Analysing the benefits of hybridisation and storage in a hybrid solar gas turbine plant

ABSTRACT

A dynamic model of a tower-driven, hybrid solar gas turbine power plant is presented to highlight the benefits of hybrid operation as well as the development a novel plant configuration to improve solar fraction by leveraging a packed-bed thermal energy storage (TES). Relative to solar-only plant, hybridisation increases solar-to-electric efficiency (STE) by 30%. Introduction of a passive packed-bed TES only leads to slight improvement in solar energy utilisation and displacement of solar load. A novel plant configuration, which utilises a recycle stream to charge TES, is presented to improve solar energy utilisation. The recycle stream gives freedom to manipulate the thermal capacity of flow in the tower collector to control collector exit temperature and direct excess solar energy to TES. Employment of the proposed plant configuration leads to a 10.8% and 11.3% improvement in yearly STE and solar fraction, respectively, relative to a plant not utilising such a control scheme.     

Co-located gas turbine/solar thermal hybrid designs for power production

This paper describes gas turbine/solar trough hybrid designs that achieve a solar contribution greater than 50% and increase the solar-to-electric efficiency while reducing gas heat rate. Two conceptual designs are explored: (1) integrating gas turbines with conventional oil heat-transfer-fluid (HTF) troughs running at 390 °C, and (2) integrating gas turbines with salt-HTF troughs running at 450 °C and including thermal energy storage (TES). The latter system is also representative of molten-salt power towers, although the power towers run at temperatures near 565 °C and would require selection of an appropriate gas turbine to provide waste heat at those temperatures. Using gas turbine waste heat to supplement the TES system provides operating flexibility while enhancing the efficiency of gas utilization. The analysis indicates that the hybrid plant designs produce solar-derived electricity and gas-derived electricity at lower costs than either system operating alone.     

Design and performance analysis of a de-coupled solid oxide fuel cell gas turbine hybrid

Hybrid solid oxide fuel cells (SOFC) cycles of varying complexity are widely studied for their potential efficiency, carbon recovery and co-production of chemicals. This study introduces an alternative de-coupled fuel cell-gas turbine hybrid arrangement that retains the high efficiency thermal integration of a topping cycle without the high temperature heat exchanger of a bottoming cycle. The system utilizes a solid-state oxygen transport membrane to divert 30%–50% of the oxygen from the turbine working fluid to the intermediate temperature SOFC. Thermodynamic modeling delineates design trade-offs and identifies a flexible operating regime with peak fuel-to-electric efficiency of 75%. Co-production of electricity and high purity hydrogen result in net energy conversion efficiencies greater than 80%. The potential to retrofit existing turbine systems, particularly micro-turbines and stand-by ‘peaker’ plants, with minimal impact to compressor stability or transient response is a promising pathway to hybrid fuel cell/turbine development that does not require turbomachinery modification.     

Thermal performance analysis of gas turbine engines based on different compressor configurations

In this study, the performance of several gas turbine engines has been investigated using computational modelling based on the actual manufacturer's data. Further, the study focuses on evaluating the impact of varying the configuration of the compressor on overall engine performance based on the first and second laws of thermodynamics. The results confirm that the main source of irreversibilities occurs in the combustion chamber in all cases. The exergetic efficiency of the gas turbine engine significantly varies with compressor configurations, type of compressors, load variation, climatic condition, and isentropic efficiency. The engine capacity and high‐pressure turbine inlet temperature govern the gas turbine performance, and higher values are more favourable. The gas turbine exergetic efficiency drops off when the power setting adjusted at part‐load and at high ambient temperature. The most optimal gas turbine performance is located at the single axial compressor case, followed by the axial‐centrifugal compressor and then the centrifugal–centrifugal compressor.     

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.     

Test and evaluation of a solar powered gas turbine system

This paper describes the test and the results of a first prototype solar powered gas turbine system, installed during 2002 in the CESA-1 tower facility at Plataforma Solar de Almería (PSA) in Spain. The main goals of the project were to develop a solar receiver cluster able to provide pressurized air of 1000 °C and solve the problems arising from the coupling of the receivers with a conventional gas turbine to demonstrate the operability of the system. The test set-up consists of the heliostat field of the CESA-1 facility providing the concentrated solar power, a pressurized solar receiver cluster of three modules of 400 kWth each which convert the solar power into heat, and a modified helicopter engine (OST3) with a generator coupled to the grid. The first test phase at PSA started in December 2002 with the goal to reach a temperature level of 800 °C at the combustor air inlet by the integration of solar energy. This objective was achieved by the end of this test phase in March 2003, and the system could be operated at 230 kWe power to grid without major problems. In the second test phase from June 2003 to August 2003 the temperature level was increased to almost 1000 °C. The paper describes the system configuration, the component efficiencies and the operation experiences of the first 100 h of solar operation of this very successful first test of a solar operated Brayton gas turbine system.     

Thermal performance of a triple-pass solar air collector

This communication presents a mathematical model for the thermal performance of a triple-pass solar air heater. The model predicts a rise of 4–22°C in the temperature of air (corresponding to efficiencies of 0.37–0.46) during a typical day in Nsukka, Nigeria in April; the predictions have been compared with the reported experimental results of Ezeike [Energy in Agriculture, Vol. 5, pp. 1–20 (1986)]     

Thermal performance of a new solar air heater

A solar air heater, part of a food drying system using solar energy as a renewable energy source for heat, was developed and tested for several agricultural products (i.e., sultana grapes, green beans, sweet peppers, chilli peppers). Drying processes were conducted in the chamber with forced natural air heated partly by solar energy. Solar air heater performances were discussed along with estimates of energy efficiency of the system. The obtained results indicate that the present system is efficient and effective.     

微型燃气轮机涡轮背盘冲击冷却特性研究

受可靠性和成本制约,微型燃气轮机冷却技术的发展和应用一直较为缓慢,已成为其进一步提升热效率的主要瓶颈。针对此问题,提出了一种简单可靠的径流涡轮新型冷却技术-背盘冲击冷却,使用气热耦合的方法对该冷却技术的冷却特性进行了仿真研究。结果表明:背盘冲击冷却可以大幅降低径流涡轮背盘的温度。当冷却气体流量为主流的2%时,冷却流体温度从473.0降到323.0 K,背盘平均温度降低了143.0～202.0 K;当冷却温度为323.0 K时,冷却气体消耗量从主流质量流量的1%增加到4%时,背盘平均温度降低150.0～252.0 K。冷却流体流入主流后会对其产生一定的影响,每增加1%的冷却流量,涡轮机效率下降约1%。     

Exergy based performance analysis of a solid oxide fuel cell and steam injected gas turbine hybrid power system

This paper presents exergy analysis of a hybrid solid oxide fuel cell and gas turbine (SOFC/GT) system in comparison with retrofitted system with steam injection. It is proposed to use hot gas turbine exhaust gases heat in a heat recovery steam generator to produce steam and inject it into gas turbine. Based on a steady-state model of the processes, exergy flow rates are calculated for all components and a detailed exergy analysis is performed. The components with the highest proportion of irreversibility in the hybrid systems are identified and compared. It is shown that steam injection decreases the wasted exergy from the system exhaust and boosts the exergetic efficiency by 12.11%. Also, 17.87% and 12.31% increase in exergy output and the thermal efficiency, respectively, is demonstrated. A parametric study is also performed for different values of compression pressure ratio, current density and pinch point temperature difference.     

Thermal modeling of a solid oxide fuel cell and micro gas turbine hybrid power system based on modified LS-SVM

For a solid oxide fuel cell (SOFC) integrated into a micro gas turbine (MGT) hybrid power system, SOFC operating temperature and turbine inlet temperature are the key parameters, which affect the performance of the hybrid system. Thus, a least squares support vector machine (LS-SVM) identification model based on an improved particle swarm optimization (PSO) algorithm is proposed to describe the nonlinear temperature dynamic properties of the SOFC/MGT hybrid system in this paper. During the process of modeling, an improved PSO algorithm is employed to optimize the parameters of the LS-SVM. In order to obtain the training and prediction data to identify the modified LS-SVM model, a SOFC/MGT physical model is established via Simulink toolbox of MATLAB6.5. Compared to the conventional BP neural network and the standard LS-SVM, the simulation results show that the modified LS-SVM model can efficiently reflect the temperature response of the SOFC/MGT hybrid system.     

Combustion performance of hydrogen in a small gas turbine combustor

Combustion characteristics of gaseous hydrogen fuel in a can type gas turbine combustor are presented. These are the results of a research program sponsored by CDND/DSS/NRCC^*. Combustion performance of hydrogen is compared with that of other (liquid) fuels using the same combustion hardware. Hydrogen combustion is characterized by high combustion efficiency, ease of ignition, and good flame stability; however it can also result in relatively high metal temperatures which can impact on liner durability, and high NO_x, emissions. Effects of two different hydrogen fuel injector designs on performance of the combustor are discussed. Impact of individual operating parameters on combustor performance with hydrogen is identified.     

Thermal performance of a water-phase change material solar collector

A new type of solar collector was developed and its short term thermal performance was investigated. The solar collector, which exhibited a net solar aperture area of 1.44 m², consisted of two adjoining sections one filled with water and the other with a phase change material with a melting and freezing range of about 45–50°C, i.e. paraffin wax in this study. The phase change material functioned both as an energy storage material for the stabilisation, theoretically, of the water temperature and as an insulation material due to its low thermal conductivity value. The results of the study indicated that the water temperature exceeded 55°C during a typical day of high solar radiation and it was kept over 30°C during the whole night. Covering the collector surface with an insulation blanket at a time when the water temperature was at its maximum improved the energy conservation of the water significantly. The instantaneous thermal efficiency values were between about 22% and 80%. The present solar collector was much advantageous over the traditional solar hot water collectors in Turkey in terms of total system weight and the cost in particular.     

Thermal performance of a novel rooftop solar micro-concentrating collector

Concentrating solar thermal systems offer a promising method for large scale solar energy collection. Although concentrating collectors are generally thought of as large-scale stand-alone systems, there is a huge opportunity to use novel concentrating solar thermal systems for rooftop applications such as domestic hot water, industrial process heat and solar air conditioning for commercial, industrial and institutional buildings. This paper describes the thermal performance of a new low-cost solar thermal micro-concentrating collector (MCT), which uses linear Fresnel reflectors, and is designed to operate at temperatures up to 220 °C. The modules of this collector system are approximately 3 m long by 1 m wide and 0.3 m high. The objective of the study is to optimise the design to maximise the overall thermal efficiency. The absorber is contained in a sealed enclosure to minimise convective losses. The main heat losses are due to natural convection inside the enclosure and radiation heat transfer from the absorber tube. In this paper we present the results of a computational and experimental investigation of radiation and convection heat transfer in order to understand the heat loss mechanisms. A computational model for the prototype collector has been developed using ANSYS–CFX, a commercial computational fluid dynamics software package. The numerical results are compared to experimental measurements of the heat loss from the absorber, and flow visualisation within the cavity. This paper also presents new correlations for the Nusselt number as a function of Rayleigh number.     

Aerodynamic performance prediction of a 30 kW counter-rotating wind turbine system

In the present work, the aerodynamic performance prediction of a unique 30 kW counter-rotating (C/R) wind turbine system, which consists of the main rotor and the auxiliary rotor, has been investigated by using the quasi-steady strip theory. The near wake behavior of the auxiliary rotor that is located upwind of the main rotor is taken into consideration in the performance analysis of the turbine system by using the wind tunnel test data obtained for scaled model rotors. The relative size and the optimum placement of the two rotors are investigated through use of the momentum theory combined with the experimental wake model. In addition, the performance prediction results along with the full-scale field test data obtained for C/R wind turbine system are compared with those of the conventional single rotor system and demonstrated the effectiveness of the current C/R turbine system.     

A methodology for improving the performance of molten carbonate fuel cell/gas turbine hybrid systems

In the present article a molten carbonate fuel cell (MCFC) system has been developed, modeled and implemented in Matlab language. It enables definition of the optimal operating conditions of the fuel cell, in terms of electrical and thermal performance, when it is a part of a hybrid plant composed of an MCFC system, a gas turbine and a possible heat recovery system. The thermal energy, which is recoverable from the adequately treated anodic exhaust gases, is utilized in a gas turbine plant to reduce its fuel consumption. Therefore, in the present article a methodology is illustrated to calculate the optimal values of some parameters characterizing the MCFC/gas turbine integrated system in terms of the electrical, first law and equivalent efficiencies. A choice is made among the sets of values of parameters investigated to improve the performance of the same integrated system according to its use (for the production of electric energy only or for the contemporary production of electric and thermal energy). Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal performance of a solar pressure cooker based on evacuated tube solar collector

This paper presents the thermal performance of a community type solar pressure cooker based on evacuated tube solar collector. The developed design of solar pressure cooker has separate parts for energy collection and cooking unit and both are coupled by heat exchanger. The paper has presented the performance results of experimental study conducted on solar pressure cooker and a simulation model has been developed for predicting the cooker performance under a variety of operating and climatic conditions. The theoretical model is validated against the experimental results. The obtained results have suggested a possibility of several batches of solar cooking on a clear sunny day under typical conditions of Delhi.     

燃气轮机运行中的性能监测

本文结合苏州高达热电有限公司两台PG6551B型燃气轮机发电机组几年来运行中性能监测情况，阐述燃气轮机性能测试方法，数据整理，性能评估等问题，以资参考。     

Optimal integration strategies for a syngas fuelled SOFC and gas turbine hybrid

This article aims to develop a thermodynamic modelling and optimization framework for a thorough understanding of the optimal integration of fuel cell, gas turbine and other components in an ambient pressure SOFC-GT hybrid power plant. This method is based on the coupling of a syngas-fed SOFC model and an associated irreversible GT model, with an optimization algorithm developed using MATLAB to efficiently explore the range of possible operating conditions. Energy and entropy balance analysis has been carried out for the entire system to observe the irreversibility distribution within the plant and the contribution of different components. Based on the methodology developed, a comprehensive parametric analysis has been performed to explore the optimum system behavior, and predict the sensitivity of system performance to the variations in major design and operating parameters. The current density, operating temperature, fuel utilization and temperature gradient of the fuel cell, as well as the isentropic efficiencies and temperature ratio of the gas turbine cycle, together with three parameters related to the heat transfer between subsystems are all set to be controllable variables. Other factors affecting the hybrid efficiency have been further simulated and analysed. The model developed is able to predict the performance characteristics of a wide range of hybrid systems potentially sizing from 2000 to 2500 W m⁻² with efficiencies varying between 50% and 60%. The analysis enables us to identify the system design tradeoffs, and therefore to determine better integration strategies for advanced SOFC-GT systems.