• Energy Research

Abstract In an increasingly decentralized energy market, micro gas turbines are seen with great potential due to their low emissions and fuel flexibility, which aligns with growing environmental concerns. Although presenting a relatively low efficiency, these machines could be improved by coupling it with an organic Rankine cycle. This manuscript covers the thermoeconomic design and optimization of such bottoming cycle for a 100 kWe micro gas turbine. The tool employed for such calculations is extensively described and was developed using solely open resources. The results shown that the saturation temperature at ambient pressure was an important variable when the minimum pressure is constrained above ambient and that a high degree of superheating was favored when the recuperated cycle is heated directly by the microturbine flue gases. Pentane was flagged as the best working fluid, generating 14.1 kWe of additional power and increasing the overall electric efficiency from 30 to 34.2%. The Authors show that at the current state of the art an efficiency of around 35% is the upper practical limit for such microturbine organic Rankine cycle combination.

During the design of a gas turbine it is required the analysis of all possible operating points in the gas turbine operational envelope, for the sake of verification of whether or not the established performance might be achieved. In order to achieve the design requirements and to improve the engine off-design operation, a number of specific analyses must be carried out. This paper deals with the characterization of a small gas turbine under development with assistance from ITA (Technological Institute of Aeronautics), concerning the compressor variable geometry and its transient operation during accelerations and decelerations. The gas turbine is being prepared for the transient tests with the gas generator, whose results will be used for the final specification of the turboshaft power section. The gas turbine design has been carried out using indigenous software, developed specially to fulfill the requirements of the design of engines, as well as the support for validation of research work. The engine under construction is a small gas turbine in the range of 5 kN thrust / 1.2 MW shaft power, aiming at distributed power generation using combined cycle. The work reported in this paper deals with the variable inlet guide vane (VIGV) transients and the engine transients. A five stage 5:1 pressure ratio axial-flow compressor, delivering 8.1 kg/s air mass flow at design-point, is the basis for the study. The compressor was designed using computer programs developed at ITA for the preliminary design (meanline), for the axisymmetric analysis to calculate the full blade geometry (streamline curvature) and for the final compressor geometry definition (3-D RANS and turbulence models). The programs have been used interatively. After the final channel and blade geometry definition, the compressor map was generated and fed to the gas turbine performance simulation program. The transient study was carried out for a number of blade settings, using different VIGV geometry scheduling, giving indication that simulations needed to study the control strategy can be easily achieved. The results could not be validated yet, but are in agreement with the expected engine response when such configuration is used.

ABSTRACTThis paper presents a review of the various aeronautical air conditioning systems that are currently available and discusses possible system configurations in the context of the aeronautical environmental control systems. Descriptions of the standard vapor compression cycle and air cycles are provided. The latter includes, simple-cycle, bootstrap-cycle, simple-bootstrap cycle (3-wheel) and condensing cycle (4-wheel). Water separation and air recirculation systems are also explored. A comparison between vapor compression cycles and air cycles is provided, as well as a comparison between different air cycles. Air cycle units are far less efficient than vapor compression cycle units, but they are lighter and more reliable for an equivalent cooling capacity. Details regarding the aircraft conceptual design phase along with general criteria for the selection of an air conditioning system are provided. Additionally, industry trends and technological advances are examined. Conclusions are compiled to guide the systems engineer in the search for the most appropriate design for a particular application.

Abstract Growing environmental concerns are driving the energy market toward the development of thermodynamic cycles to harness renewable energy and waste heat. This manuscript introduces the novel organic Rankine flash cycle, which combines the organic Rankine cycle with the trilateral cycle, merging their advantages in terms of high specific power output and low heat transfer irreversibility, respectively. By comparing the organic Rankine flash cycle to the organic flash cycle, it was found that the proposed architecture reaches a peak exergy efficiency at a more realistic value of two-phase expansion volume flow ratio, consistently achieves higher energy and exergy efficiencies, presents a lower cost, and is not constrained to operate close to the working fluid saturation temperature, promising easier operability. Considering pentane as working fluid, the exergy efficiency of the organic Rankine flash cycle is 18%p higher for a heat source temperature of 150 °C, 12%p for 175 °C, and 4%p for 200 °C. The attractive thermoeconomic performance of the proposed organic Rankine flash cycle highlights the potential of such a cycle as a new paradigm in the ORC panorama, encouraging further investigation towards practical demonstration.

This manuscript provides an exergy-based parallel between combined- and steam-cycle power plant configurations burning blast furnace gas (BFG). The combined cycle (CC) was based on a currently operational power plant located in Rio de Janeiro, Brazil. The steam cycle (SC) was created by replacing the gas turbines (GTs) for steam generators (SGs) that handled the same amount of fuel. The results show that the combined cycle achieved 21.25% higher exergy efficiency, although emitting twice as much nitrogen oxide. The combined cycle generated 52.08% less steam while wasting 78.86% less exergy, which indicated that steam generators benefit from a higher amount of excess air. The gas turbine combustion chamber high exergy efficiency indicates that burning low-grade fuels is beneficial for reducing the intrinsic waste of chemical reactions. However, the compression process required prior to combustion undermines this benefit. Ultimately, this manuscript provides a comparison between two options to avail blast furnace gas.

Poor part-load performance is a well-known undesirable characteristic of gas turbines. Running off-design, both compressor and turbine lose performance. Flow misalignment at the various rows causes losses to increase sharply, thereby decreasing net output faster than decreasing fuel consumption. To bring the flow to alignment with the blade passages, it is required to restagger the blades both at the compressor and at the turbine. To avoid mechanical complexities, it is generally accepted to restagger only the stators. This work deals with a numerical approach to the simulation of a gas turbine equipped with variable stators at the compressor and at the turbine, enabling the search for better-performance operation. A computer program has been developed to simulate virtually any gas turbine having variable stators at the compressor stages and turbine nozzle guide vanes. Variable-inlet guide vanes (VIGVs), variable-stator vanes (VSVs), variable-nozzle guide vanes (VNGVs), variable-geometry compressors (VGCs) and variable-geometry turbines (VGTs) are the focus in this work, which analyses a one-shaft free power turbine for power generation in the search for performance improvement at part load.

Industry and universities around the world invest time and money to develop digital computer programs to predict gas turbine performance. This study aims to demonstrate a brand new digital model developed with the ability to simulate gas turbine real time high fidelity performance. The model herein described run faster than 30ms per point, which is compatible with a high-definition video refresh rate: 30 frames per second. This user-friendly model, built in Visual Basic in modular structure, can be easily configured to simulate almost all the existing gas turbine architectures (single, 2 or 3 shaft engines mixed or unmixed flows). In addition, its real time capability enables simulations with the pilot in the loop at earlier design phases when their feedback may lead to design changes for improvements or corrections. In this paper, besides the model description, it is presented the model run time capability as well as a comparison of the simulated performance with a commercial gas turbine tool for single, 2 and 3 shaft engine architecture.

During a gas turbine development phase an important engineer task is to find the appropriate engine design point that meet the required specifications. This task can be very arduous because all possible operating points in the gas turbine operational envelope need to be analyzed, for the sake of verification of whether or not the established performance might be achieved. In order to support engineers to best define the engine design point that meet required performance a methodology was developed in this work. To accomplish that a computer program was written in Matlab®. In this program was incorporated the thermoeconomic and thermodynamic optimization. The thermodynamic calculation process was done based in enthalpy and entropy function and then validated using a commercial program. The methodology uses genetic algorithm with single and multi-objective optimization. The micro gas turbine cycle chosen to study was the recuperated. The cycle efficiency, total cost and specific work were chosen as objective functions, while the pressure ratio, compressor and turbine polytropic efficiencies, turbine inlet temperature and heat exchange effectiveness were chosen as decision variables. For total cost were considered the fixed costs (equipment, installation, taxes, etc.) and variable costs (fuel, environmental and O&M). For emissions were taken into account the NOx, CO and UHC. An economic analysis was done for a recuperated cycle showing the costs behavior for different optimized design points. The optimization process was made for: single-objective, where each objective was optimized separately; two-objectives, where they were optimized in pairs; three-objectives, where it was optimized in trio. After, the results were compared each other showing the possible design points.

Las centrales eléctricas que funcionan en ciclo combinado presentan una mayor eficiencia térmica (más del 60%) y una mayor generación de energía en comparación con los ciclos simples tradicionales, como las turbinas de gas o vapor que funcionan solas. Teniendo en cuenta que la central eléctrica evaluada en este documento ya está operativa, se requiere un desarrollo adicional relacionado con el sistema de control de la central eléctrica para evaluar las perturbaciones y variaciones de frecuencia generadas por la red eléctrica durante el funcionamiento normal, ya que las cargas aplicadas a las turbinas están intrínsecamente asociadas a la frecuencia de la red. Se desarrolló un programa informático capaz de simular el sistema de control para hacer frente a estas inestabilidades y garantizar la protección necesaria para el funcionamiento de la central eléctrica. El programa de desarrollo se realizó utilizando MATLAB Simulink®. Los componentes principales de la central son 2 turbinas de gas de 90 MW cada una y una turbina de vapor de 320 MW, totalizando 500 MW. En primer lugar, los componentes principales de la central eléctrica se construyeron por separado. Una vez obtenidos los modelos estables, el escape de la turbina de gas se conectó al ciclo agua-vapor a través del generador de vapor de recuperación de calor. Los principales parámetros necesarios para ajustar el modelo, como ganancias, límites y constantes, se obtuvieron a partir de los datos operativos de la central eléctrica. Los resultados de la simulación permitieron evaluar algunos parámetros clave; otros son posibles pero no se muestran, como la potencia, la temperatura de los gases de escape, el flujo de combustible y los ángulos variables del estator durante las inestabilidades de la red. Los estudios se realizaron probando la robustez, el tiempo de respuesta, el análisis de transitorios, el análisis de estado estacionario y la confiabilidad del modelo propuesto. Les centrales électriques fonctionnant en cycle combiné présentent une efficacité thermique plus élevée (plus de 60 %) et une production d'énergie accrue par rapport aux cycles simples traditionnels, tels que les turbines à gaz ou à vapeur fonctionnant seules. Étant donné que la centrale électrique évaluée dans cet article est déjà opérationnelle, un développement ultérieur concernant le système de contrôle de la centrale électrique est nécessaire afin d'évaluer les perturbations et les variations de fréquence générées par le réseau électrique en fonctionnement normal, car les charges appliquées aux turbines sont intrinsèquement associées à la fréquence du réseau. Un programme informatique capable de simuler le système de contrôle a été développé pour faire face à ces instabilités et garantir la protection nécessaire au fonctionnement de la centrale. Le programme Develop a été réalisé à l'aide de Matlab Simulink®. Les principaux composants de la centrale se composent de 2 turbines à gaz de 90 MW chacune et d'une turbine à vapeur de 320 MW, totalisant 500 MW. Tout d'abord, les principaux composants de la centrale ont été construits séparément. Une fois les modèles stables obtenus, l'échappement de la turbine à gaz était connecté au cycle eau-vapeur via le générateur de vapeur à récupération de chaleur. Les principaux paramètres nécessaires pour ajuster le modèle tels que les gains, les limites et les constantes ont été obtenus à partir des données opérationnelles de la centrale. Les résultats de la simulation ont permis l'évaluation de certains paramètres clés ; d'autres sont possibles mais non illustrés, tels que la puissance, la température des gaz d'échappement, le débit de carburant et les angles variables du stator pendant les instabilités du réseau. Les études ont été menées en testant la robustesse, le temps de réponse, l'analyse des transitoires, l'analyse de l'état d'équilibre et la fiabilité du modèle proposé. Power plants operating in combined cycle present higher thermal efficiency (over 60%) and increased power generation when compared to traditional simple cycles, such as gas or steam turbines operating alone. Considering that the power plant evaluated in this paper is already operational, a further development concerning to the power plant control system is required in order to evaluate disturbances and frequency variations, generated by the electrical grid during normal operation, as the loads applied to the turbines are intrinsically associated to the grid frequency. A computer program able to simulate the control system was developed to cope with these instabilities and to guarantee the necessary protection to the power plant operation. The develop program was made using MATLAB Simulink®. The main components of the power plant consists of 2 gas turbines of 90 MW each and a steam turbine of 320 MW, totalizing 500 MW. Firstly, the power plant main components were constructed separately. Once obtained stable models, the exhaust from the gas turbine was connected to the water-steam cycle through the heat recovery steam generator. The main parameters necessary to adjust the model such as gains, limits and constants were obtained from the power plant operational data. The simulation results allowed the evaluation of some key parameters; others are possible but not shown, such as power, exhaust gas temperature, fuel flow and variable stator angles during grid instabilities. The studies were conducted by testing the robustness, response time, transient analysis, steady state analysis and reliability of the proposed model. تقدم محطات الطاقة التي تعمل في الدورة المركبة كفاءة حرارية أعلى (أكثر من 60 ٪) وزيادة توليد الطاقة عند مقارنتها بالدورات البسيطة التقليدية، مثل التوربينات الغازية أو البخارية التي تعمل بمفردها. بالنظر إلى أن محطة الطاقة التي تم تقييمها في هذه الورقة تعمل بالفعل، يلزم إجراء مزيد من التطوير فيما يتعلق بنظام التحكم في محطة الطاقة من أجل تقييم الاضطرابات وتغيرات التردد، التي تولدها الشبكة الكهربائية أثناء التشغيل العادي، حيث أن الأحمال المطبقة على التوربينات ترتبط ارتباطًا جوهريًا بتردد الشبكة. تم تطوير برنامج كمبيوتر قادر على محاكاة نظام التحكم للتعامل مع حالات عدم الاستقرار هذه ولضمان الحماية اللازمة لتشغيل محطة الطاقة. تم إعداد برنامج التطوير باستخدام MATLAB Simulink®. تتكون المكونات الرئيسية لمحطة الطاقة من توربينين غازين بقدرة 90 ميجاوات لكل منهما وتوربين بخاري بقدرة 320 ميجاوات، بإجمالي 500 ميجاوات. أولاً، تم بناء المكونات الرئيسية لمحطة الطاقة بشكل منفصل. بمجرد الحصول على نماذج مستقرة، تم توصيل العادم من التوربينات الغازية بدورة بخار الماء من خلال مولد بخار استرداد الحرارة. تم الحصول على المعلمات الرئيسية اللازمة لضبط النموذج مثل المكاسب والحدود والثوابت من البيانات التشغيلية لمحطة الطاقة. سمحت نتائج المحاكاة بتقييم بعض المعلمات الرئيسية ؛ والبعض الآخر ممكن ولكن لم يتم عرضه، مثل الطاقة ودرجة حرارة غاز العادم وتدفق الوقود وزوايا الجزء الثابت المتغيرة أثناء عدم استقرار الشبكة. أجريت الدراسات من خلال اختبار المتانة ووقت الاستجابة والتحليل العابر وتحليل الحالة الثابتة وموثوقية النموذج المقترح.