What is you opinion about WDE kiln ?

[rerednaw]

What is you opinion about WDE-maspel vacuum kiln ? Somebody use it ?

ps: sorry for my english

[Den Socling]

Welcome to the forum. Your English is fine.

I don't know what the arrangement is/was but Maspell's technology is sold in the US as VacuTherm.

[rerednaw]

Thanks about VacuTerm i know a lot

[DanG]

Welcome to the ForestryForum, Rerednaw!  We would like to hear more about you, what you do, and how things are in your country.  It helps us to learn more about our industry to know how things are on the other side of the world.

Please don't worry about your English.  We will figure out what you are saying. You are much better in English than most of us would be in your language.

[rerednaw]

Now i try to start business to produse finger jointed board for customer who made fillet for picture from it. But drying is a big problem. Oldest air drying chamber what we have as heritage from USSR is totaly unuseful   As i see a vacuum drying tehnology is future in drying business. so i decide to buy a vac kiln WDE sell his kiln in or country near 80000 Eur. in USA a litle bit cheap, but to high for me. So i have only one choice - bulid kiln by myself for first time i think what this is totaly imposible. i dont find any info about it in russian internet. but when i find this forum i see what a lot of people are joined hand-maded vac kiln and at least 30 years in USA you use it

[Den Socling]

Rerednaw,

I've seen some old Maspell/VacuTherms that looked 30 years old but these 'hand-made' vac kilns are new to the US. I know how to build one but too many people need one but can't afford one. So, if you are the kind of guy who can fix his own tools or build his own tools, join in! Maybe we can get a couple running.

Den

[rerednaw]

I think what I guy of this kind I read a lot of post about discontinuous vac kiln and have some questions.I decide to build a continuous vac kiln. At this time I have a tank-wagon from gas with these parameters:
Diameter 3m (9 foot), length 4.5m (14.7 foot), capacity is near 30 m3 (935 cubic foot ?). it is from steel with thickness from 8 to 11 mm. And 10 ears old vacuum pump bush 138063 (20 mbar, 3 hp, 41 cfm).
1. Can anybody who get vac klin to run send to me photos of you kiln ? im interesting in door construction and heating/condensing system construction.

2. Wich is drying time for 2” pine in you kiln ?

3. is 8-11mm steel enough to stand vacuum near 20 mbar ?

4. is the pump with 41 cfm enough for continuous vac ? Den, in you post you write what 1 gallon of water produce near 227 cubic foot of vapor and we need pump enough to evacuate this from chamber. If we have in chamber wood with temperature near 40C and temperature of wall of chamber near 20-25C is it not enough for condensing vapor on the wall of chamber ? or  if it is not enough we must put in chamber something like small refrigerator (or pipe with could water) for condensing vapor ? so I suppose what by one of this method we can pour out 1 gallon of water but not 227 cubic foot of vapor ?

5. heating. As in our country electricity is cheapest when aluminum heating plates like use WDE (800$ each as I hear) I decide to made electrical heating plates. I plan take 2 aluminum plate and put inside nichrome (?) wire (I don’t know what is it in english. This is alloy from nickel and chrome and used for example in iron to produce heat). Another way is try to use carbon fiber material between plates. It is also produce heat when connected to electricity. But I don’t have any experience with both types of these materials. Den, did you try something of this ?

6. Measuring. Where in wood you measure the temperature? On the side where is heating plates? In center of board or in the side where is not heating plates?

[Den Socling]

Rerednaw,

I think what kind of guy you are is one with a lot of questions!  

I don't know what a 'tank-wagon from gas' is but I'm guessing that it's a tank designed to carry liquefied petroleum gas down the highway. If so, that could be a chamber. The thickness is normal for a vacuum chamber but too light for a pressure vessel.

I didn't look up the pump but 20 millibar is very low pressure (or high vacuum).

You should note that continuous vac doesn't work unless you use our 'methods' and I can't tell you what they are. I would reconsider discontinuous if I were you.

Drying time depends entirely on how well your system works and has nothing to do with the species IF that species is permeable. You could dry soft wood in 2 days.

Condensation on the kiln chamber does assist the vacuum pump. WoodMizer, for example, thought that a very small vacuum pump could work because they were thinking like you. If you are always drying softwood and if the chamber is always in cold air, you can factor in the condensation. If you want additional condensation, hang fin pipe inside and pump cold water through it. However, if you ever dry any hardwood, the low humidity from the condensation could cause a lot of damage to the wood.

I worked with WoodMizer on the problems with electric heat. The main problem is regulating the temperature. The temperature is going to vary across the plate because wet wood will cool an area while dryer wood will not cool as much. How can you keep the temperature where it belongs when you might be monitoring a cool or a hot spot?

I usually put RTD's for temperature measurement into the center of the board.

[rerednaw]

Den,
Big thanks for you answers, it’s very useful for me

'tank-wagon for gas' is a tank designed to carry liquefied petroleum gas by railroad (it’s opinion of my electronically English translator)

20 mbar I see on the tablet on the pump, but I don test it. Which  pressure and temperature usually you use with discontinuous vac ?

What you mean “on how well your system works” ? fully automated process ? how many time I need to heat wood ? or how high vac can make my pump ?

I always dry pine and rarely alder. Max temperature of chamber wall is near 30C, usually 20-25C. it is enough for condensation ?

In which way woodmizer plan to make his electric plates and how they plan to heat it ? “wet wood will cool an area while dryer wood will not cool as much”. if I understand right, we will have board what in one spot will be 40C and in another spot 45C ? if we have it, which kind of problem we will get ? crack of wood or no vaporization in some spot of board ? if only no vaporization we can pull down vac in advance to lower when needed.

About measuring: I plan to put one RTD direct between wood and plates to control heating temperature and one RTD on the up of wood to control temperature of wood. Is it right ?

If you think what I must first build kiln and next ask about drying technological questions just say

[Den Socling]

You are welcome to the answers. Lets see if I can give a couple more.

If you learn to use the following page from our website, you will see the 'basic' idea. Our kilns are 'continuous' vac but the basics apply to both types of vac kilns.
http://www.pcspecialties.com/torroconvHC.html
The chart on that page shows that, at 29'C, the vapor pressure of water is 39.9 m bar. If you heat wood to 29'C and pull the chamber pressure down to 39.9 m bar, all of the water in the wood will evaporate. All of the water doesn't actually evaporate because, when water starts evaporating, the temperature is going to drop and the chamber pressure is going to go up. If your system works well, you will add heat as it is used and you will pull vapor as fast as they fill the 'vacuum'. If your system is well designed and well controlled, you will add only the heat you need for a desired drying rate.

Your chamber wall is not going to give you a lot of condensation because, if your room temperature is 20-30'C, the chamber is going to warm up as water condenses. WoodMizer tried to increase the condensation by building an air plenum around the chamber and blowing air through the plenum. It helps.

WoodMizer's heating blankets were thin, flexible aluminum with a mylar-like material covering the aluminum. They were supplied with low voltage, high current. The supply was regulated with SCR's. The SCR's were fired by a microprocessor that read the blanket temperature from thermistors.

The problem was this: if the thermister was kept cool with a wet board, it would keep turning on the power. It there was an area where the wood was dry, it kept getting hotter. It could get so hot that the wood could begin to burn. In the vacuum, it would just turn black but, if you opened a kiln expecting to find dry wood, you might find a fire instead. RTD's are better than thermisters but you will have the same problem.

And wood temperature, in a continuous vac, is set by chamber pressure.

You've got things in the right order. Ask lots of questions before you start building. You sound very 'capable' (a guy who can build and fix his own) but I think that discontinuous is the way you will go after asking enough questions.   But hold on to that tank!

[rerednaw]

Can you tell me approx how quickly temperature drop (if we no add heat) and how quickly pressure up for 10 m3 of wood ? is it seconds, minutes, hours ? Maybe you have some diagram of this process? And how many heat (approx) we need to add to up temperature of 1m3 of wood for 1C?

Can you tell me what exactly is this “mylar-like” material ? or it is something designed by woodmizer and for woodmizer ? What mean SCR and RTD abbreviation ?

What will be with wood (spot dry spot wet) if I will control temperature of plates in area what not covered by wood and try to stable temperature in this area of plates at 40C for example. Did wood warm up to 40C? Or by this way I can’t provide so heat as wood need? You say what dry wood always will be hottest when wet if we add equivalent portion of heat to both (I understand right?) but I still don’t understand why. I think what dry must be only get warmed thoroughly slowly when wet)

I get this tank to metal workshop and at Monday I hope I will have welding door at this

[Jason_WI]

SCR = Silicon Controlled Rectifier

http://www.americanmicrosemi.com/tutorials/scr.htm

RTD = Resistance Temperature Detectors

http://www.omega.com/rtd.html



Jason

[Den Socling]

Rerednaw,

The timing is determined by the design of your system. You should size the heating and vacuum components to give you minutes or parts-of-hours. If, for instance, you want to dry 10 m3 of softwood at a rate of 1% per hour, you might need to move around 9 gallons per hour. To vaporize 9 gallons, you need to get about 73,000 btu's into the water. Then your vacuum system needs to move about 2045 cubic feet of vapor. (Excuse me for leaving the metric system.) If you are doing a discontinuous vac and you want to spend 1/2 hour heating and 1/2 hour pulling vacuum, then you need to move that 2045 cubic feet in 30 minutes. So, you need a vacuum pump capable of 2045/30 minutes = 68CFM. That's about 1926 liters per minute. That's how the 'times' are set.

Mylar is a tough, clear plastic that is or was used in electronic applications. It's purpose was to protect the blankets but they still got torn. I don't know if it was mylar but you would want something that was strong even when it was very thin.

Trying to control temperature where it was not being affected by wood may be a good idea. If you add heat to wet wood in a chamber with reduced pressure (vacuum), the water can boil at low temperature. When the water boils, it carries the heat away toward the vacuum pump. When the water is all boiled away, the heat will start warming the wood. With no water, the wood can now go to 40C.

OH OH!   Another space race. This guy could get his door on ahead of the Americans.

[Don_Lewis]

I don't agree that a vacuum kiln is the right choice for what you are doing. If you are dryin 25mm stock to make frames and such, I am quite sure you will have problems with quality. There are about 30,000 kilns in North America and 99+ % of them are conventional or dehumdification kilns. There is a reason. One reason is quality and another is cost both capital and operating. People get really hung up on speed of drying and that is fine but it not worth the offsets. There are places where vacuum kilns work well but 25-50 mm stock is not the place. I will now log off and miss the screams...

[Den Socling]

Don,

You, like Gene, keep thinking of the vacuum kilns of the past. They were built by companies who didn't understand the dynamics. They thought that low pressure meant low temperature and that would mean low degrade. It's not that simple. They blew a lot of money on worthless details and missed the details that needed addressed.

I'm working with a company in New Zealand that wants to dry a species that New Zealand thinks is impossible to dry. I've been drying 25 mm stock in 72 hours without degrade. It knocked their socks off. In a very short time you will be seeing that 99+% of conventional and DH kilns start losing their share very quickly. The new vac kilns are so fast and quality is so good that payback, even with a fancy system running at less than 100%, is less than 3 years. Not everybody can afford a fancy system or even a DH kiln. For them, I hope I can make this discontinuous vac work. They can build it themselves and it will far surpass conventional or DH kilns.

This post is becoming one that should be at PCS's forum and not at the ForestryForum so now I'll log off.

Den

[old3dogg]

Don.
Im a vac kiln operator and I would have to agree with you.
Vacuum drying is fast but does not work in all areas of drying.

[Den Socling]

Mike,

You're right. If you can put 5 or 6 million bf into airdrying sheds, vac kilns aren't for you.  

Den

[old3dogg]

Oh boy.I feel like Im trying to get in the middle of a fight here.
I will leave now.

[Den Socling]

Absolutely no fights here. But I will 'discuss' any point against vacuum drying. And, except for those who can tie up beaucoup bucks airdrying, I don't know anybody who couldn't use vacuum drying.

But again, I don't want that discussion at the Forestry Forum. move it to PCS.

[old3dogg]

Wait a minute!
Im not or will I ever be "against" vacuum drying.
BUT! If I was to get into drying a lot of thin soft wood I would have to go with DH or steam drying.