Home made vac kiln

Den Socling · April 20, 2015, 10:32:12 AM

What I really need to know is whether it's porous or occluded. I've dried French Oak that was supposed to be White Oak and it was porous and dried like Red Oak. If John's oak is occluded, this is going to be tough because he doesn't have steam to raise the humidity.

Den Socling · April 20, 2015, 03:03:37 PM

If you're interested, we discovered that it is Quercus robur which is English Oak, French Oak and German Oak. I've successfully dried French and German so I gave John my schedules and we are looking over his equipment for anything that would explain the problem with his two slabs. We'll get it.

boardmaker · April 21, 2015, 04:43:40 AM

I have been wondering what the condenser in the rear of the vacuum chamber is?

Also, in the 2nd to last picture of the build. There are several boxes to the right of the control panel. They don't look familiar?

These guys did an outstanding job! I also gotta hand it to you Den to help someone so much even when the info you're sharing is something you've earned with your own blood sweat and tears.

John.Howard · April 21, 2015, 07:54:25 AM

Thanks Boardmaker.

That is the kiln condenser at the back, but at the moment I'm working on the opposite problem.

The main box to the right of the control panel is a domestic consumer unit (a type of distribution board, you may call it something different), with RCD's and MCB's. This is where I split the incoming power to the lights, plug sockets and all the different pumps, 24v DC power supply etc. Each component can therefore be individually isolated outside of the control panel. Then there is the electric meter so we know how much juice we're using. It only flows left to right which is why it looks like an octopus reaching over its head with it's left arm to pick up something on the consumer unit to it's right. The other box is just to split the armoured cable to the 'tails' which go into the meter then on to the consumer unit. I'm sure there's probably a better way of doing things, this was just the most familiar to me.

And yeah, Den's been great.

boardmaker · April 21, 2015, 09:58:13 AM

I never realized you would need a condenser. I assumed that all water removed would go through the drain and be removed in the shell and tube exchanger.

Would you explain why you're using the condenser?

Also, what brand of HMI is that? I see most the the other components are Automation Direct, but I know that's not a CMore.

John.Howard · April 21, 2015, 10:44:54 AM

Quote from: boardmaker on April 21, 2015, 09:58:13 AM
Would you explain why you're using the condenser?

I probably won't. I think it's mainly used if drying maple.

The HMI is a weintek MT6070iE and yes, most of the other components are from Automation Direct.

beenthere · April 21, 2015, 11:18:24 AM

I think the water first comes from the wood by evaporation and is in the air, not liquid until the air is passed through a condenser where it changes. Like an air conditioner works...

Maybe different in a vacuum kiln...

John.Howard · April 21, 2015, 11:45:01 AM

Yes, vacuum kilns reduce the pressure which reduces the boiling point of water. When ambient pressure and vapour pressure are the same, water boils. It increases in volume 1700x when it vaporises, which raises the pressure inside the kiln to a set point at which the PLC activates the vacuum pump, which draws the vapour through the shell and tube heat exchanger, where it condenses and falls down into the catchment tank, from where it is pumped away.

Den Socling · April 21, 2015, 01:01:26 PM

And if you are drying something that can go really fast like maple or cherry, you can condense vapor inside the chamber. That causes a shrinkage of 1700X. That leaves the vac pump with less work to do. And that leaves you with an even lower drying cost.

John.Howard · April 21, 2015, 05:55:19 PM

Does sycamore dry like that, Den? What with it being a maple. I know if you stand a sycamore log upright it will soon produce a pool of water. By sycamore I am referring to Acer pseudoplatanus, not Platanus occidentalis, which is a plane.

Den Socling · April 21, 2015, 06:06:02 PM

From what I've seen with local Sycamore, the wood likes to warp. Usually, slow drying with a vac kiln causes warp. However, I dried a load of Sycamore a couple years ago with a slightly slower schedule and it turned out perfectly flat. If you want to dry some, I'll send you my schedule.

John.Howard · May 02, 2015, 06:54:21 AM

Made a couple of amendments but the second load has come out less than perfect, though better than last time. Pretty much what I was expecting. Some salvageable timber for personal use but not something I want to sell. I'm pretty confident I know what's wrong and how to fix it. Back to work and we'll fire her up in a couple of weeks. Third time lucky maybe?

GeneWengert-WoodDoc · May 02, 2015, 08:21:12 AM

Let me share a bit of my philosophy and experience with vacuum drying of lumber. Hopefully, Den and others will correct my thoughts or fine tune my statements, as needed. I am not referring to John directly, as he has indeed done his homework.

I have seen at least 20 different vacuum kilns during my career (and ran one using electric blankets for heating for a year too) throughout the world and only two of them have worked well on thick lumber of various species...Den's operation and Vacu-Therm in Warren, Vermont. Some of the claims of these other operations were amazing to me, but the claims were not proven to be true.

So, here is my philosophical statements...There is considerably more to successful vacuum drying than just pulling a vacuum. I listened to Den talk for over an hour in Louisville, and then visited his operation and learned more, but still do not have a complete understanding of his successful approach. (Probably any vacuum kiln can dry an easy drying wood like pine and can dry thin veneer. My discussion refers to lumber, especially thick lumber, and many different species, with high quality requirements.)

Vacuum drying of lumber has been tested for over 100 years, yet commercial success has been limited. I think that vacuum drying is a complicated process and the details of the successful process are not well known and not widely known. In fact, Den's technical approach may not work well on different equipment...you need both good equipment features and good operating techniques. That is what you get when you buy a vacuum kiln from the two mentioned. It is also probably why their equipment is rather expensive.

I suggest that if vacuum drying were easy, we would have seen successful operations throughout the world in the past century that could dry a variety of species and thicknesses. At the same time, as mentioned, we do have two really good operations here in North America, so vacuum drying can be done.

Some years ago there was a conference on vacuum drying of wood (United Nations or FAO sponsorship?) in Europe with a thick publication. Den has been sharing his knowledge too...listen very closely to him. At the same time, be aware of the pitfalls.

Den Socling · May 02, 2015, 08:31:32 AM

We think John has met every requirement except humidity. He is trying to dry a relatively small amount of wood in a relatively large chamber. There is not enough water vapor being made to elevate humidity. He is going to add still more equipment - a steam generator to start the load.

Den Socling · May 03, 2015, 12:16:55 PM

Gene, If you are working with the right equipment, vacuum kilns are very easy to use. I almost always use the same chamber pressure settings (vacuum). Thick White Oak is the only species that needs some care. If I'm drying 12/4 Red Oak, I set the controls to ramp from 100'F to 140'F in 240 hours. If I'm drying Hard Maple bat billets, I ramp from 100'F to 150'F in 144 hours. If I'm drying 12/4 Black Walnut, I ramp from 104'F to 160'F in 216 hours. There are no other settings. There are no samples to check. There are no adjustments to make. What could be easier?

GeneWengert-WoodDoc · May 03, 2015, 03:54:42 PM

Can't beat that for simplicity.

Den Socling · May 04, 2015, 10:00:45 PM

I should mention, Gene, that VacuTherm has to air dry oak before they put it in their vacuum kilns. You shouldn't put us in the same category as VacuTherm.

John.Howard · May 06, 2015, 07:38:56 PM

Well their machines certainly look interesting and I'd sure like to have a good look at one. I can't quite work out what's going on in the pictures, it almost looks like a shell and tube heat exchanger on it's side. Wish I could get a closer look.

Den Socling · May 06, 2015, 09:22:28 PM

I think it's for heat.

John.Howard · May 08, 2015, 06:49:30 PM

They obviously spend a lot of money on marketing, but a VacDry kiln is far superior

Den Socling · July 02, 2015, 10:07:45 PM

Hi Gene,

Quick Question.

Isn't VacuTherm Maspell? Isn't Maspell an Italian company? I believe we are the only US company building vac kilns.

John.Howard · July 22, 2015, 07:20:34 AM

Yeah, from the Maspell website, it seems clear that VacuTherm are just their US distributor. Bit misleading!

Anyway, here are some pics I took a while ago of the steam and cooling systems. We are on our 4th run. Each time we learn more and each time is better, but not quite right... Maybe this time?

james04 · July 22, 2015, 08:36:53 AM

Wow is all I can say! The complexity that goes into this is amazing. Do you have a guess as to how much money has gone into it? What is the unit in the shed with all the tubing going into the top?

James

John.Howard · July 22, 2015, 09:15:43 AM

Thanks James. The materials must be about £20,000! The unit in the shed is a beer cooler from an old pub. Next to it is a steam cooler from an old brewery and on top of the tank is an old beer keg!