efficiency question

[John Burton]

This season while boiling i borrowed a friend infared thermometer climed on my roof and measured my stack temprature , it was 765f and I got to thinkingif wter boils at 212(approx) and syrup is 7.1 degrees above that . most stove pipe thermometers say 350 to 575 is the "clean burn" or non soot zone when you run temps at 750 or more arent you wasting at least 250degrees or more of heat up the stack? I understand that to maintain a good boil you want a raging fire and all but it just seems as though we should be trying to extract more heat from less wood...am I crazy

[Fred Henderson]

Not crazy, but exactly right. That is one of the many things that I like about the way my evap is built. I got to work really hard to get that stack temp over 500 drg.

[maple flats]

If you had higher efficiency you would not keep your sugar bush properly thinned and your sugar bush would not be as healthy.

[ibby458]

I had a guy remark to me one time that he's amazed people are trying to extract heat from 212 degree steam in their preheaters, but totally ignore the 1000 degrees going up the stack.

I've lost track of him, but as I recall, he was planning a 2x16 evaporator (with forced draft), knowing full well it wouldn't boil full lenght, but should extract as much heat from the wood as possible.

I wonder if he ever did it, and how it worked out?

I've toyed with the idea of a "pre-boiler". Direct the stack fire/fumes thru some 3" tubing in a seperate pan situated higher than the flue pan. It should boil like crazy, but cleaning might be a problem.

[John Burton]

ibby your reading my mindwith your exhat gas pre heater. ive also wondered how an evaporator would run if the pans were reversed. not sure how it would act but i would think that you would get more even heat on the syrup pan... just have always wondered why guys were so amazed at high stack temps when it actually represents inefficent operation.

[brookledge]

That is why when I bought my new evaporator I went from a 3X8 to a 3X12. The fire box is the same size and I burn the same amount of wood but utilize more of the heat. If you have a choice between evaporators I'd always go with the longer. Once you go wider then the fire box is wider and it takes more wood
Keith

[danno]

Keith - it was that exact post you made a month or two ago that steered me away from 4x10's and back towards 3x12's. I'm already burning enough wood in my 2.5x8, than to almost double the width of my arch but I'd love to get another 4' of pan at the end of my rig.

By the way, still shopping for a 3x12 (or RO):) Bascoms had a 3x12 for sale at a decent price, but flues were pretty shallow.

[markcasper]

I was at a large producer aqaintence of mine, about 20 miles away. Hes got a 6x 20 and you could put your hand on the base stack on the rear when he was operating and hold it there. The forced air was cranked!! Now thats efficiency. Wish they made a 4x20!

[ibby458]

I've also wondered why they make the syrup pan bigger than necessary. On many 2x6 evaporators, the syrup pan is 3' long, when it would be much better to have a 2x2 syrup pan, and 2x4 flue pan. I'll bet it's to keep the cost down. False economy, in the long run, though.

[John Burton]

talked with leader at the open house about this. Brads response was that while the liquid will boil at a lower temp, you would be wood efficient... however the evaporator is not boiling to peak capacity claims that they tested this out by measuring temp in base stacks, they pushed the rigs slow at first monitering evaporation rate.then increased the stack temp untill there was no longer a significant gain in evaporation and that is how 1000 degree base temp number was reached.I thought he said the number was around 500 for oil fired . to sum it up wood efficient is not evaporator efficient and vice versa. still not 100 percent positive that pushing all that extra heat into the sky is a great thing to do.with all that heat being wasted

[ibby458]

The simplest idea I came up with for preboiling the incoming sap was to have a stainless base stack with welded seams. Over this would be a stainless 55 gallon drum with the stack going thru it. Obviously, the drum would have to be welded to the tank. A float switch would activate a pump to keep the drum filled, and a tap on the bottom of the drum would attach to the regular float box on the back pan.

Several problems would need to be overcome. That much weight in the air would need to be supported on legs or suspended from the ceiling. Burnt sugar would build up on the stack as it exits above sap level. Cooling off the stack in that one area might lead to creosote problems.

In the past, I would have thought the big equipment producers would have researched these ideas and discarded them as impractable, but with everyone's experience with this years SS 5/16 bucket spouts, I'm forced to wonder how much (if any) research they do on new ideas?

Leader's 11 inch flues represent increased heat extraction, but that's not really a NEW idea - just a logical extension to a very old design. Aside from ROs and Steamaways, when was the last truly new design that increased evaporation rate in the evaporator itself? Is the flue pan design truly the epitome of heat transfer/evaporation rate?

[Fred Henderson]

The Leader with the 11" flues is no more than a rasied flue, drop flue built together. Coming out of the float box is two pipes one each suppying each flue pans. So now you have to have a bigger fire box for a little more wood or more gph nozzle.

[archangel_cpj]

If one wanted to remove more heat out of the flue gasses why not build a recirulating heat exchanger running pipes across the chimney from top to bottom and utilizing a pump to recirulate the sap from a steel storage tank through the chimney heat exchanger and them back into the sap tank. would probably get sap well over 100 deg and if one used a heavier pipe say sch 40 steel it would hold the heat more like cast iron. It could then come out of the tank again to the chimney but around a copper tubing hung outside and covered with mineral wool and then to the float or pan etc. might work and if its SS chimbey weld the pipes in would have to be induced draft though as all that tubing may interfere with the draft otherwise.

[Fred Henderson]

This is only my opinion and that is that Leader's new evap is some proudcers idea. The most efficent evap thus far in my opinion was the old Vermont, no longer made of course. GH Grimm worked for Vermont at one time and that is where a lot of his ideas came from.

[3% Solution]

Hi everyone,
Just something I happened to think of; when you increase the temperature of the sap (I think above 50 degrees) the bacteria starts to grow and multiply. I would not be a bit surprized that when you get to a certain temperature all hell breaks loose and those little critters really grow.
Now that will effect your syrup grade, right?
You would have to get the sap in storage to the point to kill the critters and keep it there while it is in storage.
Now, am I thinking with an area besides my brain?
What do you folks think?

Dave

[fred]

absolutely, that is why you keep sap as cold as possible until it stays at the evaporator. you will end up with more headaches than it is worth

[3% Solution]

Yup thought so!
Thanks Fred

Dave

[maplecrest]

dave, that is what they make u/v lights for. jeff

[fred]

a uv light would never kill bacteria in 100 deg sap

[RileySugarbush]

Regarding pulling more heat out of the stack and into the raw sap:

It seems there is little advantage if you have a steam hood and preheater working well already. If so, your incoming sap is over 200 deg already and it does not help to heat it up sooner back in the tank.

If you want to increase heat transfer from the flue gases, it's better to do that in the flue pan where it evaporates water, and thats done by increasing surface area with the deeper flues or a longer sap pan. With the increasing use of forced draft, my guess is that there is a lot to be gained by increasing the length of the flue pan. A doubling of the flue length should nearly double the evaporation rate, right?..... and effectively make use of the 600deg plus flue gases that are in the stack now.

I'm guessing the traditional length was based on how long they could be and still get reasonable natural draft for a good burn. That is not a significant limitation with a blower and airtight arch.

I'd like to try a 2x10 or 12 and check the efficiency! Anybody want to loan me a 2x4 drop flue pan in the name of science?????

[mapleman3]

I dont think you can keep increasing the length of the flue pan with out widening or making longer the syrup pan... I think at some point you wouldnt be able to keep up with the drawoff... and risk the pan becoming all syrup and burning... too much sugar coming off the flue pan would be a problem I would think... if not count me in on making the flue pan longer... my 2x6 fits in my SH fine, I would have room to lengthen it just not much side to side room. The other thing is you would have to increase the size of your firebox to be able to get enough heat for the extra length.. seems like alot of work

[RileySugarbush]

Too much sugar, too fast would be a problem most of us would want to deal with! But there is probably something to the ratio of flue pan and syrup pan.....

The ideas of efficiency and production rate are at cross purposes. And human nature usually will drive you towards production rate at the cost of efficiency. If we take your 2x6 as an example, if you fire it more slowly you may get more syrup per gallon of oil, but who wants to spend the time? The natural thing to do is to crank it up for max rate, but that is wasteful. Lengthening your sap pan would extract more of the heat and improve the rate some and efficiency probably quite a bit, as long as you don't crank up the heat even more. But there is always a tendency to do just that when we see the back end of the pan not boiling as hard as the front. For a given heat input, best efficiency is when the stack temp is low, and the only way to do that is to take the heat out with a longer heat exchanger.

A good analogy is driving your car. We all know we could get better milage by taking it very easy on the throttle. Best economy is accelerate slowly and drive at reasonable speeds, best "production" is to floor it and to drive faster. You know what most will choose!

[TapME]

What would happen if you increase the depth of the flues as the pan lengthens to get more heat from the flame? Start with a 4" flue and have it tapper to 8" at the back of the pan. Just a thought.

[WESTVIRGINIAMAPLER]

I think there are some 2x12's out there somewhere. I would love to have a 2x12 with a 3' syrup pan. I don't see any concerns as I have a 2x8 with a 3' syrup pan and 3' more on the flue pan wouldn't increase the sugar content that much more in my opinion, especially in my case boiling 50+ to 1 ratio sap.

[RileySugarbush]

I guess if you think about it, an RO does the same thing as the extra long flue pan would do. Do they cause an issue with too rich a feed into the syrup pan?

[WESTVIRGINIAMAPLER]

I would think you would be feeding much higher sugar content with an RO vs a 9' flue pan.

[RileySugarbush]

I agree, so a long flue pan shouldn't cause problems in the syrup pan. I'd like to hear from someone who runs a 2x10 or 2x12. I that could be the most efficient setup around in terms of gallons per cord if you kept the stack temp down to 300 or 400 F . But of course the temptation would be to increase the heat input for more gph, and off we go again......

Brandon, my rig has a big syrup pan (33" long) and a 36 inch long drop flue with forced draft of about 100 cfm. I get about 30gph when I have the stack temp between 600 to 900F. How does that compare to your evaporation rate? I'm going to have to keep track of wood consumption this year.

[WESTVIRGINIAMAPLER]

John,

I run about 50gph with the preheater and inferno arch pushing about 265 cfm. I am installing a 780 cfm blower on it for next year, so we'll see how that works. As far as stack temp, I have no idea but plan on installing a stack thermometer before next year.

Are you running a preheater also??

[RileySugarbush]

Yes, my preheater puts out 190F sap when we are at max rate. I think I under estimated my blower capacity, probably 190cfm, but not as much as you have now. If you put in that big blower, I bet you will get a much greater evaporation rate, but will really go through the wood, per hour and per gallon of syrup. It's that production vs. efficiency thing again. Cost of wood vs cost of time boiling, or maybe time boiling traded for time cutting and splitting!

Heat up the stack is heat wasted, but it does save boiling time.

[brookledge]

If you increase your length you will get more efficient. In my case I went from a 3X8 to a 3X12 and still used the same amount of wood but drasticly increased my evap. rate. If you lengthen out a 2X6 to a 2X8 or longer you will increase your evap. rate while still using the same amount of wood.
Once you go wider then your fire box becomes bigger and then you use more wood
Keith