Process and device for cryogenic air fractionation

Abstract

The process and the device serve for cryogenic air fractionation, in particular for supplying an oxygen-enriched (product stream to an oxyfuel power plant. The distillation column system for nitrogen/oxygen separation has a high-pressure column ( 26 ) and a low-pressure column ( 32 ). The high-pressure column ( 26 ) and the low-pressure column ( 32 ) are thermally coupled via a condenser-evaporator ( 37 ). Feed air ( 1 ) is compressed in an air compressor ( 3 ), cooled at least in a first post-cooler ( 6 ) and purified in a purification device ( 22 ), cooled in a main heat exchanger ( 23 a, 23 b, 23 c ) and introduced at least in part ( 25, 29 ) into the high-pressure column ( 26 ). At least one liquid stream ( 33, 35 ) is introduced from the high-pressure column ( 26 ) into the low-pressure column ( 32 ). An oxygen-enriched product stream ( 41, 45, 46,47, 48 ) is taken off from the low-pressure column ( 32 ). A first nitrogen stream ( 63, 64, 65, 66 ) is withdrawn from the high-pressure column ( 26 ) and warmed to a temperature of at least 280 K ( 6 ). The warmed first nitrogen stream ( 67 ) is work-expanded ( 72 ) in a first warm expansion engine ( 68 ). The first nitrogen stream ( 70, 71 ) which is expanded in the first warm expansion engine ( 68 ) is work-expanded in a second warm expansion engine ( 72 ).

1 . A process for cryogenic fractionation of air in a distillation column system for nitrogen-oxygen separation, which has a high-pressure column ( 26 ) and a low-pressure column ( 32 ), in which
 the high-pressure column ( 26 ) and the low-pressure column ( 32 ) are thermally coupled via a condenser-evaporator ( 37 ),   feed air ( 1 ) is compressed in an air compressor ( 3 ), cooled at least in one first aftercooler ( 6 ) and cleaned in a cleaning apparatus ( 22 ), cooled in a main heat exchanger ( 23   a,    23   b,    23   c ) and at least partly introduced ( 25 ,  29 ) into the high-pressure column ( 26 ),   at least one liquid stream ( 32 ,  35 ) from the high-pressure column ( 26 ) is introduced into the low-pressure column ( 32 ),   an oxygen-enriched product stream ( 41 ,  45 ,  46 ,  47 ,  48 ) is withdrawn from the low-pressure column ( 32 ),   a first nitrogen stream ( 63 ,  64 ,  65 ,  66 ) from the high-pressure column ( 26 ) is drawn off and warmed ( 6 ) to a temperature of at least 280 K, and   the warmed first nitrogen stream ( 67 ) is expanded ( 72 ) to perform work in a first warm expansion machine ( 68 ), characterized in that   the first nitrogen stream ( 70 ,  71 ) expanded in the first warm expansion machine ( 68 ) is expanded to perform work in a second warm expansion machine ( 72 ).   
     
     
         2 . The process as claimed in  claim 1 , characterized in that the first nitrogen stream is warmed using residual heat, especially the warming of the first nitrogen stream being performed at least partly in the first aftercooler ( 6 ) and the first nitrogen stream ( 66 ) is brought into indirect heat exchange there with feed air ( 5 ) downstream of the air compressor ( 3 ). 
     
     
         3 . The process as claimed in  claim 2 , characterized in that the first nitrogen stream ( 66 ,  67 ) is warmed in the first aftercooler ( 6 ) upstream of the first warm expansion machine ( 68 ), then expanded in the first expansion machine ( 68 ) to an intermediate pressure, and the first nitrogen stream ( 70 ) expanded to the intermediate pressure is heated in a second aftercooler ( 8 ) and then expanded in the second warm expansion machine ( 72 ) to an end pressure which is lower than the intermediate pressure. 
     
     
         4 . The process as claimed in  claim 3 , characterized in that the first and second aftercoolers ( 6 ,  8 ) are connected in parallel on the air side. 
     
     
         5 . The process as claimed in  claim 1 , characterized in that the first nitrogen stream ( 74 ) expanded to perform work in the second warm expansion machine ( 72 ) is used at least partly as regeneration gas ( 58 ,  59 ) in the cleaning apparatus ( 22 ). 
     
     
         6 . The process as claimed in  claim 1 , characterized in that
 a second nitrogen stream ( 52 ) drawn off from the high-pressure column ( 26 ) is warmed to an intermediate temperature in the main heat exchanger ( 23   c ),   the second nitrogen stream ( 53 ) warmed to the intermediate temperature is expanded to perform work in a cold expansion machine ( 54 ) and then warmed again in the main heat exchanger ( 23   c ).   
     
     
         7 . The process as claimed in  claim 6 , characterized in that the second nitrogen stream ( 57 ) expanded to perform work is used at least partly as regeneration gas ( 58 ,  59 ) in the cleaning apparatus ( 22 ). 
     
     
         8 . An apparatus for cryogenic fractionation of air
 comprising a distillation column system for nitrogen-oxygen separation which has a high-pressure column ( 26 ) and a low-pressure column ( 32 ),   the high-pressure column ( 26 ) and the low-pressure column ( 32 ) being thermally coupled via a condenser-evaporator ( 37 ),   comprising an air compressor ( 3 ) for compressing feed air ( 1 ), a first aftercooler ( 6 ) for cooling compressed feed air ( 4 ), a cleaning apparatus ( 22 ) for feed air, arranged downstream of the first aftercooler ( 6 ), a main heat exchanger ( 23   a,    23   b,    23   c ) for cooling cleaned feed air ( 23 ) and a main air line ( 25 ) for introducing cooled feed air into the high-pressure column ( 26 ),   comprising means for withdrawing at least one liquid stream ( 33 ,  35 ) from the high-pressure column ( 26 ) and introduction thereof into the low-pressure column ( 32 ),   comprising an oxygen product line for withdrawing an oxygen-enriched product stream ( 41 ,  45 ,  46 ,  47 ,  48 ) from the low-pressure column, comprising a first nitrogen line for withdrawing a first nitrogen stream ( 63 ) from the high-pressure column ( 26 ),   comprising means ( 6 ) for warming the first nitrogen stream ( 65 ,  66 ) to a temperature of at least 280 K and   comprising a first warm expansion machine ( 68 ) for work-performing expansion of the warmed first nitrogen stream ( 67 ), characterized by a second warm expansion machine ( 72 ) for work-performing expansion of the first nitrogen stream ( 70 ,  71 ) expanded in the first warm expansion machine ( 68 ).   
     
     
         9 . The apparatus as claimed in  claim 8 , characterized in that the means for warming the second nitrogen stream comprise the first aftercooler ( 6 ), which is configured for indirect heat exchange between the first nitrogen stream ( 66 ) and compressed feed air ( 5 ). 
     
     
         10 . The apparatus as claimed in  claim 9 , characterized in that a second aftercooler ( 8 ) is arranged between the first warm expansion machine ( 68 ) and the second warm expansion machine ( 72 ) and is configured for indirect heat exchange between the second nitrogen stream ( 70 ) and compressed feed air ( 7 ). 
     
     
         11 . The apparatus as claimed in  claim 10 , characterized in that the first and second aftercoolers ( 6 ,  8 ) are connected in parallel on the air side. 
     
     
         12 . The apparatus as claimed in  claim 8 , characterized by means for supplying the first nitrogen stream ( 74 ) expanded to perform work in the second warm expansion machine ( 72 ) as regeneration gas ( 58 ,  59 ) to the cleaning apparatus ( 22 ). 
     
     
         13 . The apparatus as claimed in  claim 8 , characterized by a second nitrogen line for withdrawing a second nitrogen stream ( 52 ) from the high-pressure column ( 26 ), in which the second nitrogen line leads through the main heat exchanger ( 23   c ), leaves the main heat exchanger ( 23   c ) at an intermediate site and continues through a cold expansion machine ( 54 ) and leads again through the main heat exchanger ( 23   c ). 
     
     
         14 . The apparatus as claimed in  claim 13 , characterized by means for supplying the second nitrogen stream ( 57 ) expanded to perform work as regeneration gas ( 58 ,  59 ) to the cleaning apparatus. 
     
     
         15 . An oxyfuel power plant comprising a combustion chamber and a cryogenic air fractionation plant, in which the cryogenic air fractionation plant is configured as an apparatus as claimed in  claim 8  and the oxygen I product line ( 48 ) is connected to the combustion chamber. 
     
     
         16 . A process for operating an oxyfuel power plant which a combustion chamber and a cryogenic air fractionation plant, in which the cryogenic air fractionation plant is operated according to any of  claims 1  to  7   claim 1  and the oxygen-enriched product stream ( 48 ) is supplied at least partly to the combustion chamber.