RO High-Brix Sap Causing Foam and Surging Issues In Evaporator?

[maple marc]

Got my new RO system up and running this week. I was supplying my evaporator feed tank with 4 to 9 brix sap. First issue was lots of foam in the syrup pan's take-off compartment. I increased my defoamer rate but to no avail. I had to put some defoamer in the take-off compartment sometimes which I hate to do. Then I got really bad temperature surges at take-offs. Suddenly overshooting my take-off temperature, then trying to take off as much as quickly as possible, then taking some light syrup off to compensate, hoping to get back close to the proper brix. I've had some surge issues in the past, but not his bad. I've learned to sort of "ride the curve" of temperature, taking off a little early and staying open as the temperature slowly rises through the right temperature. This was crazy.

I'm wondering if these issues were related to feeding the evaporator with the high brix sap. My evaporator:
Leader 2x6 WSE (drop flue 4-foot flue pan, 3 compartments syrup pan)
Sap depth about 1.5" slightly above tunnels
Stoking every 8 minutes.
Defoaming: usually 4 drops in flue pan near float box each stoke, but increased it to 5 or 6 drops and still getting a lot of foam in take-off compartment
Stack temperature 800-900 degrees

This was early season first run sap. The RO really cut down my boiling time, and I was expecting things to happen fast, but this was a bad take-off day. Does high-brix sap do this? I'm hoping you all can help me figure this out. Should I be making some changes in depth, more defoamer, anything else? Been making great syrup on this evaporator for years. Thanks for any ideas.

Marc

[JoeJ]

This will be my 18th year boiling and I have never had as much foam as I did on my first boil sweetening the pans. Even though I put in a normal amount of defoamer at the start, I couldn't believe how much the sap foamed up. Has to be something with the first run sap this year.

Joe.

[SeanD]

Ditto. It was like a bubble bath in the flue pan when I started my first boil. My concentrate coming in was over 10%. Eventually as the amount of defoamer worked its way through the pan, it settled down. I have to admit, boiling with high concentrate feels easier than the 6-8% I was boiling before. The syrup comes off faster and it seems to even out my draws.

The surges through draws are something to get on top of, but it sounds like you know what you are doing. Once you get into a heavy/light cycle it takes a few rounds to get it evened out. Sometimes, that's just how it goes. I override my thermometer when I see syrup in the middle channels, but sometimes I guess wrong and I pull too early. Then there are issues with firing. I've learned that's a big part of it too. Some firings are just hotter than others and that kind of messes up the flow, too.

The last thing to watch is depth. Don't run deeper with concentrate. That leads to more foam. Boil high brix concentrate the same way you would raw sap.

Good luck.

[DrTimPerkins]

Sorry, but I had a good chuckle after seeing your subject line

RO High-Brix Sap Causing Foam and Surging Issues In Evaporator?

and then reading the sentence....


I was supplying my evaporator feed tank with 4 to 9 brix sap.

I was expecting someone writing about 25+ Brix sap. We run our concentration up to 35-36 Brix in our Lapierre HyperBrix. I can tell you that foams like crazy too, especially the first time you boil to sweeten the pans. Turn on your defoamer as soon as you turn on the concentrate going into the pans. Otherwise you have a pan full of concentrate, but little or no defoamer there.

Sometimes there isn't a good transition of defoamer from the backpan to the frontpan, so you need to use a little in the frontpan as well. Put it in just after the floatbox going from the back to the front. If needed, use defoamer sparingly as you get closer to the drawoff partition.