Impacts on Blowoff by a Variety of CRZs Using Various Gases for Gas Turbines (original) (raw)
Related papers
2015
This paper presents a series of experiments and numerical simulations using commercial software (ANSYS) to determine the behaviour and impact on the blowoff process with various geometries and simulated syngas compositions at fixed power outputs. Experiments were performed using a generic premixed swirl burner. The Central Recirculation Zone and the associated turbulent structure contained within it were obtained through CFD analyses providing details of the structures and the Damkolher Number (Da) close to blowoff limits. The results show how the strength and size of the recirculation zone are highly influenced by the blend, with a shift of Da and turbulence based on carbon-hydrogen ratio, shearing flows and Reynolds number. Instabilities such as thermoacoustics, flashback, autoignition and blowoff are highly affected by the flow structures and chemical reactions/diffusivity. Moreover, it has been observed that turbulence close to the boundaries of the central recirculation zone, a...
Coherent Structure Impacts on Blowoff using Various Syngases
Energy Procedia
Swirl stabilized combustion is one of the most successful technologies for flame and nitrogen oxides control in gas turbines. However, complex fluid dynamics and lean conditions pose a problem for stabilization of the flame. The problem is even more acute when alternative fuels are used for flexible operation. Although there is active research on the topic, there are still various gaps in the understanding of how interaction of large coherent structures during the process affect flame stabilization and related phenomena. Thus, this paper approaches the phenomenon of lean premixed swirl combustion of CH4/H2/CO blends to understand the impacts of these fuels on flame blowoff. An atmospheric pressure generic swirl burner was operated at ambient inlet conditions. Different exhaust nozzles were used to alter the Central Recirculation Zone and observe the impacts caused by various fuel blends on the structure and the blowoff phenomenon. Methane content in the fuel was decreased from 50% to 10% (by volume) with the remaining amount split equally between carbon monoxide and hydrogen. Experimental trials were performed using Phase Locked PIV. The Central Recirculation Zone and its velocity profiles were measured and correlated providing details of the structure close to blowoff. The results show how the strength and size of the recirculation zone are highly influenced by the fuel blend, changing stability based on the carbon-hydrogen ratios. Nozzle effects on the shear flow and Re numbers were also observed. Modelling was carried out using the k-ω SST CFD model which provided more information about the impact of the CRZ and the flame nature close to blowoff limit. It was observed that the model under-predicts coherent structure interactions at high methane fuel content, with an over-prediction of pressure decay at low methane content when correlated to the experimental results. Thus, complex interactions between structures need to be included for adequate power prediction when using very fast/slow syngas blends under lean conditions.
54th AIAA Aerospace Sciences Meeting, 2016
Lean premixed combustion is one of the most successful technologies for flame control in low NOx systems. The characteristics of these flows its good mixing performance, stability and the low emissions. The potential of using new alternative fuels presents a problem in terms due to heating value changes, flame parameters and reactivity. Bio-renewable processes and industrial systems requiring waste gases are just a few examples. The biggest challenge to fuel-flexibility is the large differences between natural gas and the proposed alternative fuels which causes variations in the stability profiles of the combustion process. In this paper, combustion of CH4/H2/CO mixtures was experimentally and numerically studied to understand the impacts of these fuels on the blowoff process. Atmospheric pressure and ambient temperature were used at moderate swirl number. Various nozzles were used to determine the impact of the blends on the Central Recirculation Zones. Methane content in the fuel was decreased from 50% to 0% (by volume) with the remaining amount split equally between carbon monoxide and hydrogen. The Central Recirculation Zone and its turbulence were numerically characterised using the k-ω turbulence model providing details of the structure close to blowoff. The results show how the strength and size of the recirculation zone are highly influenced by the blend, carbon/hydrogen ratio, nozzle geometry and Re numbers.
Stable Combustion under Carbon Dioxide Enriched Methane blends for Exhaust Gas Recirculation (EGR)
DEStech Transactions on Environment, Energy and Earth Sciences
Exhaust gas recirculation (EGR) is one of the main techniques studied over the years to enable the use of oxyfuel combustion for carbon capture and storage (CCS). However, the use of recirculated streams with elevated carbon dioxide poses different challenges from the control of the flow rates and flue stream characteristics to the suppression of unwanted instabilities during the combustion process. Therefore, this study evaluates the use of various CO2 enriched methane blends and their response towards the formation of a great variety of structures that appear in swirling flows, which are the main mechanism for combustion control in current gas turbines systems. The study uses a 100kW acoustically excited swirlstabilised burner to investigate the flow field response. The results showed improved thermal efficiency of the system with high swirl and forcing while the blend of CO2 with methane balanced the heat release fluctuation with a corresponding reduction in the acoustic amplitudes of the system for a smooth running, suggesting that certain CO2 concentrations in the fuel can provide more stable flames at a certain carbon dioxide concentration.
Flue gas recirculation in gas turbine: Investigation of combustion reactivity and NOx emission
Proceedings of ASME …, 2009
Flue gas recirculation (FGR) is a promising technology for the optimization of post-combustion CO 2 capture in natural gas combined cycle (NGCC) plants. In this work, the impact of FGR on lean gas turbine premix combustion is predicted by analytical and numerical investigations as well as comparison to experiments. In particular the impact of vitiated air condition and moderate increase of CO 2 concentration into combustion reactivity and NO x emission is studied. The influence of inlet pressure, temperature and recirculated NO x are taken as parameters of this study. Two different kinetic schemes are used to predict the impact that FGR has on the combustion process: the GRI3.0 and the RDO6_NO, which is a newly compiled mechanism from the DLR Stuttgart. The effects of the FGR on the NO x emissions are predicted using a chemical reactor network including unmixedness as presumed probability density function (PDF) to account for real effects.
FLUE GAS RECIRCULATION OF THE ALSTOM SEQUENTIAL GAS TURBINE COMBUSTOR TESTED AT HIGH PRESSURE
Concerning the efforts in reducing the impact of fossil fuel combustion on climate change for power production utilizing gas turbine engines Flue Gas Recirculation (FGR) in combination with post combustion carbon capture and storage (CCS) is one promising approach. In this technique part of the flue gas is recirculated and introduced back into the compressor inlet reducing the flue gas flow (to the CCS) and increasing CO 2 concentrations. Therefore FGR has a direct impact on the efficiency and size of the CO 2 capture plant, with significant impact on the total cost. However, operating a GT under depleted O 2 and increased CO 2 conditions extends the range of normal combustor experience into a new regime. High pressure combustion tests were performed on a full scale single burner reheat combustor high-pressure test rig. The impact of FGR on NO x and CO emissions is analyzed and discussed in this paper. While NO x emissions are reduced by FGR, CO emissions increase due to decreasing O 2 content although the SEV reheat combustor could be operated without problem over a wide range of operating conditions and FGR. A mechanism uncommon for GTs is identified whereby CO emissions increase at very high FGR ratios as stoichiometric conditions are approached. The feasibility to operate Alstom's reheat engine (GT24/GT26) under FGR conditions up to high FGR ratios is demonstrated. FGR can be seen as continuation of the sequential combustion system which already uses a combustor operating in vitiated air conditions. Particularly promising is the increased flexibility of the sequential combustion system allowing to address the limiting factors for FGR operation (stability and CO emissions) through separated combustion chambers. 2 2 ~ sum of higher alkane volumes fraction in natural gas mixture
Effects of geometry and gas composition on swirling flow
2015
Lean premixed swirl stabilised combustion is regarded as one of the most successful technologies for flame control and NOx reduction in gas turbines. Important characteristics of these flows are good mixing, flame stability through the formation of a Central Recirculation Zone, and low emissions at lean conditions as a consequence of the low operating temperature. This project presents a series of experiments and numerical simulations using commercial software (ANSYS) to determine the behaviour and impact on the blowoff process at various swirl numbers, nozzle geometries and gas compositions at same power outputs using confined and open conditions. Experiments were performed using a generic premixed swirl burner. The Central Recirculation Zone and the associated turbulent structure contained within it were obtained through CFD analyses providing details of the structures and the Damkolher Number (Da) close to blowoff limits. The results show how the strength and size of the recircul...
2017
It has become increasingly cost-effective for the steel industry to invest in the capture of heavily carbonaceous BOF (Basic Oxygen Furnace) or converter gas, and use it to support the intensive energy demands of the integrated facility, or for surplus energy conversion in power plants. As industry strives for greater efficiency via ever more complex technologies, increased attention is being paid to investigate the complex behavior of by-product syngases. Recent studies have described and evidenced the enhancement of fundamental combustion parameters such as laminar flame speed due to the catalytic influence of H2O on heavily carbonaceous syngas mixtures. Direct formation of CO2 from CO is slow due to its high activation energy, and the presence of disassociated radical hydrogen facilitates chain branching species (such as OH), changing the dominant path for oxidation. The observed catalytic effect is non-monotonic, with the reduction in flame temperature eventually prevailing, and...