Steam power?

[Sugar-me-Timbers]

There is a producer near me that say they run their evaporators with steam. Watched a you tube video with a producer in Vermont 40 K taps http://www.youtube.com/watch?v=RGHdQQKpzh4 Producer states "We boil it using the steam evaporating system".
Never seen this, anyone know about this system, how is it powered, what are the mechanics of this process?
Thanks,
Phil

[Teuchtar]

Isn't the evaporator just powered by a saturated steam boiler with the steam under slight pressure ? Just need to keep the saturation temp somewhere about 250F, so there's a corresponding saturation pressure with it, of 15 psi gauge. Variations exist.
This means the steam will condense on the wall of the tank/pan containing the boiling sap at that temperature. Condensing steam has a ferociously unbelieve capacity for heat transfer, even at what seems like a low temperature compared to the flame of burning, steam has a remarkable ability to transfer heat when condensing.
The steam-side of the pan is sealed, so the steam can't escape to atmosphere, and contains that pressure. The condensate that rains down off the boiling pan gets picked up by the boiler feed pump and reinjected into the boiler.
An alternative design, is to pipe the steam through pipes immersed in the flue pan. The pipes would be sloping like a helix to allow condensate to drain down to the steam exhaust.

There are lots of food processing industries that use saturated steam for cooking and processing. For example, some (most ?) distilleries use steam boilers fired by heavy fuel oil to produce steam for the stills. My uncle ran the Allt-á-Bhainne distillery on night shift himself. Supervised the boiler, checked the mash, ran the still, and pushed the Stop button if things got hectic. He was able to draw off about 20,000 L of Chivas Regal by 7:00 am. The miracle of process automation.
Advantage: you can start the boiler and have it hot and ready while you fiddle with the RO, filters, drums etc. Once you push the Cook button, things start happening pretty fast. Boiler controls have common commercial automation, and are readily maintained/repaired by specialists. The heat transfer surface remains very clean, since steam doesn't soot up and degrade the heat transfer process. Thus effectiveness doen't fall off like it does when burning wood.
Disadvantage: Even a "cheap" saturated boiler costs more than your house is worth. Plus you need someone with a boiler operators license to look after it. And a heated building to keep it in. And mandatory state/insurance inspections. Not a hobby operation.

[Thompson's Tree Farm]

I have not personally seen it but have heard of an operation that uses an old powdered milk dehydrater that operates with steam heat to make syrup from a large number of taps.

[Dave Y]

While making syrup with steam is interesting it is very inefficient. you must heat water to boil sap.

[Teuchtar]

Hmm, I wonder.
The most efficient power plants are combined cycle gas turbine with steam turbine bottoming cycle. Net thermal efficiency is presently 60% (gas BTU's to KW on the outgoing feeder). My diesel tractor with a pto generator might get as high as 30%. The steam bottoming cycle (driving a steam turbine at 1100F, 2400psi from a boiler off the gas turbine's exhaust) is a very efficient and economical way to recover energy.
Using steam doesn't mean inefficient, unless that specific application is poorly designed. In the case of power plants as well as large process industries, steam offers the advantage of being a readily available working fluid which is comparitively safe to handle. (versus say ammonia or propane, or R12) which maybe have superior thermal properties, but are hazardous and expensive in those large quantities.
If someone with a steam evaporator could share their steady-state oil consumption rates with us, maybe we can compare with gas or oil fired published rates.

Oh, one other advantage of steam. You cannot scorch the pans. Saturated steam is "guaranteed isothermal". its always 250F at 15psi, and you don't get hotspots, (unlike a direct oilfired unit) plus the heat is distributed pretty much evenly everywhere.

Lets see what the steam-evaporator guys have to say.

[sapman]

Don't Bascom's use steam? I may be mistaken. There's that one big pan, plus the RO's, or so I thought.

[rchase]

bascom does use steam and its a very effiecient way to boil. i think his steam is over 100psi. i way be wrong but i think hes only using 1/3gal of oil for a gallon of syrup. you can make that nasty commercial syrup and not burn you pan too.