Innovations in line-of-site gas detection

by Jean Berthold, CMSO, VP

Open Path Gas Detectors (OPGD) using NDIR laser detection techniques have been in use since the late 1980’s and are widely accepted for many Oil & Gas, Petrochemical and other industrial hazardous gas detection applications.

“At the heart of the ELDS technique are two technologies, harmonic fingerprinting and real-time multiple wavelength measuring that improve sensitivity for hydrocarbon gases three (3) orders of magnitude (1000 X)”

In transmitter/receiver configurations, OPGD systems are currently used to monitor hydrocarbon gas leaks at offshore and onshore oil and gas production facilities, refineries, petrochemical plants, and gas transmission stations.

OPGD detectors are proven to provide significantly higher probabilities for the detection of hazardous gases over fixed point detectors for a number of reasons: wide area coverage, much lower sensitivity levels, and 1-2 second response times of OPGD provide increased safety integrity and reduced risk.

However, these traditional NDIR OPGD systems have reached a technology plateau that includes a variety of problems: detector susceptibility to noise interferences, difficult alignment setups, costly false alarms, expensive and risky maintenance schedules, and failure to provide consistent performance when exposed to direct sunlight or adverse weather conditions. But these problems pale beside their inability to detect some target gases before reaching critical explosive or toxic levels.

1)  ELDS open path gas detector installation

Newly introduced open path gas detectors with Enhanced Laser Diode Spectroscopy (ELDS^TM) technology set a new standard for monitoring both flammable and toxic gases in the most demanding environments.

At the heart of the ELDS technique is harmonic fingerprinting and real-time multiple wavelength signal integration that improves sensitivity for hydrocarbon gases three (3) orders of magnitude (1000 X). ELDS will detect low ppm level hydrocarbon gases as compared to % LEL by traditional OPGDs.

With ELDS, the system detects the target gas at the earliest point of detection when the gas leak is small, allowing operators time to initiate remediation procedures that avoid, or virtually eliminate the possibility of gas leak levels reaching dangerous thresholds. It is now possible for users to monitor and track the progression of rising atmospheric levels of gas before they reach the critical stage.  Awareness of target gas concentrations at low levels can add literally hours of time to determine a leak source or shut down a hot spot to prevent an accident.

ELDS OPGD is a collection of advanced techniques with benefits to match

Harmonic Fingerprints are so specific that only absorption by the target gas produces a signal. Electronic noise and other atmospheric interferences do not to interfere with the detector's ability to detect its target gas, enabling an ELDS-based gas detector to effectively eliminate false alarms.

Multiple wavelength measurement and detection has long been the technique of choice in controlled scanning spectroscopy applications. ELDS has been described as providing this level of laboratory analysis in a process application. In the harshest environments, ELDS gas detectors measure the harmonic fingerprints at several different harmonic levels and in some cases, across several wavelengths, enabling simultaneous, interference-free, multiple wavelength confirming gas measurements. ELDS detectors can simultaneously detect two gases with dual isolated out put signals for applications such as sour gas (Methane + H2S), resulting in up to a 60% lower capital expenditure for a multi-gas detection system. 

ELDS features substantially better obscuration and misalignment tolerance, along with faster, easier commissioning.  ELDS OPGD remains in full operation, even in conditions causing up to 98% obscuration of the beam - resulting in much improved operation in fog, rain, snow, dust, and blowing sand. Traditional NDIR systems will often drop into beam block or initiate a false alarm with as little as a 60% reduction in signal intensity from obscuration or misalignment.

Reducing cost of ownership by simplifying risky detector functionality testing

Traditionally, routine maintenance and functional detector testing consume a major part of any fixed gas detector system justification and operation. Harmonic fingerprinting with multiple wavelength measurements form the technology basis for SimuGas^TM, a technology that eliminates the requirement for field testing of detectors to verify operation.

2) SimuGas technology enables remote, electronic, and automatic gas detector functionality testing, eliminating risks and costs associated with field testing.

SimuGas is the ELDS technique that utilizes the system's ability to directly control the laser's output to provide an exact simulation of the laser diode drive waveforms that distinguish each target gas. Each ELDS detector contains proprietary SimuGas technology and an internal target gas reference cell that together provide remote, electronic, and automatic gas detector functionality bump testing every day, or even hourly, to constantly assure full functionality of the system.

ELDS unit functional testing requires no test filters, no gassing cells, no hazardous calibration gases or technician time in the field. SimuGas enables OPGD system owners to substantially lower the risks of personal exposure by eliminating traditional field testing requirements for detector functionality, replacement of electrochemical cells for toxic gases, and associated personnel labor and risks.

3) Unique harmonic fingerprint generated by controlled scanning of a H2S  gas absorption line

Heavy duty for operation in rough environments.

ELDS OPGD innovation extends beyond gas detection technology. To meet the rigorous demands of the oil and gas industry, ELDS detectors are designed to mitigate risks in oil rigs, refineries and other operations located anywhere around the world and in the most inhospitable environments.

Where traditional fixed detectors require complicated installations with multiple components for each unit, ELDS has an integral stainless steel bracket and junction box. Each ELDS detector unit is completely self-contained to ensure the simplest possible installation and long-term reliability.

Fit-and-forget reliability begins with high quality 316L stainless steel, IP67 ingress protection, and fully integrated terminal compartments for corrosion resistance and extended operating lifetime to as much as 12-15 years.  The system contains no moving parts of any kind offering significant confidence that the system will not require repair in the field by the end user at any time.

ELDS Open Path Gas Detectors are certified for Hazardous Area Class 1, Division 1, and Zone 1 by FM Global to the FM, ATEX and CSA Standards for OPGD for both hazardous area safe operation and performance.

Conclusion

While Open Path Gas Detectors (OPGD) using NDIR laser detection techniques have been in use for decades, only current ELDS fulfills the promise of line-of-site detector technology for reliably monitoring and detecting hazardous gases before they reach critical thresholds.

4) Unique harmonic fingerprint generated by controlled scanning of a Methane gas absorption line.