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Saving Fuel in Corn Drying
Bill Wilcke,
Minnesota Extension Engineer
The combination of low corn prices and high fuel prices
makes it especially important to consider ways to save fuel
while drying corn this fall. Prices for both liquefied
petroleum gas (LPG; mostly propane) and natural gas are
expected to be higher this fall than in the past. Typical
heated-air corn dryers fueled by LPG use about 0.02 gallons
of LPG per bushel per percentage point of moisture removed.
This means that every point of moisture removal that can be
avoided in these dryers will save about 0.02 gallons of LPG
per bushel of corn harvested.
Here are some possible approaches for reducing fuel use
in corn drying:
- Harvest whole-plant corn silage or high-moisture
ear corn instead of shelled grain that must be dried.
Farmers who raise ruminant animals might consider
altering their rations and feeding more silage or ground
ear corn. Farmers who don’t have the necessary
harvesting equipment might be able to hire custom
harvesters. Farmers who don’t have storage
facilities for these crops might be able to use silage
bags or temporary bunkers.
- Store ensiled high-moisture corn. Instead of
artificially drying shelled corn, livestock producers who
can feed high-moisture corn might consider storing some
of their crop in silos or in silage bags as ensiled or
fermented, high-moisture corn. The naturally occurring
bacteria that cause fermentation need high moisture
levels to become active, so corn should be harvested at
25 to 30% moisture. One of the most common problems that
occurs during storage of high-moisture corn is that corn
dries to less than 25% moisture in the field before the
silo is full. Corn stored at less than 25% moisture is
often too dry for bacteria to cause fermentation, but
it’s at an ideal moisture for fungi to cause mold
damage. If you plan to store high-moisture corn, start
harvest early and make sure the silo is full before the
corn gets too dry. Attempts to rewet shelled corn that is
too dry to ensile are usually unsuccessful.
- Delay harvest to take advantage of drying in the
field. But only consider this option if it’s
early in the season, you have good drying weather, and
you don’t have disease or insect problems that are
causing stalks to lodge or ears to drop. Harvesting corn
at lower moisture means less water must be removed. For
corn that will be fed during winter, livestock producers
who delay harvest until temperatures drop to near
freezing might be able to avoid drying altogether. If
corn can be aerated in storage to keep its temperature
near 30°F, it can be safely stored at up to 18%
moisture or so through the winter months. But wet corn
must be fed or dried by spring! If there’s any
chance that corn will be stored into warm weather the
following spring and summer, make sure that its moisture
is 15% or less when it is stored.
- Reduce overdrying. Corn buyers usually prefer
corn at 14 to 15% moisture, and with proper storage
management, corn can be safely stored for six to nine
months at these moisture levels. Although some stored
grain managers intentionally dry corn to lower moisture
levels to reduce storage risk, this is an expensive
strategy. Overdrying increases drying costs (especially
when fuel costs are high), it reduces dryer capacity (the
number of bushels that can be dried per day), and it
reduces the number of bushels that are available for sale
(because grain is sold by weight, and you are removing
water that could be sold at the price of corn). Overdried
corn is also more susceptible to cracking and breaking
during handling.
- Switch to in-storage cooling. If corn is
currently dried at high temperatures and then rapidly
cooled in the dryer, some fuel can be saved by switching
to cooling corn in the storage bin instead of in the
dryer. Almost no moisture is lost when freshly dried corn
kernels are rapidly cooled immediately after drying. But,
if corn is unloaded from a dryer while it is still hot
and is transferred to storage where it is cooled slowly
using the storage bin’s aeration fan, the corn will
lose one to two percentage points of moisture during the
cooling process. This means that if the final target
moisture is 15%, the dryer can be unloaded when the corn
reaches 16 to 17% moisture instead of drying it all the
way to 15% moisture. In-storage cooling saves the fuel
that would be needed to remove the last one to two points
of moisture and it reduces the amount of time that corn
spends in the dryer, which greatly increases dryer
capacity. For more information, contact the University of
Minnesota Biosystems and Agricultural Engineering
Department and ask for the bulletin Dryeration and
In-Storage Cooling for Corn Drying.
- Use dryeration. Dryeration is similar to
in-storage cooling, except that corn is intentionally
left hot (called steeping or tempering) for 4 to 12
hours. During this tempering period, moisture and
temperature gradients equalize within freshly dried
kernels, which enables the kernels to lose two to three
percentage points of moisture during cooling. Compared to
rapidly cooling corn in the dryer, dryeration reduces
energy use, increases dryer capacity, and improves corn
quality (better test weight and fewer cracked kernels).
It is best to transfer corn from the bin where cooling
takes place to a different storage bin after it goes
through the dryeration process to avoid problems that
might be caused by condensation on the inside walls of
the cooling bin. For more information, contact the
University of Minnesota Biosystems and Agricultural
Engineering Department and ask for the bulletin
Dryeration and In-Storage Cooling for Corn
Drying.
- Consider using natural-air drying instead of
heated-air drying. Natural-air drying is an in-storage
drying process that uses bins equipped with full
perforated drying floors and fairly large fans
(approximately 0.75 to 1.0 fan horsepower per 1000
bushels of corn for bins that are no deeper than about 18
ft). Natural-air drying works well in the upper Midwest,
but harvest must be delayed until corn moisture drops to
about 22% moisture in the field and drying requires
several weeks of fan operation. In many years, drying is
not completed before winter and corn is kept cold during
winter and drying is finished in early spring. Although
natural-air drying uses no LPG or natural gas, it does
use an average of about 1 kWh of electricity per bushel
of corn to operate the drying fan. Cost effectiveness of
natural-air drying compared to heated-air drying depends
on the relative costs of LPG or natural gas and
electricity and on how favorable the weather is during
the drying season. For more information, see the
University of Minnesota Extension Service bulletin
Natural-Air Corn Drying in the Upper Midwest,
BU-6577.
- Use combination drying. If you do not like
some of the limitations of natural-air drying, you can
partially dry corn to about 20% moisture in a heated-air
dryer and then finish drying it in a bin equipped for
natural-air drying. Combination drying allows you to
harvest corn earlier than you can with just natural-air
drying, but it uses less fuel and produces better corn
quality than complete heated-air drying. For more
information, contact the University of Minnesota
Biosystems and Agricultural Engineering Department and
ask for the bulletin Combination High-Speed,
Natural-Air Corn Drying.
- What about alternative energy sources?
Solar. Quite a bit of solar grain drying research
was conducted about 20 years ago. Because solar energy is a
fairly diffuse source of energy (not many British Thermal
Units or Btus of energy are available per square foot of
surface area per day), it is not a good replacement or
supplement for the fuel used in high-speed, heated-air
dryers. These types of dryers use millions of Btus per hour
and it would take very large solar collectors to replace the
LPG or natural gas needed to produce this amount of energy.
Solar energy could be used as a supplemental heat source for
low-temperature, in-storage drying systems that operate over
a period of several weeks. But, research has shown that
these types of dryers actually work fairly well without any
supplemental heat. In fact, there are some disadvantages to
adding supplemental heat--including potential overdrying of
the crop and the cost of building and maintaining the solar
collectors.
Biomass. Some research on using biomass fuels such
as wood, hay, and crop residues for drying corn was also
conducted about 20 years ago. Use of biomass fuels showed
some promise, but energy prices stabilized and research
funds dried up before the equipment and systems for using
biomass were fully developed. Biomass fuels are attractive
because they are renewable, some biomass fuels are fairly
energy dense (significant number of Btus produced per pound
of fuel), and producing biomass fuels might reduce farmer
dependence on fluctuating energy prices and supplies or even
present the opportunity for farmers to sell fuel. Here are
some questions to consider if you are interested in using
biomass fuels to dry corn:
- Can biomass be harvested ahead of corn harvest, or
will time and labor for harvesting fuel compete with time
and labor for harvesting corn?
- What is the expected moisture content of the biomass
fuel, and will you need to dry it before you burn it? The
higher the fuel moisture content, the lower the net
energy production per wet pound of fuel.
- Is special equipment and facilities needed to
harvest, transport, and store the biomass fuel or can you
adapt equipment and facilities that you already own? If
you have to buy special equipment, don’t forget to
include the cost of that equipment in your cost per Btu
calculations.
- How hard is the fuel to handle? Does the fuel flow on
its own and can the fuel supply system be automated, or
will a lot of labor be required to keep the burner
supplied with fuel? For example, it might be relatively
easy to set up an automatic fuel supply system for a fuel
in pellet or granular form, but it would be more
difficult to set up an automatic system that uses logs or
large bales.
- Can you buy a burner that will handle the fuel you
have in mind and that will supply the number of Btus per
hour that are needed? Several companies produce small
biomass burners, but not many companies produce the
larger sizes needed for heated-air corn dryers. If you
decide to build your own burner, keep in mind that it can
be difficult to come up with a design that provides the
right amount of air for complete combustion, is easy to
feed, can withstand high temperatures for long periods of
time, and provides for convenient removal of ash,
clinkers, or slag.
- Will removal of biomass from the land reduce soil
quality and make it vulnerable to erosion? For example,
using all the cobs from a crop of corn might not have a
very large effect on the soil, but removing all of the
corn stalks would.
- Is there a positive net energy balance for using the
biomass fuel? When you subtract all the energy required
to grow, harvest, and transport the biomass fuel from the
energy produced by burning it, how much are you
gaining?
- Is the biomass material that you are considering more
valuable as food, feed, or an industrial feed stock than
it is as a heating fuel?
- Is use of the biomass fuel cost effective? When you
add up the costs for equipment, labor, and other inputs
for producing, harvesting, transporting, storing, and
burning the biomass product, is the cost per Btu
competitive with other alternatives?
For more information on any of these topics, contact Bill
Wilcke in the University of Minnesota Biosystems and
Agricultural Engineering Department in St. Paul, Minnesota
(wilck001@umn.edu or
612-625-8205).
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