Many applications including emissions monitoring, ethylene purity, ammonia slip, hydrocarbon gas composition, and more require the measurement of the concentration of various components in a gas mixture.
One technology used to perform this measurement is tunable diode lasers and laser absorption spectrometry (TDLAS). This fast, high resolution detects and identifies a range of molecules in the mid-infrared wavelength. Emerson’s Quantum Cascade Laser (QCL) analyzer is based on this TDLAS technology. Another technology, Tunable Diode Laser (TDL) spectroscopy technology identifies a range of molecules in the near-infrared band. Here are some common molecules requiring concentration measurements in industrial processes:
In an Industrial Automation Asia article, Advanced Hybrid Laser Technology Breaks New Ground In Gas Analysis, Emerson’s YeeTiong Koh describes how the combination of QCL and TDL technologies in the Rosemount CT5000 Series of analyzers expands gas analysis to both the near and mid-infrared range to enhance process insight, improve overall gas analysis sensitivity and selectivity, remove cross interference, and decrease response time.
YeeTiong opens highlighting the importance of gas measurement in many applications including:
…process control, product certification, and emissions monitoring — are so critical to industrial companies’ bottom line that tried and true, proven technology is required.
He notes that although combining QCL & TDL technologies into a single analyzer has not been around as long as other technologies, they are:
…already seeing rapid adoption for ethylene production purity, continuous emissions monitoring, NOx reduction/ammonia slip, natural gas, and hydrogen purity in industries such as petrochemical, oil and gas, power, gas processing, and research and development.
The lasers work by emitting:
…light at a desired wavelength and are made to scan a spectrum using a laser chirp technique.
The laser chirp:
…lasts about one microsecond and in this time a spectrum of between 1-3 wavenumbers is scanned.
The frequency of this chirp can be:
…up to 100 KHz, enabling many thousands of spectra to be gathered in a few seconds and processing these spectra gives a strong signal with a good signal-to-noise ratio.
Although suitable for many gases, inert gases are not a good fit. The do not provide enough spectral response in the near- or mid-infrared range.
YeeTiong shared an example of a refinery testing the use of a Rosemount CT5000 Series analyzer in a continuous emissions monitoring system (CEMS) application.
They first set up the QCL CT5400 continuous gas analyser from Emerson to perform all of the refinery’s CEMS measurements in a single unit. This included NO, NO2, O2, CO, CO2, and SO2. The CT5000 series has the ability to ‘chirp’ multiple lasers to fire sequentially with each chirp being under 1 millisecond, enabling thousands of spectra to be collected each second. They chirped six lasers through the entire range of their gases.
Read the article for the results of this testing, the compact & rugged packaging of these analyzers, and the ease of ongoing maintenance and upgrading.
You can also connect and interact with other analyzer experts in the Analytical group in the Emerson Exchange 365 community.
