Gas analysis expert Servomex (Crowborough, England) has launched a compact Tunable Diode Laser (TDL) analyzer specifically optimized for the most accurate and fastest-response measurement of ammonia (NH3).

The new SERVOTOUGH Laser 3 Plus NH3 analyzer plays a major role for operators looking to balance emissions reduction with operational costs, while still complying with increasingly tough regulations across the world.

The burning of coal and other fossil fuels, like natural gas, is widely used in the power industry for electrical generation, but particulate matter, carbon monoxide and nitrogen oxides (NOx) are released into the atmosphere as part of the combustion process.

NOx and dust are the leading cause of human respiratory issues, and government agencies worldwide are releasing stronger regulatory measures designed to reduce this air pollution.

The main NOx control strategies used in the power industry are Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR). For lower emissions limits, SCR is a must. Both processes rely on accurate ammonia or urea dosing levels to reduce NOx formation and prevent downstream equipment fouling.

NH3 overdosing (called NH3 slip) causes the formation of ammonium bisulfate (ABS), a white powder that deposits on and eventually plugs the NOx reduction catalyst. This excess NH3 shows up in the fly ash and is detrimental to those plants looking to sell their fly ash to the cement industry, as it results in sub-standard product which is no longer fit for use. ABS is very acidic and causes corrosion in the boiler and other downstream piping and equipment.

Traditionally, NH3 slip monitoring has used extractive sampling techniques with an infrared (IR) based analyzer. A sample of the gas must be transported to the analyzer, with the use of a sample pump resulting in response time delays of greater than 90 seconds in the reported NH3 value.

As mentioned above, the production of the ABS power eventually will plug the sampling line, requiring added measurements to ensure that the sample is present. The sample gas must be kept very hot (>290oC) in order to keep ABS and sulfuric acid (H2SO4) from forming and damaging the analytic equipment. The high flow rate and particulate loadings of coal-fired combustion also makes a single-point extractive sampling system unreliable as a process control trigger.

Gas sampling simplicity is one of the reasons that TDL-based analyzers have taken over from traditional extractive systems as the industry standard for monitoring the NH3 slip and feeding the results back to the control process.

Installed directly on the process stack or equipment, they provide an instantaneous signal that is averaged across the duct, providing greater accuracy in the NH3 reading, even if the flow through the stack is uneven. The use of insertion tubes or a slotted pipe allows the analyzer to be used in very heavy dust loadings.

Rapid and accurate monitoring of the NH3 slip saves the power and other industrial plants millions by providing a feedback process loop that reduces ABS and acid gas formation, extending the life of the catalyst.

Click to view ServomexDiagram2Click on the image at right for a chart detailing SERVOTOUGH's NOx Reduction Feedback Control Strategy.

The compact lightweight Laser 3 Plus occupies only a fraction (one-tenth) of the footprint of its competitors. And while other TDL analyzers require two to three people to install and align the analyzer, the Laser 3 Plus only requires one or two people to install and completely tune the analyzer in just a few hours.

As there is no physical or mechanical interaction with the process, the Laser 3 Plus offers a highly stable and fast measurement response, even in hot, wet, corrosive and dusty process conditions. It offers the longest intervals between calibrations or cleaning on the market today, making it an ideal system where analyzer downtime is critical.

Other new and unique features include a signal processing routine that provides highly stable, repeatable results with minimal cross-interference from other gases or dust loading compared to any other TDL or IR analyzer on the market.

It also incorporates a unique 'line lock' technology that prevents the analyzer losing the gas signal that it is monitoring even when the analyte or moisture is not present in the gas stream, providing a much higher level of stability even during start-up and shutdown events.

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