PEFTEC 2017 - Abstract

Abstract Title: New applications for near- and mid-infrared in-situ TDLS sensors
Abstract Type: Oral
Presenter Name: Dr Peter Geiser
Company/Organisation: NEO Monitors AS
Session Choice: Online & Process Monitoring

Abstract Information :

In this presentation, we will report on new challenging applications for near- and mid-infrared tunable diode laser spectroscopy (TDLS). In the last decades, TDLS has proven to be an excellent choice for many applications - even under very harsh conditions - where measurements directly in the process (in-situ) are required.

The Claus process is one of the most commonly used processes to recover elemental sulfur from gaseous hydrogen sulfide (H2S). To regulate the sulfur recovery process, it is necessary to measure the ratio of hydrogen sulfide concentration and sulfur dioxide (SO2); the latter is generated during the recovery process.

Currently, measurements of H2S and SO2 for tail gas analysis are typically performed by gas chromatographs or heated UV analyzers. While the measurement setups are fairly straightforward, they have high demands on maintenance and the generated sulfur is frequently clogging the extraction pipes. Consequently, in-situ measurements are desirable to avoid these issues.

In-situ TDLS measurements of H2S in the near-infrared and SO2 in the mid-infrared were performed in a German sulfur recovery plant. During the measurement campaign, a co-located extractive UV analyzer was used as reference system. Excellent agreement between both measurement systems was achieved, thus demonstrating that it is feasible to regulate a Claus process with in-situ instrumentation.

Another challenging task is the continuous emission monitoring of tetrafluoromethane (CF4), CF4 is a very strong greenhouse gas that contributes to global warming despite its low atmospheric concentration level. The aluminum smelting process is one of the largest anthropogenic contributors to atmospheric CF4. According to spectroscopic databases, CF4 does not absorb in the near- but only in the mid-infrared with a strong band located at around 7.79 µm. A quantum cascade laser (QCL) sensor was developed using a unique Wavelength Modulation Spectroscopy (WMS) approach. During laboratory assessment, a detection limit of well below 10 ppb.m was demonstrated. Afterward, the CF4 sensor was installed at an Alcoa aluminum smelter. A co-located Fourier Transform Infrared Spectrometer allowed direct comparison measurements and general agreement between the two methods was observed. This led to the conclusion that the developed in-situ quantum cascade laser based sensor has the potential to continuously measure CF4 at aluminum smelters.