evaporating sap in a vacuum?

[Machinist67]

Has anyone experimented with evaporating sap in a vacuum chamber?

[DrTimPerkins]

Has anyone experimented with evaporating sap in a vacuum chamber?

Yes, there has been a lot of work with this. Evaporation with vacuum can be achieved with much lower temperatures. It is used in some processes in sugarcane and beet sugar processing. The problem (in maple) is that it doesn't allow for much of any color or flavor development (desirable in other sugar industries) due to the near complete lack of caramelization.

[BreezyHill]

Provided I can rap up my remodel project we will beading vacuum to our flue pan system. For the last 30 plus years our sugar house had a fan that pressurized the boiling room to force steam out thru two stacks. One was for the finish pan the other was for the flue pan. Last season during a late night boil it suddenly hit me that one factor that was slowing our boiling rate was the room being pressurized. We have a candy thermometer that has an adjustable mark plate. It is always slide to the highest point to meet the results of the hydrometer. Thru a little experimenting I found I could drop my finish temp by 6degrees that night by turning of the fan.

So the remodel project started into design mode. I have a 24" Chicago fan that I was going to use for air over fire but it is going to be used to suck the steam from the pans. I use the steam of the flue pan to preheat sap so the C fan will be up stairs and pull the steam thru the preheater. The finish pan will also be on the same fan thru a tee with a gat valve.

The goals of the system will be:
remove steam from the sugar house
preheat the sap to the 180 achieved in the past design
increase the boiling rate
reduce the amount of wood burned in the arch
don't collapse the flue pan.

The goals are simple but the return of meeting the goals will be huge. We also have a goal of .5 gallon/ tap to increase our .47 from 2013.

On paper the inclusion of a slight vacuum on the flue pan will provide a 10% increase in boiling rate, while the addition of the pressure was reducing our rate by 20%. I am optimistic and will settle for nothing less than reaching, in two years, an increase of 50% in our boiling rate. There are several changes that will be made to achieve this goal but the current growth in sales will force us to double the boiling rate thru this rig or buy another.

I have designed in a fail safe for the flue pan as I was warned by another producer that you can collapse a flue pan.

How were you thinking of setting up to boil?

Ben

[Machinist67]

Ben,

It is good to here your ideas. I do agree that collapsing the pans would be a major concern.
I sell industrial equipment in all types of application and was doing some reading on super heated steam doing some research I found this chart. One of the engineers I was working with said "why not boil under vacuum". So I found this, boiling point of water under vacuum www.jbind.com/pdf/Cross-Reference-of-Boiling-Temps.pdf‎Cached
So my Idea is to remove more water before the finishing pan by making a vessel that would be like a "steam away" that would be under vacuum.

Dr Tim,
Does anyone have any research in print I could review their findings?
Eric

[DrTimPerkins]

Does anyone have any research in print I could review their findings?

There is a copious amount of research and methods description for vacuum evaporation in the sugarcane industry.

[DrTimPerkins]

"why not boil under vacuum".

The "why not" primarily boils down (pardon please) to two factors:

1. Current maple evaporators are not designed to boil under partial pressures, and could result in pan collapse unless either the evaporator is constructed to withstand the vacuum or close monitoring and a vacuum relief system is used to avoid that possibility.

2. The "flavor" profile of maple syrup includes some degree of caramelization. If boiling is done at temperatures too low to allow this to happen (which really is not very much lower than the boiling point of syrup), then the product you will end up with will be very clear and almost flavorless. This is exactly what the sugarcane and beet sugar industries strive for (producing a very light-colored product that will require little "refining" to produce crystal sugar), however this is not what the maple industry and its customer base requires.

[noreast maple]

Why couldnt you put a couple of ss tubes crossways in your pan to keep from sucking sides in? then maybe a automatic damper to open slightly when vac reaches a certain level, dont know, just throwing a couple of ideas out there.

[lpakiz]

If you put your pan under vacuum, you will also need a very robust float valve to hold back the sap. And your hood would need to withstand the pull, also.
I doubt that you can generate enough vacuum, especially with a paddle type fan, to really influence the evap rate. Not that I'm against trying this. I guess you could screw a vac gauge into a fan inlet and plug the inlet to see how far the needle moved.
Years ago, I wondered if anyone tried vacuum, in addition to heat, in a clothes dryer. It works in evacuating an A/C system to remove moisture by lowering the boiling point below ambient temperature.

[Machinist67]

I was thinking about a vacuum pump not a Positive Displacement fan. I also was think of only using it on the area before and above the back pan, just to remove more water from the sap. I might be able to use the heat of the evaporator pan to raise the temp enough to only have to pull 10-15in/Hg to cause the sap to start the boil off process. Do not know if the energy used to pull the vacuum will warrent the energy savings to remove the water. Just trying to make the rigs more efficient.

As DR Tim has said, I do not want to mess with the color or the taste of good syrup.

[Brian Ryther]

I have worked with vacuum evaporators in the limestone slurry industry. I have thought it would work well as a pre concentrator for maple sap. If I were to build one it would be a vertical shell and tube design. You need steam to get the process up and running. Once up and running the steam created from the evaporation is pumped into the tubes of the shell and tube. This pump (turbo fan) does two things. It creates a vacuum in the sap side and pressurizes the steam on the tube side. The pressurized steam is super hot and very effective at boiling. This process is very energy efficient. The only energy needed is the turbo fan, once up and running.

[BAP]

The "why not" primarily boils down (pardon please) to two factors:


2. The "flavor" profile of maple syrup includes some degree of caramelization. If boiling is done at temperatures too low to allow this to happen (which really is not very much lower than the boiling point of syrup), then the product you will end up with will be very clear and almost flavorless. This is exactly what the sugarcane and beet sugar industries strive for (producing a very light-colored product that will require little "refining" to produce crystal sugar), however this is not what the maple industry and its customer base requires.
This is similar to concentrating too much with an R/O and not enough boiling time. I've tasted syrup in drums at Bascom's from the Great North that were supper light colored and very little flavor even though they were the right density. Needles to say, we didn't buy it and it stayed there.

[Brent]

A fellow in the fruit concentrates in the Toronto area tried vacuum on sap.
Got some great looking syrup ... almost clear ... and tasted just like sugar cane syrup.
As the Doc said ... you gotta boil it.

[markct]

I have heard rumors or speculation that the process Bascoms use for making the granular maple sugar is done under vacuum. This would be logical as it would allow boiling at a lower temp thus less troubles with it wanting to scorch at the near done stage.

[BreezyHill]

Machinist67,
Sorry got swamped with all the cold and snow with the farm and feed mill.
I think that sounds like a good experiment. You could use a electric solenoid to open to bring in sap as the system would process and need filling.
A second solenoid to split the vessel so that when the float needed sap it would be supplied with a third solenoid at the float to allow the sap to exit.
now the steam exiting would need to be on a separate elevated section of the vessel to get the water vapor evacuated without loosing all the vacuum of the unit. This will be tricky but possible another set of solenoids to cycle to release the vapor.

I do like the idea of doing this to make sugar and this could be easier than syrup production. It has been some time since I made sugar/candy but we will be needing to make a good amount of this for a market that we secured in the past week.

Can you pm me that boiling point of water link it seems to be broken.

Remember failure is simply a step in the road to success!

Ben

[Cedar Eater]

I know this is an old thread, but I dredged up an even older report on a method of using vacuum called mechanical vapor compression (http://www.fs.fed.us/ne/newtown_square/publications/research_papers/pdfs/scanned/ne_rp385p.pdf). I don't see how they keep oil out of the distillate, but I can see how the color and taste of the syrup would be equal to atmospheric boiling. It uses electric heaters, but that could be tinkered with.