GPH Boil Rate Calculation

[JDP]

Can anyone confirm the boil rate is based on surface area and every 10 sq inches equals 1GPH rate of boil???

Thanks in advance for your help!

[jmayerl]

Yes boil rate is by area exposed to flame. A general rule of thumb is 1-1.5gph per sq foot. This can go up of down slightly depending on how intense the fire is under the pan.

[optionguru]

My two evaporators so far have averaged 1gph per square foot of surface area with consistent firing.

[JDP]

Thanks jmayer1. I have an old heavy duty diesel fuel tank (been empty and full of water for 20 years)for next years fire box that I want to drop a 30 inch by 60 inch pan onto. That should allow me to boil 18 plus gallons an hour. I need to calculate how many trees to tap that I can process the sap without spending 12 hour days boiling. I think around 50 taps producing a gallon a day gives me a 3 hour boil time to process it. That means I can boil every other day for 6 hrs and keep up. I work shifts on the fire dept and work 24 hrs each shift so my buddy can collect sap when I work. So boiling every other day will be workable. Thanks again. Just a newby figuring things out. Anyway my bathtub evaporator this year has produced over 10 gallons of finished syrup and still counting. I want to up the ante next year and lesson the time staring at boiling sap. Super forum to ask questions and get answers.

[11-Nick]

I'll piggyback a few questions onto this thread since it is applicable....
1 gph per sq foot of surface area is the rule of thumb.
How much do you gain with a preheater? What percentage of a boost would you get in gph if you trickled in sap at ambient temp ~40 degrees, to using same setup with a preheater that trickled it in at ~150 degrees?
How about a fan? What percentage gain would you expect with a fan vs without a fan on an otherwise identical setup?
Not looking for exact mathematical calculations. Just looking for rough answers that came from experience.
Thanks

[VTmaplehobby]

A blower will boost evaporation rate dramatically, in the 100% range. It will also raise fuel efficiency alot. That said, you will use alot more wood. In a single steam pan that only had a 2 square foot surface area, we could evaporate 4-5 gallons per hour with a high pressure blower under the fire. The sides of the pan were in the flame too, so that helped with evaporation rate as well. We ran a preheater pan last year on our barrel evaporator. I'm sure it helped because it didnt reduce the boil when sap was added. As far as numbers though I'm not sure.

[sams64]

With a good blower and preheater I can push my 2'x 3.5' to 15gph pretty easily and 18 or better if I really stay on it hard. Without a preheater and blower I would be lucky to hit 10. Preheaters can be tricky, but, fans should be a no brainer. I keep meaning to make a video of mine rig with the blower running and not running to post whenever people ask if they should install one.

sam

[BreezyHill]

Our rig is a 2x6 air tight grimm.

We have a season long competition between myself and my sons for the best boiling rate with bragging rights to the winner. For the third year running the winner is my youngest son. This season he hit 37 GPH for a 3 hour stretch.

Our sap is preheated by the steam from the flue pan that is plumbed to a wooden chamber that surrounds a 1.5" SS pipeline to feed the flue pan. This season I was back to pressurizing the sugar house to evacuate steam rather than a Chicago fan to pull the steam away. Fan was creating a condensation night mare due to its location in a space above the sugar house. Next season will be trying fans in the ducts.

I built an auto draw off controller with a switch to power the unit with the AUF fan in on or off. We often had to shut off the fan when drawing of as the temp would rise several degrees As soon as the temp stopped rising and dropped a couple tenths it would go back on.

We do run an RO and that helps to explain our higher than average rates...higher sugar content in faster draw off from the finish pan.

His record day we had a lot going on and there was no time to sit and relax. We would fire the rig, get an arm full off wood squeegee the concrete floor, fire the rig, check the RO sugar content for passing sugar, fire the rig, check the collection tank, get wood, fire the rig. I was in a truck delivering feed for our mill and he was by himself, 17 yrs old on spring break week. Sap was flowing very well on a sunny 48 degree day after a nice 24 night.
He was afraid he would have to switch collection tanks if the RO could not keep up. So he was adjusting the pressure on here to squeeze out as much water as possible.
When I returned he had only 10 gallons left in the Evap tank and had just texted me to ask how low to go before pulling from the RO to get some more.
In four hours he had started the rig, boiled off 140 g of the 150 gallon E tank and pulled off nearly 15 gallons of syrup, and had burned nearly 3/4 of a cage of wood. Not one time did he turn of the AUF fan and the preheater was kicking out 165 degree sap. Usually it is warmer but he was cracking the sap thru the preheater pretty fast. We start with a bucket of coals from the outside wood furnace and the pans are dropped 1 hole for the finish pan and two for the flue form shut down the boil before. This reduces the time it takes to get the rig running...a lot. We can be up to temp in around 20 minutes with good small wood. All sap levels are taken of the E tanks measuring stick and wrote on a carbon paper with check times.

Next season I plan on a stack temp PID that will help in the rig firing. Stack temp drops we need more fuel. Our stack runs cooler than most but I modified the arch to get all the flame and air thru the flues to get the most of the wood.

Brushing the flues is a huge factor. I can always tell when a poor brushing occurred. The rig just doesn't seem to want to get going. I am looking to make a brush that can be used during the day as we are often running for 8-10 hours now that we expanded our bush again and have another 500 to add for next season.

Keeping the steam hood closed is also a huge factor in boiling rate. Open it up and the rate drops right off. We slide it to check for foaming now. Open 1/2 inch and close it right up.

The records of the other two boilers this season were 34 for the middle son and 31 for me.

The youngest loves to split his wood, cost me a $40 hatchet for him but was worth every penny!

I also get doing other things: helping filter syrup, repairs, running the RO and don't fire as often as I should...thus the stack temp will have a light to flash and signal fuel needed. My mother in law thinks the lights should be led rope lights so it is prettier...LOL

We are looking at AOF and bubblers for the pans for next season. Bubblers to reduce the dark end of season syrup as we have a market for only medium and dark. Early light gets blended with dark to increase our medium quantity.

The fire fan for us is a huge increase...I would guess in the 40% range. This season we had a slightly larger fan and plan a large fan for next season.

Preheated sap is also huge as is foam on the float box that insulates the sap when it enters. I also plan to wrap the float box for next season as the sap in entering is warmer than the sap in the box.

Everything you can do to positively affect your boiling rate is worth the cost...over time it will save you fuel and time.

Good Luck!

Ben

[nymapleguy607]

I run a 2x6 Leader Patriot raised flue evaporator, I have a 4' flue pan with the standard 7.5" flues. I'm boiling on a home made intensofire style arch. Last year with just the pans and preheater I was boiling about 40-45 GPH average including start up and shut down. This year I added a Steamaway to the mix and am now boiling about 72 GPH with start up and shut down. Wood size and as much air you can get in seem to really crank up the GPH. I will say I no longer cringe at the sight of a full 400 gallon tank.

[jmayerl]

I will say I no longer cringe at the sight of a full 400 gallon tank.

Wait until you get a RO and laugh because you can't even start until you have 500 gallons and then it's all gone in 3 hours!

[ennismaple]

Wait until you get a RO and laugh because you can't even start until you have 500 gallons and then it's all gone in 3 hours!
Or 2,000 gallons in our case! We started with 1500 in the raw sap tank on Sunday when we fired up the RO. By the time I'd collected the remaining 5,000 gallons the RO had shut off for 10 minutes before I got the last 500 gallons to the camp and we were eating into our 100 gallon "cushon" of concentrate that we keep in case we need to do some RO maintenance.

To stay on thread - we have a 3.5x14 forced air = 49 ft^2 of bottom area (3.5x10 flue pan, 3.5x4 syrup pan) and we get about 200GPH so 4GPH/ft^2.

[JDP]

Again' I'm a newby so could someone explain how to add a blower to your fire.
Are we talking a hair dryer volume for CFM or do you need a squirrel cage blower like on a power vented water heater? Sorry. I can rig something up but need a few basics. Would love to increase GPH and also realize the full potential of the fuel / wood. Wood is not an issue.....but cutting it is!!!! LOL
My evaporator is presently an modified overturned bathtub but we are working on a 250 gallon tank with a 2x5 ft pan installed onto it. Appreciate any advise to increase my GPH.

Thanks

[Sugarmaker]

We have seen a lot of unique evaporators but the overturned bath tub might top them? Any pictures?
Keep stoking the fire, and plan your next larger rig.
I have not calculated the surface area of our pans. 3 x 10 King, boiling around 150 GPH with steam away, AOF, and AUF.
Regards,
Chris

[JDP]

If you go to "Redneck Bathtub Evaporator" thread in Homemade Maple Equipment I posted a pic and description. Works good but limited to boil rate of 8-10 GPH so far.

[ennismaple]

Again' I'm a newby so could someone explain how to add a blower to your fire.
Are we talking a hair dryer volume for CFM or do you need a squirrel cage blower like on a power vented water heater? Sorry. I can rig something up but need a few basics. Would love to increase GPH and also realize the full potential of the fuel / wood. Wood is not an issue.....but cutting it is!!!! LOL
My evaporator is presently an modified overturned bathtub but we are working on a 250 gallon tank with a 2x5 ft pan installed onto it. Appreciate any advise to increase my GPH.

Thanks

JDP - I forget how many CFM's our blowers (x2, primary and secondary air) push out but it's a lot!!! When they are at full speed it is tough to hear yourself think in the sugar camp. Any air forced under the grates will help. On our old Waterloo 5x16 we used an old box fan meant to ventilate a barn that got piped beneath the grates. You noticed a difference when it was on vs off.