The rapid electrification through natural gas in Mexico; the interest of the country to mitigate the effects of climate change; and the opportunity for rolling out Enhanced Oil Recovery at national level requires an important R&D effort to develop nationally relevant CCS technology in natural gas combined cycle power plants. Post-combustion carbon dioxide capture at gas-fired power plants is identified and proposed as an effective way to reduce CO2 emissions generated by the electricity sector in Mexico. In particular, gas-fired power plants with carbon dioxide capture and the sequential combustion of supplementary natural gas in the heat recovery steam generator can favourably increase the production of carbon dioxide, compared to a conventional configuration. This could be attractive in places with favourable conditions for enhanced oil recovery and where affordable natural gas prices will continue to exist, such as Mexico and North America. Sequential combustion makes use of the excess oxygen in gas turbine exhaust gas to generate additional CO2, but, unlike in conventional supplementary firing, allows keeping gas temperatures in the heat recovery steam generator below 820°C, avoiding a step change in capital costs. It marginally decreases relative energy requirements for solvent regeneration and amine degradation. Power plant models integrated with capture and compression process models of Sequential Supplementary Firing Combined Cycle (SSFCC) gas-fired units show that the efficiency penalty is 8.2% points LHV compared to a conventional natural gas combined cycle power plant with capture. The marginal thermal efficiency of natural gas firing in the heat recovery steam generator can increase with supercritical steam generation to reduce the efficiency penalty to 5.7% points LHV. Although the efficiency is lower than the conventional configuration, the increment in the power output of the combined steam cycle leads a reduction of the number of gas turbines, at a similar power output to that of a conventional natural gas combined cycle. This has a positive impact on the number of absorbers and the capital costs of the post-combustion capture plant by reducing the total volume of flue gas by half on a normalised basis. The relative reduction of overall capital costs is, respectively, 9.1% and 15.3% for the supercritical and the subcritical combined cycle configurations with capture compared to a conventional configuration. The total revenue requirement, a metric combining levelised cost of electricity and revenue from EOR, shows that, at gas prices of 2$/MMBTU and for CO2 selling price from 0 to 50 $/tonneCO2, subcritical and supercritical sequential supplementary firing presents favourably at 47.3-26 $/MWh and 44.6-25 $/MWh, respectively, compared with a conventional NGCC at 49.5-31.7 $/MWh. When operated at part-load, these configurations show greater operational flexibility by utilising the additional degree of freedom associated with the combustion of natural gas in the HRSG to change power output according to electricity demand and to ensure continuity of CO2 supply when exposed to variation in electricity prices. The optimisation of steady state part-load performance shows that reducing output by adjusting supplementary fuel keeps the gas turbine operating at full load and maximum efficiency when the net power plant output is reduced from 100% to 50%. For both subcritical and supercritical combined cycles, the thermal efficiency at part-load is optimised, in terms of efficiency, with sliding pressure operation of the heat recovery steam generator. Fixed pressure operation is proposed as an alternative for supercritical combined cycles to minimise capital costs and provide fast response rates with acceptable performance levels.

abstract: Modern day gas turbine designers face the problem of hot mainstream gas ingestion into rotor-stator disk cavities. To counter this ingestion, seals are installed on the rotor and stator disk rims and purge air, bled off from the compressor, is injected into the cavities. It is desirable to reduce the supply of purge air as this decreases the net power output as well as efficiency of the gas turbine. Since the purge air influences the disk cavity flow field and effectively the amount of ingestion, the aim of this work was to study the cavity velocity field experimentally using Particle Image Velocimetry (PIV). Experiments were carried out in a model single-stage axial flow turbine set-up that featured blades as well as vanes, with purge air supplied at the hub of the rotor-stator disk cavity. Along with the rotor and stator rim seals, an inner labyrinth seal was provided which split the disk cavity into a rim cavity and an inner cavity. First, static gage pressure distribution was measured to ensure that nominally steady flow conditions had been achieved. The PIV experiments were then performed to map the velocity field on the radial-tangential plane within the rim cavity at four axial locations. Instantaneous velocity maps obtained by PIV were analyzed sector-by-sector to understand the rim cavity flow field. It was observed that the tangential velocity dominated the cavity flow at low purge air flow rate, its dominance decreasing with increase in the purge air flow rate. Radially inboard of the rim cavity, negative radial velocity near the stator surface and positive radial velocity near the rotor surface indicated the presence of a recirculation region in the cavity whose radial extent increased with increase in the purge air flow rate. Qualitative flow streamline patterns are plotted within the rim cavity for different experimental conditions by combining the PIV map information with ingestion measurements within the cavity as reported in Thiagarajan (2013). / Dissertation/Thesis / M.S. Mechanical Engineering 2013

The resolution of differential equations of diverse degree of complexity is necessary to simulate the phenomena present in the complex turbomachinery flows and in particular, requires accounting for unsteady effects that may have a preponderant role. Today, only the LES (Large Eddy Simulation) fully compressible approach has the required accuracy to predict the physics associated to reactive and turbulent flows in such complex geometries. This work covers the numerical modelling of physics in the near-wall region of a high-pressure turbine blade with special focus on thermal predictions. This work was supported by the European project COPA-GT, dedicated to the numerical multi-physics simulation of a complete gas turbine.

Dans le contexte aéronautique, cette thèse, financée par Safran Helicopter Engine, s’intéresse à l’application de l’approche Simulations aux Grandes Échelles (SGE) pour les systèmes de refroidissement de turbine. Le système de refroidissement industriel complexe est divisé en cas académiques plus simples donnant accès à des caractérisations expérimentales de la dynamique et de la thermique. Le jet impactant est traité en tant que système interne et l’écoulement de protection au bord de fuite en tant que système externe. Après une brève introduction du contexte lié au refroidissement de turbine et des objectifs scientifiques, ce manuscrit est divisé en 3 parties. La 1ère partie traite d’un écoulement de jet impactant sur plaque plane représentatif de l’impact à mi-corde. Elle se concentre sur la validation et la qualification des outils et modèles ainsi que sur l’analyse physique de l’écoulement. Les différentes instationarités de l’écoulement sont reliées à la thermique de paroi à l’aide de diagnostics statistiques et d’analyses modales. La 2ème partie s’intéresse à l’impact sur paroi concave représentatif de l’impact au bord d’attaque. Cette étude se concentre principalement sur la caractérisation de l’effet de courbure pour le jet impactant. Contrairement, au consensus actuel sur l’effet de courbure, la réduction des transferts thermiques est observée pour le cas d’étude de cette thèse. Au vu de ces résultats, une discussion est proposée pour tenter d’expliquer cet écart. Finalement, la 3ème partie de ce manuscrit contient une application de la SGE à un système de protection du bord de fuite par film isolant. Dans ce dispositif, des effets de groupe sont mis en évidence. L’impact des choix de modélisation tels que l’hypothèse de périodicité dans la direction de l’envergure est alors évalué. Il est montré que cette hypothèse de périodicité influe sur la prédiction locale de l’efficacité en forçant l’écoulement. En revanche, la prédiction de l’efficacité globale du système de protection n’est pas impactée.

Eolus recently developed, sold and now manage a wind farm consisting of four 2 MW wind turbines located in the northern half of Sweden. Soon after commissioning it was noticed that they were underperforming in terms of production and availability. It was suspected that one turbine was underperforming relative to the manufacturers’ power curve. Furthermore, the de-icing systems were discovered to be problematic, causing a lot of unplanned downtime. The main goals of this project are to determine the causes of the discrepancies in availability and production at the wind farm. As part of the investigation, the malfunctioning de-icing systems are also investigated. Initially, the background of the wind farm was researched. Important contracts, maintenance reports and other documentation was reviewed. Moreover, interviews were performed with four people involved with the wind farm. These revealed that problems first began during the construction phase. Delays and poor construction quality in general led to problems being carried over to the operations stage. Complications with the de-icing systems and blade drainage holes contributed to underperformance during the first year of operation. The second year of operation was marked by the de-icing system electrical cabinet detaching in the hub of turbine 2. Analysis of the turbine data and status files confirmed and elaborated on the information provided by the qualitative analysis. Investigation of the production and lost production figures revealed that the main problems have been related to the pitch systems, low temperature kits, sonic anemometers, PT-100 sensors, and the software for the controllers. Furthermore, a significant proportion of the lost production and downtime in years one and two can be attributed to tests and repairs performed on the de-icing systems. However, early indications in year three suggest that the single active de-icing system in turbine 3 is functioning as it should. Year three began with a significant improvement in availability, all turbines have experienced monthly availabilities of at least 90%. Overall, it appears that the fact that only one de-icing system is active has had a significant impact on the availability and production figures. However, organisational issues with the manufacturer still need to be resolved, as do the technical issues.

No description available.

It is preferable that control and bearing condition monitoring are integrated, as the condition of the system should influence control actions. As wind turbines mainly work in remote areas, it becomes necessary to develop a wireless platform for the control system. A fuzzy system with self-tuning mechanism was developed. The input speed error and speed change were selected to control the shaft speed, while the kurtosis and peak-to-peak values were used as another set of inputs to monitor the bearing conditions. To enhance effectiveness, wait-and-see (WAS) logic was used as the pre-processing step for the raw vibration signal. The system was implemented on the LabVIEW platform. Experiments have shown that the system can effectively adjust motor rotating speed in response to bearing conditions. For future studies, more advanced fault detection methods can be integrated with proper tuning mechanisms to enrich the performance and function of the controller.

Distributed energy production in the form of renewable energy sources are expected to increase in the coming years, a consequence of this is instability of the power grids due to the stochastic nature and lack of inertia of renewable energy sources. In addition, small and local, so called island grids, are on the rise and these system may present an even higher sensitivity to frequency fluctuations. In these applications gas turbines are an attractive option owing to the quick start capabilities, flexible fuel options and reliable operation. The aim of this thesis is to evaluate the transient capabilities of the Siemens SGT-750 double shaft and SGT-800 single shaft industrial gas turbines in island grid settings, through simulations of substantial load increases in varying ambient settings. Furthermore the possibility of using hydrogen fuel as a renewable option to the standard natural gas will be evaluated. This thesis provides a model of a simple island grid for load sharing between two or three turbines. The model was tuned to real life test data for the two gas turbines considered. In order to evaluate the capabilities of the turbines simulations were run in cold (-30 oC), hot (30 oC) and ISO (15 oC) conditions, evaluating the maximum instant load increase capabilities. Case studies were also run on island grids containing two or three turbines in order to determine the frequency response in case of an event. Case A regarded a scenario in which two turbines ran on 50% of rated power and one tripped, case B regarded three turbines working on 33% of rated power and one tripped out. Lastly, the maximum load increase cases with hydrogen fuel mixes (25, 50, 75 and 100% hydrogen by volume) were considered. The results suggest that the SGT-750 and SGT-800 gas turbines are capable of handling scenarios on reasonably dimensioned power systems, with both machines capable of recovering instant load increases of over 50% of the rated power. The findings shows thats hort periods (<10 s.) of allowed overfiring temperatures are necessary for the transient performance for the most extreme scenarios of high ambient temperatures and large loadincreases (around 50% of rated power). Furthermore an empirical κ-parameter, related to inertia and operational stability is discussed in order to compare GT load increase capability. The relevance of inertia and dynamic response is discussed and conceptually simulated to highlight the their role in gas turbine transient response. The hydrogen simulations, aside from the 75% case, showed little difference from natural gas in transient scenarios. The 75% hydrogen fuel consisting of high amounts ofinert gas however, rendered the turbine unable to withstand substantial load increases. The hydrogen simulation results are suggested to be accounted for by the rather simple combustion system and the energy densities of the gases.

No description available.

Intimate knowledge of ammonia fueling gas turbines is of crucial importance for power generation sectors, owing to its carbon-free nature and high hydrogen capacity. Anticipated challenges include, among others, the difficulty to stabilize ammonia flames and on top of that the propensity of ammonia flames to produce large quantities of nitrogen monoxide emissions. In gas turbine devices, combustion in practice occurs in a turbulent swirl flow and at elevated pressure conditions. The stability of ammonia flames and the production of NO emissions are sensitive to such parameters. This body of work focuses on the development of a swirl combustor, ~30kW thermal power, for investigating behaviors of flame stability limits and NO emissions from the combustion of ammonia fuel with mixtures of hydrogen or methane at pressure conditions up to 5 bar. Data show that increasing the ammonia addition increases the equivalence ratio at the lean blowout limit but also reduces the flames’ propensity to flashback. If the volume fraction of ammonia in the fuel blend exceeds a critical value, increasing the equivalence ratio at a fixed bulk velocity does not yield flashback and rich blow-out occurs instead. This significantly widens the range of equivalence ratios yielding stable ammonia flames. Regardless of the fuel blend, increasing the pressure increases the propensity to flashback if the bulk velocity remains constant. Pure ammonia-air flames are stable under elevated pressures, and the stable range of equivalence ratio becomes wider as the pressure increases. The NO emissions are measured for large ranges of equivalence ratios, ammonia fractions, and pressures. Regardless of the ammonia fraction, data show that competitively low NO emissions can be found for slightly rich equivalence ratios. Good NO performance is also found for very lean ammonia-hydrogen-air mixtures, regardless of the pressure. NO mole fractions for lean ammonia mixtures can be reduced as pressure increases, demonstrating the strong potential of fueling gas turbines with ammonia-hydrogen mixtures.