Piggy back evaporator for maple syrup evaporator apparatus or the like

A piggy back evaporator coupled in stacked overlying position to a syrup evaporator apparatus including an upright box flue pan carrying syrup for evaporation subject to an underlying fire to boil off vaporazable constituents thereof, said piggy back evaporator comprising:

• a drip pan sized to the flue pan, mounted to the flue pan and overlying said flue pan, said drip pan including an oblique condensate drain sheet plate extending over the major length of the same, a steam hole within said condensate drain plate, a piggy back pan sized to and mounted to the top of the drip pan, said piggy back pan being upwardly open and including a corrugated bottom wall defining a series of laterally spaced troughs therein interiorly of the piggy back pan and a series of vertical flues on the exterior of the piggy back pan bottom wall facing said drip pan, a hood covering an open top of said piggy back pan, being sealed about edges thereof to said piggy back pan, said drip pan, said piggy back pan and said hood comprising a vertically stacked assembly, at least one steam exhaust chimney carried by said hood and extending upwardly therefrom, a plenum assembly mounted to said hood, said plenum assembly including a high pressure air blower, an air inlet passing through said hood and connected to said blower, a plenum chamber internally of said hood and connected to said air inlet, said piggy back evaporator further comprising a plurality of downpipes projecting downwardly from said plenum chamber and opening to the interior of the plenum chamber and a plurality of sparging tubes extending the length of the piggy back pan and being connected to respective downpipes, said sparging tubes being located within the bottoms of said troughs, longitudinally spaced holes within said sparging tubes, means for feeding sap to the piggy back pan of the piggy back evaporator and the flue pan of the evaporator apparatus, means for drawing off concentrate from the piggy back pan and adding the drawnoff concentrate to the flue pan, and means for drawing off concentrate from the flue pan and wherein, the capacity of the blower, the number and size of the holes within said sparging tubes, the size of said at least one steam exhaust chimney and the vertical length of said at least one chimney are such that the steam from the flue pan is caused to condense on the bottom wall of the piggy back pan to effectively boil off the sap within the piggy back pan, and nearly all of the steam resulting from boiling off water content of the sap within the flue pan condenses on the undersurface of the piggy back pan due to the application of sparging air flow via said blower, said plenum chamber and said sparging tubes to the surface of the upper side of the piggy back pan, scouring the metal surfaces of the troughs within the piggy back pan bottom wall and creating an effective frothing action with the sap to form a sap and air mixture whereby the air in passing through the sap is effectively heated and saturated with moisture with the resulting evaporation of the moisture captured by the air consuming a large quantity of heat to maintain the temperature differential between the sap and air mixture and the condensing steam under the piggy back pan at a level to insure that almost all of the steam is condensed in the area between the drip pan and the piggy back pan to increase liquid concentration of the sap processed thereby.