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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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