1、684Theoretical Study For The Effect Of Different Fuels On The Perfomance Of Open Gas Turbine Power PlantMohamed F. Thabit Al-DawoodiDepartment of Mechanical Engineering, Al-Qadissiya University, Al-Qadissiya, IraqAbstract The use of gas turbine is increasing day by day for producing electricity and
2、for various industrial applications. Its well-known that thermal efficiency of open gas turbine varies with the fuel used in the combustion process. In this work an investigation for the effect of different hydrocarbon, alcohol and hydrogen fuels on the performance of simple and modified gas turbine
3、 has been studied. A computer program was written in Quick basic Language has been accomplished to calculate the thermal efficiency, work ratio, specific fuel consumption.etc. in gas turbine working with different types of fuels. Its found that specific fuel consumption is margined according to the
4、fuel used because its dependency on the enthalpy of reaction of the fuel. Also its noted that hydrogen fuel has higher thermal efficiency and lower fuel consumption than other fuels, but its requires high pressure to insert it to combustor. Therefore we must use methane as fuel in the plant since it
5、 is more common type than other. . . . . . , , NomenclatureSymbol Definition UnitT Temperature KCp Specific Heat at Constant Pressure kJ/kg.KC1,C2 Parameters of Fuels -h Specific Enthalpy kJ/kgf Fuel to Air Ratio -W Work kJ/kgS.F.C. Specific Fuel Consumption Kg/kW.hrPR Pressure Ratio -Greek SymbolsS
6、ymbol Definition UnitSpecific Heat RatioEfficiencyHEnthalpy of Reaction per unit Mass kJ/kgJournal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(19): 2011685Subscript Symbol Definitiona Airb Burnerc Compressorg Gasm Mechanicalmax. Maximum n Netr Ratiot TurbineIntroductionThe wide use
7、 of electrical energy is one of the most important characters of each century and its large consumption considered and a feature of highly developed countries. Most of the governments and companies to complete the production of electrical energy and its distribution to help users employ it for diffe
8、rent purposes: domestic, industrial and commercial. Although the thermal efficiency of closed gas turbine cycles was independent of the fuel used in the combustion process. (leung E., 1985) presented in his paper an investigation about the performance of open gas turbine. The principle result of his
9、 study was a correlation between the variation of the thermal efficiency with both hydrocarbon fuel and alcohol, and the fuel parameter C1+C2 taken from the equation of reaction. Practical and theoretical study of performance of simple gas turbine cycle for power generation performed by (Badran, 199
10、7), for two power stations “Rehab and Rasha stations” at different load. The result showed that an increase in compressor inlet temperature yields to decrease in the efficiency where mechanical efficiency macTCpW/*1/2 m(3)2. Combustion Chamber: This part is represented in process 2-3 of (T-S) diagra
11、m. In Figure (2). The combustion chamber is designed to burn a mixture of fuel and air to deliver the resulting gases to the turbine at a uniform temperature. The gas temperature of the turbine must not exceed the allowable structure temperature of the turbine (Jack, D.1998) .A schematic of combusti
12、on chamber is shown in Figure (3). Since the process is adiabatic with no work transfer, so the energy equation, (Cohen, 1989) is simply ;(4)0.,/23, tfihhmNow making the enthalpy of reaction at a reference temperature of 25 oc, so equation can be expanded in the usual way (Cohen, 1989) to get;(5)029
13、8.298298.1 /253 fftatgt TCpTCpHfTCpfBy simplifying equation (5) the theoretical fuel to air ratio will be:(6)25131/1Tpfgat The actual (fuel / air) ratio for given temperature difference is given by;(7) 3. Turbine: The purpose of turbine is to extract kinetic energy from the expanding gases which flo
14、w from the combustion chamber (Jack, D.1998). The kinetic energy is converted to shaft horse power to drive the compressor and other components. Nearly three-forth of all energy available from the product of combustion is required to drive the compressor. This part is represented in process 3-4- of
15、(T-S) diagram In Figure (2). aaRPT1121btaf/688During the isentropic expansion process (Easjop T.D.,1978):(8) Similarly the isentropic efficiency of compressor is defined as the ratio of actual work output to the isentropic work output between P3 and P4 (9)Then the turbine work output is:(10)The net
16、work output is determine by subtracting equation (10) from equation (3). The work ratio is defined as the ratio of net work output to turbine output work (Easjop T.D.,1978):.(11)tnRWThe specific fuel consumption is given by;(12)Then the cycle thermal efficiency is found there from the equation below
17、 (Jack, D.1998);(13)25*.360HCFSthThe following Correlation was obtained to get maximum thermal efficiency (leung E., 1985) where %ln.*32.*.2947.5 21max CJJ 10lnmaxTJ(14)ggPRT113443/Tt/43*TCpgtnafCFS360.Journal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(19): 2011689The above equati
18、on examined the variation of maximum thermal efficiency with both hydrocarbon and alcohol fuels with fuel parameter taken from the equation of 21Creaction:(15)OHCOfuelC2212Simulation Of Modified CyclePossible modification to the basic cycle can be made (Cohen, 1989), such as Intercooling (use more c
19、ompressor), reheating (use more combustor), and heat exchanger which uses some of the energy in the turbine exhaust gases to preheat the air entering the compressor. In this work we should summarized these modification as follows:1. Intercooling: When the compression process is performed in two stag
20、es with an intercooler, then the work input for a given pressure ratio and mass flow is reduced. The task of intercooler is to reduce the outlet temperature of low pressure compressor which is equal to the temperature inlet to high pressure compressor at the same pressure. The system of intercooling
21、 and (T-S) diagram are shown in Figure (4) and Figure (5) respectively. To get the work input is a minimum, we must make the pressure in each stage of compression is the same, when the temperature of air is cooled in the intercooler, back to the inlet to the unit (plant) So:(16) During the isentropi
22、c processes (1-2-) (20)2. Reheat: The expansion process is very frequently performed in two separate stages. The high pressure turbine driving the compressor and low pressure turbine providing the useful power output. The work output of the low pressure turbine can be increased by raising the temper
23、ature at the inlet of the stage. This can be done by placing a second combustion chamber between the turbine stages (Cohen, 1989), in order to heat the gases leaves the 3412P13TmatocCpW/*3/41/2690high pressure turbine. This system with the (T-S) diagram are shown in Figure.(6), and Figure (7). The h
24、igh pressure turbine must be exactly equal to the work input for the compressor with the following equation (21)For the first combustion chamber, the energy equation is used (Cohen, 1989)(22)The first theoretical fuel/air ratio is calculated from expanding equation (22) as follows(23)The same proced
25、ure is used for second combustion chamber;(24)0.2/4, ftihhmThe second fuel/air ratio is then calculated as follows;(25)0298.29898.1 /42552 fftgtgt TCpTCpHfTCpfThen the total fuel/air ratio is given by;(26)21,tttoffThe net work of the plant is equal to work output of low pressure turbine(27)/652.TCpW
26、gtn3.Heat Exchanger: The exhaust gases leaving the turbine at the end of expansion are still at a high temperature (high enthalpy). If these gases are allowed to pass into atmosphere, this represent a loss of available energy, this energy can be recovered by passing the gases from the turbine throug
27、h a heat exchanger, where the heat transfer from the gases is used to heat the air leaving the compressor. Therefore the function of heat exchanger is to heat the outlet air from compressor (T/2 to T3) and to cooled the exhausted gases from turbine (T/5-T6) as shown in Figure.(8) and Figure (9), so
28、the ideal heat exchanger have (T/2=T6) and (T3=T/5) which is assumed in this work.The other performance parameters are repeated with the same procedure applied in simple cycle.Results And Discussion /431/2 TCpTpgma0.1/23, ftihh0298.29898.1 1/2513 fftatgt TCpTCpHfTCpfJournal of Babylon University/Pur
29、e and Applied Sciences/ No.(2)/ Vol.(19): 2011691The layout of the results is divided into two sections, these explain the effect of maximum temperature and pressure ratio on the performance of simple and modified of open gas turbine plant respectively. In this work we studied different types of fue
30、ls which are (H2, CH4, C3H6 , C6H6, CH3OH) that are used in gas turbine cycle. Figure (10) shows the relation between maximum plant temperature with different types of fuels. Equation (14) is used to draw this plot. It can be seen that when maximum cycle increased, the maximum efficiency also increa
31、sed. When we make comparison between the fuels used, it can be noted that hydrogen and methyl alcohol have the same higher maximum efficiency than other fuels at the same operating conditions, this is because they have greater fuel parameter (C1+C2), see table (1). Figure (11) shows the effect of ma
32、ximum cycle temperature which was varied from (1100-2000) Ko on the thermal efficiency for all fuels considered. In general the thermal efficiency increases with increase in temperature of cycle. The hydrogen curve is on the top of the plot because it has higher enthalpy of reaction (lower calorific
33、 value) then methane., with methyl alcohol which came last because it has lower energy than other fuels. Figure (12) represent the relation between maximum cycle temperature with the specific fuel consumption. It can be noted that hydrogen fuel has minimum specific fuel consumption than other fuels
34、and this expected because hydrogen has higher thermal efficiency and according to equation (13) hydrogen fuel must has minimum specific fuel consumption followed by methane, propen, benzene, and finally methyl alcohol. Now the graphs of thermal efficiency and specific fuel consumption are repeated f
35、or all fuels selected, but for variable pressure ratio (4-9), and for fixed maximum temperature 1600 Ko, see Figure (13) and Figure (14). When pressure ratio is increased, the thermal efficiency increased for all fuels but hydrogen and methane fuels remain in the top of the plot. In the graphs of mo
36、dify open gas turbine power plant which include (intercooling, reheat, and heat exchanger), Only hydrogen and methane fuels is graphed, since methane fuel is the more common type used in gaseous plant, and hydrogen is promising fuel which have maximum efficiency, and minimum fuel consumption than ot
37、her fuels. The use of hydrogen as a fuel appears to promise a significant improvement in performance of gaseous plants and reduces the emissions of Greenhouse gases, nitrogen oxide, and smoke. Another driving force behind the need to use hydrogen fuels is the rapid depletion rate of currently used f
38、ossil fuels. Figure (15) and Figure (16) shows the effect of maximum temperature and pressure ratio on the thermal efficiency and S.F.C. of intercooling cycle operating on hydrogen and methane fuels respectively. It can be noted from Figure (15) the thermal efficiency increase with increase in maxim
39、um temperature for a fixed pressure ratio (PR=4), this increase is greater than in simple cycle about 12 % . Also there is a reduction in S.F.C. bout 35% as compared with simple cycle this because increase in net work and thermal efficiency for both fuels selected. Figure (16) shows the effect of pr
40、essure ratio variation on the thermal efficiency and specific fuel consumption with maximum temperature equal to 1600 Ko Its observed that when pressure ratio increased, the thermal efficiency increased, until reaches to maximum value then starts to decrease indicating that there is an optimal press
41、ure ratio equal 7 at which the maximum thermal efficiency is 0.360255 and specific fuel consumption is 0.08327 ( kg/kW.hr) for hydrogen fuel. The same behavior is observed for methane fuel when PR=7, thermal efficiency and S.F.C. are 0.3537 Hydrogen fuel is ideal promising fuel in the gaseous plant
42、which has greater thermal efficiency, and hence minimum S.F.C. than other selected fuels. Greater improvement in the performance of modified gas turbine power plant occurred with intercooling and heat exchanger rather than simple and reheat cycle.ReferencesBadran O. “ Study in gas turbine performanc
43、e improvements” ,Journal of Eng. Sciences Vol.4, No.2, 1997.Chiesa, P., Lozza G., Mazzocchi, L.“using hydrogen as gas turbine fuel“, Journal of Eng. For gas turbine and power, Jan.,Vol. 127, 2005Cohen H,Rogers ,“gas turbine theory”, john wily,1989.Easjop T.D. ”Applied thermodynamics for Eng. Technol
44、ogy”, 1978.Foster R.W. “A small air turbine power plant fired with coal in an atmospheric fluid bed” Journal of Eng. Science for gas turbine and power, Jan. 1990.Gulder O.L. “Combustion gas properties and prediction of partial pressures of CO2 & H2O in combustion gases of aiation and diesel fuels”,
45、Journal of Eng. Science for gas turbine and power, July, 1986.Jack, D. Mattingly, “Element of gas Turbine“, 1998.Kreutz, T. G. et al., (Production of hydrogen and electricity from coal with CO2 capture,“ Proc. Of the sixth international conference on “ Green gas control Technologies“, Kyoto, Japan, 2002. Lefebve A.H. “fuel effect on gas turbine combustion ignition stability and combustion efficiency”, Journal of Mechanical Eng., 1985.Leung E.Y.W. “Universal Correlation for the thermal efficiency of open gas turbine by using differ
