Preheater fab

[wiam]

Hello

Perhaps a stupid question but I will ask....why wouldn't a couple of small pipes (SS sched 80) across the exhaust gas flowpath pick up more heat (possibly too much) and be a simpler/cheaper solution? Kind of like a feedwater economizer on a large utility boiler

There are stories of burning sap in pipes near the flue "stack". Also the preheater intue steam hood will give you a supply of hot water. Which is not usually available in a sugarhouse.

[johnallin]

Here's a picture of the pre-heater I put in last year. It's made by Leader. Note the drip tray. Good luck with your project. John

IMG_2641 - Copy.jpg

[Bucket Head]

Remember, warm sap turns into bad sap and bad sap gets nasty. I always flush my preheater out with water after shut down. I rinse my head tank out and then I put some water in it to flush out the preheater, letting this water drain out into a pail to dump. Your rig and the sap in it stays warm for some after shutdown and that allows sap to "stew" in the pipes if it's left in there.

[Aa2tn]

Keep in mind that the sap only moves as fast as your evaporation rate, which is a trickle at best on most rigs. It's in those tubes for a long time.

I figured out that my preheater with 7 2" diameter tubes at about 36" long each will hold about 3.5 gallons of sap. So at 21 gallons an hour evaporation rate the sap would only be in the preheater for 10 minutes.

[Maplebrook]

Dang it! I thought more copper would mean more heat, but then you are right, there is a lot more sap volume in 3/4".....pondering another trip to the plumbing supply store now..

I was wondering about insulating the vent. If your system is closed, doesn't that negate the vent all together? I thought the purpose of the vent was to allow any inadvertent steam to escape, and prevent the pre-heater pipes from bursting catastrophically?

Hi Guys,

I'm no stationary engineer, But I don't think you can boil sap in a preheater that is heated with steam. Even if it did, steam would still have the float box to vent or even push back through the feed line from the tank and gurgle into the sap tank. I've never had an issue with pressurized steam with this set-up.

On my old home made evaporator with two 25' runs of 3/8" copper wrapped tight around the smoke pipe, pressurized steam was an issue. And a vent was required. And I burned sugar inside the 3/8" when the sap started to run out. This set-up would boil sap in the preheater.

I think we get mixed up between direct heat preheaters (pipes containing sap against a flame heat source) and steam preheaters. They are two completely different creatures.

[Maplebrook]

Dang it! I thought more copper would mean more heat, but then you are right, there is a lot more sap volume in 3/4".....pondering another trip to the plumbing supply store now..

Also, for my preheater manifold headers, I drilled 5/8" holes (the o/s diameter of 1/2" copper pipe) at 1 or 11/2" spacing and soldered the 1/2" preheater tubes into them. It was a lot more compact, a lot cheaper and a lot less soldering.

[bmbmkr]

Hello

Perhaps a stupid question but I will ask....why wouldn't a couple of small pipes (SS sched 80) across the exhaust gas flowpath pick up more heat (possibly too much) and be a simpler/cheaper solution? Kind of like a feedwater economizer on a large utility boiler

I've read that a couple member have stainless pre heaters running through their exhaust, and I know there is one manufactured for the wood furnace that i heat my house with to augment the electric water heater. I have these tidbits registered in my nugget for sure! For now, this is my first arch, my skills, and resources are limited, but a good idea for sometime down the road.

[bmbmkr]

Also, for my preheater manifold headers, I drilled 5/8" holes (the o/s diameter of 1/2" copper pipe) at 1 or 11/2" spacing and soldered the 1/2" preheater tubes into them. It was a lot more compact, a lot cheaper and a lot less soldering.

That's a great idea, wished I'd known that,maybe I should have addressed these questions ahead of time, before i went out and bought and cut up 40' of 3/4" lol Thanks for the idea!

[maplesyrupstove]

DSC02255.jpg 3/4 pipe with 5/8 holes for 1/2 inch copper pipe

[maplesyrupstove]

DSC02257.jpg 7 runs of pipe 45 inches long for preheater