Reflux of demethenization columns

Abstract

A process for the separation of the components of a gas mixture to be treated comprising methane, nitrogen and at least one hydrocarbon having at least two carbon atoms, or a mixture of these hydrocarbons, including introducing the gas mixture to be treated into a first distillation column, thereby producing, in the column bottom, a first liquid stream enriched in hydrocarbon having at least two carbon atoms and, at the column top, a first gas stream enriched in methane; and introducing the first liquid stream enriched in hydrocarbon having at least two carbon atoms resulting from stage a) into a second distillation column, thereby producing, at the top of this column, a second gas stream rich in methane and, in the bottom of this column, a second liquid stream comprising at least 85 mol % of the hydrocarbons having at least two carbon atoms initially present in the mixture to be treated.

1 .- 13 . (canceled) 
     
     
         14 . A process for the separation of the components of a gas mixture to be treated comprising methane, nitrogen and at least one hydrocarbon having at least two carbon atoms, or a mixture of these hydrocarbons, comprising the following stages:
 a) introducing the gas mixture to be treated into a first distillation column, thereby producing, in the column bottom, a first liquid stream enriched in hydrocarbon having at least two carbon atoms and, at the column top, a first gas stream enriched in methane;   b) introducing the said first liquid stream enriched in hydrocarbon having at least two carbon atoms resulting from stage a) into a second distillation column, thereby producing, at the top of this column, a second gas stream rich in methane and, in the bottom of this column, a second liquid stream comprising at least 85 mol % of the hydrocarbons having at least two carbon atoms initially present in the mixture to be treated;   
       wherein a portion of the second gas stream rich in methane resulting from stage b) at the outlet of the top of the second distillation column is compressed to a pressure at least greater by 1 bar than the pressure of said second distillation column and then condensed in order to be introduced, for one portion, into the upper part of the first distillation column and, for the other portion, into the upper part of the second distillation column in order to carry out the reflux of said distillation columns. 
     
     
         15 . The process as claimed in  claim 14 , wherein a portion of the second gas stream is reduced in pressure in a turbine to a pressure at least lower by 1 bar than the pressure of said second distillation column. 
     
     
         16 . The process as claimed  claim 14 , wherein the nitrogen content of said second gas stream is at least 1.5 times lower than the nitrogen content of the first gas stream. 
     
     
         17 . The process as claimed in  claim 14 , further comprising stage c): introduction of said first gas stream enriched in methane resulting from stage a) into a denitrogenation unit in order to separate the nitrogen. 
     
     
         18 . The process as claimed in  claim 17 , wherein the second gas stream resulting from stage b) is not treated by the denitrogenation unit. 
     
     
         19 . The process as claimed in  claim 18 , wherein from 5 mol % to 30 mol % of the methane initially present in the gas mixture to be treated is comprised in the first liquid stream enriched in hydrocarbon having at least two carbon atoms resulting from stage a). 
     
     
         20 . The process as claimed in  claim 14 , wherein from 10 mol % to 20 mol % of the methane initially present in the gas mixture to be treated is comprised in the first liquid stream) enriched in hydrocarbon having at least two carbon atoms resulting from stage a). 
     
     
         21 . The process as claimed in  claim 14 , further comprising, prior to stage a), the following stages:
 at least partially condensing said gas mixture to be treated in order to obtain a two-phase mixture;   injecting the vapor phase from said two-phase mixture into said first distillation column;   injecting the liquid phase from said two-phase mixture into said second distillation column.   
     
     
         22 . The process as claimed in  claim 14 , wherein the gas stream, extracted from the first distillation column in stage a), comprises at most half of the amount of hydrocarbons having more than two carbon atoms present in the feed gas. 
     
     
         23 . The process as claimed in  claim 14 , wherein the liquid, extracted from said first distillation column during stage a), comprises at least 90 mol % of the hydrocarbons having at least two carbon atoms and preferably at least 95%. 
     
     
         24 . The process as claimed in  claim 14 , wherein said gas mixture to be treated comprises 70 mol % of methane, at least 4 mol % of nitrogen and 2 mol % of hydrocarbons having at least two carbon atoms. 
     
     
         25 . The process as claimed in  claim 14 , wherein, during stage b), the liquid stream enriched in hydrocarbon having at least two carbon atoms resulting from stage a) is introduced into said second distillation column at a theoretical stage below the top of this said second column. 
     
     
         26 . The process as claimed in  claim 14 , wherein said gas stream resulting from stage b) is extracted directly from said second distillation column) at a pressure of greater than 20 bara and comprises 95 mol % of methane.