Introduction

The reduction of gas emission from industrial plants is now a global concern for the environment as climate change, deforestation and respiratory diseases are endangering present and future generations.

With 10 years of experience in Ammonia gas detection by UV spectroscopy and hundreds of on-line analyzers installed, we have now extended our technology to a wide range of UV-absorbing gases.

Key requirements for successful on-line analysis - such as stability, low maintenance and low operating cost - have oriented our design to the DOAS (Differential Optical Absorbance Spectroscopy) method based on the Beer-Lambert law. No sampling system is needed, reducing maintenance and installation costs. An air purge circuit maintains the optics clean.

Typical applications are SCR and SNCR processes where simultaneous measurement of NO, NO2 and NH3 is necessary to control the DeNOx process, as well as other chemical processes.

Based on the recognition of a specific UV gas spectrum by proprietary algorithms using Fast Fourier Transform, the system can detect up to 8 gases simultaneously with high selectivity in a complex gas matrix.

Using direct light coupling without optical fibre, measurements are possible even with high levels of dust inside the stack.

The distance between the stack and the controller is not limited as with optical fibre systems.

The use of a clamp enables a second assembly/disassembly of the emitter and receiver for checking or recalibration procedures. The emitter and receiver can be easily transferred to a special calibration tube for zero checking or a specific gas calibration.

The UV Xenon lamp is specified for 1,000,000,000 flashes, thus giving many years of continuous measurements. This significantly reduces maintenance costs and the risk of wrong measurements due to aging lamps.

An inexpensive 2-wire RS485 link is used to connect the receiver on the stack to the analyzer located in the control room.

Distances over hundreds of meters can be achieved in an electrically noisy environment.

Major emission gases like CO, CO2 and H2O are not absorbed y UV and so will not interfere with the measured gases (as opposed to FT-IR based systems).

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