MAPLE SIRUP PRODUCERS MANUAL 



59 



gallon is more than double the cost of wood at 

 $25 per cord, but the operational costs may not 

 differ greatly since oil does not require the 

 services of a fireman. 



The disadvantages of using oil as the fuel 

 source, while few, are nevertheless important: 

 (1) The initial cost (capital investment) of oil 

 burners is high; (2) oil burners require a special 

 arch (firebox) although in a new installation it 

 is not necessarily more expensive than the 

 conventional wood-burning arch; and (3) oil 

 does not make use of the cull trees that must be 

 removed each year from a well-managed sugar 

 bush. 



When oil is used as fuel, two pertinent facts 

 must be observed. The first and most important 

 is that wood and oil burn in different ways. 

 Wood burns with a luminous flame (long fire 

 path) throughout the length of the evaporator, 

 including the area under the flue pans as well 

 as under the sirup pan; oil, on the other hand, 

 burns as a ball of flame in only a relatively 

 small space. Secondly, of the two forms of heat 

 transfers — radiant and convection — used in a 

 sap evaporator, radiant heat accounts for ap- 

 proximately 80 percent of the heat transfeiTed 

 to the liquid, whereas convection heat (that 

 which is derived from the hot flue gases passing 

 over the surface of the pans and flues) supplies 

 approximately 20 percent. Therefore, to make 

 use of the radiant heat from the oil fire, the ball 

 of burning oil must illuminate the entire under- 

 surface of the pans. This necessitates properly 

 positioning the ball of burning oil and eliminat- 

 ing any obstructions that will prevent illumina- 

 tion of the entire undersurface of the pans. This 

 requirement will be met only through the 

 proper design of arches made for the burning of 

 oil as fuel. 



A wood-burning arch cannot be successfully 

 converted to an oil-burning arch without major 

 changes. The principal fault of such a conver- 

 sion is that the slope of the wood-burning arch 

 behind the firebox does not permit illumination 

 of the entire underside of the sap or flue pan by 

 the ball of burning oil and, consequently, the 

 sap will not boil. 



Size of Burner 



The size of burner to use is determined by 

 two factors: (1) The length and width of the 



evaporator (the vertical area of the flues has a 

 minor effect) and (2) the quantity of sap to be 

 evaporated per hour. If the rated capacity of 

 the evaporator in gallons of sap per hour is 

 known, it can be divided by 13 (the approximate 

 number of gallons of water evaporated per hour 

 by 1 gallon of oil) to obtain the size of burner 

 (g.p.h. = gallons of oil per hour) required for a 

 specific evaporator. 



The rated capacity of an evaporator burning 

 wood cannot be accurately equated to that of 

 an evaporator burning oil. Therefore, this 

 method of calculation may indicate a burner 

 that is too large. However, this is not serious 

 since the amount of oil burned per hour can be 

 changed, within limits, by changing the size of 

 the nozzles. 



To prevent damaging the pan by firing with 

 an oversize burner, it is recommended that for 

 the first trials a nozzle size 20 percent smaller 

 than indicated by the above calculation be used. 

 The burning rate (nozzle size) can then be 

 increased as needed. An empirical method for 

 determining nozzle size is to divide the surface 

 area (length times width) by .5. Thus, a 5- by 12- 

 foot evaporator would require an oil burner 

 nozzle of 12 g.p.h. 



Tyite of Burner 



With few exceptions, high-pressure oil burn- 

 ers that use No. 2 oil are recommended. They 

 are available with different nozzle sizes to fit 

 evaporators of all sizes. Their lower initial cost 

 offsets any advantage gained by using burners 

 that require the heavier grades of oil. 



Muniber of Burners per Arch 



Only one burner is required for each evapora- 

 tor (fig. 88). It must be correctly positioned 

 under the evaporator and the combustion 

 chamber must meet certain minimum stand- 

 ards. Use of a single burner reduces the capital 

 investment and installation costs. For example, 

 the capital investment and installation costs for 

 an evaporator requiring 12 gallons of fuel per 

 hour supplied by a single burner would be 

 approximately half that for an evaporator sup- 

 plied by two 6-gallon-pei--hour burners. In addi- 

 tion, the two smaller burners will require more 

 servicing and attention than will the larger 

 one. 



