2x8 CDL traditional evaporator questions....

[SyrupHog]

Started using my 'new to me' raised flue 2x8 CDL traditional evaporator last night for the first time and I've got a couple of newbie questions I could use some help with.

Quick background...I didn't get the sugar shack built in time for this year, so yes, I'm setup outside again for another season...ugh. Anyways, as such, my stack length is limited since I don't have any way to brace a taller chimney properly. Stack length is currently only about 8', but I plan on trying to rig up another section to bring it up to 13'. That will be the best I can do for this year.

My evaporation rate on the unit was poor. I figure I was averaging about 65-70 litres (15ish gallons) per hour. I'm sure stack length has something to do with it, but wondered about these other things:

1) The evaporator is on small legs/feet at the firebox/ash bin area. This means there are four open sides at the bottom, about 1.5 -2" in height, allowing a lot of uncontrolled air to enter the firebox. Is this normal, or is it preferable to somehow close these sided up with something? As I see it right now, the draft damper door at the front of the firebox has no functional control of air flow unless those sides are closed up.

2) When building and maintaining your fire in the evaporator, do you tend to keep the fire only in the firebox area (over the grates), or do you end up with wood going up the ramp? I found it difficult to keep a hot fire going without pushing the wood further back into the evaporator, hence I had a lot of coals building up on the ramp. Normal?

3) Speaking of coals...I found I had a lot of coals! In an effort to keep a hot fire going I was trying to add wood every 10ish minutes. I found that I was constantly shuffling coals around trying to keep the firewood area 'flat', otherwise the wood was going in to a firebox that was raised with coals at the back, making the firewood slip down towards the doors (does that description makes sense?).

So, curious to know of other peoples experiences with similar naturally aspirated evaporators and I'm all ears to hear for any tips and guidance!

Thanks!

[ecolbeck]

I suspect that the stack and coal issues are related. The lack of draw means that the wood burns slowly and coals build up. The coals block the grates, making the problem worse. Adding a blower would make the stack height irrelevant.

I added a sheet metal bottom to the ash box on my evaporator to make an enclosed space. I’ve never understood why manufacturers don’t do this. There’s literally no point in have a draft door if the bottom is completely open anyway! There’s also no point in adding a blower until that area is sealed off too.

[darkmachine]

A good rule of thumb is the stack should be 2x the length of your arch, that's out of your control for this season, it has a lot to do with draft. Since you can't increase your stack height, maybe consider sealing up that gap with some earth or bricks and introducing some forced air under the grates. It's like night and day. Second I would say check the moisture content of your fuel. With our 2x6 moisture content makes the difference between boiling at 15gph and in the high 30's. We feed every 5 min on a timer, oak strips from a sawmill, wrist size or smaller, criss-crossed to allow it to burn hot, forced air, and keep the firebox full, don't miss a fireing. If you have enough air, either through natural draft or forced air there will be very little coals. If i don't add wood for 10 min, the only thing left in the firebox is a hand full of coals. Just my experience.

[SyrupHog]

Thanks for the ideas. @darkmachine, I will seal up that gap with some bricks/earth for this season and will check the moisture content of the wood. It's a mix of maple and birch that's been split and drying for 2 years, but I'll try making the pieces smaller perhaps. Right not they are about the size of my fist. @ecolbeck, I like the idea of a sheet metal bottom, definitely something I'll do when the evaporator makes it up to the new sugar house when it's ready. Contemplated a forced air idea too, but seems to me I'd have to change the doors and draft door to be something air tight, no? Or would adding some simple thin door gasket be enough? Hoping to boil again later today, so I'll post with an update after implementing these suggestions.

[SeanD]

It sounds like your fire/heat is not getting pulled back to the flue pan where the vast majority of evaporation happens. The added stack height will be a big help and you'll see a big difference getting to 13'. More is better, but 13' should be a big improvement over the 8'.

The bricks to semi-close the gap will allow you to use the draft door to control the air intake, though the fire you describe sounds more like it needs more air not less. The boil in your back pan should resemble a jacuzzi. Coals shouldn't really be piling up over the duration of the boil. I typically start the fire with everything right up front, close to the door. That first wood is smaller and thinner. I fire every six minutes (with a timer) gradually getting to full-sized pieces of wood over the next 1-2 firings. Those first 1-2 firings get piled on top of what's left of the firing before right at the door. Then when the box is good and hot, the wood burns more quickly and cleanly. At that point and for the rest of the boil I:
-Get the first piece of wood in my hand and the second in my lap.
-Open the door and use the piece of wood in my hand to push what's left of the burned wood back onto the bottom of the ramp below the ends of the (drop) flues.
-Quickly reload the front of the firebox in a log cabin right up against the door. Air/spacing is most important. Fill as high as I can.
-Get the whole job done as quickly as possible - 15-20 seconds? I don't know. I try to be fast.
-Slam the door shut, reset the timer, and add defoamer.

With this method, I have the newest wood maintaining the boil in the front pan and the overall heat of the firebox while the wood I pushed back gets used up and keeps the flue pan raging. On the next firings the wood that was in the back is gone and there's room to push more wood back. There are no coals building up over the boil.

Sometimes, I get out of sync or the wood I happen to have at the start is bigger than I want and it takes more firings to get it burning cleanly, but eventually it gets into a rhythm. You have a new rig, so it will take a little time to get to know what works best for it.

[darkmachine]

Contemplated a forced air idea too, but seems to me I'd have to change the doors and draft door to be something air tight, no? Or would adding some simple thin door gasket be enough? Hoping to boil again later today, so I'll post with an update after implementing these suggestions.. Depends on the volume of air you put in, I've seen it work ok with out air tight doors, it would be worth experimenting with. Small fan with some aluminum duct to the draft door might work.

[SyrupHog]

Update: I was able to boil for a few hours today and adding the extra length of stack helped for sure. I split the wood into smaller pieces too, so that likely helped as well. Never did find my moisture meter, so not sure what that number might be, but the wood seems dry. Coals were not a problem today! So all in all, seemed to go better.

@SeanD - I was following a fairly similar procedure when firing, though I was still probably firing every 10ish minutes. I think I'll see about decreasing that firing interval and use your idea of pushing the mostly burned wood to the back to keep the flue pan going. I did notice that every time I'd reload, my boil would take a real hit and it would be several minutes before it would bounce back.

With regards to the flue pan, do you guys get a raging boil throughout most of the pan, or just in one area? I seem to get that good 'jacuzzi' type boil right at the front of the flu pan (first 12 inches maybe), but then it really tapers off to almost nothing after that. I wondered if part of that could be that my opening for the smoke/gases to get to the base stack is too small/narrow. By that I mean, my vermiculite build up under the flue pan (which is covered with ceramic blanket) is ramped down towards the base stack opening over approximately the last 8". This was done as per a CDL video I'd seen on bricking the evaporator. But I then add a 4" spacer plate between the back of the flue pan and the base stack opening, which would make that area narrower. Could that be possibly restricting draft? Ugh...tough to describe...wish I could draw!

[RFM]

SyrupHog,
A few Options for your Evaporator. We ran a 2x8 CDL approximately 10 yrs. 1st recommendation is set up a stack thermometer. We fired to 1400 degrees F before we realized we were dumping fuel up the stack. This turns your stainless stack a pretty purple color. We ended up running between 850 and 1000 degrees. Running 12% concentrate, we could get over 100 gallons syrup per full cord (of split Locust wood). next keep the Ceramic Blanket approx. 1 in. below the bottom of the flues. We installed a plate dampener in the rear to force the heat to drop into the cavity under the base stack. It will always boil the hardest at the top of the arch ramp 12-16 inches back from the syrup pans. We had to make a stainless-steel shield to prevent the sweet form jumping out of the evaporator pan (at the top of the arch) when we finally added the Air under Fire Option. We manufactured a 3-pipe manifold which laid where the original grates were. a Dayton blower (Grainger) was used with an intake dampener controlled by vernier cable. This closed manifold allowed firing without shutting the Blower off. We Made 486 gallons of syrup it's best year. (2019). Cross Flow syrup pans work better if you boil concentrate. You have a great rig. Good Luck learning and tweaking it. I will try to attach a picture