Section 2: Study on the flat-bed dryer in the Mekong River Delta of Viet Nam pptx

17





Section 2
Study on the flat-bed dryer in the Mekong River Delta of
Viet nam
18

Section 2. Study on the flat-bed dryer in the Mekong River Delta
of Viet nam
ABSTRACT
The study, including experiments and survey on the flat-bed dryer, focused on the cracking of
paddy grains, and on comparing the air reversal mode. Results showed that, in both the 8-ton
production-scale dryer and the 20-kg laboratory dryer, the effect of air reversal was very
apparent in reducing the final moisture differential; however, its effect on the drying time or
the drying rate was not statistically significant. Mechanical drying, whether with or without
air reversal, was superior to sun drying in terms of reducing rice crack. However, compared
to shade control drying, drying (with or without air reversal) did decrease the head rice
recovery and increase the crack; the causing factor was not apparent, most suspected reason
was the drying rate. The decrease in head rice recovery was inconsistent, slightly lower or
higher in each specific pair of experiments with and without air reversal; this was not
expected in line with data on the final moisture differential. Testing of a 4-ton dryer at Long-
An equipped with the solar collector as supplementary heat source resulted with good grain
quality and confirmed the good economic potential. Major findings from the survey on the
current status on the use of flat-bed dryers in 7 Provinces were: The trend for increased
drying capacity, the role of local manufacturers and local extension workers, government
support with interest reduction for dryer loans, the drying during the dry-season harvest, and
especially the unbalance between drying costs and drying benefits.

INTRODUCTION
Flat-bed dryers have been with the rice agriculture of the Mekong Delta of Viet Nam for a
long time. From the first flat-bed dryers in the 1980’s to about 6500 units in 2007 is quite a
good progress. But not all is optimistic. Acceptance varies among provinces, even among
districts or communes in the same province. Finding the interrelated factors affecting the
dryer acceptance is quite complex. Within the context of the CARD Project 026/VIE-05 with
focus on the cracking of paddy grains in the area, the study on the flat-bed dryer from 2006 to
2008 included the following objectives:

19

• Conduct experiments under laboratory controlled drying conditions and under actual
production conditions to evaluate the effect of air reversal on the rice crack and other
drying outputs.
• Conduct experiments on the 4-ton flat-bed dryer, using solar energy as supplementary
heat source.
• Conduct a Participatory Rapid Rural Appraisal (PRRA) survey to update on the use of
flat-bed dryer in the Mekong Delta.

REVIEW OF RELEVANT INFORMATION
The following information is based on data by various Provinces presented during different
seminars, on an integrated assessment study by the Ministry of Agriculture-Rural
Development in collaboration with DANIDA in 2004, and on the first author’s working
experience with flat-bed dryers in the past 25 years.

Development of the flat-bed dryer
The Mekong Delta in Southern Viet Nam, with 2.7 million hectares of rice land, is producing
about 50 % of Viet Nam total rice output. With 16 million people or about less than 20 % of
the total population, this region has accounted for more than 90 % of Vietnamese rice export

in the past decade. Average farm size is about 1 ha per household, although in some newly-
reclaimed districts, 3 - 10 ha per household is not uncommon.
Rice drying became an issue in Mekong Delta in early 1980’s when a second crop was
promoted, of which the harvest fell into the rainy season. Different dryer models were tried
by various agencies; only one model was accepted by the production sector, namely the flat-
bed dryer (FBD). The first FBD was installed in Soc-Trang Province in 1982 by the
University of Agriculture and Forestry (now renamed Nong-Lam University NLU). Farmers
in Soc-Trang copied/ modified/ improved this FBD using cheap local materials. In 1990,
there were about 300 FBD units in the Mekong Delta, half of which were in Soc-Trang.
Other Provinces began to adopt these dryers. In 1997, a survey conducted by a Danida-
assisted Project reported a total of 1500 FBD in all Mekong Delta, with 3 leading Provinces
(Kien Giang, Soc-Trang, Can-Tho) accounted for 850 units; all remaining 10 Provinces
shared the balance of 650 units.
The above Danida-assisted Project in Can-Tho and Soc-Trang doubled the FBD in each
Province from about 250 to 500 units in the two-year span of 1998-1999, through a credit
20

scheme and extension activities. The Project terminated in 2001, and replaced by a Program
managed by the Ministry of Agriculture, but still assisted by Danida, then with only extension
activities. The Program terminated in mid-2007. The number of FBD dryer rose rapidly,
about 3000 units in 2002 and 6200 units in 2006. The dryers in the Mekong Delta account
for more than 95 % of all dryers in Viet Nam.
The technical development of the FBD in the past 25 years followed an interesting pattern.
First, a design was released by a research institution, NLU in this case. Next, farmers/
mechanics copied/ modified/ improved the design. Next, NLU monitored those modifications
and came up with a major design change and improvement. The cycle repeats.
The landmarks for these major design releases by NLU have been:
1982: Conventional FBD with central air inlet to the plenum chamber, using flat-
grate rice husk furnace with precipitation chamber (Fig.1).
1994: Conventional FBD with side-duct plenum (Fig.2), rice husk furnace with

vortex and central-pipe precipitation chamber (Fig.3).
2001: Reversible FBD (Fig.5 & 6).
(expected):
2006: Automatic rice husk furnace (model NLU-IRRI-Hohenheim, Fig.4)
2007: Solar collector for FBD
Major modifications /improvements by farmer-mechanics have been:
1987: Rice husk furnace with inclined grate.
2004: Drying bin for reversible dryer, with distributed central inlet.
2006: Raking mechanism under the rice husk hopper for more uniform husk feeding.

Figure 1. Conventional FBD with central air inlet to
the plenum chamber.

Figure 2. Conventional FBD with side-duct
plenum.
21


Figure 3. Rice husk furnace with vortex and
central-pipe precipitation chamber.

Figure 4. The automatic rice husk furnace for
SRA-4 reversible flat-bed dryer.

Drying Air
UP
Grain
CONVENTIONAL SHG
FLAT-BED DRYER
Floor: 50 sq.m / 8 ton

0.3m

Drying Air
UP
Drying Air
DOWN
Grain Grain
REVERSIBLE SRA DRYER
0.6m
Floor: 25 sq.m / 8 ton

Figure 5. Principle of reversible-air dryer.

Figure 6. The SRA-10 reversible air dryer (10 tons per batch).

NLU have taken the leading role in releasing efficient dryer fans, both for conventional and
reversible dryers, with transfer of design and fabrication technology to 15 manufacturers in
the Mekong Delta, among them 7 have built fan test ducts according to JIS Standards.

Quality of paddy dried by the flat-bed dryer
The quality of dried paddy is judged by several criteria:
 The paddy is not contaminated with black ashes from the furnace.
 The paddy final moisture content is uniform at the desired level for storage.
 For seed grain, the germination is high.
 For commercial grain, the dried grain crack is minimized.
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The first criterion (no ash mixed with grain) has been met after some years, due to gaining of
experience in furnace building, and competition among furnace builders, to deal with

farmers’ first-visual reactions.

The second criterion is difficult to meet due to the inherent principle of flat-bed drying. A
final moisture differential of 1.5 % (between the top and the bottom layer) is considered
good, while in continuous-flow mixing-type dryer, 1.0 % is normal. For flat-bed dryers,
farmers rely on manual mixing. Technically, a good high airflow rate at moderate
temperature (below 44
o
C) helps reducing the differential. The air-reversal principle
introduced since 2002 also reduces the non-uniformity. All these technical features should be
re-evaluated / confirmed in this current CARD Project.

The preserved seed germination is well established by Seed Companies in using a safe drying
temperature below 42
o
C, and most importantly to dry the grain within 12 hours after harvest.
For commercial grain, the dried grain crack is a big issue. A report (Phan Hieu Hien, 1998)
based on surveys of a few rice mills in Can-Tho and Long-An showed a reduction of 5 to 7 %
of farmers’ profit due to more broken rice due to improper drying. This high loss was due to
the habit of field drying in the dry-season harvest, and estimated to be about 20 million US$
per harvest in the Mekong Delta. However, data and estimates were based on a few
interviews, and not on systematic testing. Thus, in this CARD Project, the need is to confirm
or reject based on solid test data.

MATERIALS AND METHODS
Testing
Testing of dryers followed standard procedures described in RNAM (1991) and ASABE
(2006). Measurement equipment included different thermometers, moisture meter and drying
oven, power meter etc.
For the 8-ton dryers, the drying temperature was at 2 levels: a) Constant at 43

o
C; and b) At
50
o
C for the first hour, and afterwards constant at 43
o
C. In reality, due to the furnace
configuration, the temperature rarely exceeded 50
o
C, and was about 48
o
C at most. In all
tests, the focus was to compare two drying modes: WITH air reversal, and WITHOUT air
23

reversal. Some experiments also compared with sun drying on the cement drying yard with a
7-cm paddy layer, as popularly practiced by local farmers.

The crack analysis and head rice analysis was first done at the Vinacontrol, an accredited
agency in charge of certifying rice quality for export, and later at the Rice Quality Laboratory
of the NLU Chemical Technology Department, following procedures adopted by
International Rice Research Institute and the University of Queensland. Each treatment was
analyzed by 3 samples, each consists of 50 grains taken at random; each paddy grain was
hand-husked and examined under the magnifying glass for fissure. The increase in crack or
decrease in head rice of each treatment based were on the control shade drying (or further
shade drying to 14 %MC).

The biggest problem for testing has been the input paddy. We encountered severe difficulties
in securing batches of the same quantity or initial moisture content. This was apparent with
the 8-ton batches. But even scale-down to 1-ton batch, the 3-factor experiments could not be

run, due to different initial MC. Finally, from the “lumpsum” conclusions with 8-ton dryers,
we had to concentrate on and be contented with 20-kg batches in paired experiments (block)
of Air reversal and No air reversal.

For experiments on the use of solar heat for paddy drying, a 4-ton popular flat-bed models
fabricated by a local mechanical shop was selected, and added with a solar collector designed
at the NLU Center for Agricultural Energy and Machinery.

Survey
The objectives of the surveys were: (i) to update the role of flat-bed dryers in reducing post-
harvest losses and in preserving rice quality; (ii) to identify operating factors of the flat-bed
dryer which contribute to the reduction of rice crack; and (iii) to identify problems with the
flat-bed dryer that the CARD Project could possibly help.

The survey used the Participatory Rapid Rural Appraisal (PRRA) method, through
interviewing different people class, from farmers to rice millers to governmental officials etc.
But it also relied heavily on both available data gathered in the past 10 years by various
24

agencies, and on personal experience of the people involved with the dryer at NLU over the
past 20 years.

Four Provinces were selected in 2006, namely Can-Tho City, Kien-Giang, Long-An, and
Tien-Giang. The first three Provinces have sites which had been selected by the CARD
Project for all related experiments, demonstrations, and extension activities. The fourth
Province is adjacent to Long-An, and also planned as site for rice milling survey, so facts and
data on the dryer would be relevant. In 2007, we visited more Provinces such as Hau-Giang,
An-Giang, Kien Giang, Soc-Trang…, with resulted with additional findings.
RESULTS AND DISCUSSSION
TESTING

Experimental results on the 8-ton dryer, the laboratory dryer, the solar-assisted dryer, as well
as the survey results are presented in the following sections.
The 8-ton dryer
Two 8-ton dryers were selected for experiments. One was a NLU-designed air-reversible
dryer installed at Tan-Phat-A Cooperative, Tan-Hiep District, Kien Giang Province in July
2006 (Figs. 7&8). The other was an air-reversible dryer made by a local manufacturer
installed at Tan-Thoi Cooperative in Can-Tho Province, with the design patterned on the
SRA-8 of NLU; the difference was the under-plenum duct inside the drying bin, “ong gio
chim” in Vietnamese (Fig.9), in order to distribute the airflow evenly.

Figure 7. The 8-ton dryer at Tan-Phat-A
Cooperative, Kien Giang

Figure 8. The 8-ton dryer with the air for
downward direction .
25


Figure 9: The 8-ton flat-bed dryer at Tan-Thoi Cooperative, Can-Tho Province

Experiments from Kien-Giang were under more control thus more results are reported here,
while results at Can-Tho are supplementary. Refer to Phan Hieu Hien (2006, 2007, 2008) for
testing details.
In Kien-Giang experiments were conducted in two wet seasons (July 2006, and July- August
2007), and two dry-seasons (March 2007, and March 2008). Major findings are as follow:

• The drying temperature is stable and can be kept within ± 3
o
C, usually from the nominal
value of 43

o
C.
• The effect of air reversal was very apparent in reducing the final moisture differential.
When operated correctly, this differential was less than 2.2 % with air reversal, but over
4.6% without air reversal. More MC differential means more rice cracking during
milling. This explains why dryers installed since 2003 have been more and more of the
reversible principle.
• However the effect of air reversal on the drying time or the drying rate was not clear
because of several other factors involved (Fig.10).








Dr ying r ate
0.0
0.5
1.0
1.5
2.0
2.5
3.0
20 22 24 26 28 30
Initial MC, %wb
Air Reversal
No air reversal

Fig.10: Effect of air reversal on the drying rate.
26


Data on the crack of rice upon milling in March 2007, and July 2007 with three pairs of
drying batches (With Air reversal, and Without air reversal) showed that:
• Mechanical drying, whether with or without air reversal, was superior to sun drying in
terms of less crack percentage or more head rice recovery. About 3- 4 % less cracking,
and about 4 % more head rice recovery were main data obtained from .March 2007
experiments.
• The grain cracking in Air-reversal batches were lower than No-air-reversal batches
(Fig.11). This is a basic result.
• However, the decrease in head rice recovery was inconsistent, slightly lower or higher in
each specific pair (Fig.12). This is confirmed by the statistical comparison on the head
rice recovery with t-test between batches of Air reversal and No air reversal, which did
not show significant difference at 5% level. This was not expected in line with the above
data on Final MC differential. The reason was probably due to the sample milling; the
whitening time was only 1 minute, thus some slightly cracked kernels might not be
broken during milling.
• In both cases (Air reversal and No air reversal) drying did decrease the head rice recovery
and increase the crack. The causing factor was not apparent, due to so many factors
involved in a large mass of 8 tons of grain: paddy non-uniformity, drying rate…. Most
suspected reason was the drying rate (Fig.13), data pointed to an optimum drying rate in
the 1.0– 1.2 %/hr range, but this has to be confirmed by further elaborate experiments, or
from laboratory scale experiments.
Crack % INCREASE (Kien Giang 2007 wet-season)
0
5
10
15

20
25
30
35
40
B2 & B5 B1 & B6 B9 & B6 Ave(3batches)
Batches
Crack %
Air reversal No air reversal
Figure 11. Crack% INCREASE, Kien-Giang, wet-
season 2007.
Head rice, Kien Giang 2007 Wet-season
(AR = Air Reversal; NAR = No air reversal. B2 = Batch No2)
0
10
20
30
40
50
60
70
AR B2
AR B9
NAR B5
NAR B6
StDev(AR
)
Head Rice Before drying, % Head Rice After drying, %
Figure 12. Head rice Before and After drying.
27

Effect of Drying rate (AR & NAR)
0
4
8
12
16
20
24
28
32
36
0.8 1.0 1.2 1.4 1.6 1.8 2.0
Drying rate, % /hr
Crack Increase,
Head rice Decrease, %
Grain Crack Increase, % Head Rice Decrease , %

Figure 13. The effect of the drying rate on the crack increase or the head rice recovery.


The laboratory dryer
The effects of two factors were studied: Factor A was the final MC with two levels (14%
coded X14, and 17% coded X17). Factor B was the air reversal mode with two levels (Air
Reversal AR, and No Air reversal NoAr). Each four treatments (or factor combinations)
were in one block of experiment that is, conducted at the same time. This was possible
thanks to 2 identical laboratory dryers running in parallel. Each batch contains 20 kg of
paddy. Four replications (or 4 blocks) were made.
The total thickness of the paddy layer in the AR batches was 0.51 m while that of NoAr
batches was 0.31 m. Paddy was sampled at three layers –Bottom, Middle, and Top layer— in

3 specific trays, with other buffer trays in-between.
In each block of experiment, the dependent variables were: the drying rate (shown by the
drying curve), the uniformity of the final MC (shown by the MC of the bottom, middle, and
top layers), the head rice recovery, and the grain crack. Data in one typical block are graph in
Fig.14, 15, 16&17. Results are statistically analyzed as a RCBD (randomized complete block
design) with data compiled in Table 1.

From the results and the statistical analysis, the following remarks can be derived:
a. The final MC differential:
The effect of both the reversal mode and the final MC was statistically significant at 5%
alpha level. Air reversal yielded less final MC differential than No air reversal (Table 1,
Fig.14). Also, drying stop at 14% MC gave less final MC differential than at 17% MC.
However, since the interaction effect is significant, comparisons should be made from each
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treatment, that is between factor combinations. For example in Table 1, treatment NoArX14
and AR_X17 had similar MC differential.
20-8-2008I: 43
o
C
10
11
12
13
14
15
16
17
18
19

20
21
22
23
AR X14 NoArX14 AR X17 NoArX17
AR = Air Reversal; NoAr = No Air reversal.
X14 = Average Final MC 14%
X17 = Average Final MC 17%
Final MC, %w
b
Upper
Middle
Lower

Figure 14. Moisture non-uniformity.

20-8-2008I: 43
o
C. Final MC 17%
10
12
14
16
18
20
22
24
26
28
30

024681012
Drying time, hr
MC , % wb
NoArX17-Bottom
NoArX17-Middle
NoArX17-Top
AR X17-Bottom
AR X17-Middle
AR X17-Top Layer

Figure 15. Drying curves down to 17% MC of the Top, Middle, and Bottom layers.
AR = Air Reversal; NoAr = No Air reversal.
X14 = Average Final MC 14%. X17 = Average Final MC 17%
29

20-8-2008I: 43
o
C. Final MC 14%
10
12
14
16
18
20
22
24
26
28
30
024681012

Drying time, hr
MC , % wb
NoArX14-Bottom
NoArX14-Middle
NoArX14-Top
AR X14-Bottom
AR X14-Middle
AR X14-Top Layer

Figure 16. Drying curves down to 14% MC of the Top, Middle, and Bottom layers.

b. Drying rate:
The effect of both the reversal mode and the final MC was not statistically significant at 5%
alpha level. However, at 10% alpha level, drying down to 14% MC was significantly at
slower rate than down to 17% MC (Table 1, Fig.15 &16).

-6.38
-8.56
-12.92
22
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2

0
NoArX14 AR X14 NoArX17
A
Decrease in Head rice
r
y, compared to shade drying,
% (decrease = - )
AR = Air Reversal; NoAr = No Air reversal.
X14 = Average Final MC 14%
X17 = Average Final MC 17%

Figure 17. % Decrease in head rice recovery.
30


Table 1. Data from experiments with the laboratory dryers. AR = Air Reversal; NoAr = No Air reversal;
X14 = Final MC 14%; X17 = Final MC 17%.
DRYING RATE,
%/hr
FINAL MC
DIFFERENTIAL, %
% DECREASE IN
HEAD RICE
RECOVERY
GRAIN CRACK, %
A =
Final
MC

B =

Reversal mode
A =
Final
MC
B =
Reversal mode
A =
Final
MC
B =
Reversal mode
A =
Final
MC
B =Reversal
mode


NoAr AR

NoAr AR

NoAr AR

NoAr AR Ctrl
X14
1.00 0.88
X14
4.20 2.00
X14

-2.99 -5.96
X14
8.00 11.33 11.33
1.37 1.54 6.30 4.00 -10.02 -9.26
0.00 7.33 4.00
1.46 1.35 7.00 4.90 -7.50 -9.32
0.00 2.00 0.67
1.59 1.53 7.89 3.90 -5.02 -9.70
0.67 8.00 1.33
Av: 1.35 1.32 Av: 6.35 3.70 Av: -6.38 -8.56 Av:
2.17 7.17 1.83
X17
1.11 1.05
X17
5.30 3.70
X17
-14.18 -5.70
X17
18.67 24.00 3.00
1.47 1.49 11.70 9.60 -10.27 -10.18
19.33 8.67 0.67
1.60 1.36 8.90 4.80 -21.83 -25.70
4.00 9.00 0.00
1.59 1.71 10.30 6.60 -5.77 -8.41
2.00 1.33 0.00
Av: 1.55 1.52 Av: 10.30 7.00 Av: -13.01 -12.50 Av:
11.00 10.75 0.92
Statistical Analysis Results (at 5% significance level):
Interaction AB:
No

Interaction AB: Yes Interaction AB: Yes Interaction AB: Yes
A: non-significant LSD = 2.14% LSD = 7.70% LSD = 7.73%
B: non-significant (between treatments)


c. Decrease in head rice recovery and Rice crack
Drying, whether with air reversal or not, did decrease the head rice recovery and increase the
rice crack compared to control shade drying. The reason was suspected as too high drying
rate (over 1.3 %/hr). But the regression analysis and graphing (Fig.18) showed no definite
trend. More crack and lower head rice recovery at 17% as expected because paddy was
milled with the laboratory mill at that MC which was not the optimum.

31

Effect of Drying rate on rice crack
0
5
10
15
20
25
0.8 1.0 1.2 1.4 1.6
Drying rate , %wb /hr
Rice crack, %
NoAr
AR

Figure 18. Effect of the Drying rate on Rice crack.

In theory, more head rice recovery corresponds to less rice cracks; and more head rice and

less crack correspond to more MC differential. The less final differential with Air Reversal
compared to No Air reversal was expected to go with less decrease in head rice and less
crack, but data showed the contrary (Table 1).
In summary even with the laboratory experiments, the experimental data were still hard to
analyze for balanced and good-looking results, with the possible reason traced to the
variability between the individual grains.

The 4-ton solar-assisted dryer
A 4-ton popular flat-bed models (named SDG-4 dryer) fabricated by a local mechanical shop
was selected. This is a collapsible unit, which consists of the following components:
i.) A two-stage axial fan, a design transferred by NLU, powered by a 15 HP Chinese diesel
engine.
ii.) A coal furnace, with coal consumption adjustable within 5 to 12 kg/hr.
iii.) A drying bin, with the grain floor size 4.50 m *3.27 m made from bamboo slat and nylon
net. The bin is supported on 7 metal legs, thus can be easily installed on rough land. The
airflow can be upwards (Fig.19), or downward (Fig.20) with a covering tarpaulin.
iv.) A solar collector (designed at NLU) consisting of 2 cylindrical plastic collector (Fig.19
&20). Each cylinder is φ1.0 m * 27 m long. Inside the transparent plastic layer is the
black PE layer for absorbing heat. The two cylinders converged into a transition box,
32

which also received heat from the coal furnace. The collector used cheap materials such
as bamboo slats and plastic wires, and was installed on the open ground instead on the
rooftop, thus the investment cost was significantly reduced compared to the steel-frame
collector of the macaroni dryer (Phan Hieu Hien et.al, 2007).
The solar collector and the coal furnace can be used separately or in combination. Tests
were done at Long-An Province in March 2007, the driest month of the year.
Figure 19. The SRA-4B dryer with the upward
airflow.
Figure 20. The SRA-4B dryer with the downward

airflow, using solar heat.

Five drying batches were tested in March 2007: Batch 1 with heat from coal only; Batches 2
& 3 with heat from solar energy only, Batches 4 & 5 with heat combined from both coal and
solar energy.

Results are summarized as follow:
• The capacity was 3.8 – 4.1 ton per batch of 7- 12 hours, with moisture reduction (average
± standard deviation) from 23.8 ±1.7 % MC down to 14.2 ± 0.8 % .
• The drying temperature could be adjusted within 38- 44
o
C using coal. With solar heat,
the drying temperature could reach 38
o
C with good sunshine (over 800 W/m
2
radiation),
or only 36
o
C in cloudy weather (about 500 W/m
2
radiation, which is also typical in the
wet-season). With less sunshine, the 12-hr drying time as in Batch 3 was expected.
• The combination of solar and coal heat is handy in ensuring to finish one batch within the
day. The harvest season in one village or commune usually lasts less than 25 days, thus
can not allow the “luxury” of 2-day drying batch.
• The head rice recovery in all batches were comparable to “shade” drying; or even slightly
better with 2 batches with solar energy, possibly to slightly lower drying temperature.

33

The contribution of solar energy is analyzed using data of Batch 4 and Batch 5, both with
combined heat from coal and solar energy; the following can be drawn:
 Solar energy could contribute to a cost saving of 43– 78 % from reducing the coal
consumption.
 The saving translated into US$ 3– 5 per batch, or US$ 0.7– 1.3 per ton)
# # #

 For estimation, assume that in one year, the dryer is used for 100 batches or 400 tons, of
which ½ totally use solar energy, and ½ use supplementary solar energy with 50 %
saving, or US$1.6 and US$0.8 per ton respectively. Thus the total saving would be
US$480 per year.
 Compared to the additional investment for the solar collector of about US$ 560, with the
replacement of the plastic sheet costing about US$120 after every 7 months, the payback
period is about 2 years.
 For stand-alone dryer owner, he/she might not be able to dry for 100 batches per year. In
contrast, dryer owner-cum-rice miller can surpass that quantity easily. Thus the solar
collector would aim practically more for the rice milling compound.

In the Mekong Delta of Viet Nam, farmers currently use the flat-bed dryer mostly for paddy
harvested in the wet-season. For the dry-season harvest, people mainly rely on the pavement
natural sun drying to save the cost of fuel for drying. Thus paddy crack in the dry-season
harvest is even more severe, as repeatedly warned by research and extension agencies without
many results, obviously due to the very low drying cost under sunshine.
Thus, from test data, solar energy has been used to dry paddy at a production scale; early
attempts in the 1980’s dealt with 50- 300 kg/ batch lasting 2 days The test has proved the
quality of the dried paddy. Economically, it could refute the popular saying that “Solar
energy is free but not cheap” with the fact that the owner can recover the additional
investment for the solar collector in about 2 years. Environmentally, solar energy is clean.
The problem remains to introduce the solar heat to the integrated rice mill with dryers. The

test has proved the function of the solar collector in saving fuel cost, especially in the dry-
season harvest.



# # #
Converted from 16 300 VN dong
≈
US$1 (In 2007).
34

SURVEY
Background data
The 4 Provinces under study have similar data in terms of climate and other agricultural
featuresm typical of the Mekong Delta. All have the average monthly temperature of
27- 28
o
C, with the average maximum of 29
o
C in April and minimum of 25
o
C in January.
But the temperature difference between daytime and night time is more pronounced, say
between 25 and 36
o
C in hot months, or 23 and 33
o
C in cooler months.

The rainy season in the region occurs from May to October, the remaining months are dry

season and there is not four seasons such as the Spring, Summer, Winter like in Northern
Provinces. The annual rainfall is 1 400 mm in Long-An, and higher in Can-Tho and Kien-
Giang, 1600 and 1800 mm respectively.

The average annual relative humidity is 80- 82 %. This just says that is typical tropical
humid climate, and not specific enough about its significance in post-harvest. Earlier
compilarion (Phan Hieu Hien, 1998) showed that in a typical day of March (dry season) and
of August (rainy season) in of the Mekong Delta, the relative humidity during the night time
(21h00 PM to 7h00 AM) is very high, over 90%. This is totally different with Australia,
where the Rh is below 70 % even in night time. The implication is the moisture re-absorption
of the grain during storage.

Specific data pertaining to each Province are shown in Table 2.
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Table 2. Selected data of the 4 Provinces under survey.
Can-Tho Kien-Giang Long-An Tien-Giang
Population (2005), million 1.14 1.65 1.41 1.70
of which % in agriculture/ rural area 50 76 83 85
Rice Yearly PLANTED area, ha 231 000 596 000 430 000 252 000
Rice production, million ton 1.23 2.90 1.93 1.31
of which % harvested in rainy months 47 48 35 60
Number of flat-bed dryers
≈350
1100 580
#
300
##
% of wet-season paddy dried by machines
≈15

(10- 20)
24 22 12
Source: General Statistics Office, Ha-Noi, Viet Nam, (2005)
Danida ASPS Report (2004)
# Mr. Con, Office of Long An Rural Development (2006) .
## Mr. Viet, Post-harvest Advisor at Tien-Giang Province(2006)

Post-harvest and drying status
a) The number of flat-bed dryers in the 4 Provinces is listed in Table 3. Long-An and Tien-
Giang are more backward in terms of dryer development.
b) The flat-bed dryer was first installed in these Provinces in the early 1990’s. These were
“first-generation” conventional flat-bed dryer with central air inlet to the plenum
chamber, using flat-grate rice husk furnace with precipitation chamber (Fig.1). Later,
“second-generation” flat-bed dryer with side-duct plenum (Fig.2) and improved rice husk
was installed between 1995 and 1997 in these Provinces. Last, the “third-generation”
reversible dryer (the principle is shown in Fig.5), with its advantage of saving labor and
land space, was introduced first at Long-An in 2000, and at Tien-Giang and Kien-Giang
in 2002. There are now about 400 reversible dryers in the Mekong Delta, among which
30 units are from original design and installed by NLU, which include about 15 units in
the 4 Provinces under study.
c) The percentage of mechanically dried paddy is not evenly distributed within each
Province. For example, Kien-Giang with an average of 24%, yet in many villages, only
3 % of the paddy harvested in the wet-season is mechanically dried.
d) The percentage of mechanically dried paddy might not proportional to the number of
dryers, but also depends on the weather. That is why in Can-Tho, different sources quote
different percentage, from 10 to 20 %.
36

e) Mechanical drying not only reduces post-harvest losses, but also preserves grain quality.
This fact is widely recognized now by farmers, rice millers, governmental officials, which

is a different view compared to about 10 years ago.
f) Despite the above salient advantage, the majority still practice sun drying. For example,
in Can-Tho, while the installed drying capacity can meet 25 % of the harvest, yet
only 15 % is dried by machine. One source even says that 90 % are sun drying,
consisting of 40% on earthen yard, 40 % on cement yard, and 10 % on roadside.
g) The reason lies with the drying cost, while the quality factor does not account much under
the present agricultural production and trading system. Our data gathered from Long-An
resulted in Table 3.

Table 3. Drying cost under different settings.
Mode VNdong /kg US$ /ton
SRA-4 (reversible, 4-ton/batch) dryer, with rice husk furnace 98 6.1
SRA-8 (reversible, 8-ton/batch) dryer, with rice husk furnace 79 4.9
SDG-4 (reversible, 4-ton/batch) dryer, rice husk furnace
#
1 80 5.0
SDG-4 (reversible, 4-ton/batch) dryer, COAL furnace 130 8.1
Sun drying, in the dry-season harvest
70 4.4
Sun drying, in the wet-season, normal (moderate) weather 140 8.8
Sun drying, in the wet-season, ADVERSE weather 210 13.1
Note: #1: SDG-4 = A “lower-cost” reversible 4 ton/batch dryer, made by a local manufacturer in Dong-Thap
Province (described in solar-assisted experiments).

From Table 3, the following remarks can be made:
• In the dry season, the mechanical drying cost of the SRA-4 dryer (8.1 US$/ton) is still
higher than the manual sun drying cost.
• In the wet season, the mechanical drying cost is lower than sun drying cost. Thus a
charged drying fee of 5 % of paddy value, or about 8 US$/ton, would enable the dryer
owner to recover the investment after 2- 4 years, depending on the investment.

• From the farmer’s (paddy owners) standpoint, they would not spend more than sun
drying in the normal weather, and surely the paid fee is cheaper than sun drying in the
worst, adverse weather. This has not yet taken into account the cost of paddy
deterioration, as reflected in the sale price drop of 10- 20 %, or 16- 32 US$/ton.
37

• SRA-8 dryer, with rice husk furnace, and SDG-4 dryer with rice husk furnace are
alternatives to further reduce the drying cost.
• However, the SDG-4 dryer with coal
furnace is not recommended, since the drying
cost is so high that makes the operation unprofitable for the dryer owner to recover
the investment.
• The drying cost does not include yet the transportation cost charged to the grain
owner, which is about 0.6- 0.7 US$/ton or about 10 % of the proper drying cost.

h) The Danida-assisted Project in Can-Tho and Soc-Trang Provinces in 2001-2006, and its
expanded Program in the whole Mekong Delta has done a good job in promoting the
dryer various people in the rice sector, with a strong and well organized network of
people and facilities. Extension in drying, which used to be a limiting factor in promoting
dryers in the 1990’s, appeared to be well fulfilled in 2000’s. If resistance to using dryers
persists, then it should be traced to other factors.

Further surveys in 2007 resulted with the following additional findings:
• There is a trend in increase the drying capacity to 12- 20 ton/batch; this is reflected in the
number of 10- 16 ton dryers in the last two years compared to 5 years ago with 4- 8
tons/batch; and in different requests for 20 tons/batch dryer in 2007.
• The role of local manufacturers and local extension workers: Provinces with rapid dryer
development such as An-Giang and Tien-Giang have strong manufacturers providing
reliable and efficient dryers to farmers as well as “instant” after-sale service. Extension
workers with solid knowledge in dryer construction and operation are important in

spreading a new design.
• Government support, specifically with interest reduction for dryer loans, is another key
factor in promoting the dryer.
• In the dry-season harvest, there are now places where mechanical drying is popular with a
percentage ranging from 30- 90 % such as Giong-Rieng District of Kien-Giang Province,
Ke-Sach and My-Tu Districts of Soc-Trang Province, Go-Cong and Cho-Gao Districts of
Tien-Giang Province… Farmers just sell wet rice. In Soc-Trang the division of labor is
more and more clear-cut. Ten years ago among the following jobs: paddy growing,
paddy buying, paddy drying, rice milling, there might be a person doing 2 jobs. But
38

nowadays, these jobs are more and more specialized, in which the farmer-grower no
longer dry his/her own paddy.
• The cooperative as an administrative or business unit in paddy drying has not shown an
established role or image in the Mekong Delta. More social study might be needed to
find out the reason.

Problems to be addressed from 2007
The above facts and analysis point to a single major problem in drying at the Provinces under
study, which is: The unbalanced between drying cost and drying benefits
.

While the drying cost is real and quantified, the drying benefits might not be so. Better
quality rice due to mechanical drying may not be bought by traders with a price higher
enough to compensate for the drying cost. Different possible reasons are:

 The output grain was not good due to improper dryer operation.
 Even with proper dryer operation, the output grain was not really good, because farmers
only brought paddy to the dryer as a last recourse when paddy was about to deteriorate
after days of rain.

 The good-quality dried rice was mixed with the bad sun-dried rice, for convenience in
transporting in a same boat-load.
 The quality of the mechanically-dried grain was not yet appreciated enough by the
market. A few percentage point more of head rice recovery might not command a paddy
price superior enough to compensate for the drying cost.
 Even in case the mechanically-dried grain obtained higher price, its effects did not benefit
the farmer growing rice, because the rice miller got practically all advantages from the
head rice recovery. Farmers own paddy, while rice millers and traders own white rice !
Thus the drying problem in 2007 differs from that of 1997: It is no longer (or much less in
scope) of quantity
post-harvest losses, it is more on quality post-harvest losses.

Possible measures for the drying problem from 2007
Given the status in drying as above-analyzed, the proposed activities could be grouped into 3
aspects:

39

a) Technology: There is the need to improve the dryer design so that the quality (in terms of
more head rice recovery, or less crack) is ensured and less dependent on the manual
judgment of the operator. This is not easy, due to the age-old constraint on the drying
cost. The theme of the current CARD Project seems to be in line with these requirements.

b) Extension: In light of the “new” recognition on quality, the extension activities should be
geared more on dryer utilization to preserve quality, not just on reducing quantitative
post-harvest losses. Not just to build dryers to save the crop, but to demonstrate the effect
of more head rice and less rice crack through milling. In another words, farmers not only
see the dried paddy, but also see the white whole grain. Thus a stand-alone dryer does
not help much in the 2007 period.

c) Policy: The above factors (technology and extension) are just necessary conditions, but
not sufficient. A system to induce the dryer utilization for quality should be enhanced.
From the end of the chain, the market should be created for quality rice, with clear
distinction in price. Next, the benefit from high-priced rice should be distributed rightly
to the due contribution of both farmers and rice millers/ traders. The policy should gear
to encouraging the adoption of these practices through financial measures.

The policy affecting the whole rice system is complicated and not easy to alter in a few
months. But as far as the CARD Project is concerned, an integrated system from paddy
supply to drying to milling, which involves farmers, should be established as demonstration
sites at various Provinces.

CONCLUSIONS
 Testing of two 8-ton reversible dryer in Kien-Giang and Can-Tho Provinces; analysis of
the rice cracks in the dry and the wet season harvests, in the actual production. Testing
under laboratory controlled drying conditions with 20-kg dryers in two modes of air
reversal, and two final moisture contents. In both test sets, air reversal reduced the final
MC differential but not the drying time. The effect of air reversal on the head rice
recovery and rice crack was not consistent and involved interactions with the final MC
and possibly with other factors.

40

 Testing of a 4-ton dryer at Long-An equipped with the solar collector as supplementary
heat source showed good grain quality and good economic potential.

 Rapid survey on the current status on the use of flat-bed dryers in 7 Provinces. Among
major findings are: The trend for increased drying capacity, the role of local
manufacturers and local extension workers, the government support with interest
reduction for dryer loans, and the drying during the dry-season harvest.

One main proposal from these activities: To study on ways to integrate the dryer in the
whole chain of rice post-harvest, so that the benefit and paddy drying reflect back to increase
farmers’ income by their active participation.

41

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