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LIBRARY .
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Univufity

   

This is to certify that the

thesis entitled

CONTINUOUS-FLOW DRYING OF SOYBEANS

presented by

Valdecir Antoninho Dalpasquale

has been accepted towards fulfillment
of the requirements for

M.S. degree in AB

.:: 7 /Z/‘/)/
’t/CZZA ' “((1 414.;

Major professor

 

 

Date 05.16.79

 

 

 

1 ENE a 5.?

K-hi {‘1

2.1

95"?”

1 ,7 RS.

5“ 0" «,8

CONTINUOUS-FLOW DRYING OF SOYBEANS
BY

Valdecir Antoninho Dalpasquale

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Agricultural Engineering

1979

ABSTRACT
CONTINUOUS-FLOW DRYING OF SOYBEANS
BY

Valdecir Antoninho Dalpasquale

The feasibility of drying soybeans continuously at
high temperatures is the main topic of this study. In
the United States, the adoption of this practice will
permit harvesting of soybeans at higher moisture contents,
thus reducing the losses at harvesting. Field losses due
to adverse weather conditions will also be reduced. In
Brazil, besides the advantages already mentioned, early
harvesting will make the practice of double cropping
(soybeans-wheat) more attractive.

A one-stage concurrent flow dryer was used in the
laboratory to dry soybeans at different temperatures. In
the first test, soybeans at 14.18 percent wet basis moisture
content were dried at 121.1°C for 2.5 hours. In the second
test, two stages were simulated by letting the soybeans to
temper for two hours between runs. For the first stage,
121.1°C was used as the drying air temperature, and for the
second stage, 93.3°C. In the third test, two stages were
simulated and the inlet drying air temperatures were 148.9°C
and 121.1°C for the first and second stages, respectively.
In all tests, the overall dryer efficiencies fell between
4200 and 5100 kJ/kg of water removed. Germination, cracks

and splits were the quality parameters evaluated; the

Valdecir Antoninho Dalpasquale

obtained values after drying were considered satisfactory.
Continuous flow drying of soybeans was also studied

by the use of a newly developed crossflow dryer computer

model. The lack of precise thin—layer drying equations and

equilibrium moisture content equations was noted. Neverthe-

less, an acceptable crossflow dryer model was developed for

air and soybean conditions typical of the United States

as well as Brazil.

MM/u/W

Major Professor

.5“- $4977

r~

 

Department Chairman

Chapter

II

III

IV

TABLE OF CONTENTS

INTRODUCTION .

1.1 Production, Perspectives and Importance
of Soybeans in the United States and

Brazil.

1.2 When and Why Soybeans Must Be Dried .

1.3 How Soybeans Are Dried.

OBJECTIVES

LITERATURE REVIEW.

3.1 Soybean Quality

3.2 Continuous Flow Drying.

CONCURRENT FLOW DRYING .

4.1 Experimental.

4.

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+4 hard h‘rd hard #4

tom-amateurs:

l.

1

Dryer.
Soybeans
Soybean flow rate.

Temperature and relative humidity.

Air flow rate.
Liquid propane gas
Moisture content
Germination tests.
Cracks and splits.

4.2 Test Procedure.

iii

Page

11

22

24
24
24
26
26
29
29
31
31
32

33

Chapter
V

VI

VII

VIII

CROSSFLOW DRYING .

5.1 Crossflow Model Development

5.

UICfi UICfl m
H +4 H +4 H

1.

(5)01;th

l

Thin-layer equations

Equilibrium moisture content
Specific heat.

Latent heat of vaporization.

Air and other soybean properties

Energy and static pressure
equations.

RESULTS AND DISCUSSION .

6.1 Concurrent Flow Dryer

6.2 Crossflow Simulation.

CONCLUSIONS.

SUGGESTIONS FOR FURTHER STUDIES.

APPENDICES

A

B

LISTING OF THE COMPUTER PROGRAM.

SCHEMATIC OF THE COMMERCIAL UNIT SIMULATED
IN THIS THESIS . . . . . . . . . .

EQUILIBRIUM MOISTURE CONTENT RESULTS FROM
ROA EQUATION FOR RELATIVE HUMIDITY HIGHER
THAN 90 PERCENT FOR SEVERAL TEMPERATURES

GERMINATION, CRACK AND SPLIT RESULTS AND
TEMPERATURE RESULTS. . . . . . .

D.1 Germination, crack and split results
for Test No. l (121.11°C) .

D.2 Germination, crack and split results
for Test No. 2 (121.11-93.33°C)

D.3 Germination, crack and split results
for Test No. 3 (148.89-121.11°C).

D.4 Temperature results (°F) for the
concurrent flow dryer .

iv

Page

36
38
48
63
63
63

64

66
66

77
84

86

88

98

99

100

100

101

102

103

APPENDICES Page
' E CONVERSION FACTORS. . . . . . . . . . . . . . . 104

REFERENCES.......................106

Figure

10

11

LIST OF FIGURES

Block diagram of a 3—stage cross flow dryer
with partial air recycling (Lerew et al.,
1972). . . . . . . .

Block diagram of a 2-stage concurrent flow
dryer with counterflow cooler (Brook, 1977).

Relation between energy required and initial
moisture content of rice when the drying air

temperature is 48.89°C (120°F) (Bakshi et al.,

1978). . . . . . . .

Product and air temperatures versus depth for
a single-stage concurrent flow dryer (Brook,
1977). . . . . . . . . . . . . . . . . .

Block diagram of concurrent flow dryer with
counter flow cooler (Brooker et al., 1974)

Schematic of the pilot-scale concurrent flow
dryer used in the laboratory, showing the
thermocouple locations (dots) (Walker, 1978)

Response of the Overhults thin-layer drying
equation for soybeans when the drying para-
meters are estimated by the White equation

Response of the Overhults thin-layer drying
equation for soybeans when the drying para-
meters are estimated by the White equation

Response of the original Overhults thin—layer
drying equation for soybeans

Response of the Roa-Macedo thin-layer drying
equation for soybeans. . . . . . . . .

Soybean equilibrium moisture content predic-

tion according to Alam, Henderson-Thompson,
Chung-Pfost, and Sabbah equations, at 10°C .

vi

Page

13

14

16

23

25

44

45

46

47

51

Figure Page

12 Soybean equilibrium moisture content predic-
tion according to Alam, Henderson-Thompson,
Chung-Pfost, and Sabbah equations, at 21.1°C . . 52

13 Soybean equilibrium moisture content predic-
tion according to Alam, Henderson-Thompson,
Chung-Pfost, and Sabbah equations, at 32.2°C . . 53

14 Soybean equilibrium moisture content predic-
tion according to Alam, Henderson-Thompson,
Chung-Pfost, and Sabbah equations, at 43.3°C . . 54

15 Soybean equilibrium moisture content predic-
tion according to Alam, Henderson-Thompson,
Chung-Pfost, and Sabbah equations, at 54.4°C . . 55

16 Soybean equilibrium moisture content predic-
tion at 43.3°C using a combination of the
Henderson-Thompson and Sabbah equations. . . . . 58

17 Soybean equilibrium moisture content predic-
tion at 21.1°C using a combination of the
Henderson-Thompson and Sabbah equations. . . . . 59

18 Soybean equilibrium moisture content predic—
tion using the average between the Henderson-
Thompson and Sabbah equations at five levels

of temperature . . . . . . . . . . . . . . . . . 60
19 Soybean equilibrium moisture content predic-

tion according to the Roa equation for five

levels of temperature. . . . . . . . . . . . . . 62

vii

Table

LIST OF TABLES

Production of soybeans in the United States
and Brazil during the period of 1968 to 1978.

Proposed standard conditions for the perform-
ance evaluation of automatic batch and con—
tinuous-flow grain dryers, drying shelled
corn. . . . . . . . . . .

Monitoring instruments.

Air and soybean properties treated as
constant in the simulation program.

Soybean germination, crack and split
variations after drying in a concurrent
flow dryer.

Input and results for the crossflow dryer
simulation, first stage

Input and results for the crossflow dryer
simulation, second stage.

Input and results for the crossflow dryer
simulation, third stage

Input and results for the crossflow dryer
simulation, fourth stage.

viii

Page

18

27

65

76

78

79

80

81

EMC

fg

K II: D" O

LIST OF SYMBOLS

heat capacity of dry air, BTU/1b °F or otherwise
specified

heat capacity of dry product, BTU/lb °F or other-
wise specified

heat capacity of water vapor, BTU/lb °F or other-
wise specified

heat capacity of liquid water, BTU/1b °F or other-
wise specified

efficiency rating, lbs of water removed by 1000 BTU
of fossil energy

energy consumption, BTU

equilibrium moisture content, dimensionless
dry airflow rate, lb/hr-ft2
grain flow rate lb/hr-ft2 or kg/hr-m2

latent heat of water in grain, BTU/lb or kJ/kg

humidity ratio, lb of water/1b of drying air

moisture content, decimal wet basis or otherwise
specified

moisture equilibrium, decimal dry basis or
otherwise specified

initial moisture content, decimal wet basis or
otherwise specified

air water vapor pressure deficit, kgf/m2
volumetric airflow, cfm/bu
universal gas constant, 1.987 cal/kg °K

Reynolds number, dimensionless

ix

RH

amb

i3

relative humidity of drying air, decimal or other-
wise specified

ambient air relative humidity, decimal

moisture removal, lb

static pressure due to airflow, inches of water
drying air temperature, °F or otherwise specified
drying time, hr

drying air temperature, °R

ambient temperature, °C

node position

column depth, ft

weight of grain at moisture M, lb

grain temperature, °F or otherwise specified

dry bulk density of grain, lb/ft3

CHAPTER I

INTRODUCTION

Artificial drying of a wide variety of crops is a
practice that gives satisfactory results for most uses.
Drying soybeans (Glycine max, L., Merril) requires the know-
ledge of the parameters which determine the quality of the
dried product. Some requirements are already known. For
instance, several studies showed that at low air humidity
(below 40 percent RH) cracking of the seed coat and separa-
tion of the cotyledons are likely to happen to soybeans.
Preserving the seed quality during the drying process results
in a better product for storage, avoids seeds with low

germination and, consequently, low yields.

1.1 Production, Perspectives and Importance of Soybeans in
the United States and Brazil

In the United States, soybeans are planted by about
600,000 farmers. It is the second largest crop by volume.
The production has increased over the years to 1.81 billion
bushels in 1978 (approximately 49 million metric tonnes).
Most of this is used as animal feed but it is also consumed
as human food. Soybeans and soybean derivatives exported
in 1978 generated $4.75 billion, i.e., 17.4 percent of the

value of all agricultural products exported during that

1

period of time. The future trend is likely to be a smooth
increase in the production due to better yields through the
adoption of more sophisticated agricultural techniques.

In Brazil, soybean production has increased by more than
ten times since 1968, when it was a practically unknown
culture. In 1978, 9.35 million metric tonnes of soybeans
were grown on Brazilian farms and the projection for 1979
is a record production of more than 12.0 million tonnes.

The Brazilian economy is greatly dependent on agricultural
products with soybeans playing a major role. As in the
United States, the production tends to increase each year

but at higher rates mainly because Brazilian farmers are
expanding their acreages by expanding the country's frontiers.

Table 1 presents the American and Brazilian soybean
production during the last ten years. In 1968 the Brazilian
production was about 2 percent of that produced in the United
States; this proportion has increased to about 19 percent

ten years later.

1.2 When and Why Soybeans Must Be Dried

Soybean drying is a practice that can usually be
avoided by American farmers because of the favorable weather
conditions at harvest time. The crop is left in the field
until the moisture content reaches a level that is safe for
storage, i.e., around 11-12 percent or even less, depending
on the storage time. Rather recently, some soybean growers
in the Corn Belt have started harvesting at 15-17 percent

moisture content followed by artificial drying to about

Table 1: Production of soybeans in the United States and
Brazil during the period of 1968 to 1978.

 

 

Year United States Brazil
In 1000 ton
1968 30,121 655
1969 30,833 1,057a
1970 30,669 1,509a
1971 32,000 1,977a
1972 34,575 3,223a
1973 42,100 5,135a
1974 33,156 7,876a
1975 42,071 9,892a
1976 35,048 10,810
1977 47,946 12,000
1978 49,252 9,350

 

Source: Agricultural Statistics, USDA (1978) and
a: Os Verdadeiros Numeros do Brasil, ed Bloch (1975).

12 percent. Low temperature drying has been most often
used.

The Brazilian situation is quite different. Almost all
soybeans must be artificially dried in one way or another
after harvesting. Since a significant percentage of the
soybean growers double crop wheat, the time between the
harvest of soybeans and the planting of wheat is not long
enough to permit drying of the soybeans in the field.
Another important point is that the sooner the product is
sold, the better is the market price and the less interest
is paid for the borrowed money. Brazilian farmers are more
concerned about interest because it is much higher in Brazil
than in the United States. In fact, it may determine the
profitability of the business.

Drying soybeans in Brazil is an operation practiced
mainly by the cooperatives and by the processing industry.
Only a very small amount is dried and/or stored on farms.
This is due to the lack of knowledge of post-harvest tech-
niques on the part of the farmers and because of the high
initial investment of the necessary equipment. In general,
soybeans require better controlled storage conditions than
other crops such as corn and wheat. At tropical conditions

these requirements are more pronounced.

1.3 How Soybeans Are Dried
The conventional field drying practiced in the United
States is satisfactory as far as keeping quality and storage

are concerned. However, it is a weather dependent practice

and often leads to excessive losses because of the brittle-
ness of the bean stalks and pods. Under unfavorable condi-
tions of humid weather, the beans suffer deterioration prior
to the harvest.

Harvesting soybeans at high moisture content levels
requires that the amount of water in the beans is decreased
down to safe storage quantities. This can be done in several
ways.

The oldest drying method, which is still extensively
used in the United States, is natural drying in the field.
It is highly dependent upon the weather conditions. Artifi-
cial drying is a safer method to decrease the excessive
moisture in the crop. There are several methods which fall
in this category. Forced air is the most common. The
resulting drying rate is a function of the product moisture
content, product. equilibrium moisture content, mass flow rate,
air temperature and relative humidity. The equilibrium
moisture content of a product is the lowest moisture which
the product can reach under given air conditions. The rate
of drying is controlled by the amount of heat that is added
to the air. The drying process falls into two categories:
low- and high-temperature drying.

The low-temperature process is being used specially
for seed drying where the viability of the crop must be
preserved. With the increase in energy costs, this method
is being preferred by some researchers. In some cases, no

heat is added, and ambient (natural) air is used. When the

initial moisture content of the crop is high and the weather
is unfavorable, the drying time during natural air drying may
be so long that some deterioration takes place before the
desired low moisture level is reached.

High-temperature drying is a faster process and is
less dependent upon the weather conditions. The raising of
the air temperature is expensive and creates a management
problem. If too high, the soybeans may crack, thereby
increasing the chances of molding and deterioration and making
storage more difficult. If too low, the water removed will
be less than the desirable amount, i.e., the end product
will not have the desirable quality.

Low- and high-temperature processes have advantages and
disadvantages. The utilization of one or the other will be

decided by the particular characteristics of each situation.

CHAPTER II

OBJECTIVES

The general objective of this thesis is to retain the
soybean quality during continuous flow drying at high air
temperatures.

The specific objectives are:

1. To verify the feasibility of continuous-flow high—
temperature drying of soybeans in a concurrent flow dryer.

2. To maintain soybean quality at high drying tempera-
tures using the concurrent flow dryer.

3. To develop a computer model for simulating soybean
drying in a continuous cross flow dryer to be used in optimiz-

ation studies.

CHAPTER III

LITERATURE REVIEW

3.1 Soybean Quality

Soybeans are classified in different grades according
to their visual and physiological conditions. The latter is
represented mainly by the germination capability of the seeds
although the amount of free fatty acids is sometimes con-
sidered. By the visual conditions is meant the external
appearance of the seeds, including cracking of the seed
coat and broken and/or separated cotyledons.

Several investigators have studied the factors which
alter the quality parameters. White et a1. (1978) carried
out thin-layer experiments using three initial moisture con-
tents (16, 20 and 24 percent, wet basis), seven dew-point
temperatures ranging from 8 to 38°C, and five drying tempera-
tures (from 30° to 70°C). Drying data was analyzed by
fitting an exponential drying model containing two empirical
drying parameters. The drying damage was analyzed and class-
ified according to seed coat and cotyledon or cleavage
cracks. Seed coat cracks were found to be correlated to
the initial moisture content, drying air relative humidity,
the difference between the vapor pressure of the drying air

and the saturated vapor pressure at the wet bulb temperature,

8

the dew-point depression, the difference between the initial
and equilibrium moisture content, and the two empirical
drying values contained in the drying model.

The relative humidity of the drying air must be kept
above 40 percent, regardless of the air temperature, if
soybeans are to be used for seed. Below 40 percent relative
humidity, severe cracking damage can occur to the beans,
especially at high air drying temperatures. In order to
avoid germination losses, the seed temperature cannot be
greater than 43.33°C (110°F). To prevent cracking, the
temperature limit may be increased to 54.44-60°C (130-140°F),
although some splitting will have occurred at that tempera-
ture level (Rodda, 1974).

Pfost (1975) studied the effects of varietal and
environmental factors on the cracking of soybeans in the
range of 90 to 150°F. Seventeen varieties were tested and
significant differences were found among them. In general,
cracking decreased with an increase in the final moisture
content and relative humidity of the drying air, and increased
with an increase in air temperature, drying rate and initial
moisture content. For any given variety, the most signifi-
cant factor affecting cracking was the relative humidity of
the drying air. Pfost also observed that most of the cracks
formed during the first five minutes of drying.

Ting et a1. (1978) investigated the occurrence and
extent of drying damage in remoistened soybeans at different

depths in a laboratory-type deep-bed dryer. The position of

10

the soybeans in the bed was found to be the most significant
factor affecting the drying damage. The farther the soy—
beans were located from the air inlet, the lower the damage.
Thus, the drying damage produced in soybeans at varying loca—
tions in a deep-bed dryer will be different. Besides the
position in the drying bed, initial moisture content, air
flow rate and air drying temperature were all found to
significantly affect the drying damage.

Sabbah et a1. (1976) applied the reversed-direction-
air-flow technique to a batch-in-bin drying system and claimed
considerable improvements in soybean seed quality over the
conventional one-direction-air-flow method. In this system,
the final moisture content was uniform throughout the bed
due to the periodic reversal of the air flow direction.

Due to the better uniformity of the moisture content,
fewer overdried and underdried seeds were observed. This
resulted in less cracking and mold activity inside the mass
of beans. Another advantage of this drying method is the
avoidance of mechanical stirring equipment which is fre-
quently used in order to obtain a more uniform final mois-
ture content. Stirring of a bin of soybeans usually increases
the mechanical damage of the dried product.

White et a1. (1976) reported that the physical damage
experienced by soybeans when dried with heated air can have
pronouced effects on their long term storability and quality.
Soybeans dried by means of high air temperature are more
prone to mold development and, also, to an increase in the

fatty acid content.

ll

Chanchai et a1. (1976) studied the influence of heated
air drying on soybean impact damage using temperatures from
75 to 165°F. Heated air drying resulted in considerable
damage to the soybeans and was related to subsequent impact
damage during handling. Tests showed that the higher the
drying temperature, the higher the number of cracks and
splits. However, Hall (1974) studying damage caused by
handling of soybeans, observed-that artificial drying will
not cause an increase in damage during handling. A similar
observation was made by Matthes and Welch (1974) who con-
cluded that it is feasible to dry high moisture content
soybean seeds with heated air and obtain a finished product
of acceptable quality.

Soybean seeds which did not lose quality significantly
during the drying process still can be deleteriously affected
if subsequent handling and storage operations are not
properly performed. Rodda and Ravalo (1978) stored soybeans
in four types of containers at ambient temperatures and in
sealed metal containers at constant temperatures. Samples
at low initial moisture content maintained the original
characteristics satisfactorily under tropical conditions.
0n the other hand, samples with poor initial quality did

not store well even at temperatures as low as 3°C.

3.2 Continuous—Flow Drying
For the purpose of this thesis, only cross flow and
concurrent flow drying processes will be considered. Cross

flow drying is the most commonly used continuous-flow drying

12

technique. The concurrent flow dryer has recently been
developed.

In a cross flow dryer, the directions of the grain and
air flow are perpendicular. As a rule, grain nearest the
air exhaust tends to remain wet, and grain near the air inlet
tends to overdry and overheat. However, commercial cross
flow dryers with air recycling and reversed air flow over-
come these disadvantages somewhat. These so-called modified
cross flow dryers reduce the moisture and temperature gra-
dient problems and are also more efficient than the conven-
tional cross flow dryers (Lerew et al., 1972). Additional
changes in the basic cross flow dryer design will be needed
in order to overcome the problems related to energy effi-
ciency and the quality of the end product. A diagram of a
modified cross flow dryer is presented in Figure 1.

In a concurrent flow dryer, air and grain flow in the
same direction, resulting in an equal drying treatment of
the product. The air temperature decreases rapidly because
the warmest air encounters the wettest grain causing evapora-
tion to occur at high rates. The reason for the popularity
of this kind of dryer is the advantage it represents over
the conventional cross flow dryer with regard to energy
efficiency, product quality and air pollution. A diagram
of a two-stage concurrent flow dryer is presented in Figure 2.

A grain dryer is a device which uses ambient air and
a source of heat to create a flow of heated air to remove

water from a grain. Its performance is affected by several

13

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partial air recycling (Lerew et al.

Figure 1:

14

GRAIN IN

 

 

HEATER FAN AMBIENT AIR

V

CONCURRENT
DRYING

 

 

 

 

[TEMPERING J
r HEATER AMBIENT AIR

CONCURRENT
DRYING

 

 

 

 

 

 

 

1” EXHAUST

 

 

 

COUNTER
FLOW
COOLING

 

 

 

 

* FAN AMBIENT AIR

GRAIN OUT

Figure 2: Block diagram of a 2-stage concurrent flow dryer
with counterflow cooler (Brook, 1977).

15

factors including: (1) the air temperature and relative
humidity, (2) the initial grain temperature, (3) the initial
and final moisture content of the grain, (4) the resistance
to air flow through the grain mass, (5) the throughput of
the dryer, (6) the grain variety, and (7) the design factors
of the burner, fans, and ducting systems. All these para-
meters act together.

Generally, the higher the initial moisture content of
the drying product, the faster the drying rate will be in
terms of water removed vis-a-vis energy inputs. This is
explained by the fact that at higher moisture contents
water is removed more easily from the individual grain
kernel, i.e., water is less highly held by the grain.

Figure 3 shows the relation between energy required and the
initial moisture content of rice when the drying air tempera-
ture was 48.89°C (120°F). As expected, at the higher initial
moisture contents less energy per pound of water removed

was required than at lower moisture contents.

The air conditions can drastically alter the drying
efficiency. They are the most easily manageable parameters
in a drying system, especially the temperature. Together
with the air flow, the air condition is responsible for the
amount of water removed in a dryer and also determines the
quality of the end product.

Air flow resistance, usually expressed as the pressure
drop across a bed of the drying product, can have a signifi-

cant effect on the airflow rate and thus on the drying rate.

98 f3 38 08

(80 ‘HDVLNHDHHd) LNHLNOO HHHLSIOW TVILINI
86

(.0
0

Figure 3:

16

ENERGY (BTU/LB OF WATER)

 

H H H m m m

:35 O3 00 O N A

O O O O O O

O O O O O O
l l I r* l r I I

 

3°68°8F HHOLVHHdWHL HIV

 

 

 

Relation between energy required and initial mois—
ture content of rice when the drying air tempera-
ture is 48.89°C (120°F)(Bakshi et al., 1978).

17

For a given fan size, the cleaner the mass, the higher the
airflow and the drying rate will be.

The grain variety may affect the total water removed
by a dryer. Bakker-Arkema et a1. (1978) observed that some
corn varieties dry at different rates. They defined a new
quantity, named the "hybrid drying factor”, which accounts
for the characteristic drying behavior of a lot of corn.

This factor is the ratio of the specific drying rate to the
standard drying rate of a lot of corn used in an experimental
dryer test. Similar observations were made by Keener and
Glenn (1978). Tests to determine thin-layer drying constants
will result in specific values for each hybrid corn variety.
The hybrid factor should be defined for other crops than

corn and thus also for soybeans.

A standard method for testing grain dryer performance
has not been established. The importance of such a method
cannot be overemphasized since comparison between different
dryers will only be realistic if the dryers are tested under
the same conditions.

Bakker-Arkema et a1. (1978) proposed standard conditions
for the performance evaluation of automatic batch and con-
tinuous-flow dryers. The variables that have to be monitored
are the inlet and outlet grain moisture content and tempera-
ture, the ambient air temperature and relative humidity,
the presence of foreign materials and the time period of
testing. The proposed values for drying shelled corn are

listed in Table 2.

18

Table 2: Proposed standard conditions for the performance
evaluation of automatic batch and continuous-flow
grain dryers, drying shelled corn.

 

Average inlet grain moisture content, % wb 25.0 i 1.5
Average outlet grain moisture content, % wb 15.0 t 0.5
Average ambient air temperature, °F 50 t 10
Average ambient air relative humidity, % 50 i 10
Average inlet grain temperature,°F 50 t 10
Inlet grain BCFM, % 3.0
Outlet grain temperature, °F above ambient 15

Time period of testing, h 24

 

Source: Bakker-Arkema et a1. (1978).

19

Keener and Glenn (1978) proposed a method to standardize
the measurement of performance of crop dryers using rates
of moisture removal and energy requirements. The following

formulas are suggested in the evaluation of these parameters.

Mo M

RM (l-Mo ' l-M)

- (l—M) - w

E = 3 - 3414 - electrical energy (kWh/test) + heat of
combustion of fossil fuel per test

e = 1000 . RM - E

where,
RM = moisture removal (lbs)
M = initial moisture content (w.b., decimal)
M = final moisture content (w.b., decimal)
W = weight of grain at moisture M dried by the system
during the test (lbs)
e = efficiency rating (lbs of water removed by 1000

Btu of fossil energy)

Bakshi et a1. (1978) compared various drying conditions
in an attempt to evaluate the energy needed for drying rice
in a cross flow dryer. A laboratory-scale model was used and
results checked against the Michigan State Cross Flow com-
puter model. Good results were attained especially when the
exhaust air was recycled. Recycling resulted in lower energy
requirements for rice drying and affected the milling
yields beneficially.

Walker (1978) reported that rice can be dried at temp-

eratures as high as 65.55°C (150°F) as long as the air flow

20

is less than 0.17 m3/hr and the grain flow rate higher than
2.27 m3/min. A single-stage concurrent flow pilot-scale
dryer was used but two- and three-stage dryers were simu-
lated. Satisfactory energy efficiencies were achieved.

Bakker—Arkema et a1. (1977) conducted tests in one-,
two- and three-stage laboratory concurrent flow wheat dryers
at high temperatures. Results showed that hard wheat can
be dried in concurrent flow dryers at temperatures as high
as 121°C (525°F) provided the kernel temperatures remain
below 63°C (145°F). At the same time, comparisons of the
three kinds of dryers tested indicated that multistage
concurrent-flow dryers have advantages over a single-stage
model. The advantages are: (1) higher energy efficiency,
(2) higher capacities, (3) lower operating costs, (4) lower
investment per unit of capacity, and (5) improved grain
quality.

Brook and Bakker-Arkema (1977) investigated the optimum
operational parameters and dimensions of multistage concurrent
flow dryers. A dynamic programming optimization scheme was
used. It was concluded that, on a per-square-meter-of—
column-area basis, the single-stage concurrent flow dryer
is more expensive to operate than a two- or three-stage
similar model. This was attributed to the increased grain
flow rate used in the multistage units. When compared with
a cross flow dryer, the concurrent flow dryer is less costly
and also produces an end-product of better quality. With

regard to energy costs, the three-stage concurrent flow

21

dryer, with recirculating air, presented advantages over
the two-stage dryer. The added capital required for the
equipment necessary for conducting the exhaust air was not
considered. Although these conclusions are drawn for corn,

similar results may be expected for soybeans.

CHAPTER IV
CONCURRENT FLOW DRYING

Concurrent flow drying is one of the three main grain
drying techniques. The other two, cross flow and counter
flow, will not be discussed here.

The characteristic behavior of concurrent flow drying
is schematically represented in Figure 4. Due to the high
rates of evaporation and the short period of time during which
the product is exposed to the high drying temperatures at
the grain inlet side of the dryer, the kernel temperature
remains considerably below the air temperature in that
region (Farmer et al., 1972). In the subsequent portions
of the dryer, the grain and the air temperatures both slowly
,decrease. This tempering process is an important charac-
teristic of the concurrent flow dryers because it leads to
a uniform high quality product at the end of the drying pro-
cess. The end-product has fewer stress cracks and has also
less tendency to mechanical damage by subsequent handling.
In short, concurrent flow drying results in superior grain
quality.

The high evaporation rate which occurs in the first
layers of the dryer permits the use of inlet temperatures

as high as 121.11°C (250°F) in the concurrent flow dryer

22

23

 

300

 

 

 

 

 

 

 

550
500
250
450
£3 E:
o o 400 .
‘4 200 ‘“
52“ 8
D a 350
B
a 3
ca- 150 ca 300 AIR
m - m
2 2
m m
B B 250
100 200
150
50
100
PRODUCT
L l 1 L 1 l
2 3 4' 5 6 8 9
DEPTH (feet)
L, l L 1
0.5 1.0 1.5 2.0 2. 3.0
DEPTH (meters)
Figure 4: Product and air temperatures versus depth for a

single-stage concurrent flow dryer (Brook,

1977).

without damaging the grain mass, when corn is used. The

use of high drying air temperatures results in better energy
efficiencies for the dryer. Brook (1977) reported that
energy efficiencies between 4185 (1800 BTU/lb) to 5120

(2200 BTU/1b) kJ/kg of water evaporated are common for

concurrent flow grain dryers.

4.1 Experimental
During the fall of 1978, soybeans were dried in a
single-stage concurrent flow dryer in the laboratory. Two-

stage drying was also simulated.

4.1.1 Dryer

Soybeans were dried in a pilot scale concurrent flow
dryer in the Processing Laboratory in the Agricultural
Engineering Department at Michigan State University. The
dryer consists of a single-stage concurrent flow dryer with
a counter flow cooling section. The cross sectional area is

0.00366 m2

(1.0 ftz) and the concurrent drying section has
a length of 0.91 m (3.0 ft). The dryer is represented

schematically in Figure 5.

4.1.2 Soybeans

An unknown variety of soybeans harvested during the
1978 season served as the drying material for the experiments.
The beans were stored in a cold room at 4°C for several weeks
before the tests were performed. By the time the soybeans
were dried, the initial moisture content varied from 13 to

15 percent w.b. The non-uniformity in the moisture level

25

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GRAIN IN
8:] AIR IN
AIR
HEATING
CONCURRENT FLOW
DRYING
L1 DRTING AIR OUT
_)
COOLING AIR OUT
)
r. Y
COUNTERFLOW
COOLING
1?»
1J

 

 

GRAIN OUT AIR IN

Figure 5: Block diagram of concurrent flow dryer with
counter flow cooler (Brooker et al., 1974).

26

made the analysis among the tests more difficult because
the energy required (Figure 3) and the end product quality

are functions Of the initial moisture content.

4.1.3 Soybean flow rate

An AC motor (1750 rpm) powers the cross auger from the
base of the concurrent section. This system is responsible
for the control of the mass flow rate. Previously, the auger
was attached to a variable speed DC motor which allowed mass
flow rate variations. However, problems with the motor speed
control forced the change to the AC motor. As a result,
only one mass flow rate (432.48 kg/hr) could be used. Deter-
mination of the mass flow rate was accomplished by recording
the weight of the soybeans and the unloading time.

According to Kalchik (1977), the designer of the dryer,
0.207 m3 of soybeans are required to fill the dryer. In
order to fill the cooler and the cross auger, an additional

volume of 0.083 m3 is required.

4.1.4 Temperature and relative humidity

The drying air temperature is sensed by an iron-constan—
tan thermocouple (type J) which accuracy is :2.2°C (:4.0°F).
This thermocouple is connected to a two channel Texas Instru-
ment recorder. The characteristics of this instrument and
of the others used in this experiment are presented in
Table 3. Copper-constantan thermocouples (type T), accuracy
of :0.8°C ( :1.5°F), are used on the dryer; these temperatures

are recorded by means of a 24 channel Texas Instrument

27

Table 3: Monitoring instruments.

 

INSTRUMENTS DESCRIPTION-ACCURACY

 

1. Recorder Texas Instrument twenty-four channel,
Model EMWTGB, accuracy 30.75°F,
linearity :0.3°F.

2. Recorder Texas Instrument two channel,
Model P 502 W6A, accuracy 12°F,
linearity :0.3°F.

3. Moisture tester Steinlite Model 400 G, accuracy
10.5% moisture content wet basis.

4. Drying oven Blue M Electric Company, Model
OV510, mercury in steel thermo—
meter, accuracy :2.5°F.

5. Pitot Tube Accuracy 0.01 inch.

6. Scale Toledo Scale Company, style 0891,
accuracy $0.25 lb.

7. Scale Mettler P160N, accuracy :10 mg.

8. Scale Mettler, accuracy 30.1 mg.

 

28

recorder. The soybean temperature was evaluated by inserting
a mercury-in-glass thermometer (smallest division 1.11°C)
into the grain mass as it left the dryer.

The inlet dry and wet bulb air temperatures are measured
in three different positions. First, at the inlet air stream
of the fan. This position was chosen in such a way that no
turbulence was present, i.e., directly on the inlet air
streamlines. The second point is located after the fan
outlet and before the laminar flow element. The thermo—
couples detect the rise in temperature of the air due to
turbulence inside the fan. Whenever the inlet air temperature
is used in energy efficiency calculations, this temperature
is used. A third thermocouple is placed after the burner
in the plenum before the concurrent drying section. This
is the only iron-constantan thermocouple used in the tests.

Dry and wet bulb temperatures are also sensed at the
drying air outlet and at the cooling outlet. By periodically
checking these temperatures during the tests, it is possible
to calculate the exit air relative humidity and, consequently,
the amount of drying in the concurrent section and in the
_ cooler. Dry bulb temperatures are measured at three levels
-in the concurrent section, at 15.24 cm, 30.48 cm and 60.90 cm
from the grain inlet. In addition, two thermocouples are
installed above the concurrent section, one at 30.48 cm
from the top of the dryer and the other at 91.44 cm from the
same position. The latter one served as a check for air

leakage through the hopper. Air leakage is possible if the

Figure 6:

Legend:

Schematic of the pilot-scale concurrent flow
dryer used in the laboratory, showing the thermo-
couple locations (dots) (Walker, 1978).

Bucket elevator

Grain storage hopper

Natural grain airlock

’Heating air and grain boundary area

1
2
3
4
5. Concurrent drying section
6 Dryer exhaust

7 Burner

8 Grain flow rate metering auger
9 AC motor

10. Cooler exhaust

ll. Cooling section

12. Cooling air entrance

l3. Cooling section discharge auger

14. Cooler base

30

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(y -_-
\/

 

 

Figure 6: Schematic of the pilot-scale concurrent flow dryer
used in the laboratory, showing the thermocouple
locations (dots) (Walker, 1978).

31

is now possible because the new regulator allows very accu-
rate adjustment Of the gas flow rate.
In order to find the quantity of gas used in a complete

run, the gas tank was weighed before and after each run.

4.1.7 Moisture content

The original moisture content was obtained by sampling
the soybeans as the dryer was being filled. Subsequent
samples were taken during the tests by collecting material
at the unloading auger at a regular time interval.

A Steinlite electronic moisture tester served as an
indicator of the soybean moisture content. These moisture
.values were used as a check for the amount of drying that
was being carried out. The soybean moisture contents used
in the results of this experiment were evaluated according
to the ServiCe and Regulatory Announcements NO. 147 of the
United States Department of Agriculture. Ground samples
of 4-5 grams were dried at 130°C for one hour. The samples
were cooled at room temperature inside a silica-gel contain-
ing jar. The final moisture content of the samples was

calculated from the moisture loss during the oven drying.

4.1.8, Germination tests

Soybean germination tests were conducted in the labora-
tory of the Crop and Soil Sciences Department at Michigan
State University. Two hundred seeds of each dried sample
were germinated in two lOO-seed lots. Normal seedlings and

the seeds which had begun germinating without abnormal

32

symptoms were counted as germinated. All others were class-
ified as dead seeds because of their incapacity to produce
normal seedlings. Seeds that showed any sign of viability
loss were avoided in order to eliminate the influence of

elements other than temperature in the final results.

4.1.9 Cracks and splits

In this thesis, soybeans are classified as falling in
one of the following categories:

a. undamaged -- no visual evidence of physical damage;

b. cracked -- a crack in the seed coat of the soybeans
with the seed coat still on the bean and the cotyledons
intact;

0. split -- a crack which has advanced to the cotyle-
dons, with the seed coat Off and the cotyledons separated
into two individual parts, and small broken or fractured
parts of the beans.

Two samples Of 25—35 grams each were obtained for each
moisture content sample. After being weighed on a Mettler
P160N scale, the material was separated and classified.

Any foreign material was removed from the original samples.
The quantity of soybeans in each category was recorded and
the corresponding percentages evaluated. All tests were
performed by the author in order to maintain consistency

throughout the tests.

33

4.2 Test Procedure

Dryer operations involved only one person after a small
modification was performed at the bucket elevator inlet.

A bean storage hopper was installed at the inlet which
allowed the Operator to take samples and check temperatures
and instrumentation between consecutive fillings of the inlet
hopper to the dryer.

To start the drying process, the concurrent section was
filled with soybeans until the micro-switches on top of the
dryer indicated that it was full. The fan on the concurrent
section was turned on and the burner ignited and adjusted
to the desired temperature by manual regulation of the liquid
propane (LP) gas controls. By this time, all recorders
had been switched on, as well as the cross auger.

The dryer can be used in simulating a multi-stage
concurrent dryer because the output from the concurrent sec-
tion can be diverted from the machine before the beans reach
the cooler. A description of the procedures for simulating
this system follows.

Soybeans were dried without cooling to a moisture con-
tent below 13 percent and were placed in a container to
temper for about two hours. During this time, the moisture
diffuses uniformly inside the beans. The drying operation
was then repeated with the cooling section used during the
second drying operation.

Samples were taken at regular time intervals during a

dryer test and conditioned in sealed plastic bags, identified

34

and stored in a cold room at 4°C. Moisture content and germ-
ination tests were determined later as was the evaluation of
cracks and splits.

In this thesis, a pass means each time the soybeans go
through the dryer once, and a run means one of the three
tests performed. Using these definitions, it is necessary
to point out that several passes were needed before a complete

run was completed.

CHAPTER V

CROSSFLOW DRYING

Among the continuous-flow grain dryer configurations,
the crossflow is the most common and, therefore, has been
the topic of much research.

In the crossflow configuration, air and product flow
in perpendicular directions. The product usually uses
gravity to move through the dryer; the air passes through
the grain horizontally.

In order to overcome the efficiency and quality problems
of the basic crossflow configuration, many modifications have
been tested. One Of them is the use of the warm exhaust
air from the cooling section as the heater inlet air for
the drying section. The advantage of this process is an
increase in the dryer efficiency, since part Of the sensible
heat of the grain is recovered (Brooker et al., 1974). The
technique of reversing the airflow halfway through the
drying section was tested and, although a reduction of 60-75
percent in the moisture content gradient across the column
of the dryer was reported, there was also a decrease in the
dryer efficiency and capacity. An advantage of reversing
airflow is the lower average grain temperature (Bakker-Arkema

et al., 1978).

35

36

Figure 1 presents a block diagram of a three-stage
crossflow dryer with reversing airflow and air recycling.
This dryer, commercially available, uses the mixture of
the exhaust air from the second drying section and the first
cooling section (after re-heating) as the inlet drying air
for the first and second drying sections. As a result,
the energy use is approximately half that used in the basic
crossflow configuration. The moisture content gradients
at the outlet are significantly smaller than of the conven-

tional crossflow dryer (Bakker—Arkema et al., 1978).

5.1 Crossflow Model Development

Thompson et a1. (1969) developed a series of semi-
theoretical grain dryer models which have been used success-
fully. More general and fundamental models have been
developed by researchers at Michigan State University,
starting in 1966. These models are based on the basic
laws of heat and mass transfer and, because of their theor-
etical nature, are described by a rather complicated system
of differential equations. The solution to these systems
of equations can be Obtained numerically with the help of
a digital computer.

Bakker-Arkema et a1. (1976) studying in-bin solar
drying, concluded that the air and product temperatures can
be.set equal at the low airflow rates used in solar drying.
Later research with crossflow dryer models led to similar
conclusions. The same simplification is used in the present

thesis. The advantage of this assumption is that considerable

 

 

 

37

computer time is saved in the simulation Of the model.
The three basic equations describing heat and mass

transfer in a crossflow dryer are (Bakker-Arkema et al.,

1976):
p (c + Mc ) 23 + G (c + H0 ) 32 + g [(c -c ) (212-T)
p p W at a a v 3x a w V
BE _
8M 3H _
01;» 9‘1? + Ga 6; " 0 <2)
3M =

Equations (1) through (3) can be written in finite
difference form and rearranged as explicit functions of

H with x being the node position in the dryer width, and

x,t’
t being the drying time.
The basic finite difference equations of the crossflow

model used in this thesis are:

 

-AtGa(hx,t-Hx-Ax,t) (hfg+212(cW-cv))
+ ppr(cp+cwa,t-At)Tx,t-At + GaAt(ca+chx-Ax,t)
Tx—Ax,t
Tx,t = (4)
-GaAt(Hx,t-Hx-Ax,t) (CW-CV) + ppr(cp+°wa,t-At)

+ GaAt(ca+chx-Ax,t)

p A
= _ .E_§ -
Hx,t Hx-Ax,t Ga t (Mx,t Mx,t-At) (5)
Mx,t = f(Tx,t’ Hx,t) (6)

38

Other assumptions (besides the product and air tempera—
tures being equal) made in the development of the present
crossflow dryer model simulation are:

1. There is no volume shrinkage during the drying
process;

2. The grain flow and airflow are uniform (plug-type);

3. The dryer walls are adiabatic, with negligible heat
capacity;

4. aT/Bt and aH/at are insignificant as compared to
BT/Bx and aH/ax;

5. There is no temperature gradient within the indivi-
dual grain particles;

6. The heat capacities of grain and of the moist air
.do not vary over short periods of time;

7. All transfer processes are reversible without

hysteresis.

5.1.1 Thin-layer equations

The practical importance of the thin-layer equation
in the dryer simulation models is considerable. The equa-
tions are obtained from data Obtained in thin-layer drying
experiments in which a very small quantity of the original
material is used. In simulation, the drying process is
described by assuming the entire mass to consist Of a series
of thin layers of the product. An accurate equation describ-
ing the moisture behavior of the thin layers is thus very
important in order to accurately simulate the multi-layer

drying process.

39

Sabbah et a1. (1976) developed a thin-layer drying
equation for soybeans based on the premise that the drying
is controlled by the rate of diffusion within the seed and
by the rate of mass convection at its surface. Two govern-
ing equations for convection and mass diffusion developed
in the range 32.2-43.3°C are coupled, resulting in the
following semi-empirical equation:

MHM

M -M = 0.608(1 - exp(—K2t))(exp(-Klt)

o e (7)
+ 025 exp(-4Klt)) + exp(-K2t)

 

The variable K1 is evaluated by Equation (8):

K1 = 4R2D/d2 (8)

The term d in Equation (8) is the equivalent seed diameter,
assuming the seed to be a sphere. The validity of this
assumption has been confirmed by Chu and Hustrulid (1968)
who stated that two solids of different shapes can be con-
sidered equivalent for drying if their volume-to-surface-
area ratios are the same provided none of the solids are
originally spheres. Values for the seed equivalent diameter
of soybeans can be obtained from the following empirical
equation:

d = 0.6279 + 0.1255-M (9)
where M is the moisture content expressed in decimal, dry
basis. A second empirical equation was used to evaluate the
mass diffusion coefficient D in Equation (8).

D = (0.0493 exp(-O.59/(Mo-Me)) + 0.0181(M—Me)) -

exp(-3137.6/£8+273)) (10)

40

K2, the convection parameter in Equation (7), is defined as:

K2 = GF - AF - GAF (11)

where GF is the grain factor:

CF = a S/B (12)
a = 558.99 - 196.19 0 M (13)
B = 675.10 + 464.54 0 M (14)

S = 1.0 (shape factor)

AF is the air factor:

AF = 1.342 . 10‘6 GaRH-1(T+273)1'54/(0.514+0.0036-T)0'67
.(15)
and GAF is the grain-air factor:
GAF = xRey(RHamb-RH)/(M-Me) (16)
where
x = 0.91 and y = 0.51 for Re < 50.0 and

x = 0.61 and y

0.41 for Re‘: 50.0

Equations (7) through (16) were originally written in SI units.

The Sabbah equation was at first selected for use in
this study because it was developed using a reversed-air
drying system.

When the Sabbah equation was added to the MSU crossflow
computer simulation program in order to fulfill the require-
ments of Equation (6), serious instability problems arose.

A more careful evaluation of the Sabbah equation showed
that the moisture ratio cannot decrease below 0.73, no matter
how large the drying time becomes.

Brooker et a1.(1974) presented a semi-theoretical

drying equation with a logarithmic behavior:

41

———M I: = exp(-kt) (17)
0 e

where k is a drying constant expressed in hr"l or see-1
Overhults et a1. (1973) Observed that a logarithmic drying
model of the type in Equation (18) does not adequately
describe the thin-layer drying process for soybeans. The

following modified logarithmic model was proposed:

M - Me n

M__:—M—' = exp(-(kt) ) (18)
o e

M = moisture content (dry basis, decimal)

t = drying time (hr)
k and t are drying constants described by:
n = 0.3529 + 0.00136 . T (19)

T = drying temperature (°F)

In R = 11.752 - 7912.7/Tabs if Mo = 20% (20)

1n k = 10.906 - 7357.0/Tabs if M0 = 23% (21)

In k = 10.375 - 6779.3/Tabs if Mo = 33% (22)
with

Tabs = absolute temperature (°R)

In the development of the Overhults equation, drying data of
hand-harvested soybeans at initial moisture contents in the
range of 20-33 percent w.b. and with drying temperatures from
37.8-104.4°C were used.

White et a1. (1978) derived two empirical equations for
evaluating the n and k parameters in the Overhults equation:

n = 0.33 + 0.0025 RH + 0.003 T (23)

42

k = -0.207 + 3.57-10‘3 T + 2.16-10‘3 MO
+ 2.61-10'3 RH + 3.20210"6 MO T (24)
where
RH = relative humidity (percent)
T = temperature (°C)
M0 = initial moisture content (percent d.b.)

Air temperatures for the White et a1. experiments varied from
30—70°C, initial moisture contents from 16-24 percent, wet
basis, and dew point temperatures from 8-38°C.

Pinheiro-Filho (1976) also developed empirical equations
to evaluate the parameters n and k in the Overhults equation
for two temperatures (32 and 54.5°C) and two levels of
moisture content (15 and 19 percent, w.b.):

n = 0.5526 + 1.7742 - T'1 (25)

1n k = 03.5187 + 0.3333-10‘1 - T (26)
T = drying temperature (°F)
Pinheiro-Filho pointed out that some restriction must be
put on these equations because of the small number of experi-
ments on which the regression was based.

Roa and Macedo (1976) obtained a thin-layer drying

equation for carioca beans:

M - Me n q
M_—:_M_' = exP("'11(va"pv) t ) (27)
o e
where
M = product moisture content (decimal, dry basis)

M = initial moisture content (decimal, dry basis)

3
II

equilibrium moisture content (decimal, dry basis)

43

"U
l
"U
<1
ll

air water vapor pressure deficit (kgf/kg)

d
ll

time (hours)

m,n and q drying constants of the product

Roa et a1. (1977) evaluated the drying constants of
Equation (27) using drying data for soybeans obtained at
47.7°C and 28 percent relative humidity:

m = 0.01448

n = 0.47088

q = 0.51168
The Roa-Macedo soybean drying equation is presented in
Figure 10 for five temperatures.

Initially, it was decided to use the Overhults equation
as the thin-layer drying equation for the simulation in this
study, together with White values for n and k (Equations (23)
and (24)). After careful analysis, it was observed that the
moisture ratio decreases as the air relative humidity in-
creases. The opposite effect should be predicted by the
equation. The behavior of the Overhults-White equations
(Equations 18, 23, and 24) can be observed by comparing the
results in Figures 7 and 8. It was finally decided to use
Overhults equation as the thin-layer drying equation together
with Equations (19) through (22) for the evaluation Of its
parameters. This equation is not affected directly by the
air relative humidity, only by the air temperature. Its

behavior at five temperatures is presented in Figure 9.

44

HRzEXPi-[KTMxN]

 

 

8 stun": wnznrncoo mu:
_: INITIBL mam caurnum rem: as
D
‘5’
co.
H
g.—
G:
“‘8
Lu . .
05:)" some cc:
:3
p.
03
Ho mums:
2':
o‘
”(32.ch
8 unmade:
:-
130““.40)
:3
‘3
I I I I I
:11.00 2.00 4.00 6.00 8.00 10.00

TIME - HOURS

Figure 7: Response of the Overhults thin-layer drying
equation for soybeans when the drying parameters
are estimated by the White equations.

45

HRzEXPI-(KTJXXNJ

 

 

8 scum: HUHIOITYa-SS me
' INITIAL HOIBTURE CONTENTaZZ PERC H8
CI.
:3
9
42°.
h-l
p.
CE
05::
co
LI.J°.1
05C)
:3
p.
a:
H
OS
2 .‘ summon
c:
7ort21.1c)
3 907132.ch
o-
unrua.ac
130Ft84. '
c:
(D
. I I 'I l 1
‘b.00 2.00 4.00 6.00 8.00 10.00
TIME - HOURS
Figure 8: Response of the Overhults thin-layer drying

equation for soybeans when the drying parameters
are estimated by the White equations.

46

MR:EXP(-(KTJ¥&NJ

INITIflL ”DISTURE courenrszz PERC H3
RELBTIVE NUHIOITYSO - 100 PERC

 

 

 

 

C3 .
C? 1 - TEflPERflTUREI BDFII0.0CI
,_ z - TWERRTURE: 709121.10)
3 - TEMPERATURE: 90FI32oZC)
4 - TEflPERflTURE: llOFI‘S-SC)
5 - TEflPERflTUREx 130f(84o461
I - TEMPERRTUREB ISOFIBSoSCJ
fig 7 - TEMPERRTURE: 170F178o881
0‘ 6 " WWW IWI”07CI
‘:3C3 0 - TERPERBTURE: 210Ft90.8¢)
I—l
p..
CE
“‘8
LL] .q 1
crgca
E? 2
03
H
<D° 3
2":
° 4
.5
83
a 6
CD
CD . .___
ca 1.
I I I 7
cb.00 2.00 4.00 8.00 10.00

6.00
TIME - HOURS

Figure 9: Response of the original Overhults thin-layer
drying equation for soybeans.

ROB-MRCEDO DRYING EQURTION

INITIHL BOISTURE CONTENT=22 PERC HI
RELRTIVE HUHIDITYBO - 100 PERC

 

 

0
C3 1 - TEMPERRTURfiz 50F(10.0C)
,3- 2 - mmnmne: 70F(21.ICJ
8 - TEMPERRTURfis 80F(32.203
4 - TERPERHTURE: 110Ft43.3¢)
8 - TEMPERRTURE: 130FI84.4C)
D
0
1:39"1
H
1...
(I
0:0
(D
m .-
cr:€3
::
p_.
03
HO
CD‘-
:5q
0
N
5'1
0
C3
. I l r T l
:11.00 2.00 4.00 6.00 6.00 10.00
TIMEIHOURS)

Figure 10: Response of the Roa-Macedo thin-layer drying
equation for soybeans.

48

5.1.2 Equilibrium moisture content

There are several equilibrium moisture content equations
available for soybeans. Some are specific for soybeans and
others can predict moisture equilibrium for several agri-
cultural products by varying one or more coefficients in
the equations.

An equation which accurately describes equilibrium
moisture content is important for computation of the drying
and desorption rates because it determines the driving force
for these processes. Nevertheless, variations in the Me
values reported for one product at the same relative humidity
and temperature are common. Some of the causes which may
be responsible for the variation are: l) differences in
moisture equilibrium determination methods; 2) experimental
errors in moisture equilibrium determination, resulting from
difficulties in maintaining and measuring relative humidities
and temperatures while the samples equilibrate; 3) inadequate
measurement of the moisture content and relative humidity;
and 4) product from different varieties and with different
histories.

Henderson (1952) proposed a semi-theoretical equation
based on the thermodynamic relationships for adsorption to
calculate the equilibrium moisture content:

1 - RH = exp(-A TabsMeB) (28)
where

A and B are product constants

Tabs = ambient temperature ( R)

49

RH

relative humidity (decimal)

M

e moisture equilibrium (percent, dry basis)

Values for A and B were determined by Henderson for several
products. For soybeans at 25°C, A and B are equal to

3.20-10-5 and 1.52, respectively. These parameters were

reevaluated by Alam (1972) and found to be A = 4.667-10-5
and B = 1.48234, at the same temperature. A restriction of
the Henderson type equation is that it fails to give accept-
able Me predictions for relative humidities above 80 percent.
Alam (1972) also determined the values for the constants

of soybeans in the Sabbah moisture equilibrium equation

originally developed for corn:

Me = a - RHb/Tc (29)
where, for soybeans:
a = 1.617-10’4
b = 2.85274
RH = relative humidity (percent)
T = temperature (°F)

Reasonable predictions for the equilibrium moisture content

were obtained for relative humidities above 70 percent.
Alam (1972) also developed a third order polynomial

equilibrium moisture content equation for soybeans:

2 2
5RH + CGRH T

3 3
RH + cllRH T

RH2T3

Me = c1 + czRH + 03

2 2 2 2
+ C7T + c8RH T + 09RH T + 010

3 2 3 3

RH T + 013T + 014RH T + 015
3 3

RH T (30)

T + c4RH T + c

+ 612

+ 016

50

where c1 = 2.98305 69 = 0.52060-10"5
c2 = 0.29107 °10 = 0.75358-10‘4
c3 = 0.10662 cll = 0.23991-10"5
c4 = 0.12514-10'1 012 = --0.36882-10‘7
05 = -0.65510-10‘2 013 = --0.48010-10"5
06 = -0.34487-10‘3 014 = 0.68246-10'6
c7 = 0.131125-10'4 c15 = -0.19123-10"7
c8 = -0.18787-10"3 016 = 0.13494-10‘9

T = temperature (°C)

RH = relative humidity (percent)

M
e

equilibrium moisture content (percent
Alam reported that the equation was developed for the desorp-
tion isotherms over the entire range of relative humidities
and for temperatures ranging from 5°C (41°F) to 55°C (131°F).
However, the results could not be duplicated by the author
who found negative moisture equilibrium values at low rela-
tive humidities for temperatures higher than 32.2°C (90°F).
These results may be observed in Figures 12 through 14.

Pfost et al. presented an equilibrium moisture content
equation which can be utilized for several products:

Me = E - F ln(-R(T + C) ln(RH)) (31)
where, for soybeans

E = 0.375314

0.066816
= 24.576

universal gas constant (1.987 cal/kg °K)

0-3 :1! O ’31
II

= temperature (°C)

51

 

 

D
Z- TEMPERQTUREzsoF 11001
“3 1 - RLRH EOUHTION
2 - HENDERSON-THOMPSON EWHTIUN
3 - WNHFWT EQUITY!“
4 - 383m EWHIION
3
653-
C9.
l—o
29
Ha
:5
C3
L)
1—8
2:3-
ON
2:
Jo /
"‘c:
D o
38‘ /
DJ
8
I 00 20.00 40.00 60.00 8'0.00 £00.00
Cb RELRTIVE HUMIDITY(PERCJ
8
15
7a

Figure 11: Soybean equilibrium moisture content prediction

according to Alam, Henderson-Thompson, Chung-
Pfost, and Sabbah equations, at 10°C.

52

C3
D
é. TEMPERRTURE: 70F [21.10)

1 - flLflfl EQURTION

2 - HENDERSON-THWSON EHURTIOII
3 - CHUNG-PFBBT EOURTIDN

4 - 88088" ERURTION

12.00

1

EQUIL MOIST CON;

2.00

 

 

8.00

 

0 .00 ab .00 4B .00 6'0 .00 6'0 .00 1‘00 .00
RELRTIVE HUMIDITY(PERC)

Figure 12: Soybean equilibrium moisture content prediction
according to Alam, Henderson-Thompson, Chung-
Pfost, and Sabbah equations, at 21.1°C.

53

TEMPERRTURE: 90F [32.2C]

1 - RUM EQURTION

2 - HENDERSON-THOMPSON EOURTION
3 - CflUNO-PFBGT EWRTIUN

4 - sauna" EQURTION

/

 

d3-00

’8 000

 

'l.‘!'/ 1
F 20.00 40.00 60.00 60.00 100.00
RELRTIVE HUMIDITYIPERC]

Figure 13: Soybean equilibrium moisture content prediction

according to Alam, Henderson-Thompson, Chung-
Pfost, and Sabbah equations, at 32.2°C.

40.00

32.00

24.00

l

16.00

1

L MOIST CONTENT.0.B.
8.00

I
0

2:)CD

0

E
:9.

 

54

TEMPERRTURE:110F [43.30]

1 - flLflfl EBUHTIUN

2 - HENDERSON-THOMPSON EEURTION

3 - CHUNG-PFUST EGURTIDN 1 ‘
4 - 80890“ EflUflTIOI

 

 

:0 20.00 40.00 60.00 80.00 100.00
RELRTIVE HUMIDITY(PERC)

Figure 14: Soybean equilibrium moisture content prediction

according to Alam, Henderson-Thompson, Chung—
Pfost, and Sabbah equations, at 43.3°C.

55

c:
9
53-
53
&. TEMPERRTURE:130F [54.40)
on 1 - 01.1111 EOURTIDN
2 - neuoensou-rnoursou 5000710»
3 - cause-Pros? enunrrou
c: 4 - anaaau EQURTION
c3 .
4.
N

16.00

I

 

/
/

l//

.02 20.00 40.00 60.00 60.00 100.00
RELHTIVE HUMIDITYTPERC)

l

8.00

.CNJ

 

l

EQUIL MOIST CONTENT.D.B.

()0

-8.
l

 

-16.00

Figure 15: Soybean equilibrium moisture content prediction
according to Alam, Henderson-Thompson, Chung-
Pfost, and Sabbah equations, at 54.4°C.

56

RH relative humidity (decimal)

Me = moisture equilibrium (decimal d.b.)
The Pfost equation has the same limitation as Equation (30)
since it predicts negative Me values at low relative humidi-

ties for temperatures between 10 and 54.44°C.

Pfost et a1. (1976) also calculated the constants for
the Henderson-Thompson type equilibrium moisture content

equation for soybeans:

Me = (ln(l - RR)/(-k(T+C)100)N‘1 (32)
where

T = temperature (°C)

k = 0.000503633

c = 43.016

N = 1.3628

Although the Henderson-Thompson equation does not have a
sigmoidal shape (which is characteristic of the equilibrium
moisture content curve for biological products), it does not
give negative values. This is an important characteristic
when the Me is part of a computer simulation program. At
relative humidities higher than 95 percent, the Me calculated
with Equation (32) is overestimated, a behavior which requires
a bound on the Me values for simulation.

Most of the research conducted on soybean drying has
been conducted at low temperatures. Thus, most of the
equilibrium moisture content equations for soybeans were
developed for low temperatures. As a result, all EMC equa-

tions presented here have restrictions in one way or another

57

when used in high drying temperature simulations. Equations
(29) through (32) were plotted in the entire range of rela—
tive humidities and for five temperatures, from 10-54.44°C.
The results are shown in Figures 11 through 15. By analyz-
ing these plots, one can observe that the Sabbah and Hender-
son-Thompson equations do not give moisture equilibrium
values lower than zero. It was attempted to combine the
Sabbah and Henderson-Thompson equations. Equation (32)

was used from zero to 70 percent relative humidity and
Equation (29) above 70 percent. Figure 17 shows what happens
at the transition region at 43.3°C. The transition from

one region to another may be relatively smooth and acceptable
for computer simulation (see Figure 16). However, when the
combined equations are plotted at 21.1°C, a discontinuity
occurs at the transition which leads to instability in the
simulation results (see Figure 17).

To solve the instability problem at the transition point,
the average equilibrium moisture content was calculated from
Equations (29) and (32)- Although the "average" equation
does not show any discontinuity it under-estimates the equi-
librium moisture content for.relative humidities below 70
percent because of the limitations of Equation (29). The
under-estimation of the equilibrium moisture content contri-
butes to instability of the results when the average EMC
is utilized in the computer program. Figure 18 presents
the average equilibrium moisture content curves for tempera-

tures from 10-54.44°C thus obtained.

 

 

58

TEMPERRTURE:110F [43.30)

mall-WWII“! EMTIBN

 

9
=0.00

Figure 16:

20.00 40.00 60.00 60.00 100.00
RELHTIVE HUMIDITY(PERCJ

Soybean equilibrium moisture content prediction
at 43.3°C using a combination of the Henderson-
Thompson and Sabbah equations.

59

TEMPERRTURE: 70F (21.101

WWWWBMRW IGNITION

 

 

 

c0.00

Figure 17:

20.00 40.00 60.00 60.00 100.00
_RELRTIVE HUMIDITY(PERCJ

Soybean equilibrium moisture content prediction
at 21.1°C using a combination of the Henderson—
Thompson and Sabbah equations.

6O

RVERRGE EMC

 

 

1 - Itnrenaruaz=sar 110.001
2 - TEMPERRTURE=7OF 121.101
:3 a - rearsxnrunsesor 132.201 1
u? 4 - IznrznaIUREsiior 143.301
ca‘ 6 - TEMPERRTUREsISOF (64.601
as 2
(:15?
1-‘31
I:
LLJ
p.
I:
:18
U .-
c:
L.
00
H
c:
c:
:9:
_J:F
H
:3
C3
LL]
:3
F.
o.
//
o 1
D
.‘ I I r T’ I
c0.00 0.20 0.40 0.60 0.80 1.00

RELRTIVE HUMIDITY

Figure 18: Soybean equilibrium moisture content prediction
using the average between the Henderson-Thompson
and Sabbah equations at five levels of temperature.

61

At late stage of this research, an additional equili-

brium moisture content equation became available (Roa et al.,

1977):
M = (p RH + p RHZ + p RH3) exp<<q + (q RH + q RH2
e 1 2 3 o l 2
4
+ qBRH3 + q4RH ) (T + q5>) (33)
where
Me = equilibrium moisture content (decimal, dry basis)
RH = relative humidity (decimal)
T = temperature (°C)

p1 = 0.3167048
p2 = -0.4084806

p3 = 0.4687752
q0 = -0.0106576
q1 = -0.06349201
q2 = 0.2160320
q3 = -0.3108765

q4 = 0.1684076

q5 = -14.04595
Equation (33) was derived in the temperature range of 20-60°C.
The equation is plotted in Figure 19 for five temperatures.
It can be Observed that the curves have a common point at
87 percent relative humidity. Because the Me values are
over-estimated above that point, the results in that range

are presented in Appendix C.

0.30

0.25
J

0.20

l

0.15

l

l

EQUILéfigIST.CONT.(DEC..DB)

 

 

62

R08 EMC EOURTION

1 - TEMPERRTURE: ”(10.03)
2 - WWREI 70FIZIJC)
3 - TEMPERRTURKI ”(32.26)
4 - WWI"!!! 110fl434301
8 - WWW“: 130F18444CJ

 

In
9
cf
:1
9
c0.00 0020 0140 0160 0080 1000
REL.HUMIDITY(0EC)
Figure 19: Soybean equilibrium moisture content prediction

according to the Roa equation for five levels
of temperature.

63

5.1.3 Specific heat

Alam (1972) carried out specific heat determinations
by a calorimetric procedure. The specific heat values
obtained at various moisture levels are linearly related,

resulting in the following empirical equation:

cp = 0.39123 + 0.0046057 M (34)
where

cp = specific heat (cal/g°C)

M = moisture content (percent, d.b.)

5.1.4 Latent heat of vaporization

The energy required to evaporate moisture from a product
being dried is called the latent heat of vaporization.
0thmer (1940) proposed the following equation for the latent
heat of vaporization:

hfg = hfg' (1 + A exp(B)) (35)

Alam and Shove (1973) determined the constants for the
latent heat equation from equilibrium moisture content data
for soybeans in the range of 5.66 to 27.51 percent dry basis
and temperatures from 5-55°C:

h = (2502.1 - 2.386 0) ° (1 + 0.216 exp(-6.233 M)) (36)

f8

5.1.5 Air and other soybean properties

A psychrometric model developed by Brooker et a1. (1974)
permits the calculation Of any property of moist air given
any other two properties. The model, known as SYCHART, is
stored on a permanent file on the CDC 6500 computer at

Michigan State University.

64

The grain and air properties listed in Table 4 are

treated as constants.

5.1.6 Energy and static pressure equations
The energy to heat the drying air can be calculated by
an enthalpy balance on the air flowing through the heater

apparatus:

E = (Ga(ca + cV Hin) ~ (T - Tamb))/Gp (37)

Pressure drop evaluation is based on the Shedd curves
which are represented by the following pressure-flow rela-

tionship (Brook, 1977):

0a = A (SP/x1)B (38)
where, for soybeans

A = 75.2

B = l/l.431

Qa = airflow rate (cfm)

x1 = column depth (ft)
Rearranging Equation (38) leads to:

1.431

89 = x1(Qa/75.2) (39)

A copy of the computer program partially developed for

this thesis is presented in Appendix A.

65

Table 4: Air and soybean properties treated as constants
in the simulation program.

 

Dry bulk density, kg/m3 929.000
Specific heat of soybeans, kJ/kg °C 1.675
Specific surface area, mz/m3 1522.300
Specific heat of dry air, kJ/kg °C 1.013
Specific heat of water vapor, kJ/kg °C 1.884

 

Source: Brook (1977).

CHAPTER VI
RESULTS AND DISCUSSION

6.1 Concurrent Flow Dryer

The analysis of the concurrent flow dryer is based on
the data acquired during the test runs in the laboratory.
The calculations assume LP gas to have 45,226.741 kJ/kg
(19444 BTU/1b), air to have a specific heat Of 0.000239
J/kg°K (0.25 BTU/lb9F), the air density to be the same for
one entire test, and a test weight Of 57 1b/bushe1.

The set of tests consisted of three runs at different
drying air temperatures at the same product flow rate.
Samples were taken at the grain outlet at equally spaced
time intervals and the moisture content, germination, cracks
and splits were analyzed. The results are:

FIRST TEST: 12.13.78

inlet air temperature: TIN: 121.11°C (250°F)

inlet moisture content, wet basis, percentage — XMIN: 14.18
outlet moisture content, wet basis, percentage - XMOUT: 12.58
grain flow rate - GFR: 543.48 kg/hr (1200 lb/hr)

inlet grain temperature - TGIN: 11.67°C (53°F)

outlet grain temperature - TGOUT: 28.33°C (83°F)

ambient temperature, dry bulb - TAMB: 24.44°C (76°F)

ambient temperature, wet bulb - TAMBW: 15°C (59°F)

66

67

LP gas used - 2.26 kg (5 lb)
drying time - TIME: 2.58 hr

dry matter - DM

DM GFR (l-XMOUT)

543.48 (1-0.1258)

475.11 kg/hr (1049.04 lb/hr)
water in grain (in) - WIN
WIN = DM - XMIN/(l-XMIN)
= 475.11 - 0.1418/(l-O.l418)
= 78.50 kg/hr (173.33 1b/hr)
water in grain (out) - WOUT
WOUT = GFR - XMOUT
a 543.38 - 0.1258
= 68.37 kg/hr (150.96 lb/hr)
specific volume (air) - sv = 0.857 m3/kg (13.70 cu ft/lb)
water removed - WR
WR = WIN - WOUT
= 78.50 - 68.37
= 10.13 kg/hr (22.37 1b/hr)
LP gas consumption - LPG
LPG = LP/TIME
= 2.26/2.58
= 0.88 kg/hr (1.93 lb/hr)
energy used - EN

EN = LPG ° 45,226.77

0.88 - 45,226.77

39,799.54 kJ/hr (37,772.58 BTU/hr)

68

efficiency - EFF

EFF

EN/WR

39,799.54/10.13

3928.88 kJ/kg of water removed
(1688.77 BTU/1b)
For the second test, as well as for the third one,
two stage drying was simulated. For the first stage drying
the cooler was turned off and the drying process was continued
for 1.5 hr. A tempering time of two hours was established,
after which the second stage drying was started. The
results for the second test follow:
SECOND TEST: 12.22.78
First Stage: TIN = 121.ll°C (250°F)
XMIN = 14.69
XMOUT = 13.24
GFR = 432.48 kg/hr (1200 lb/hr)
TGIN = 11.67°C (53°F)
TGOUT = 28.33°C (83°F)
TAMB = 23.33°C (74°F)
TAMBW = 13.89°C (57°F)
sv = 0.851 m3/kg (13.60 cu ft/lb)
LP = 1.47 kg (3.25 lb)
TIME

2.0 hr
dry matter -

DM

543.48 (1-0.1201)

478.21 kg/hr (1055.88 lb/hr)

69
water in grain (in) -
WIN = 478.21 - 0.1469/(1-0.1469)
= 82.35 kg/hr (181.82 lb/hr)

water in grain (out) -

WOUT

543.48 . 0.1324

71.96 kg/hr (158.88 lb/hr)
water removed -
WR = 82.35 - 71.96
= 10.39 kg/hr (22.94 lb/hr)
LP gas consumption -

LPG = 1.47/2.0

.74 kg/hr (1.62 lb/hr)
energy used -

EN = 0.74 - 45,226.74

33,467.79 kJ/hr (31,763.30 BTU/hr)
efficiency -

EFF = 33,467.79/10.39

= 3221.15 kJ/kg of water removed
(1384.56 BTU/lg)

Second Stage:

TIN = 93.33°C (200°F)

XMIN = 13.24

XMOUT = 12.01

TIME = 1.50 hr

LP = 0.91 kg/hr (2.0 lb/hr)

70

water in grain (out) -

WIN = 543.48 ° 0.1201

65.27 kg/hr (144.12 1b/hr)
water removed -
WR = 71.96 - 65.27
= 6.69 kg/hr (14.77 lb/hr)
LP gas consumption -
LPG = 0.91/1.5
= 0.61 kg/hr (1.34 lb/hr)

energy used -

EN 0.61 ' 45,226.74

27,588.31 kJ/hr (26,183.26 BTU/hr)
efficiency -
EFF = 27,588.31/6.69
= 4123.81 kJ/kg of water removed
(1772.56 BTU/lb)
overall dryer efficiency -

OEFF

(EN(first stage) + EN(second stage))/

(WR(first stage) + (WR(second stage))

(33.467.79 + 27,588.31)/(10.39 + 6.69)

3574.71 kJ/kg of water removed

(1536.53 BTU/1b)

The third test produced the following results:
THIRD TEST:
First Stage: TIN = 148.89°C (300°F)
XMIN = 13.52
XMOUT = 12.73

71

GFR = 543.38 kg/hr (1200 lb/hr)
TGIN = 5.56°C (42°F)

TGOUT = 23.33°C (74°F)

TAMB = 24.44°C (76°F)

TAMBW = 15.00°C (59°F)

sv = 0.854 m3/kg (13.65 cu ft/lb
m:

H

.13 kg (2.50 lb)

TIME 1.5 hr
dry matter -

DM = 543.48 (1-0.1124)

482.39 kg/hr (1065.12 lb/hr)
water in grain (in) -
WIN = 482.39 . 0.1352/(1-0.1352)
= 75.42 kg/hr (166.52 lb/hr)
water in grain (out) -
WOUT = 543.48 - 0.1273
69.19 kg/hr (152.76 lb/hr)

water removed -

WR 74.42 - 69.19

6.23 kg/hr (13.76 lb/hr)

LP gas consumption -

LPG = 1.13/1.5
= 0.75 kg/hr (1.66 lb/hr)
energy used -
EN = 0.75 - 45,226.74

33,920.06 kJ/hr (32,192.54 BTU/hr)

72

efficiency -
EFF = 33,920.06/6.23
= 5444.63 kJ/kg of water removed
(2340.29 BTU/lb)
Second Stage:
TIN = 121.ll°C (250°F)

SMIN = 12.73

XMOUT = 11.24

TIME = 1.5 hr

LP = 1.02 kg (2.25 lb)
water in grain (out) -

WOUT 543.48 ° 0.1124

61.09 kg/hr (134.88 lb/hr)
water removed -

WR = 69.19 b 61.09

8.10 kg/hr (17.88 lb/hr)

LP gas consumption -

LPG 1 02/1 5

0.68 kg/hr (1.50 lb/hr)
energy used -
EN = 0.68 - 45,226.74
= 30,754.19 kJ/hr (29,187.90 BTU/hr)

efficiency -

EFF 30.754.19/8.10

3796.81 kJ/kg of water removed
(1632 BTU/lb)

73

overall efficiency

OEFF

(33.920.06 + 30,754.19)/(6.23 + 8.10)

4513.21 kJ/kg of water removed

(1939.93 BTU/1b)

Excellent control was achieved for the inlet drying air
temperatures in all three tests. Special consideration of
the wet bulb temperature depression is necessary. The maxi-
mum wet bulb depression is Obtained when the air velocity
through the wet wick is above 4.57 m/s (15 ft/sec) (Brooker
et al., 1974). Because the cross sectional area of the con-
current and counterflow exhaust ducts are both 0.0081 1112
(0.0873 ftz), the minimum airflow necessary to overcome the
velocity requirements is 2.23 m3/min (78.54 cfm). As the
airflow rate through the cooler is only 0.60 m3/min (21 cfm),
the measured wet bulb temperature of the cooler exhaust is
too high. In the concurrent exhaust, the wet bulb tempera-
ture is correctly measured because the airflow was at least
3.83 m3/min (135 cfm).

An average flow rate of 543.48 kg/hr (1200 lb/hr),

r 3.2 kg/hr (7 lb/hr), was measured for the three tests.

The LP gas measurement presented a problem. The gas
consumption was estimated by the tank weight variation
before and after each test. A Toledo scale was utilized
as the weighing device. Because the tank was installed
outside the building, precise weight readings were difficult
to Obtain due to the wind effects. The author feels that

this explains the discrepancy between the LP gas consumption

74

data for the first, second and third tests. In theory,

all three values should have been equal for the stages in
which the same inlet drying temperature was used. However,
variations from 0.88 kg/hr to 0.68 kg/hr were recorded for
the LP gas.

_The soybean moisture content was evaluated according
to Service and Regulatory Announcements No. 147 of the
United States Department of Agriculture. Besides the error
in the weight measurements due to the limited scale accuracy,
a rounding-Off error occurred in the calculations because
the scale was accurate to only two decimal places. The
author feels that a scale accurate to four decimal places
should have been used because relatively small samples (about
5 grams) were involved. Another error present in the
moisture content evaluations is due to sampling. Samples
were taken as the dryer was being filled and accepted as
representative of the dryer load. Nevertheless, analyzing
the moisture content at several times during the drying
tests, it was observed that the initial moisture content
by as much as :2 percent.

A value of 3.83 m3/min (135 cfm) was obtained for the
airflow through the drying section. However, as the airflow
was Checked from the energy calculations, the following
results were attained:

1. first test

- air flow: 5.61 m3/min (197.96 cfm)

75

2. second test
2.1 first stage

- air flow: 4.64 m3/min (163.63 cfm)

N

.2 second stage

air flow: 5.40 m3/min (190.61 cfm)
3. third test

3.1 first stage

air flow: 3.71 mB/min (130.78 cfm)

3.2 second stage

air flow: 4.08 m3/min (144.06 cfm)

The discrepancy in these results is assumed to be caused
by the incorrect values measured in weighing the LP gas
consumption. The value of 3.83 mB/min was thus accepted
as the airflow reference value.

Germination, cracks and splits results are presented
in Table 5 for the extreme cases. The values for germination,
cracks and splits at the beginning of the drying tests
are expected to be similar for all three tests because they
are the soybean characteristics before any drying was per-
formed. Because the initial crack and split values are
significantly different, the results in Table 5 indicate
that the soybean sample was not originally homogeneous.

An expected decrease in the percentage of germination and
an increase in splits and cracks percentage was observed
for all tests. The complete results are presented in

Appendix D.

76

Table 5: Soybean germination, crack and split variations
after drying in a concurrent flow dryer.

 

121.ll°C 121.11-93.33°C 148.89-121.11°C

 

Germination (%)

initial 91.00 95.50 93.00

minimum 83.50 84.00 75.50
Cracks (%)

initial 2.77 3.83 8.51

maximum 15.63 21.05 18.18
Splits (%)

initial 1.20 3.57 3.87

maximum 4.48 5.68 6.60

 

77

The measured efficiency values fall in the interval
expected for concurrent flow dryer, i.e., from 4185 kJ/kg
Of water removed (1800 BTU/lb) to 5120 kJ/kg of water
removed (2200 BTU/lb). The high values encountered for
the efficiency in the first stage of the third run is the
result of the low inlet soybean temperature for that test.
As a result, part of the heat available for removing water
from the soybeans was used to warm up the product, diminish-
ing the amount of water removed. The data show that the
concurrent flow dryer is an efficient device for drying

soybeans.

6.2 Crossflow Simulation

The crossflow dryer simulated in this thesis is commer-
cially available. The air and product conditions represent
typical conditions Of the harvesting season. A schematic of
the commercial unit is presented in Appendix B.

The computer simulation program permits a choice of
the reversal of airflow, of a different number of stages of
different lengths, and of variable inlet air temperatures
and airflows. Recirculating airflow may be simulated after
a quick hand evaluation of the new inlet conditions is made.

The results obtained from the simulation are presented
in Tables 6 through 9. The inlet conditions for each stage
are presented at the top of each table.

Besides the minimum, maximum and average moisture
contents and temperatures, the outlet soybean mOisture equi-

librium, and the air relative humidity and humidity ratio

78

Table 6: Input and results for the crossflow dryer simulation,

first stage.

EXEC BEGUN.08.20.33.

TYPE OF PRODUCT<C0RN31 OR SOYBEAN82)32. 2.0000

CROSSFLOU GRAIN DRYER SIMULATION
USING THE OVERHULTZ THINLAYER EQUATION FOR SOYBEAN
AND ENC BY ROA

INPUT CONDITIONS FOR STAGE 1:

INLET AIR TEMP! F {130. 130.0000
INLET AMBIENT TEMP! F :60. 60.0000
TYPE OF FUEL USED (18N0.2 FUEL
Z‘NRTOGASI 3'L!P.GAS):10 100000
CALCULATED AMBIENT ABS HUN- .0068
CALCULATED INLET ADS HUNI .0087
AIRFLOU! CFN/DU (AT DRYING TENP):110. 110.0000
INLET GRAIN TEMP! F360. 60.0000
INLET MOISTURE! NET BASIS PERCENT322. 22.0000
COLUHN UIDTH! IN812. 12.0000
COLUMN LENGTH! FT323.5 23.5000
GRAINFLOU! DU/HR/SG FT320. 20.0000
OUTPUT INTERVAL! FT31. 1.0000
HYBRID DRYING FACTOR!DEC€1. 1.0000
N0.0F STAGESCDRYER+COOLER):4. 4.0000
PRELIMINARY CALCULATED VALUES
AIRFLOU! CFN/SG FT 88.4244
DRY AIRFLOH RATE! LD/HR-FT2 388.5833
INLET MC(DRY BASIS DECINAL) .2821
GRAIN FLOU RATE! 8USHELS/HR-FT2 20.0000
GRAIN FLOU RATE! FT/HR 24.8800
TINE DEPTH MOISTURE-88 TENPERATURE
HR FT NAV MIN MAX TAVG THIN TNAX HOUT RH NEOUT
.02 .50 .2196 .2114 .2231 65.2 60.0 116.5 .0111 98.21 .2656
.06 1.49 .2195 .2049 .2226 70.7' 60.9 125.8 .0116 99.20 .2715
.10 2.49 .2192 .2004 .2233 75.8 62.4 127.5 .0123 99.16 .2728
.14 3.48 .2188 .1967 .2238 80.4 65.0 128.0 .0135 99.04 .2748
.18 4.48 .2181 .1936 .2242 84.2 68.8 128.3 .0153 98.63 .2761
.22 5.47 .2173 .1908 .2246 87.1 72.8 128.5'.0175 98.02 .2759
.26 6.47 .2163 .1883 .2250 89.3 74.2 128.7 .0193 97.48 .2749
.30 7.46 .2151 .1860 .2253 91.1 74.5 128.8 .0204 97.13 .2739
.34 8.46 .2138 .1838 .2256 92.5 74.8 128.9 .0209 96.95 .2733
.38 9.45 .2125 .1818 .2259 93.8 75.1 129.0 .0211 96.87 .2729
.42 10.45 .2112 .1799 .2260 95.0 74.7 129.0 .0211 96.82 .2726
.46 11.44 .2098 .1781 .2262 96.1 75.2 129.1 .0211 96.79 .2724
.50 12.44 .2084 .1764 .2263 97.2 74.8 129.1 .0210 96.80 .2724
.54 13.44 .2070 .1747 .2265 98.3 75.3 129.2 .0210 96.76 .2721
.58 14.43 .2056 .1732 .2266 99.3 75.0 129.2 .0209 96.77 .2721
.62 15.43 .2042 .1717 .2268 100.3 75.6 129.2 .0208 96.74 .2718
.66 16.42 .2027 .1702 .2269 101.3 75.2 129.3 .0208 96.76 .2719
.70 17.42 .2012 .1688 .2270 102.3 75.1 129.3 .0207 96.72 .2716
.74 18.41 .1997 .1675 .2272 103.2 75.7 129.3 .0206 96.72 .2714
.78 19.41 .1982 .1662 .2273 104.2 75.4 129.4 .0206 96.73 .2714
.82 20.40 .1967 .1649 .2274 105.1 75.3 129.4 .0205 96.70 .2712
.86 21.40 .1951 .1637 .2275 106.0 75.9 129.4 .0204 96.69 .2711
.90 22.39 .1936 .1625 .2276 106.8 75.8 129.4 .0203 96.72 .2712
.94 23.39 .1920 .1613 .2277 107.7 75.6 129.4 .0203 96.73 .2712
.96 23.88 .1914 .1608 .2280 108.6 78.5 129.4 .0154 71.52 .1505
AVERAGE AIR EXHAUST TENP! F 75.1951
AVERAGE AIR EXHAUST HUN.RATIO .0187
ENERGY SUPPLIED! BTU/SO FT 157204.4265
HATER REMOVED! L8/SO FT-HR 65.3743
EFFICIENCY! BTU/L3 H20 2404.6830
TOTAL DRYER HATER REMOVED! LDISG FT-HR 65.3743
TOTAL DRYER EFFICIENCY! 8TU/L8H20' 2404.6830
INLET MOISTURE EQUILIBRIUM-UR .0207
DRY AIRFLOH RATE! LB/HR FT2 388.5833
STATIC PRESSURE! IN H2O 1.2609
TOTAL HORSE POUER! HP/FT2 OF UIDTH 1.6505

79

Table 7: Input and results for the crossflow dryer simulation,

second stage.

CROSSFLOU GRAIN DRYER SIMULATION
USING THE OVERHULTZ THINLAYER EQUATION FOR SOYBEAN
AND EMC BY RDA

INPUT CONDITIONS FOR STAGE
INLET AIR TEMP! F 2130.
INLET AMBIENT TEMP! F :60.

AMBIENT REL HUM! DEC 3.6

CALCULATED AMBIENT ABS HUM-
CALCULATED INLET ABS HUM.

AIRFLOH! CFM/DU (AT DRYING TEMP)8110.
COLUMN LENGTH! FT:23.5

~90
130.0000
60.0000
.6000
.0068
.0087
110.0000
23.5000

TYPE OF ARRAY CONVERSION
(1'NO CHANGES! 2=REVERSE AIRFLOH):2.

TIME
HR
.02
.06
.10
.14
.18
.22
.26
.30
.34
.38
.42
.46
.50
.54
.58
.62
.66
.70
.74
.78
.82
.86
.90
.94
.96

DEPTH
PT
.50

1.49
2.49
3.48
4.48
5.47
6.47
7.46
8.46
9.45

10.45

11.44

12.44

13.44

14.43

15.43

16.42

17.42

18.41

19.41

20.40

21.40

22.39

23.39

23.88

AVERAGE AIR

HATER REMOVED!

EFFICIENCY!
TOTAL DRYER HATER REMOVED! LD/SO FT-HR
TOTAL DRYER EFFICIENCY! BTU/LDH2O
INLET MOISTURE EQUILIBRIUM-H8

MOISTURE-H8

MAV
.1895
.1877
.1864
.1852
.1841
.1819
.1809
.1799
.1790
.1780
.1770
.1760
.1750
.1741
.1731
.1722
.1712
.1703
.1694
.1685
.1676
.1667
.1659
.1654

MIN
.1602
.1594
.1587
.1581
.1576
.1573
.1570
.1567
.1566
.1565
.1564
.1563
.1561
.1560
.1558
.1556
.1553
.1550
.1547
.1544
.1541
.1538
.1534
.1530
.1529

MAX
.2252
.2146
.2119
.2077
.2042
.2011
.1984
.1959
.1937
.1917
.1898
.1880
.1863
.1847
.1831
.1816
.1802
.1789
.1776
.1763
.1751
.1739
.1728
.1717
.1711

EXHAUST TEMP! F
AVERAGE AIR EXHAUST HUM.RATIO
ENERGY SUPPLIED!

BTU/LB H2O

BTU/SO FT
LBISO FT-HR

2.0000

TEMPERATURE

TAVG
105.9
102.2
100.2

98.7

97.9

97.8

98.4

99.5

101.0
102.7

104.5

106.3
107.8

109.2.

110.3
111.3
112.1
112.8
113.4
114.0
114.5
115.0
115.4
115.8
116.0

TMIN
73.4
77.6
81.1
82.5
83.3
84.0
84.5
84.9
85.3
85.6
86.0
87.4
89.6
92.0
94.4
96.4
98.1
99.5
100.7
101.7
102.6
103.4
104.1
104.7
105.0

TMAX
127.1
123.7
126.9
127.8
128.2
128.4
128.6
128.7
128.8
128.9
129.0
129.1
129.1
129.2
129.2
129.2
129.3
129.3
129.3
129.3
129.4
129.4
129.4
129.4
129.4

HOUT
.0269
.0234
.0168
.0153
.0148
.0145
.0143
.0142
.0141
.0141
.0141
.0141
.0140
.0140
.0140
.0139
.0138
.0138
.0137
.0136
.0135
.0135
.0134
.0133
.0133

99.9437

.0150

157204.4265
55.5476 .
2830.0865
120.9219
2600.0995

.0207

RH
28.81
29.04
24.34
25.81
29.24
33.69
39.00
44.55
49.16
51.61
51.42
49.13
45.80
42.34
39.26
36.72
34.69
33.07
31.74
30.64
29.69
28.86
28.12
27.45
27.13

MEOUT
.0498
.0510
.0454
.0483
.0542
.0620
.0715
.0820
.0914
.0967
.0963
.0914
.0846
.0779
.0721
.0676
.0640
.0613
.0590
.0572
.0556
.0542
.0530
.0519
.0514

DRY AIRFLOH RATE! LB/HR FT2
STATIC PRESSURE! IN H2O
TOTAL HORSE POHER! HP/FT2 OF HIDTH

388.5833
1.2609
3.3009

80

Table 8: Input and results for the crossflow dryer simulation,

third stage.

CROSSFLOH GRAIN DRYER SIMULATION

USING THE OVERHULTZ THINLAYER EGUATION FOR SOYBEAN
AND EMC BY ROA

INPUT CONDITIONS FOR STAGE 3:

INLET AIR TEMP! F :60. 60.0000
INLET AMBIENT TEMP! F :60. 60.0000
AMBIENT REL HUM! DEC 3.6 .6000'
CALCULATED AMBIENT ABS HUM- .0068
CALCULATED INLET ABS HUMI~ .0068
AIRFLOH! CFM/BU (AT DRYING TEMP):110. 110.0000
COLUMN LENGTH! FT37.85 7.8500
TYPE OF ARRAY CONVERSION
(IINO CHANGES! 2=REVERSE AIRFLOH):1. 1.0000
TIME DEPTH MOISTURE-HB TEMPERATURE
HR FT MAV MIN MAX TAVG TMIN TMAX HOUT RH MEOUT
.02 .50 .1650 .1527 .1706 111.5 79.8 121.8 .0113 22.87 .0450
.06 1.49 .1643 .1523 .1695 105.3 61.6 116.7 .0107 21.43 .0428
.10 2.49 .1636 .1519 .1686 99.5 60.1 113.0 .0100 19.94 .0405
.14 3.48 .1631 .1514 {1680 93.8 60.0 110.1 .0095 18.64 .0385
.18 4.48 .1627 .1510 .1677 88.4 60.0 107.8 .0089 17.61 .0369
.22 5.47 .1624 .1505 .1675 83.2 60.0 106.0 .0085 16.98 .0360
.26 6.47 .1621 .1501 .1675 78.2 59.9 104.2 .0081 17.04 .0363
.30 7.46 .1619 .1497 .1674 73.7 59.9 100.7 .0077 18.09 .0384
.32 7.96 .1618 .1495 .1674 71.7 59.9 98.3 .0076 19.10 .0403
AVERAGE AIR EXHAUST TEMP! F 104.8688
AVERAGE AIR EXHAUST HUM.RATIO .0091
ENERGY SUPPLIED! BTU/SO FT 0.0000
HATER REMOVED! LB/SG FT-HR 7.4742
EFFICIENCY! BTU/LB H20 0.0000
TOTAL DRYER HATER REMOVED! LB/SG FT-HR 128.3960
TOTAL DRYER EFFICIENCY! BTU/LBH2O 2448.7431
INLET MOISTURE EQUILIBRIUM-HS .1239
DRY AIRFLOH RATE! LB/HR FT2 389.8055
STATIC PRESSURE! IN H2O 1.2609

TOTAL HORSE POHER!

HP/FT2 OF HIDTH

3.8522

81

Table 9: Input and results for the crossflow dryer simulation,

fourth stage.

CROSSFLOH GRAIN DRYER SIMULATION
USING THE OVERHULTZ THINLAYER EQUATION FOR SOYBEAN

AND EMC BY ROA

INPUT CONDITIONS FOR STAGE 43

INLET AIR TEMP! F 360. 60.0000
INLET AMBIENT TEMP! F 360. 60.0000
AMBIENT REL HUM! DEC 3. .6000
CALCULATED AMBIENT ABS HUMI .0068
CALCULATED INLET ABS HUMll .0068
AIRFLOH! CFM/BU (AT DRYING TEMP)3110. 110.0000
COLUMN LENGTH! FT37.85 7.8500
TYPE OF ARRAY CONVERSION
(18NO CHANGES! 2IREVERSE AIRFLOH)32. 2.0000
TIME DEPTH MOISTURE-H8 TEMPERATURE
HR FT MAV MIN MAX TAVG TMIN TMAX HOUT RH MEOUT
.02 .50 .1618 .1495 .1674 70.7 59.9 89.7 .0074 65.89 .1397
.06 1.49 .1616 .1495 .1674 70.4 60.0 85.0 .0074 65.36 .1382
.10 2.49 .1615 .1495 .1673 70.0 60.1 81.9 .0074 64.25 .1349
.14 3.48 .1614 .1495 .1673 69.5 60.0 79.6 .0074 61.15 .1262
.18 4.48 .1613 .1495 .1671 68.9 60.0 77.6..0074 56.08 .1131
.22 5.47 .1612 .1494 .1669 67.9 60.0 76.0 .0073 50.21 .0994
.26 6.47 .1611 .1494 .1667 66.8' 60.0 74.7 .0073 45.13 .0886
.30 7.46 .1610 .1494 .1666 65.5 59.9 73.5 .0072 41.94 .0823
.32 7.96 .1610 .1494 .1665 64.8 59.9 73.0 .0072 41.20 .0809
AVERAGE AIR EXHAUST TEMP! F 64.9376
AVERAGE AIR EXHAUST HUM.RATIO .0073
ENERGY SUPPLIED! BTU/SQ FT‘ 0.0000
HATER REMOVED! LB/SQ FT-HR 1.7237
EFFICIENCY! BTU/LB H2O 0.0000
TOTAL DRYER HATER REMOVED! LB/SQ FT-HR 130.1197
TOTAL DRYER EFFICIENCY! BTU/LBH2O 2416.3039
INLET MOISTURE EQUILIBRIUM-H8 .1239
DRY AIRFLOH RATE! LB/HR FT2 389.8055
STATIC PRESSURE! IN H2O 1.2609
TOTAL HORSE POHER! HP/FT2 OF HIDTH 4.4036

THIS IS THE END OF CROSSFLOH

STOP

82

at the outlet conditions, some additional quantities are
evaluated after each stage. Some values refer to the stage
just simulated and others are cumulative results. Belonging
to the first group are: (l) the average air exhaust temp-
erature, (2) the average air exhaust humidity ratio, (3) the
energy supplied, (4) the water removed, (5) the energy effi-
ciency of the stage, (6) the dry airflow rate, and (7) the
static pressure. In the second group fall: (1) the total
dryer water removed, (2) the total dryer efficiency, and

(3) the total horsepower. These figures permit the reader
to observe how the soybeans and the air behave inside the
dryer.

At the bottom of Figure 9, the total dryer efficiency
is tabulated. In the simulated case, the overall efficiency
is 5620.31 kJ/kg of water removed (2416.3 BTU/lb), a typical
value for a crossflow dryer. The overall efficiency can
be improved if some changes are made in the cooler dimen-
sions (in the present dryer only a small amount of water
is removed by the cooling air). It should be noted that
the efficiency only includes the energy used to increase
the drying air temperature. The electricity required to
run the fans is not included in the efficiency calculations.

The results in Tables 6 through 9 are a sample of the
features of the crossflow model. They are characteristics
of the input conditions. The output will be different if
one or more input parameters change.

English units are used in the simulation of this dryer

83

because the American grain dryer industry is not yet using
the SI units. The appropriate unit conversion factors can

be found in Appendix E.

CHAPTER VII
CONCLUSIONS

1. Drying air temperatures up to l48.89°C (300°F) may
be used to dry soybeans in a concurrent flow dryer without
a significant reduction in the product quality (germination,
cracks and splits), provided the mass flow rate is at
least 540 kg/hr.

2. The increase in cracks and splits is due to the
combined effect of drying and handling (two augers moved
the beans through and out of the dryer). However, it was
not possible to determine which of these effects was the
most important. Previous studies showing a decrease in the
crack percentage in favor of an increase in splits was not
confirmed on this research. The results here reported
show an increase in both figures, a more logical behavior.

3. An efficient crossflow dryer model resulted from
the soybean drying simulation.

4. Continuous flow drying of soybeans at high temp-
eratures is a feasible practice. The adoption of such a
practice will stimulate early harvest of soybeans which
results in less field and harvesting losses. Besides,
early harvested soybeans reach the market when the price

is higher. In Brazil, anticipation of the harvesting

84

85

season will have one additional advantage, i.e., there will
be more time for planting the next crop, thus making the

practice of double cropping more attractive.

CHAPTER VIII

SUGGESTIONS FOR FURTHER STUDIES

1. Future experimental work with the concurrent flow
drying of soybeans should include variations in the air
and mass flow rates.

2. Initial moisture content on the order of 16-22
percent should be tested because the feasibility of continu-
ous soybean drying will be greatly increased if the drying
process can start at those levels of moisture content.

3. Special care must be taken in the moisture evalua-
tion of the product. A scale accurate to four decimal places
should be used because small variations in the weight read—
ings may cause significant error in the moisture content
calculations.

4. A statistical sampling method should be used.

~5. An equilibrium moisture content equation should be
developed to assist in the dryer simulation that uses high
air temperatures. The available equilibrium moisture con-
tent equations are acceptable for low temperature drying
simulations but may not describe the drying behavior ade-
quately at higher temperatures than for which they were

developed.

86

87

6. A thin—layer equation which accounts for the
moisture diffusion inside the soybeans should be developed
because it describes the drying process in a more realistic
way.

7. An equation which predicts the germination loss

of the soybeans would be valuable in drying simulations.

APPEND I CES

APPENDIX A

LISTING OF THE COMPUTER PROGRAM

88'

APPENDIX A
LISTING OF THE COMPUTER PROGRAM

3n 3 .9; .y .r a 2; 50303000.. .0001 ..030COr..0..,Y0080000.,6000....000n.00rJC000CCC0.00026 603:0.0000000000
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G D MNMMMNN!HLEJIDGENDNCLINTNDNNDNNDNNDN NLNNDNNDNNDN:MNDNNDNNDNEENDNEcL
0 MEMMMMMMHAMT DTTIAIRL(I IAIIAIIAIIAI ILIIAIIAIIAIOTIAIIAIIAI(MIAINNE
R GLOOCOOOOEI( ASORERPAFRORERRERRERRERIRARRERRERRERMIRERRERRERFTRERIPV
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89

continued:

APPENDIX A,

245.5 Ad. .Co. .a. .A.

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AND INITIALIZE ALL ARRAY POSITIONS NECESSARY
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90

continued:

APPENDIX A ,.

0000 00 005 08000000005000000 00000000000005.00050000
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60

91

APPENDIX A, continued:

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92

continued:

APPENDIX A,

CO009300000000000000000000000005000000500050000000000000050000000000

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C C 9C CC C C1 6 7 £5

93

continued:

APPENDIX A,

05000500060050000579000OOOOOOOCOOOCOOOOO
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O
1

94

continued:

APPENDIX A,

000000000000000000000000000000000000UOOOOOOOOOOOOOO00009000OOOOOOOUOOCOOOOOO0
67 cr 95123656789 a .1236567899123L5678901236567890123656739n .123‘56789 31§Eo673901.. ..
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continued:

APPENDIX A,

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APPENDIX B
SCHEMATIC OF THE COMMERCIAL UNIT SIMULATED IN THIS THESIS

98

 

 

 

 

 

T

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D - GRAIN (corn)

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Inv

 

 

APPENDIX C
EQUILIBRIUM MOISTURE CONTENT RESULTS FROM ROA EQUATION
FOR RELATIVE HUMIDITY HIGHER THAN 90 PERCENT
FOR SEVERAL TEMPERATURES

EQUILIBRIUM MOISTURE CONTENT RESULTS FROM ROA EQUATION
FOR RELATIVE HUMIDITY HIGHER THAN 90 PERCENT

APPENDIX C

99

FOR SEVERAL TEMPERATURES

 

 

 

Relative Temperature ng)
Humidity (%) 50 70 90 110 130
Me (percent, dry basis)

90 31.13 32.21 33.33 34.48 35.68
91 32.63 34.19 35.82 37.54 39.33
92 34.25 36.37 38.82 41.02 43.56
93 36.00 38.78 41.78 45.00 48.48
94 37.90 41.46 45.34 49.59 54.24
95 39.97 44.43 49.38 54.88 61.00
96 42.23 47.74 53.98 61.02 68.99
97 44.69 51.45 59.22 . 68.18 78.48
98 47.38 55.60 65.24 76.55 89.82
99 50.33 60.27 72.16 86.40 103.44
100 53.58 65.53 80.15 98.04 119.92

 

APPENDIX D
GERMINATION, CRACK AND SPLIT RESULTS
AND TEMPERATURE RESULTS

100

APPENDIX D

Table D.1: Germination, crack and split results for
Test No. 1 (121.11°C).

 

 

Sample No. Germination (%) Cracks (%) Splits (%)
1 85.0 2.77 1.20
2 90.0 5.85 2.73
3 90.0 6.82 3.17
4 91.0 6.70 2.58
5 88.5 7.54 3.55
6 83.0 6.38 3.03
7 83.0 4.86 3.65
8 86.0 6.40 2.53
9 84.5 6.54 3.18

10 84.0 5.97 3.47
11 85.0 5.79 2.50
12 87.0 10.02 2.16
13 89.0 8.64 3.39
14 84.0 6.34 3.21
15 85.5 11.41 3.94
16 86.5 14.84 3.63
17 83.5 15.63 4.48

 

101

APPENDIX D

Table D.2: Germination, crack and split results for Test
No. 2 (121.11—93.33°C).

 

 

Sample No. Germination (%) Cracks (%) Splits (%)
1 95.5 3.83, 3.57
2 95.0 5.34 3.44
3 91.5 6.74 3.87
4 85.0 6.83 4.13
5 81.0 5.49 4.38
6 90.5 4.84 3.90
7 87.0 5.65 4.38
8 88.0 9.01 3.61
9 84.0 9.65 4.25

10 87.0 6.51 2.25
11 87.0 8.48 5.68
12 85.0 8.15 2.92
13 89.5 8.99 5.47
14 86.0 10.49 3.39
15 88.0 11.98 4.11
16 87.0 9.56 3.41
17 86.0 10.10 5.41
18 85.5 11.29 3.38
19 85.0 12.33 5.28
20 89.0 21.05 4.87

 

102

APPENDIX D

Table D.3: Germination, crack and split results for Test
No. 3 (148.89-121.11°C).

 

 

Sample No. Germination (%) Cracks (%) Splits (%)
1 87.5 8.51 3.87
2 90.5 6.31 2.23
3 92.0 5.12 4.66
4 86.5 10.38 3.34
5 93.0 10.06 5.12
6 80.5 9.62 2.41
7 82.0 9.71 3.42
8 81.0 10.05 4.23
9 81.5 14.46 3.87

10 84.5 12.80 5.36
11 88.0 10.29 3.26
12 83.5 10.69 3.59
13 81.0 11.65 5.01
14 83.0 16.20 4.76
15 75.5 12.29 6.18
16 79.5 18.18 5.04
17 82.0 16.06 6.60

 

103

APPENDIX D

Table D.4: Temperature results (°F) for the concurrent
flow dryer.

 

Test No. 1 Test No. 2 Test No. 3

 

Inlet drying air 250 250-200 300-250
Drying section:

1 ft depth 104 104 112

2 ft depth 103 103 110

3 ft depth 101 101 106
Outlet air, dry bulb 112 107 124
Outlet air, wet bulb 95 98 101

Cooling section:

inlet air, dry bulb 78 74 74
inlet air, wet bulb 61 61 55
outlet air, dry bulb 93 92 87

outlet air, wet bulb 84 81 75

 

APPENDIX E
CONVERSION FACTORS

104

APPENDIX E

CONVERS ION FACTORS

 

 

Unit Conversions English or Metric SI
Area 1 ft2 9.290x10-2m2
Convective Heat-Transfer l BTU/h ft2 °F 5.678 W/m2°C
Coefficient
Density 1 lb /ft3 1.602x10kg/m2
Energy 1 kcal 4. 187x103J
1 BTU 1.055x10 J
Enthalpy, specific 1 BTU/1b 2.326x103J/kg
Force 1 1bf 4.448 N
Heat Flux l kcal/h m2 1.163 W/m2
1 BTU/h ft2 3.155'W/m2
Heat Release Rate (mass) 1 BTU/h lb 6.461xlo‘1wnsg
length 1 ft 3. 048xlo‘1m
Mass 1 1b 4.536x10’lkg
l tonne 1.000x10
1 ton 1.016x103kg
Power 1 BTU/h 2.931xlo'1w
1 hp 7.457x102W
pressure 1 standard atnnsphere 1 . 013x105N/mg
1 bar 2 1.000x10 /m2
1 lbf/in 6.895x10 /m2
1 in water 2.491x10 /m2
1 am Hg 1.333xl /m
Surface per Unit Volume 1 ftz/ft3 3.280 mz/m3
Specific Heat 1 BTU/1b F 4.187x103J/kgK

Tauperature Difference
Thermal Conductivity

1 deg F (deg R)
1 B’IU/h ft2 ("E/ft)

5/9 deg C (deg K)
1.731 W/mz (°C/m)

105

APPENDIX E, continued:

 

 

Unit Conversions English or Metric SI
Velocity 1 ft /h 8.467x10'5m/s
Viscosity, absolute 1 1b/ft h 4.134x10‘4kg/m s

(or dynamic)

Viscosity, kinematic 1 ftz/h 2.581x10-5m2/s
Volume 1 bu (volume) 3.523x10:2 3
1 ft3 2.832x10_3m3
1 U.S. gal 3.785x10
Airflow 1 cfm ' 2.83mojmg/min
].cfin 2 4.7MbflDLfn/Sec
1 cfm/ft2 3.048x10_3m/min
1.cfimflt SJMIRQO nusa:

 

REFERENCES

REFERENCES

Alam, A. 1972 Drying simulation of soybeans. Unpublished
Ph.D. thesis. University of Illinois: Urbana, IL.

Alam, A. and Shove, G. 1973. Simulation of soybean drying.
Trans. ASAE 16:134-136.

Bakker-Arkema, F. W., Lerew, L. E., DeBoer, S. F., and
Roth, M. G. 1974. Grain Dryer Simulation. Research
Report 224. Agr. Exp. Sta., Michigan State University:
East Lansing, MI.

Bakker-Arkema, F. W., Lerew, L. E., Brook, R. C., and
Brooker, D. B. 1978. Energy and capacity performance
evaluation of grain dryers. ASAE Paper No. 78-3523.
Am. Soc. Agr. Eng.: St. Joseph, MI.

- Bakker-Arkema, F. W., Brook, R. C., and Lerew, L. E. 1978.
Cereal grain drying. In: Advances in Cereal Science
and Technology, ed. by Y. Pomeranz, pp. 1-90. Amer-
ican Association of Cereal Chemists, Inc: St. Paul, MN.

Bakker-Arkema, F. W., Brooker, D. B., and Roth, M. G. 1976.
Feasibility study of in-bin corn drying in Missouri
using solar energy. USDA Special Report.

Bakker-Arkema, F. W., and Green, R. 1977. High temperature
wheat drying. ASAE Paper No. 77-3527. Am. Soc. Agr.
Eng.: St. Joseph, MI.

Bakshi, A. S., Singh, R. P., Wang, C. Y., and Steffe, J. F.
1978. Energy costs of a conventional and air recycling
crossflow rice dryer. ASAE Paper No. 78-3011. Am.
Soc. Agr. Eng.: St. Joseph, MI.

Brook, R. G. 1977. Design of multistage grain dryers.
Unpublished Ph.D. thesis. Michigan State University:
East Lansing, MI.

Brook, R. G., and Bakker-Arkema, F. W. 1977. Design of
multistage grain dryers using computer simulation.
ASAE Paper No. 77—3529. Am. Soc. Agr. Eng.: St. Joseph,
MI.

106

107

Brooker, D. B., Bakker-Arkema, F. W., and Hall, C. W. 1974.
Drying Cereal Grains. AVI: Westport, CT.

Chanchai, R., White, G. M., Loewer, 0. J., and Engli, D. B.
1976. Influence of heated air drying on soybean impact
damage. Trans. ASAE 19:372-377.

Farmer, D- M., Bakker-Arkema, F. W., DeBoer, S. F., and
Roth, M. G- 1972. Simulation and optimal design of
a commercial concurrent-counterflow grain dryer -
the Anderson model. ASAE Paper No. 72-847. Am. Soc.
Agr. Eng.: St. Joseph, MI.

Hall, G. E. 1974. Damage during handling of shelled corn
and soybeans. Trans. ASAE 17:335-338.

Henderson, S. M. 1952. A basic concept of equilibrium
moisture. Agr. Eng. 33(1).

Kalchik, S. V. 1977. Drying of soybeans in a pilot scale
concurrent flow dryer. Unpublished M.S. thesis.
Michigan State University: East Lansing, MI.

Keener, H. M., and Glenn, T. L. 1978. Measuring performance
of grain drying systems. ASAE Paper No. 78-3521.
Am. Soc. Agr. Eng.: St. Joseph, MI.

Lerew, L. E., Bakker-Arkema, F. W., and Brook, R. C. 1972.
Simulation of a commercial crossflow dryer: The Hart-
Carter model. ASAE Paper No. 72-829. Am. Soc. Agr.
Eng.: St. Joseph, MI.

Matthes, R. K., and Welch, G. B. 1974. Heated air drying
of soybean seed. ASAE Paper No. 74-3001. Am. Soc.
Agr. Eng.: St. Joseph, MI.

0thmer, D. F. 1940. Correlation vapor pressure and latent
heat data. Ind. Eng. Chem. 32:841-846.

Overhults, D. G., White, G. M., Hamilton, H. E., and Ross,
I. J. 1973. Drying soybeans with heated air. Trans.
ASAE 16:112-113.

Pfost, D. L. 1975. Environmental and varietal factors
affecting damage to seed soybeans during drying.
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