Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Using Hydrogen as Gas Turbine Fuel: Premixed Versus Diffusive Flame Combustors

[+] Author and Article Information
Matteo Gazzani

e-mail: matteo.gazzani@mail.polimi.it

Emanuele Martelli

Energy Department,
Politecnico di Milano,
Via Lambruschini 4,
Milano 20156, Italy

Iarno Brunetti

Enel Ingegneria e Ricerca,
via A. Pisano 120,
Pisa 56121, Italy

In addition, a selective catalytic removal process can be adopted for NOx abatement from exhaust gases of gas-turbine power plants. This technique can be applied to H2-fueled gas turbines, as well as for conventional units, but it does not affect at all the combustion process and gas-turbine operations, and therefore it will be totally neglected in this analysis.

In the calculation model, this technological level is identified by the cross-sectional area of the spent coolant-ejecting holes. Hence, TIT is reduced as long as the resulting cooling flow can be ejected through the stipulated area in the most critical row of the expander (which always turned out to be the first rotor).

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received October 21, 2013; final manuscript received November 22, 2013; published online January 2, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(5), 051504 (Jan 02, 2014) (10 pages) Paper No: GTP-13-1381; doi: 10.1115/1.4026085 History: Received October 21, 2013; Revised November 22, 2013

This work aims at estimating the efficiency gain resulting from using lean premixed combustors in hydrogen-fired combined cycles with respect to diffusive flame combustors with significant inert dilution to limit NOx emissions. The analysis is carried out by considering a hydrogen-fired, specifically tailored gas turbine whose features are representative of a state-of-the-art natural gas–fired F-class gas turbine. The comparison between diffusion flame and lean premixed combustion is carried out considering nitrogen and steam as diluents, as well as different stoichiometric flame temperatures and pressure drops. Results show that the adoption of lean premixed combustors allows us to significantly reduce the efficiency decay resulting from inert dilution. Combined cycle efficiency slightly reduces from 58.5%–57.9% when combustor pressure drops vary in the range 3%–10%. Such efficiency values are comparatively higher than those achieved by diffusive flame combustor with inert dilution. Finally, the study investigated the effects of decreasing the maximum operating blade temperature so as to cope with possible degradation mechanisms induced by hydrogen combustion.

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Grahic Jump Location
Fig. 1

Variation of the isentropic expansion enthalpy drop and turbine inlet volumetric flow due to the use of hydrogen with/without diluents with respect to natural gas operation (for fixed TIT and pressure ratio). The variation is plotted as a function of the stoichiometric flame temperature when diluting hydrogen with nitrogen and steam.

Grahic Jump Location
Fig. 2

The combined cycle-plant layout for hydrogen-fueled cases; in the upper part of the figure, the GT and HRSG are represented. The bottom part of the figure reports the plant features for the three scenarios considered: (a) premixed flame combustor, (b) diffusive flame combustor with nitrogen dilution, and (c) diffusive flame combustor with steam dilution.

Grahic Jump Location
Fig. 3

Comparison between blade-temperature profiles of the reference case (solid line) and a modified case (dashed line), where a reduction ΔT is applied to the gas stream and to the blade material

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Fig. 4

(a) Combined cycle electric efficiency for all the cases at nominal TIT: the efficiency for steam- and nitrogen-diluted combustors is plotted as function of the STFT (bottom x-axis), while the efficiency for the premixed combustor is plotted as function of the combustor relative pressure loss (upper x-axis). (b) Electric efficiency for all the simulated cases as a function of the maximum blade-metal temperature; moving left to right: premixed combustor, nitrogen-diluted combustor, and steam-diluted combustor.




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