Thermodynamic optimization of a reheat chemically recuperated gas turbine

The feasibility of integrating a commercially available reheat gas turbine with a methane steam reformer is analyzed. A slight modification to the original reheat design is proposed to improve the methane conversion rate in the reforming process and, consequently, the efficiency in recovering waste exhaust heat from the gas turbine.Two solutions are proposed for the heat recovery scheme: a first reformer has a single pressure level while the second has two in order to match the different pressures of the combustors. While the single pressure scheme gives good performance with respect to the stand alone gas turbine, the dual pressure reformer can give a further benefit, as far as an accurate optimization of the steam management is performed.     

Modular approach to analysis of chemically recuperated gas turbine cycles

Current research programmes such as the CAGT programme investigate the opportunity for advanced power generation cycles based on state-of-the-art aeroderivative gas turbine technology. Such cycles would be primarily aimed at intermediate duty applications. Compared to industrial gas turbines, aeroderivatives offer high simple cycle efficiency, and the capability to start quickly and frequently without a significant maintenance cost penalty. A key element for high system performance is the development of improved heat recovery systems, leading to advanced cycles such as the humid air turbine (HAT) cycle, the chemically recuperated gas turbine (CRGT) cycle and the Kalina combined cycle. When used in combination with advanced technologies and components, screening studies conducted by research programmes such as the CAGT programme predict that such advanced cycles could theoretically lead to net cycle efficiencies exceeding 60%. In this paper, the authors present the application of the modular approach to cycle simulation and performance predictions of CRGT cycles. The paper first presents the modular simulation code concept and the main characteristics of CRGT cycles. The paper next discusses the development of the methane–steam reformer unit model used for the simulations. The modular code is then used to compute performance characteristics of a simple CRGT cycle and a reheat CRGT cycle, both based on the General Electric LM6000 aeroderivative gas turbine.     

Proposal and analysis of a dual-purpose system integrating a chemically recuperated gas turbine cycle with thermal seawater desalination

A novel cogeneration system is proposed for power generation and seawater desalination. It combines the CRGT (chemically recuperated gas turbine) with the MED-TVC (multi-effect thermal vapor compression desalination) system. The CRGT contains a MSR (methane-steam reformer). The produced syngas includes plenty of steam and hydrogen, so the working medium flow increases and NO_x emissions can achieve 1 ppm low. However, the water consumption is large, ∼23 t/d water per MW power output. To solve this problem and produce water for sale, MED-TVC is introduced, driven by exhaust heat. Such a dual-purpose plant was analyzed to investigate its performance and parameter selection, and compared with four conventional cogeneration systems with the same methane input. Some main results are following: In the base case of the CRGT with a TIT of 1308 °C and a compression ratio of 15, the MED-TVC with 9 effects, the specific work output, performance ratio and CRGT-consumed water ratio are 491.5 kJ/kg, 11.3 and 18.2%, respectively. Compared with the backpressure ST (steam turbine)/CC (combined cycle) plus MED/MSF (multistage flash), the CRGT + MED has better thermal performance, lower product cost and shorter payback period, which indicates the CRGT + MED dual-purpose system is a feasible and attractive choice for power and water cogeneration.     

Basic chemically recuperated gas turbines—power plant optimization and thermodynamics second law analysis

One of the proposals to increase the performance of the gas turbines is to improve chemical recuperated cycle. In this cycle, the heat in the turbine exhaust gases is used to heat and modify the chemical characteristics of the fuel. One mixture of natural gas and steam receives heat from the exhaust turbine gases; the mixture components react among themselves producing hot synthesis gas. In this work, an analysis and nonlinear optimization of the cycle were made in order to investigate the temperature and pressure influence on the global cycle performance. The chemical composition in the reformer was assumed according to chemical equilibrium equations, which presents good agreement with data from literature. The mixture of hot gases was treated like ideal gases. The maximum net profit was achieved and a thermodynamic second law analysis was made in order to detect the greatest sources of irreversibility.     

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.     

Exergetic and engineering analyses of gas turbine based cogeneration systems

This paper presents exergetic and engineering analyses as well as a simulation of gas turbine-based cogeneration plants consisting of a gas turbine, heat recovery steam generator and steam turbine. The exergy analysis is based on the first and second laws of thermodynamics. The engineering analysis is based on both the methodology of levelized cost and the pay back period. To simulate these systems, an algorithm has been developed. Two cogeneration cycles, one consisting of a gas turbine and the other of a gas turbine and steam turbine and process to produce electricity and process heat have been analyzed. The results showed good agreement with the reported data.     

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%.     

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.     

Exergetic and economic evaluation of control strategies for a gas turbine plant

In this paper, a thermoeconomic approach is applied to a gas turbine based power plant in order to analyze the performance of its control system when variations in the operating condition, due to some internal or external causes, occur. Different control strategies are compared by quantifying, first, their effect on the performance of the components. Then, their economic impact on the management is determined, by also evaluating the impact of the control system on the components lifetime.     

考虑实际气体性质的三轴燃气轮机中冷循环性能优化

考虑实际气体的热力性质,建立了三轴燃气轮机中冷循环的热力模型,以循环功率和效率为优化目标,对中间压比(或低压压气机压比)的分配进行了优化,同时分析了低压压气机进口气流温度、中冷度和总压比对循环性能的影响。研究发现,与不考虑实际气体热力性质的研究结论相比,循环功率或效率最大时的中间压比并不等于高压压气机压比。     

Simulated process integration of wastewater electrooxidation with recuperated micro gas turbine for energy recovery

Electrooxidation (EO) is a promising wastewater treatment technology that is plagued with high energy consumption. This study simulates the energy recovery potential from EO by process integration with recuperated micro gas turbine (RMGT). Gainful utilization of hydrogen produced at cathode is key to it. Percent recoverable energy (PRE) from EO would be strongly influenced by the cathodic current efficiency (CCE) and interelectrode potential (IP) and was likely to vary from a high of 46% to a low of 14%. Simulations suggested that process integration with RMGT could potentially recover 72.4% of this energy – 30.7% as electricity and 41.7% as thermal energy in the form of hot water at 353 K. This translated to 6.3%–9.7% electricity saved in EO besides recovered thermal energy. Energy dynamics was found to be highly sensitive to recuperator performance of the RMGT. Better recuperator performance made energy recovery through process integration more electricity driven at the cost of recovered heat and total energy recovery.     

燃气轮机中冷循环功率和功率密度优化比较

计入高低温侧换热器和中冷器的热阻损失、压气机和涡轮机中的不可逆压缩和膨胀损失及管路中压力损失,用有限时间热力学方法导出了变温热源条件下不可逆闭式燃气轮机中冷循环功率和功率密度（功率与循环中最大比容之比）的解析式;分别以功率和功率密度为目标,优化了中间压比、高低温侧换热器及中冷器热导率分配,并对结果进行了比较.     

Estimation of exergy-based sustainability index and performance evaluation of a novel intercooled hybrid gas turbine system

This paper contributes a novel sustainability index and modified exergy indicators for conventional gas turbines and solid oxide fuel cell integrated gas turbine (SOFC-GT) hybrid power cycles. In this work, an intercooled gas turbine (Ic-GT) cycle is considered as a base cycle, which gives an additive advantage in lowering the power required for the compressor. Moreover, on SOFC integration with Ic-GT, the qualitative and quantitative performance are examined. Numerical modeling is done using MATLAB and an exclusive comparison has been made based on energy-exergy and sustainability analysis for the system and its components. On comparing the first law efficiency at turbine inlet temperature, TIT 1250K and rp = 18 for Ic-GT, intercooled recuperated gas turbine (Ic-RGT), and Ic–SOFC–RGT, it is 25.82%, 36.04%, and 64.78%, respectively. Similarly, second law efficiency is 11.43%, 22.33%, and 61.11% and the overall sustainability index is 1.12, 1.28, and 2.57 for Ic-GT, Ic-RGT, and Ic–SOFC–RGT, respectively. Nine other modified exergy-based parameters are used to identify the role of fuel and product exergy and then compare the most affected component in three configurations.     

Exergetic evaluation of methods for improving power generation efficiency of a gas turbine cogeneration system

A cogeneration system generating both heat and power for district heating and cooling is required to be more efficient to improve its economy. In this paper, three typical methods for improving the power generation efficiency of a gas turbine cogeneration system are evaluated by examining exergy flow at various points of the system. The three methods investigated are: (a) to raise turbine inlet temperature, (b) to incorporate a regenerative cycle, and (c) to introduce a dual-fluid cycle. Exergy flows at various points of each cogeneration system have been evaluated. It has been shown through quantitve analyses of exergy flows (1) what kind of energy loss of the system can be reduced by introducing each efficiency-improving method, (2) that the method of incorporating a regenerative cycle is highly useful in improving exergy efficiency of the cogeneration system. © 1997 by John Wiley & Sons, Ltd.     

Cost numerical optimization of the triple‐pressure steam‐reheat gas‐reheat gas‐recuperated combined power cycle that uses steam for cooling the first GT

Optimization is an important method for improving the efficiency and power of the combined cycle. In this paper, the triple‐pressure steam‐reheat gas‐reheat gas‐recuperated combined cycle that uses steam for cooling the first gas turbine (the regular steam‐cooled cycle) was optimized relative to its operating parameters. The optimized cycle generates more power and consumes more fuel than the regular steam‐cooled 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 heat recovery steam generator (HRSG) and the costs of the additional operation and maintenance, installation, and fuel. Constraints were set on many operating parameters such as air compression ratio, the minimum temperature difference for pinch points (δT_ppm), the dryness fraction at steam turbine outlet, and stack temperature. The net additional revenue and cycle efficiency were optimized at 11 different maximum values of turbine inlet temperature (TIT) using two different methods: the direct search and the variable metric. The optima were found at the boundaries of many constraints such as the maximum values of air compression ratio, turbine outlet temperature (TOT), and the minimum value of stack temperature. The performance of the optimized cycles was compared with that for the regular steam‐cooled cycle. The results indicate that the optimized cycles are 1.7–1.8 percentage points higher in efficiency and 4.4–7.1% higher in total specific work than the regular steam‐cooled 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 21 million U.S. dollars for a 439 MW power plant. Increasing the maximum TOT to 1000°C and replacing the stainless steel recuperator heat exchanger of the optimized cycle with a super‐alloys‐recuperated heat exchanger could result in an additional efficiency increase of 1.1 percentage point and a specific work increase of 4.8–7.1%. The optimized cycles were about 3.3 percentage points higher in efficiency than the most efficient commercially available H‐system combined cycle when compared at the same value of TIT. Copyright © 2008 John Wiley & Sons, Ltd.     

Exergetic optimization of flat plate solar collectors

In this paper, an exergetic optimization of flat plate solar collectors is developed to determine the optimal performance and design parameters of these solar to thermal energy conversion systems. A detailed energy and exergy analysis is carried out for evaluating the thermal and optical performance, exergy flows and losses as well as exergetic efficiency for a typical flat plate solar collector under given operating conditions. In this analysis, the following geometric and operating parameters are considered as variables: the absorber plate area, dimensions of solar collector, pipes' diameter, mass flow rate, fluid inlet, outlet temperature, the overall loss coefficient, etc. A simulation program is developed for the thermal and exergetic calculations. The results of this computational program are in good agreement with the experimental measurements noted in the previous literature. Finally, the exergetic optimization has been carried out under given design and operating conditions and the optimum values of the mass flow rate, the absorber plate area and the maximum exergy efficiency have been found. Thus, more accurate results and beneficial applications of the exergy method in the design of solar collectors have been obtained.     

Thermodynamic optimization of reheat regenerative thermal-power plants

A first- and second-law procedure for the optimization of the reheat pressure level in reheat regeneration thermal-power plants is presented. The procedure is general in form and is applied for a thermal-power plant having two reheat pressure levels and two open-type feedwater heaters. The second-law efficiency of the steam generator, turbine cycle and plant are evaluated and optimized. The irreversibilities in the different components of the steam generator and turbine cycle sections are evaluated and discussed. Additional constraints such as the steam qualities at the exits of the different turbine stages are considered.     

燃气轮机燃烧室内部流场的冷态模拟与优化设计

利用流体分析软件STAR-CD对一个燃气轮机燃烧室的内部流场完整真实的几何结构进行了三维的冷态模拟；得出其内部的流场分布，对其加以分析，找出原设计中存在的问题，并加以改进，得出更加合理的流场分布，从而指导燃烧室的结构设计。改进后的数值模拟结果表明，改进措施的效果是十分明显的，所建立的流动分析系统为燃气轮机燃烧室的优化设计提供了强有力的计算分析工具。     

Power optimization of an endoreversible closed intercooled regenerated Brayton cycle

In this paper, power is optimized for an endoreversible closed intercooled regenerated Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite-time thermodynamics (FTT) or entropy generation minimization (EGM). The effects of some design parameters, including the cycle heat reservoir temperature ratio and total heat exchanger inventory, on the maximum power and the corresponding efficiency are analyzed by numerical examples. The analysis shows that the cycle dimensionless power can be optimized by searching the optimum heat conductance distributions among the hot- and cold-side heat exchangers, the regenerator and the intercooler for fixed total heat exchanger inventory, and by searching the optimum intercooling pressure ratio. When the optimization is performed with respect to the total pressure ratio of the cycle, the maximum dimensionless power can be maximized again.     

Exergetic optimization of solar collector and thermal energy storage system

This paper deals with the exergetic optimization of a solar thermal energy system. This consists of a solar collector (SC) and a rectangular water storage tank (ST) that contains a phase change material (PCM) distributed in an assembly of slabs. The study takes into account both conduction and convection heat transfer mode for water in the SC, and also the phase change process for the PCM in the ST. An analytical solution for the melting process in the PCM is also presented. The results of the study are compared with previous experimental data, confirming the accuracy of the model. Results of a numerical case study are presented and discussed.