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CIRCULAR No. 443 _ a
UNITED STATES DEPARTMENT OF AGRICULTURE Le sf S|
WASHINGTON, D.C.

ARTIFICIAL DRYING OF FORAGE CROPS* -

By E. D. Gorpon and W. M. Horst, associate agricultural engineers, Division of
Mechanical Equipment, Bureau of Agricultural Engineering

CONTENTS
Page ; Page
INeedifor forageidriens "2-22 28 ae ee 1] Use of driers—Continued.
LV DES OM GIONS 22 — aoa ae eee eee Lee 2 UENaCe and We Sa aa ee 13
ARESTSIOL GRICTSe 2 aoe as ee ee oa SD 4) Sa LOWer LEGUIneIMeN (Ss === eee 15
Wserohadnicrs sss! — eran ae see 12} Operation of driers and cost of drying_-__ _---- 16
Capacityeate ne: Sas ee ee Ad eae CN ea 12 | Feeding value of artficially dried forage_-___-_- 20

NEED FOR FORAGE DRIERS

The production and curing of forage crops is an important part of the
program of farm operations in most parts of the United States. Not
only is forage a basic ingredient of livestock rations but it also has
an important place in crop rotation and in the conservation of soil
fertility. Since it is desirable to bring quality production in line
with profitable operation, attention is being given to the curing of
forage artificially. The reason for this comparatively new under-
taking lies in the results of feeding experiments which show that for-
age of high grade (U. S. grade) is usually superior in feeding value
to low-grade forage.

Feeding experiments have demonstrated (p. 21) that with artificial
drying forage of superior quality can be obtained from a crop that
otherwise, under unfavorable weather conditions, would be of inferior
quality. "Methods and equipment employed in harvesting, curing,
and subsequent processing operations govern to a large degree the
value of the product for feed. This is especially true in the more
humid areas. Overdrying, leaf shattering, and discoloration by rain
and dew, reduce the returns to the grower regardless of whether the
hay is used on the farm or is sold. Occasionally unfavorable condi-
tions result in practically a total loss of the crop.

The use of green, leafy alfalfa hay and of alfalfa meal as a source
of vitimin A has also stimulated interest in artificial drying. When
the crop is cut at the proper stage and dried artificially without
injury, hay or hay products equivalent to U. S. No. 1 Extra Green,
Extra Leafy alfalfa may be obtained. The carotene content, source
of vitamin A activity, usually is higher in hay artificially dried than
in sun-cured hay of the same grade. Artificial drying also tends to
preserve the protein and mineral elements of hay by eliminating the

1 The investigation on which this report is based was conducted under cooperation between the Bureaus

of Agricultural Engineering, Animal Industry, Dairy Industry, Plant Industry, and Agricultural Eco-
nomics.

151358 °—37—_1

De CIRCULAR 443, U. S. DEPARTMENT OF AGRICULTURE

possibilities of leaf shattering in handling and of leaching due to
weathering in the field.
TYPES OF DRIERS

The artificial drying of forage crops has been practiced to a limited
extent in some localities in the United States for many years. Avail-
able information does not indicate the exact date of the first hay drier
in this country. However, about 1909 an experimental drier was
constructed and used in Missouri for alfalfa. Also, a machine was
constructed for drying native grasses in Louisiana as early as 1910.
Since that date many attempts have been made by commercial, State,

Air from fan | mixed Air return Air from fan 2 mixed
with hot gases from furnace | to fan 2 __withhot gases from furnace 2

FIGURE 1.—Apron-conveyor type of forage drier.

and Federal agencies to develop satisfactory forage driers, but few
were developed beyond the experimental stage.

The design of many of the early machines indicated a radical
departure from established practices in the utilization of heat for
evaporating moisture from damp or wet materials. In other cases
slight changes in design and alterations were made of equipment
typical of that used for drying materials other than hay. The most
common types were those generally known as apron-conveyor and
revolving-drum driers. An apron-conveyor drier of the type com-

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FIGURE 2.—Revolving-drum type of forage drier, single-drum design.

monly used for hay is diagrammatically illustrated in figure 1, and
drum driers in figures 2 and 3.

The principles involved in these machines are not new, but the
direct exposure of material to be dried to the furnace gases is a practice
that has been closely associated with the development of hay driers
of various types in the United States. Previously steam was com-
monly used, the material to be dried being brought into direct contact
with or exposed to air heated by steam radiators. Higher efficiency
in the utilization of heat and elimination of the expense and trouble
commonly associated with steam boilers are factors frequently cited
in favor of direct application of furnace gases.

In the apron-conveyor type (fig. 1) the green forage is loaded on an
endless screen-wire apron and conveyed through the drying chamber

ARTIFICIAL DRYING OF FORAGE CROPS 3

where hot air or furnace gases are circulated through the layer of forage
on the apron by means of one or more fans. Driers of this type may
have a single endless conveyor, or several conveyors one above the
other. As the drying air becomes saturated with moisture it is drawn
or allowed to escape from the machine into the atmosphere. The forage
may be fed into the drier whole, crushed, or chopped. Drying the for-
age whole is more satisfactory in single- -apron machines, especially if
the plants are small and light as is usually the case with alfalfa, some
clovers, and grasses. The crushing operation is intended to be suffi-
cient only for cracking open the heavier stemmy plants including weeds.
The crushing-roll pressure should not be sufficient for complete r macera-
tion. In connection with experimental work the crushing was done by
passing undried soybean plants between a pair of rollers, one of which
was steel and the other rubber coated. The drying was noticeably
more uniform through the “mattress” of hay as compared with the un-

{—™~)

FIGURE 3.—Revolving-drum type of forage drier, triple-drum design.

crushed hay plants. The chopped material offers more resistance to the
movement of air than do the whole plants, crushed or uncrushed, and
many of the finely chopped particles fall through the screen apron.

Drum driers of the single-drum type (fig. 2) used for drying granular
substances such as salt have the feed end slightly elevated. As the
drum revolves the material is picked up by baffles or flights fastened to
the inside of the shell and then allowed to fall. Each time some of the
material is picked up it falls somewhat closer to the discharge end due
to the sloping position of the drum. In drying hay the drum is placed
in a horizontal position and a current of heated air or furnace gases re-
lied upon both for drying and for moving the forage through the ma-
chine. With drum driers it is necessary to chop the forage before it is
fed into the machine. In some driers of this type the dry material is
drawn into a chamber at the discharge end, from which it is conveyed
mechanically to a storage structure. In most cases, however, the dry
hay passes through the exhaust fan and is blown to a dust collector
from which it may be sacked or conveyed to a haymow.

In the single-drum drier (fig. 2) the chopped hay passes directly
from the wet end (feed end) to the discharge end (dry end). In the
triple-drum drier (fig. 3) the material moves through the center shell,
back through the second, and out through the third, thus traveling ap-
proximately three times ‘the length of the drier before it passes to the
exhaust fan.

The apron-conveyor drier is a relatively low-temperature drier in
which the material remains for a considerable period of time. The
temperature of the drying air or furnace gases entering the machine

4 CIRCULAR 443, U. S. DEPARTMENT OF AGRICULTURE

is usually held at from 250° to 350° F., and the period of exposure may
vary from 15 to 45 minutes, depending i in part upon the initial mols-
ture content of the forage. The temperature of the hay remains much
lower than that of the surrounding gases due to the cooling effect of
evaporation. The temperature of the forage also tends to coincide
with the wet-bulb temperature of the drying air, which, in a hay
drier, is much below the dry-bulb temperature.

Apron- -conveyor driers are usually much larger machines than drum
driers, due in part to the long period of exposure. Single apron-
conveyor driers for hay are frequently 150 to 200 feet in length with
the equivalent of 10 by 10 feet in section.

Drying the plants without chopping or chopping them in long
pieces also tends to increase the time during which the material must
remain in the machine. The leafy portions and fine stems dry
quickly, whereas considerable time is required for drying the long,
coarse stems. The overdrying of some parts of the plant and heat
losses from the long tunnel may result in a low thermal efficiency
for some machines of the apron-conveyor type.

The drum drier when used for hay may be classed as a high tem-
perature machine, necessitating a short period of exposure to prevent
charring or burning of the hay. The temperature of the furnace gases
entering the machine is usually held at from 1,000° to 1,500° F., by
means of adjustments on the secondary air inlet to the furnace or its
quantity of fuel supplied to the burner. The material remains in a
drier of the drum type for approximately 1 to 3 minutes, or even less,
depending somewhat upon the initial moisture content of the forage.
However, as is the case with the apron-conveyor type, the tem-
perature of the hay is much below that of the drying gases.

The chopping of the hay into short pieces enables it to dry quickly
and thereby makes possible the use of high temperatures in drum
driers. As the air is used for moving the material through the drier,
the light particles move more rapidly than the stemmy material,
which is helpful in preventing overdrying.

The use of high temperatures and a short period of exposure in
drum driers makes possible a rather small, compact unit in comparison
with the apron-conveyor type. Single-drum driers are usually 40 to
60 feet in length and from 7 to 9 feet in diameter. Double- or triple-
drum driers may be somewhat shorter than single drum units, as the
use of multiple drums increases the length of the drying zone with
reference to over-all length.

In drum driers there seems to be a definite relation between the
temperature of the exhaust gases and the moisture content of the
hay as it is discharged from the machine. An exhaust-gas tempera-
ture of about 200° to 250° F. is usually maintained by controlling
the rate of feed of undried hay. If the moisture content of the forage
entering the drier is high (65 to 75 percent) the exhaust temperature
should be kept at the high point of the range. With moisture contents
around 50 percent the exhaust temperature can be held at the lower
end of the range. The high exhaust temperature represents a con-
siderable loss of heat which tends to reduce the thermal efficiency
of drum driers.

TESTS OF DRIERS

Investigational work by the United States Department of Agricul-
ture was begun in 19380 in a study of the mechanics of artificial drying

ARTIFICIAL DRYING OF FORAGE CROPS 5

of forage crops, the elements of cost, and the feeding value of artifi-
cially dried forage. A small apron-conveyor drier of the type com-
monly used in drying cotton linters was set up on the Iberia Live-
stock Experiment Station at Jeanerette, La., for experimental use in
drying crops for feeding trials (fig. 4). This machine was approxi-
mately 46 feet long, 11 feet wide, and 9 feet high. The drying chamber
was approximately 8 by 36 feet, and the machine would usually
evaporate from 500 to 1,000 pounds of water per hour under the

Furnace manifold

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at fans 2 and5
CROSS SECTIONS

FIGURE 4.—Apron-conveyor drier used in forage-drying experiments at Iberia Livestock Experiment
Station. Drying air enters fan 1 from furnace manifold and is discharged above apron, is drawn through
apron by fan 2 and released above it in seccnd compartment, and then is drawn again through apron by
fan 3 and released outside the drier. Circulation through fans 4, 5, and 6 is similar.

at fans 3and6

conditions in which it was operated. This drier was used for several
seasons, but its capacity was insufficient for drying the forage needed
for feeding trials. It was unsatisfactory also for drymeg coarse-
stemmed crops such as soybeans.

In all the experimental driers discussed herein, electric power was
used for operating the machinery and fuel oil was used for heat, because
of the ease of measuring the quantities used and of controlling
operations.

After the conveyor-type drier had been used for a few years, a
revolving-drum drier was installed. ‘This machine consisted of a
single shell 6 feet in diameter and 24 feet in length, mounted hori-
zontally. Flights or flanges were attached to the inside of the shell,
for picking up and dropping the chopped forage as the drum revolved.

6 CIRCULAR 448, U. S. DEPARTMENT OF AGRICULTURE

A furnace was connected to one end of the drum and an exhaust fan
to the other. The dried forage passed from the drum through the
fan and was blown into a dust collector or cyclone. This machine was
inefficient because of the short drying zone or length of travel and
period of exposure of the material in the drier.

For increasing the efficiency of this machine a cylinder 2 feet in
diameter and 20 feet long was installed inside and concentrical with
the large drum (fig. 5). This cylinder was connected to the furnace
and to the feeder for the undried material at the furnace end of the
drier. At the opposite end the 2-foot cylinder was open and ended
3 feet from the end of the outer cylinder. An exhaust fan was con-
nected to the outer shell at the furnace end in such a manner as to
move the furnace gases together with the chopped hay first through
the inner cylinder and back through the outer cylinder. The dried
forage, after passing through the fan, was blown into a dust collector.

Conveyor for

FIGURE 5.—Revolving-drum drier used in forage-drying experiments at Iberia Livestock Experiment
tation.

This reverse current or two-pass system lengthened the evaporating
zone and greatly increased the efficiency of the machine.

From 1931 to 1936, inclusive, the apron-conveyor and double-drum
driers, were used in drying about 300 tons of hay, including alfalfa,
pasture grass, clovers, andsoybean hay. Approximately 250 tons were
used in feeding tests with dairy animals, and the remaining portion
with beef cattle. In operating these experimental driers records were
kept of the tonnage handled, the power, labor, and fuel requirements,
and the moisture content of the forage before and after drying. As
time permitted, trips were made to farms operating forage driers in
Louisiana, where similar data were obtained.

Observations of the various factors entering into the dehydration of
forage takes into account a large number of factors, many of which are
rather difficult to measure with any degree of precision. A drying
machine handling such a bulky product as forage must of itself be large
and any attempt to measure air velocities, temperatures, or make
hydrometric measurements of the drying gases are only an approxima-
tion. It is furthermore impossible to make check runs on the average
lot of forage because of the wide range of moisture contents which it
has before entering the drier. The presence of weeds and mixtures of
other kinds of forage enter into the actual test work and provide data
which are somewhat difficult to interpret.

The performance of the apron-conveyor and rotary driers located at
Iberia Livestock Experiment Station were observed especially as to
the power, labor, and fuel requirements for various kinds of crops, for

ARTIFICIAL DRYING OF FORAGE CROPS a

crops of different maturity, and for different methods of processing.
Other factors incidental to these observations were time length of the
drying run, drier-inlet and exit-gas temperatures, moisture content
of forage entering and leaving the drier, the weight of the material
entering the drier, and if possible the weight of the material leaving the
drier. When it was not practicable to obtain the weight of the
material both entering and leaving the drier the unknown weight was
computed from the known weight and the moisture content of the
forage (wet basis) before and after drying. Under normal operating
conditions it is assumed that the difference between the weight of the
forage as it enters and leaves the drier represents the water evaporated
and that the quantity of dry matter is constant.

From observations and tests of the two driers at the Iberia Station,
which have been summarized in tables 1 and 2, the following is noted:

1. In drying alfalfa (whole) on the apron-conveyor drier the average
percentage loss in weight is about the same for the seasons 1932 and
1934. Not much forage was dried during the 1933 season. The
power consumed per unit weight of material dried, and per unit weight
of water evaporated was reduced in 1934 from that shown during the
1932 season. The same holds true for the heat requirements of the
drier per unit weight of material dried and per unit weight of water
evaporated, although the hourly output and evaporation weight do not
show an increase. This more efficient utilization of power and heat
in the apron-conveyor drier was due to the scheme of blowing the air
counter current to the apron travel for the first half of the apron length.
The intake and exhaust system on the apron-conveyor drier was
arranged so that the drying gases after first being forced through a
section of the apron might be drawn into a fan and then forced through
another section of the apron either toward the feed end or discharge
end of the drier. If the air moved toward the feed end the counter-
current system was obtained. If toward the discharge end (fig. 4), the
air moved concurrently with the hay. The air velocity through the
mat of forage ranged from 80 to 150 feet per minute in all of these
observations.

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CIRCULAR 443, U. S. DEPARTMENT OF AGRICULTURE

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12 CIRCULAR #8, U. S. DEPARTMENT OF AGRICULTURE

When the apron-conyeyor drier was used to dry chopped soy-
bea hay, the drying proved to be very uneven and poor, the average
discharge moisture content being approximately 20 percent. At this
moisture content it is doubtful if artificially dried forage will keep in
good condition, free from mold and spoilage.

3. Cowpea hay in the apron-conyeyor drier presented much the
same problem as to nonuniformity of drying as did soybean hay.

4, The data for the 1935 season for the rotary drier were taken when
the material was further reduced by passing it through a hammer mill
after it had been cut in a silage cutter. The power requirements per
1,000 pounds of water evaporated were greater for drying soybean hay
in 1935 than in 1934. The heat required per unit of material dried was
about the same, but the hourly evaporation was increased from 770
to 866 pounds or an increase of 13 percent. In drying alialfa there also
appears to be an increase in thermal efficiency as well as capacity of
ae drier due to the shredding of the undried forage with a hammer

5. Data taken on the effect of maturity on power and fuel require-
ments showed that the 120-day growth Otootan soybean hay required
slightly less power and fuel for dehydration than 80-day growth hay
of the same variety. This difference was not due to initial moisture
content of the green material.

6. The thermal capacity for evaporating moisture is affected
materially when the forage is reduced to fine particles. The inner
parts of the forage plant come in more direct contact with the drying
gases when chopped and shredded than when left whole as they are in
the apron-conveyor drier.

Data were also taken on several commercial driers operating on
neighboring plantations. The performance of these driers are sum-
marized in table 3 under the heading of “Single-drum” and “Triple-
drum.’ So far as the data show the large commercial driers were some-
what more efficient in the utilization of heat than the small experi-

mental units.
USE OF DRIERS

CAPACITY

Alfalfa when cut for hay may contain more than 70 percent moisture.
When such material is hauled to the drier and dried immediately, as
much as 3,860 pounds of water must be evaporated to produce 2,000
pounds of hay containing 12 percent moisture (fig. 6). Ti the hay is
left in the swath for several hours its moisture content may be reduced
to about 55 percent. Under such conditions it will be necessary for
the machine to evaporate approximately 1,930 pounds of water to
produce a ton of hay at 12 percent moisture. In the latter case the
capacity of the drier in tons of hay per hour may be twice as great as
with 70-percent moisture content forage.

The capacity of a dryer will also depend somewhat upon the kind
of forage and the degree of processing before it is fed to the machine.
With drum dryers the fineness and uniformity of chopping greatly
influence the performance of the machine. Alfalfa, some varieties of
clover, and meadow grasses usually dry much easier than soybean hay
or other coarse-stem plants. The capacity of a hay drier is frequently
referred to in terms of tons of dried material delivered per hour. While
this method gives an indication as to what tonnage may be expected

ARTIFICIAL DRYING OF FORAGE CROPS 13

Loss in weight (percent)

Entering moisture content (percent)

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moisture contents.

under some conditions, it may be misleading unless reference is also
made to the initial moisture content and kind of forage dried.

Forage driers may be obtained with rated capacities ranging from
approximately 1,000 to 6,000 pounds of water per hour. However, a
machine capable of evaporating 3,000 pounds of water per hour
approaches the lower limit of capacity for practical purposes under
the conditions hay driers are usually operated in the United States.

FURNACE AND FUELS

A properly designed furnace of ample size is important for a forage
drier, as air much in excess of that required for complete combustion
is drawn through the furnace. The capacity of the furnace should be
large enough, and the size of the openings great enough so as not
unduly to increase resistance to the flow of the drying gases. With a
drum drier the air requirements at the discharge fan are taken roughly
as the equivalent of 1.2 cubic feet of dry air per minute per pound of
water evaporated per hour. Since the temperature of the drying gases
at the discharge end is in the neighborhood of 250° F. and that at the
drier inlet is about 1,500°, the inlet volume is about three times ereater
than the volume at dischar ge. Therefore, a dryer with an evaporative
capacity of about 3,000 pounds of w ater per hour should allow the
passage of about 10 800 cubic feet of air per minute at the inlet. The
entrance velocity should not greatly exceed 1,500 feet per minute,

14 CIRCULAR #48, U. S. DEPARTMENT OF AGRICULTURE

With a thermal efficiency of 60 percent the evaporation of 3,000 pounds
of water will require in the neighborhood of 5,500,000 B. t. u. This
quantity of heat would be supplied by 40 to 45 gallons of fuel oil or
5,500 cubic feet of natural gas fuel.

In practice final dilution of furnace gases takes place at the second-
ary alr inlet. This inlet is so arranged that the atmospheric air is
warmed by passing over heated portions of the exterior of the com-
bustion chamber (note drawing of Dutch-oven type of furnace, fig. 7).
The furnace gases may be still further diluted by providing an opening
just ahead of the drier inlet although this is not essential.

Brick

Secondary air
pesseges

wt

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a
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Inspection
[* door

FicguRe 7.—Duich-oven furnace.

Furnace design may be either of the cylindrical or rectangular cross
section (figs. 7 and 8). The rectangular cross-section furnace is
usually termed the Dutch-oven type and can be built more eco-
nomically than the cylindrical type of furnace because only the stand-
ard shaped firebrick are required in the combustion chamber. The
outer wall can be built of ordinary second-hand construction brick.
These two general types of furnaces are adaptable for burning either
oil or gas fuels.

The problem of utilizing solid fuels in drying forage is one requiring
special consideration, so that the drying gases are rendered smokeless
and do not contain incandescent particles of flying ash. Ouil- or gas-
burning equipment possesses advantages that place the coal- or coke-
burning furnace at a disadvantage for hay driers unless a mechanical
stoker Is available.

In order not to localize the combustion of the fuel in too small a
space it has been found that, with the fuel oil used at Jeanerette, from
1.75 to 2 pounds of oil may be fired per hour per cubic foot of com-
bustion space. This quantity of oil has a heat value of about 33,000
B. t. w.

In drying hay it required the combustion of a fuel capable of gener-
ating approximately 5,500,000 B. t.u. of heat energy to evaporate 3,000
pounds of water per hour. On the above basis 1t would require a com-
bustion chamber with a volume of from 165 to 175 cubic feet. For
practical purposes the dimensions might be as follows: Width 4 feet,
height to top of arch 5 feet, and length to bridge wall 10 feet.

The combustion of gaseous fuels is relatively simple, requiring only
a suitable mixing carburetor. For oil fuels it is essential that there
be smokeless combustion which can be accomplished only by thorough
atomization of fuel. Under ordinary conditions, satisfactory results
are more certain if oil having a specific gravity greater than 0.93 is not
used. This specific gravity corresponds to 20.6° (American Petroleum
Institute). Fuels heavier than this usually require preheating equip-
ment in order to insure proper combustion.

ARTIFICIAL DRYING OF FORAGE CROPS 15

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FIGURE 8.—Cytindrical furnace, with sliding rings for controlling air flow.

POWER REQUIREMENTS

In a forage drying plant, power is needed for the following purposes:

(1) Processing the undried forage. This includes chopping, chop-
ping and shredding, or crushing depending upon the type of drier and
the operator’s preference.

(2) Transporting the dried forage to a storage structure or proces-
sing plant either by a drag conveyor or a pneumatic system or a com-
bination of both.

(3) Conveying the drying gases to the drier from the furnace, and
removing them after they have performed their work in vaporizing
the moisture from the forage.

(4) Miscellaneous uses such as operating fuel pump and blower for
the burner, rotating the drum or actuating the apron conveyor of the
drier, operating the unloading hoist, baling or grinding the dried
material, etc.

The choice of the power unit depends somewhat on its availability
and the cost per unit of energy. From the standpoint of convenience,
electric power has the advantage. Where electric energy is available,
in most instances the rates are low enough so that it can be used
profitably.

Apron-conveyor driers are not adapted to handling finely chopped
forage, especially the single-apron machines, because the apron screen
allows a considerable portion of the material to drop through and

16 CIRCULAR 448, U. S. DEPARTMENT OF AGRICULTURE

unless it is placed in a comparatively thin layer the chopped hay
forms a mattress practically impervious to the passage of the drying
gases. However, crushing of the forage by running it through a
crushing device patterned after a clothes wringer and cracking the
stems, especially the nodes, is found to be of appreciable assistance in
drying the forage. i

The ordinary silage cutter can be adapted for chopping the forage
by slowing down the feed table so that the forage is cut into lengths less
than three-eighths of an inch long. A combination silage cutter and
hammer mill has been found suitable for processing the undried mate-
rial. No screens are used in the hammer mill and it is set to receive
the chopped forage directly from the silage cutter. The impact of the
hammers on the chopped green forage has been found sufficient to
crack open the stemmy sections and further aid the evaporation of
water in the drier.

Examination of table 3 shows that the power requirements for the
experimental apron-conveyor drier ranged from 22 to 28 kilowatt-
hours per 1,000 pounds of water evaporated. The power requirements
are distributed approximately as follows:

Percent
Moving apron and auxiliary conveyors______________._----- 11
Moving dryiie -ensesi. 9 28 5.0 ee a ee, ee 83
Ori“ burner OperahiOn.. fet 5 PF oF. ee § ee ee ee 6

For an experimental rotary drier the power requirements ranged
from 11 to 19 kilowatt-hours per 1,000 pounds, distributed roughly as
follows:

Percent
Chopping forage. 254 - ptf as a Es 25 to 35
Moying drying eases. fate 26 ee eee 2 eee 45 to 60
Onl-purner Operation. “2. Shel 2 ee ee ee ee eee 4to 8
Rotating drum and conveying forage___________________ 10 to 15

With these figures in mind it will be found that a drum drier capable
of evaporating 3,000 pounds of water per hour will need motive power
equivalent to 35 or 40 horsepower to run it. This would be divided
as follows:

Horsepower
@hopper 2 eos 2. a epee shed 15
Pancand ceirinm 30 awe. Ge Ss ett he Oe ee ee 20
[BUY Ue 1) ee eee ce mao oe BO rege ure OL a colle EE RY Soe rs Ss Se 146

A danger in motor installation is to overmotorize. Induction-type
electric motors running underloaded heat up badly as well as deliver
power at low efficiencies, thus increasing the power consumption.
Where electric power is not available, power distribution to the vari-
ous places about the drier may be accomplished by means of a long
countershaft. The motive power in this case may be in the form of a
tractor or a stationary gas, oil, or Diesel engine.

OPERATION CF DRIERS AND COST OF DRYING

By care in the planning of a forage-drier installation, economies
can be effected in all of the important items that go to make up the
cost of operation. The cycle of operations comprises unloading the
trucks or wagons, feeding the wet forage into a chopper or directly
into the drier, and disposing of the dried material at the pomt where
it is discharged from the drier system. Ordinarily the material is

ARTIFICIAL DRYING OF FORAGE CROPS LY

blown or conveyed into a bin or haymow. The problem of bagging the
chopped forage is aggravated by the fact that comparatively small
quantities of it can be packed in a bag. Chopped forage can be baled
by using especially rugged balers. Baling of artificially dried forage
is, however, not recommended for either chopped or whole hay with
present available equipment. ‘The leafy and fine stem portions of the
whole hay shatter badly if baled as it emerges from the drier. Chopped
hay from a drier, due to its short length, is more difficult to bale than
chopped field-cured hay.

The unloading of trucks and wagons can be accomplished in several
ways by means of a power hoist or horse-drawn unloading fork. The
ereen forage can be placed convenient for those who feed the chopper
or drier. Oftentimes trucks or wagons are provided with dump bodies.
By means of the hay-carrier fork and track system, bunches of hay
can be picked up after they are dumped and placed conveniently
near the cutter. However, there are a great variety of schemes by
which the material can be brought close to the point where it is re-
quired. In anchoring the chopper, for instance, it can be so placed
that the feeding conveyor is practically at the round level, thereby
saving a great amount of lifting of wet forage. The use of machines
in process of development by commercial firms for harvesting, chop-
ping, and loading into a wagon or truck in the field will doubtless
reduce labor requirements at the drier.

The following points should be kept in mind regarding drier opera-
tion:

1. For a drum drier the forage should be reduced to a uniform size,
the size of the particles not being greater than about three-eighths
of an inch in any one dimension.

2. The inlet temperature should be kept as high as possible, pref-
erably around 1,400° to 1,500° F. Temperatures in excess of these
can be used although corrosion of the brick and steel work may occur
more readily at temperatures in excess of 1,500°.

3. The temperature of the exhaust gases should range between
200° and 250° F. for a drum drier, depending upon the initial moisture
content of the forage.

4. The furnace, drum, fan, and dust collector should be close-
coupled to eliminate piping resistance.

5. Conveying chopped forage pneumatically may be accomplished
at the expenditure of slightly greater amounts of power than by drag
conveyors. Pneumatic conveying of the dried product allows for
ereater flexibility than do drag methods. However, from the stand-
point of fire prevention, any smoldering sparks of forage will be more
readily detected in the open conveyor than in other systems of con-
veying. For horizontal runs of pneumatic systems the air velocity
should be in the neighborhood of 4,000 feet per minute.

6. The matter of fire prevention is important at the forage-drying
plant. Unforeseen stoppages and break-downs may result in fire
outbreak. Convenient garden-hose connections with short pieces of
hose will repay themselves many times over in extinguishing fires in
their incipiency. Forage driers should not be placed in barns or
buildings where quantities of inflammable farm products are stored.
An inexpensive fire-resistant shelter for the drying plant can_ be
made from second-hand steel pipe and corrugated sheet-metal roofing.

18 CIRCULAR 445, U. 8. DEPARTMENT OF AGRICULTURE

7. It is very important that the forage be thoroughly dried down
to its safekeeping moisture content, which for practical purposes
should approximate 12 percent. Too often the inexperienced operator
attempts to increase the output of the drier beyond its capacity or
without due regard to the heat input. The result is a partially dried
product that may mold or may heat sufficiently to cause spontaneous
combustion. Whole field-cured hay usually can be stored with a
moisture content of from 15 to 25 percent, depending upon locality,
without danger of heating. Experience indicates that artificially
dried hay, especially when chopped, should have a lower moisture
content. Such material, when conveyed directly to a mow from the
drier, has a higher temperature than that of the atmosphere and there
is likely to be some variation in the moisture content of the particles.

The cost of operating a drier (power, labor, and fuel) depends in
part upon the thermal efficiency of the drier; the initial moisture
content of the forage; the unit costs of power, labor, and fuel; and the
kind of forage to be dried. However, results of tests made by the
Department of Agriculture in Louisiana on several commercial and
experimental driers shown in table 3 will give an indication of what
may be expected in this connection. The labor was computed at
20 cents per man hour, fuel oil at 3.5 cents per gallon, and electric
current at 4.7 cents per kilowatt-hour.

Barr ? shows from 20 to 29 kilowatt-hours, 16 to 26 gallons of oil,
and from 0.97 to 4 man-hours per 1,000 pounds of water evaporated
in various types of driers. With the same unit costs for power, labor,
and fuel as shown in table 3 the cost per 1,000 pounds of water evapo-
rated ranged from $1.69 to $3.07.

Clyde ® gives as the cost of drying per ton of dry hay (2,400 pounds
water evaporated at an over-all thermal efficiency of 65 percent for
the drier) the following items exclusive of overhead charges:

Huet.:29) .callons' oil-atsy. Cents a ean = oe eae © MERE, Sree eee eee ee $2. 07
Labor, 3 men, 1.35 hours at 40 cents, 30 cents, and 30 cents____________ 1. 35
Power, 20.4:kilowatt-hours ate3 centsi22 25. 285 15 “Seer Paes . 61
Repairs:-estimatedist: rae ee sh eee a eh ee i EO CR ee rey.

4, 20

In using the same unit costs for power, labor, and fuel as previously
indicated the cost would approximate $1.23 per 1,000 pounds of water
evaporated.

At the Lewisburg, Tenn., station of the Bureau of Dairy Industry,
approximately 170 tons of hay were dried artificially with a commercial
rotary-drum drier during the 1935 season, as shown in table 4. The
total cost of drying the hay, including the harvesting in the field and
mowing in the barn, but not including interest or depreciation on the
equipment, was $11. 77 per ton of dry hay. Repairs (labor and parts)
accounted for $3.20 of the above cost, the major portion of which was
spent on the upkeep and repairs on field-harvesting machinery.
Much of this expense appears to be due to the fact that this equipment
was manufactured for handling dry hay and was not strong enough to
handle the heavier green material. ;

2 BaRR, H.T. ARTIFICIAL CURING OF FORAGE CROPS. La. Agr. Expt. Sta. Bull. 261, 14 pp., illus. 1935,
3 CLYDE, A. W. NEW DEVELOPMENTS IN HAY DRIERS. Agr. Engin. 14: 127-129, illus. 1933.

19

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20 CIRCULAR 4438, U. 8S. DEPARTMENT OF AGRICULTURE

In addition to the cost of operating a drier, the cost of harvesting
and hauling the material to the machine must be considered, and the
overhead charges. With suitable equipment, the cost of harvesting
and loading should approximate that for field-cured hay except for
the larger tonnage in hauling wet forage instead of dry hay. Over-
head charges per 1,000 pounds of water evaporated depend in large
measure upon the initial cost of the drier and the tonnage of hay
handled each year.

TaBLeE 4.—Hay crops dried at the Lewisburg, Tenn., station during the 1935 season

Moisture content
akaait Fuel oil
Hay Rate of uantity | per ton
Before After drying dried of hay
drying drying
Pounds
Percent Percent per hour Tons Gallons
TA Tialignseis © ee A een a ele Sed 62.9 11.6 1, 674 - 65 £32:
WGOSPO COZ Alen segs nee een eee eee 3iA 5.9 2, 352 21 183°
SOroMUM Soak Bake eet ae ee eee ee 67.5 4.6 1, 201 13 46.0
Soybean. 222 22 = (2 ooo ea: ee eee 60. 7 10. 4 1, 632 71 31.6

1 Korean, common, and L. sericea.

The initial cost of a drum drier installed approximates $2,000 per
1,000 pounds-per-hour evaporating capacity. On this basis and as-
suming 6 percent interest on the average investment (one-half the
initial cost), 10 percent annual depreciation, and 5 percent for taxes,
insurance, and repairs, the overhead cost would approximate $360
per 1,000 pounds-per-hour evaporating capacity, or $1,080 per year for
a drier capable of evaporating 3,000 pounds of water per hour.

The overhead cost of a drier is, for all practical purposes, a fixed
annual cost, but when computed on a per-ton basis decreases as the
total volume of hay dried per season increases. With a $6,000 invest-
ment in a drier and only 100 tons of hay dried annually, the overhead
cost would approximate $10.80 per ton. If the drier handled 1,000
tons per year the overhead would approximate $1.08 per ton. From
this it can be seen that the cost of drying may be excessive unless a
large quantity of hay is dried annually.

FEEDING VALUE OF ARTIFICIALLY DRIED HAY‘

The progress of the feeding tests in which the dehydrated forage
was fed to beef cattle and dairy animals at the Iberia Livestock
Experiment Station, has shown that, as compared with the sun-cured
product, it will produce slightly greater gains in weight; that the cost
of producing the dehydrated product is somewhat greater, thus mak-
ing the cost of animal gain a trifle higher; that the market grade of
the dehydrated product is generally higher; that results of chemical
anaylses of comparable grade of hay show but slight variations in
favor of the artificially dried product.®? However, the carotene con-
tent of the artificially dried hay was considerably higher than that of

4 This section was prepared in collaboration with R. R. Graves, Chief, Division of Dairy Cattle Breed-
ing, Feeding, and Management, Bureau of Dairy Industry.

5 If the average field-cured hay at the Jeanerette station were used in making the comparative chemical
analyses, the results would undoubtedly be considerably in favor of the artificially dried product for the
reason that much of the field-cured hay is badly damaged by unfavorable weather conditions during curing.

If this loss in quality were taken into consideration, the cost of the good field-cured hay would be greatly
increased.

ARTIFICIAL DRYING OF FORAGE CROPS pA hi

the sun-cured based on a limited number of tests from the Jeanerette

station as shown in table 5.

TABLE 5.—Grade and carotene content of samples of the same lot of forage sun-
cured and artificially dried

Sun-cured Artificially dried
Crop
United States grade Carotene United States grade Carotene
Parts per Parts per
f million million
Alfalfa____- U.S. No. 2, Heavy Grass Mixed_- 36 | U.S. No. 2, Heavy Grass Mixed_- 104
Soybean___| U.S. No. 1, Extra Green__________ 523] U.S. No: i xtra Green = == — 75
Dez = AWE SOS LE = oes 2) Ee pete ee SBS AT URS ERINO S222 © SERa Ee Ses ees 27
Doe aaa 1G Sree oo ie aes ea 43 | U.S. No. 1, Extra Green___-___---- 64
|

1 Slightly scorched while drying.

In sampling the forage at Jeanerette on which grade and carotene
determinations were made, a portion of an undried lot of forage was
spread on a screen bottom tray and set in the sun to dry. This ma-
terial was put under shelter at night and also when rains occurred.
The remaining portion of the forage was put through the drier and a
sample obtained as it came from the machine. This procedure, while
providing comparable samples, resulted in obtaining higher-quality
sun-cured hay than would have been possible under prevailing weather
conditions at Jeanerette, La.

The protein content of the dehydrated product from the Jeanerette
station ran about 1 percent higher than for the sun-cured forage,
although this did not hold true in every instance. It should be borne
in mind that no feeding value is added in the dehydration of forage.
Obviously the manner in which the hay is harvested and artificially
dehydrated makes for more complete conservation of the feeding value
of the forage in that the leaf loss is minimized. Since one advantage
of artificial drying is to prevent weathering and reduce leaf loss, espe-
cially with alfalfa, dehydrated forage is likely to be rich in protein and
calcium as these elements are formed principally in the leaves.

With grade Aberdeen Angus beef cattle there was a slight advantage
in favor of the artificially dried forage under prevailing test conditions
at Jeanerette as to gain per hundredweight of feed consumed. This
advantage amounted to about 2.5 to 6 percent.

In feeding trials with dairy cattle at Jeanerette six Jersey bull
calves were castrated and placed on a ration consisting entirely of
artificially dried roughage, at 6 months of age. They gained an aver-
age of only 148 pounds each from 6 to 12 months of age, which was
only 60 percent of normal. Between 12 and 18 months of age, how-
ever, they made normal gains but, of course, were below normal weight
at 18 months of age because of the small gains made between 6 and
12 months.

In an experiment now in progress five Jersey heifers were started on
artificially dried roughage with no grain at 12 months of age. They
have maintained slightly more than normal gains between 12 and 18
months of age. These and other experiments indicate that if Jersey
heifers are at normal weights at 1 year of age they can maintain normal
gains from that time on when fed machine-dried roughage of high
quality.

29 CIRCULAR 443, U. 8S. DEPARTMENT OF AGRICULTURE

In feeding dairy animals when the entire ration consists of dehy-
drated forage, the production of milk and butterfat is about 60 to
70 percent of the production made on a full-grain ration. In an experi-
ment conducted by the Bureau of Dairy Industry at the Lewisburg,
Tenn., station, 16 registered Jersey cows made 17 lactation-period
records on rations restricted to machine-dried hay (largely legume)
and pasture. Their average production, calculated to a mature-
equivalent basis, for an average lactation period of 361 days was
6,333 pounds of milk and 329 pounds of butterfat. The average loss
in body weight was 33 pounds to the end of the lactation, but this
does not take into consideration gains that normally would be made
during the dry period prior to the next calving. The same cows made
comparable records under register-of-merit testing conditions when
they were fed machine-dried legume hay, pasture, and liberal amounts
of a grain mixture. Under these conditions the same cows produced
an average of 9,656 pounds of milk and 527 pounds of butterfat with
an average gain of 70 pounds in body weight to the end of their lacta-
tion period. On the roughage-alone ration the cows produced 66 per-
cent as much milk and 62 percent as much butterfat as they produced
under the register-of-merit conditions. During the time the cows
received hay without pasture they consumed an average of 28.6 pounds
of hay per cow a day, or at the rate of 3.44 pounds of hay per 100
pounds of body weight.

However, in feeding forage to animals, the question of palatability
is an important factor and artificially dried hay is very palatable to
animals. Some forage plants such as the clovers and alfalfa appear to
be more readily consumed by the animals than the coarser, heavy-
stemmed legume forages such as soybeans and cowpeas. Artificially
dried hay will be uniformly good if the hay is cut at the proper stage
of maturity, while much of the nutritive value of field-cured hay
may be lost in any given year due to unfavorable weather conditions
for field curing. Machine drying is an insurance against losses in
quality of hay that results from unfavorable weather conditions for
field curing.

Two experiments, conducted at the Western Washington Experi-
ment Station by the Bureau of Dairy Industry and the Washington
Experiment Station, have a bearing on the nutritive value of artifi-
cially dried pasture grasses. These experiments were conducted with
a small experimental rotary-drum drier. In view of the fact that the
drying material is not expected to attain a higher temperature than
that of the gases at the outlet from the drier, the outlet temperatures
in these experiments were taken as the temperature of drying. How-
ever, as the material dried in passing from the feed end to the dis-
charge end of the machine it was subjected to temperatures in excess
of that indicated as the exhaust temperature.

Artifically dried roughage that has a minimum of exposure to sun-
light after cutting is thought likely to be deficient in vitamin D. The
first experiment ® was conducted to determine the comparative cal-
cifying powers of similar samples of green, artificially dried, and sun-
cured pasture herbage. It was found that pasture herbage when fed
in a green, artificially dried, or sun-cured form, constituting 3 percent
of the dry matter in the ration, caused a significantly greater degree
of calcification in rats than did the basal diet. Increasing the amount

6 HopGson, R. E., and KNoTT, J. C. THE CALCIFYING PROPERTIES OF GREEN, ARTIFICIALLY DRIED AND
‘SUN-CURED PASTURE HERBAGE. Jour. Agr. Research 48: 439-446. 1934.

ARTIFICIAL DRYING OF FORAGE CROPS 23

of the grass fed did not result in a greater degree of calcium deposition.
Either the green or the artificially dried grass was as efficient in pro-
ducing calcification as was similar grass that was cured by exposure
to 15 hours of sunlight. The results of this experiment are not in
accord with the results of an experiment conducted by Bechdel’ at
the Pennsylvania station who found that there was an appreciable
difference in the antirachitic potency of artificially dried alfalfa hay
and sun-cured alfalfa hay when fed to 6-month-old dairy calves. A
severe rachitic condition developed during a 6-month feeding period
when 1 pound of artificially dried hay was added to the basal diet,
and a miid rachitic condition developed when 1 pound of sun-cured
hay was added. As much as 2.5 pounds of artificially dried hay did
not prevent the development of a mild rachitic condition, while the
same amount of sun-cured hay prevented the appearance of rickets.
Perhaps the calcifying power of the artificially dried pasture herbage
was due to the fact that the grasses were immature and growing
rapidly at the time of cutting.

In the second experiment ° digestion trials were conducted with
sheep on mixed pasture grasses that were artificially dried at exhaust
gas temperatures of 250°, 300°, 350°, and 400° F. to determine the
effects of these temperatures on the digestibility and availability of
the nutrients in the pasture herbage. The results were that the
percentage of apparent digestibility of the feed constituents of the
rations of sun-cured grass and of the grass dried artificially at exhaust-
gas temperatures of 250°, 300°, and 350° showed no significant differ-
ences, indicating that artificial : drying under these conditions had no
depressing effect on the availability of the nutrients. The percentage
of apparent digestibility of the nutrients in the sun-cured and in the
artificially dried grasses at 250°, 300°, and 350° averaged for dry
matter, 76; for crude protein, 76; for crude fiber, 83; for ether extract,
73; for ‘nitrogen-free extract, 83; "and for ash, 44,

The results of the feeding trials of the material dried at 400° F.
showed that this temperature for the exhaust gas from the drier had
a depressing effect on the apparent digestibility of the crude protein,
dry matter, and nitrogen-free extract. There was also evidence of
the burning of some portions of the more leafy material when dried
at the outlet temperature of 400° F. The apparent digestibility of
most constituents was somewhat lower for the green grass than for
the material dried at 250°, 300°, 350°. As the exhaust temperature
of drying was increased by 50° intervals there was a definite lowering
of the percentage of natural color in the herbage. That dried at
400° had only 76.3 percent as much color as that dried at 250°.

7 BECHDEL, S. L., pnd otners. RICKETS INCALVES. Pa. Agr. Expt. Sta. Bull. 291, 41 pp., illus. 1933.
8 HODGSON, R. E., K ort, J. C., GRAVES, R. R., and MuRER, H. K. EFFFCT OF TEMPERATURE OF

ARTIFICIAL DRYING ON SC AND AVAILABILITY OF NUTRIENTS IN PASTURE HERBAGE. Jour. Agr.
Research 50: 147-164; illus. 1935.

ORGANIZATION OF THE UNITED STATES DEPARTMENT OF AGRICULTURE
WHEN THIS PUBLICATION WAS LAST PRINTED

Sectetary ofp Agreculiute= 2) = tee Ey Henry A. WALLACE.

Onder Secretar ities: 0 os pied Le re Beads M. L. Witson.

AL SSESL CIE IS CERCLORE S253 lak he hee ee Harry L. Brown.

Director of Extension Work___.------------ C. W. WARBURTON.

Director Of F tnaqee onc IA el Tepe nee ee W. A. Jump.

Director iop-laifermatione: 0-1 ie AS td M. 8. EISENHOWER.

Dizcetorof personel 25 22 ae ts W. W. STocKBERGER.

Director ap tecsearelt = 2. San see es cera Be James T. JARDINE.

SOLU AGEN ee eG Behe Pes a Ss aa a wi Mastin G. WHITE.

Agricultural Adjustment Administration____- H. R. Toiuey, ADMINISTRATOR.
Bureau of Agricultural Economics __--_------ A. G. Buack, Chief.

Bureau of Agricultural Engineering__-_------ S. H. McCrory, Chief.

Bureau of Animal Industry__-------------- JoHN R. Mouser, Chief.
Bureau of Biological Survey__------------- Tra N. GAaBRIELSON, Chief.
Bureau of Chemistry and Sotls____--------- Henry G. Knieut, Chief.
Commodity Exchange Administration_______- J. W. T. Duvet, Chief.
Bureau\of Dairy, Indusiry ss 42 G8 weigh O. E. REep, Chief.

Bureau of Entomology and Plant Quarantine. Len A. StronG, Chief.

Office of Experiment Stations____________---- JAMES T. JARDINE, Chief.

Food and Drug Administration_-_----------- WaLtTeR G. CAMPBELL, Chief.
Boresh Serurce ae ssid ch = Wa A a, Be ie, pe ot FERDINAND A. Srtcox, Chief.
Bureau of Home Economics____------------ Louise STANLEY, Chief.

dis) f) ee ae SNL RT Py ees SP rene? plas Zee CLARIBEL R. Barnett, librarian.
Burecauof Plant Indusizg=: 26 Ses Arie ae FreDERIcK D. Ricuey, Chief.
Bureau of Public Boadss tt) i ipa r eA ers Tuomas H. MacDonatp, Chief.
Resettlement Administration. _~_____-------- W. W. ALEXANDER, Administrator.
Sail. Conservation Servree 2 sat in ae Se H. H. Bennett, Chief.

Weathé; Burcats. 85-42 A Sees Wiuus R. Greae, Chief.

This circular is a contirbution from

Bureau of Agricultural Engineering____--_-- S. H. McCrory, Chief.
Division of Mechanical Equipment_-___-- R. B. Gray, Chief.
24

U.S. GOVERNMENT PRINTING OFFICE: 1937

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