A number of manufacturers now make stoves which will burn shelled corn.
Although similar to wood stoves, these new corn burning stoves have been specifically
designed to burn a dry granular fuel, such as shelled corn. Corn burning
stoves & burners have a combustion air fan and a fuel stoker, both of which
are not common in standard wood stove construction.
Why burn corn?
In Ontario we have an abundant source of dry shelled corn. The corn used as a fuel in corn stoves does not have to be Grade No. 1, but can be of
lower quality. There are however two requirements of this corn fuel:
- The shelled corn must be dry, preferably 15% moisture content or
less. Corn which is higher in moisture will have a lower heat value
per unit weight than "dry" corn. Moist corn may also cause
flow problems through the fuel loading auger.
- The shelled corn must be free of fines. Dirty corn which has a lot
of fines and cob pieces will cause problems with the fuel loading
auger.
The storage, moving and handling of grain corn has evolved to a point
where there are very few unknowns. Every year farmers harvest, dry,
convey, and store millions of bushels of corn. The equipment to do all
these things is readily available. Consequently putting a corn storage
system together for a home heating set up is possible with augers,
conveyors and storage bins which are readily available.
Two reasons it is so attractive as a heat source are that dry shelled
corn is so easily handled and in plentiful supply. Shelled corn also has a
high heat energy per unit weight. Here's how shelled corn measures up to
other solid fuels.
Table 1. Heat Energy of On-Farm Fuel Sources
|
Shelled Corn |
7000 BTU/lb (16,200 kJ/kg) at 15% Moisture Content |
|
Straw |
6550 BTU/lb (15,200 kJ/kg) Air Dried |
|
Corn St over |
7540 BTU/lb (17,500 kJ/kg) Air Dried |
|
Wood |
8000 BTU/lb (18,500 kJ/kg) Air Dried |
You can see from this table that shelled corn has heat energy close to that of wood.
Basics of Corn Stoves & Burners
Corn burning stoves are specifically designed to burn a granular fuel. Because
this fuel is metered into the burning chamber, most stoves have a storage
hopper to contain a supply of fuel. In some ways corn burning stoves are
very similar to pellet burning stoves. In both cases, corn and pellets are
very dense. Consequently, neither of these fuels will burn readily in an
open pile in a fire chamber.To get these fuels to burn, some manufacturers use a small combustion chamber into which the corn is fed and combustion air is pumped through.
The corn can be either dribbled into this combustion chamber from above,
or it can be stoked into the chamber from below by means of an auger. The
feed rate of this auger can be adjusted to regulate the amount of corn
burned, which in turn controls the amount of heat produced. The second
requirement for burning to occur is oxygen. In order to support
combustion, oxygen is blown into the combustion chamber by means of a
small fan. The combustion air is usually brought in from outside, not room
air. This combustion chamber is actually quite small and could easily fit
into a child's lunch box.As corn burns it produces a clinker. Because of the small size of the
combustion chamber the clinker should be removed daily. With practice, the
removal of the clinker can be done without having to shut down and then
relight the stove. A specially designed poker is used to upend the
clinker, then tongs are used to remove it.
Inside the corn stove, a heat exchanger is used to remove heat from the flue
gases and heat the room air. A fan is used to move the room air through
the stove where it is warmed. This fan may also help in moving the heat
further away from the stove.
A different style of corn stove also exists which does not use augers to
feed in the corn or fans to provide combustion air or move heated air to
the room. By careful design, these stoves will burn corn at the bottom of
a hopper and radiate heat to the surrounding room. Unlike the previous
type where electricity is used to stoke the fire and move the heat to the
room, these stoves are not affected by electrical power outages.The type of flue pipe required to vent the exhaust gases from the stove
will depend on the design of the stove or corn burning appliance. These
flue pipes can range from those commonly used in wood stoves to
through-the-wall vent pipes which actually preheat the combustion air by
removing heat from the flue gases. Follow the manufacturer's
recommendations regarding the type of flue pipe required. It is best to
keep the flue pipe as short and straight as possible (keep the number of
elbows to a minimum) to maximize the stove's performance.
Types of Corn Stoves
A number of different manufactures are presently making corn burning
stoves. They are available in a variety of sizes and styles. Here are some
of the configurations available:
- Stove (some can be modified as a fireplace insert)
- Space heater
- Hot air furnace
- Hot water boiler
The size of fuel hoppers also varies greatly. This hopper size can
range from holding one day to ten days supply of fuel.One thing to consider with the freestanding stove or space heaters is
the surface temperature of exposed metal parts. This is especially
important if there are small children in the house.
Cost of Heating with Corn
Before you can accurately compare heating with corn to other heating
fuels you have to look at a number of factors. Not only is price of the
fuel important, but also the heating efficiency of the heating system and
the energy content of a unit of each fuel.
Here is a formula which you can use to calculate your cost per Million
BTU's of useable energy. This formula takes into account all these
factors:
- Cost per unit of fuel
- Energy content per unit of fuel
- Seasonal heating efficiency
Cost per Million BTU's of useable energy =
(Cost Per Unit Of Fuel x 1,000,000) ÷ (Energy Content Per Unit Of Fuel
(BTU) x Seasonal Heating Efficiency)
Where: Cost per unit of fuel is in Dollars Energy Content Per Unit of
Fuel in BTU's Seasonal Heating Efficiency is in decimal form ie (70% =
0.7)
Example: Lets look at an example where you are using corn at $2.50 per
bushel in a stove which has a seasonal heating efficiency of 60%. What is
the cost per million BTU's of useable energy?
Corn Cost = $2.50 per bushel
Energy content per bushel = 7000 BTU/lb x 56 lb/bu. = 392,000 BTU
Seasonal Heating Efficiency = 60% = .6
Dollars per Million BTU's Useable Energy =
(Cost per unit of fuel ($) x 1,000,000) ÷ (Energy Content Per Unit Of
Fuel (BTU) x Seasonal Heating Efficiency)
=($2.50 x 1,000,000) ÷ (392,000 x .6)
= $10.63
Therefore to supply one million BTU's of heat to the house costs $10.63
when this stove operates at 60% efficiency, burning corn at $2.50 per
bushel. The average older home requires approximately 100 million BTU's of
useable energy per year. When you do the calculations for your situation,
keep in mind that the price charged per bushel of corn may vary from the
market price when small quantities are purchased. Check the prices
carefully before doing these calculations.
Table 2. Heat Content and Heating Efficiency of Various Fuels
|
Fuel Type |
Energy Content per Unit |
Seasonal Heating Efficiency |
|
Shelled Corn |
7000 BTU/lb. (16,200 kJ/kg) |
70% - 85% |
|
56 lb./Bushel |
392,000 BTU/56 Pound Bushel |
|
|
48 lb./Bushel |
336,000 BTU/48 Pound Bushel |
|
|
Furnace Oil |
36,700 BTU/L (38,700 kJ/L) |
70% - 85% |
|
Propane |
25,300 BTU/L (26,900 kJ/L) |
70% - 85% |
|
Natural Gas |
35,700 BTU/M3 (37,700 kJ/M3) |
70% - 85% |
|
Electricity-Resistance |
3413 BTU/KWh (3600 kJ/kwh) |
100% |
|
Air Source Heat Pump |
C.O.P. = 2.75 |
275% |
|
Water Source H.P. |
C.O.P. = 4.0 |
400% |
|
Wood |
8000 BTU/lb. (18,500 kJ/kg) |
60% |
Limitations of Burning Corn for Heat
Possibly the first and most important limitation of corn as a fuel is
the stove itself. If the stove uses augers to feed the corn into the
combustion chamber and fans to maintain combustion and move heated air to
the room then an electrical power interruption will shut the stove down.
Very simply with this style of stove, no electrical power means no heat
from your corn stove. Some stoves require a manual reset after a power
interruption, as a safety feature. Second, since most house layouts do not allow the free movement of air
through the house, a centrally located stove will not heat the whole
house. If this is your case, size the stove to heat the room where the
stove is located. Oversizing the stove will result in the room housing the
stove becoming unbearably hot.
Corn Stove Buying Criteria
When purchasing a corn stove there are some questions which you should
answer:
- (What is the heat output of the stove? Do you know how much heat you
require to maintain the heated space at the desired temperature?
If you are trying to heat your whole house with a stove or space
heater, does the house layout allow for the convective movement of
heat through the whole house? Most newer houses are not built to allow
convective air movement.
What is the size of the fuel hopper? Will it require filling on a
daily, weekly or biweekly schedule?
What is the seasonal heating efficiency of the corn stove?
Does the unit meet UL and CSA standards?
Does the unit have hot exposed surfaces which could cause burns to
skin?
What type of exhaust venting is required? Does it require a chimney
with a flue liner or can a combination flue/fresh air vent pipe be
used?
Are you prepared to clean out the clinker daily and clean the heat
exchanger of ash on a weekly basis?
Will the stove handle granular solid fuels other than shelled corn?
This is important in the event that the economics of burning corn
become unattractive or an alternative low cost pelleted fuel becomes
available.
Will this corn burning appliance be a primary heat source or act as
a supplementary heat source? Stoves with small fuel hoppers will not
keep a house warm for long periods of time, unattended.
- How will corn be stored for winter operation?
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