Methods and apparatuses for liquefying hydrocarbon streams

Abstract

Methods and apparatuses for liquefying hydrocarbon streams are provided. In one embodiment, a method for liquefying a hydrocarbon stream includes expanding the hydrocarbon stream with a turbo expander to form an expanded hydrocarbon stream. The method includes compressing a first refrigerant with the turbo expander. Further, the method includes cooling the expanded hydrocarbon stream with the first refrigerant to form a liquid hydrocarbon stream.

What is claimed is: 
     
         1 . A method for liquefying a hydrocarbon stream, the method comprising the steps of:
 expanding the hydrocarbon stream with a turbo expander to form an expanded hydrocarbon stream;   compressing a first refrigerant with the turbo expander; and   cooling the expanded hydrocarbon stream with the first refrigerant to form a liquid hydrocarbon stream.   
     
     
         2 . The method of  claim 1  further comprising separating the expanded hydrocarbon stream into a liquid stream and a vapor stream, wherein cooling the expanded hydrocarbon stream with the first refrigerant comprises cooling the liquid stream and the vapor stream with the first refrigerant. 
     
     
         3 . The method of  claim 1  further comprising cooling the first refrigerant in a cooling cascade arrangement before cooling the expanded hydrocarbon stream with the first refrigerant. 
     
     
         4 . The method of  claim 1  further comprising cooling the first refrigerant with a second refrigerant before cooling the expanded hydrocarbon stream with the first refrigerant. 
     
     
         5 . The method of  claim 1  wherein compressing the first refrigerant with the turbo expander comprises compressing a mixed refrigerant with the turbo compressor. 
     
     
         6 . The method of  claim 1  further comprising cooling the first refrigerant with a second refrigerant before cooling the expanded hydrocarbon with the first refrigerant. 
     
     
         7 . The method of  claim 1  further comprising:
 cooling the first refrigerant with a second refrigerant before cooling the expanded hydrocarbon stream with the first refrigerant, wherein cooling the first refrigerant with the second refrigerant comprises exchanging heat from the first refrigerant to the second refrigerant at a stage in a cooling cascade arrangement. 
 
     
     
         8 . The method of  claim 7  wherein cooling the expanded hydrocarbon stream with the first refrigerant comprises exchanging heat from the expanded hydrocarbon stream to the first refrigerant at a later stage in the cooling cascade arrangement. 
     
     
         9 . The method of  claim 1  wherein cooling the expanded hydrocarbon stream with the first refrigerant comprises exchanging heat from the expanded hydrocarbon stream to the first refrigerant at a stage in a cooling cascade arrangement. 
     
     
         10 . The method of  claim 9  wherein the cooling cascade arrangement includes a last stage and an upstream stage, and wherein the method further comprises expanding the first refrigerant upstream of the last stage and downstream of the upstream stage. 
     
     
         11 . The method of  claim 9  further comprising passing the first refrigerant through cooling stages in an upstream cooling cascade before passing the first refrigerant through the cooling cascade. 
     
     
         12 . The method of  claim 1  further comprising:
 removing contaminants from the hydrocarbon stream before expanding the hydrocarbon stream to form a contaminant stream; and 
 exchanging heat from the hydrocarbon feed stream to the contaminant stream. 
 
     
     
         13 . A method for liquefying a hydrocarbon stream, the method comprising the steps of:
 transferring heat from a mixed refrigerant to a second refrigerant at an upstream stage in a cooling cascade;   expanding a hydrocarbon stream with a turbo expander to form an expanded hydrocarbon stream; and   transferring heat from the expanded hydrocarbon stream to the mixed refrigerant at a downstream stage in the cooling cascade.   
     
     
         14 . The method of  claim 13  further comprising transferring heat from an entering stream of the mixed refrigerant to an exiting stream of the mixed refrigerant at an additional stage in the cooling cascade. 
     
     
         15 . The method of  claim 13  further comprising:
 compressing the mixed refrigerant with the turbo expander to form a compressed mixed refrigerant; and 
 cooling the compressed mixed refrigerant before feeding the mixed refrigerant to the cooling cascade. 
 
     
     
         16 . The method of  claim 13  further comprising:
 compressing the mixed refrigerant with the turbo expander to form a compressed mixed refrigerant; and 
 cooling the compressed mixed refrigerant in a first cooling cascade before feeding the mixed refrigerant to the cooling cascade. 
 
     
     
         17 . The method of  claim 13  wherein the cooling cascade is located in a cold box, and wherein the method further comprises:
 withdrawing the mixed refrigerant from the cold box after transferring heat from the mixed refrigerant to the second refrigerant; 
 expanding the mixed refrigerant; and 
 after expanding the mixed refrigerant, feeding the mixed refrigerant to the downstream stage in the cooling cascade in the cold box. 
 
     
     
         18 . The method of  claim 13  further comprising:
 circulating the first refrigerant through a first loop passing through the cooling cascade; 
 circulating the second refrigerant through a second loop passing through the cooling cascade; 
 feeding the expanded hydrocarbon stream to the cooling cascade; and 
 withdrawing a liquid hydrocarbon stream from the cooling cascade. 
 
     
     
         19 . The method of  claim 18  wherein
 circulating the mixed refrigerant through the first loop comprises circulating the mixed refrigerant through a first cooling cascade and through a compressor zone of the turbo expander. 
 
     
     
         20 . An apparatus for liquefying a hydrocarbon stream, the apparatus comprising:
 a turbo expander having an expansion zone and a compression zone;   a first refrigerant loop including a cooling cascade, wherein the first refrigerant loop passes through the compression zone of the turbo expander;   a second refrigerant loop, wherein the second refrigerant loop passes through a first stage in the cooling cascade; and   a hydrocarbon stream path, wherein the hydrocarbon stream path passes through the expansion zone of the turbo expander and through a second stage in the cooling cascade.