An apparatus and method for producing liquefied natural gas. A liquefaction plant
may be coupled to a source of unpurified natural gas, such as a natural gas pipeline
at a pressure letdown station. A portion of the gas is drawn off and split into
a process stream and a cooling stream. The cooling stream passes through a turbo
expander creating work output. A compressor is driven by the work output and compresses
the process stream. The compressed process stream is cooled, such as by the expanded
cooling stream. The cooled, compressed process stream is divided into first and
second portions with the first portion being expanded to liquefy the natural gas.
A gas-liquid separator separates the vapor from the liquid natural gas. The second
portion of the cooled, compressed process stream is also expanded and used to cool
the compressed process stream. Additional features and techniques may be integrated
with the liquefaction process including a water clean-up cycle and a carbon dioxide
(CO2) clean-up cycle.
