MAPLE SIRUP PRODUCERS MANUAL 



63 



pan only and should be installed ahead of and 

 in series with the complete evaporator (see 

 chart 13). The supplemental flue pan arches are 

 constructed in exactly the same manner as the 

 one for the complete evaporator. To connect the 

 supplemental flue pans in series with the evap- 

 orator requires only one point at which the raw 

 sap is fed and one point at which the partly 

 evaporated sap or sirup is removed for transfer 

 to the finishing pan or bottling tank. In the 

 multiple unit assembly, the flat pan of the 

 evaporator continues to serve as the semifinish- 

 ing or finishing pan (fig. 90). 



Efficiency af Heat 



A study of the use of oil as fuel for the 

 evaporation of maple sap in an open evaporator 



was reported by Phillips and Homiller (87). 

 They showed that commercial maple sap evapo- 

 rators fired with oil haye an efficiency of 66 to 

 74 percent. Their data were obtained with a 

 smaller-than-average evaporator; larger evapo- 

 rators would be expected to be slightly more 

 efficient. The efficiency of the open pan evapo- 

 rator compares favorably with commercial 

 steam generating plants, for which a combus- 

 tion efficiency of 80 percent is considered good. 

 The efficiencies obtained by Strolle and oth- 

 ers (111) in evaporating 45 to 55 gallons of 3°- 

 Brix sap to standard-density sirup are given in 

 table 6. These data indicate that efficiency de- 

 creases as the rate of sap feed (gallons of sap 

 evaporated per hour) increases and that oil cost 

 per hour also increases. However, from further 



Figure 90.— In one of the most economical and efficient types of evaporators, an oil fire and four fine pans are used for 

 evaporation; high-pressure steam is used for the last stage of evaporation. 



