Systems and Methods of Removing Contaminants in a Liquid Nitrogen Stream Used to Liquefy Natural Gas

A method of producing liquefied natural gas (LNG), the method comprising:

• providing a natural gas stream from a supply of natural gas;
• providing a liquid nitrogen stream from a liquid nitrogen supply;
• compressing the natural gas stream in a natural gas compressor to a pressure of at least 135 bara to form a compressed natural gas stream;
• cooling, through indirect heat exchange with an ambient fluid in a natural gas cooler, the compressed natural gas stream to form a cooled compressed natural gas stream;
• passing the cooled compressed natural gas stream and an at least partially vaporized nitrogen stream through a first heat exchanger that exchanges heat between the at least partially vaporized nitrogen stream and the cooled compressed natural gas stream to additionally cool the cooled compressed natural gas stream to form an additionally cooled compressed natural gas stream;
• expanding, in a work producing natural gas expander, the additionally cooled compressed natural gas stream to a pressure less than 200 bara, but no greater than the pressure to which the natural gas compressor compresses the natural gas stream, to thereby produce a chilled natural gas stream;
• and
• liquefying the chilled natural gas stream by passing the chilled natural gas stream and the liquefied nitrogen stream through a second heat exchanger that exchanges heat therebetween, wherein the liquefied nitrogen stream passes through the second heat exchanger to form the at least partially vaporized nitrogen stream;
• and
• further comprising removing greenhouse gas from the at least partially vaporized nitrogen stream using a greenhouse removal unit, wherein the greenhouse gas removal unit comprises a distillation column and a heat pump condenser and reboiler system, and further comprising:
• increasing a pressure and condensing temperature of an overhead stream of the distillation column;
• cross-exchanging the overhead stream of the distillation column and a bottoms stream of the distillation column to affect both an overhead condenser duty and a bottom reboiler duty of the distillation column;
• reducing a pressure of the distillation column overhead stream after the cross-exchanging step to produce a reduced pressure distillation column overhead stream;
• and
• separating the reduced pressure distillation column overhead stream to produce a first separator overhead stream, wherein the first separator overhead stream is gaseous nitrogen that exits the greenhouse gas removal unit having greenhouse gases removed therefrom.