Who has experience with piggyback systems?

[Russ]

If any of you have read the description of our new evaporator, you know that we cannabalized our old 5x16 Vermont-style evaporator and had a 5x18 custom built. We had the guy that designed and built it add a piggyback over the 8' flue pan; the piggyback pan itself is probably 6' long. The flues are triangular, not rectangular; I don't have the design with me and the sugar shack is 210 miles away, so I don't know how deep they are (let's guess they are 6" deep). I think there are 19 flues; each will have an aerator tube. There is a 72' foot long 2" diameter continuous tube preheater feeding the piggyback pan.

My questions:

1. How deep do you run your piggyback? So far I've heard everything from less than the depth of the flues to 2" over the top of the flues.

2. What temperature of sap do you get coming out of the piggyback?

3. What sugar concentration improvement do you get from what goes into the piggyback compared to what comes out?

Steam hoods and a few miscellaneous parts should arrive in 1.5 weeks, so we are looking forward to our test boil in the next few weeks.

[Maple Hill Sugarhouse]

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[powerdub]

Are you talking piggyback or steam-a-way? they are two different beasts.

[Russ]

Well then, let's start with the definitions and differences....

[Maple Hill Sugarhouse]

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[Russ]

Well if a steamaway uses tubes to transport the steam in a heat exchanger fashion, then what we have is different.... a piggyback system? Since Piggyback and Steamaway are registered trade names, our fabricator calls his design the Piglet. I'll try to explain how ours is set up.

The footprint of the piggyback exactly matches the 5' x 8' flue pan. It sits on top, with steel tabs on the sides than extend down along the flue pan to prevent the piggyback from sliding from side to side. If I could draw a decent cross section, you would see, from the bottom up, a drip pan with a 12" opening across the width at the back; this allows steam from the flue pan to enter the piggyback and catches condensation from the pre-heater and the underside of the piggyback flues. Next comes the pre-heater; 72' of SS tubing (either 1.5" or 2", I don't remember) zig-zagged under the piggyback pan. Yes, the preheater is below the piggyback in order to get the full impact from the flue pan steam. Next up is the piggyback pan, which has triangular flues. Steam will travel from back to front, between the drip pan and the bottom surface of the piggyback flues and amongst the preheater tubing. In the front of the piggyback pan is a 12" opening across the width that will allow the steam to go up into the steam hood and out the steam chimney. In each of the flues will be an aerator tube fed off a pressurized air chamber mounted in the steam hood, which is the last layer. We'll experiment with the exact type of fan unit once we get the steam hoods and air injector unit; we're starting with a 2-speed electric leaf blower mounted outside the building to reduce noise inside. We have a small concern over the longevity of a leaf blower motor when it is run for hours and hours with some back pressure.

Is this what the rest of you call a piggyback? My Internet searches seemed to indicate that Piggyback and Steamaway units were similar, just different trade names.

[syrupmaker]

Russ...I used a vacuum cleaner motor on my bubbler. Picked it up at Graingers for $60 Stock number is 4M941. This one is 110v but they also have them in 220v if you have the higher voltage available. It would cut your power consumption in half for that part of the operation.

Rick

[howden86]

RUSS

I HAVE A 5 X 10 PIGGYBACK ON TOP A THUNDERBOLT. I HAVE ASKED THE SAME QUESTIONS ABOUT MINE. DEALERS AND SALES PEOPLE CAN'T EVEN AGREE ON THE DEPTH OF SAP. MY MEASUREMENT SHOWED ME IT DOES NOT MATTER IN 2 INCHES ABOVE OR BELOW THE TOP OF THE FLUES. ONE PERSON SAYS THE HOTTER THE BETTER AND THE NEXT SALES PERSON SAY IT SHOULD ONLY BE 180-185 FOR MAX EFFIENCY.
AS FAR AS SAP CONCENTRATION IF IT WENT IN AT 2 BRIX IT CAME OUT ABOUT 3.0- 3.3 BRIX. TO ME IT IS JUST A GLORIFIED PREHEATER. IT JUST SEEMS WHAT EVER I CHANGE DOES NOT MAKE ANY DIFFERENCE.

[Russ]

Well, the test boil on Saturday may give us a clue as far as temperature gains, but not concentration impact. Depending on how much time and water we have, we'll try different depths. The piggyback is a little more than a pre-heater in that you are actually getting rid of some water content instead of just heating it. Since our sap is usually at 2-2.5, I'll take that extra .8-1 point going into the flue pan. I'm actually hoping for 3.8 or better, since the pre-heater should already have the sap hot before it goes into the piggyback. We'll have to wait and see...

most people get the best results out of there piggyback with sap levels about 1" below top of flues. I should bubble up over the top.

You should run the piggyback at atleast 180 for maximum effecincy most sugarmakers who boil hard can feed all the sap for the evaporator through the piggyback and maintain 180 plus.

A piggyback should increase your evaporation rate by 65-75%

[Russ]

Thanks... that's what we were thinking. Just high enough that the bubbles reach the top of the flues. We have a variety of things we want to try to measure the trade-off, if any, between temperature and concentration results.