| HEAT
ENERGY CONTENT OF SHELLED CORN |
The energy content of shelled corn is not a constant value because of
biological variability and management factors. Generally the energy content
of corn is in the range of 8,000 to 8,500 BTU per pound of dry matter.
A BTU (British Thermal Unit) is a unit measure of energy. One BTU is the
amount of heat energy needed to heat one pound of water one degree Fahrenheit.
The factors that may influence the energy content of corn include variety
of corn, soil fertility, weather conditions during growing season and
at harvest, stage of maturity at harvest, drying method, and storage conditions.
It needs to be emphasized that the energy content of shelled corn is in
the range of 8,000 to 8,500 BTU per pound of dry matter, based on bomb
calorimeter studies. The term "dry matter" refers to material
that is "bone dry." The standard moisture content of shelled
corn is 15.5 % moisture on a wet basis. This means that each pound of
shelled corn will actually consist of 0.845 pound of dry matter and 0.155
pound of water. Using a median energy content value of 8,250 BTU per pound
of dry matter, the energy content of one pound of shelled corn at 15.5%
moisture is then 6,971 BTU (8,250 BTU per pound dry matter x 0.845). The
figure of 6,970 BTU per pound is referred to as the Higher Heating Value
(HHV).
The HHV needs to be further reduced because of the energy required to
vaporize the 0.155 pound of water in the shelled corn, since this energy
is unavailable for heating purposes. The energy to evaporate the water
is approximately 163 BTU (1,050 BTU per pound water x 0.155 pound). The
net available energy content of a pound of shelled corn with a moisture
content of 15.5 % is then 6,810 BTU. This value of 6,810 BTU per pound
of shelled corn is known as the Lower Heating Value (LHV), a reduction
of nearly 17.5 % when the moisture content is taken into account. The
actual energy content of shelled corn would be even lower if pieces of
cob, husk, or stalks are mixed in with the shelled corn.
The tradition in the United States is to compare the thermal energy content
of various fuels on the basis of HHV whereas in Europe the standard practice
is to use the LHV. In the Energy Selectors at this web site, the energy
content for shelled corn is assumed to be of 6,970 BTU per pound of shelled
corn for all the analysis, along with an assumed overall seasonal thermal
efficiency of 75%. Whenever reviewing commercial literature, be especially
cautious of the recommendations and conclusions if the analyses are based
on an energy content of the corn higher than 7,500 BTU per pound of shelled
corn and/or an overall thermal efficiency of 80% or higher.
Unfortunately, some manufacturers of corn stoves use the energy content
figures of 8,000 to 8,500 BTU per pound as though these figures were the
energy content of the actual shelled corn itself. They frequently multiply
energy content by the number of pounds in a bushel (56 pounds) and then
report an energy content of 448,000 to 476,000 BTU per bushel of shelled
corn. I have seen figures as high as 10,000 BTU per pound or 560,000 BTU
per bushel used in some analyses. Whenever these exaggerated energy contents
are used in any analysis, there will be considerable distortion in the
results. |
