how much gain with preheater/hood...

[tuckermtn]

how many GPH gain could we possibly expect with a hood and a copper pipe preheater (not a steamaway)?

we have a 2.5 x 5.5 flu pan currently.

Anyone else with a similar size evap. that could give me some #'s?

We currently get 50-55gph on our stock evap. set-up.

thanks-

Eric

[Haynes Forest Products]

Eric I dont think a hood is going to help with the evaporation rate (could be wrong) unless you use it to keep the heat on a preheater. Your rig is perfect for a preheater. What does your fluepan look like when your boiling do you have a cold spot as the sap comes in from the float box? If you can get your sap from 45 degrees to 120 150 your going to help the boil rate. Its all about the BTUs the higher the boil rate in the flue pan the better. What type of preheater are you thinking of?

[RileySugarbush]

The copper pipe preheater uses the heat in the water vapor to preheat the incoming sap. The hood helps by holding the water vapor around the copper pipes long enough to transfer that heat effectively. If the sap coming in is near boiling, the evaporator doesn't need to heat the sap so all the heat from the flue gasses can be used to evaporate water. Preheaters help, but only so much.... Here is a simple estimate:

It takes about 180 BTU to raise the temperature of 1 lbm of water (or sap) from 32°F to 212°F. It takes 975 BTU to vaporize it from 212°F. So the best improvement you can hope for is about 19% if your sap is coming in near freezing.

In practice, the sap is usually not that cold and your preheater doesn't get to 212°F, so maybe 10% to 12% increase in productivity can be expected. Not fantastic, but it is free energy once you get it set up! Plus you get all that nice hot distilled water condensing on your preheater for cleanup.

[Haynes Forest Products]

I would like to hear about other preheaters that people are useing. I started out with simple copper tubes over the flue pan. Then went to a hood and a preheater with a drip pan to catch the condensate but the pan blocked the heat and it didnt help that much. I then went a totaly differant way. I now have the coils in the flue stack that circulates hot water (not the sap) with a pump into a plate heat exchanger. The sap gravity feeds thru the exchanger into the float box. Im having the best luck with this setup. I dont have any plumbing in my hood so its easy to remove. With my 3x10 get about 20 gallons advantage. I do think that your evaporator is like your car when it comes to performance. To get good gas mileage you make alot of little changes and the gas milage goes up. Air in the tires,new air filter,tuneup, good catalitic converter ,good gas

[RileySugarbush]

Haynes,

What was your evaporation rate with and without your preheater? Did you see about the 12 to 15% improvement?

The regular preheaters in hoods work best if you have a damper on the steam stack to hold the water vapor in the hood so it can transfer heat to the tubes. This is a case where too good a draft hurts you.

The flue gases in the stack are another source of free (waste) heat that you can take advantage of, and several people here have talked about running copper tubes around or even through the stack. That should be super efficient, but if you run your feed sap that way and shut down the flow for some reason, at best you can burn the sap in the tubing, at worst it can boil and burst the tube or shoot boing sap around the sugar house. I'm too scared to try it. Your rig with continuously circulating water sounds safer.

[Haynes Forest Products]

Riley
I have no records that i kept from one type of preheater to the next . But what i feel is that with the plate heat exchanger i get hotter sap into the fluepan and that has helped increase my evaporation rates. I would say over 15%. I dont know the amount but most of the steam is made in the fluepan so it only stands to reason to have hot sap comeing in so all the fluepan is boiling. I can tell you that all it takes to burn sap in a coil is to have large air bubbles form and bingo burnt sap nasty smell and taste. There are differant dynamics when it comes to boiling sap in a open evaporator and sap in a closed copper coil. When sap is running down a tube using gravity and it boiles the bubbles try and run up stream and get bigger and slower and that is when it burns and causes air lock. You mentioned the steam and that is when things get dicey. My system uses water on the flue stack side and it is a closed system with a pressure relief valve and it vents to the floor. With a closed system you will not make steam as quick as with a open system. If I run out of sap the temp in the water side jumps up fast and without the sap to cool the water it will start to make steam. I have a low pressure water valve that keeps the system full but it still blowes the relief at times .

[WESTVIRGINIAMAPLER]

Figure 10% with a hood and stanard copper preheater and if you get more, then be thankful.

[Haynes Forest Products]

WESTVER
Saw your preheater set up and with it open without a catch tray isnt it counter productive having the condensate dripping back into the fluepan?

[WESTVIRGINIAMAPLER]

I have a stainless drip pan underneath the preheater slightly wider and the entire length of the preheater. I is aprox 12 to 14 gauge stainless and it has a lip on each end which allow the condensation to go right into the condensation channel inside my hood and the lip sits right down into the channel and the channel supports the drip pan and preheater and the drip pan has adjustable brackets that the preheater sits right into. It's a very good design as the preheater just lays in the stainless brackets that have aprox 3" of vertical adjustment and my preheater has about 3" of lift from the low end being the incoming end to the high end being the exit end.

I agree that without a drip pan, it would be a waste or close to it anyways. Besides, most of the condensation you get from the hood comes off of the preheater.

[Haynes Forest Products]

WESTVERG
What do you think your heat gain is? Plus what is your GPH sap Chuck

[WESTVIRGINIAMAPLER]

I have never checked it as I went to an inferno arch the same time as a preheater, but I would guess 10% and others Ihave talked to that have tracked it better than me have come up with about the same #'s.

[RileySugarbush]

We all may only get about 10% gain with preheaters, but it is a very satisfying 10%! Low cost, low maintenance, free hot water, and the good feeling of adding nice hot sap instead of ice cold to the flue pan.

[Haynes Forest Products]

WESTVER
With my old plate exchanger I was converting 42 degree sap to about 85 degree was wondering what kind of heat rise others are getting and how thair doing it. workng on the next bigger and badder system

[RileySugarbush]

For what it's worth, my set up is over a 2x3 drop flue with a tight hood, 7" steam stack straight up into the cupola. The preheater is 3/4" copper, with 16' of length in serial flow. I should change it to parallel.

When running steady at about 40gph ±, the output sap is between 180°F and 200°F, almost regardless of inlet sap temperature, though that is usually in the 40's. When I shut down the draft for firing, there is a big surge in inlet flow and the boil drops down, and a slug of cool sap comes through until things get ripping again and the inlet flow settles down.

[WESTVIRGINIAMAPLER]

I run from 140 to 180 degrees coming out of the preheater and I agree, it is all free heat and free hot water. I am not complaining at all. At the end of a 10 hour day, it saves me aprox 1 hour boil time and that amount of wood and an extra gallon of syrup.

If I run my damper closed, I could probably easily reach 200, but the flue pan is going so crazy anyways with pushing 760 cfm thru the arch.

[Gary R]

I have seen Sugarmaker's preheater. I believe he has around 200 degree sap temp on his 3X10. He made his, patterned off of a commercial unit. It is copper, 1" lower and upper manifold, 3/4" parrallel flow tubes. Can't remember the number or length, but about 20' of 3/4 overall. No pan under the tubing. Instead under each tube is an angle laid so it forms a "V" under the tube. Each one of these goes to another "V" under the lower manifold and out to drain. It also has vapor lock vent and drain petcock so the lines don't freeze when not in use. It is VERY nice looking. If I every get to a head tank, I'll try make one of those.

[WESTVIRGINIAMAPLER]

I would think if you could have a "V" tray underneath each preheater pipe, it would have to be more efficient due to allowing better steam travel around each one.

[Sugarmaker]

Brandon & GaryR & folks,
Yes that was my thought to, so I abonded the standard pan under the copper preheater and made the "v/s" to catch the condesate. Sap goes from 40 degs F to 200 deg entering the rear pan, IF if you keep the wood to it. Probably adds 5-10% to the efficency of or evaporator. We can boil off between 80-90 GPH.

Regards,
Chris

[TapME]

I have a question. Are these pipes in the pre heaters cut in half or are they whole and can build pressure? Excuse my non knowledge on this subject, but with the gain in taps this may be an option to help speed up processing.

[brookledge]

Tap me
The sap travels in copper or stainless pipes inside the enclosed flue pan (under the hood). The fuel that you burned to turn the water into steam is lost once the steam leaves the pan. The pre heater captures this heat and warms the cold incoming sap. When the hot steam hits the cold pipes the steam condenses back to liquid. This is the point that you need to drain the now condensed water out of the flue pan so that it does not drip back into the sap or you have not gained anything.
Some pre heaters use pans underneath the preheater to collect the condensate and others like sugarmakers post have designed V shaped channels underneath the preheater pipes to collect the condensate and carry it out of the hood
That is where you get 10-15% gain in efficiency
Keith

[WESTVIRGINIAMAPLER]

Most preheaters are on a slope with the sap coming in at the lowest end and the head pressure forces it uphill. This way, the sap is preheating evenly and not taking the path of least resistance if it was level.

[TapME]

This could be next years project. The science seems simple enough. Is the volume of the heater a consideration when building one?
Dave has a EVU I believe. What is the difference?

[brookledge]

As for the size, it is important to have the proper size. If it is too small the sap will not heat up as much as posibble. and if it is too big the sap can begin to boil in the tubes and vaporize. Most pre heaters are desighned with a parrallel flow. I otherwords the sap comes into a manifold and then disperses and travels through pipes side by side and then into another manifold bringing the hot sap back to just one pipe. The parrallel style allows for alot of pipe to get good heat exchange with out creating alot of restriction like a series style would do.
Keith

[Sugarmaker]

Big differrence in Daves EVU and a preheater: he should be able to turn 2% sap into 4% sap. The preheater will not do that, it just gets to cold sap up near the boiling point so you don't need as much wood.

Chris