With the transition to more use of renewable forms of energy in Europe, grid instability that is linked to the intermittency in power generation is a concern, and thus, the fast response of on-demand power systems like gas turbines has become more important. This study focuses on the injection of compressed air to facilitate the improvement in the ramp-up rate of a heavy-duty gas turbine. The steady-state analysis of compressed airflow injection at part-load and full load indicates power augmentation of up to 25%, without infringing on the surge margin. The surge margin is also seen to be more limiting at part-load with maximum closing of the variable inlet guide vane than at high load with a maximum opening. Nevertheless, the percentage increase in the thermal efficiency of the former is slightly greater for the same amount of airflow injection. Part-load operations above 75% of power show higher thermal efficiencies with airflow injection when compared with other load variation approaches. The quasi-dynamic simulations performed using constant mass flow method show that the heavy-duty gas turbine ramp-up rate can be improved by 10% on average, for every 2% of compressor outlet airflow injected during ramp-up irrespective of the starting load. It also shows that the limitation of the ramp-up rate improvement is dominated by the rear stages and at lower variable inlet guide vane openings. The turbine entry temperature is found to be another restrictive factor at a high injection rate of up to 10%. However, the 2% injection rate is shown to be the safest, also offering considerable performance enhancements. It was also found that the ramp-up rate with air injection from the minimum environmental load to full load amounted to lower total fuel consumption than the design case.

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.

The development of gas turbine combustors is expected to consider the effects of radiation heat transfer in modeling. 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 regard 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 reduce 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.

No abstract

No abstract