Oil and gas production handbook An introduction to oil ... - ABB Group

o Dual mixed refrigerant (Liquefin Axens)
o Mixed fluid cascade process (MFCP) (Statoil/Linde)
• Expander cycle
o Kryopak EXP ® process
Each process has different characteristics in scalability, investment cost and
energy efficiency. For smaller installations, e.g., to handle stranded gas or
isolated small gas fields, a single cycle process is preferable due to its low
CAPEX (and possibly lower weight for floating LNG), even if energy
efficiency is significantly lower than the best cascade or DMR processes,
which cost more but also allow the largest trains typically, 7.8 million tons per
annum and lowest energy consumed per energy unit LNG produced.
Most processes use a mixed refrigerant (MR) design. The reason is that the
gas has a heat load to temperature (Q/T) curve that, if closely matched by
the refrigerant, will improve stability, throughput and efficiency (see the figure
below). The curve tends to show three distinct regions, matching the precooling,
liquefaction and sub-coiling stages. The refrigerant gas composition
will vary based on the individual design, as will the power requirement of
each stage, and is often a patented, location-specific combination of one or
two main components and several smaller, together with careful selection of
the compressed pressure and expanded pressure of the refrigerant, to
match the LNG gas stream.
Figure 13. LNG Q/T diagram
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