The main cryogenic heat exchanger is critical to the operation of an LNG train. The refrigerant used in this heat exchanger undergoes multiple stages of compression in its cycle. The low pressure mixed refrigerant (MR) suction drum receives refrigerant vapour flow from the main cryogenic heat exchanger and separates entrained liguids to protect the MR compressor from damage. Operationally, the low pressure MR suction drum is characterised by high gas volume with low liquid flow (typically less than 1% by mass). The high gas flow drives the size requirements of the vessel and, as a result, these vessels tend to be quite large. As such, the low pressure MR suction drum is a good candidate for optimisation through the careful selection of process internals. Consider the design basis outlined in the low pressure MR suction knock out' sidebar in this article (p. 52). The resultant vessel diameter is nearly 34 ft.
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