the Gasmet™ CMM – regular instrument air is sufficient.

 

KEY ADVANTAGES

  • Very low detection limit with CVAF technique (ng/Nm3)
  • Specific for mercury – Virtually no interference from other gases such as SO2, HCl
  • Low operating costs – No need for separate chemicals, gold amalgamation concentrators, acid scrubbers, or additional gases
  • Direct sampling with sample dilution and effective filter blowback system – simple probe design
  • Reliable system with low need for maintenance

AREAS OF APPLICATION

Coal-fired power plants

  • Monitors the mass emission of mercury per amount of energy produced (mg/BTU)
  • Measures low µg/Nm3 concentrations of mercury in moderate to high SO2 matrix

Waste incinerators (Hazardous and municipal waste)

  • Monitoring mercury emissions from 0–15 µg/Nm3
  • Compliant with EU Integrated Emissions Directive and quality assurance standard EN 14884

Industrial processes with mercury in process and flue gases

  • Applicable to a wide variety of industries such as mining, metal refining, and sulphuric acid production
  • Managing mercury as an impurity arising from raw materials

Technical Data

General parameters
Measuring principle: Cold vapour atomic fluorescence (CVAF) with extractive filtration, dilution, and thermal conversion
Performance: Minimum range 0 – 10 µg/m3, tested range up to 0 – 1000 µg/m3. Minimum detection limit for total mercury 0.02 µg/m3 (complete system, with dilution)
Operating temperature: 5 – 40 °C, non-condensing, dust free ambient air
Storage temperature: -20 – 60 °C, non-condensing
Response time, T90: Typically < 120 s, depending on the sample line length and measurement time
Power supply:  100 – 115 or 230 V / 50 – 60 Hz

 

Spectrometer with integrated thermal converter
Operation principle: Direct cold vapour atomic fluorescence (CVAF) in vacuum pressure
Detector: Photon detection unit with photon counting
Source: Low pressure mercury vapour lamp
Operation wavelength: 253.7 nm
Sample conversion: Integrated high temperature thermal converter

 

Calibrator for Hg0 and/or HgCl2
Operation principle (Hg0):  Vapour generation from saturated source and dilution
Operation principle (HgCl2): HgCl2 solution dosing and
evaporation
Calibration gas: Dried, and Hg scrubbed instrument air
Dilution gas flow control: MFC 0 – 20 l/min
Span gas flow control: MFC 0 – 20 ml/min
Hg source temperature: 0 – 15 °C
Calibration concentration ranges converted to Hg0: 
Saturated Hg source: 1 – 200 µg/m3
HgCl2 solution dosing: 1 – 1000 µg/m3

 

Measurement parameters
Zero point calibration: 24 hours
Span calibration: 24 hours
Calibration linearity test: 1 week
Zero point drift: < 2% of measuring range per calibration interval
Sensitivity drift: < 2% of measuring range per calibration interval
Linearity deviation: < 2% of measuring range
Temperature drifts: < 2% of measuring range

 

Instrument air preparation
Instrument air inlet: 6 – 10 bar, 80 l/min, 8 mm Swagelok fittings
Instrument air filtration: 3-stage filter unit
Nitrogen generator: Capacity 99 % N2, 8 l/min, 5-6 bars, efficiency ratio 20 %
Calibration gas drying: Absorption dryer, capacity -30 °C
Mercury scrubber: Absorption scrubber
Vacuum pump: WOB-L Piston twin headed

 

Alarm outputs
System alarm: Gasmet CVAF mercury analyzer and application software
Service request Gasmet CVAF mercury analyzer and application software
Maintenance status: Gasmet CVAF mercury analyzer and application software
Result valid: Gasmet CVAF mercury analyzer and application software
Concentration alarm: Gasmet CVAF mercury analyzer and application software

 

Air conditioning
Cooling capacity:  A35 °C / A35 °C 1500 W
Internal circulation:  500 m3/h

 

Dilution probe
Operating principle: Ejector with critical orifice
Material: SS 316, glass coated sample wetted parts
Operating temperature: Maximum 250 °C
Filter element: Glass coated SS 316, 2 µm
Dust load: < 2 g/m3

 

Heated probe tube
Material: SS 316, glass coated sample wetted parts
Temperature: Maximum 250 °C
Length: 122 cm
Other materials, lengths, and temperatures are available on request.

 

Heated line
Tube size: 2 * 6/8 mm
Core material: PFA Teflon core
Temperature: Maximum 200 °C
Fittings: 8 mm Swagelok
Power supply: 230 VAC or 115 VAC
Power density: 200 watts/meter
The maximum length for the heated line is 30 m with 230 VAC and 15 m with 115 VAC power supply. Analyzer and calibrator are connected to dilution probe with combined heated line which divides into two parts on both ends. There are also 2 unheated 4/6 mm lines for dilution and blowback gases.

 

Electrical connections
Main supply: 3 * 16 A
Power consumption: ~ 6 kW (the full CMM with heated lines, 20 m)

 

Measuring data outputs
Gasmet measuring system is equipped with analog output representing the result total Hg concentration.
Analog output range:  4 – 20 mA

 

Enclosure
Material: Bake painted steel
Dimensions (mm): 2030 * 600 * 600 (cooling unit on top)
Weight: ~ 500 kg (full system)
Protection: Cabinet IP 54, air conditioning unit IP 34

Gasmet Technologies Oy shall not be liable for technical or editorial errors or omissions contained herein. The information in this document is provided “as is” without warranty of any kind and is subject to change without notice. Should you find any errors, we would appreciate if you notified us. 

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