2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 174 -
Abstract
-- The main purpose of this research was to
comparative study effect of drying with three different heat
sources on drying kinetics and qualities of medium-grain
parboiled rice (Leb Nok Pattani rice variety). Drying
temperature for all experiments was varied between 60 and
100
q
C. Power of infrared heat source was fixed at 1,000 and
1,500 W and inlet air flow rate of heat convection was fixed
at 1.0±0.2 m/s. The three drying composed of infrared (IR)
drying, hot air (HA) drying and combined HA+IR drying.
Before determination of mathematical thin-layer drying
model, the equilibrium moisture content was evaluated. The
experimental results were fitted in five conventional EMC
models and the results stated that the GAB’s model was the
best fitting to the experimental results. By non-linear
regression analysis, the thin-layer drying model following
the Fick’s diffusion law
was simulated. The results showed
that an effective diffusion coefficient of parboiled rice
drying was in ranges 0.67
u
10
-9
to 3.2
u
10
-9
m
2
/s. To
determine quality of dried parboiled rice samples with three
different heat sources, the conclusion stated that head rice
yield using HA+IR drying yielded a higher value than HA
and IR drying, respectively while yellowness and whiteness
of rice are significantly affected by drying temperature and
drying strategy. The yellowness value increases with
increase drying temperature. In contrast, the whiteness
decreases with increase drying temperature.
Index Terms
—
Parboiled rice, Rice qualities, Combined
HA+IR drying, Energy consumption.
I.
NOMENCLATURE
IR
Infrared radiation
HA
Hot air
HA+IR
Combined hot air
d.b.
Dry-basis
M
eq
or EMC
Equilibrium moisture content, decimal
RH
Relative humidity, %
T
Temperature,
q
C
A, B, C, k and M
m
Constants.
R
2
Correlation coefficient
RMSE
Root mean square error
D
eff
Effective diffusion coefficient
r
o
Radius of parboiled rice, 0.00141 x 10
-3
m
t
Drying time, min
HRY
Head rice yield, %
b*
Yellowness of parboiled rice
W
Whiteness of parboiled rice
GC
Gel consistency, mm
AS
Alkali spreading value
AMC
Amylose content, %
PC Protein content, %
LC Lipid content, %
SEC
Specific energy consumption, MJ/kg water
evaporated
M
in
Initial moisture content, % dry-basis
M
f
Final moisture content, % dry-basis
W
d
Dry weight, g
P
Total amount of energy consumed during drying
process, kW-h
X
predicted,i
and
X
observed,i
Predicted and experiment value,
respectively.
N
Number of data
GT
Gelatinization temperature,
q
C
II.I
NTRODUCTION
Rough rice or paddy that is subjected to hydrothermal
treatment prior to milling is defined as parboiled rice.
Traditional parboiling involves soaking in cold water,
steaming and drying [2]. Parboiling is practiced in many
parts of the world such as India, Bangladesh, Pakistan,
Myanmar, Malaysia, Sri Lanka, Guinea, South Africa,
Italy, Spain, Thailand, Switzerland, USA and France
[13]. Moreover, parboiled rice product in Thailand tends
to increase, especially in health food and green organic
products. The advantage of parboiled rice is because
during the parboiling process, grain changes its physical
properties as starch gelatinizes correlated to a high
milling yield. In addition, parboiled rice reduces nutrient
loss during milling and cooking [15, 20]. In Southern part
of Thailand, many rice varieties has a lot of loss among
post-harvesting period because its harvesting on rainy
season and high relative humidity environment [19]. To
get added value of product, the rice parboiling process is
interesting. Moreover, parboiling to minimize the loss is
important to improve product price. Leb Nok Pattani rice
variety, mild white belly, is widely produced in the south
of Thailand. A few works on local rice parboiling was
reported. Parboiling process consists of 3 steps which
were mentioned above and the drying was the most
Comparative Study between Hot Air and
Infrared Drying of Parboiled Rice:
Kinetics and Qualities Aspects
O. Bualuang
*
, S. Tirawanichkul
**
and Y. Tirawanichkul
***
*Faculty of Engineering, Prince of Songkla University,
(Thailand)
**Discipline of Excellent of Chemical Engineering,
Faculty of Engineering, Prince of Songkla University,
(Thailand)
***Energy Technology Resaecrh Center (ETRC), Faculty of Science,
Prince of Songkla University,
(Thailand)
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