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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

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.

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.