The Best Leak Detection Technology for LNG Plants

LNG Oil and GasWe know that LNG is central in the processing and transportation of natural gas. As a result, it’s important to understand the safety risks involved in LNG and the optimal protections available to guard against those risks. While LNG itself isn’t dangerous, any liquid released into the open will quickly turn to gas and that can cause fire or explosion, precipitating jet flames, fireballs, flash fires, vapor cloud explosions, and pool fires. Refrigerants like ethylene, ethane, polypropylene, and butane are often used in liquification, and these increase risk, while a hydrogen sulfide release can result from the purification process.

 

Here is a brief description of the three main options for gas detection in LNG facilities, particularly marine terminals.

 

Catalytic Detectors

Simple in design and easy to manufacture, catalytic detectors respond to the greatest possible range of combustible gases (including hydrogen) and offer good reliability and accuracy, as well as fast response times. Catalytic sensors are able to detect ethylene in concentrations well below the lower explosive limit (LEL).

 

Due to their wide compass, catalytic detectors are installed in fractionation columns (scrub columns) before liquefication at a main exchange, near propane pre-cooling vessels or near refrigerant compressors. Catalytic detectors are also useful for the protection of process pumps.

 

Infrared (IR) Gas Detection

IR gas detection provides high integrity and reliability in point and open path configurations, which are essential methods for safety applications. As optical gas detection is a physical technique, high-target gas concentrations for prolonged periods and oxygen level changes do not degrade sensor performance. Most importantly, IR devices are failsafe. Both point and open path IR detectors are used in marine terminals to monitor LNG transfer pumps and storage tanks.

 

Ultrasonic Leak Detection

Unlike fixed point catalytic, point or open path IR detection, which primarily detect gas accumulations, ultrasonic gas leak detection responds to the ultrasonic noise generated at the leak source itself. It therefore has the potential to compensate for the limitations in effectiveness of traditional gas detection systems since it responds instantaneously and is impervious to wind and gas dilution. Use of ultrasonic is limited to high pressure leaks producing acoustic emissions higher than the level of any background noise. Ultrasonic gas leak detectors can be installed in gas turbines for fuel gas compressors and refrigerant compressors.

 

A Detection Plan

Detection coverage at LNG facilities should be based on a process hazard analyses that takes into account the advantages and limitations of the detection technologies. All point detectors, for example, are limited to detecting gas at a specific location and can be foiled if placed in a spot where air stagnates or if an obstruction prevents the hazardous gas from reaching the detector element. Similarly, ultrasonic gas leak detectors cannot detect low pressure gas releases such as those produced by LNG spills. The best strategy appears to be deployment of these techniques in combination, so that devices may comprise a broader range of gas release scenarios while mitigating vulnerabilities.

 

What leak detection approaches do you use?