Boil rate for backyard boiler.

[manif001]

Hello all

I am new this year to sugaring. I have been trying to figure out what a good boil rate would be for a backyard boiler. I have been looking but most the threads talk about larger operations getting couple hundred gph.

I built a rocket stove out of 55 gallon drum and use 30 qt stock pot. If I keep the fire stoked in the chamber I can get upward of 12-15 gph. The norm however is probably around 8-10 gph.

Is the pretty normal for a backyard boiler. If not I think I'm going to build an arch or different design for next year.

Thanks

[Hannah]

Out of a stock pot? I would have to say it is near unbelievable due to the restricted surface area. I use a 18"x30" flat pan and am doing good @8gph with 4-6 gph the norm. A mason 2x4 XL is rated at 15 gph. If your getting that much out of your rocket stove than I believe your doing very very well.

[CBLA]

That's great! with my 3 propane burner set up with a 2x2 flat pan I can get 5gph

[Sinzibuckwud]

That's a really good rate for a stock pot, I run a barrel stove with a 2x2 flat pan a pre heater and auf and I chug along at 5-8 gph

[Clinkis]

I get 8-10 gph out of my 16x48 propane evaporator with a flue pan. 8-10 gph seems impossible with a stock pot. Are you sure your calculations are correct? If so, then let me know where you got your rig from cause I'll buy one.

[manif001]

Ok thanks you for your input. Happy to hear my rocket stove is working well.

I was able to get more surface area due to the internal pot skirt that is only 2 cm off the pot forcing the heat all the way up the sides of the pot. Also due to the huge amount of insulation I installed very little heat escapes without going by the pot first.

Again thanks for the info.

[325abn]

I wouldn't think physics allow for a 12 - 15 or even 10 GPH from a round stock pot. It would be great to see this rig in action, maybe a video. Maybe I will build some type of rocket stove form my pan.

[Daveg]

My rig has 5,600 square inches of surface area and I get about 20 gph, so your stock pot with 500 square inches is doing very well indeed. I would like to add a skirt like yours. Can you post any pictures?

[manif001]

So after looking at your guys rates And seeing mine looked high. I decided to go back to my excel spreadsheet where I have been keeping all my data for the year.

I checked my formulas and found a typo. I have change the typo and have gotten more realisitic numbers. My actual rate with the correct formula is about 6 gph with a max of 10 gph. This seems more reasonable to me.

Thanks again for the info and helping me catch my typo.

I think i am going to build a double rocket stove next year so I can use a flat pan to bump up the evaporation rate. I really like the rocket stove due to its efficiency. I get very little smoke and have barely used any wood due to a more efficient burn.

Thanks again for your input.

[325abn]

I keep track of the number of feed tank fills I do in a given boiling time IE: 12 feed tank fills in 5 hours. I also keep track of individual feed tank times into the pan. I have marks on the feed tank and use a stop watch to time rate between marks. Then average everything out also accounting for what it takes to fill the pan.

[TooManyIrons...]

I have built rocket stoves so I know where you are coming from - those things are blow torches when they work properly.

I incorporated stock pots in my arch design to save money until the design was proven ($60 for six off-the-shelf stock pots versus $450-$500 for a custom built SS preheat pan and a main boil pan). My arch using sunken stock pots boils off at 5 gph with stoke rate every half hour, but I can get 8 gph with vigilant stoking (every 15 minutes religiously). I think 8-10 gph with your set up is very possible, but the fire must need almost constant stoking. You also must have to be constantly topping off the stock pot level to avoid scorching or mineral scale burn-on on the heated sides of the stock pot. If you are constantly adding cold sap that would really knock down the gph. I can see your concept working very well for bulk reducing, but it must get a little tricky to use once sap starts getting concentrated.

The thing to keep in mind about his/her rocket stove concept is that the stock pot is being heated on the sides as well as the bottom. What is interesting about my design of using 6 sunken stock pots is that there is actually more surface area directly exposed to heat than if I were using flat pans over the stove's entire top surface area. Of course this problem is resolved by having pans built with angled bottoms to create more surface area, but that adds significantly to the pan cost. I am in a dilemma at this point, the stock pot concept was just for testing the arch design, but the cost for the pans is hardly justifiable for a hobbyist. I will probably cough up the money to get them built but I will not be happy about it.

For a backyard setup I would be thrilled to have a consistent 10 gph. For me, a bridge too far...

manif001 - I would love to see a pic or two of your rig. :)

[DuncanFTGC/SS]

I am using a 25 by 48 inch flat pan, over propane, I am getting a solid 9 gph for two boils so far. I am sure that with a little more tweaking and a preheater and a few other minor additions, I will be getting over 10. I was pretty impressed with that for my homebuilt rig! LOL

[Daveg]

The formula I use is: "gallons boiled" divided by "hours" equals "gph". For example, my last boil was 94 gallons and it took me 4 hours and 15 minutes, so: 94÷4.25=22.
KISS



So after looking at your guys rates And seeing mine looked high. I decided to go back to my excel spreadsheet where I have been keeping all my data for the year.

I checked my formulas and found a typo. I have change the typo and have gotten more realisitic numbers. My actual rate with the correct formula is about 6 gph with a max of 10 gph. This seems more reasonable to me.

Thanks again for the info and helping me catch my typo.

I think i am going to build a double rocket stove next year so I can use a flat pan to bump up the evaporation rate. I really like the rocket stove due to its efficiency. I get very little smoke and have barely used any wood due to a more efficient burn.

Thanks again for your input.

[Daveg]

What material do you use for insulation in your rocket stove sap evaporator? Refractory bricks, refractory blanket, refractory cement, a combination? Every rocket stove I've seen has the insulation "dialed-in" to focus the flames at the target. Also, I'm curious as to what your stock pot is made out of and if you get any soot on it?



Ok thanks you for your input. Happy to hear my rocket stove is working well.

I was able to get more surface area due to the internal pot skirt that is only 2 cm off the pot forcing the heat all the way up the sides of the pot. Also due to the huge amount of insulation I installed very little heat escapes without going by the pot first.

Again thanks for the info.

[DuncanFTGC/SS]

The formula I use is: "gallons boiled" divided by "hours" equals "gph". For example, my last boil was 94 gallons and it took me 4 hours and 15 minutes, so: 94÷4.25=22.
KISS

Using Excel does not necessarily make something complicated. In the long run it makes things easier, you just have to get your formula's setup correctly. :D

[Daveg]

You could make you own pans and "sink" them as well. Get some 22 gauge stainless and some silver solder and have some fun. $56 for a sheet of 2'x4' mirror finish 304 stainless. Then, if the pans were sunk, and not just sitting on top you would increase your surface area.

[Daveg]

DuncanFTGC/SS: We agree the calculations need the correct formula. I don't think their calculations were sullied by Excel. That's why I offered my formula for gph.:lol:

[saphound]

I'd like to see a few pics of this setup too.

[DuncanFTGC/SS]

DuncanFTGC/SS: We agree the calculations need the correct formula. I don't think their calculations were sullied by Excel. That's why I offered my formula for gph.:lol:

Ahhh, I understand now. I thought you meant that using excel was making things too complicated :)

[Clinkis]

The problem with sinking pans in and having heat on the sides is they will burn once your concentrate gets higher. I've have issues with my syrup pan one the sides from heat coming up from my propane burners.

[Cedar Eater]

I've been under the impression that the pan-to-sap surface area is not nearly as important as the air-to-sap surface area. Moving the vapor away from the surface of the sap is evaporation. If your boil is so vigorous that it is launching droplets out of the pan and over the side, you're losing sugar. There was a number being quoted last year as a theoretical max rate per square foot of air-to-sap surface area. If you are exceeding that rate, it doesn't matter if you're using a rocket stove or a nuclear reactor to get the heat into the sap, you're still losing sugar. If I remember correctly, that rate was around 1.7 gph/sqft, but that's really hard to achieve without air movement across the surface.

[motowbrowne]

I've been under the impression that the pan-to-sap surface area is not nearly as important as the air-to-sap surface area. Moving the vapor away from the surface of the sap is evaporation. If your boil is so vigorous that it is launching droplets out of the pan and over the side, you're losing sugar. There was a number being quoted last year as a theoretical max rate per square foot of air-to-sap surface area. If you are exceeding that rate, it doesn't matter if you're using a rocket stove or a nuclear reactor to get the heat into the sap, you're still losing sugar. If I remember correctly, that rate was around 1.7 gph/sqft, but that's really hard to achieve without air movement across the surface.

I'm gonna disagree with you here. If sap to air exposure is more important than sap to pan exposure (aka pan to fire exposure) then flue pans wouldn't exist. We'd all be boiling on huge flat pans. Not only do you get in incredible increase in evaporation rate and efficiency by adding a flue pan with 7" flues, but now there's evaporator manufacturers making pans with flues that are 16". If there wasn't any further evaporation rate to be gained by adding extra sap to pan exposure, this wouldn't work.

My rig does 70 gph when I'm really cooking. My 2x2'syrup pan might do 4-5 gph based on the one gallon per hour per square foot rule for flat pans. That means my 2x8 flue pan is doing 65 gph, or 4 gallons per hour per square foot exposed to the air.

[Cedar Eater]

I'm gonna disagree with you here. If sap to air exposure is more important than sap to pan exposure (aka pan to fire exposure) then flue pans wouldn't exist. We'd all be boiling on huge flat pans. Not only do you get in incredible increase in evaporation rate and efficiency by adding a flue pan with 7" flues, but now there's evaporator manufacturers making pans with flues that are 16". If there wasn't any further evaporation rate to be gained by adding extra sap to pan exposure, this wouldn't work.

My rig does 70 gph when I'm really cooking. My 2x2'syrup pan might do 4-5 gph based on the one gallon per hour per square foot rule for flat pans. That means my 2x8 flue pan is doing 65 gph, or 4 gallons per hour per square foot exposed to the air.

But isn't a flue pan designed to produce fountains that won't launch the sugar over the sides? The fountains increase the air-to-sap surface area which increases evap rate by making a two dimensional interface into a three dimensional interface. I get the same effect above the heating element in my electric evaporators. And flue plans are used at the fresh sap start of the boil when the sugar content is lower than it will reach in a stock pot. They also have taller sides to block sugar loss and redirect the sap back into the boil. Those sides are not heated as the sides of a stock pot would be. With a stock pot in a super hot flame, you have to either scorch sap on the sides or run with very deep sap, as if it's one giant drop tube with nothing to contain the single large fountain.

[Daveg]

The sap in a pan can change state from a liquid to a gas at the bottom of the pan. We can see the bubbles forming on the bottom. The gas then rises to the surface where it joins a gaseous environment, the atmosphere, and escapes. Steam engines harness that change of state of liquid to gas to power machinery, but instead of boiling in a pan, the boiling is in a sealed boiler filled with tubes to increase the ratio of metal-to-water contact. The change of state (boiling) is higher if the ratio of surface area of metal-to-liquid contact is higher. The lower the surface area ratio, the slower the boil. My 2x6 has 5,600 square inches of metal-to-sap surface area, because it has 7 flues and can crank along at 26gph. Without the flues it would only have 1200 square inches. A friend with a 2x4 flat pan gets only 5gph. Even though their atmospheric contact area is only 50% less than mine, my boiling rate is 420% more. Operating a fan to blow across one's pan doesn't increase evaporation rate because the change of state has already occurred, before the steam even breaks the surface of the sap. A fan will actually slow down the evaporation rate.

[Daveg]

The problem with sinking pans in and having heat on the sides is they will burn once your concentrate gets higher. I've have issues with my syrup pan one the sides from heat coming up from my propane burners.


It depends on the geometry of your rig and if you are batch boiling or continuously drawing off. If the set-up keeps the sap deep and if the heat source isn't concentrated then having heat on the sides of the pan is desirable to increase surface area/boiling rate.

[Cedar Eater]

The sap in a pan can change state from a liquid to a gas at the bottom of the pan. We can see the bubbles forming on the bottom. The gas then rises to the surface where it joins a gaseous environment, the atmosphere, and escapes.

And when that happens the bubble bursts and if the boil is vigorous enough, it launches sugary drops up and sideways, where it falls on the ground. No matter how much heat you pour into a stock pot, the max evap rate is fixed by the ability to get water molecules up and away from the interface without losing too much sugar. Boiling increases the size of the liquid-air interface, but you can only increase it so much without losing too much sap overboard. Those who finish on a kitchen stove learn all about sugar launched from a stock pot.

[Daveg]

And when that happens the bubble bursts and if the boil is vigorous enough, it launches sugary drops up and sideways, where it falls on the ground. No matter how much heat you pour into a stock pot, the max evap rate is fixed by the ability to get water molecules up and away from the interface without losing too much sugar. Boiling increases the size of the liquid-air interface, but you can only increase it so much without losing too much sap overboard. Those who finish on a kitchen stove learn all about sugar launched from a stock pot.
The interface that matters the most in determining boiling rates is the metal-to-sap interface, not the sap-to-atmosphere interface. If a stockpot was built with flues that increased the surface area of the metal-to-sap contact, then the boiling rate would increase. A round-bottommed stockpot with a diameter of say, 14", has 154 square inches of interface. If you added 4-4"x10" flues to the stock pot it would have 320 sq. in. the gph would double. And if the sides were raised at the same time the sugar would stay in the pot.

[1220']

Hello all

I am new this year to sugaring. I have been trying to figure out what a good boil rate would be for a backyard boiler. I have been looking but most the threads talk about larger operations getting couple hundred gph.

I built a rocket stove out of 55 gallon drum and use 30 qt stock pot. If I keep the fire stoked in the chamber I can get upward of 12-15 gph. The norm however is probably around 8-10 gph.

Is the pretty normal for a backyard boiler. If not I think I'm going to build an arch or different design for next year.

Thanks

Wow that's really good evaporation rate.

[Cedar Eater]

The interface that matters the most in determining boiling rates is the metal-to-sap interface, not the sap-to-atmosphere interface.

That is only true to a point. Your ability to put more heat into the liquid through tricks like drop tubes becomes moot when you reach the limit of the pan to move water molecules away without losing an unacceptable amount of sugar, unless you're just stupidly willing to launch sugar all over your backyard, but that is not evaporation. That is loss of sugar that only looks like evaporation on paper if you don't include a sugar balance. You can't get around that by changing the design of the bottom of the pan.

[motowbrowne]

That is only true to a point. Your ability to put more heat into the liquid through tricks like drop tubes becomes moot when you reach the limit of the pan to move water molecules away without losing an unacceptable amount of sugar, unless you're just stupidly willing to launch sugar all over your backyard, but that is not evaporation. That is loss of sugar that only looks like evaporation on paper if you don't include a sugar balance. You can't get around that by changing the design of the bottom of the pan.

Cedar eater, "things like drop tubes" and flues aren't "tricks". They are proven technology that's been around more than a hundred years. Increasing the surface area exposed to the fire saves firewood and increases boiling rate. That's all there is to it. If your sap is jumping out of the pan, you need higher sides.

[lpakiz]

Cedereater,
Mowtobrowne is right. Why do you think all large evaporators have flues?
And why do you think we all spend big money to build or buy these flues? Have we been thinking wrong all these years? Or just throwing our money away? Look around at every large evaporator.
It's the amount of total surface area at the sap/heat interface. My 24 inch wide flue pan with includes 16 FEET of material, folded up so its 24 inches wide. I would have to see a 12 inch high flat pan and arch that could boil hard enough to throw sap out.
If you are sending sap over the side, build higher sides or reduce the heat.

[Cedar Eater]

Cedar eater, "things like drop tubes" and flues aren't "tricks". They are proven technology that's been around more than a hundred years. Increasing the surface area exposed to the fire saves firewood and increases boiling rate. That's all there is to it. If your sap is jumping out of the pan, you need higher sides.

Please go back and read the OP. It is about a rocket stove and a stock pot. There is no doubt that boiling harder increases the liquid-air interface and therefore the evap rate, but putting a stock pot in a flame so hot that it heats the sides will not magically increase the evap rate beyond the natural limit of the pan design without blowing sugar over the sides. If that was not the case, we could build very small diameter cylindrical pans with very high sides and blast pure water out at super sonic velocities. Even flue pans, which by design have a higher max limit than flat pans and stock pots, have a natural upper limit beyond which adding more heat will only blow sugar up and over the sides or into the condensate trays or somewhere other than where you want it to stay. You can increase the max limit through design but each design will have a max limit beyond which adding more heat is the wrong thing to do. Agreed?

[Cedar Eater]

Cedereater,
Mowtobrowne is right. Why do you think all large evaporators have flues?
And why do you think we all spend big money to build or buy these flues? Have we been thinking wrong all these years? Or just throwing our money away? Look around at every large evaporator.
It's the amount of total surface area at the sap/heat interface. My 24 inch wide flue pan with includes 16 FEET of material, folded up so its 24 inches wide. I would have to see a 12 inch high flat pan and arch that could boil hard enough to throw sap out.
If you are sending sap over the side, build higher sides or reduce the heat.

Please read my response to motowbrowne and feel free to answer the question I asked him.