Blowing a lot of hot air… -...
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Applying Technology for Agriculture Blowing a lot of hot air…
Transcript of Blowing a lot of hot air… -...
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Blowing a lot of hot air…
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• Aeration vs NAD vs hot air drying
• Safe storage times
• How does storage of canola differ from other grains?
• NAD and equilibrium moisture content
• PAMI’s automatic control strategy
• Potential benefits/savings with automatic systems
• Other control strategies
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• Hot/wet grain will “spoil”
• Insects, fungal molds, mites thrive in hot (>15⁰C) and wet (>10% for canola) conditions
• Hot air dries grain more effectively than cold air
• Greater vapour pressure difference = faster moisture movement from kernel to air
• Warmer air has a greater ability to hold moisture than cooler air
• Grain conditioning and storage requires careful management
• Dry grain first (if possible), then cool it and monitor regularly
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• Temperature variations = moisture variations
• Temperature variations caused by
• Ineffective air distribution systems
• Natural convection driven by outside temp
• Especially problematic for larger diameter bins
• Can be minimized by aeration
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Source: SK Ag & Food extension document (1997) Note: Canola is considered “dry” at 10%
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• Aeration = cooling/conditioning
• Airflow rate ~ 0.1-0.2 cfm/bu
• If air is cooler than grain, grain will cool
• At 0.1 cfm/bu, it will take about 200 hrs (8 days) of fan operation to equalize the temp in the bin
• Natural air drying (or near ambient drying) = reducing the moisture in the grain
• Airflow rate ~ 1-2 cfm/bu
• If air has “capacity to dry”, grain will dry
• At 1 cfm/bu, it will take 7-14 days of continual fan operation to dry wheat from 16.5% to 14.5% (highly dependent on ambient conditions!)
• Upward vs downward air movement
• Turn fans on and let them run continuously…?
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• Hot air drying
• High temperature, high airflow rate (8-15 cfm/bu), low retention time
• NAD relies on ambient air’s capacity to remove moisture from grain
• Adding heat to ambient air will increase it’s capacity to remove moisture
• General recommendation is to increase temp by 10⁰C or less and to a maximum of 20⁰C • Minimizes cost and chance of overheating the grain
• Effective way to “extend” the NAD season
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Pros of NAD Cons of NAD
• Energy savings
• Smaller investment
• Higher quality grain
• Slow
• Requires management
• Dependent on
ambient conditions
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L/s per m3 cfm per bushel
1-2 Aeration 0.1-0.2
13-26 NAD 1-2
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• Airflow rate from a specific fan depends on the
static pressure (resistance to airflow)
• Static pressure depends on
• Grain type (size of voids)
• Smaller seeds = smaller voids = increased resistance to
airflow
• Depth of grain
• Greater depths = greater resistance to airflow
• Type of distribution system
• Floor and ducts should be at least 10% perforated
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2000 cfm
5 in
H2O
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• Airflow rate from a specific fan depends on the
static pressure (resistance to airflow)
• Static pressure depends on
• Grain type (size of voids)
• Smaller seeds = smaller voids = increased resistance to
airflow
• Depth of grain
• Greater depths = greater resistance to airflow
• Type of distribution system
• Floor and ducts should be at least 10% perforated
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Source: SK Ag & Food extension document (1997)
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Source: SK Ag & Food extension document (1997)
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• PAMI tested several types of distribution systems for hopper bottoms
• Univision Ultra Dry, Taylor, Naicam, Grain Guard GG 7000, Keho Cyclone, Bader Hooded, Grehi, Harvest Hopper, Trail Rite V Aeration, Univision In-Line, Westeel Boot
• Static pressure to achieve 1 cfm/bu in a 2000 bushel bin ranged from 2.5 to 8.2 inches H2O
Images from www.GrainGuard.ca
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Bin "A" Bin "B"
Diameter 22 ft 18 ft
Grain depth 10 ft 15 ft
Grain volume 3000 bu 3000 bu
Expected static pressure @ 0.75 cfm/bu 3.5 in 7.5 in
Typical fan required 3 hp 5 hp
Source: SK Ag & Food extension document (1997)
General Guidelines for NAD
Bin size (bu) Fan size (hp)
2000 3
3500 5
5000 7-10
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• Aeration: 0.1-0.2 cfm/bu
• NAD: 1-2 cfm/bu
• Airflow from a fan depends on static pressure
• Static pressure depends on
• Air distribution system
• Grain type
• Grain depth
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• Simply connect a flexible,
transparent tube (minimum
inside diameter ¼ inch) to the
transition duct
• The difference in water height =
static pressure in inches
Source: SK Ag & Food extension document (1997)
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• Bin fill • Grain naturally piles into a cone
• Grain spreaders can be used to minimize this cone and even distribute fines which will help make the temperature variation more even
• Exhaust vents • Help expel moist air from top of bin, preventing condensation
under roof or on top of grain
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• Sensitive to spoilage lower target MC
• Canola “respires” for up to 6 weeks after harvest, requiring aeration even if dry
• Resistance to airflow = higher static pressure
• A system sized for NAD of wheat can be used for canola but bin should only be half or two thirds full
• Fully perforated floors recommended for canola
• Oil content can degrade in adverse (high temp) storage conditions
• PAMI study shows that oil degradation after 2 months of storage still within tolerance limits. Longer storage periods might result in significant oil degradation
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• Shorter safe storage times (3 months vs 5 months)
• Longer-term storage studies currently underway
• PAMI trials showed no danger of compaction or oil extrusion for grain depths up to 100 ft
• Oils are susceptible to degradation
• High oil content canola behaved the same as regular
canola during those 2 months
• Lower target MC for high oil content canola
(8% vs 10%)
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• NAD systems are common but not used efficiently
• Through-dry means grain at bottom is over dry
• Fan running but not drying (or cooling) • Air needs to have
“capacity to dry”
• Manual control involves a lot of guess work
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• To develop a control system that will
automatically turn fans on/off
• “Set it and forget it”
• Prevent over-drying of grain
• Reduce energy costs (and GHG emissions)
• The envisioned control system should
• Be proactive rather than reactive
• Allow estimation of moisture content profile
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• “Moisture content” of the air in the grain voids
will be equal to the moisture content of the grain
• Moisture content of the air can be calculated
from air temperature (T) and relative humidity
(RH) using “Equilibrium Moisture Content” (EMC)
equations
N
dbCTK
RHMC
1
)(
)1ln(Henderson EMC:
ASAE Standard D245.5, 2005
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Temp Relative Humidity (%)
⁰C 35 40 45 50 55 60 65 70 75 80 85
-2 6.7 7.5 8.2 8.9 9.7 10.5 11.3 12.2 13.2 14.3 15.7
2 6.4 7.0 7.7 8.4 9.1 9.9 10.7 11.6 12.5 13.6 14.9
5 6.1 6.8 7.4 8.1 8.8 9.5 10.3 11.1 12.0 13.1 14.3
8 5.9 6.5 7.1 7.8 8.5 9.2 9.9 10.7 11.6 12.6 13.8
10 5.7 6.3 7.0 7.6 8.3 8.9 9.7 10.5 11.3 12.3 13.5
13 5.5 6.1 6.7 7.3 8.0 8.6 9.4 10.1 11.0 11.9 13.1
15 5.4 6.0 6.6 7.2 7.8 8.5 9.2 9.9 10.7 11.7 12.8
18 5.2 5.8 6.4 7.0 7.6 8.2 8.9 9.6 10.4 11.3 12.4
22 5.0 5.6 6.1 6.7 7.3 7.9 8.5 9.3 10.0 10.9 12.0
26 4.8 5.4 5.9 6.5 7.0 7.6 8.2 8.9 9.7 10.5 11.6
28 4.8 5.3 5.8 6.3 6.9 7.5 8.1 8.8 9.5 10.4 11.4
If air has 50% RH and 5 deg C and it is passed over canola for a length of time, the canola
will eventually equilibrate to 8.1% moisture content…whether it started at 10% or 6%.
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Bin 1
Bin 3
Bin 2
Bin 6
Bin 5
Bin 4
HT1 HT3 HT5 HT11 HT13 HT15
HT21 HT4 HT10
HT6
HT7
HT8
HT9
HT16
HT17
HT18
HT19
HT20HT14HT12
FS1 FS2 FS3 FS4 FS5 FS6
L1 L2 L3 L4 L5 L6
P1 P2 P3 P4 P5 P6
Monitoring in all bins
Mass, temp/RH at inlet, temp/RH at outlet,
static pressure, fan speed
Monitoring in bins 3 and 6
Grain temp/RH at 4 depths
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Actual MC
16.7
14.7
14.4
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N
dbCTK
RHMC
1
)(
)1ln(Henderson EMC:
With the adjustment regression, predicted wheat MC was within
1% of actual wheat MC (between 13% and 17% wb)
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Temp Relative Humidity (%)
⁰C 35 40 45 50 55 60 65 70 75 80 85
-2 11.5 12.2 13.0 13.7 14.5 15.3 16.0 16.9 17.7 18.7 19.8
2 11.1 11.9 12.6 13.4 14.1 14.9 15.6 16.4 17.3 18.2 19.3
5 10.9 11.7 12.4 13.1 13.8 14.6 15.3 16.1 17.0 17.9 19.0
8 10.7 11.5 12.2 12.9 13.6 14.3 15.1 15.8 16.7 17.6 18.7
10 10.6 11.3 12.0 12.7 13.4 14.2 14.9 15.7 16.5 17.4 18.5
13 10.4 11.1 11.8 12.5 13.2 13.9 14.6 15.4 16.2 17.1 18.2
15 10.3 11.0 11.7 12.4 13.1 13.8 14.5 15.2 16.1 17.0 18.0
18 10.1 10.8 11.5 12.2 12.9 13.6 14.3 15.0 15.8 16.7 17.7
22 9.9 10.6 11.3 11.9 12.6 13.3 14.0 14.7 15.5 16.4 17.4
26 9.7 10.4 11.1 11.7 12.4 13.0 13.7 14.4 15.2 16.1 17.1
28 9.6 10.3 11.0 11.6 12.3 12.9 13.6 14.3 15.1 15.9 16.9
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MCgrain Max
= MCmin
(14-14.9%)
MCambient
= Neutral
(14-14.5%)
MCambient
= Wet
(>14.5%)
MCambient
= Dry
(<14%)
MCgrain Max
= MCmid
(15-16.9%)
MCgrain Max
= MCdry
(13-13.9%)
MCgrain Min
= MCoverdry
(<13%)
MCambient
= Wet
(>14.5%)
MCambient
= Neutral
(14-14.5%)
MCambient
= Wet
(>14.5%)
MCambient
= Dry
(<14%)
Fan ON Fan ON Fan OFFFan OFF
Fan ON
Fan OFF Fan ON
Does any MCgrain = MCmax (>17%)? Yes
No
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• Wheat (15.8% wb) loaded Sept 15
• Grain was “average” dry (14.4%) on Sept 27
• 12 days total
• Fan was on 45% of time (137 of 306 hrs)
• Testing of re-wetting cycle started on Sept 30
• Final calculated moisture contents
Bottom 14.4%
Middle 12.3%
Top 14.6%
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0
2
10
11
12
13
14
15
16
0 24 48 72 96 120 144
Fan cycle (0
= off, 1
= on
)
Gra
in M
C (
%w
b)
Time (hrs)
Effect of fan cycle on grain moisture content (bottom grain)
0
2
0
2
4
6
8
10
12
14
16
18
20
0 24 48 72 96 120 144
Fan cycle (0
= off, 1
= on
) Am
bie
nt
Air
MC
(%
wb
)
Time (hrs)
Effect of ambient air moisture content on fan cycle
The diurnal variation of ambient
air moisture content meant that air
had “potential to dry” from
approximately 10 am to 10 pm on
most days.
Drying occurred when the fan was
on. When the fan turned off, some
equilibration or slight rewetting
occurred.
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• 5 hp fan running continuously for 30 days =
2,980 kW-hr of electricity
• Cost to run fan continuously (10 cents per kW-
hr) = $300 per month
• By optimizing the operating cycle of the NAD
fan, a farmer can save approximately $150 per
operating month per fan
• Also, reduced chance of grain spoilage or
overdrying and reduced labour (more $$
impacts)
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• 2000 bushel bin of canola dried to 8% MC (average)
• Equals 1.07 tonnes of lost saleable water
• @ $567/tonne, this represents $607 of lost
revenue (plus the cost of running the fan)
• Overdrying is about as costly as selling tough grain
(drying costs @ elevator ~ $10/t)
• 2000 bushels @ 12% = 50.4 tonnes
• @ $10/tonne, this represents $504 in penalties
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• Canola harvested at 6% moisture content
• Assume 1000 bu
Rewet to
(average)
Added water (tonnes
per 1000 bushels)
Added revenue*
(per 1000 bushels)
7% 1.7 $964
8% 2.0 $1134
10% 2.6 $1474
*assumes price of canola is $567/tonne
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• Each bin would require
• At least 4 temp/RH sensors (three in-grain
and one at inlet)
• Relays to switch fan on/off
• Each set up (for up to 10 bins) would require
• Controller to execute algorithm
• Interface for input information (grain type,
starting MC, etc.)
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• OPI-integris (Calgary
based)
• Control of aeration,
drying (with heat) and
ventilation
• Designed for large bins
(100,000 bushels +)
• Complex, costly system
• Aeration Control
(Australia)
• Drying, aeration, and
conditioning control for
large silos
• In-grain moisture
predicted based on info
during loading and
weather during fan
hours
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• PAMI
• CFD, discrete modeling of airflow in bin
• Useful for design and optimization of new inlet/outlet
configurations
• Indian Head Research Farm (IHARF)
• Mass balance approach for control strategy
• Initial results suggest more water is lost during evening hours than day time hours (article in Western Producer)
• Side by side trials in fall, 2011
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• Control strategy work
• Side by side small scale and full scale testing
• Optimization of control strategy (setpoints, frequency of decision routine, cooling cycles, etc.)
• Development and refinement of calculations to calculate grain moisture content for different grains (including canola)
• Analysis of the impact of starting and stopping the fan on the drying/cooling front
• Analysis of buffer capacity of grain at bottom
• Other grain storage work
• Potential for adding aeration to grain bag storage
• Natural ventilation systems
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• Aeration = cooling (low airflow), NAD = drying
(high airflow)
• Measure static pressure to gauge airflow
• Grain storage requires good management
• Canola storage requires extra management
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• Currently, NAD systems require guess work
• In-grain temp/RH can be used to calculate grain MC
• Control strategy based on grain and inlet MC was implemented
• Full scale run suggests that fans should operate only 45% of time
• More development and refinement required
• Existing products not feasible for small producers
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• SK Min of Ag NAD guide
• AAFC (Storage of Canola by J.T. Mills, 1996
revised by M. Hartman, 2011)
• PAMI Test Reports (500, 578, 588)
• PAMI Notes GD-10 and GD-11
