Method of treating a hydrocarbon stream comprising methane, and an apparatus therefor

Abstract

A wet hydrocarbon stream comprising at least methane and water is dried thereby forming an effluent stream and a wet disposal stream. Before drying the wet hydrocarbon stream is cooled by indirectly heat exchanging against the effluent stream followed by indirectly heat exchanging against an auxiliary refrigerant stream. The effluent stream is subsequently passed to a further heat exchanger where the effluent stream is cooled against an evaporating refrigerant stream which is subsequently discharged from the further heat exchanger as a spent refrigerant stream. A refrigerant stream in compressed condition is formed by compressing the spent refrigerant and the auxiliary refrigerant stream that is discharged from the indirectly heat exchanging with the wet hydrocarbon stream, whereby allowing direct heat exchanging between the discharged auxiliary refrigerant stream and the spent refrigerant stream before said compressing.

1 . Method of treating a hydrocarbon stream comprising methane, the method comprising:
 providing a wet hydrocarbon stream at a first temperature, said wet hydrocarbon stream comprising at least methane and water;   cooling of the wet hydrocarbon stream thereby lowering the temperature from the first temperature to a second temperature, wherein said cooling of the wet hydrocarbon stream comprises indirectly heat exchanging against an effluent stream followed by indirectly heat exchanging against an auxiliary refrigerant stream;   withdrawing from the wet hydrocarbon stream, in a water removal device at the second temperature, a wet disposal stream comprising water from the wet hydrocarbon stream and an effluent stream comprising the wet hydrocarbon stream from which the wet disposal stream has been removed;   passing the effluent stream to a further heat exchanger, said passing of the effluent stream to the further heat exchanger comprising heating the effluent stream by indirectly heat exchanging against the wet hydrocarbon stream in a wet feed heat exchanger;   cooling the effluent stream in the further heat exchanger by indirect heat exchanging against an evaporating refrigerant fraction;   cycling a refrigerant in repetitive cycles, wherein a single pass of the refrigerant through the cycle comprises the following consecutive steps:
 providing a refrigerant stream in a compressed condition; 
 passing the refrigerant stream in said compressed condition through a condenser whereby at least partially condensing the refrigerant stream in said compressed condition, thereby forming source refrigerant stream comprising a liquid phase at a refrigerant temperature and a refrigerant pressure; 
 obtaining the evaporating refrigerant fraction comprising expanding at least a part of a part of the source refrigerant stream to a pressure lower than the refrigerant pressure; 
 passing the evaporating refrigerant fraction to the further heat exchanger; 
 forming a spent refrigerant from the evaporating refrigerant fraction by absorbing heat from at least the effluent stream in the further heat exchanger; 
 discharging said spent refrigerant from the further heat exchanger; 
 passing said spent refrigerant to a refrigerant compressor; 
 discharging from the refrigerant compressor said refrigerant stream in compressed condition; 
   wherein during said single pass the cycle further comprises the following consecutive steps:
 splitting the source refrigerant stream into said auxiliary refrigerant stream and said part of the source refrigerant stream wherein said auxiliary refrigerant stream comprises at least a part of said liquid phase; 
 indirectly heat exchanging the auxiliary refrigerant stream against said wet hydrocarbon stream whereby passing heat from the wet hydrocarbon stream to the auxiliary refrigerant stream as part of said cooling of the wet hydrocarbon stream whereby discharging a discharged auxiliary refrigerant stream containing said heat from the wet hydrocarbon stream; 
 directly heat exchanging the discharged auxiliary refrigerant stream with the spent refrigerant being passed to the refrigerant compressor; 
 forming the refrigerant stream in compressed condition by compressing the spent refrigerant and the discharged auxiliary refrigerant stream whereby allowing said direct heat exchanging before said compressing in each single pass. 
   
     
     
         2 . The method according to  claim 1 , wherein said condenser is provided in the form of an ambient heat exchanger and wherein providing of the wet hydrocarbon stream comprises passing said wet hydrocarbon stream through a wet feed ambient heat exchanger thereby heat exchanging said wet hydrocarbon stream against ambient and thereby providing the wet hydrocarbon stream at said temperature equal to the first temperature;
 and wherein said condensing of said refrigerant stream in said compressed condition comprising heat exchanging said refrigerant stream in said compressed condition against ambient, thereby providing said source refrigerant stream at a refrigerant temperature equal to a third temperature, which is within 10° C. from the first temperature.   
     
     
         3 . The method according to  claim 2 , further comprising:
 admitting the effluent stream into the further heat exchanger via a first tube bundle inlet;   
       and wherein said obtaining of said evaporating refrigerant fraction during said single pass of the refrigerant through the cycle comprises:
 passing said part of the source refrigerant stream to the further heat exchanger while maintaining its temperature essentially equal to the third temperature; 
 admitting the part of the source refrigerant stream into the further heat exchanger via least one second tube bundle inlet; and 
 cooling the part of the refrigerant stream in the further heat exchanger against the evaporating refrigerant fraction; 
 
       followed by said expanding. 
     
     
         4 . The method according to  claim 3 , wherein the temperature of the effluent stream in the first tube bundle inlet is essentially the same as the temperature of the effluent stream that was reached by said indirectly heat exchanging against the wet hydrocarbon stream at essentially said first temperature in the wet feed heat exchanger, and wherein the temperature of the effluent stream and the temperature of the part of the source refrigerant stream in the first and second tube bundle inlets in the further heat exchanger are less than 10° C. apart from each other. 
     
     
         5 . The method according to  claim 1 , wherein during said single pass after said splitting and before said indirectly heat exchanging of the auxiliary refrigerant stream against said wet hydrocarbon stream, 
       the auxiliary refrigerant stream is expanded. 
     
     
         6 . The method according to  claim 1 , wherein the temperature of the effluent stream is matched to the first temperature as close as the warm end approach temperature of the wet feed heat exchanger by said heating of the effluent stream by indirectly heat exchanging against the wet hydrocarbon stream in the wet feed heat exchanger during said passing of the effluent stream to the further heat exchanger. 
     
     
         7 . The method according to  claim 1 , wherein the water removal device comprises a separator vessel for separating precipitated components from the wet hydrocarbon stream and, downstream thereof, a sorbing device sorbing at least water. 
     
     
         8 . The method according to  claim 1 , wherein the first temperature of the wet hydrocarbon stream, before said indirect heat exchanging against the effluent stream, is controlled by heat exchanging against said ambient stream; and wherein the at least part of the source refrigerant stream has a temperature within 10° C. from the first temperature. 
     
     
         9 . The method according to  claim 1 , wherein said directly heat exchanging of the discharged auxiliary refrigerant stream with the spent refrigerant comprises injecting the discharged auxiliary refrigerant stream into the spent refrigerant being passed from the further heat exchanger to the refrigerant compressor. 
     
     
         10 . The method according to  claim 9 , further comprising passing the discharged auxiliary refrigerant stream and the spent refrigerant both through a single suction drum, drawing from the suction drum a refrigerant compressor vapour feed stream and passing the refrigerant compressor vapour feed stream to the refrigerant compressor without condensing any part of the refrigerant compressor vapour feed stream during any single pass from the suction drum to the refrigerant compressor. 
     
     
         11 . The method according to  claim 1 , wherein the spent refrigerant is discharged from the further heat exchanger at a fourth temperature and wherein the discharged auxiliary refrigerant stream immediately after its indirectly heat exchanging against the wet hydrocarbon stream is at a fifth temperature, wherein said fifth temperature is lower than the forth temperature. 
     
     
         12 . The method according to  claim 1 , wherein the auxiliary refrigerant stream flows at an stream flow rate and wherein the spent refrigerant stream flows at a spent refrigerant stream flow rate, wherein the auxiliary refrigerant stream flow rate is less than 10% of the spent refrigerant stream flow rate. 
     
     
         13 . The method according to  claim 1 , wherein the wet hydrocarbon stream comprises natural gas, and wherein at least part of the effluent stream is cooled to form liquefied natural gas. 
     
     
         14 . Apparatus for treating a hydrocarbon stream comprising methane, the apparatus comprising:
 a supply conduit for providing a wet hydrocarbon stream that comprises at least methane and water;   a wet feed heat exchanger connected to the supply conduit, and arranged to receive the wet hydrocarbon stream from the supply conduit, and to lower the temperature of the wet hydrocarbon stream by indirect heat exchanging against an effluent stream;   an auxiliary heat exchanging arrangement arranged to further lower the temperature of the wet hydrocarbon stream discharged from the wet feed heat exchanger by indirect heat exchanging against an auxiliary refrigerant stream;   a water removal device, arranged to receive the wet hydrocarbon stream downstream of the auxiliary heat exchanging arrangement, and comprising a wet disposal stream outlet for discharging a wet disposal stream comprising water from the wet hydrocarbon stream, and a vapour outlet for discharging an effluent stream comprising the wet hydrocarbon stream from which the wet disposal stream has been removed;   a further heat exchanger provided with a first tube bundle inlet for receiving the effluent stream from the water removal device, and a first tube bundle outlet for discharging a cooled hydrocarbon stream, wherein the first tube bundle outlet is internally in the further heat exchanger connected with the first tube bundle inlet via a first tube bundle, and wherein said first tube bundle is arranged in a heat exchanging relationship with an evaporating refrigerant fraction inside the further heat exchanger;   first connecting means connecting the vapour outlet of the water removal device with the first tube bundle inlet of the further heat exchanger, which first connecting means passes through the wet feed heat exchanger in indirect heat exchanging interaction with the wet hydrocarbon stream;   a refrigerant circuit arranged to cycle a refrigerant in repetitive cycles, said refrigerant circuit, when being considered following the flow of the refrigerant during a single pass through the refrigerant circuit starting from a discharge outlet of a refrigerant compressor, comprising:
 a condenser arranged to receive a refrigerant stream in a compressed condition and to extract heat from the refrigerant stream in said compressed condition whereby at least partially condensing the refrigerant stream in said compressed condition thereby forming a source refrigerant stream comprising a refrigerant stream in a compressed condition and comprising a liquid phase; 
 a first expansion device arranged to receive and expand at least a part of a part of the source refrigerant stream thereby obtaining the evaporating refrigerant fraction; 
 the further heat exchanger arranged to receive the evaporating refrigerant fraction from the first expansion device, in which further heat exchanger a cooling zone is provided wherein the evaporating refrigerant fraction is arranged in indirect heat exchanging contact with at least the effluent stream in the first tube bundle whereby the evaporating refrigerant fraction is transformed into spent refrigerant, said further heat exchanger comprising a shell outlet to discharge the spent refrigerant from the cooling zone; 
 a spent refrigerant line connecting the shell outlet to the refrigerant compressor, the discharge outlet of the refrigerant compressor arranged to discharge said refrigerant stream in said compressed condition; 
 a splitter, arranged to split the source refrigerant stream into the auxiliary refrigerant stream and the part of the source refrigerant stream, wherein said auxiliary refrigerant stream comprises at least a part of said liquid phase; 
 a combiner arranged to bring the spent refrigerant and a discharged auxiliary refrigerant consisting of the auxiliary refrigerant discharged from the auxiliary heat exchanging arrangement together in direct heat exchanging contact, whereby the auxiliary heat exchanging arrangement is arranged in the auxiliary refrigerant stream between the splitter and the combiner, said combiner being between the auxiliary heat exchanging arrangement and the refrigerant compressor, wherein said refrigerant stream in compressed condition contains both the discharged auxiliary refrigerant stream and the spent refrigerant stream. 
   
     
     
         15 . The apparatus according to  claim 14 , further comprising:
 a wet feed ambient heat exchanger arranged in the supply conduit arranged to receive the wet hydrocarbon stream and to exchange heat between the wet hydrocarbon stream and an ambient stream wherein the wet feed heat exchanger is connected to the supply conduit via the wet feed ambient heat exchanger, wherein there is essentially no separate heat exchanger present between the wet feed ambient heat exchanger and the wet feed heat exchanger;   wherein the first connecting means is essentially free from any separate heat exchanger between the wet feed heat exchanger and the first tube bundle inlet of the further heat exchanger;   wherein said condenser is provided in the form of an ambient heat exchanger;   wherein the further heat exchanger is further provided with at least one second tube bundle outlet for discharging at least one cooled refrigerant stream, wherein the at least one second tube bundle outlet is internally in the further heat exchanger connected with the second tube bundle inlet via a second tube bundle arranged in the cooling zone;   second connecting means connecting the condenser with the second tube bundle inlet, for receiving at least the part of said source refrigerant stream, said second connecting means being essentially free from any separate heat exchanger.