64 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



FLOW DIAGRAM 

 OF MULTIPLE UNIT EVAPORATOR 



OIL 

 FIRED 



FINISHING PAN 

 (GAS FIRED) 



TO 

 POLISHING FILTER 

 AND CANNING TANK 



Chart 13. — Flow diagram of multiple-unit evaporator. 



calculations and rough extrajX)lations the data 

 in table 7 were obtained. 



These data show that sirup production in- 

 creases as the amount of fuel burned increases. 

 The increase in cost of fuel per gallon of sirup is 

 slight and is more than compensated for by the 

 improvement in the gi-ade of the sirup and the 

 reduction in evaporation time and cost of labor. 



Table 6. — Efficiency of oil-fired experimental 

 evaporator in evaporating sap of 3° Brix to 

 standard-density sirup 



Sap evaporated per 

 hour (gallons) 



Oil burned per 

 hour 



Efficiency 



45 

 50 

 55 



Gallons 

 3.9 



4.7 

 5.3 



Percent 

 74 

 69 

 66 



Table 7. — Extrapolated efficiency of oil-fired 

 evaporator 



Sap evapo 

 rated per 



hour 

 (gallons) 



Cost of 

 Oil Sirup oil per 



burned made gallon of 

 per hour per hour sirup 

 produced 



Time re- 

 quired to 

 evapo- 

 rate 550 

 gallons 

 of sap 



Effi- 

 ciency 



Galloyis Gallons Dollars Hoiirs Percent 



65 6.7 



60 6.0 



55 5.3 



50 4.7 



45 3.9 



2.36 1.00 8.5 59.6 



2.18 .96 9.2 62.6 



2.00 .93 10.0 66 



1.82 .91 11.0 69 



1.64 .84 12.2 74 



The maximum efficiency that could theoret- 

 ically be obtained from an oil-fired evaporator 

 would utilize all the British thermal units 

 (B.t.u.'s) of a gallon of oil. This heat would raise 

 the temperature of the feed sap to its boiling 

 point and then vaporize the water in the sap to 

 steam. Assuming that the temperature of the 

 sap is 35° F. and its boiling point is 210°, the 

 heat (B.t.u.'s) required to evaporate 34.4 gallons 

 of sap with a density of 2.5° Brix to yield 1 

 gallon of standard-density sirup can be calcu- 

 lated. Knowing the B.t.u.'s of No. 2 fuel oil 

 (139,000), the number of gallons of oil required 

 to produce this gallon of sirup at maximum 

 efficiency is 2.2 gallons. Since no oil burner is 

 100-percent efficient, and oil-fired evaporators 

 are only 60- to 75-percent efficient, the fuel 

 required per gallon of sirup is 3+ gallons of oil. 



To measure the efficiency of burners, arches, 

 and evaporators, a number of factors must be 

 carefully obtained. These are: 



