Optimal Design of a Gas Turbine Cogeneration Plant by a Hierarchical Optimization Method With Parallel Computing

To attain the highest performance of energy supply systems, it is necessary to rationally determine types, capacities, and numbers of equipment in consideration of their operational strategies corresponding to seasonal and hourly variations in energy demands. Mixed-integer linear programming (MILP) approaches have been applied widely to such optimal design problems. The authors have proposed a MILP method utilizing the hierarchical relationship between design and operation variables to solve the optimal design problems of energy supply systems efficiently. In addition, some strategies to enhance the computation efficiency have been adopted: bounding procedures at both the levels and ordering of the optimal operation problems at the lower level. In this paper, as an additional strategy to enhance the computation efficiency, parallel computing is adopted to solve multiple optimal operation problems in parallel at the lower level. In addition, the effectiveness of each and combinations of the strategies adopted previously and newly is investigated. This hierarchical optimization method is applied to an optimal design of a gas turbine cogeneration plant, and its validity and effectiveness are clarified through some case studies.

An Introduction Into the Clearance Management of Ansaldo GT36 From Development to Validation

The optimization and evaluation of blading clearance is important for gas turbine efficiency and performance. The Ansaldo GT36 gas turbine offers high efficiency together with outstanding flexibility across a large load range. Active management of engine clearances during the complete development process followed by a thorough validation on the Ansaldo test plant facility in Birr, Switzerland enables the GT to attain ambitious clearance targets. The clearance at baseload must be minimized but is limited by the pinch point clearance during cold, warm and hot start-ups — including normal and fast ramp-up and/or shutdown. Therefore transient analysis is necessary for covering the different operating conditions. A well-established process of 2d finite element modelling of the whole engine model (WEM) comprised of axis-symmetric and plane stress elements was used during the design process from concept to detailed design to optimize the clearances. It delivers the transient stator and rotor deformation and together with the compressor and turbine airfoil deformation based on 3D models the basic clearance evaluation process is defined. The GT engine design was significantly influenced, starting with a simplified version of the WEM for identification of the most promising variants. Subsequently a detailed WEM was developed which is fully validated against measurements on the test engine. Different 3D effects are considered separately at identified critical transient conditions and overlaid on the 2d clearances which lead to the final optimized clearances. In addition to this, limitations from each step of the manufacturing process were identified and improved to reduce tolerances and uncertainties to their minimum. The results of the calculation and clearance prediction process are compared against clearance measurements during all kinds of GT operation and cooldown. Passive clearance indicators showing the remaining gap till rubbing would occur and rub marks, in areas that tolerate it, further validate the clearances and clearance prediction process.

Experimental and Numerical Investigation of Early Phase of Laser Ignition Under Stoichiometric and Lean Conditions

Forced ignition, the initiation of combustion processes by rapid and localized introduction of energy, is central to the successful operation of many combustion systems. It is therefore of interest to investigate this process, starting from the introduction of energy to the emergence of self-sustained flame or the quenching of an otherwise initialized flame kernel. Since the process is highly non-equilibrium and involves various complex kinetic phenomena, it is important to understand the key aspects that control failed or successful ignition. Detailed studies of the early phases of the ignition process can lead to knowledge of more general characteristics of the problem so that reduced models of the ignition process can be developed. These reduced versions can be used in less costly computational studies to assess various ignition events. This paper reports an experimental and numerical investigations of the early phase of laser ignition. The gas mixtures, air, methane/N2 and methane/air are considered to bring out the effect of heat release on the early flow field. The mixtures are studied at three different energy levels and the Jones blast wave theory is used to deduce the energy responsible for the development of the attendant shock waves. This energy is also used to specify initial conditions for the simulations of air and methane/air processes. Additionally, interferometry is used to resolve the density field within the plasma kernel. For the methane/air simulation two chemical models are used, a global reaction model supplemented by an ignition model and a two-step mechanism. The sensitivity of the simulations to the initial geometry of the laser spark is also investigated. The blast wave and interferometry results show that in the reacting methane/air mixture the resulting shock wave is strengthened by early heat release. It is also shown that the shock wave trajectory is not strongly affected by the initial spark geometry, but it has an impact on the velocity field and on the distribution of thermodynamic properties.

A Highly Flexible Approach on the Steady-State Analysis of Innovative Micro Gas Turbine Cycles

Steady state simulations are an important method to investigate thermodynamic processes. This is especially true for innovative micro gas turbine (MGT) based cycles as the complexity of such systems grows. Therefore, steady state simulation tools are required which ensure large flexibility and computation robustness. As the increased system complexity result often in more extensive parameter studies also a fast computation speed is required. While a number of steady state simulation tools for micro gas turbine based systems are described and applied in literature, the solving process of such tools is rarely explained. However, this solving process is crucial to achieve a robust and fast computation within a physically meaningful range. Therefore, a new solver routine for a steady state simulation tool developed at the DLR Institute of Combustion Technology is presented in detail in this paper. The solver routine is based on Broyden’s method. It considers boundaries during the solving process to maintain a physically and technically meaningful solution process. Supplementary methods are implemented and described which improve the computation robustness and speed. Furthermore, some features of the resulting steady state simulation tool are presented. Exemplary applications of a hybrid power plant, an inverted Brayton cycle and an aircraft auxiliary power unit show the capabilities of the presented solver routine and the steady state simulation tool. It is shown that the new solver routine is superior to the standard Simulink algebraic solver in terms of system evaluation and robustness for the given applications.

Numerical Investigation of an Inverted Brayton Cycle Micro Gas Turbine Based on Experimental Data

Residential buildings account for approximately one fifth of the total energy consumption and 12 % of the overall CO2 emissions in the OECD countries. Replacing conventional boilers by a co-generation of heat and power in decentralized plants on site promises a great benefit. Especially, micro gas turbine (MGT) based combined heat and power systems are particularly suitable due to their low pollutant emissions without exhaust gas treatment. Hence, the overall aim of this work is the development of a recuperated inverted MGT as heat and power supply for a single family house with 1 kWel. First, an inverted MGT on a Brayton cycle MGT was developed and experimentally characterized, in previous work by the authors. This approach allows exploiting the potential of using the same components for both cycles. As a next step, the applicability of the Brayton cycle components operated in inverted mode needs to be evaluated and the requirements for a component optimization need to be defined, both, by pursuing thermodynamic cycle simulations. This paper presents a parametrization and validation of in-house 1D steady state simulation tool for an inverted MGT, based on experimental data from the inverted Brayton cycle test rig. Moreover, a sensitivity analysis is conducted to estimate the influence of every major component on the overall system and to identify the necessary optimizations. Finally, the component requirements for an optimized inverted MGT with 1 kWel and 16 % of electrical efficiency are defined. This work demonstrates the high potential of an inverted MGT for a decentralized heat and power generation when optimizing the system components.

Environmental Impact on the Life Cycle for Turbine Based Biomass CHP Plants

Biomass CHP plants represent a viable option to produce distributed energy in a sustainable way when the overall environmental benefit is appraised on the whole life cycle. CHP plants for bioenergy conversion may consist of a gasification (IGC – Integrated Gasification Cycle) or pyrolysis (IPRP – Integrated Pyrolysis Regenerated Plant) pre-treatment unit, producing a syngas that feeds an internal combustion engine or a gas turbine. The external combustion mode is also an option, where exhaust gases from biomass combustion provide heat to either a traditional steam cycle, an ORC (Organic Rankine Cycle) or an EFGT (Externally Fired Gas Turbine). This paper focuses specifically on turbines based technologies and provides a LCA comparison of 4 main technologies suitable for the small scale, namely: EFMGT, ORC, IGC and IPRP. The comparison is carried out considering 3 different biomasses, namely a Short Rotation Forestry, an agricultural residue and an agro industrial residue at 2 different scales: micro scale (100 kw) and small scale (1 MW), being higher scales barely sustainable on the life cycle. From data derived from the Literature or experimental campaign (tests at the IPRP and gasification facilities at the University Perugia), LCA analysis were carried out and the different scenarios were compared based on two impact categories: global warming and human health. Input and output of the derived LCI are referred to the functional unit of 1 kWh electric for upstream, core and downstream processes. Results show the contribution of main processes and are discussed comparing scale, technology and feedstock.

The Heron Fan: Concept Description and Preliminary Aerothermodynamic Analysis

The Heron Fan is a new concept of a fuel powered jet engine that does not utilize a conventional core engine. The fan, a single axial compressor of high diameter, creates thrust, similar to a turbofan. Its blades are hollow with inner channels to transport the core air from the hub to the tip, inducing radial compression. The combustion chamber is located in the casing region, either integrated in the blades or in an external ring. After burning, the core air is returned to the blades and is blown out through an expansion device with a large component in circumferential direction. This propels the fan in the opposite direction. The expansion device may be realized by nozzles integrated in the blade trailing edge or by turbine stages integrated in the blade tip region. Subsequently, the core air mixes with the bypass air, which passes the fan axially, and ejects through the main nozzle, producing thrust. To achieve higher compression ratios, it is possible to install core air compressor stages ahead of the fan. The main purpose of this concept is to reduce weight and complexity of the engine, leading to lower production and operating costs. This is achieved by simplifying the engine architecture, integrating the functions and shortening some of the components. In particular, the core engine has been rearranged, thus eliminating the second and in some cases the third shaft. Further, the complete expansion and parts of the compression have been integrated in the fan blade. To assess the aero-thermodynamic parameters, a preliminary cycle analysis has been done, where the most influential parameters were varied. The results show, that the above listed benefits can be achieved while maintaining an efficiency comparable to conventional turbofans. Further, a feasibility study in terms of geometry, internal flow, component implementation and installation has been done, in order to qualify the concept and to identify the most critical aspects. To incorporate the corresponding thoughts and results, as well as to find and eliminate conceptual conflicts and opposing trends, a CAD model has been generated. Overall, the results are sound and encouraging, hence justifying future investigations. However, the Heron Fan concept also brings structural, thermal and aerodynamic challenges which are illustrated and briefly discussed, but still need detailed investigation.

HRSG Duct Firing Revisited

Duct firing in the heat recovery steam generator (HRSG) of a gas turbine combined cycle power plant is a commonly used method to increase output on hot summer days when gas turbine airflow and power output lapse significantly. The aim is to generate maximum possible power output when it is most needed (and, thus, more profitable) at the expense of power plant heat rate. In this paper, using fundamental thermodynamic arguments and detailed heat and mass balance simulations, it will be shown that, under certain boundary conditions, duct firing in the HRSG can be a facilitator of efficiency improvement as well. When combined with highly-efficient aeroderivative gas turbines with high cycle pressure ratios and concomitantly low exhaust temperatures, duct firing can be utilized for small but efficient combined cycle power plant designs as well as more efficient hot-day power augmentation. This opens the door to efficient and agile fossil fuel-fired power generation opportunities to support variable renewable generation.

Performance Enhancement of a Molten Carbonate Fuel Cell/Micro Gas Turbine Hybrid System With Carbon Capture by Off-Gas Recirculation

The demand for clean energy continues to increase as the human society becomes more aware of environmental challenges such as global warming. Various power systems based on high-temperature fuel cells have been proposed, especially hybrid systems combining a fuel cell with a gas turbine, and research on carbon capture and storage technology to prevent the emission of greenhouse gases is already underway. This study suggests a new method to innovatively enhance the efficiency of a molten carbonate fuel cell/micro gas turbine hybrid system including carbon capture. The key technology adopted to improve the net cycle efficiency is off-gas recirculation. The hybrid system incorporating oxy-combustion capture was devised, and its performance was compared with that of a post-combustion system based on a hybrid system. A molten carbonate fuel cell system based on a commercial unit was modeled. Externally supplied water for reforming was not needed as a result of the presence of the water vapor in the recirculated anode off-gas. The analyses confirmed that the thermal efficiencies of all the systems (MCFC stand-alone, hybrid, hybrid with oxy-combustion capture, hybrid with post-combustion capture) were significantly improved by introducing the off-gas recirculation. In particular, the largest efficiency improvement was observed for the oxy-combustion hybrid system. Its efficiency is over 57% and is even higher than that of the post-combustion hybrid system.

Thermal Stability Analysis of Gevo Jet Fuel Using Ellipsometry

Thermal stability is an important characteristic of alternative fuels that must be evaluated before they can be used in aviation engines. This characteristic is of great importance to the effectiveness of the fuel as a coolant and to the engine’s combustion performance. In this work, the thermal stability of Gevo fuel, an alcohol to jet fuel made from plant derived feedstock, was studied. This analysis was used to comment on the effectiveness of the current thermal stability test standard. This work was performed using a spectroscopic ellipsometer to measure the thickness of deposits left on aluminum substrates. It was observed that Gevo deposit thickness increased slowly up to 375 °C and much more rapidly after that point. Similar behavior was observed in JP-8 fuel. Comparisons were also made between color standard ratings and ellipsometric thickness measurements, and it was found that in some cases, darker colors did not indicate thicker deposits. Reference tubes were used to validate the optical models used in this work, and different optical constants were found to best model the results than what are published in the ASTM D3241 test method for thermal stability.