pressure which for air is 38 bar but more preferably 56 bar at ambient temperature u2248 298 k the main process gas stream 31 35 enters inlet 31 from which point it is directed through a first heat exchanger 100 and is cooled progressively by the cold recovery circuit 120 htf passing through passage 52 the htf in the cold recovery circuit 120 may comprise gas or a liquid at high or low pressure in the preferred case a gas such as nitrogen at a pressure of 5 bar is used the cold recovery circuit 120 consists of a means of circulation 5 such as a mechanical blower a second heat exchanger 101 is provided in addition to the first heat exchanger 100 described above the htf is circulated around the cold recovery circuit by the mechanical blower and enters the second heat exchanger 101 at 185 k the htf is progressively cooled by virtue of its proximity to the waste stream of lng 60 passing through the first heat exchanger and exits the second heat exchanger at around 123 k the htf is then directed to the first heat exchanger 100 through which it passes via passage 52 providing cooling to the high pressure main process gas stream 31 35 by virtue of its proximity thereto at point 35 the main process gas stream 31 35 has been cooled to a temperature of between 110 135 k but in the preferred case 124 k and continues to pass through the first heat exchanger 100 in which it continues to.