Front Cover
 Title Page
 Table of Contents
 Investigation of present drying...
 Experimental equipment and infrared...
 Static pressure determinations
 Experimental drying tests
 Storage tests
 Proposed tung nut dryer

Group Title: Bulletin
Title: Investigation on dehydration of tung nuts
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00003376/00001
 Material Information
Title: Investigation on dehydration of tung nuts
Series Title: Bulletin - Florida Engineering and Industrial Experiment Station ; 21
Alternate Title: Dehydration of tung nuts
Physical Description: 35 p. : ill. ; 23 cm.
Language: English
Creator: Leggett, James T. ( James Thomas ), 1916-
Gilbert, Seymour G ( Seymour George )
University of Florida -- Engineering and Industrial Experiment Station
Publisher: Florida Engineering and Industrial Experiment Station :
U.S. Field Laboratory for Tung Investigations
Place of Publication: Gainesville, Fla.
Publication Date: 1948
Subject: Tung nut -- Drying -- Equipment and supplies   ( lcsh )
Tung oil industry -- Florida   ( lcsh )
Genre: bibliography   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (p. 35).
General Note: "July, 1948."
Statement of Responsibility: by James T. Leggett and Seymour G. Gilbert.
 Record Information
Bibliographic ID: UF00003376
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA4532
ltuf - AJN3644
oclc - 27179416
alephbibnum - 001809785

Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
    Title Page
        Page 1
        Page 2
        Page 3
        Page 4
    Table of Contents
        Page 5
        Page 6
        Page 7
        Page 8
    Investigation of present drying methods
        Page 9
        Page 10
    Experimental equipment and infrared drying tests
        Page 11
        Page 12
        Page 13
    Static pressure determinations
        Page 14
    Experimental drying tests
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
    Storage tests
        Page 27
        Page 28
        Page 29
    Proposed tung nut dryer
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
Full Text

Investigation on



Assistant Research Engineer
Mechanical Engineering Section
Florida Engineering and Industrial Experiment Station


Associate Plant Physiologist
U. S. Field Laboratory for Tung Investigations

July, 1948

Bulletin No. 21

College of Engieering University of Florida Gainesville


The Engineering Experiment Station was first approved by
the Board of Control at its meeting on May 13, 1929. Funds
for the Florida Engineering and Industrial Experiment Station
were appropriated by the Legislature of the State of Florida in
1941. The Station is a Division of the College of Engineering
of the University of Florida under the supervision of the State
Board of Control of Florida. The functions of the Florida En-
gineering and Industrial Experiment Station are:
a) To develop the industries of Florida by organizing and
promoting research in those fields of engineering, and the re-
lated sciences, bearing on the industrial welfare of the State.
b) To survey and evaluate the natural resources of the
State that may be susceptible to sound development.
c) To contact with governmental bodies, technical societies,
associations, or industrial organizations in aiding them to solve
their technical problems. Provision is made for these organ-
izations to avail themselves of the facilities of the Engineering
and Industrial Experiment Station on a co-operative financial
basis. It is the basic philosophy of the Station that the indus-
trial progress of Florida can best be furthered by carrying on
research in those fields in which Florida, by virtue of its loca-
tion, climate, and raw materials, has natural advantages.
d) To publish and disseminate information on the results
of experimental and research projects. Three series of pamphlets
are issued: Bulletins covering the results of research and in-
vestigations by staff members; Technical Papers, reprinting
papers or reports by staff members which have been published
elsewhere; and Leaflets, reprinting articles by staff members
which have been published in the more popular periodicals.
For copies of Bulletins, Technical Papers, Leaflets or infor-
mation on how the Station can be of service, address:
The Florida Engineering and Industrial Experiment Station
College of Engineering
University of Florida
Gainesville, Florida

Investigation on



Assistant Research Engineer
Mechanical Engineering Section
Florida Engineering and Industrial Experiment Station


Associate Plant Physiologist
U. S. Field Laboratory for Tung Investigations

College of Engineering
University of Florida


Burean of Plant Indusiry, Soils, and Agricultural Engineering
Agricultural Research Admnistration
United States Departmenl of Agriculture

Bulletin No. 21 -July. 1948

Peorissiop. is gien to reproduce orquote any
portion of this nibHlatio provlin a credit line
is given acknowledging the sore of the ijfor-

The tung oil industry in Florida ranks third among southern
states in commercial tree acreage. Solution of problems and
new developments in this industry are of interest to many
of its citizens.
A milling problem of the tung oil industry has been proper
drying of the nuts which have a high moisture content. In pres-
ent practice the tung fruit is left on the ground until it has dried
sufficiently to be placed in storage for further drying. This
process takes several months. This bulletin describes mechani-
cal equipment which has been devised for dehydrating the nuts
preparatory to milling. The new procedure permits use of the
hulls for fertilizer in the field, reduces hauling costs, makes pos-
sible more efficient miilling, and ultimately results in a better
grade of oil.
Working plans for such a tung nut dryer are described and
pictured herein. Data on various experimental drying and stor-
age tests are included along with results of an investigation of
present drying methods.
It is hoped that this information will be of value to the tung
oil industry in maintaining its economic stability and that its
application will be of benefit to Florida citizens.

The authors wish to acknowledge and express appreciation
for the aid and helpful criticisms of Professor N. C. Ebaugh,
Head of the Mechanical Engineering Department, College of
Engineering, University of Florida; Dr. R. A. Morgen, Director,
Florida Engineering and Industrial Experiment Station, Univer-
sity of Florida; Dr. F. S. Lagasse, Senior Pomologist, and Dr.
George F. Potter, Principal Physiologist, of the U. S. Field Lab-
oratories for Tung Investigations, Bureau of Plant Industry,
Soils, and Agricultural Engineering, Agricultural Research
Administration, United States Department of Agriculture, at
Gainesville, Florida, and Bogalusa, Louisiana, respectively.
Appreciation is also expressed to Dr. R. S. McKinney, Senior
Chemist, Tung Oil Laboratory, Bureau of Agricultural and In-
dustrial Chemistry, United States Department of Agriculture.
Gainesville, Florida, for suggestions and for use of the laboratory
huller, and to Professor Ford L. Prescott, Mechanical Engineer-
ing Department, College of Engineering, University of Florida,
for aid in the design and drawing of the dryer.
Appreciation is expressed to the American Tung Oil Associ-
ation and to the General Tung Oil Corporation, who partially
defrayed the expenses of the research reported in this bulletin.

INTRODUCTION ...... .......... ..... ......... .....-...-.... .....--....... 7


Natural Drying _................ .. ... ............... 9

Artificial Drying ..--............-.. ...................... 10

EXPERIMENTAL EQUIPMENT ................ ...- ......... ...... 11

INFRARED DRYING TESTS .......... ......... ............... ...... 11

STATIC PRESSURE DETERMINATIONS ---...........---...;.---. 14

EXPERIMENTAL DRYING TESTS ...---.....-..............---- 15

STORAGE TESTS ..-.......-................... .............. 27

Procedure ....................... ...... ..... ........ ... 27

Results of Storage Studies ..-... ..-.......................-. 29

PROPOSED TUNG NUT DRYER ......... ..-......-............-......- 30

CONCLUSIONS ---...... -_. ...................-................ 33


Dehydration of Tung Nuts

On April 21, 1945, representatives of the American Tung
Oil Association and of the General Tung Oil Corporation met
with representatives of the Florida Engineering and Industrial
Experiment Station to discuss the possibility of initiating a re-
search project on the dehydration of tung nuts. This conference
resulted in a project which was started under the joint spon-
sorship of these three organizations.
Since the U. S. Field Laboratory for Tung Investigations,
located on the University of Florida campus, was interested in
the storage problems of tung nuts, it was asked to cooperate
and make studies of the storage properties of tung nuts which
would be dried under experimental conditions.
This bulletin therefore includes the results of storage studies
made by the U. S. Field Laboratory for Tung Investigations as
well as drying data and dryer design as determined and devel-
oped by the Florida Engineering and Industrial Experiment
The tung industry in the United States has developed rap-
idly since the introduction of the species from China in 1905,
although not without many trials and hazards.
It is estimated that there are now about 175,000 acres under
care. The present distribution of the tree population among
the states in the tung belt, based on the 1940 Census, is approxi-
mately as follows: Mississippi 75 per cent, Louisiana 14 per
cent, Florida 10 per cent, with Alabama, Georgia, and Texas
having the remainder of the commercial acreage.
This approximately 30-year-old orchard industry produced
a crop of fruit* totaling 66,700 tons in 1947** valued at about
From the above brief review of the size and value of the
tung crop, it is apparent that any economy that can be intro-
* The term fruit as used in this bulletin refers to the entire or unhulled
fruit just as it drops from the tree. The term nut refers to the hulled
fruit. The term kernel refers to the seed from which the hull and
shell have been removed.
** Taken from Louisiana Crop Reporting Service Bulletin released January
13, 1948, Department of Agricultural Economies, Baton Rouge La.

duced relative to its production and storage will have a consid-
erable monetary value.
The development of the Reed' portable tung fruit huller
seemed to give promise of a considerable saving by reducing
by about 50 per cent the volume of material to be handled in
the field. This, however, was dependent upon whether the hulled
nuts obtained could be stored without deterioration until they
could be milled. The study reported herein concerns this prob-
Harvested tung fruit undergoes changes during storage
which may affect the recovery of oil, either by expulsion or sol-
vent extraction. It is a common experience among the Ameri-
can millers that tung fruit stored during the summer months
deteriorates to a considerable extent. This spoilage is shown
by changes in color of kernel and by the failure of the meal to
form a satisfactory cake during the expelling process. As a
consequence of the last mentioned change, such fruit held longer
than June or July following harvest is usually unsalable.
A second type of change, found principally in fruit or nuts
stored when the moisture content is too high, is the formation
of free fatty acids. This may result from the growth of molds,
since nuts with intact shells or in whole fruits usually store
satisfactorily in bins in the fall and winter even when the
moisture content of the kernel is about 10 per cent, while the
kernels of nuts with broken shells develop extremely high free
acidity (acid number) if not dried to about 5 per cent moisture
within a few days after the shells are broken.'
Since the kernels themselves contain an enzyme' which can
hydrolyze tung oil to free fatty acids, an increase in acid number
can also occur without mold action. This is the condition that
occurs in intact nuts and fruit of about 30 per cent moisture
content during warm weather as part of the germination process
of the seed in the spring.
At the mill the fruit is usually put through a Bauer hulling
machine just before the oil is expelled. This huller breaks 75
per cent or more of the nut shells, and such hulled nuts have not
been kept for extended periods because of the danger from spoil-
age (acidity formation) during storage. At least two-thirds of
the storage space required for whole fruit could be saved by the
storage of the nuts instead of the fruit if a safe procedure could

SSee bibliography.

be found. Drying of the nuts to a safe moisture content appears
as one of the most likely possibilities.
With the development of the Reed portable huller, a new
factor has entered the harvest picture. This machine hulls the
fruit in the field, leaving the hulls under the trees as a source
of organic fertilizer, and reduces the haulage costs approxi-
mately 50 per cent. Of great importance is the fact that about
90 per cent of the nuts have unbroken shells. Such nuts have
been successfully air dried'; but an economically feasible drying
system would permit the storage of such material with a greater
margin of safety and greater saving of space. Drying equip-
ment could also be used for nuts processed in a Bauer huller if
storage of partly shelled nuts of low moisture content was found
to be satisfactory.

A field survey of the tung industry in Florida, Georgia, Ala-
bama, Mississippi, and Louisiana was made to discuss the dry-
ing problem with the tung mill operators and to inspect existing
drying methods.

Natural Drying
The practice of permitting the fruit to dry partially in the
field, followed by further drying in naturally ventilated storage
sheds is in widespread use, particularly by the smaller growers.
The dried tung fruit is then hauled to the mill for hulling and
processing. There are several disadvantages to this method.
The cost of hauling tung fruit is approximately twice that of
hauling only the nuts. The hulls must be disposed of by the
miller, whereas if they are hulled at the grove the hulls are
useful as mulch and fertilizer. The moisture content of the fruit
varies widely within a given storage bin, and also fruit delivered
to the mill by one grower may vary considerably in moisture
content from that delivered by another. The latter considera-
tion reduces the efficiency of mill operation. During wet sea-
sons, this natural drying practice has necessitated the milling
of nuts that contain too much moisture for efficient processing.
These disadvantages of the natural drying process have led
several of the mill operators to consider methods of artificially
drying the tung nuts.

Artificial Drying
Several static dryers of the type commonly employed in dry-
ing cottonseed have been built These dryers were of several
sizes-some holding as little as 15 tons and others as much as
100 tons of tung nuts, while the depth of nuts in the dryers
varied from four to twenty feet. While these dryers have proved
of considerable value, especially during wet seasons, they have
several operating characteristics that make them unsuitable for
the satisfactory drying of tung nuts. Tung nuts, being larger
in size and harder than cottonseed, pack with considerably larger
voids. Therefore, air being drawn through a mass of tung nuts
in dryers of this type has a tendency to channel and leave areas
in which little or no drying occurs. Progressive drying also
occurs in which the moisture content varies from a minimum at
the top of the nut bed to a maximum at the bottom or air outlet.
The degree of variation is dependent upon the depth of the nut
bed, being least in those dryers with a relatively shallow depth.
Even with depths of four feet, the moisture differences due to
progressive drying usually are too great for efficient milling.
As an experiment, a pilot infrared dryer was constructed at
one of the mills. This dryer consisted of a battery of drying
lamps placed over a screw conveyor. Coarsely ground tung nuts
passing through the conveyor remained under the lamps for a
period of ten minutes. It is reported that little or no moisture
was removed. Although the temperature of the metal parts of
the conveyor rose considerably, only a small portion of the avail-
able energy was absorbed by the ground nuts.
The LaRow Investment Corporation has installed a vertical
Hess No. 2 grain dryer which was converted for drying tung
nuts. The cooling section was removed and replaced with an
equivalent drying section. It has a holding capacity of 3000 lbs
of tung nuts and may be operated as either a static or a con-
tinuous dryer.
It is reported that this dryer will dry 15 tons of tung nuts
from 20 per cent moisture content to 6 to 8 per cent in 24 hours;
10 tons of nuts from 25 per cent moisture content to 6 to 8 per
cent moisture content in 24 hours; and 9 to 10 tons of nuts from
28 per cent moisture content to 6 to 8 per cent in 24 hours.
The field survey of the tung milling industry indicated that
there was a definite need for an improved low cost method of
drying tung nuts. An efficient dryer should be capable of sup-

plying tung nuts dried to an average moisture content of 6.5
per cent to 7 per cent on the dry basis; and, the moisture varia-
tion in each batch should be low, i.e., not over 3 percentage units.

The principal pieces of equipment utilized in the experimental
work carried out at the Station consisted of the following items:
1. Dryer. The experimental dryer was constructed of 18-
gauge galvanized sheet metal. The dryer body was 15
inches long, 12 inches wide, and 12 feet high. The floor
was made of 1/4 inch mesh galvanized hardware cloth.
Two-inch pipe couplings, serving as sampling holes, were
welded into the side of the dryer body in the positions
shown on Figure 1.
Air was supplied by a Clarage No. 8, Type CI, fan with
a Type C wheel. The fan was driven at 2900 rpm, deliver-
ing 2270 cfm of standard air at 7 inches of water static
pressure drop. The fan inlet was connected to the suction
side of the dryer. Air flow was controlled by a damper
on the end of the fan discharge duct. Air volume was
determined by calculation from the pressure drop across
a calibrated orifice placed in the fan discharge duct. Heat
was supplied from a steam coil placed at the air entrance
of the dryer. Air temperature entering the dryer was con-
trolled by a thermostatically operated modulating steam
flow valve located in the steam supply to the coil.
2. Sampling Device.-The sampling thief consisted of a two-
inch brass tube with saw teeth filed into one end. By
pushing and rotating the thief through the pipe coupling
into the dryer body, samples of 50 to 100 nuts were ob-
3. Moisture Oven.-Moisture determinations were made in a
DeKhotinsky type vacuum oven in the presence of phos-
phorus pentoxide.
4. Miscellaneous Equipment.-Various thermometers, in-
clined manometers, and balances were also used in con-
ducting the tests.
While an experimental bin type dryer was being constructed,
tests were made to determine the feasibility of drying tung nuts







Figure 1.-Experimental Tung Nut Dryer.

with infrared drying lamps.
The nuts for these tests were from the 1944-45 crop. As
they were already dry, it was necessary to soak them in water
before drying tests could be made. It was realized that the data
obtained from rewetted nuts might not agree with these ob-


trained from nuts containing their natural moisture, but the trend
to be expected from freshly harvested nuts should be indicated.
A bank of six 250-watt infrared drying lamps was used to
dry small samples of whole tung nuts, whole tung kernels, and
a ground mixture of commercially hulled tung nuts. The bank
of lamps was suspended 31 inches above a sheet of insulating
board. The nuts and kernels were placed under the lamps in one
nut thicknesses while the layer of ground mixture was one-
fourth of an inch thick. Data showing typical results obtained
from tests conducted under these conditions are presented in





8l s ^--
a. \--1--- *

Figure 2 -Infrared drying of tung nuts.

Figure 2. The variations in moisture content in the three
samples at the beginning of the test was caused by resoaking
dry nuts for use in these tests.
Reference to Figure 2 shows that, in each sample, the rate
of moisture removal was high during the first ten minutes of
the test, while the rate dropped off appreciably during the last
five minutes. The curve of moisture content versus time for
whole nuts is of particular interest. The moisture removed dur-
ing the first ten minutes of this test was probably surface moist-
ure and possibly some diffused moisture near the surface. The
moisture removed during the last five minutes was primarily
dependent upon the rate of moisture diffusion from within
the nut to the surface. This part of the curve indicates that it
is not economically feasible to dry tung nuts by infrared energy
which involves high cost electricity.

In order to eliminate guesswork in fan selection for dryer
design, it was necessary to determine static pressure drops
through different thicknesses of tung nuts at various air veloc-
ities. Since fan horsepower requirements are based on static
pressure drop and air volume, the economical fan selection will
be a function of face velocity and depth of nut bed.
Static pressure drop tests were conducted on tung nuts in
depths from one foot to ten feet at one foot intervals. Face
velocities of from 50 feet per minute to 250 feet per minute in
intervals of 50 feet per minute were used. Figure 3 shows the
relation of static pressure drop to the depth of the nut bed at
the various face velocities. The data were corrected to standard
air conditions, i.e., 68' F and 29.92 inches Hg barometer pressure.
Correction was also made for the effect of humidity on air
The nuts for the static pressure drop determinations were
already dry and had been commercially hulled in a Bauer huller.
They contained the usual number of broken nuts, shells, and
other material present in the discharge of this machine. The
amount of broken material present will materially affect the size
of voids and thus the static pressure drop. Pressure drops ob-
served during drying tests on nuts hulled in a laboratory huller
(approximately 99 per cent whole nuts) were less than those
determined in these tests.

The temperature of the air entering the nut bed also affects
the pressure drop. A close approximation of static pressure drop
at any temperature may be determined by substitution in the
following equation:

Ps d,
where Pe = Static pressure drop at desired temperature
Ps = Static pressure drop at standard air conditions
dT = Density of air at desired temperature
ds = Deanity of standard air (70 F and 29.92" barometer pressure)

From Figure 3, the static pressure drop at 100 feet per minute
face velocity and two feet depth of nuts is 2.52 inches of water
at standard air conditions. At 150' F, neglecting humidity, the
density dt would equal 0.065 pounds per cubic foot. At standard
air conditions, neglecting humidity, d- equals 0.075 pounds per
cubic foot. By substituting in Equation 1, the static pressure
drop at 150 F would be:
P. dr
Pc =
2.52 x 0.065
Po =
P= = 2.18 in. of water


Experimental drying of tung nuts in the laboratory dryer
(Figure 1) was conducted on nut beds two feet in depth, at a
face velocity of 100 feet per minute and at air temperatures of
150" F, 175' F, and 200" F. The two-foot depth of nut bed and
face velocity of 100 feet per minute were chosen by virtue of
the reasonable static pressure drop that would be encountered.
According to Figure 3, the maximum static pressure drop to be
expected at these values would be 2.5 inches of water. Fan
horsepower requirements are a reasonable value at this pressure
drop. Moreover, the two-foot depth of nut bed was chosen in
order to limit the differential in the final moisture content of
the nuts between the top and bottom layers of the bed.



O 100 200 300

Figure 3.-Static pressure drop through various thicknesses of tung nuts.

Drying tests were made on tung nuts from several orchards.
Tests numbered 3 through 7 were on nuts hulled in a laboratory
huller (99 per cent whole nuts) while tests numbered 8 and 9
were made on nuts hulled in a Bauer huller (approximately 37
per cent whole nuts). During the tests, samples for moisture
determinations were taken at the beginning of the test and at

hourly intervals (in some tests at one-half hour intervals).
Samples were taken through the sampling openings at the top,
middle, and bottom of the nut bed. Data were also taken of
entering air temperature, air temperature at the middle of the
nut bed, exit air temperature, and static pressure drop. This
information is included in Tables I through VII.
Each sample (consisting of 50 to 100 nuts) was ground and
thoroughly mixed so that a representative moisture determina-

s80 I --I I [ F r I r I I ]r [ -I I




Figure 4.Conversion curve, dry to wet basis.

tion sample could be obtained. Samples of approximately 10
grams were weighed out in covered aluminum dishes. These
were transferred to the vacuum oven and dried at 158' F and
28 inches of mercury vacuum for eight hours. The oven was
allowed to cool to room temperature under vacuum before remov-
ing the samples. This was done to prevent oxidation of the oil
in the samples at the elevated temperature.
Moisture determinations were calculated on the dry basis,
i.e., pounds of moisture per 100 pounds of moisture-free or bone-
dry nuts. Figure 4 is a curve for converting from the dry basis
to the wet basis, i.e., pounds of moisture per 100 pounds of origi-
nal sample.
The tung nuts for all hot air drying experiments included
in this section were from the 1945-46 crop asreceived from the

Drying Test at 200' F Entering Air Temperature (Test No. 3)
Tung nuts for this test were hulled in a laboratory huller
and contained approximately 99 per cent whole nuts. The nuts
as charged into the dryer contained 19.45 per cent moisture on
the dry basis.

Test Number 3
Nut Depth 2 ft-Air Velocity 100 fpm-Air Temperature 200*
Laboratory Hulled Nuts
Time Moisture Content Bin Air Temperature Pressure
b/100 lb Dry Nuts Deg. F Drop
Bottom Middle Top Enter- Middle
Hours Layer Layer Layer ing Layer Exit In. of Water
0 19.45 19.45 19.45 199 156 127 -
1 12.03 8.01 6.03 199 180 140 1.00
2 6.73 2.57 331 202 198 179 1.00
3 3.61 1.71 1.73 206 203 190 0.95
4 2.32 0.78 1.22 205 202 192 0,95
5 1.32 0.62 0.81 208 208 201 1,05

The results of this test are shown on Figure 5 and Table I.
Figure 5 is a curve of moisture content plotted against time
showing the drying of tung nuts at the top, middle, and bottom
layers under the conditions of this test. Reference to Figure 5
shows that, while drying at this temperature is accomplished


Figure 5.-Drying at 200 F, test No; 3.

at a high rate, there is a wide difference in moisture content
between the top and bottom layers. This difference exists until
the moisture content is below 5 per cent, which is too low for
efficient expelling. The top layer reaches a moisture content of
6 per cent in approximately one hour at which time the bottom
layer has approximately 12 per cent moisture content. This is
one characteristic of static drying that is undesirable. In addi-
tion to wide moisture differences as indicated by the drying
test, subsequent storage tests showed that nuts dried at 200" F

entering air temperature cannot be safely stored for an appre-
ciable length of time.
To reduce the moisture difference between the top and bot-
tom layers subsequent tests were conducted at entering air tem-
peratures below 200' F.

Drying Tests at 150' F Entering Air Temperature
(Tests No. 4, 6, and 9)
In test No. 4, the initial moisture content was 33.49 per cent
on the dry basis. After five hours of drying, the moisture con-
tent dropped to 5.75 per cent in the top layer and 8.04 per cent
in the bottom layer with an average moisture content of 6.63
per cent. The results of this test are shown in Figure 6 and
Table H.
Test Number 4
Nut Depth 2 ft-Air Velocity 100 fpm-Air Temperature 150 F
Laboratory Hulled Nuts
Time Moisture Content Bin Air Temperature Pressure
lb/100 Ib Dry Nuts Deg. F Drop
Bottom Maddle Top Enter- Middle
Hours Layer Layer Layer ing Layer Exit In. of Water
0 33.49 33.49 33.49 165 96 70 1.30
1 25.98 23-72 16.47 158 142 119 0.90
2 16.10 17.15 14.19 157 151 132 0.90
3 16.58 12.45 8.83 156 153 139 0.90
4 12.71 8.27 721 157 154 143 0.90
5 8.04 6.12 5.73 158 156 146 0.90
6 6.84 5.19 5.23 156 155 148 .98

For purposes of better comparison, it was desirable to run a
drying test at entering air temperature of 150 F on nuts of
approximately the same moisture content as those used in the
200' F entering air temperature test. This was done in Test
No. 6 in which nuts were used containing an initial moisture
content of 19.35 per cent on the dry basis.
Figure 7 contains curves of moisture content versus time
for drying tung nuts under conditions of the test. Observed and
calculated data are included in Table III. At the end of a four-
hour drying period, the moisture content varied from 5.85 per
cent in the top layer to 8.27 per cent in the bottom layer. The
average moisture content was 6.59 per cent. Comparison of
Figures 5 and 7 indicates that drying at 200 F entering air

a 4 4 5
Figure 6,-Drying at 150- F, test No. 4

temperature is much faster than at 150 F; however, the varia-
tion in moisture content between the top and bottom layers at
expellable moisture content is much less at the 150" F drying
The nuts for Tests No. 4 and 6 were hulled in the laboratory
huller and consisted of approximately 99 per cent whole nuts.
It was deemed desirable to compare these data with data ob-
tained from drying commercially hulled nuts from a Bauer
huller under the same drying conditions. Test No. 9 was con-

Figure 7. Drying at 150 F, test No. 6.

ducted under the same conditions as Tests No. 4 and 6 except
that nuts containing approximately 37 per cent whole nuts
were used.
The results of this test are included in Figure 8 and Table
IV. Examination of Figure 8 shows that, with an initial mois-
ture content of 19.6 per cent on the dry basis, approximately
three hours would be required to dry nuts with considerable
quantities of broken shell to an average moisture content of 7
per cent. This time is one hour less than that required to dry
whole nuts under essentially the same conditions.

Test Number 6
Nut Depth 2 ft-Air eloity 10 pir reoit 1 fp- Temperature 150' F
Laboratory Hulled Nuts
Time Moisture Content Bn Air Temperature Pressure
]b/100 Ib Dry Nuts Deg F Drop
Bottom Middle Top Enter Middle
Hours Layer Layer Layer ing Layer Exit In. of Water
0 19.35 19.35 19.35 160
1 16.79 14.14 12.29 145 138 127 1.20
2 13.54 11.05 6.63' 151 149 137 1.10
3 11.68 7.58 7.31 158 156 147 1.00
4 8.27 5.67 585 155 155 148 0.95
5 6.05 4.66 5.65 156 156 152 0-90
Probably m error.


Test Number 9
Xut Depth 2 ft-Air Velocity 100 fpm-Air Temperature 150 F
Commercially Httled Nuts


Moisture Content
Ib/100 ib Dry Nuts
Bottom Middle Top
Layer Layer Layer
19.60 19 60 19.60
15.79 15.39 11.89
13.32 10.43 10 26
10.46 9.68 8.46
9.62 7.71 641
6.92 5.86 6.55
6.58 5.35 4.18
5.67 4.79 4 60

Bi Air Temperature'
Deg. F
Enter- Middle
ing Layer Exit
170 73 65
165 126 85
153 142 115
146 143 124
155' 135' 119
158 148 139
145 132 135
148 140 125

In. of Water

Temperature control valve not functioning properly.
Steam pressure off for approximately 10 minutes. Did not stop fan,
therefore temperature dropped.
*Probably in error.

Drying Tests at 175' F Entering Air Temperature
(Tests No. 5, 7, and 8)
The results of Test No. 5 are shown in Figure 9 and Table
V. The nuts for this test and Test No. 7 (Table No. VI) were
hulled in the laboratory huller. As is shown in Figure 9, a dry-
ing time of three hours was required to dry the batch from
18.73 per cent moisture content to an average of 6.8 per cent
moisture. The variation in moisture content at this stage was
3.4 percentage units.


0 2 4



Test Number 5
WNt Depth 2 ft--Ar eloelty 100 fpm---Ar Tempena 175- F
Laboratory Huled Nuts
Time Morslture Content Bin Air Temperatre Pressure
Ib/lW0 b Dry Nuts Deg. F Drop
Bottom Middle Top Enter- Middle
Hours Layer Layer Layer ing Layer Exit In. of Water
0 18.73 18.73 18.73 175 115 78
1 15.77 13.01 11.64 162 146 23 120
2 11.74 8.42 7.74 177 169 142 0.90
3 8.41 7.06 5 00 170 168 152 0.90
34 6.26 5-0 4.75 180 178 159 0.90
4 5.43 3.93 3.26 180 174 159 0.90
4. 4.22 321 3.43 187 183 167 0.90
5 4.10 2 76 3 05 186 184 170 0.90
TimenisueCnet BnArTmeaue Pesr
_____ b10 bD-Nt Dg.FDo





S3 4 5

Figure 9.Drying at 17 F. test No 5.


Test NuWmenr 7
N-t Depth 2 ft--Air Velocity 100 fpm--Alr Temperature 175- F
Laboratory Hulled Nuts

Moisture Content
lb/100 Ib Dry Nuts

Bm Air Temperature
Deg. F

Bottom Middle Top Enter- Middle
Hours Layer Layer Layer ing Layer Exit In. of Water
0 20.78 20.78 20.78 -
1 18.63 1424 9.99 174 169 150 1.15
2 14.97 9.44 6.99 17T 172 163 0.90
3 11.46 717 7 71 174 172 167 0.85
3'1 9.24 4.87 4.99 174 173 168 0.90

Figure 10 includes drying data for Test No. 8. The observed
and calculated data are included in Table VII. The nuts for this
test were commercially hulled in the Bauer huller. They con-
sisted of approximately 37 per cent whole nuts. From an initial
moisture content of 19.16 per cent to an average moisture con-
tent of 6.36 per cent required 2.5 hours drying time. The mois-
ture variation between the top and bottom layers at this point
was 2.9 percentage units.


0 \ \
0 \-
z \
if\ \
La0 \ \ N- -----

^ ~ \ n:^ '. \
8 I-__ ^

Figure 10.-Drying at 175Y F test No. .8

[ 2 1

Test Number 8
Nut Depth 2 ft-Air Velocity 100 [pn-Air Temperahare 175- F
Commercially Hulled Nuts

Moisture Content Bin Air Temperature Pressure
Time lb/100 Ib Dry Nuts Deg. F Drop
Bottom Middle Top Enter- Middle
Hours Layer Layer Layer ing Layer Exit In. of Water
0 19.16 19.16 19.16 176 78 65 2-10
19 04 16.28 13.66 175 153 109 170
1 14.07 1174 9.11 172 166 136 1.50
11 10.99 944 6.58 174 168 147 1.30
21' 8.16 5.67 5.26 174 172 155 1.30
3 7.07 4.85 3.81 170 172 160 1.30
3% 6.21 4.02 3.48 171 174 163 1.30
4 4.47 2.54 2.67 172 175 166 130

Table VIII summarizes the results of drying Tests No. 3
through No. 9, indicating probable drying times for optimum
final moisture content. It is important to note that the drying
time is influenced by the initial moisture content and the method
of hulling.

Summary of Drying Test at Nut Depth of 2 ft-Air Fare Velocity 100 fpm

Initial Moisture
Test Air Moisture Drying Variation Nut
Number Temp lb/100 lb Time lb/100 lb Condition'
*F Dry Nuts Hours Dry Nuts
3 200 19.5 1.5 4.6- 9.2 Laboratory Hulled
4 150 33.5 50 5.7- 8.0 Laboratory Hulled
6 150 19.4 4.0 5.8 8.3 Laboratory Hulled
9 150 196 3.0 6.0 8.0' Commercially Hulled
5 175 19.5 3.0 5.0 8.0" Laboratory Hulled
8 175 19.2 2.5 5.3 8 2 Commercially Hulled
Laboratory hulled nuts were approximately 99% whole. Commercially
hulled nuts had approximately 37% intact nuts and about 63% whole
or broken kernels from which all or part of the shell had been re-
SMolsture variation between top and bottom layers at drying time in-


After drying in the experimental bin dryer, the nuts were
stored in sacks on a low shelf on the first floor of a two-story

unheated building. This same storage condition had been found
to be unusually satisfactory^ for nuts from the 1944 crop stored
until January, 1946.


Changes During Storage of Bin-Dried Tung Nuts in Dry Weight,
Oil Content of Kernel, and 0 Characteristics
Drying No of hO Oil Refractive Aid
Test Temperature Days Ib/100 1b lb/100 lb Index Number
No. Deg. F Stored Dry Kernels Dy No 25* C omg.
BKernel KOH/gm
3 200 0 2 7 71.3 1.521 0.3
18 3.1 710 1.519 0.1
57 1.5 69.2 1.518 0.9
72 2.4 668 1.517 0.5
117 2.4 56.1 516 0.1
219 35 38.8 1516 2A
4 150 0 4.7 62.6 1.519 0.9
38 4.8 62.5 1518 0.2
63 3.9 63.3 1.517 0.6
108 4.5 618 1.518 0.1
210 5.2 54.8 1.516 0.5
5 175 0 3.1 65.5 1.518 0.3
36 3.8 63.7 1.518 0.4
61 3.5 64.0 1518 1.1
106 4.2 64.8 1518 0.1
208 5.8 56.6 1.516 0.5
6 150 0 4.7 62.5 1.518 01
17 4.9 64.2 1519 0.5
42 5.1 63.3 1.518 0.7
87 4.8 63.7 1519 0.4
189 5.6 59.6 1517 0.4
175 0 4.5 63.7 1.518 0.3
17 4.5 62.5 1518 0.2
42 3.8 63.0 1.518 0.9
87 4.4 62.8 1.518 0.2
189 5.4 60.0 L518 0.5
9 150 0 4.4 67.7 1.518 0.1
73 4.3 68.1 1518 0.2
175 4.9 63.5 1516 0.3
8 175 0 3.2 67.7 1.518 0.2
74 4.2 66 3 L517 0.3
176 4.6 63.7 1.517 0.2

Duplicate lots of 100 nuts each were taken at the stated inter-
vals (Table IX). The shells were removed by hand and the ker-
nels flaked in a mechanical device. Oil was determined by the
Blendor method of Hamilton and Gilbert'.


Acid number was determined by titration of either a 50-ml
aliquot of the hexane solution of oil obtained in the Blendor
process or by titration of the oil after removal of the solvent.
Twenty-five ml of U. S. P. alcohol were added to either the oil
solution or free oil (1 gm) and titrated with 0.03 N alcoholic
KOH to the first pink tint of the phenolphthalein end point. Re-
fractive indices were determined with an Abbe' refractometer,
the readings being corrected to 25' C by the temperature factor
of = 0.0004 units per degree difference from 25" C. The mois-
ture content of the kernels was determined by drying 10-gram
aliquots of the flaked kernel for five hours at 158- F and 4 mm
pressure in a vacuum oven containing P,20,. The oven was then
allowed to cool to room temperature for two hours before releas-
ing the vacuum and removing the samples. This procedure was
found necessary for the material dried at 200' F since, as shown
by gain in weight, the usual practice of removal of the samples
from the oven while at 158' F promoted oxidation before the
samples could be weighed. The nuts dried at lower than 200' F
did not show so great a sensitivity to oxidation, but a uniform
procedure was used for all samples.
The oil obtained from the 200' F lot was also different from
that extracted from the other lots in that it showed a marked
tendency to polymerize on the steam bath when the last traces
of the hexane were being removed from the oil extracts. The
other oil extracts could be safely steamed for 15 minutes after
practically all the solvent had been removed.
The 50-ml oil extracts from the 200' F samples were concen-
trated to about 2 ml of solvent on the steam bath and the last
portions of the solvent were removed by heating for a half hour
in a vacuum oven at 158' F and 10-mm pressure. Oil free from
visible polymerization was thus obtained.

Results of Storage Studies
The data in Table IX show the results of the storage experi-
ments. The first column gives the drying test number, the sec-
ond column the air temperature used in drying, and the third
column the number of days of storage after drying. The re-
maining columns present the results of the analysis of the ker-
nels for moisture content, oil content, the refractive index, and
the acid number of the solvent extracted oil.
It should first be noted that very little change in the mois-

ture content of the kernel occurred during the storage period.
Fluctuations in the moisture content of the nut are more marked
(data not shown), the changes being due to variations in mois-
ture content of the shell with varying climatic conditions.
The great variation in the amount of solvent extractable oil
occurred in the lot dried at 200" F. After storage for two
months, a definite decrease of about 2 percentage units of oil
was found. After about four months, the oil content had de-
creased to 56.1 per cent. Seven months' storage produced a
change to 38.8 per cent extractable oil which represents only
about half of the original oil content of the kernel.
Only slight decreases were found in the refractive index of
the extracted oils after storage following the various. drying
treatments. The lowest values, however, are above the A.S:T.M.
minimum for tung oil.
A definite, although not extreme, increase in free acidity
(acid number 2.4) was found after seven months' storage.
Drying at the lower temperatures (175F and 150" F) re-
suited in nuts of better keeping quality than did the 200 F
treatment. No appreciable changes were noted for at least three
months. After six months, a drop of about 2 to 3 percentage
units of oil was noted, and after seven months about 8 percent-
age units. The nuts from the Bauer huller showed about the
same response to drying, about 4 percentage units less of oil
being extracted after nearly six months' storage. These nuts
in contrast to the others, had only about 37 per cent of nuts
with intact shell. No significant changes in either acid number
or refractive index were found in nuts stored after drying at
150 F and 175" F.

For the commercial drying of a low-value commodity such
as tung nuts, it is essential that the drying costs be held as low
as possible. Drying cost must include the cost of moving the
nuts to and from the dryer, the cost of heating the air, the cost
of moving the air, and depreciation on the drying equipment.
Not only must drying cost be considered in design, but also,
the nuts must be dried to a condition in which they may be
safely stored and efficiently milled.
Figures 11 and 12 show outside and internal views of the
dryer under consideration. The experimental data included in

[3 ]

previous sections of this bulletin indicate that a two-foot layer
"of nuts will be satisfactory from the standpoint of static pres-
sure drop and moisture variation.







Figure 11.-Tung nut dryer.

In order to conserve floor space, it is proposed that the two-
foot layer be placed in a vertical position as shown in Figure 12.
A vertical column two feet wide by six feet long by ten feet high
will hold 4200 pounds of dry tung nuts weighing 35 pounds per
cubic foot. To double capacity of the dryer without increasing
the height or length dimension or the static pressure against
which the fan must operate, an identical section is placed adja-




Figure 12.-Internal construction of tung nut dryer.

cent to the first separated by an air space to act as the hot air
plenum chamber. This increases the holding capacity of the
dryer to 8400 pounds. The coil for heating the air is mounted
on the back side of the dryer at the entrance to the central air
plenum chamber. Attached to the outside of each nut column
is an air outlet box which is connected to the fan by means of
a short duct as shown. Air enters the dryer thru the heating
coil into the hot-air plenum, flows horizontally thru the vertical
nut column into the air outlet boxes and is 'then discharged thru
the double width double inlet fan to the surrounding atmos-


The dryer is loaded with nuts thru the charging doors located
on the top deck. The nuts may be raised to this level by a 10-
inch screw conveyor. They are discharged thru a hopper sus-
pended under each of the vertical nut columns, and may be re-
moved from the area by a screw conveyor of the same size as
that used in loading.
The frame of the dryer is of welded angle iron construction
while the walls are of 14-gauge hot rolled sheet steel.
Control of air temperature may be obtained either manually
by a globe valve or automatically by a thermostatically con-
trolled steam valve located in the steam supply line to the
Reference to the drying data indicates that at 175" F the
time required for drying will probably be from two to three and
one-half hours depending on the moisture content of the nuts
upon entering the dryer. With allowance of one-half hour for
loading and unloading the dryer (this is ample when using a
10-inch screw conveyor), the cycle period would be from two
and one half to four hours. Under these conditions, the drying
capacity would vary from 25 to 40 tons per 24 hours.
To maintain an air velocity of 100 feet per minute at 175' F
would require 12,000 cubic feet per minute of air at the same
temperature. This is equivalent to approximately 11,000 cubic
feet per minute at standard air conditions. Reference to the
static pressure drop data indicates that two inches of water
pressure drop is a safe value at 100 feet per minute face ve-
locity and a two-foot depth of nut bed. The connecting duct
work, heating coils, etc., should add approximately 1A inch of
water -pressure, giving a total static pressure drop of 2% inches
of water. The motor horsepower required for the fan would
be either 7.% HP or 10 HP, depending on the fan selected.
Complete working drawings of the dryer as pictured in Fig-
ures 11 and 12 are available from the Florida Engineering and
Industrial Experiment Station. These plans include complete
specifications of material and equipment required for construc-
tion of the dryer.

1. The results of preliminary tests indicate that the drying
of whole tung nuts by utilizing infrared energy is not economi-
cally feasible.


2. Static pressure drop tests at nut depths greater than
three to four feet indicate that break-through or channeling of
the air through the nut bed may occur. This will result in areas
of uneven drying.
The static pressure drop will vary depending on the condi-
tion of the nuts loaded into the bin. Other conditions remaining
constant, the pressure drop will be less for a loading of 100 per
cent whole nuts than for a loading which includes nuts with
broken shells.
The static pressure drop will decrease as the nut charge be-
comes heated and the discharge air temperature rises. This re-
sults in a decreasing horsepower requirement for the drying
3. Drying tests conducted on two-foot layers of tung nuts
at air velocities of 100 feet per minute indicate that the most
satisfactory drying temperature is from 150" F to 175' F. The
time required for drying will vary according to the entering air
temperature and the initial moisture content of the nuts. Ref-
erence to the drying curves and data indicate in general the time
that niay be required.
Drying at entering air temperatures of 200' F is rapid, but
the variation in the moisture content of the top and bottom
layers is too wide for efficient expelling. Reference to the stor-
age data indicates poor results on storage of nuts dried at this
4. The proposed dryer Should dry tung nuts to a moisture
content that will allow efficient milling and in a period of drying
time that will make the process economical. Since safe storage
can be accomplished, the tung fruit can be harvested early. The
fruit can be hulled at the grove and only the nuts need to be
hauled to the mill.
5. A temperature of 200' F or more is to be avoided in the
drying of tung nuts for storage. Although no definite changes
in amount of extractable oil were noted at the end of 18 days
of storage and only slight decrease in oil extracted after 57 days,
there was a noticeably greater tendency for the oil to oxidize
and polymerize both in the meal and after extraction. It is be-
lieved that these changes may possibly affect the milling and
storage properties of the oil.
Drying temperatures of 150 F and 175' F produced nuts
of good keeping quality as determined by the tests made. Stor-
[ 34

age for as much as four months produced no measurable changes
while only moderate deterioration was noted after seven months'
These tests indicate that nuts with considerable broken shell,
such as are produced in the Bauer huller, can be safely stored
for over two months if the moisture content of the kernel is re-
duced to about 5 per cent by drying at 150" F to 175- F imme-
diately after hulling.
While data from previous studiesW indicate the possibility of
curing the whole nut by proper air drying, the uncertainties of
climatic conditions require more extensive trials before the
method can be recommended. From the data of the drying
studies in this bulletin, it appeals quite likely that drying at
150' F to 175' F will provide safe economical conditioning of
the nuts for storage, both for whole nuts from the Reed huller
and for partly shelled nuts from the Bauer huller. Studies on the
expelling of nuts that were dried in a large laboratory dryerW
indicate that drying at temperatures ranging from 150 F to
175 F does not significantly decrease the percentage of oil ex-
pelled, after as much as three months' storage.

1. REED. I F and JEZEK. R. E. "USDA Portable Tung Nut Decorticator."
Proceedings of the Anerican Tungy Oil Association, pp. 69-72. 1945.
2. GIBERT, S. G., LOUSTALuT. A. J., and PoTTER, G. F. "Storing Tung Nuts
Safely." Tung World, p. 8. February. 1947.
3. JOHNSTON, F. A, JR. and SELL, H. M. "Changes in Chemical Compo-
sition of Tung Kernels During Germination." Plant Physiology. Vol. 19,
pp. 694-695. 1944.
4. HAMILTON, and GILBET, S. G. "A Rapid Method of Determining Oil
Content of Tung Kernels." Anal. Chem., Vol. 19, pp. 453-456. July, 1917.
5. HOLMES, P. F., PACK, F, and GiLBEBT, S G. "Effect of Drying and Stor-
ing Tung Seed on Quality of the Oil and Mlling Characteristics of the
Seed," Journal of tle American Oil Chenmists' Society, pp. 311-314.

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