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Post in 'The Boiler Room - Wood Boilers and Furnaces' started by avc8130, Sep 24, 2012.
Iwas waiting for this reply.
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Wood has an auto ignition of 572*
Got enough property to cut all my wood, cut all the lumber I need, shoot at will and this year I've killed three deer within 200-yards of the house.
I wouldnt be able to speculate on your knowledge of physics. But my point was our boilers are going to do what they do once we light the match. Whether we understand why they are doing what they are doing or not.... So be safe!
Sounds like an experiment is in order. Do you have ir thermometer?
I DID, but the WG burned the leads of my cheap thermocouple.
If someone had an IR thermometer it would be easy to prove. Just open the lower door and shoot the refractory while the WG is "off/idle". Plot the temp vs time and THEORETICALLY, if the cement remains 650F+, the fire could literally be "out" and re-kindle.
This subject has been discussed and beat to death and so far I've been able to keep my mouth shut and stay out of it. But....Here's my take on what happens:
When the boiler's heat is satisfied and/or the cycle timer shuts it down, all air is choked off to the fire. The fire sits and smolders and smolders and smolders and glowing embers remain inside the firebox. If, and only if there are a couple of these glowing embers left when the boiler kicks back on the fire will rekindle itself and start to actively burn again. The firebrick is hot but when you think about it, this brick is meant to transfer heat to the water jacket. Its not meant to be a heat-sink or retain that much heat. I agree that the center swirl chamber is very hot especially while it's burning and even if it did retain that kind of heat, it would be below the fuel and with the intake air being pulled across this fuel and down through the swirl chamber, this residual heat wouldn't have a chance to get to the fuel. Unless there are glowing embers left in your fire box, you're hitting it with a torch to relight. No magic, no tricks and no gremlins unless you call a little glowing ember a gremlin.
Now this is me ducking!
Actually, I think fire brick/refractory is intended for just the opposite - to insulate the fire box from the cold water jacket, not transfer heat to it. The fire therefore burns better the more heat is kept in it.
I'd agree with the ember take on it though.
The refractory is NOT to transfer heat to the water. If it did that, you would NEVER get gassification.
In fact, there is an INSULATING fiberglass blanket under the refractory between it and the water jacket. Even the ends of the refractory are open and do not touch the water jacket.
Here's a dare: put a piece of "1 x" lumber in your kitchen oven. Turn it to broil. Do NOT let the wood touch the heating element. You let me know how long it takes until you have the fire department there. No match, no torch, no glowing embers.
Sounds like are in agreement then on the refractory - the above post 583 (holy crap that's a lot of posts) was the first I had heard mention of refractory used to transfer heat to the water. Don't think I'll try the wood in the oven trick here, thanks. It would be pretty interesting to know how hot the refractory stays in the WG over time, and how hot it still is at the end of the longest 'idling' times that are typically seen, when the fire re-ignites. Also would be interesting to see that temp info on other units too.
I've got an infrared thermometer....When I get home tonight I'll fire the boiler up for a good long time on the purge timer and reset the cycle timer like it has just shut off. I'll go back downstairs just before its set to come back on, rake away the coals and take a temperature reading of the refractory unit. Any bets on what it'll read?
No bets here.
Is your IR gun pretty good? I got one but it seemed to always read too low or too high - forget now which since I put it on the shelf & haven't used it for quite a while.
Maybe we could have Effecta User wire up his monitoring gear to a WG and plot a graph of refractory temps over time between shut down & re-activation - even more interesting.
Doesn't really matter what it reads. Does it? The refactory is an insulator, that is what any "brick" are usually used for. To keep the heat where you want it. In the fire box. (Heat transfers at the latter stage.) To keep that ember you are talking about as hot as it can for as long as it can. You are right about that ember, just like Fred was a long time ago. And I think it works pretty well. I still have not bought the cycle timer and it is keeping my house nice and toasty. Just have to be careful to try to not lose it to bridgeing, or poor coal bed, etc.
One of the few Wood Gunners that's not embarrasing himself.
Oh look, the "former" guy is back in the owners party.
Just open the lower door when the unit is "off" and shoot the refractory from the front. No need to move the coals around.
I've got a pretty good one. I'll check it against a "known" like the hot-water outflow just to proof it. I'll fire it for 10 minutes and let it sit for 70 minutes, 10 minutes short of the cycle timer firing back up and two tall rye and gingers, and check it inside the fire box and below inside the lower door.
I'm going to say it'll be 325 degrees after 70 minutes.
1500-325 is quite a temp drop...
Does the refractory itself get to 1500 though?
Place yer bets everyone!
(I'll take 400 )
Nine years operating one under my belt. Hot concrete always ignites wood when you blow cold air on it and that's a fact
Only if it is over the kindling temp.
Either way. It doesn't matter. The boiler works, the house is warm, I still have all of my "oil money".
Where is the majority of the heat transferred in this unit?
SUPPOSEDLY in the "fire tube/swirl chamber".
"The super heated gases pass through the interconnected refractory tunnels and in to our uniquely designed swirl chamber. This is where the bulk of heat exchange takes place."
Then check that temp again about 15 minutes after it fires back up. After being off for more than an hour. Or off more than two hours. Or,sometimes, off more than three hours. I am still impressed.
The gassers we own today sure can throw some serious heat. Wood Gun, EKO, Attack, Varm, etc. Nice wood burning machines.