Grain Drying (cont.)
Heaters, Costs, Safety and Managing Stored
Grain
 Selecting
a Heater
Drying System Cost
Grain Handling
Systems
Safety Considerations
Managing Stored
Grain
Other Drying and Storage
Information Available
Introduction
Drying Advantages and
Disadvantages
Recommended Storage Moisture Contents and
Estimated Allowable Storage times
Influence of Drying Conditions
Types of Dryers and Drying
Natural
Air/Low Temperature Drying
Layer Drying
High Temperature Bin Drying
Column Dryers
Combination Drying
Dryeration and In Storage Cooling
Energy, Quality, Fire, Moisture and Fans
Energy
Efficiency
Selecting a Drying System
Maintaining Quality During Drying
Drying Fire Hazard
Moisture Determination
Moisture Shrink
Selecting Fans
The amount of heat required to heat the drying air can be determined from the equation:
BTU/hr = cfm x 1.10 x temperature increase desired. If we want to increase the temperature
of 4364 cfm of air from the preceding example 10F, we would need a heater capable of
delivering about 48,004 BTU/hr (4364 x 1.10 x 10).
1 gallon propane = 88,000 BTU
1 KWH = 3413 BTU/hr
Approximately 30 percent of the energy is lost in a heat exchanger dryer where the
combustion gases and heated air heat an exchanger that heats the drying air. Approximately
10 percent of the energy is lost in a direct-fired dryer where the combustion gases go
through the grain being dried. All the energy enters the grain as heat from an electric
heating element.
The calculated heat requirement needs to be adjusted based on the heating efficiency.
The actual heat requirement for a direct fired dryer would be about 1.10 x the calculated
value. For the preceding example, the heat needed considering the 10 percent heat loss
would be 48,004 x 1.10 = 52,804 BTU/hr.
In a natural air drying system, the heat requirement comes from the air and to a
limited extent from the energy supplied by the fan motor if the air passes over the motor.
With a heated air system, the heat can be supplied from an electric heater, a LP gas
burner, a fuel oil burner, from coal or wood, burning crop residue, or a solar collector.
The LP gas burner and electric heater are the most common types.
Research on solar heating for grain drying has been primarily on low temperature
systems to minimize the cost of the collector. To dry 1000 pounds of sunflower from 18
percent to 8 percent in one hour requires the removal of about 109 pounds of water. Using
3000 BTU/pound of water removed, a typical energy requirement for a high temperature
continuous flow dryer, means that 327,000 BTUs of energy must be supplied. A solar
collector with an area of at least 3,800 square feet, 5 x 760 ft., would be required to
provide the heat. The maximum solar energy reaching the earth's surface at solar noon
during the harvest season is about 290 BTU/hr per square foot of solar collector. Since
solar collectors are only about 30 percent efficient when heating air 100F, only 87 BTU/hr
per square foot are captured. At solar noon, 327,000 BTU/hr � 87 BTU/hr – sq. foot =
3759 square feet of collector is required. Less heat would be collected at other times
because the solar energy reaching the collector decreases to zero at sunset. With a low
temperature drying system, a much smaller collector can be used since the heating needs
are spread over a much longer time period.
Information on solar collector and grain drying systems are available in Midwest Plan
Service Handbook MWPS-22, "Low Temperature and Solar Grain Drying."
Biomass burners are another option. A pound of dry crop residue or wood contains about
7,000 BTUs of heat. Generally a biomass dryer will use a heat exchanger with an efficiency
of about 70 percent. Therefore, to provide the heat for the preceding example using a
biomass type dryer would require about 67 pounds of dry crop residue or wood per hour,
327,000 � 0.70 � 7000 = 66.7.
The cost of drying systems fluctuate with dryer, energy and other prices so actual
values will not be given. Generally, the less supplemental heat required, the less
expensive the system will be. However, the speed of drying will be slower. Several items
must be considered to calculate the cost of a drying system. These would include ownership
costs such as interest, depreciation and insurance, and operating expenses such as fuel
and electricity. The labor required and the amount of grain to be dried are also important
factors to consider. For more information request the NDSU Extension Circular AE-923
Calculating Grain Drying Cost.
The addition of grain drying to a farm operation will normally increase the grain
handling required. Increased handling makes hopper type storage structures and good
handling equipment more important.
Handling the grain can be done by portable equipment, permanent equipment or a
combination. When using portable conveyors, circular bin arrangements are satisfactory,
enabling one conveyor to reach all the bins from the center of the bin circle. However, if
permanently installed handling equipment is planned, a straight-line arrangement is more
suitable. Straight-line bin arrangements lend themselves more readily to drive through
unloading facilities, ease of expansion, and efficient use of permanently installed
loading and unloading equipment.
In planning, it is necessary to consider the grain flow pattern. This needs to include
the time factor as well as where the grain goes. For example, when using a portable batch
or continuous flow dryer, both wet and dried grain holding bins are necessary to enable
efficient use of the dryer. Generally speaking, the continuous flow drying process
requires a more complex grain handling system than the batch system. The batch drying
system requires larger equipment since large quantities of grain are handled in fairly
short periods of time.
Several factors need to be considered in selecting equipment. Table 11 lists some
information on bins and Table 12 lists information on conveyors.
Table 11. Bin Types, Sizes and Uses.
-----------------------------------------------------------------------
Grade Level Grade Level Overhead or Elevated
Description Discharge Flat Discharge Hopper Discharge Hopper
Bottom Bin Bottom Bin Bottom Bin
-----------------------------------------------------------------------
Name Storage Bin Bulk Bin Work Bin
-----------------------------------------------------------------------
Usually fill once Fill & unload
Use Pattern per year & unload Fill & unload many daily. Value is
over a relatively times/year; mostly in choke-fed
long time period. weekly to monthly gravity flow.
-----------------------------------------------------------------------
Large Medium Small
Size 1000's of bushels 3-30 Tons; can be 1/4-2 Tons
(Relative) or 100's of tons large & storage bins
-----------------------------------------------------------------------
Table 12. Conveyor Types.
--------------------------------------------------
Type of Type of Horsepower
Conveyor Material Capacity Requirement Cost
--------------------------------------------------
Screw ground medium low to medium
(Auger) granular medium
or
chopped
Advantages:
1-can be used a mixer or for uniform flow feeder
2-good for unloading bulk storage
3-wide range available
Disadvantages:
1-size of material limited
2-single sections limited in length
3-medium to heavy wear factor
--------------------------------------------------
Bucket ground medium low medium
granular to high to high
or lumpy
Advantages:
1-efficient
2-high capacity for vertical lift
Disadvantages:
1-limited speed range
2-difficult to erect
3-expensive
--------------------------------------------------
Belt beans high low high
grain
Advantages:
1-can be used for long distances
2-low power requirement
Disadvantages:
1-limited in angle of elevation
2-expensive
--------------------------------------------------
Pneumatic grain variable high medium
ground to high
feed,
chopped
forage
Advantages:
1-flexibility of installation
2-easily cleaned
3-mechanical parts at ground level
Disadvantages:
1-high power requirement
2-conditions of operation vary with type of material
3-noisy
--------------------------------------------------
Mass Flow grain medium low high
granular to high
Advantages:
1-nearly self cleaning
2-reliable
Disadvantages:
1-expensive
2-some types can only operate on small inches
--------------------------------------------------
Four types of grain handling systems for drying are shown in Figures 16, 17, 18 and 19.
Figure 16 uses portable augers for conveying grain into a drying bin. The batch-in-bin
dryer in Figure 17 is contained in a circular bin arrangement. Figure 18 shows a system
for a continuous flow dryer, and Figure 19 shows a completely mechanized grain
handling-drying system using permanently installed equipment. Table 13 shows the
dimensions for a circular bin arrangement for some bin diameters.
Figure 16. Handling system for a bin dryer using
portable augers. Overhead conveyors connect to several storage bins.
(8KB b&w diagram)
Figure 17. Circular bin arrangement for use with
portable conveyors.
(12KB b&w diagram)
Figure 18. Portable conveyors handle grain to and
from a continuous flow dryer.
(8KB b&w diagram)
Figure 19. A completely mechanized grain
handling-drying system using all permanently installed handling equiment.
(18KB b&w diagram)
Table 13. Dimensions for Circular Bin
Arrangements.
(see graphic below table)
---------------------------------------------
Circular bin arrangement working from center
filling location.
R = radius from central dump to center of bins
A = distance between bins
B = distance from inside of bin to central dump
C = opening for back-in, the number listed is
an approximate figure
All numbers are in feet
---------------------------------------------
18 Ft. Diameter Bins
---------------------------------------------
No. of Bins 6 8 7 9
R 26 32 30 35
A 2 2 2 2
B 17 23 21 26
C 35 35 35 35
Min. Auger Lgth 36 40 41 45
Bin Height 24 24 28 28
---------------------------------------------
21 Ft. Diamter Bins
---------------------------------------------
No. of Bins 6 8 6 8
R 29 36 29 36
A 2 2 2 2
B 18.5 25.5 18.5 25.5
C 35 35 35 35
Min. Auger Lgth 38 44 41 46
Bin Height 24 24 28 28
---------------------------------------------
24 Ft. Diameter Bins
---------------------------------------------
No. of Bins 5 7 5 7
R 28 36 30 36
A 2 2 2 2
B 16 24 18 24
C 30 30 30 30
Min. Auger Lgth 37 43 41 46
Bin Height 24 24 28 28
---------------------------------------------
27 Ft. Diameter Bins
---------------------------------------------
No. of Bins 5 7 5 7
R 30 39 30 39
A 2 2 2 2
B 16.5 25.5 16.5 25.5
C 30 30 30 30
Min. Auger Lgth 39 46 41 48
Bin Height 24 24 28 28
---------------------------------------------
More information on handling systems is available in Midwest Plan Service Handbook
MWPS-13, "Grain Drying, Handling and Storage Handbook," available from Extension
Agricultural Engineering, P.O. Box 5626, Fargo, ND 58105.
Safety Considerations
Safety should be a part of all grain drying and handling operations. Use proper
shielding of all moving parts. Avoid high voltage power lines when locating or moving
equipment. Contact your electric power supplier before constructing a grain drying system
for assistance with electric service.
Bottom unloading equipment and grain bins have a special suffocation hazard. As this
equipment is unloaded, the grain flows off the top and down the center withdrawal cone.
Anyone entering the withdrawal cone will be pulled down and may suffocate if they become
covered. The only way to prevent this type of accident is to be absolutely sure no one is
inside a grain bin, hopper bottom bin, truck box, or wagon when unloading takes place.
For best results in storing dried grain, an accurate moisture test is needed to
determine that the grain is dry and an aeration system is necessary for controlling grain
temperature. The drying fan can be used for cooling if the grain is stored in the bin in
which it is dried. If the grain is placed into a different bin, it should be equipped with
an aeration system to control grain temperature during storage. It is imperative that the
grain be cooled during storage to control insects and reduce moisture migration. Request
NDSU Extension Circular AE-791, "Crop Storage Management," for grain storage
management and aeration system design and operation information.
Other Drying and Storage Information Available
Other information on grain drying and storage is available from the county extension
offices and from Extension Agricultural Engineering at North Dakota State University. Some
of the literature available is listed below. Many plans are also available.
------------------------------------------------
AE-791 Crop Storage Management
AE-808 Crop Dryeration and In-Storage Cooling
AE-850 Pneumatic Grain Conveyors
AE-905 Grain Moisture Content Effects
and Management
AE-84 Temporary Grain Storage on the Farm
AE-93 Approved Seed Cleaning Plants
AE-94 Grain Drying Tables
AE923 Calculating Grain Drying Cost
AE945 Equivalent Weights of Grain and Oilseeds
AE1044 Grain Stream Sampling and Sampler Construction
EB-35 Natural Air/Low Temperature Crop Drying
EB-45 Insect Pest Management for Farm
Stored Grain
EC-801 Determining Grain Storage Cost
MWPS-13 Grain Drying, Handling and Storage
Handbook
MWPS-22 Low Temperature and Solar Grain Drying
Handbook
NCH-14 Energy Conservation and Alternative
Energy Sources for Corn Drying
------------------------------------------------
B A C K
Introduction
Types of Dryers and Drying
Energy, Quality, Fire, Moisture and Fans
AE-701 (Revised), November 1994
NDSU Extension Service, North Dakota State University of Agriculture and Applied
Science, and U.S. Department of Agriculture cooperating. Sharon D. Anderson, Director,
Fargo, North Dakota. Distributed in furtherance of the Acts of Congress of May 8 and June
30, 1914. We offer our programs and facilities to all persons regardless of race, color,
national origin, religion, sex, disability, age, Vietnam era veterans status, or sexual
orientation; and are an equal opportunity employer.
This publication will be made in alternative format upon request 701/231-7881.
North Dakota State University
NDSU Extension Service |
