Using Tunable Diode Laser (TDL) gas analysis in clean air strategies for industry
Jul 12 2023
Gas analysis plays an essential role in industrial clean air strategies, not only by measuring harmful emissions but by helping to significantly reduce them through improved process efficiency.
Among all the processes relevant to clean air, an efficient combustion reaction is essential, as it can reduce the amount of pollutants emitted, save on fuel consumption, and improve safety.
Combustion efficiency depends on keeping the ratio between fuel and air at the optimum level, which in turn relies on accurate measurements of oxygen (O2) and combustibles (COe) concentrations.
Accurately measuring the levels of O2 and COe – and particularly the combustible, carbon monoxide (CO) – means that operators can balance the air-to-fuel ratio to ensure process safety and achieve optimal fuel efficiency. Controlling the combustion reaction in this way can also significantly reduce emissions of the oxides of nitrogen (NOx) and sulphur (SOx), along with CO, and carbon dioxide (CO2).
Multiple oxygen analysers are often used for combustion monitoring on large-scale furnaces, as it is understood that these larger processes have different zones of combustion, with the effects of layering and convection giving different concentrations along the length of the furnace.
Tunable Diode Laser (TDL) sensing technology measures across the stack, providing an average result for gas concentration rather than a single-point result, and ensures a better overall picture of conditions within the fired heater.
Servomex’s SERVOTOUGH Laser 3 Plus range is designed to make TDL sensing easy to install and use, for clean air applications across the power generation and hydrocarbon processing markets.
The Laser 3 Plus Combustion model provides in-situ cross-stack measurements of O2, CO, or CO and methane (CH4), delivering exceptional performance benefits and providing a rapid-response measurement for safety in gas-fired heaters and boilers.
The Laser 3 Plus Process version provides the most stable, repeatable results for the measurement of O2 in process temperatures up to 500°C. This makes it ideal for applications including oxidation control, inerting, safety monitoring, process control, flare gas monitoring, combustion control below 500°C, and coal-to-chemical processes.
However, combustion efficiency is just one part of a comprehensive clean air strategy. Gas clean-up – the removal of harmful substances from process gases to ensure they cannot then be emitted by the plant – is another key phase.
DeNOx (ammonia slip) treatment is a prime example, with ammonia (NH3) or urea used to suppress harmful NOx emissions created by combustion. An accurate NH3 measurement is essential to ensure that NOx emissions are properly suppressed without forming the damaging ammonium bisulphate by-product.
The Laser 3 Plus Environmental model is designed to measure NH3 in this application. Installed directly into the process ducts, it provides a highly sensitive, average measurement across the duct, so the NH3 reading is accurate even when flow conditions are inconsistent.
The analyser also meets all uptime and performance requirements for the US EPA PS18 standard, for reliable CEMS monitoring of NH3 as a precursor to harmful particulates.
All Laser 3 Plus analysers can be installed, configured, and calibrated by just one person, with a multi-directional mounting assembly that ensures precision alignment from the outset. This combines with the quick-release mechanism to help make reinstallation simple after maintenance.
A built-in line lock cuvette system helps to ensure measurement reliability, which is particularly key to process control and safety applications. A secondary detector, targeted on a cuvette filled with the required gas, enables the main detector to stay locked in, delivering an accurate measurement even if the measured gas is zero.
These qualities ensure that the Laser 3 Plus TDL range forms an essential part of any wide-ranging clean-air strategy.
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