Question

What factors contribute to boil-off gas (BOG) generation in LNG storage tanks?

Accepted Answer

Several factors contribute to boil-off gas (BOG) generation in LNG storage tanks. The most significant factor is heat leak from the surrounding environment into the tank. Despite the insulation, some heat inevitably penetrates the tank walls and roof, warming the LNG. This heat input causes a portion of the LNG to vaporize, creating BOG. The rate of heat leak depends on the effectiveness of the insulation, the surface area of the tank, and the temperature difference between the LNG and the ambient environment. Another factor is flashing. When LNG is transferred into the storage tank, there is often a slight pressure drop. This pressure drop can cause some of the LNG to vaporize instantaneously, creating flash gas. The amount of flash gas depends on the temperature and pressure difference between the incoming LNG and the tank conditions. Tank agitation or mixing can also contribute to BOG generation. If the LNG in the tank is not homogenous in terms of temperature and composition, mixing can cause warmer layers to come into contact with colder layers, leading to vaporization. Ingress of moisture into the tank or insulation system can also increase BOG generation. Moisture can condense and freeze, creating thermal bridges that increase heat leak. Finally, pump operation and other equipment inside the tank can generate heat, contributing to BOG generation.

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What factors contribute to boil-off gas (BOG) generation in LNG storage tanks?