Drying Times for Newbie

[sisyphus]

I am trying to work out the fastest way to dry mixed species of timber and would very much appreciate some thoughts.

The background is that I am doing some financial forecasting for a charity in the UK which intends to recycle complete trees which would otherwise be dumped in landfill. It will do this by acquiring a sawmill and planking the trees. There is likely to be a wide range of species, the most common being Ash, Beech, Birch, Chestnut, Elm, Lime, Maple, Oak, Poplar and Sycamore.

To maximise the output from selling dried timber, a kiln is needed. I have spoken to a number of suppliers, all of whom assure me that their product will do exactly what I want. However, when I go into details, the picture is less than clear. For example, assume that the charity needs to sell 10 cu m ( say 4200 bf ) a month. A kiln with this capacity would appear to be suitable but not if the drying time were more than 30 days. Alternatively, a kiln with a third of this capacity would be OK if it dried the timber in 10 days or less because I could get three loads of one third of a cu m done in a month.

I appreciate that the time involved depends on the thickness of the timber and how dry it is when it is put in the kiln. I am assuming that the bulk of the output will be 4/4 or 8/4 boards. I have no idea how wet the timber will be when we get it but am happy to work on the basis that the trees were felled the day before we got them and we planked and kilned them the day after. I assume that this has to be the worst case scenario in terms of speed. I am also assuming that the trees
we will be given will be a mixed lot each month and that it will be necessary to dry mixed batches, certainly in the initial stages of the operation.

Once the project is up and running, I feel that we will be able to air dry timber for a period before using the kiln. We cannot do this at the start as the bank wants its money back as quickly as possible so we need the added value from the kiln. I have looked at a number of publications, from various sources on the web, which give drying schedules. It seems to me that it will always take more than 30 days to dry oak so I would prefer to air dry this. I think Sycamore is best left on end to air dry but I would want to kiln dry the other species.

I know that I have to decide on either a conventional kiln or a dehumidifier ( current thinking is conventional as the electricity cost of running the dh would be enormous ) but my problem is deciding on whether to spend a lot of money on buying a big kiln or a lot less on a smaller one. The critical point seems to be the actual drying times, and if I can get several cycles a month out of a small kiln, I would prefer to do this.

Can anyone give me some advice on this question?

[scsmith42]

Welcome to the forum!

A couple of observations...

In conventional or DH kilns, it is usually a bad idea to mix different species and/or thickness in the same load.  The problem is due to the fact that different species dry at different rates, and you need to adjust the kiln during the drying process.  If you adjust it for the quicker drying species, you risk damaging the slower drying species, etc.

DH kilns are fairly economical to operate; contact the folks at Nyle for some cost forecasting info.

To proide you with some estimates, in my Nyle L200 it typically takes around 25 days to dry 4/4 oak boards from green to 8%.  The actual amount varies depending upon how much wood is in the kiln.  A load of 8/4 oak would require somewhere between 60 - 90 days drying from green.

If your climate will support it, some solar kilns may be a better alternative for you.  You could bring the wood from green down to 20% (or thereabouts) in the solar kiln, and then transfer it to a DH for final drying and sterilization.

I would suggest contacting the folks at Nyle for their recommendations, and a copy of their drying charts.  They sell kilns all over the world and are well versed in the different power requirements in various countries.  Their reputation is excellent too.

Good luck with your project!

Scott

[ellmoe]

   I think that you will find that a DH klin will be less expensive to operate and more forgiving. ;D  Once you put your first charge in the kiln green, the rest of you loads can be airstacked and allowed to partially air dry. This will shorten your drying time for the following loads. If you properly cover the air drying wood you can get some cheap drying, saving expenses and allowing the use of a smaller (cheaper) kiln. Since you will be drying a mixture of species and thicknesses, consider buying a smaller kiln now and another later. With this option you will have more flexibility and an easier time drying your variety of lumber. Purchasing two kilns will be more expensive than one larger kiln. However, after you ruin several thousand feet trying to dry a variety of wood in the large kiln, the cost savings will be gone, up in smoke (vapor) :D.

   Good luck.

Mark

[sisyphus]

Many thanks for your comments. Ironically, they confirm my initial view which was that we should have two small kilns as opposed to one big one in order to deal with mixed species. I was then seduced into thinking big by talking to a kiln manufacturer.

I'll go back to basics and have a chat with Nyle.