WO1998057110A1 - Appareil et procede de regulation de l'humiditie d'un materiau particulaire - Google Patents

Appareil et procede de regulation de l'humiditie d'un materiau particulaire Download PDF

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Publication number
WO1998057110A1
WO1998057110A1 PCT/US1998/011594 US9811594W WO9857110A1 WO 1998057110 A1 WO1998057110 A1 WO 1998057110A1 US 9811594 W US9811594 W US 9811594W WO 9857110 A1 WO9857110 A1 WO 9857110A1
Authority
WO
WIPO (PCT)
Prior art keywords
gas flow
flow path
gas
moisture
supply
Prior art date
Application number
PCT/US1998/011594
Other languages
English (en)
Inventor
W. John Gillette
Paul M. Frank
Original Assignee
Novatec, Inc.
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.)
Filing date
Publication date
Application filed by Novatec, Inc. filed Critical Novatec, Inc.
Priority to CA002294016A priority Critical patent/CA2294016A1/fr
Priority to JP50289499A priority patent/JP2002504034A/ja
Priority to EP98926318A priority patent/EP0988498A4/fr
Publication of WO1998057110A1 publication Critical patent/WO1998057110A1/fr

Links

Classifications

    • 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
    • F26B21/06—Controlling, e.g. regulating, parameters of gas supply
    • F26B21/08—Humidity
    • F26B21/083—Humidity by using sorbent or hygroscopic materials, e.g. chemical substances, molecular sieves

Definitions

  • This invention relates to moisture control in a material handling system, and more particularly to an apparatus and method used to control the moisture content of solid particulate material, such as plastic pellets used for making thermoplastic molded articles and extrusions.
  • a typical system for controlling the moisture content in a particulate bed supplies moisture- controlled air to the particulate bed and uses a dessicant to dehu idify air returning from the particulate bed.
  • This system causes very low dew point air to be supplied to the particulate bed.
  • the material in the particulate bed comprises resins such as certain homopolymer and copolymer polyamides and some polyesters (e.g., nylon 6 and 6.6)
  • the resins may be over-dried undesirably. Some moisture content is required to maintain desired impact resistance and flexibility in finished products produced from the resins.
  • an apparatus for controlling the moisture content of a material in a material handling system comprises a supply gas flow path to supply moisture-controlled gas to the material handling system; a return gas flow path to extract gas from the material handling system; a dehumidifying system having a first gas flow path including a dryer and a second gas flow path devoid of a dryer; and a selector to alternatively connect one of the first gas flow path, the second gas flow path, and both of the first and second gas flow paths between the supply and return gas flow paths to thereby provide a closed-loop circuit of moisture- controlled gas to control the moisture content of the material.
  • a method for controlling the moisture content of material in a material handling system uses a dehumidifying system having a first gas flow path including a dryer and a second gas flow path devoid of a dryer.
  • the method comprises providing a supply gas flow path to supply moisture-controlled gas to the material handling system; providing a return gas flow path to extract gas from the material handling system; and alternatively connecting one of the first gas flow path, the second gas flow path, and both of the first and second gas flow paths between the supply and return gas flow paths to thereby provide a closed-loop circuit of moisture-controlled gas to control the moisture content of the material.
  • Figure 1 is a schematic diagram showing process air flow in accordance with the invention when air returning from a feed hopper is dehumidified.
  • Figure 2 is a schematic diagram showing process air flow in accordance with the invention when air returning from the feed hopper is not dehumidified.
  • Figure 3 shows a front elevational view of dehumidifying apparatus of the invention.
  • Figure 4 shows a rear elevational view of the dehumidifying apparatus of the invention.
  • Figure 5 shows a top view of the dehumidifying apparatus of the invention.
  • Figure 6 shows a rear elevational sectional view of the dehumidifying apparatus of the invention taken along the line 6-6 in Figure 5.
  • a stream of air of controlled humidity from a dehumidifying apparatus 100 is supplied to a feed hopper 30, or like container, containing a bed of particulate material 80, e.g., pellets of a synthetic thermoplastic resin, and is returned to the dehumidifying apparatus 100.
  • the invention is conveniently applied, for example, to controlling the moisture content of pellets of thermoplastic synthetic resin in the feed hopper 30 that are output through a discharge outlet 40 to a thermoplastic molding machine or extrusion apparatus (not shown) .
  • Dehumidified air is supplied to the feed hopper 30, typically near the bottom, and passes through an air diffuser 50, e.g., a spreader cone, and through the bed of particulate material 80, taking up moisture from the particulate material.
  • the process air is then returned to the dehumidifying apparatus 100 where its moisture content is reduced by passage through a dryer, namely a bed of dessicant 90. (As later described, the invention employs two dessicant beds, alternately.)
  • the air passing through the dehumidifying apparatus is then re-supplied to the feed hopper 30 after passing through an inlet air heater 70, which heats the air from the dehumidifying apparatus to a temperature selected in accordance with the type of particulate material.
  • the air heater may be an electric unit or an indirect, gas-fired unit.
  • the moisture content in the particulate material 80 in the feed hopper 30 is determined by monitoring the humidity (or dew point) of the return air leaving the hopper.
  • a suitable dew point or humidity sensor 10 located in an exit conduit (not shown) of the hopper provides a signal to control circuitry in a control box 106 of the dehumidifying apparatus 100.
  • the control circuitry may include a PLC processor. As the moisture level in the particulate material 80 decreases, the dew point of the return air from the feed hopper 30 also decreases.
  • the control circuitry of the dehumidifying apparatus 100 moves a diverter (selector) valve 134 to a bypass position. As shown in Fig. 2, the stream of process air then bypasses the dessicant bed 90 and is re-supplied to the feed hopper 30 without dehumidification. Because the process air does not pass through the dessicant bed, moisture will not be removed from the process air, and the process air will absorb little or no moisture from the particulate material (or may even add moisture) , depending on the state of equilibrium between the process air and the particulate material 80. The dew point of the process air will increase as additional moisture-bearing particulate material is inserted at the top 20 of the hopper to replace particulate material 80 discharged from outlet 40 at the bottom, and as humid environmental air invades the system.
  • control circuitry When the dew point of the return air increases to a value corresponding to a pre-selected upper limit of moisture content of the particulate material 80, the control circuitry repositions the diverter valve 134 to again permit the process air stream to pass through the dessicant bed 90.
  • a dew point sensor has a predetermined dew point range (e.g., 0 degrees F to -40 degrees F (-17.8 C degrees to -40 C degrees)) and the operator selects an appropriate value in that range. The operator also selects an appropriate drying temperature. Once an appropriate drying temperature is selected, the air heater 70 is controlled to regulate the temperature, using a temperature sensor (not shown), e.g., a thermocouple.
  • a dew point sensor 60 is preferably provided between the outlet of the dehumidifying apparatus 100 and the air heater 70. However, the dew point sensor 60 could be located elsewhere in the supply air flow path.
  • the dehumidifying apparatus 100 of the invention comprises two dessicant towers 102 and 104, only one of which is used, i.e., "on-process," at a given time.
  • the on- process dessicant bed is monitored and automatically regenerated when the dessicant nears saturation, and the other bed, which has been regenerated is brought on-process.
  • a control box 106 which includes control circuitry for the system, is mounted between and supported on dessicant towers 102, 104 by brackets 107.
  • the front panel of the control box 106 supports the displays and controls -for the operating parameters of the system.
  • the displays preferably show all major component functions, including temperature settings, dew points and other process variables, in a graphic, schematic format.
  • the values of the operating parameters may also be provided to an external communications port.
  • the apparatus is also preferably provided with a fail-safe over-temperature alarm and dryer shut-down controls.
  • return air enters the dehumidifying apparatus 100 through inlet 158 and passes through a process air cooler 154, which is preferably provided in this embodiment .
  • the process air cooler 154 contains a cooling coil, typically cooled by circulating cool water through inlet and outlet connections 156. This cooling coil in the return air line lowers the temperature of the moisture-laden return air before it enters the dessicant, so that the dessicant may perform effectively.
  • the process air cooler 154 can be omitted if the return air in a particular system is already cool enough.
  • the process air After passing through the cooler 154, the process air then passes through a filter unit contained in a housing 112.
  • the filter unit can include a high-efficiency air filter to trap entrained dust particles.
  • a cyclonic filter which can trap particles as small as one micron in diameter, can be added.
  • the process filter units may have monitors to signa-1 when filter cartridges need to be cleaned and replaced.
  • the process air After passing through the filter unit, the process air passes through an air conduit 114 to a process air blower 108 driven by a motor 110.
  • the process air passes from the blower 108 into an upper 4-way valve 116, which directs the air into the on-process dessicant bed in one of the dessicant towers 102 or 104, through one of air conduits 122 or 120, respectively.
  • the state of the valve 116 is adjusted by the actuator arm 124.
  • actuator arms are shown on each side of the 4-way valve. However, it will be understood that such an actuator arm is actually needed only on one side of the valve .
  • the process air passes downward through the on-process dessicant bed to the bottom of the bed, which is located at about the level of the air conduits 130 and 132.
  • the dessicant beds in the illustrated apparatus fill only the upper portion of the dessicant towers 102 and 104, the lower portion of the towers being provided for mechanical support.
  • the process air then passes through the appropriate conduit 130 or 132 to a lower 4-way valve 118.
  • the state of the lower 4-way valve 118 is adjusted by its actuator arm 126 (shown duplicated for clarity of illustration) . From the lower 4-way valve 118, the dehumidified air passes through conduit 140 to diverter valve 134.
  • the diverter valve 134 is positioned, e.g., by an actuating air cylinder 136, to direct the process air to the outlet 142, from which it proceeds to a material handling apparatus, such as the feed hopper 30 containing the pellets to be dried. After passing through the feed hopper 30, and absorbing moisture from the particulate matter therein, the process air returns to the dehumidifying apparatus 100 through a conventional return air conduit (not shown) .
  • the humidity or dew point of the process air leaving the hopper 30 is measured by a sensor 10 as described previously.
  • the sensor 10 is preferably located at the hopper, but may be located in the return air conduit or at the inlet to the dehumidifying apparatus 100.
  • the circuitry in the control box 106 senses when the dew point signal from the sensor 10 has fallen to a value corresponding to the desired lower limit of moisture content for the particulate material as described previously. At this time, the circuitry in the control box 106 actuates air cylinder 136 to reposition the diverter valve to a state which blocks air coming from a dessicant bed via conduit 130 or 132 and the lower 4-way valve 118, and opens air conduit 138 from the process air blower 108 to the diverter valve
  • the diverter valve may prevent air from entering a dessicant bed, or two diverter valves may be used to block air entering and leaving a dessicant bed.
  • the return air from the hopper 30 bypasses the dessicant bed in both of the dessicant towers 102, 104 and is sent directly to the outlet 142 of the diverter valve 134, to be reheated and re-supplied to the hopper for another pass through the particulate material.
  • the control circuitry When the dew point of the air leaving the hopper 30 indicates that the moisture content has reached a predetermined upper limit, the control circuitry is activated to return the diverter valve 134 from its bypass state to its normal dehumidifying state, and the process air is then again dehumidified at each pass through the dehumidifying apparatus 100.
  • the moisture content of the process air (and, e.g., the moisture content of the material in the hopper) is kept within a predetermined range merely by setting the controls on the front panel of the control box 106, under control of the operator.
  • the on-process bed in one of the dessicant towers 102 and 104 is switched out of the process air loop and the fresh, off-process bed in the other of the two dessicant towers 102 and 104 is placed on-process.
  • This is accomplished under control of the control circuitry which actuates the 4-way valve actuator 162, which in turn repositions the 4-way valves 116 and 118 through their actuator arms 124 and 126, which are connected to each other and to the valve actuator 162 by mechanical linkages 164.
  • the process air is then directed from the blower 108 through the other of the dessicant towers 102 and 104, and the air so dehumidified is sent to the particulate material.
  • a regeneration cycle may be performed in the following manner.
  • a regeneration air filter unit in a regeneration air filter housing 146.
  • the regeneration filter unit may have a monitor to signal the need for cleaning or replacing a filter cartridge.
  • Air passing through the regeneration filter unit is moved by a regeneration air blower 144, driven by a motor 148, through a regeneration air heater housing 150.
  • the heater housing 150 is preferably externally mounted to allow easy access for maintenance.
  • a heating element within the heater housing 150 warms the regeneration air so that the moisture adsorbed by the dessicant bed can be released.
  • the heated regeneration air then passes from the heater housing 150 through conduit 152 to the lower 4-way valve 118, which directs the regeneration air into the off-process bed through the appropriate conduit 130 or 132.
  • the heated regeneration air passes upward through the dessicant bed to release the adsorbed moisture therein by thermal regeneration.
  • the moist regeneration air then leaves the off-process bed through the appropriate upper conduit 120 or 122 to the upper 4-way valve 116.
  • the moist regeneration air is then discharged to the environment through the regeneration air outlet 128 on the lower port of the upper 4-way valve 116.
  • Appropriate sensors can be incorporated into the regeneration loop to control the temperature of the regeneration air.
  • the regeneration cycle preferably has a dynamic cooling period during which the heater is turned off and the blower 144 is left on.
  • blower 144 is turned off to provide static cooling, thus permitting a smooth shift between the on- process and off-process beds.
  • the method and apparatus of the invention provide a convenient way to control the humidity of particulate material such as pellets of thermoplastic molding or extrusion resins, within a desirable predetermined range.
  • components such as the process air blower can be mounted on a floor stand near the material handling hopper if the dryer is some distance from the hopper.
  • a single air drying unit can also serve as a central dehumidifying system to deliver unheated, controlled dew point air to one, or several, remote heater/blowers on one, or several, hoppers, each with an individually set drying temperature.
  • the dehumidifying apparatus of the invention can also serve as a source of dry air for air conveying systems that use the air as a conveying medium to distribute materials to one, or several, different molding or extrusion machines, for example.
  • the diverter valve is positioned by an air cylinder in the foregoing description, the diverter valve could be positioned by other means, such as a hydraulic cylinder or a gear motor. If, e.g., a gear motor is employed, the diverter valve can be used to provide a modulated supply of air from a dessicant bed and air returning from the particulate material. That is, air that is dehumidified in the dessicant bed can be mixed with the moist air returning from the particulate material in a manner that more precisely controls moisture content of the air supplied to the particulate material. In such a system (and others) , signals from both sensors 10 and 60 can be used for control .

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Drying Of Gases (AREA)
  • Drying Of Solid Materials (AREA)
  • Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)

Abstract

On peut réguler la teneur en humidité d'un matériau, tel que des pastilles thermoplastiques (80) dans une trémie (30), en amenant de l'air déshumidifié provenant d'un lit de déshydratant (90) jusqu'à la trémie (30) et en faisant ensuite retourner l'air de la trémie (30) au lit de déshydratant. Un capteur de point de rosée (10) dans le trajet de retour de l'air détermine la teneur en humidité du matériau (80) dans la trémie (30) et, lorsque le point de rosée tombe à un niveau préétabli, une chicane (134) amène le flux d'air de retour à contourner le lit de déshydratant (90) et à retourner à la trémie sans déshumidification. Deux lits de déshydratants sont prévus, l'un est alimenté en continu alors que dans l'autre, le déshydratant est régénéré.
PCT/US1998/011594 1997-06-13 1998-06-12 Appareil et procede de regulation de l'humiditie d'un materiau particulaire WO1998057110A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
CA002294016A CA2294016A1 (fr) 1997-06-13 1998-06-12 Appareil et procede de regulation de l'humiditie d'un materiau particulaire
JP50289499A JP2002504034A (ja) 1997-06-13 1998-06-12 粒状材料の水分調整用装置および方法
EP98926318A EP0988498A4 (fr) 1997-06-13 1998-06-12 Appareil et procede de regulation de l'humiditie d'un materiau particulaire

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US4949897P 1997-06-13 1997-06-13
US60/049,498 1997-06-13

Related Child Applications (2)

Application Number Title Priority Date Filing Date
US09445773 A-371-Of-International 1999-12-13
US09/739,770 Continuation US6289606B2 (en) 1997-06-13 2000-12-20 Apparatus and method for moisture control of particulate material

Publications (1)

Publication Number Publication Date
WO1998057110A1 true WO1998057110A1 (fr) 1998-12-17

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EP (1) EP0988498A4 (fr)
JP (1) JP2002504034A (fr)
CA (1) CA2294016A1 (fr)
WO (1) WO1998057110A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014122178A1 (fr) 2013-02-07 2014-08-14 Bayer Materialscience Ag Procédé de production de compositions d'abs à surface améliorée après un stockage dans des conditions de chaleur et d'humidité

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4974337A (en) * 1989-10-30 1990-12-04 The Conair Group, Inc. Apparatus and method of drying and dehumidifying plastic

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5172489A (en) * 1991-04-30 1992-12-22 Hydreclaim Corporation Plastic resin drying apparatus and method
DE19531446A1 (de) * 1995-08-26 1997-02-27 Motan Holding Gmbh Vorrichtung mit mindestens einem Vorratsbehälter für zu behandelndes Gut, vorzugsweise Kunststoffgranulat

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4974337A (en) * 1989-10-30 1990-12-04 The Conair Group, Inc. Apparatus and method of drying and dehumidifying plastic

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP0988498A4 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014122178A1 (fr) 2013-02-07 2014-08-14 Bayer Materialscience Ag Procédé de production de compositions d'abs à surface améliorée après un stockage dans des conditions de chaleur et d'humidité
US9714324B2 (en) 2013-02-07 2017-07-25 Covestro Deutschland Ag Method for the production of ABS compositions having an improved surface following storage in a warm-humid environment

Also Published As

Publication number Publication date
JP2002504034A (ja) 2002-02-05
EP0988498A1 (fr) 2000-03-29
EP0988498A4 (fr) 2000-11-15
CA2294016A1 (fr) 1998-12-17

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