Controlling temperature spikes

[Bruce L]

Had the auto draw off set at 219.2 yesterday,but noticed during draw offs that temperature would sometimes spike to 220.3 before coming back down. I put the sliders in place every fire to keep the pan from mixing,got thinking overnight that maybe I have the draw off valve too far open at 1/2 and dropping the pan too quickly,I remember Bruce Gillilan saying something about syrup coming off the size of a lead pencil?

[DrTimPerkins]

Don't use the sliders if you can avoid it. Be sure you have a valve between your pans and the drawoff valve. That valve should be cracked open only about 1/2 way. That way you will never draw the liquid level down beyond that point and it'll reduce the chances that you burn your pans. Secondly, what kind of auto draw are you using? Some of them are on/off, some are modulating. Modulating is better to reduce that kind of issue as it'll open just a tiny crack as it approaches the setpoint and open further if you meet or exceed the setpoint. That way the stream of syrup coming off is proportional to the temperature. You can usually set the temperature for it to open just a tiny bit and the temperature to open all the way.

If you have a solenoid (on/off) auto draw and your temps are spiking, turn the setpoint down a bit lower to compensate. It'll draw off a touch light at first, but the heavy syrup coming later will even it out.

By using the sliders, you're actually letting the syrup in that partition get denser since there is no incoming syrup that is lighter coming in to mix in and compensate by thinning it out.

When you first do these adjustments, raise the liquid level a little with your floats to give you a little extra margin of safety. Then as you get it figured out you can drop the level again if you want.

Ideally, as you were told, you want just a tiny stream of syrup coming off the evaporator continuously. It'll never quite perfectly get there, but will some tweaking you can get it to operate pretty close to that.

[Bruce L]

Hi Dr. Tim, I do have a valve between the pan and the solenoid valve,it is at 1/2 open,maybe I should close it to 1/3? It is a Marcland open and close,not modulating. I have found the sliders useful to keep the syrup from mixing while I am firing,firing only takes one minute or less,as I would observe the temperature to be say 218.1, then I fire and temperature could go down to say 216.5 for example,then I would end up with darker syrup and a large batch,as opposed to 1/2 gallon to 1 gallon at a time which I prefer. When I use the sliders I find the temperature doesn’t drop near as much when I fire. I know the syrup pan got running lower than I prefer yesterday,as syrup was coming off every ten minutes,hardly enough time for pan to recover

[TapTapTap]

I typically have at a least a couple of draw-offs for each boil where this happens. For me it often happens as I'm bringing the cold rig up to boiling temperature and the gradient hasn't yet established a balanced condition. My process now involves a series of short manual drawoffs below syrup temperature/density as the temperature is rising and getting to syrup. This procedure helps establish a gradient in the syrup pan. I then use this light batch to get the filter press hot, primed with DE, and verified. The filtered product goes back into the flue pan until i reach syrup on the outlet.

I also have a Vortec (30"x10') with raised flue and revolution pan. I think the channels in my 30" wide syrup pan are a little narrow with somewhat small openings in the dividers - and that constricts the flow somewhat during drawoff which obviously doesn't help. The Vortec is like a race car running on rocket fuel and it's not the easiest rig to control, especially compared to an oil burner! I'm even amazed at other wood-fired rigs when I see how calm and gentle they run compared to my Vortec.

Ken

[ennismaple]

Bruce - We leave our valve before the auto-runoff only half full which helps avoid extra large runoffs. With wood fired it is hard to avoid batching unless you are able to manage the temps in your fire box to a tight range. The other factor is defoamer - regular use of defoamer keeps our runoffs small.