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Tobacco: Tobacco Barn Retrofit

Fuel Cost and Consumption

Adapted from comments made by Dr. Mike Boyette, NCSU:

The relative benefits (cost or otherwise) of fuel oil vs LP or natural gas in curing barns is a concern of all growers. There is no simple answer to this question except maybe, "it depends".

LP gas is a by-product of the natural gas industry and consists primarily of propane and butane. It contains approximately 90,500 Btu per gallon. Under moderate pressure (60-70 psi) LP gas is a liquid at room temperature.

No. 2 fuel oil (i.e. diesel fuel) contains approximately 138,000 Btu per gallon. It is produced by the refining of crude oil and in terms of volume produced, is second only to gasoline.

A gallon of fuel oil contains: (138,000/90,500) = 1.52 times as much energy as a gallon of LP gas. Another way of stating this is; if a gallon of LP sells for $1.00, then a grower could pay $1.52 per gallon for fuel oil to get the same $/Btu.

The cost per gallon of both LP and fuel oil fluctuates from season to season and year to year. Because they may be freely substituted in many applications, they do, however, tend to track each other and remain at parity most of the time. Locally, you may be able to find LP cheaper than fuel oil (on a $/Btu basis) this year but next year it may be opposite. Year in and year out, there is probably little advantage of one over the other. The best prices for either type of fuel are to be had by contract buying in bulk lots.

In theory, the combustion efficiency of LP and fuel oil should be the same. In practice, LP tends to be slightly better because LP gas and air mix better during combustion than fuel oil and air.

The bottom line is that in the long run, there is little difference in the use of oil vs gas. Most growers that were using LP will probably continue as will most growers that were using fuel oil.

The following table list a comparison of fuel cost.

LP Gas

Fuel #2

Natural Gas

($/Gallon)

($/Gallon)

($/Therm)

0.50
0.76
0.55
0.55
0.84
0.61
0.60
0.91
0.66
0.65
0.99
0.72
0.70
1.07
0.77
0.75
1.14
0.83
0.80
1.22
0.88
0.85
1.30
0.94
0.90
1.37
0.99
0.95
1.45
1.05
1.00
1.52
1.10
1.05
1.60
1.16
1.10
1.68
1.22
1.15
1.75
1.27
1.20
1.83
1.33
1.25
1.91
1.38
1.30
1.98
1.44
1.35
2.06
1.49
1.40
2.13
1.55
1.45
2.21
1.60
1.50
2.29
1.66
1.55
2.36
1.71
1.60
2.44
1.77
1.65
2.52
1.82
1.70
2.59
1.88
1.75
2.67
1.93
1.80
2.74
1.99
1.85
2.82
2.04
1.90
2.90
2.10
1.95
2.97
2.15
2.00
3.05
2.21
2.05
3.13
2.27
2.10
3.20
2.32
2.15
3.28
2.38
2.20
3.35
2.43
2.25
3.43
2.49
2.30
3.51
2.54
2.35
3.58
2.60
2.40
3.66
2.65
2.45
3.74
2.71
2.50
3.81
2.76
2.55
3.89
2.82
2.60
3.96
2.87
2.65
4.04
2.93
2.70
4.12
2.98
2.75
4.19
3.04
2.80
4.27
3.09
2.85
4.35
3.15
2.90
4.42
3.20
2.95
4.50
3.26
3.00
4.57
3.31
 

Consumption

Will your fuel consumption increase with the installation of a heat exchanger? The answer depends. It will be more if both direct fired and heat exchanger burners were operating at their maximum efficiency. But it may be the same if the burner used in the direct fire was operating at low efficiency and the new heat exchanger has been tested to operate at maximum efficiency.

You will here reports of heat exchangers installed in bulk tobacco barns burning the same or less LP gas than before the retrofit was installed. This is because of burner efficiency.

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