EMISSION AND PERFORMANCE TESTING OF A CROSSFLOW GRAINDRYER WITHOUT EMISSION CONTROL

L. Otten1, R. Brown1, A. W. Gnyp2, C. C. St. Pierre2, and D. S. Smith2

'School ofEngineering, University ofGuelph, Guelph, Ontario NIG 2W1, and Wellington Engineering Ltd.,Guelph, Ontario NIG2X2; and department ofChemical Engineering, University of Windsor, Windsor, Ont.

N9B 3P4.

Received 2 September 1982, accepted 4 February 1983

Otten, L., R. Brown, A.W. Gnyp, C. C. St. Pierre, and D. S. Smith. 1983. Emission and performance testingof a crossflow grain dryer without emission control. Can. Agric. Eng. 25: 111-118.

This paper describes a study to determine the emission and performance characteristics of a commercial crossflowdryer, ACE Model 2165-D. The dryer was not fitted with optional equipment tospecifically control particulate emission.The emission results showed that the average rate ofemission was 1.3 ± 0.4 kg/h or4.7 ± 1.4 kg/100 m3 ofdriedcorn when precleaned grain corn was dried. These results have been accepted by the Ontario Ministry ofthe Environmentfor impingement concentration calculations.

INTRODUCTION

Noise and dust emissions from countryelevators have become an increasingsource of complaints for the Ontario Ministry of the Environment (OME) duringthe past 10 yr. Much of the problem iscaused by an influx of commuters who areattracted by lower housing costs and otheradvantages of living in small communities. Subsequent growth of the communities frequently causes a conflict with established agricultural operations, including farms and elevators.

In contrast with industrial processes,OME has few data on the source of particulate emission from country elevators.Nevertheless, grain dryers are consideredto be the main source because they emita light, flaky, reddish material duringdrying of grain corn. This material, whichis known as 'red-dog' or 'beeswings,' ishighly visible and will be carried vast distancesby the wind. In an attempt to obtain

some quantitative information on particulate formation in dryers, OME negotiated a study with the Schoolof Engineering, University of Guelph. Although thestudy identified the type of particulatematerial and the main areas in the dryerwhere it is generated, it did not considerthe emission into the environment (Meier-ing et al. 1977).

A simultaneous survey of the literaturealso failed to provide the data needed toestablish guidelines for setting acceptableemission levels. The lack of emission datais due to the difficulties encountered insampling when the exhaust air containslarge particles and exits over a large areaat relatively low velocities. As illustratedby the summary in Table I, the emissionrates depend on dryer design as well as thesampling method. Myers (1973) performed multiple studieson two Aeroglidedryers and found that the measured emission varied with the sampling train used

TABLE I. SUMMARY OF EMISSION TESTS

to collect the particulate material. Despitethe variation in results caused by samplingtechniques, it is clear that the addition ofemission control equipment to the Aeroglide rack dryers resulted in a reduction ofparticulate emission.

Faced with an increasing number ofcomplaints and hampered by a lack of reliable data, OME decided to use the big-stick approach by requiring emission control equipment on all new dryers installednear buildings which are not part of theelevator complex. However, even this requirement might still produce emissionconcentrations at those impingementpoints which exceed the ambient air quality criterion of 200 |xg/(h.m3 of air) usedby OME (O'Keefe 1982, pers. commun.).It was therefore decided in 1979 to con

duct a study to determine the total particulate emission rate from a commonly usedcrossflow dryer with emission controlequipment. The work was carried out by

Capacity

Emission rate

(kg/100 m3 ofDryer Control system (m3/h) Sampling method (kg/h) dried corn) References

Rack dryersAeroglide None 375 UPO train 49 31 Myers (1973)

JOY-EPAt train 13 35 Myers (1973)Aeroglide rack None 725 Not specified 60 83 Anonymous (1971)Aeroglide rack Wiedermann Screen 100 EPA* hi-vol 45 45 Shannon et al. (1973)Model 2010C/GLH Kleen (34-mesh) train (43.3 m3/h)Aeroglide rack Wiedermann Screen 145 UPO train 42 9 Myers (1973)

Kleen (50-mesh) JOY-EPA train 2.3 2 Myers (1973)Hess rack DAY-VAC dust filter 36 EPA* method 2.7-4.5 8-13 Anonymous (1973a)

Crossflow dryersZimmerman

Model 8AP-1200

None 375 Rader hi-vol train 2.4 6 Anonymous (1971)

Mathews CompanyModel 900

None 145 Rader hi-vol train 1.2 8 Shannon et al. (1973)

ACE Behlen ROTO-VAC 250 JOY-EPA train 0.8 3 Gnypetal. (1980)

tJOY-EPA, Joy Manufacturing Agency Company's Emission Parameter Analyzer.^Environmental Protection Agency.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER 1983 111

Gnyp et al. (1980) on a new ACE Model2165-D dryer equipped with a Behlen Ro-tovac.

In the Rotovac equipment particle-ladenair exhausting from the dryer is passedthrough a 62-mesh (0.32-mm-diameteropenings) polyester filter which is attached to a drum rotating at 120 r/h. Thedeposited particles are continuously removed from the outer surface of the filterby vacuum nozzles and collected in highefficiency cyclones for disposal.

In the 1979 study three complete emission tests were carried out according to theOME Source Testing Code (Anonymous1973b) on the exhaust air leaving the filtersystem. It was found that the average Rotovac emission rate was 0.82 ± 0.01 kg/h or 3.39 ± 0.17 kg/100 m3 of dried grain.

The capital cost of installing the Rotovac system increases the cost of an ACE

OVERFLOW

(^DRYER LEG^^>

Model 2165-D by about 40%. In addition,the fine starch particles in the saturated airexhausted from the dryer caused operatingproblems during the 1979 drying season.For these reasons, the dryer manufacturer,Dorssers Welding Company Ltd., commissioned a second study with the objective of obtaining emission and performance data on an uncontrolled ACE dryerusing precleaned corn.

The emission data have been reviewedand accepted by OME for calculation ofthe impingement concentration contoursof ACE Model 2165-D installations.

This paper presents a description andresults of the study.

GENERAL INFORMATION

Project SiteA flow diagram of the country elevator

selected for the study is presented in Fig.

SCREENINGS

DUST

(^TOP AUGEFt^)

/\—SAMPLING POINTS

Figure 1. Grain handlingsystemat the test site.

1. Wet grain is dumped into an unloadingpit and elevated to a cleaner (Western Gyrating Cleaner, by A.T. Ferrell and Co.,Saginaw, Mich.) on the second floor ofthe elevator house. Cleaned grain is gravity-fed into an automatic dump scale whilethe cleaner tailings are removed to the dustor screening bins. Because the intake capacity of 110 m3/h is much greater thanthe dryer capacity, grain from the scalesis elevated into one of several wet storagesilos. Grain transferred from the holdingsilos to the dryer must pass through anaspirator cleaner (Dorssers Welding Co.Ltd., Blenheim, Ont.) in which red dogand other light particulate matter is removed. Dried grain is put into silos forfinal cooling and storage.

ACE Model 2165-D Grain DryerA side view of the crossflow dryer is

shown in Fig. 2 and a summary of the design characteristics is given in Table II.As the result of an earlier study (Otten etal. 1980), the dryer is designed to recirculate all of the cooling air and part of theexhaust drying air to the fan. By recyclingair, some of the unused energy is recovered and less particulate matter isemitted.

In an attempt to reduce the amount ofparticulate matter leaving the grain columns, the manufacturer used screens with2.0-mm-diameter openings instead of thestandard 2.8-mm openings. This was oneof the recommendations made by Meier-ing et al. (1977) but it had not been implemented until the construction of thisdryer.

With a limited supply of natural gas atthe elevator site, the 37 x 106 kJ/h burneris fueled by a mixture of natural gas andpropane. The proportion of each fuel depends on the availability of natural gas.

It was necessary to modify both sidesof the dryer to allow proper sampling ofthe particle-laden exhaust. As illustratedin Fig. 2, each louvred opening was covered with an assembly consisting of threesampling duct extensions. The assemblywas originally built for the 1979 Newburyproject (Gnyp et al. 1980).

Details of a typical extension are shownin Fig. 3. The egg-crate flow straightenersprovide nine 0.09-m2 sampling areas ineach of which two sampling points arespaced 100 mm apart. Each samplingpoint is located two equivalent diametersupstream and downstream of flow disturbances. With three duct extensions on eachside of the dryer and 18 sampling pointsper extension, a total of 108 points is usedto collect samples.

112 CANADIAN AGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER 1983

Figure 2. Side view of the dryer with the sampling duct extensions.

General Description of the TestsA complete evaluation of the emission

characteristics of a grain dryer requiresknowledge of the operating conditions ofthe dryer and the quality of the grain. Forthis reason the tests were planned so thatemission and performance data were obtained simultaneously. Thus, while theUniversity of Windsor group collectedemission samples, Wellington Engineering Ltd. and University of Guelph personnel collected grain samples and performance data.

The emission tests included evaluation

of (1) total particulate loading in the exhaust air; (2) particulate matter emissionrate on a dry air basis at 25°C and 101.0kPa; (3) particle size distribution of particulate matter in the exhaust air (4) average volumetric flow rate of exhaust air;(5) volumetric flow rate of air from eachsampling extension; (6) temperature andhumidity of exhaust air and ambient air;and (7) wind speed and direction.

The performance tests included evaluation of (1) inlet and outlet average moisture content of corn; (2) inlet and outletcracked corn and foreign material (CCFM)and quality of corn; (3) corn flow rate; (4)specific energy consumption; (5) dry andwet bulb temperatures of the drying air,cooling air, recirculating air, exhaust airand ambient air streams; and (6) cleaningefficiency of the aspirator and cleaner.

Before a test was started, the dryer was

FLOW

10 cm-DIAMETERSAMPLINGHOLES

SAMPLING PORTS

10cm-DIAMETERMETAL DUCTS

\

FLOW STRAIGHTENER

ELEVATION

•« -1-5 -

0-9rr ^

—m

* -#

•

/XX X X x X"

X X X X XX

X X X x XX

/FRONT

Figure 3. Details of a typical sampling duct extension.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER 1983

x-SAMPLING POINTS

IB

TABLE II. ACE MODEL 2165-D DESIGN CHARACTERISTICS

Grain column

Length (height) 20 m

Width 6.4 m

Thickness 0.3 m

Capacity per column 40 m3

Number of columns 2

Length drying section 13.4 m

Length cooling section 6.6 m

Screen panel size 0.3 x 0.9 m

Perforation size 2.0 mm

Gauge 18

Open area fraction 40%

Corrosion protection Oxide primer paint

Drying fanType DWDI Dorssers CentrifugalDiameter 1.7 m

Speed 9.2 r/sec

Motor size HOkW

Electrical demand (running) 100-107 kW

Static pressure (operating) 690 Pa

Rated capacity 197 000 m3/h @ 500 PaAirflow rate 400 (L/sec)/m2 of screen

Cooling fanCooling is proovided by drying fan at a static pressure of 300 Pa.

Burner

Type MAXON Model NP 136B

Fuel Natural gas and propaneRated capacity 37 GJ/h

Control system Manual thermostat; high-temperature limit switch; oneflame detector

Grain movement

Elevation (input and discharge) Bucket conveyorsMetering device Fluted meter rolls driven by variable speed hydraulic motorDischarge mechanism 0.23-m diam. screw conveyorRated capacity 36 m3/h at 10 percentagepoints moisture removal

operated for several hours to ensuresteady-state conditions. Since the OMEcompliance program requires three sets ofloading data for the dryer, both sides ofthe dryer were sampled on 18 and 25 Oct.1980 to obtain two sets of data. The third

set was obtained by sampling the south-side of the dryer on 21 Oct. and the north-side on 29 Oct.

Emission TestingEmission data acceptable for submis

sion to OME must be obtained accordingto their Source Testing Code (Anonymous1973b). The Code specifies the composition and qualifications of the samplingteam, locations of sampling sites in thestack or duct, number and distribution ofsampling points, sampling time and volume per point, type and operating procedure of equipment, laboratory analysis ofsamples, and reporting procedure.

Since the particulate matter emittedfrom grain dryers is not specifically mentioned in the Code and because the numberand location of sampling points deviatedfrom those specified in the Code, it wasnecessary to review the project with theAir Management Branch of OME prior toconducting the source sampling tests.

The sampling train employed for solidparticulate matter acquisition is shownschematically in Fig. 4. It was manufactured by the Western Precipitation Division of Joy Manufacturing and sold underthe trade name Emission Parameter Ana

lyzer (Joy-EPA). This model is approvedby OME and the U.S. Environmental Protection Agency. To ensure accurate measurements with the sampling train, the S-type Pitot tube-sampling nozzle combination, orifice rate meter and dry total gasmeter were calibrated according to standard procedures (Environment Canada1974).

To determine the particle-loading of theexhaust air, the duct extensions were traversed using the cumulative samplingmethod. This involved sampling for 150sec at each point, collecting about 8.5 m3of exhaust air. After a point was sampled,the probe was quickly moved to the nextpoint and the sampling flow rate was adjusted to match the velocity of the undisturbed exhaust stream at the samplingpoint. Velocity matching or isokineticsampling is necessary to ensure that notmore or less exhaust enters the train thanwould normally cross the probe area. Eachduct extension was traversed at the three

levels shown in Fig. 3, each time startingwith the point closest to the far wall.

After sampling a set of three or six extensions, depending upon whether one orboth sides of the dryer was sampled thatday, the contents of the first three im-pingers were sealed until sample analysisin the laboratory. The filter assembly,nozzle, probe and cyclone were alsosealed and transported to the laboratoryfor subsequent sample recovery and analysis.

An Andersen cascade impactor wasused in three separate tests to determinethe particle size distribution of the emittedsolids. As with the loading determinations, it was necessary to provide isokinetic conditions at the sampling points.

Performance TestingAll measurements needed to obtain the

performance of the dryer were made usinga procedure developed over the past 5 yrwhile testing various farm and industrialgrain dryers (Otten et al. 1980). All temperature, energy consumption and moisture content readings were recorded athalf-hour intervals.

Natural gas consumption was recordedwith a Roots Meter (Model 7M125) whilepropane consumption was measured witha Canadian Meter Co. Ltd. gas meter(Model AL12300).

Electrical demand and usage were determined from voltage and current measurements and the performance curves ofthe motors.

The grain flow rate was determined atleast once for each test by weighing about110 m3of wet corn into an empty silo. Themass flow rate was calculated from the

weight and the time required to dry thecorn. Conversion to volumetric flow rate

required use of the average test density ofdried grain.

Grain samples were collected beforeand after the aspirator, cleaner, and dryer(sample points 1 through 5 in Fig. 1). Thesamples were used to determine moisturecontent, CCFM, test density, and amountof kernel damage, all according to standard methods recommended by the Canadian Grain Commission.

RESULTS

Emission Results

The results of the particulate emissiontests are summarized in Table III. The ambient conditions are from measurements

at the beginning and end of each experiment, while the exhaust conditions represent the average of those observed ateach sampling point. The emission rate is

114CANADIAN AGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER 1983

HEATED AREA F|LTERHOLDER THERMOMETER 7 CHECK

/ VALVE

^PROBE L

VACUUMLINE

Figure 4. Schematic diagram of the Joy-Emission Parameter Analyzer sampling train.

calculated from the total particulate mattercollected and the averaged exhaust conditions measured while traversing one orboth sides of the dryer. All data reductionand analysis were done according to theOME Source Testing Code (Anonymous1973b).

Although the ambient conditions reported in Table III are necessary to calculate the emission concentration contours

away from the dryer, the most importantresults are the emission rates. By combining the results of all the tests, the averageemission rate of the dryer was 1.3 ± 0.4kg/h.

Particle size distributions of the emitted

particulate matter, as determined by theAndersen cascade impactor, are summarized in Table IV on a cumulative mass

basis.

Over 75% of the emitted material con

sisted of particles whose diameter exceeded 10 \xm. About 12% of the particleshad a diameter of less than 1 fxm. Thesesize distributions were confirmed by therelative amounts of solids collected in the

various components of the sampling train.

Dryer Performance ResultsAlthough temperature, energy con

sumption and moisture content data were

TABLE III. EMISSION RESULTS

Test no.

1 2 3 4

Ambient conditions

Wind speed (km/h) 5-13 6-8 6-11 3-10Wind direction wsw WNW N NNE

Temperature (°C) 13.6 16.7 9.3 4.4

Moisture content (vol. %) 1.15 1.12 0.91 0.55

Exhaust conditions

Dry bulb temp. (°C) 34.8 34.0 33.8 33.0Wet bulb temp. (°C) 34.1 34.0 33.8 32.6Flow rate 24 600 12 800 20 700 9 800

Emission results

Side of dryer N&S s N&S N

Particulate collected (mg) 76.1 65.0 67.1 52.5Emission rate (kg/h) 1.17 1.01 1.01 0.80Specific dryer emission

(kg/100 m3 of dried corn) 3.82 6.89 3.18 4.82

collected at half-hour intervals duringeach test, only those data and samples obtained during the mass flow rate determinations were used.

As shown in Table V, three completetests were run on 18, 25, and 29 Oct.However, difficulties in scheduling thetests made it necessary for the emissionsampling team to run a test on the southside of the dryer on 21 Oct. when personnel of Wellington Engineering Ltd. couldnot be present. The grain samples and

mass flow rate data were collected by theelevator manager of Taylor Grain Co. Ltd.

The total energy consumption was calculated assuming that the average heatingvalues of natural gas and propane are37.28 and 94.84 MJ/m3, respectively. Inthe energy efficiency calculation it wasassumed that the heat of vaporization is3020 kJ/kg of water removed.

The range of initial moisture contentspresented in Table V demonstrates thevariability in the moisture content of the

CANADIAN AGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER1983 115

TABLE IV. PARTICLE SIZE DISTRIBUTIONS OF PARTICULATE EMISSIONS ON A MASSBASIS

Anderseni AndersenL Andersen

Test 1 Test 2 Test 3

DP ^P D?(u.m) %<DV (fjim) %<DV (ixm) <%<DV

9.40 26.3 9.70 24.0 9.10 22.3

5.90 18.8 6.10 23.0 5.80 12.8

4.00 14.2 4.10 19.9 3.90 9.1

2.80 12.8 2.90 18.9 2.90 9.1

1.70 11.5 1.80 18.4 1.60 8.3

0.89 10.1 0.92 15.8 0.84 7.9

0.53 8.9 0.55 15.3 0.50 7.9

0.36 8.7 0.37 15.3 0.34 7.9

Dp = particle diameter.

TABLE V. DRYER PERFORMANCE TEST RESULTS

Date

80/10/18 80/10/21 80/10/25 80/10/29

Air conditions

Ambient temp. (°C) 12.2 -8.3 5.0

Ambient rel. hum. (%) 64 -79 62

Drying temp. (°C) 109-

110 110

Cooling temp. (°C) 30-

28 26

Cooling rel. hum. (%) 74-

80 91

Energy consumptionNatural gas (m3/h) 298.99 -

324.32 360.83

Propane (m3/h) 55.50 -

42.85 29.15

Electricity (kW) 100-

102 107

Total consumption rate (GJ/h) 16.78-

16.52 16.60

Corn parametersInlet/outlet MC (% WB) 29.8/16.1 29.8/16.9 29.8/17.6 27.9/16.9

Range of inlet MC (% WB) 25.9-34.9 28.4-31.2 27.4-34.2 24.5-29.7

Inlet/outlet temp. (°C) 18/38 -

15/16 6/33

Inlet/outlet CCFM (%) 0.64/0.93 -1.25/1.83 1.43/1.82

Inlet/outlet test density (kg/m3) 653/695 626/688 644/675 649/676

Damaged kernels (%) 0.85 0.53 0.53 0.88

Mass flow rate, wet dry, (tonne/h) 25.1/21.0 23.6/20.0 24.9/21.2 25.7/22.2

Volumetric flow rate, wet/dry (m3/h) 38.9/30.6 38.1/29.3 39.0/31.8 39.8/33.2

Specific energy consumptionMoisture removal rate (kg/h) 4110 3670 3690 3400

Specific energy consumption (kJ/kg) 4080-

4480 4880

Overall energy efficiency (%) 74-

67 62

within the limits established for No. 2

corn.

The results showed a significant increase in CCFM as the grain was dried.

This increase was expected because laboratory tests have established that dryinggenerates new particulate matter.

The wet and dry capacity results werecalculated from the weighed runs and thecorresponding wet and dry test densities.The variation in capacities for the fourtests is due to the difference in the amount

of moisture removed and the different am

bient conditions. In any case, if the resultsare converted to 10 percentage points ofmoisture removal, the lowest recorded capacity is 36 m3/h of dry grain and the highest one is 41 m3/h of dry grain.

The specific energy consumption results in Table V vary consistently with theambient and grain conditions. Since someof the energy put into the air is used tobring the drying air and the wet grain upto the drying temperature, this energy isnot available for drying. Therefore, thelower the ambient and wet grain temperatures, the higher the specific energy useand the lower the overall efficiency.

Performance of Aspirator and CleanerOn 25 and 29 Oct. three sets of samples

were collected before and after the aspirator (points 3 and 4 in Fig. 1). Each setcontained about 4.5 kg of grain which wascollected over a period of 30 min. Sampleswere taken simultaneously from the bottom of the dryer leg and from the spoutleading from the aspirator to the dryer.The results for each of the six tests shownin Table VI are the average of four moisture content and CCFM determinations oneach set of samples. The percent reductionin CCFM obtained by passing cornthrough the aspirator varied from 18 to37%.

Similarly, grain samples were collectedat 5-min intervals while grain from a single source was being unloaded on 25 and29 Oct. The sampled shipments were atleast 10 tonnes. Four moisture content and

CCFM tests were run after mixing the sub-samples for each day. The averaged results in Table VI indicate that about

different loads of grain received by theelevator during normal operation. Although the variations cause some difficulty in controlling the dryer, experiencedoperators are generally able to obtain adried product at the desired final moisturecontent by blending relatively wet and drygrain as it enters the dryer.

The moisture content of the grain leaving the dryer was greater than 16%and thetemperature exceeded 32°C. These conditions are consistent with the practice atTaylor Grain Co. Ltd. to cool the grain toambient conditions in the storage bins.This delayed-cooling approach uses thesensible heat of the grain to remove another 0.5-1 percentage point of moisture.

The grain quality parameters of testdensity, CCFM, and kernel damage are

TABLE VI. PERFORMANCE OF ASPIRATOR AND GRAIN CLEANER

116

CCFM CCFM Percent

Test Date of MC before after reduction

number test (% WB) (%) (%) in CCFM

Aspirator1 80/10/25 30.4 2.89 2.36 18.3

2 80/10/25 28.5 1.53 1.15 24.8

3 80/10/25 27.3 0.99 0.62 37.3

4 80/10/29 29.8 0.93 0.64 31.2

5 80/10/29 29.8 1.83 1.25 31.7

6 80/10/29 27.9 1.82 1.43 21.4

Cleaner

1 80/10/25 26.9 1.13 0.35 69.0

2 80/10/29 28.7 1.41 0.60 57.5

CANADIAN AGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER 1983

60-70% of the broken kernels, harvesttrash and other foreign material was removed by the cleaner.

To obtain an estimate of the size of the

material removed by the aspirator andcleaner, 2-kg samples of streams 6 and 7were also collected. The values in Table

VII are the average of four separate sieveanalyses. Before the distribution testswere run on cleaner screenings, all piecesof cobs and stalks were removed.

A visual examination of the material

removed by the aspirator from cleanedcorn showed that about half of the material

was red-dog. The particle size analysis indicated that at least 27% of the particlesare greater than 2.4 mm in size, or arelarger than the screen perforations of 2.0mm. However, most of the material removed by the aspirator is small and lightenough to be emitted from the dryer.

In addition to the pieces of cobs andstalks, 43% of the material removed bythe cleaner exceeds a particle size of 2.4mm in diameter, and 84% exceeds 1.2mm. The screenings consisted mostly ofbrokenkernels which have a specific gravity of about 1.2. In view of the large particle size and the specific gravity, most ofthe screenings would either be retained bythe dryer screens or settle out in the exhaust plenum.

DISCUSSION

The emission rates are the most important part of the study because they areneeded to calculate the particulate concentration contours around the dryer (Anonymous 1980). OME has accepted the result of the study and uses it to determinethe impingement concentration at thenearest dwelling when an application toerect an ACE Model 2165-D dryer is received. If the impingement concentrationis less than 200 |xg/h.m3 of air), approvalis given; if it is greater, pollution controlequipment must be used or the sitechanged (O'Keefe 1982, pers. commun.).

The specific emission rate of 4.7 ±1.4kg/100 m3 of dried grain is of the samemagnitudeas the 3.4 ± 0.2 value reportedby Gnyp et al. (1980) for an ACE Model2165-D equipped with emission controlequipment. Although the Rotovac equipment does reduce the amount of particulate matter emitted, the decrease is considerably smaller than expected. The netresult is that an uncontrolled dryer withthe specification shown in Table II is acceptable for elevator sites which previously would only be approved if pollutioncontrol equipment were included.

One important item of the dryer specifications is the use of screens with 2.0-

TABLE VII. PARTICLE SIZE DISTRIBUTION OF CLEANINGS-PERCENT BY WEIGHT

Source ofParticle size (mm)

cleanings >2.4 1.2-2.4 0.6-1.2 0.3-0.6 0.15-0.3 <0.15

1. Screeningsfrom cleaner

2. Cleanings fromaspirator

43.3

26.9

40.6

28.4

10.9

16.2

4.0

10.0

0.9

9.0

0.3

9.5

mm-diameter openings. The size distribution results of the samples from thecleaner and aspirator show that a considerable amount of fine material is removedbefore corn enters the dryer.

Drying conditions are probably moreimportant in determining the emission ratethan may be evident from the results. Ifthere is extensive condensation in the col

umn enclosure, particulate matter may actas nuclei for condensation or come in con

tact with the wet walls. In either case theparticles will probably stay inside the enclosure. Indeed, visual examination of theenclosure showed a considerable amountof condensation and particulate matter onthe walls, floors, screen supports and, toa lesser extent, on the screens.

The same observation was also made byHoefkes (1976) when he performed emission studies on a pilot scale dryer at theUniversity of Guelph. He concluded thatdrying corn with a low initial moisturecontent (<20% WB) resulted in less vaporcondensation and higher emission rates.

Wet corn used in the present study hada moisture content range of 25-35% WB,which represents the normal range encountered during the harvest season.

Since the emission rates were obtainedwith precleaned grain, any new plant mustalso have a cleaner and aspirator. It is interesting to note that the south-side emission rate obtained in Test 3 was only 5%higher than that of the north-side, eventhough uncleaned corn was being driedduring the south-side sampling period.This small increase is readilyexplainedbythe fact that the cleaner was shown to remove broken kernels rather than the fineswhich could pass through the dryerscreens.

The importance of the aspirator isclearly illustrated by the reduction inCCFM and the type of material removed.Although much of the material has a particle diameter greater than the screenopenings, it consists mostlyof red dog andother fragile particles which are easilyfractured during drying.

The dryer performance results showthat the dryer was operated at uniformconditions throughout the study. The capacity was nearly constant at 39 m3of wet

corn per hour and a moisture removal of11-12 percentage points which is higherthan the rated capacity of 36 m3at 10 percentage points removal. The specific energy consumption values are of the samemagnitude as those observed in an earlierstudy of an ACE dryer under comparableambient and harvest conditions (Otten etal. 1980). The decrease in overall energyefficiency with a decrease in ambient andwet grain temperature is as expected.

CONCLUSIONS

The main conclusions drawn from the

project results are as follows.1. The results of the compliance tests

showed that the average emission rate ofthe dryer operated with precleaned No. 2grain corn was 1.3 ± 0.4 kg/h or 4.7 ±1.4 kg/100 m3 of dried corn.

2. The grain cleaner removed about60-70% of the CCFM in the wet corn.About 84% of the screenings had a particlesize greater than 1.2 mm diameter.

3. The aspirator removed between 18and 37% of the CCFM before the grainentered the dryer. The bulk of the removedfines was 'red dog' with a particle sizegreater than 1.2 mm diameter.

4. The dryer capacity was at least 10%greater than the rated capacity of 36 m3 ofwet grain per hour.

ACKNOWLEDGMENTSWe wish to thank Mr. V. Ozvacic, P.Eng.,

AirResources Branch,OMEfor reviewing andauthorizing the design of the sampling ductextensions and the number and location ofsampling points. The cooperation of Mr. W.P. Suboch, P.Eng. andMr. H. Wong, P.Eng.,WasteManagement Branch,OMEduringsampling is also appreciated. Above all, we are indebted to Mr. Bill Dorssers for his permissionto publish the results of the study.

REFERENCES

ANONYMOUS 1971. Background information for federal performance standards.Grain handlingand milling. ProjectCPA70-142. PEDCO. Environmental SpecialistsInc., Cincinnati, Ohio.

ANONYMOUS 1973a. EPA emission testingreport 73-GRN-Y, Part I. Summary of results. National Technical Information Service, U.S. Dep. Commerce, Springfield, Va.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER 1983117

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