Hydrate formation risk exists in gas/LNG processing plants when wet gas streams are cooled within the process. This can lead to blockages which impact flows, pressure drops, and can lead to potential process safety risks (e.g., overpressure due to blocked discharge). As ongoing injection of hydrate inhibitors into the gas phase is generally not practical, the standard way of managing hydrate risk is maintaining temperatures in the process 3 – 5°C above the predicted hydrate formation temperature (normally based on the most conservative composition and operating conditions).
Introduction and Objective
For natural gas production and LNG processing, one of the most significant risks to operation is unexpected or unknown solid formation and deposition, which can be in the form of hydrates, but also waxes or asphaltenes. Blockage of pipelines or process units can lead to system shutdown with significant safety and economic implications. For hydrates, prevention via chemical inhibition is effective for subsea production lines. However, challenges persist in detecting and managing solids within topside and liquefaction infrastructure. Minor process upsets can trigger freeze-out events, yet delayed indicators such as pressure drop and invasive inspections remain the primary means of diagnosing internal deposition. This project investigated two technologies for monitoring hydrate deposition, based on microwave and acoustic technology. The UWA JT Expansion Flow Loop facility was employed to replicate, at pilot scale, a range of hydrate formation scenarios that are commonly encountered in a live facility, to assess the performance of the sensor technologies.
Project Findings
The in-line toroidal microwave resonator demonstrated ability to distinguish deposit type and depth in sensitivity testing. Furthermore, it demonstrated measurement of hydrate and water fractions consistent with the experimental conditions across all tests. The acoustic sensor signal was dominated by throttling for the absolute energy source and was not influenced by external noises. A model relating absolute energy of a dry gas stream to differential pressure across the JT valve was established to provide insight into the flow conditions of the apparatus. It demonstrated detection of flow reduction in cases where hydrate was expected to form. Overall, both sensors were capable of detecting hydrates with complimentary insights; the in-line toroidal resonator could detect hydrate deposition and also estimate phase volume fractions, and the acoustic sensor could monitor flow reduction.
Recommendations
Further testing should be conducted on a continuous flow loop, to investigate sensor performance over longer time periods and study the sensitivity to accumulation of solids and dynamically changing gas/water/hydrate fractions. The acoustic sensor would benefit from a reduced operating range of absolute energies, reducing uncertainty in the flow reduction model.
Based on the findings from the tests performed in this project, these sensors can provide valuable information on changes on phase within the flow, as deviations from steady state can be reliably identified. A key advantage of the in-line microwave solid deposition sensor is that it can determine the deposit type and volume fraction in the sensing region. Therefore, it is a useful monitor of solid accumulation in problematic points along a plant. It is recommended to consider applications where the sensors are located at high-risk locations for hydrate (or other solids) formation, such as downstream of an expansion valve, changes in flow direction, shut-in locations, and wherever there is significant subcooling to cause hydrate formation.
Project researchers
- Dr Paul Stanwix
- Prof. Eric May
- Dr Liam Tenardi
Project Status
Complete
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