Process and apparatus for low temperature refrigeration

Claim 2

A low temperature refrigeration procEss employing a working fluid having at least two components comprising the steps of a. compressing said working fluid; b. countercurrently passing the compressed working fluid in indirect contact heat exchange relationship with at least one returning stream having a lower temperature, whereby said working fluid is cooled; c. substantially isentropically expanding said cooled working fluid to provide a vapor-liquid mixed working fluid; d. separating the uncondensed vapor fraction from the condensed liquid fraction of said mixed working fluid; e. returning the separated uncondensed vapor fraction to said heat exchange step and passing said vapor fraction countercurrently with the working fluid, as one of said returning streams; f. delivering the separated condensed liquid fraction to an evaporating zone and evaporating said liquid fraction to deliver refrigeration; g. returning the evaporated liquid fraction to said heat exchange step and passing said evaporated fraction countercurrently with the working fluid, as one of said returning streams; and h. combining the returned evaporated fraction with the returned separated vapor fraction of step (e) to comprise said working fluid.

Claim 3

The refrigeration process as defined by claim 1, further comprising the step (k) of removing a portion of the working fluid at a point in the refrigeration cycle where the most volatile component of the working fluid is most highly concentrated.

Claim 4

The refrigeration process as defined in claim 1, wherein said working fluid comprises predominant portions of nitrogen and methane and a minute portion of helium.

Claim 5

The refrigeration process as defined by claim 1, wherein said compression step (a) comprises a plurality of separate compression stages and wherein said expansion step (c) provides the energy to carry out at least one of said compression stages in step (a).

Claim 6

The refrigeration process as defined by claim 1, further comprising the steps of (f1) passing the evaporated liquid fraction of step (f) into a separation zone and separating any unevaporated liquid therefrom and (f2) recovering such liquid prior to returning the evaporated liquid fraction according to step (g).

Claim 7

The refrigeration process as defined by claim 5, wherein said refrigeration is delivered in step (f) to a second fluid and further comprising the step of (i) introducing a vapor fraction of said second fluid into said working fluid.

Claim 8

The refrigeration process as defined by claim 6, further comprising the step (j) of introducing the liquid recovered in step (f2) into said second fluid being refrigerated.

Claim 9

The refrigeration process as defined by claim 6, wherein the vapor fraction of said second fluid is a boil-off gas stream from a LNG storage tank and further comprising the step (n) of passing said vapor fraction countercurrently with the working fluid in said heat exchange step (b), as one of said returning streams.

Claim 10

The refrigeration process as defined by claim 6, wherein said second fluid being refrigerated is liquefied natural gas (LNG).

Claim 11

The refrigeration process as defined by claim 9, wherein the refrigeration is delivered to a boil-off gas stream of a LNG storage tank to condense said gas and further comprising the step (l) of combining a stream of the stored LNG with said boil-off gas stream to be condensed prior to delivery of said refrigeration.

Claim 12

The refrigeration process as defined by claim 10, further comprising the step (m) of separating any uncondensed, highly volatile LNG constituents from the combined boil-off gas stream and stored LNG stream subsequent to refrigeration of said combined streams and introducing said separated, uncondensed LNG constituents into the working fluid.

Claim 13

The refrigeration process as defined by claim 3, wherein said second fluid is a LNG input stream to be pre-cooled before introduction into a LNG storage vessel.

Claim 14

The refrigeration procEss as defined by claim 12, wherein said second fluid further comprises a recirculated stream of LNG from said storage vessel.

Claim 15

Apparatus for low temperature refrigeration comprising a first compressor for compressing a working fluid having at least two components; a first heat exchanger for cooling the compressed working fluid by countercurrent indirect contact with at least one returning stream having a lower temperature; a means for substantially isentropically expanding the cooled working fluid to provide a vapor-liquid mixed working fluid; a first separator for separating the uncondensed vapor fraction from the condensed liquid fraction of the mixed working fluid; conduit means for returning the separated uncondensed vapor fraction through said first heat exchanger countercurrent to said working fluid and for joining said returned vapor fraction with said working fluid at a point before the working fluid enters said first compressor; a second heat exchanger for receiving the separated condensed fraction of the mixed working fluid and for indirectly contacting said working fluid fraction with a second fluid, whereby the working fluid fraction is evaporated and refrigeration is delivered to said second fluid; and conduit means for returning said evaporated working fluid fraction through said first heat exchanger countercurrent to said working fluid and for joining said evaporated working fluid fraction with the working fluid at a point before the working fluid enters said first compressor.

Claim 16

Apparatus for low temperature refrigeration comprising a first compressor for compressing a working fluid having at least two components; a first heat exchanger for cooling the compressed working fluid by countercurrent indirect contact with at least one returning stream having a lower temperature; a means for substantially isentropically expanding the cooled working fluid to provide a vapor-liquid mixed working fluid; a first separator for separating the uncondensed vapor fraction from the condensed liquid fraction of the mixed working fluid; conduit means for returning the separated uncondensed vapor fraction through said first heat exchanger countercurrent to said working fluid and for joining said returned vapor fraction with said working fluid at a point before the working fluid enters said first compressor; a second heat exchanger for receiving the separated condensed fraction of the mixed working fluid and for indirectly contacting said working fluid fraction with a second fluid, whereby the working fluid fraction is evaporated and refrigeration is delivered to said second fluid; and conduit means for returning said evaporated working fluid fraction through said first heat exchanger countercurrent to said working fluid and for joining said evaporated working fluid fraction with the working fluid at a point before the working fluid enters said first compressor.

Claim 17

The apparatus as defined by claim 14, further comprising means for coupling the mechanical energy from said expanding means with said first compressor.

Claim 18

The apparatus as defined by claim 14, further comprising a third compressor for further compressing said working fluid exiting from said first compressor.

Claim 19

The apparatus as defined by claim 14, further comprising a second separator for separating any unevaporated working fluid fraction exiting from said second heat exchanger.

Claim 20

The apparatus as defined by claim 17, further comprising a third heat exchanger for receiving said separated condensed fraction of the mixed working fluid exiting from said second heat exchanger and for further indirectly contacting said fraction with a stream of said second fluid incoming to said storage vessel; and means intermediate said second and third heat exchangers for introducing into said second fluid (1) unevaporated working fluid fraction separated in said second separator, and (2) a portion of said second fluid contained in said storage vessel.

Claim 21

The apparatus as defined by claim 17, further comprising a fourth compressor for compressing the vapor fraction of said second fluid as it exits from the storage vessel; means for conveying a portion of the compressed vapor fraction of said second fluid exiting from said fourth compressor to said second heat exchanger; means for conveying a liquid fraction of said second fluid contained in said storage vessel to said second heat exchanger to be mixed therein with said compressed vapor fraction; a third separator for separating any uncondensed components of said mixed fractions exiting from said second heat exchanger; and means for conveying separated condensed liquid from said third separator back to the storage vessel.

Claim 22

The apparatus as defined by claim 17, further comprising a storage vessel for said second fluid and conduit means for conveying a vapor fraction of said second fluid through said first heat exchanger countercurrent to said working fluid and for joining said vapor fraction with the working fluid at a point before the working fluid enters said first compressor.

Claim 23

The apparatus as defined by claim 20, wherein said conduit means for the vapor fraction includes a second compressor for compressing the vapor fraction exiting from the first heat exchanger.