ISSN: X Tikrit Journal of Engineering Sciences available online at:

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1 Aadel Abdulrazzaq Alkumait/Tikrit Journal o Engineering Sciences 22(1) (2015) ISSN: X Tikrit Journal o Engineering Sciences available online at: Parametric Simulation on Enhancement o the Regenerative Gas Turbine Perormance by Eect o Inlet Air Cooling System and Steam Injection Aadel Abdulrazzaq Alkumait Mechanical Engineering Department, College o Engineering, Tikrit University (Received 21 May 2014, Accepted 12 August 2014, Available online 1 April 2015) ABSTRACT Iraq being one o the developing countries o the world considers energy eiciency and the impact o its generation on the environment an imperative process in improvement o its power generation policies. Iraq bearing high temperatures all year long results in reduction o air density, thereore, Inlet air Cooling and Steam Injection Gas Turbines are a striking addition to the regenerative gas turbines. Regenerating Gas turbines tend to have a high back work ratio and a high exhaust temperature, thus, it leads to a low eiciency in power generation in hotter climate. Moreover, STIG and IAC through og cooling have known to be the best retroitting methods available in the industry which improve the eiciency o generation rom 30.5 to 43% and increase the power output rom 22M to 33.5M as the outcomes o computer simulations reveal. Additionally, this happens without bringing about much extensive change to original eatures o the power generation cycle. Furthermore, STIG and spray coolers have also resulted in power boosting and exceeding generation eiciency o gas turbine power plant. Keywords: heat pipe, constant conductance heat pipe, eect o working luid quantity o heat pipe perormance. Introduction Industrial Power Plant also known as Gas turbines power plants are used extensively in every orm o industry or the purpose o generation o electricity as well as power the turbines, compressors or power pumps needed to run those industries[1]. Moreover, Gas turbines are also reerred to as naval gas turbines when used in aircrats. Gas turbines are the most common orm o power generation resource available to many industries, but they are usually made to work or long time periods, under conditions that do not necessarily agree to their design speciications [2]. Thus, understanding the true working o Gas turbines is one o the most important actors on the economy o a developing country [3]. As power generation is directly proportional to the working o industry, hence or appropriate optimization o any industry, the proper working o a gas turbine needs to study [4]. It is the main source o power production in any industry [5]. A gas turbine consists o three distinctive components which are compression, chamber and turbine. The individual and speciic evaluation o these components consists o thermodynamic processes like compression, expansion and combustion. Furthermore, the thermodynamic analysis o any gas turbine includes measurements o perormance parameters like thermal eiciency, power output and particular uel consumption and can be executed with the help o Brayton cycle [6]. Gas turbines results in huge amount o exhaustion o gases, thus leading to loss o huge amounts o energy into the environment (which are exposed to the atmosphere 400 o C to 500 o C). Although, a great amount o heat energy is recovered rom exhaust gases, some o it is used into regeneration o power through their gas turbines. Turbine work is extensively

2 39 used to compress the inlet-air in the compressor o the gas turbine to urther boost its own perormance [7, 9]. Moreover, many retroitting methods are used such as Li-Br-water rerigeration system and spray cooling system (evaporating cooling), which cool the inlet compressor air to urther reduce the work o the turbine and increase its eiciency. Furthermore, STIG is also an eective method used to recover energy o the exhaust gases. STIG and inlet air spray cooling system are engaged with regenerating gas turbine cycle to increase its eiciency. Enhancement o power generation is a result o these two retroitting methods. This urther helps in developing the economy as well, as economy is directly proportional to the working o industries [8, 10]. Thereore, proper implementation o these techniques need to done and we need to understand the proper working o the two ways. Spray cooling systems sprays water at normal condition into air by the help o which the transer o heat within air and water takes place. Furthermore, the increase o water usage and demineralization o water reduces the environmental riendly nature o the turbines towards the society. Subsequently, these two systems result in a great increase o power generation and boost to its power output. System Description Figure 1 shows a regenerative cycle two-shat gas turbine system. It primarily consists o compressor, combustor, gas turbine and a generator. The system shown in the igure is incorporated with both injection gas turbine and inlet air cooling. It is also installed with an evaporative og cooling system (FCS) to reduce the temperature o ambient air to state point 0. A standard og cooling system includes an array o maniolds present at some distance across the compressor inlet duct; these maniolds are ed by a high pressure pump skid. In order to create cooling eect, og cooling being an active system uses special atomizing nozzles that eject extremely small droplets o water under high pressure; these nozzles are ound at distinct spots across the inlet duct at high pressure. There are a speciic number o nozzles in these maniolds which release high pressure water into the inlet air. Factors such as dry and wet bulb ambient conditions are vital or monitoring the amount o og introduced to get the required amount o cooling. Each nozzle produces approximately 2.8 billion droplets per second and its discharge is 2.8ml/s. These mini droplets are in act og itsel which, because o their ineness evaporate rapidly and drop the inlet air temperature. Other than its basic components, a gas turbine such as this also installed with a heat recovery steam generator (HRSG) located at the downstream exit o the turbine (state point 7); the purpose it to salvage the heat rom the exhaust gases. The superheated steam yielded by HRSG is divided in two parts, where only a raction o it is used or STIG (state point 10) and the rest is taken up or various processes. Fig.1: Regenerated gas turbine cycle with og cooling and STIG Thermodynamic Model and Analysis Alterations in the inlet air cooling system and steam injection o the gas turbine have been thoroughly studied under the light o thermodynamics; comprehensive energy analysis has been carried out to examine the Baiji mobile gas turbine plant. The energy calculations o the gas turbine, steam injection system and inlet air cooling system are carried out. The ollowing points [1-3] sum up the assumptions made or the study o the gas turbine and cooling system: 1. The temperature dierence between lue gas and superheated steam, also known as Terminal Temperature Dierence (TTD) is assumed to be 20 C in the HRSG. 2. Any decrease in pressure in the combustion chamber and HRSG is ignored.

3 40 3. Any heat losses incurring in the combustion chamber, turbines and HRSG are also ignored. 4. Following atmospheric conditions are assumed: Temperature, 288K Pressure bar Relative humidity 60% 5. The maximum temperature o steam cycle is taken to be 833K. 6. Compressor and gas turbines have 85% isentropic eiciencies. 7. 3% o the uel lower heating value is taken to be the heat loss in the combustion chamber [11]. All other components are supposed to be adiabatic. 8. Tap, approach point is taken to be 5 C in HRSG. 9. The minimum temperature dierence between the lue gas and the saturated steam, also known as pinch points (Tpp), are taken as 15 C in HRSG [12]. 10. Pressure in the condenser is supposed to be 0.12 bar. 11. All process are assumed to be steady-state and steady low. 12. Fog cooling system has been maintained or 100% saturation o ambient air at wet bulb temperature o air. 13. Constant temperature has been maintained in combustion chamber. 14. It is assumed that the uel injected into the combustion chamber is natural gas. 15. It is supposed that the nozzle discharges water into the evaporative cooling chamber at a pressure o 140 bar when it transorms into og (tiny droplets). It absorbs latent heat o air through adiabatic mixing. Using a set o steady-state equations which include mass, energy balances using control volume analysis serially or compressor, combustor, gas turbine and HRSG, MATLAB has made a code to compute and simulate the retroitting methods over simple gas turbine power plant. A set o equations which inluence a particular component n may be called Mass Rate Balance: m in n mout, n in out, (1) Thereore, Energy rate Balance is: cv n cv n outm h out n out n h,,,, inmin, n in, n (2) Regenerator is a signiicant kind o heat exchanger, the unction o which is to heighten the energy o the hot stream rom the compressor beore it enters the combustion chamber. Preheating enhances combustion [13]. T T T T 2 (3) In the heat recovery boiler, heat transer between the condensed water and exhaust gases takes place and super-heated steam is produced. mexh h 7 h 8 mwhsteam hwater (4) here: mexh= mass low rate o exhaust gases o turbine mw= mass low rate o condensate water h 7, h 8, hsteam and h w= enthalpies o exhaust gases at state 6 and 7, super-heated steam and condensate water respectively. The equation representing heat transer that occurs in an evaporative cooling system or a og cooling system is: m h h m h h m m h h evw here: v1 w0 air air0 air1 steam air v0 v1 m evw = mass low rate o cooling water h w0 = enthalpy o cooling water ma= mass low rate o dry air h h = enthalpy change o water v0 v1 vapour during cooling h h = enthalpy change o dry air air0 air1 (5) The ollowing equation represents the thermal energy (ɳth) o a thermal system: th (6) It is the ratio o work output to heat input o the uel. here: = work output = total heat input o the uel Generation eiciency (ɳ gen) o a thermal

4 41 system is represented as: gen (7) It is deined as the ratio o electrical power output ( ) to the total heat input o the uel ( ). HR (8) (HR) Heat Rate is the ratio o heat produced by the uel to the electrical power output o the thermal system. Based on cost eectiveness, another actor considered to measure the thermodynamic perormance o a cogeneration system is the ratio o power to heat [14]: P RH (9) eva prod Cost is directly related to the amount o power such a system can produce in return o the amount o process heat added. The ratio o mass o uel to the work output is called Speciic Fuel Consumption (SFC) [13, 14]: m SFC (10) It is reciprocal o speciic work ( spec). According to the irst law o thermodynamics, thermal eiciency (η I) is the ratio o all the useul energy absorbed rom the system (electricity and process heat) to the energy o uel input. pro I (11) here: ( pro)= process heat rate First-law thermal eiciency may also be called Fuel Utilization Eiciency or Utilization Factor or Energetic Eiciency. The ratio o useul energy (work output and process heat) to the heat supplied by the uel is known as the Energy Utilization Factor (EUF) [15]: pro EUF COH (12) The energy output to the total energy output o the power generation system is called the Fuel Energy Saving Ratio (FESR) [11, 15]: pro HRSG pro HRSG GT F ESR (13) GT Results and Discussion Following are the our conigurations with retroitting that have been investigated in relation to simple gas turbine cycle: 1- Regenerative gas turbine cycle 2- Regenerative gas turbine cycle with inlet air cooling (IAC) 3- Regenerative gas turbine cycle with STIG 4- Regenerative gas turbine cycle with both IAC and STIG. The systems listed above were run on a computer program in MATLAB or perormance analysis. hile doing computations, turbine blade cooling was neglected or steady state operations. Fig. 2: Net work output or retroitted cycles in comparison to simple GT cycle Fig. 2 shows how the perormance measures o simple gas turbine cycle contrasts with other combinations cycle. The compositions and

5 42 proportions o gases and many estimated perormance parameters are taken into account or calculation o temperature, pressure and gas concentration in each component. Perormance parameters such as system eiciencies, heat rate and speciic power output etc., are greatly improved with the incorporation o evaporative cooler in a regenerative cycle. The resulting power generation eiciency and output or regenerative cycle are 6.99% and 21.8 M respectively. Gas turbine inlet air ogging uses very small droplets, sizes varying rom 3 to 16 microns o og converted rom de-mineralized water which is projected by special atomizing nozzles working at 140 bar to cool the intake air. Because o the miniscule size o the droplets in the intake duct the air temperature drops and subsequently improves power perormance by increasing the moist air mass low rate. Approximately 100% evaporation eectiveness can be achieved in terms o attaining saturation conditions and wet bulb temperature at the compressor inlet. Thereore, change in the ambient temperature aects the exhaust temperature o the compressor, the internal and external temperature o the turbine, the mass low, the speciic work, the speciic uel consumption and power. The power supplied by the machine is inversely proportional to ambient temperature; as the ambient temperature decreases, the power supplied increases. Hence, it is important to cool the compressor inlet air to achieve a higher supply o electric power which also reduces the work to be done by the compressor. Hence, evaporative cooling is employed as an eective way o cooling inlet air rom 25 o C and 60% RH up to o C. In dry summers, the inluence o evaporative cooling will be higher in Iraq when there is greater dry bulb temperature and lesser RH. Figs.2 and 3 draw the comparison between a regenerative cycle gas turbine with og and one without og cooling. The power output adds up by 6.1% and many other eiciencies increase by 0.91%, whereas the heat rate drops by 2.1%. Figs. 2 and 3 also weigh regenerative cycle gas turbine with STIG and without STIG; again, the power output and thermal eiciency escalate by 24% and 4% respectively whereas 11.5% o drop in heat rate is observed. The temperature at the outlet o the stack, shown in Fig.1 at state point 7 is maintained above the dew point temperature o acid, i.e. 131 o C. The purpose o this control is to avoid condensation o SO2 and NO2 which ultimately hydrolyse into sulphuric acid (H2SO4) and nitric acid (HNO3) respectively and cause damage to the air pre-heater o HRSG such as scaling and corrosion. Under these conditions, generated superheated steam at K and 22bar has a the highest low rate o around kg/s when the pinch point and approach point or current investigation are taken as 15 o C and 5 o C respectively. There is an impressive range o STIG available to optimize the power cycle; generated steam injected into the combustor (STIG only) yields a maximum injection ratio (msteam/mair) o around 0.2 which is quite considerable. The power output can be raised to 34.15M by pumping as its value is 2 to 3 orders lower than that o a compressor; the power output produced by the steam is, thus quite high as compared to that o air per unit mass low rate. The pump itsel can make STIG alone to create proound impact. Other than that, the superheated steam has almost twice speciic heat as compared to air and the enthalpy o steam is greater than that o air at a particular temperature. The STIG method quite successully increases the power output and increases the overall eiciency o the gas turbine. System eiciencies get sizably enhanced in a regenerative gas turbine cycle with STIG (or steam injection ratio 0.2). eighing regenerative cycle gas turbine with og cooling and STIG against one without og cooling and STIG reveals that power output shoots up by 11.9% and thermal eiciency, by 9.81%, the heat rate, however, decreases by 11.2%. It may thereore be concluded that incorporation o simple cycle with STIG and og cooling greatly enhances system perormance. Fig. 3 shows the comparison drawn between generation eiciencies or simple, regenerative and enhancing cycles.

6 43 Fig. 3: Generation eiciencies or simple, regenerative and enhancing Fig. 4: Eect o steam injection ratio on irst-law eiciency and generation eiciency or regenerative GT combined with og cooling and STIG. Fig.4 reveals how generation eiciency is inluenced by STIG; it also shows its eects on irst law o eiciency or ixed inlet air conditions under maximum o 100% air saturation because o the cooling caused by og. In simple cycle gas turbine, the incorporation o ogging and STIG is seen to improve the system perormance according to both irst and second laws. For retroitted combined cycle (og cooling and STIG), the maximum generation eiciency achieved is 45.21% with injection ratio 0.2. Figure 5 shows that the rate o reduction o process heat is steeper than the slope o energy eiciency. As a result the irst law eiciency decreases with increasing amount o steam injection ratio. At 0.2, the maximum injection ratio is still below the allowable injection limit as recommended by the manuacturer or the available industrial turbines because the energy extracted rom HRSG restricts the maximum amount o injection steam. Fig.5: Eect o steam injection ratio on the process-heat or regenerative GT combined with og cooling and STIG Conclusions ith the rapidly increasing demand or electricity in the developed countries like Iraq, and the expected shortage in power supply due to delays in the major power projects, retroitting regenerative gas-turbines with inlet air pre-cooling and STIG are attractive investment opportunity. Recovering the energy rom the exhaust gas o a regenerative cycle can be used back to the system to improve the system perormance. Steam injection and inlet air evaporative cooling are well-proven technology that can eectively improve power output and power generation eiciency or a regenerative cycle gas turbine. In the present work, a regenerative cycle gas turbine has been investigated. An existing simple cycle gas turbine was considered as the basic system and has been converted into modiied retroitted system with regenerative, inlet air cooling, and STIG. The steam needed in the STIG eature is generated rom the energy recovered rom the system s own exhaust gases. Under the average local weather conditions (25 o C and 60% RH), the beneit o adding the STIG eature can substantially improve the power output rom the 22 M to 33.5 M and power generation eiciency rom 30.5 to 43 %. It also reveals that the degree o energy wasting and thermal pollution can be reduced through retroitting. Although the perormance o spray coolers is deeply inluenced by the ambient temperature and humidity, they operate eiciently during hot and dry climatic conditions.

7 44 Acknowledgements The author would like to thank University o Tikrit or providing laboratory acilities and inancial support. Reerences 1. Jaber,.M., Jaber J.O. and Khawaldah M.A. Assessment o Power Augmentation rom Gas Turbine Power Plants Using Dierent Inlet Air Cooling Systems Jordan Journal o Mechanical and Industrial Engineering, Vol. 1, Number 1, pp. 7-15, Sep Rahim, K. J., Galal M. Z. and Majed M. A. Thermo-Economics Analysis O Gas Turbines Power Plants ith Cooled Air Intake Yanbu Journal o Engineering and Science, Vol. 1, pp.26-42, October EL-AAD M. M. A computer-based model or gas-turbine power augmentation by inlet-air cooling and water/steam injection STROJN ICKY CASOPIS, 59, pp , El-Awad M. M., Siraj, M. A. and Saeed, H. A. Feasibility o Gas Turbine's Inlet-Air Cooling by Air ashing and Evaporative Cooling in the Dry and Hot Climate UoKEJ Vol.2, Issue 1, pp , February Behdashti, A., Ebrahimpour, M., Vahidi, B., Omidipour, V., Alizadeh, A. Field Experiments and Technical Evaluation o an Optimized Media Evaporative Cooler or Gas Turbine Power Augmentation Journal o Applied Research and Technolo gy, Vol. 10, pp , June AL-Salman, K.Y., Rishack,.A., and AL-Mousawi, S.J. Parametric Study O Gas Turbine Cycle ith Fogging System J.Basrah Researches (Sciences) Vol. 33. No.4.(16-30)DEC.(2007). 7. Al-Ibrahim A. M. and Varnham, A., A review o inlet air-cooling technologies or enhancing the perormance o combustion turbines in Saudi Arabia Applied Thermal Engineering, Vol. 30, pp Sanaye S., and Tahani M. Analysis o gas turbine operating parameters with inlet ogging and wet compression processes Applied Thermal Engineering, Vol. 30, pp , Kyoung, H. K., Hyung-Jong, K., Kyoungjin K., and Horacio P-B., Analysis o water droplet evaporation in a gas turbine inlet ogging process Applied Thermal Engineering, Vol , pp , Alhazmy, M.M. and Najjar, Y.S.H., Augmentation o gas turbine perormance using air coolers Applied Thermal Engineering, Vol. 24, pp , Farzaneh-Gord, M. and Deymi-Dashtebayaz, M., Eect o various inlet air cooling methods on gas turbine perormance Energy, Vol. 36, pp , Ashley, D. S. and Al Zubaidy, S., Gas turbine perormance at varying ambient temperature Applied Thermal Engineering, Vol. 31, pp , Naeim, F., Liu, S., and aisar, H., Eect o Ambient Temperature on the Perormance o Gas Turbines Power Plant IJCSI International Journal o Computer Science Issues, Vol. 10, Issue 1, No 3, pp , January ang, F.J. and Chiou, J.S., Integration o steam injection and inlet air cooling or a gas turbine generation system Energy Conversion and Management, Vol. 45, pp , Zadpoor, A. A. and Golshan, A. H., Perormance improvement o a gas turbine cycle by using a desiccant-based evaporative cooling system Energy, Vol. 31, pp , 2006.