Abstract:Industrial gas turbines are now required to operate more flexibly as a result of incentives and priorities given to renewable forms of energy. This study considers the extraction of compressed air from the gas turbine; it is implemented to store heat energy at periods of a surplus power supply and the reinjection at peak demand. Using an in-house engine performance simulation code, extractions and injections are investigated for a range of flows and for varied rear stage bleeding locations. Inter-stage bleedin… Show more
“…It shows good agreement with the publicly available OEM data, 6 having the highest percentage error of 2% for one temperature; the mean error across the nine cases is 0.2%. Further details of the design and off-design calculations are provided in Igie et al., 18 MacMillan, 21 and Pellegrini et al. 22 Figure 2.Off-design validation of engine model – varying ambient temperatures.…”
Section: Set-up Under Investigationmentioning
confidence: 99%
“…Igie et al. 18 focus on the stand-alone GT with respect to an assumed CAES. This study shows the performance benefits of different injection air temperatures, as well as the influence of the design stage pressure ratio distribution on stall margin.…”
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.
“…It shows good agreement with the publicly available OEM data, 6 having the highest percentage error of 2% for one temperature; the mean error across the nine cases is 0.2%. Further details of the design and off-design calculations are provided in Igie et al., 18 MacMillan, 21 and Pellegrini et al. 22 Figure 2.Off-design validation of engine model – varying ambient temperatures.…”
Section: Set-up Under Investigationmentioning
confidence: 99%
“…Igie et al. 18 focus on the stand-alone GT with respect to an assumed CAES. This study shows the performance benefits of different injection air temperatures, as well as the influence of the design stage pressure ratio distribution on stall margin.…”
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 impact of compressed air injection is now being examined more widely for power augmentation and ramp-up rates improvement, within power generation. Injecting compressed air into a gas turbine engine provides additional mass flow for power augmentation [8,9,10,11] in steady-state and can be used to improve the transient ramp rate performance [8,12]. For augmentation, Coriolano S. [13] examines the augmentation benefit of combining a small CAES system in two configurations.…”
Section: Figure 2 Power Demand and Renewable Energy Generation For A Given Period Of The Daymentioning
confidence: 99%
“…The article shows a storage efficiency of 70% for the best operating scenario and confirms an adequate surge margin of 8% during air injection. Igie et al [9] evaluate the implication of energy storage demand (extractions and injections) on the performance and operability of a single shaft gas turbine. The study indicates an increase in power output of over 40% with an air injection rate of 20% (wrt inlet), also proposing a maximum of 17.5% as safer for stall avoidance shown in the rear stages of the multi-stage model.…”
Section: Figure 2 Power Demand and Renewable Energy Generation For A Given Period Of The Daymentioning
The transition to more renewable energy sources of power generation is associated with grid instability and the need for backup power, due to their intermittency. This provides an opportunity for gas turbine engines, especially the aeroderivative (AD) types that generally have higher ramp rates than heavy-duty engines. Nonetheless, higher ramp rates are still necessary to meet more stringent grid requirements, with increased renewables subscription. The study examines ramp rate improvements and performance enhancement through compressed air injection at the back of the high-pressure compressor (HPC). Two configurations of AD engines are considered in the investigation. In-house gas turbine performance simulation software has been used to simulate the steady-state and transient operations for design and off-design performance. Compressed air injection in the study is facilitated by an assumed compressed air storage or an external compressor. The steady-state analysis for power augmentation shows that for the two-spool engine with fixed speed low-pressure compressor (LPC), a 16% increase in power is obtained with 8% of flow injection. The other engine that is intercooled and consists of a variable speed LPC with power turbine shows a 21% increase in power for the same injection amount. Above 8% injection, the HPC of both engines tends towards an adverse rise in pressure ratio. However, up to 15% of flow injection is allowed before the surge point. It is seen generally that the operating point of the LPC moves away from surge, while the opposite is the case for the HPC. For transient simulations focused on ramp rates, the better improvements are shown for the intercooled engine that runs at variable speed. This is a ramp rate improvement of 100% with air injection, while that of the other engine increases by 85%.
“…Ref [12] only presents a technical review of the potentials of extraction for MEL and not the methodology of the analysis. The stand-alone GT is the focus of Igie et al [13] that investigates the impact of flow extractions at 3 consecutive rear stage locations, using a single-shaft engine model of 10 compressor stages. The study was conducted at full load extraction and reports that extracting after the last stage proved safer with regards to surge margins of the compressor.…”
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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