Patent GB-560193-A (GB)
Title: Improvements in or relating to the fractionation of mixtures of gaseous hydrocarbons
IPC: F25J3/02
Filed: 1941-12-18
Abstract: 560,193. Distilling hydrocarbons. STANDARD OIL DEVELOPMENT CO. Dec. 18, 1941, No. 16344. Convention date, Jan. 2, 1941. [Class 321 Mixtures of saturated and unsaturated hydrocarbons of the boiling range of gasoline and lower, e.g. the mixtures of gases and low boiling hydrocarbons obtained in cracking hydrocarbons, are fractionally separated into a gasoline fraction of high aromatic content and into fractions comprising : (a) hydrogen, methane and less than 50 per cent ethylene; (b) more than 50 per cent ethylene ; (c) mainly C3 hydrocarbons ; (d) mainly C4 hydrocarbons ; by first compressing and cooling the mixture to condense the higher boiling constituents, separating the condensate from the gases, compressing the gases, and passing the condensate and the compressed gases into a separating zone from which a gasoline condensate is separated while the gaseous fractions are subjected to further fractionation with the aid of compression and a refrigerating agent to separate them into C1, C2, and C3 fractions, the refrigerating agent being preferably a liquified fraction separated from the mixture. (1) Cracking stage to produce the gaseous mixture and gasoline. Crude oil is pumped through line 10 and vaporiser coil 14 to separator 22 where the vapours are mixed with steam from line 23; the separated vapours are cracked in coil 32 at 1200‹ F. and after reduction of temperature by addition of a quenching oil through line 38 are passed into the lower separator part 43 of a tower 45 from which condensate is withdrawn through line 54. (2) Separation of water and gasoline constituents. The mixed vapours issuing from the top of tower 45 are cooled in condenser 56 and passed to separator 58 from which water is withdrawn as bottom layer through line to pot 62 while hydrocarbon condensate is withdrawn through line 64. Gaseous constituents are withdrawn through line 66, compressed in 76, and cooled in 78, and the products mixed with the hydrocarbon condensate in separator 86, where further water and hydrocarbon condensate are separated, the water being taken off through line 88. The constituents still in gaseous form are led off through 'line 94 and subjected to further compression and cooling whereafter they are mixed in separator 108 with the condensate withdrawn through line 92 ,and a further separation of ,water is effected through line 112 and condensate through line 114, the still gaseous fraction passing off through line 116. (3) Debutanisation of the liquid condensate. The condensate is passed through preheater 122 into a conventional debutaniser tower 124 provided with reboiler 133 in which volatile fractions are separated overhead and recovered in receiver 152 while a stabilised gasoline having a large aromatic content is recovered from the reboiler 132 and passed through the preheater 122 to storage tank 144. The gaseous phases from line 116 and receiver 152 are mixed and, with or without purification by scrubbing in vessel 162, are indirectly cooled in 'heat exchanger 168 by means of liquefied propylene to remove heavier constituents which are separated in -vessel 178 and returned through line 176 to the separator 108. (4) Dehydration and separation of gaseous fractions. This is effected as shown in Fig. 1a the gases being first subjected to dehydration by contact With powdered alumina to remove residual water and then fractionated .in three stages with the aid of a refrigerating agent. The gases pass through line 178 to one of a pair of towers 182, 183 filled with alumina and provided with the necessary connections so that while one tower is on stream the other may be freed from water and regenerated with the aid of purging gases. (5) Separation of the gaseous fractions. The dried vapors pass through line 192 to compressor 194, cooler 196, and refrigerator 198 and thence successively through fractionating towers 202, 242, 258, and 316. The towers are similarly constructed having each reboiler element 228, reflux cycle system 212 and double top plates 204, 212, joined by a pipe 208 providing a refluxing element. Temperature conditions in the tower 202 are controlled by refrigerant in heat exchanger 218 so as to isolate a gaseous fraction comprising mainly hydrogen, methane, and ethane which is withdrawn through line 224 and cooler 356 and may be fed through line 426 for cooling the dehydrators prior to putting these on stream. The temperature conditions in tower 242 are similarly controlled to recover overhead a concentrated ethylene fraction withdrawn through line 282. Similarly in tower 258 a propylene fraction is recovered overhead to receiver 292, and thence to storage tank 300. The condensate from tower 258 is passed to tower 316 where a fraction comprising mainly-C4 hydrocarbons is recovered from the reboiler 338. Tables showing,the proportions of the various hydrocarbons recovered from the towers are given in the Specification. (6) Refrigeration cycle. The C3 (propylene fraction with some ethane) is used as refrigerant for the cooling system .of the towers and is cycled as shown in thick lines through the heat exchangers 218, 276, 198 and 168.