Ratio Of NH3 Research Articles

Effect of oxygen enrichment and NH3 pre-cracking on laminar burning velocity and intrinsic instability of NH3/bio-syngas

This paper investigates the laminar burning velocity (SL) and instability of NH3/bio-syngas under different bio-syngas contents, oxygen enrichment factors (Ω), and the cracking ratio of NH3 (ζ) using a constant-volume combustion bomb. The results show that increasing bio-syngas, Ω, and ζ effectively enhance the SL of the fuel. Around ζ = 60%, the relationship between SL and the NH3 content before cracking is reversed. Increasing the bio-syngas and ζ enhance SL through the chemical effect, while Ω primarily enhances SL through the thermal effect. When Ω = 50%, the contribution of thermal effect can reach up to 94.53%. Linear stability analysis indicates that increasing the bio-syngas content and ζ reduces the critical Peclet number (Pec), while Ω increases Pec. As the bio-syngas content and ζ increase, the growth rate of perturbation (∑) monotonically increases, indicating instability. Ω, on the other hand, decreases ∑, making it negative.

An experimental investigation into the characteristics of ammonia dissociation in a Bubbling Fluidised Bed

Ammonia (NH3) dissociation is of an initial and very important step during its combustion process. This study therefore systematically investigates the effect of reaction temperature (650–950 °C), fluidisation number (0.83–2.50) and static bed depth (0–25 mm) on NH3 dissociation in a laboratory-scale Bubbling Fluidised Bed (BFB). By analysing the concentrations of H2 and N2 in the effluent using gas chromatography, results show that the conversion ratio of NH3 in BFB was merely 0.26%–0.29% at 650 °C but increased significantly to 18.1%–25.3% at 950 °C. This highlights the importance of temperature in promoting NH3 dissociation. However, as fluidisation number increased from 1.0 to 2.5, attributing to a decrease in gas – solid contact time, the conversion ratio of NH3 decreased correspondingly from the highest 20.7%–5.7%. Moreover, as static bed depth increased from 15 mm to 25 mm, the conversion ratio of NH3 increased slightly from 21.5% to 26.8%, both of which were found to be higher than that without bed particles. Clearly, NH3 dissociation is enhanced by the bed material depth but is also dependent on the gas – solid contact time. In addition, by measuring the temperature distribution in the BFB reactor, a temperature drop of ca. 20 °C near the distributor was confirmed, showing a strong effect of endothermicity during NH3 dissociation. These would provide an improved comprehension on the mechanisms of NH3 dissociation and offer theoretical guidance for optimising the combustion processes in BFB burning NH3.

Numerical investigation on the combustion characteristics and NOx emission of non-premixed H2/NH3/air in vase-shaped micro combustor

Hydrogen and ammonia, as currently popular zero carbon fuels, have received widespread attention. These two fuels have complementary advantages in combustion characteristics, cost, safety, etc. Based on the vase shaped micro combustor, a new structure proposed for application in micro thermophotovoltaic systems in our previous work. This article numerically investigated the combustion characteristics and NOx emission of non-premixed H2/NH3/Air in vase shaped micro combustor which proposed in our previous work. The variation patterns of flame temperature, wall temperature, flammability limit, and NOx emission with the blended ratio of NH3 and equivalence ratio were obtained. It was found that the flame cannot move and stabilize when the mixing ratio is 0.6. The rate of production (ROP) and sensitivity of NO and N2O were analyzed. Four precursors of NO, HNO, NH, N, N2 have been discovered. Under the conditions of this article, HNO is the key component affecting NO emissions. When the blending ratio is greater than 0.3, the lower reaction rate of HNO leaded to a decrease in NO. The elementary reaction R63: NH + NON2O + H is the key elementary reaction that affects NO consumption and N2O generation. The blending ratio of 0.4 and the equivalence ratio of 1.2 are the optimized operating conditions with the highest comprehensive performance.

Numerical study on the effects of adding NH3 into syngas/NH3 mixtures on combustion characteristics and NOx emissions in diluted hot co-flows

NH3 is a carbon-free fuel with good storage and transport characteristics. Applying Moderate or Intense Low-oxygen Dilution (MILD) combustion to NH3/syngas blended fuel is expected to achieve clean and low-carbon combustion. This work explores the impacts of changing the NH3/syngas ratio and O2 content in co-flow on the combustion characteristics and the NOx formation and transformation mechanisms. As the proportion of NH3 increases, the flame is gradually lifted, while the rise of H2 in syngas reduces the lifted height. As the O2 proportion is increased to 15%, almost the entire computational domain is transformed from MILD to high-temperature combustion when the ratio of NH3 to syngas is 3:7. NH that is derived from the decomposition of NH3 participates more actively in the consumption process of NO and N2O. N radicals are more likely to generate N2 when O2 content in hot co-flow increases.

Role of methane in ammonia combustion in air: From microscale to macroscale

Ammonia (NH3) has gained increasing recognition as a carbon-free fuel. To enhance NH3 combustion, reactive gases, like methane (CH4), are usually added to the combustion system. In this work, the role of CH4 in NH3 combustion is systematically studied. A series of reactive force field molecular dynamic (ReaxFF MD) simulations are implemented to investigate effects of CH4 addition on the consumption of NH3 and the yields of nitrogen oxides (NOx) from the atomic perspective: CH4 accelerates the consumption of NH3 by shortening the decomposition time of the first NH3 molecule and increasing the translational kinetic energy of the system; CH4 modifies the yield of NOx by complicating the elementary reactions and introducing additional intermediates. The fuel ratio of CH4 and NH3 between 0.5 and 1 is suggested for a cleaner and enhanced NH3 combustion. By summarising the findings from the latest publications and the present work, the role of CH4 in NH3 combustion is comprehensively analysed from the macroscale and microscale perspectives: CH4 accelerates the progress of NH3 combustion flame, activates chemical reactions, and aggravates NOx emissions at a low CH4 content. Taking the NH3/CH4 combustion as an example, this study provides an exclusive perspective to understand combustion phenomena from the microscale events to macroscale observations.

Experimental study of CO2/H2/NH3 influence on CH4 flameless combustion process in semi-industrial furnace

A flameless combustion mode was employed in a semi-industrial furnace to investigate the effect of NH3 on CH4, which was diluted by CO2/H2 combustible mixtures, serving as the primary fuel. Emission characteristics, as well as toxic compounds and temperature distribution maps, were presented for selected fuels. The combustion system was tested at a constant firing rate of 150 kWth and a constant fuel bulk velocity of 85 m/s. We investigated the effects of equivalence ratio, fuel composition and volume share of NH3 in the fuel. It was found that the equivalence ratio and NH3 amount have the most significant impact on the emission of fuel nitric oxide in the flameless combustion process. The dilution of CH4 with CO2 affects the stretch rate, resulting in an increase in CO levels as well as promoting NO level growth. The calculated dimensionless Conversion Factor (CF) shows that the dilution gas, CO2, significantly impacts the reduction of NH3 to NO, but only for low-content fuel-bound nitrogen (up to 1%). The lowest values of CF were measured for a high equivalence ratio, corresponding to the typical oxygen content for flameless combustion process.

Influence of swirl intensity on combustion dynamics and emissions in an ammonia-enriched methane/air combustor

Ammonia (NH3) has been widely considered as a promising carbon-free energy and hydrogen carrier for various applications. The large-scale direct utilization of NH3 as fuel in gas turbine engines is currently attracting significant interest, with strong focuses on improving the efficiency and stability of the system and reducing the emissions of pollutants. The present study experimentally examined the impacts of swirl intensity on combustion stability and emissions in an NH3-enriched premixed swirl-stabilized CH4/air combustor under a wide range of equivalence ratios. Simultaneous high-speed OH* chemiluminescence and particle image velocimetry measurements suggested that increasing swirl intensity resulted in more compact flame shapes and expanded the recirculation zone, which promoted flame stability at higher NH3 ratios. However, under specified conditions, enhancing swirl intensity could increase the instability frequency and amplitude of pressure oscillations. The flame dynamics exhibited different behaviors depending on the swirl intensity. At high swirl intensity, the flames underwent high-frequency, small-amplitude periodic motion. At low swirl intensity, the flames oscillated axially with large amplitude and low frequency. For flow dynamics, the stability of the vortex at high swirl intensity contrasted with the periodic vortex shedding at low swirl intensity. Furthermore, the two-dimensional Rayleigh index indicated that the dominant positive thermoacoustic coupling regions were located near the flame shear layers and flame tail at low and high swirl intensities, respectively. Finally, the experimental results showed that swirl intensity affected pollutant emissions by influencing the temperature of combustion chamber and gas mixing efficiency. The pathway of fuel-type NOx was found to be dominant in the NOx emission of the NH3/CH4/air flames.

Numerical analysis of flow and combustion of Coal-Ammonia blend in coal-fired furnace

Co-firing ammonia (NH3) in coal-fired power plants presents an attractive method to expedite the global decarbonization process. Nevertheless, the challenge lies in reconciling the need for higher temperatures within the furnace with the imperative of maintaining low nitrogen oxides (NOx) emissions, which limits the widespread use of NH3 as a fuel. In this article, the flow and combustion of coal-NH3 blends in a 3 × 700 MW tangentially-fired utility coal boiler furnace are investigated using Computational Fluid Dynamics (CFD). The impact of NH3 blending ratios is examined through numerically simulated combustion involving five co-firing ratios (CRs) of NH3, including 0%, 10%, 20%, 30%, and 50%. Various combustion properties are assessed, including the furnace’s temperature profile, flow distribution, species emissions, pollutant formation, and heat generation. To validate the approach, single coal and coal blend simulations performed depicted reasonable agreement in predicting furnace flame temperatures. The predicted flue gas temperature exhibited a decrease with an increase in NH3 CR, leading to a reduction in the furnace’s heat generation. Regarding flow characteristics, there was a notable increase in velocity as the concentration of NH3 was raised. The elevated NH3 content correlated with an observed rise in oxygen (O2) residue in the rear pass, coupled with a decrease in both carbon dioxide (CO2) and carbon monoxide (CO) concentrations. Pollutant formation, assessed in terms of nitrogen oxide (NO) emissions, revealed an increase in concentration with the rise in NH3 CR. Indeed, these findings suggest a promising strategy for adopting NH3 as a viable alternative to coal, representing an effective carbon-neutral fuel for the future.

Study on the equilibrium constants and initial formation temperature of NH4HSO4 and (NH4)2SO4 in coal‐fired flue gas

AbstractWith the development and utilization of high‐sulfur coal, generating ammonium bisulfate (ABS) and ammonium sulfate (AS) during the coal combustion process has garnered increasing attention. This study examined the formation of ABS and AS under varying temperatures and different initial reactant ratios of SO3 and NH3 by establishing a self‐constructed experimental setup. Based on the experimental data, the equilibrium constant change diagram for the ternary reactions leading to ABS and AS formation was derived. The initial temperatures for forming gaseous ABS and AS were estimated to be approximately 416.33°C and 393.56°C, respectively. Consequently, this study fills the data gap of the equilibrium constant of gaseous ABS formed at high temperatures and furnishes the selective catalytic reduction (SCR) system with quantifiable and notably expedient means of technical analysis.

Significant Increase in Ammonia Emissions in China: Considering Nonagricultural Sectors Based on Isotopic Source Apportionment.

Isotopic source apportionment results revealed that nonagricultural sectors are significant sources of ammonia (NH3) emissions, particularly in urban areas. Unfortunately, nonagricultural sources have been substantially underrepresented in the current anthropogenic NH3 emission inventories (EIs). Here, we propose a novel approach to develop a gridded EI of nonagricultural NH3 in China for 2016 using a combination of isotopic source apportionment results and the emission ratios of carbon monoxide (CO) and NH3. We estimated that isotope-corrected nonagricultural NH3 emissions were 4370 Gg in China in 2016, accounting for an increase in the total NH3 emissions from 7 to 31%. As a result, compared to the original NH3 EI, the annual emissions of total NH3 increased by 35%. Thus, in comparison to the simulation driven by the original NH3 EI, the WRF-Chem model driven by the isotope-corrected NH3 EI has reduced the model biases in the surface concentrations and dry deposition flux of reduced nitrogen (NHx = gaseous NH3 + particulate NH4+) by 23 and 31%, respectively. This study may have wide-ranging implications for formulating targeted strategies for nonagricultural NH3 emissions controls, making it facilitate the achievement of simultaneously alleviating nitrogen deposition and atmospheric pollution in the future.

Pure ammonia direct decomposition using rod-electrode-type microwave plasma source

This paper presents the experimental results of ammonia (NH3) decomposition without catalyst and dilution using a rod-electrode-type microwave plasma source (MPS) at atmospheric pressure. The direct decomposition ratio of pure NH3 was investigated in relation to the flow rate into the rod-electrode-type MPS and the average transmission power to the rod-electrode-type MPS. The decomposition ratio increased with decreasing the flow rate and with increasing the average transmission power. For example, the decomposition ratio was demonstrated to exceed 40 % at the flow rate of 0.2–0.8 L/min and the average transmission power of about 63–166 W. The highest decomposition ratio was approximately 84 % at the flow rate of 0.2 L/min and the average transmission power of approximately 112 W, and the hydrogen yield was approximately 90 %.

Electron repulsion tuned electronic structure of TiO2 by fluorination for efficient and selective photocatalytic ammonia generation.

The photocatalytic conversion of nitrogen into high-value ammonia products holds tremendous potential in the global nitrogen cycle. However, the activation of N2 and competition of hydrogen evolution limit the improvement of nitrogen fixation performance. In this study, we developed a fluorinated TiO2 (F-TiO2) using a hydrothermal-annealing method. The incorporation of F dopants not only enhances the adsorption and activation of N2 through electronic structure regulation, but also facilitates an in situ increase in active sites via the electron repulsion effect between F and Ti atoms. In addition, the presence of F on the surface effectively improved the nitrogen supply problem and optimized the nitrogen fixation selectivity for its hydrophobic modulation. The NH3 yield of the F-TiO2 photocatalyst reached 63.8 μmol h-1 g-1, which was 8.5 times higher than that of pure TiO2. And the selectivity experiment showed that the electronic ratio of NH3 to H2 production reached 0.890. This research offers valuable insights for the design of highly efficient and selective nitrogen-fixing photocatalysts.

Influence of Al2O3/SiNx Rear-Side Stacked Passivation on the Performance of Polycrystalline PERC Solar Cells

In recent years, polycrystalline passivated emitter and rear cell (PERC) solar cells have developed rapidly, but less research has been conducted on the preparation process of their rear side passivation layers on standard solar cell production lines. In this work, a Al2O3/SiNx rear side stacked passivation layer for polycrystalline PERC solar cells was prepared using the plasma- enhanced chemical vapor deposition (PECVD) method. The effects of different Al2O3 layer thicknesses (6.8~25.6 nm), SiNx layer thicknesses (65~150 nm) and SiNx refractive indices (2.0~2.2) on the passivation effect and electrical performance were systematically investigated, which were adjusted by TMA flow rate, conveyor belt speed and the flow ratio of SiH4 and NH3, respectively. In addition, external quantum efficiency (EQE) and elevated temperature-induced degradation experiments were also carried out to check the cell performance. The results showed that the best passivation effect was achieved at 10.8 nm Al2O3 layer, 120 nm SiNx layer and 2.2 SiNx layer refractive index. Under the optimal conditions mentioned above, the highest efficiency was 19.20%, corresponding Voc was 647 mV, Isc was 9.21 A and FF was 79.18%. Meanwhile, when the refraction index was 2.2, the EQE of the cell in the long-wavelength band (800–1000 nm) was improved. Moreover, the decrease in conversion efficiency after 45 h LeTID was around 0.55% under the different refraction indices. The above results can provide a reference for the industrial production of polycrystalline PERC solar cells.

Field experiments on chemical and biological changes of thin-layer oyster shells capping sediments in dense aquaculture area

Thin-layer oyster shell capping has been proposed as a method for improving contaminated coastal environments. Field experiments were conducted to investigate the effects of oyster shell capping on nutrient concentrations, microorganisms, and macrobenthic communities. The concentration of PO4-Pin the experimental area decreased by approximately 38% more than in the control, due to phosphorus fixation of oyster shells and the presence of Proteobacteria. Ammonia-oxidizing bacteria such as the order Pirellulales (phylum Planctomycetes) were related to the low ratio of NH3–N found in dissolved inorganic nitrogen in the experimental area, indicating nitrification promotion. The reduction in annular benthic organisms observed in the experimental area indicates a decline in sediment organic matter, which could potentially mitigate eutrophication. Oyster shell capping was confirmed to be an effective material for restoring coastal sediments by improving their chemical and biological properties.

Numerical study on the effects of co-firing ratio and stoichiometric ratio on biomass/ammonia co-firing

Co-firing of biomass and NH3 can generate positive effect on the energy and environment. However, there is limited research in this area. In this work, Ansys Fluent, a computational fluid dynamics software, was utilized to simulate the two-dimensional combustion process of mixed wood (MW) particles with NH3 in a 15 KW furnace under various operating conditions. Various models such as turbulence, species transport, particle phase, radiation, and pollutant were reasonably considered, and the reliability of these selected models was also evaluated by comparing with the experimental results obtained from the 15 KW furnace. The four combustion cases with different NH3 ratios (NRs) of 0%, 40%, 50%, and 60% were investigated (partial MW replaced by NH3 with equivalent calorific value). Moreover, the effects of stoichiometric ratios (SRs) of 0.8, 0.9, 1.1, and 1.3 on the combustion behavior was also explored at a fixed NR of 60%. The velocity, flame shape, furnace temperature, and emissions of pollutants (CO2 and NO) were described and analyzed. The findings show that the temperature at the center of outlet can reach 1209.0 K when the SR and NR are 0.9 and 60%, respectively, which exhibits the highest value among all operating conditions. The average value of CO2 concentration is 3.7% at the outlet under the condition of SR = 1.3 and NR = 60%, which presents the lowest level among all cases, while the average value of NO concentration presents a lowest value of 111 ppm under the condition of SR = 0.8 and NR = 60% at the outlet. In summary, these numerical simulation results can provide important support for further studies of the co-firing of biomass/NH3.

Growth and pre-cooling doping of semiconducting C-doped hBN as a sensitive thermistor

This letter describes the growth of hexagonal boron nitride (hBN) on plateau and terrace regions of nickel foil by tuning the V/III ratio of NH3 and B2H6, followed by pre-cooling carbon doping with CH4. The V/III ratio = 120 with a growth duration of 30 min is good to grow ∼ 14 nm-thick hBN for the application requiring it as an insulator. Pre-cooling doping by CH4 is possible because crystallizing BN prevents carbon from diffusing into bulk nickel and allows the substitution of nitrogen atoms. The C-doped hBN is having a lowered bandgap of 5.79/5.47 eV, sub-bandgap of 2.86 eV, narrowed Raman E2g peak on plateau and terrace regions, a slight decrease in nitrogen atomic%, and reduced thickness. These convert hBN from an insulator into a semiconductor. The C-doped hBN is a very sensitive thermistor with a temperature coefficient of resistance up to –0.037 K−1.

Knock Mitigation and Power Enhancement of Hydrogen Spark-Ignition Engine through Ammonia Blending

Hydrogen and ammonia are primary carbon-free fuels that have massive production potential. In regard to their flame properties, these two fuels largely represent the two extremes among all fuels. The extremely fast flame speed of hydrogen can lead to an easy deflagration-to-detonation transition and cause detonation-type engine knock that limits the global equivalence ratio, and consequently the engine power. The very low flame speed and reactivity of ammonia can lead to a low heat release rate and cause difficulty in ignition and ammonia slip. Adding ammonia into hydrogen can effectively modulate flame speed and hence the heat release rate, which in turn mitigates engine knock and retains the zero-carbon nature of the system. However, a key issue that remains unclear is the blending ratio of NH3 that provides the desired heat release rate, emission level, and engine power. In the present work, a 3D computational combustion study is conducted to search for the optimal hydrogen/ammonia mixture that is knock-free and meanwhile allows sufficient power in a typical spark-ignition engine configuration. Parametric studies with varying global equivalence ratios and hydrogen/ammonia blends are conducted. The results show that with added ammonia, engine knock can be avoided, even under stoichiometric operating conditions. Due to the increased global equivalence ratio and added ammonia, the energy content of trapped charge as well as work output per cycle is increased. About 90% of the work output of a pure gasoline engine under the same conditions can be reached by hydrogen/ammonia blends. The work shows great potential of blended fuel or hydrogen/ammonia dual fuel in high-speed SI engines.

On the feasibility and performance of the ammonia/hydrogen/air rotating detonation engines

A series of numerical simulations were performed to investigate the feasibility and performance of the premixed ammonia/hydrogen/air rotating detonation engines. A 19 species and 80 reactions ammonia/hydrogen/air mechanism is adopted and validated for detonation simulations. The effects of injection total temperatures (T0) and ammonia/hydrogen equivalence ratios (φNH3 and φH2) are analyzed under a fixed global equivalence ratio of 1. The propagation map of rotating detonation waves is numerically outlined. The result indicates that a higher injection total temperature and a lower ammonia equivalence ratio are beneficial to the successful propagation of rotating detonation waves. The maximum φNH3 with successful propagation of rotating detonation waves reaches 0.6, achieved at T0 = 1000 K. High total temperatures and ammonia equivalence ratios can lead to lower detonation wave speeds. The detonation height is found to account for around 20%–36% of the engine axial length. The critical accommodated detonation cell number for successful propagation of rotating detonation waves is 5.9, below which the rotating detonation wave will have difficulty maintaining propagation. Mass-flow-averaged and area-averaged methods are adopted to evaluate the pressure gain performance of NH3/H2/air RDE. The results of the two methods both indicate that the total pressure gain is significantly affected by the injection total temperature but less affected by the equivalence ratio of NH3. In addition, it is found that NOx emission is dominated by NO. The NOx emission increases with increased injection total temperatures and ammonia equivalence ratios. Negligible NOx emission is produced in pure hydrogen-fueled RDE while it reaches the maximum (0.037) at φNH3 = 0.6 and T0 = 1000 K.

Insight into the action mechanism of ammonia in one-pot synthesis of hermetic Al@Ag core–shell particles via deposition model

In this study, Al@Ag particles with hermetic silver shell were successfully prepared by a facile one-pot electroless plating method and the effect of NH3·H2O in reaction process was investigated. The result shows that the concentration ratio of NH3·H2O to Ag+ from 18:1–55:1 triggers a continuous transition of the silver coating from raspberry-like granule to hermetic and then loose. This transition is mainly dependent on the suppression of Ag deposition as increasing NH3·H2O concentration. It was confirmed using silver deposition kinetic and electrochemistry tests. Based on these experimental results, a deposition model was proposed to quantify the specific behavior of NH3·H2O in inhibiting Ag deposition from the perspective of interfacial reaction between active center and [Ag(NH3)2]+. The deposition model was fitted well with experimental results and the effective chemical reaction rate (keff) at solid-liquid interface were calculated, which is the critical factor affecting nucleation and coating quality. As CNH3·H2O:CAg+= 48:1, keff is 0.0117 mol L−1 min−1, a compact core-shell Al@Ag particle is realized and the resistivity as low as 1.21 × 10−4 Ω·cm even with Ag content is 15.61 wt%. This work revealed the dual role of NH3·H2O in complexing Ag+ and regulating keff to control silver grain size and distribution.

Manufacturing of Gallium Nitride Thin Films in a Multi-Wafer MOCVD Reactor

Abstract Gallium nitride (GaN) thin films have attracted considerable attention for manufacturing optical and electronic devices. They have wide bandgap and superb performance in these applications. The reliability and durability of optoelectronic devices depend on the quality of the GaN thin films. The metal-organic chemical vapor deposition (MOCVD) process is a common manufacturing technique for fabricating high-quality thin films. By manipulating the operating conditions and the reactor design, one can control the deposition rate and the uniformity of the thin film. In this paper, the manufacturing process for GaN thin films in a multi-wafer MOCVD reactor is simulated based on the three-dimensional computational model of an experimental system which provides data for validation as well as realistic design parameters. The reactor pressure and the flow rate of the precursor, trimethyl-gallium (TMG), significantly affect the deposition rate and film uniformity. The incursion of impurities in the deposition can be reduced by increasing the volumetric ratio of NH3 to TMG (V/III) and reducing the reactor pressure. The deposition rate and quality of the thin film are enhanced using an appropriate mixture of H2 and N2 as the carrier gas. The design of the inlet can also be varied to improve the utilization of metal-organic precursors and increase the deposition rate. This paper presents and discusses results on these aspects for this important manufacturing process. Thus, it leads to a better understanding of the basic mechanisms involved and provides guidelines for obtaining high deposition rates with high film quality in practical chemical vapor deposition reactors.