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Aeration Details

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					  Aeration & Grain Quality
Management Systems Engineering
  Ronald T. Noyes, Ph.D., P.E.
 Grain Storage Engineering, LLC
Stored Product Management Engineering
 Stillwater, Oklahoma USA 74074-1116
 (Extension Agricultural Engineer, Emeritus
        Oklahoma State University)
    Aeration System Engineering
Aeration system design -- General
   Design factors to consider:
· Coarse vs small grain? – determines air resistance
· Type of storage structure & grain depth?
· Geographic location /harvest date?
· Available cooling energy/time?
· Cooling Speed vs Energy Costs?
· Cool as fast as you can afford – 1/5 cfm/bu is 2X
 faster than 1/10 cfm/bu.
    Aeration System Engineering
Aeration system design - - Specific
         Design factors to consider:
· Airflow rate (fast cooling = storage insurance!)
· Airflow resistance of grain (size/shape/depth) – Wheat
  generates over 2X static pressure vs corn or soybeans
· Aeration fan type & size (propeller vs centrifugal)
· Airflow direction (suction vs pressure)
· Air distribution system (floor ducts or perforated floor)
· Fan control - - manual vs automatic
    Aeration System Components
       Design components:
·   Fans -- airflow rate vs static pressure
·   Transition and supply ducts
·   Floor distribution system
·   Roof vents & exhaust fans
·   Controls to regulate fan operation
·   Use negative air pressure safety switch for
    suction fan systems!!
    Aeration Airflow Rates
    Airflow rate - - depends on:
•   Type of grain – coarse vs small grain -- or both
•   Grain moisture content
     • Dry: 12-14% m.c. -- 1/10 to 1/4 cfm/bu
     • Moist/wet: 15-25% m.c. – 1/2 to 2 cfm/bu
•   Air distribution floor design
•   Required cooling time vs available weather
•   Climatic conditions - - sub-tropic (warm) vs
    temperate (cool)
Aeration Airflow Rates (Dry Grain)
     Current Recommendations
• Upright Storage Structures:
  • Under 50 ft deep: 1/5 – 1/3 cfm/bu

  • Over 50 ft deep: 1/15 – 1/5 cfm/bu

• Horizontal Storage Structures:
  • 1/5 – 1/3 cfm/bu
Aeration Cycle -- Cooling Time
     Total hours or days
Depends on:
• Airflow rate
• Grain surface - - level vs peaked
• Dockage/fines/foreign material (FM)
• Test weight of the grain – grain density
• Airflow distribution – cooling uniformity
• Climatic conditions - time of year/location
Aeration Cycle Time
Time calculation for all grains:
         15          TW
 AT = ---------- x -----------
        AR            60
Where:
 AT = aeration time, hours/cycle
 AR = airflow rate, cfm/bu
 TW = test weight, lb/bu
Effect of Airflow Rate (cfm/bu) and
Test Weight on Aeration Cycle Time
                      500
                      450                                   0.025
 Aeration Cycle (h)




                      400                                   0.05
                      350                                   0.1
                      300
                                                            0.2
                      250
                      200                                   0.25
                      150                                   0.5
                      100                                   0.75
                       50                                   1
                        0
                            32     48          56      60
                                 Test Weight (lb/bu)
                                                        Airflow vs. Pressure Drop

                           3



                          2.5
Pressure Drop (inch/ft)




                           2
                                                                                                                    Wheat
                                                                                                                    Sorghum
                          1.5
                                                                                                                    Corn
                                                                                                                    Soybeans
                           1



                          0.5



                           0
                                1   2   3   4   5   6   7     8     9    10      20   30   40   50   60   70   80

                                                            Airflow (cfm/ft^2)
        Airflow Direction
Negative pressure (suction) systems:
·Needs 15-25% larger transition/duct cross-section
 area to reduce excessive static pressure loss,
 especially in flat storage
·Roof damage from vacuum when vents freeze
    ·
   Need headspace negative pressure switch for
   aeration in freezing conditions
    ·
   Steel bin roof eave gaps Do Not provide
   adequate safety when roof vents freeze or are
   sealed/covered
     Airflow Direction
  Negative pressure (suction) systems:
·Reduced condensation under steel roofs
·Top grain heat moves down through all grain
  ·When warm grain added to cool grain
  ·Upper level grain mold heat pulled through all grain
  ·NOTE: Hot air in the headspace is negligible - -
   compare 2-3 minutes to replace headspace air to
   several hours of continuous cooling which follows
     Airflow Direction
Negative pressure (suction) systems:
·checkingzone recording fanestimated by
 Cooling
          and
              movement is
                           exhaust air
  temperatures
· Outdoor grain pile covers may require
  continuous suction or use of a wind speed
  switch which can operate suction fans
  during high winds
       Airflow Direction
  Positive pressure (push) systems:
· “Heat of compression” increases cooling air 3-10 F
                                                 o


· Condensation problems under steel roofs
· Air distribution in flat storage is more uniform
· Can add warm grain w/o heating cool grain
· Aeration zone finished when surface grain cools
· Less plugging of perforated floors or ducts
     Fan Selection & Sizing
·Centrifugal vs Axial Fans
·Performance factors
  ·Power & efficiency
  ·Multiple fans (parallel and series)
  ·Heat of compression
·Fan selection - - use FANS program
 from U. Minnesota & Purdue U.
        Fan Types
·Axial-flow Fans
 ·Vane-axial (fixed or adjustable pitch blades)
 ·Tube-axial (small fans -- 2 HP or less)
·Centrifugal Fans
 ·Low speed - - 1750 rpm/60 Hz; 1460 rpm/50 Hz
 ·High speed & In-line centrifugal
   ·3500 rpm/60 Hz; 2900 rpm/50 Hz
        Axial-flow Fans
· Low cost
· Noisy
· 3- 5 inches w.c.,
  static pressure (SP)
· More airflow per
 HP than centrifugal
 fans -- up to 4” SP
         Centrifugal Fans
· Higher cost than axial fans
· Quieter than axial fans
· More airflow per HP than
  axial fans above 5” SP
· Low-speed: 7-8” SP
· High-speed: 12-18” SP
· In-line: 10-12” SP
 Fan Heat of Compression
· Heat energy added to air during pressure fan
 compression to build SP to force air through
 grain resistance
· Raises air temp 0.75-1.0   oF/inch   w.c. SP
  · Ambient air + 2-5 F for vane-axial fans
                     o

  · Ambient air + 5-10 F for centrifugal fans
                         o


· Lowers Air RH and EMC in push aeration
     Fan Performance
The airflow volume (CFM) a fan delivers
across its static pressure (SP) range
·All Fan manufactures should provide fan
 performance data
·Air Moving and Conditioning Assoc.
 (AMCA) certified fan data is best
    Fan Performance Curves
18000

16000

14000

12000                                          vane axial

10000
                                               low speed
 8000                                          centrifugal
                                               high speed
 6000                                          centrifugal
 4000

 2000
CFM 0

        0   2    4    6    8    10   12   14
            Static Pressure (in of H20)
Fan Performance Conversion
 To convert fan performance data for 60
 Hz to fan data for 50 Hz, multiply…
  Speed (RPM) x (50/60)
  Airflow (CFM) x (50/60)
  Static Pressure (Inches w.c.) x (50/60)2
  Motor Power (HP or KW) x (50/60)3
          Fan Selection
Select Fans Based on:
· Optimum fan performance
· Efficiency of fan in terms of airflow per unit
  of energy (CFM/HP or m /min/kW)
                            3

· Noise, cost, reliability, mounting factors, etc.
   Air Distribution System Design

· Transitions, supply ducts, manifold pipes
· Perforated ducts, pads or false floors
· Roof venting or roof exhaust fan systems
 (often not well designed)
 Fan Transitions



·Transition taper angle of 30° or less
·No obstructions in the bin foundation
 duct entrance
        Fan Transitions - - Avoid
    Abrupt Air Direction Changes from
          Transition to Tunnel
             Air Tunnel



Foundation

         Transition
                          A baffle must be added to
                  Fan     guide the air as shown
 Fan Transition Differences

             Air
             Duct
                     When the transition is
                     narrower than the air
Foundation
                     duct tunnel, no
                     modification to guide
       Transition    the air is needed!

               Fan
    Transition and Supply
     Duct Air Velocities
· Maximum design air velocity:
  · Positive pressure system: 2500 fpm
  · Negative pressure system: 2000 fpm
· Preferred design air velocity:
  · Positive pressure system: 1500-2000 fpm
  · Negative pressure system: 1000-1500 fpm
Perforated Air Distribution
      Duct Velocities
 ·Perforated duct design velocity:
   ·Upright Storages:   2000 fpm
   ·Flat Storages:      1500 fpm
Perforated Duct Grain
Exhaust/ Entry Surface
Velocity

· Ideal(0.5 ft/sec) grain entrance velocity: 30
  fpm
        surface to

· Max. preferred surface to grain velocity:
     45-60 fpm (0.75-1.0 ft/sec)
· Recommended 120 fpm (2.0 ft/sec) surface to
  grain velocity:
                   never exceed (NE)
Perforated Ducts, Pads, Floors
·Duct systems
  ·In-floor - - removable planks, must support
   vehicles in flat storages and large steel bins
  ·On-floor (damaged by front loaders)
· Perforated pad (maximize square area)
· Perforated floor (removable planks)
· Sloped/hopper bottom bins, tanks, silos,
 flats - - half-round or round ducts
         Airflow Path Ratio
Airflow Path
•Shortest path = C -- duct to grain
surface/wall intercept or peak.
•Longest path = A + B =
    horizontal + vertical.                 C       A
                                      C
•Airflow Path Ratio (APR) -- A
Compare longest airflow path
(A + B) to shortest airflow path,     B
                                               B
C
•APR should not exceed 1.5 : 1            A+B <= 1.5 C
Round Bin Aeration Floor Layouts

                 Pad
                   .




Square “Y”   .         Double “T”
Round Bin Aeration Floor Layouts

             Double Pad




Double “H”                Quad “F”
              Layout of Bin Vertical
              Aerator with Cored Peak
· Big bins with Dia. to than
  sidewall ratio greater
    2.5:1 need vertical aerator
    (VA).
·   VA w/ 6 ft dia. x 20 ft perf.
    cylinder and separate fan
    aerates 20-25% of center
    grain.
·   Coring Peaks to 1/4 Dia.
    inverted cone ridge to
    improve airflow from VA
    in center of bin.
     Peak Aerator With
     Separate Fan
· For new bins, vertical                                                  Centrifugal fan -- 50% air flow




    aerator (VA) can be
    included in initial                                                 Floor aeration duct s




    airflow fan design.
·
                             Ver tical aerat or pedestal 2 -3 ft from                           Cent rifugal fan for vertical aerator
                             center unload slide gate                                           added to exist ing aerat ion system




    For existing large bin   Unload conveyor slide gates



    aeration systems, use                                               Alt ernative solid air duct for vertical


    separate fan and duct                                               aer ator added to ex isting bin wit h floor duct s


                                                                            Aeration and unload conveyor tunnel


    for vertical aerators.

                                                                        Centrifugal fan -- 50% air flow
Duct layout in flats
· Duct spacing is critical to
                                               50 to 70 ft




  uniform airflow delivery.
· Flats require non-uniform                                  Up to 100 ft




  air distribution.
· Cross ducts -- low airflow
                                 70 to 90 ft




  under grain ridges.
· Need more airflow under
                                                             Up to 150 ft




                                                                             c



  peaks than near walls.
· Match duct layouts to bldg.   90 - 150 ft




  width and length.                                                         c




                                                             Repeat Pattern -- No Limit
In-Floor Aeration Duct Design



                 Use 3/32 (0.093)” dia. perf. for
                 cereal grains; Use 3/64-1/16
 In-floor Duct   (0.047-0.063)” for small seeds
 Calculating Duct Air Flow Volumes
Example: 3 ft2, 39 in (3.25 ft) wide x 30 ft long
 perforated in-floor duct
Horizontal/Tunnel Airflow Through Duct
·Perforated duct air volume at entrance
    3 ft2 x 2000 ft/min = 6000 ft3/min (cfm)
Vertical Flow Through Perf Duct Surface
·Surface area exhaust volume (to/from grain)
 Rectangular duct 3.25 ft wide @ 30 ft. long,
 3.25 x 30 = 97.5 ft2 x 60 ft/min = 5,850 ft3/min
Roof Venting – Inlet & Exhaust
 Pressure (exhaust vent) system:
1 ft2 vent cross-section area per 1000-1500 cfm
 Suction (inlet vent) system:
1 ft2 vent cross-section area per 800-1000 cfm
  Note: Keep static pressure in bin head
   space - - 1/8” SP or less!
Roof Venting
· Place one or more vents on
  fill cap or near peak.
· Example: 100,000 bu bin @ 0.2
  cfm/bu, = 20,000 cfm = 20 sq ft
  vent area @ 1,000 ft/min.
                                    “Mushroom” Vent
· At 1.8 sq ft/vent, 11-12 vents
                                                      .




  needed. Put 1-2 vents at peak
  with other vents uniformly
  spaced around roof mid-point
  - - not at eave.
         Gooseneck Vent
· Economical
· Open flow
· Horizontal screen
  design for rain shield
· Wind Directional –
 High wind can blow rain
 against roof slope, and
 directly into open vent.
Mushroom Vent
· More expensive than
  gooseneck vents
· Non-directional – rain
    less affected by wind
    direction
·   Grain dust cakes in
    vent screens, on roof
    w/pressure aeration
Roof Exhausters -- Power Vents
· Brace Roof Exhaust Fans (RF) to
  roof sub-structure
· Operate Roof Exhaust Fans (RF)
  when aeration fans run
· Run RF for 15-20 minutes after
    aeration fans shut off to prevent
    head space condensation, using RF
    timer operated by aeration controller
·   Size exhaust airflow at 200-250% of
    aeration rate for 100-125% dilution
      Roof Exhaust Fan and Vents
                          “Inlet” Vents

· Up-flow aeration                    Roof Exhaust Fan
    w/roof exhaust
    fans - - roof vents
    are inlets
·   When using roof
    exhausters, size
    vents @ 1000
    ft/min
Roof, Fans and Vents Design
· Mount:
  Exhaust fans mid-roof
  Gravity vents high/low
· Seal roof/sidewall eave
 gaps (permanent foam)
  Improve fumigation kill
  Reduce fumigation labor
Aeration Fan Controllers
Electro-mechanical fan control
  High /low limit thermostats
  With/without humidity control
  NEMA 4R (rain-tight) housing
  Hour meter and selector switch
  Time delay relays --multiple fans
  Use off-the-shelf components
  Local electricians can fabricate and
   service
Aeration Fan Controllers
Partial List of Commercial Temperature
 and RH Based Aeration Controllers
 GSI Corp, Assumption, IL
 Caldwell/Chief-Agri, Kearney, NE
 The Boone Group, Boone, IA
 OPI Systems, Inc, Calgary, AL, Canada
 AgriDry Rimik Pty, Ltd, Toowoomba, Qld, AUS
Closed Loop Fumigation (CLF)
Phosphine Gas Recirculation System



                     Four 200,000 bu bins w/two 1.5
                     blowers @ 1600 cfm = 1/500 cfm


 1.5 HP CLF blower   Total Cost = $0.0068/bu. in 1992
 w/6” suction, 4”
 pressure PVC pipe
Closed Loop Fumigation (CLF)
       Phosphine Gas
    Recirculation System




        150’ x 500’ x 30’, 3 million bu flat
        storage w/CLF @ 1/500 cfm/bu --
        Tulsa Port of Catoosa, OK
Closed Loop Fumigation (CLF)
Phosphine Gas Recirculation System
         · 300,000 bu welded steel
           tank w/two 1/12 HP CLF
           blowers = 1/6 HP @ 350
           cfm = 1/850 cfm/bu.
         · 150’ W x 500’ L Flat @ 3
           million bu w/six 2 HP
           CLF blowers = 12 HP @
           6,000 cfm = 1/500 cfm/bu
         · Flat vs Round = 10 X grain ,
           17 X airflow, 72 X HP - -
           both excellent CLF systems
  Closed Loop Fumigation (CLF)
Phosphine Gas Recirculation System
· CLF in concrete silos
    eliminates “turning”
    grain to fumigate.
·   Sealed under roof
    exterior vents, spouts,
    conveyors and other
    leak points improves
    kill with <50% dosage.
·   Interior vents allow
    gas flow from one bin.
        Comparative Costs of Aeration
            and CLF Equipment
· Aeration System
  @ 6.0-12.0c/bu
· Aeration
    Controller @ 0.3-
    1.0c/bu
·   CLF @ 0.6-1.5c/bu.
·   Temp. Cables @
    0.3-1.0c/bu
 Temperature Monitoring Systems –
 Quality Grain Management Tool
Thermocouple or Thermistor Cable Systems
 Manual readout with manual data log book
 Data logger records temps @ manual plug-in
  terminal; periodically down-load temperature
  data to computer
 Computer interfaced temperature cable system
  w/thermistor or thermocouple cables.
   - Automatic monitoring w/data warning/alarm
     system if temperatures exceed alarm set-
     points.
OPIGIMAC Temperature and Insect
Monitoring, Aeration Fan Control System OPI
Systems, Calgary, Canada
-Thermistor  temp-
 erature sensors
-Infrared insect
 detectors
-Individual
 fan controls
  Chilled Aeration
Grain Chilling Unit
Uniform temperatures in
 warm weather
Fast cooling, 24 hours/day
Minimum moisture
 shrinkage
Non-chemical insect
 control:
 @ 70oF, slows reproduction,
 @ 60oF stops insect growth,
 @ 50oF kills insects –
 dehydration
Fluidized Duct Aeration
Self-Cleanout Floor
KanalSystemTM Aeration-
  unloading system
  minimizes bin/silo entry.
Aeration duct airflow @ 215
  cfm/ft, 16 in. w.c. SP.
Special perforation ducts @
  13% open area.
Aeration airflow rate of 0.1-0.3
  cfm/bu
Manifold valves direct air to
  floor duct sections
      Coring Bins to Lower Peak
          Improves Aeration
Periodic “coring” cleans
  dockage and f.m. from
  “core of fines” in bins.
“Coring” bins to 1/4 -1/3
  bin dia inverted cone
  reduces cooling 20-30%.
Single “coring” full bin
  not = multiple coring
  but improves cooling.
Dryeration – High Temperature Drying
With High Speed Aeration Cooling
Higher corn quality – fewer stress cracks,
  less breakage, better test weight
Transfer hot grain to
  temper/cooling bin
Temper 6-12 hours
Cool 8-12 hrs @ 1/2 - 1
 cfm/bu removes 1.5 -
 2.5%m.c. , increases
  capacity 70-100%
New Theory -- Old Technology
     Dryeration W/Continuous Flow
Tempering/Cooling Bin = Higher Efficiency
                                                                               Dryeration Fan @
                                                                                 1/2 - 1 cfm/bu
      Insulated Continuous Flow
       Tempering/Cooling Bin to




                                                    MC
         Hold 24 Hour Drying                                                       Saturated Air-




                                                     %
                                                 -18
               Capacity                                                            140F/100%RH




                                              16
                                             @
     Wet Corn in




                                         0F
                                                                           Temper Zone -




                                       14




                                                                                                    C
     @ 22-30% MC                                         Hot Corn--140F




                                                                                                  M
                                                                           Hot 6-10 Hours




                                         -
                                      orn




                                                                                                %
                                                                                             /2
                                                                                             51
                                    tC




                                                                                           -1
                                  Ho
                                                         Hot Corn--140F




                                                                                         14
                                                                                         @
                                                                                    F
                                                         Hot Corn--130F




                                                                                    60
                                                                                  n-
                                  Cooling Zone




                                                                                or
                                                         Warm Corn--100F




                                                                              lC
 Batch or Continuous              - - 8-12 Hours                                             Continuous Dry Grain




                                                                            oo
                                                         Cool Corn - 70F                      Transfer to Storage




                                                                           C
 All Heat Grain Dryer
@ 230-260F - - 70-100%
  Increased Capacity
                                                                            Ambient Air- 60F/50%RH
             -- New Theory --
     Closed Loop Aeration (CLA)
· Internal recirculation of air in sealed bin
· Uses CLF fan & plumbing system                Seal Eaves,
· Permanent wall/roof eave-gap seal             Augers

· Temp/seal roof vents, and base                and Other

· & wall openings                               Bin Leak
                                                Points

                  CLF Gas Recir-
                  culation Fan

   Aeration Fan Sealed
              -- New Theory --
        Closed Loop Aeration (CLA)
· Supplemental, low airflow internal recirculation system
· Operates in sealed storage @ 1/200-1/500 cfm/bu.
· Purpose - - maintain uniform grain temperature.
· Eliminate convection air currents - - moisture migration.
· Uses CLF fan and piping system 24 hrs/day,2-6 months.
· No additional capital cost - - small operating cost.
· Gradual grain cooling w/o moisture loss in sealed bin.
· Will require periodic monitoring of insects/grain/temps
       -- New Technology --
    Low Airflow Suction Aeration
    System Added to Concrete Silos
Low power economical suction aeration system
Incorporated with CLF system
1/60-1/100 cfm/bu. = 500-900 hours/cooling cycle
Install aeration manifolds in silo discharge
  spouts between R&P slide gates and tunnel
  wall or ceiling
    New Theory -- Old Technology
        Cross-Flow Aeration
Cross-flow aeration provides
  fast cooling at 10-15% of the
  power of vertical aeration.
Four - duct cross-flow aeration
  technology in figure at right
                                   Dead Air Zone




  has “dead air zone” in center.
  --New Theory --
Cross-Flow Aeration
Optimum 4-duct method -- use
 1 inlet and 3 outlet ducts.
Alternate between inlet ducts,
 A & C, with ducts B & D used
 as dedicated exhaust ducts.
Horizontal airflow in long
 seeds (corn, wheat, barley,
 rice, sunflowers, etc.) requires
 60-70% as much power for
 horizontal vs vertical airflow.
Grain Quality Monitoring Systems
 USDA Electronic Insect Monitoring
  System now Commercialized by OPI
  Systems, Calgary, ALB, Canada
 Purdue U. researching mold sniffing
  system to provide early warning
  (much faster than temperature cable
  system) of mold development by
  CO2 detection.

				
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