Ammonia Blended Fuels – Energy Solutions for a Green Future (original) (raw)
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Ammonia/Hydrogen/Methane Characteristic Profiles for Atmospheric Combustion Applications
Ammonia has become a chemical of interest for the economic distribution and storage of hydrogen. Utilization of this molecule has been conceived in systems that range from small Fuel Cells to large gas turbines and furnaces. Ammonia characteristics enable the reduction of carbon emissions whilst ensuring long term storage and distribution of hydrogen produced from renewable sources. However, the use of ammonia as a combustion fuel also presents various issues mainly related to low flame speed and elevated nitrogen-based emissions. Therefore, further understanding of this molecule and its combustion characteristics is required before replacement of fossil fuels using ammonia can be accomplished at large scale. Therefore, this work presents a series of experiments that depict the characteristic profiles of various ammonia/hydrogen/methane blends intended to serve as replacement of pure fossil-based fuelling sources. The study is approached through a generic tangential swirl burner which has been commissioned to burn a great variety of blends at various power outputs. Temperatures, operability, chemiluminescence of various species (OH*, NH2*, CH* and NH*), spectrometry profiles, and emissions were determined for comparison purposes at various equivalence ratios and blending conditions.
Combustion Characteristics of Ammonia as a Promising Renewable Fuel
Proceedings of the World Congress on Momentum, Heat and Mass Transfer, 2016
Introduced as a renewable energy source in many studies, ammonia (NH3) is known as a potential fuel to be combusted in power engines. With its high hydrogen density and already existing infrastructure, it is believed to be an excellent green fuel that can be used in energy generation and transportation systems. Combustion of ammonia has certain challenges (associated with its low flame speed and fuel bond NOx emissions) that need to be addressed before its widespread use in practical systems. A comprehensive numerical study is accomplished focusing on the major combustion characteristics of ammonia and ammonia-hydrogen flames in a wide range of conditions.
Frontiers in chemical engineering, 2021
Ammonia has been proposed as a replacement for fossil fuels. Like hydrogen, emissions from the combustion of ammonia are carbon-free. Unlike hydrogen, ammonia is more energy dense, less explosive, and there exists extensive experience in its distribution. However, ammonia has a low flame speed and combustion emits nitrogen oxides. Ammonia is produced via the Haber-Bosch process which consumes large amounts of fossil fuels and requires high temperatures and pressures. A life cycle assessment to determine potential environmental advantages and disadvantages of using ammonia is necessary. In this work, emissions data from experiments with generating heat from tangential swirl burners using ammonia cofired with methane employing currently available technologies were utilized to estimate the environmental impacts that may be expected. Seven ammonia sources were combined with two methane sources to create 14 scenarios. The impacts from these 14 scenarios were compared to those expected from using pure methane. The results show that using ammonia from present-day commercial production methods will result in worse global warming potentials than using methane to generate the same amount of heat. Only two scenarios, methane from biogas combined with ammonia from hydrogen from electricity and nuclear power via electrolysis and subsequent ammonia synthesis using nitrogen from the air, showed reductions in global warming potential. Subsequent analysis of other environmental impacts for these two scenarios showed potentially lower impacts for respiratory organics, terrestrial acidification-nutrification and aquatic acidification depending on how the burner is operated. The other eight environmental impacts were worse than the methane scenario because of activities intrinsic to the generation of electricity via wind power and nuclear fission. The results show that generating heat from a tangential swirl burner using ammonia currently available technologies will not necessarily result in improved environmental benefits in all categories. Improvements in renewable energy technologies could change these results positively. Other means of producing ammonia and improved means of converting ammonia to energy must continue to be explored.
Counterflow flame extinction of ammonia and its blends with hydrogen and C1-C3 hydrocarbons
Applications in Energy and Combustion Science
Ammonia as a fuel offers the potential to avoid carbon emissions, but its combustion is hindered by low reactivity. Here, the extinction limits of NH 3 and NH 3 plus reactivity enhancers were measured in the counterflow laminar non-premixed flames. A stable NH 3-N 2 flame was established with an oxygen-enriched oxidizer stream, and when the fuel was blended with CH 4 , C 2 H 6 , C 3 H 8 , and H 2. For blended mixtures, results showed that CH 4 has the least potential to enhance the stability of NH 3 flames compared to the other additives. The extinction limits of C 2 H 6 and C 3 H 8 blended NH 3 flames are nearly identical. At low percentage addition, H 2-blended flames extinguish earlier than those blended with C 1-C 3 hydrocarbons, but this trend is reversed at higher H 2 blends. Experimental conditions were simulated using Okafor et al. 2018 model and an extended Zhang et al 2021 model developed here. The models captured the measured trends, including the crossover between NH 3-H 2 and NH 3-C 2 /C 3 hydrocarbon fuels. Quantitatively, both models under-predicted the extinction limits of NH 3-N 2 /enriched oxidizer flame. Better quantitative agreement is observed for the blended fuels using the model developed here. Discrepancies have been observed in the reported rates for reactions involving HNO (+OH, H), and if addressed, could improve models' capability in predicting extinction behavior in non-premixed flames. Numerical analyses were carried out to understand the kinetic coupling between NH 3 and H 2 /C 2-C 3 in counter-flow flames. Extinction limits of NH 3-C 2-C 3 /H 2 flames are shown to be affected by H abstraction and NH 3 related chain termination reactions, heat producing reactions, and chain branching reactions. It has also been observed that at high blending ratios, C 2 H 6 /C 3 H 8 addition in NH 3 flames reduced the peak H and OH concentration via recombination and termination reactions, which compete with branching pathways. H 2-blended flames are mostly influenced by reactions producing active radicals.
Science and technology of ammonia combustion
Proceedings of the Combustion Institute, 2018
This paper focuses on the potential use of ammonia as a carbon-free fuel, and covers recent advances in the development of ammonia combustion technology and its underlying chemistry. Fulfilling the COP21 Paris Agreement requires the de-carbonization of energy generation, through utilization of carbon-neutral and overall carbon-free fuels produced from renewable sources. Hydrogen is one of such fuels, which is a potential energy carrier for reducing greenhouse-gas emissions. However, its shipment for long distances and storage for long times present challenges. Ammonia on the other hand, comprises 17.8% of hydrogen by mass and can be produced from renewable hydrogen and nitrogen separated from air. Further more, ther mal properties of ammonia are similar to those of propane in terms of boiling temperature and condensation pressure, making it attractive as a hydrogen and energy carrier. Ammonia has been produced and utilized for the past 100 years as a fertilizer, chemical raw material, and refrigerant. Ammonia can be used as a fuel but there are several challenges in ammonia combustion, such as low flammability, high NOx emission, and low radiation intensity. Overcoming these challenges requires further research into ammonia flame dynamics and chemistry. This paper discusses recent successful applications of ammonia fuel, in gas turbines, co-fired with pulverize coal, and in industrial furnaces. These applications have been implemented under the Japanese 'Cross-ministerial Strategic Innovation Promotion Program (SIP): Energy Carriers'. In addition, fundamental aspects of ammonia combustion are discussed including characteristics of laminar premixed flames, counterflow twin-flames, and turbulent premixed flames stabilized by a nozzle burner at high pressure. Furthermore, this paper discusses details of the chemistry of ammonia combustion related to NOx production, processes for reducing NOx, and validation of several ammonia oxidation kinetics models. Finally, LES results for a gas-turbine-like swirl-burner are presented, for the purpose of developing low-NOx single-fuelled ammonia gas turbine combustors.
2017
Sustainble solutions are needed to be increasingly applied to the energy sector in order to prevent the detrimental effects of fossil fuels on the enviroment. Ammonia (NH3) is, recently, identified as a carbon free sustainable fuel, and anticipated as a hydrogen energy carrier because of the higher hydrogen capacity of 17.8% in weight. Nevertheless, much lower laminar burning velocity [1-2] and high fuel NO generation in the combustion, because NH3 contains nitrogen itself than that of conventional hydrocarbon fuels, hindered the use of NH3 as a commercial fuel. However, recent studies of Somarathne et al. [3-4] and Hayakawa et al. [5] have numerically and experimentally illustrated that by introducing swirl flow, and thereby making a recirculation near the downstream of swirler, NH3/air turbulent premixed flames have successfully achieved a stable combustion at the atmospheric pressure and various turbulent intensities at the initial mixture temperature of 500 K and 300 K. Moreover...
2020
Ammonia is a promising sustainable fuel, however, its low reactivity creates challenges in industrial applications. In this study, ammonia/methane mixtures were considered for premixed and non-premixed counterflow flames. The extinction stretch rate was measured over a wide range of ammonia/methane mixing ratios and compared to 1D numerical results from four different mechanisms. Additionally, for counterflow premixed twin flames, quantitative analysis based on the comparison of experimental and numerical FWHM of OH and NO profiles was performed. Results showed that in premixed flames, all the mechanisms investigated were inadequate for predicting the extinction stretch rate, specifically for lean flames. In non-premixed flames, Okafor's mechanism was accurately predicting the extinction stretch rate. For the FWHM analysis, the numerical mechanisms overpredicted both OH and NO apparition in the flame, except for Tian's mechanism which underpredicted OH apparition. GRI Mech 3...
Combustion analysis of Ammonia and hydrogen as aviation fuel
2020
The current project is an attempt to make a contribution to ICAO's one of the aspirational goals for sustainable aviation. The project aims to perform analysis on combustion characteristics and NO emissions for the combustion of a mixture of Ammonia and Hydrogen as carbon-free alternatives to existing aviation fuel. The work will be also compared with different mechanisms and with experimental data.
Transfer Functions of Ammonia and Partly Cracked Ammonia Swirl Flames
Energies
The replacement of hydrocarbon fuels by ammonia in industrial systems is challenging due to its low burning velocity, its narrow flammability range, and a large production of nitric oxide and nitrogen dioxide when burned close to stoichiometric conditions. Cracking a fraction of ammonia into hydrogen and nitrogen prior to injection in the combustion chamber is considered a promising strategy to overcome these issues. This paper focuses on evaluating how different levels of ammonia cracking affect the overall burning velocity, the lean blow-off limit, the concentration of nitric oxide and nitrogen dioxide, and the flame response to acoustic perturbations. Swirl stabilized premixed flames of pure ammonia–air and ammonia–hydrogen–nitrogen–air mixtures mimicking 10%, 20%, and 28% of cracking are experimentally investigated. The results show that even though ammonia cracking is beneficial for enhancing the lean blow-off limit and the overall burning velocity, its impact on pollutant emis...
Ammonia often occurs in combustion gases as a product of fuel-nitrogen. Since either NO or N 2 may predominate as the product of ammonia oxidation, there is considerable interest in understanding the factors responsible for selecting the final products. In flames the selectivity is known to depend on whether the reaction zones are premixed or non-premixed. This paper reports on a combined experimental and modeling investigation of ammonia chemistry in a hot combustion environment that is below flame temperatures, such as in post combustion gases. Experiments that mix highly diluted ammonia-methane and oxygen-water streams are interpreted in terms of a plug-flow model, a simplified mixing reactor model, and a two-dimensional direct numerical simulation. The study finds that the final products of ammonia oxidation remain sensitive to mixing even at temperatures below those of self-sustaining flames. At low temperatures ammonia oxidation occurs in a premixed reaction zone, but at sufficiently high temperatures a nonpremixed reaction zone may develop that produces significantly less NO than the equivalent premixed system. A direct numerical simulation is required to predict the behavior over the full range of conditions investigated experimentally, while a simplified mixing reactor model captures the essential features as long as the radial gradients are not too steep.