EXERGY ANALYSIS OF BOILER IN COGENERATION BAGASSE PLANT
Lakshmi Naga Swetha Yanamandra & Sethupathy Rethinasamy
Halmstad University, Sweden
loss from sugar handling, is one of the biomass build-ups utilized as fuel. It
would thus be able to be a valuable inexhaustible asset for vitality which
likewise guarantees to keep away from the natural discharges of energy age from
petroleum derivatives. The bagasse plant at Ratchasima Sugar Mill, Thailand is
considered for our project. The sugar process forms 30,000 tons of sugarcane
for each day. The power plant, joined to the sugar process, is of cogeneration
compose. The vitality and water adjust demonstrate that 272 tons of bagasse can
create 342 tons of steam at 420C utilized as a part of the sugar procedure and
around 25.5 MWh of power. Consequently, bagasse can be a naturally neighbourly
crude material for control age and has high potential as another, sustainable
source of energy. This work is mainly energy and exergy investigation of sugarcane
bagasse boilers. The technique depends on the standard and genuine responses
which permits the count of the enthalpies. The strategy is given utilizing a
case genuine information from a sugarcane bagasse plant.
Cogeneration plant, Boiler, Exergy, Energy, Bagasse
conventional energy resources and mounting pressure to reduce carbon emissions
together make the conservation of energy and the identification of new and/or
renewable energy sources the prime challenge for industry and the public at
large today. Resourceful usage of energy becomes more important in
our world where the fossil fuels are limited. Industrial
consumers of energy resources must implement energy saving techniques as a
means for achieving cost reductions and competitive advantage.
The cogeneration of power and steam (combined heat and
power – CHP) is a proven method of energy cycle optimization. The main process
industry segments that benefit from CHP are textiles, paper, food, district
heating and sugar production. The last decade witnessed a huge momentum in
sugar cogeneration, with many opting for CHP plants. The primary model
envisioned power as a by-product to sugar production and a shield against the
cyclical nature of sugar price between the production season and the off
The advantages obtained
by using cogeneration system are:
1. Due to usage of
electricity where it is generated, there is no loss of transfer and by
regaining the heat energy, the cost of energy is kept low.
2. Saving from the
primary fuel in proportion to regained heat energy, the limited sources are
used efficiently furthermore emission harm is reduced to minimum.
3. National electricity
generation is supported.
WHY BAGASSE USED IN POWER
Bagasse is the fibrous
material that comes after sugarcanes are crushed to extracting the juice for
sugar production process. This sugarcane juice is a product of the process of manufacturing sugar. The
bagasse can either be a sale or captively
consume for generating the steam as a fuel in a boiler. So literally, it’s a biofuel. Apart from power
generation, the sugarcane trash(Bagasse) used for manufacturing of pulp and
paper products. Every 10 tons of
sugarcane can give around 3 tons of natural bagasse (50% of wet). Bagasse is
the by-product of sugar production industry. Moreover, the main use of bagasse
is to avoid the use of fossil fuels like coal and gasoline and reduce the
carbon dioxide emissions from the stack. Globally, the bagasse has already begun
to use in the cogeneration power plant
which has boiler, steam, and turbine. So, the carbon dioxide emission will be achieved by the help of bagasse.
Over the years, as the sugar mills have tended towards
cogeneration, combustion technology has also advanced. Today supplementary
fuels are used along with bagasse, namely coal, biomass and biogas (a
by-product in an integrated sugar mill). Using a by-product – bagasse – as an
energy source and producing combined heat and power (CHP) to meet their sugar
mills’ demand makes immense sense for customers. In addition, surplus
electrical power from the cogeneration process can be exported to the state
1: Schematic diagram of a bagasse plant
EXERGY: It’s known that energy can’t be created nor
destroyed due to the first law of thermodynamics, only converted. In an
irreversible process, the quality of energy decreases according to the second
law of thermodynamics. This is described by the concept of entropy. If the
entropy increases in a system, then the quality of the energy decreases. Exergy
(E) is defined as the maximum theoretical work (W) that can be extracted from a
system, meaning that entropy and exergy pretty much explain the same thing.
Based on the information
accessible for the Ratchazima Sugar Factory in Nakorn Ratchazima, Thailand, the
plant limit is 30,000 tons of sugarcane every day consistently amid the crushing
season. The power plant is cogeneration sort with 2 water-tube boilers and 2 steam
Demineralized water is
used in the boilers at start-up operation and condensate water from sugar
processes is reused from there on. Steam created in the boilers is used in the
sugar processes and steam turbines. This control plant by and large operates at
24 MW, using 16 MW for the sugar production line and power plant.
For the project work we
have taken single boiler for analysis.
Schematic representation for Boiler
are classified as a high-pressure boiler
(or) low pressure and steam-boiler (or) hot water boiler. The high-pressure boiler can operate higher than 160psig.
High-temperature hot water boiler has a minimum temperature of above 120
celsius or pressure minimum of 160psig.
Low-temperature hot water boiler has not greater than 120
Celsius or pressure higher than 160psig. The casting of the boiler is usually
iron, bronze (or) brass during their construction. Those that are insulated
uses of steel, brass, and copper with steel is the most common material.
The following definitions
are acknowledged for analysis calculations of the cogeneration system:
• Equipment are systems
having continuous flow.
• Boiler, pipes and components of other
installations are considered with heat losses.
• The fuel enters boiler
under environmental conditions.
• Reference state T0 = 298 K and P0 = 1 bar
Feed water= 637t/h @ 108oc
Flue gas=833981.1m3/hr @141.5oc
analysis of Boiler:
Energy balance: EW+Eb=Eflue+Esteam+Eash+Eloss
of Feed water:
h= 452.84 KJ/Kg
? (feed water) = 637 t/h
Calorific value= 1750
Kcal/Kg= 7.32 GJ/ton
?(steam)= 605 t/h
of flue gas:
?(flue)= 833981.1 m3/hr
flue gas temp= 141.5°c
Mean gas specific heat=
of flue gas = 133.10 GJ/hr
2% of total heat=
6.7% of total heat=
analysis of Boiler:
Analysis of bagasse
composition of Ratchasima Sugar Factory:
(?) = 7.5
Chemical exergy of
Exch= = 2377.53Kcal/Kg
h,c,o,s are the mass
fractions of hydrogen, carbon, oxygen and sulphur respectively.
Molar mass of bagasse=
Po= 1 bar
of feed water:
of flue gas:
Composition of Flue gas
in the stack:
(?) = 9172.54
emission from the boiler is not considered, it doesn’t contribute global
Considering each case,
of NO2= 0.62KJ/s
exNO2+ exCO= 698.50KJ/s
of flue gas @141.5oc
Chemical analysis of the
sugarcane bagasse ash:
into molar fraction:
Exergy of SiO2=7.9*0.0194=0.1532*103KJ/s
Total molar mass of ash=?=25.06mol/s
Total chemical exergy of ash=exch=633.98KJ/s
Exergy of ash=Ex,ash=?*exch=15887.56.
E/Q of steam=( =0.11
E/Q of water=
Substituting the values obtained,
Exergy of boiler= 21%
In this study, exergy analysis is done by
taking the values of measurements of a cogeneration system located in Thailand
into consideration. In the table below,
the energy and exergy accordingly are given.
Considering different temperatures
exergy and energy efficiencies are determined and calculated on the data basis
of a sugarcane cogeneration plant in Thailand.Analysis of calculations shows
values of exergetic efficiency essentially less then corresponding energetic efficiency.
Calculated value of energy is 84%, at the same time value of exergy is equal to
21%. That shows quite low degree of thermal energy potential use in given
technological scheme and working conditions.
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