Ammonia slip downstream from NOX reduction reactions indicates a host of problems (utility waste, pollution, and ammonium bisulfate plugging). The OMA-300-DNX continuously monitors the health of a DeNOX process stream, displaying real-time concentrations of ammonia and NOx. Unlmited alarms can easily be configured to alert the DCS the instant that any concentration thresholds are crossed.
STANDARD ANALYTE(S): NH3 NO2 NOx NO

DeNOx is the conversion of NO and NO2—two hazardous nitrogen oxides known generically as NOx—to nitrogen and water. In the selective catalytic reduction method (SCR) of DeNOx, ammonia is injected upstream from a catalyst to act as a reducing agent:

4NO + 4NH3 + O2 >>> 4N2 + 6H2O

The term "ammonia slip" refers to the unreacted ammonia found in the effluent stream from this reaction.

FIRST PRIORITY: AMMONIA MONITORING

Ammonia slip indicates excess NH3 injection and, therefore, complete reduction of NOx. However, using more ammonia than what the stoichiometry demands is a sign of a few glaring problems:

  • NH3 is an expensive utility to waste;
  • downstream NH3 will react with SO3 to create ammonium bisulfate--a corrosive, tarlike solid notorious for plugging economizers and fouling surfaces;
  • the fly ash from NOx reduction flue gas is often sold to manufacturers of concrete for added profitability, but fly ash contaminated with NH3 makes concrete with unacceptable odor and is avoided by manufacturers;
  • and NH3 is a nonpoint source pollutant of water systems and contributes to particulate matter (PM) in the atmosphere.

SECOND PRIORITY: NOx MONITORING

Monitoring the SCR effluent for the presence of NO and NO2 (constituents of NOx) is the most dependable method for verifying efficent NOx reduction. Furthermore, a sudden spike in NOx concentration downstream from the reaction is a good indication of catalyst bed failure.

SOLUTION: THE OMA-300 AMMONIA SLIP ANALYZER

Continuously monitoring ammonia slip and NOx in the pipeline post-reaction, the OMA-300 is the ultimate tool for fine-tuned, highly efficient SCR. The absorbance structures of NO, NO2, and NH3 all overlap heavily in the UV wavelength region; while cross-interference cripples the accuracy of most analyzers, this type of scenario is precisely what the OMA-300 was engineered for.

General Performance

Measurement Technology

nova-II™ UV-VIS diode array spectrometer

Light Source

Pulsed xenon lamp (~5 year lifespan); deuterium and tungsten sources available

Sample/Analyzer Interface

Flow cell (various materials and path lengths available)

Sample Conditioning

If required; customized per DeNOx application

Accuracy

**Custom measurement ranges available for all components; typical ranges specified below.

NH3 (ammonia)
0-10 ppm: ±5 ppm
0-1,000 ppm: ±1% of reading, full scale
0-1%: ±1% of reading, full scale
0-50%: ±1% of reading, full scale

NO (nitric oxide)
0-100 ppm: ±1% of reading, full scale
0-500 ppm: ±1% of reading, full scale

NO2 (nitrogen dioxide)
0-100 ppm: ±1% of reading, full scale
0-500 ppm: ±1% of reading, full scale

NOX (nitrogen oxides)
Simple sum of NO and NO2 readings

Photometric Accuracy

±0.004 AU

Multi-Component Capability

Up to 5 stream chemicals measured simultaneously

Calibration

For many applications, factory calibrated with certified calibration gases; for safety reasons, some applications require on-site calibration

Verification

Easy verification/validation with standard certified gas samples and neutral density filters
Operating Conditions

Ambient Temperature

0 to 55 °C (32 to 131 °F)
[Optional upgrade: -20 to 55 °C (-4 to 131 °F)]

Sample Temperature

Using immersion probe: -20 to 150 °C (-4 to 302 °F)
Using flow cell: -20 to 150 °C (-4 to 302 °F)

Sample Pressure

Using immersion probe: 100 bar (1470 psig)
Using flow cell: 206 bar (3000 psi)

Analyzer Environment

indoor/outdoor (no shelter required)
Hardware

Size

Analyzer enclosure (standard): 24" H x 20" W x 8" D (610mm H x 508mm W x 203mm D)
Sample conditioning system enclosure (standard): 24" H x 30" W x 8" D (610mm H x 760mm W x 200mm D)

Weight

Analyzer (standard): 32 lbs. (15 kg)
Sample conditioning system: highly variable

Wetted Materials

Analyzer (standard): stainless steel 316/316L; K7 glass; Viton
Sample conditioning system (standard): stainless steel 316/317; quartz; Viton

Outputs

one galvanically isolated 4-20mA output per component; modbus TCP/IP (optional); RS232 (optional); Fieldbus, Profibus, and HART (all optional); two digital outputs for fault and sampling system control (user programmable)

Electrical Requirements

85 to 264 VAC 47 to 63 Hz

Power Consumption

45 watts

Area Classification

General Purpose (standard) / Class I, Div. 2 (optional) / Class I, Div. 1 (optional) / ATEX Exp II 2(2) GD (optional)
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