Thermo-environmental analysis of an open cycle gas turbine power plant with regression modeling and optimization

In this paper, a gas turbine cycle is modeled to investigate the effects of important operating parameters like compressor inlet temperature (CIT), turbine inlet temperature (TIT) and pressure ratio (PR) on the overall cycle performance and CO₂ emissions. Such effects are also investigated on the exergy destruction and exergy efficiency of the cycle components. Furthermore, multiple polynomial regression models are developed to correlate the response variables (performance characteristics) and predictor variables (operating parameters). The operating parameters are then optimized. According to the results, operating parameters have a significant effect on the cycle performance and CO₂ emissions. The largest exergy destruction is found in the combustion chamber with lowest exergy efficiency. The regression models have appeared to be a good estimator of the response variables. The optimal operating parameters for maximum performance have been determined as 288 K for CIT, 1600 K for TIT and 23.2 for PR.     

Energy,exergy, and sustainability a novel comparison of conventional gas turbine with fuel cell integrated hybrid power cycle

In this paper, six novel modified exergy relations are explored to determine the precise estimation of exergy destruction and to identify which component has the most improvement potential. For this, three power generation cycles are considered, i.e., simple gas turbine (SGT), recuperated gas turbine (RGT), are compared with a novel hybrid system (SOFC-RGT: Solid Oxide Fuel Cell-RGT), which operates with fuel flexibility as well as enhanced work-output and thermal efficiency. For energy, exergy, and sustainability studies, numerical modeling is conducted using MATLAB. At r_p = 4, TIT = 1250 K, an exclusive comparison has been made between proposed configurations based on thermodynamic modeling and exergy-based sustainability index. It is found that with the inclusion of a recuperator and a fuel cell in the proposed cycles, the thermal and sustainability performance tend to increase significantly. Whereas, exergy destruction increases but has minimal impact on comparing thermal performance and sustainability index. In terms of sustainability, RGT is 30.76% more sustainable than SGT, while SOFC-GT is 63.39% more sustainable than RGT.     

Gas turbine steam injection and combined power cycles using fog inlet cooling and biomass fuel: A thermodynamic assessment

The results of energy and exergy analyses of two biomass integrated steam injection cycles and combined power cycles are reported. Fog cooling, steam injection and adding steam turbine cycles to gas turbine cycles can enhance the performance of power generation systems. Even with its lower heat value, biomass can be substituted for fossil fuels. The performances of the cycles are assessed under the same conditions. The assessments show that the combined cycle has a higher efficiency at lower values of compressor pressure ratio but the steam injection plant is advantageous at higher pressure ratio values. The steam injection plant has a higher net power under the same conditions, while the exergy loss rate is higher for the combined cycle at all pressure ratios. But the exergy destruction rate is higher for the steam injection cycle at lower compressor pressure ratios, and for the combined cycle at higher pressure ratios.     

Energy and exergy analyses of an externally fired gas turbine (EFGT) cycle integrated with biomass gasifier for distributed power generation

Biomass based decentralized power generation using externally fired gas turbine (EFGT) can be a technically feasible option. In this work, thermal performance and sizing of such plants have been analyzed at different cycle pressure ratio (r_p = 2−8), turbine inlet temperature (TIT = 1050–1350 K) and the heat exchanger cold end temperature difference (CETD = 200–300 K). It is found that the thermal efficiency of the EFGT plant reaches a maximum at an optimum pressure ratio depending upon the TIT and heat exchanger CETD. For a particular pressure ratio, thermal efficiency increases either with the increase in TIT or with the decrease in heat exchanger CETD. The specific air flow, associated with the size of the plant equipment, decreases with the increase in pressure ratio. This decrease is rapid at the lower end of the pressure ratio (r_p < 4) but levels-off at higher r_p values. An increase in the TIT reduces the specific air flow, while a change in the heat exchanger CETD has no influence on it. Based on this comparison, the performance of a 100 kW EFGT plant has been analyzed for three sets of operating parameters and a trade-off in the operating condition is reached.     

Modeling,numerical optimization,and irreversibility reduction of a triple-pressure reheat combined cycle

The main methods for improving the efficiency of the combined cycle are: increasing the inlet temperature of the gas turbine (TIT), reducing the irreversibility of the heat recovery steam generator (HRSG), and optimization. In this paper, modeling and optimization of the triple-pressure reheat combined cycle as well as irreversibility reduction of its HRSG are considered. Constraints were set on the minimum temperature difference for pinch points (PP_m), the temperature difference for superheat approach, the steam turbine inlet temperature and pressure, the stack temperature, and the dryness fraction at steam turbine outlet. The triple-pressure reheat combined cycle was optimized at 41 different maximum values of TIT using two different methods; the direct search and the variable metric. A feasible technique to reduce the irreversibility of the HRSG of the combined cycle was introduced. The optimized and the reduced-irreversibility triple-pressure reheat combined cycles were compared with the regularly designed triple-pressure reheat combined cycle, which is the typical design for a commercial combined cycle. The effects of varying the TIT on the performance of all cycles were presented and discussed. The results indicate that the optimized triple-pressure reheat combined cycle is up to 1.7% higher in efficiency than the reduced-irreversibility triple-pressure reheat combined cycle, which is 1.9–2.1% higher in efficiency than the regularly designed triple-pressure reheat combined cycle when all cycles are compared at the same values of TIT and PP_m. The optimized and reduced-irreversibility combined cycles were compared with the most efficient commercially available combined cycle at the same value of TIT.     

Energetic and exergetic performance analyses of a combined heat and power plant with absorption inlet cooling and evaporative aftercooling

In this paper, exergy method is applied to analyze the gas turbine cycle cogeneration with inlet air cooling and evaporative aftercooling of the compressor discharge. The exergy destruction rate in each component of cogeneration is evaluated in detail. The effects of some main parameters on the exergy destruction and exergy efficiency of the cycle are investigated. The most significant exergy destruction rates in the cycle are in combustion chamber, heat recovery steam generator and regenerative heat exchanger. The overall pressure ratio and turbine inlet temperature have significant effect on exergy destruction in most of the components of cogeneration. The results obtained from the analysis show that inlet air cooling along with evaporative aftercooling has an obvious increase in the energy and exergy efficiency compared to the basic gas turbine cycle cogeneration. It is further shown that the first-law efficiency, power to heat ratio and exergy efficiency of the cogeneration cycle significantly vary with the change in overall pressure ratio and turbine inlet temperature but the change in process heat pressure shows small variation in these parameters.     

Thermodynamic analysis of an LNG fuelled combined cycle power plant with waste heat recovery and utilization system

This paper has proposed an improved liquefied natural gas (LNG) fuelled combined cycle power plant with a waste heat recovery and utilization system. The proposed combined cycle, which provides power outputs and thermal energy, consists of the gas/steam combined cycle, the subsystem utilizing the latent heat of spent steam from the steam turbine to vaporize LNG, the subsystem that recovers both the sensible heat and the latent heat of water vapour in the exhaust gas from the heat recovery steam generator (HRSG) by installing a condensing heat exchanger, and the HRSG waste heat utilization subsystem. The conventional combined cycle and the proposed combined cycle are modelled, considering mass, energy and exergy balances for every component and both energy and exergy analyses are conducted. Parametric analyses are performed for the proposed combined cycle to evaluate the effects of several factors, such as the gas turbine inlet temperature (TIT), the condenser pressure, the pinch point temperature difference of the condensing heat exchanger and the fuel gas heating temperature on the performance of the proposed combined cycle through simulation calculations. The results show that the net electrical efficiency and the exergy efficiency of the proposed combined cycle can be increased by 1.6 and 2.84% than those of the conventional combined cycle, respectively. The heat recovery per kg of flue gas is equal to 86.27 kJ s^?1. One MW of electric power for operating sea water pumps can be saved. The net electrical efficiency and the heat recovery ratio increase as the condenser pressure decreases. The higher heat recovery from the HRSG exit flue gas is achieved at higher gas TIT and at lower pinch point temperature of the condensing heat exchanger. Copyright © 2006 John Wiley & Sons, Ltd.     

Thermodynamic performance assessment of an indirect intercooled reheat regenerative gas turbine cycle with inlet air cooling and evaporative aftercooling of the compressor discharge

This study provides a computational analysis to investigate the effects of cycle pressure ratio, turbine inlet temperature (TIT), and ambient relative humidity (φ) on the thermodynamic performance of an indirect intercooled reheat regenerative gas turbine cycle with indirect evaporative cooling of the inlet air and evaporative aftercooling of the compressor discharge. Combined first and second‐law analysis indicates that the exergy destruction in various components of gas turbine cycles is significantly affected by compressor pressure ratio and turbine inlet temperature, and is not at all affected by ambient relative humidity. It also indicates that the maximum exergy is destroyed in the combustion chamber; which represents over 60% of the total exergy destruction in the overall system. The net work output, first‐law efficiency, and the second‐law efficiency of the cycle significantly varies with the change in the pressure ratio, turbine inlet temperature and ambient relative humidity. Results clearly shows that performance evaluation based on first‐law analysis alone is not adequate, and hence more meaningful evaluation must include second‐law analysis. Decision makers should find the methodology contained in this paper useful in the comparison and selection of gas turbine systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Exergy analysis of two cryogenic air separation processes

Two process designs of a cryogenic ASU (air separation unit) have been evaluated using exergy analysis. The ASU is part of an IGCC (integrated gasification combined cycle); it is supplying oxygen and nitrogen to the gasifier and nitrogen to the gas turbine. The two process designs separate the same feed into products with the same specifications. They differ in the number of distillation columns that are used; either two or three. Addition of the third column reduced the exergy destruction in the distillation section with 31%. Overall, the three-column design destroyed 12% less exergy than the two-column design. The rational exergy efficiency is defined as the desired exergy change divided by the total exergy change; it is 38% for the three-column design and 35% for the two-column design. Almost half of the exergy destruction is located in compressor after-coolers. Using this heat of compression elsewhere in the IGCC can be an important way to increase the IGCC efficiency. It is proposed to use it for the pre-heating of ASU products or for the production of steam, which can be used as part of the steam turbine cycle.     

Energy and exergy analysis of steam cooled reheat gas–steam combined cycle

This paper deals with parametric energy and exergy analysis of reheat gas–steam combined cycle using closed-loop-steam-cooling. Of the blade cooling techniques, closed-loop-steam-cooling has been found to be superior to air-film cooling. The reheat gas–steam combined cycle plant with closed-loop-steam-cooling exhibits enhanced thermal efficiency (around 62%) and plant specific work as compared to basic steam–gas combined cycle with air-film cooling as well as closed-loop-steam cooling. Further, with closed-loop-steam-cooling, the plant efficiency, reaches an optimum value in higher range of compressor pressure ratio as compared to that in film air-cooling. It has also been concluded that reheat pressure is an important design parameter and its optimum value gives maximum plant efficiency.Component-wise inefficiencies of steam cooled-reheat gas–steam combined cycle based on the second-law-model (exergy analysis) have been found to be the maximum in combustion-chamber (≈30%), followed by that in gas turbine (≈4%).     

Exergy analysis of Joule–Thomson cryogenic refrigeration cycle with an ejector

In this paper, exergy method is applied to analyze the ejector expansion Joule–Thomson (EJT) cryogenic refrigeration cycle. The exergy destruction rate in each component of the EJT cycle is evaluated in detail. The effect of some main parameters on the exergy destruction and exergetic efficiency of the cycle is also investigated. The most significant exergy destruction rates in the cycle are in the compressor and ejector. The ejector pressure ratio and compressor isothermal efficiency have a significant effect on the exergetic efficiency of the EJT cycle. The exergy analysis results show the EJT cycle has an obvious increase in the exergetic efficiency compared to the basic Joule–Thomson refrigeration cycle. A significant advantage from the use of the ejector is that the total exergy destruction of the EJT cycle can be reduced due to much more decreasing of the exergy destruction rates in the compressor and expansion valve. The exergy analysis also reconfirms that applying an ejector is a very important approach to improve the performance of the Joule–Thomson cryogenic refrigeration cycle.     

Analysis and cost optimization of the triple‐pressure steam‐reheat gas‐reheat gas‐recuperated combined power cycle

Increasing the inlet temperature of gas turbine (TIT) and optimization are important methods for improving the efficiency and power of the combined cycle. In this paper, the triple‐pressure steam‐reheat gas‐reheat recuperated combined cycle (the Regular Gas‐Reheat cycle) was optimized relative to its operating parameters, including the temperature differences for pinch points (δT_PP). The optimized triple‐pressure steam‐reheat gas‐reheat recuperated combined cycle (the Optimized cycle) had much lower δT_PP than that for the Regular Gas‐Reheat cycle so that the area of heat transfer of the heat recovery steam generator (HRSG) of the Optimized cycle had to be increased to keep the same rate of heat transfer. For the same mass flow rate of air, the Optimized cycle generates more power and consumes more fuel than the Regular Gas‐Reheat cycle. An objective function of the net additional revenue (the saving of the optimization process) was defined in terms of the revenue of the additional generated power and the costs of replacing the HRSG and the additional fuel. Constraints were set on many operating parameters such as the minimum temperature difference for pinch points (δT_PPm), the steam turbines inlet temperatures and pressures, and the dryness fraction at steam turbine outlet. The net additional revenue was optimized at 11 different maximum values of TIT using two different methods: the direct search and variable metric. The performance of the Optimized cycle was compared with that for the Regular Gas‐Reheat cycle and the triple‐pressure steam‐reheat gas‐reheat recuperated reduced‐irreversibility combined cycle (the Reduced‐Irreversibility cycle). The results indicate that the Optimized cycle is 0.17–0.35 percentage point higher in efficiency and 5.3–6.8% higher in specific work than the Reduced‐Irreversibility cycle, which is 2.84–2.91 percentage points higher in efficiency and 4.7% higher in specific work than the Regular Gas‐Reheat cycle when all cycles are compared at the same values of TIT and δT_PPm. Optimizing the net additional revenue could result in an annual saving of 33.7 million US dollars for a 481 MW power plant. The Optimized cycle was 3.62 percentage points higher in efficiency than the most efficient commercially available H‐system combined cycle when compared at the same value of TIT. Copyright © 2007 John Wiley & Sons, Ltd.     

Comparative studies of augmentation in combined cycle power plants

The attractive features of a combined cycle (CC) power plant are fuel flexibility, operational flexibility, higher efficiency and low emissions. The performance of five gas turbine‐steam turbine (GT‐ST) combined cycle power plants (four natural gas based plants and one biomass based plant) have been studied and the degree of augmentation has been compared. They are (i) combined cycle with natural gas (CC‐NG), (ii) combined cycle with water injection (CC‐WI), (iii) combined cycle with steam injection (CC‐SI), (iv) combined cycle with supplementary firing (CC‐SF) and (v) combined cycle with biomass gasification (CC‐BM). The plant performance and CO₂ emissions are compared with a change in compressor pressure ratio and gas turbine inlet temperature (GTIT). The optimum pressure ratio for compressor is selected from maximum efficiency condition. The specific power, thermal efficiency and CO₂ emissions of augmented power plants are compared with the CC‐NG power plant at the individual optimized pressure ratios in place of a common pressure ratio. The results show that the optimum pressure ratio is increased with water injection, steam injection, supplementary firing and biomass gasification. The specific power is increased in all the plants with a loss in thermal efficiency and rise in CO₂ emissions compared to CC‐NG plant. Copyright © 2013 John Wiley & Sons, Ltd.     

Exergy analysis of renewable light olefin production system via biomass gasification and methanol synthesis

The conceptual light olefin production system from biomass via gasification and methanol synthesis was simulated and its thermodynamic performance was evaluated through exergy analysis. The system was made up of gasification, gas composition adjustment, methanol synthesis, light olefin synthesis, steam & power generation and cooling water treatment. The in-depth exergy analysis was performed at the levels of system, subsystem and operation component respectively. The gasifier and the tail gas combustor were the main sources of irreversibility with exergy destruction ratios of 17.0% and 16.8% of the input exergy of biomass. The steam & power generation subsystem accounted for 43.4% of the overall exergy destruction, followed by 41.0% and 5.69% in the subsystems of gasification and gas composition adjustment respectively. The sensitivity evaluation of the operation parameters of gasifier indicates that the system efficiency could be improved by enhancing syngas yield and subsequent yield of light olefins. The overall exergetic efficiency of 30.5% is obtained at the mass ratios of steam to biomass and O₂-rich gas (95 vol%) to biomass (S/B and O/B) of 0.26 and 0.14 and gasification temperature at 725 °C.     

Exergy and Energy Analysis of Combined Cycle systems with Different Bottoming Cycle Configurations

The paper deals with thermodynamic analysis of cooled gas turbine‐based gas‐steam combined cycle with single, dual, or triple pressure bottoming cycle configuration. The cooled gas turbine analyzed here uses air as blade coolant. Component‐wise non‐dimensionalized exergy destruction of the bottoming cycle has been quantified with the objective to identify the major sources of exergy destruction. The mass of steam generated in different configurations of heat recovery steam generator (HRSG) depends upon the number of steam pressure drums, desired pressure level, and steam temperature. For the selected set of operating parameters, maximum steam has been observed to be generated in the case of triple pressure HRSG = 19 kg/kg and minimum in single pressure HRSG = 17.25 kg/kg. Plant‐efficiency and plant‐specific works are both highest for triple‐pressure bottoming cycle combined cycle. Non‐dimensionalized exergy destruction in HRSG is least at 0.9% for B3P, whereas 1.23% for B2P, and highest at 3.2% for B1P illustrating that process irreversibility is least in the case of B3P and highest in B1P. Copyright © 2012 John Wiley & Sons, Ltd.     

Energy and exergy analyses of a CFB‐based indirectly fired combined cycle power generation system

Combined cycle configuration has the ability to use the waste heat from the gas turbine exhaust gas using the heat recovery steam generator for the bottoming steam cycle. In the current study, a natural gas‐fired combined cycle with indirectly fired heating for additional work output is investigated for configurations with and without reheat combustor (RHC) in the gas turbine. The mass flow rate of coal for the indirect‐firing mode in circulating fluidized bed (CFB) combustor is estimated based on fixed natural gas input for the gas turbine combustion chamber (GTCC). The effects of pressure ratio, gas turbine inlet temperature, inlet temperatures to the air compressor and to the GTCC on the overall cycle performance of the combined cycle configuration are analysed. The combined cycle efficiency increases with pressure ratio up to the optimum value. Both efficiency and net work output for the combined cycle increase with gas turbine inlet temperature. The efficiency decreases with increase in the air compressor inlet temperature. The indirect firing of coal shows reduced use with increase in the turbine inlet temperature due to increase in the use of natural gas. There is little variation in the efficiency with increase in GTCC inlet temperature resulting in increased use of coal. The combined cycle having the two‐stage gas turbine with RHC has significantly higher efficiency and net work output compared with the cycle without RHC. The exergetic efficiency also increases with increase in the gas turbine inlet temperature. The exergy destruction is highest for the CFB combustor followed by the GTCC. The analyses show that the indirectly fired mode of the combined cycle offers better performance and opportunities for additional net work output by using solid fuels (coal in this case). Copyright © 2009 John Wiley & Sons, Ltd.     

Two new high-performance cycles for gas turbine with air bottoming

The objective of this research is to model steam injection in the gas turbine with Air Bottoming Cycle (ABC). Based on an exergy analysis, a computer program has been developed to investigate improving the performance of an ABC cycle by calculating the irreversibility in the corresponding devices of the system. In this study, we suggest two new cycles where an air bottoming cycle along with the steam injection are used. These cycles are: the Evaporating Gas turbine with Air Bottoming Cycle (EGT-ABC), and Steam Injection Gas turbine with Air Bottoming Cycle (STIG-ABC). The results of the model show that in these cycles, more energy recovery and higher air inlet mass flow rate translate into an increase of the efficiency and output turbine work. The EGT-ABC was found to have a lower irreversibility and higher output work when compared to the STIG-ABC. This is due to the fact that more heat recovery in the regenerator in the EGT-ABC cycle results in a lower exhaust temperature. The extensive modeling performed in this study reveals that, at the same up-cycle pressure ratio and turbine inlet temperature (TIT), a higher overall efficiency can be achieved for the EGT-ABC cycle.     

Study of humid air turbine cycle with external heat source for air humidification

In this paper, through introducing an external heat source to the conventional humid air turbine (HAT) cycle, we have studied the performances of the improved humid air gas turbine cycle mainly by exergy analysis method. In order to attain the performance of the humid air gas turbine with external heat source, we compare it with the conventional HAT cycle in detail with different factors such as the pressure ratio, turbine inlet temperature (TIT) and the external circulating water mass flow. The results showed that the specific work of the new system and the humidity ratio of saturator are all increased in some degree. For example, in the same pressure ratio and TIT, when the ratio of the external circulating water mass flow rate with that of the internal water is 0.2, the specific work increases more than 15.2 kJ kg⁻¹a, and the humidity raises at least 2.0 percent points. By introducing the external circulating water into the system, though thermal efficiency of the new HAT cycle is lower than that of the conventional HAT cycle, the exergy efficiency exhibits different results. Generally, when the pressure ratio is over 8, the exergy efficiency for the proposed HAT cycle is higher than the conventional HAT cycle; while less than 8, whether or not the exergy efficiency increases will mainly depend on TIT. In addition, the exergy destructions of components in systems were investigated. Through the comparison of the new system with the conventional HAT cycle, it was found that the exergy loss proportion in combustion declines for the new system, and the proportion of exhaust loss increases. From the viewpoint of total energy system, the HAT cycle with utilization of external heat source is a beneficial way to improve the overall performances of energy utilization. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparative exergoeconomic analyses of the integration of biomass gasification and a gas turbine power plant with and without fogging inlet cooling

Inlet cooling is effective for mitigating the decrease in gas turbine performance during hot and humid summer periods when electrical power demands peak, and steam injection, using steam raised from the turbine exhaust gases in a heat recovery steam generator, is an effective technique for utilizing the hot turbine exhaust gases. Biomass gasification can be integrated with a gas turbine cycle to provide efficient, clean power generation. In the present paper, a gas turbine cycle with fog cooling and steam injection, and integrated with biomass gasification, is proposed and analyzed with energy, exergy and exergoeconomic analyses. The thermodynamic analyses show that increasing the compressor pressure ratio and the gas turbine inlet temperature raises the energy and exergy efficiencies. On the component level, the gas turbine is determined to have the highest exergy efficiency and the combustor the lowest. The exergoeconomic analysis reveals that the proposed cycle has a lower total unit product cost than a similar plant fired by natural gas. However, the relative cost difference and exergoeconomic factor is higher for the proposed cycle than the natural gas fired plant, indicating that the proposed cycle is more costly for producing electricity despite its lower product cost and environmental impact.     

Effects of evaporative inlet and aftercooling on the recuperated gas turbine cycle

Inlet air cooling and cooling of the compressor discharge using water injection boost both efficiency and power of gas turbine cycles. Four different layouts of the recuperated gas turbine cycle are presented. Those layouts include the effect of evaporative inlet and aftercooling (evaporative cooling of the compressor discharge). A parametric study of the effect of turbine inlet temperature (TIT), ambient temperature, and relative humidity on the performance of all four layouts is investigated. The results indicate that as TIT increases the optimum pressure ratio increases by 0.45 per 100 K for the regular recuperated cycle and by 1.4 per 100 K for the recuperated cycle with evaporative aftercooling. The cycles with evaporative aftercooling have distinctive pattern of performance curves and higher values of optimum pressure ratios. The results also showed that evaporative cooling of the inlet air could boost the efficiency by up to 3.2% and that evaporative aftercooling could increase the power by up to about 110% and cycle efficiency by up to 16%.