US 5,471,842 AGranted

Cryogenic rectification method and apparatus

AssigneeThe BOC Group, Inc.

InventorsRobert A. Mostello, Sidney S. Stern

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Abstract

A cryogenic rectification method for producing a product stream from a gaseous mixture having higher and lower volatility components and heavy impurities. In accordance with the method, the mixture is separated by a cryogenic rectification process employing one or more columns having plates, trays or packing for intimately contacting ascending vapor and descending liquid streams within the column. The mixture to be separated after having been compressed is combined with the recycle stream to produce a combined stream which is purified in a prepurification unit that is designed to remove the heavy contaminants. The combined steam is divided into major and minor streams. The major stream is then cooled and separated into liquid and vapor phases. Heavy impurities concentrate in the liquid phase taken as the recycle stream, which is then pumped to a high enough pressure for vaporization of the impurities. The resulting vapor is then reduced in pressure and combined with the incoming gaseous mixture. The concentration of heavy impurities in the vapor phase is reduced to a sufficient extent such that a product stream concentrated in the lower volatility component will have a reduction in its heavy impurity concentration. The product stream is pumped to pressure and vaporized against a portion of mixture using a boosted pressure subsidiary stream made up of a minor portion of the gaseous mixture.

Claims14

Dependent claims

A method of separating a gaseous mixture comprising higher and lower volatility components and heavy impurities to obtain a product stream predominantly containing said lower volatility components of said gaseous mixture, said method comprising:

subjecting said gaseous mixture to a cryogenic rectification process to produce said product stream, said cryogenic rectification process having compression, cooling and distillation stages and a prepurification stage located between said compression and cooling stages;
forming a recycle stream from a liquid concentrated in said heavy impurities;
pumping said recycle stream to a sufficient pressure that said heavy impurities will vaporize with said liquid;
vaporizing and then pressure reducing said recycle stream to a pressure about equal to that of said gaseous mixture between said compression and prepurification stages;
combining said recycle stream with said gaseous mixture to be separated to form a combined stream and then, introducing said combined stream into said prepurification stage;
introducing at least a major part of said combined stream into said cooling stage and after said at least a major part of said combined stream is cooled, concentrating said heavy impurities contained within said at least a major part of said combined stream into said liquid used in forming said recycle stream so that a vapor is formed lean in said heavy impurities;
introducing said vapor into said distillation stage to produce said product stream, whereby said product stream will have a reduced concentration of said heavy impurities below a concentration that would otherwise have been obtained had said heavy impurities been not concentrated within said liquid.

4 more elements

An apparatus for separating a gaseous mixture comprising higher and lower volatility components and heavy impurities to obtain a product stream predominantly containing said lower volatility components of said gaseous mixture, said apparatus comprising:

cryogenic rectification means for producing said product stream, said cryogenic rectification means having compression, cooling and distillation stages and a prepurification stage located between said compression and cooling stages;
said cryogenic rectification means also having,
a pump for pumping a recycle stream formed from a liquid concentrated in said heavy impurities to a sufficient pressure that said heavy impurities will vaporize with said liquid;
said pump connected to said cooling stage so that said recycle stream vaporizes within said cooling stage;
a pressure reduction valve in communication with said cooling stage and said prepurification stage so that said recycle stream combines with said gaseous mixture to be separated to form a combined stream flowing through said prepurification stage;
said cooling stage connected to said prepurification stage so that at least a major part of said combined stream flows through said cooling stage;
and
means connected to said cooling stage and said distillation stage for concentrating said heavy impurities contained within said combined stream in said liquid so that said recycle stream and a vapor lean in said heavy impurities are formed and said vapor flows into said distillation stage to produce said product stream, whereby said product stream will have a reduced concentration of said heavy impurities below a concentration that would otherwise have been obtained had said heavy impurities not been concentrated within said liquid.

5 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/292,126Filed 17 Aug 1994
Granted: 5 Dec 1995
Term ends: Not estimatedThe source records don’t support an estimate.

Classification11 codes

F25J 3/04854
Operation, control and regulation of the process; Instrumentation within the process: safety aspects of operation
F25J 3/04078
Providing pressurised feed air or process streams within or from the air fractionation unit: providing pressurized products by liquid compression…
F25J 3/0409
Providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression: of oxygen
F25J 3/04284
Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion: using internal refrigeration by open-loop…