EXERGYANALYSIS OF BOILER IN COGENERATION BAGASSE PLANTLakshmiNaga Swetha Yanamandra & Sethupathy RethinasamyHalmstadUniversity, Sweden ABSTRACTBagasse,the 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 whichlikewise guarantees to keep away from the natural discharges of energy age frompetroleum derivatives. The bagasse plant at Ratchasima Sugar Mill, Thailand isconsidered for our project. The sugar process forms 30,000 tons of sugarcanefor each day. The power plant, joined to the sugar process, is of cogenerationcompose. The vitality and water adjust demonstrate that 272 tons of bagasse cancreate 342 tons of steam at 420C utilized as a part of the sugar procedure andaround 25.
5 MWh of power. Consequently, bagasse can be a naturally neighbourlycrude material for control age and has high potential as another, sustainablesource of energy. This work is mainly energy and exergy investigation of sugarcanebagasse boilers. The technique depends on the standard and genuine responseswhich permits the count of the enthalpies. The strategy is given utilizing acase genuine information from a sugarcane bagasse plant.Keywords:Cogeneration plant, Boiler, Exergy, Energy, Bagasse INTRODUCTIONExhaustingconventional energy resources and mounting pressure to reduce carbon emissionstogether make the conservation of energy and the identification of new and/orrenewable energy sources the prime challenge for industry and the public atlarge today.
Resourceful usage of energy becomes more important in our worldwhere the fossil fuels are limited. Industrial consumers of energy resourcesmust implement energy saving techniques as a means for achieving cost reductionsand competitive advantage.Co-generation is the concept ofproducing two forms of energy from one fuel. One of the forms of energy mustalways be heat and the other may be electrical or mechanical energy. In aconventional power plant, fuel is burnt in a boiler to generate high-pressuresteam which is used to drive a turbine, which in turn drives an alternatorthrough a steam turbine to produce electrical power. The exhaust steam isgenerally condensed to water which goes back to the boiler. As the low-pressuresteam has a large quantum of heat which is lost in the process of condensing,the efficiency of conventional power plants is only around 35%.
In acogeneration plant, very high efficiency levels, in the range of 75%–90%, canbe reached. This is so, because the low-pressure exhaust steam coming out ofthe turbine is not condensed, but used for heating purposes in factories orhouses. The cogeneration of power and The primary model envisioned power as aby-product to sugar production and a shield against the cyclical nature ofsugar price between the production season and the off season.Theadvantages obtained by using cogeneration system are: 1.Due to usage of electricity where it is generated, there is no loss of transferand 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 limitedsources are used efficiently furthermore emission harm is reduced tominimum. 3.National electricity generation is supported.
WHYBAGASSE USED IN POWER GENERATION PLANT?Bagasseis the fibrous material that comes after sugarcanes are crushed to extractingthe juice for sugar production process. This sugarcane juice is a product of the process of manufacturing sugar. Thebagasse can either be a sale or captivelyconsume for generating the steam as a fuel in a boiler. So literally, it’s a biofuel. Apart from powergeneration, the sugarcane trash(Bagasse) used for manufacturing of pulp andpaper products. Every 10 tons ofsugarcane can give around 3 tons of natural bagasse (50% of wet). Bagasse isthe by-product of sugar production industry. Moreover, the main use of bagasseis to avoid the use of fossil fuels like coal and gasoline and reduce thecarbon dioxide emissions from the stack.
Globally, the bagasse has already begunto use in the cogeneration power plantwhich 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 havetended towards cogeneration, combustion technology has also advanced. Todaysupplementary fuels are used along with bagasse, namely coal, biomass andbiogas (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 theirsugar mills’ demand makes immense sense for customers. In addition, surpluselectrical power from the cogeneration process can be exported to the stategrid.
Fig 1: Schematic diagramof a bagasse plant EXERGY: It’s known that energy can’t be created nordestroyed due to the first law of thermodynamics, only converted. In anirreversible process, the quality of energy decreases according to the secondlaw of thermodynamics. This is described by the concept of entropy. If theentropy 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 asystem, meaning that entropy and exergy pretty much explain the same thing.SYSTEM DESCRIPTION:Basedon the information accessible for the Ratchazima Sugar Factory in NakornRatchazima, Thailand, the plant limit is 30,000 tons of sugarcane every dayconsistently amid the crushing season. The power plant is cogeneration sortwith 2 water-tube boilers and 2 steam turbines.
Demineralizedwater is used in the boilers at start-up operation and condensate water fromsugar processes is reused from there on. Steam created in the boilers is usedin the sugar processes and steam turbines. This control plant by and largeoperates at 24 MW, using 16 MW for the sugar production line and power plant. Forthe project work we have taken single boiler for analysis. Flue gas Feed water Steam Steam Bagasse Ash Fig: Schematicrepresentation for Boiler BOILER: TYPES: I.
Fire-tube boiler II. Water-tube boilerBoilers are classified asa high-pressure boiler (or) low pressureand steam-boiler (or) hot water boiler. The high-pressureboiler can operate higher than 160psig. High-temperature hot water boiler has aminimum temperature of above 120 celsius or pressure minimum of 160psig.Low-temperaturehot water boiler has not greater than 120 Celsius or pressure higher than160psig. The casting of the boiler is usually iron, bronze (or) brass duringtheir construction. Those that are insulated uses of steel, brass, and copperwith steel is the most common material.
Thefollowing definitions are acknowledged for analysis calculations of thecogeneration system: •Equipment are systems having continuous flow. • Boiler, pipes and components of otherinstallations are considered with heat losses. •The fuel enters boiler under environmental conditions. • Reference state T0 = 298 K and P0 = 1 bar• Feedwater= 637t/h @ 108oc• Bagasse=272t/h• Steam=605t/[email protected]• Fluegas=833981.
1m3/hr @141.5oc• Ash=39.82GJ/hrEnergy analysis ofBoiler:Energybalance: EW+Eb=Eflue+Esteam+Eash+ElossEnergy of Feedwater: h=452.84 KJ/Kg?(feed water) = 637 t/hEw=h*?= 288.45 GJ/hrEnergy forbagasse:Calorificvalue= 1750 Kcal/Kg= 7.32 GJ/ton?(bagasse)=272t/hEb=1991.04GJ/hrEnergy of steam:h=3.
26GJ/t?(steam)=605 t/hEsteam=1972.3GJ/hrEnergy of fluegas:?(flue)=833981.1 m3/hrfluegas temp= 141.
5°cMeangas specific heat= 0.00137 J/m3°cEnergy of flue gas= 133.10 GJ/hrEnergy of Ash:2%of total heat= 39.82GJ/hrEnergyloss:6.7%of total heat= 134.29 GJ/hrEnergy Efficiencycalculation: Exergy analysis ofBoiler:Exergy of Bagasse:Analysisof bagasse composition of Ratchasima Sugar Factory: COMPONENT WEIGHT VALUE (%) MASS FLOWRATE (Kg/s) MOLAR MASS (Kmol/s) Carbon 41.
54 28.4 2.36 Hydrogen 5.40 3.69 3.
66 Oxygen 33.14 22.7 1.42 Nitrogen 1.83 1.23 0.
088 Sulphur 1 0.685 0.021 Total (?) = 7.5 Ex,fuel= Chemicalexergy of fuel: Exch== 2377.
53Kcal/Kgh,c,o,sare the mass fractions of hydrogen, carbon, oxygen and sulphur respectively. Molarmass of bagasse= 7.5 Kmol/sReferencetemperature and pressure:To=25oc= 298kPo=1 barho=104.89KJ/kgSo=0.
3674KJ/kg.kExergy of feed water:T=108och=452.89s=1.3964?=160.52kg/sEx,feedwater=?(h-ho-To(s-so))= 6639.10KJ/sExergy of steam:T=420och=3263.73KJ/Kgs=6.864KJ/Kg.
k?=152.45kg/sEx,steam=?(h-ho-To(s-s0))=186426.97KJ/sExergy of flue gas:Ex,fluegas=?(h-ho-To(S-So)+exch) Compositionof Flue gas in the stack: PARAMETER FLOW RATE (Kg/s) MOLAR MASS (Mol/hr) SO2 0.22 3.43 NO2 1.
86 40.4 CO 255.7 9128.71 Total (?) = 9172.54 *co2emission from the boiler is not considered, it doesn’t contribute globalwarming.
Consideringeach case,1) SO2:SO2=0.22Kg/hMolar mass=64.0628kg/kmolExergy of SO2=0.298KJ/s 2) NO2:NO2= 1.86kg/hMolar mass= 46.
0055kg/kmolExergy of NO2=0.62KJ/s 3) CO:CO=255.7kg/hMolar mass=28.0105kg/kmolExergy of CO=697.58KJ/s Exch=exSO2+exNO2+ exCO= 698.
50KJ/s Exergy of flue [email protected]= 141.5och=2735.81KJ/kgs=6.916KJ/Kg.
kEx,flue gas=?(h-ho-To(S-So)+exch)=3513.72 Ash:Chemicalanalysis of the sugarcane bagasse ash: COMPONENT WEIGHT VALUE (%) MASS FLOWRATE (Kg/s) SiO2 85.5 1.17 Al2O3 2.
29 0.03 Fe2O3 1.21 0.016 TiO2 0.20 0.00274 CaO 4.05 0.0554 P2O5 3.
01 0.041 SO3 2.28 0.031 K2O 1.33 0.018 MnO 0.8 0.010 Convert into molarfraction: 1) SiO2=1.
17kg/sMolarmass=60.085kg/kmolExergyof SiO2=7.9*0.0194=0.1532*103KJ/s 2) Al2O3=0.03/101.
65KJ/s4) TiO2=2.74*10-3/79.90=0.731KJ/s5) Cao=0.0554/56.08=0.
1087*103KJ/s6) P2O5=0.041/283.8=0.1188103KJ/s7) SO3=0.031/80.06=0.0964103KJ/s8) K2O=0.
018/94.20=0.0789103KJ/s9) MnO=0.010/70.93=0.0167103KJ/s Totalmolar mass of ash=?=25.
06mol/s Totalchemical exergy of ash=exch=633.98KJ/s Exergyof ash=Ex,ash=?*exch=15887.56. ExergyEfficiency: Where,To=25oc=298k E/Qof steam=( =0.11 E/Qof water= Substitutingthe values obtained, Exergyof boiler= 21% Exergydestruction: RESULTS AND DISCUSSION:Inthis study, exergy analysis is done by taking the values of measurements of acogeneration system located in Thailand into consideration. In the table below, the energy and exergyaccordingly are given.
Parameter Energy Exergy Feed water 288.45 6639.10 Bagasse 1991.04 17947.97 Steam 1972.3 186426.
97 Flue gas 133.10 3513.72 Ash 39.
86 15887.56 Efficiency 84% 21% Consideringdifferent temperatures ExergyEfficiency:When To=25oc, To=20oc, To=15oc, To=10oc, CONCLUSION:An exergy and energyefficiencies are determined and calculated on the data basis of a sugarcanecogeneration plant in Thailand.Analysis of calculations shows values ofexergetic efficiency essentially less then corresponding energetic efficiency.Calculated value of energy is 84%, at the same time value of exergy is equal to21%. That shows quite low degree of thermal energy potential use in giventechnological scheme and working conditions. REFERENCES: 1) EXERGY(Second Edition-2013) Energy, Environment and Sustainable Development byIbrahim Dincer and Marc A. Rosen. ISBN 978-0-08-097089-9.
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