Patent ID: 7185514
Filing Date: 2007-03-06
Classification: F25J

Abstract:
1. A method of fractionating a gas produced by the pyrolysis of hydrocarbons, encompassing hydrogen and C 1 to C 4 hydrocarbons including ethylene, ethane and methane, and possibly water and CO 2 , into at least a first current enriched in hydrogen and methane, and possibly at least a second current essentially consisting of water, the method comprising: a) compressing and drying the gas, passing the gas into a series of compressors, each connected to respective a cooler and a respective separator and further comprising a CO b) progressively cooling and partially liquefying the compressed gas produced by the compressing and drying operation a), caused by successively passing the gas into a cryogenic exchanger and separating the gas in separators into (i) liquids respectively enriched in C (ii) gases respectively depleted in C c) forming the gas undergoing the progressive cooling and partial liquefaction operation b) with the gas produced in the compression and drying operation a), d) distilling in a column, supplied at various levels with liquids collected during operation b) and partially expanded, the column allowing separation, into a relatively colder upper part, of a gaseous top current enriched in methane and depleted in ethylene and ethane, and, into a relatively less cold lower part, of a liquid bottom current depleted in methane and enriched in ethylene and ethane, recycling the top current during operation a) upstream of the compressor, the feed pressure of which is closest to the operating pressure of the distilling column, at the bottom current and collecting and making up a third current containing most of the other C e) feeding of LNG into the cryogenic exchanger at a temperature that is variable from minus 89° C. to minus 160° C.; f) heating the separator gas produced by the last separator, the top current and the bottom current in the cryogenic exchanger.