CA2864368A1

CA2864368A1 - A method and apparatus for controlling cooling temperature and pressure in wood veneer jet dryers

Info

Publication number: CA2864368A1
Application number: CA2864368A
Authority: CA
Inventors: Bryan Wolowiecki; Irven J. Mcmahon
Original assignee: USNR Kockums Cancar Co
Current assignee: USNR KOCKUMS CANCAR HOLDINGS ULC
Priority date: 2007-02-09
Filing date: 2008-02-07
Publication date: 2008-08-09
Anticipated expiration: 2028-02-07
Also published as: CA2577979A1; CA2620499C; CA2864367C; CA2864368C; CA2864367A1; CA2620499A1

Abstract

An apparatus for drying wood veneer includes an elongate drying chamber including a conveyor for conveying material to be dried from an input end to an output end; and a cooling section for cooling veneer leaving the output end of the drying chamber, the cooling section including a pressure controller for maintaining a pressure in the cooling section that is slightly higher than pressure in the drying chamber while maintaining a near-zero pressure differential between the drying chamber and the cooling section.

Description

A METHOD AND APPARATUS FOR CONTROLLING COOLING TEMPERATURE AND
PRESSURE IN WOOD VENEER JET DRYERS
Field of the Invention This invention relates to the field of producing wood veneer and in particular to a method and apparatus for controlling the temperature and pressure in the cooling sections of wood veneer j et dryers.
Background of the Invention Applicant is aware of United States Patent No. 5,603,168 which issued to McMahon, Jr. on February 18, 1997 for a Method and Apparatus for Controlling a Dryer wherein it is taught that the cooling section cools into the material exiting the drying chamber of the dryer by blowing ambient air around the material as it travels through the cooling section. A
control is provided for maintaining the pressure within the cooling section at a level greater than the pressure in the drying chamber. By operating the cooling section at a slightly higher pressure, leakage of exhaust gases from the drying chamber into the cooling section is inhibited. An automatic control for maintaining the required pressure differential between the cooling section and the drying chamber pressure is described. Pressure sensors are disclosed for monitoring the pressure in the drying chamber and the pressure in the cooling section. A

controller was suggested to be connected to the pressure sensors and operatively coupled to a damper for controlling the flow of cooling air thereby controlling the pressure within the cooling section. Alternately, the speed of a cooling air blower may be adjusted. Applicant is also aware of United States Patent No. 4,439,930 which issued April 3, 1984 to McMahon, Jr.
Conventionally, the last structural units (sections), typically one to four, sections of veneer jet dryers comprise the cooling zone. They are typically fitted with vane axial-type supply air fans and motors delivering outside air to nozzle systems for direct cooling of the veneer passing through the heating and cooling sections. It is typically desirable to utilize the cooling zone to drop the surface temperature of the veneer to a specified level. This has typically been accomplished by turning certain sections of the cooling zone "on or off' as necessary to achieve the desired temperature, or to utilize an alternating current (AC) variable speed drive on the fan motors to vary the speed of the fans and, thereby, vary the veneer temperature. Being that these cooling sections are typically connected directly, that is, in fluid communication with the heated sections of the dryer, with only a baffle wall separating the two, there has not been the ability to control the flow of cooling zone air into or out of the dryer.
This has resulted in either "cool" air being pushed into the heated drying process or heated process air flowing into the cooling zone specifically when the damper described in Patent No.
5,603,168 is not present or set too far open.
The present invention contemplates an improved automatic control for maintaining the required pressure differential between the cooling section and the drying chamber. Pressure sensors are disclosed for monitoring the pressure in the drying chamber and the pressure in the cooling section. A controller connected to the pressure sensors is operatively coupled to a damper for controlling the flow of cooling air out of the dryer thereby controlling the pressure within the cooling section above dryer pressure. Alternately, the speed of a cooling air blower may be adjusted.

2 =
Summary of the Invention Among its various objects, the present invention provides for automatically balancing the pressure between an enclosed veneer dryer and its associated cooling section by adjusting the pressure in the first cooling section, both up and down, as needed to inhibit airflow between the adjacent sections.
Thus, in one aspect of the present invention, the first cooling section, which is attached directly to the last heated dryer section, is modified to create a "pressure seal" for minimizing both the flow of heated process air from the dryer into the cooling zone or the flow of cool air from the cooling zone into the enclosed heated dryer. In one embodiment the first cooling section is fitted, in its discharge vent, with a tube-axial extractor fan and motor controlled by a frequency drive, conjoined with a modulating, balanced-blade damper. The section is mechanically sealed from both the enclosed dryer and second cooling section by two sets of baffle-like "stop-offs" that are mounted between the dryer rolls at the beginning and end of the section, restricting the movement of air in and out of the first cooling section. The stop-offs extend laterally across the veneer flow path and work in conjunction with the veneer conveying rolls. They, therefore, only allow restricted leakage or entrance of air past the pressure seal section entrance and exit.
Pressure-sensing manifolds are mounted on either side of the stop-offs between the enclosed dryer and first cooling section and are piped to a pressure transducer, which continuously monitors the differential pressure between the heated dryer and first cooling section. The signal from the transducer is processed in the dryer programmable logic controller (PLC) using a PM loop, described below, with split range control and a "near zero"
set point, which produces a signal that both modulates the damper through the first half of the control range and controls the speed of the tube-axial extractor fan through the second half of the control range. The effect of this control is to maintain a slightly higher pressure in the first cooling section with a "near zero" pressure differential between the enclosed dryer and first

3 cooling section, that is the "pressure seal" section, under all operating conditions. The resulting controlled condition minimizes pitch buildup in the dryer and cooler, minimizes volatile organic carbon (VOC) in the cooler vent and improves the drying process thermal efficiency.
In an additional embodiment, the cooler section air supply fans are controlled either by one or individual frequency drives receiving a signal from a proportional-integral-derivative (PID) loop in the dryer PLC and having an operator-established veneer temperature "set point" and a "process variable" measured by an infrared scanner mounted at the dry veneer moisture detector. If reduced cooling is required the air supply fans slow to satisfy the temperature set point. This action lowers the pressure in the in the first cooling section and its discharge damper closes to again balance the pressure in this the cooler "seal" and the extractor fan stops. If increased cooling is required, the air supply fans increase in speed and the pressure seal discharge damper modulates to full open at the end of the first half of the control range and, as more cooling is required, in the second half of the control range the extractor fan begins to increase in speed to satisfy the near-zero pressure "set point" of the first cooling section.
The supply and exhaust air for the cooling sections are normally taken from and vented to atmosphere, for example above the factory roof, thereby allowing the cooling zone of the dryer to have a "net zero" impact on makeup air to the factory.
In summary, the wood veneer dryer according to the present invention may be characterized in one aspect as including an elongate drying chamber having an input end and an output end and defining a path of movement between the ends. A conveyor conveys product to be dried along the path of movement through the drying chamber. The chamber includes a plurality of juxtaposed heating units sections, each heating unit defining a circulation path for heated air, the path being substantially transverse to the path of movement of the product to be dried. Nozzles forming part of each of the heating units direct heated air

4 into an impinging relationship with the path of movement. An exhaust system extracts gases from an adjacent heating sections. A first pressure sensor senses a pressure in the output end of the drying chamber; a cooling section cools the veneer leaving the output end of the drying chamber. The cooling section includes pressure controlling means for maintaining a pressure in the cooling section that is higher, for example slightly higher than the pressure in the drying chamber while maintaining a near-zero pressure differential between the drying chamber and the cooling section. A second pressure sensor senses a pressure in the cooling section downstream of and adjacent to the output end of the dryer. A flow controller adjusts the rate of the exhaust flow as a function of the difference in pressure sensed by the first and second pressure sensors.
In one embodiment the flow controller includes a forced air input and a forced air extractor arranged laterally opposed across the path of movement in the first cooling section, and a damper cooperating with the air extractor.
Thus in the present invention, the method for controlling a wood veneer dryer, may be characterized as including the steps of:
a) providing a drying chamber having at least one drying section and corresponding upstream input and downstream output ends, b) providing a cooling section at an output end of the drying chamber;
c) monitoring a first pressure of dryer gases at the output end;
d) comparing the first pressure with a second pressure in the cooling section;

5 e) adjusting a flow rate of cooling air in the cooling section so that the second pressure is greater than the first pressure and the pressure differential between the first and second pressures is near-zero.
In one embodiment the control is provided by the use of a PID loop using a split range controller wherein in a first, lower range, that is below the split, the position of the cooling section exhaust damper is controlled to control the pressure differential, and in the second, upper range, above the split, a forced air mover is also employed in a graduated fashion.
Brief Description of the Drawings With reference to the drawings in which similar characters of reference denote corresponding parts in each view:
Figure 1 is, in plan view, the wood veneer dryer cooling sections according to the present invention.
Figure 2 is, in side elevation view, the cooling sections of Figure 1.
Figure 3 is a sectional view along line 3-3 in Figure 2.
Figure 4 is a sectional view along line 4-4 in Figure 1.
Figure 5 is a sectional view along line 5-5 in Figure 2.

6 Detailed Description of Embodiments of the Invention First cooling section 10 is mounted directly to the last, that is most downstream, heated dryer section 12. Section 10 is modified to create a pressure seal for minimizing both the flow in direction A of heated process air from the dryer air into the cooling zone commencing in section 10 or the flow in the opposite direction of cool air from the cooling zone into the enclosed heated dryer. In one embodiment first cooling section 10 is fitted, in its discharge vent 14, with a tube-axial exhaust fan 16 and motor 18 controlled by a frequency drive, conjoined with a modulating, balanced-blade damper 20. Section 10 is mechanically sealed from both the last dryer section 12 and a downstream second cooling section 22 by two sets of stop-offs 24 that are mounted between the dryer rolls 26 in both the upstream and downstream ends of section 10, thereby restricting the movement of air into and out of first cooling section 10.
Pressure-sensing manifolds (not shown) are mounted on either side of stop-offs 24 between dryer section 12 and first cooling section 10 and are piped to a pressure transducer (not shown), which continuously monitors the differential pressure between the heated dryer and first cooling section. The signal from the transducer is used for predictive control and in particular is processed in a programmable logic controller (PLC) using a proportional-integral-derivative (PH)) loop. As would be known to one skilled in the art, the ND
loop automates what an intelligent operator with a gauge and a control knob would do. The operator would read a gauge showing the output measurement of a process, and use the knob to adjust the input of the process until the process's output measurement stabilizes at the desired value on the gauge. The position of the needle on the gauge is the "process variable"
as used herein.
The desired value on the gauge is referred to as the "setpoint" herein. The difference between the gauge's needle and the setpoint is the "error".
A control loop consists of three parts: measurement by a sensor connected to the process; decision in a controller element; and, action through an output device or actuator

7 such as the extractor fan and damper herein. As the controller reads the sensor measurement, it subtracts this measurement from the setpoint to determine the error. It then uses the error to calculate a correction to the process's input variable so that this correction will remove the error from the process's output measurement. In a PID loop, correction is calculated from the error in three ways: cancel out the current error directly (Proportional), the amount of time the error has continued uncorrected (Integral), and anticipate the future error from the rate of change of the error over time (Derivative). The sum of the three calculations constitutes the output of the PID controller.
In the present invention the PID loop has a split pressure range control and a near-zero pressure differential set point. The PLC PID loop produces a signal that both modulates the actuation of damper 20 and its associated drive motor 28 through the first half of the control signal range and controls the speed of the tube-axial extractor fan 16 through the second half of the control signal range. The effect of this control is to maintain a near-zero pressure differential between the dryer section 12 and first cooling section 10, that is the pressure seal section, under all operating conditions. The control minimizes pitch buildup in the dryer and cooling sections 10, 22 and 30 minimizes volatile organic carbon (VOC) in the cooling section vents and improves the drying process thermal efficiency.
In an additional embodiment, the cooling section fans are controlled either by one or individual frequency drives receiving a signal from a PID loop in the dryer PLC and having an operator-established veneer temperature set point and a process variable measured by an infrared scanner (not shown) mounted at the dry veneer moisture detector (not shown).
If reduced cooling is required the cooling section supply fans slow which lowers the pressure in the seal section and damper 20 adjusts toward closed to maintain the pressure balance in the seal section 10 and the extractor fan 16 stops. If increased cooling is required, the cooling section supply fans increase in speed, damper 20 modulates to full open and, as more cooling is required to maintain the veneer temperature setpoint and the extractor fan 16 begins to increase in speed to meet the cooling section pressure setpoint.

8 The first cooling section includes a provision for controlling the rate of exhausted cooling air such that a pressure is maintained in the cooling section that is greater than the pressure in the drying chamber. As a result, the flow of exhaust gas from the drying chamber to the cooling section is inhibited. Cooling air flowing from the inlet duct through the cooling section supply fan and enters an inlet chamber. As is conventional, the cooling air flows through jet nozzles and around the multiple levels of sheet material traveling through the cooling section and ultimately enters an exhaust chamber. From the exhaust chamber, the cooling air is exhausted through the outlet stacks. A damper assembly is positioned between the exhaust chamber and outlet stacks and controls the, flow rate of the cooling air. Pressure sensors are positioned in the last drying section and also in the cooling section near the entrance to the cooling section. A differential pressure monitor or controller connected to the pressure sensors monitors for automatically controlling the position of the damper assembly so that a slightly positive pressure at the entrance to the cooling section, as compared to the drying sections, is maintained. As long as the pressure sensed by the sensor is greater than the pressure sensed by the drying section sensor, exhaust gases from the drying chamber will be inhibited from flowing into the cooling section. The position of the damper assembly is controlled by an electrically-operated rotary actuator.
The supply and exhaust air for the cooling sections is obtained and vented to atmosphere, for example above the factory roof, thereby allowing the cooling zone of the dryer to have a "net zero" impact on makeup air to the factory.
Cooling section 10 differs from cooling sections 22 and 30 in that cooling section 10, being the pressure seal section, includes exhaust fan 16 and damper 20 controlled by the PD loop. The intake side of cooling sections 10, 22 and 30 each, however, include ambient air intakes 32 so as to intake ambient air in direction B from intake stack 34. A hood 36 may be mounted atop each intake stack 34. Ambient air is drawn down through intake ducts 32 by supply fans 38 driven by drive motors 40.

9 Ambient air passes through fans 38 downwardly into supply chambers 44 so as to be turned in direction C. The ambient cooling air is thereby forced between the sheets of veneer passing downstream in direction A on rollers 26 thereby cooling the veneer.
Once the cooling air has passed between and over the sheets of wood veneer on roller 26, the now warmed air is turned in direction D in exhaust chamber 46.
The warmed air then passes through damper 20 and continues upwardly in direction E
through extractor fan 16 so as to be vented from discharge vent 14 through outlet stack 48.
In the illustrated embodiment, and in order put the scale of the diagrams into perspective, a ladder 50 and guard rail 52 are illustrated.
The scope of the claims should not be limited by the embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

Claims

WHAT IS CLAIMED IS:

1. A method for controlling a wood veneer dryer, wherein the wood veneer dryer includes a drying chamber having at least one drying section and corresponding upstream input and downstream output ends and a cooling section at the output end of said drying chamber having a forced air extractor, the method comprising:
monitoring a first pressure in the drying chamber at said output end;
comparing said first pressure with a second pressure in said cooling section;
and adjusting operation of the forced air extractor to maintain a predetermined pressure differential between the cooling section and the drying chamber, wherein said second pressure is greater than said first pressure.

2. The method of claim 1, wherein the cooling section further comprises a forced air input and a damper, and wherein adjusting operation of the forced air extractor includes operating the forced air extractor with the damper in an open position.

3. The method of claim 2, wherein the cooling section further comprises a forced air input, the method further including:
detecting a veneer temperature downstream of the drying chamber;
determining a difference between the detected veneer temperature and a temperature setpoint; and adjusting operation of the forced air input based at least on said difference.

4. The method of claim 3, wherein the forced air input includes a supply fan, and adjusting operation of the forced air input includes increasing or decreasing a speed of the supply fan.

5. The method of claim 1, wherein the predetermined pressure differential setpoint is a near-zero pressure differential.

6. The method of claim 1, further including providing a controller with a control loop, said adjusting being performed automatically by the controller based at least on the difference between the detected pressure differential and a predetermined pressure differential setpoint.

7. The method of claim 6, wherein said controller is a programmable logic controller (PLC) and the control loop is a proportional integral derivative (PID) loop having a split control signal range, the PID loop configured to control the damper position over a first portion of the range and to control the exhaust fan speed over a second portion of the range.

8. The method of claim 7, wherein the cooling section further includes a forced air input, the method further including:
detecting a veneer temperature downstream of the drying chamber;
determining, by the controller, a difference between the detected veneer temperature and a temperature setpoint; and adjusting operation of the forced air input, by the controller, based at least on said difference.

9. The method of claim 1, further including providing a first seal system coupled with an input end of the cooling section, the first seal system configured to restrict airflow between the drying chamber and the cooling section.

10. The method of claim 9, wherein the predetermined pressure differential setpoint is a near-zero pressure differential.

11. The method of claim 9, wherein the forced air exhaust includes a damper and an exhaust fan, and adjusting operation of the forced air exhaust includes one or more of adjusting a position of the damper and adjusting a speed of the exhaust fan.

12. The method of claim 9, further including providing a controller with a control loop, said adjusting being performed automatically by the controller based at least on the difference between the detected pressure differential and a predetermined pressure differential setpoint.

13. The method of claim 12, wherein the controller is a programmable logic controller and the control loop is a proportional-integral-derivative (PID) loop having a split control signal range, the PID loop configured to control a position of the damper over a first portion of the range and to control a speed of the exhaust fan over a second portion of the range.

14. The method of claim 13, wherein the cooling section further includes a forced air input, the method further including:
detecting a veneer temperature downstream of the drying chamber;
determining, by the controller, a difference between the detected veneer temperature and a temperature setpoint; and adjusting operation of the forced air input, by the controller, based at least on said difference.

15. The method of claim 9, wherein the cooling section is a first cooling section and the wood veneer dryer includes a second cooling section coupled with an output end of the first cooling section, the method further including providing a second seal system coupled with an output end of the first cooling section, wherein the second seal system is configured to restrict airflow from the first cooling section to the second cooling section.

16. The method of claim 15, wherein the predetermined pressure differential setpoint is a near-zero pressure differential.

17. The method of claim 15, wherein the forced air exhaust includes a damper and an exhaust fan, and adjusting operation of the forced air exhaust includes one or more of adjusting a position of the damper and adjusting a speed of the exhaust fan.

18. The method of claim 17, further including providing a controller with a control loop, the controller configured to perform said adjusting automatically based at least on the difference between the detected pressure differential and a predetermined pressure differential setpoint.

19. The method of claim 18, wherein the controller is a programmable logic controller (PLC) and the control loop is a proportional-integral-derivative (PID) loop with a split control signal range, and the PID loop is configured to control a position of the damper over a first portion of the range and to control a speed of the exhaust fan over a second portion of the range.

20. The method of claim 17, wherein at least one of the cooling sections further includes a forced air input, the method further including:
detecting a veneer temperature downstream of the drying chamber;
determining, by the controller, a difference between the detected veneer temperature and a temperature setpoint; and adjusting operation of the forced air input, by the controller, based at least on said difference.

21. The method of claim 20, wherein the forced air input includes a supply fan, and adjusting operation of the forced air input includes increasing or decreasing a speed of the supply fan.

22. A method of operating a veneer dryer, wherein the veneer dryer includes a drying chamber with at least one drying section and corresponding input and output ends and a cooling section at the output end having a forced air intake and a forced air exhaust;
detecting a pressure differential between the drying chamber and the cooling section;
determining a difference between the detected pressure differential and a predetermined pressure differential setpoint; and adjusting operation of the forced air exhaust, based at least on said difference, to maintain a positive pressure within the cooling section relative to the drying chamber.

23. The method of claim 22, wherein the predetermined pressure differential setpoint is a near-zero pressure differential.

24. The method of claim 22, wherein the cooling section further includes a damper and the forced air exhaust includes an exhaust fan, and adjusting operation of the forced air exhaust includes adjusting a speed of the exhaust fan.

25. The method of claim 22, further including:
detecting a veneer temperature downstream of the drying chamber;
determining a difference between the detected veneer temperature and a temperature setpoint; and adjusting operation of the forced air intake based at least on said difference.

26. The method of claim 24, further including providing a controller with a control loop operatively coupled with the forced air exhaust, said adjusting being performed automatically by the controller based at least on the difference between the detected pressure differential and a predetermined pressure differential setpoint.

27. The method of claim 26, wherein said controller is a programmable logic controller (PLC) and the control loop is a proportional integral derivative (PID) loop having a split control signal range, the PID loop configured to control the damper position over a first portion of the range and to control the exhaust fan speed over a second portion of the range.

28. The method of claim 26, further including:
detecting a veneer temperature downstream of the drying chamber;
determining, by the controller, a difference between the detected veneer temperature and a temperature setpoint; and adjusting operation of the forced air intake, by the controller, based at least on said difference.

29. The method of claim 22, further including providing a first seal system coupled with an input end of the cooling section, the first seal system configured to restrict airflow between the drying chamber and the cooling section.

30. The method of claim 29, wherein the predetermined pressure differential setpoint is a near-zero pressure differential.

31. The method of claim 29, wherein the forced air exhaust includes a damper and an exhaust fan, and adjusting operation of the forced air exhaust includes one or more of adjusting a position of the damper and adjusting a speed of the exhaust fan.

32. The method of claim 20, further including providing a controller with a control loop operatively coupled with the forced air exhaust, said adjusting being performed automatically by the controller based at least on the difference between the detected pressure differential and a predetermined pressure differential setpoint.

33. The method of claim 32, wherein the controller is a programmable logic controller and the control loop is a proportional-integral-derivative (PID) loop having a split control signal range, the PID loop configured to control a position of the damper over a first portion of the range and to control a speed of the exhaust fan over a second portion of the range.

34. The method of claim 32, further including:
detecting a veneer temperature downstream of the drying chamber;
determining, by the controller, a difference between the detected veneer temperature and a temperature setpoint; and adjusting operation of the forced air intake, by the controller, based at least on said difference.

35. The method of claim 29, wherein the cooling section is a first cooling section and the forced air intake is a first forced air intake, the method further including providing a second seal system coupled with an output end of the first cooling section, the second seal system configured to restrict airflow between an output end of the first cooling section and one or more second cooling sections downstream of the first cooling section.

36. The method of claim 35, wherein the predetermined pressure differential setpoint is a near-zero pressure differential.

37. The method of claim 35, wherein the forced air exhaust includes a damper and an exhaust fan, and adjusting operation of the forced air exhaust includes one or more of adjusting a position of the damper and adjusting a speed of the exhaust fan.

38. The method of claim 37, further including providing a controller with a control loop operatively coupled with the forced air exhaust, said adjusting being performed automatically by the controller based at least on the difference between the detected pressure differential and a predetermined pressure differential setpoint.

39. The method of claim 38, wherein the controller is a programmable logic controller and the control loop is a proportional-integral-derivative (PID) loop having a split control signal range, the PID loop configured to control a position of the damper over a first portion of the range and to control a speed of the exhaust fan over a second portion of the range.

40. The method of claim 27, further including:
detecting a veneer temperature downstream of the drying chamber;
determining, by the controller, a difference between the detected veneer temperature and a temperature setpoint; and adjusting operation of the forced air intake, by the controller, based at least on said difference.

41. The method of claim 40, wherein the forced air intake includes a supply fan, and adjusting operation of the forced air intake includes increasing or decreasing a speed of the supply fan.

42. A method of modifying a veneer dryer, wherein the veneer dryer includes a drying chamber having at least one drying section and corresponding input and output ends and a cooling section at the output end of the drying chamber, the method comprising:
providing a forced air extractor in the cooling section; and operatively coupling the forced air extractor with a controller, wherein the controller is configured to adjust operation of the forced air exhaust to maintain a positive pressure within the cooling section relative to the drying chamber.

43. The method of claim 42, further including operatively coupling the controller with a first pressure sensor positioned to detect a first pressure in the output end of the drying chamber and a second pressure sensor positioned to detect a second pressure in the cooling section, the controller configured to adjust operation of the forced air exhaust based at least on a pressure differential between the first and second pressures and a predetermined pressure differential setpoint.

44. The method of claim 42, wherein providing the forced air extractor includes installing an extractor fan in the cooling section.

45. The method of claim 44, wherein the cooling section includes an exhaust vent, and providing the forced air extractor includes positioning the extractor fan in the exhaust vent.

46. The method of claim 45, wherein the cooling section further includes a damper positioned within the exhaust vent, and providing the forced air extractor includes positioning the extractor fan in the exhaust vent downstream of the damper.

47. The method of claim 42, wherein the cooling section further includes a forced air intake, and the controller is further configured to adjust operation of the forced air intake.

48. The method of claim 47, further including operatively coupling the controller with a veneer temperature sensor, wherein the controller is further configured to adjust operation of the forced air intake based at least on a difference between a detected veneer temperature and a temperature setpoint.

49. The method of claim 42, wherein the controller has a control loop with a split control signal range, the controller configured to control the damper position over a first portion of the range and to control the exhaust fan speed over a second portion of the range.

50. The method of claim 42, further including providing a first seal system coupled with an input end of the cooling section, the first seal system configured to restrict airflow between the drying chamber and the cooling section.

51. The method of claim 50, further including providing a second seal system coupled with an output end of the cooling section, the second seal system configured to restrict airflow through the output end of the cooling section.

52. A method of modifying a veneer dryer, wherein the veneer dryer includes a drying chamber having at least one drying section and corresponding input and output ends and a cooling section at the output end of the drying chamber, the method comprising:
providing a first seal system coupled with an input end of the cooling section, wherein the first seal system is configured to restrict airflow from the cooling section to the drying chamber; and providing a forced air extractor in the cooling section, wherein the forced air extractor is selectively operable to adjust a rate of airflow from the cooling section to thereby maintain a positive pressure within the cooling section relative to the drying chamber.

53. The method of claim 52, wherein providing the forced air extractor includes installing an extractor fan in the cooling section.

54. The method of claim 53, wherein the cooling section includes an exhaust vent, and providing the forced air extractor includes positioning the extractor fan in the exhaust vent.

55. The method of claim 54, wherein the cooling section further includes a damper positioned within the exhaust vent, and providing the forced air extractor includes positioning the extractor fan in the exhaust vent downstream of the damper.

56. The method of claim 52, further including operatively coupling a controller with the forced air extractor, wherein the controller is configured to control operation of the forced air extractor based at least on a difference between a first pressure in the output end of the drying chamber and a second pressure in the cooling section.

57. The method of claim 56, wherein the cooling section further includes a forced air intake, and the controller is further configured to adjust operation of the forced air intake.

58. The method of claim 57, further including operatively coupling the controller with a veneer temperature sensor, wherein the controller is further configured to adjust operation of the forced air intake based at least on a difference between a detected veneer temperature and a temperature setpoint.

59. The method of claim 56, wherein the cooling section includes a damper and the forced air extractor includes an extractor fan, and the controller has a control loop with a split control signal range, the controller configured to control the damper position over a first portion of the range and to control the exhaust fan speed over a second portion of the range.

60. The method of claim 59, wherein the controller is a programmable logic controller (PLC) and the control loop is a proportional-integral-derivative (PID) loop.

61. The method of claim 52, further including providing a second seal system coupled with an output end of the cooling section, the second seal system configured to restrict airflow through the output end of the cooling section.

62. The method of claim 61, wherein the cooling section is a first cooling section, the method further including coupling a second cooling section with a downstream end of the first cooling section, wherein the second seal system is configured to restrict airflow from the first cooling section to the second cooling section.

63. An apparatus for drying wood veneer, comprising:
an elongate drying chamber including means for conveying material to be dried from an input end to an output end;
a cooling section for cooling veneer leaving said output end of said drying chamber, said cooling section including temperature and pressure controlling means for varying a rate of air flow through said cooling section as a function of temperature within the cooling section while maintaining a near-zero pressure differential between said drying chamber and said cooling section.

64. A dryer system comprising:
a drying chamber having an output end and a first pressure sensor;
a first cooling section having an input end, an output end, a first forced air intake, a forced air exhaust, and a second pressure sensor, the input end connected to the output end of the drying chamber;
a first seal system coupled to the input end of the first cooling section, the first seal system configured to restrict airflow between the drying chamber and the first cooling section;
a second cooling section with an input end, an output end, and a second forced air intake, the input end of the second cooling section coupled to the output end of the first cooling section;
a second seal system coupled to the output end of the first cooling section, the second seal system configured to restrict airflow between the first and second cooling sections; and a controller operatively coupled to the forced air exhaust, the controller configured to maintain a positive pressure in the first cooling section, respective to the drying chamber, according to a predetermined pressure differential setpoint.

65. The dryer system of claim 64, the forced air exhaust including an exhaust fan and a damper disposed upstream of the exhaust fan.

66. The dryer system of claim 64, further including a third cooling section with an input end, an output end, and a forced air intake, the input end of the third cooling section coupled to the output end of the second cooling section.

67. The dryer system of claim 65, wherein the second cooling section lacks a forced air exhaust.

68. The dryer system of claim 65, wherein the controller is operable to process pressures detected by the first and second pressure sensors according to a proportional-integral-derivative (PID) loop with a split pressure control signal range.

69. The dryer system of claim 68, wherein the control signal range has a first portion and a second portion, the PID loop configured to modulate operation of the damper in the first portion of the control signal range and to modulate operation of the exhaust fan in the second portion of the control signal range.

70. The dryer system of claim 64, further including a temperature sensor disposed in the first cooling section, the controller operatively coupled to the forced air intake and configured to adjust operation of the forced air intake based at least on a predetermined temperature setpoint.