6-024 (O) The Joint International Conference on “Sustainable Energy and Environment (SEE)”
1-3 December 2004, Hua Hin, Thailand
Environmental Profile of Power Generation from Rice Husk in Thailand
1
1,*
2
1 The Joint Graduate School of Energy and Environment , King Mongkut’s University of Technology Thonburi,, Bangkok, Thailand
2 Department of Mechanical Engineering, King Mongkut’s Institute of Technology North Bangkok, Bangkok 10800, Thailand
Abstract : The use of fossil fuels causes environmental and energy security problems. Renewable energy is being looked at as an alternative for Thailand. Biomass from agriculture, especially rice husk, is a very promising renewable energy source since it is indigenous and is considered to have environmental benefits. However, the environmental profile of the electricity production from biomass must be assessed to ensure reduced environmental damage. This article considers the environmental evaluation of a 10 MW pilot plant using rice husk as feedstock. The environmental impacts from rice husk energy power plant are evaluated using the Life
Cycle Assessment (LCA) methodology. Energy, material and carbon balances have been determined for tracing the system flow. Most impact potentials from rice husk energy are lesser than fossil fuels plants; except the photo-oxidant formation potential from CO. The performance of rice husk power plants can be enhanced by improving the combustion efficiency.
Keywords: Fossil Fuel, Environmental Impact, Renewable Energy, Rice Husk, Life Cycle Assessment (LCA).
Thailand’s energy supply comes mostly from consumption of fossil fuels, a large percentage of which are imported from other countries causing concern for energy security. In addition, fossil fuels combustion is associated with emissions of CO
2
, SO
2
and NO
X
leading to environmental impacts. The proposed solution for these problems is using renewable energy sources instead of conventional (fossil) energy sources
[1, 2]. In addition, the Energy Conservation Promotion Fund committee (ENCON Fund) authorized the Energy Policy and
Planning Office (EPPO) to subsidize Small Power Producers
(SPP) producing biomass energy [3]. This paper is focused on rice husk power plant because rice husk is the one major energy sources from the agro-industrial sector. Rice husk is considered to be an environmentally friendly fuel because it can mitigate CO
2
, SO
X
and NO
X
emissions when compared with conventional energy [4]. However, the emissions have not been assessed in quantitative way in Thailand. To answer that, LCA has been used to evaluate the environmental profile of energy production from rice husk.
Rice is grown in every region of Thailand. The by-product of the milling process is rice husk, which accounts for 20% by weight of the rice. A large amount of rice husk is dumped as waste that brings waste disposal problem and methane emissions. Moreover, rice husk can cause breathing problem due to its characteristics. To maximize advantage of the waste and also to reduce the problems, some of rice husk is used as additive in cement industries [5], fertilization [6] in fields and chicken incubation [7]. These ways are not enough to significantly reduce the disposal problem. The alternative way that has been proposed is to utilize rice husk for energy.
Rice husk can be converted to a useful form of energy to meet the thermal and mechanical energy requirement for the mills themselves.
The Northeastern region is particularly important as one of the major rice growing belts of the country [2]. Due to the environmental and economic scenarios, the Thai government has supported renewable energy production from indigenous sources. One project that has been conducted under this support is the Roi-Et Green Project in Roi-Et province, using
Corresponding author: shabbir_g@jgsee.kmutt.ac.th
rice husk as feedstock.
Approximately 255 tons of rice husk supplied from Sommai rice mill, 138 tons of Shi river water and 24 MWh of electricity are required for power production in one day. The maximum power production capacity is 10.2 MW and the minimum is 6.5 MW, depending on raw materials load. The surplus electricity will be sold to EGAT for the commitment under SPP scheme for 21 years. Raw water is pretreated by demineralization before feed to boiler and cooling tower.
Waste water comes from boiler blow down (flash tank) and cooling tower blow down, and then sent to treatment. Waste water treatment including pH balance, coagulation and demineralization. Solid wastes are sludge from waste water treatment, bottom ash and fly ash.
LCA methodology is divided into 4 phases: Goal definition and scoping, Inventory analysis, Impact assessment and
Interpretation [8].
4.1 Goal Definition and Scoping
Goal Definition and Scoping is the first phase of LCA, which is used for defining the objectives of the study and the system boundaries for providing environmental information
[8]. The goal for this study is to collect environmental data on the electricity production from rice husk at a 10 MW power plant in Thailand based on the entire life cycle. Energy and material balances will be conducted to evaluate the efficiency of power production. Data on emissions will yield the environmental impacts potentials .
Since rice husk is considered as a waste of the rice production, the system boundary includes only energy generation. Transportation, construction, and emissions in water as also emissions from rice cultivation and production are not included in the boundary. Functional unit for this study is 1 MWh of electricity. All resources, materials and energy consumed and potential environmental impacts will be identified.
4.2 Inventory Analysis
Inventory Analysis is the identification and quantification of energy, water and materials usage and environmental releases.
The step starts from list of inventories, data collection then calculation of material and energy balances, carbon balance and, data analysis.
According to the conservation law, matter and energy can not be created or destroyed [9]. Hence, material/energy inputs must be equal to material/energy outputs. The balances are

6-024 (O) The Joint International Conference on “Sustainable Energy and Environment (SEE)”
1-3 December 2004, Hua Hin, Thailand presented in Figs 1 and 2, which have been calculated and listed from material flow and energy flow [10].
M
WE
: 0.53 t/h
M
A
: 70.97 t/h
59,495.67 m 3 /h, 31.8
° C
M
RH
: 10.63 t/h
Power plant
M
FG
: 76.14 t/h
81,523.60 m 3 /h, 160 ° C
M
FA
: 1.56 t/h, M
BA
: 0.32 t/h
M
RW
: 5.84 t/h M
WD
: 5.27 t/h
Fig. 1 Material balance of rice husk energy production.
E
WE
: 79.16 GJ/h
E
R&Ub
: 11.32 GJ/h
E
RH
: 146.40 GJ/h
E
ST
: 0.39 GJ/h
Power plant
E
FG
: 10.77 GJ/h
E
FA
: 0.82 GJ/h, E
BA
: 0.23 GJ/h
E
Elec
: 34.2 GJ/h
E
WD
: 0.64 GJ/h
Fig. 2 Energy balance of rice husk energy production.
The calculation of material balance is represented by Eq. (1) and Eq. (2), and energy balance is Eq. (3).
M
RH
+ M
A
= M
FA
+ M
BA
M
RW
= M
WE
+ M
WD
,
+ M
FG
, (1)
(2)
E
RH
= E
FA
+ E
+ E
Elec
Where,
BA
+ E
FG
+ E
WE
+ E
WD
+ E
R&Ub
+ E
ST
(3)
M
RH
= Mass flow rate of rice husk
M
A
= Mass flow rate of air inlet
M
FA
M
BA
M
RW
= Mass flow rate of fly ash
= Mass flow rate of bottom ash
= Mass flow rate of raw water
M
WE
M
WD
E
RH
E
FA
E
BA
E
FG
E
WE
= Mass flow rate of water evaporation
= Mass flow rate of water discharge
= Energy in rice husk
Energy fly in ash ash
= Energy in flue gas
= Energy in water evaporation
E
WD
E
R&Ub
E
ST
E
Elec
Energy water
= Radiation and unaccounted loss at boiler
= Loss at steam turbine
Electricity
The difference in material input and output works out to
3.58 t/h, which is about 4.4 % of the total material input. This may be due to averaging of measurement. The difference in water and steam input and output is 0.04 ton/hr or 0.68%.
From Fig. 2, the difference in input and output energy is about
6.06 % which may be due to loss in pipes and tubes.
The principle of balance is applied to material/energy flow analysis in LCA for checking the consistency of the collected data. The balances are necessary to understand the whole process of energy production. Also, the quantification of material and energy flows indicates where the difference between inputs and outputs is exchanged to the environmental as emissions and losses.
Fig. 3 Sankey diagram of rice husk energy production.
A useful way of charting energy flow is to use a Sankey diagram. Fig. 3 is the Sankey diagram of rice husk energy production, which can be used for describing the losses at every sub process of rice husk energy production. Heat input is the energy from rice husk which is defined as 100%. The recycled energy is the energy content in air inlet and feed water, which was heated by the flue gas. At the steam turbine, there is loss during conversion of thermal energy to mechanical energy and mechanical energy to electricity along with the waste heat during condensation amounting to 54 %.
The total loss of 22.57 % shown in Fig. 3 includes heat loss in flue gas, fly ash, bottom ash, radiation loss, water blow down discharge loss, loss at steam turbine , and in pipes and tubes.
The energy in the form of electricity is about 23 % of the total energy input.
4.3 Carbon Balance
The proximate and ultimate analysis of rice husk from the study site is shown in Table 1. The data show that the main components of rice husk are carbon and oxygen, and there is little nitrogen and sulphur content. In the Table 2, the stack emissions data have been presented. The main emission is
CO
2
, while CO, SO
2
and NO
2
are very low. The carbon balance for the study is shown in Fig. 4 and Eq. (4).
C
RH
= C
FG where,
+ C
FA
+ C
BA
, (4)
C
RH
C
FG
= Carbon in rice husk
= CO
C
FA
C
BA
2
and CO in the flue gas
= Carbon in fly ash
= Carbon in bottom ash

6-024 (O) The Joint International Conference on “Sustainable Energy and Environment (SEE)”
1-3 December 2004, Hua Hin, Thailand
C
RH
: 4,483.96 kg-C/h
Power
Plant
C
FG
: 4,403.30 kg-C/h,
C
FA
: 20.28 kg-C/h
C
BA
: 6.56 kg-C/h
Fig. 4 Carbon balance for the combustion of rice husk.
The difference between input and output is 53.82 kg-C or
1.2% of carbon input. This difference is very small and may be due to minor variations in rice husk characteristics and averaging of measurements.
Table 1 Components analysis of rice husk sample
[8]:
EP ( j ) i
=
i
Q i
×
Where EP(j) i
is the emission’s potential contribution to the environmental impact category (j), Q is the magnitude of i emission of substance (i) and EF(j) is the substance’s equivalency factor for the environmental impact category (j).
Table 3 Environmental impact potentials from rice husk and fossil fuels power production
Impact category
EP
Global warming
(kg CO
2
-eq/MWh)
Acidification
(kg SO
2
-eq/MWh)
( j ) i
(5)
Rice husk [10] Fossil fuels**
17.27 734.41
0.92 2.34
Parameter Result Unit Basis
C 42.2
a % dry
Photo-oxidant formation
(kg C
2
H
4
-eq/MWh)
0.34 0.01
H 5 a
O 36 a
% dry Nutrient enrichment
(kg N-eq/MWh)
0.39 0.73
% dry
N 0.7
a % dry
a: Result from laboratory test.
b: Result from reference [10].
*: Below detection limit of instrument (0.01 %)
Table 2 Emission data from the study site [10]
Solid waste
(kg ash/MWh)
198.21 n.a.
S *
Total moisture
Ash content
Heating value
Volatile matter
Fixed carbon
CO
2
NO
2
13 a
16.10
a
13,778.5
a
59.87
b
18.56
b
% dry
% dry kJ/kg dry
% dry
% dry
** Combined value of 76.42 % natural gas, 23.56 % coal
and 0.02% oil [11].
n.a. Not available.
Table 3 shows the comparison of environmental impact potentials of rice husk power plant and Thailand’s fossil fuels power plants [11]. Thailand’s fossil fuels power plants are a combination of natural gas plants (76.42 %), coal plants
(23.56 %) and oil plants (0.02 %).
4.5 Interpretation
The results from inventory analysis indicate that material and energy balance is consistent. The difference of inputs and outputs in the material balance is of about 4.4 % may occur from unsteady state of the production. The water and steam flow in the plant is balanced. The raw water input is reservoir water from the Shi river. The water and steam outputs are evaporated water from cooling tower and blow down water discharge.
The energy balance scheme and Sankey diagram can indicate the overall efficiency of this plant, which is about
SO
2
16
23 %. They can also be used for improvement of the power plant efficiency, by identifying the source and amount of
TSP
Fly ash
12.7 ppm
1,560 kg/h
1.03
1,560 losses. The maximum heat loss occurs during water condensation and conversion of steam turbine and generator.
Bottom ash 323 kg/h 323
The impact assessment results show that the impact of global warming potential of rice husk energy is far less than
The value of SO
X
is not measured because the sulphur content in rice husk is very small.
4.4 Impact Assessment
Based on the emissions data in Table 2 and priorities in
Thailand, the environmental impact categories selected for this study are global warming, acidification, photo-oxidant formation, nutrient enrichment and solid waste.
To assess the environmental impact potential by LCA fossil fuels plants because CO
2
from biomass is considered as greenhouse gas neutral. Sulphur and nitrogen contents in rice husk are small. In addition, the combustion temperature of rice husk is lower than 900 ˚ C, preventing the formation of thermal
NO
X
. Hence, acidification and nutrification potential of rice husk energy are lesser than fossil fuels plants even though fossil fuels plants have NO
X alled.
and SO
X
removal equipment inst
Photo-oxidant formation is from CO emissions of rice husk which are higher than fossil fuels plants. This may be due to methodology all emissions have to be calculated by Eq. (5) the low combustion efficiency of the rice husk power plant and moisture content in rice husk.

6-024 (O) The Joint International Conference on “Sustainable Energy and Environment (SEE)”
1-3 December 2004, Hua Hin, Thailand
For solid waste potential only the data from rice husk power plant is available. Hence the comparison can not be made. The results present that most environmental impacts potentials from rice husk are lesser than the fossil fuels plants.
The objective of this study is to investigate the material/ energy balances and impact assessment of power generation from rice husk in a life cycle perspective.
The comparison of impact potentials between study site and
Thailand’s fossil fuels plants shows that the most impact potentials from rice husk are lesser. Only the photo-oxidant formation potential is higher due to high CO emission. That may result from low combustion efficiency and moisture content in rice husk itself.
The conversion technology should be improved to reduce energy loss and CO emission and increase electricity production. The waste heat at condenser may be utilized for drying rice husk before combustion, which could improve combustion efficiency as well as reduce wastage of energy.
This would improve the overall efficiency of the rice husk power plant, and also its environmental profile.
The authors gratefully acknowledge the contribution of the
Energy for Environmental Foundation for information about
Roi-Et Green power plant, and also the Joint Graduate School of Energy and Environment for providing the grant for this study.
[1] Wibulswas, P. and Chungpaibulpatana, S. (1996)
Development of alternative sources of energy,
Proceedings of GMS 2000 . Chiang Mai, Thailand.
[2] National Energy Policy Office (2001) Thailand Biomass
- Based Power Generation and Cogeneration Within
Small Rural Industrie: Final Reprt.
Bangkok, Thailand.
[3] Sajjakulnukit, B., Manneekhao, V., and Pongnarintasut, V.
(2002) Policy analysis to identify the barriers to the development of bioenergy in Thailand, Energy for
Sustainable Development , 4 , 3, pp. 21-30.
[4] Gonzales, A.D. and Mathias, A.J. Demonstration and market implementation of bio-energy for heat and electricity in Southeast Asia: Financing Issues and CDM potential , http://www.cogen3.net/doc/articles/DemonstrationMarketI mplementBio-Energy.pdf, 18 October, 2004.
[5] Ajiwe, V.I.E., Okeke, C.A. and Akigwe, F.C., (2000)
A preliminary study of manufacture of cement from
rice husk, Bioresource Technology , 73 , pp. 37-39.
[6] Hui-lian, X.
(2001) Effects of a Microbial Inoculant and
Organic Fertilizers on the Growth, Photosynthesis and
Yield of Sweet Corn, Nature Farming and Microbial
Application , 3 , 1, pp. 183-214.
[7] Roy, B.C., Ranvig, H., Chowdhury, S.D., Rashid,
M.M.and Faruque, M.R. (2004) Production of day-old chicks from crossbred chicken eggs by broody hens, rice husk incubator and electric incubator, and their rearing up to 6 weeks, Livestock Research for Rural
Development , 16 , 3, ISSN 0121-3784.
[8] Wenzel, W., Hauschild, M. and Alting, L
(1997) Environmental Assessment of Products , 1 ,
Kluwer Academic, London, England.
[9] Pirunkaset, M. (2000) Thermodynamics 2 Handbook ,
Se-education, Bangkok, Thailand (in Thai).
[10]EGCO Green Co. Ltd., (2002) Information and Operation
Report , Roi-Et, Thailand.
[11]Lohsomboon, P. and Jirajariyavech, A. (2001) Final
Report for the Project on Life Cycle Assessment , Business and Environmental Program, Thailand Environment
Institute, Thailand.