Keywords: Ultrasonic Gas Leak Detector (UGLD), Emerson Process Management, Groveley Detection.
Owner-operators in upstream and midstream natural gas environments are facing more challenging operational, environmental and regulatory issues as they strive to bring natural gas and other hydrocarbons to market, safely, efficiently, and profitably. Gas leak detection is critical to personnel and plant safety. However, in hazardous or harsh operating environments and in applications where weather has an impact, conventional point gas detection technologies may not provide adequate protection. This is because air flow within a facility and other environmental factors may adversely impact detection performance. As a result, ARC Advisory Group believes a comprehensive gas detection strategy should involve three critical layers:
Layer 1 – Ultrasonic gas detectors to rapidly detect pressurized gas leaks in open environments and inaccessible locations
Layer 2 – Point detectors to identify and quantify leaks
Layer 3 – Line of sight devices for perimeter protection and cross-plant cloud detection
No Silver Bullet, No One Perfect Solution
Many operating companies in the UK, Australia, Indonesia, Malaysia and Oman have already embraced a comprehensive strategy for gas leak detection that combines traditional technologies such as infrared point detection with newer, complimentary technologies such as ultrasonic to provide more complete leak protection. With this strategy, the ultrasonic gas leak detectors provide the first line of defense by detecting leaks before these can develop into serious problems. This is particularly critical in open environments and inaccessible locations.
Although traditional systems that require direct contact with the gas are very accurate, their effectiveness is limited in open environments where factors such as wind can dissipate the gas before it reaches the sensor. Other factors such as gas dilution and leak direction can also hamper a point detector's ability to effectively detect leaks.
Ultrasonic gas leak detectors can serve as an effective complimentary technology to traditional systems to help ensure a more comprehensive approach to gas detection and minimize the risks of exposure to plant personnel, assets, and the surrounding environment. Users must understand that there is no single, perfect gas leak detection system. The ideal solution requires a comprehensive, multi-layered approach that employs a combination of conventional point detectors, ultrasonic detectors, and line-of-sight detectors, coupled with sophisticated alarm escalation techniques. One such example might be ultrasonic detector alarms plus increasing LEL (lower explosive levels (LELs) observed on point and line-of-sight devices.
Mapping Surveys Are Critical to Success
Installing detectors without a comprehensive plan will limit their effectiveness. Mapping surveys are critical to identify the number of detectors required as well as their optimum placement. ARC advises users to work with suppliers with a proven track record in conducting effective mapping surveys. The suppliers' experienced technicians typically utilize mapping tools and software to measure background noise level in the location under normal operating conditions. Mapping also helps determine the coverage range of each detector and estimate the number of detectors required for maximum coverage. For example, an ultrasonic leak detector's coverage area would be larger with background noise level of 74 dB compared to noise levels of 84 dB, for the same gas release.
The ultrasound generated by a gas leak depends on a number of factors including upstream gas pressure and temperature, ambient temperature, gas type and leak size. These factors are crucial to determine proper detector installation. Utilizing mapping software, suppliers such as Emerson can calculate detector coverage area and model detector behavior for various leak sizes and types. Mapping and leak characterization ensures a sufficient number of detectors are installed at optimum locations to provide the broadest coverage.
A New Approach to Gas Leak Detection
GDU-Incus ultrasonic gas leak detectors (UGLD) from Emerson Process Management (via the recent Groveley acquisition) do not measure gas concentration in terms of percent LEL or ppm (parts per million) as do traditional detectors utilized in catalytic, infrared, or electrochemical-based systems, respectively. With GDU-Incus detectors, it is not necessary for the gas to make contact with the sensor to be detected. It utilizes innovative (patent-pending) floating piezo ceramic resonant sensors to detect ultrasonic sound in the 25 kHz to 100 kHz frequency range. Each detector includes four independent sensing heads with the detector responding to the differential in ultrasound generated from a pressurized gas leak and the normal plant process noise. Due to the ability to detect the leak rather than the gas plume, the GDU-Incus offers the potential to provide early warning of a leak.
The chemical-resistant sensor has no moving parts and is calibrated for life. Each sensor is ceramically sealed to keep it from becoming clogged with salt spray, moisture, sand, or dust. According to the company, the sensor will not age, drift, or need replacing during normal working conditions, thus requires minimal maintenance. The quad sensor head provides a detection range of up to 40 meters depending on ambient noise. The SIL 2 rating makes GDU-Incus suitable for critical applications involving continuous gas monitoring in open areas for all types of toxic or combustible pressurized gas leaks, including hydrocarbon and hydrogen gases. The robust physical packaging provides IP66/67 ingress protection against dust and forceful water during operation. A variety of configurations are available to accommodate a broad range of operating environments and system integration.
According to the company, the technology is impervious to wind, rain, fog, poisoning, or gas dilution, making it reliable in outdoor installations anywhere in the world. It can be utilized in an advisory capacity when operated as a standalone unit or as part of a system controlled by the digital control system. Where toxic gases and asphyxiants are involved, zero time delay in detection can mean the difference between a minor incident and major catastrophe. In the case of flammable gases, unwanted alarms can be avoided with a time delay. According to the company, their technology enables GDU-Incus gas detectors to detect sound from very small pressurized leaks, provided a detailed assessment of the application is made. However, detecting pressurized leaks greater than 7 bar is more common.
For manufacturers to minimize the risks associated with the accidental release of harmful gases, ARC recommends a multi-layered approach to gas detection that includes multiple technologies for specific purposes: ultrasonic pressurized leak detection, point detectors to identify and quantify leaks, and line-of-sight devices for cloud detection. A site survey including identification of background noise helps ensure appropriate numbers of ultrasonic detectors are utilized and located to provide optimum area coverage. Operating companies should partner with experienced gas detection professionals to obtain the highest possible return on investment and the greatest level of protection.
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