Process for purification of natural gas

Claim 2

A process in accordance with claim 1 in which the partial condensation of the second interstage stream as recited in step (j) of said claim 1 is accomplished by direct mixing of at leaSt a portion of said second interstage stream with the expanded subcooled natural gas mixture referred to in step (d) of said claim 1.

Claim 3

A process in accordance with claim 1 in which step (a) thereof is carried out by passing separate portions of the natural gas mixture through parallel heat exchanger means in separate heat exchange relation with at least a portion of the first and second product streams passed separately through said parallel heat exchanger means.

Claim 4

A process in accordance with claim 4 in which that portion of the first product stream passed through the heat exchanger means in heat exchange relation to a portion of the natural gas mixture is repressurized to a relatively higher pressure in the liquid phase prior to its passage through said heat exchanger means.

Claim 5

A process in accordance with claim 5 in which the partial condensation of the second interstage stream as recited in step (j) in claim 1 is accomplished by direct mixing of at least a portion of said second interstage stream with the expanded subcooled natural gas mixture referred to in step (d) of claim 1.

Claim 6

A process in accordance with claim 1 in which the temperature in the first stage separation zone in maintained at a predetermined level so as to achieve a controlled predetermined composition of the first product stream.

Claim 7

A process in accordance with claim 1 in which the temperature in the second stage separation zone is maintained at a predetermined level so as to achieve a controlled predetermined composition of the second product stream.

Claim 8

A process in accordance with claim 1 in which the partially warmed natural gas mixture and the cooled second interstage stream referred to in step (e) of said claim 1 are subjected to a partial separation of liquid and gaseous phases thereof prior to discharge into said first stage separation zone.

Claim 9

A process in accordance with claim 1 in which the expansion of the subcooled natural gas mixture referred to in step (c) of said claim 1 is carried out so as to produce external work.

Claim 10

A process in accordance with claim 1 in which a portion of the liquid phase from the second stage separation zone is removed as a liquid product and the balance of the liquid phase removed from the second stage separation zone is used for the cooling step referred to in step (k) of said claim 1.

Claim 11

A process in accordance with claim 1 in which the expansion of the subcooled natural gas mixture recited in step (c) of said claim 1 is carried out with the production of external work and a portion of the liquid phase in the second stage separation zone is removed as a liquid product and the balance of the liquid phase removed from the second stage separation zone is used in the heat exchange step referred to in step (k) of said claim 1.

Claim 12

Apparatus for separating a high pressure normally gaseous natural gas mixture comprising predominantly nitrogen and methane into a first product stream containing a substantially higher proportion of methane than the mixture and a second product stream containing a substantially higher proportion of nitrogen than the mixture, the apparatus comprising: a. heat exchanger means, b. means for passing the natural gas mixture through the heat exchange means in heat exchange relation to a first and second product stream, c. subcooler means and means for passing at least a portion of the cooled mixture in heat exchange relation to a first interstage stream in the subcooler means so as to subcool and at least partially liquefy the cool natural gas mixture, d. means for expanding the subcooled natural gas mixture to a first reduced pressure, e. intercooler means and means for passing at least a portion of the expanded subcooled natural gas mixture in heat exchange relation to a second interstage stream in the intercooler means, f. first stage separation vessel means and means for introducing the partially warmed natural gas mixture from the intercooler means and the cooled second intErstage stream into the first stage separation vessel means to produce therein a single methane-rich liquid phase and a single nitrogen-rich gaseous phase in approximate thermal equilibrium at substantially said first reduced pressure, g. means for withdrawing from the first stage separation vessel means separate streams of the methan liquid phase as the first interstage stream and the nitrogen-rich gaseous phase as the second product stream and for introducing said first interstage stream into the subcooler means recited in (c) in heat exchange relation to the cooled natural gas mixture, h. second stage separation vessel means and means for introducing the partially vaporized first interstage stream into the second stage separation vessel means to produce therein a single methane-rich liquid phase richer in methane than the first interstage stream and a single nitrogen-rich gaseous phase in approximate thermal equilibrium at a second reduced pressure, i. means for continuously and separately withdrawing from the second stage separation vessel means separate streams of the methane-rich liquid phase as the first product stream and the nitrogen-rich gaseous phase as the second interstage stream, j. means for passing at least a portion of the second interstage stream in heat exchange relation to the expanded mixture in the intercooler means recited in (e), k. means for introducing the partially condensed second interstage stream into the first stage separation vessel means as recited in (f), and l. means for passing at least a portion of the second product stream and at least a portion of the first product stream in heat exchange relation to the natural gas mixture in the heat exchanger means recited in (a).