Stack Melt Down

[ecolbeck]

I've seen frequent references on the forums to the idea that running too high a stack temperature (red hot) can cause it to "melt down." I assume this means some sort of catastrophic failure. I'm wondering if this has ever happened to anybody and what the results were.

[Cjadamec]

Prolonged temperatures of 1000 degrees F, or higher, will cause the steel in the stack to become plastic and loose its ability to hold its shape. A lot depends on the thickness of the steel and type of steel. A dull red color of steel typically indicates 1200F, a bright cherry red color is around 1500F.

Depending on how the stack is built and supported this can lead to dramatic failure at a very in-convenient time.

It is a good idea to have a stack temp gauge to help prevent damage to your stack.

[Sugarmaker]

Ok I might be guilty of saying this phrase. I can give you some examples: If you heat steel with a torch to about red hot you can bend it easily. Now on our evaporator stack, when we were burning pallets we had a nephew firing the rig. and he fired it like a locomotive. I walked back the the stack and it was red hot and glowing. I believe if I had a screwdriver, I could have poked it through the stack. We idled the firing way back. Put on a stack thermometer and kept a eye on the temp after that.
No I have never actually heard of a stack melt down. Oh the other thing was I almost burned down the sugarhouse because of the stack being to hot and the wood roof not insulated well enough. Was real lucky to have a hose there to put out the fire. Put up a stainless sleeve around the stack in the roof area.
Currently my stack temps are half of what they used to be due to new pans that draw most of the heat out of the fire before it gets to the stack.
Hot stacks, yea too hot to handle. Be safe!
Regards,
Chris

[Bruce L]

Have to hijack this thread,my stack is a brick chimney that has been standing for 127 years now,where would I get a stack thermometer with a long enough probe to go through the brick into the centre of the chimney where the flue gases are?

[mol1jb]

I have seen kiln thermometers that are longer because they go through thick walls on a kiln. That might work for you.

[Ntatar]

Here she is with the fan on high at night. I ran it hot just for the picture, this is not how I normally,run her. Only took 30 seconds to get,there! 19654

[Sugarmaker]

Ntatar,
Ahhhh, you have a potential problem! Your only 30 seconds away from disaster! Dial that puppy back a little! I thought I saw a glow in the night sky last night in the east!:) You need to get that fire under some good pans on a real arch!
Thanks for the picture. Keep the garden hose close by too!

Yes what you have there is a real good start to stack melt down IMO!
FYI, my stack temp (external) was about 400 F last night.
Regards,
Chris

[steve J]

The problem with small 2x3 or 2x4 is the blowers trow to much air for the size of the evaporator. So your blowing most of the heat up chimney thus red hot stack. I put a 3 speed switch in mine and I am fine unless I go to High and than my elbow and lower stack will look like yours.

[Chickenman]

Mine looks like that most all the time. I get 2 years from black single wall stove pipe. I know that I'm over firing a tad but yesterday I started with 38 gallons of 5% sugar. Start to finished cool down was 2 and 1/2 hours. Pan depth stayed right at 1 1/2 inches the whole time. So I'm guessing that I'm near 15 gallons plus evaporation rate on a 2x3 Mason. Stack temp was 500 on low end and upto 900 degrees on the high end by magnetic stove thermometer on the pipe out the back of the arch.. Should be 5.5 gallons in the pan.

[Bucket Head]

Ntater,

Wow, that is the hottest stack I,ve ever seen! Good thing that is outdoors, and that car in the background is upwind of it!! Like Chris said, you need to dial that in better. Entirely way too much heat going up and out.

Steve

[Ntatar]

Just did this for a fun picture :-) I don't ever run it this hot.

[ennismaple]

That's red hot for sure! Our rig boils best between 750 and 800 F using an internal temperature probe. Anything hotter than that any you're blowing BTU's up the stack.

[ecolbeck]

That's red hot for sure! Our rig boils best between 750 and 800 F using an internal temperature probe. Anything hotter than that any you're blowing BTU's up the stack.

Ennismaple, I'm glad you posted this because I'm curious about it. It seems like if you ask 100 sugar makers you will get 100 different answers about stack temperatures. There seems to be a common theme that says if your stack temp gets past a certain threshold (different for everyone) you are "wasting BTUs".

What puzzles me is that BTUs are going up the stack as soon as you light a match. More BTUs on the pans is good but it automatically means more BTUs up the stack. Does anybody really know where the transition between efficiency and waste occurs?

[mol1jb]

Does anybody really know where the transition between efficiency and waste occurs?

You’ll probably get 100 different answers on this as well.

[Woody77]

I have a smokey lake 2×6 raised flue . I built my arch with smokey lakes pre made front door assembly. I made a few changes to the arch. Of witch one was a damper at the back of the arch. I run my rig hot enough to turn my fire brick red inside the fire box. Adjusting the damper and the amount of air I put in I got over 50 gph consistently. My stack temps were just over 500° that's very little waste up the chimney.

[ennismaple]

Not sure exactly when you go from efficient boiling to losing BTU's up the stack - but it does boil faster! I know for my rig I'm boiling too hard when I get smoke or sparks out the chimney. We added the stack thermometer so we could see at a glance when we need to fire. If I drop below 700 F the front pan doesn't boil hard enough and I get batching rather than regular runoffs.

[JohnsSugarShack]

When I had my 2x6 it ran great at 625-650. Now on my 2x4 I was running 800, if it dropped to 700 my boil in the syrup pan would drop off.

[RileySugarbush]

Just like a car, you can be efficient and slow or inefficient and fast. So you need to decide if you want to minimize your time boiling or splitting wood. Which is more fun for you?