KD vs. Seasoned

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Kwehme09

Member
Sep 7, 2011
76
Northern N.H.
I am looking for solid resources that compare BTU outputs of kiln dried hardwoods vs. seasoned. Obviously, moisture content and species play a large role, but there must be some comparisons out there.

I am doing research for a commercial operation that currently burns 60-70 cords of KD a year in a wood gasification boiler, trying to calculate the cost savings of buying greenwood and seasoning it for one year on site.

I am using 21,000,000 BTU per KD cord, with 80& efficiency for a net of 16,800,000 BTU per KD cord as a starting point.

Any input is appreciated!
 
KD to what MC? KD is mostly marketing. In many cases, wood is just being heat treated in a kiln and passed off as KD.
 
The KD moisture content has varied but 10% is a safe estimate.
 
You don't say what hardwoods and given that even Poplar is a hardwood, results could be all over the map. To get most green hardwoods down to 10% MC in one year using mere stacking could be a challenge. To do so with 60 or 70 cord would be even more so to the point of labour costs possibly out-weighing any cost benefit.

There are some that say 10% MC is too dry for a wood gasification boiler so you may need to first determine ideal MC for your particular application. Of course anything that takes a wood burning appliance out of the sweet spot can effect efficiency buy the following Wiki article ( http://en.wikipedia.org/wiki/Wood_drying ) suggests only a 5% penalty.

Where I work, we have a huge biomass boiler that burns tons of fuel every day. I should have asked the design engineers what effect MC has on its efficiency.
 
Well here is what I have so far:

What I am using now is a mix of good hardwoods... ash, maple, some oak, a little paper birch... it's tough to narrow down the species given the huge quantity. It's KD down to roughly 10%. As a base I am using 21,000,000 BTU per cord...

We burn with a GARN 3200. I am giving that 80% efficiency as a rough guess, but I am curious if anyone has an opinion on that...

So, 21,000,000 at 80% nets me 16,800,000 BTU per cord. We move the wood with a loader, and because of the size of our GARN building, etc., it's easiest for me to use shipping pallets with rough lumbers sides, and the loader forks to move it. I stack about 70cf on each pallet. Factoring in the cost of the KD, plus the labor of palatalizing, moving, feeding, etc. it comes out being $20.54 for 1 million BTUs.

Let's say I can get 20,000,000 BTU out of 18% MC seasoned. At 80% efficiency on the boiler that's 16,000,000 BTU net. Given the cost of a green cord, and hardly any difference in labor (I am already palatalizing the wood), I am calculating $17.58 for 1 million BTUs.

Compare that to boilers giving me 87% efficiency. With #2 heating oil giving 138,500 BTU per gallon, that means 120,495 BTUs net per gallon. At $3.78 per gallon (last delivery) that means $32.12 for 1 million BTUs.

Follow me so far? Anyone see any drastic error in these numbers? Any input is appreciated.
 
It sounds like you have it figured out pretty good, I dont think green hardwoods will season cubed on pallets unless you stack them in single rows witch would add an extra handeling step in your setup.
I don't know what type of business you are in but I hope what your doing doesn't catch on around my neck of the woods because there wouldn't be any left for me.
 
scotvl said:
I dont think green hardwoods will season cubed on pallets...
+1
Laying out all 70 cord on pallets for a year has to be more labour than spotting KD deliveries onto pallets. I'm assuming the KD wood is not one huge 70 cord delivery.
 
Some questions that come to my mind is who is kiln drying the wood and the cost of the wood/s being compared? If you are drying the wood then of course that cost has to be folded in but could be a savings to you. If you buy kiln dried pre cut to size so there is less handling then anything you purchase to split, stack and season is going to have to be figured against that cost. Unless you have a very economic source I think it would be hard to compare to the kiln dried stuff unless the kiln source is very high. I can have 3 cord cut to length, split to my preferrence and delivered for around $500 and all of the better wood varieties that you have mentioned. It still has to be stacked and dried. A tree service here also sells 20 face cord loads for $45 per face (1/3 cord=face cord) that is usually 16" lengths split to the size they figure is right. Sorry I don't know of a source that will give you the hard data you need for cost comparisons however I would suggest that you get 10 cord to let season (do your own moisture readings and don't trust to what the supplier says is seasoned) and then do an analysis of burn times and output and emissions efficiencies of the two wood sources. Your resource expenses would not be astronomical that way and then you would have your own data without really jeopardizing company resources. If the cord wood is cheap enough you could possibly do a mixed quantities burn and still save money.
 
I guess I wasn't aware that there were people kiln drying firewood to that low of a MC. I was under the assumption that they were kiln drying ony long enough to kill off any bugs in the wood to provide for safe transport over what otherwise would be restricted boundaries.
 
They are 24" pieces, so stacking two deep on pallets doesn't seem as though it would affect drying too much, especially in a big, open, windy location.

Right now I get 4 cord deliveries at $300 per KD cord (dried, split and delivered) I get the deliveries all winter, and will be spot stacking it on pallets to move up to the GARN building, all winter. Now, if I was going with green wood $200 per (maybe less), cut in the fall, split and delivered in spring, I'd be able to do all the palatalizing at once, throwing numerous bodies at it in nicer weather. I think that may actually be less labor than spot stacking all winter...
 
Kwehme09 said:
We burn with a GARN 3200. I am giving that 80% efficiency as a rough guess, but I am curious if anyone has an opinion on that...Compare that to boilers giving me 87% efficiency. With #2 heating oil giving 138,500 BTU per gallon, that means 120,495 BTUs net per gallon. At $3.78 per gallon (last delivery) that means $32.12 for 1 million BTUs.

Follow me so far? Anyone see any drastic error in these numbers? Any input is appreciated.

Our stove has a rated efficiency of 70%, but to be honest, I reckon we probably average out at more like 50 or 60% as I'm not using it under perfect laboratory conditions.

I'd beware of trying to work anything out at maximum possible efficiency all the time, but I don't worry because our wood is free.......

And I know that when I'm out there splitting it I'm certainly not working at maximum efficiency ;-)
 
Your settings may come in to play but in my gasser lighter woods do not function as well as more dense woods do (charcoal chunks get blown through the nozzle instead of suppling "gas" for best efficiency). Gasifier requirement fluctations of 20-25% max MC can easily allude to moisture deviations punking burn stability. Some with gassers have warned of too small of splits and or too dry of wood effecting boiler output by over "riching" the mix. It is possible that the low MC you are getting is actually costing more in fuel (I wonder if the drier exhaust is carrying as much heat mass as higher MC exhaust gasses would). Something properly installed instrumentation would better ascertain than the best guessitmology. The man handling end sounds covered though.
 
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