Reducing moisture in granular resin material using inert gas

Abstract

An apparatus for drying granular resin material in a hopper including a first sub-system, including a membrane and a heater receiving drying gas from the membrane to be heated, the first sub-system supplying dried heated gas to a first portion of the hopper; and a second sub-system, including a mixing device and a heater for receiving drying gas from the mixing device to be heated, the mixing device inducing withdrawal of gas from the hopper and mixing the withdrawn gas with gas supplied from the first subsystem, the mixed gases being heated and supplied to a second portion of the hopper, the improvement comprising a gas separation membrane for separating inert gases from air supplied to the apparatus and providing the separated inert gas in the first subsystem; a heater for heating air supplied to the apparatus; and a thermostat for controlling the heater and thereby maintaining the supplied air at a selected temperature.

Claims

1. In a method of drying granular resin material in a hopper including supplying a first portion of air to a membrane; heating gas supplied by the membrane and supplying the heated supplied gas to a first portion of the hopper; supplying a portion of incoming compressed air independently of the membrane to a mixing device; withdrawing heating gas from the hopper and using the mixing device to mix the withdrawn heating gas with incoming compressed air; and supplying the resulting mixture of gases to a second portion of the hopper to heat granular resin material in hopper, the improvement comprising: a) furnishing inert gas from a gas separation membrane as the first portion of heating gas; and b) regulating temperature of the gas separation membrane by controlling temperature of compressed air supplied thereto to maintain the gas separation membrane at a preselected temperature.

2. The method of claim 1, wherein the improvement further comprises passing heated drying gas through the granular resin material in the hopper in a direction opposite that of granular resin material travel through the hopper.

3. The method of claim 2 wherein the improvement further comprises withdrawing inert heating gas from the hopper in an amount several times the amount of compressed air supplied to the mixing device.

4. The method of claim 1 further comprising passing the compressed air through the mixing device to induce withdrawal of inert heating gas from the hopper.

5. The method of claim 1 further comprising supplying an air-inert gas mixture to the second portion of the hopper in an amount several times the amount of inert gas supplied to the first portion of the hopper.

6. An apparatus for drying granular resin material in a hopper including a first sub-system, including a membrane dryer and a heater receiving drying gas from the membrane dryer to be heated, the first sub-system supplying dried heated gas to a first portion of the hopper; and a second sub-system, including a mixing device and a heater for receiving drying gas from the mixing device to be heated, the mixing device inducing withdrawal of gas from the hopper and mixing the withdrawn gas with gas supplied from the first subsystem, the mixed gases being heated and supplied to a second portion of the hopper, the improvement comprising: a) a gas separation membrane for separating inert gases from air supplied to the apparatus and providing the separated inert gas to the first and second subsystems; b) a heater for supplying heat to the gas separation membrane; and c) a thermostat for controlling the gas separation membrane heater and thereby maintaining the gas separation membrane at a selected temperature.

7. In a method of drying granular resin material in a hopper including supplying a first portion of gas to a membrane dryer; heating gas dried by the membrane dryer and supplying the heated drying gas to a first portion of the hopper; supplying a second portion of heating gas independently of the membrane dryer to a gas mixing device; withdrawing heating gas from the hopper and using the mixing device to mix the withdrawn gas with the second portion of gas; and supplying the mixed gases to a second portion of the hopper to heat granular resin material in hopper, the improvement comprising: a) furnishing inert gas from a gas separation membrane as the first and second portions of heating gas; and b) regulating temperature of the gas separation membrane by controlling application of heat thereto to maintain the gas separation membrane at a preselected temperature.

8. The method of claim 7, wherein the improvement further comprises passing heated drying gas through the granular resin material in the hopper in a direction opposite that of granular resin material travel through the hopper.

9. The method of claim 8 wherein the improvement further comprises withdrawing inert gas from the hopper in an amount several times the amount of the second portion of inert gas supplied to the mixing device.

10. The method of claim 7 further comprising passing the second portion of inert heating gas through the mixing device to induce withdrawal of inert heating gas from the hopper.

11. The method of claim 7 further comprising supplying mixed inert gases to the second portion of the hopper in an amount several times the amount of inert gas supplied to the first portion of the hopper.

12. An apparatus for drying granular resin material in a hopper including a first sub-system having a membrane dryer and a heater receiving drying gas from the membrane dryer to be heated, the first sub-system supplying dried heated gas to a first portion of the hopper; and a second sub-system having a mixing device and a heater for receiving drying gas from the mixing device to be heated, the mixing device inducing withdrawal of gas from the hopper and mixing the withdrawn gas with gas supplied from the first subsystem, the mixed gases being heated and supplied to a second portion of the hopper, the improvement consisting of: a) a gas separation membrane separating inert gases from air supplied to the apparatus and providing the separated inert gas to the first and second subsystems; b) a heater supplying heat to the gas separation membrane; and c) a thermostat for controlling the gas separation membrane heater to maintain the gas separation membrane at a selected temperature.

13. In a method of drying granular resin material in a hopper including supplying a first portion of gas to a membrane dryer, heating gas dried by the membrane dryer and supplying the heated drying gas to a first portion of the hopper; supplying a second portion of heating gas independently of the membrane dryer to a gas mixing device; withdrawing heating gas from the hopper with the mixing device mixing the withdrawn gas with the second portion of gas; and supplying the mixed gases to a second portion of the hopper to heat granular resin material in hopper, the improvement consisting of: a) furnishing inert gas from a gas separation membrane as the first and second portions of heating gas; and b) controlling application of heat to the gas separation membrane to maintain the gas separation membrane at a preselected temperature.

14. An apparatus for drying granular resin material in a hopper, comprising: a conduit configured to direct inlet air to the apparatus; a first heater in fluid communication with the conduit and configured to heat substantially all of the inlet air supplied to the apparatus; a gas separation membrane in fluid communication with the first heater, the gas separation membrane being configured to receive no more than a first portion of the inlet air exiting the first heater, and to separate inert gases from the first portion of the inlet air; a second heater in fluid communication with the gas separation membrane and the hopper, the second heater being configured to heat the inert gases, and to supply the heated inert gases to a first portion of the hopper; a mixing device in fluid communication the first heater and the hopper, the mixing device being configured to induce withdrawal of gas from within the hopper, and to mix the withdrawn gas with a second portion of the inlet air exiting the first heater; and a third heater in fluid communication with the mixing device and the hopper, the third heater being configured to heat the mixture of the withdrawn gases and the second portion of the inlet air, and to supply the heated mixture to a second portion of the hopper.

15. An apparatus for drying granular resin material in a hopper, comprising: a conduit configured to direct inlet air to the apparatus; a first heater in fluid communication with the conduit and configured to heat substantially all of the inlet air supplied to the apparatus; a gas separation membrane in fluid communication with the first heater, the gas separation membrane being configured to receive substantially all of the inlet air exiting the first heater, and to separate inert gases from the inlet air; a membrane dryer in fluid communication with the gas separation membrane, the membrane dryer being configured to receive no more than a first portion of the inert gases exiting the gas separation membrane, and to dry the first portion of the inert gases; a second heater in fluid communication with the membrane dryer and the hopper, the second heater being configured to heat the first portion of the inert gases, and to supply the heated inert gases to a first portion of the hopper; a mixing device in fluid communication the gas separation membrane and the hopper, the mixing device being configured to induce withdrawal of gas from within the hopper, and to mix the withdrawn gas with a second portion of the inert gases exiting the gas separation membrane; and a third heater in fluid communication with the mixing device and the hopper, the third heater being configured to heat the mixture of the withdrawn gas and the second portion of the inert gases, and to supply the heated mixture to a second portion of the hopper.

Description

DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a schematic diagram of granular resin material drying apparatus manifesting aspects of the invention.

(2) FIG. 2 is a schematic diagram of an alternative embodiment of the granular resin material drying apparatus shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(3) The apparatus shown in FIG. 1 is designed such that a drying inert gas, preferably nitrogen or argon, supplied to a bed of particulate material, namely granular resin material, is passed through the granular resin material contained in a drying chamber, such as a drying hopper DH, which receives the granular resin material via an inlet 10 at the top of the drying hopper DH. The granular resin material preferably moves slowly downward through drying hopper DH, passes through an outlet valve 12, and is discharged via an outlet 14. The residence time of the granular resin material in hopper DH depends on the particular granular resin material being dried and the desired level of dryness to be achieved.

(4) Still referring to FIG. 1, as the granular resin material moves downwardly through hopper DH, the moisture content of the granular resin material is reduced by a flow of preferably low dew point, namely about −75° Fahrenheit dew point, inert gas that is passed upwardly through hopper DH. The gas is supplied to the hopper via one or more flow paths.

(5) As illustrated in FIG. 1, the inert gas used to dry the granular particulate resin material is furnished by one or more gas separation membranes, one of which has been numbered 100. Pressurized air applied to gas separation membrane 100 results in membrane 100 dividing the compressed air into two streams. One of the streams is gas having molecule size that of oxygen or smaller. These molecules pass easily through the gas separation membrane. The second stream is that of gases having molecule size greater than that of oxygen. The second stream, having molecule size greater than that of oxygen, is typically largely composed of nitrogen, with argon also being present but in a small percentage relative to the nitrogen. Other gases may also be in the second stream. However, because these other gases are present in the atmosphere only in very minute amounts, the second stream will always be principally nitrogen with a lesser amount of argon and minimal amounts of other gases having molecule size larger than that of oxygen.

(6) A heater 102, which is preferably electrically powered and is controlled by a thermostat 104, is positioned in an inlet air conduit 50, which conveys compressed air received at inlet 16, through valve 17 and filters 18 and 19, to heater 102.

(7) The compressed air flows through the schematically illustrated conduit 50 past an unnumbered “T” which splits the compressed air stream into two portions, with one portion going to pressure regulator 20 and a second portion going to membrane 100.

(8) Gas separation membrane 100 is preferably supplied with pressurized air via conduit 50 from a compressed air supply (not shown). In practice, the compressed air inlet 16 may be connected to a manufacturing facility's existing compressed air system for powering pneumatic equipment. Such compressed air systems often include a refrigerant type dryer which provides partially dehumidified air having a dew point of from +40° Fahrenheit to +50° Fahrenheit. Conventional filters 18 and 19 are installed after a conventional valve 17 leading from inlet 16, to remove undesirable contaminants from the compressed air stream before the air stream reaches heater 102.

(9) Continuing to refer to FIG. 1, a portion of the compressed air received from conduit 50 is supplied, via a first flow path FP1, to a first sub-system SS1 that includes membrane 100 and a heater EH′.

(10) In a preferred embodiment membrane 100 provides relatively low dew point inert gas output which is passed to the heater EH′ via a pressure regulator 21 and a flow-regulating orifice 22, providing a desired pressure and inert gas flow rate through drying hopper DH. The heater EH′ may use any suitable heat source, such as an electric heater as shown in FIG. 1.

(11) The low dew point inert gas from electric heater EH′ is fed to a first portion of the drying hopper DH, with the inert gas being introduced into drying hopper DH at a lower portion of drying hopper DH, flowing through the granular resin material in hopper DH, and drawing off moisture from the granular resin material therein.

(12) Still referring to FIG. 1, a second flow path FP2 for the compressed air extends through a pressure regulator 20 to a second sub-system SS2 that includes a mixing device 30 and a heater EH. The mixing device is preferably a pneumatic amplifier, such as the amplifier sold by Nortel Machinery, Inc. of Buffalo, N.Y., although other types of gas mixing devices, such as venturis and ejectors, can be used. Compressed air supplied via a portion of conduit 50 downstream of pressure regulator 20 to a first inlet 32 of the mixing device induces flow of recirculating inert drying gas from an upper portion of drying hopper DH, preferably via a filter 26, to a second inlet 31 of mixing device 30, which mixes inert gas supplied thereto through inlet 31 with air supplied via inlet 32. The resulting gas mixture exits outlet 33 of mixing device 20 and is supplied to the drying hopper DH via heater EH, which may be an electric heater as shown in the drawing. The heated gas mixture enters hopper DH via a diffuser 34, which may be a pipe with a screened outlet, and is supplied to hopper DH via a diffuser 34 located at a second, higher portion of the hopper, above diffuser 36.

(13) As shown in FIG. 1, mixing device 30 combines the inlet stream of inert gas and the inlet stream of air at a predetermined volumetric ratio, which can be adjusted. An appropriate ratio for any given application may readily be determined by trial and error by anyone of skill in this art.

(14) The use of drying gas recirculation is advantageous in that it permits a reduction in the amount of inert gas, and hence the amount of compressed air needed to generate the inert gas required for the drying process; it also allows use of a smaller membrane 100.

(15) In the embodiment of the invention depicted in FIG. 1, most of the drying is affected in the upper portion of hopper DH by the mixture of drying gas received from diffuser 34, which mixture of drying gas is supplemented by the inert drying gas from diffuser 36. The remainder of the drying is affected near the bottom of drying hopper DH by the inert gas from diffuser 36. A relief valve 37 connected to vent 39, venting to atmosphere, prevents undesired pressure build-up in drying hopper DH.

(16) A number of the temperature and pressure indicators and controls depicted in FIG. 1 have not been specifically discussed. Their purpose and function will be readily understood by those skilled in the art. For example, pressure switch PS can shut off air to mixing device 30 when pressure of the drying gas in drying hopper DH is above or below an appropriate value.

(17) While a preferred embodiment of the invention has been shown and described, it will be appreciated by those skilled in the art that various modifications can be made in keeping with the basic principles of the invention. For example, instead of a single membrane 100, a plurality membranes 100 may be used, as indicated by dashed lines in FIG. 1. Further, provisions may be included to control the amount of drying more precisely, such as by providing a detector to monitor the dew point of inert drying gas exiting hopper DH and a pressure controller to adjust pressure of compressed air furnished to membrane 100, depending on the detected humidity, to control the dew point.

(18) Also, instead of supplying compressed air directly to inlet 31 of mixer 30, the output of membrane 100 can be split, so that flow path FP2 to the inlet 32 of air mixer 30 extends from membrane 100. For example, FIG. 2 depicts one possible embodiment, in the form of a granular resin material drying apparatus 110, in which the inlet 32 of air mixer 30 is supplied with inert gases from the membrane 100. Components of the apparatus 110 that are identical to those of the apparatus described above and depicted in FIG. 1 are identified with identical reference characters.

(19) In the apparatus 110, the heater 102, controlled by the thermostat 104, is connected to the gas separation membrane 100 to control the temperature of the gas separation membrane 100. Unlike the apparatus depicted in FIG. 1, the entirety of the pressurized air supplied to the apparatus 110 and received at inlet 16 passes through the membrane 100. The second stream of gas, namely, the inert gas separated out by gas separation membrane 100, is split after leaving gas separation membrane 100, with the resulting two flows traveling through the schematically illustrated conduits to pressure regulator 20 and to a membrane dryer MD, respectively. As discussed above, the first stream of gas, which is largely oxygen separated out by gas separation membrane 100, is preferably vented to atmosphere at gas separation membrane 100.

(20) Continuing to refer to FIG. 2, one of the flows of inert gas received from gas separation membrane 100 is supplied, via a first flow path FP1a, to a first sub-system SS1a that includes a membrane dryer MD and the heater EH′.

(21) In a preferred embodiment, dryer MD is a membrane dryer. Low dew point, typically 10° Fahrenheit to −20° Fahrenheit, inert gas output from membrane dryer MD, is passed to the heater EH′ via the pressure regulator 21 and the flow-regulating orifice 22, to provide a desired pressure and inert gas flow rate through drying hopper DH.

(22) As discussed above in relation to the apparatus of FIG. 1, the warmed, low dew point inert gas from electric heater EH′ is fed to a first portion of the drying hopper DH, with the inert gas being introduced into drying hopper DH at a lower portion of drying hopper DH and flowing through the granular resin material in hopper DH, drawing off moisture from the granular resin material therein.

(23) Still referring to FIG. 2, a second flow path FP2a for inert gas from membrane 100 extends through the pressure regulator 20 to a second sub-system SS2a that includes the mixing device 30 and the heater EH. Inert gas supplied from membrane 100 to the first inlet 32 of the mixing device 30 induces a flow of recirculating inert drying gas from an upper portion of drying hopper DH, preferably via the filter 26, to the second inlet 31 of mixing device 30, which mixes inert gas supplied thereto through the inlets 31 and 32. The mixture of inert gas exits the outlet 33 of mixing device 20 and is supplied to the drying hopper DH via the heater EH, which may be an electric heater as shown in the drawing. The heated mixture of inert gas is supplied to and enters hopper DH via the diffuser 34, which may be a pipe with a screened outlet located at a second, higher portion of the hopper, above diffuser 36.

(24) As shown in FIG. 2, mixing device 30 combines the two inlet streams of inert gas at a predetermined volumetric ratio, which can be adjusted. An appropriate ratio for any given application may readily be determined by trial and error by anyone of skill in this art.

(25) The use of drying inert gas recirculation is advantageous in that it permits a reduction in the amount of inert gas, and hence the amount of compressed air, needed to generate the inert gas required for the drying process; it also allows use of a smaller membrane dryer MD.

(26) In the embodiment of the invention depicted in FIG. 2, most of the drying is effected in the upper portion of hopper DH by the inert drying gas from diffuser 34, which is supplemented by the inert drying gas from diffuser 36. The remainder of the drying is effected near the bottom of drying hopper DH by the inert gas from diffuser 36. This system configuration provides excellent drying performance. A relief valve 37 connected to vent 39 venting to atmosphere prevents undesired pressure build-up in drying hopper DH.

(27) A number of the temperature and pressure indicators and controls depicted in FIG. 2 have not been specifically discussed. Their purpose and function will be readily understood by those skilled in the art. For example, pressure switch PS can shut off membrane dryer MD when pressure of the inert gas received from gas separation membrane 100 is above or below an appropriate value.

(28) While a preferred embodiment of the invention has been shown and described, it will be appreciated by those skilled in the art that various modifications can be made in keeping with the basic principles of the invention. For example, instead of a single membrane dryer MD, a plurality of MD membrane dryers may be used, as indicated by dashed lines in FIG. 2. Also, instead of supplying inert drying gas directly to inlet 31 of gas mixer 30, the output of membrane dryer MD can be split, so that flow path FP2a to the inlet 32 of gas mixer 30 extends from membrane dryer MD. Further, provisions may be included to control the amount of drying more precisely, such as by providing a detector to monitor the humidity of inert drying gas exiting hopper DH and a pressure controller to adjust pressure of inert drying gas furnished to membrane dryer MD, depending on the detected humidity, to control the dew point.

(29) Although membrane dryers denoted MD are preferred for use in practicing the invention, other types of dryers may also be employed. While one of the advantages of the invention is that it avoids certain drawbacks of desiccant dryers, it is also possible and appropriate to use a desiccant-type dryer in sub-system SS1a in conjunction with sub-system SS2a.

(30) Although schematic implementations of the invention and at least some of its advantages are described in detail hereinabove, it should be understood that various changes, substitutions and alterations may be made to the apparatus and methods disclosed herein without departing from the spirit and scope of the invention as defined by the appended claims. The disclosed embodiments are to be considered in all respects as being illustrative and not restrictive, with the scope of the invention being indicated by the appended claims rather than by the foregoing description. All changes coming within the meaning and range of equivalency of the claims are intended to be embraced therein. Moreover, the scope of this patent application is not intended to be limited to the particular implementations of apparatus and methods described herein, nor to any methods that may be described or inferentially understood by those skilled in the art to be present herein.

(31) As discussed above and from the foregoing description of an exemplary embodiment of the invention, it will be readily apparent to those skilled in the art to which the invention pertains that the principles and particularly the compositions and methods disclosed herein can be used for applications other than those specifically mentioned. Further, as one of skill in the art will readily appreciate from the description of the invention as set forth hereinabove, apparatus, methods, and steps presently existing or later developed, which perform substantially the same function or achieve substantially the same result as the embodiments described and disclosed hereinabove, may be utilized according to the description of the invention and the claims appended hereto. Accordingly, the appended claims are intended to include within their scope such apparatus, methods, and processes that provide the same advantage or result, or which are, as a matter of law, embraced by the doctrine of the equivalents respecting the claims of this application.

(32) As respecting the claims appended hereto, the term “comprising” means “including but not limited to”, whereas the term “consisting of” means “having only and no more”, and the term “consisting essentially of” means “having only and no more except for minor additions which would be known to one of skill in the art as possibly needed for practice of the claimed invention.” The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description and all changes that come within the range of equivalency of the claims are to be considered to be embraced by the claims. Additional objects, other advantages, and further novel features of the invention will become apparent from study of the appended claims as well as from study of the foregoing discussion and description of the invention, as that study proceeds.