Patent EA-003854-B1 (EA)
Title: Method of separating a hydrocarbon stream
Inventor: CAMPBELL ROY E
IPC: F25J3/02
Filed: 1999-11-24
Abstract: 1. In a process for the separation of a gas stream containing methane, C2 components, C3 components and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile fraction containing a major portion of said C2 components, C3 components and heavier hydrocarbon components, in which process (a) said gas stream is treated in one or more heat exchange steps and at least one division step to produce at least a first feed stream that has been cooled under pressure to condense substantially all of it, and at least a second feed stream that has been cooled under pressure; (b) said substantially condensed first feed stream is expanded to a lower pressure whereby it is further cooled, and thereafter supplied to a fractionation tower at a top feed point; (c) said cooled second feed stream is expanded to said lower pressure, and thereafter supplied to said fractionation tower at a mid-column feed point; and (d) said cooled expanded first feed stream and said expanded second feed stream are fractionated at said lower pressure whereby the components of said relatively less volatile fraction are recovered; the improvement wherein (1) a liquid distillation stream is withdrawn from said fractionation tower and heated; (2) said heated distillation stream is returned to a lower point on said fractionation tower that is separated from said withdrawal point by at least one theoretical stage; and (3) the quantities and temperatures of said feed streams to said fractionation tower are effective to maintain the overhead temperature of said fractionation tower at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered. 2. In a process for the separation of a gas stream containing methane, C2 components, C3 components and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile fraction containing a major portion of said C2 components, C3 components and heavier hydrocarbon components, in which process (a) said volatile residue gas fraction is re-compressed and a portion is withdrawn to form a compressed first feed stream; (b) said compressed first feed stream is cooled under pressure to condense substantially all of it; (c) said substantially condensed first feed stream is expanded to a lower pressure whereby it is further cooled, and thereafter supplied to a fractionation tower at a top feed point; (d) said gas stream is treated in one or more heat exchange steps to produce at least a second feed stream that has been cooled under pressure; (e) said cooled second feed stream is expanded to said lower pressure, and thereafter supplied to said fractionation tower at a mid-column feed point; and (f) said cooled expanded first feed stream and said expanded second feed stream are fractionated at said lower pressure whereby the components of said relatively less volatile fraction are recovered; the improvement wherein (1) a liquid distillation stream is withdrawn from said fractionation tower and heated; (2) said heated distillation stream is returned to a lower point on said fractionation tower that is separated from said withdrawal point by at least one theoretical stage; and (3) the quantities and temperatures of said feed streams to said fractionation tower are effective to maintain the overhead temperature of said fractionation tower at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered. 3. The improvement according to claims 1 or 2 wherein said liquid distillation stream is pumped after being withdrawn from said fractionation tower. 4. The improvement according to claim 3 wherein (a) said pumped liquid distillation stream is divided into at least a first portion and a second portion; (b) said first portion is heated; and (c) said heated first portion is returned to a lower point on said fractionation tower that is separated from said withdrawal point by at least one theoretical stage. 5. The improvement according to claims 1 or 2 wherein said liquid distillation stream is directed in heat exchange relation with at least a portion of said gas stream or said feed streams, to supply said cooling thereto and thereby heat said liquid distillation stream. 6. The improvement according to claim 3 wherein said pumped liquid distillation stream is directed in heat exchange relation with at least a portion of said gas stream or said feed streams, to supply said cooling thereto and thereby heat said pumped liquid distillation stream. 7. The improvement according to claim 4 wherein said first portion is directed in heat exchange relation with at least a portion of said gas stream or said feed streams, to supply said cooling thereto and thereby heat said first portion. 8. The improvement according to claims 1 or 2 wherein the quantity and temperature of said heated distillation stream and the heating supplied to said fractionation tower are effective to maintain the bottom temperature of said fractionation tower at a temperature to reduce the quantity of carbon dioxide contained in said relatively less volatile fraction. 9. The improvement according to claim 3 wherein the quantity and temperature of said heated distillation stream and the heating supplied to said fractionation tower are effective to maintain the bottom temperature of said fractionation tower at a temperature to reduce the quantity of carbon dioxide contained in said relatively less volatile fraction. 10. The improvement according to claim 4 wherein the quantity and temperature of said heated first portion and the heating supplied to said fractionation tower are effective to maintain the bottom temperature of said fractionation tower at a temperature to reduce the quantity of carbon dioxide contained in said relatively less volatile fraction. 11. The improvement according to claim 5 wherein the quantity and temperature of said heated distillation stream and the heating supplied to said fractionation tower are effective to maintain the bottom temperature of said fractionation tower at a temperature to reduce the quantity of carbon dioxide contained in said relatively less volatile fraction. 12. The improvement according to claim 6 wherein the quantity and temperature of said heated distillation stream and the heating supplied to said fractionation tower are effective to maintain the bottom temperature of said fractionation tower at a temperature to reduce the quantity of carbon dioxide contained in said relatively less volatile fraction. 13. The improvement according to claim 7 wherein the quantity and temperature of said heated first portion and the heating supplied to said fractionation tower are effective to maintain the bottom temperature of said fractionation tower at a temperature to reduce the quantity of carbon dioxide contained in said relatively less volatile fraction.