The SERVOTOUGH Laser 3 Plus Environmental allows ammonia monitoring applications to benefit from Tunable Diode Laser (TDL) sensing precision via a cost-effective, low-maintenance platform.
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The importance of robust DeNOx and ammonia measurement cannot be understated. Adhering to strict environmental legislation requires reducing NOx emissions from combustion processes, making this an area of growing importance for the hydrocarbon processing and power generation markets.
NOx is a generic term that refers to the nitric oxide (NO) and nitrogen dioxide (NO2) produced due to the reaction of excess nitrogen and oxygen during combustion, particularly at high temperatures.
NOx must be effectively controlled in order to meet legislative requirements and avoid potential fines. Its effective management also enhances the efficiency and effectiveness of a combustion process.
The removal of waste NOx (referred to as a DeNOx process) in power plants and other combustion processes is generally done via either selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR).
The SCR process injects ammonia (NH3) or urea-NH3 into the flue gas stream from the combustion process. This NH3 or urea reacts with NOx in the flue gas on a catalyst surface, resulting in the formation of water (H2O) and nitrogen (N2).
The SNCR process requires a hotter environment and a longer pathway to allow NH3 or urea to react with the NOx in the flue gas, requiring that temperatures be maintained at 1472-1742 °F (800-950 °C).
Temperature control is key to this process because low temperatures can lead to a surplus of unreacted NH3. This is typically referred to as ‘ammonia slip.’
Ammonia slip is generally measured downstream from the SCR catalyst unit, or downstream of the NH3 injection point for SNCR.
This must be accurately measured in DeNOx equipment for several reasons.
For example, high levels of unreacted NH3 have implications for the plant operator, including wasted resources and increased expenses. Ammonia slip can also have a major impact on deposition and catalyst plugging, and may result in corrosion of downstream equipment, such as the air preheater used in power generation.
Excessive ammonia slip in a coal-fired power plant can lead to the creation of fly ash with high levels of NH3. This would render the fly ash unfit for sale as a mineral filler in cement or asphalt plants.
The level of ammonia slip also offers useful diagnostic information on the function of the SCR/SNCR system and NOx reduction process, allowing operations personnel to accurately determine the appropriate time to replace the catalyst.
Ammonia slip is typically maintained at less than 2 parts per million (ppm) in order to optimize the process. This low level makes it difficult to control without direct measurement, particularly due to the number of parameters that could potentially influence the slip. These parameters include inlet NOx concentration, catalyst performance, fuel composition, and nozzle plugging.
These measurements have historically been difficult to achieve with extractive techniques, despite the high cost, operational, and safety benefits of measuring and managing ammonia slip.
The comparatively reactive nature of NH3 means that wetted components greatly affect the analyzer measurements. These must be non-adsorbing and be kept hot. These analyzers are also impacted by a range of interferents, including the presence of high levels of dust and the sulfur dioxide (SO2) or water (H2O) formed by the process.
Extractive systems have historically been used to measure ammonia slip, but measurement uncertainty can occur due to the adsorption of NH3 upon the wetted materials, and the increasing demand for ultra-low measurements with higher sensitivity and a more rapid response. These factors mean that extractive systems have become increasingly unable to meet the demands of this process.
TDL Sensing: A Superior Solution for NH3 Measurement
Advanced Tunable Diode Laser (TDL) technology represents an effective and comprehensive solution for accurate ammonia slip control.
TDL technology is comprised of a tunable diode laser light source, transmitting optics, receiving optics, and a detector. This powerful instrumentation is suitable for in-situ, cross-duct measurements, with a system commonly made up of a laser transmitting module and receiver module mounted across the flue stack or process duct.
The gas concentration information is acquired via the gas absorption line shape, which is collected by scanning the laser wavelength over the NH3 absorption line under investigation.
Should NH3 be detected in the beam path, a photodiode will detect a reduction in signal intensity, converting this into the NH3 gas concentration. TLD is a spectroscopic absorption measurement technique, meaning that it effectively counts molecules, or the number density of molecules, that fall within the beam.
When the analyzer is installed across a stack or duct, it will produce an average concentration reading as opposed to the point readings acquired via an extractive sample. This allows NH3 concentration levels to be measured with far greater certainty in the TDL measurement versus the extraction measurement.
It is also important to note that the NH3 sample never leaves the process, thus avoiding the complications associated with sample transport in extractive methods and the contamination issues prompted by the heat, dust, and water.
Not only are TDL measurements significantly more accurate, but they also allow plant operators to avoid a large portion of the downtime necessary for cleaning extractive systems.
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Servomex’s Next-Generation NH3 Measurement Solution
The SERVOTOUGH Laser 3 Plus Environmental leverages TDL absorption spectroscopy analysis to deliver accurate NH3 measurements in DeNOx processes, allowing operators to take control of their combustion emissions.
This extremely compact gas monitor can be directly installed into process ducts, making it ideally suited to monitoring ammonia slip during a range of NOx reduction processes, including Selective Catalytic Reduction (SCR) or Selective Non-Catalytic Reduction (SNCR). This monitor enables the level of ammonia slip to be maintained between 2-3 parts per million.
Acquiring an average NH3 measurement across the duct returns precise readings and avoids stratification issues, even during inconsistent flow conditions. Auto-validation software also ensures ongoing QA/QC requirements and accuracy, meaning that the Laser 3 Plus Environmental offers a powerful combination of industry-leading installation flexibility, as well as cost and performance benefits.
It is also important to highlight that TDL technology offers a non-depleting measurement that does not require a sample conditioning system.
The compact design of the Laser 3 Plus Environmental significantly reduces installation time, with its intuitive alignment capabilities ensuring easy setup and maintenance while lowering costs at all stages. The instrument also features full Ethernet communications for commissioning, troubleshooting, and diagnostics.
The analyzer’s hardware advances are supplemented by advanced Wavelength Signal Modulated Spectroscopy processing software, while line-lock technology eliminates drift over extended operation.
This innovative technology automatically tracks the NH3 absorption line from a sealed reference cuvette, ensuring highly accurate and reliable operation over long periods and boasting calibration frequencies of over 12 months for many applications.
Its sturdy, general-purpose design has been specifically optimized for hazardous areas, ensuring that the Laser 3 Plus Environmental can function in even the most challenging of settings, including particulate-rich environments. The instrument is also IP66-rated and meets IECEx, ATEX, and North American hazardous-area approvals.
Acknowledgments
Produced from materials originally authored by Rhys Jenkins from Servomex Group Limited.
This information has been sourced, reviewed and adapted from materials provided by Servomex.
For more information on this source, please visit Servomex.