AU619255B2 - Creation of Inventions and Patents with Artificial Intelligence

AU619255B2 – Drying method and apparatus
– Google Patents

AU619255B2 – Drying method and apparatus
– Google Patents
Drying method and apparatus

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Publication number
AU619255B2

AU619255B2
AU30746/89A
AU3074689A
AU619255B2
AU 619255 B2
AU619255 B2
AU 619255B2
AU 30746/89 A
AU30746/89 A
AU 30746/89A
AU 3074689 A
AU3074689 A
AU 3074689A
AU 619255 B2
AU619255 B2
AU 619255B2
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AU
Australia
Prior art keywords
vessel
particulate matter
drier
gas
heated gas
Prior art date
1988-02-26
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)

Ceased

Application number
AU30746/89A
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AU3074689A
(en

Inventor
Granville J. Hahn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)

Permian Research Corp

Original Assignee
Permian Research Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1988-02-26
Filing date
1989-02-24
Publication date
1992-01-23

1989-02-24
Application filed by Permian Research Corp
filed
Critical
Permian Research Corp

1989-08-31
Publication of AU3074689A
publication
Critical
patent/AU3074689A/en

1992-01-23
Application granted
granted
Critical

1992-01-23
Publication of AU619255B2
publication
Critical
patent/AU619255B2/en

2009-02-24
Anticipated expiration
legal-status
Critical

Status
Ceased
legal-status
Critical
Current

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Classifications

F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

F26—DRYING

F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM

F26B17/00—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement

F26B17/18—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by rotating helical blades or other rotary conveyors which may be heated moving materials in stationary chambers, e.g. troughs

F26B17/22—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by rotating helical blades or other rotary conveyors which may be heated moving materials in stationary chambers, e.g. troughs the axis of rotation being vertical or steeply inclined

B—PERFORMING OPERATIONS; TRANSPORTING

B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL

B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS

B29B13/00—Conditioning or physical treatment of the material to be shaped

B29B13/06—Conditioning or physical treatment of the material to be shaped by drying

B29B13/065—Conditioning or physical treatment of the material to be shaped by drying of powder or pellets

B—PERFORMING OPERATIONS; TRANSPORTING

B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL

B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS

B29B7/00—Mixing; Kneading

B29B7/30—Mixing; Kneading continuous, with mechanical mixing or kneading devices

B29B7/32—Mixing; Kneading continuous, with mechanical mixing or kneading devices with non-movable mixing or kneading devices

B—PERFORMING OPERATIONS; TRANSPORTING

B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL

B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS

B29B7/00—Mixing; Kneading

B29B7/30—Mixing; Kneading continuous, with mechanical mixing or kneading devices

B29B7/58—Component parts, details or accessories; Auxiliary operations

B29B7/72—Measuring, controlling or regulating

B—PERFORMING OPERATIONS; TRANSPORTING

B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL

B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS

B29B7/00—Mixing; Kneading

B29B7/74—Mixing; Kneading using other mixers or combinations of mixers, e.g. of dissimilar mixers ; Plant

B29B7/7476—Systems, i.e. flow charts or diagrams; Plants

B29B7/748—Plants

B—PERFORMING OPERATIONS; TRANSPORTING

B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL

B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS

B29B7/00—Mixing; Kneading

B29B7/80—Component parts, details or accessories; Auxiliary operations

B29B7/82—Heating or cooling

B29B7/826—Apparatus therefor

B—PERFORMING OPERATIONS; TRANSPORTING

B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL

B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS

B29B9/00—Making granules

B29B9/16—Auxiliary treatment of granules

F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

F26—DRYING

F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM

F26B17/00—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement

F26B17/12—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed solely by gravity, i.e. the material moving through a substantially vertical drying enclosure, e.g. shaft

F26B17/14—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed solely by gravity, i.e. the material moving through a substantially vertical drying enclosure, e.g. shaft the materials moving through a counter-current of gas

F26B17/1433—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed solely by gravity, i.e. the material moving through a substantially vertical drying enclosure, e.g. shaft the materials moving through a counter-current of gas the drying enclosure, e.g. shaft, having internal members or bodies for guiding, mixing or agitating the material, e.g. imposing a zig-zag movement onto the material

F26B17/1466—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed solely by gravity, i.e. the material moving through a substantially vertical drying enclosure, e.g. shaft the materials moving through a counter-current of gas the drying enclosure, e.g. shaft, having internal members or bodies for guiding, mixing or agitating the material, e.g. imposing a zig-zag movement onto the material the members or bodies being in movement

F26B17/1483—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed solely by gravity, i.e. the material moving through a substantially vertical drying enclosure, e.g. shaft the materials moving through a counter-current of gas the drying enclosure, e.g. shaft, having internal members or bodies for guiding, mixing or agitating the material, e.g. imposing a zig-zag movement onto the material the members or bodies being in movement the movement being a rotation around a vertical axis

F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

F26—DRYING

F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM

F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects

F26B21/14—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects using gases or vapours other than air or steam, e.g. inert gases

B—PERFORMING OPERATIONS; TRANSPORTING

B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL

B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS

B29B9/00—Making granules

B29B9/16—Auxiliary treatment of granules

B29B2009/168—Removing undesirable residual components, e.g. solvents, unreacted monomers; Degassing

B—PERFORMING OPERATIONS; TRANSPORTING

B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL

B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS

B29K2067/00—Use of polyesters or derivatives thereof, as moulding material

Description

COMMONWEALTH OF AUSTRALI Patent Act 1952 6 1 92 COMPLETE SPECIFICATION
(ORIGINAL)
Class Int. Class Application Number Lodged Complete Specification Lodged Accepted Published Priority :26 February 1988 Related Art i i Krl 1-.
q Name of Applicant Address of Applicant Actual Inventor/s Address for Service :PERMIAN RESEARCH CORPORATION 3400 W. 7th Street, Big Spring Texas 79720 United States of America Granville J. Hahn F.B. RICE CO., Patent Attorneys, 28A Montague Street, BALMAIN 2041.
Complete Specification for the invention entitled: DRYING METHOD AND APPARATUS The following statement is a full description of this invention including the best method of performing it known to us/ME S00c~57i 13 24 02 z89 Technical Field This invention relates to a drying method and apparatus, and more particularly, to a method and apparatus for use in drying polymers. One aspect of the invention particularly relates to a method and apparatus for drying crystalline polymers such as polyethylene terephthalate pellets or granules. Another 00 ooo. aspect of the invention relates to a method and apparatus for 0000 oGoo aftercondensing polycondensed polymers such as polyesters and 0 *00 polyamides.
oo0000 ooo 09 00 Background Art The need for driers that can effectively and efficiently o 0o reduce the moisture content of finely divided materials is well o. known. One problem commonly encountered in drying such materials is clumping or agglomeration. Some prior art methods and apparatus 06 0* 6 have utilized rotating shafts and stirring arms to stir particulate matter during drying. Others have utilized hot gas 0:00 15 injected under high pressure to fluidize a bed of particulate 00oo -matter during drying. Still others have employed stirring 0* devices in combination with the injection of hot gas to effect drying. However, problems are still encountered with the conventional, commercially available driers, and their methods of use.
I
Such problems include, for example, packing of moist particulate matter by the rotating stirring arms; channeling that leads to incomplete drying, agglomeration and spot overheating; carryover of entrained solids from driers into filters and overhead recovery systems; inability to effectively remove undesirable reaction products; excessive energy use; and the like.
Drying is often required in order to satisfactorily prepare j l”4 amorphous or crystalline polymers for subsequent molding or I° il 10 extrusion operations. For example, polyethylene terephthalate (PET) pellets used in molding carbonated beverage bottles is typically dried prior to injection molding the parisons from which the bottles are later blown.
Conventional methods and apparatus for the aftercondensation S’ 15 of amorphous polymers are disclosed in U.S. 4,585,366, and the references cited therein. Two primary problems previously encountered in the aftercondensation of amorphous polymers, and polyesters in particular, are agglutination and the removal of tundesirable gaseous reaction products such as acetaldehydes. The S, 20 ‘removal of aldehydes from a static bed of crystalline PET by 1 forced air or inert gas is specifically addressed in U.S.
4,230,819.
In previously disclosed methods and systems designed to overcome these two primary problems, other problems have been encountered which have also limited their usefulness and efficiency. Thus, rotary drum driers have been employed to limit agglutination, but their effectiveness has been hampered by dust formation, high energy consumption, and the need for operating in a batch rather than continuous process.
The use of simple shafts or columns as drying vessels has resulted in agglomeration of the granulate in the upper portions of such vessels, necessitating the use of crushing or peeling devices in the discharge section to break up the clumps, which 44…again boosts energy consumption and causes dust formation.
10 To avoid such problems, others have employed fluidized beds for precrystallizing the polymer prior to recondensation. With fluidized beds, however, it is difficult to control residence time of the particles. Energy requirements are also great, and separate vessels are required for each step of the two-stage 15 process.
:In U.S. 4,584,366, the inventors disclose an apparatus comprising a single vessel with two stacked sections. The upper section contains an agitator preferably comprising a rotary shaft having flat stirring bars appended thereto. The lower section, 2’into wihthe polymer flows under gravitational force from the upper section, is merely a cylindrical vessel through which the polymer flows without separation or interruption. Hot inert gas is injected into the lower portion of each section, and flows upwardly through the polymer bed to a collection system where it is filtered, dried, reheated and recirculated to the vessel.
However, the apparatus disclosed in U.S. 4,584,366 requires a residence time of 5 hours to adequately dry and recondense PET granulate.
A polymer drier, drier system and method of operation are therefore needed that will permit finely divided particulate matter, and more particularly, polymer materials such as PET pellets or granulate to be dried in a much shorter time than five hours, thereby achieving correspondingly greater P”I Ythroughput. This advantage should desirably be attained without ee o 10 increasing the required capital investment and operating expenses eat9 re^ to such an extent that the resultant advantage in throughput is S* more than offset by these other factors. Also, the advantage in throughput must be achieved without sacrificing the physical properties of the product. With PET granulate intended for use 15 in food grade applications, for example, this means that the 4 49 acetaldehyde level of the recondensed polymer should be 4- maintained below a specified maximum level. Also, moldability and structural integrity of the products to be molded from the recondensed polymer may require that the intrinsic viscosity of dried and recondensed polymer be maintained within a specified acceptable range.
According to the present invention, a drier, drier system and method are provided that achieve all of the foregoing advantages without any associated disadvantages that would negate the benefits to be achieved through use of the invention.
Summary Of The Invention The drier of the present invention is designed to contact particulate matter flowing downward through a cylindrical vessel with a countercurrent flow of heated gas.
According to one embodiment of the present invention, an improved single-stage polymer drier is provided that employs a specially designed rotary agitator in cooperation with a plurality of specially designed baffles and foraminous separators 6*09 e’ to achieve improved drying and polymer throughput without Qo• agglomeration. The rotary agitator utilized in the invention 1o 0 preferably comprises a centrally disposed rotatable shaft having attached in fixed relation thereto a plurality of axially-spaced arrays of circumferentially-spaced, downwardly inclined stirring ,arms. When used in accordance with the method of the invention, a It the subject apparatus demonstrates excellent effectiveness in drying and removing gaseous reaction products from polycondensates.
According to another embodiment of the invention, an improved drier system is disclosed that utilizes the novel single-stage drier of the invention in combination with a specially designed gas flow control mechanism to prevent overheating or agglomeration of particulate matter residing in the drier during a cessation of flow through the drier outlet.
According to another embodiment of the invention, a method is disclosed for drying polymers through use of the subject drier and drier system. According to a particularly preferred embodiment of the subject method, beneficial results are achieved by contacting the downwardly flowing polymer with an upwardly flowing stream of air or inert gas such as nitrogen at a temperature ranging between about 340 and 385 deg. F. (about 170- 200 deg. in a ratio of from about 1.0 to about 1.5, and most preferably about 1.3, cubic feet of gas per minute to 1 pound per hour of polymer.
bola Brief Description Of The Drawings The invention is further described and explained in relation 0 0 o to the following drawings wherein like numerals are used to 10 identify like parts in each figure: i 0 0 0 Figure 1 is a simplified flow diagram depicting the drier system of the invention; S Figure 2 is a sectional elevation view depicting the S internal structure of the drier of the invention; 15 Figure 3 is a sectional plan view of the drier of the invention taken along line 3–3 of Figure 2; Figure 4 is a plan view depicting shaft anchor plate 116 of V the drier of the invention as shown in Figure 2; and j r Figure 5 is a plan view depicting the gas flow control plate employed with the gas flow control mechanism of the drier system of the invention.
Description Of The Preferred Embodiments Drier system 10 preferably comprises drier 14, and the related auxiliary equipment depicted in simplified form in Figure 1. Referring to Figure 1, drier system 10 preferably also includes feed hopper 12, cyclone 34, filter 38, overhead condenser 40, blower 46, gas flow control mechanism o desiccators 64, 68, directional inlet flow control valve 0! oo directional outlet flow control valve 74, and gas heater 78.
S °,Particulate material is supplied to drier 14 o o0 S0°.oo from feed hopper 12 through feed inlet 22. The particulate So 10 feedstock can comprise any of numerous types of relatively finely divided particulate solid material or mixtures thereof including, j 0 0 for example, grain and grain products; sand; wood flour; 00 fertilizer and other granular chemical compounds; polymer granules, flakes or pellets (whether amorphous, partially crystalline or crystalline, and whether virgin or regrind); and the like.
Particulate matter entering drier 14 through feed inlet 22 flows downwardly through the vessel by gravity flow, eventually V exiting through outlet 24. Hot gas is blown into drier 14 from gas supply line 26 through gas inlet port 28. The hot gas preferably comprises air or a relatively inexpensive inert gas such as nitrogen.. The hot gas rises through the particulate matter inside drier and 14, heating and drying the particulate matter while picking up moisture, fines and, in some cases reaction products.
After passing upward through the particulate matter, the spent gas exits through gas outlet port 30, and flows through cyclone 34 and microfilter 38 to first remove entrained fine particulate matter. The filtered gas then flows into condenser which is preferably cooled by cooling tower water, to condense out much of the liquid prior to entering desiccators 61, o.9n 68. The condensed liauid flows out of condenser 40 through 0a0s B” 10 condensate drain 42, and the uncondensed gas passes overhead io ooo* through blower feed line 44 to blower 46. Blower 46 discharges the gas through blower exhaust line 48, gas flow control mechanism 50, and desiccator feed line 52.
o, The flow of gas through desiccator feed line 52 is j 15 alternately directed to one or the other of desiccators 64, 68 by So o directional inlet flow control valve 60. Two desiccators are S preferably employed in drier system 10 in order that one desiccator can be utilized to remove additional water vapor from the gas while the other desiccator is undergoing regeneration.
‘According to one preferred embodiment of the invention, desiccators 64, 68 each contain about 1050 pounds of 4 ADG 1/8″ 4 pellets of MicroSeive -dessicant marketed by Union Carbide Corporation, and flow is diverted from one desiccator to the other about every four hours during continuous operation. After each four hour cycle, the desiccant material in the desiccator not then in use is regenerated by means of a conventional auxiliary heater and blower system that is not shown in Figure 1.
After passing through the desiccant bed, the gas exits the desiccator through the applicable outlet line 70, 72, and directional outlet low control valve 74 into heater feed line 76.
Heater feed line 76 supplies the filtered and dried gas to heater 78, in which the gas is once again heated to the desired temperature for injection through gas supply line 26 and inlet I a 10 port 28 into drier 14. Any make-up gas required by the o recirculating gas system to compensate for leakage or other loss is desirably introduced into the system adjacent the inlet to c**o blower 46. Depending upon the particulate matter being dried, o a and the applicable temperatures and flow rates, further energy o l conservation may be obtained in some instances by circulating gas leaving desiccators 64, 68 through a conventional gas-gas heat *exchanger adapted to transfer thermal energy from the overhead gas stream at a point between drier 14 and condenser 40 prior to 0 entering gas heater 78.
Drier 14 is further described with reference to Figures 2 t through’4 of the drawings. Drier 14 is preferably a I “t substantially cylindrical vessel comprising top wall 80 and side wall 82. The upper portion of side wall 82, which comprises a major portion of its length, is preferably substantially j 25 cyclindrical. The lower portion of side wall 82, which comprises a minor portion of its length, is preferably inwardly inclined as it extends downwardly from the substantially cylindrical upper portion of side wall 82. The lower portion of side wall 82 thereby defines a frustoconical section having a top diameter that corresponds to the diameter of the upper portion and a bottom diameter that corresponds to the diameter of outlet 24.
Agitator shaft 16 is preferably rotatably mounted coaxially with the vertical axis of side wall 82.
i. According to a preferred embodiment of the invention, shaft i 16 is 5 inches in diameter. The lower end of shaft 16 is #Ott disposed inside the vessel near outlet 24, and is supported by 10 bearings 114 bolted to shaft anchor plate 116. Referring to Figure 4, shaft 16 extends downward through orifice 3.18, and S’ bearings 114 are bolted to shaft anchor plate 116 through bolt i holes 123. The top of shaft 16 extends upward through top wall as shown in Figure 1, and is driven by motor 18 through chain i 15 drive 20, According to a preferred embodiment of the invention, motor 18 is rated at 20 horsepower.
A plurality of axially-spaced sets of circumferentiallyspaced stirring arms are preferably connected in fixed relation to shaft 16. The number and spacing of the stirring arms can vary in relation to the overall size of drier 14, but according to one preferred embodiment of the invention, the configuration A depicted in the drawings can be satisfactorily employed with an apparatus having a throughput of about 1000 pounds of polymer per hour.
Referring to Figures 2 and 3, the uppermost set of stirring arms comprises stirring arms 84, 85, 86, which are preferably connected to shaft 16 at a point disposed near, and most preferably, slightly below the level within drier 14 to which particulate material is to remain filled during continuous operation. Each stirring arm is preferably of smaller diameter than shaft 16, and is downwardly inclined so as to form an included angle with shaft 16 of from about 40 to about degrees. End caps 88 are provided at the end of each stirring 10 arm 84, 85, 86. Support rods 90, 92, 94 extend transversely between stirring arms 84, 85, 86 to provide lateral structural oo00 o support. The length of stirring arms 84, 85, 86 is preferably such that the arms will extend to within about 2.5 inches of the a inwardly facing surface of side wall 82.
15 The next axially-spaced set of circumferentially-spaced stirring arms comprises stirring arms 102, 104 and a third S”stirring arm disposed beneath stirring arm 85 that is not visible in Figures 2 or 3. Each of stirring arms 102, 104 and the third stirring arm further comprises an end cap 106. The third axially-spaced set of stirring arms comprises stirring arms 108, 110 and a third stirring arm disposed beneath stirring arm Sthat is not visible in Figures 2 or 3. Each of stirring arms 108, 110 and the third stirring arm further comprises an end cap 112.
While the axially-spaced sets of stirring arms shown in Figure 1 are depicted in stacked alignment for ease of illustration, it will be understood that each respective axially-spaced set of stirring arms can be attached to shaft 16 in positions that are circumferentially rotated relative to the next adjacent set of stirring arms so as to obtain a more overlapped stirring pattern within the vessel. It will also be understood that while o each axially-spaced set of stirring arms shown in Figure 1 et 04 comprises three stirring arms, the number of stirring arms can be 10 varied in each axially-spaced set. According to a preferred oo embodiment of the invention, the stirring arms in each axially- S0 spaced set are evenly spaced circumferentially around shaft 16, Sand all stirring arms in drier 14 are fabricated from 1 inch diameter Schedule 80 pipe.
V *15 As shown in Figure 2, the length of the stirring arms in t j each of the two lower sets of stirring arms is shorter than the length of the stirring arms in the set or sets above it.
According to a preferred embodiment of the invention, the length of the stirring arms in each axially-spaced set will be equal, “and will be such that the radial distance between the outermost extending part of the stirring arm and the next closest portion of the stationary internal structure of polymer drier and recondenser 14 will be between about 1 and about 3 inches, and most preferably, between about 2 and 2.5 inches. Depending upon the length and diameter of the stirring arms, and the magnitude a o« 0 a *1 e f o 0* o o e 4 0000 00 0 0 00 0 0* o o o e 0 00 0r0 0 0 00 o 0 0 0 of the forces exerted on them during agitation, lateral support rods for the shorter stirring arms may be required.
Referring again to Figures 2 and 3, drier 14 preferably further comprises primary flow separator 124, which is preferably a frustoconical, foraminous metal structure defined by top edge 128 and bottom edge 130, having a first upwardly and inwardly facing surface and a second downwardly and outwardly facing surface, and having a thickness of about 1/8 inch. Top edge 128 is preferably fixed such as by welding to side wall 82 at a point 10 above the level at which side wall 82 becomes inwardly inclined.
Bottom edge 130 is preferably coextensive with the top edge of cylindrical outlet flow separator 126. Outlet flow separator 126 is desirably fabricated from the same metal as primary flow separator 124 and is connected in fixed relation thereto, such as 15 by welding or other similarly effective means.. The base of outlet flow separator 126 is preferably connected in fixed relation to shaft anchor plate 116 radially outside of polymer orifices 120, either by welding or by bolting a flange (not shown in Figure 2) along its bottom edge through holes 122. Primary 20 ‘flow separator 124 and outlet flow separator 126 are each preferably perforated across their surfaces with 1/8 inch diameter holes 132, 134, respectively, drilled in a diamond pattern on 3/16 inch spacing. The diameter of holes 132, 134 can vary from the size stated herein depending upon the average particle diameter of the particulate matter, and is preferably about the same size as or slightly smaller than the average particle diameter. To simplify illustration, only representative holes 132, 134 are shown in Figures 2 and 3.
When primary flow separator 124 and outlet flow separator 126 are constructed as disclosed herein, they cooperate to define plenum 154 in which relatively dry heated gas introduced through gas inlet port 28 is distributed over substantially the entire S o cross-sectional area of drier 14 so as to rise through the S polymer distributed across its cross-sectional area. The I 10 circulation and distribution of heated gas within plenum 154 can be further assisted by the installation of conventional baffles (not shown) within plenum 154, which baffles can be attached to the interior of side wall 82.
Auxiliary separator 136 is another frustoconical, foraminous S. 15 metal structure preferably disposed within side wall 82 of drier 14, and is adapted to cooperate with the stirring arms discussed 1 above and primary flow separator 124 in establishing beneficial i| contact between the downwardly flowing particulate matter and the upwardly flowing heated gas, while simultaneously retarding I 1 20 “agglomeration. Bottom edge 142 of auxiliary separator 136 is I preferably spaced about 3 inches away from the upward facing S.:surface of primary flow separator 124. Auxiliary separator 136 is preferably supported by and maintained in fixed relation to primary flow saparator 124 by a plurality of mounting brackets 138 circumferentially spaced around bottom edge 142. Top edge
I
140 of auxiliary separator 136 is preferably closely adjacent to, but not contacting, shaft 16. Auxiliary separator 136 is preferably perforated across substantially all of its surface with 1/8 inch diameter holes 144 having 3/16 inch spacings.
Where the particle size of the particulate matter is too great to permit any appreciable downward particle flow through auxiliary separator 136, a plurality of spaced holes 144 having a diameter larger than the average particle size of the particulate matter I:vb can be interspersed with small diameter holes 144 to provide better flow distribution through drier 14.
root Downwardly inclined deflector shield 146 is preferably I attached to rotating shaft 16 slightly above top edge 140 of auxiliary separator 136, and extends radially outward therefrom sufficiently to prevent downwardly flowing particulate matter from channelling through the gap between top edge 140 and shaft 16. When installed in this manner, deflector shield 146 also i functions to prevent the heated gas from channeling upward along shaft 16.
1 Triangularly shaped baffle plates 96, 98, 100 welded to stirring arms 84, 85, 86 and shaft 16 are also effective for ‘4 limiting the channeling of upwardly flowing heated gas along shaft 16, and provide additional lateral support for the stirring arms as well. A similar function could of course be satisfactorily achieved by installing additional axially-spaced deflector shields such as deflector shield 146, possibly of varying diameters, at other points along shaft 16.
When constructed as described herein, drier 1. can be effectively operated according to the method of the invention.
According to a preferred embodiment of the method of the invention, crystalline PET pellets are introduced into drier 14 through feed inlet 22 at a flow rate of about 1000 pounds per hour. Experience has shown that desirable results are achieved when the lower end of feed inlet 22 is disposed approximately ca q 10 inches below top wall O00 Agitator shaft 16 is controlled so as to rotate at less than 0o about 10 revolutions per minute, and preferably at about revolutions per minute.
Heated gas, preferably air or nitrogen at a dew point 1, o o0o 15 ranging between about -30 deg. F. and about -60 deg. and most preferably about -50 deg. is heated in heater 78 to a 4 I Stemperature between about 340 and about 385 degrees and most preferably about 380 degrees F. The heated gas is then introduced into plenum 154 of drier 14 at a flow rate ranging ‘between about 1000 and about 1500 cubic feet per minute, and most preferably, about 1350 feet per minute. This flow rate corresponds to a range.of from about 60 to about 90 cubic feet of heated gas per pound of particulate matter, and preferably, about 80 cubic feet of heated gas per pound of particulate matter.
As the particulate matter flows downward through drier 14, it is subjected to stirring agitation by rotating shaft 16, and the attached stirring arms. The particulate matter is simultaneously contacted by the heated gas as it rises through the vessel. The force exerted by the heated gas on the downward flowing particulate matter is desirably sufficient to penetrate the entire drier 14, and contact each particle without being so Sgreat as to fluidize the particulate matter or entrain any Sappreciable amount of particulate (other than fines) in the (othe 4 10 exhaust gas passing through gas outlet port Ite When PET pellets are dried according to this method, r ,excellent results are achieved in obtaining dried product having satisfactorily high intrinsic viscosities and satisfactorily low to acetaldehyde levels in comparison to comparable prior art devices.
According to another preferred embodiment of the method and system of the invention, damper mechanism 50 depicted in simplified form in Figures 1 and 5 is desirably employed to restrict the flow of heated gas through drier 14 during any prolonged cessation of particulate flow through outlet 24.
Si 20 Damper mechanism 50 preferably comprises gas flow control plate i 150, which is connected in fixed relation to rotable spindle 148.
j Gas flow control plate 150 is desirably disposed inside blower Soutlet line 48, and the diameter of gas flow control plate 150 is preferably slightly less than the inside diameter of blower outlet line 48. Rotatable spindle 148 desirably extends through the walls of blower outlet line 48, and is adapted by conventional, commercially available electromechanical control means (not shown) to be selectively rotated between a first position wherein the major surfaces of gas flow control plate 150 do not significantly impede the flow of gas through blower outlet line 48, and a second position where the major surfaces of gas flow control plate 150 are substantially transverse to the direction of flow of gas through blower outlet line 48. Gas flow #Oct control plate 150 is preferably further provided with a plurality ft., of orifices 152 adapted to permit about half, and preferably Ot0o from about 40 to about 60 percent, of the gas flow past damper mechanism 50 whenever gas flow control plate 150 is in the e& o transverse position as compared to the amount of gas that can otherwise flow past damper mechanism 50 whenever gas flow control Go 0 s 15 plate 150 is in the first position.
According to a preferred method of the invention employing C damper mechanism 50, the subject drier system is started up by opening feed ii.let 22 and actuating motor 18 to rotate shaft 16 within drier 14. Blower 46 is also actuated and gas heater 78 is -set so as to heat the circulating gas to the desired temperature.
The drier system is desirably operated in this manner for about 1 hour with the outlet 24 closed to heat up drier 14 and approach steady-state operating conditions. Outlet 24 is then opened and the discharge of dried particulate matter commences. If it later becomes necessary to stop the discharge of dried particulate matter from outlet 24, the amount of heat and/or agitation imparted to material within drier 14 during such stoppage or cessation of flow can be selectively controlled by controlling the rotational rate of shaft 16, by controlling damper mechanism 50 to restrict the gas flow rate, and by controlling the temperature of the circulating gas.
Where the particulate matter is PET pellets, and outlet 24 is adapted to flood feed an injection molding machine, the method 0444 of the invention has been successfully employed during short 0o 10 stoppages of the injection molding machine as follows. First, o44 employing well known, commercially available devices in the o’o method of the invention, a toggle switch triggers a delay timer 00 whenever the injection molding machine is stopped. For stoppages of under two minutes, no change is effected in the operation of the drier system of the invention. After a stoppage of two 4 °4 minutes, hcwever, a conventional microprocessor signals motor 18 O° to shut down, thereby stopping the rotational motion of shaft 16 and the stirring arms within drier 14. The microprocessor simultaneously signals damper mechanism 50, which is so adapted by conventional means such as air cylinders well known to those of ordinary skill in the art, to rotate gas flow control plate 150 to its transverse position, thereby restricting the gas flow rate to approximately 650 cubic feet per minute, compared to approximately 1350 cubic feet per minute during continuous operation. For stoppages substantially longer than two minutes, it may also be desirable to lower the temperature setting of gas heater 78 to avoid scorching the PET pellets w:chin drier 14.
Once the injection molding machine receiving material from outlet 24 is restarted, the aforementioned steps are reversed, and the temperature is brought back up, gas flow control plate 150 is rotated to its open position, and motor 18 is actuated, commencing rotation of shaft 16.
I The subject method and apparatus are particularly effective for reducing the acetaldehyde level in injection molded PET parts 10 made from PET pellets dried as disclosed herein. Acetaldehyde levels lower than 3 parts per million are consistently achieved in injection molded PET parts made from PET pellets dried in the apparatus of the invention while practicing the subject method utilizing air as the heated gas, a gas inlet temperature of about i 15 380 degrees a gas flow rate of about 1350 cubic feet per t 0 Sminute, a PET flow rate of about 1000 pounds per hour, and a shaft rotation rate of about 3.5 revolutions per minute.
Moreover, through use of the present invention, these highly desirable results are achieved at an energy savings of about “in comparison to the closest comparable conventional driers. The significant improvements in energy efficiency experienced through use of the present invention are believed to be attributable to the improved contact and thermal energy transfer between heated gas and particulate matter that is achieved through improved agitation and flow distribution within the subject drier in cooperation with particularly beneficial gas flow rates. Such energy savings are easily translated into significantly reduced operating costs which, coupled with the highly desirable physical properties of the resultant product, offer molders attractive economic incentives for utilizing the method and apparatus of the invention.
Other alterations and modifications of the subject drier, system and method will become obvious to those of ordinary skill in the art upon reading the subject disclosure, and it is I 10 intended that the present invention be limited only by the i broadest interpretation of the appended claims to which the I inventor may be legally entitled.
ti
C.

Claims (18)

1. A drier for particulate matter, said drier comprising: An enclosed vessel having an upper section with a vertically oriented, substantially cylindrical sidewall, and a coaxially aligned lower section with a downwardly and inwardly tapered frustoconical sidewall, the bottom edge of said upper section being substantially coextensive with the top edge of said lower section; A rotatable shaft coaxially disposed within said vessel and extending substantially the entire interior length of said vessel; Means for rotating said shaft within said vessel; A plurality of axially spaced arrays of circumferentially spaced, radially extending, downwardly inclined stirring arms connected to said shaft in fixed relation to said shaft and in substantially fixed relation to each other; Inlet means near the top of said vessel for introducing particulate matter to be dried into said vessel; Outlet means at the bottom of said vessel for discharging dried particulate matter from said vessel; or Means for introducing a heated gas into the lower section of said vessel; and 25 At least two perforated substantially frustoconical separator means coaxially disposed within said vessel in fixed relation to each other and to the sidewalls of said vessel: said first separator means tapering inwardly in S the downward direction and having a top edge substantially 30 coextensive with the sidewall of said vessel and a bottom edge terminating near the bottom of said vessel, said first separator means comprising a first inwardly and upwardly facing surface and a second downwardly and outwardly facing surface, said second surface further cooperating with the sidewall of said vessel to define an 23 annular plenum within the lower section of said vessel, said plenum being adapted to receive said heated gas introduced into the lower section of said vessel and to distribute said heated gas upwardly through said vessel, the perforations in said first separator means being adapted to permit the passage of heated gas upwardly therethrough and not being substantially larger than the average particle size of said particulate matter; said second separator means boing inverted relative to said first separator means and having a top edge closely adjacent to but spaced apart from said shaft, and a bottom edge disposed inwardly of and below the top edge of said first separator means but spaced sufficiently above the interiorly facing surface of said first separator means to permit the passage of particulate matter therebetween, at least some of the perforations in said second separator means being sufficiently large to permit the passage of I particulate matter therethrough.

2. The drier of claim 1 wherein said stirring arms in at least one of said arrays are further connected by means j adapted to provide lateral support to said stirring arms during rotation within said vessel. S 3. The drier of claims 1 or 2 wherein at least one 1 deflector means is connected in fixed relation to said I 25 shaft to prevent said heated gas from rising through said i vessel along said shaft. S4. The drier of any one of claims 1-3 wherein the lower end of said shaft is rotatably mounted within and near the bottom of said vessel and is maintained in coaxial alignment with said vessel by means of bearings secured to an anchor plate adapted to permit the downward passage of particulate matter therethrough. The drier of any one of claims 1-4 wherein said vessel is adapted to accommodate a flow of about 1000 pounds of particulate matter per hour and a flow of about 24 1350 cubic feet of heated gas per minute.

6. The drier of any one of claims 1-5 wherein said particulate matter is polymer pellets, and said heated gas is selected from the group consisting of nitrogen and air.

7. A drier system for particulate matter, said system comprising the drier of claim 1, means for introducing particulate matter and heated gas into said drier, means for recovering gas from said drier and for filtering, condensing, drying, reheating and recirculating said gas to said drier; means for receiving dried particulate matter discharged from said drier; and means for restricting the flow of recirculating gas through said drier following a cessation of particulate matter flow through said drier.

8. The drier system of claim 7 wherein said means for restricting the flow of recirculating gas is a damper mechanism adapted to limit the flow of recirculating gas following a cessation of particulate matter flow through said drier for a predetermined period.

9. The drier system of claim 7, further comprising means for downwardly adjusting the temperature of said recirculating gas following a cessation of particulate matter flow through said drier for a predetermined period. The drier system of claim 7, further comprising means for downwardly adjusting the rate of rotation of said shaft following a cessation of particulate matter flow through said drier for a predetermined period.

11. A method for drying particulate matter, said method comprising the steps of: Introducing said particulate matter into a vessel having a vertically disposed substantially cylindrical upper section and a frustoconical lower section, said vessel further comprising a coaxially disposed rotatable shaft extending downwardly through said vessel for substantially the entire length of said vessel; a C C CC iL I 25 plurality of axially spaced arrays of circumferentially spaced, radially extending, downwardly inclined stirring arms connected to said shaft; and a plurality of perforated substantially frustoconical separator means coaxially disposed within said vessel in fixed relation to each other and to the sidewalls of said vessel, said first separator means tapering inwardly in the downward direction and having a top edge substantially coextensive with the sidewall of said vessel and a bottom edge terminating near the bottom of said vessel, said first separator means comprising a first inwardly and upwardly facing surface and a second downwardly and outwardly facing surface, said second surface further cooperating with the sidewall of said vessel to define an annular plenum within the lower section of said vessel, said plenum being adapted to receive said heated gas introduced into the lower section of said vessel and to distribute said heated gas upwardly through said vessel, the perforations in said first separator means being adapted to permit the passage of heated gas upwardly therethrough and not being substantially larger than the average particle size of said particulate matter; said second separator means being inverted relative to said first separator means and having a top edge closely adjacent to but spaced apart from said shaft, and a bottom edge disposed inwardly of and below the top edge of said first separator means but spaced sufficiently above the interiorly facing surface of said first separator means to permit the passage of particulate matter therebetween, at least some of the perforations in said second separator means being sufficiently large to permit the passage of particulate matter therethrough and said separators cooperating with said stirring arms to retard agglomeration of said particulate matter within said vessel; I If I 1 0 90 O 04 044 949,o 4 4944 44i 0 S 0 0 44 0 9 I 26 Introducing relatively dry, heated gas into the lower section of said vessel in such manner that it is distributed over substantially the entire cross-sectional area of said vessel and directed upwardly through said vessel; Contacting said downwardly flowing particulate matter with said upwardly directed heated gas while agitating said particulate matter by rotating said shaft; Discharging said particulate matter through an outlet 10 disposed in the lower section of said vessel; Recovering said heated gas through an outlet in the top of said vessel; Filtering entrained particulate matter from said recovered gas; 15 Condensing water vapor from said recovered gas; Drying said recovered gas; Reheating said recovered gas; and Recirculating said reheated gas to said vessel.

12. The method of claim 11 wherein said particulate matter comprises a polymer.

13. The method of any one of claims 11 or 12 wherein said particulate matter is selected from the group consisting of polycondensates.

14. The method of any one of claims 11-13 wherein said particulate matter is selected from the group consisting of polyesters. The method of any one of claims 11-14 wherein said particulate matter is selected from the group consisting of polyethylene terephthalate pellets, polyethylene terephthalate granules, polyethylene terephthalate flakes, and mixtures thereof.

16. The method of any one of claims 11-15 wherein the heated gas introduced into said vessel has a dew point ranging between -30 degrees F. and -60 degrees F.

17. The method of any one of claims 11-16 wherein said iA 27 heated gas has a dew point of about -50 degrees F.

18. The method of any one of claims 11-17 wherein said heated gas further comprises a major portion oy an inert gas.

19. The method of claim 18 wherein said inert gas is nitrogen. The method of any one of claims 11-19 wherein said heated gas is introduced into said vessel at a temperature ranging between 170 degrees C. and 200 degrees C. oo 10 21. The method of any one of claims 11-20 wherein the o amount of heated gas introduced into said vessel ranges *too between 60 and 90 cubic feet per pound of particulate sa matter.

22. The method of any one of claims 11-21 wherein the 04 40 o 15 amount of heated gas introduced into said vessel is about cubic feet per pound of particulate matter.

23. The method of any one of claims 11-22 further comprising the step of restricting the flow rate of said .oP heated gas by about one half upon cessation of flow of S 20 said particulate matter through said vessel.

24. The method of any one of claims 11-23 further comprising the step of reducing the temperature of said heated gas upon cessation of flow of said particulate matter through said vessel.

25. The method of any one of claims 11-24 further comprising the step of reducing the rate of rotation of said shaft upon cessation of flow of said particulate matter through said vessel. Dated this 25 day of October 1991. PERMIAN RESEARCH CORPORATION Patent Attorneys for the Applicant: A ~F B RICE CO j

AU30746/89A
1988-02-26
1989-02-24
Drying method and apparatus

Ceased

AU619255B2
(en)

Applications Claiming Priority (2)

Application Number
Priority Date
Filing Date
Title

US07/160,521

US4839969A
(en)

1988-02-26
1988-02-26
Drying method and apparatus

US160521

1993-12-01

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AU3074689A

AU3074689A
(en)

1989-08-31

AU619255B2
true

AU619255B2
(en)

1992-01-23

Family
ID=22577225
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Priority Date
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AU30746/89A
Ceased

AU619255B2
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1988-02-26
1989-02-24
Drying method and apparatus

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EP
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CN
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Also Published As

Publication number
Publication date

US4839969A
(en)

1989-06-20

JPH024501A
(en)

1990-01-09

AU3074689A
(en)

1989-08-31

KR920002380B1
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1992-03-23

KR890013066A
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1989-09-21

CN1037207A
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1989-11-15

CN1018672B
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1992-10-14

EP0333329A3
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1991-09-04

EP0333329A2
(en)

1989-09-20

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