thoughts on a preheater

[phil]

I just picked up a new evaporator. i don't have a steam hood or preheater. so i was thinking of just building a preheater out of copper and sitting on top of my flue pan. or will the condensation dripping back in just defet the whole thing? Can't think of away to put a tray under it and the steam to still get out.

[spencer11]

what you are describing is what evaporators with steam hoods have on them. so it should work fine.


spencer

[phil]

ya but they have a tray under them to catch the dips dont they

[500592]

Yes they do and to make them effective you should have a hood

[jmayerl]

You need a hood and a drip tray, preheater does nothing without them.

[TimJ]

I think one can get away without a hood (less efficient of course) - but the drip tray is required for it to be more efficient than without.

The simple way to make a tray is one large pan - and this is where a hood is needed. Or one can build channels under each copper tube and then have those collect in one place/drain off.

We just build a hood/preheater with a used oven range hood and some copper pipe and a large cake/catering pan. The preheater sits inside the hood and also inside the hood but under the preheater is the tray.

[lenny]

I will add my few cents worth. I made a preheater with 10- 1/2" copper tubes so that the overall demencions are 24" X 36". I used 3/4" copper tees. and connected them with very short 3/4" copper pipe. In other words the ends are 3/4 inch copper fittings and the length is 1/2" copper pipe. I boiled 370 gallons of sap this weekend keeping track of how much I boiled each hour as my head tank is calibrated. There was a tremendous amount of condensation on the tubes. At one point I estimated 80 big drips. I also checked the temperature of the sap as it flowed from the preheater into the float box. It was 71 to 72 degrees. That did not seem very significant to me. The last 3 hours of the day I took off the preheater. I increased my evaporation about a gallon per hour. I did a few other things to increase evaporation such as increasing the stack temperature a little and adding wood with fewer pieces more often so maybe all of the change was not due to the preheater removal?

Bottom line for me is I will not put the preheater back on unless I learn of a better way. I do not want to use a hood because I want to see and feel the sap when it is boiling.

[TimJ]

I will add my few cents worth. I made a preheater with 10- 1/2" copper tubes so that the overall demencions are 24" X 36". I used 3/4" copper tees. and connected them with very short 3/4" copper pipe. In other words the ends are 3/4 inch copper fittings and the length is 1/2" copper pipe. I boiled 370 gallons of sap this weekend keeping track of how much I boiled each hour as my head tank is calibrated. There was a tremendous amount of condensation on the tubes. At one point I estimated 80 big drips. I also checked the temperature of the sap as it flowed from the preheater into the float box. It was 71 to 72 degrees. That did not seem very significant to me. The last 3 hours of the day I took off the preheater. I increased my evaporation about a gallon per hour. I did a few other things to increase evaporation such as increasing the stack temperature a little and adding wood with fewer pieces more often so maybe all of the change was not due to the preheater removal?

Bottom line for me is I will not put the preheater back on unless I learn of a better way. I do not want to use a hood because I want to see and feel the sap when it is boiling.

Adding a preheater without siphoning off the condensation will produce the results you see - no improvement. If you can draw off the condensation without it falling into the pans to be reheated and re-evaporated then you will be net positive.

Without a hood placed down low on the pan, the efficiency of a preheater/hood drops.

[PerryW]

I think the hood is designed to be steeper than a certain angle so the condensation clings to the metal and runs downhill to the drip trays (one on each side) instead of dripping back into the pan.

[Asthepotthickens]

My set up is small so I made a steel stand and I put a pot up very close to my chimney. The heat from the chimney heats the sap to about body temp. Works for me

[Peepers]

Hey Phil, what did you end up rigging up for a preheater? I'm working on a bigger pan right now and have been noodling through some preheater design options. My pot sitting next to the stack helps a bit but I'd sure like to enjoy the added efficiency of feeding my evap 150+ degree sap. :)

[Asthepotthickens]

Did anybody ever try to wrap copper tubing around the stack? Say space it an inch away and trickle sap through it?

[Pibster]

Did anybody ever try to wrap copper tubing around the stack? Say space it an inch away and trickle sap through it?
I have 3/8" copper tubing wrapped around my stove pipe. It does help warm the sap slightly. I would wrap it fairly tight, no space needed. When the sap runs out, you'll have to flush the tubing with water.

[phil]

I ended up piping around the smoke stack with 3/4 copper as close as i could get it. just tapped on the weekend havent got enuf sap too test it yet. i used 1/4" last year on a smaller rig and it worked great still had to add sap to pan too keep up. hopeing the sap runs all night tonight

[b116757]

I just made a paralell flow preheated this year out of 3/4 stainless pipe 5 lines 6.5' long and a drip pan out of 24 gauge stainless bent angles out of the 24 ga to under each run of pipe to collect the condensation on the maden run we didn't get the catch pan installed and the system still improved overall gph because boil on the back pan was much better with 130 degree sap entering instead of 34 degree sap killing the boil this was with a tight fitting hood.

[Springfield Acer]

I have a combination of preheating. My homemade block arch has a steel covering at the back since the flue goes out the back end and then elbows up. For the last two years, we have pan fed all the sap from pans dipped full and placed on that steel "shelf". When needed, we pour the preheated sap into the little 3 gal head tank that we keep at one to two gallons.From there it gravities thru a trickle valve into the pan (20 x 40 w/three compartments). This year I added four 1/2" copper tubes with 1/2" headers and small SS gutters high in the hood. My pan entering sap temp varies from 120 to 150* depending on sap temp and air temp. I have gained evaporation from somewhere north of 13 gal/hr to as high as 15+ gal/hr. This is with OFA and feeding small amounts of small wood often. If the front door isn't glowing, we need wood!