• 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.

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.

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.

The association of turbochargers with piston engines is widespread since both the efficiency and the power output of an engine could be improved. However, a piston engine operational range is wide and highly variable. This characteristic imposes challenges for the project and application of a turbocharger that should perform properly within the operational range. An important tool used to evaluate the performance of both turbine and compressor, which compose a turbocharger, is the characteristic map. The map condenses the main performance parameters into a single graphic that allow the evaluation of the machine characteristics, such as the operational width. A typical characteristic map relates the pressure ratio, mass flow rate, rotation and efficiency for each operational condition. The present work provides a technique to obtain the characteristic map of a turbocharger centrifugal compressor with reduced time consumption through steady state simulation using a fully unstructured mesh. Evaluation of the results indicated good accuracy for the predicted mass flow rate and pressure ratio. However, the resulting efficiency presented considerable discrepancy, which was aggravated when simulating extreme operational conditions or when the mass flow was used as a boundary condition. At last, the porter shroud and volute were evaluated within the entire range to provide an insight into the compressor operation.