Turbulent Flame Structure of Methane-Hydrogen Mixtures at Elevated Temperature and Pressure

The effect of hydrogen addition to methane on premixed turbulent flame has been investigated. Lean, stoichiometric and rich flames have been tested using a Bunsen burner at 3 bar and 7 bar absolute pressures, and 473 K, 573 K and 673 K temperatures. Two important turbulent flame structure characterstics, namely flame brush thickness δ T and flame surface density Σ have been quantified and analysed. Coefficients of the equations which relate flame brush thickness with progress variable are deduced. Flame surface density and the Bray-Moss-Libby model coefficient g/(σ y L y ) for the fuel mixtures studied have been found

Improving the Performance of Gas Turbine Power Plant by Modified Axial Turbine

Computer-based optimization techniques can be employed to improve the efficiency of energy conversions processes, including reducing the aerodynamic loss in a thermal power plant turbomachine. In this paper, towards mitigating secondary flow losses, a design optimization workflow is implemented for the casing geometry of a 1.5 stage axial flow turbine that improves the turbine isentropic efficiency. The improved turbine is used in an open thermodynamic gas cycle with regeneration and cogeneration. Performance estimates are obtained by the commercial software Cycle – Tempo. Design and off design conditions are considered as well as variations in inlet air temperature. Reductions in both the natural gas specific fuel consumption and in CO2 emissions are predicted by using the gas turbine cycle fitted with the new casing design. These gains are attractive towards enhancing the competitiveness and reducing the environmental impact of thermal power plant

Burning velocities of alternative gaseous fuels at elevated temperature and pressure

This study has been undertaken to investigate turbulent burning velocities of alternative gaseous fuels at elevated temperature and pressure using the established Bunsen burner method. The experiments were conducted in the industrial scale high-pressure optical chamber at the Gas Turbine Research Centre of Cardiff University. Five different gaseous fuels, methane, two methane-carbon dioxide mixtures, and two methane-hydrogen mixtures were studied. Experiments were conducted at two different temperatures (473 K and 673 K) and two different pressures (3 bara and 7 bara). Analysis of measurements made using 100% methane showed anticipated burning velocity trends with variation in temperature and pressure. The results reported here showed reasonable agreement with the available turbulent burning velocity correlations, although the burning velocities recorded by the other researchers were somewhat higher. The stoichiometric flames considered were all purposely contained within one flame regime on the Borghi-Peters diagram, namely the corrugated flamelet regime, through appropriate choice of operating conditions. Hydrogen enrichment and carbon dioxide dilution of methane show some expected trends. As expected, dilution of methane with carbon dioxide reduces the measured burning velocity. However, increasing pressure and temperature in this case have competing effects, with temperature raising the burning velocity and pressure reducing it. Comparison of the methane-carbon dioxide mixture results presented here are consistent with the qualitative trends recently reported by the group of researchers, but exhibit quantitative differences thought to be due to experimental and data analysis differences. Hydrogen enrichment of the methane leads to a significant increase in the measured burning velocity compared with methane, as anticipated. Comparison of the methane-hydrogen mixture results reported here show reasonable agreement with the measurements of other researchers. Our measurements show that increases in temperature and pressure independently lead to increased turbulent burning velocity, with a more pronounced effect of pressure for lean flames. Copyright © 2009. by Cardiff University and QinetiQ

Comparative Analysis of Isochoric and Isobaric Adiabatic Compressed Air Energy Storage

Adiabatic Compressed Air Energy Storage (ACAES) is regarded as a promising, grid scale, medium-to-long duration energy storage technology. In ACAES, the air storage may be isochoric (constant volume) or isobaric (constant pressure). Isochoric storage, wherein the internal pressure cycles between an upper and lower limit as the system charges and discharges is mechanically simpler, however, it leads to undesirable thermodynamic consequences which are detrimental to the ACAES overall performance. Isobaric storage can be a valuable alternative: the storage volume varies to offset the pressure and temperature changes that would otherwise occur as air mass enters or leaves the high-pressure storage. In this paper we develop a thermodynamic model based on expected ACAES and existing CAES system features to compare the effects of isochoric and isobaric storage. Importantly, off-design compressor performance due to the sliding storage pressure is included by using a second degree polynomial fit for the isentropic compressor efficiency. For our modelled systems, the isobaric system round-trip efficiency (RTE) reaches 61.5%. The isochoric system achieves 57.8% even when no compressor off-design performance decrease is taken into account. This fact is associated to inherent losses due to throttling and mixing of heat stored at different temperatures. In our base-case scenario where the isentropic compressor efficiency varies between (Formula presented.) and (Formula presented.), the isochoric system RTE is approximately 10% lower than the isobaric. These results indicate that isobaric storage for CAES is worth further development. We suggest that subsequent work investigate the exergy flows as well as the scalability challenges with isobaric storage mechanisms.</p