Experimental study on the effect of pressure on single and two stage combustion of decomposed ammonia (NH3-H2-N2) blends over a swirl stabilized burner

Ammonia (NH3) is a practical hydrogen vector for gas turbine power generation, but struggles to be deployed commercially due to many unresolved technical and fundamental challenges. This experimental investigation focuses on combustion of fuel blends representatives of various NH3 decomposition (or cracking) ratios in a combustor fitted with a swirl-stabilized burner, exploring pressures ranging from atmospheric to 10 bar. The study presents measurements of flame stability and emissions of NOx and N2O in combustor strategies relevant to both conventional single lean operation and staged with a rich primary zone, as a function of decomposition ratios (DR) and primary zone equivalence ratio. The findings reveal a notable pressure-dependency of nitrogen oxides (NOx) during combustion of ammonia containing fuels. For a fully decomposed mixture (H2 single bondN2 at 75/25 %vol.), NOx emissions increase with increasing pressure. Conversely, when ammonia is present in the fuel, the trend reverses. However, the majority of NOx reduction occurs within a limited range of pressure increase and reaches a plateau thereafter. The transition at which the pressure effect declines depends on other factors, and was seen to occur between 5 and 9bar in the conditions of this study. Notably, NOx levels in flames containing NH3 are significantly higher, rendering the pressure sensitivity on NOx primarily governed by NH3 presence, irrespective of its concentration in the fuel (i.e. DR). Furthermore, the study reveals a non-monotonic relationship between NOx emissions and NH3 concentration in the fuel, peaking at mid-decomposition ratios. All factors tending to weaken flame stability (e.g. increasing fuel NH3 content, approaching lean/rich blow off limits, or increasing burner exit velocity) favour emissions of N2O emissions. As a general trend, it appears that longer residence times, increased pressure, and rich primary zone operation are all parameters limiting NOx formation from all partially decomposed blends of ammonia, but that they only positively add to a certain limit of a few hundred ppm. This NOx plateau level being higher at higher NH3 content in the fuel. Finally, the fuel obtained by perfectly decomposing ammonia appears to be the optimal fuel associating strong flame stability and low NOx propensity, even for the non fully premixed burner type of this study.publishedVersio

Experimental study on high pressure combustion of decomposed ammonia: How can ammonia be best used in a gas turbine?

Hydrogen, a carbon-free fuel, is a challenging gas to transport and store, but that can be solved by producing ammonia, a worldwide commonly distributed chemical. Ideally, ammonia should be used directly on site as a fuel, but it has many combustion shortcomings, with a very low reactivity and a high propensity to generate NOx. Alternatively, ammonia could be decomposed back to a mixture of hydrogen and nitrogen which has better combustion properties, but at the expense of an endothermal reaction. Between these two options, a trade off could be a partial decomposition where the end use fuel is a mixture of ammonia, hydrogen, and nitrogen. We present an experimental study aiming at finding optimal NH3-H2-N2 fuel blends to be used in gas turbines and provide manufacturers with guidelines for their use in retrofit and new combustion applications. The industrial burner considered in this study is a small-scale Siemens burner used in the SGT-750 gas turbine, tested in the SINTEF high pressure combustion facility. The overall behaviour of the burner in terms of stability and emissions is characterized as a function of fuel mixtures corresponding to partial and full decomposition of ammonia. It is found that when ammonia is present in the fuel, the NOx emissions although high can be limited if the primary flame zone is operated fuel rich. Increasing pressure has shown to have a strong and favourable effect on NOx formation. When ammonia is fully decomposed to 75% H2 and 25% N2, the opposite behaviour is observed. In conclusion, either low rate or full decomposition are found to be the better options. Copyright © 2021 by ASME.publishedVersio

Emission characteristics of a novel low NOx burner fueled by hydrogen-rich mixtures with methane

The use of hydrogen-rich fuels may be challenging for burner designers due to unique properties of hydrogen compared to conventional fuels such as natural gas. Burner retrofit may be required to use hydrogen-enriched fuels in combustion systems that are designed for natural gas combustion. This study aimed to experimentally investigate NOx emissions from a novel low NOx burner fueled by methane-hydrogen mixtures. The burner was tested in a cylindrical combustion chamber at atmospheric pressure. Burner thermal load of 25 kW (LHV) and air-fuel equivalence ratio of 1.15 were maintained throughout the experimental campaign. The influence of burner design parameters on NOx emissions was tested for various fuel compositions using a statistically cognizant experimental design. The study revealed that shifting the burner head upstream can deliver NOx emission reduction. In contrast, supplying fuel to the burner through secondary fuel ports increases NOx emissions, particularly when the burner head is shifted upstream. The lowest predicted NOx emissions from the burner are below 9 ppmvd at 3% of O2 and 14 ppmvd at 3% of O2 for 5% and 30% mass fraction of hydrogen in the fuel, respectively.Open Access article

Predicting radiative heat transfer in oxy-methane flame simulations: An examination of its sensitivities to chemistry and radiative property models

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Experimental and Numerical Results of a Non-DLE Aeroderivative GT Combustion System Burning Methane-Ammonia Blends at Intermediate Pressures

Ammonia is considered as a practical hydrogen carrier, as it can be stored in liquid form at moderate pressures and temperatures and is commonly produced and transported today. Ammonia could be used directly as a Gas Turbine fuel to replace current hydrocarbon-based fuels, but its low reactivity and propensity to produce high NOx will require major combustor design changes. Alternatively, ammonia can be fully or partially converted back into hydrogen and nitrogen before using it as a fuel with additional equipment and penalty on cycle performance. Another option is to replace only part of the natural gas with ammonia to minimize the changes of combustion properties and hence combustor design. Although this only partially decarbonizes the fuel, it may be a viable intermediate step to reduce the gas turbine footprint in the short term and with minimum hardware changes to the GT. This experimental and numerical study investigates combustion of methane-ammonia blends with a simplified version of the non-DLE Siemens Energy SGT-A35 turbine combustion system (Rich-Quench-Lean system, RQL) at pressures up to 8 [bar] and powers up to 100 [kW]. The effect of ammonia/methane ratios and Primary Zone Equivalence Ratio (PZER) on emissions of NOx, CO and N2O has been investigated for different pressures and power. A pressure exponent has been extracted based on this experimental data to provide an order of magnitude of NOx emissions at engine conditions. To complement these experimental results, a simple Chemical Reactor Network (CRN) has been used to support the experimental results further. The experimental results showed that even small amounts of ammonia in methane result in unacceptably high NOx emissions for all Primary Zone temperatures and pressures investigated. Although increasing pressure reduces NOx emissions (as previously reported), extrapolation to engine conditions showed that the order of magnitude of NOx emissions will remain unacceptably high. It is also shown that flame stability becomes insufficient for fuels containing more than 40–50 [% by vol.] of NH3 as blow out occurred for these fuels. Furthermore, the results showed that N2O emissions are very low for rich Primary Zone Equivalence Ratios and increase approximately exponentially with decreasing equivalence ratios, but remained below 10 [ppm] for cases at higher pressures. Finally, the CRN results reproduced the experimental trends qualitatively well for %NH3 variations but PZ ER variations and absolute values could not be matched for all cases simultaneously without re-tuning of the CRN.Experimental and Numerical Results of a Non-DLE Aeroderivative GT Combustion System Burning Methane-Ammonia Blends at Intermediate PressuresacceptedVersio

Predicting Radiative Heat Transfer in Oxy-Methane Flame Simulations: An Examination of Its Sensitivities to Chemistry and Radiative Property Models

Measurements from confined, laminar oxy-methane flames at different O2/CO2 dilution ratios in the oxidizer are first reported with measurements from methane-air flames included for comparison. Simulations of these flames employing appropriate chemistry and radiative property modeling options were performed to garner insights into the experimental trends and assess prediction sensitivities to the choice of modeling options. The chemistry was modeled employing a mixture-fraction based approach, Eddy dissipation concept (EDC), and refined global finite rate (FR) models. Radiative properties were estimated employing four weighted-sum-of-gray-gases (WSGG) models formulated from different spectroscopic/model databases. The mixture fraction and EDC models correctly predicted the trends in flame length and OH concentration variations, and the O2, CO2, and temperature measurements outside the flames. The refined FR chemistry model predictions of CO2 and O2 deviated from their measured values in the flame with 50% O2 in the oxidizer. Flame radiant power estimates varied by less than 10% between the mixture fraction and EDC models but more than 60% between the different WSGG models. The largest variations were attributed to the postcombustion gases in the temperature range 500 K–800 K in the upper sections of the furnace which also contributed significantly to the overall radiative transfer

Low carbon power generation for offshore oil and gas production

Emission reductions in power generation for offshore oil and gas activities are key in order to reach climate targets in regions with this industry. This study presents a review of both established and immature low carbon power generation concepts, an analysis of their potential for greenhouse gas (GHG) emission reduction, and an evaluation of their offshore applicability. The potential for GHG emission reduction is quantified by estimating CO2 equivalent intensity for implementation on the Norwegian Continental Shelf. The offshore applicability is evaluated with emphasis on weight, infrastructure requirements, process heat availability, technical maturity, as well as health, safety, and environment (HSE). It is shown that power from shore is the only technically mature concept with potential for very high emission reductions (>95 %, provided that low GHG electric power is available). There are several alternative concepts under development that also can give significant emission reductions (>70 %), including fuel switching, CO2 capture and storage, and renewable power combined with energy storage. Combined cycle gas turbines and offshore wind power combined with gas turbines are technically mature and can achieve partial emission reductions (around 15–50 %, with the assumed system configurations). Other concepts offering partial emission reductions are under development, but do not show clear advantages over those already mentioned. It is pointed out that, to enable reaching the net zero emission targets, only efficiency improvements and power from shore are not enough, and there is a need to develop additional low emission technologies not yet on the market. The present study has compiled a large database of specifications for assessing low carbon power production concepts and proposes a methodology that is valuable in screening a large number of commercial and immature technologies.publishedVersio