Performance Of Combined Cycle Research Articles

An efficient methanol pre-reforming gas turbine combined cycle with integration of mid-temperature energy upgradation and CO2 recovery: Thermodynamic and economic analysis

An innovative design has been developed to optimize the performance of the gas turbine combined cycle (GTCC) by integration with a decarbonized methanol steam reforming (MSR-deCO2) system based on the principle of the cascade utilization of chemical and thermal exergy. In the integrated system, the primary fuel is reformed with the steam extracted from GTCC and decarbonized before combustion. The reforming process leads to a significant reduction of exergy loss in the combustor. Introducing methanol as a viable turbine fuel presents an opportunity for recuperating mid-temperature heat as chemical energy through endothermic MSR and redeeming it as high-grade thermal energy in the combustor. By such incorporation, the power generation of the mid-temperature heat in the bottoming cycle is significantly enhanced, and most of the CO2 is removed as the liquid phase. Based on a 530 MW GTCC plant, thermodynamic analysis reveals a 4.6% energy efficiency increase, a 4.3% exergy efficiency boost, and an 82.2% CO2 recovery with a 0.354 MJ/kgCO2 energy penalty. The proposed design yields 454.4 M$ more profit than the reference power plant throughout its lifespan. Additionally, sensitivity analysis indicates optimal conditions for MSR at approximately 250 °C, a 1:1 water-to-methanol ratio, and a higher reaction pressure preference.

Energy, Exergy & Environmental Analysis of a Combined Cycle with Pre-combustion CO2 Capture and N2 Injected into the Compressor of the Gas Turbine

Power plants are a major source of CO2 emissions in the environment, which cause global warming; due to this issue, CO2 capture from hydrocarbon fuels is one of the key technology options to reduce greenhouse gases. Pre-combustion capture of CO2 in the combined gas and steam turbine cycle has been investigated in this paper. The first step in the pre-combustion method is to react the fuel with oxygen, which comes from the air separation unit and produces a mixture of hydrogen and carbon monoxide. The CO is converted to CO2 in a water-shift reactor, and a physical absorbent removes the CO2; a hydrogen-rich fuel is produced, which can be burnt in a gas turbine with minimal CO2 emissions. This paper presents a thermodynamic cycle analysis, where pre-combustion CO2 capture is applied in a combined cycle where the main goal is to reduce the CO2 emission into the atmosphere. The main parameters are varied to examine the influence on cycle performance. The cycle performance results for the combined cycle with CH4 as fuel are presented and compared to the combined cycle with precombustion CO2 capture, both with and without Nitrogen injection into the compressor. An exergy analysis is carried out to determine which case has more exergy destruction. The results indicate that at 45 oC the combined cycle efficiency is raised by around 3 % when the pre-combustion CO2 capture without Nitrogen injection into the compressor is used, and the power output has been increased by 29 %. The performance of combined cycle with CO2 capture can be further enhanced by the N2 acquired from the air separation process and injected into the compressor’s middle stage. The results demonstrate a good improvement in the performance; the power output increases by 48 % and efficiency by 4.2 %. However, exergy destruction is increased when the CO2 capture, both with and without N2 injection into the compressor is used. Nevertheless, pre-combustion capture requires large monetary investment for a new-build plant where also the CO2 emission is reduced by 100 %.

Effects of excess oxidizer coefficient on RBCC engine performance in ejector mode: A theoretical investigation

This study investigates the effects of the primary rocket’s excess oxidizer coefficient (EOC) on the performance of a kerosene-fueled rocket-based combined cycle (RBCC) engine operating in ejector mode using the diffuser and afterburning (DAB) cycle. Employing complete mixing and chemical equilibrium assumptions, a quasi-one-dimensional model is developed to simulate combustion processes in the primary rocket chamber, mixer, and afterburner. Experimental data and full three-dimensional simulation validate the model’s accuracy. Results indicate that increasing EOC mitigates thermal choking effects at the mixer exit, decreasing mixing and Rayleigh losses, enhancing the entrainment ratio, and providing more oxygen for secondary combustion. However, the gas mixture’s compression ratio and total temperature decrease, rendering secondary combustion more susceptible to thermal choking in a constant cross-sectional afterburner. As the flight Mach number increases from 0.8 to 2.5, the optimum EOC for maximum specific impulse shifts from 0.725 to 2.375. While the optimum EOC for maximum thrust remains consistently around 2.0. The findings underscore the necessity of a higher EOC to fully unlock the DAB cycle’s thrust augmentation potential.

An efficient methanol pre-reforming gas turbine combined cycle with mid-temperature energy upgradation: Thermodynamic and economic analysis

A novel design has been developed to optimize the performance of the gas turbine combined cycle (GTCC) plant by integration with a methanol steam reforming (MSR) system based on the principle of the cascade utilization of chemical energy. In the integrated MSR-GTCC system, the methanol fuel releases its chemical energy through two successive processes: the thermal reforming reaction of primary fuel in the MSR, and the combustion reaction of reformate syngas in GTCC. The energy required for the endothermic MSR is provided by a portion of mid-temperature heat (MTH), which is extracted from the bottoming cycle of GTCC. By such incorporation, the loss in the conversion from chemical energy to physical energy is reduced and the power generation capability of MTH is improved effectively. Based on a 530 MW GTCC plant, the thermodynamic analysis reveals that the energy and exergy efficiencies are promoted by 7.3 % and 7.2 %, respectively. Besides, the profit of the integrated design is 193.9 M$ higher than that of the conventional system over the lifespan. Furthermore, sensitivity evaluation indicates that the non-reflux MSR process is suitable when the reaction temperature exceeds 250 °C and the optimal water-to-methanol ratio is approximately 1.0 for the integrated MSR-GTCC system.

Performance enhancements and NOx emission reductions using novel exhaust-driven hybrid gas turbine inlet air-cooling techniques

For combined cycles, gas turbine inlet air-cooling (GTIAC) increases the mass flow rates of both air and the generated steam of the heat recovery steam generator and hence power output. The introduction of exhaust gas recirculation (EGR) to reduce NOx emissions necessitates the application of GTIAC to overcome the adverse effects of gas turbine (GT) inlet air heating that accompany EGR. For a hot-humid climate, the r5egular cooling methods consume a significant amount of energy while desiccant and inlet-fogging are not effective. The main purpose of this study is to introduce innovative exhaust-driven hybrid GTIAC techniques that can reduce effectively the inlet temperature of the combined cycle in a hot-humid climate without consuming a substantial amount of energy and examine the effects of applying such techniques on the performance and NOx emissions. In this paper, a thorough analysis for the effect of increasing ambient temperature ( To) and relative humidity ( RHo) on the performance and NOx emissions of the air-cooled GT combined cycle (ACGTCC) is presented and the novel exhaust-driven hybrid (NE-DH) GTIAC systems of desiccant-ejector, ejector-refrigeration, and desiccant-ejector-refrigeration are applied to ACGTCC and optimized for maximum power output. The 1-D model at the double choking was used to model the performance of the ejector GTIAC technique. The results indicate that applying NE-DH GTIAC techniques results in gains in power, which vary between 0.31% and 0.6% per °C rise in To and an efficiency improvement of up to about 0.5 percentage point and significant reductions in both capital and maintenance costs compared with applying the refrigeration GTIAC system. The introduction of ejector and desiccant cooling decreases NOx emissions further and adds no additional equipment cost if implemented together with EGR or some CO2 capture techniques. A suggested plan for GTIAC that reduces NOx emissions by up to 25% is presented.

Cascading the Transcritical CO2 and Organic Rankine Cycles with Supercritical CO2 Cycles for Waste Heat Recovery

Concentrating solar power (CSP) applications can benefit from the superior thermophysical and chemical properties of supercritical CO2 (sCO2), which offers greater cycle efficiency in contrast to supercritical or superheated steam cycles. The transcritical CO2 (TCO2 cycle) excels in low-grade waste heat recovery (WHR), while the organic Rankine cycle (ORC) is also a potential option for WHR from sCO2 cycles. This study focuses on the thermodynamic assessment and optimization of combined power cycles, incorporating multiple bottoming cycles, to enhance overall thermal efficiency. The configurations employed include recompression, partial cooling, and main compression intercooling within the sCO2 cycle. Waste heat recovery is achieved using both TCO2 and ORC. The parametric analysis explores key variables such as turbine inlet temperature, main compressor inlet temperature, recuperator effectiveness, pressure ratios in the bottoming cycles, and condensation temperatures of the bottoming cycles. Furthermore, this research conducts performance analysis of the proposed combined cycle configurations. The results underscore the substantial enhancement of combined cycle performance with regard to thermal and exergy efficiency. A rise in the highest temperature that can occur in the sCO2 cycle leads to improved thermal efficiency. The Main Compressor Inlet Temperature (MCIT) exhibits an efficiency increase of up to 40°C–45°C, attributed to pseudocritical effects, followed by a decline. Among the various configurations, the combined partial cooling cycle generates the highest net output power. The study finds that the combined main compression model consistently outperforms other layouts, yielding a 2-2.5% increase in efficiency. Optimization of the intermediate pressure value for the partial cooling (PC) and main compression (MC) cycles at 10 MPa further contributes to enhanced performance. This study not only presents the optimized operating conditions for each combined cycle but also offers a comparative analysis of these models under different boundary conditions. The findings from this research significantly advance the utilization of waste heat and the development of clean power generation.

Reducing the Energy Penalty of Retrofit Decarbonization in Combined Cycle Power Plants

Abstract This study is a continuation of previous work aimed at elucidating the effect of hydrogen-cofiring and exhaust gas recirculation (EGR) on combined cycle (CC) performance. The thermodynamic analysis was expanded to include postcombustion capture (PCC) by means of mono-ethanolamine (MEA). Attention was paid to net power output and thermal efficiency. Part-load operation of the CC without carbon capture was taken as a reference. Decarbonization solutions, in ascending order of complexity, included the following: (1) adding a PCC unit; (2) combining EGR with PCC, so as to exploit the increase in the flue gas CO2 concentration while reducing the exhaust gas flow delivered to the absorber; (3) including hydrogen cofiring at the largest capability dictated by the gas turbine (GT) combustion system, with the opportunity to explore a wider range of EGR rates, while still relying on PCC of the residual CO2 in flue gas, before discharge into the environment. Scenarios were first discussed under the same GT load for consistency with the published literature, thus enabling the validation of the modeling procedure. Then, CC net power production was assumed as the basis of comparison. The third solution was found to be the most promising thus minimizing both the energy penalty due to carbon capture and CO2 emission intensity (EI).

Assessment of single rotor expander-compressor device in combined organic Rankine cycle (ORC) and vapor compression refrigeration cycle (VCR)

An environmental degradation due to consumption of fossil fuel based high grade energy releasing greenhouse gases is a pressing issue around the world. The use of low-grade heat from renewable energy sources using organic Rankine cycle is an attractive solution to reduce of emission of greenhouse gases and protect the environment. This paper investigates the potential of a new single rotor expander-compressor device in a combined Vapor Compression Refrigeration (VCR) cycle and an organic Rankine cycle (ORC). The numerical model of combined ORC-VCR is developed and validated. The thermal performance of combined cycle has been evaluated under the influence of evaporation temperature of ORC (62.75 °C–89.7 °C) and VCR (−20 °C–5 °C), condensation temperature of ORC (20 °C–45 °C) and rotor speed (500–3000 rpm) at a constant hot source (water) temperature of 95 °C. The maximum cooling effect, heat-to-cooling efficiency, and exergy efficiency achieved are found to be 5.38 kW, 56% and 63% when the evaporation temperature of ORC and VCR is 62.75 °C and −5 °C, and condensation temperature of ORC is 20.5 °C. Moreover, cooling effect increases linearly with the rotor speed, however, the heat-to-cooling efficiency and exergy efficiency are not affected by the rotor speed.

Effect of gas turbine intake air temperature regulating heat exchanger on combined cycle performance based on three-dimensional deformed tube

Effect of gas turbine intake air temperature regulating heat exchanger on combined cycle performance based on three-dimensional deformed tube

Simulation studies on GAX based absorption cooling and power cycle using a mixture of ammonia-water working fluid and aluminium oxide nano particles

The present work is focused on analyzing the influence of nano material aluminium oxide on the performance of generator absorber heat exchange ammonia-water absorption refrigeration system. Matlab code has been used to simulate the performance of the combined cycle. The effect of refrigeration, absorber and condenser temperatures on the combined cycle performance have been studied. The results of the analysis indicate that the performance of the combined cycle is higher by 15 to 20% when Al2O3 nano particles were added when compared to the same cycle without the addition of nano particles.

Off-design performance analysis of a gas-supercritical carbon dioxide combined cycle under multi-stage mass flow cooperative operation

• A gas-supercritical carbon dioxide combined cycle was employed for load balance. • A reduction coefficient was proposed to build multi-stage mass flow cooperative operation. • Off-design performance models were proposed to present the performance of combined cycle. • Transcritical CO 2 cycle became more important under low-load operating conditions. • The combined cycle had good off-design performance under cooperative operation strategy. Renewable energy power plants have widely installed to supply electrical energy to power grids, which could lead to a grid load-balancing problem owning to the uncertainty of wind and solar power generations. To solve the issue of load balancing, a gas-supercritical carbon dioxide (CO 2 ) combined cycle, which has the advantages of compactness and flexibility, is employed and operated under off-design conditions with load-following operating strategies. A reduction coefficient is assumed to elucidate the multi-stage mass flow cooperative operation strategy of the combined cycle. Furthermore, off-design performance models and a solution procedure are proposed to present the off-design performance of the combined cycle under a cooperative operation strategy. The results from off-design simulations show that a large amount of recovered waste heat ensures that the transcritical CO 2 (t-CO 2 ) cycle becomes more important under low-load operating conditions. Additionally, the power ratio of the t-CO 2 cycle to the cascaded CO 2 cycle can be greater than 90% when the inlet guide vane is closed to the minimum opening, whereas the variation in the efficiency of the cascaded CO 2 cycle is relatively smooth. In general, the gas-supercritical carbon dioxide combined cycle has good off-design performance under multi-stage mass flow cooperative operation in terms of its wide load-following range and remarkably thermal efficiency improvement.

System Performance and Pollutant Emissions of Micro Gas Turbine Combined Cycle in Variable Fuel Type Cases

This study focuses on an investigation of the operating performance and pollutant emission characteristics of a micro gas turbine combined cycle using biomass gas, replacing natural gas. The models of both recuperative cycle micro gas turbines with a waste heat utilization system and a micro gas-steam turbine combined cycle system are established. When the gas turbine works at 100 kW and the same types of fuel are burnt, the recuperative cycle system consumes less fuel than the gas-steam combined cycle system. The electric efficiency of the recuperative cycle system can reach more than 29%, which is higher than 24% of the gas-steam combined system. The combined cycle thermal efficiency of the recuperative system is as high as 66%, with 36% waste heat utilization efficiency. The electrical efficiency of the recuperative cycle system in the biomass gas case decreases, while that of the gas-steam combined cycle system undergoes little change. When the gas turbine power output increases from 50 kW to 100 kW, the electrical efficiency and combined cycle thermal efficiency increases, but the thermal efficiency of waste heat utilization of recuperative cycle decreases, the NOX and SO2 emissions gradually rise. Under the same working conditions, the NOX emissions of the recuperative cycle system are greater than that of the steam-gas combined cycle system.

Influence of operating parameters on the performance of combined cycle based on exergy analysis

This paper presents the energy and exergy analysis for actual data of the triple-pressure combined cycle power plant (CCPP). This study was carried out to evaluate each component's power plant efficiency and destruction rate. Furthermore, to investigate the effect of operating parameters on a combined cycle power plant using an engineering equation solver (EES) program. The result shows that the net energy and exergy efficiency is calculated at 56%and 54%, respectively. Also, by exergy analysis, the major source of exergy destruction among components occurs in the combustion chamber with a value of 314.6 MW which is 58% of the total exergy destruction in power plants. The exergy destruction was significantly affected by the increased ambient temperature. The heat transfer rate can be reduced with the high-pressure ratio in the gas turbine, leading to an increase in the overall efficiency. Besides that, the high turbine inlet temperature increased the steam cycle's generated power and the power plant's overall efficiency. Reducing the exergy destruction rate will increase the power output and efficiency of the combined cycle power plant. Therefore, maximum efficiency could be achieved by decreasing the ambient temperature and increasing the turbine inlet temperature.

Energy and Exergy Analysis on a Blast Furnace Gas-Driven Cascade Power Cycle

Blast furnace gas is the major combustible by-product produced in the steel industry, where iron ore is reduced by coke into iron. Direct combustion of blast furnace gas after simple treatment for power generation is a common utilization method nowadays. However, this method suffers from low efficiency and high carbon intensity. The use of gas-steam combined cycle is an excellent method to improve the efficiency of blast furnace gas for power generation. However, there is a problem of insufficient utilization of low product heat, and the addition of CCS system can further reduce the power efficiency. To solve these issues, a new blast furnace gas power generation system with a Brayton cycle with supercritical CO2 and a Rankine cycle with transcritical CO2 is proposed in this work. The new system is then thermodynamically simulated by Aspen Plus, after the sub-modules are validated. The effects of molar ratio of steam to carbon, selexol/CO2 mass ratio, compression ratio, turbine import temperature and turbine inlet pressure on the system are investigated. A comparison is also performed between the new combined cycle system and the traditional combined cycle power generation system. The results show that in the new power generation system, net power efficiency of 53.29%, carbon capture efficiency of 95.78% and sulfur capture rate of 94.46% can be achieved, which is significantly better than the performance of the conventional combined cycle.

Assessment on energy and exergy of combined supercritical CO2 Brayton cycles with sizing printed-circuit-heat-exchangers

The supercritical carbon dioxide Brayton cycle is one of the alternative thermal schemes for advanced energy systems. In this study, ammonia absorption Refrigeration-reheat supercritical carbon dioxide Brayton combined cycle is constructed, and the thermodynamic performance of reheat supercritical carbon dioxide Brayton cycle with ammonia absorption refrigeration cycle are analyzed. The characteristics of Brayton cycle and ammonia absorption refrigeration cycle configuring with Printed Circuit Heat Exchanger are analyzed. The result shows that under controlled freezing-point storage condition, optimized combined cycle energy and exergy efficiency is 46% and 64.98%, electricity output and refrigeration capacity is 11.4 MW and 1.78 MW. Under air-conditioning refrigeration condition, optimized combined cycle energy and exergy efficiency is 50.28% and 65.04%, and electricity output and refrigeration capacity is 11.4 MW and 3 MW. Compared with combined cycle performance before optimization, average improvement of cycle energy efficiency, exergy efficiency and exergy destruction is 4.19%, 0.73% and 3.64%, which shows obvious improvement of cycle performance after optimization. Comparative analysis of printed circuit heat exchanger applied at recuperator and subcooler shows that heat transfer performance of single-faced etched printed circuit heat exchanger in straight channel is better than that of double-faced etched printed circuit heat exchanger for same heat transfer and pressure drop.

Peak regulation performance study of the gas turbine combined cycle based combined heating and power system with gas turbine interstage extraction gas method

Improving the peak regulation performance of the gas turbine combined cycle (GTCC)-based combined heating and power (CHP) system helps to increase the integration of renewable energy. A new method of the gas turbine (GT) interstage extraction gas is proposed to improve the peak regulation performance of the GTCC-based CHP system. The effect of the GT interstage extraction gas method on both the gas turbine expansion ratio and gas turbine extraction gas temperature are studied, and the heat and power operation regions of the GTCC-based CHP system are obtained. Finally, using a heating characteristic day as an example, the peak regulation performance and natural gas consumption changes of the GTCC-based CHP system are analysed. The results indicate that the GT interstage extraction gas method helps to expand the heat and power operation regions of the GTCC-based CHP system under the same output power. During the entire heating season from Nov.15th to Mar.15th, under the GT interstage extraction gas method, the integration of renewable energy is increased by 72071 MW, the natural gas consumption is decreased by 861.74 × 104 m3 and the profit is decreased by $4.72 × 105.

Design, modeling and multi-objective techno-economic optimization of an integrated supercritical Brayton cycle with solar power tower for efficient hydrogen production

Solar-driven hydrogen production systems are environmentally benign alternatives to gain more benefits of green hydrogen. In this work, a novel power generation plant based on supercritical Closed Brayton Cycle (CBC) driven by solar heliostat field is designed and optimized to be integrated with an electrolyzer for green hydrogen production. To improve the CBC performance, its waste heat is recovered by an organic Rankine cycle (for additional power generation) and an absorption chiller for compressor inlet cooling. Thermoeconomic models are developed to evaluate the proposed hydrogen production plants and to compare the proposed combined cycle performance with that of standalone CBC-based system, in terms of hydrogen production rate, solar-to-hydrogen exergy efficiency and levelized cost of produced hydrogen. Then, a bi-objective optimization is conducted to attain minimum hydrogen cost and maximum exergy efficiency. The results revealed superior performance of the combined cycle over the CBC-based system. Under the optimum operating condition, the combined cycle yields around 15.8% higher hydrogen production rate and solar-to-hydrogen efficiency, and approximately 4.2% lower hydrogen cost. This implies that, the additional expenditures imposed by adding the bottoming cycles are totally compensated by extra hydrogen production, which in this case it costs 7.01$/kgH2. A comparison with a solar tower-based previous system proved superiority of the present plant by around 5% based on solar-to-hydrogen exergy efficiency.

Design and analysis of a novel solar compression-ejector cooling system with eco-friendly refrigerants using hybrid photovoltaic thermal (PVT) collector

• A novel solar cooling system is designed and analyzed. • The solar cooling efficiency increased by 33.1 %. • The COP of the refrigeration cycle is improved by 8.23 %. • R290 has the best performance in the system. World faces cold crunch and solar energy exploitation plays a vital role in facing this problem. This study aims at improving the performance of combined solar ejector vapor compression refrigeration cycles ( EVRC ) with two evaporators using a photovoltaic thermal ( PVT ) collector. The PVT collector supplies the system's required power, such as compressor and water circulator pump. The outgoing water is further used to cool the condenser and subcool the condenser outlet refrigerant to improve the system efficiency. This work also investigates the utilization of the environmentally friendly refrigerants of R1234yf, R600a, and R290 to reduce the global warming issue by replacing the typical R134a refrigerant. The results showed that the optimal water flow rate for the highest system efficiency and the lowest exergy destruction is 0.05 kg/s. With the passage of water (with optimal flow rate), the collector's electrical efficiency, total solar cooling efficiency, and refrigeration cycle performance coefficient ( COP ) can be increased by 11%, 33.1%, and 8.23%, respectively, compared to the non-cooling state. The R290 refrigerant also performs best in terms of maximum efficiency and lowest system exergy destruction, among other refrigerants, with COP and solar cooling efficiency of 3 and 0.52, respectively, which is 4.8% and 4.6% higher in comparison with the R134a.

Techno-Environmental Evaluation of a Liquefied Natural Gas-Fuelled Combined Gas Turbine with Steam Cycles for Large Container Ship Propulsion Systems

Restrictions on emissions are being imposed by regional and international shipping organisations, which raise the question of which marine fuel and technology can most effectively replace heavy fuel oil and diesel engines. The aim of this study is to find appropriate advanced combined gas and steam turbine cycles for marine propulsion systems in a large container ship with respect to the evolving maritime environmental regulations. The selection criteria are the thermodynamic performance, emissions, size, and weight of advanced combined gas and steam turbine cycles in a large container ship. Two baselines are used: a diesel engine using marine diesel oil and a combined gas and steam turbine system using liquefied natural gas and marine diesel oil. Then, liquefied natural gas cycles are examined based on fuel replacement and enhanced to assess the benefits of liquefied natural gas over marine diesel oil. The results show that the enhanced liquefied natural gas combined gas and steam turbine cycles are the most efficient, at up to 1.6% higher than the other cycles. Regarding the size and weight, the combined gas and steam turbine propulsion system is approximately 24.7% lighter than the original diesel engine propulsion system.

Air bottoming combined cycle performance analyses by the combined effect of variable parameters

Air bottoming combined cycle performance analyses by the combined effect of variable parameters