Hydrogen Blending Into Ansaldo Energia AE94.3A Gas Turbine: High Pressure Tests, Field Experience and Modelling Considerations

Fuel flexibility in gas turbine development has become increasingly important and modern engines need to cope with a broad variety of fuels. The target to operate power plants with hydrogen-based fuels and low emissions will be of paramount importance in a future focusing on electric power decarbonization. Ansaldo Energia AE94.3A engine acquired broad experience with operation of various natural gas and hydrogen fuel blends, starting in 2006 in the Brindisi (Italy) power plant. Based on the exhaustive experience acquired in the field, this paper describes the latest advancements characterizing the operation of the AE94.3A burner with high pressure combustion tests adding hydrogen blends ranging from 0 to 40% in volume. The interpretation of the test results is supported by reactive and non-reactive simulations describing the effects of varying fuel reactivity on the flame structure as well as the impact of fuel / air momentum flux ratio on the fuel / air interaction and fuel distribution in the combustion chamber. As expected, increasing amounts of hydrogen in the fuel are also associated with higher amounts of NOx production, however this effect could be countered by optimization of the fuel staging strategy, based on the mentioned CFD considerations and feedback from high pressure tests.

Experimental Investigation of Fuel Staging Effect on Modal Dynamics of Thermoacoustic Azimuthal Instabilities in a Multi-Nozzle Can Combustor

This paper analyzes the dynamics of unstable azimuthal thermoacoustic modes in a lean premixed combustor. Azimuthal modes can be decomposed into two counter rotating waves where they can either compete and potentially suppress one of them (spinning) or coexist (standing), depending on the operating conditions. This paper describes experimental results of the dynamical behaviors of these two waves. The experimental data were taken at different mass flow rates as well as different azimuthal fuel staging in a multi-nozzle can combustor. It is shown that at a low flow rate with uniform fuel distribution, the two waves have similar amplitudes, giving rise to a standing wave. However, the two amplitudes are slowly oscillating out of phase to each other, and the phase difference between the two waves also shows oscillatory behavior. For an intermediate flow rate, the dynamics show intermittency between standing and spinning waves, indicating that the system is bistable. In addition, the phase difference dramatically shifts when the mode switches between standing and spinning waves. For a high flow rate, the system stabilizes at a spinning wave most of the time. These experimental observations demonstrate that not only the amplitudes of two waves but also the phase difference plays an important role in the dynamics of azimuthal mode. For non-uniform azimuthal fuel staging, the modal dynamics exhibit only an oscillatory standing wave behavior regardless of the mass flow rate. Compared to the uniform fuel staging, however, the pressure magnitude is considerably reduced, which provides a potential strategy to mitigate and/or suppress the instabilities.

Combustor Development and Engine Demonstration of Micro-Mix Hydrogen Combustion Applied to M1A-17 Gas Turbine

Kawasaki Heavy Industries, LTD. (KHI) has research and development projects for a future hydrogen society. These projects comprise the complete hydrogen cycle, including the production of hydrogen gas, the refinement and liquefaction for transportation and storage, and finally the utilization in a gas turbine for electricity and heat supply. Within the development of the hydrogen gas turbine, the key technology is stable and low NOx hydrogen combustion, namely the Dry Low NOx (DLN) hydrogen combustion. KHI, Aachen University of Applied Science, and B&B-AGEMA have investigated the possibility of low NOx micro-mix hydrogen combustion and its application to an industrial gas turbine combustor. From 2014 to 2018, KHI developed a DLN hydrogen combustor for a 2MW class industrial gas turbine with the micro-mix technology. Thereby, the ignition performance, the flame stability for equivalent rotational speed, and higher load conditions were investigated. NOx emission values were kept about half of the Air Pollution Control Law in Japan: 84ppm (O2-15%). Hereby, the elementary combustor development was completed. From May 2020, KHI started the engine demonstration operation by using an M1A-17 gas turbine with a co-generation system located in the hydrogen-fueled power generation plant in Kobe City, Japan. During the first engine demonstration tests, adjustments of engine starting and load control with fuel staging were investigated. On 21st May, the electrical power output reached 1,635 kW, which corresponds to 100% load (ambient temperature 20 °C), and thereby NOx emissions of 65 ppm (O2-15, 60 RH%) were verified. Here, for the first time, a DLN hydrogen-fueled gas turbine successfully generated power and heat.

Application of Large Eddy Simulation for HA_Class Combustion System Design to Mitigate Combustion Instabilities (Frequency, and Amplitude)

Enabled by national commercialization of massive shale resources, Gas Turbines continue to be the backbone of power generation in the US. With the ever-increasing demand on efficiency, GT combustion sections have evolved to include shorter combustion lengths and multiple axial staging of the fuel, while at the same time operating at ever increasing temperatures. This paper presents the results of very detailed Large Eddy Simulations of one (or two) combustor can(s) for a 7HA GE Gas Turbine Engine over a range of operating parameters. The model of the simulated combustor can(s) includes (include) all the details of the combustor from compressor diffuser to the end of the stationary part of the first stage of the turbine. It includes the geometries of multiple pre-mixers within the combustion can(s) and the complete design features for axial fuel staging. All simulations in this work are performed using the CharLES flow solver developed by Cascade Technologies. CharLES is a suite of massively parallel CFD tools designed specifically for multiphysics LES in high-fidelity engineering applications. Thermo acoustic results from LES were validated first in the physical GE lab and then in full-engine testing. Both the trend as well as the predicted amplitudes for the excited axial dominant combustion mode matched the data produced in the lab and in the engine. The simulations also revealed insight into the ingestion of hot gases by different hardware pieces that may occur when machine operates under medium to high combustion dynamics amplitudes. This insight then informed the subsequent design changes which were made to the existing hardware to mitigate the problems encountered.

New Generation Aero Combustor

The purpose of this study is to identify the technology for next generation aero combustors, and to propose totally new combustor design approaches. Next generation aero combustors need very high combustion air fraction, that brings idle lean blow out (LBO) problem. The present study suggests several measures to solve this problem, including: pilot and main two concentric combustion zones with separation, aerodynamic design to have main air slipping by pilot combustion zones, etc. For high fuel air ratio (FAR) combustor, the present authors propose using angled main fuel co-axial air plain jet injection. Make use of different penetration to meet the need for low power and high power conditions. For low emissions combustor, the present authors use small scale close contact fuel-air mixing with fuel staging to have low emissions at the same time to have good idle, good high altitude ignition, etc. Brand new cooling designs are proposed for outliner and inner liner. This chapter is mainly a survey of present author’s own research. The results of this study will provide guideline for the development of next generation aero combustors.

Canonical Validation of a Modeling Strategy for Carbon Monoxide Emissions in Staged Operation of Gas Turbine Combustors

Canonical validation of a holistic modeling strategy for the prediction of CO emissions in staged operation of gas turbine combustors is subject of this study. Results from various validation cases are presented. Focus is on operating conditions that can be considered typical for modern, flexible gas turbines that meet the requirements of the upcoming new energy age. Reducing load in gas turbines is usually achieved by redistributing fuel referred to as fuel staging. Fuel-staged operation may lead to various mechanism like strong interaction of the flame with secondary air leading to quenching and elevated CO emissions and is - due to technical relevance - stressed in this work. In the recent past, our group published a new modeling strategy for the precise prediction of heat release distributions as well as CO emissions. An extension to the CO modeling strategy that is of high relevance for the introduced validation cases is addressed by this work. The first part of this study presents relevant aspects of the overall modelling strategy. Furthermore, a validation of the models is shown to demonstrate the ability of precisely predicting CO in two different multi-burner cases. Both validation cases feature a silo combustion chamber with 37 burners. The burner groups are switched off at partial load leading to intense interactions between hot and cold burners. Major improvement in comparison to CO predictions from the flamelet-based combustion model can be achieved as the modeling strategy is demonstrated to be capable of predicting global CO emissions accurately. Furthermore, the model’s precision in fuel staging scenarios are demonstrated and discussed.

Effects of Fuel Staging on the Hydrodynamic Stability of Multinozzle Swirl Flows

Hydrodynamic instability in lean premixed gas turbine combustors can cause coherent flow velocity oscillations. These can in turn drive heat release oscillations that when favorably coupled with combustor acoustic modes can result in combustion instability. The aim of this paper is to understand the impact of fuel staging on the characteristics of hydrodynamic modes in multinozzle combustors. We extend our recent numerical study on the hydrodynamic stability characteristics of a multinozzle combustor having three nozzles in a straight line with uniform fuel–air ratio in each nozzle, to the nonuniform fuel–air ratio case. As before, we construct the base flow model for this study by superposing contributions from individual nozzles, determined using a base flow model for a nominally axisymmetric single nozzle, at every point in the computational domain. The impact of fuel staging is captured by changing the burnt to unburnt gas density ratio parameter in the individual contribution from each nozzle. We investigate the characteristics of the most locally absolutely unstable mode for two cases. The first one is when the middle nozzle is made fuel rich when compared to the side nozzles and the second is when the side nozzles are made fuel rich relative to the middle nozzle. The impact of nonuniform fuel/air ratio on the local absolutely unstable temporal eigenvalues is seen to be small. However, significant changes in the spatial structure of the flow oscillations associated with the hydrodynamic eigenmodes are observed. In the first case, the flow oscillations with a different locally azimuthal nature on the middle nozzle when compared to the side nozzles emerge as the middle nozzle is made richer. In the second case, the oscillations on the two side nozzles are suppressed leaving the middle nozzle in a state that closely matches that of a single unconfined nozzle with the same nominal base flow velocity field. These types of internozzle variations in flow oscillation characteristics can explain the emergence of nonuniformity in heat release oscillation characteristics between individual nozzles in multinozzle combustors.

Quantification of Variation in Combustion Instability Amplitude in a Multi-Nozzle Can Combustor

In this work, we quantify the level of variation in unstable combustion oscillation amplitudes and identify the source of this variation in a multi-nozzle can combustor. At conditions where pollutant emissions are reduced, lean-premixed combustors can undergo thermoacoustic instability when pressure and heat release rate oscillations couple. A commonly used method for suppressing instability is fuel staging, which is a method where fuel is unevenly distributed between nozzles in a multi-nozzle combustor. Our work follows others who have characterized the effect of fuel staging on combustion instability and the mechanisms by which it works during both steady-state and transient operation. One of the outcomes from our previous work was that certain instability operating points display a high level of pressure oscillation amplitude variation. Instead of oscillating at a constant limit-cycle amplitude, the pressure oscillation amplitude varies significantly in time. In this work, we use the concept of permutation entropy to quantify the level of variation in the pressure fluctuation amplitude. We correlate the level of variation with a number of state variables over a range of operating conditions, 291 test cases in all. These state variables include mixture equivalence ratio; transient timescale, amplitude, and direction; hardware temperatures; gas temperatures; and thermoacoustic damping and growth rates. Significant pressure oscillation amplitude variation occurs when the thermoacoustic damping rate is low. The damping and growth rates can be low for a number of reasons, but they are highly correlated with the metal temperature of the centerbody, where the flames are anchored; lower temperatures result in lower damping rates during stable operation and lower growth rates during unstable operation. These results show the importance of the thermal boundary condition on the time-dependent behavior of the thermoacoustic instability.