Method of preparing a cooled hydrocarbon stream and an apparatus therefor

Abstract

A partially condensed hydrocarbon feed stream is sent to a column. An overhead vapour hydrocarbon stream from the column is then partially condensed by indirect heat exchanging against an expanded cooling fluid flowing through a first section of a cold side heat exchanging channel. The cooling fluid consists of a mixed refrigerant composition, and liquid from the expanded cooling fluid is continuously transformed to vapour thereby forming a residual liquid portion of not evaporated expanded cooling fluid. The residual liquid is used to progressively condense the hydrocarbon feed stream to produce the partially condensed hydrocarbon feed stream that is sent to the column, by allowing the hydrocarbon feed stream to lose heat to the residual liquid passing through a second section of the cold side heat exchanging channel. The liquid component that is condensed out of the overhead vapour hydrocarbon stream is used as reflux for the column.

What is claimed is: 
     
         1 . A method of preparing a cooled hydrocarbon stream from a hydrocarbon feed stream, comprising:
 circulating a cooling fluid consisting of a mixed refrigerant composition in a loop along a circulation direction wherein, in consecutive order,
 passing the cooling fluid through an expander to provide an expanded cooling fluid, 
 allowing the expanded cooling fluid to progressively evaporate as the expanded cooling fluid flows through a cold side heat exchanging channel, by allowing the expanded cooling fluid to flow through a first section of the cold side heat exchanging channel in contact with a first cold surface of a first heat exchanging fluid barrier whereby liquid from the expanded cooling fluid is continuously transformed to vapour thereby forming a residual liquid portion of not evaporated expanded cooling fluid, and subsequently allowing the residual liquid portion to continue its flow through a second section of the cold side heat exchanging channel in contact with a second cold surface of a second heat exchanging fluid barrier whereby the residual liquid is continuously vaporized, 
 compressing the vapour and the vaporized residual liquid to provide a compressed vapour, 
 transferring heat from the compressed vapour to ambient, and 
 closing the loop by again passing the cooling fluid through the expander; 
   progressively cooling a hydrocarbon feed stream as it flows through a second warm section of a warm side heat exchanging channel in contact with a second warm surface of said second heat exchanging fluid barrier, thereby forming a pre-cooled hydrocarbon feed stream consisting of a mixture of vapour and liquid phases, by allowing the hydrocarbon feed stream to lose heat to the evaporating residual liquid passing through the second section of the cold side heat exchanging channel;   passing the pre-cooled hydrocarbon feed stream into a column;   drawing an overhead vapour hydrocarbon stream from the column;   progressively condensing the overhead vapour hydrocarbon stream as it flows through a first warm section of the warm side heat exchanging channel in contact with a first warm surface of said first heat exchanging fluid barrier, until the overhead vapour hydrocarbon stream is partially condensed and forms a partially condensed hydrocarbon stream, by allowing the overhead vapour hydrocarbon stream to lose heat to the evaporating expanded cooling fluid passing through the first section of the cold side heat exchanging channel;   separating the partially condensed hydrocarbon stream into a liquid component and a vaporous component, wherein the vaporous component comprises the cooled hydrocarbon stream;   feeding the liquid component into the column as reflux stream.   
     
     
         2 . The method of  claim 1 , wherein the first heat exchanging fluid barrier and the second heat exchanging fluid barrier are both located within a single heat exchanger. 
     
     
         3 . The method of  claim 1 , wherein the first warm section, comprising the first heat exchanging fluid barrier, is located within a first heat exchanger and the second warm section, comprising the second heat exchanging fluid barrier, is located within a second heat exchanger, wherein the first heat exchanger is fluidly interconnected with the second heat exchanger to allow fluid communication from the first section to the second section of the cold side heat exchanging channel. 
     
     
         4 . The method of  claim 3 , wherein the residual liquid portion is passed from the first section of the cold side heat exchanging channel to the second section of the cold side heat exchanging channel without changing the pressure of the residual liquid portion by more than 1 bar anywhere between these first and second sections. 
     
     
         5 . The method of  claim 3 , wherein the residual liquid portion is passed from the first section of the cold side heat exchanging channel to the second section of the cold side heat exchanging channel without changing the composition of the residual liquid portion anywhere between these first and second sections. 
     
     
         6 . The method of  claim 3 , wherein the residual liquid portion is passed from the first section of the cold side heat exchanging channel to the second section of the cold side heat exchanging channel without changing the flow rate of the residual liquid portion anywhere between these first and second sections. 
     
     
         7 . The method of  claim 3 , wherein during any single pass of cooling fluid through the loop the cooling fluid does not pass through any phase separator between the expander and the second section of the cold side heat exchanging channel. 
     
     
         8 . The method of  claim 1 , wherein during any single pass of cooling fluid through the loop the cooling fluid does not pass through any phase separator between the expander and the second section of the cold side heat exchanging channel. 
     
     
         9 . The method of  claim 1 , further comprising, between said transferring of heat from the compressed vapour to ambient and said closing the loop by again passing the cooling fluid through the expander, progressively cooling the compressed vapour as it flows through an auxiliary warm side heat exchanging channel, whereby flowing through the auxiliary warm side heat exchanging channel comprises:
 flowing through a third warm section in contact with a third warm surface of a third heat exchanging fluid barrier, by allowing the compressed vapour to lose heat to the evaporating residual liquid passing through the second section of the cold side heat exchanging channel and subsequently   flowing through a fourth warm section in contact with a fourth warm surface of a fourth heat exchanging fluid barrier, by allowing the compressed vapour having passed through the third warm section to lose heat to the evaporating expanded cooling fluid passing through the first section of the cold side heat exchanging channel.   
     
     
         10 . The method of  claim 1 , further comprising indirectly heat exchanging the vaporous component from the partially condensed hydrocarbon stream against an evaporating main cooling fluid. 
     
     
         11 . The method of  claim 10 , further comprising circulating the main cooling fluid in a main refrigeration loop, wherein the main refrigeration loop is separate from the loop in which the cooling fluid is circulated. 
     
     
         12 . The method of  claim 11 , wherein said compressing of the vapour and the vaporized residual liquid is performed with a first compressor train comprising at least one first compressor, and wherein said circulating of the main cooling fluid comprises compressing the main cooling fluid in a second compressor train comprising at least one second compressor and, further wherein a common drive shaft mechanically drives the at least one first compressor and any other compressor in the first compressor train as well as the at least one second compressor and any other compressor in the second compressor train. 
     
     
         13 . The method of  claim 1 , wherein the hydrocarbon feed stream comprises natural gas and wherein the cooled hydrocarbon stream is a liquefied natural gas stream. 
     
     
         14 . An apparatus for preparing a cooled hydrocarbon stream from a hydrocarbon feed stream, comprising:
 a cooling fluid consisting of a mixed refrigerant composition;   a loop containing the cooling fluid for circulating the cooling fluid in a circulation direction, which loop, described in consecutive order in the circulation direction, comprises:
 an expander to provide an expanded cooling fluid, 
 a cold side heat exchanging channel comprising a first section and a second section, wherein the first section is fluidly connected to the expander to receive the expanded cooling fluid, wherein the first section comprises a first heat exchanging fluid barrier with a first cold surface facing into the first section of the cold side heat exchanging channel and arranged to allow passage of the expanded cooling fluid in contact with the first cold surface of the first heat exchanging fluid barrier, and wherein the second section of the cold side heat exchanging channel is arranged to receive at least a residual liquid portion from the first section of the cold side heat exchanging channel, and wherein the second section comprises a second heat exchanging fluid barrier with a second cold surface facing into the second section of the cold side heat exchanging channel and arranged to allow passage of the residual liquid in contact with the second cold surface of the second heat exchanging fluid barrier, 
 a first compressor train in fluid communication with at least the second section of the cold side heat exchanging channel and comprising at least one first compressor for compressing vaporised expanded cooling fluid and vaporized residual liquid originating from the cold side heat exchanging channel to provide a compressed vapour, 
 an ambient heat exchanger arranged to receive the compressed vapour and to transfer heat from the compressed vapour to ambient, and 
 a cooling fluid connection fluidly extending between the ambient heat exchanger and the expander by which the loop is closed; 
   a warm side heat exchanging channel comprising a first warm section and a second warm section, whereby a first warm surface of said first heat exchanging fluid barrier faces into the first warm section, which first warm surface is in heat exchanging contact with the first cold surface through the first heat exchanging fluid barrier; and whereby a second warm surface of said second heat exchanging fluid barrier faces into the second warm section of the warm side heat exchanging channel, which second warm surface is in heat exchanging contact with the second cold surface through the second heat exchanging fluid barrier;   a hydrocarbon feed stream;   a source of the hydrocarbon feed stream;   a column, comprising an overhead discharge outlet, and comprising a first column inlet and a second column inlet, which column is fluidly connected to the source of the hydrocarbon feed stream via the first column inlet and via the second warm section of the warm side heat exchanging channel to allow passage of the hydrocarbon feed stream from the source to the column in contact with the second warm surface whereby forming a pre-cooled hydrocarbon feed stream consisting of a mixture of vapour and liquid phases;   a reflux separator comprising a separator inlet and a liquid discharge outlet and a vapour discharge outlet, whereby said reflux separator is in fluid communication with the column via the overhead discharge outlet, the separator inlet and via the first warm section of the warm side heat exchanging channel to allow passage of an overhead vapour hydrocarbon stream from the column to the reflux separator in contact with a first warm surface, whereby said first warm section of the warm side heat exchanging channel extends between the overhead discharge outlet and the separator inlet;   a reflux conduit fluidly connecting the reflux separator and the column via the liquid discharge outlet and the second column inlet;   a cooled hydrocarbon stream conduit connected to the vapour discharge outlet of the reflux separator arranged to remove a vaporous component from the reflux separator which vaporous component comprises the cooled hydrocarbon stream.   
     
     
         15 . The apparatus of  claim 14 , wherein the first heat exchanging fluid barrier and the second heat exchanging fluid barrier are both located within a single heat exchanger. 
     
     
         16 . The apparatus of  claim 14 , wherein the first warm section, comprising the first heat exchanging fluid barrier, is located within a first heat exchanger and the second warm section, comprising the second heat exchanging fluid barrier, is located within a second heat exchanger, wherein the first heat exchanger is fluidly interconnected with the second heat exchanger to allow fluid communication from the first section to the second section of the cold side heat exchanging channel. 
     
     
         17 . The apparatus of  claim 16 , wherein the loop does not comprise any phase separator between the expander and the second section of the cold side heat exchanging channel when the loop is considered in a circulation direction and in a single pass. 
     
     
         18 . The apparatus of  claim 14 , wherein the loop does not comprise any phase separator between the expander and the second section of the cold side heat exchanging channel when the loop is considered in a circulation direction and in a single pass.