New technology is reducing the risk of compressor and other plant failures. National Grid in the UK has recently published its findings on testing a camera-based system to detect liquid and solid contamination in gas flows. LineVu provides live video streams that show activity in high pressure pipelines for both gas processors and gas networks. This information provides an extra dimension in understanding and allows actionable insights to be made for process control and gas quality.
Gas/liquid separators are not 100% efficient 100% of the time. In fact, their performance is one of the most common causes of problems and capacity constraints.
Foaming, flow surges, start-up, shutdown, and flow ramping are all common causes of liquid carry-over. Liquids in a gas network collect at low points that cause corrosion, compressor failures, or even explosions. Undetected liquids cost the industry $Millions every year in damage, lost revenue and labour costs.
While dewpoint meters and gas chromatographs monitor gas quality, amine and glycol are most likely to carry over into the sales gas lines when separator performance is compromised, and these liquids are not currently monitored.
Within a plant, poor separator performance can be a real problem. When a dew pointing system is fitted to remove condensate, glycol carry-over can freeze and cause blockages.
Molecular sieves and mercury absorber beds can be destroyed by liquid carry-over. More importantly, their life is insidiously reduced by small, constant, undetectable liquid carry-over.
Compressor Failures
The lack of liquid carry-over monitoring frequently means that liquid contamination is not known until it is too late and a compressor fails. Dry Gas Seals (DGS) within gas compressors rely on a supply of clean process gas to ensure lift-off between static and rotating components. When liquids enter the gap between the rotating seat and stationary face, high shearing forces generate heat. The generated heat leads to gap instability, causing contact between the rotating seat and stationary face, damaging the seal faces and resulting in a seal failure. In a survey of 71 compressor failures, 100% of failures reported liquid ingress to the DGS. The health and safety report went on to state that:
“DGS failures are not normally directly hazardous but have the potential for escalation. Resulting in an uncontrolled excessive release of hydrocarbon gas.”
Gas Safety Management Regulations (GS(M) R) in the UK and Federal Energy Resource Council (FERC) in the USA require that gas in transmission networks should not contain liquids or solids. This is impossible to determine with current technology at custody transfer at the gas entry points to a network.
Ensuring a contaminant free gas in networks also extends the asset life by reducing the threat of corrosion. When liquids are present in a network, they pool at low points and corrode the pipeline to the point of rupture, as at Carlsbad, New Mexico.
Fiscal Measurements
When contamination occurs in dry gas flows, orifice plate and ultrasonic flow meters overread, significantly increasing the uncertainty from <0.5% to around 2%. As calorific value and hydrocarbon dewpoint measurements are taken from the gas phase only, any liquids at the bottom of the pipe are not included in these measurements.
A New Understanding
As more systems are installed worldwide, data from this patented technology is bringing a better understanding of how gas and contamination interact within a pipeline. Much of the real-world data gathered from large diameter pipelines do not agree with established fluid dynamic models. While most CFD models treat liquids in a pipeline as homogenous, separation of different density liquid flows has been observed at high pressure, and lighter end liquids have been seen being drawn off of a stationary mass of contamination, leaving a dry material behind. LineVu brings a new approach to monitoring liquid carryover that provides certainty about gas pipeline contamination levels.
When liquid flows occur, they are often not one flat stream but, depending on their density, could be a worm-like shape or many small streams. Operators are provided with a live view of pipeline activity, and image processing is used to alarm if contamination is present. Implementing this technology enables compliance with regulations, improves process safety, and has several financial benefits.
LineVu’s “Camera Can” is certified for use in hazardous areas and normally mounted vertically on a standard tapping point and views down to the pipe floor below reporting activity on the pipe floor and in the gas flow between the camera and the pipe floor. By continuously monitoring the effectiveness of gas/liquid separators, more effective maintenance is possible, and the threats posed by contamination are decreased.
The National Grid trial effectively validated the video detection system, and LineVu is now providing video-based liquid detection systems for in-pipe monitoring.
The camera and illumination system is configured to take video and images of the pipeline through the isolation valve. With a live link to the control room, operators better understand gas quality and the impact of process changes.
The standard flange is a Class 900 3” RTJ. The Camera Can has a secondary containment vessel to prevent loss of containment upon a window or seal failure. The secondary containment vessel is constantly monitored for pressure and temperature.
The SIM card in the interface unit allows connection to the mobile phone network via a secure link to enable technical support, including:
- Remote system commissioning, setting camera and illumination for optimum results.
- Continuous health checks.
- Upload of software updates.
- Fault diagnosis.
- Remote technical resources able to view live data to aid operational decisions.
- Data monitoring
Greater process confidence is gained when operators can see events in highpressure systems. When the alarm is raised, LineVu automatically starts recording data. It continues to record until no further contamination is detected.
The interface unit and LineVu controller are mounted in a safe area, with an ethernet connection between them. All data is saved on-site with sufficient space in the LineVu Controller to save up to a year of data. The system has proved to be highly sensitive to mist flows and liquid streams in a pipe with alarm thresholds set at a high sensitivity level with notification emails set up.
The interface unit and LineVu controller are mounted in a safe area, with an ethernet connection between them. All data is saved on-site with sufficient space in the LineVu Controller to save up to a year of data. The system has proved to be highly sensitive to mist flows and liquid streams in a pipe with alarm thresholds set at a high sensitivity level with notification emails set up.
In addition to the alarm function, LineVu provides extra functionality beyond the detection of contamination. In normal operation, LineVu is set to store a still shot once a minute. It automatically compiles these shots into a time-lapse video which can be downloaded every 24 hours. Replaying these videos at 1500x speed highlights and reveals low-level contamination (under alarm threshold) for further investigation.
Threshold alarms and system alarms can be configured for notification via:
- Relay activation.
- Email notification – with still shots.
- Text notification – with still shots.
- Push notification – with still shots.
As the system has access to the mobile phone network, cybersecurity has been considered in its design. There are several levels of security. The systems can operate independently of the operational or data networks operated by the end-user; all connections are via a secure link, and all data uses high-level encryption. In addition to alarm notification, each system provides a web interface that can be accessed with the correct credentials and user authentication. Users can:
- View live video
- View historical video
- Export sections of footage
- Export snapshots and PDF reports
A mobile phone app is also available via a secure and authenticated link.
Conclusion
With a LineVu system installed, threats to asset integrity such as compressors, and corrosion can be better managed; sources of contamination can be better understood and therefore reduced. Uncertainties on fiscal measurements of both flow and calorific value can be better managed. Clean-up costs after a contamination event can be correctly allocated to the source.
Process Vision Ltd.
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