A
BSTRACT
The use of a rice husk gasifier as a cook stove is
limited to the domestic sector of developing countries
primarily because it needs electrical energy to drive a
blower for the gasification process. To solve this
problem, we investigated the feasibility of attaching
commercial thermoelectric (TE) modules made of
bismuth–telluride materials to the gasifier’s side wall,
thereby creating a TE generator system that utilizes a
proportion of the gasifier’s waste heat. A rice husk
gasifier TE generator (TE-RSG) having an internal
diameter of 16 cm was fabricated and tested. The TE
generator system consisted of two commercial TE
modules, a metal sheet wall which acted as one side of
the gasifier’s structure and served as the hot side of the
TE modules and a rectangular fin heat sink at the cold
side of the TE modules. A blower was used to suck the
ambient air to cool the heat sink and blow the air from the
heat sink to the reactor of the gasifier. Gasification was
conducted in a temperature range of 500-700
C and
gasification agent, air feeding rate of 18.6 m
3
/h. The
results revealed that the electrical power output and the
conversion efficiency depend on the temperature
difference between the cold and hot sides of the TE
modules. At the temperature difference of approximately
60
C, the unit achieved a power output of 3.9 W and a
conversion efficiency of 2.01%. Through a comparison of
results between the theoretic model and the experimental
system, the reasonability of this system model has been
verified.
Keywords: Conversion efficiency, Thermal efficiency
Reactor
I
NTRODUCTION
The demand for renewable sources of energy is
increasing due to an elevated concern about global
warming, climate change and the decline of fossil fuel
reserves. Compared with other renewable energy
resources, biomass is huge. Its annual production rate is
high and it is geographically widespread throughout the
world. In general, paddy, or rice, is one of the earths’
most prolific crops. Rice husk is a residue from rice
farming and is considered an agricultural waste. In
Thailand, where the average gross rice production is
approximately 32.09 Mtons/yr., 6 Mtons of rice husk is
produced and around 600 thousand tons of ash is
generated by burning the rice husk [1]. Currently, rice
husk is widely used in stall mats, compost and fillers.
However, due to increasing demands for utilization of
waste-to-energy, many researches are actively involved in
researching ways to use rice husk as a fuel.
Approximately 2.4 billion people depend on wood, dung,
charcoal and other biomass fuels for cooking. Most of
these people cook on open fires that burn poorly leading
to low thermal efficiency and high pollution emissions.
The current patterns of use cause significant negative
impact of several types, including human morbidity and
mortality, outdoor air pollution, climate change and
deforestation. One interesting alternative to these
inefficient cooking methods is a rice husk gasifier; it is
more efficient than biomass cook stoves [2]. However,
electrical power is needed to drive a blower that is part of
the rice husk gasifier system. Individual thermoelectric
(TE) power generators coupled with rice husk gasifier
offer an interesting option to provide electricity. In past
years, TE generators have been coupled with biomass
stoves. As the examples, Nuwayhid et al. [3] considered
the prospect of applying TE modules located on a wood
stove-top to produce power. That system is well known
and could be useful in regions with unreliable electricity
supply. The stove-top TE system produces a maximum
power output of 2.7 W per module. A heat sink composed
of a thermosyphonic heat pipe has been adapted to further
improve the power output of a TE module [4]. These
developments revealed that a commercially available TE
module could provide over 3 W of power with a
temperature difference between the hot and cold side of
the TE module of 70-80
C. Experiments have also been
conducted on the side-walls of cook stove. Stove wall
temperatures are likely to be in the range of 150-300
C.
Lertsatitthanakorn [5] investigated a combined biomass
cook stove thermoelectric (BITE) generator. The results
of that investigation showed that the BITE produces a
maximum power output of 2.4 W at a temperature
difference of 150
C. The conversion efficiency of 3.2%
was enough to drive a low power incandescent light bulb
or a small portable radio. Meanwhile, the payback period
of the BITE is 0.74 years if compared with batteries
supplying power to a 1.8 W load with an annual operating
time of 365 hours. Champier et al. [6] studied a TE
generator incorporated in a multifunction wood stove to
produce electrical power from the exhaust gas of the
wood stove. One-dimensional heat flow was used to
predict the system’s performance. The TE module
produced maximum power output of 9.5 W. An economic
analysis showed that the price of TE modules varied with
order volume. By comparison between the cost per watt
Study of Combined Rice Husk Gasifier Thermoelectric
Generator
C. Lertsatitthanakorn
1
, J. Jamradloedluk
1
, and M. Rungsiyopas
2
1
Thermal Processes Research Laboratory, Faculty of Engineering, Mahasarakham University, Khantarawichai,
Mahasarakham 44150 (
Thailand
)
2
Mechanical Engineering Department, Faculty of Engineering, Burapha University, 169 Long-Hard Bangsaen Road,
Saensuk, Muang, Chonburi, 20131 (
Thailand
)
2013 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 896 -
