Tobacco Barn used as a kiln

[SawyerTed]

I have access to a bulk tobacco barn and have found NCSU's Extension Service instructions on repurposing a bulk barn for drying lumber.  Barns are selling now for less than $2000 and many are $1000 or less.

James Kea at the Martin County, NC Extension Service Office authored the instructions that follow.  I'd be interested in feedback on this as a viable method for drying lumber and heat treating air dried lumber.  Keep in mind that the author was trying to find secondary uses for existing barns as a profit source for farmers.

Instructions from NCSU:

Bulk Tobacco Barn: (1) Check the maximum weight that the perforated floor can carry. Pine lumber weighs approximately five pounds per board foot (1″ X 12″ X 12″). Hardwood would weigh between 5 and 7 pounds per board foot. (2) Weigh a sample board while it is green. Mark it as a reference board for determining when your lumber is dry. (3) Paint the ends of lumber to reduce splitting. Use oil based paint. Lumber should have 1″ stickers (ie. tobacco sticks) placed every 2 feet of each layer. Place stickers directly over those in the previous layer. Leave about an inch between boards in each layer. The pile should be as level and flat as possible. A foot wide chimney needs to be left in the center and a cover such as plywood placed on stickers on top of the pile. The idea is to spread the air flow from the chimney out between the layers. (4) The first day run at 120° dry bulb and 110° wet bulb. The second-day run 120°dry bulb and 105° wet bulb. The third fourth and fifth days run at 130° – 140° dry bulb and 90° wet bulb or less with no water added. Continue at this schedule if not dry for one more day. Thin lumber (less than 1″ thick) may need weight on top to reduce twisting and warping of the top layers. Stack this lumber in lower layers of random size lumber with large timbers on top. Eggs and adults of wood boring insects should be killed with this schedule. (5) Wood should weigh three pounds or less per board foot when dry at 20% moisture content. Moisture content will change to match relative humidity. (6) Dry lumber can be stored without stickers, but must be kept flat. Store in a dry place.

[Southside]

I presume you are talking about the modern propane fired metal barns?  

[SawyerTed]

Yes. It is a Powell.  Looks like a shipping container.

This is actually my heat  treatment plan for the flooring we discussed

[DR Buck]

I don't know anything about these modern tobacco barns.   However, the specific wet bulb dry bulb settings specified ARE NOT EVEN CLOSE to a proper species drying schedule.   If you try drying green  hardwood lumber in 5 days you will be making firewood.

[scsmith42]

I don't know anything about these modern tobacco barns.   However, the specific wet bulb dry bulb settings specified ARE NOT EVEN CLOSE to a proper species drying schedule.   If you try drying green  hardwood lumber in 5 days you will be making firewood.

The schedule listed is for SYP, which should be ok.  You are 100% correct about that schedule trashing hardwood though.
Ted, how far are you from Raleigh?  I've been operating a shipping container kiln since 2003 and always thought that the metal tobacco barns would make a good, small dry kiln for lumber.

[SawyerTed]

I don't know anything about these modern tobacco barns.   However, the specific wet bulb dry bulb settings specified ARE NOT EVEN CLOSE to a proper species drying schedule.   If you try drying green  hardwood lumber in 5 days you will be making firewood.

This is is great feedback and good information.  It's in this vein that I need more information to determine if it's worth the time and money to pursue using a tobacco barn.  Could you elaborate on appropriate hardwood drying times and temps?  I know it isn't a formula but a combination of art and science.  I'm having trouble getting target temps and ballpark times for kiln drying hardwoods.
Scsmith42 - I'm a couple hours west of Raleigh.  

[DR Buck]

I have the earlier Wood-Mizer version of the Nyle 200 DH kiln.     This link is the the user manual for the current Nyle 200.     Section 2 of the user guide covers drying schedules.

https://www.nyle.com/wp-content/uploads/L200Manual_Web.pdf

[Don P]

These are a couple more standards, there are conventional kiln tables in them they might be more in the temp ranges you'll be hitting. The Dry Kiln Operators Manual is sort of the bible for conventional kiln ops.

https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr118.pdf
https://www.fpl.fs.fed.us/documnts/usda/ah528.pdf?q=hardwood

I'm assuming you have vents you can open and close to run heat/vent cycles.. sorry my experience ended with handing sticks up in the barn, ok not that sorry it ended there :D

[samandothers]

Neat idea!  I look forward to hearing how this turns out.  Are these gas fired?

[SawyerTed]

Thank you for the links to the kiln operation guides and drying schedules. I am brand new to this.

 I recognize that just like curing tobacco or hams, it's part science and part art.  It certainly is not a "set it and forget it" operation.

DonP, after the trailers were full of tobacco I had either the offbearer job (taking a stick upon which the stringer sewed leaves for hanging in the barn) or the housing job at the barn (hanging sticks of tobacco leaves on tier poles in a barn).  Those were good days but I don't want to go back either, at least not to that.  Yes the bulk tobacco barns have options for venting, adding humidity and heat.  The bulk barns are easier to control that the old log or frame barns.

Samandothers, yes these are propane fired burners.  The original barns were direct fired, later barns used heat exchangers to prevent hydrocarbon residues from accumulating on the tobacco leaves.  

I've been around these barns for 30 years, I believe the greatest drawbacks will be loading and unloading and capacity.  But if you have no kiln but access to a bulk barn (for less than building a solar kiln) you've got a lot to gain if you can figure out how to dry lumber in a bulk barn.  

[btulloh]

There are a lot of these sitting around doing nothing these days if this is feasible. 

[Matt Mckinnon]

Lot of them around here.  I know some people that have used them to dry lumber.  I also know of a pallet maker here that uses one.  

[SawyerTed]

Here's an update.

I met with my neighbor about using his bulk tobacco barn.  The deal is I pay fuel and electricity costs.  Use of the barn is free. He hasn't used it in over 10 years.  We did start it so it runs. 

We discussed control of air, humidity and temperature.  While the controls are analog they are automatic.   The issue of controlling the air through the perforated floor has to be addressed.  I believe I can lay plywood over the areas not covered by stacks of lumber.  

Winter time drying may present efficiency challenges.  

Looking from this from an entrepreneurial standpoint, it is worth the risk. It will cost fuel, electricity, and time.  It might cost a stack or two of experimental lumber (mine before I try a customer's lumber).

[Southside]

Are those insulated or just the metal? I have never seen the inside of one.  

[samandothers]

If this works out there could be a run on tobacco barns!

[SawyerTed]

The one I'm looking at is insulated.  It is a sandwich of metal outside, foam in the middle and plywood inside.   It is on a 6" concrete slab on rigid foam insulation as well. 

I'm wondering why the barn manufacturers haven't branched in this direction.

[GeneWengert-WoodDoc]

There are basically two types of tobacco barns.  Both are disappearing...NC used to have 500,000 but now is under 10,000.  They were typically about 20' x 20'.  One type, the most popular, was an air drying shed; that is, there was no added heat.  Outside air was naturally convected through the leaves.  The plentiful vents to the outside were open in the daytime when humidities were low, but then closed at night with the high humidities.  The second type used a furnace to accelerate drying.  Typically the furnace put hot flue gasses directly into the barn using a large set of ducts.  The fuel was almost always southern pine logs.  A leaf is about 80% water when first cut.  This means that the leaf temperature was close to the wet-bulb for most of the time.  Very hot temperatures were avoided, especially at the end of drying.  The leaves did get coated with the chemicals in the flue gasses...we might call it creosote...affecting quality.  So, not all grades of leaves were heat cured.

  Incidentally, the leaves were hung on racks in order to facilitate drying.

When we use the word "kiln" or "kiln drying" in our lumber business, we usually think of a room that has carefully controlled temperature and humidity with fans that blow air through a lumber pile.  Because of the fans, we do not need a chimney in the pile and we do not need spacing between the lumber pieces in the same layer.  Further, we generally avoid mixing thicknesses in the same pile.  For Southern pine we also avoid over-drying, as we will see a lot more warp.  Warp is a big issue with syp and with construction lumber.  The "schedule" quoted in the document
https://martin.ces.ncsu.edu/twigs/drying-green-lumber/
Is not reasonable for syp for this reason.  Likewise, the stacking method with chimney and spacing and 1" stickers is not the best idea.

I think we might indeed be more accurate if we called this a dryer rather than a kiln.  You can indeed dry wood in many ways, but for quality, even syp will benefit by regulated drying conditions that especially avoid over drying.  

In fact, the phrase "kiln drying" when referring to syp graded lumber means temperatures used in drying were over 150 F.

[Don P]

That sounds more like burley barns and the older flue curing barns, take a look at bulk tobacco barns for what Ted is describing. Off to the haybarn myself, it's dumping snow here, again!

[Wudman]

Doc,

SawyerTed is referring to a "modern" bulk tobacco barn.  They look like a shipping container and are insulated.  The older barns were direct fired with propane burners.  The newer ones used a heat exchanger to limit the amount of petrol by-products on the tobacco.  They have adjustable vents, fans, and a method to control humidity (to some extent).  You can steam in them.  I think you could dry SYP without too much issue in one.  More finicky hardwoods may present more of a challenge. 

Wudman

[PC-Urban-Sawyer]

I lived in North Florida while I was a teenager. We had tobacco farmers there and the barns were all flue cured design with propane heat.

One of the farmers wanted my Dad to build them a dining room set. He asked Dad if he could use some of the "fence row" (black) cherry to make the set. Dad said sure, so the guy cut a dozen or so large cherry trees (about 1 Mbf of 4/4 lumber) to use. He knew that it needed to be dry and didn't want to wait for it to air dry so he stacked it in one of his old tobacco barns and cranked the heat / blowers up to full blast. "Dried" (baked) them for two weeks (figured it took a week to dry tobacco so he have the cherry two weeks... That was some of the worst lumber we ever tried to work with.  It was case hardened and every cut on the table saw pinched the blade enough to burn the cherry and it was so hard you had to pre-drill if you wanted to put in a finishing nail. After building the drop leaf dining table we started on chairs and after a couple of weeks my Dad went to see him and told him we couldn't finish the set because the wood was too bad to work with. Gave him the table at no charge and he told us to throw out the rest of the lumber.

Herb

[SawyerTed]

What I am working with is, indeed, a modern bulk tobacco barn.  

What Dr Wengert is discussing are air cured or flue cured log or frame barns.  I do in fact have 1200 bdft of white oak stored in a frame flue cured tobacco barn within sight of my house.  We actually have two frame flue cured tobacco barns and four log flue cured tobacco barns on our farm.  I'm very much in agreement that these are good for air drying lumber but will not serve well for a kiln.  Tobacco was a way of life on this farm and in this family for over 100 years.

After careful study of the drying schedules in Drying Hardwood Lumber (corrected, I referenced the wrong source originally) Chapter 7, I believe the modern tobacco bulk barn has the capability and controls for temperature and humidity to be a viable alternative to a purpose built kiln with minimal modification.  While the controls are analog they are fairly sophisticated.  For example the controls can be set for dry and wet bulb temperature control, temperatures can be programmed to increase/decrease by increments over time. Opening and closing of the vents is typically a manual operation.

The pine drying schedule contained in the Martin County document I originally referenced isn't viable.  However, if the guidance in Chapter 7 is to be relied upon (and of course it can), then the modern tobacco bulk barn can meet the temperature and relative humidity outlined for both hardwoods and softwoods I will be milling. Two hundred plus degrees is obtainable.

There are challenges that need to be overcome. These are the ones I'm aware of right now.

First is the square footage of the barn I'm going to use will be excessive for the amount of lumber I will typically load.  This will have to be managed.  The simplest will be controlling the airflow and heat through the perforated floor and directing that flow to the stacks of lumber.  Other ideas will include some type of baffling for partitioning.  Modification costs will be far less than purchase or construction of a purpose built kiln.

Tobacco is a summer crop.  Curing is normally a warm weather process.  Drying lumber in colder months may present inefficiencies too costly to justify.

Loading the barn will be a challenge as well.  Initially and until the feasibility can be proven, loading will be manual.  I envision kiln carts on tracks eventually.  

The modern bulk tobacco barn is well advanced beyond the old log or frame tobacco barns that were used extensively at one time - whether they were drying sheds for burley tobacco or the more common flue cured barns.

[SawyerTed]

One additional caveat-remember my business is very new.  The idea of using the tobacco barn is an alternative along the lines of a solar kiln. It is a low cost way to meet a need for the short term.  It isn't intended to be a high production solution. 

[Southside]

Ted - 

Given what you have there, moving the air across the stack and baffling the excess area will basically duplicate what a purpose built DH kiln does, assuming of course you are relieving the moist air out of the system.  So, I don't see a difference there at all, warm, dry air, is warm dry air, be it from a heat pump, or a nuclear reactor gone bad.  

As you said the key is control and you have that in the system.  If it works well for you then including a PLC and some relays into the controls would not be a big deal at all.  Four functions, fan, heat, vent, and steam is all the PLC output needs along with two inputs - dry and wet bulb, which probably would have to be upgraded to digital, but is not a big deal to do.  

For winter use, just insulate over the outside of the unit and re-shell it. 

[SawyerTed]

The first photo is an example of an old log flue cured tobacco barn. 

The following two images are of bulk barns similar to the one I am repurposing.  The barn loads from the end pictured under the shelter. The width is 9'8" and the interior length is 33'.  There is a divider down the middle that divides the barn into two "rooms".  The divider presents some loading challenges.  The vented end houses the burner and other controls.  

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