Apparatus and method for moisture control of particulate material

• US 6,289,606 B2
• Filed: 12/20/2000
• Issued: 09/18/2001
• Est. Priority Date: 06/13/1997
• Status: Expired due to Term

• Current Assignee: Novatec Incorporated
• Original Assignee: Novatec Incorporated
• Inventors: Gillette, W. John, Frank, Paul M.
• Primary Examiner(s): WILSON, PAMELA ANNE
• Application Number:
  US09/739,770
• Publication Number:
  US 20010003874A1
• Time in Patent Office: 272 Days
• Field of Search: 344/67, 344/72, 344/74, 344/78, 344/79, 344/80, 345/51, 345/57, 345/66, 34/79, 34/80, 34/81, 342/12, 342/15, 342/18, 342/19, 344/73, 341/65, 341/66, 341/68, 341/69
• US Class Current: 34/472
• CPC Class Codes: B29B 13/065 of powder or pellets
• CPC Class Codes: B29B 9/16 Auxiliary treatment of granules
• CPC Class Codes: F26B 21/083 by using sorbent or hygroscopic materials, e.g. chemical substances, molecular sieves

Abstract

An apparatus and method for control of moisture content of material such as thermoplastic pellets (80) in a hopper (30) is controlled by supplying dehumidified air from a dessicant bed (90) to the hopper (30) and returning air from the hopper (30) to the dessicant bed (90). A dew point sensor (10) in the return air path determines the moisture content of the material (80) in the hopper (30), and when the dew point drops to a pre-set level, a diverter (134) causes the return air flow to bypass the dessicant bed (90) and to be re-supplied to the hopper (30) without dehumidification. Two dessicant beds are provided, one of which is on-process while the dessicant in the other is regenerated.

Claims

1. An apparatus for controlling the moisture content of material in a material handling system, comprising:

a supply gas flow path to supply moisture-controlled gas to said material handling system;

a return gas flow path to extract gas from said 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 operative to alternatively connect one of said first gas flow path, said second gas flow path, and both of said first and second gas flow paths between said 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.

2. An apparatus according to claim 1, further comprising:

a sensor to output a signal based on the moisture content of the material; and

control circuitry to cause said selector to operate based on said signal.

3. An apparatus according to claim 2, wherein said sensor is provided in the return gas flow path.

4. An apparatus according to claim 1, wherein said dryer in said first gas flow path includes a dessicant.

5. An apparatus according to claim 4, wherein when said selector connects only said second gas flow path between said supply and return gas flow paths, said selector causes gas flow through said dryer to be blocked.

6. An apparatus according to claim 1, wherein the selector includes a valve.

7. An apparatus for controlling the moisture content of material in a material handling system, comprising:

a supply gas flow path to supply moisture-controlled gas to said material handling system;

a return gas flow path to extract gas from said material handling system;

first and second dessicant towers to remove moisture from the gas extracted from said material handling system;

a first valve to input the extracted gas to a selected one of said first and second dessicant towers;

a second valve to output gas from the selected one of said first and second dessicant towers to a third valve; and

a bypass gas flow path to supply the extracted gas to said third valve and thereby bypass said first and second dessicant towers, wherein said third valve alternately directs, to said supply gas flow path, gas from a selected one or the other of said bypass gas flow path and the output from said second valve and alternately blocks a non-selected one or the other of said bypass gas flow path and said output from said second valve, to thereby provide moisture-controlled gas to control the moisture content of the material.

8. An apparatus according to claim 7, further comprising:

a sensor, provided in the return gas flow path, to output a signal based on moisture content of the material; and

control circuitry to control said third valve based on the signal from the sensor.

9. An apparatus according to claim 8, further comprising:

a sensor, provided in the supply gas flow path, to output a signal based on the dew point of the moisture-controlled gas,

wherein said control circuitry controls said first and second valves to select the other of the first and second dessicant towers based on the signal from the sensor provided in the supply gas flow path.

10. An apparatus according to claim 9, further comprising:

a regeneration heater, controlled by said circuitry, to regenerate the dessicant in the first and second towers.

11. A method for controlling the moisture content of material in a material handling system using a dehumidifying system having a first gas flow path including a dryer and a second gas flow path devoid of a dryer, comprising:

providing a supply gas flow path to supply moisture-controlled gas to said material handling system;

providing a return gas flow path to extract gas from said material handling system; and

alternatively connecting one of said first gas flow path, said second gas flow path, and both of said first and second gas flow paths between said 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.

12. A method according to claim 11, further comprising:

sensing the moisture content of the material, wherein the alternative connecting is based on said sensing.

13. A method according to claim 12, wherein said sensing senses the moisture content of gas in the return gas flow path.

14. A method according to claim 11, wherein said dryer in said first gas flow path includes a dessicant.

15. A method according to claim 14, wherein when only said second gas flow path is connected between said supply and return gas flow paths, gas flow through said dryer is blocked.