QCL Technology Provides Never Before Achievable Performance in Gas Purity Measurement

By Amanda Gogates, Cascade Global Product Manager, Emerson Automation Solutions

Precise and cost-effective measurement of gas purity significantly impacts the bottom line in a number of industrial applications. I’d like to share a new technology with you that will overcome many of the most common problems manufacturers face in this area, including poor sensitivity, costly consumables, and outmoded equipment requiring high levels of technician resourcing to operate and maintain. You may be aware of the Emerson line of Quantum Cascade Laser (QCL) technology for measurement applications such as Continuous Emission Monitoring or CEMS. Now, this remarkable technology has been extended to some of the most demanding markets in the world and is a quantum leap over previous generation solutions.

First, a little background on the technology. Emerson’s QCL technology offers fast, high-resolution spectroscopic detection to identify a range of compounds. QCLs operate in the mid-infrared spectral region, where molecules typically exhibit strong absorption bands that can be exploited to improve measurement sensitivity. Coupled with Tunable Diode Laser (TDL) spectroscopy, a single instrument is now able to broaden measurement capability and exploit both the near- and mid-infrared regions.  The result is that a single analyzer is able to monitor an increased number of compounds compared to preceding technologies. The system uses what is called a laser chirp technique. In this technique, a QCL is pulsed with electrical energy and heats up and as the temperature increases, the wavelength of the emitted light also increases. A laser chirp lasts about one microsecond, and in this time a spectrum of between one and three wavenumbers is scanned, sufficient to detect unique absorption features from one or multiple gases. This data can then be interpreted in terms of absolute concentration, minimizing the need for complex and frequent instrument calibration. QCLs can be chirped at a frequency of up to 100 KHz, enabling many thousands of spectra to be gathered in a few seconds, resulting in a high signal-to-noise ratio, while maintaining a rapid response time.

As a result of this unique design, the new CT5800 enables highly accurate measurement of concentrations of impurities down to sub-ppm levels in a variety of gas streams. This makes it ideal for hydrogen purity, nitrogen purity, and ethylene purity applications. With up to six laser modules housed inside the same enclosure, the CT5800 analyzer can measure up to twelve components simultaneously, greatly reducing the need for multiple analyzers while still meeting the real-world analysis needs of these markets.

The key outcome of this new technology is that the combination of this measurement performance and analyzer capabilities has not been possible before – not with existing lasers or other measurement technologies. Of course, not every application needs this level of performance, but when taking the example of ethylene product quality, time and product contamination is money in this volatile industry. When multiple, highly sensitive measurements can be made in seconds by a QCL, excursions in the product quality can be rapidly detected, facilitating decisions to suitably manage plant operation, and minimize losses. QCL technology provides a speed and quality level never before possible. Likewise, the low levels of detection not only improve product quality for the user, but they also open up wider market options and help meet guidelines.

Over the next months, I’ll be sharing about ways to optimize gas analysis in different critical markets. For now, if you have questions about how QCL technology might work for you, please contact me at Amanda.gogates@Emerson.com.

How do you currently measure gas purity?

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