Article energies Two-Stage Evaporative Inlet Air Gas Turbine Cooling Article Obida Zeitoun 1,2 Two-Stage Evaporative Inlet Air Gas Turbine Cooling 1 Obida Zeitoun 1,2 2 1 Mechanical Engineering Department, College of Engineering, King Saud University, Riyadh 11421, Saudi Arabia; ozeitoun@ksu.edu.sa K.A.CARE Energy Research and Innovation Center at Riyadh, Riyadh 11421, Saudi Arabia Mechanical Engineering Department, College of Engineering, King Saud University, Abstract: Gas turbine inletozeitoun@ksu.edu.sa air-cooling (TIAC) is an established technology for augmenting gas tur Riyadh 11421, Saudi Arabia; 2 Energy Research and InnovationinCenter at Riyadh,TIAC Riyadhusing 11421,evaporative Saudi Arabia cooling is suitable for bineK.A.CARE output and efficiency, especially hot regions. hot, dry regions; however, the cooling is limited by the ambient wet-bulb temperature. This study Abstract: Gas turbine inlet air-cooling (TIAC) is an established technology for augmenting gas investigates two-stage evaporative TIAC under the harsh weather of Riyadh city. The two-stage turbine output and efficiency, especially in hot regions. TIAC using evaporative cooling is suitable evaporative TIAC however, system consists of indirect direct evaporative In theThis indirect for hot, dry regions; the cooling is limitedand by the ambient wet-bulb stages. temperature. studystage, air is precooled using water cooled in a cooling tower. In the direct stage, adiabatic saturation investigates two-stage evaporative TIAC under the harsh weather of Riyadh city. The two-stage cools the air. This investigation conducted forand thedirect GE 7001EA gas stages. turbineInmodel. Thermoflex evaporative TIAC systemwas consists of indirect evaporative the indirect stage, air software was used tousing simulate GE in 7001EA gastower. turbine using different TIAC systems including is precooled waterthe cooled a cooling In the direct stage, adiabatic saturation cools the evapora air. This investigation was conducted the GE 7001EA gas turbine model. Thermoflex software tive, two-stage evaporative, hybridforabsorption refrigeration evaporative and hybrid vapor-com was used to simulate the GE 7001EA gas turbine using different TIAC systems including evaporative, pression refrigeration evaporative cooling systems. Comparisons of different performance parame two-stage hybrid absorptionThe refrigeration evaporative vapor-compression ters of gasevaporative, turbines were conducted. added annual profitand andhybrid payback period were estimated refrigeration evaporative cooling systems. Comparisons of different performance parameters of gas for different TIAC systems. turbines were conducted. The added annual profit and payback period were estimated for different TIAC systems. Keywords: gas turbine; inlet cooling; two-stage; evaporative cooling Keywords: gas turbine; inlet cooling; two-stage; evaporative cooling Citation: Zeitoun, O. Two-Stage Citation: Zeitoun, O. Two-Stage Evaporative Inlet Air Gas Turbine Evaporative Inlet Air Gas14, Turbine Cooling. Energies 2021, 1382. Cooling. Energies 2021, 14, x. https://doi.org/10.3390/en14051382 https://doi.org/10.3390/xxxxx Academic Editor: 1. Introduction 1. Introduction Gas turbine power plants have relatively low cost, require less space and are quick turbine power Gas plants have relatively cost, require less spacethat anddraws are quick to beGas commissioned. turbines (Figurelow 1) have a compressor air in and to be commissioned. Gas turbines (Figure 1) have a compressor that draws air in and compresses it and a fuel combustor that heats the compressed air. Combustion products compresses it and a fuel combustor that heats the compressed air. Combustion products at at high temperatures and pressure are through passed through thewhere turbine, high temperatures and pressure are passed the turbine, theywhere expandthey and expand and develop motive force for turning the turbine rotor. develop motive force for turning the turbine rotor. AndrzejEditor: Teodorczyk Academic Andrzej Teodor- czyk Received: 22 January 2021 Accepted: 26 February 2021 Fuel Combustion chamber Received: 22 January 2021 Published: 3 March 2021 Accepted: 26 February 2021 Published: 3 March 2021 Publisher’s Note: MDPI stays neutral Generator with regard to jurisdictional claims in Publisher’s MDPI stays neupublishedNote: maps and institutional affiltral iations. with regard to jurisdictional claims in published maps and institutional affiliations. Compressor Gas turbine Copyright: © 2021 by the author. Licensee MDPI, Basel, Switzerland. Copyright: © is 2021 by the authors. This article an open access article Ambient air distributed under the terms and Submitted for possible open access conditions of the Creative Commons publication under the terms and con- Chimney Attribution (CC BY) Commons license (https:// ditions of the Creative Atcreativecommons.org/licenses/by/ tribution (CC BY) license (http://crea4.0/). tivecommons.org/licenses/by/4.0/). Figure Simplecycle cycle turbine unit. Figure 1.1.Simple gasgas turbine unit. Energies 2021, 14, 1382. https://doi.org/10.3390/en14051382 Energies 2021, 14, x. https://doi.org/10.3390/xxxxx https://www.mdpi.com/journal/energies www.mdpi.com/journal/energies Energies 2021, 14, x FOR PEER REVIEW The capacity and efficiency of gas turbine systems highly depend 2 ofon 17 ambie perature and pressure. In a relatively hot climate, such as in the Kingdom of Saud (KSA), turbine capacities can fluctuate as much as 20% between summer and win Energies 2021, 14, x FOR PEER REVIEW cause a capacity gas turbine is a constant volumetric flow rate machine. The output The and efficiency of gas turbine systems highly depend on ambient tempera-of a gas ture and pressure. a relatively hot climate, such as in the Kingdom Saudi Arabia (KSA), decreases as theInair mass flow rate decreases owing to anofincrease in the ambient turbine capacities can fluctuate as much as 20% between summer and winter, because a gas ature. The power output ofand theefficiency GE 7001EA turbine can highly fall from 84.4onMW at The capacity of gasgas turbine systems depend ambien turbine is a constant volumetric flow rate machine. The output of a gas turbine decreases and pressure. In a relatively hotConsequently, climate, such as incooling the Kingdom of Saudi A 69.0 MW at perature an ambient temperature of 45 °C. the incoming as the air mass flow rate decreases owing to an increase in the ambient temperature. The (KSA), turbine capacities can fluctuate as much as 20% between summer and winte ◦ increase theof gas power output byfall20%. power output theturbine GE 7001EA gas turbine can from 84.4 MW at 15 C to 69.0 MW at cause a gas turbine is a constant volumetric flow rate machine. The output of a gas tu ◦ an ambient of 45 C.inlet Consequently, cooling using the incoming air can increase theand mec Air attemperature the compressor can be cooled evaporative cooling decreases asby the20%. air mass flow rate decreases owing to an increase in the ambient te gas turbine power output or thermal refrigeration. The evaporative cooling (Figure 2) is desirable The power of the GE 7001EA gassystem turbine can fall mechanical from 84.4 MW at 15 Air at theature. compressor inlet output can be cooled using evaporative cooling and ventional cooling techniques owing to the low cost and the low energy needed toa 69.0 MW atThe an ambient temperature 45 °C.(Figure Consequently, coolingfor theconincoming or thermal refrigeration. evaporative cooling of system 2) is desirable increase the gasowing by the the system. Using either aturbine wetted or a20%. water sprayneeded system, the cooling ventional cooling techniques to power themedium lowoutput cost and low energy to operate Air at the compressor inlet can be cooled using evaporative cooling anddry mech evaporative cooling solely on difference between the ambient a the system. Using eitherdepends a wetted medium or the a water spray system, the cooling effect or thermal refrigeration. The evaporative cooling system (Figure 2) is desirable fo in evaporative cooling depends solely on the difference between the ambient dry and bulb temperatures. To cool the air below ambient wet-bulb temperature, a mu ventional To cooling techniques to the low cost and the lowaenergy needed to op wet-bulb temperatures. cool the air belowowing ambient wet-bulb temperature, multistage evaporativethe system, introduced by [1], can be used (Figure 3). In the first stage,efa system. Using by either a wetted medium a water system, the cooling evaporative system, introduced [1], can be used (Figureor3). In the spray first stage, a cooling tower cools the water used to precool a heat exchanger. In the dry secon cooling depends solely onair thein difference the ambient and tower cools theevaporative water used to precool the air in a the heat exchanger. In thebetween second stage, direct bulb temperatures. To cool the air below ambient wet-bulb temperature, a mult direct evaporative cooling is used to further cool the air. evaporative cooling is used to further cool the air. Energies 2021, 14, 1382 evaporative system, introduced by [1], can be used (Figure 3). In the first stage, a co tower cools the water used to precool the air in a heat exchanger. In the second Combustion direct evaporative used to further cool the air. Fuel cooling is chamber Combustion chamber Fuel Generator Generator Evaporative cooler Compressor Evaporative cooler Ambient air Gas turbine Compressor Ambient air Gas turbine Make up water Make up water Chimney Chimney Figure 2. Gas turbine with inlet cooling. Figure 2.2.Gas turbine with evaporative inletevaporative cooling. Figure Gas turbine with evaporative inlet cooling. Combustion Fuel Combustion chamber chamber Fuel Cooling tower Cooling tower Generato r Generato r a Ambient air a Ambient air Cooling tower make up water 1 Ambient air b Cooling tower make up water b 1 Ambient air Evaporative cooler 4 Evaporative 3 cooler Compressor 0 0 0 3 exchanger Heat Compressor Gas turbine Gas turbine 4 0 0 0 Evaporative cooler make up water Heat exchanger Chimney Evaporative Figure 3. Gas turbine with two-stage evaporative inlet cooling. Figure 3.cooler Gas turbine with two-stage evaporative inlet cooling. make up water Chimney Vapor-compression or absorption refrigeration systems commonly provide ref ation. The vapor-compression refrigeration system will be driven using work fro Figure 3. Gas turbine with two-stage evaporative inlet cooling. Energies 2021, 14, 1382 3 of 17 Energies 2021, 14, xPEER FOR REVIEW PEER REVIEW Energies 2021, 14, x FOR 3 of 1 Vapor-compression or absorption refrigeration systems commonly provide refrigeration. The vapor-compression refrigeration system will be driven using work from the turbine atexpense expense of aincrease power output increase because theHowever, inlet air cooling. turbine atturbine the expense athe power output because of the inlet air at theof of a power output increase because of cooling. theofinlet air cooling. How vapor-compression refrigeration is typically characterized by a relatively high vapor-compression refrigeration isrefrigeration typically characterized by a relatively high initial cost ever, ever, vapor-compression is typically characterized by a relatively high initia cost and relatively power consumption, compared with evaporative and relatively highrelatively power consumption, compared with evaporative which hascooling, cost and high high power consumption, compared withcooling, evaporative cooling, whic has relatively low power consumption. For a medium-sized gas turbine (typically relatively has lowrelatively power consumption. a medium-sized turbine (typically in the output low power For consumption. For a gas medium-sized gas turbine (typically in th output of heat 20–60 exhaust heat is suitable in quantities and temperatur range of 20–60 MW), exhaust is MW), suitable inheat quantities andintemperatures fortemperatures power output rangerange of 20–60 MW), exhaust is suitable quantities and fo power absorption refrigeration systems. absorption refrigeration cycle systems. power absorption refrigeration cyclecycle systems. To reduce refrigeration capacity and needed work ortoheat needed to operate the inl To reduceTorefrigeration capacity and work or heat operate inlet air- inlet reduce refrigeration capacity and work or heat needed tothe operate the air cooling system, hybrid refrigeration evaporative cooling, similar to that shown in F cooling system, hybrid refrigeration evaporative cooling, similar to that shown in cooling system, hybrid refrigeration evaporative cooling, similar to that shown in Figure 4 and 5, can be used. As shown in Figures 4 and 5, an absorption or a vapor-compr Figures 4 4and 5, can be used. As shown in Figures 4 and 5, an absorption or a vaporand 5, can be used. As shown in Figures 4 and 5, an absorption or a vapor-compressio refrigeration system used to produce to the in heat exch compression refrigeration system isisused to chilled water to precool precool the inaaexchange refrigeration system is used to produce chilled waterwater to precool the air inair aair heat heat exchanger before using evaporative cooling. Both systems condensers’ is before evaporative cooling. condensers’ water is cooled cooled before usingusing evaporative cooling. Both Both systems condensers’ waterwater is cooled usingusing coolinc using cooling towers. Al-Aansary et al. [2] introduced a hybrid turbine inlet cooling system towers. Al-Aansary et al. [2] introduced a hybrid turbine inlet cooling system comb towers. Al-Aansary et al. [2] introduced a hybrid turbine inlet cooling system combinin combining the benefits of evaporative cooling with vapor-compression refrigeration. This the benefits of evaporative cooling with vapor-compression refrigeration. This sysi the benefits of evaporative cooling with vapor-compression refrigeration. This system system isbased based on a two-step cooling process, in which mechanical vapor-compression based on a two-step cooling process, in which mechanical vapor-compression firs on a two-step cooling process, in which mechanical vapor-compression first pre first precools the air which is further cooled using evaporative cooling. cools the air which is further cooled using evaporative cooling. cools the air which is further cooled using evaporative cooling. CoolingCooling tower tower air AmbientAmbient air Combustion Combustion chamberchamber Fuel Fuel Condenser Condenser tower make CoolingCooling tower make up waterup water Generator Generator Generator Generator Absorber Evaporator Absorber Evaporator Evaporative Evaporative cooler cooler Chilled water Chilled water 1 1 air AmbientAmbient air 3 3 Compressor Compressor 4 4 00 0 0 0 Gas Gas turbine turbine 0 Heat exchanger Heat exchanger Evaporative Evaporative cooler cooler make upmake waterup water Chimney Chimney Figure 4. Gas with evaporative-absorption refrigeration inlet cooling. Figure Gas turbine with evaporative-absorption refrigeration inlet cooling. Figure 4. turbine Gas4.turbine with evaporative-absorption refrigeration inlet cooling. Cooling Cooling tower tower Ambient Ambient air air Fuel Condenser Condenser Cooling tower Cooling tower make up water make up water Fuel Combustion Combustion chamber chamber Generator Generator Compressor Compressor Evaporator Evaporator Evaporative cooler Evaporative cooler Compressor Compressor Chilled water Chilled water 1 1 Ambient air Ambient air 3 3 0 0 4 0 0 0 Gas Gas turbine turbine 4 0 Heat exchanger Heat exchanger Evaporative cooler Evaporative cooler make up water make up water Chimney Chimney Gas turbine with evaporative vapor-compression refrigeration inlet cooling. FigureFigure Gas5. turbine withevaporative evaporative vapor-compression refrigeration inletcooling. cooling. Figure 5.5.Gas turbine with vapor-compression refrigeration inlet Energies 2021, 14, 1382 4 of 17 Gas turbine inlet air cooling (TIAC) is a well-known technology that is used to improve gas turbine performance [1–4], where gas turbine power increases at a low cost per kW. Various approaches for cooling the turbine inlet air have been used. Gas turbines have ambient temperature sensitivity, where both the capacity and efficiency decrease as the ambient temperature increases. The compressor section of the gas turbine’s power demand is proportional to the absolute temperature of the inlet air. The compressor mass flow rate capacity is proportional to the air density at the compressor inlet, which is inversely proportional to the absolute temperature. Therefore, high ambient temperature negatively affects both the capacity and efficiency of the turbine. Gas turbines are rated at ISO conditions, 15 ◦ C (59 ◦ F), which is approximately the global average temperature. Single or simple cycle turbines working at full load in KSA have an efficiency of 22–28% [5]. Various approaches for cooling turbine inlet air have been implemented. Al-Ibrahim et al. [6] and Deng et al. [7] conducted extensive reviews of gas turbine inlet air cooling systems. Hot dry air can be cooled using water evaporation. For turbine inlet cooling, this can be accomplished either with wetted media or using water spray systems. Both evaporative cooling techniques share the attribute that the difference between dry-bulb and wet-bulb temperatures limit cooling. The biggest advantage of evaporative cooling is the low installation cost. Typically, this system’s weakness is water availability, particularly in dry regions. Investigators, including [1–4,8–13], studied evaporative gas turbine inlet cooling. Ali et al. [3] and Zeitoun et al. [4] simulated evaporative cooling for the GE7001EA gas turbine using Thermoflex software for different evaporation techniques. The results showed that the net power output could reach 12%, but the efficiency increased only by a maximum of ~2.5%. Alhazmy and Najar [8] reported that evaporative cooling could boost the power output and enhance the efficiency of gas turbines less expensively as compared to the cost of chilling systems. Although the performance of evaporative coolers depends highly on ambient conditions, they operate efficiently under hot and dry conditions. The analysis of Alhazmy and Najar [8] has shown that evaporative cooling reduces the temperature of incoming air by 3–15 ◦ C, enhancing the power by 1–7% and improving the efficiency by 3%. Gas turbine evaporative inlet cooling, according to Wang and Braquet [9], indicated a potential of 10% enhancement in power output in warm, dry conditions. Wang and Braquet [9] reported that the installation cost of the evaporative inlet cooling system was 57% lower in cost than buying new gas turbines. Ehyaei et al. [10,13] investigated the effect of fogging on gas turbine efficiencies and emissions and social cost. The model of [10] indicated that the first- and secondlaw efficiencies increased from 5.5% to 7%, and the social cost of air pollution dropped by 4%. Mahto and Pal [11] studied the effect of fogging on combined cycles of different configurations and concluded that the optimum configuration was the combined cycle with a triple-pressure heat recovery steam generator. Carmona [12] conducted thermodynamic and economic investigations using evaporative cooling in hot humid regions. According to [12], evaporative cooling can improve the performance of gas turbines, even in tropical areas. Saghafifar et al. [14] recommended using the Maisotsenko cooler for gas TIAC in hot and humid climates, where gas turbine waste heat was used for desiccant regeneration. Absorption and vapor-compression refrigeration can also be used for the compressor inlet cooling by passing relatively hot ambient air over a coil cooled by chilled water (or brine). The main advantage of such systems is that air can be cooled to temperatures below the wet-bulb temperature. The use of vapor-compression or absorption refrigeration in gas TIAC was investigated by [15–24]. Erickson et al. [15] reported that a 300-refrigeration ton aqua-ammonia refrigeration unit was required to cool the inlet of a 5-MW gas turbine from 35 ◦ C to 5 ◦ C. Cooling increases the power output by 1 MW, and the added power is at a marginal efficiency of 39%, compared with 29% for the base turbine power. Turbine Energies 2021, 14, 1382 5 of 17 power increases at a lower cost per kilowatt than the turbine alone and improves the heat rate [16,17]. According to Ondryas et al. [18], gas turbine power augmentation using inlet air chilling can be used to boost peak power at high ambient temperatures. Ondryas et al. [18] concluded that the benefits from on-peak power production can outweigh the cost of the chillers’ expensive equipment. According to Alhazmy et al. [19], the mechanical refrigeration used in turbine inlet cooling improved power output but appreciably dropped in thermal efficiency. Marzouk and Hanafi [20] reported that using chillers could increase the annual power gained by 36%, compared with evaporative cooling, while the net cash flow was 16% lower than evaporative cooling. Kodituwakku [21] investigated the use of a two-stage absorption system to cool the GE MS5001R turbine. The cost of the exhaustdriven absorption chiller system was $736 per ton of refrigeration, with a payback period of 11 years. Mohapatra and Sanjay [22] reported that vapor-compression refrigeration inlet air cooling could improve the plant-specific work by 18.4% and efficiency by 4.18%, compared with 10.48% and 4.6%, respectively, for evaporative cooling. However, evaporative inlet air cooling might be preferred over vapor-compression cooling for higher plant efficiency. Barakat et al. [23] investigated the use of geothermal energy in inlet air cooling of gas turbines. As reported by [23], the output power and thermal efficiency increased by 9% and 4.8%, respectively, with a payback period of 1.2 years. The comparison of El-Shazly et al. [24] indicated that the absorption chiller achieved an augmentation of 25.47% and 33.66% in power and efficiency, respectively, while the evaporative cooler provides only an increase of 5.56% and 1.55% in power and efficiency, respectively. The effect of a combined cycle inlet cooling using absorption and vapor-compression refrigeration was investigated by [25,26]. Yang et al. [25] concluded that absorption chilling was preferable in ambient temperature zones (25 ◦ C) and with a relative humidity higher than 40%. Mohapatra and Sanjay [26] conducted a comparison study to investigate the impact of inlet air cooling using vapor-compression and absorption refrigeration. It was observed by [26] that the benefits of using absorption refrigeration were superior to vaporcompression refrigeration. As reported by [26], the optimum value of the compressor inlet temperature was 20 ◦ C for both absorption and vapor-compression refrigeration schemes. Thermal energy storage (TES) systems incorporated in inlet air-cooling systems of gas turbines were investigated by [27,28]. TES systems are based on chilled water or ice thermal storage charged during low-load nighttime using mechanical chillers. Chilled water or ice is used on the hot day during high-load hours to cool inlet air to the compressor. The thermo-economic analysis of [29] indicated that the payback period of using media evaporative, fogging and absorption refrigeration TIAC systems were 1.4, 1.14 and 5.7 years, respectively. The economic analysis of [20] revealed that the payback period were 0.66 and 3.3 years for evaporative and vapor compression refrigeration TIAC systems, respectively. Al-Ansary et al. [2] and Dizaji et al. [30] investigated hybrid inlet cooling systems. As reported by Al-Ansary et al. [2], hybrid inlet cooling systems typically required significantly smaller amounts of makeup water than conventional evaporative cooling systems because the amount of water that must be added initially is significantly lower. When compared with mechanical vapor-compression, the hybrid system cools the air to an intermediate temperature, significantly lowering the required chilling/refrigerating capacity. Thus, the required chillers can have smaller comparative capacities and consume relatively less power. Two-stage evaporative cooling is a new technology used in air conditioning applications. This technology can cool ambient air below its wet bulb temperature. In this investigation, the feasibility of the two-stage evaporative cooling technique as a TIAC system was examined. This study focused on investigating the performance of a real gas turbine incorporated with a two-stage evaporative TIAC system (Figure 3) under the hot dry weather conditions of Riyadh city. Comparisons of the proposed system and evaporative and hybrid refrigeration evaporative TIAC systems (Figures 2, 4 and 5) were conducted. Energies 2021, 14, x FOR PEER REVIEW 6 of 17 Energies 2021, 14, 1382 6 of 17 weather conditions of Riyadh city. Comparisons of the proposed system and evaporative and hybrid refrigeration evaporative TIAC systems (Figures 2,4,5) were conducted. 2. Gas Turbine Simulation Thermoflex (part of THERMOFLOW software) is a well-known simulation software 2. Gas Turbine Simulation with a graphical interface, allowing the assembly of a thermal system model from icons Thermoflex (part of THERMOFLOW software) is a well-known simulation software representing more than 175 components. The program covers both the design and offwith a graphical interface, allowing the assembly of a thermal system model from icons design simulation of real systems and models all types of power plants, including gas representing more than 175 components. The program covers both the design and offturbine, combined and conventional steam cycles. The simulation procedure is presented design simulation of real systems and models all types of power plants, including gas in [3,4]. turbine, combined and conventional steam cycles. The simulation procedure is presented The software was validated by simulating ISO [3,4] and the commission conditions of in [3,4]. the GE turbine (Figure 5). Table 1 lists the comparison data showing the high capability of The software was validatedreal by gas simulating Thermoflex software to simulate turbines.ISO [3,4] and the commission conditions of the GE turbine (Figure 5). Table 1 lists the comparison data showing the high capability of Thermoflex software to simulate real prediction gas turbines. Table 1. Comparison between Thermoflex and contract conditions of a GE 7001EA gas turbine. Table 1. Comparison between Thermoflex prediction and contract conditions of a GE 7001EA gas turbine. Plant Summary Thermoflex Contract Ambient pressure Plant Summary Ambient temperature Ambient pressure Ambient temperature Ambient RH Ambient RH Ambient wet-bulb temperature Ambient wet-bulb temperature Net power Net power Net electric efficiency (LHV) Net electric efficiency (LHV) Net heat rate (LHV) Net heat rate (LHV) bar 0.94 Thermoflex Contract 50 0.94 50 10 10 23.23 23.23 60,203 60,361 60203 60361 30.39 30.39 11,848 11,817 11848 11817 ◦C bar °C % % ◦C °C kW kW % % kJ/kWh kJ/kWh 3.3.Investigated InvestigatedGas GasTurbine TurbineInlet InletCooling CoolingSystems Systems GE 7001EA gas turbine performances with GE 7001EA gas turbine performances withand andwithout withoutdifferent differentinlet inletcooling coolingtechtechniques, including evaporative cooling (Figure 2), two-stage evaporative cooling (Figure 3), niques, including evaporative cooling (Figure 2), two-stage evaporative cooling (Figure hybrid absorption refrigeration evaporative cooling (Figure 4) and hybrid vapor3), hybrid absorption refrigeration evaporative cooling (Figure 4) and hybrid vapor-comcompression refrigeration evaporative cooling (Figure were simulated the monthsof pression refrigeration evaporative cooling (Figure 5), 5), were simulated forfor the months of the year under weather conditions of Riyadh (Table In this investigation, the year under thethe weather conditions of Riyadh (Table 2). 2). In this investigation, the the perperformances between the gas turbine with the mentioned inlet cooling techniques and formances between the gas turbine with the mentioned inlet cooling techniques andthe the same samegas gasturbine turbinewithout withoutinlet inletcooling coolingare arecompared compared(Figure (Figure6). 6). Figure6.6.Thermoflex Thermoflexmodel modelofofthe theGE GE7001EA 7001EAgas gasturbine. turbine. Figure TableTable 2. Average weather conditions of Riyadh [31]. [31]. 2. Average weather conditions of Riyadh High HighTemperature Temperature Mean C MeanDaily DailyValue, Value, ◦oC Relative Humidity Mean Value, % Jan.Jan. Feb.Feb.Mar.Mar.Apr.Apr.MayMayJun.Jun. Jul.Jul. Aug. Aug. Sep. Sep. Oct. Oct. Nov. Nov. Dec. Dec. 20.220.2 22.922.927.6 27.632.3 32.3 38.738.7 41.541.5 42.842.8 42.5 42.5 40.1 40.1 34.6 34.6 27.4 27.4 21.7 21.7 18 24 37 46 50 40 35 33 22 14 15 14 Relative Humidity Mean Value, % Relative Humidity Energies 2021,Value, 14, 1382 % Mean 50 40 35 33 22 14 15 14 18 24 37 46 50 40 35 33 22 14 15 14 18 24 46 737 of 17 Figure 7 shows a schematic of the turbine and inlet cooling system as presented in Thermoflex for gas turbines with evaporative inlet cooling (Figure 2). The surrounding Figure 7 shows a schematic thestate turbine and inlet cooling as presented ambient air (7) is cooled from stateof 4 to 2, as it is humidified in system the evaporative coolei Figure 7 shows a schematic of theevaporative turbine and inlet cooling system as presented in Thermoflex for gas turbines with inlet cooling (Figure 2). The surroundin (5) using a water source (8). The temperature at the evaporative cooler exit, state 2, is lim Thermoflex turbinesfrom withstate evaporative inlet cooling (Figure 2). The surrounding ambient airfor (7)gas is cooled 4the to state 2, as it is humidified in the evaporative coole ited by air the wet-bulb temperature ofstate ambient air. ambient (7) is cooled from state 4 to 2, as it is humidified in the evaporative (5) using a water source (8). The temperature at the evaporative cooler exit,cooler state 2, is lim (5) using a water source (8). The temperature at the evaporative cooler exit, state 2, is ited by the wet-bulb temperature of the ambient air. limited by the wet-bulb temperature of the ambient air. Figure 7. Gas turbine with evaporative inlet cooling. Figure 7. 7. Gas turbine with evaporative inlet cooling. Figure Gas turbine with inlet cooling. Given the benefits ofevaporative the two-stage cooling cycle, it would be desirable to provide two-stage evaporative method for turbine cooling to reduce inlet air dry Given the benefits ofcooling the two-stage cooling cycle, inlet it would be desirable to the provide Given the benefits of the two-stage cooling cycle, it would be8desirable to provideo bulb temperature below the inlet air wet-bulb temperature. Figure shows a a two-stage evaporative cooling method for turbine inlet cooling to reduce the inletschematic air two-stage evaporative cooling method for turbine inlet coolingfor toareduce the inlet airtwo dry the turbine and inlet cooling system presented in Thermoflex gasa turbine with dry-bulb temperature below the inlet air wet-bulb temperature. Figure 8 shows schematic bulb temperature below the inlet air wet-bulb temperature. Figure 8 shows a schematic stage evaporative inletcooling cooling introduced by [1] (Figure 3). The ambient aio of the turbine and inlet system presented in Thermoflex for asurrounding gas turbine with theisturbine and from inletinlet cooling system in Thermoflex for The a gasairturbine with two two-stage evaporative cooling introduced by [1] (Figure 3). The surrounding ambient (7) precooled state 6 to state 5presented in the heat exchanger (9). cooling is com stage evaporative inlet cooling introduced by [1] (Figure 3). The surrounding ambient a air (7) isfrom precooled state2,6as toitstate 5 in the heat exchanger (9). The air cooling is a wate pleted state 5from to state is humidified in the evaporative cooler (5) using completed 5 tostate state 62,(10) as state itcools is humidified in required the evaporative (5) using a (9). (7) is precooled from to 5 the in the heat exchanger (9).cooler The air cooling is com source (8).from The state cooling tower water for the heat exchanger water source The5cooling the water for the heat exchanger (9). a wate pleted from(8). state to statetower 2, as (10) it iscools humidified inrequired the evaporative cooler (5) using source (8). The cooling tower (10) cools the water required for the heat exchanger (9). Figure 8. Gas turbine with two-stage evaporative inlet cooling. Figure 8. Gas turbine with two-stage evaporative inlet cooling. Figure 9 shows a schematic of the turbine and inlet cooling system presented in Figure 8. Gas with two-stage cooling. Figure 9 turbine shows a schematic ofevaporative the turbineinlet and inlet cooling systeminlet presented Thermoflex for a gas turbine with hybrid absorption refrigeration evaporative cooling in Ther moflex4). forThe a gas turbine ambient with hybrid (Figure surrounding air (7)absorption is precooledrefrigeration from state 6 toevaporative state 5 in the inlet heat cooling Figure 9 shows a schematic of the turbine and inlet cooling system presented in The exchanger (6). The air cooling is completed from state 5 to state 2, as it is humidified in (Figure 4). The surrounding ambient air (7) is precooled from state 6 to state 5the in the hea moflex for a gas turbine with hybrid absorption refrigeration evaporative inlet evaporative cooler (5) using a water source (8). The absorption chiller (3) cools the water exchanger (6). The air cooling is completed from state 5 to state 2, as it is humidifiedcoolin in th needed for4). the heat exchanger The generator absorption chiller (3)6was assumed (Figure The surrounding air (7)of isthe precooled from state to(3)state 5 in hea evaporative cooler (5) using(6). aambient water source (8). The absorption chiller cools thethe wate ◦ toexchanger operate using aThe hotair water source (12) of 100 C, which will5 be heated using gas turbine (6). cooling is completed from state to state 2, as it is humidified in th needed for the heat exchanger (6). The generator of the absorption chiller (3) was assumed exhaust gases. The design absorption coefficient of the chiller’s performance was assumed evaporative cooler (5) using a water source (8). The absorption chiller (3) cools the wate needed for the heat exchanger (6). The generator of the absorption chiller (3) was assume exhaust gases. The design absorption coefficient of the chiller’s performance was assumed temperature rise in the chilled water in the heat exchanger (6) was assumed as 7 °C. This hot water is heated using gas turbine exhaust gases. The condenser of the absorption chiller (3) is water-cooled using a cooling tower (10). Energies 2021,as 14,0.67. x FORThe PEERmaximum REVIEW Energies 2021, 14, 1382 8 of 17 of 17 turbine to operate using a hot water source (12) of 100 °C, which will be heated using8 gas exhaust gases. The design absorption coefficient of the chiller’s performance was assumed as 0.67. The maximum temperature rise in the chilled water in the heat exchanger (6) was assumed as maximum 7 °C. Thistemperature hot water isrise heated gas turbine gases. The condenser as 0.67. The in theusing chilled water in theexhaust heat exchanger (6) was assumed as 7 ◦ C. This hot (3) water is heated usingusing gas turbine exhaust gases. The condenser of the absorption chiller is water-cooled a cooling tower (10). of the absorption chiller (3) is water-cooled using a cooling tower (10). Figure 9. Gas turbine with hybrid absorption refrigeration evaporative inlet cooling. Figure 10 shows a schematic of the turbine and inlet cooling system presented in Figure 9. Gas turbine with hybrid absorption refrigeration evaporative inlet cooling. Thermoflex for a Figure gas turbine with with hybrid vapor-compression refrigeration evaporative 9. Gas turbine hybrid absorption refrigeration evaporative inlet cooling. inlet cooling (Figure 5).Figure The surrounding ambient air (7) is precooled from state 1 state in 10 shows a schematic of the turbine and inlet cooling system to presented Figure 10 shows a schematic of the turbine and inlet cooling system presented in Thermoflex for a air gas cooling turbine with hybrid vapor-compression evaporative 2 in the heat exchanger (6). The is completed from state 2 refrigeration to state 3, as it is a gas turbine with hybrid vapor-compression refrigeration inlet cooling for (Figure 5).(3) The surrounding ambient air (7)The is precooled from state 1 to evaporative state humidified in the Thermoflex evaporative cooler using a water source (5). vapor-compression 2 in the heat exchanger (6). The air cooling ambient is completed from state 2 to state 3,state as it is inlet cooling (Figure 5). The surrounding air (7) is precooled from chiller (12), an electrically driven system using gas turbine output, cools the water needed 1 to state in exchanger the evaporative (3)cooling using a water source (5).from The vapor-compression 2humidified in the heat (6). cooler The air is completed state 2 to state 3, as it is for the heat exchanger (6). The maximumdriven temperature risegas inturbine the chilled water in the heat chiller (12), an electrically system using output, the water needed humidified in the evaporative cooler (3) using a water sourcecools (5). The vapor-compression exchanger (6) was assumed as 7 °C. The design coefficient of the chiller’s performance was for the heat exchanger (6). The maximum temperature rise in the chilled water in the heat chiller (12), an electrically driven system using gas turbine output, cools the water needed exchanger (6) of wasthe assumed as 7 ◦ C. The designchiller coefficient the chiller’s performance was assumed as 3. Thefor condenser vapor-compression (12)ofis water-cooled the heat exchanger (6). The maximum temperature rise in isthe chilledusing water inathe heat assumed as 3. The condenser of the vapor-compression chiller (12) water-cooled using a cooling tower (10). exchanger (6) was assumed as 7 °C. The design coefficient of the chiller’s performance was cooling tower (10). assumed as 3. The condenser of the vapor-compression chiller (12) is water-cooled using a cooling tower (10). Gas turbine hybrid vapor-compression refrigeration evaporative inlet cooling. Figure 10.Figure Gas 10. turbine with with hybrid vapor-compression refrigeration evaporative inlet cooling. FigureFor 10.the Gasabove turbine withthe hybrid vapor-compression refrigeration evaporative inlet cooling. cases, saturation efficiency of evaporative coolers was assumed as ◦ above95%, cases, efficiency evaporative as andthe thesaturation heat exchanger minimumofpinch point was coolers assumed was as 2 assumed C. For the For the minimum above cases,pinch the saturation efficiency of as evaporative coolers was assumed as 95%, and the heat exchanger point was assumed 2 °C. 95%, and the heat exchanger minimum pinch point was assumed as 2 °C. Energies 2021, 14, x FOR PEER REVIEW 9 of 17 Energies 2021, 14, 1382 9 of 17 4. Simulation Results and Discussions The simulation of the above cases was conducted for the GE 7001EA gas in 9 ofturbine 17 4. Simulation andnet Discussions Riyadh. Figure 11Results shows the output power of the gas turbine with and without differsimulation of the above cases was that conducted for the GE ISO-rated 7001EA gas turbine ent inletThe cooling techniques. The results indicate the turbine power, 84 MW, Riyadh. Figure 11MW shows the and net output power of the gas with and fluctuates between 64.6 in June 75.9 MW in December. Forturbine evaporative inletwithout cool4.in Simulation Results and Discussions inletpower cooling techniques. Theconducted results indicate that the power, ing,different the fluctuates between 74.5 and 78.8 For turbine two-stage evaporative Theturbine simulation of the above cases was for theMW. GE 7001EA gas turbine in ISO-rated 84 MW, fluctuates between 64.6 MW in June and 75.9 MW in December. For evaporative inlet cooling, the power fluctuates andwith 78.8 and MW. For hybrid Riyadh. Figure 11turbine shows the net output powerbetween of the gas76.5 turbine without differ-absorpinlet the turbine fluctuates 74.5 andISO-rated 78.8 ForMW. two-stage ent inletcooling, cooling techniques. Thepower results indicate thatbetween the turbine power, 84 MW, tion evaporative inlet cooling, the turbine power fluctuates between 76.5MW. and 81 For evaporative inlet cooling, the turbine power fluctuates between 76.5 and 78.8 fluctuates between 64.6 MW inevaporative June and 75.9inlet MW in December. evaporative inlet cool- MW. hybrid vapor-compression cooling, theFor turbine power fluctuates be-For ing, the turbine power fluctuates between 74.5 and 78.8 MW. For two-stage evaporative hybrid evaporative cooling, the turbine power fluctuates between 76.5 tween 76.5absorption and 80.6 MW. Figure 12 inlet shows the monthly percentage increase in the turbine’s inlet cooling, theFor turbine power fluctuates betweenevaporative 76.5 and 78.8 MW. absorpand 81 MW. hybrid vapor-compression inlet For cooling, the turbine power net power output for the different cooling techniques, referenced tohybrid the turbine without tion evaporative inlet cooling, the80.6 turbine power fluctuates between 76.5 and 81 MW. For increase fluctuates and 12 augmentation shows the monthly inlet cooling. between The data76.5 in Figure 12 MW. showFigure that the in thepercentage turbine’s output hybrid vapor-compression evaporative inlet cooling, the turbine power fluctuates beinreach the turbine’s netsummer. power output for the different cooling techniques, referenced can the The two-stage evaporative inlet cooling system (Figure to 12)the tween 76.520% andin 80.6 MW. Figure 12 shows the monthly percentage increase in the turbine’s turbine without inlet cooling. The data in Figure 12 show that the augmentation in performs infor June, andcooling Augusttechniques, than the other techniques. Figurewithout 13 shows thethe net powerbetter output the July different referenced to the turbine turbine’s output can reach 20% in the summer. The two-stage evaporative inlet cooling annual added The electric owing to inlet compared the uncooled inlet cooling. dataenergy in Figure 12 show that cooling, the augmentation inwith the turbine’s outputturbine. system (Figure 12) performs better in June, July and August than the other techniques. can reach 20% in the summer. The two-stage evaporative inlet cooling system (Figure 12) (1) ∆ = − Figure 13 shows the annual owing to inlet cooling, compared with performs better in June, July andadded Augustelectric than theenergy other techniques. Figure 13 shows the the uncooled turbine. annual added electric energy owing to inlet cooling, compared with the uncooled turbine. where Ewic and Eic are the annual energy generated without and with an inlet cooling sys∆E = Eic − Ewic (1) tem, respectively. The annual added∆energy percentages are 10 % for the evaporative (1) cool= − ing,where 11.3 % forand the Etwoare stage cooling, 12.5 %without for the and hybrid absorption and Ewic the evaporative annual energy generated with an inlet cooling where Ewic and Eic are icthe annual energy generated without and with an inlet cooling sys12.4system, % for respectively. the hybrid vapor compression TIAC systems. The two hybrid refrigeration The annual added energy percentages are 10 % for the evaporative tem, respectively. The annual added energy percentages are 10 % for the evaporative coolmethods are better than the two evaporative methods owing to satisfactory cooling, 11.3 % for the twoevaporative stage evaporative cooling, 12.5 fortheir the hybrid absorption and ing, 11.3 % for the two stage cooling, 12.5 % for the%hybrid absorption and performance in the winter. 12.4 % for the hybrid vapor compression TIAC systems. The two hybrid refrigeration meth12.4 % for the hybrid vapor compression TIAC systems. The two hybrid refrigeration ods areare better than the methodsowing owing their satisfactory performance methods better than thetwo twoevaporative evaporative methods toto their satisfactory perforin 85,000 theinwinter. mance the winter. Energies 2021, 14, x FOR PEER REVIEW 80,000 75,000 Power, kW Power, kW 85,000 80,000 75,000 70,000 70,000 65,000 65,000 60,000 60,000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar AprEvaporative May Jun Jul Aug Sep Two Octstage Nov Evaporative Dec No cooling No cooling Evaporative Two stage Evaporative Absorption Vapor Compression Absorption Vapor Compression Figure 11. 11. Effect of inlet cooling on turbine power output. Figure Effect of inlet cooling on turbine power output. Figure 11. Effect of inlet cooling on turbine power output. 25 25 Added AddedPower, Power, % % 20 20 15 15 10 10 5 5 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Evaporative Jan Feb Mar Apr May Jun Two Jul stage Aug Evaporative Sep Oct Nov Dec Absorption Vapor Compression Evaporative Two stage Evaporative Absorption Vapor Compression Figure 12. Added power output. Energies 2021, 14, x FOR PEER REVIEW 10 of 17 Energies 2021, 14, x FOR PEER REVIEW 10 of 17 Energies 2021, 14, 1382 10 of 17 Figure 12. Added power output. Figure 12. Added power output. 80,000 energy, MW h/year Added annual electric energy,annual MW h/year Added electric 80,000 60,000 60,000 40,000 40,000 20,000 20,000 0 0 Evaporative Two stage Absorption Evaporative Two stage Absorption Vapor Vapor Evaporative Compression Evaporative Compression Figure 13. Added Added annual electric energy (MW h/year). Figure 13. 13. Added annual electric energy (MW(MW h/year). Figure annual electric energy h/year). Figures 14 15 the net rate and net based on Figures 14and and 15show show theheat net heat heatand rateturbine and turbine turbine net efficiency efficiency based on network, network, Figures 14 and 15 show the net rate net efficiency based on network, respectively. Figure 16 shows the percentage increase in gas turbine efficiency with respectively. Figure 16 shows the percentage increase in gas in turbine efficiency with inlet respectively. Figure 16 shows the percentage increase gas turbine efficiency withinlet inlet cooling systems compared gas without inlet system. cooling systems compared withwith gas turbines without inlet cooling system. cooling systems compared with gasturbines turbines without inletcooling cooling system. ∆η ∆η∆η η − η η − wic η % = = =ηic − η100 %100 (2) (2) 100 %% (2) η η η %% η ηη wic wic ηic are efficiencies without and with an inlet cooling system, respectively. where ηwic ηand wic and ηic are efficiencies without and with an inlet cooling system, respectively. where where ηwic and ηic are efficiencies without and withcan an inlet cooling by system, respectively. TheThe gas gas turbine efficiency withwith the inlet cooling system becan increased 4.3%byin4.3% the in the turbine efficiency the inlet cooling system bebe increased The gas turbine efficiency with the inlet cooling system can increased by 4.3% in summer. summer. the summer. 12,000 Heat rate, kJ/kWh Heat rate, kJ/kWh 12,000 11,500 11,500 11,000 11,000 10,500 10,500 10,000 10,000Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec No cooling Evaporative Two stage Evaporative No cooling Absorption Energies 2021, 14, x FOR PEER REVIEW VaporEvaporative Compression Two stage Evaporative Vapor Compression Figure 14. Absorption Effect of inlet cooling on turbine heat rate. Figure 14. Effect of inlet cooling on turbine heat rate. Efficiency, % 35 14. Effect of inlet cooling on turbine heat rate. Figure 30 25 Jan No cooling Feb Mar Evaporative Apr May Jun Jul Two stage Evaporative Aug Figure 15. Effect of inlet cooling on gas turbine efficiency. Figure 15. Effect of inlet cooling on gas turbine efficiency. 5 Sep Absorption Oct Nov Dec Vapor Compression 11 of 17 25 Jan No cooling Feb Mar Evaporative Apr May Jun Jul Two stage Evaporative Aug Sep Oct Absorption Nov Dec Vapor Compression Energies 2021, 14, 1382 11 of 17 Figure 15. Effect of inlet cooling on gas turbine efficiency. Efficiency increase, % 5 4 3 2 1 0 Jan Feb Evaporative Mar Apr May Jun Two stage Evaporative Jul Aug Absorption Sep Oct Nov Dec Vapor Compression Figure 16. Percentage increase in gas turbine efficiency. Figure 16. Percentage increase in gas turbine efficiency. Water consumption for inlet cooling systems is critical in dry regions. For simulated inlet cooling systems, water needed to operate evaporative cooling sections and cooling Water consumption foris inlet cooling systems is critical in dry regions. For simulate towers. Figures 17 and 18 show the total water consumption using evaporative coolers inlet cooling systems, water is needed to operate evaporative cooling sections and coolin and cooling towers at daily and yearly rates. The two-stage evaporative cooling system towers. Figures 17 and 18the show theabsorption total water usingsystems. evaporative consumes less water than hybrid andconsumption vapor-compression The coole andcooling cooling towers at daily and yearly rates. two-stage evaporative cooling tower of the absorption refrigeration systemThe consumes larger amounts of water than system other systems to release highthe condenser heat to the surrounding. The hybrid absorption consumes less water than hybrid absorption and vapor-compression systems. Th Energies 2021, 14, x FOR PEER REVIEW 12 system needs 80%, 130% and 240% more water than the hybrid vapor-compression, the cooling tower of the absorption refrigeration system consumes larger amounts of wate two-stage evaporative and the high evaporative TIACheat systems, respectively. than other systems to release condenser to the surrounding. The hybrid absorp Water cosumption, m3/day tion system needs 80%, 130% and 240% more water than the hybrid vapor-compressio 600 evaporative and the evaporative TIAC systems, respectively. the two-stage Figure 19 shows that the fuel consumption of the gas turbine with inlet cooling sy 500 tems increases, compared with the gas turbine without a cooling system. The increase fuel consumption is related to the increase in the compressor airflow rate owing to inl 400 cooling. Figure 20 shows the annual increase in fuel consumption. 300 ∆ = , − ( , 200 where mf,wic and mf,ic are annual fuel consumption without and with inlet cooling system 100 respectively. 0 Jan Evaporative Feb Mar Apr May Jun Two stage Evaporative Jul Aug Sep Absorption Oct Nov Dec Vapor Compression Figure consumption of different inlet cooling Figure17.17.Water Water consumption of different inlet systems. cooling systems. ual water cosnumption, m3/year 160,000 120,000 80,000 40,000 Annual fuel consumption,Annual fuel consumption, Annual water cosnumption, Annual water cosnumption,Water cosumption, m3/da ton/year ton/year m3/year m3/year 0 500 Energies 2021, 14, 1382 Jan 400 Evaporative 300 Feb Mar Apr May Jun Two stage Evaporative Jul Aug Sep Absorption Oct Nov Dec Vapor Compression 12 of 17 Figure 17. Water consumption of different inlet cooling systems. 200 100160,000 0 Jan Feb Mar Apr May Jun 120,000 Evaporative Two stage Evaporative Jul Aug Sep Absorption Oct Nov Dec Vapor Compression 80,000 Figure 17. Water consumption of different inlet cooling systems. 40,000 160,000 0 120,000 Evaporative Two stage Evaporative Absorption Vapor Compression 80,000 Figure Annual water consumption of different inlet cooling Figure18.18. Annual water consumption of different inletsystems. cooling systems. Figure 19 shows that the fuel consumption of the gas turbine with inlet cooling systems 40,000 180,000 increases, compared with the gas turbine without a cooling system. The increase in fuel consumption is related to the increase in the compressor airflow rate owing to inlet cooling. Figure 20 shows the annual increase in fuel consumption. 0 160,000 Evaporative∆m =Two stage Vapor m f ,ic − m f ,wic Absorption (3) f Evaporative Compression where mf,wic and mf,ic are annual fuel consumption without and with inlet cooling 140,000 systems, respectively. Figure 18. Annual water consumption of different inlet cooling systems. 120,000 180,000 100,000 160,000 No cooling Evaporative Two stage Absorption Vapor Evaporative Compression 140,000 Figure 19. Annual fuel consumption of different inlet cooling systems. 120,000 100,000 No cooling Evaporative Two stage Absorption Vapor Evaporative Compression Figure19.19. Annual consumption of different inletsystems. cooling systems. Figure Annual fuelfuel consumption of different inlet cooling Energies 2021, Energies 2021, 14,14,x 1382 FOR PEER REVIEW 13 of 17 13 Annual increase in fuel consumption, ton/year 20,000 16,000 12,000 8000 4000 0 Evaporative Two stage Evaporative Absorption Vapor Compression Figure Annual increase in fuel of different cooling systems. Figure20.20. Annual increase inconsumption fuel consumption of different cooling systems. 5. Economic Analysis 5. Economic Analysis The feasibility of the investigated inlet cooling systems depends on their annual total Thetotal feasibility of the investigated inlet cooling their cost. The costs include installation and operating costs. systems Regardingdepends operatingon cost, the annual added annual profit AAP because of using inlet cooling systems can be estimated from cost. The total costs include installation and operating costs. Regarding operating cos added annual profit AAP because of using inlet cooling systems can be estimated fro AAP = Sa − Ca = (4) − where Sa is the added annual sale value of added energy and Ca is the added annual fuel and water added annual sale valueofofadded added energy energy because of the using inlet annua where Sa costs. is the The added annual sale value and Ca is added cooling systems can be estimated from and water costs. The added annual sale value of added energy because of using inlet ing systems can be estimated from Sa = ∆E Tae (5) =isΔTa = 0.048 $/kWh [32]. The added The current tariff of electricity in Saudi Arabia e annualThe costcurrent because of using inlet cooling systems was estimated tariff of electricity in Saudi Arabia is Tafrom e = 0.048 $/kWh [32]. The ad annual cost because of using inlet cooling LHV systems was estimated from Ca = ∆m f C =Δ Pf + mw Pw (6) + where LHV is the low heating value of used natural gas, LHV = 44,472 kJ/kg and Pf is the price of natural gas fuel [33]. where LHV is the low heating value of used natural gas, LHV = 44472 kJ/kg and Pf i price of natural gas fuel [33]. Pf = 2.6346$/million Btu (7) 2.6346 C is a conversion factor, mw is the = total water$⁄ consumption and Pw is the water 3 price (Pw = 1.6 USD/m ) [34]. Figure 21 shows the added annual operating profit (AAP) C is a conversion factor, mw is the total water consumption and Pw is the water produced using inlet cooling systems. The average AAP is USD 2 million per year. The 3) [34]. Figure 21 shows the added annual operating profit (AAP) (Pw = 1.6 USD/m evaporative and hybrid vapor-compression inlet cooling systems produced AAP of 9% duced inlet The average AAP USD 2 million per and year. The e and 7.5%using less than thecooling average systems. AAP, respectively. However, theistwo-stage evaporative hybrid absorption inlet cooling systems produced AAP of 3% and 6.5% higher than the of 9% orative and hybrid vapor-compression inlet cooling systems produced AAP average AAP, respectively. 7.5% less than the average AAP, respectively. However, the two-stage evaporative hybrid absorption inlet cooling systems produced AAP of 3% and 6.5% higher tha average AAP, respectively. Annual operation profit in Million $/year FOR PEER REVIEW Energies 2021, 14, 1382 14 of 14 17of 17 2.5 2 1.5 1 0.5 0 Evaporative Figure 21. Annual added profit. Two stage Evaporative Absorption Vapor Compression Figure 21. Annual added profit. Ahmadzadehtalatapeh and Rashidi [29] reported on the initial investment costs of Ahmadzadehtalatapeh and Rashidi [29] reported on the initial investment costs of evaporative cooling, vapor-compression and absorption inlet cooling systems. As shown, evaporative cooling, andadded absorption inlet systems. the vapor-compression initial investment costs per power are USDcooling 89, 259 and 267 perAs kWshown, for evaporathe initial investment per added power USD 89, vapor-compression 259 and 267 per kW evapotive, costs water-cooled absorption andare water-cooled inlet for cooling systems, respectively. For and hybrid absorption and vapor-compression systems, investment rative, water-cooled absorption water-cooled vapor-compression inlet cooling sys-costs should include both evaporative and refrigeration cooling equipment costs. The initial tems, respectively. For hybrid absorption and vapor-compression systems, investment investment cost was estimated from costs should include both evaporative and refrigeration cooling equipment costs. The inCi = Re Cev + (1 − Re )Cr (8) itial investment cost was estimated from where Ci is USD per added and−Cr are (8) = kW, C+ ) initial investment costs per added kilowatt ev (1 for evaporative and refrigeration systems, respectively, and Re is the ratio between the Ci is USD per added sensible kW, Cevevaporative and Cr arecooling initialtoinvestment costs per added kilowatt maximum total maximum cooling: where for evaporative and refrigeration systems, respectively, and Re is the ratio between the (9) e = Q e / ( Q e + Qr ) maximum sensible evaporative cooling to total Rmaximum cooling: For the two-stage evaporative inlet cooling system, investment costs should include (9) = ⁄( + ) both direct and indirect evaporative cooling equipment costs. The initial investment costs of the evaporative two-stage evaporative inlet cooling system will be far less than those of absorption For the two-stage inlet cooling system, investment costs should include and vapor-compression chillers and in the cost range of the direct evaporative inlet cooling both direct and indirect evaporative cooling equipment costs. The initial investment costs system. In this analysis, it was assumed that the costs of direct and indirect evaporative of the two-stage evaporative inlet cooling system will investment be far lesscost than those of absorption cooling are similar. Consequently, the total (USD) of inlet cooling systems and vapor-compression chillers and in the cost range of the direct evaporative inlet coolwas estimated from Ccap costs = Ci Pof adddirect and indirect evapora-(10) ing system. In this analysis, it was assumed that the tive cooling are similar. Consequently, the total investment inlet The cooling where Padd is the maximum monthly added power cost owed(USD) to inlet of cooling. payback periodfrom (PBP) was estimated from systems was estimated = PBP = Ccap /AAP (10)(11) Table 3 lists the investment cost, annual and payback period. The monthly added capital power owed toadded inlet profit cooling. The payback where Padd is the maximum payback period falls between 0.5 and 1.1 years. The PBP for evaporative and two-stage period (PBP) was estimated from evaporative systems is ~50% of the hybrid refrigeration inlet cooling systems. The data in = ⁄ (11) Table 3 lists the investment capital cost, annual added profit and payback period. The payback period falls between 0.5 and 1.1 years. The PBP for evaporative and two-stage Energies 2021, 14, 1382 15 of 17 Table 3 show the good feasibility of investment in inlet cooling systems. However, for hot, dry regions such as the city of Riyadh, evaporative and two-stage evaporative inlet cooling systems compete strongly with hybrid refrigeration inlet cooling systems. Table 3. Initial cost and payback period. Padd Cev Cr kW USD/kW USD/kW Evaporative 10,839 89 Two-stage evaporative 12,979 89 Hybrid absorption 12,492 Hybrid vapor-compression 12,462 TIAC System Re Ci Ccap AAP PBP USD/kW Million USD Million USD Year 1 89 0.964 1.8289 0.527 89 0.429 89 1.155 2.0634 0.560 89 259 0.538 167.5 2.093 2.1520 0.973 89 267 0.567 166.1 2.070 1.8699 1.107 6. Conclusions Evaporative, two-stage evaporative, absorption refrigeration evaporative and vaporcompression refrigeration evaporative TIAC systems were investigated for GE 7001EA gas turbine model under the weather conditions of the city of Riyadh. Thermoflex software was used to simulate the performance of the GE 7001EA gas turbine using different TIAC systems. This investigation was conducted to examine the feasibility of the two-stage evaporative TIAC system in hot dry regions. This system can cool the inlet air below the wet-bulb temperature. The simulation data indicate the competitive performance of the gas turbine incorporated with the two-stage evaporative TIAC system, where the power output in summer months increases by 20% compared with turbines without TIAC systems. However, using evaporative, hybrid absorption and hybrid vapor-compression TIAC systems increases the power output in summer months by 16.8, 19.3 and 19.3%, respectively. Regarding water consumption, the hybrid absorption system consumes 80%, 130% and 240% more water than the hybrid vapor-compression, the two-stage evaporative and the evaporative TIAC systems, respectively. The added annual profit of using the twostage evaporative TIAC system is 10% higher than evaporative TIAC, 7% higher than the hybrid vapor-compression TIAC and 4% lower than the hybrid absorption TIAC systems. The payback period of the two-stage evaporative TIAC system is 42% and 50% less than the than the hybrid vapor-compression and the hybrid absorption TIAC systems, respectively. Funding: This work was supported by King Saud University, Deanship of Scientific Research and Research Center College of Engineering. Institutional Review Board Statement: Not Applicable. Informed Consent Statement: Not Applicable. Data Availability Statement: Not Applicable. Acknowledgments: The author thanks the Deanship of Scientific Research and RSSU at King Saud University and Research Center College of Engineering for their technical support. Conflicts of Interest: The author declares no conflict of interest. Abbreviations AAP Ca Ccap Cev Cev Eic Ewic added annual profit, $/year added annual fuel and water costs, $/year total investment cost ($) of inlet cooling system investment cost of evaporative TIAC system per added kW power, $/kW investment cost of refrigeration TIAC system per added kW power, $/kW annual energy generated with TIAC system, MWh/year annual energy generated without TIAC system, MWh/year Energies 2021, 14, 1382 16 of 17 HR LHV mf,ic mf,wi mw P Padd PBP Pf Pw Qe Qr Sa Re Tae TIAC ηic ηwic Heat rate, kJ/kWh low heating value of used natural gas, 44,472 kJ/kg annual fuel consumption with TIAC system, ton/year annual fuel consumption without TIAC system, ton/year total water consumption, m3 /year Power, kW maximum monthly added power, kW payback period, year price of natural gas fuel, $/million Btu water price (Pw = 1.6 $/m3 ) sensible cooling load of evaporative TIAC sensible cooling load of refrigeration TIAC added annual sale value of added energy, $/year the ratio between evaporative cooling to total cooling current tariff of electricity in Saudi Arabia, 0.048 $/kWh turbine inlet air cooling efficiency with TIAC system efficiency without TIAC system References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 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