Two stage membrane dryer
AssigneePraxair Technology, Inc.
InventorRavi Prasad
Life of this patent
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Abstract
This invention uses a first or roughing stage to remove the bulk of moisture and a second or polishing stage to complete the drying. The first stage can use a relatively small membrane area and a relatively low quality purge gas whereas the second stage can use a large membrane area and high quality purge gas, such as some product back purge. The arrangement provides efficient usage of available high quality purge gas, such as product, while minimizing product contamination. This two stage purging arrangement is especially attractive for those processes or systems where multigrade purge gases are available.
Claims15
A process for drying wet gas streams in a membrane system, said process comprising steps of:
- (a) passing a feed gas stream containing wet components under pressure to at least one first stage membrane having about 6% to about 80% of the total membrane surface area in the system;
- (b) passing a gas stream from an external source comprising a foreign gas to at least one low pressure, permeate side of said at least one first stage membrane to carry the permeated wet components away from the permeate side thereof;
- (c) passing the partially dried feed gas stream resulting therefrom under pressure to at least one second stage membrane having about 20% to about 94% of the total membrane surface area in the system;
- (d) passing at least a portion of the resulting dried product gas from said at least one second stage membrane to at least one low pressure, permeate side of said at least one second stage membrane to carry the permeated wet components away from the permeate side thereof, wherein step (d) is carried out at a cleaning ratio of less than about 4;
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- (e) recovering the remaining portion of the dry product gas.
A process for drying high purity wet nitrogen gas streams in a membrane system, said process comprising:
- (a) passing a high purity nitrogen gas stream containing wet components under pressure to at least one first stage membrane having about 6% to about 80% of the total membrane surface area in the system,
- (b) passing a gas stream containing a foreign gas from an external source to at least one low pressure, permeate side of said at least one first stage membrane to carry the permeated wet components away from the permeate side thereof;
- (c) passing the partially dried high purity nitrogen gas stream resulting therefrom under pressure to at least one second stage membrane having about 20% to about 94% of the total membrane surface area in the system;
- (d) passing at least a portion of the resulting dried high purity nitrogen product gas from said at least one second stage membrane to at least one low pressure, permeate side of said at least one second stage membrane to carry the permeated wet components away from the permeate said thereof;
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- (e) recovering the remaining portion of the dried high purity nitrogen product gas.
A membrane capable of drying a wet gas stream, said system comprising:
- at least two membrane modules connected in series, each having at least four gas ports and at least one membrane having at least one non-permeate side and at least one permeate side, with a defined membrane area, the combined membrane area of said at least two membrane modules being based on the total membrane area in the system, wherein an earlier module is connected to an external purge gas source containing a foreign gas to provide purging means containing a foreign gas on the permeate side of said at least one membrane thereof and a later module is provided with a reflux purging means to direct a gas derived from the non-permeate side to the permeate side of said at least one membrane thereof and wherein the earlier module has a smaller membrane area than the later module.
Dependencies are inferred from the claim text.