Badak LNG plant utilizes Multi Component Refrigerant (MCR) as cooling medium for natural gas liquefaction. In the process system, a heat exchanger is serving as compressor aftercooler that cools down this MCR (gas with mostly Methane and Ethane) by means of sea cooling water. This particular heat exchanger is constructed with Rod-Baffle design with Titanium tubes. The design also incorporates a vapour belt at shell inlet/outlet that is functioned as flow distributor.

Badak LNG has 8 plants called process trains; with each process train has one MCR aftercooler. The aftercooler at each train has difference in terms of vapour belt design.

During plant operations, vibration problem has repetitively occurred in all MCR aftercooler and caused tube leaks. However, a computational fluid dynamics study revealed that the fluid velocity was low enough to generate tube vibrations. However, Rod-Baffle design uses single support direction per baffle. With 4 axis of support (X+, X-, Y+, Y-), one direction support will repeat at the 5th support, 10th support, and so on.

Calculation was then made to confirm the effect if one of the baffle failed to support. This condition will increase the length between baffle by 2 times. Consequently, the fluid critical velocity will decrease by 4 times.

This approach was then compared with the fluid velocity pattern inside the exchanger shell. It concludes that the fluid velocity is above its critical velocity. Thus, the exchanger is vulnerable to vibrations.

Each MCR aftercooler has different vulnerability to vibrations due to vapour belt different designs. The study has concluded the comparison of vulnerability of the exchangers. Exchanger A has 25.9 % tubes having tubes vulnerable to vibrations, while Exchanger F (with different vapour belt design) has only 1.92 % tubes vulnerable to vibrations. With 2000 tubes quantity, the effect to process conditions is significantly different between exchangers.

This paper concludes that design of vapour belt can significantly improve the reliability of Rod-Baffle type heat exchanger.

Volume Subject Area:
Vibration, Acoustics and Wave Propagation
Topics:
Heat exchangers, Liquefied natural gas, Vibration, Design, Belts, Fluids, Trains, Cooling, Shells, Compressors, Computational fluid dynamics, Flow (Dynamics), Leakage, Liquefaction, Methane, Natural gas, Refrigerants, Reliability, Seas, Titanium, Water
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