flat bed drying including survey results on the drying costs of various drying methods practiced in mekong delta ''''

FLAT BED DRYING INCLUDING
SURVEY RESULTS ON THE DRYING
COSTS OF VARIOUS DRYING METHODS
PRACTICED IN MEKONG DELTA "




SECTION 3


FLAT BED DRYING INCLUDING SURVEY RESULTS ON THE DRYING COSTS
OF VARIOUS DRYING METHODS PRACTICED IN MEKONG DELTA

93




CARD Project
FLAT-BED DRYER
Sub-Component
2006/2007 Report
Reporting period:
from 15 May 2006 to 28 Feb 2007


Compiled by: Phan Hieu Hien, Ph.D.

with contributions from staff
of the NLU Center for Agricultural Energy and Machinery:
Le Quang Vinh,
Tran Thi Thanh Thuy,
Tran Van Tuan,
Nguyen Thanh Nghi.


March 2007








94
CONTENTS
CARD PROJECT, FLAT-BED DRYER SUB-COMPONENT 2006 REPORT 96
1 INTRODUCTION 96
2 INSTALLATION OF THE 8-TON FLAT-BED DRYER 96
3 EXPERIMENTS WITH THE 8-TON DRYER UNDER ACTUAL
PRODUCTION CONDITIONS.
98
3.1 Objectives 98
3.2 Materials and methods 98
3.3 Results and discussion: 98
3.3.1 July 2006 experiments 98
3.3.2 March 2007 experiments 98

4 FABRICATION OF A LAB (MINI) DRYER FOR EXPERIMENTING
UNDER CONTROLLED CONDITIONS.
99
4.1 Objective 99
4.2 Materials and methods 99
4.3 Results and discussion (1-to dryer) 104
5 THE PRRA SURVEY ON THE USE OF FLAT-BED DRYER AND THE
COST OF VARIOUS DRYING METHODS IN THE MEKONG DELTA.
110
5.1 Background 110
5.2 Objectives 110
5.3 Method 110
5.4 Result and discussion 110
5.4.1 Background data 110
5.4.2 Post-harvest and drying status 112
5.4.3 Conclusions 114
6 EXTENSION MATERIALS FOR TRAINING COURSES, BASED ON THE
OUTCOME OF THE SURVEY AND EXPERIMENTS
115
7 CONCLUSIONS AND FURTHER PROPOSALS 116
8 EVALUATION OF FARMERS’ PRACTICE 117
8.1 Value losses due to field drying and sun drying 117
9 REFERENCES 118
10 APPENDIX 119
10.1 Appendix 1 : Paddy milling quality analysis (procedure by IRRI) 119


95
CARD Project, FLAT-BED DRYER Sub-Component
2006 Report

(from 15 May 2006 to 28 February 2007)
1 INTRODUCTION
The sub-component of CARD Project 026/VIE-05 on the flat-bed dryer study, as specified in
the contract, consists of the following activities:
• Select the site and supervise the installation of an 8-ton flat-bed dryer for experiments.
• Conduct experiments with the 8-ton dryer under actual production conditions.
• Build a lab (mini) dryer and other needed tool for experimenting under controlled
conditions.
• Conduct experiments to determine the optimum drying conditions for the flat-bed dryer
(with or without air reversal) using the lab mini-dryer at the Nong-Lam University or a
nearby location.
• Conduct a Participatory Rapid Rural Appraisal (PRRA) survey on the use of flat-bed
dryer in the Mekong Delta.
• Write extension materials for future training courses, based on the outcome of the survey
and experiments.
The above activities can be clustered into 3 groups:
- The 8-ton dryer
- The 1-ton dryer
- Survey, training, and extension
This is the final report of the above-mentioned activities, covering the period from 15 May
2006 to 28 Feb 2007. It is compiled from 2 earlier Progress Reports, and updated with most
recent data and findings, thus conclusions from this report supercede the earlier reports for
any discrepancies.
2 INSTALLATION OF THE 8-TON FLAT-BED DRYER
Together with the Project Leader, Dr. Truong Vinh, we selected the site for installing the
8-ton flat-bed dryer; the site was Tan-Phat-A Cooperative, located in Tan-Hiep District,
Kien Giang Province.
At first, we intended to contract from a local dryer builder for a typical dryer in the region,
adding features needed for the experiment, but no contractor was willing to meet the needs
they considered too time-consuming with these added features in a miscellaneous contract for

their business. So, the research team decided to build an 8-ton air-reversible dryer which is a
SRA-8 design from NLU with slight modifications.
The installation of the dryer was completed in mid-July 2006 (Fig.1 & 2), just in time for the
wet-season harvest and for experimental purposes.



96

Figure 1: The 8-ton dryer at Tan-Phat-A Cooperative, Kien Giang

Figure 2: The 8-ton dryer with the air for downward direction .



97
3 EXPERIMENTS WITH THE 8-TON DRYER
UNDER ACTUAL PRODUCTION CONDITIONS.
3.1 Objectives
To determine the performance of the dryer under actual production conditions, for different
drying regimes.
3.2 Materials and methods
The experiments were conducted in July 2006 Tan-Phat-A Cooperative, Tan-Hiep District,
Kien-Giang Province. Eight experiments were done, with 2 factors under study.
• Air reversal at 2 levels: a) YES , and b) NO
• Drying temperature 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.
Each treatment was replicated twice. However, due to severe difficulty in securing batches of
the same quantity or initial moisture content, the experiments were not strictly factorial. The
arrangement of factor levels is for systematic observation only.
Due to different views on milling analysis, data on head rice recovery were discarded. Thus
in March 2007, another set of experiment was replicated, with focus on comparing the crack
and head rice recovery of 2 different drying modes, namely
with and without air reversal. Sun
drying on the cement drying yard with a 7-cm paddy layer, as popularly practiced by local
farmers, was replicated as control treatment.
The crack analysis was done at the VINACONTROL, an accredited agency in charge of
certifying the rice quality for export. Each treatment was analyzed by 3 samples, each
consisting of 30 grains taken at random; each paddy grain was hand-husked and examined
under the magnifying glass for fissure.
The head rice recovery analysis was done at the Rice Quality Laboratory of the NLU
Chemical Technology Department, following procedures adopted by International Rice
Research Institute (see Appendix) and the University of Queensland.
3.3 Results and discussion:
3.3.1 July 2006 experiments
The experiment results are summarized in Table 1. Figures 3 and 4 show the moisture
reduction curves. Remarks:
- The effect of air reversal is very apparent in reducing the final moisture differential.
When operated correctly, this differential is less than 2 % with air reversal, but at least

5% 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.
- Air reversal also decreased the drying time.
- The drying temperature is stable and can be kept within ± 3
o
C.
3.3.2 March 2007 experiments
Results are in Table 2. All 3 above observations hold with these new experiments.
Data on the crack of rice upon milling show that:

98
a) Mechanical drying, whether with or without air reversal, is 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 are main data obtained from this set of experiments.
b) Mechanical drying
with air reversal resulted in less Final MC differential (2.2 %)
compared to
without air reversal (4.6 %)
c) The increase in crack percentage between mechanical drying
with and without air differed
by only 1 %; while judged by the head rice recovery, the difference was only 0.4 %, or
almost no difference (Table 2). This was not expected in line with the above data on
Final MC differential. Thus more experiments should be conducted in the future to
confirm the trend.


4 FABRICATION OF A LAB (MINI) DRYER
FOR EXPERIMENTING UNDER CONTROLLED CONDITIONS.
4.1 Objective

To determine the performance of the 1-ton dryer under controlled conditions.
4.2 Materials and methods
A lab mini-dryer of maximum capacity of 1 ton was designed and fabricated for
experimenting under controlled conditions (Fig.5)
(a)
(b)
Figure 5: The 1-to dryer: Airflow upward; (b) Downward reverse airflow

99
Table 1: Summary of 8 drying batches (July 2006 )
Date /2006
23-7
25-
26/7

25-7 30-7 24-7 27-7 23-7 29-7
Batch Number 1 5 4 8 3 6 2 7
Ave
Temperature, oC 43 43 43 43
48
x43
48
x43
48
x43
48
x43

Air reversal
Yes Yes No No Yes Yes No No

Drying time, h+xx/100 10.42 6.00 10.50 8.75 10.00 3.58 5.75 11.67
Air reversal time, minute 10 15 15 10
Break-down time, minute 60
Initial MC, % 27.4 19.3 21.5 24.5 25.6 20.7 25.6 26.0

Final MC: Bottom, Max: 9.1 13.9 11.7 13.2 13.4 14.1 8.1 12.8
Final MC: Bottom, Min: 5.9 12.1 11.2 11.2 12.2 13.1 6.1 10.6
Final MC: Bottom, Ave,%: 8.2 13.4 11.6 12.0 12.7 13.6 7.6 11.3

Final MC: Top, Max: 15.5 14.9 23.1 22.7 17.3 15.2 13.0 22.6
Final MC: Top, Min: 15.2 13.3 15.2 15.5 15.8 14.4 12.2 17.8
Final MC: Top, Ave, %: 15.3 14.2 18.9 19.1 16.5 14.8 12.5 20.4

Final MC differential, % 7.1 0.8 7.3 7.1 3.8 1.2 4.9 9.1
Air SUPERFICIAL Velocity
Average , m /minute 10.13 9.72 10.23 9.62 10.23 9.78 9.78 9.71
9.90
± Std. Dev., m /minute 0.28 0.22 0.16 0.17 0.16 0.22 0.15 0.20
AIR FLOW, m3/s 5.31 5.10 5.37 5.05 5.37 5.13 5.13 5.10
5.19
Av. Drying temp, oC 42.8 42.5 43.3 41.4 42.2 44.8 42.2 44.3 42.9
± Std.Dev, oC 2.0 2.8 2.4 2.8 3.6 2.8 3.6 3.2
2.9
Temp. Increase, oC 16.2 16.25 12.41 12.14 12.0 11.83 12.0 12.20
13.1
Bulk density:Before, kg/m
3
521 505 529 495 529 525 522 523
519
After drying, kg/m

3
480 484 465 493 498 515 477 503
489
Paddy : BEFORE, kg 8338 7246 8185 7860 8805 8724 5307 9438

AFTER drying, kg 6946 6564 7368 7462 7706 4599 8307
Grain depth: BEFORE, m 0.508 0.456 0.491 0.504 0.528 0.528 0.323 0.573
AFTER drying, m 0.459 0.431 0.474 0.475 0.475 0.306 0.524

Husk consumption: Total, kg 416.4 206.4 220.9 282.2 371.5 138.9 160.5 373.0
kg/ hour 39.95 34.40 21.04 36.41 37.16 38.80 27.92 31.96 33.45
Diesel consump. :Total, Lit 18.0 17.0 16.6 12.0 17.00 6.0 9.50 17.0
Lit/ hour 1.73 2.83 1.58 1.55 1.70 1.68 1.65 1.46 1.77


100

101

Table 2: SUMMARY results of March 2007 experiments: Comparison of 2 drying batches
Batch 1 (46+43 oC, with air reversal). Batch 2 (46 x43 oC, WITHOUT air reversal)
(46 x43 = 46 oC in first 1,5 hours, &43 oC in remaining time)
Place Tan Phat A Cooperative, Ken Giang Province. Date: March 2007
Batch Number Batch 1 Batch 2
Air reversal Yes No
Drying temperature (oC) ± StDev
43.3
± 3.1
43.0
± 2.9

START date-time
08-03-07 10:30 10-03-07 11:30
END date-time
08-03-07 16:30 10-03-07 17:30
Drying time, h+xx/100 6.00 6.00
Air reversal time, minute 15
Laborer for air reversal 2
Initial MC, % (Ave ± StDev)
23.86
± 0.71
20.41
± 0.45
Final MC % (Ave ± StDev) 14.94 16.07

Top layer 13.92 0.31 18.23 0.75
Middle layer 16.16 1.05 16.38 0.7
Bottom layer 14.75 0.63 13.59 0.47
MC differential Top-Bottom, % 0.83 4.64
MC differential Middle-Top , % 2.24
AIRFLOW (20 points)

Airflow, m3/s 5.88 5.70
Superf. vel. (Ave ±StDev), m/min 11.20 ± 0.30 10.85 ± 0.37
Rice husk consumption: kg /batch 171.2

215.2

Rice husk consumption: kg / hr 28.5

35.9

Diesel consumption, liter /h 1.70 1.75
Initial Paddy mass, kg 9276 9197
Initial Paddy Layer (Ave±StDev), mm 517.8 15.6 507.8 7.5
Crack BEFORE drying, % 12.00 Differ 21.00 Differ
Crack AFTER drying, % 13.75
1.75
23.75
2.75
Crack, Sun drying on Cement yard,
7-cm layer, %
17.80
5.80
26.80
5.80
Head Rice Recovery, %

Head Rice %, BEFORE drying 62.72
Differ
59.12
Differ
Head Rice %, AFTER drying 59.39
-3.33
56.21
-2.91
Head Rice %, Sun drying 55.58
-7.14
52.12
-7.00
Difference (Sun & Mechanical) . % -3.81 -4.09

BATCH 1 ( 43
o
C, With air reversal )

BATCH 4 ( 43 oC, Without air reversal)

BATCH 5 ( 43
o
C, With air reversal )

BATCH 8 ( 43 oC, Without air reversal)

Mẻ 1, Đảo gió, 43 oC
0
5
10
15
20
25
30
0 2 4 6 8 10 12
Thời gian sấy Drying time, h
Ẩm độ MC %(wb)
Dưới 1
Dưới 2
Dưới 3
Dưới 4
Dưới 5
Trên 1

Trên 2
Trên 3
Trên 4
Trên 5
MẺ 4 (sấy 43 oC, KHÔNG đảo gió)
0
5
10
15
20
25
30
024681012
Thời gian sấy Drying time, h
Ẩm độ MC %(wb)
Dưới 1
Dưới 2
Dưới 3
Dưới 4
Dưới 5
Trên 1
Trên 2
Trên 3
Trên 4
Trên 5
MẺ 5 (sấy 43 oC, CÓ đảo gió)
0
5
10
15

20
25
30
0123456
Thời gian sấy Drying time, h
Ẩm độ MC %(wb)
Dưới 1
Dưới 2
Dưới 3
Dưới 4
Dưới 6
Trên 1
Trên 2
Trên 3
Trên 4
Trên 6
Mẻ 8 (sấy 43 oC, KHÔNG đảo gió)
0
5
10
15
20
25
30
0123456789
Thời gian sấy Drying time, h
Ẩm độ MC %(wb)
Dưới 1
Dưới 2
Dưới 3

Dưới 4
Dưới 5
Trên 1
Trên 2
Trên 3
Trên 4
Trên 5
Figure 3: Moisture reduction curves at 43
o
C



102
BATCH 3 (48
o
C + 43
o
C, With air reversal )

BATCH 2 (48
o
C + 43
o
C, Without air reversal )

BATCH 6 (49
o
C + 43
o

C, With air reversal )

BATCH 7 (48
o
C + 43
o
C, Without air reversal )


103
MẺ 2 (sấy 50oC + 43oC, KHÔNG đảo gió)
0
5
10
15
20
25
30
0123456
Thời gian sấy Drying time, h
Ẩm độ MC %(wb)
Dưới 1
Dưới 2
Dưới 3
Dưới 4
Dưới 5
Trên 1
Trên 2
Trên 3
Trên 4

Trên 5
MẺ 7 (sấy 50 oC +43 oC, KHÔNG đảo gió)
0
5
10
15
20
25
30
024681012
Thời gian sấy Drying time, h
Ẩm độ MC %(wb)
Dưới 1
Dưới 2
Dưới 3
Dưới 4
Dưới 5
Trên 1
Trên 2
Trên 3
Trên 4
Trên 5
Figure 4: Moisture reduction curves at 48
o
C in the first hour, and 43
o
C afterwards.

MẺ 3 (sấy 50 oC + 43oC, CÓ đảo gió)
0

5
10
15
20
25
30
02468101214
Thời gian sấy Drying time, h
Ẩm độ MC %(wb)
Dưới 1
Dưới 2
Dưới 3
Dưới 4
Dưới 5
Trên 1
Trên 2
Trên 3
Trên 4
Trên 5
Mẻ 6 (sấy 50 oC +43 oC, CÓ đảo gió)
0
5
10
15
20
25
30
01234
Thời gian sấy Drying time, h
Ẩm độ MC %(wb)

Dưới 1
Dưới 2
Dưới 3
Dưới 4
Dưới 5
Trên 1
Trên 2
Trên 3
Trên 4
Trên 5

104
.The SRA-1 dryer fan was tested for the performance (Fig.6)
SRA-1 FAN
0
5
10
15
20
25
30
35
40
0.8 0.9 1.0 1.1 1.2
Airflow, m
3
/s
Stat.Pressur, mmH2O ;
Efficiency, %
0.0

0.5
1.0
1.5
2.0
Power, kW
Stat ic
Pressure,
mmH2O
Static.Eff , %
Mech. Eff, %
Power
kW

Figure 6: Fan performance of the SRA-1 dryer
Originally, three factors were planned for study:
− Air reversal at 2 levels: a) YES , and b) NO
− Drying temperature 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.
− Final moisture content at 2 levels: a) 14.5 % ; and b) 17.0%.
Thus there would be 8 treatments, arranged in blocks, so that the initial moisture contents in
each block are similar.
However, in actual conditions, it was impossible to arrange for the blocks with same moisture
content since the paddy belongs to the owner or the rice miller. Eight experiments would last
at least 4- 8 days, thus even if the same paddy field were booked for the test, the initial MC

would be different. With different input MC, the final MC at 2 levels would not make sense,
at different drying rates.
So we decided to conduct paired experiments, based on the first variable, namely
with or
without


The experiment results are summarized in Table 3. Figures 7 and 8 show the moisture
reduction curves.
4.3 Results and discussion (1-to dryer)
air reversal. Each pair was combined with a level of the second variable (drying
temperature). Each pair draw from the same lot of paddy input, thus could be assumed as
having the same initial MC.

Table 3: Summary of 8 drying batches
Nong-Lam University

TESTS: drying paddy with SRA-1 dryer (CARD
Project)
Date 09-16/ Dec.2006
Center for Agr. Energy & Machinery

8 drying batches
Place : Le- Minh BRVT Rice Mill Pers: : TTT Thuy, NV Quy

Batch
1
Batch 2 Batch 3 Batch
4
Batch 5 Batch 6 Batch

7
Batch 8
Note
No Drying conditions
50+43o
C
with
Air
Reversal
50+43oC
Without
Air
Reversal
43oC
Without
Air
Reversal
43oC
with
Air
Reversal
43oC
with Air
Reversal
43oC
Without
Air
Reversal
50+43
oC

with
Air
Reversal
50+43oC
Without
Air
Reversal

1 Date 10 /12
/06
11 /12 /06 11-
12/12/06
12 /12
/06
13-
14/12/06
14/12/06 15/12/06 16/12/06
2
Paddy MC Before drying (%)
24.71 18.84 24.35 21.10 27.70 27.35 25.97 21.83

3
Paddy MC After drying (%)
13.43 12.82 12.62 13.65 13.53 13.35 12.49 12.64

4 Ave. Final MC, Top layer
13.9 12.9 13.6 13.6 12.8 13.3

5 Ave. Final MC, Bottom layer
11.8 11.2 11.7 11.4 11.0 11.1

6
Final MC Differential = Top - Bottom
2.1 1.7 1.9 2.2 1.8 2.2

7 Layer thickness before drying (m)
0.364 0.243 0.248 0.246 0.379 0.261 0.405 0.249

8 Layer thickness after drying (m)
0.321 0.230 0.208 0.219 0.350 0.230 0.361 0.220

9 Fresh /Dried before air reversal - Top Layer
1.11 1.14 1.10 1.19

10

Fresh /Dried after drying - Top Layer
1.22 1.07 1.18 1.20 1.25 1.23 1.29 1.13

11 Fresh / Dry Ratio before air reversal - Bottom L.
1.36 1.23 1.34 1.41

12 Fresh / Dry Ratio after drying - Bottom Layer
1.39 1.11 1.26 1.25 1.36 1.38 1.45 1.20

13 Coal consumption (kg)
22 10 18 9 20 8 17

14 Coal consumption (kg / hr)
1.93 2.50 2.25 0.84 1.74 1.23 1.55 0.00

Table 3 (continued)

105

Batch
1
Batch 2 Batch 3 Batch
4
Batch 5 Batch 6 Batch
7
Batch 8
Note
No Drying conditions
50+43
o
C
with
Air
Reversa
l
50+43oC
Without
Air
Reversal
43

o
C
Without
Air
Reversal
43
o
C
with
Air
Reversa
l
43
o
C
with Air
Reversal
43
o
C
Without
Air
Reversal
50+43
o
C
with
Air
Reversal
50+43

o
C
Without
Air
Reversal

18 Air SUPERFICIAL Velocity, Ave (m/minute)
11.46

19
Air SUPERFICIAL Velocity,
Std.Dev., m/minute)
0.42

20
Air Flow, m3 / s 0.76 > 0.80 > 0.79 > 0.80

21
Air flow rate (m3 /s / ton) > 1.39 1.32 > 0.99 > 1.43

22
Mass of Paddy Before Drying (kg) 893 572 576 606 803 560 851 586

23
Mass of Paddy After Drying(kg) 665 474 420 434 556 381 620 486

24
Mass Reduction, Actual (kg) 228 98 155 172 247 179 231 100

25

Mass Reduction, from MC calc.(kg) 116 39 77 52 132 90 131 62


Ratio Reduction: Actual/ MC Calc. 2.0 2.5 2.0 3.3 1.9 2.0 1.8 1.6

26
Drying time (hr) 11.42 4.00 8.00 10.67 11.50 6.50 11.00 7.20

27
Time of Air Reversal, after (hr) 7.00 7.00 9.00 9.00

28
Bulk Density WET, kg / m
3
613 588 581 616 530 535 525 588

29
Bulk Density DRIED , kg / m
3
695 621 692 692 573 608 590 666

30
Note Batch 1 &2 for
tune-up
Lots of immature,
green grains.
Batch 3 & 3: from
same input paddy
- Very wet paddy, forced
aeration for 1.5 hr to obtain

desired initial MC
- Lots of immature grains &
impurities
-Batch 5, 6& 7: from same
input paddy
Good grain, little impurities


106

BATCH 3 ( 43
o
C, Without air reversal)
Batch 3 ( 43 oC, Without Air Reversal )
10
12
14
16
18
20
22
24
26
28
0123456789101112
Drying time, hr
T1
T2
T3
T4

T5
D1
D2
D3
D4
D5

BATCH 4 ( 43
o
C, with Air reversal)
Batch 4 (43 oC, with Air Reversal )
10
12
14
16
18
20
22
24
26
28
0123456789101112
Drying time , hr
T1
T2
T3
T4
T5
D1
D2

D3
D4
D5

Batch 6 (43 oC, Without Air Reversal )
Batch 6 (43 oC, Without Air Revers al )
10
12
14
16
18
20
22
24
26
28
0123456789101112
Drying time, hr
T1
T2
T3
T4
T5
D1
D2
D3
D4
D5

Batch 5 (43 oC, with Air Reversal )

Batch 5 (43 oC, with Air Reversal )
10
12
14
16
18
20
22
24
26
28
0123456789101112
Drying time, hr
Moisture content, %
T1
T2
T3
T4
T5
D1
D2
D3
D4
D5

Figure 7 : Moisture reduction curves at 43
o
C drying temperature

107

108
Batch 8 (50 oC + 43 oC, WITHOUT Air Reversal
Batch 8 (50 oC + 43 oC, WITHOUT Air Reversal
10
12
14
16
18
20
22
24
26
28
0123456789101112
Drying time, hr
Moisture content, %
T1
T2
T3
T4
T5
D1
D2
D3
D4
D5

Batch 7 (50 oC + 43 oC, with Air Reversal )
Batch 7 (50 oC + 43 oC, with Air Reversal )

10
12
14
16
18
20
22
24
26
28
0123456789101112
Drying time, hr
Moisture content, %
T1
T2
T3
T4
T5
D1
D2
D3
D4
D5

Figure 8 : Moisture reduction curves. at 50
o
C + 43
o
C drying temperature

The following remarks could be pointed out:
- The effect of air reversal was very apparent in reducing the final moisture differential
(FMD). Without air reversal this FMD was larger than 2 % point. With air reversal, it
was less than 2 % point; even that the grain quantity dried was much more than the
former case.
- For this lab dryer, air reversal did not decrease the drying time, because for the same
airflow, with less grain on the floor, the specific airflow rate (per ton) was higher in the
case air was not reversed. .
- The drying temperature is stable and can be kept within ± 2
o
C.
The above remarks do not offer much new findings; yet the tests give specific and handy data
for preparing training materials on rice drying, as part of the Project activities.
The problem of non-uniformity of the input materials for testing is reflected with data on the
bulk density of the input (wet) as well as the output (dried) paddy (Fig 9)

SRA-1, Ba-Ria VT, Dec.2006 (Wet paddy)
520
540
560
580
600
620
640
18 20 22 24 26 28
Moisture content, % wb

Bulk density, kg /m
3
kg/ m3
Regression

(a)
SRA-1, Ba-Ria VT, Dec.2006 (DRIED paddy)
500
550
600
650
700
12.0 12.5 13.0 13.5 14.0
Moisture content, % wb
Bulk density, kg /m3
(b)
Figure 9: Bulk density of the wet (a) and dried paddy (b) used in the tests.

The learning experience from the tests have been: A balanced set of experimental data for
drying treatments of even 1 ton each is difficult to obtain under actual field conditions.
Perhaps, a quantity of around 20 kg each is more appropriate. Even so, cold storage room is
needed for conditioning the grain for one-week-long testing. Miscellaneous equipment such
as cleaner is also needed. All these rigorous procedures would give pure academic results,
which in fact do not reflect the realities, as the graph on the bulk density showed.
Thus in the future, an alternative that several drying researchers followed would be
modeling of the drying process. This hopefully can cope with diversities in material
conditions as well as ambient conditions.
Another constraint was the laboratory milling equipment for milling analysis (for head rice
recovery) could not be standardized for proper operation at the time.
Page 109

5 THE PRRA SURVEY ON THE USE OF FLAT-BED DRYER
AND THE COST OF VARIOUS DRYING METHODS IN THE MEKONG
DELTA.

By the terms of the contract, two other activities were conducted: The survey using the
Participatory Rapid Rural Appraisal (PRRA) method on the use of flat-bed dryer in the
Mekong Delta and the cost of drying; and the writing of extension materials for future
training courses, based on the outcome of the survey and experiments.
5.1 Background
The flat-bed dryer has been with the rice agriculture in the Mekong Delta of Viet Nam since
early 1980’s. Its development over the past 25 years and its current status need to be
examined in the context of the CARD Project 026/VIE-05 with focus on the cracking of
paddy grains in the area. Thus a survey using the PRRA method on the use of flat-bed dryer
in selected Provinces of the Mekong Delta was conducted.
5.2 Objectives
- To confirm the role of flat-bed dryers in reducing post-harvest losses and in preserving
rice quality.
- To identify operating factors of the flat-bed dryer which contribute to the reduction of
rice crack.
- To identify problems with the flat-bed dryer that the CARD Project could possibly help.
5.3 Method
The survey used the PRRA method, through interviewing different people class, from farmers
to rice millers to governmental officials… But it also relied heavily on both available data
gathered in the past 10 years by various agencies, and on personal experience of the people
involved with the dryer at NLU over the past 20 years.
Four Provinces were selected, 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.
Note: Can-Tho = Can-Tho City, which used to be part of Can-Tho Province, and is about half
of the latter in terms of rice land.
5.4 Result and discussion
5.4.1 Background data
The 4 Provinces under study have similar data in terms of climate and other agricultural
features. 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.
Page 110
The rainy season in the region occurs from May to October, the remaining months are dry
season (no 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 (1 600 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. Figure 10
presents average variation of a typical day of March (dry season) and of August (rainy
season) in Can-Tho, which is very similar to that of other places in the Mekong Delta.
Whether in rainy or dry season, 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.
Temperature and Rel.Humidity, CAN-THO (average 1988- 1992)
22
24
26
28
30
32
34
36
38
40
42
0 3 6 9 12 15 18 21 24
Time of the day (12= noon ; 24 = midnight)
Temperature, oC
0
10
20
30
40
50
60
70
80
90
100
Rel.Humidity, %

oC-March oC-August %RH-March %RH-August

Figure 10. Weather data of a typical day in March and August,
at Can-Tho Province (average 1988- 1992)
Specific data pertaining to each Province are shown in Table 4.
Table 4: 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) .
Page 111
## Mr. Viet, Post-harvest Advisor at Tien-Giang Province(2006)

5.4.2 Post-harvest and drying status
a) The number of flat-bed dryers in the 4 Provinces is listed in Table 4. 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.11). Later,
“second-generation” flat-bed dryer with side-duct plenum (Fig.12) 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.13), 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 %.
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 5.

Table 5: Drying cost under different settings (the details of the raw data will be provided later)
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:
Page 112
#1: SDG-4 = A “lower-cost” reversible 4 ton/batch dryer, made by a local manufacturer in
Dong-Thap Province. This dryer uses the fan design transferred by NLU, but with a devised drying
bin which reduces material costs, while still ensuring airflow uniformity through a “distributed center
tube” from the fan outlet (Fig. 14).
From Table 5, the following remarks can be made:
• In the dry season, the mechanical drying cost of the SRA-4 dryer (98 VND/ kg) 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 130 VND/kg, 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 270- 540 VND/ kg.
• 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 10- 12 VNdong /kg or US$0.6- 0.7 or about 10 % of the proper
drying cost.


Figure 11: Conventional FBD with central air inlet to
the plenum chamber

Figure 12: Conventional FBD with side-duct
plenum

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 13: Principle of reversible-air dryer
Page 113

Figure 14: SDG-4 (reversible, 4-ton/batch) dryer, shown with the coal furnace,
and the solar collector (a new development at NLU in early 2007)

5.4.3 Conclusions
The above facts and analysis point to a single major problem in drying at the four 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. 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. Thus this
CARD project is timely because it addresses this issue. It will take sometime before the
farmers and traders will realise that the quality is as important as quantity and the price of
the paddy will also be determined by both factors. This is also a matter of policy from the
relevant institutions to encourage the adoption of these practices through financial
measures, although 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
Page 114
established as demonstration sites in all the Provinces in Mekong Delta after successful
implementation of current project in three cooperatives in three provinces.
6 EXTENSION MATERIALS FOR TRAINING COURSES,
BASED ON THE OUTCOME OF THE SURVEY AND EXPERIMENTS
Based on the outcome of the survey and experiments (Section 3, 4, and 5) a hand-out for
training has been prepared in Vietnamese, which includes the following topics:
- Development of flat-bed dryers in the Mekong Delta in the past 25 years and
problems solved by mechanical dryers.
- The issue of the rice grain crack and the consequent post-harvest losses.
- Ways to avoid rice cracking with mechanical drying.
- Current research from CARD Project relating to rice crack.
- Preliminary results with the eight-ton-per-batch SRA-8 dryer (version 2006).
- Economic calculation for the SRA-8 dryer at Tan-Phat A Cooperative.
The hand-out was used for a training course held at Tan-Phat-A Cooperative in 25 and 26
February 2007, with about 50 participants including farmers, rice millers, and governmental
extension staff (Fig.15).

Figure 15: Training course on drying at Tan-Phat-A Cooperative, February 2007
Page 115
7 CONCLUSIONS AND FURTHER PROPOSALS

In the first year of the Project (actually within 10 months), the sub-component on the flat-bed
dryer has completed a number of activities:
- Installation and testing of an 8-ton reversible dryer in Kien-Giang Province.
- Installation of two 4-ton dryers for the Go-Gon Cooperative (instead of one 8-ton dryer).
One dryer equipped with the solar collector has already been installed by the time this
report is being submitted. This new collector was developed at Nong-Lam University in
2006 for macaroni, and also tested on the STR-1 with promising result (Fig.16). The
other 4 ton dryer is being installed.
- Installation of one 8-ton reversible dryer at Tan-Thoi Cooperative, Can-Tho City, which
is another selected by the CARD Project for experimentation and demonstration.
- Fabrication of the 1-ton mini-dryer for basic testing at Ba-Ria Vung-Tau near Nong-Lam
University
- Rapid survey on the current status on the use of flat-bed dryers in 4 Provinces.
- Writing of the hand-out for use as training materials, based on the outcome of the survey
and experiments.
-
During the coming second year of the Project, the following activities for the flat-bed dryer
Sub-Component is being implemented:
 To conduct more test and analyze the rice cracks in the dry and the wet season harvest, at
various actual dryers in the production.
 It is time now to be applied at production scale, especially during the dry season harvest.
Paddy crack in the dry-season harvest is even more severe, as people rely more on the
pavement natural sun drying to save the cost of fuel for drying.
 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, as analyzed in Section 5.4.3 and 5.4.4


Figure 16: Solar collector tested with STR-1 dryer in Moc Hoa (Long An), 2006
Page 116