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This study reports measurements of stability limits and exhaust NO mole fractions of technically-premixed swirl ammonia-air flames enriched with either methane or hydrogen. Experiments were conducted at different pressures from atmospheric to 5 bar, representative of commercial micro gas turbines. The full range of ammonia fractions in the fuel blend, xNH3, was considered, from 0 (pure methane or hydrogen) to 1 (pure ammonia), covering very lean (φ = 0.25) to rich (φ = 1.60) equivalence ratios. Results show that increasing pressure widens the range of stable equivalence ratios for pure ammonia-air flames. Regardless of pressure, there is a critical ammonia fraction above which the range of stable equivalence ratios suddenly widens. This is because flashback does not occur anymore when the equivalence ratio is progressively increased towards stoichiometric and rich blowout occurs instead. This critical ammonia fraction increases with pressure and is larger for ammonia-hydrogen than for ammonia-methane. Provided that enough hydrogen is blended with ammonia (xNH3

This study reports on the lean stability limits and exhaust emissions of ammonia-methane-air swirl flames with varied ammonia fuel fractions. A reduced-scale burner was manufactured, inspired by Ansaldo’s micro gas turbine AE-T100 burner, and it was installed inside a high-pressure combustion duct to operate at 4.5 bar. This pressure corresponds to that found at full-load in the actual micro gas turbine’s combustion chamber. The lean stability limits were measured by igniting the flame at an equivalence ratio of ϕ = 0.85 and then progressively decreasing the equivalence ratio until lean blowout. Emissions of CO2, NO, and N2O were recorded for different equivalence ratios and ammonia fractions. Rich flames at an equivalence ratio of ϕ = 1.20 were also considered. Results show that the equivalence ratio at lean blowout increases when the ammonia fraction increases and that all the ammonia fractions tested lead to flames more prone to lean blowout than the pure methane reference flame. The CO2 emissions are monotonically reduced by increasing the ammonia fraction, both for lean and rich flames. The NO emissions exceed many regulations limit regardless of the ammonia fraction for all lean equivalence ratios. N2O emissions are almost negligible, except for very lean equivalence ratios where the N2O mole fraction in the exhaust reaches unacceptably high values. Only rich ammonia-methane-air flames show good NO and N2O performance. Therefore, FTIR analysis was carried out to quantify the amount of the unburnt NH3 in the exhaust for these flames. Results show that unburnt NH3 concentration is invariant, around 200 ppmv, between 0.70 ≤ XNH3 ≤ 0.95. Data reported in this study provide insights for future work on combustors and after-treatment systems towards zero-emissions micro gas turbines.

Hydrogen is a promising carbon-free fuel for power generation in gas turbines. However, this raises some challenges associated with the storage and distribution of pure hydrogen. Storing hydrogen chemically in the form of ammonia is a safe and efficient alternative. However, ammonia as a fuel features a low chemical reactivity compared to hydrogen and natural gas and, as a consequence, stabilizing turbulent ammonia-air flames is challenging. Offsetting this low reactivity by enriching ammonia with some amount of hydrogen, which is much more reactive, is a promising strategy. In this study, the stability limits of technically-premixed ammonia-hydrogen-air flames are measured in a laboratory-scale swirl combustor for a wide range of ammonia fractions in the ammonia-hydrogen fuel blend. Results are compared to that obtained in the same combustor for reference methane-hydrogen-air mixtures. Data show that increasing the ammonia fraction in the fuel blend promotes lean blowout but reduces the flames’ propensity to flashback. The latter effect is even more pronounced if the volume fraction of ammonia in the fuel blend exceeds 0.7. In that case, increasing the equivalence ratio at a fixed bulk velocity does not yield flashback and rich blowout occurs instead, yielding a much wider range of stable equivalence ratios. This study also reports exhaust NO mole fractions, measured for large ranges of equivalence ratio and ammonia fraction in the fuel blend. Regardless of the ammonia fraction, data show that competitively low NO emissions occur for slightly rich equivalence ratios of φ ≥ 1.05, which is consistent with earlier studies. Stable flames and good NO performance are also found for very lean ammonia-hydrogen-air mixtures with φ ≤ 0.50, demonstrating the strong potential of fueling gas turbines with ammonia-hydrogen blends.

The global demand for energy is on the rise and in order to eliminate the associated emissions, carbon capture utilization and storage is deemed as one of solutions to achieve this target.1 Furthermore, the development of renewable energy alternatives including: solar, wind, geothermal, etc., is one of the potential long-term options to eliminate additional emissions.2 Although electricity generation from renewable sources is on the rise, it is going to be a long journey for renewables to take over the traditional power generation routes.2

To investigate the oxidation of ammonia (NH3)/hydrogen (H2) mixtures at intermediate temperatures, this work has implemented jet-stirred reactor (JSR) oxidation experiments of NH3/H2 mixtures at atmospheric pressure and over 800-1280 K. The H2 content in the NH3/H2 mixtures is varied from zero to 70 vol% at equivalence ratios of 0.25 and 1.0. Species identification and quantification are achieved by using Fourier-transform infrared (FTIR) spectroscopy. A kinetic model for pure NH3 and NH3/H2 mixtures is also developed for this research, and validated against the present experimental data for pure NH3 and NH3/H2 mixtures, as well as those for pure NH3, H2/NO, H2/N2O, NH3/NO, NH3/NO2 and NH3/H2 mixtures in literature. The model basically captures the experimental data obtained here, as well as in literature. Both measured and predicted results from this work show that H2 blending enhances the oxidation reactivity of NH3. Based on the model analysis, under the present experimental conditions, NH3 + H = NH2 + H2 proceeds in its reverse direction with increasing H2 content. The H atom produced is able to combine with O2 to produce either O and OH via a chain-branching reaction, or to yield HO2 through a chain-propagation reaction. HO2 is an important radical under the present intermediate-temperature conditions, which can convert NH2 to OH via NH2 + HO2 = H2NO + OH; H2NO is then able to convert H to NH2 and OH. In this reaction sequence, NH2 and H2NO are chain carriers, converting HO2 and H to two OH radicals. Since the OH radical is the dominant radical to consume NH3 under the present conditions, the enhanced OH yield via H + O2 = O + OH, NH2 + HO2 = H2NO + OH and H2NO + H = NH2 +OH, with increasing H2 content, promotes the consumption of NH3. For NOx formation, non-monotonous trends are observed by increasing the content of H2 at the 99% conversion of NH3. These trends are determined by the competition between the dilution effects and the chemical effects of H2 addition. Nitrogen related radicals, such as NH2, NH and N, decrease as H2 increases, and this dilution effect reduces NOx formation. For chemical effects, the yields of oxygenated radicals, such as O, OH and HO2, are enhanced with increasing H2 content, which results in enhancing effects on NO formation. For N2O formation, the enhanced oxygenated radicals (O, OH and HO2) suppress its formation, while the enhanced NO promotes its formation.

Saudi Aramco and General Electric have been jointly developing oxy-combustion technology with CO 2 capture for difficult to burn liquid fuels. The technology enables direct combustion of such fuels while addressing CO 2 emissions concerns in a cost effective way. A 15 MW thermal testing campaign was performed in Windsor, CT firing heavy asphalt in air and oxy mode. The testing campaign results show a significant improvement in fuel combustibility in oxy mode compared to air firing in addition to 50% reduction in NO x emissions. The test results were used to validate a CFD model enabling simulation of various configuration for scale-up studies. The test results were considered in the basis of design for a 2800 MW OHR oxy-fired power plant with CO 2 capture. The technology is ready for demonstration at a larger scale in a refining environment where it can synergistically be integrated with the refinery optimizing its operation and performance.

Ammonia is a promising fuel for heat and power generation because it is carbon-free and it can be produced from abundant chemicals and renewable energy sources. However, ammonia-air mixtures feature a low reactivity and stabilizing turbulent ammonia-air flames is challenging. In this study, the stability limits of technically-premixed ammonia-methane-air mixtures are measured for a wide range of ammonia additions in a laboratory-scale swirl burner. Results are compared to that obtained for baseline methane-air mixtures. Data show that increasing the ammonia addition increases the equivalence ratio at the lean blowout limit but also reduces the flames’ propensity to flashback. If the volume fraction of ammonia in the fuel blend exceeds a critical value, experiments also show that increasing the equivalence ratio at a fixed bulk velocity does not yield flashback and rich blow-out occurs instead. This significantly widens the range of equivalence ratios yielding stable flames. The critical ammonia volume fraction is a function of the Reynolds number and is xNH3 = 0.42 for Re = 7000 and xNH3 = 0.70 for Re = 3000. Because the ability to stabilize ammonia-methane-air flames is not practically relevant if NOx emissions are too large compared to that of conventional methane-air flames, exhaust NO concentrations are also measured. Consistent with previous studies, data show that, for non-marginal ammonia fuel fractions, good NO performances are not found for lean ammonia-methane-air mixtures and can only be achieved with slightly rich mixtures, which are within measured stability limits.

An ilmenite oxygen carrier was tested in a laboratory scale chemical-looping reactor with a nominal thermal capacity of 300 Wth. Ilmenite is a mineral iron-titanium oxide, which has been used extensively as an oxygen carrier in chemical-looping combustion. Two different kinds of fuels were used, a sulfur-free kerosene and one kerosene that contained 0.57 mass% sulfur. Both fuels were continuously evaporated and directly fed into the chemical-looping reactor. Experiments were conducted for 50 h with the sulfur-free kerosene and for 30 h with the sulfurous kerosene. CO2 yields above 99% were achieved with both types of fuel. A significant and lasting improvement in the oxygen carrier's reactivity was observed, presumably an effect of using sulfurous kerosene. No evidence of sulfur was found on the particles' surface.

A project devoted to establishing chemical-looping combustion with liquid fuels currently being conducted by Chalmers University of Technology with support from Saudi Aramco is presented. The ultimate goal of the project is to develop technology capable of utilizing and processing heavy residual oils with inherent CO2 capture. Up to this point, a continuously operating reactor with the nominal effect 300W has been designed, constructed, and successfully operated with nickel-, manganese-, copper- and iron-based oxygen-carrier particles using non-sulfurous and sulfurous kerosene as fuel. The results so far are very promising, and 99% conversion of fuel carbon to CO2 has been demonstrated with all four kinds of oxygen carrier materials. Chemical-looping reforming for synthesis gas production was also demonstrated using kerosene and the Ni-based oxygen carrier. Here, complete hydrocarbon conversion to CO and H2 was achieved. Future work includes design and construction of a larger 10kW reactor system for direct combustion of heavier fuels such as fuel oil and heavy vacuum residues, as well as a techno- economic study. This paper provides an overview of the project and presents the main results and conclusions so far.

International audience; Air cooling and dehumidification can be performed by different means, at various energy costs. Absorption and adsorption cycles are widely used at various temperature ranges. For air dehumidification at negative temperatures (especially less than -20 °C), the adsorption and absorption systems present some drawbacks such as for the energy regeneration cost of the solid desiccant in the case of adsorption and the liquid desiccant loss by evaporation (generally glycol) in absorption, limiting the continuous operation of the system. In classical absorption systems, the brine dilution (due to water transfer from air to liquid) is compensated by adding salts (CaCl 2, LiCl...). A new absorption method is proposed to dehumidify air to -40 °C with a continuous operation without adding salts to re-concentrate the brine solution. The solution is re-concentrated by evaporating the condensed water on a separate cooling tower around ambient temperature. The energy consumption of the system is compared to other possible concentration processes: water boiling and membrane separation.

International audience

International audience

CD Rom

International audience; Six widely differing, novel capture processes, currently under development in Europe are described. These processes cover the range of postcombustion, precombustion and denitrogenation and show favourable possibilities for integration with power plants. They can be regarded as potential break-throughs in technical performance and/or costs.