Browsing by Author "Hamilton, Richard"

Now showing 1 - 6 of 6
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    Aerodynamic limits air injection for heavy-duty gas turbine: compressor aerodynamic limits for power augmentation and ramp-up capabilities
    (SAGE, 2022-04-24) Szymanski, Artur; Igie, Uyioghosa; Hamilton, Richard
    Improved operational flexibility of gas turbines can play a major role in stabilising the electric power grid, by backing up intermittent renewable power. Gas turbines offer on-demand power and fast dispatch of power that is vital when renewable power reduces. This has brought about increasing demand to improve the ramp-up rate of gas turbines. One approach is through the injection of compressed air from energy storage or an auxiliary compressor. This method is the focus of the present work, which shows for the first time, the implications and limits of compressor air injection in a high-fidelity Computational Fluid Dynamics model (CFD). The 3D multi-stage model of the compressor was developed in ANSYS CFX v19.2, while the boundary conditions related to the injection cases have been obtained from a corresponding 0D engine model. The upper limits to air injection determine how much air can be injected into the engine, providing indicative values of power augmentation and ramp-up rate capabilities. These have been previously addressed by the authors using 0D models that do not consider the compressor aerodynamics in great detail. The CFD study has shown that for power augmentation, 16% of compressed air (based on compressor exit) is allowed based on the onset of stall. It also shows that increasing air injection amplifies losses, blockage factor and absolute velocity angle. Also, about 30% of the blade span from the hub is dominated by a rise in the total pressure loss coefficient, except the outlet guide vane for which separation occurs at the tip. For the ramp-up rate analysis, up to 10% air injection is shown to be sustainable. The work shows that the improvements in the 0D analytical engine model are plausible, in addition to demonstrating similar limits at different ambient temperatures.
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    Aerodynamic limits of gas turbine compressor during high air offtakes for minimum load extension
    (Elsevier, 2021-02-18) Szymanski, Artur; Igie, Uyioghosa; Abudu, Kamal; Hamilton, Richard
    Renewable energy sources (RES) have become a favoured alternative to fossil fuel energy generation that has been driven by environmental concerns. Their intermittent nature has meant that gas turbines have remained relevant to support them as a backup. Current grid operation requires gas turbines to operate at as low power as possible when their demand drops, and also ramp-up quickly when power generation from renewables declines. Air extraction from a gas turbine compressor can address the first requirement, as this mechanism reduces the load or power of the engine while storing the air for further pressurised reinjection, related to ramp-up rate improvements. This study demonstrates the aerodynamic implications and the limits to air extraction behind the last stage of the compressor, to achieve further minimum load reduction. To achieve this, a zero-dimensional (0D) analytical model of an engine at design and off-design conditions (air extraction) has been used to determine the boundary conditions for a 3D compressor Computational Fluid Dynamics (CFD) model. The multi-stage CFD model shows the aerodynamic implications of low to high air extractions that are limited by choke, high flow separation, and loss in the pressure at the hub region of OGV and last stage stator. As such, the back of the compressor was more affected than the earlier stages. Based on these, the limit of flow extraction is 18% (of the compressor discharge). The compressor of the analytical engine model showed similarity in trends for comparable conditions with the stand-alone 3D compressor, however, more optimistic than the latter. The work has shown that the compressor is capable of high airflow extractions to reduce the minimum load further.
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    Gas turbine minimum environmental load extension with compressed air extraction for storage
    (Elsevier, 2020-08-14) Abudu, Kamal; Igie, Uyioghosa; Minervino, Orlando; Hamilton, Richard
    The fact that most renewable forms of energy are not available on-demand and are typically characterised by intermittent generation currently makes gas turbine engines an important source of back-up power. This study focuses on one of the capabilities that ensure that gas turbines are more flexible on the electric power grid. The capability here is the minimum environmental load that makes it possible to keep a gas turbine engine on the grid without a shut-down, to offer grid stability, adding inertia to the grid in periods when there is no demand for peak power from the engine. It is then desirable to operate the engine at the lowest possible load, without infringing on carbon monoxide emissions that becomes dominant. This paper demonstrates this potential through the extraction of the pressurised air from the back end of the compressor into an assumed energy storage system. The simulation of the engine performance using an in-house tool shows the additional reduction of the power output when the maximum closing of variable inlet guide vane is complemented with air extractions. However, the identified key strategy for achieving a lower environmental load (with same carbon monoxide emission limit) is to always maintain the design flame temperature. This is contrary to the conventional approach that involves a decrease in such temperatures. Here, a 34% reduction in load was achieved with 24% of flow extraction. This is shown to vary with ambient temperatures, in favour of lower temperatures when the combustor inlet pressures are higher. The emission models applied were based on empirical correlations and shows that higher combustor inlet pressures, high but constant flame temperatures with core flow reduction is crucial to obtaining a low environmentally compliant load. The compressor analysis shows that choking is a noticeable effect at a higher rate of extractions; this is found to occur at the stages closest to the extraction location
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    Impact of gas turbine flexibility improvements on combined cycle gas turbine performance
    (Elsevier, 2021-02-20) Abudu, Kamal; Igie, Uyioghosa; Roumeliotis, Ioannis; Hamilton, Richard
    The improvement of gas turbines flexibility has been driven by more use of renewable sources of power due to environmental concerns. There are different approaches to improving gas turbine flexibility, and they have performance implications for the bottoming cycle in the combined cycle gas turbine (CCGT) operation. The CCGT configuration is favourable in generating more power output, due to the higher thermal efficiency that is key to the economic viability of electric utility companies. However, the flexibility benefits obtained in the gas turbine is often not translated to the overall CCGT operation. In this study, the flexibility improvements are the minimum environmental load (MEL) and ramp-up rates, that are facilitated by gas turbine compressor air extraction and injection, respectively. The bottoming cycle has been modelled in this study, based on the detailed cascade approach, also using the exhaust gas conditions of the topping cycle model from recent studies of gas turbine flexibility by the authors. At the design full load, the CCGT performance is verified and subsequent off-design cases from the gas turbine air extraction and injection simulations are replicated for the bottoming cycle. The MEL extension on the gas turbine that brings about a reduction in the engine power output results in a higher steam turbine power output due to higher exhaust gas temperature of the former. This curtails the extended MEL of the CCGT to 19% improvement, as opposed to 34% for the stand-alone gas turbine. For the CCGT ramp-up rate improvement with air injection, a 51% increase was attained. This is 3% point lower than the stand-alone gas turbine, arising from the lower steam turbine ramp-up rate. The study has shown that the flexibility improvements in the topping cycle also apply to the overall CCGT, despite constraints from the bottoming cycle.
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    Minimum environmental load extension through compressed air extraction: numerical analysis of a dry low NOx combustor
    (Elsevier, 2023-02-17) Wiranegara, Raditya Yudha; Igie, Uyioghosa; Ghali, Pierre; Abudu, Kamal; Abbott, David; Hamilton, Richard
    The operational flexibility of gas turbine (GT) engines is a key requirement to coexist alongside increasing renewable energy that is often intermittent. One of the GT flexibility criteria is the Minimum Environmental Load (MEL). This is the lowest load the engine can be operated, without infringing on emissions limits (particularly CO) and is relevant to periods when there is a priority to renewable generation or low power demand. This study along with a series of related works of the authors proposes compressor air extraction for MEL extension. Here, a stand-alone three-dimensional numerical dry low NOx combustor demonstrates the technical viability concerning combustor performance and emissions. In addition, supplemented with low-order models for durability and stability evaluations. For the first time, there is evidence to show that the combustor can handle the 18% compressed air extraction to sustain a new MEL. This operation is characterised by a 12.3% reduction in CO through an increase of the fuel split ratio by 2% after design exploration cases. However, at the expense of a smaller overall rise in NO emissions by 5%. The durability analysis focused on the wall liner temperature assessments, which show no unusually high temperature rise for the new MEL. Similarly, the thermoacoustic instability frequencies and gains are around the normal operation mode. When benchmarked against previous related engine-level analysis, the evidence shows that the new MEL is a 7% points reduction of load.
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    Numerical study of radiation and fuel-air unmixedness on the performance of a dry low NOx combustor
    (American Society of Mechanical Engineers (ASME), 2022-11-11) Wiranegara, Raditya Yudha; Igie, Uyioghosa; Ghali, Pierre; Zhao, Rang; Abbott, David; Hamilton, Richard
    The development of gas turbine combustors is expected to consider the effects of radiation heat transfer in modelling. However, this is not always the case in many studies that neglect this for adiabatic conditions. The effect of radiation is substantiated here, concerning the impact on the performance, mainly the emissions. Also, the fuel-air unmixedness (mixing quality) influenced by the combustor design and operational settings has been investigated with regards to the emissions. The work was conducted with a Mitsubishi-type Dry Low NOx combustor developed and validated against experimental data. This 3D computational fluid dynamics study was implemented using Reynolds-Averaged Navier Stokes simulation and the Radiative Transfer Equation model. It shows that NO, CO and combustor outlet temperature reduces when the radiative effect is considered. The reductions are 17.6% and below 1% for the others respectively. Thus, indicating a significant effect on NO. For unmixedness across the combustor in a non-reacting simulation, the mixing quality shows a direct relationship with the Turbulence Kinetic Energy (TKE) in the reacting case. The most significant improvements in unmixedness are shown around the main burner. Also, the baseload shows better mixing, higher TKE and lower emissions (particularly NO) at the combustor outlet, compared to part-load.