My first masonry rocket stove maple syrup boiler

Built this boiler setup mostly out of stuff we had laying around or got for free. Bought the stove pipe and the restaurant 6" deep full pans and some perforated strap.

Burning blown down birch & maple, boiling maple sap from some local trees here in East central MN. We shall see how it all goes...

Hi Simeon;  
Welcome to Permies!
Great Looking RMS stove you have built there!
I suspect / hope that you have a sugar shack planed to cover that boiler up for rainy season.
Have you boiled down sap before?
It has been a lifetime since I was in a working sugar shack but I remember the large amount of raw sap it took to produce a gallon of syrup.
We still used the gallon tin cans back then, and I gained an appreciation of the work involved to fill each can.
To this day I never balk at the current cost of buying maple syrup, its just too good!

thomas rubino wrote:Hi Simeon;  
Welcome to Permies!
Great Looking RMS stove you have built there!
I suspect / hope that you have a sugar shack planed to cover that boiler up for rainy season.
Have you boiled down sap before?

Thanks! It was designed mostly based on what was laying around.

Setup is temporary, will be taken apart when sugaring off is done, no shack is planned yet.

Last time I boiled syrup was in highschool, mid 1970s. A friend showed me a few things and I decided to give it a try- Farmer near me has a sugar bush but nobody tapped those trees for 50 years, he let me tap them.

Holy Sugar Tap!
That is one fancy I/V unit you have there!
A long way from the tin pails and spikes they used in the mid-seventies when I was last in a sugar shack!
That looks like (work) but fun!
Sadly not enough sugar maples in Western Montana to warrant a sugaring operation.

thomas rubino wrote:A long way from the tin pails and spikes they used in the mid-seventies when I was last in a sugar shack!

My friend who got me (re) started on syrup making has set up a reverse osmosis (RO) rig to remove about 50% of the water from his maple sap before cooking it down- Can't post video but here is a screen grab of RO rig, he ran 14 five gallon pails of 3.2 - 5% sugar content sap (he tested) through his RO rig for me, reduced it to 6 five gallon pails of over 8% sugar by weight. That took about 4 hours and the energy to run a 500W pump, 2KW hours electrical power energy is TINY compared to heat energy required for boiling away 40 gallons of water...

In picture, pump is barely visible at far right, it's the type of high pressure (piston, not centrifugal) pump RVs use for "on demand" shower/sink water pressure. The large black cylinder is a 5 micron filter to protect the  reverse osmotic membranes,  which are in the 4 white cylinders at far left.

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(Later on, we are going to genetically engineer the Maple trees to grow taps by themselves and wirelessly inform us that it is time to collect sap from them. We'll probably have to give them a cut of the profits and eventually, they'll demand the right to vote, but it'll be worth it!)

Very cool Simeon;
Syrup-making has really made some improvements in the last 40 years!
Gallons of water were removed in 4 hrs that is incredible!

Yes, it is inevitable that soon your maple trees will unionize.
Personally, being an Operating Engineer with 25 years in the Union I think that is a great thing for the maples.
It may hurt your bottom dollar, but think about how the standard of living will improve for them!
Happy Maple trees will devote their life to sharing their sap and making plenty of little Maple trees to carry on the tradition!

After running the first 15 gallons of reverse osmosis concentrated maple sap, I was reasonably happy with my physical layout (EXCEPT for realizing I have to lie flat on the ground to stoke properly every 15 minutes!) and quite happy with the fuel efficiency, I am using about 1/3 the quantity of wood my acquaintances use in traditional "steel wood stove with a pan on top" evaporators.

I was not as pleased with the RATE at which water was being evaporated and so, before second run, I tried modifying the space above the rocket stove flue top and below the pans, where the heat from fire is transfered to boil sap.

My initial theory was that I wanted fast moving gasses exiting the rocket stove to slow down and have more "dwell" time in the passage under those pans, so I built that space 5" tall X 20" wide (cross section of 100 square inches) with the flue leading in being 6.5" X 9" (68.5 square inches in cross section). After that space is 8' length of 6" Dia.  stove pipe for draft (cross section approximately 28.3 square inches)

For second run I cut the 5" height of that passage under pans down to 1.5" high by filling most of it in with a layer of 3.5" thick bricks. Cross section now being 30 square inches... And the evaporator performance improved DRAMATICALLY. Guys in a certain rocket stove forum told me that this was wrong, flue exit had to be equal or greater than vertical chimney. The fire disagreed, this mod caused fire to draft harder, made a somewhat louder "roar" and the sap  heated faster & to higher temperatures. I also had to stoke every 10 minutes rather than every 15.

My friend (who is not an engineer, just a guy who boils down a few thousand gallons of sap every Spring) had told me to forget such theories about efficiency, that I wanted as hot a fire and fast moving as possible hot gasses/flame under my evaporator pans during the primary part of boiling down as I could manage- Guess what, he was correct!

To understand scale in picture, those 5 core "face" bricks making up evaporator support walls and now also filling in floor are approximately 3.5" tall X 3.625" thick X 11" long. The area 3 evaporator pans (6" deep "full" steam table pans, 24 gauge 304 stainless) sit in is 20.125" wide and 38" long. For this purpose, the cheapest, thinnest SS steam table pans will be best as far as heat transfer, SS is a fairly lousy conductor of heat. These pans don't get lifted while full, I transfer liquids by scooping/labeling, only remove mostly empty pans to wash & etc..

The disc propped up on brick pieces above rocket stove flue is to divert flue gasses (fire!) from striking first pan directly and making a "hot spot" on center of first pan/burning sugar onto pan bottom. It is the re purposed bottom of a cheap azz Wally Mart 22 quart stock pot which fell off that pot after I forgot it & boiled it dry on an electric stove, just a handy chunk of metal from my pile of "bits & bobs".