Kiln design question

[BeeGuy]

Question for you more experienced guys with mid sized kilns. I'm currently designing a kiln to dry at max 15k bdft of SYP at a time. Now, let's say I only have a 5k bdft run every once in a while that doesn't fill the kiln. Do I just need to center the load under the fans, spread it all out evenly for the full length of the kiln minus plenum, or what? Thoughts? At the moment the design for the kiln is 32ft long x 18 wide, four fans, and the Nyle HT18. We primarily deal with SYP down here. I'm not completely sold on the Nyle HT18 so If you have any recommendations on another brand/model I'm all ears.

The Nyle reps have been awesome to work with just wanted to see if there are better products out there for this size of kiln. Also, thoughts on getting a smaller unit and still running the same 15k bdft? What happens in that scenario, does it just take longer to dry?

Thanks in advance!

[K-Guy]

If you buy a smaller unit you will get mold, the smaller unit won't remove the amount of water you need to. Also if you are drying SYP make sure you have lots of airflow.

[BeeGuy]

What if I pre dry the SYP outdoors prior to putting it into the kiln? We are a small manufacture and can only process around 6k bdft a week from exiting the kiln to assembled finished product. Originally my thought was to stage 2 weeks in advance, so have 12k bdft in the kiln at a time. That way when the lumber is done drying we are just finishing up the first load. That being said, if I can reduce that time in the kiln down to a week and only bring in 6k bdft each week then I'm golden. Thoughts?

[customsawyer]

First off I don't think your chamber is going to be big enough to get 15,000 bf. inside of it, unless you are going to be stacking pretty high. My chamber is 15X20 I can squeeze 5,000 bf into it, if it is cut at 9/4. If you are drying 4/4 lumber than you will have twice as many stickers than I do with 9/4. I'm going to guess that since 32' came into the size of the chamber that you are planing on putting packs of 16' lumber end to end. If this is the case I would recommend a minimum of 34' or 35' or even 40' would be better. If it were my operation I would feel more comfortable with 2 or 3 Nyle 200 units in different chambers than I would trying to fill one 15,000 bf chamber. If you are air drying the pine before you go into the kiln then you can put more than 2000 bf in the Nyle 200. I regularly air dry pine to 20% and stick 4000bf in my Nyle 200. I can run this size load every 10 to 12 days. It does take some extra heat sources during the sterilization cycle as my unit is around 20 years old.  

[YellowHammer]

SYP is not ideally suited for a DH kiln.  Green, it releases so much water that it will cause the production numbers of the DH unit to drop by 75%.  Or you have to add and vent excess heat to increase the capacity.  

If the SYP is air dried, then it will work better, but why not get a kiln with such fast drying properties that it is optimized for fast drying species such as pine and polar?

Typically, that would be some sort of direct or indirect fired system.  Lots of heat in, lots of moisture out.  Full loads of green.  Fast drying for wood that can handle high moisture removal rates.  

I'df also highly recommend purchasing a system that exceeds your current drying requirements, so you can dry the loads you need, then let it sit idle.  Design the kiln for at least 50% more capacity than you currently need now, or in a few years, you'll be getting another one.  Then as you grow, your kiln can handle the increased loads.

The cost of the kiln unit itself is pretty cheap, its all the other stuff that costs money, so over build on the building and facility, and you won't have to incur those high costs twice.    

[BeeGuy]

Customsawyer, yes. We have height in our advantage, our ceilings start at 18ft and go up, that's how I'm getting that amount of bdft in that space. No we will not be putting 16' lumber in the chamber. We load from the short side in. Also, 16' lumber is a pain to deal with length wise in production. We prefer to use 12ft and 8ft lengths, thus the reason for the 18ft entrance (16ft door way).

Typically, that would be some sort of direct or indirect fired system.  Lots of heat in, lots of moisture out.  Full loads of green.  Fast drying for wood that can handle high moisture removal rates.

We have access to a major gas line running through the property. It sounds like you have something in mind, what system do you recommend? Let's say currently we are at 6k bdft/week this and next year. So 50% is worst case scenario, which puts us at 9k bdft of SYP at a time.

Another thought has come across my mind while reading some past posts. Why not use a steam boiler? We produce plenty of scrap/sawdust that could be converted to fuel for the boiler. I'm just thinking out loud. Does anyone on here have any experience with steam boilers that have any input on a small unit?

[BeeGuy]

I've attached a simple sketch as to the layout of the kiln. This is the only location in the shop it can fit. I have designated 40'x25' for the kiln but am trying to conserve some space since I only currently need around 6k bdft per week. That's why I went with 32'x18'. Anything less length wise is just wasted floorspace. As I mentioned before the ceilings start at 18' from the outer walls and work their way up so I have height to my advantage.

[YellowHammer]

Direct or indirect fire typically use propane or such.  An outdoor wood boiler uses waste wood as a source of heat.  The heat is transferred as heated water or superheated steam. Or use your existing steam system such as in a conventional kiln.  All will work.  With forgiving and fast drying wood you have lots of options. 

[customsawyer]

One other thing I would do is add two more fans. I have 4 in my 20' kiln and I wouldn't want any less. I wired them up in pairs, so that if I have a smaller load I don't have to run all of them. If I have a full load I have the air flow that I need. The nice thing about pine is you can dry it as hard and fast as you want or can. One of the down sides to they L200 kilns is that they can't dry over 130 degrees. So if all you are drying is pine go with a kiln that will dry at higher temps. Nyle makes some as I have researched them before. What moisture are you needing to get to?

[BeeGuy]

What moisture are you needing to get to?

That is an excellent question that I should know but don't have a clear answer for. It's an issue we deal with. Currently we purchase 35M mdft at a time of 1x12x16 or 1x12x12 with some 1x12x8, just depending what they have. Our stuff comes ready to go and heat treated from George Pacific currently. I believe it's right around 19% when it leaves the kiln, I'll have to check the markings but I'm pretty sure they read KDHT19.

We are in Arkansas so humidity and heat are high in the summer. We typically process and build or stack indoors as soon as the trucks come in. I have noticed though that some of the top boards on the stacks will begin to warp (which become scrap). Warping is an issue for us as we transition from May into June and July. We assume its humidity/temp related. So that's a pain to work with.

The thought behind the kiln for us is, we can regulate the humidity and temp better for our operation to match the local region we are in (reducing scrap) and to cut down the cost of the lumber increase from this past year. Kinda two birds one stone scenario for us.