Systems for drying moisture-containing work pieces and methods for drying same

• US 7,194,822 B2
• Filed: 05/11/2004
• Issued: 03/27/2007
• Est. Priority Date: 05/11/2004
• Status: Active Grant

• Current Assignee: American Wood Dryers, LLC
• Original Assignee: American Wood Dryers, Inc.
• Inventors: Kolari, Gary L.
• Primary Examiner(s): Lu; Jiping
• Application Number:
  US10/843,728
• Publication Number:
  US 20050252027A1
• Time in Patent Office: 1,050 Days
• Field of Search: 344/87, 344/88, 344/89, 344/91, 344/92, 345/14, 345/15, 345/65, 345/66, 345/69, 34/86, 341/91, 342/12, 342/15, 342/18, 342/19, 165/59, 165/240, 236/44.C
• US Class Current: 34/489
• CPC Class Codes: F26B 21/026 by reversing fan rotation
• CPC Class Codes: F26B 21/12 Velocity of flow; Quantity of flow , e.g. by varying fan speed, by modifying cross flow area F26B21/004 takes precedence; changing air flow pattern F26B21/022
• CPC Class Codes: F26B 2210/16 Wood, e.g. lumber, timber
• CPC Class Codes: F26B 23/002 recovered from dryer exhaust gases F26B23/022 takes precedence
• CPC Class Codes: Y02P 70/10 Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working

Abstract

A system and method are provided for controllably drying moisture-containing work pieces. The system comprises a drying compartment defining an internal workspace for housing and drying the moisture-containing work pieces by introducing heat into the internal workspace and heating the moisture-containing work pieces located in the internal workspace by removing heated moisture from the work pieces and absorbing the heated moisture into the air in the workspace to produce heated humidified air. A multi-directional air flow heat exchanger is employed for receiving heated humidified air and atmospheric air and for recycling waste heat from exhaust air from the drying compartment, and for heating the atmospheric air in the heat exchanger using recovered heat extracted from the heated humidified air to a temperature higher than ambient temperature thereby reducing energy costs and drying time and preventing the loss of circulation air. First and second reversible variable speed fans are also included in the system. Each of the fans is independently controllable at respective intake and exhaust modes and at variable air flow rates, without employing a damper for controlling the flow of exhaust air and atmospheric air to and from the heat exchanger.

Claims

1. A method for controlling drying conditions in a dry kiln including a workspace by venting and recycling waste heat from exhaust air from the workspace, said workspace housing and drying high moisture-containing work pieces, which comprises:

introducing heat into said workspace;

heating the high moisture-containing work pieces located in said workspace;

removing heated moisture from the high moisture-containing work pieces and absorbing said heated moisture into the air in the workspace to produce heated humidified air thereby forming working pieces which are substantially uniformly dried;

providing a multi-directional air flow heat exchanger for receiving heated humidified air and atmospheric air;

providing first and second reversible variable speed fans, each of said fans being independently controllable at either one of an intake and exhaust mode and at variable air flow rates, without employing a damper for controlling the flow of exhaust air and atmospheric air to and from said heat exchanger;

providing a humidity control system including sensors for monitoring the conditions in the workspace, including air temperature before and/or after the heat exchanger, and sending a control signal;

providing variable frequency drives interfaced with said humidity control system to set the speed of the first and second reversible variable speed fans which proportionately increase or decrease the speed of the first and second reversible variable speed fans to increase or decrease the air flow through the dry kiln in response to the control signal sent by said control system;

controllably exhausting said heated humidified air from the workspace into said heat exchanger using said first variable speed and/or said second variable speed fan;

supplying atmospheric air at ambient temperature into said heat exchanger using said first variable speed and/or said second variable speed fan;

heating the atmospheric air in the heat exchanger to a temperature higher than ambient temperature using recovered heat extracted from the heated humidified air thereby reducing energy costs and drying time and preventing the loss of circulation air;

controllably exhausting said heated humidified air, after heating the atmospheric air, from said heat exchanger using said first variable speed and/or said second variable speed fan to maintain the dry kiln at steady state operating conditions;

controllably correcting pressure imbalance in the workspace by running the fan at intake mode, and the fan at exhaust mode, at different respective speeds; and

replacing the humidified air transferred from the workspace with the heated atmospheric air using said first variable speed and/or said second variable speed fan, the dry kiln operation being conducted at any level from 0 to 100% of required output to sustain the dry kiln operation at a predetermined output level for maintaining said steady state operating conditions.

2. The method of claim 1, wherein said first and second reversible variable speed fans are operated at varying speeds to control the flow of air into and out of the workspace using a programmable controller.

3. The method of claim 2, wherein said programmable controller is a programmable logic controller.

4. The method of claim 1, wherein said first and second reversible variable speed fans are operated at varying speeds to control the flow of air into and out of the workspace based on the temperature of the atmospheric air.

5. The method of claim 1, wherein said first and second reversible variable speed fans are operated at varying speeds to control the flow of air into and out of the workspace based on the temperature in the workspace.

6. The method of claim 1, wherein said first and second reversible variable speed fans are operated at varying speeds to control the flow of air into and out of the workspace based on the humidity in the workspace.

7. The method of claim 1, wherein said first and second reversible variable speed fans are operated at varying speeds to control the flow of air into and out of the workspace based on the temperature of the atmospheric air before and/or after the heat exchanger.

8. The method of claim 1, wherein said first and second reversible variable speed fans are operated at varying speeds to control the flow of air into and out of the workspace based on the temperature of exhaust air before and/or after the heat exchanger.

9. The method of claim 1, wherein said first and second reversible variable speed fans are operated at varying speeds to control the flow of air into and out of the workspace based on the temperature of atmospheric air entering the area surrounding the high moisture-containing work pieces and/or the temperature of the exhaust air exiting the area surrounding the high moisture-containing work pieces and/or the relative humidity in the workspace.

10. A dry kiln system for controllably drying moisture-containing work pieces, which comprises:

a drying compartment defining an internal workspace for housing and drying said moisture-containing work pieces by introducing heat into said internal workspace and heating the moisture-containing work pieces located in said internal workspace by removing heated moisture from the work pieces and absorbing said heated moisture into the air in the workspace to produce heated humidified air;

a multi-directional air flow heat exchanger for receiving heated humidified air and atmospheric air and for recycling waste heat from exhaust air from the drying compartment, and for heating the atmospheric air in the heat exchanger using recovered heat extracted from the heated humidified air to a temperature higher than ambient temperature thereby reducing energy costs and drying time and preventing the loss of circulation air; and

first and second reversible variable speed fans, each of said fans being independently controllable at respective intake and exhaust modes and at variable air flow rates, without employing a damper for controlling the flow of exhaust air and atmospheric air to and from said heat exchanger; and

a humidity control system including sensors for monitoring the conditions in the workspace, including air temperature before and/or after the heat exchanger. and sending a control signal;

variable frequency drives interfaced with said humidity control system to set the speed of the first and second reversible variable speed fans which proportionately increase or decrease the speed of the first and second reversible variable speed fans to increase or decrease the air flow through the dry kiln in response to the control signal sent by said control system,

said first variable speed and/or said second variable speed fan controlled by said humidity control system and (a) controllably exhausting said heated humidified air from the drying compartment into said heat exchanger, (b) introducing atmospheric air at ambient temperature into said heat exchanger, (c) controllably exhausting said heated humidified air from said heat exchanger after heating the atmospheric air, (d) replacing the humidified air transferred from the drying compartment with the heated atmospheric air, and (e) controllably correcting pressure imbalance in the workspace by running the fan at intake mode, and the fan at exhaust mode, at different respective speeds, the drying operation being conducted at any level from 0 to 100% of required output to sustain the dry kiln operation at a predetermined output level for maintaining a steady state operating conditions.

11. The system of claim 10, wherein said first and second reversible variable speed fans are operable at varying speeds to control the flow of air into and out of the workspace using a programmable controller.

12. The system of claim 11, wherein said programmable controller is a programmable logic controller.

13. The system of claim 10, wherein said first and second reversible variable speed fans are operable at varying speeds to control the flow of air into and out of the workspace based on the temperature of the atmospheric air.

14. The system of claim 10, wherein said first and second reversible variable speed fans are operable at varying speeds to control the flow of air into and out of the workspace based on the temperature in the workspace.

15. The system of claim 10, wherein said first and second reversible variable speed fans are operable at varying speeds to control the flow of air into and out of the workspace based on the humidity in the workspace.

16. The system of claim 10, wherein said first and second reversible variable speed fans are operable at varying speeds to control the flow of air into and out of the workspace based on the temperature of the atmospheric air before and/or after the heat exchanger.

17. The system of claim 11, wherein said first and second reversible variable speed fans are operable at varying speeds to control the flow of air into and out of the workspace based on the temperature of exhaust air before and/or after the heat exchanger.

18. The system of claim 10, wherein said first and second reversible variable speed fans are operable at varying speeds to control the flow of air into and out of the workspace based on the temperature of atmospheric air entering the area surrounding the high moisture-containing work pieces and/or the temperature of the exhaust air exiting the area surrounding the high moisture-containing work pieces and/or the relative humidity in the workspace.

19. The system of claim 10, wherein the heat exchanger has first and second air flow channels that allow hot moist air flow to pass on a first side of a transfer surface and for the cool dry air flow to pass on a second side of the transfer surface.

20. The system of claim 10, wherein said first and second reversible variable speed fans have substantially the same air flow characteristics in each direction for controlling air flow through the heat exchanger.

21. The system of claim 10, wherein said first and second reversible variable speed fans are reversible air foil fan.

22. The system of claim 10, without auxiliary elongate conduits or ducts for transporting the flow of atmospheric air to said drying compartment.

23. The system of claim 10, wherein said first and second reversible variable speed fans are controlled at a predetermined speed for maintaining a predetermined moisture level in the workspace.

24. A method for controlling drying conditions in a kiln for drying wood by venting and recycling waste heat from exhaust air from the workspace defined by said kiln, which comprises

providing a kiln including said workspace for housing and drying wood;

introducing wood into said workspace;

introducing heat into said workspace for drying said wood;

heating the wood located in said workspace;

removing heated moisture from the wood and absorbing said heated moisture into the air in the workspace to produce heated humidified air thereby forming wood which is substantially uniformly dried;

providing a multi-directional air flow heat exchanger for receiving heated humidified air and atmospheric air;

providing first and second reversible variable speed fans, each of said fans being independently controllable at either one of an intake and exhaust mode and at variable air flow rates, the first and second reversible variable speed fans being run at different speeds which preserves a balanced pressure inside the workspace, without employing a damper for controlling the flow of exhaust air and atmospheric air to and from said heat exchanger;

providing a humidity control system including sensors for monitoring the conditions in the workspace, including air temperature before and/or after the heat exchanger, and sending a control signal;

providing variable frequency drives interfaced with said humidity control system to set the speed of the first and second reversible variable speed fans which proportionately increase or decrease the speed of the first and second reversible variable speed fans to increase or decrease the air flow through the dry kiln in response to the control signal sent by said control system;

controllably exhausting said heated humidified air from the workspace into said heat exchanger using said first variable speed and/or said second variable speed fan;

supplying atmospheric air at ambient temperature into said heat exchanger using said first variable speed and/or said second variable speed fan;

heating the atmospheric air in the heat exchanger to a temperature higher than ambient temperature using recovered heat extracted from the heated humidified air thereby reducing energy costs and drying time and preventing the loss of circulation air;

controllably exhausting said heated humidified air, after heating the atmospheric air, from said heat exchanger using said first variable speed and/or said second variable speed fan;

controllably correcting pressure imbalance in the workspace by running the fan at intake mode, and the fan at exhaust mode, at different respective speeds; and

replacing the humidified air transferred from the workspace with the heated atmospheric air using said first variable speed and/or said second variable speed fan, the dry kiln operation being conducted at any level from 0 to 100% of required output to sustain the dry kiln operation at a predetermined output level for maintaining steady state operating conditions.