Method and apparatus for polymer drying using inert gas

Abstract

Method and apparatus for drying granular resin material by heating compressed air to a temperature prescribed for gas separation membrane operation, presenting the heated compressed air to a membrane separating out oxygen-size and smaller molecules to provide a stream of gas molecules of at least nitrogen-size at a pressure substantially that of the compressed air, heating the stream of gas molecules of at least nitrogen-size to a temperature at which dew point of the stream is no higher than -40 degrees F., and introducing the heated stream of gas molecules into a chamber for upward flow to atmosphere through granular resin material in the chamber.

The following is claimed: 
     
         1 . A method for drying granular resin material, comprising:
 a) heating compressed air to a temperature prescribed for gas separation membrane operation;   b) presenting the heated compressed air to a membrane separating out oxygen-size and smaller molecules to provide a stream of gas molecules of at least nitrogen-size at a pressure substantially that of the compressed air;   c) reducing pressure of the stream of gas molecules to less than  1 . 0  psig;   d) heating the stream of gas molecules of at least nitrogen-size to a temperature at which dew point of the stream is no higher than - 40  degrees F.; and   e) introducing the heated stream of gas molecules into a chamber for upward flow to atmosphere through granular resin material in the chamber, the stream drying the granular resin material by drawing moisture therefrom during contact therewith.   
     
     
         2 . A method for drying granular resin material, comprising:
 a) dividing a stream of compressed air into two streams;   b) heating one of the streams to a temperature prescribed for gas separation membrane operation;   c) presenting the heated stream to a membrane separating out oxygen-size and smaller molecules to provide a stream of gas molecules of at least nitrogen-size;   d) allowing the stream of gas molecules to expand thereby reducing pressure of the stream of gas molecules to less than 1.0 psig;   e) heating the stream of gas molecules of at least nitrogen-size to a temperature at which dew point of the stream is no higher than −40 degrees F.;   f) introducing the heated stream of gas molecules into a chamber for upward flow to atmosphere through granular resin material in the chamber, the heated stream of gas molecules drying the granular resin material by drawing moisture therefrom during contact therewith;   g) drawing a portion of the heated stream of gas molecules out of the chamber at a point between introduction of the heated stream of gas molecules into the chamber and gas venting to atmosphere with an ejector powered by the remaining stream of air;   h) combining at least a part of the remaining stream of air with the portion of the heated stream of gas molecules drawn from the chamber;   i) heating a combined flow of the remaining stream of air and the portion of the heated stream of gas molecules gas drawn from the chamber to reduce the dew point of the combined flow; and   j) introducing the heated combined flow into the chamber to join the upward flow of the heated stream of gas molecules to atmosphere through granular resin material in the chamber, further drying the granular resin material in the chamber by drawing moisture therefrom during contact therewith.   
     
     
         3 . A method for drying granular resin material, comprising:
 a) heating air to a temperature prescribed for a gas separation membrane;   b) presenting the heated air to a membrane separating out oxygen-size and smaller molecules to provide a collection of gas molecules of at least nitrogen-size;   c) dividing the collection of gas molecules into two portions;   d) allowing the stream of gas molecules to expand thereby reducing pressure of the stream of gas molecules to less than 1.0 psig;   e) heating the first portion of gas molecules to a temperature selected to reduce dew point to no higher than minus 40 degrees F.;   f) introducing the heated first portion of gas molecules into a chamber for upward flow to atmosphere through granular resin material in the chamber, the reduced dew point gas drying the granular resin material by drawing moisture therefrom during contact therewith;   g) drawing a portion of the reduced dew point gas out of the chamber at a point between gas introduction into the chamber and gas venting to atmosphere with an ejector powered by the second portion of gas;   h) combining the second potion of gas with the portion of reduced dew point gas drawn from the chamber;   i) heating a combined flow of the second portion of gas and the portion of gas drawn from the chamber, to reduce the dew point of the combined flow; and   j) introducing the heated combined flow into the chamber to join the upward flow of drying gas to atmosphere through granular resin material in the chamber, further drying the granular resin material in the chamber by drawing moisture therefrom during contact therewith.   
     
     
         4 . Apparatus for drying polymer resin prior to molding or extrusion, comprising:
 a) a first conduit adapted for connection at one end thereof to a supply of compressed air;   b) a first heater for heating compressed air supplied thereto through the first conduit;   c) a housing including a membrane receiving heated compressed air from the heater, the membrane having apertures therethrough of size allowing passage of gas molecules of oxygen size and smaller, the housing having internal structure allowing release to ambient of gas molecules passing through the apertures while funneling gas molecules too large for passage through the apertures to a heating gas outlet;   d) a conduit connected to the housing and receiving a stream of the large size gas molecules therefrom;   e) a valve positioned in the conduit for reducing pressure of the received gas stream to less than  1  psig;   f) a second heater for heating the reduced pressure gas received from the conduit to a dew point no greater than minus  40  degrees F.; and   g) a resin drying hopper for holding polymer resin to be dried, the resin drying hopper receiving the heated reduced pressure gas from the second heater, for drying the resin.   
     
     
         5 . Apparatus for drying polymer resin prior to molding or extrusion, comprising:
 a) a first conduit adapted for connection at one end thereof to a supply of compressed air, and dividing the received supply of compressed air into two portions;   b) a first heater for heating a first portion of the compressed air supplied thereto through the first conduit;   c) a housing including a membrane receiving heated first portion of compressed air from the first heater, the membrane having apertures therethrough of size allowing passage of first portion gas molecules of oxygen size and smaller, the housing having internal structure allowing release to ambient of gas molecules passing through the apertures while funneling first portion gas molecules too large for passage through the apertures to a heating gas outlet;   d) a conduit connected to the housing and receiving a stream of the larger size gas molecules therefrom;   e) a valve positioned in the conduit for reducing pressure of the received gas stream to less than 1 psig;   f) a second heater for heating first portion gas molecules received from the heating gas outlet of the housing to a temperature at which the dew point of the first portion gas molecules is no greater than minus 40 degrees F.;   g) a drying hopper for holding polymer resin to be dried, the resin drying hopper receiving heating first portion gas molecules for drying the resin from the second heater;   h) an ejector receiving the second portion of the compressed air;   i) a takeoff conduit connecting an upper portion of the drying hopper with the ejector for flow of heating gas from the hopper to the ejector;   j) a third heater receiving a mixture of heating gas and air from the ejector; and   k) a conduit supplying the heated mixture of heating gas and air from the third heater to the drying hopper.   
     
     
         6 . Apparatus for drying polymer resin prior to molding or extrusion, comprising:
 a) a first conduit adapted for connection at one end thereof to a supply of compressed air;   b) a first heater for heating the compressed air supplied thereto through the first conduit;   c) a housing including a membrane receiving heated portion air from the first heater, the membrane having apertures therethrough of size allowing passage of gas molecules of oxygen size and smaller, the housing having internal structure allowing release to ambient of gas molecules passing through the apertures while funneling gas molecules too large for passage through the apertures to a heating gas outlet;   d) a conduit receiving the larger size gas molecules from the heating gas outlet of the housing and dividing the received gas into two portions;   e) a valve positioned in the conduit for reducing pressure of the received gas stream to less than 1 psig;   f) a second heater for heating the received gas stream received from the conduit to a temperature at which dew point of the stream is no greater than minus 40 degrees F.;   g) a drying hopper for holding polymer resin to be dried, the resin drying hopper receiving first portion gas molecules for drying the resin from the second heater;   h) an ejector receiving the second portion of the larger size gas molecules from the conduit connected to the heating gas outlet of the housing;   i) a takeoff conduit connecting an upper portion of the drying hopper with the ejector for recycle flow of heating gas from the hopper to the ejector;   j) a third heater receiving a mixture of recycle heating gas and second portion of larger size gas molecules from the ejector; and   k) a conduit supplying the heated gas from the third heater to the drying hopper.