Sweep gas for membrane-based dehydration modules

Abstract

An air dehydration membrane module is provided with a sweep gas which is taken from the waste gas of a pressure swing adsorption (PSA) unit. No additional compressor is required, other than the compressor forming part of the PSA unit. In another embodiment, the sweep gas includes the combination of dried product gas, taken from the dehydration membrane module, and a supplemental gas, which may be ambient air, or permeate gas from an air separation membrane, or waste gas from a PSA unit. An air ejector combines the streams, without the use of an additional compression step, and the combined gas is used as a sweep stream for the dehydration module. The invention also includes the method of selecting an optimum point at which the sweep gas is injected into the module.

Description

BACKGROUND OF THE INVENTION[0001]This invention pertains to the drying of wet feed gases. In particular, the invention provides various techniques for making a sweep gas for use in a membrane-based dehydration module.[0002]Polymeric membranes have been shown to be effective for the removal of condensable gases, especially water, from otherwise desirable gas streams. A membrane module, containing a plurality of polymeric fibers, is typically used to dry a wet air stream, thereby providing dry air for use in a subsequent process.[0003]The effectiveness of a membrane in gas separation depends not only on the inherent selectivity of the membrane, but also on its capability of handling a sufficiently large product flow. Gas permeates through the membrane due to the pressure differential between one side of the membrane and the other. Thus, to maintain the pressure differential, it is advantageous to remove the permeate gas from the vicinity of the fibers, after such gas has permeated thr...

AI Technical Summary

Benefits of technology

[0012]In one embodiment, the present invention comprises a system for drying a feed gas and for producing a purified product gas, the product gas being a component of the feed gas. The system comprises an air dehydration membrane module and a pressure swing adsorption (PSA) unit connected to receive product gas from the dehydration membrane module, the PSA unit providing a product stream and a waste stream. The waste stream from the PSA unit is connected, through a buffer, to the dehydration membrane module, so that the waste stream can function as a countercurrently flowing sweep gas for the module. The term “countercurrent” means that the sweep gas flows in a direction opposite that of the feed gas entering the module. The system requires no compressor, other than that which is included in the PSA unit.

[0018]The invention also has an object of enhancing the production of dried gas with a dehydration membrane module, by using a sweep gas which is formed in an economical manner.

[0020]The invention has the further object of reducing the cost of producing dried gas, by entraining a dry gas with a supplemental gas, without the use of a separate compression step, so as to make a sweep gas for a dehydration membrane module.

Problems solved by technology

Both of the above approaches incur the cost of operating a compressor.

Alternatively, it is possible to remove water from air by using a refrigeration dryer, but the refrigeration process also consumes power.

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