2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 137 -
Energy Consumption Analysis of NR
Producing Skim Block Rubber
J. Tasara*, S. Tirawanichakul * and Y. Tirawanichakul **
*Department of Chemical Engineering, Faculty of Engineering, Prince of Songkla University, Songkhla 90112, (
Thailand
)
** Plasma and Energy Technology Research Laboratory, Department of Physics, Faculty of science,
Prince of Songkla University, Songkhla 90112, (
Thailand
)
*Authors to correspondence should be addressed via email:
Abstract
The objectives of this research were to investigate the
drying strategies on evolution of moisture transfer of skim
rubber and to study effect of drying strategies on physical
quality of skim rubber such as specific mass flow rate, inlet
drying temperature and percentage of air recirculation etc.
The mathematical near equilibrium drying model was
developed and used for prediction drying kinetics and
specific energy consumption. The experiments were carried
on in various drying strategies and comparative studied
with simulated results. The results showed that the
simulated result has good agreement with all experiment
results. Moreover, the simulated results using drying with
the percentage of recycled air ranging between 85 and 95
corresponding to the lowest specific energy consumption.
From the experimental results of quality determination, the
suitable drying strategy of skim block rubber was the two
stages drying which the 1
st
stage drying with 130
q
C and the
2
nd
stage drying with 110
q
C at operating periods of 40 and
140 min, respectively.
Keyword
:
Equilibrium moisture content / Fixed-bed drying /
Mathematical model / Skim block rubber
I.
NOMENCLATURE
MR
NR
SR
SEC
DR
RMSE
SEE
Y
exp
Y
cal
Y
exp
N
M
in
M
f
m
p
m
w
c
a
c
v
c
r
T
f
Moisture ratio
Natural rubber
Skim rubber
Specific energy consumption
Drying rate
Root mean square error
Standard error of estimate
Measured in the experiment
Calculated using the models
Mean of the measured in the experiment data
Number of data points
Initial and final moisture content (% dry-basis)
Final moisture content (% dry-basis)
Dry mass of product (kg of dry rubber)
Mass of water evaporated from rubber
(kg of water)
Specific heat capacity of dry air (kJ/kg-°C)
Specific heat capacity of water vapor
(kJ/kg-°C)
Specific heat capacity of wet rubber (kJ/kg-°C)
Air temperature of dry air (°C)
T
mix
T
r
W
mix
W
f
h
fg
M
eq
T
DT
RH
TDT
Air temperature of water vapor (°C)
Air temperature of wet rubber (°C)
Humidity ratio of dry air before drying
(kg of H
2
O/kg of dry air)
Humidity ratio of dry air after drying
(kg of H
2
O/kg of dry air)
Specific evaporated enthalpy (kJ/kg)
Equilibrium moisture content (% dry-basis)
Drying temperature (K)
Drying time (min)
Relative humidity
Total drying time (min)
II.INTRODUCTION
Thailand is the largest export of natural rubber in the
world. The type of natural rubber export are namely
produced in form of ribbed smoke sheet (RSS), air dried
sheet (ADS), concentrated latex (percentage of dry rubber
content (DRC) of 60-65%), block rubber with 6 Standard
Thai Rubber (STR) types. Presently the export of natural
rubber made from natural crumb rubber following various
STR grades and concentrated latex rapidly grow faster
than the other NR products. One of interesting by-product
of concentrated latex factory is skim rubber (SR) which is
normally defined as rubber scrap (sponge-liked)
extracting from latex waste water. It has low dry rubber
content (about 3-10%) and composes of small rubber
particles. Therefore, SR is a low grade rubber scrap and
mostly used as mixing matter with other natural rubber
(NR) (such as RSS3, USS3, STR5L, STR20, ADS, etc.)
The SR manufactures consist of several processes
such as cleaning, shredding, size reduction, drying and
packaging and all of processes have huge energy
consumption including to electrical energy and heat
energy. Electrical energy consumption is used for driven
blowers while diesel fuel or liquefied natural gas (LNG)
is used for heating up air during drying process. From the
previous works, over 80% of total energy consumption in
natural rubber producing STR factory is consumed at
drying process. Thus drying process should be evaluated
and make good decision for saving energy consumption
whilst high qualities product still be maintained. There
have been very few studies relating to SR drying and its
production process, thus the design of this drying system
