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A case study on printed cycle heat exchanger adoption for reliable and enhanced ethane recovery at QatarEnergy LNG facilities.

Number: 47

Author(s) : AL-HUSSAINI N.

Summary

Natural Gas Liquid (NGL) recovery unit is designed in QatarEnergy LNG facilities to produce lean gas and NGL products. The units operate at cryogenic temperatures where Brazed Aluminum Heat Exchanger (BAHX) is one of the key equipment utilized in the process to achieve efficiently the required NGL recovery at high heat rates. Particularly for this case study, AKG-1 Train is designed to produce sales gas and ethane+ (C₂+) to meet domestic and industrial demand in the State of Qatar. It recovers 99% ethane (C2) as per design via Ortloff Recycle Split Vapor (RSV) process licensed by UOP.
Between 2019 and 2021, QatarEnergy LNG facilities experienced multiple Tier-1 and Tier-2 process safety incidents resulting from BAHX failures of core bursts, joint and nozzles cracks, that led to Loss of Primary Containment (LOPC) and minor ignition events. As confirmed by Root Cause Analyses (RCAs), these failures were mainly because of medium to high thermal fatigues because of repeated events of temperature rate of change (T-ROC) and temperature difference above ALPEMA® and API 668 limits of 1 °C during steady-state, 5 °C during transient conditions and 30 °C, respectively. Hence, several enhanced mitigation measures were implemented such as maintaining operation within the Integrity Operating Window (IOW) defined by ALPEMA® and API 668, establishing proactive surveillance programs to ensure better monitoring and compliance with these limits, developing inspection strategies, and installing online gas detection systems.
Comprehensive BAHX integrity assessments were conducted across the NGL units to identify risks associated with the thermal stress. For this case study covering AKG-1, the Demethanizer Side Reboiler (136-E004) was identified as a medium “yellow” risk due to frequent exceedances of TROC limits. This risk restricts AKG-1 C₂ production to approximately 70% of its design rate of 67 T/H. The Side Reboiler (136-E004) is particularly exposed to thermal fatigue risk due to AKG-1’s dynamic operations, which involve frequent changes in sales gas and C₂ production rates based on customer demand governed by QatarEnergy. These variations in production rates cause changes
in feed gas flow and Demethanizer temperature profile, resulting in continuous temperature fluctuations that directly contribute to the observed T-ROC exceedances beyond the advised limits. In a feasibility study for AKG-1 C₂ maximization project, several options were checked to debottleneck this limitation. Therefore, replacing Demethanizer Side Reboiler from BAHX to PCHE was studied and considered as the optimum option. Since PCHE offers significant advantages due to its material properties and manufactuing process, which provide higher resilience against thermal stress failure mechanisms for the asset dynamic operations.
The material used for new PCHE is stainless steel (grade: SS 304L), has a higher tensile strength (500-700 MPa), providing robustness to withstand thermal and mechanical stress before failure. Additionally, it exhibits a lower coefficient of thermal expansion by (25 x 10⁻⁶ /K) which helps it to restrict dimension changes during temperature fluctuations. Also, the material has greater stiffness, indicated by Young's Modulus: 190-200 GPa) provides a strong resistance against deformations. PCHE manufacturing process is diffusion bonding which eliminates transient joints, as the core is manufactured via diffusion bonding. This process enables the heat exchanger components to merge at an atomic level, creating a monolithic structure with a common grain boundary.
In contrast, the BAHX (for the existing heat exchanger) is constructed from an aluminum alloy (Al 5083). This material has a high thermal conductivity (Al 5083: 121 W/(m·K) vs. SS 304L: 16.2 W/(m·K)), which directly enables a more compact design and a higher heat transfer area per unit volume for an equivalent thermal duty. However, this aluminum alloy is also more prone to thermal stress due to its mechanical properties: a lower tensile strength (~300 MPa), a higher coefficient of thermal expansion (25 x 10⁻⁶ /K). Higher thermal expansion causes greater dimensional changes, deformation and cracks in response to continuous temperature changes. It has a lower stiffness, indicated by Young's Modulus: ~70 GPa. Furthermore, the BAHX is manufactured by vacuum brazing, a process that uses a filler metal to join the components (fins, parting sheets, side bars) into a single structure. This method creates transient joints which can act as weak points under thermal cycling, demonstrated by multiple historical failure reports in these locations.
 

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  • Original title: A case study on printed cycle heat exchanger adoption for reliable and enhanced ethane recovery at QatarEnergy LNG facilities.
  • Record ID : 30034660
  • Languages: English
  • Subject: Technology
  • Source: 21st International Conference & Exhibition on Liquefied Natural Gas (LNG2026)
  • Publication date: 2026/02/05

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