Process and apparatus for separating hydrocarbon

Abstract

To provide a process for separating hydrocarbons capable of recovering ethane or propane, including improved cold heat recovery enabling a reduction in compressor power. A process for separating hydrocarbons, in which a residual gas enriched with methane or ethane and a heavy fraction enriched with a lower volatile hydrocarbon are separated, includes: a) partially condensing the feed gas by cooling using the residual gas and another refrigerant as a refrigerant, followed by vapor-liquid separation; b) depressurizing and supplying the liquid obtained from step (a) to the distillation column; c) expanding a part or all of the gas obtained from step (a) by an expander to cause partial condensation, followed by vapor-liquid separation; d) feeding the liquid obtained from step (c) to the distillation column after using it as the further refrigerant in step (a); e) feeding a part or all of the gas obtained from step (c) to the distillation column; and f) obtaining the residual gas from the top of the distillation column and the heavy fraction from the bottom of the distillation column.

What is claimed is: 
     
         1 . A process for separating hydrocarbons, wherein a feed gas containing at least methane and a hydrocarbon less volatile than methane is separated into a residual gas enriched with methane and lean in a hydrocarbon less volatile than methane and a heavy fraction lean in methane and enriched with a hydrocarbon less volatile than methane using a distillation column, the process comprising:
 a) partially condensing the feed gas by cooling using the residual gas and one or more other refrigerants as refrigerants, followed by vapor-liquid separation;   b) depressurizing and supplying a liquid obtained from step (a) to the distillation column;   c) expanding a part or all of a gas obtained from step (a) by an expander to cause partial condensation, followed by vapor-liquid separation;   d) feeding a liquid obtained from step (c) to the distillation column after using the liquid as one of the one or more other refrigerants in step (a);   e) feeding a part or all of a gas obtained from step (c) to the distillation column; and   f) obtaining the residual gas from the top of the distillation column and the heavy fraction from the bottom of the distillation column,   wherein a portion of the gas obtained from step (c) is supplied to step (e), the remainder of the gas obtained from step (c) is compressed and cooled by heat exchange with the residual gas to be totally condensed, and the totally condensed liquid is depressurized and supplied to the distillation column.   
     
     
         2 . A process for separating hydrocarbons, wherein a feed gas containing at least ethane and a hydrocarbon less volatile than ethane is separated into a residual gas enriched with ethane and lean in a hydrocarbon less volatile than ethane and a heavy fraction lean in ethane and enriched with a hydrocarbon less volatile than ethane using a distillation column, the process comprising:
 a) partially condensing the feed gas by cooling using the residual gas and one or more other refrigerants as refrigerants, followed by vapor-liquid separation;   b) depressurizing and supplying the liquid obtained from step (a) to the distillation column;   c) expanding a part or all of the gas obtained from step (a) by an expander to cause partial condensation, followed by vapor-liquid separation;   d) feeding the liquid obtained from step (c) to the distillation column after using the liquid as one of the one or more other refrigerants in step (a);   e) feeding a part or all of the gas obtained from step (c) to the distillation column; and   f) obtaining the residual gas from the top of the distillation column and the heavy fraction from the bottom of the distillation column,   wherein a portion of the gas obtained from step (c) is supplied to step (e), the remainder of the gas obtained from step (c) is compressed and cooled by heat exchange with the residual gas to be totally condensed, and the totally condensed liquid is depressurized and supplied to the distillation column.   
     
     
         3 . The process according to  claim 1 , wherein all of a gas obtained from step (a) is supplied to step (c). 
     
     
         4 . The process according to  claim 1 , wherein a portion of the gas obtained from step (a) is supplied to step (c), the remainder of the gas obtained from step (a) is cooled by heat exchange with the residual gas to be totally condensed, and the totally condensed liquid is depressurized and supplied to the distillation column. 
     
     
         5 . A separation apparatus for hydrocarbons, wherein a feed gas containing at least methane and a hydrocarbon less volatile than methane is separated into a residual gas enriched with methane and lean in a hydrocarbon less volatile than methane and a heavy fraction lean in methane and enriched with a hydrocarbon less volatile than methane, the separation apparatus comprising:
 a distillation column discharging the residual gas from the top of the distillation column and the heavy fraction from the bottom of the distillation column;   a heat exchange means for partially condensing the feed gas by cooling, comprising a refrigerant flow path in which the residual gas flows as a refrigerant, and one or more other-refrigerant flow paths in which other refrigerants flow respectively;   a first vapor-liquid separator for vapor-liquid separation of the partially condensed feed gas obtained from the heat exchange means;   a line for supplying the liquid obtained from the first vapor-liquid separator to the distillation column via a pressure reducing valve;   an expander for expanding and partially condensing part or all of the gas obtained from the first vapor-liquid separator;   a second vapor-liquid separator connected to an outlet of the expander;   a line for supplying the liquid obtained from the second vapor-liquid separator to the distillation column via one of the one or more other refrigerant flow paths;   a line for supplying part or all of the gas obtained from the second vapor-liquid separator;   a line for supplying part of the gas obtained from the second vapor-liquid separator to the distillation column;   a compressor for compressing the remainder of the gas obtained from the second vapor-liquid separator;   a condenser for cooling and totally condensing the gas compressed by the compressor by heat exchange with the residual gas;   a pressure reducing valve for decompressing the totally condensed liquid in the condenser; and   a line connecting an outlet of the pressure reducing valve for decompressing the totally condensed liquid in the condenser to the distillation column.   
     
     
         6 . A separation apparatus for hydrocarbons, wherein a feed gas containing at least ethane and a hydrocarbon less volatile than ethane is separated into a residual gas enriched with ethane and lean in a hydrocarbon less volatile than ethane and a heavy fraction lean in ethane and enriched with a hydrocarbon less volatile than ethane, the separation apparatus comprising:
 a distillation column discharging the residual gas from the top of the distillation column and the heavy fraction from the bottom of the distillation column;   a heat exchange means for partially condensing the feed gas by cooling, comprising a refrigerant flow path in which the residual gas flows as a refrigerant, and one or more other-refrigerant flow paths in which other refrigerants flow respectively;   first vapor-liquid separator for vapor-liquid separation of the partially condensed feed gas obtained from the heat exchange means;   a line for supplying the liquid obtained from the first vapor-liquid separator to the distillation column via a pressure reducing valve;   an expander for expanding and partially condensing part or all of the gas obtained from the first vapor-liquid separator;   a second vapor-liquid separator connected to an outlet of the expander;   a line for supplying the liquid obtained from the second vapor-liquid separator to the distillation column via one of the one or more other refrigerant flow paths;   a line for supplying part or all of the gas obtained from the second vapor-liquid separator;   a line for supplying part of the gas obtained from the second vapor-liquid separator to the distillation column;   a compressor for compressing the remainder of the gas obtained from the second vapor-liquid separator;   a condenser for cooling and totally condensing the gas compressed by the compressor by heat exchange with the residual gas;   a pressure reducing valve for decompressing the totally condensed liquid in the condenser; and   a line connecting an outlet of the pressure reducing valve for decompressing the totally condensed liquid in the condenser to the distillation column.   
     
     
         7 . The apparatus according to  claim 5 , comprising a line for feeding all of the gas obtained from the first vapor-liquid separator to the expander. 
     
     
         8 . The apparatus according to  claim 5 , comprising:
 a line for feeding part of the gas obtained from the first vapor-liquid separator to the expander;   a condenser for cooling and totally condensing the remainder of the gas obtained from the first vapor-liquid separator by heat exchange with the residual gas;   a pressure reducing valve for decompressing the totally condensed liquid in the condenser; and   a line connecting an outlet of the pressure reducing valve for decompressing the totally condensed liquid in the condenser to the distillation column.   
     
     
         9 . The apparatus according to  claim 6 , comprising a line for feeding all of the gas obtained from the first vapor-liquid separator to the expander. 
     
     
         10 . The apparatus according to  claim 6 , comprising:
 a line for feeding part of the gas obtained from the first vapor-liquid separator to the expander;   a condenser for cooling and totally condensing the remainder of the gas obtained from the first vapor-liquid separator by heat exchange with the residual gas;   a pressure reducing valve for decompressing the totally condensed liquid in the condenser; and   a line connecting an outlet of the pressure reducing valve for decompressing the totally condensed liquid in the condenser to the distillation column.   
     
     
         11 . The process according to  claim 2 , wherein all of the gas obtained from step (a) is supplied to step (c). 
     
     
         12 . The process according to  claim 2 , wherein a portion of the gas obtained from step (a) is supplied to step (c), the remainder of the gas obtained from step (a) is cooled by heat exchange with the residual gas to be totally condensed, and the totally condensed liquid is depressurized and supplied to the distillation column. 
     
     
         13 . The process according to  claim 1 , wherein the one or more other refrigerants in step (a) comprise a side stream of the distillation column and/or an external refrigerant. 
     
     
         14 . The process according to  claim 2 , wherein the one or more other refrigerants in step (a) comprise a side stream of the distillation column and/or an external refrigerant. 
     
     
         15 . The process according to  claim 13 , the external refrigerant comprises a propane refrigerant. 
     
     
         16 . The process according to  claim 14 , the external refrigerant comprises a propane refrigerant. 
     
     
         17 . The apparatus according to  claim 5 , wherein the one or more other refrigerants flowing respectively in the one or more other-refrigerant flow paths comprise a side stream of the distillation column and/or an external refrigerant. 
     
     
         18 . The apparatus according to  claim 6 , wherein the one or more other refrigerants flowing respectively in the one or more other-refrigerant flow paths comprise a side stream of the distillation column and/or an external refrigerant. 
     
     
         19 . The apparatus according to  claim 17 , wherein the line for supplying the liquid obtained from the second vapor-liquid separator to the distillation column via one of the one or more other-refrigerant flow paths supplies the liquid obtained from the second vapor-liquid separator to the one of the one or more other-refrigerant flow paths directly without undergoing pressure reduction. 
     
     
         20 . The apparatus according to  claim 18 , wherein the line for supplying the liquid obtained from the second vapor-liquid separator to the distillation column via one of the one or more other-refrigerant flow paths supplies the liquid obtained from the second vapor-liquid separator to the one of the one or more other-refrigerant flow paths directly without undergoing pressure reduction. 
     
     
         21 . The apparatus according to  claim 17 , wherein the external refrigerant comprises a propane refrigerant. 
     
     
         22 . The apparatus according to  claim 18 , wherein the external refrigerant comprises a propane refrigerant.