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final moisture percentage

Started by Raym, June 22, 2019, 04:50:13 AM

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Raym

Should I adjust the target % knowing that during sterilization (48 hours at 140) it will loose more moisture. I have noticed that drying to a target of 8% and then raising the temp with compressor off, I still loose 3-6% moisture content.
'14-LT40 super, nyle l200m kiln, vintage case 480E loader.

It's not the fool that askith, it's the fool that agreeith.

GeneWengert-WoodDoc

What species are you drying and what thickness?  It would be, for most species and 4/4 and thicker, very unusual to lose 6% MC in 48 hours when you are already around 8% MC.  Lumber does not dry that fast at low MCs.

How are you measuring the MC?  If a moisture meter, what brand and what equipment?  With a pin meter with insulated needles, it might be that the temperature correction of 140 F is not correct.  Also, pin meters cannot measure under 6.5% MC, so you could not measure more than an 1.5% MC loss...certainly not a 6% MC loss that you indicate.  With a pinless meter, which can measure down to 4.5% MC (3.5% MC loss from 8% MC) but the low value can be because the surface is extremely dry, and the average MC is a lot higher.  So, it is indeed possible that you do not have the low MCs you indicate.

Are you able to get to 140 F within an hour or does it take longer?  Faster heating will shorten sterilization time.  As you know, the target temperature for sterilization is 133 F throughout the wood.  So you have an 7 F difference between the air at 140 F and the target.  If you heat the kiln to 146, it will take about half as long as you will have a 14 F temperature difference between the air and the target.  At 151 F, the time is 1/3.

What MC is you lumber when it goes into the kiln?  Assuming you are drying hardwoods, the only insect that you are worried about is the lyctid powderpost beetle.  This insect does not come into wood wetter than about 20% to 25% MC, so in most cases of air drying before going into the kiln, the lyctid PPB or it's eggs, are not in the wood when it enters the kiln.  Therefore, no matter what temperature you use, it will not be in the lumber when you are done kiln drying.  All other insects cannot live in wood drier than 12% to 20% MC, so again, at the end of drying, they are not alive.  The bottom line: special sterilization is not needed in most situations.  Do you have a special situation that makes you think that a special sterilization cycle is needed?  Also, remember that finding the lyctid PPB in dry lumber is most certainly due to infestation AFTER drying.  Sterilization cycles in the kiln do not stop reinfestation, although the lyctid PPB prefers 8% MC and wetter for living in kiln dried wood.

There is no question that 8% MC wood at 140 F will dry if the humidity is under 50% RH, which is a 25 F depression.  To achieve even a 4% MC loss in 48 hours, you would need humidities under 20% RH (over 45 F depression). So, add some water to the air to avoid the low humidity...a bucket of water on the floor perhaps...you have to see how much water you need, and if you need to add some more water after 12, 24 and 36 hours.  Hotter than 140 F is faster sterilization, but it is also an even lower RH.  (Generally, we do not enter a kiln at 140 F or hotter, as it is too hot and there is not enough oxygen for humans.  You need some sort of remote way to add humidity safely.  You also need a way to estimate the RH.)  Note that if you add water initially to boost the humidity, a very tight building will keep that water inside as there is no way for the moisture to exit.  So, does you kiln have leaks...if so, fix them.

How much lumber do you have in the kiln?  If you have 1000 BF of oak, the lumber will release about 4 gallons of water for each 1% MC loss.  So, for an average of just a 4% MC loss during sterilization, you will have 16 gallons of water added to the kiln air.  In a tight kiln, this will be enough to keep the humidity quite high, as the water released cannot get out of the kiln.  So, in your case, the moisture must be escaping...you need to figure out how and fix that leak.

Questions?
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

busenitzcww

So, as far as the ppb they can survive in 8% Mc wood but won't lay eggs in wood under 20% Mc? Or did I misunderstand?

GeneWengert-WoodDoc

The lyctid PPB eggs can be laid at 20% MC but not much higher.  And 20% MC is a low air drying MC.  They can survive at lower MCs.  They are unable to create a new generation at under 8% MC as that is too dry. And the wood is basically too hard for their jaws.  At about 110 up to 130 F, they are not active, but do survive.

Most of the data on the lyctid PPB is for more dense species.  It is possible that low density species may need a slight modification.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

firefighter ontheside

Would there be anything wrong with doing the sterilization when the wood is at around 15%.  Then dialing in on the target % after sterilization.
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doc henderson

FF, I think of it like this. you will be heating the wood plus the extra water.  so it will take more heat.  if you have a low rh, the water will evaporate consuming (storing) that heat to keep it in the vapor (evaporated state).  so if you have a leak and loose humidity, then some of the heat is being used to keep the water in a higher energy state as it is driven toward the gradient of humidity (low rh promotes evaporation) and that heat is lost if vapor leaves the kiln/hot box.  so it may take longer to get to your goal temp.  It takes heat to go through a phase change, liquid to gas.  wood with more water, has a higher overall density.  Temp is heat density.  I am not sure about damage to wood fibers.  @GeneWengert-WoodDoc 
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

GeneWengert-WoodDoc

Sterilization of lumber during or at the end of kiln drying is not done very often, as most kilns can get hot enough to automatically perform sterilization without the need for an extra step.  So, it is only with small kilns that do not get kiln temperatures over 130 F which need to consider sterilization.  Once you analyze the need and process, it is cheaper, more efficient and less damaging on equipment (mechanical and structure equipment) to have a separate chamber that is used for sterilization.  You would not need fans, so this chamber can be very small.  The design also facilitates cleaning out the dust, so the fire hazard is reduced to almost zero.  It can be used for storage which then frees the kiln to do drying of another load.

In almost every case that I have been involved with regarding the lyctid PPB, the point of infection is in the storage after drying.  There is usually some foreign wood or bamboo that is infected adjacent to the kiln dried lumber and this is the source of the insect.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Raym

What species are you drying and what thickness?  It would be, for most species and 4/4 and thicker, very unusual to lose 6% MC in 48 hours when you are already around 8% MC.  Lumber does not dry that fast at low MCs.

How are you measuring the MC?  If a moisture meter, what brand and what equipment?  With a pin meter with insulated needles, it might be that the temperature correction of 140 F is not correct.  Also, pin meters cannot measure under 6.5% MC, so you could not measure more than an 1.5% MC loss...certainly not a 6% MC loss that you indicate.  With a pinless meter, which can measure down to 4.5% MC (3.5% MC loss from 8% MC) but the low value can be because the surface is extremely dry, and the average MC is a lot higher.  So, it is indeed possible that you do not have the low MCs you indicate.

I was trusting the probes on the Nyle 200. I did go back and measure with my Delmhorst and it read about 4% higher, however this was several days after removal and stored. (in conditioned basement).

What MC is you lumber when it goes into the kiln?  Assuming you are drying hardwoods, the only insect that you are worried about is the lyctus powderpost beetle.  This insect does not come into wood wetter than about 20% to 25% MC, so in most cases of air drying before going into the kiln, the lyctus PPB or it's eggs, are not in the wood when it enters the kiln.  Therefore, no matter what temperature you use, it will not be in the lumber when you are done kiln drying.  All other insects cannot live in wood drier than 12% to 20% MC, so again, at the end of drying, they are not alive.  The bottom line: special sterilization is not needed in most situations.  Do you have a special situation that makes you think that a special sterilization cycle is needed?  Also, remember that finding the lyctus PPB in dry lumber is most certainly due to infestation AFTER drying.  Sterilization cycles in the kiln do not stop reinfestation, although the lyctus PPB prefers 8% MC and wetter for living in kiln dried wood.

This was a load of Poplar that was 18% going in. I just assumed that it needed to be sterilized at the end. Maybe I don't need to be concerned but I thought if eggs were laid, they could hatch once the material was used for its end product. I use a lot of poplar for different products and trim that I sell to residential builders and didn't want any issues down the road. I do recall a customer (not mine) that had an issue with their HW flooring(oak) that had these mysterious sawdust holes show up a couple of years after they moved in. I "assumed" the wood used for flooring wasn't sterilized. The floor was purchased and installed by a reputable retail company.

How much lumber do you have in the kiln?  If you have 1000 BF of oak, the lumber will release about 4 gallons of water for each 1% MC loss.  So, for an average of just a 4% MC loss during sterilization, you will have 16 gallons of water added to the kiln air.  In a tight kiln, this will be enough to keep the humidity quite high, as the water released cannot get out of the kiln.  So, in your case, the moisture must be escaping...you need to figure out how and fix that leak.


I try and get at least 2000 ft in at a time. Its a 18x22 "basement" and the only area that could have moisture escape is through the power vent option for this unit which has an intake and exhaust.
The local weather here is usually very humid but the weather pattern during this drying cycle was usually dry.





Sterilization of lumber during or at the end of kiln drying is not done very often, as most kilns can get hot enough to automatically perform sterilization without the need for an extra step.  So, it is only with small kilns that do not get kiln temperatures over 130 F which need to consider sterilization.
 

I can get the temps up to 140 but that is about it. I use a hot water exchanger feed by an OWB. The shut of for it is 165 and I'm scared to crank it up more than that. The settings for the drying cycle was dry bulb 120 and wet bulb 75 based on suggestions from schedules that came with Nyles paperwork.


'14-LT40 super, nyle l200m kiln, vintage case 480E loader.

It's not the fool that askith, it's the fool that agreeith.

K-Guy

Hi Raym

Stan from Nyle here. I think Gene is right, you have a leak somewhere in the chamber, probably around the doors. This will also affect your heat. By itself the kiln should be able to heat the chamber to a maximum of 160°F. Adding heat from a OWB should speed it up.
Nyle Service Dept.
A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.
- D. Adams

YellowHammer

Quote from: Raym on June 22, 2019, 04:50:13 AM
Should I adjust the target % knowing that during sterilization (48 hours at 140) it will loose more moisture. I have noticed that drying to a target of 8% and then raising the temp with compressor off, I still loose 3-6% moisture content.
You dry to 8% then raise the temp, then lose an additional 3 to 6% which wood bring the wood down to 2%?  What time frame is this?  This seems like an instrumentation issue. I don't see how the wood can actually do this this.   
 
I generally raise my temps to 150.  I take a day to get there, a day to hold, and a day to cool off.  I do this for several reasons, one being that it really "wet noodles" the wood, and makes it noticeably more relaxed.  However, I will only lose 1%, maybe 1.5% ish, and it won't get the wood less than 6% or so which is borderline too low.  
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

GeneWengert-WoodDoc

The moisture several days after finishing drying does not change very fast.  If you lost 4% in a couple of days, at low MCs after drying, why even use a kiln?  So, there is some sort of issue with the MC measuring equipment indeed.

If you sterilization in the kiln, once you take it out of the kiln it can become infected.  Note that the lyctid PPB does not like smooth woods like yellow poplar...not enough knocks and crannies to lay eggs.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

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