IL28868A

IL28868A - Process for liquefaction of natural gas and transportation by marine vessel

Info

Publication number: IL28868A
Application number: IL28868A
Authority: IL
Original assignee: Williams V; Simonds O
Priority date: 1966-11-02
Filing date: 1967-10-31
Publication date: 1971-06-23
Also published as: FR1542232A; NO124796B; BE705963A; OA02527A; ES346651A1; GB1170329A; US3400547A; JPS535321B1; NL6714932A

Description

S Patents Form 3 PATENTS AND DESIGNS f FOR LIQUEFACTION OF NATURAL GAS AND TRANSFORATION BY MARINE n State United States of United Ste do hereby dec 1 are the nature of this invention and in what manner the same is to be to be particularly described aud in and by the following There two classes of natural gas produced from gas wells and natural gas produced association with crude Much of this gas production occurs in vast in the ing countries and cannot be transported economically b pipeline to these world Because of only a fraction of the natural gas resources are at usefully It is one thing to flare or release natural gas at great it is mother to reduce it to manageable transport store and sell it in competition with other One way to deal with a large volume of gas is to liquefy natural which is largely cannot be liquefied by simply the as has been the case critical temperature of methane is which is the temperature above which it impossible to liquefy methane regardless of the sure At atmospheric the methane will be at its normal boiling point of the techniques of liquefying end handling natural gas are within the scope of the of cryogenic The liquefaction of natural gas requires the removal of energy in the form of sensible and latent This process can be accomplished by mechanical refrigeration where heat is by a series of re rigerants to a ect ambient level This method uses what is referred to as a cascade cycle or Another method is that of compressing and expanding the using This is known as an expander The most widely used cycle the cascaded vapor pression This based on refrigeration uses commercially available refrigerants whose thermodynamic and of natural gas is most economical in its liquefied As a natural gas will occupy approximately l 600th of its gaseous volume under standard conditions cu ft of gas at ard temperature and pressure 1 cu ft liquid at normal boiling of interests show need fo storage of liquefied natural The area interest lies in transporting gas from to areas in insulated whereby storage depots at both the ield site and the market site are In such th storage facility is essentially a surge tank smoothing put the nonuniform demand and fuel delivery In this it is not preserve the liquefied natural in the tank for long nce it is passed on to distribution within a short period of The second area of interest is in the continued growth and expansion of the natural gas industry which has resulted in the need storage of large volumes of gas near metropolitan areas to meet winter this liquefied natural gas is stored for relativel long periods of time and used during only a few days of the heat influx must be held to a A great deal of research is at present being devoted to finding and efining industrial processes which will make continuous use of the large amounts of The main sibilities here lie in the development of major industrial cations as the production by air rectification of liquid to make the maximum use of cold it Tho cold should which is very expensive compared to mild refrigeration the low temperatures needed in the production of cryogenic The overall cost of refrigeration in the liquefaction of the natural gas is a major part of tho final sales There another manner of approaching the use of the available This would be to consider the as an inherent part of the process thus making it the not selling or something derived from but building its use into the process technology reduce the investment and operating costs and thus to increase the of a natural gas distribution Summary of the By means of this a process has been devised for liquefaction of nitrogen at the market site against the liquefied natural gas and returning the liquid nitrogen in the insulated transport tanks in the marine vessel to the field site where it is employed in liquefaction of the natural which is then loaded on marine vessel shipment to the The availability of the cold in the liquid nitrogen reduces the equipme at The cycle is a constant repetition of these two shipping liquid gas to the market and liquid nitrogen back to the and the refrigeration effect at both and the markot sites of the lique gas shipped to the site to liquefy tho gas shipped from the Nitrogen may be separated from air at the market site by air recti thus producing which at the is of great use in the chemical and metallurgical auxiliary liquefaction means are needed at the field site and all of the energy necessary for li uefaction o the natural as is rovided throu h the li u d It is also possible to employ liquid air because of its major proportion of nitrogen instead of liquid nitrogen in this cycle for sh to the field because of its high percentage of has substantially similar thermal to Zn this case the liquid storage tanks would require purging with nitrogen to remove the oxygen containing atmosphere to avoid possible explosive mixtures of natural gas and This purged nitrogen is obtainable from an auxiliary suppl or from fractionation of the liquid air either at the field site or the market The large refrigeration complexes required to liquefy the natural gas at the field site are thus and wise the capital equipment located in the foreign field site is reduced to a very The process is initiated for each ship by sending outbound from market site to field site one cargo of liquid nitrogen which can be accumulated by any economical means in the above features are objects of this invention and further objects will appear in the detailed description which and will be otherwise apparent to those skilled in the Fo the purpose of there are shown in the accompanying drawings examples of the process of this It is to be understpod that these drawings are for the example only and that the invention is not limited the drawingsj Figure 1 is a flow sheet showing a typical site process for liquefaction of natural i Figure 2 is a flow sheet showing a typical market site process for the liquefaction of Figure 4 is a graph showing the heat transfer in the market sito heat Figure 5 is a graph showing a typical pressure ship at the field sito for the proportion of nitrogen to needed for Figure 6 is a graph showing the vapor pressure curves Figure 7 is a flow sheet of a modi ied process ing higher pressures and showing a typical field site process for liquefaction of natural Figure 8 is a block diagram showing the arrangement of the equipment employed i the sheet of Figure Figure a graph illustrating th flow of heat in the field site exchangers Figure 10 is a flow sheet of the modified example ing higher pressures and showing a typical market site 11 is block diagram showing the arrangement of the equipment for the marke site process of Figure Figure 12 is a graph showing the flow o heat in the market site exchangers of Figure Figure 13 is a schematic view of the tankers employed in the transfer of nitrogen from the market site to the field site and the return tanker shipment transferring liquefied natural gas from the ield site to the market pisclosure Natural which is comprised principally of methane with small percentages of and minimal percentages of carbon dioxide and is in many places in the but in most cases the markets for this gas ar industrial countries remote from the eld many situations pipe lines used to transport tho gas from the source to the there are circumstances where line transportation is technically and economically Such cases for the transportation of Arabian or Algerian gas to England or and Venezuelan or Mexican gas to Florida or the east coast of the United or the Worth Sea It has been proposed to liquefy natural gas at the site and take it by barge or ship to the market At the market site it would be and pumped into the bution 2n tho instant invention the great refrigeration able in the liquid natural gas is employed to liquefy nitrogen at the market site by evaporating the natural gas in heat exchange relation with tho The liquid nitrogen then returned to the transport tanks in insulated marine although it will be understood that other insulated such as railroad tank cars and the may be for transport to th At the field site the liquefied nitrogen turned in tho or other is employed in liquefying the natural which is then returned in the tanker to the By this invention the marine vessel is not deadheaded when it is returned from the market site back to the field and the cycle a constant repetition of taking the liquid natural gas to market and liquid nitrogen back to the Nitrogen is separated from air at the market such as by air ca and oxygen gas is produced as a which is of great use in the chemical and metallurgical The then becomes a valuable and a premium factor for the cycle of this In considering the illustration of the it although above stated other insulated such tank truck and the also bo 1 The basis chosen for illustration of this invention is tha receipt at the site of one pound cf which is the major constituent of natural gas and for practical poses is considered in calculations this process and the two terms be used In the air fication at the market site the may as an pounds will produce pounds of nitrogen and of purity The market site process for nitrogen liquefaction obtained through heat exchange relation with the by evaporation from the liquefied gas is carried out on the of the use of one pound of methane to pounds of The methane vaporizes and moves or is pressed into the market pipe for The liquid i nitroge produced is put into the insulated storage tanks of the tanker and s back to the field Xn this tion about percent of the nitrogen is lost by thereby del vering about of the nitrogen liquefied at the market site to the field The field site cycle evaporates the liquefied nitrogen against condensing methane and the liquid methane is then put in to the insulated storage tanks of the This cycle uses about to pounds of nitrogen to pounds of The lower 1 pound of nitrogen 1 pound of methane represents the optimum for ship construction but requires a greater pressure cf methane employed at the field In the limit for tank filling storage capacity on tha shipping about 2 pounds of nitrogen can be carried per pound of As the pressure is reduced at the field represent economies in the ratio of nitrogen to is increased deviates from values for ship Figure 5 shows a typical curv for the cycles shown in Figures 1 and 2 for the effect of pressure on the relat on being returned to the market in the tanker loses about by so pound is delivered to the market site where it is evaporated in heat exchange relation nitrogen to produce liquid nitrogen shipment of the liquefied nitrogen in the same tanker back to the The program and process consists of repetition of these basic Some intermediate storage may be employed at both the market and the field sites for transfe poses through insulated tanks employed to prevent loss of the site flow sheet of Figure 1 and the arket site flow sheet of Figure the cycles employed at these two sites are In the site it will be noted that the features employed use liquefied nitrogen in heat exchange tionship with the natural followed by expansion and quent cooling of the after which the nitrogen is again used heat exchange relation with the natural gas to obtain the fullest possible effect of refrigeratio The nitrogen may be vented to the atmosphere upon the completion of the field site process or used in any other fashion In the market site process the fullest possible effect of tion from the liquefied natural is employed by sending pressed nitrogen in heat relation with the liquefied natural gas expanding a major portion of this to reduce the pressure and the nitrogen to ortion of the nitrogen is drawn off and used in heat before it is passed into heat relation with the fied natural this manner a highly efficient use refrigeration is made available to liquefy the At the field the liquid nitrogen is ou the storage tanks of the or other and is replaced with liquid It is a signi of two nitrogen and in process of this that the quantities demanded in the heat change stages on a mass basis for heat balance are also acceptable balance o a liquid volume The design of the various elements in the cycles of this invention is in accordance with the thermodynamic properties of the individual data given in the examples are dealt with graphically to satisfy the requirements of the first and second of thermodynamics and also to have real cant temperature differences that permit of economic design of the heat Field Site Process The field site process of Example 1 is shown in Figure 1 and graphically shown for the field site exchanger heat flow values in Figure the field site liquefied nitrogen at atmospheric pressure is returned by the insulated tanker from the market site to the field and is pumped to working sure by a liquid The cold nitrogen heat exchanges currently against methane which thus is brought to a condensed liquid state at atmospheric This liquid methane is then put into the tanker for shipping tothe market make one pound of methane available at the market pound is shipped he field and pound is lost through vaporization or vented used as in an engine or In the process of Figure liquid nitrogen is charged to an intermediate insulated storage tank the insulated tank pounds of liquefied nitrogen is charged at and atmospheric psia to pump 18 where it is compressed to 800 for purpose of to The still liquid nitrogen is then charged through line 20 to heat exchanger where it passes in countercurrent relationship to natural The nitrogen passes through the heat exchanger in pass 24 and leaves at 55 and about 800 psia where it is expanded through a turbine expander 26 to 50 psia and The nitrogen under these is charged through line 28 to pass 29 in the heat and in the process is heated at at 50 psia and is vented in line The natural gas from the field site in the amount of pounds at and at 800 psia is charged into the heat exchanger in line It goes through the heat exchanger in pass 34 and leaves as liquefied natural gas at atmospheric pressure at The thus liquefied natural gas is charged in line 36 to insulated storage tank 12 and from it can be charged to the carrier such tanker or the In the the turbine expander delivers BTU of which must be absorbed and the heat exchanger transfers 385 In many cases the field site natural pressure is below 800 psia and the turbine work may be convenientl used in a compressor to raise the natural gas pressure to 800 As an example of alternate pressures and quantities of nitrogen employed the pounds of nitrogen may be employed at 1500 in which case the turbine expanders will deliver 89 BTU of work and the heat exchanger will transfer 375 Market Site Process The market site process of Example 1 is shown site 1 pound of liquefied natural gas is taken from the carrier in line 40 and charged to the intermediate tank One pound of liquefied natural gas is taken from storage tank line and charged to the heat exchanger 44 at and atmospheric The liquefied natural gas passes through pass 46 the heat exchanger and in heat exchange relation with the nitrogen leaves in line 47 at where it can be passed to distribution systems or storage tanks or the like for ultimate use and sale at the market The nitrogen employed in this system can be obtained from air as will be well understood in the and process leaves available oxygen for industrial Nitrogen in the amount of pounds is since this provides pounds at the field site since there is loss of nitrogen in shipping back to the fidd through evaporation or the This nitrogen is charged through the line 48 at and at 250 psia through pass 50 in the heat vhere it is cooled to To this is pound of a compressed flash stream of so that in line pounds nitrogen are The nitrogen is cooled and densed to liquid at while the methane vaporizes at and superheats to at 15 The liquid nitrogen in line 52 is subcooied from to against pounds of flash gas which warms from to line This process is effected in heat exchanger The gas slip stream is then compressed from 15 psia at in compressor 58 to 250 psia at and is added in line 60 to the feed stream of pounds of which originally enters the process through line The pull off from the separator bottle in lire 64 provides pounds of liquid nitrogen at atmospheric pressure and at temperature of The liquefied nitrogen is charged from line 64 to the nitrogen refrigerant is then charged through heat exchanger which along with heat exchanger 114 and all used in the nitrogen refrigerant stream as will be later are in heat exchange relationship with the methane heat exchanger the heat exchanger 110 the nitrogen at a temperature of passes through turbine expander 120 to a reduced pressure of and a reduced temperature of The turbine pander 120 is matched with a compressor 122 which is employed to the methane in the feed stream as will be later described The nitrogen refrigerant from the turbine expander 120 then passed through heat exchanger 112 in further heat exchange with the methane heat exchanger 118 from which it is then introduced to another turbine expander 124 where the pressure is reduced to 30 psia and the temperature is reduced to about The turbo expander 124 is matched with a compressor 126 in the nitrogen which later the downstream nitrogen as will be From the turbine expander the nitrogen stream is duced into heat exchanger 114 in heat exchange relation with the methane heat exchanger 118 in the same fashion as the previous From the heat exchanger the nitrogen refrigerant is introduced to the compressor 126 where it is compressed and then cooled in aftercooler An additional compressor 130 is also employed to further increase the pressure and work is vided through turbine expander which will be further scribed in the nitrogen the compressor further cooling is effected in cooling unit 133 after w the nitrogen stream is passed through heat exchanger 134 to obtain a ature of The nitrogen is then introduced at 200 psia to the turbine expander 132 it is expanded to 18 psia and This nitrogen is then passed through he last heat exchanger 116 heat exchange relation with the methane heat exchanger e nitrogen refrigerant leaving heat exchanger then passes through heat exchanger and is exhausted through line 138 for any eventual desired usage 18 psia and methane stream is intreduced into the field site process through line 140 at 800 psia and in an for the process shown of pounds The methane is further compressed in the 122 with work being through the nitrogen turbine expander as previously Auxiliary refrigeration is provided through cooler 142 and methane is then introduced at and at a pressure of 1500 psia into the methane heat exchanger After leaving the heat exchanger the consequent cooling by the four nitroge refrigerant heat exchang units 114 and the methane is passed through heat exchanger 108 for a phase of heat exchanger cooling in heat exchange relation with the nitrogen heat exchanger The nitrogen i3 passed through the turbine expander 104 for further reductio in pressure to 15 psia and a temperature of provide the pounds of in lique work provided in the turbine i expander 104 is to drive the pump as previously Figure 8 the site process block diagram with a matching of the and turbine expanders in simplified further the heat transfer in the various heat exchange units tie work provided in the matched turbine panders and compressor The graph of Figure 9 illustrates the ollowing of the second law of thermodynamics in the eld site process b having real temperature differences with the refrigerant nitrogen always at a lower temperature than the The employed bo diaphragm cooled machines with a ratio of isothermal to isentropic ideal work3 of but corrected to actual work by the The isentropic work is at Market Site Process market site process of 2 is shown in 11 arid 10 is a schematic diagram and sheet of the nitrogen and methane while Figure 11 is a block diagram illustrating the work output and input ing of the turbine expanders and compressors to provide for efficiency and economy in the Figure 12 is a showing the heat between the nitrogen and methane provide a real temperature di between these streams and illustrates colder temperature of the methane for abstraction of heat from the nitrogen the market site process are based on of nitrogen feed at 1 atmosphere pressure and against pound of methane in liquefied which is being vaporised and the market site the is vaporized and delivered into the pipe line grid at 600 The heat required for this vaporisation is used to condense nitrogen gas or which is then returned to the eld as source of eration to quefy the natural Of the two the eld site and the market the latter is the more difficult to There are workable t being mixed gas heat straight heat pumping this nitrogen heat all of which are novel in the invention as described with air employed there is also the possibility for fractionation the cycle to deliver liquid nitrogen and oxygen gas an added tha process as shown in Figures 10 and pound of methane in saturated liquid at psi and is introduced in tha process through line 150 where it is split into a first in line 152 and a stream in line Tha first stream in tha of pound methane is passed through heat exchanger which is in heat exchange relation heat exchangers and as be later The after passing heat exchanger is at a temperature of when it is introduced into it is compressed to 600 psia and a of in The 262 is matched with a turbine is provided in the second stream of as will be more clearly described This matching that the 165 output the turbo expander is supplied to the pressor 162 part of the powe 164 is combined in final outpu with a second stream output to provide pound methane at 600 psi and The second liquid methane stream in an amount of pounds methane is pressured by 168 to 1500 psia and a of of the required fo the pump is vided through turbine 170 in the nitrogen will be clearly described The liquid methane pumped by the pump 163 is introduced through line 172 to methane heat which is in heat exchange relation with nitrogen heat 176 and as more clearly described below in the sion of the nitrogen stream The methane from heat exchanger 174 is introduced at a temperature of to superheater exchanger 176 where it is to a of The exhaust gas from a makeup power which may be used for the pressor ISO in the nitrogen to be later may be used as a source heat in the su erheater exchan The methane the superheater exchanger is introduced to the turbine pander previously for to 600 psi at temperature where it is then introduced to the final output 166 for distribution to the natural gas and the pipeline grid at GOO The nitrogen introduced into the process through line 130 in tho amount cf pounds nitrogen at 15 psia and This is passed through heat exchange 176 with cycled nitrogen it is introduced in line to compressor The nitrogen in line is at 15 psia and and is pressed by the compressor to 265 psia and a of total stream the nitroge introduced the system the recycled nitrogen is in the of pounds combined stream in line 184 is passed to heat exchanger and is then passed through exchangers 160 and for further The nitrogen passed through the turbine 170 for reduction in pressure and further cooling and introduced into separator the separator liquefied nitrogen in th amount of pounds is stream 190 at a pressure of 15 psia and for delivery to the tanker bound for the field A recycle nitrogen stream taken the separator 183 in line 192 and passed recycle heat exchangers and 153 for combination with the initial feed nitrogen in as previously This provides further cooling for the Figure 12 graphically shows the real temperature in the with refrigerant nitrogen and s employed in the process always being colder than the nitrogen which heat is being the process the compressors utilized in the cycle may be cold suction high gas density centrifugal are high in this particularly for the axial flow machines and can be taken as net powe supply to the market site process may be in the form of a makeup machine which may be a gas turbine for the compressor 180 as previously the exhaust being heat source in the superheater exchanger The heat exchanger unit and 160 may be a multipass condenser The maximum pressure of psia used in these units allow the use of pressure The heat exchanger 186 194 for the nitrogen may also be of this while the higher pressure heat exchanger 176 and 178 may be of the wound mandrel Heat exchanger the low pressure gaseous nitrogen heat exchanger ma be installed in duplicate form with the of heat transfer surface from heat exchanger 174 to act as a water and carbon dioxide knockout surface the incoming pressure nitrogen or when one of the duplicate surfaces is rimmed the heat exchanger surface is to the other duplicate in the called heat in the cryogenic rimmed surface is heated and preparatory to the next By means expensive drying system on the feed nitrogen is Shipping stage of the nitrogen refrigerant and natural gas is on a mass For analysis on the basis of 1 pound of methane and nitrogen there would be shipped from the market site to the pounds liquid nitrogen liquid in the I outbound which would provide cubic feet of The receipt at the field allowing for some is considered as pounds of liquid In the reverse ment from the field site to the market pounds of liquid methane would be provided on the outbound which would constitute cubic feet of liquid since the density of liquid is of the liquid At the site there would be after allowing for abut pound of liquid methane or natural Figure 13 there is shown a schematic diagram trating the aforementioned which may be used in both Examples 1 and Th outbound vessel from the market to the eld site carrying the liquid nitrogen is indicated by the reference numeral while the return vessel from ld site to the market site carrying the liquefied methane is indicated by the reference numeral After arrival from the market site at the field site with all four hold tanks only full in the vessel hold tank containing pound liquid would be pump transferred to a field site land storage Hold tank 2 liquid nitrogen would be pumped into the methane liquifier proces and pounds of liquid representing of total charge of be put into empty hold tank This process would be repeated for each hold tank in turn and then finally the 0 25 pound of liquid nitrogen in the field site land storage tank would go into the methane liquefier process to deliver the pound liquid methane representing the last quarter charge of liquefied to hold tank The ship is filled with the pound liquid used a base for purpose of for its trip from the field site to the k te It is to ba that the land storage w ch no field site turn around lost for tho liquid is cubic feet This is o eighth the volumetric equivalent of the liquid methane ship of four hold at cubic feet each or cubic double tanks could bo built for 2 and 3 hold tanks in the middle of the vessel and they could then bo with liquid nitrogen fo the trip to the field while tanks 1 and 4 would empty or head on this purging of the vessel or hold storage tanks at both the field cite and the market site deserves At tha field site a tank which contained liquid air over which the equilibrium vapor associated with that liquid air is maintained all of that liquid have a vapor of nitrogen content at one atmosphere According to k this would hava vapor would with any amount of methane be for the eld no special purging conditions are on re the tanks with liquid when they a emptied of liquid air providing tho above are tha market tho liquid methane after from the vessel tanks will leave a hold full of methane Since the hold is relatively warm compared to the of air e the cool down of the hold tank would initially vaporise come of the liquid air charge and this direct itself across tho tip of tho flammable it would be necessary to perform the tank cool down with liquid nitrogen at tho market as the liquid methane is pumped from ship the overlaying methane can be nitrogen vapor to an essentially nitrogen vapor So long as the pumped out tank has a methane content of leas than n the vapor liquid air can be in directly and have the tank space in the Various changes and modi ications may be made within this process as will bo readily apparent to those skilled in the As an o is principally composed of can used process instead of and speaking of nitrogen it is to be understood that other gases air in which the major constituent is nitrogen can be v the therma characteristics of the gas are similar o suc changes and modi are within the scope teaching of th s as by the claims appended insufficientOCRQuality

Claims

1. 28868/2 Claims; ΐ. A method foi» transportation of natural gas from a field site to a market site, which method comprises liquefying natural gas at the field site by heat exchange with a liquid refrigerant which is evaporated to obtain a refrigeration effect, said refrigerant being composed principally of nitrogen, transferring the liquefied natural gas to an insulated transport carrier for transport to the market site, transferring to the field site liquefied refrigerant from an insulated transport carrier, which carrier is also used as a carrier for liquefied natural gas, for use in the step of liquefying natural gas at the field site, said liquefied refrigerant being obtained b passing liquefied natural gas in heat exchange relation with the refrigerant gas to liquefy the refrigerant, said liquid refrigerant being compressed before it is passed in heat exchange relation with the natural gas at the field site and after said heat exchange being expanded to a lowe pressure and lower temperature and passing the cooled refrigerant in a second heat exchange stage into heat exchange relation with the natural gas. 2i A method according to claim 1 in which the liquid refrigerant transported to the field site is in the ratio of about 1·0 pounds to 2·ΐ pounds for 1.05 pounds of liquefied natural gas transferred from the ield site to the market site. 28868/2 3. A method according to claim 1 or claim 2 in which the quantities of refrigerant and natural gas passed in heat exchange relation on a mass basis for heat balance are also in balance on a liquid volume basis. k* A method according to any one of the preceding claims In which the expansion of the refrigerant is carried out in a turbine expander. 5. A method according to any one of the preceding claims wherein the refrigerant at the market site is split into a liquefied product stream and a recycle stream* the recycle stream being passed in heat exchange relation with the main stream of refrigerant before the pressure is reduced and is then compressed and added to the refrigerant gas passed in heat exchange relation with the liquefied natural gas to form the main stream of refrigerant. 6· A method according to any one of the preceding claims wherein said natural gas is compressed at the field site before it is passed in heat exchange relation with the refrigerant and after said heat exchange is expanded to a lower pressure» the work provided in the expansion of the natural gas being used in the compression of the refrigerant and the work provided in the expansion of the refrigerant being used in the compression of the natural gas* 7. A method according to claim 6 in which the refrigerant is passed in heat exchange relation with the natural gas in a multiplicity of passes from substantially the same temperature. 8. A method according to any one of the preceding claims wherein said lique ied natural gas "being split at the market site into first and second streams, said first stream being passed in heat exchange relation with the refrigerant and subsequently compressed for discharge in a natural gas product stream, said second stream being compressed and passed in heat exchange relation with the refrigerant, said second stream being subsequently expanded to a lower pressure and combined in the natural gas product stream. 9· A method according to claim 8 in which the work provided in the expansion of the second stream of natural gas is used in the compression of the first stream. iiO* A method according to claim 8 or claim 9 in work which the ^provided in the expansion of the refrigerant is used in the compression of the second stream and the work provided in the expansion of the second stream of natural gas is used in the compression of the first stream* 1 . The method of claim 1 in which the natural gas is split into a multiplicity of separate paths and the compressed liquid refrigerant after being passed in heat exchange relation with the first path of the natural gas is expanded in a multiplic ty of stages and after each of said expansions is passed in heat exchange relation with the other separate split paths of natural gas. - :28δ6¾/2' 12. The method of claim 11 in which work provided by an expansion of the refrigerant in an earlier stage is employed to compress the refrigerant before any stage of expansion. Attorney for Applicants