Method and apparatus for controlling a regrigerant compressor, and use thereof in a method of cooling a hydrocarbon stream

Abstract

A method of controlling one or more refrigerant compressors ( 12 ) for one or more gaseous streams ( 10 ) at a normal operating temperature. At least one refrigerant compressor ( 12 ) has a vapour recirculation line ( 30 ). A compressor feed stream ( 10 a ) is provided from a combination of a vapour recirculation stream ( 30 ) from the vapour recirculation line ( 30 ) and an at least partly evaporated refrigerant stream ( 8 ). The compressor feed stream ( 10 a ) is passed through a suction drum ( 11 ) to provide a compressor gaseous stream ( 10 ), which is passed through the refrigerant compressor (s) ( 12 ). The inlet temperature T 1 of the compressor gaseous stream ( 10 ) is determined, and cooling of a refrigerant stream is controlled in response to temperature T 1 to provide the compressor gaseous stream ( 10 ) at the normal operating temperature of at least one refrigerant compressor ( 12 ).

1 . A method of controlling one or more refrigerant compressors for one or more gaseous streams at a normal operating temperature, at least one refrigerant compressor having a vapour recirculation line, the method at least comprising the steps of:
 (a) providing a compressor feed stream from a combination of a vapour recirculation stream from the vapour recirculation line and an at least partly evaporated refrigerant stream;   (b) passing the compressor feed stream through a suction drum to provide a compressor gaseous stream;   (c) passing the compressor gaseous stream through the refrigerant compressor(s);   (d) determining the temperature T 1  of the compressor gaseous stream at the inlet of at least one refrigerant compressor; and   (e) cooling of one or more of the group consisting of: the vapour recirculation stream, the at least partly evaporated refrigerant stream, the compressor feed stream and the compressor gaseous stream; said cooling being controlled in response to the temperature T 1  to seek to provide the compressor gaseous stream at the normal operating temperature of at least one refrigerant compressor.   
     
     
         2 . The method as claimed in  claim 1 , comprising at least two refrigerant compressors, and two, three, four or five compressor gaseous streams. 
     
     
         3 . The method as claimed in  claim 2 , wherein two or more of the compressor gaseous streams have mutually different pressures. 
     
     
         4 . The method as claimed in  claim 3 , wherein four compressor gaseous streams at four different pressures pass through two refrigerant compressors. 
     
     
         5 . The method as claimed in  claim 1 , wherein the refrigerant stream is essentially comprised of propane. 
     
     
         6 . The method as claimed in  claim 1 , wherein at least one of the refrigerant compressors has multiple pressure sections. 
     
     
         7 . The method as claimed in  claim 1 , wherein said controlling comprises maintaining the temperature T 1  of the compressor gaseous stream within +10° C. of the normal operating temperature of the refrigerant compressor. 
     
     
         8 . The method as claimed in  claim 1 , wherein said cooling being controlled in response to the temperature T 1  comprises controlling the operation of one or more valves which influence the cooling of one or more of the streams defined in step (e). 
     
     
         9 . The method as claimed in  claim 8 , wherein the one or more valves control one or both of the flow and expansion of a cold stream or cooling stream used for cooling of one or more of the steams defined in step (e). 
     
     
         10 . The method as claimed in  claim 1 , wherein said cooling in step (e) comprises cooling against a cooler stream or a cooling stream in a heat exchanger. 
     
     
         11 . The method as claimed in  claim 1 , wherein said cooling in step (e) comprises adding one or more cold streams or cooling streams to said one or more streams of the group. 
     
     
         12 . The method as claimed in  claim 11 , further comprising the steps of:
 (f) dividing the compressed refrigerant stream into at least a first continuing stream and a vapour recirculation stream;   (g) cooling the first continuing stream to provide an at least partially condensed first continuing stream;   (h) dividing the at least partially condensed first continuing stream into a second continuing stream and a second recirculation stream;   (i) allowing at least part of the second continuing stream to evaporate to form the at least partly evaporated refrigerant stream of step (a);   (j) using the second recirculation stream as one or more of the cold streams or cooling streams.   
     
     
         13 . The method as claimed in  claim 12 , wherein the second recirculation stream is added to the vapour recirculation stream. 
     
     
         14 . The method as claimed in  claim 1 , where step (e) comprises cooling of the vapour recirculation stream. 
     
     
         15 . A method for the cooling of a hydrocarbon stream, comprising:
 passing a compressor gaseous stream through at least one refrigerant compressor having a vapour recirculation line, to provide a compressed refrigerant stream;   providing a hydrocarbon feed stream;   cooling the hydrocarbon feed stream by heat exchange against a refrigerant stream that has passed through the at least one refrigerant compressor to provide a cooled hydrocarbon stream and at least part of an at least partly evaporated refrigerant stream;   providing a compressor feed stream from a combination of a vapour recirculation stream from the vapour recirculation line and the at least partly evaporated refrigerant stream;   passing the compressor feed stream through a suction drum to provide the compressor gaseous stream;   determining the temperature T 1  of the compressor gaseous stream at the inlet of at least one refrigerant compressor; and   cooling of one or more of the group consisting of: the vapour recirculation stream, the at least partly evaporated refrigerant stream, the compressor feed stream and the compressor gaseous stream; said cooling being controlled in response to the temperature T 1  to seek to provide the compressor gaseous stream at the normal operating temperature of the at least one refrigerant compressor.   
     
     
         16 . The method as claimed in  claim 15 , further comprising the step of liquefying the hydrocarbon feed stream, thereby providing a liquefied hydrocarbon stream. 
     
     
         17 . An apparatus for controlling one or more refrigerant compressors for one or more gaseous streams at a normal operating temperature, the apparatus at least comprising:
 a suction drum to receive a compressor feed stream from a combination of a vapour recirculation stream and the at least partly evaporated refrigerant stream, and to provide a compressor gaseous stream;   at least one refrigerant compressor having an inlet for the compressor gaseous stream and an outlet for providing a compressed refrigerant stream;   one or more pathways for re-circulating part or all of the compressed refrigerant stream as a vapour recirculating stream through the refrigerant compressor; and   a temperature controller to determine the temperature T 1  of the compressor gaseous stream at the inlet of the refrigerant compressor, and to control either:   (i) one or more coolers to cool one or more of the group consisting of the vapour recirculation stream, the at least partly evaporated refrigerant stream, the compressor feed stream and the compressor gaseous stream, to seek to provide the compressor gaseous stream at the normal operating temperature; or   (ii) one or more streams cooler than the vapour recirculating stream to be combined with one or more of the group consisting of: the vapour recirculation stream, the at least partly evaporated refrigerant stream, the compressor feed stream and the compressor gaseous stream, to seek to provide the compressor gaseous stream at the normal operating temperature; or   (iii) one or more at least partially liquid streams to be combined with one or more of the group consisting of: the vapour recirculation stream, the at least partly evaporated refrigerant stream, the compressor feed stream and the compressor gaseous stream, to seek to provide the compressor gaseous stream at the normal operating temperature; or   (iv) a combination of two of more of (i)-(iii);   
       in response to the temperature T 1 . 
     
     
         18 . Use of the apparatus as claimed in  claim 17  for cooling of a hydrocarbon stream comprising cooling the hydrocarbon feed stream by heat exchange against a refrigerant stream that has passed through the at least one refrigerant compressor to provide a cooled hydrocarbon stream and at least part of the at least partly evaporated refrigerant stream. 
     
     
         19 . The method as claimed in  claim 2 , wherein said two or more refrigerant compressors consist of two refrigerant compressors. 
     
     
         20 . The method as claimed in  claim 19 , wherein four compressor gaseous streams at four mutually different pressures pass through the two refrigerant compressors. 
     
     
         21 . The method as claimed in  claim 2 , wherein said two or more refrigerant compressors consist of four refrigerant compressors. 
     
     
         22 . The method as claimed in  claim 21 , wherein four compressor gaseous streams at four mutually different pressures pass through the four refrigerant compressors. 
     
     
         23 . The method as claimed in  claim 9 , further comprising the steps of:
 (f) dividing the compressed refrigerant stream into at least a first continuing stream and a vapour recirculation stream;   (g) cooling the first continuing stream to provide an at least partially condensed first continuing stream;   (h) dividing the at least partially condensed first continuing stream into a second continuing stream and a second recirculation stream;   (i) allowing at least part of the second continuing stream to evaporate to form the at least partly evaporated refrigerant stream of step (a);   (j) using the second recirculation stream as one or more of the cold streams or cooling streams.   
     
     
         24 . The method as claimed in  claim 23 , wherein the second recirculation stream is added to the vapour recirculation stream. 
     
     
         25 . The method as claimed in  claim 16 , wherein the hydrocarbon stream is a natural gas stream and the liquefied hydrocarbon stream is LNG. 
     
     
         26 . A method of liquefying a hydrocarbon stream using two or more refrigerant compressors, comprising:
 providing at least one refrigerant compressor having a vapour recirculation line;   providing a hydrocarbon feed stream;   cooling the hydrocarbon feed stream by heat exchange against a refrigerant stream to provide a cooled hydrocarbon stream and at least part of an at least partly evaporated refrigerant stream;   providing a compressor feed stream from a combination of a vapour recirculation stream from the vapour recirculation line and the at least partly evaporated refrigerant stream;   passing the compressor feed stream through a suction drum to provide a compressor gaseous stream;   passing the compressor gaseous stream through the at least one refrigerant compressor, to provide a compressed refrigerant stream;   obtaining the refrigerant stream for said cooling the hydrocarbon feed stream from said compressed refrigerant stream;   determining the temperature T 1  of the compressor gaseous stream at the inlet of the at least one refrigerant compressor; and   cooling of one or more of the group consisting of: the vapour recirculation stream, the at least partly evaporated refrigerant stream, the compressor feed stream and the compressor gaseous stream;   controlling said cooling of the one or more streams of the group, comprising controlling the operation of one or more valves with influence the cooling of one or more of the one or more of the streams in the group, in response to the temperature T 1  to seek to provide the compressor gaseous stream at the normal operating temperature of the at least one refrigerant compressor.   
     
     
         27 . The method according to  claim 26 , wherein said cooling of said one or more streams of the group at least comprises cooling the vapour recirculation stream.