LEADER EVAPORATOR WSE Evaporator
2018
Page:
3
INTRODUCTION: THEORY OF OPERATION
A maple syrup evaporator works under the principal of a gradient. As the sap boils, it concentrates. As it concentrates,
the volume is reduced and the solids (sugar concentration) increase. As the volume is reduced the liquid works to
maintain the levels across the evaporator so less concentrated sap flows into areas where there is more concentrated
sap. During the evaporation process the percent of sugar will change from the incoming (approximately 2%) to the draw
off (approximately 66%).
FORMING THE GRADIENT
When the evaporator is first filled, the concentration of the sap is the same throughout. The gradient is formed as the
water is evaporated from the sap in the syrup pan and the flue pan, and as the new sap enters the flue pan.
As the sap boils it loses moisture and becomes denser / more concentrated. As it is becoming concentrated it loses
volume. As it loses volume additional sap will try to keep the levels constant and at the same concentration. This is
occurring in both the flue pan and the syrup pan.
In the flue pan less concentrated sap enters through the float box into the first flue pan compartment and begins to
concentrate. As it concentrates it moves toward the second compartment of the flue pan. Early in the boil the second
compartment will become denser as the “fresh” sap entering the first compartment from the float box keeps pushing
the denser sap around.
As the syrup pan boils, the sap becomes denser. The flue pan sap is pushed into the syrup pan making sap in the first
syrup pan compartment less dense. The sap from the first syrup pan compartment is pushed to the next compartment
where the sap is denser and then to the densest compartment , the “syrup” compartment. The syrup is drawn off the
evaporator from this compartment and more sap flows across all the compartment s of the evaporator to replace the
volume of syrup drawn off.
With a good gradient in place there will be a measureable difference in the liquid levels between one side of the syrup
pan and the other. You may note a difference of ½”.
PROPER OPERATIONS TO MAINTAIN GRADIENT:
Firing
Defoamer
Minimize Reversal Effects
During operations you will be working to maintain a consistent gradient. This is done through firing level, control of
foaming, and minimizing the effects of reversal
.
Firing
During firing you are seeking to maintain the same boil all the time. By doing so the liquid “push” in the pans will remain
consistent. If the boil reduces, the syrup pan flow will reverse and flow to the flue pan. In order to maintain the boil the
following should be of concern:
1.
Wood to use
a.
Mix of hardwood (longer lasting, more BTUs) and softwood (quicker, intense heat).
b.
Avoid slabs as they do not allow heat to evenly reach the pan
c.
Split wood 2” to 3” in diameter and approximately 24” in length
2.
Loading wood into the arch
a.
Wood should stay on the grates and 2” to 5” inside from the door so wood fire does not heat the arch
face
b.
Criss-cross the wood as best possible so oxygen can reach all wood efficiently
c.
Do not hit the flues when loading wood