This paper presents numerical predictions of the flow field in the swirl-stabilized OP16 DLE combustor using hydrogen as a fuel. Computational Fluid Dynamics (CFD) simulations employing unsteady Reynolds-Averaged Navier-Stokes (URANS) and Wall Modelled Large Eddy Simulations (WMLES) are performed without including reaction mechanisms. The objective is to gain insights into scalar mixing predictions of the two approaches when hydrogen and air undergo shear-driven turbulent mixing. Accurate scalar mixing predictions are crucial in the combustors’ design process to assess the uniformity of fuel-air mixing as localized regions of high fuel concentrations can lead to increased NOx emissions and to identify locations with a propensity for Boundary Layer Flashback (BLF). Results are compared and analyzed in terms of time-averaged equivalence ratio, unmixedness and Turbulent Kinetic Energy (TKE) profiles. TKE predictions are lower in URANS, leading to significantly lower fuel-air mixing levels than WMLES, indicating differences in their predictions of shear-layer interactions in the mixing region and the swirl section of the combustor.@en

To support increasing renewable capacity for a net-zero future, energy storage will play a key role in maintaining grid stability. In this paper, all current and near-future energy storage technologies are compared for three different scenarios: (1) fixed electricity buy-in price, (2) market-based electricity buy-in price, and (3) energy storage integrated into a fully renewable electricity system. In the first part of this study, an algorithm is devised to simulate strategic buy-in of electricity for energy storage. This analysis yields a qualitative decision-making tool for a given energy storage duration and size. Building upon the first part’s findings, an integration study gives insight into expected power prices and expected storage size in a typical northwestern European fully renewable energy system. The integration study shows significant need for electricity storage with durations spanning from one to several days, typically around 40 h. Pumped Hydro Storage and Pumped Thermal storage surface as the best options. The overall levelized costs of storage are expected to be in the USD 200–500/MWh range. Integration of storage with renewables can yield a system-levelized cost of electricity of about USD 150/MWh. Allowing flexibility in demand may lower the overall system-levelized cost of electricity to USD 100/MWh.@en

Hydrogen is presently emerging as a convenient, chemically simple and carbon-free chemical for large-scale energy transport and storage with good balancing potential in future energy systems dominated by unsteady, non-dispatchable renewable power generation from solar and wind resources. Therefore, the capability to operate with hydrogen-enriched fuels reliably, cleanly and efficiently is an increasingly important requirement for gas turbines combustion systems. In this context, the innovative FlameSheet™ combustion system platform, developed by PSM with continued technology refinements by Thomassen Energy, both sister Hanwha companies, represents a competitive Dry Low Emission (DLE) device that has already proven able to handle gaseous fuel blends with high hydrogen fractions at 1350 C gas turbine firing conditions and above. This is mainly due, among a number of crucially important characteristics, to a carefully designed fuel-injection system and to an aerodynamic flame-stabilization strategy characterized by a unique flow pattern (U-bend) of the premixed reactants, ultimately resulting in increased resistance to premixed flame flashback. In the present work, we report a joint research effort consisting of a comprehensive numerical modelling study and of a experimental measurements campaign conducted on a geometrically simplified “FlameSheet^TM-like” burner fired with hydrogen-air mixtures at varying equivalence ratios. A two-dimensional, planar version of FlameSheet^TM (originally a cylindrical burner) is developed at TU Delft in collaboration with Thomassen Energy to enable better optical access and improved diagnostics of the turbulent reactive flow. Massively parallel Large Eddy Simulation (LES) of several geometrically simplified FlameSheet^TM configurations are performed at SINTEF in conjunction with detailed chemical kinetics and a Partially Stirred Reactor (PaSR) model for the turbulence-chemistry interaction. The LES results are validated against the experimental measurements and used, jointly with the latter, to provide new insights about the physical mechanisms that lead to stable flames or, alternatively, to the occurrence of flashback. It is found that, depending on the shape of the tip of the inner combustor-liner wall, flashback takes place along an inner route, around the blunt-shaped tip, or follows an outer route along the outer wall of the U-bend, for a sharp-shaped tip. Furthermore, as the critical equivalence ratio is approached, the amplitude of acoustic pressure fluctuations, excited by the interaction of the flame with the vortex-shedding immediately downstream of the U-bend, significantly increases ultimately leading to abrupt upstream flame displacement and to the occurrence of flashback. Finally, the LES model predictions confirm that the ratio of the channel thickness confining the flow upstream and downstream of the U-bend represents one of the main tuning parameters in flashback control.

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Hydrogen is considered as a promising zero carbon battery fuel to deliver balancing power for the future electricity system with an increasing share of variable renewable power generation. Flame flashback is one of the main challenges for the application of hydrogen in gas turbines. Lean premixed hydrogen combustion is more prone to flashback than natural gas combustion due to higher flame speed and Lewis number effect. The TU Delft developed a boundary layer flashback model based on a previous work by TU Munich. The TU Delft model includes amongst others the effect of the laminar flame speed, boundary layer profile, Lewis number and adverse pressure gradient of the mean flow. The model was successfully validated on academic experiments from TU Munich. In the present paper the turbulent flame speed closure in the TU Delft flashback model is updated for gas turbine like conditions using experimental data from the University of California, Irvine (UCI). This updated model is validated against data from the Paul Scherrer Institute (PSI) and back tested on the original academic experiments from TU Munich. The updated TU Delft boundary layer flashback model and the flashback model from the Paul Scherrer Institute (PSI) have been applied to a scaled version of the Flamesheet^TM combustor. The outcome of the PSI flashback model correlates very well with test results from the TU Delft laboratory, the TU Delft flashback model only with the original flame speed correlation.

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Industry is a major contributor to the rise in global CO2 emissions, constituting one fifth of the global energy consumption, of which a significant amount is provided by fossil fuel combustion. Following the Paris agreement, emphasis has been made on the decarbonization of the industrial sector. This study focuses on industrial decarbonization by employing Carbon Capture and Storage for Combined Heat and Power (CHP) gas turbine plants. The scope of this study includes conceptual modelling and thermodynamic analysis of potential decarbonization options for zero carbon CHP plants. The studied options include post-combustion capture, exhaust gas recirculation, precombustion capture and oxyfuel combustion. As conventional air Brayton cycles are not applicable for oxy-fuel combustion in gas turbines, different working fluids and cycle configurations are proposed and thermodynamic performance is evaluated. Selected cycles were then compared based on thermodynamics, economics and off-design performance at a typical constant power to heat ratio of 0.78. It was observed that oxyfuel CHP cycle with CO2 working fluid is a promising solution for zero carbon CHP with relatively low costs and 100% CO2 capture. However, this solution requires new turbomachinery design.

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New technologies are being developed to produce electricity cleaner and more efficient. Promising technologies among these are the solid oxide fuel cell and the supercritical carbon dioxide Brayton cycle. This study investigates the potential of integrating both technologies. The solid oxide fuel cell is known as a potentially clean and highly efficient technology to convert chemical energy to electricity. The high operating temperatures (600–1000 °C) allow the possibility of a bottoming cycle to utilize the high quality excess heat and also facilitate reforming processes, making it possible to use higher hydrocarbons as fuel. The supercritical carbon dioxide Brayton cycle has received attention as a promising power cycle. It has already been identified as a suitable cycle for relatively low temperature, compared to traditional gas turbines, heat sources for several reasons. Firstly because of the high efficiency, around 40%–45% for the common simple recuperative cycle. Secondly, because the turbine inlet temperature of a supercritical carbon dioxide is around 700 °C is low, compared to well over 1000 °C for a common air Brayton cycle. This is especially of interest because solid oxide fuel cell developers are targeting lower operating temperatures to avoid the use of exotic and expensive materials. And thirdly, the cycle can operate entirely above the critical point. Therefore the temperature increases gradually with the energy added to the cycle. This is more suitable for waste heat because the exergy loss decreases and more low temperature heat can be utilized compared to a steam Rankine cycle where most of the heat is added above the relatively high boiling point of pressurized water. A thermodynamic model of the solid oxide fuel cell- supercritical carbon dioxide Brayton cycle hybrid system is developed to explore and analyze different concepts of integration. Several conclusions are drawn. Firstly it is found that recirculating cathodic air increases the efficiency of the system and decreases the size of the heat exchangers. Secondly, applying a pinch point optimization decreases the size of the heat exchangers but increases the complexity of the system while the efficiency is not much affected. Thirdly, applying the recompression cycle in stead of a simple recuperative supercritical carbon dioxide cycle increases the efficiency of the system but not as significantly when operating the supercritical carbon dioxide as a stand-alone system while the complexity of the system increases even more. And finally, compared to a directly coupled solid oxide fuel cell-gas turbine system the solid oxide fuel cell- supercritical carbon dioxide Brayton cycle hybrid system is more efficient but significantly more complex.

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The combustion properties of hydrogen make premixed hydrogen-air flames very prone to boundary layer flashback. This paper describes the improvement and extension of a boundary layer flashback model from Hoferichter et al. (2017, "Prediction of Confined Flame Flashback Limits Using Boundary Layer Separation Theory," ASME J. Eng. Gas Turbines Power, 139(2), p. 021505) for flames confined in burner ducts. The original model did not perform well at higher preheat temperatures and overpredicted the backpressure of the flame at flashback by 4-5×. By simplifying the Lewis number-dependent flame speed computation and by applying a generalized version of Stratford's flow separation criterion (Stratford, 1959, "The Prediction of Separation of the Turbulent Boundary Layer," J. Fluid Mech., 5(1), p. 1), the prediction accuracy is improved significantly. The effect of adverse pressure gradient flow on the flashback limits in 2 deg and 4 deg diffusers is also captured adequately by coupling the model to flow simulations and taking into account the increased flow separation tendency in diffuser flow. Future research will focus on further experimental validation and direct numerical simulations to gain better insight into the role of the quenching distance and turbulence statistics.

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Todays renewables, wind and solar power, have a fluctuating nature, making the grid less stable. However, with the increasing share of intermittent sources of renewable power, novel options have to be created to stabilize the power grid. One of these options is energy storage via the conversion of excess power to hydrogen during periods of high generation from wind and/or solar. In periods of power shortages hydrogen is converted back to power. In this work, a number of high efficiency thermodynamic cycles, based upon the Graz cycle and the Toshiba Reheat Rankine cycle, both a coupled closed Brayton cycle with a Rankine cycle, are investigated and improvements are proposed leading to LHV efficiencies of 75%. Also the addition of fuel cells to the cycles is studied leading to potential LHV efficiencies of 85%. Application of pressurized H2/O2 usage leads to several improvements over conventional thermodynamic cycles and conventional fuel cells.@en

This work is focused on the process system modelling of an indirectly heated gasifier (10 MW_th) using torrefied wood as feedstock and its integration with methanol and power production using Aspen Plus®. The modelling of the gasification process along with the obtained reaction kinetics were validated with experimental data found in literature. Different processing steps such as gasification, gas cleaning and upgrading, methanol synthesis and energy conversion, were modelled and their performance was optimized through a series of sensitivity studies. The results obtained were then used to investigate the effect of different technologies and the variation of operational parameters on the overall process performance. Three cases were examined: “syngas production” (case 1), “methanol production” (case 2), and “power production” (IGCC) (case 3). Case 1 and case 2 were simulated using sand and dolomite as bed materials respectively, in order to study the incorporation of Absorption Enhanced Reforming (AER) on the syngas and methanol production efficiency. For case 3 the simulation was performed for two different configurations: a conventional Integrated Gasification Combined Cycle (IGCC) and an innovative Inverted Brayton Cycle (IBC) turbine system. Dolomite was used as the bed material for both configurations. For case 1, an increase of 5% in hydrogen yield in the product gas when AER is applied was observed. For case 2, higer values of Cold Gas Efficiency and Net Efficiency (34% and 60% instead of 33% and 55%, respectively) and a slightly lower value of Carbon Conversion (96% instead of 100%) were obtained when AER was employed. Gasification temperature was lowered by 110 °C in this scenario. For case 3, a lower value of Net Efficiency was obtained when IBC was considered (43% instead of 47%), while a value of 60% was obtained for methanol production with AE. Moreover, the results of case 3, showed that the latent heat in the hot syngas is best utilised when IBC is considered. The developed model accurately predicted the composition of the produced gas and the operational conditions of all the identified blocks within the methanol synthesis and power production processes. This way the use of this model as a generic tool to compare the utilization of different technologies on the performance of the overall process was validated.

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The combustion properties of hydrogen make premixed hydrogen-air flames prone to flashback. Several combustor concepts have been proposed and studied in the past few years to tackle the problem of flame flashback in premixed high hydrogen fuel combustors. This study looks at one of the concepts which uses the Aerodynamically Trapped Vortex to stabilize the flame. Burner concepts based on trapped vortex flame stabilization have a higher resistance towards flame blowout than conventional swirl stabilized burners. This work looks at the flow and flame behavior in the proposed Aerodynamically Trapped Vortex Combustor for 100% premixed hydrogen operation. Numerical simulations for the analysis were performed with the commercial CFD simulation package AVL FIRE^TM. The flow field characterization was focused on the investigation of the influence of both the inlet velocity and inlet turbulence intensity on the mean velocity, wall velocity gradient and turbulence intensity in the combustor. To study the flame stabilization mechanism, reactive simulations were performed at two fuel equivalence ratios. The combustion regime of the flame, turbulent flame speed and temperature distribution in the combustor were quantified from the simulation results. Combustion is modelled using a detailed chemistry solver with the k - e turbulence model to resolve turbulence. No additional turbulence-chemistry interaction model is used in the current research. To reduce chemistry computational time, the multi-zone method is employed. To capture the effect of preferential diffusion, two approaches were used to quantify the diffusion coefficient of each species. The diffusion coefficients were calculated using both mixture averaged approach and the multi component diffusion approach. The proposed design for the Aerodynamically Trapped Vortex combustor was able to stabilize a 100% premixed hydrogen flame without flashback for the simulated conditions.

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The combustion properties of hydrogen make premixed hydrogen-air flames very prone to boundary layer flashback. This paper describes the improvement and extension of a boundary layer flashback model from Hoferichter [1] for flames confined in burner ducts. The original model did not perform well at higher preheat temperatures and overpredicted the backpressure of the flame at flashback by 4-5x. By simplifying the Lewis number dependent flame speed computation and by applying a generalized version of Stratford’s flow separation criterion [2], the prediction accuracy is improved significantly. The effect of adverse pressure gradient flow on the flashback limits in 2◦ and 4◦ diffusers is also captured adequately by coupling the model to flow simulations and taking into account the increased flow separation tendency in diffuser flow. Future research will focus on further experimental validation and direct numerical simulations to gain better insight into the role of the quenching distance and turbulence statistics.@en

The rapid growth of renewable generation and its intermittent nature has modified the role of combined cycle power stations in the energy industry, and the key feature for the operational excellence is now flexibility. Especially, the capability to start an installation quickly and efficiently after a shutdown period leads to lower operational cost and a higher capacity factor. However, most of existing thermal power stations worldwide are designed for continuous operation, with no special focus on an efficient start-up process. In most current start-up procedures, the gas turbine controls ensure maximum heat flow to the heat recovery steam generator, without feedback from the steam cycle. The steam cycle start-up controls work independently with as main control parameter the limitation of the thermal stresses in the steam turbine rotor. In this paper, a novel start-up procedure of an existing combined cycle power station is presented, and it uses a feedback loop between the steam turbine, the boiler and the gas turbine start-up controls. This feedback loop ensures that the steam turbine can be started up with a significant reduction in stresses. To devise and assess this start-up methodology, a flexible and accurate dynamic model was implemented in the Simulink environment. It contains >100 component blocks (heat exchangers, valves, meters and sensors, turbines, controls, etc.), and the mathematical component submodels are based on physical models and experimental correlations. This makes the model generally applicable to other power plant installations. The model was validated against process data related to the three start-up types (cold start, warm start, hot start). On this basis, the optimization model is implemented with feedback loops that control, for example, the exit temperature of the gas turbine based on the actual steam turbine housing temperature, resulting in a smoother heating up of the steam turbine. The optimization model was used to define the optimal inlet guide vanes position and gas turbine power output curves for the three types of start-up. These curves were used during real power station start-ups, leading to, for cold and warm starts, reductions in the start-up time of, respectively, 32.5% and 31.8%, and reductions in the fuel consumption of, respectively, 47.0% and 32.4%. A reduction of the thermal stress in the steam turbines is also achieved, thanks to the new start-up strategy.

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Combined heat and power (CHP) is a very efficient way to generate both power and heat. However due to the increase in renewable power, the position of CHP in the energy system shifts: 1) the benefits of low effective CO2 emissions and low primary fuel consumption decrease and 2) the income from the generated power will show stronger fluctuations and will generally decrease. Most CHP plants have shifted from base load operation to flexible operation on the power market to cope with these challenges. But due to the requirement for stable heat supply, flexible operation is more challenging than for a CCGT plant. Significant flexibilization of CHP plants can be achieved by the integration with power to heat (P2H): the heat supply requirement enables the opportunity to create value out of low electricity prices during periods of excess renewable power generation using hybrid CHP-P2H-operation while during hours with high electricity prices and relatively low renewable power generation the CHP plant can run economically in its original configuration. In this paper a study is executed on the implementation of P2H in an industrial CHP plant for four different configurations, varying from a ‘simple’ external electrical boiler to a full integration using air preheating and flue gas heating. The added flexibility and reduction of fuel consumption of these configurations have been calculated. The economic analysis identified the imbalance market as the most attractive option for a hybrid CHP-P2H installation. The maximum income is generated by the CHP-P2H configuration that combines an inlet air preheater with electrical duct firing. P2H appears to be a technical feasible option to make existing CHP installations fit for operation on a power market with an increasing share of renewable power.@en

The energy scenario is currently undergoing a rapid transition in the pursuit of increasing the share of renewable energy sources in order to reduce the global anthropogenic CO2 emission. However, since several of the renewable energy sources are intermittent in nature, like wind and solar, this intermittency gives rise to several problems in energy production, distribution and management. A novel solution to store and utilize excess energy from intermittent renewable energy sources (IRES) in a combined cycle power plant (CCPP) is introduced. The overall thermal to electricity conversion efficiency of the proposed method is higher as compared to other contemporary energy storage solutions. The techno-economic feasibility analysis of the proposed method indicates that it can lead to annual fuel savings up to approximately 0.8%, thereby saving 3600 tonnes of CO2 emission annually for a typical power plant. The proposed concept paves the way to change the role of a combined-cycle power plant from being solely an energy provider to a contributor in energy storage and energy management.@en

The rapid growth of renewable generation and its intermittent nature has modified the role of combined cycle power stations in the energy industry, and the key feature for the operational excellence is now flexibility. Especially, the capability to start an installation quickly and efficiently after a shutdown period leads to lower operational cost and a higher capacity factor. However, most of existing thermal power stations worldwide are designed for continuous operation, with no special focus on an efficient start-up process. In most current start-up procedures, the gas turbine controls ensure maximum heat flow to the heat recovery steam generator, without feedback from the steam cycle. The steam cycle start-up controls work independently with as main control parameter the limitation of the thermal stresses in the steam turbine rotor. In this paper, a novel start-up procedure of an existing combined cycle power station is presented, and it uses a feedback loop between the steam turbine, the boiler and the gas turbine startup controls. This feedback loop ensures that the steam turbine can be started up with a significant reduction in stresses. To devise and assess this start-up methodology, a flexible and accurate dynamic model was implemented in the SimulinkTM environment. It contains more than 100 component blocks (heat exchangers, valves, meters and sensors, turbines, controls, etc.), and the mathematical component sub-models are based on physical models and experimental correlations. This makes the model generally applicable to other power plant installations. The model was validated against process data related to the three start-up types (cold start, warm start, hot start). On this basis, the optimization model is implemented with feedback loops that control for example the exit temperature of the gas turbine based on the actual steam turbine housing temperature, resulting in a smoother heating up of the steam turbine. The optimization model was used to define the optimal inlet guide vanes position and gas turbine power output curves for the three types of start-up. These curves were used during real power station start-ups, leading to, for cold and warm starts, reductions in the start-up time of respectively 32.5% and 31.8%, and reductions in the fuel consumption of respectively 47.0% and 32.4%. A reduction of the thermal stress in the steam turbines is also achieved, thanks to the new start-up strategy.@en

This work focused on system modelling regarding the investigation of biomass gasification and its integration with methanol synthesis and power production. Indirect gasification technology was chosen and modelledusing Aspen Plus®. The gasification process along with the reaction kinetics were validated with experimental data from the literature. Different processing steps towards the conversion of biomass to methanol were identified and modelled. The identified process blocks were: Gasifier, Gas Cleaning Unit, Methanol Synthesis and the Energy Conversion Network were optimised by performing a series of sensitivity studies. The optimised model was then used to study the effect of choosing different technologies and parameters within the blocks on the overall process behaviour. Two different case studies were examined, each distinct from each other by a difference in technology of one of the blocks. The two cases concerned the impact of incorporation of Absorption Enhanced Reforming (AER) on the methanol synthesis process, simulated by using dolomite as the bed material. Sankey plots for each of these cases were drawn to visualize the energy losses in such complicated systems. The developed model accurately predicted the composition of the major product gas and operational conditions of all the identified blocks within the methanol synthesis process. The effect of incorporating AER on the overall methanol synthesis process was simulated. The developed model proved its use as a generic tool to compare the effect of different choices in technology on the performance of the overall process.@en

The increasing amount of renewable energy and emission norms challenge gas turbine power plants to operate at part-load with high efficiency, while reducing NOx and CO emissions. A novel solution to this dilemma is external Flue Gas Recirculation (FGR), in which flue gases are recirculated to the gas turbine inlet, increasing compressor inlet temperature and enabling higher part load efficiencies. FGR also alters the oxidizer composition, potentially leading to reduced NOx levels. This paper presents a kinetic model using chemical reactor networks in a lean premixed combustor to study the impact of FGR on emissions. The flame zone is split in two perfectly stirred reactors modelling the flame front and the recirculation zone. The flame reactor is determined based on a chemical time scale approach, accounting for different reaction kinetics due to FGR oxidizers. The recirculation zone is determined through empirical correlations. It is followed by a plug flow reactor. This method requires less details of the flow field, has been validated with literature data and is generally applicable for modelling premixed flames. Results show that due to less O2concentration, NOx formation is inhibited down to 10 - 40% and CO levels are escalated up to 50%, for identical flame temperatures. Increasing combustor pressure leads to a rise in NOx due to thermal effects beyond 1800 K, and a drop in CO levels, due to the reduced chemical dissociation of CO2. Wet FGR reduces NOx by 5-10% and increases CO by 10-20%.@en