WO2004080691A1

WO2004080691A1 - Polyethylene terephthalate regrind particle processing system

Info

Publication number: WO2004080691A1
Application number: PCT/US2004/006815
Authority: WO
Inventors: Robert Crawford
Original assignee: Mann & Hummel Protec Gmbh
Priority date: 2003-03-06
Filing date: 2004-03-08
Publication date: 2004-09-23
Also published as: WO2004080691A9

Abstract

A method and apparatus for producing a polyethylene terephthalate {PET} sheet in which virgin PET granules are dried with dry air in a drying air (16) at a temperature above the glass transition temperature of PET. Regrind PET material is also dried with dry air at a temperature below the glass transition temperature. Dried virgin PET granules are air cooled in a cooling hopper (32) to a temperature below the glass transition. The cooled virgin PET granules are blended with the dried PET regrind material and the blend is then extruded into a PET sheet by extruders (54).

Description

POLYETHYLENE TEREPHTHALATE REGRIND PARTICLE PROCESSING SYSTEM

BACKGROUND OFTHE INVENTION

The production of articles from polyethylene terephthalate (PET) typically results in formation of significant amounts of scrap PET. To minimize wastage and enhance production economy, it is desirable to recycle this clean scrap to the production process. Accordingly, clean PET scrap is commonly reground to produce PET particles which can be recycled to the original molding or extruding process.

PET is a hygroscopic material which absorbs moisture from the atmosphere. While low amounts of absorbed moisture can be tolerated in molding and extruding processes, excessive moisture levels tend to result in defects in the produced articles. Consequently, it is a conventional practice to heat PET regrind to elevated temperatures to drive off moisture before returning it to the molding or extruding line.

PET can exist in either an amorphous or a crystalline state, and most PET regrind consists of amorphous material. When amorphous PET is heated to high drying temperatures, it can become tacky and tends to agglomerate. This, in turn, can lead to severe fouling or blockages in production equipment. To minimize the danger of such fouling or blockages, it is conventional in the art to first crystallize regrind PET by heating it to a temperature above the glass transition temperature (approximately 170°F) before it is heated to drying temperatures, which typically are on the order of 300 to 350°F. Since crystalline PET exhibits much less tendency to agglomerate at elevated drying temperatures, the use of a separate crystallization treatment greatly reduces the likelihood that fouling or blockages will occur in the production equipment. However, the need for a separate crystallizing stage adversely affects the economics of the PET production process. In an attempt to avoid the need to crystallize and dry PET regrind, vented extruders have been developed which attempt to remove excess moisture from PET regrind during the extrusion process by applying a vacuum to the extruder chamber which contains molten PET before it is fed to the extrusion die. An example of such an approach is disclosed in Clements, US Patent No. 5,849,381. While this approach has proved useful in many cases to substantially reduce or eliminate the defects in molded or extruded PET articles caused by the presence of excessive moisture in the resin, it is not able to always prevent such problems. Accordingly, there has remained a need for better procedures for processing PET regrind.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an improved method of processing PET regrind material. Another object of the invention is to provide a method of processing PET regrind material which reduces the overall energy consumption of the process.

A further object of the invention is to provide a method for processing PET regrind material which is flexible in its operation.

An additional object of the invention is to provide an improved method for processing PET regrind material which can effect rapid changes in the material which is processed by extrusion or the like.

It is also an object of the present invention to provide a method for processing PET regrind which avoids the need to cool drying air so that acquired moisture can be removed from the drying air by a desiccant. Yet another object of the invention is to provide a process for recycling

PET regrind which avoids the need for a crystallization stage.

A still further object of the invention is to provide a method of processing PET regrind which minimizes exposure of the material to potentially damaging temperatures. Another object of the invention is to provide a method of processing PET regrind in which operator control is simplified.

Still another object of the invention is to provide a method of processing PET regrind which minimizes the amount of PET resin which is heated at any given time.

These and other objects have been achieved in accordance with the present invention by providing a method of producing a polyethylene terephthalate sheet comprising the steps of (a) drying virgin polyethylene terephthalate granules with a stream of dry air at an elevated temperature above the polyethylene terephthalate glass transition temperature; (b) cooling the dried virgin polyethylene terephthalate granules with a stream of air to a temperature below the polyethylene terephthalate glass transition temperature; (c) transporting the cooled virgin polyethylene terephthalate granules to an extruder; (d) drying polyethylene terephthalate regrind material with a stream of dry air at a temperature below the polyethylene terephthalate glass transition temperature; (e) transporting dried polyethylene terephthalate regrind material to the extruder; (f) blending dried and cooled virgin polyethylene terephthalate granules with dried polyethylene terephthalate regrind material; and (g) extruding the blended virgin polyethylene terephthalate granules and polyethylene terephthalate regrind material into a polyethylene terephthalate sheet.

In accordance with further preferred aspects of the invention, the objects are achieved by providing an apparatus for processing polyethylene terephthalate regrind particles comprising (a) a virgin polyethylene terephthalate granule dryer; (b) means for supplying said virgin granule dryer with dry heated air at a temperature above the polyethylene terephthalate glass transition temperature to dry polyethylene terephthalate granules therein; (c) a polyethylene terephthalate granule cooler for receiving dry polyethylene terephthalate granules from said virgin granule dryer; (d) means for supplying dry cooling air to said granule cooler for cooling dried polyethylene terephthalate granules to a temperature below the polyethylene terephthalate glass transition temperature; (e) a polyethylene terephthalate regrind particle dryer; (f) means for supplying said regrind particle dryer with dry air at a temperature below the polyethylene terephthalate glass transition temperature to dry polyethylene terephthalate regrind particles therein; (g) means for blending dried and cooled virgin polyethylene terephthalate granules from said virgin granule cooler and dried polyethylene terephthalate regrind particles from said regrind particle dryer; and (h) means for conveying the virgin polyethylene terephthalate granules and the polyethylene terephthalate regrind particles to an extruder.

The invention reduces equipment requirements while gaining maximum processing advantage and improved energy savings via low-temperature drying of PET regrind particles. By drying PET regrind particles separately at low temperatures for an extended residence time, it becomes unnecessary to use crystallizing equipment is not necessary. On-the-fly recovery of regrind into cooled process stream eliminates large batch blending requirements. By handling materials in this fashion, the following benefits are experienced:

• A crystallizer is not required;

^• Blending is simplified by "cutting in" regrind on demand; ^• Lower energy consumption is achieved; and

^• Flexible operation and quick-changeovers from one feed material to another are facilitated.

The usual technique for processing PET is heating by the crystallizer/dryer and then melting by the screw agitation. In contrast to this, in the invention, the bulk of the melt energy is developed by the extruder. Energy savings are achieved because the additional load of extruder energy is less than net load of crystallizing and drying circuits. Also, the drying system cooling load (because the air to be dehumidified must be cooled for desiccant efficiency) is decreased since material enters the drying system at ambient temperatures instead of hot from crystallizer. Regrind drying temperatures are low and not time critical.

Flexible operation and quick changeovers are possible because the blending of virgin granules and regrind particles can occur at the extruder throat, so there is little or no stored volume of run-critical material. Virgin material is kept in its own drying system, so one conventional dryer can be used to prepare resin for one or more extruders. Regrind material is mixed with the virgin PET only when it is delivered to the extruder feed hopper. Dedicated regrind processing systems can be provided for each color of regrind material. Consequently, regrind material of any color is always available for instantaneous processing. Color and material changes can be made in the time that it takes to run out the extruder feed hopper, and there are no end-of-run batch hopper drain-outs.

As previously noted, a crystallizer is not required. Crystallizers heat material above the glass transition phase temperature while agitating to prevent agglomeration. Once it is crystallized, PET regrind material can be dried at temperatures as high as 325°F to 350°F. In the present invention, the PET regrind particles are dried at a low temperature of only 150°F to 160°F. The dried PET regrind material enters the system after high-temp virgin granule drying. Therefore, the regrind material is never subjected to temperatures above the glass transition temperature, and no crystallizer is required to prevent undesired tackiness and agglomeration.

The virgin granules are dried at temperatures of 325°F to 350°F for about 3 to about 4 hours to a moisture content of 50 ppm or less. The dried virgin granules are then cooled before blending with the PET regrind particles which are dried at low temperature. Preferably, the virgin granule cooling hopper is located in a gravity particle flow, serial airflow arrangement to recover heat from cooling hopper exhaust. The optimized airflow achieved by the invention maximizes energy, and eliminates or virtually eliminates operator temperature adjustments. Advantageously, the drying air volume may be regulated based on the outlet air temperature when the inlet temperature of the drying air is fixed. A system of this type is described in Graeff, US Patent No. 4,413,426. It is also possible to adjust the virgin granule drying temperature based on the throughput. Flexible operation is also enhanced by using as many regrind particle drying hoppers as there are colors of regrind material. The method and apparatus of the invention also promote efficiency by making it possible for multiple lines to share a single source of dried and cooled virgin PET granules. Damage to the regrind material is avoided due to the mild conditions to which the PET regrind particles are subjected in the invention. In general, they are dried at a temperature in the range from 150° to 160°F for a period of 4 to 6 hours to a moisture content of 200 ppm or less. Due to drying below the polyethylene terephthalate glass transition temperature, no crystallizer is required. The dried PET regrind material can be "cut-in" as needed to the cooled virgin PET granule stream supplied to the extruders.

A preferred system begins with a regrind feed system either from silo or gaylord dumpers to feed a 6 hour or larger drying hopper. Each standard color that will be used at the same time in the plant will require a separate drying vessel. Where a single natural virgin resin is used, and where needed color is added at the extruder, a single virgin granule drying system can be used to process all virgin resin requirements for the facility. This reduces the need to have individual dryers for each extruder, and with different colors fully prepared before they are needed at the extruder, they can be immediately loaded to a different line when a color change is required. In those cases where an individual regrind drying system is not running at its design rate, it can still produce dry material that will not have sufficient exposure to temperature to degrade the resin.

The dry resins must be transported in a sealed pneumatic conveying system to assure delivery of properly dried resin that is not exposed to ambient air that would rewet the resin. Rather than using the usual in plant vacuum systems to deliver the resin to the extruder, a closed loop low pressure, dilute phase pneumatic conveyor is preferably used. This type of conveying system utilizes fill/pass valves that enable a single delivery system to serve several lines. It is preferred to use airlocks on the virgin and regrind drying vessels that will regulate the amount of resin to be charged into the conveying line. The first material introduction point is at the virgin drying hopper where the airlock will feed in a metered quantity material, and then proceed in the same pipe to the appropriate regrind hopper where its airlock will meter in the desired quantity of regrind particles. The resulting blended mixture will then be conveyed to the selected extruder feed hopper where the fill/pass valve is actuated to drop the conveyed resin into the hopper.

By using a pressure convey system with dry air, any potential leakage in the system will be into the room, an will protect the dry resin from possible water regain from air leaks into the system. The convey system piping is run in a loop through the plant with a fill/pass valve located in each pipe where a particular material may be utilized. This assures the delivery of the correct mixture to each line where the selected material will be used.

The conveying system control regulates the metering airlocks, blower units, and system valving. The operator will only need to verify that the selected regrind drying hopper is available, and he will then assign the required blend ratio to extruder feed hopper. The selection of the material is maintained at a very simple level for the operator by use of the method and apparatus of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinafter in further detail with reference to illustrative preferred embodiments of an apparatus according to the invention for carrying out the method of the invention shown in the accompanying drawing figures, in which: Figure 1 is a schematic illustration of a system for processing PET regrind according to the present invention;

Figure 2 is a diagram of an alternate arrangement for processing PET regrind in accordance with the present invention in which different colors of PET regrind material can be selectively supplied to an extruding line; and

Figure 3 is a drawing of a preferred vertical arrangement of a PET regrind drying vessel with vessels for drying and cooling virgin PET.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 is a schematic diagram of an installation 10 for extruding PET into sheets. Virgin PET granules from a source (not shown) are introduced through a line 12 into a vacuum feeder 14. The vacuum feeder 14 discharges through a gate valve into a drying hopper 16 a stream of dry air, preheated to approximately 300°F as described hereinafter, is filtered in a filter 18 and then further heated to approximately 350°F in a process heater 20, after which it is introduced at the base of drying hopper 16. The heated dry air passes upwardly through the downflowing virgin PET granules and extracts the moisture from the granules. The moisture level in the granules is reduced to approximately 50 ppm. The air loses heat as it passes upwardly through the PET granules in the drying hopper and is discharged at the top of the drying hopper through a line 22 to a cyclone filter 24, from whence it passes through a line 26 to a desiccant dryer 28.

The dried PET granules exit drying hopper 16 at the bottom through a rotary airlock valve 30 and pass to a cooling hopper 32. Dried air from desiccant dryer 28 passes through line 34 to the bottom of cooling hopper 32. The dry air as it enters the cooling hopper has a temperature of only about 150°F. It passes upwardly through the hot PET granules received from the drying hopper and extracts heat from the granules so that the granules are cooled. In the course of this passage, the air is preheated to about 300°F. The preheated air is then discharged from the top of cooling hopper 32 through line 34 and passes to filter 18.

Cooling hopper 32 has a dual rotary airlock valve discharge arrangement with first and second rotary airlock discharge valves 36 and 38, respectively. Valve 36 opens into a sealed pneumatic conveying line 40 supplied with pressurized air from a pump 42. Valve 38 opens into a sealed pneumatic conveying line 44 which is supplied with pressurized air by a pressure pump 46. Lines 40 and 44 lead respectively to first and second extruder feed circuits 48 and 50 from which the dried and cooled PET granules are supplied through selectively operable fill/pass valves 52 to extruders 54 which extrude the PET into sheets.

Advantageously, the extruders 54 may be vented extruders. Preferably they are vacuum vented extruders. Equipment of this type is commercially available from Welex Co. of Blue Bell, Pennsylvania, USA. PET regrind material is introduced through lines 56 and 58, respectively into vacuum feeders 60 and 62 at the top of regrind drying hoppers 64 and 66, respectively. Drying air is passed through filters 68 and 70 and desiccant dryers 72 and 74 from whence it is conveyed to the bottom of regrind drying hoppers 64 and 66, respectively. The dry air extracts moisture from the regrind particles and then is discharged from the tops of regrind drying hoppers 64 and 66 through lines 76 and 78 which recirculate the drying air back to the filters 68 and 70, respectively.

The drying air temperature in the regrind drying circuits is controlled to a temperature which is less than the glass transition temperature of PET. Preferably heating devices 80 and 82 are provided on the drying air recirculation lines to control the temperature. Heating devices 80 and 82 may be gas fired burners, but they also may be heat exchangers which pass the drying air in heat exchange relation with another process stream of appropriate temperature. The dried PET regrind particles are discharged through airlock valves 84 and 86 into the pneumatic conveying lines 40 and 44 of the PET supply circuits 48 and 50. In this way, PET regrind particles are blended with the virgin PET granules supplied to the extruders. By adjusting the relative proportions of virgin granules and regrind particles supplied to the respective supply circuits, admixtures having the desired proportions of regrind material and virgin material may be supplied to the extruders.

In the illustrated embodiment, both extruder supply circuits are supplied with virgin granules from a single dryer and cooler. In contrast thereto, separate regrind drying hoppers 64 and 66 are provided for each PET supply circuit. In this way, it is possible to supply all circuits with virgin material from a single source, and yet to supply different circuits with different colors of regrind material.

Figure 2 is a schematic diagram of a portion of a modified PET extruding installation. Like parts are identified by the same reference numerals. The arrangement and operation of the virgin PET granule dryer and cooler are identical to that in Figure 1, and for simplicity of illustration are not shown here.

The difference between the embodiments of Figure 1 and Figure 2 is that in the embodiment of Figure 2, the respective PET supply circuits 48 and 50 both supply the same bank of extruders 54. Thus, by appropriately actuating the fill/pass valves on one or the other circuit, the extruders can be supplied with PET regrind material from either one of the two regrind drying hoppers 64 and 66. In this way, the color of the PET material supplied to the extruder can be quickly changed. It is only necessary that the small supply and the extruder feed hopper be exhausted before the alternate material is introduced. This greatly increases the operating flexibility and the repeatedly of material changes in the extrusion line. Figure 3 illustrates a preferred apparatus embodiment in which a virgin granule dryer, a virgin granule cooler and a regrind particle dryer are arranged in a vertical column.

A supply of virgin PET granules is introduced through line 92 into vacuum chamber 94 and then discharged through a gate valve 96 into drying hopper 98. A stream of dry air at a temperature of approximately 350°F is introduced through line 100 to the bottom of cooling hopper 98 and passes under baffles 102 and thence upwardly through the downwardly flowing PET granules, thereby extracting the moisture from the PET granules. The air loses heat as it passes upwardly through the granules and is discharged from the top of drying hopper 98 through line 104.

The dried granules, which have also picked up heat from the drying air, are discharged from the bottom of drying hopper 98 through rotary valve 106 to the top of an underlying cooling hopper 108. Dry cooling air is introduced through line 110 to the bottom of cooling hopper 108 and passes under baffles 112 and upwardly through the dried granules, thereby extracting heat from the dried granules. The cooling air, which has picked up heat from the dried granules, is then discharged through line 114 at the top of cooling hopper 108.

As indicated in dotted lines, if desired, the dry cooling air, which has been preheated by its passage through the cooling hopper, may be used to ask the drying air supply for the virgin granule drying hopper 98. It is only necessary to pass the preheated cooling air from line 114 through a filter 116 to remove any entrained particles and through a heater 118, to increase its temperature to the requisite drying temperature, and then introduce it through line 100 into the bottom of drying hopper 98. This manner of operation recovers and conserves a large proportion of the heat removed from the dried virgin granules, thereby providing a high degree of energy efficiency.

The cooled virgin PET granules are discharged from the bottom of cooling hopper 108 through rotary airlock valve 120 and pass through a discharge line 22 to a sealed pneumatic conveying line 124 which leads to the extruders (not shown).

PET regrind material is introduced through line 126 into the top of regrind drying hopper 128. .Dry air from a desiccant dryer (not shown) is introduced through line 130 to the bottom of regrind drying hopper 128. The dry air passes underneath baffles 132 and then upwardly through the PET regrind particles, thereby extracting moisture from the regrind particles. Preferably, the moisture content of the regrind material is reduced to a level below 200 PPM. The air is then discharged from the top of regrind drying hopper 128 through line 134.

Energy efficient operation may be promoted if the drying air discharged from the regrind drying hopper is used as the cooling air introduced to the bottom of the virgin granule cooling hopper. This may be accomplished by first passing the drying air exhausted through line 134 through a suitable dehumidifier 136 and then introducing the dehumidified air through line 110 into the bottom of cooling hopper 138. In this way, the heat content of the regrind drying air may be conserved.

The dried regrind particles exit the bottom of regrind drying hopper 128 through rotary airlock valve 138 into the sealed pneumatic conveying line 124 where they are blended with the dried virgin PET granules from line 122.

The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations falling within the scope of the appended claims and equivalents thereof.

Claims

WHAT IS CLAIMED IS:

1. A method of producing a polyethylene terephthalate sheet comprising the steps of: a) drying virgin polyethylene terephthalate granules with a stream of dry air at an elevated temperature above the polyethylene terephthalate glass transition temperature; b) cooling the dried virgin polyethylene terephthalate granules with a stream of air to a temperature below the polyethylene terephthalate glass transition temperature; c) transporting the cooled virgin polyethylene terephthalate granules to an extruder; d) drying polyethylene terephthalate regrind material with a stream of dry air at a temperature below the polyethylene terephthalate glass transition temperature; e) transporting dried polyethylene terephthalate regrind material to the extruder; f) blending dried and cooled virgin polyethylene terephthalate granules with dried polyethylene terephthalate regrind material; and g) extruding the blended virgin polyethylene terephthalate granules and polyethylene terephthalate regrind material into a polyethylene terephthalate sheet.

2. A method according to claim 1, wherein the virgin polyethylene terephthalate granules are dried at a temperature in the range from about 300°F to about 350°F, preferably 325°F to 350°F.

3. A method according to claim 1, wherein the virgin polyethylene terephthalate granules are dried for a time from about 3 to about 6 hours, preferably 3 to about 4 hours.

4. A method according to claim 1, wherein the virgin polyethylene terephthalate granules are dried to a moisture content of less than 50 ppm H₂0.

5. A method according to claim 1, wherein the dried virgin polyethylene terephthalate granules are cooled to a temperature below about 170°F.

6. A method according to claim 5, wherein the dried virgin polyethylene terephthalate granules are cooled to a temperature below about 150°F.

7. A method according to claim 1, wherein the dried and cooled virgin polyethylene terephthalate granules are transported in a sealed pneumatic conveying system.

8. A method according to claim 7, wherein said sealed pneumatic conveying system is pressurized to an elevated pressure above ambient pressure.

9. A method according to claim 1, wherein the polyethylene terephthalate regrind material is dried at a temperature in the range from about 150°F to about 160°F.

10. A method according to claim 1, wherein the polyethylene terephthalate regrind material is dried for a time from about 4 to about 6 hours.

11. A method according to claim 1, wherein the polyethylene terephthalate regrind material is dried to a moisture content of less than 200 ppm H₂0.

12. A method according to claim 1, wherein the dried poryethylene terephthalate regrind material is transported in a sealed pneumatic conveying system.

13. A method according to claim 12, wherein said sealed pneumatic conveying system is pressurized to an elevated pressure above ambient pressure.

14. A method according to claim 1, wherein the virgin polyethylene terephthalate granules and the polyethylene terephthalate regrind material are blended in a common conveying line.

15. A method according to claim 14, wherein the virgin polyethylene terephthalate granules and the polyethylene terephthalate regrind material are blended by introducing a desired proportion of regrind material into a conveying line for the dried and cooled virgin polyethylene terephthalate granules.

16. A method according to claim 1, wherein the virgin polyethylene terephthalate granules and the polyethylene terephthalate regrind material are blended in an extruder feed hopper.

17. A method according to claim 1, wherein the virgin polyethylene terephthalate granules and the polyethylene terephthalate regrind material are blended in an extruder throat.

18. A method according to claim 1, wherein the extruder is vented, further comprising the step of withdrawing residual moisture through the extruder vent.

19. A method according to claim 18, wherein said vent is a vacuum vent.

20. A method according to claim 1, wherein air locks are provided on conveying lines for the polyethylene terephthalate granules and the polyethylene terephthalate regrind material, said air locks regulating the amounts of polyethylene terephthalate transported to the extruder.

21. A method according to claim 1, wherein a separate regrind dryer and conveying line are provided for each of a plurality of colors of polyethylene terephthalate regrind material.

22. A method according to claim 1, wherein polyethylene terephthalate regrind material is transported in a circuit to a plurality of extruders and selectively introduced into at least one desired extruded by activating a fill/pass valve associated with each desired extruder.

23. A method according to claim 1, wherein a single virgin polyethylene terephthalate dryer and cooler are connected to a plurality of extruders.

24. A method according to claim 23, further comprising introducing a desired colorant for the virgin polyethylene terephthalate into at least one selected extruder.

25. A method according to claim 1, wherein warmed air from the cooling of the dried virgin polyethylene terephthalate granules is used as the stream of dry air for drying the virgin polyethylene terephthalate granules.

26. A method according to claim 25, wherein the stream of air from the cooling is filtered and heated before being used to dry the virgin polyethylene terephthalate granules.

27. An apparatus for processing polyethylene terephthalate regrind particles comprising: a) a virgin polyethylene terephthalate granule dryer b) means for supplying said virgin granule dryer with dry heated air at a temperature above the polyethylene terephthalate glass transition temperature to dry polyethylene terephthalate granules therein; c) a polyethylene terephthalate granule cooler for receiving dry polyethylene terephthalate granules from said virgin granule dryer; d) means for supplying dry cooling air to said granule cooler for cooling dried polyethylene terephthalate granules to a temperature below the polyethylene terephthalate glass transition temperature; e) a polyethylene terephthalate regrind particle dryer; f) means for supplying said regrind particle dryer with dry air at a temperature below the polyethylene terephthalate glass transition temperature to dry polyethylene terephthalate regrind particles therein; g) means for blending dried and cooled virgin polyethylene terephthalate granules from said virgin granule cooler and dried polyethylene terephthalate regrind particles from said regrind particle dryer; and h) means for conveying the virgin polyethylene terephthalate granules and the polyethylene terephthalate regrind particles to an extruder.

28. An apparatus according to claim 27, wherein cooling air recovered from said virgin particle cooler is filtered and further heated and then introduced as drying air into the virgin polyethylene terephthalate granule dryer.

29. An apparatus according to claim 27, wherein drying air recovered from said polyethylene terephthalate regrind particle dryer is dehumidified and then introduced as cooling air into the virgin granule cooler.

30. An apparatus according to claim 27, wherein said virgin polyethylene terephthalate granule dryer, said virgin polyethylene terephthalate granule cooler, and said polyethylene terephthalate regrind dryer are stacked in a vertical arrangement.

31. An apparatus according to claim 27, wherein said conveying means comprise a sealed pneumatic conveying line.

32. An apparatus according to claim 31, wherein said pneumatic conveying line is a pressurized line, and further comprising an air pump for pressurizing said conveying line.

33. An apparatus according to claim 27, wherein said blending means comprise means for introducing the virgin polyethylene terephthalate granules and the polyethylene terephthalate regrind material into a common conveying line.

34. An apparatus according to claim 1, wherein said blending means comprise means for introducing the virgin polyethylene terephthalate granules and the polyethylene terephthalate regrind material into an extruder feed hopper.

35. An apparatus according to claim 1, wherein said blending means comprise means for introducing the virgin polyethylene terephthalate granules and the polyethylene terephthalate regrind material into an extruder throat.

36. An apparatus according to claim 27, further comprising means for venting the extruder.

37. An apparatus according to claim 36, wherein said venting means comprise vacuum venting means.