Gas processing methodology utilizing reflux and additionally synthesized stream optimization

Abstract

Gas processing methodology for high efficiency recovery of propane and/or ethane from a natural gas feed stream. The method is conducted without turboexpansion, and in some embodiments, without the use of a refrigeration system. A natural gas stream is processed to have gas and liquid portions. The gas portions are cooled and flow to a refluxed absorber column and the liquid portions flow to a lower pressure distillation column. Bottoms of the absorber column are depressurized into a separator, with the separator overhead vapor being used as a source of absorber column reflux. The separator liquids are fed into the lower pressure distillation column and the distillation column overhead vapor stream is used to cool the feed and/or reflux streams. The overhead vapour stream from the lower pressure distillation can be recycled to the absorber, either as a recycle or a source of reflux.

We claim: 
     
         1 . A method of processing natural gas to recover selected hydrocarbons contained therein, comprising:
 cooling and partially condensing a natural gas feed stream;   separating the cooled and partially condensed stream into a plurality of liquid streams and gas streams;   passing said gas streams into a fractionator column and said liquid streams into a distillation column;   recovering an overheads stream from said distillation column;   treating said overheads stream to form at least one overhead stream;   passing said at least one overhead stream into said fractionator column as a recycle stream or source of reflux liquids;   contacting said source of reflux liquids as a reflux stream with said natural gas feed stream in said fractionator column to liquefy hydrocarbon components present in said natural gas feed stream or recycling said recycle stream; and   recovering a bottoms stream from said fractionator column.   
     
     
         2 . The method as set forth in  claim 1 , wherein said overheads stream is treated to form a plurality of overhead streams. 
     
     
         3 . The method as set forth in  claim 1 , wherein said bottoms stream from said fractionator are depressurized in a separator. 
     
     
         4 . The method as set forth in  claim 3 , further including the step of utilizing an intermediate pressure vessel as said separator. 
     
     
         5 . The method as set forth in  claim 4 , further including treating an intermediate pressure vessel overheads stream to form at least one reflux stream. 
     
     
         6 . The method as set forth in  claim 5 , further including the step of passing at least one reflux stream into said fractionator column as a source of reflux. 
     
     
         7 . The method as set forth in  claim 3 , further including the step of depressurizing the separator bottoms into said distillation column and recovering selected hydrocarbon components from said bottoms stream. 
     
     
         8 . The method as set forth in  claim 1 , wherein said method is conducted absent the use of turboexpansion as a unit operation. 
     
     
         9 . The method as set forth in  claim 1 , wherein said treating said at least one overheads stream to form a plurality of overhead streams includes forming a plurality of reflux streams at different pressures. 
     
     
         10 . The method as set forth in  claim 1 , further including the step of varying fluid flow rates at least between said fractionator column and said distillation column. 
     
     
         11 . The method as set forth in  claim 1 , wherein said method has a turndown range between 30% and 100% of flowrate in said method where 99% recovery is maintained. 
     
     
         12 . The method as set forth in  claim 1 , wherein said method utilizes at least cooling, heat exchange, depressurization and separation unit operations, said method further including initially determining the composition of the natural gas; and selecting a sequence of said unit operations based on said composition of said natural gas for energy optimization in effecting said method. 
     
     
         13 . A gas processing plant, comprising:
 a separator for receiving a cooled and partially condensed natural gas feed stream to separate said feed stream into a liquid stream and a gas stream;   a fractionator column for receiving said gas stream and reflux streams produced from a distillation column;   an intermediate pressure vessel in fluid communication with said fractionator column for producing an overheads stream, said overheads stream being utilized in said fractionator column as said reflux streams to liquefy hydrocarbons present in said feed stream, said fractionator column producing a bottoms stream which is depressurized into a distillation column to recover selected hydrocarbons; and   a distillation column in fluid communication with said intermediate pressure vessel, said intermediate pressure vessel producing a bottoms stream for feeding into said distillation column.   
     
     
         14 . The gas processing plant as set forth in  claim 13 , further including a network of heat exchangers positioned to recover and distribute heat from all streams of said streams during processing. 
     
     
         15 . The gas processing plant as set forth in  claim 13 , wherein said overheads stream is compressed, cooled and divided into a plurality of overhead streams. 
     
     
         16 . The gas processing plant as set forth in  claim 13 , wherein at least one of said overhead streams is compressed, cooled and depressurized for use in said fractionator column as a reflux stream. 
     
     
         17 . The gas processing plant as set forth in  claim 13 , wherein said overhead streams are pressurized at a different pressure relative to one another. 
     
     
         18 . The gas processing plant as set forth in  claim 13 , wherein said overhead streams may exist in a gas, partially condensed, or liquid state. 
     
     
         19 . A method of processing natural gas with a fractionator column and distillation column in fluid communication to recover selected hydrocarbons contained therein, comprising a plurality of operations, comprising:
 a separation operation where a natural gas stream is processed to form a liquid stream and a gas stream which are separated;   an intermediate pressurization operation fluid communication with said fractionator column for producing an overheads stream;   an overheads processing and distribution operation where an overheads stream is recovered from said distillation column and processed into a plurality of overhead streams distributed into predetermined locations in said fractionator column;   a distillation operation in said fractionator column where said natural gas feed stream contacts said overhead streams to liquefy hydrocarbon components present in said natural gas stream; and   a bottoms recovery and processing operation where a bottoms stream is recovered from said fractionator column and processed by depressurization directly in said distillation column in the absence of turboexpansion to recover selected hydrocarbons.   
     
     
         20 . The method as set forth in  claim 19 , wherein said method further includes heat exchange operations between each of the separation, overheads processing and distribution, refrigeration and bottoms recovery operations to recover and distribute heat between all streams associated with said operations. 
     
     
         21 . The method as set forth in  claim 19 , wherein said distillation column is operated as a deethanizer. 
     
     
         22 . The method as set forth in  claim 19 , wherein said distillation column is operated as a demethanizer. 
     
     
         23 . The method as set forth in  claim 19 , wherein said operations are modifiable to recover ethane, propane, hydrocarbons, or a combination thereof. 
     
     
         24 . The method as set forth in  claim 19 , wherein said separation operation includes cooling and partially condensing said natural gas feed stream. 
     
     
         25 . The method as set forth in  claim 19 , wherein said bottoms recovery and processing operation includes introducing said bottoms stream at a pressure of between 500 kPag and 2000 kPag into said distillation column relative to a pressure of between 2000 and 7000 kPag prior to introduction.