Kiln design that uses a series of at least two subsections with airflow in constant but alternating directions instead of using bi-directional fans that periodically reverse directions. The uninterrupted alternating air flow may be used in continuous drying kilns (CDK) with two sets of carriages carrying spaced stacks of lumber travel in opposite directions through a sequence of chambers. The uninterrupted alternating air flow may be used with a set of at least one pathway for carriages carrying lumber to be dried where all carriages move from a first end of the kiln to a second end of the kiln.
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1. A structure for curing lumber, the structure comprising:
at least one pathway for carriages holding lumber;
a first end of the structure for ingress of carriages holding lumber;
a second end of the structure for egress of carriages holding lumber;
a first side located between the first end and the second end;
a second side located between the first end and the second end such that the at least one pathway for carriages runs from the first end to the second end between the first side and the second side;
a set of partition baffles to subdivide the structure into at least two subsections, the partition baffles operating to allow passage of carriages holding lumber towards the second end but interfere with a longitudinal flow of air from the first end towards the second end or from the second end towards the first end; and
fans operating in a unidirectional mode to cause air flow to move in one circulation direction within a subsection but in a different circulation direction opposite of the one circulation direction in an adjacent subsection so that the air flow alternates between traveling across the carriage holding lumber from the first side to the second side in one subsection and from the second side to the first side in the adjacent subsection whereby the carriages holding lumber traverse from the first end of the structure to the second end of the structure without being in a subsection where all the fans are stopped and reversed.
11. A main drying section within a structure for curing lumber, the main drying section comprising:
at least one pathway for carriages holding lumber;
a first end of the main drying section for ingress of carriages holding lumber;
a second end of the main drying section for egress of carriages holding lumber;
a first side located between the first end and the second end;
a second side located between the first end and the second end such that the at least one pathway for carriages runs from the first end to the second end between the first side and the second side;
a set of partition baffles to subdivide the main drying section into at least two subsections, the partition baffles operating to allow passage of carriages holding lumber towards the second end but interfere with a longitudinal flow of air from the first end towards the second end or from the second end towards the first end; and
fans operating in a unidirectional mode to cause air flow to move in one circulation direction within a subsection but in a different circulation direction opposite of the one circulation direction in an adjacent subsection so that the air flow alternates between traveling across the carriage holding lumber from the first side to the second side in one subsection and from the second side to the first side in the adjacent subsection whereby the carriages holding lumber traverse from the first end of the main drying section to the second end of the main drying section without being in a subsection where all the fans are stopped and then reversed.
12. A method of curing lumber wherein lumber is stacked upon a first carriage with spacers to allow air flow across the lumber to be dried, the method using a structure comprising,:
at least one pathway for carriages holding lumber to be dried;
a first end of the structure for ingress of carriages holding lumber on the at least one pathway;
a second end of the structure for egress of carriages on the at least one pathway;
a main drying section located between the first end and the second end;
the main drying section receiving heat input to dry the lumber to be dried;
a set of partition baffles to subdivide the main drying section into at least two subsections, the partition baffles operating to allow passage of carriages holding lumber to be dried towards the second end but interfere with a longitudinal flow of air from the first end towards the second end or from the second end towards the first end;
the method comprising:
advancing the first carriage carrying lumber to be dried stacked upon the first carriage with spacers to allow air flow across the lumber on the at least one pathway towards the first end of the structure; and
advancing the first carriage into the first end of the structure and continuing to move the first carriage through the structure and out through the second end of the structure to submit the lumber on the first carriage to air flow in a series of at least two subsections, with each subsection having air flow moving in only a one first circulation direction or a different circulation direction opposite of the one first circulation direction; and
such that the first carriage moving from the first end to the second end is exposed alternatively to air moving in the one first circulation direction across the lumber then to air moving in the different circulation direction without a need to reverse fans from the one first circulation direction to the different circulation direction.
0. 21. A method of curing lumber wherein lumber is stacked upon a first carriage with spacers to allow air flow across the lumber to be dried, the method using a structure comprising:
at least one pathway for carriages holding lumber to be dried;
a first end of the structure for ingress of carriages holding lumber on the at least one pathway;
a second end of the structure for egress of carriages on the at least one pathway;
a main drying section located between the first end and the second end;
the main drying section receiving heat input to dry the lumber to be dried;
a set of partition baffles to subdivide the main drying section into at least two subsections, the partition baffles operating to allow passage of carriages holding lumber to be dried towards the second end but interfere with a longitudinal flow of air from the first end towards the second end or from the second end towards the first end;
the method comprising:
advancing the first carriage carrying lumber to be dried stacked upon the first carriage with spacers to allow air flow across the lumber on the at least one pathway towards the first end of the structure; and
advancing the first carriage into the first end of the structure and continuing to move the first carriage through the structure and out through the second end of the structure to submit the lumber on the first carriage to air flow in a series of at least two subsections, with each subsection having air flow moving in only a first circulation direction or a different circulation direction opposite of the first circulation direction; and
such that the first carriage moving from the first end to the second end is exposed alternatively to air moving in the first circulation direction across the lumber then to air moving in the different circulation direction without a need to reverse an air flow circulation direction from the first circulation direction to the different circulation direction within either of the at least two subsections.
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0. 22. The method of claim 21 where the first circulation direction moves air flow across the first carriage from a first side of the structure to a second side of the structure.
0. 23. The method of claim 21 where the first circulation direction moves air flow across the first carriage from a second side of the structure to a first side of the structure.
0. 24. The method of claim 21 wherein the first carriage traveling through the main drying section is exposed to a same duration of air flow moving in the first circulation direction as to air flow moving in the different circulation direction.
0. 25. The method of claim 21 wherein the first carriage moves continuously through the structure from the first end to the second end.
0. 26. The method of claim 21 wherein the first carriage is moved intermittently from the first end to the second end.
0. 27. The method of claim 21 wherein advancing the first carriage into the first end of the structure and continuing to move the first carriage through the structure and out through the second end of the structure to submit the lumber on the first carriage to air flow in a series of at least two subsections, with each subsection having air flow moving in only the first circulation direction or the different circulation direction opposite of the first circulation direction subjects the first carriage to air flow across the lumber to be dried for an entirety of the time that the first carriage is within the structure.
0. 28. The method of claim 21 wherein the main drying section is heated by steam passing through heat exchangers exposed to moving air.
0. 29. The method of claim 21 wherein air used in the main drying section is heated through use of a direct fire burner.
0. 30. The method of claim 21 wherein the air flow moving in only the first circulation direction or the different circulation direction opposite of the first circulation direction is circulated using a set of fans located with the structure.
0. 31. The method of claim 21 wherein the air flow moving in only the first circulation direction or the different circulation direction opposite of the first circulation direction is circulated using a set of fans located in openings in a center wall that extends above a fan deck located above the at least first pathway for carriages holding lumber.
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This application claims priority to co-pending U.S. patent application Ser. No. 13/831,361 filed Mar. 14, 2013 for Uninterrupted Alternating Air Circulation for Continuous Drying Lumber Kilns. The '361 application is incorporated by reference.
This disclosure applies to systems of the continuous drying kiln (CDK) design, (also referred to as dual path or triple length kilns), in which two paths of lumber travel in opposite directions through a sequence of chambers in which wood is pre-heated, dried, equalized and then conditioned. This disclosure also applies to unidirectional kilns where one or more sets of carriages on one or more sets of pathways to convey lumber through a first end of a kiln to a second end of a kiln.
If the first set of carriages 128 enters the structure 104 through the first end 108 and exits through the second end 112, then the second set of carriages 132 enters the structure 104 through the second end 112 and exits through the first end 108. Thus, when lumber 130 is stacked on the carriages (128 and 132) and exposed to heat in the main drying section 300, the heated lumber 136 passes near lumber that has not yet been in the main drying section 300 (green lumber 140). Note the simplified drawing in
In the first end energy recovery section 310 and in the second end energy recovery section 340, the heated lumber 136 passes heat to the green lumber 140 to partially heat and dry the green lumber 140 and the green lumber 140 cools the heated lumber 136 by absorbing heat and by evaporating the moisture content of the green lumber 140.
Thus, lumber stack 156 starts as green lumber 140 stacked upon the first set of carriages 128 with spacers to allow for air flow amongst stacked lumber 136. As the first set of carriages 128 moves along the first pathway 116, the green lumber 140 is exposed to air that is circulating in the first end energy recovery section 310.
Having an appropriate pressure gradient from the high pressure side of the center wall 228 to the low pressure side will cause a desired distribution of circulating air amongst the stacked lumber across the two sets of carriages (128 and 132). Heat from heated lumber 136 on the second pathway 120 partially dries and heats the green lumber 140. Likewise the moisture from the green lumber 140 helps cool the heated lumber 136. One of skill in the art will appreciate that the heating of the green lumber 140 is going to be most pronounced as the hot air reaches the green lumber 140 directly after leaving the heated lumber 136 and before the circulating air returns to the fans 200 above the fan deck 224. Likewise, one of skill in the art will appreciate that the cooling of the heated lumber 136 is going to be most pronounced as the moist air reaches the heated lumber 136 directly after leaving the green lumber 140 and before the circulating air returns to the fans 200 above the fan deck 224.
To reduce the variability between lumber 130 on the first side 144 and the second side 148 of the first set of carriages 132 or the second set of carriages 132, the fans 200 are periodically stopped and allowed to coast to a full stop. Then the fans 200 are operated in the reverse direction to push air in the second circulation direction as shown in
Normal practice is to reverse the fan direction about once every two to four hours. The period of running the fan in one direction is often called a fan cycle. The overall time to cure the lumber is frequently 40 hours although it may be longer for wood needing extra drying. As the first end energy recovery section 310, main drying section 300, and second end energy recovery section 340 all have fans that are periodically stopped and reversed (usually at the same time), a particular stack of lumber on a carriage should expect to have the fans stop approximately 10, 13, 20, or even more times during transit through the structure 104.
When heated lumber 136 that has recently passed through the main drying section 300 and entered the first end energy recovery section 310 or the second end energy recovery section 340, there is a risk that heavily dried and heated hot spots on the heated lumber 136 may be smoldering. Fire may be less likely in the main drying section if oxygen levels are reduced from exposure to an external direct fired burning furnace. However, even a momentary lack of circulation in an energy recover section can increase fire risk as the circulation of cooler moist air from the green lumber 140 abates and a hot spot may progress to an open fire. Thus, many structures include intermediate orthogonal baffles 320 within the energy recovery sections (310 and 340) to limit the travel of oxygen rich air from the first end 108 or the second end 112 towards the lumber in the energy recovery sections (310 or 340) that has recently emerged from the main drying section 300. While first end energy recovery section 310 and second end energy recovery section 340 both are shown with a single set of intermediate orthogonal baffles 320, there may be additional intermediate orthogonal baffles 320 to subdivide the first end energy recovery section 310 and second end energy recovery section 340 into additional energy recovery subsections (314, 318, 344, and 348 in
The first end 108, and second end 112 may have some level of orthogonal baffles to limit the ingress of oxygen and loss of heat, but the structure 104 is typically far from hermetically sealed as there is a need for water vapor to leave the structure 104 at the first end 108 and second end 112 often as visible fog.
Returning to the processing of lumber stack 156 stacked upon the first set of carriages 128, eventually, the lumber stack 156 progresses from the first end energy recovery section 310 through orthogonal partitions 324 to enter the main drying section 300.
The main drying section 300 is much like the energy recovery sections 310 and 340 with a set of bi-directional fans 200 located above a fan deck 224 circulating air alternatively in the first circulation direction 204 and the second circulation direction 208. Longitudinal baffles 220 keep the circulating air from passing between the top of the lumber stacks 152 and the fan deck 224. A complication in the main drying section 300 for direct fired kilns is that an additional circulation path is needed to move air from the structure 104 to a mixing chamber where hot flue gas from a direct fired burner is mixed with the returning air from the structure 104 to create a mix within a prescribed temperature range.
This mix of heated air and flue gas is returned to the main drying section 300 to increase the temperature and decrease the humidity of the return air which is reintroduced to the main drying section 300. A blower forces heated air leaving the mixing chamber into a distribution duct that extends the length of the main drying section 300. The distribution duct may release heated air in an upward direction through apertures in the top surfaces of the fan deck 224 or it may also release heated air in a downward direction through slotted vertical ducts, which are called downcomers, that are located between the first pathway 116 and second pathway 120 below the fan deck 224. The apertures and downcomers may be tuned to promote uniform distribution of the heated air. The flue gas leaving the direct fire burner may be near 2000 degrees Fahrenheit but after mixing with the return air from the structure 104, may return to the main drying section 300 at 450 degrees Fahrenheit which is nearly twice the main drying section set point air temperature which is often between 240 degrees Fahrenheit and 260 degrees Fahrenheit.
As one can imagine, the process of stopping the fans 200 in the main drying section 300 poses special problems as circulation from the fans 200 is needed to avoid overheating the top of the lumber stacks 152. Thus, while fans 200 are slowing, stopping, and coming back up to speed in the opposite direction, the blower continues to deliver additional air to the structure 104. During this time period when fan direction is being reversed, the burner abort stack (not shown) opens momentarily and the direct fired burner (1534 in
Eventually, lumber stack 156 stacked upon the first set of carriages 128 emerges from the main drying section 300 through orthogonal partitions 324 to enter the second end energy recovery section 340. Now the lumber is heated lumber 136 giving off heat and drying green lumber 140 on carriages 132 on the second pathway 120. The heated lumber 136 is exposed to air moving in the first circulation direction 204 and in the second circulation direction 208 as the bi-directional fans 200 are periodically turned off, allowed to coast to a stop, and then restarted in the opposite direction.
The lumber stack 156 emerges from the second end 112 and is eventually removed from the carriage 132.
Lumber on carriages 132 on the second pathway 120 receive the same sequence of treatments but travel in the opposite direction from the second end 112 to the first end 108.
The process of reversing from the first circulation direction 204 to the second circulation direction 208 may take fifteen minutes or more before the fully developed air flow pattern and dry bulb set point temperatures are regained. The sequence is as follows. First, the fans 200 are de-energized and allowed to coast to a full stop. After ample time elapses for all fans 200 in all sections of the structure 104 to reliably come to a full stop, the fans 200 are restarted in the opposite direction and eventually establish circulation at the desired speed. While the time to allow the fans to coast to a stop and restart may be as short as five minutes, some interruptions in the provision of heat may be in the 15 minute range as the heating system may be turned off before the fans are de-energized and heat may not be fully resumed for a few minutes after the fans have been re-energized. While the fans 200 are not energized and providing circulation at the desired rate, several things are not happening.
Number of 15
minute transitions
for 40 hour
Percentage
Length
transit through
of time that heat is NOT
of fan cycle
the structure
being added to the structure.
2 hour fan cycle
20
1/9 - approximately 11 percent.
3 hour fan cycle
At least 13
1/13 - approximately 7.7 percent.
4 hour fan cycle
10
1/17 - approximately 5.9 percent.
While there may not be a one to one relationship between the percentage of time that heat is not being delivered to the structure 104 and a reduction from optimal throughput for the structure, the loss in throughput should be proportion to the loss of time spent heating the structure 104
The present disclosure teaches the use fans to circulate heated air to dry lumber in a kiln. The fans do not periodically stop and reverse directions as in prior art designs. Instead, the alternating direction of air flow is provided by moving the carriage of lumber from one subsection of the kiln with air always moving in a first direction to an adjacent subsection of the kiln where the air always moves in the opposite direction from the first direction. Elimination of fan reversals will enhance kiln fire safety and reduce the time and energy required to heat lumber in kilns, while improving the quality and uniformity of lumber being processed. Aspects of the teachings contained within this disclosure are addressed in the claims submitted with this application upon filing. Rather than adding redundant restatements of the contents of the claims, these claims should be considered incorporated by reference into this summary.
This summary is meant to provide an introduction to the concepts that are disclosed within the specification without being an exhaustive list of the many teachings and variations upon those teachings that are provided in the extended discussion within this disclosure. Thus, the contents of this summary should not be used to limit the scope of the claims that follow.
Inventive concepts are illustrated in a series of examples, some examples showing more than one inventive concept. Individual inventive concepts can be implemented without implementing all details provided in a particular example. It is not necessary to provide examples of every possible combination of the inventive concepts provided below as one of skill in the art will recognize that inventive concepts illustrated in various examples can be combined together in order to address a specific application.
Other systems, methods, features and advantages of the disclosed teachings will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within the scope of and be protected by the accompanying claims.
The disclosure can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.
Use with Continuous Drying Kilns.
Structure 1104 differs from structure 104 in that the main drying section 1300 has a number of orthogonal MD partitions 1504 to subdivide the main drying section 1300 which is bounded by orthogonal partitions 324.
Thus main drying section 1300 has, in this instance, four subsections 1508, 1512, 1516, and 1520. The number of main drying section subsections does not need to be four but will be at least two and will usually be an even number of subsections as there is apt to be a desire to expose the lumber to equal ranges of the main drying section operated in the first circulation direction 204 and the second circulation direction 208 (as described below).
Turning to
As lumber 130 on the first set of carriages 132 passes through the orthogonal partition 324 separating the main drying section 1300 from the first end energy recovery section 1310 (
The fans 1200 in subsections 1508 and 1516 push air in the first circulation direction 204. But fans 1200 in subsections 1512 and 1520 push air in the second circulation direction 208. Thus, lumber stack 156 on first set of carriages 128 or the second set of carriages 132 is subject to alternating circulation directions (208 and 204) without intermediate periods of no circulation as fans are de-energized, slowed to a stop, and started in the opposite direction.
The steam supply to the steam heat exchangers 2530 may be regulated with control valves as is known in the art. While steam heat exchangers 2530 are shown on both sides of the fans 1200, one of skill in the art will recognize that the steam heat exchangers 2530 could be on a single side of the fans 1200 or with additional heat exchangers between or besides the pathways (116 and 120).
Returning to
One of skill in the art can appreciate that instead of using two subsections per energy recovery section (1310 and 1340) that one could use four or other even numbers of subsections. One could also use an odd number of subsections in the energy recovery sections (1310 and 1340) potentially by changing the lengths of the subsections so that the total amount of time subject to each circulation direction (204 and 208) is maintained equal even if done in a different number of segments. Alternatively, there may be a bias to pass heat from heated lumber to green lumber or moisture from green lumber to heated lumber.
While not absolutely required, it is expected that in most instances, there will be an even number of subsections in the alternative main drying section (1300 or 2300) and there will be the same number of subsections in the first end energy recovery section 1310 as in the second end energy recovery section 1340.
The orthogonal partitions 324, 1320, and 1504 use baffles created to allow passage of a carriage loaded as intended (with lumber, spacers, and weights) but substantially conform to that profile so that longitudinal flow of air is limited. However, as the stacking of lumber, spacers, and weights may have some small variation from carriage to carriage, the baffles must have a capacity to give way when a larger than expected profile attempts to cross an orthogonal partition. The baffles are intended to be easy to adjust or replace during maintenance outages so that longitudinal air flow continues to be effectively resisted.
Placing a set of baffles on a faux partition external to the structure 1104 for pathways heading toward the structure 1104 may be useful to allow adjustments to the green lumber 140, spacers, and weights on a carriage to minimize the amount of contact with the baffles inside the structure 1104. Working for conformity with the expected profile for a loaded carriage will reduce wear on the baffles inside the structure 1104 which will mean better resistance to longitudinal air flow over time and will reduce the risk that a grossly misaligned piece of lumber or weight will be knocked off the carriage by a baffle unable to move out of the way of such a misaligned stack.
As the direction of airflow in the energy recovery subsections adjacent to the main drying section is fixed, the structure may be optimized to provide the direction of airflow in these critical sections that is most useful for preventing an outbreak of fire on the recently heated lumber. For example, it may be prudent in these energy recovery subsections nearest the main drying section to always circulate air to push air from the green lumber directly onto the heated lumber to maximize the cooling effect on the heated lumber, especially as the lumber enters subsections with oxygen contents closer to atmospheric levels. Alternatively, some installations may want to design the structure with the concept that the hot air leaving the heated lumber is pushed directly onto the green lumber without going through a circulation fan to maximize the drying effect on the green lumber. With fixed flow directions per subsection, the designer has the opportunity to optimize a design as the flow confronting each carriage of lumber will be the same for that subsection, and the order of circulation flow directions encountered by the lumber will be the same for all carriages as they pass through the drying process. A structure 104 using mirror image energy recovery sections 314 and 318 will subject the first set of carriages 128 and the second set of carriages 128 to the same sequence and durations of first circulation direction 204 and second circulation direction 208. In the event, a designer does not opt for mirror images, then the sequence will differ.
Use with Unidirectional Kilns.
The teachings of the present disclosure may be used with unidirectional kilns that have all lumber travel in a single direction. While the concept is expressed in connection with drawings that show a single set of carriages conveying lumber from a first end to the second end of a structure, the concept is applicable to structures having two or more sets of carriages conveying lumber on parallel pathways from the first end to the second end of the structure. Thus, if the drawings of
As the need for drying time in the structure may differ for one batch of lumber to another batch as the thickness, moisture content, and other parameters may differ from one batch of lumber to another batch, nothing in this disclosure should be interpreted to require that all carriages on all pathways move at the same speed or pattern so that the lumber spends the same amount of time within the structure no matter which pathway the lumber is on.
Structure 4104 differs from structure 104 in that the main drying section 4300 has a number of orthogonal MD partitions 4504 (See
The first chamber 4310 and may or may not have a capacity to provide additional heat to the lumber as first chamber 4310 may simply allow heat from main drying section 4300 to pass into first chamber 4310 to preheat the lumber. The third chamber 4340 and may or may not have a capacity to provide additional heat to the lumber as third chamber 4340 may simply allow the heated lumber exiting from the main drying section 4300 to become uniformly heated as heat passes from the exterior of the lumber to the interior and to cool down before leaving the second side 148.
Main drying section 4300 has, in this instance, four subsections 4508, 4512, 4516, and 4520. The number of main drying section subsections does not need to be four but will be at least two and will usually be an even number of subsections as there is apt to be a desire to expose the lumber to equal ranges of the main drying section operated in the first circulation direction 204 and the second circulation direction 208 (as described below).
Turning to
The main drying section 4300 may have a return duct that draws air from one or more subsections in the manner discussed in connection with
As lumber 130 on the set of carriages 3128 passes through the orthogonal partition 324 separating the main drying section 4300 from the first chamber 4310 (
The fans 1200 in subsections 4508 and 4516 push air in the first circulation direction 204. But fans 1200 in subsections 1512 and 1520 push air in the second circulation direction 208. Thus, lumber stack 3156 on the set of carriages 3128 is subject to alternating circulation directions (204 and 208) without intermediate periods of no circulation as fans are de-energized, slowed to a stop, and started in the opposite direction.
The teachings of the present disclosure may be applied to a structure that has all carriage pathways travel in a single direction and uses steam heat exchangers to provide heat to the main drying section as discussed in connection with
Returning to
One of skill in the art can appreciate that instead of using two subsections in the first chamber 4310 or the third chamber 4340 that one could use four or other even numbers of subsections. One could also use an odd number of subsections in the first chamber 4310 or the third chamber 4340 potentially by changing the lengths of the subsections so that the total amount of time subject to each circulation direction (204 and 208) is maintained equal even if done in a different number of segments.
The orthogonal partitions 324, 4320, and 4504 use baffles created to allow passage of a carriage loaded as intended (with lumber, spacers, and weights) but substantially conform to that profile so that longitudinal flow of air is limited. However, as the stacking of lumber, spacers, and weights may have some small variation from carriage to carriage, the baffles may have a capacity to give way when a larger than expected profile attempts to cross an orthogonal partition. The baffles are intended to be easy to adjust or replace during maintenance outages so that longitudinal air flow continues to be effectively resisted.
Placing a set of baffles on a faux partition external to the structure 4104 for pathways heading toward the structure 4104 may be useful to allow adjustments to the green lumber 140, spacers, and weights on a carriage to minimize the amount of contact with the baffles inside the structure 4104. Working for conformity with the expected profile for a loaded carriage will reduce wear on the baffles inside the structure 4104 which will mean better resistance to longitudinal air flow over time and will reduce the risk that a grossly misaligned piece of lumber or weight will be knocked off the carriage by a baffle unable to move out of the way of such a misaligned stack.
One should expect that all other things being equal the push rate of a structure converted from reversing fan operation to alternating single direction fan operation should increase as heat will continue to be applied to the structure without interruption for fan direction reversals. As kilns of this type are frequently used continuously for extended periods and then serviced in a maintenance outage, an increase in push rate results in an increase in production capacity without decreasing quality.
Operation of heating systems of any type are usually easier at steady state and more difficult when there are transients since monitoring equipment set points must often be altered for transient conditions but may be set to closer tolerances during steady state operation as deviations are more meaningful during steady state operation.
One should expect reduced maintenance and operation costs from running fans in a constant direction as motors and other components receive additional strain during the effort to start the motor and accelerate the fan.
One should expect a reduced risk of fire in the structure 1304 or 4304 as continuous airflow over lumber in carriages will reduce the formation of hot spots within the structure which might have occurred during a cessation of air flow during a fan direction change. Hot spots during a period without air circulation may cause a portion of the structure to move from an operating temperature of approximately 250 degrees Fahrenheit to more than 300 degrees Fahrenheit. Given that fire suppression sprinkler heads are used with thermally activated fuse links that are often designed to open between 330 degrees 360 degrees Fahrenheit, there are risks that a thermal transient from a hot spot might trigger a sprinkler which would not be useful for drying wood. More importantly, triggering fused sprinkler heads also requires and immediate shutdown to replace the one-time activated fire suppression equipment, resulting in significant production delays and loss of production efficiency. With the use of single direction fans, the set points for fire protection equipment can be dropped to respond more quickly to true fires without the risk of responding to a transient thermal hot spot.
Fire Detection Instruments may be positioned and have alarm set-points optimized for a particular subsection. Knowing the direction of air flow will allow alarms to be placed in optimized locations. Tolerances for temperature or smoke detection may be tuned to be more proactive as the instruments will not have to compensate for the conditions associated with dead air disturbed only by natural thermal convection during the absence of forced air circulation. Thus, with tighter tolerances, the fire detection and suppression equipment can react quicker to any aberrant measurement that may indicate the onset of a fire. With the air largely precluded from longitudinal movement by the orthogonal partitions, smoke concentrations will rise faster in a particular subsection than would otherwise be the case which will further assist in the early detection of a fire. Fire suppression systems can be set to react to indications of a minor fire by only applying water to the specific subsection implicated as potentially having a fire. This avoids unnecessary spoilage of lumber that is not at risk of fire. The fire suppression systems may be automatically or manually activated so that instances of activation will not necessarily require replacing equipment.
Given that the direction of air flow within a subsection is known, the fire suppression systems can be optimized for the direction of air flow. For example, side mounted fog or water deluge nozzles maybe placed to envelope or soak the upwind side of a carriage enabling water droplets to be carried by the air flow through the lumber from the upwind to downwind side of the carriage. Side mounted fog, deluge, or other nozzle arrays could be mounted on the upwind side of each of the one or more first pathways to optimize fire suppression options and to make use of uninterrupted alternating air circulation.
A structure designed with the teachings of the present disclosure may be able to achieve air movement with less fan amps as fan blades designed for unidirectional operation may be more efficient than the compromise inherent in bi-directional fan blades. Typically, the delivered CFM per motor horse power is greater for unidirectional fan blades than it is for fan blades that must be shaped and pitched to equally propel air in opposite directions based on alternating rotation.
Those of skill in the art will recognize that the direction of travel of the first set of carriages 128 on the first pathway 116 and the second set of carriages 132 on the second pathway 120 may be reversed from the directions discussed above without deviating from the teachings of the present disclosure.
While it is anticipated that many that use the teachings of the present disclosure will use unidirectional fans or will perpetually use bi-directional fans in one direction, the option remains of using bi-directional fans and reversing the direction of all the fans during a maintenance overhaul if that is perceived to have a benefit of elongating the life of any fan component.
Those of skill in the art will recognize that the formation of partitions to form subsections may be facilitated by choosing places within the structure that have structural supports such as beams, pillars, and trusses.
A number of direct fire burners may be used to provide the heat if direct fire burners are used rather than steam. The burners used for wood kilns include biomass (such as green sawdust or wood waste) direct fired burners, fossil fuel (such as coal, natural gas, or petroleum products) heating units, or other direct fired burners.
The push rate for moving carriages and the widths of subsection widths may be selected so that a carriage enters one subsection with one circulation direction and then enters the next subsection to be subject to airflow of the opposite circulation direction every two to four hours. For some installations, a three hour interval may be optimal. Those of skill in the art will recognize that a kiln using lower temperatures or flow rates, a different carriage width, or a different amount of rows and spacers may find that a different time duration is suitable, perhaps less than two hours, perhaps more than four hours.
Sub-Sections of Different Lengths.
While the figures discussed above had uniform subsections lengths from one end of the structure to the other end, this is not a requirement.
Finally, there may be times when a structure originally designed for reversing fan operation is upgraded to uni-direction operation. As there are advantages to building the structures for partitions to coincide with existing steel supports, one may make some adjustments to sub-section length to take advantage of existing structure. An important criterion is limiting the maximum time duration exposed to any one circulation direction. A particularly long distance between existing structural steel may be further subdivided into two or three subsections to avoid an overly prolonged exposure to circulation in one direction.
Turning Off Fans During a Fire Incident.
While there are advantages to having fire detection and suppression equipment tuned for a single circulation direction rather than having to compromise to accommodate both circulation directions (204 and 208), the fire suppression scheme may call for de-energizing at least some fans in the structure to minimize the oxygen fed to the fire. Even in a system that anticipates using fire suppression with the fans de-energized, there will be advantages in early detection of a fire for a system that does not have alternating circulation directions within a single subsection.
One of skill in the art will recognize that some of the alternative implementations set forth above are not universally mutually exclusive and that in some cases additional implementations can be created that employ aspects of two or more of the variations described above. Likewise, the present disclosure is not limited to the specific examples or particular embodiments provided to promote understanding of the various teachings of the present disclosure. Moreover, the scope of the claims which follow covers the range of variations, modifications, and substitutes for the components described herein as would be known to those of skill in the art.
The legal limitations of the scope of the claimed invention are set forth in the claims that follow and extend to cover their legal equivalents. Those unfamiliar with the legal tests for equivalency should consult a person registered to practice before the patent authority which granted this patent such as the United States Patent and Trademark Office or its counterpart.
Ball, Jr., Troy Eugene, Girardi, Robert, Pollock, Robert King
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