Dry kilns emissions reduction

[SenecaMike]

Do you use emissions reduction equipment to reduce VOC's from your kilns?
What type of system do you use?

[MichaelM]

I know of a couple installations with stacks to raise the exhaust and reduce local impact.  I do not know of any lumber dry kilns in the U.S. with emissions controls, such as rtos scrubbers, esps or baghouses.

[ingo wallocha]

Hi Mike,

The best way to reduce VOCs is to have a proper heat recovery system on your vents together with a smart software. This will reduce the VOC but it will of course create kiln condensate.

Does that make sense to you?

[MichaelM]

When I was working at osu, we measured the emissions before and after a heat recovery device.  There was no difference in VOC, MEOH, or COOH.  We did not measure the other MACT haps common to lumber - propionaldehyde, acrolien, and acetaldehyde.

[ingo wallocha]

The nature of the VOCs certainly stays the same. I am just saying you have less VOCs with heat recovery because the recovered heat will be transferred into kiln condensate. 

[Craig Jensen]

Ingo,
Are you talking about overall plant emissions being down because of the lower fuel consumption needed to generate heat due to increased heat efficiency?  Or are you saying that if heat use in the kiln is more efficient, than the kiln itself will emit fewer emissions from the wood drying process?
CJ

[ingo wallocha]

Hi Craig,

The water that we have to evaporate out of the lumber will always stay the same and it has to go somewhere. So when I am saying less VOC I am just referring to less steam coming out of the vents. There will be condensate instead. So I am saying that the overall plant emissions will be down and the VOCs will be down but not the kiln emissions since they are a result of evaporating the water in the wood.

Makes sense? 

[Craig Jensen]

so the emissions stay dissolved in the water, and since the water does not leave the vents, then there are fewer emissions?

is that what you are staying?

[MichaelM]

If you reduce steam use, I agree that plant emissions will be reduced because less fuel is burned.  I'm not sure that a heat recovery device reduces overall kiln emissions.

In my earlier post, I said the heat recovery device does not remove emissions.  If one pound of VOC enteres the device in the gas phase, the about one pound leaves in the gas phase.  A tiny amount goes into the condensed water based on Henry's law.  Same for HAPs.  The water is too warm to absorb volitile organic componds. 

[ingo wallocha]

when you have less steam coming out of the vents you have less VOC coming out of the vents. When a heat recovery unit reduces your energy consumption you will have less VOC. And yes, Craig, as far as I can tell the emissions stay dissolved in the water there are fewer emissions.
 

[MichaelM]

I simply cannot agree that VOCs are reduced by a heat exchange device that condenses some of the vent steam to water.  Most VOCs will stay in the gas phase.  A tiny amount will go into the water, but not enough to change a permit. 

If you need evidence of this just look at how emissions testing is done (it is an NCASI method and I don't remember the number, maybe 98 or 99).  Kiln gas is bubbled through impingers with the water  to close to 32F, then the VOCS are collected as a gas in summa cans after the impingers.  If the VOCS  were water soluble, they would go into the 32F water.  Very little does.  I have run the method.  The water in a heat exchanger is far warmer and even less of the VOCS enter the liquid phase.  Keep in mind - the pinenes, fatty acids, etc (the high molecular weight stuff) are hydrophobic to begin with and don't mix with water.
Now consider the low molecular weight stuff.  In NCASI method 105, we again use impingers to get the aldehydes (formaldehyde, acetaldehyde etc) into the water at 32F and react them with benzyl hydroxyl amine to form a high molecular weight, hydrophilic compound to keep them in the water at 32F.  Everything is keep on ice or refrigerated until lab analysis.  We can capture methanol pretty well in 32F water without a reaction, but all these low MW compounds are too volatile to ever stay in water at the temperature in a heat exchanger. 

I hope that makes it clear where I coming from on this.  Besides all that I have measured VOC before and after a heat exchanger.  The heat exchanger did not remove VOCS or methanol or formaldehyde even though water was condensed ("less steam coming out the vents").

[ingo wallocha]

Hi Mike,
Ok, I dont't want to get into such a detailed discussion with you since you are much more knowledgeable than I am. I was of the opinion that you can either have emissions out the vents in gas form or as condensate in liquid form. If the liquid condensate does not have the ability to absorb the emissions as much as the steam does that is new to me and I (again) learned something.

Can we agree on the simple fact that heat recovery reduces the energy consumption and thus does reduce the emissions?

Having said that and reading your interesting comment below where do the VOCs go after they went through the heat recovery system? Are they still in the steam just in a more condensed form? Sorry, that might be a stupid question but I just want to make sure I understood your comment below.

Thank you!

[Keith Haigh]

Hi Ingo,

it sounds like you are starting to believe your own marketing around vent heat exchangers.

they are and always have as much use as cat-flaps on elephant houses, just my opinion!
Keith Haigh

[ingo wallocha]

Keith,
As much as I value you opinion but there is nothing which saves more energy than a proper vent heat exchanging system. We have air/liquid heat exchangers which are maintenance free and super efficient. Our continuous kilns without heat exchangers are as energy efficient as any CDK. With heat exchangers we are up to 25% more efficient. So I suggest you wait until we have the first kilns up and running in Maine and you come and for the first time in your life see a real kiln.
So long,
Ingo   

[Keith Haigh]

Congratulations on the sale Ingo, I will come and visit the kiln, but you have to buy the beer !!!

[ingo wallocha]

I will buy you as many beers as you like. You will need them after having seen our kiln ;-)