Natural air and low-temperature drying systems are generally not recommended for Kentucky because of their slow drying rates. In such systems the grain near the top of the drying bin may remain undried for an extended period of time, possibly leading to grain spoilage and/or the production of aflatoxin

Bridges, Thomas C.

Fehr, Robert L.

Loewer, Otto J.

Turner, Larry W.

White, G. M.

English

University of Kentucky

University of KentuckyUKnowledgeAgricultural Engineering Energy Series Biosystems and Agricultural Engineering10-1978Energy in Agriculture: Performance Evaluation forNatural Air and Low-Temperature Drying SystemsOtto J. LoewerUniversity of KentuckyThomas C. BridgesUniversity of Kentucky, tom.bridges2@uky.eduG. M. WhiteUniversity of KentuckyRobert L. FehrUniversity of Kentucky, robert.fehr@uky.eduLarry W. TurnerUniversity of KentuckyRight click to open a feedback form in a new tab to let us know how this document benefits you.Follow this and additional works at: https://uknowledge.uky.edu/aees_reportsPart of the Bioresource and Agricultural Engineering CommonsThis Report is brought to you for free and open access by the Biosystems and Agricultural Engineering at UKnowledge. It has been accepted forinclusion in Agricultural Engineering Energy Series by an authorized administrator of UKnowledge. For more information, please contactUKnowledge@lsv.uky.edu.Repository CitationLoewer, Otto J.; Bridges, Thomas C.; White, G. M.; Fehr, Robert L.; and Turner, Larry W., "Energy in Agriculture: PerformanceEvaluation for Natural Air and Low-Temperature Drying Systems" (1978). Agricultural Engineering Energy Series. 28.https://uknowledge.uky.edu/aees_reports/28AEE99PERFORMANCE VALUATION FOR NATI,JRAI AIRAND LOW:TEMPERATI.JRE DRYING SYSTEMSO. J. Loewer, T. C. Bridges, G. M. Whitg, R. L. Fehr, and L. W. TurnerUNIVERSITY of  KENTUCKYCOLLEGE of AGRICULTUREDEPT. of AGRIC. ENGINEERINGCOOPERATIVE EXTENSION SERI/ICErncoogerolionw i l hKENTUCKYDEPARTMENTofENERGYPERFORMANCE EVALUATION FOR NATI,]RAL AIR AND LOW.TEMPERATI,JRE DRYINGSYSTEMSO. J. Loewer, T. C. Bridses, G. M. White, R. L. Fehr, and L. W. TumerNatural air and low-temperature drying systems are generally not recommended for Kentucky because of their slowdrying rates. In such systems the grain near the top of the dryingbin may remain undried for an extended period of time,possibly leading to grain spoilage and/or the production of aflatoxin. An estimate of the period of time which grain at certainmoisture contents rnay be held without significant spoilage is shown in Figure 1:? D & 9 0Au-owABLE STORAGE TIME , oAYSFigure 1. Allowable storage time for shelled corn at various temperatures and moisture contents.For a complete discussion of low temperature drying, ask your county agent for University of Kentucky CooperativeExtension Publications AEN-22 "Low Temperature Drying-Methods and Management" and AEN-23 "Low TemperatureDrying-Use and Limitations."As shown in Figure 1, the lower the grain temperature and moisture content, the longer the grain will store safely.Increasing airflow will decrease drying time as will an increase in the drying air temperature. Natural air systems use only thedrying potential of the outside air to dry the grain, although the force of the fan may increase the air temperature by 2"F.Low temperature systems add heat to the air (5-7oF), reducing its relative humidity and thereby increasing its potential fordrying. However, too much heat added to the air will result in overdrying of the bottom layers of grain unless the grain isbeing mixed within the bin. The relationship between changes in air temperature because of heating and the resulting changesin relative humidity may be found using Figure 2. Temperature changes in the heater always take place along a line parallel tothe air temperature axis or scale.|!oUJEfF|rUJo=IrJFzE(9Figure 2. Atu,"rn"r"*. *U;;. rr idity relationships.4As an example of how Figure 2 can be used, suppose the outside air temperature was 60oF with a relative humidity of80 percent. If this air were heated to 80oF, the new relative humidity could be found by extend.ing a line parallel to thebottom of the figure from the original air conditions to a point directly above the new temperature on the bottom scale. Thenew relative humidity can then be read from Figure 2; the new relative humidity for this example is 40 percent. A "ruleof thumb" is that a 20oF increase in air temperature will generally reduce the relative humidity of the air io one-half of itsoriginal value.futother point to consider is that the temperature of the air entering the grain will be two degrees or so higher than theoutside air because of the enerry added by the fan in moving the air. To better approximate the volume of air per busheldelivered by the fan, the list of other prograrns available at the end of this text should be consulted.The natural air and low-temperature drying processes usually require relatively low levels of energy use compared withhigh-temperature systems. Unfortunately, this low energy level results in extended drying times when air temperatures aresimilar to those found in Kentucky during the harvest season. Consequently, there is a relatively high probability of grainspoilage and/or aflatoxin contamination. To determine how a natural air or low-temperature drying system will function,complete the following form and retum it to:Dr. Otto J. LoewerAgricultural Engineering DepartmentUniversity of Kentuckykxington, Kentucky 40506l . NAMEADDRESS,,3 . PHONENI,JMBERTY"E OF GRAIN TO BE DRIED(Corn or Milo)TEMPERATI,JRE OF AIR USED FOR DRYING, "FNote that tlie air will increase in temperature by approximately 2oF whenit passes through the fan.RELATIVE HI.'}IIDITY OF AIR USED FOR DRYINGConsult Fig. 2 to assist you in determining the relative humidity of airafter it has been heated.TEIIIPERATT,JRE OF THE HARVESTED GRAIN BEFORE DRYING, OFThis would be approximately the average outside temperature.PERCEMMOISTI,JRE CONTENT OF THE GRAIN BEFORE DRYING.o l-l-flll'n-fl-llu flTl-n'[[i-Tl'l-l-l-lll, n-[fT-t DESIRED FINAL PERCENT MOISTUNE CONTEM OF TIIE GRAIN AFTERDRYING.AIR FLOW RATE IN CI,IBIC FT. PER IiIINUTE OF AIR ST.JPPLIED BY THEFAN FOR EACH BUSHEL OF GRAIN IN THE BIN.Typical values are: l-2 CFM/BU for full bins. You may wish to consultother programs to obtain more exact figures for your system.'o [-l-[-T-TlThe computer analysis you will receive will be similar to that shown below. A listing of terms follows the exampleoutput.Cf lRNv MLL. .0  0R $TCI f r(@!,5?IR T ' [ :HFJr65 )ft TiI.. I.ILJINfi T{A I N TEMTI. 6{3 ,/\ 61itlFr.\6,Frc0, i \  t r l{: tr t',|./ IJ LJ'l@-tNA.TL,RAL.  ATI t  T I I IY INI i7t6Td' cd @do @-'6i. 6' cd' do du4 ' 7 " 5 O  1 5 . 4 0  l 9 ' J . $  L ? , f : ] 4  C r ? . 9 C '  C , 0 . ? J .  5 ? . 7 5  0 ' 0 ? 4 ; l9 1 1 . 0 0  1 4 . J . 9  J . [ ] . 4 3  l . ? ' t ] . 3  6 4 . 9 : 3  d , 0 . e ] ' I  5 9 . 7 4  O . O 4 S l .J . 4 ; 1 . 5 0  J . 4 . L f  1 . 7 , * V  l . ? . [ ] 3  6 f i . 0 0  6 : l '  " 4 $  s . i r , 7 4  0 , 0 7 i : 9J . ? 0 . 0 0  1 4 . 1 9  1 " 6 . q ' 7  1 9 . 8 : i  6 f i . 0 0  d l 1 , 1 0  5 9 , ' 7 7  0 , o g $ c ,: J . 3 7 . 5 0  1 4 , 1 9  : L 6 . l l 4  L ? , ; 7 : i  S : i , 0 0  & 2 , ' 7 9  : i ? , 7 e ]  0 , 1 : : 4 9; l S 5 . O O  L 4 ' L ?  J . i i . : i 3  : 1 9 . 3 [ ]  C ] f i . 0 0  C , . 3 . 4 4  $ 9 . 9 C ,  0 . 1 5 0 i ). 5 3 ? , 5 0  1 4 , J . ?  L 4 . S $  l . $ . 1 5  6 r i . 0 0  6 4 . 1 0  6 0 . 6 3  0 . 1 7 1 : i. 3 8 0 . 0 0  1 4 . 1 9  1 4 . 4 0  L d . O 0  C , S i , 0 0  6 4 . C , : :  6 : i 1 . 3 4  0 .  L { : } 1 . 94 0 s , 5 0  1 . 4 , L 9  J . 4 . . 1 1 4  1 . 4 . f ; i 3  $ r i . 0 0  6 4 . t t 5  C , 3 . 5 6  0 . L { ! } 4 C r1. CORN-Type of grain to be dried (Question 4).2. AIR TEMP-Temperature of the drying air (Question 5).3. REL. HuM-Percentage relative humidity of the drying air (Question 6).4. GRAIN TEMP-The temperature of the grain to be dried (Question 7).5. WBO-The initial moisture content of the grain in percent (Question 8).6. WBF-The desired final moisture content of the grain in percent (Question 9).7. CFM/BU-The airflow rate per bushel supplied by the drying fan (Question l0).8. TIME-The time in hours from when the drying process began, i.e., when the fan was tumed on.9. WB(l)-The percent moisture content of the grain next to where the drying air enters the bin for a given time.10. WBAVE-The average percent moisture content of the grain in the bin for a given point in time.I I . WB(IO)-Ihe percent moisture content of the grain at the point where the drying air exits the grain at a given point intime.12. G(llThe temperature of the grain next to where the drying air enters the grain for a given point in time.13. GAVE-The average temperature of the grain in the bin for a given point in time.14. G(l0)-The temperature of the grain next to where the drying air exits the grain for a given point in time.15. % DM-The percentage of dry matter decomposition. When this value reaches 0.570, the market grade will be lowered tothe next level. When it reaches lVo,the grain will have spoiled.16. PROGRAM STOPPED BECAUSE-This statement indicates that the grain moisture content has nearly reached equi-librium with the drying air. In other words, for the specified air conditions very little if any additional drying can occur.If the grain temperature reaches equilibrium before the moisture content does, the statement would be, *TOP LAYERCOOLED TO WITHIN IO DEGREES OF AMBIENT.''ENERGY CONSI,JMPTION:The energy used in low-temperature or natural air drying systems may be divided into that used by the fan and thatused in adding heat to the drying air. Heat may be added by either electricity or gas. In addition, energy may be expended forstirring the grain.A. FAN EMRGY: The amount of electricity used in fan operation may be determined through the program "FanPerformance on Grain Drying Bins". An estimate of enerry consumption may be made from the followingequation:, KW-hr of . .a ,Horsepower ol ,hours of .( E l e c t r i c a l E n " r r y )  =  (  f ; '  *  ( o p e r a t i o n 'where I hp : IOOO watts. The hours of operation can be determined from the analysis of your system. Forexample,408.5 hours of fan operation were required to dry the grain from the sample analysis. Therefore,if weassume a l0 hp fan was used:K W - h r = 1 0 x 4 0 8 . 5 = 4 0 8 5If electricity costs $0,03/KW-hr, the cost for electricity would be $145.50.B. HEATING AIR ELECTRICALLY: If low-temperature drying is used with electricity providing the energy forheating the air, the quantity used is:KW-hr = .,KW rating of. .hours of .' h e a t e r  ) * ( o p e r a t i o n )The KW rating of the heater may vary because many units are multi-stage; that is, one heating unit may becomposed of several stages of heater elements. In this case, use the average rating of the heater. If the rating ofthe heater was l0 IOY and it is operated for 408.5 houn as in the sample analysis, the KW-hr consumption wouldbe 4085. The cost would be $145.50 based on $0.03/KW-hr.HEATING AIR WITH LP GAS: The amount of IJ gas that is used may be estimated by the following equation:1 I 0x(CFM/BtI)x(Bu in Bin)x(hours of operation)x(temperature rise oF)(Gal of LP Gas) =: 92,000 x (efficiency of burning, zo)From the sample analysis, an airflow rate of 2 CFM/BU is used for 408.5 hours of operation.If we assume that(l) the bin contains 3000 bu (2) we wish to have a 5"F heat rise above that supplied by the fan and (3) theefficiency of the burning process is 80 percent, then the I,P gas consumed is:(Gal of LP Gu) == 183If the cost of LPwas $0.45/gal, the cost for dryingwould be $82.35 or2.754lbu.STIRRING DEVICES: The computer analysis does not consider stirring devices. However, the effects of thesemechanisms may be estimated by using the average moisture content of the grain (item l0) ratler than themoisture content of the top layer (item l4). Similarly, use the time required to reach this average moisturecontent and the associated ry matter decomposition (item 15). The energy used in stirring may be estimated bythe following:c.D.KW-hr I Cltt?9t^lt-,- ) x (hours of operation)Llsecl ln stlrnnq'SUMMARY:The natural air or low-temperature drying process is not recommended for Kentucky because of the relatively high riskof grain spoilage and contamination by aflatoxin owing to warm temperatures and higlr moisture contents usually foundduring the harvest season. This process does not have much reserve power; that is, the drying fiont moves relatively slowlythrough the grain. At any sign of trouble, the grain strould be removed from the bin and dried as quickly as possible usingother drying techniques uch as high-temperature portable batch or continuous flow dryers. Superior management is essentialif natural air or low-temperature drying is to be successful each year for Kentucky conditions.AVAILABLE COMPUTER PROGRAMS1. BNDZN: Computer analysis of economics, energy consumption and engineering design of a grain storage system.2. CHASE: Computer model that evaluates and compares costs of selected methods of harvesting, handling, drying andstorage of corn for an individual farmstead. Energy consumption is also estimated.3. CACHE: Computer model for economic analysis of farm drying and processing systems.4. SQUASH: Computer simulation of the harvesting-delivery-drying system used to determine bottlenecks in the system.*5. ESTIMATING FAN SIZES FOR GRAIN DRYING SYSTEMS*6, GRAIN DRYING PERFORMANICE EVALUATION*7, DRYERATIONPERFORMANCE EVALUATION*8. NATUML AIR.LOW TEMPERATURE DRYING PERFORMANCE VALUATION{.9. FAN PERFORMANCE ON GRAIN DRY]NG BINSACKNOWLEDGEMENTS:*These programs were developed by:Dr. Thomas L. Thompson, ProfessorAgricultural Engineering DepartmentUnivenity of NebraskaUncoln. NebraskaOfltce. Col lege ol  Agaculture. Universi ly ol  Kentucky, Room S-105. Agricul turat Scence Bui lding-North. Lexington. Kentucky 40546l s s u e d  I n  l u r t h e r a n c e  o l  C o o p e r a l i v e  E x l e n s i o n  w o r k ,  A c t s  o l  M a y  8  a n d  J u n e  3 0 .  1 9 1 4 ,  i n  c o o p e r a t i o n  w i t h  t h e  U . S  D e p a r t m e n t  o f  A g r i c u l t u r e  C h a r l e s  E .  B a r n h a r l ,  D i r e c t o r  o fC o o p e r a t i v e  E x t e n s i o n  S e r v i c e .  U n i v e r s i t y  o f  K e n t u c k y  C o l l e g e  o t  A g r i c u l t u r e .  L e x i n g t o n .  a n d  K e n t u c k y  S t a l e  U n i v e r s i t y .  F r a n k l o r t .lssued 1O78, 3M; 5M-7-81

Energy in Agriculture: Performance Evaluation for Natural Air and Low-Temperature Drying Systems

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Energy in Agriculture: Performance Evaluation for Natural Air and Low-Temperature Drying Systems

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