Generation Of Nitrogen Oxides Research Articles

Experimental and simulation research on the lean combustion characteristics of direct-injection hydrogen engine

At a constant engine speed of 2000 r/min and 5 bar gross indicated mean effective pressure, experiments were carried out on a 1.5 L engine with a variable geometry turbocharger to examine the combustion and emission characteristics of a direct injection hydrogen engine under lean combustion conditions. Additionally, a CFD simulation model was established to investigate the formation process of the air-fuel mixture and the generation of nitrogen oxides (NOx). The findings demonstrated that the uniformity of the hydrogen-air mixture in the cylinder descended with a delay in SOI (start of injection), and that the thermal efficiency often rose initially before declining. When SOI was set at −80°CA ATDC, the engine achieved maximum indicated thermal efficiency, brake thermal efficiency, and output torque values of 40.8%, 36.22%, and 61.2 Nm, respectively. However, as the SOI was delayed, the combustion variability ascended, and when the SOI was delayed to −20°CA ATDC, there was a significant chance that abnormal phenomena like pre-ignition would occur. BTE achieves a maximum of 36.38% when λ is 2.2 and SOI is −40°CA ATDC. Under lean combustion conditions, temperature was a major factor in the generation of NOx, and homogenous combustion can substantially reduce NOx emissions. NOx emissions are always less than 100 ppm when SOI is before −80°CA ATDC.

Deterioration Valuation of Polymer Materials in UV-ozone Generator using Microwave Plasma

Various materials are used to sterilize medical instruments. Rubber and other products deteriorate owing to ozone and UV exposure. Ozone is capable of inactivating bacteria and fungi and is known to be effective in inactivating a wide range of viruses. Silent discharge is the mainstream method of ozone generation. The silent discharge method is also concerned with the generation of nitrogen oxides (NOX) caused by nitrogen molecules in the air, and the deterioration of electrodes during use poses a problem. Furthermore, nitrogen oxides react with water in the gaseous phase to produce nitric acid. Nitric acid reacts with several metals to form nitrates. A sterilization device using high concentrations of ozone has not been put to practical use because of the lack of an efficient method for decomposing ozone and the corrosion of metals. If a medical device is altered, it cannot be used as a sterilizing device. In this study, we exposed polymeric materials, which are often used in medical instruments, to ozone and UV light to determine whether their properties changed. Elution tests were conducted on polymeric medical materials from the viewpoints of their physical and chemical properties, functional decline, and biological safety. This study investigates changes in mechanical strength and surface chemical properties, representing the physical and chemical aspects.

RISING STARS: Bumps and bacteria: influence of the maternal microbiota on pregnancy outcomes.

During pregnancy, all major physiological systems undergo remarkable changes, driven largely by alterations in the maternal hormonal milieu. In healthy pregnancies, maternal cardiovascular and metabolic adaptation to pregnancy occurs to support fetal growth and maternal well-being. Impaired maternal adaptation to pregnancy is associated with a range of pregnancy complications, including gestational diabetes and preeclampsia. There is growing recognition of the importance of different maternal microbiota, including in the gut, vagina and oral cavity, in supporting normal maternal adaptations to pregnancy as well as evidence for microbial disturbances associating with pregnancy pathologies. Here, we aim to summarise emerging evidence demonstrating that differences in maternal microbiota associate with pregnancy outcomes and discuss potential therapeutic approaches under development that might restore an 'optimal' microbiome. In particular, we highlight recent work by ourselves and others exploring the role of the oral microbiome in pregnancy, given established links between poor oral health (e.g. periodontitis) and adverse pregnancy outcomes. Our research has focussed on specific nitrate-reducing oral bacteria which play a role in the generation of nitric oxide (NO) and other bioactive nitrogen oxides associated with cardiovascular health and maternal cardiovascular adaption to pregnancy. Ongoing research aims to define whether altered microbial profiles have clinical utility in the prediction of pregnancy pathologies, and whether interventions designed to optimise specific maternal microbiota could help prevent future complications.

ОЦЕНКА ЭФФЕКТИВНОСТИ ПОДАВЛЕНИЯ АММИАКА В ВОЗДУШНЫХ СРЕДАХ ПРОИЗВОДСТВЕННЫХ ПОМЕЩЕНИЙ С ИСПОЛЬЗОВАНИЕМ БАРЬЕРНОГО РАЗРЯДА

One of the main problems in the industrial production of livestock and poultry products is the neutralization of toxic gases in the air removed from livestock premises. Ozonation is used for this. Ozone is produced in dielectric barrier discharge installations. The disadvantages of the method include the dependence of the electrical characteristics of the dielectric barrier discharge on the parameters of the medium and the generation of nitrogen oxides. (Research purpose) The research purpose is determining the effectiveness of ammonia suppression by ozone generated in dielectric barrier discharge installations at various parameters of the generator operating mode. (Materials and methods) Established the effectiveness of ammonia suppression by ozone at various parameters of the ozone generator operation mode. A 25 percent aqueous solution of ammonia with controlled purging over the surface of the solution was used as an ammonia source. The dependences of the mass concentration of ozone (O3), nitrogen oxides (NOx) and hydrogen sulfide (H2S) at the generator output on the operating mode parameters were studied. It was shown that the range of changes in the concentration of gases varied within the following limits: ozone - from 180 to 4, ammonia - from 80 to 2, hydrogen sulfide - from 4 to 0, nitrogen oxides - from 0 to 130 milligrams per cubic meter. (Results and discussion) It was found that the concentration of ammonia decreased from 50 to 10 milligrams per cubic meter; the time to reach the specified values of the concentration of ammonia in the stream was 20-50 seconds; when ozone is generated in all operating modes, nitrogen oxides are formed in the weight ratio O3/NOx from 1.42/1 to 1/1. The dependences of the generation of ozone and nitrogen oxides on the input voltage of the generator power supply unit were determined. It was noted that the optimal pumping rate of plasma-forming gas (atmospheric air) ranged from 0.8 to 1.5 m/ s; the mass ratio of nitrogen oxides to ozone varies from 0.69 to 0.98, which is unacceptable for premises with permanent residence of animals and maintenance personnel. (Conclusions) It was stated that the results obtained in assessing the rational operating modes of ozonators allow us to formulate technical requirements for the development of a specialized ozone generator adapted for use in agricultural production.

О НЕОБХОДИМОСТИ ПРИМЕНЕНИЯ СЛОЖНЫХ ЧЕЛОВЕКО-МАШИННЫХ СИСТЕМ ОПЕРАТИВНОГО УПРАВЛЕНИЯ ПРОИЗВОДСТВЕННЫМИ ПРОЦЕССАМИ

The issues of organization and management of complex human-machine systems are considered in the article via heating plant example. A phenomenological controlled indicator is introduced in order to consider the ratio of electricity generation and emissions of nitrogen oxides. Approximation model of the controlled indicator via modified model of logistic function has been developed.

Sterilization Ability by Microwave UV-ozone Generator

The 253.7 nm UV light emitted from mercury lamps is known as germicidal radiation. Additionally, it emits UV light with a shorter wavelength of 184.9 nm. This UV wavelength can generate ozone (O3) from oxygen molecules (O2) in the air. Ozone has been shown to effectively inactivate various pathogenic microorganisms. However, they must decompose quickly because they are harmful to the human body. Methods for decomposing ozone include a thermal decomposition method, a chemical cleaning method, an activated carbon method, and the like. However, there is no practical or efficient treatment method. Ozone generation methods include the silent discharge method, electrolytic method, photochemical reaction method, high-frequency discharge method, and radiation method. The most efficient method is silent discharge, which is concerned with nitrogen oxide (NOX) generation caused by nitrogen molecules in the air, and deterioration of the electrodes during use is problematic. Furthermore, nitrogen oxides react with water in the gaseous phase to produce nitric acid. Nitric acid reacts with several metals to form nitrates. A sterilization device using highconcentration ozone has not been put to practical use because of the lack of an efficient method for decomposing ozone and the corrosion of metals. The UV-ozone generation method using microwave plasma used in this study can generate UV light by applying 2.45 GHz microwaves to a quartz electrodeless bulb filled with mercury. By changing the glass material and emitting UV light at different wavelengths, it is possible to develop a UV-ozone generator that can selectively generate and decompose ozone. Furthermore, since 184.9 nm UV specifically acts on oxygen molecules, NOX is not generated. Additionally, 253.7 nm UV, which is emitted at the same time as 184.9 nm UV, can easily decompose ozone into O2

The impact of hydrogen addition and OH concentration on NO emissions in high-pressure NH3/air combustion

The addition of hydrogen to ammonia enhances combustion stability and widens the flame limits. However, it also brings the drawback of increased nitrogen oxide (NO) emissions. Therefore, this study employs a chemical kinetics simulation system to investigate the effects of OH concentration and hydrogen addition on NO emissions in a laminar premixed hydrogen/ammonia/air swirling flame at high pressures. The research reveals a distinct positive linear correlation between NO emissions and the peak mole fraction of OH radicals. Within the range of 1.0≤φ ≤ 1.1 and 0≤XH2≤0.5, as hydrogen content (0≤XH2≤0.5) increases, the promoting effect of max(OH) on NO emissions continuously intensifies. Pressure, on the other hand, has virtually no impact on their correlation.Furthermore,the analysis of production rates, sensitivity, and reaction pathways indicates that NH3 primarily transforms into NO through three pathways: NH3→NH2(NH)→HNO→NO, NH3→NH2→NH→NO, and NH3→NH2→NH→N→NO. The HNO intermediate pathway is the major route for NO generation, with OH radicals significantly promoting NO production via the NH→HNO intermediate pathway. This theoretically validates the correlation between max(OH) and NO emissions. Data analysis using MATLAB yields the relationship between max(OH) and NO emissions, providing a theoretical basis for the practical application of OH chemiluminescence detection. Additionally, NNH proves to be a crucial radical in ammonia oxidation chemistry and is involved in the NO formation process in reaction R69 NNH + ONH + NO. This study sheds light on the complex interplay between OH, hydrogen content, and NO emissions, providing valuable insights into combustion dynamics and emissions control.

Economic analysis and TOPSIS approach to optimize the CI engine characteristics using span 80 mixed carbon nanotubes emulsified Sapindus trifoliatus (soapnut) biodiesel by artificial neural network prediction model

The rise in fuel use within the vehicle sector leads to a corresponding escalation in energy demand. To achieve optimal operating conditions, it is necessary to reduce energy usage. For that, the primary objective of this study is to utilize an artificial neural network (ANN) and the optimization approach as a technique for order performance by similarity to the ideal solution (TOPSIS) to forecast the optimal features of a compression ignition (CI) engine. The experiment was performed with a four-stroke mono-cylinder compression ignition (CI) engine under different load situations. The study considers six operational parameters, including brake thermal efficiency (BTE), specific fuel consumption (SFC), as well as emission characteristics including carbon monoxide (CO), hydrocarbon (HC), Nitrogen oxides (NOx), and smoke. From the ANN results, the correlation coefficients for BTE, SFC NOx, smoke, HC, and CO were 0.9712, 0.9862, 0.964, 0.941, 0.998, and 0.978, respectively. The SNBD25 + 30 mg/L SP80 + 30 mg/L CNT blend exhibited the maximum closeness coefficient under various load conditions. The maximum closeness coefficient obtained from the TOPSIS optimisation approach under full load conditions is 0.982386. From the result of the ANN prediction technique, for TOPSIS optimised blend SNBD25 + 30 mg/L SP80 + 30 mg/L CNT a 13.84% increase in BTE, 11.21% decrease in SFC, 16.67% decrease in CO, 13.87% decrease in NOx, 19.23% decrease in HC, and 32.53% decrease in smoke. Based on the outcomes obtained from the ANN and TOPSIS methodologies, it can be concluded that the SNBD25 + 30 mg/L SP80 + 30 mg/L CNT blend exhibits superior performance in terms of reduced NOx emissions and enhanced efficiency, surpassing the other blends under consideration. The incorporation of carbon nanotubes (CNTs) into a system leads to an increase in the carbon-to‑oxygen ratio, resulting in a reduction in the generation of nitrogen oxides (NOx). The cost of a mixture consisting of SNBD25 + 30 mg/L SP80 + 30 mg/L blend is 20% lower than the cost of diesel on a per-litre basis.

Study on Mechanisms of NOx Formation and Inhibition during the Combustion of NH3/CH4 and NH3/CO Mixtures

Ammonia is an ideal renewable, carbon-free fuel and hydrogen carrier, which produces nitrogen and water after complete combustion in the presence of oxygen. However, ammonia has low reactivity, slow flame-propagation speed, and carries risks of high nitrogen oxide (NOx) emissions. Co-firing ammonia with an industrial by-product gas (with CH4 and CO being the main combustible materials) is a cost-effective and convenient method of improving the combustion characteristics of ammonia, but attention still needs to be paid to the NOx generation. Currently, the research on NOx formation during co-firing of ammonia with other fuel gases is still insufficient. In this study, a high-temperature furnace reaction system was used to investigate the NOx formation and inhibition mechanisms during the combustion of NH3/CH4 and NH3/CO mixtures. By varying the ammonia blending ratio, excess air coefficient (α), temperature, residence time, and fuel concentration, the key factors influencing NOx generation and inhibition were further analyzed. The results showed that when α was no less than 1, the production of NOx initially increased and then decreased with an increasing proportion of ammonia in the fuel gas. Within the temperature range of 900 °C to 1500 °C, the amount of NOx generated during the combustion of the mixed gas gradually decreased with the increase in temperature. Under the conditions of NH3/CH4 and NH3/CO, the emissions of NOx were higher than those during pure ammonia combustion.

Microanalysis of Active Nitrogen Oxides (RONS) Generation Characteristics during DC Negative Corona Discharge at a Needle-Plate Electrode

The DC negative corona of needle-plate electrodes can generate atmospheric pressure low-temperature plasma active particles, which have important effects on biological mutagenesis. The DC negative corona discharge of an air needle-plate electrode with effective consideration of NOx particles was simulated and the Trichel pulse current was obtained, focusing on the development of particles and the distribution of active nitrogen oxides (RONS) at four moments in the pulse process. The simulation results indicate that the positive ions (N2+ and O2+) and negative ions (O− and O2−) were closely related to the current changes, and the negative ions (O− and O2−) presented a typical stratification phenomenon. RONS (H2O2, O3, and NO) were approximately uniformly distributed above the level of the plate electrode at the same instant, with H2O2 and O3 except for the area below the needle tip. They trended to a cumulative increase in concentration with time. This study provides a theoretical basis for corona discharge plasma seed treatment technology.

The methodology of decoupling fuel and thermal nitrogen oxides in multi-dimensional computational fluid dynamics combustion simulation of ammonia-hydrogen spark ignition engines

Under the paradigm of carbon neutrality, ammonia-hydrogen (NH3–H2) blended fuel presents itself as a zero-carbon alternative to petroleum-based fuels, effectively reducing carbon emissions originating from internal combustion engines. In the combustion process of conventional hydrocarbon fuels, the production of nitrogen oxides (NOX) predominantly arises from nitrogen present in the atmosphere, which occurs through the Zeldovich mechanism under high-temperature conditions. These NOX species, commonly referred to as thermal NOX, rely on inert nitrogen. However, the utilization of ammonia fuel activates the reactivity of nitrogen element, leading to the nitrogen-containing species formation, including NOX, termed as fuel NOX. Consequently, the combustion of ammonia-hydrogen fuel entails the coupling of thermally formed nitrogen oxides and fuel-derived nitrogen oxides. The generation of NOX is significantly influenced by the physicochemical environment, while the transient combustion conditions within the engine combustion chamber further complicate the process of NH3–H2 combustion and NOX formation. As a consequence, comprehensively investigating the NOX emission characteristics in NH3–H2 engines presents a considerable challenge. By decoupling fuel NOX and thermal NOX, a more profound understanding of NOX emission control strategies for ammonia-hydrogen engines can be attained. This research paper accomplishes the decoupling of fuel nitrogen elements and atmospheric nitrogen elements in three dimensional computational fluid dynamics engine combustion simulations. The results indicate that this decoupling methodology disregards the differentiation between the fuel NOX pool and the thermal NOX pool, resulting in a slight modification in NOX concentration. Nevertheless, this approach has minimal impact on the combustion process, ensuring that the NOX formation environment remains largely unchanged. Furthermore, it successfully demonstrates the spatial and temporal distribution characteristics of thermal NOX and fuel NOX, thereby furnishing an effective analytical tool for the comprehensive study of NOX emission characteristics in NH3–H2 engines.

Selective reduction of NO3− to N2 using a highly stable Cu0/Cu2O-PANI-CNTs as a photocatalyst at neutral pH

The selective photoreduction of nitrate (NO3−) to nitrogen (N2) has emerged as an energy-efficient and environmentally friendly NO3− removal route under mild conditions. However, NO3− photoreduction often suffers low NO3− removal efficiency in the absence of hole scavengers at neutral pH, the generation of undesired side products (nitrite (NO2−), ammonium (NH4+), nitrogen oxides (NOx), etc.) and poor photocatalyst stability. In this study, a novel copper/copper(I) oxide-polyaniline-carbon nanotubes (Cu0/Cu2O-PANI-CNTs) photocatalyst was prepared through a combination of in situ polymerization and liquid phase reduction processes and used to reduce NO3− to N2. In the Cu0/Cu2O-PANI-CNTs/hv system, NO3− was reduced to NO2− by photogenerated electrons (ecb−) on the surface of Cu0/Cu2O, and the generated NO2− was further reduced to N2 by PANI, resulting in high N2 selectivity. –NH– in PANI acted as photogenerated hole (hvb+) capture centres, leading to NO3− photoreduction without additional hole scavengers. Given the interaction between Cu0, ecb− and PANI, Cu0/Cu2O-PANI-CNTs show excellent repeatability. A 100% NO3− removal efficiency and 100 % N2 selectivity could be achieved by the Cu0/Cu2O-PANI-CNTs/hv system at neutral pH. With river water, secondary effluent and the fourth reuse of the catalyst, the NO3− removal efficiencies were as high as 93.0%, 91.2% and 84.4%, respectively, with 100 % N2 selectivity.

Numerical simulation study on combustion characteristics and NOx emission of COREX gas swirl burner and boiler

To tackle the problem of high nitrogen oxide (NOx) emissions and low combustion efficiency when burning COREX gas, a type of high-calorific gas that is a by-product of the Ouye furnace, a low-NOx burner with broad applicability was designed. In this study, the feasibility of flue gas recirculation technology applied to a swirl burner of COREX gas was investigated through Fluent numerical simulation, and the effect of central flue gas recirculation ratio on burner combustion characteristics and NOx generation rate was analyzed. The results indicated that the implementation of central flue gas recirculation reduced the NOx concentration from 288.4 mg/m3 to 101.48 mg/m3. To further reduce nitrogen oxide emissions, an interlayer structure for flue gas was proposed to be installed between the COREX gas and internal secondary air. Flue gas was extracted from the tail of the boiler and introduced into the interlayer structure, thereby delaying the fuel and internal secondary air mixing while achieving uniform diffusion of low-temperature and low-oxygen flue gas into the combustion zone. Compared with the structure without flue gas interlayer, the NOx concentration can be reduced from 101.48 mg/m3 to 61.54 mg/m3 by passing the flue gas through the central passage and flue gas interlayer with a mass ratio of 3:5.The study demonstrated that the low-NOx burner designed in this paper had sound inhibition effects on thermal and prompt NOx. Based on both actual operation and simulation results, it was observed that the outlet NOx concentration could be regulated within 100 mg/m3 across varying boiler loads. This marks the first application of a low-NOx burner for the combustion of COREX gas in China.

Numerical and Experimental Investigation of the Decoupling Combustion Characteristics of a Burner with Flame Stabilizer

In order to integrate renewable electricity into the power grid, it is crucial for coal-fired power plant boilers to operate stably across a wide load range. Achieving steady combustion with low nitrogen oxide (NOx) emissions poses a significant challenge for boilers burning low-volatile coal in coal-fired power plants. This study focuses on developing a decoupling combustion technology for low-volatile coal-fired boilers operating at low loads. A three-dimensional numerical simulation is employed to analyze and optimize the geometrical parameters of a burner applied in a real 300 MW pulverized coal fired boiler. Detailed analysis of the burner’s decoupling combustion characteristics, including stable combustion ability and NOx reduction principles, is conducted. The results indicate that this burner showed three stages of coal/air separation, and the flame holder facilitates the stepwise spontaneous ignition and combustion of low-volatile coal. By extending the time between coal pyrolysis and carbon combustion, the burner enhances decoupling combustion and achieves low nitrogen oxide emissions. Based on optimization, a flat partition plate without inclination demonstrates excellent performance in terms of velocity vector field distribution, coal air flow rich/lean separation, combustion, and nitrogen oxide generation. Compared with the initial structural design, the average nitrogen oxide concentration at the outlet is reduced by 59%.

Numerical Simulation of Selective Non-Catalytic Reduction Denitrification Process in Precalciner and the Effect of Natural Gas Injection on Denitrification

Cement production is the third largest source of nitrogen oxides (NOx), an air pollutant that poses a serious threat to the natural environment and human health. Reducing NOx emissions from cement production has become an urgent issue. This paper aims to explore and investigate more efficient denitrification processes to be applied in NOx reduction from precalciner. In this study, firstly, the flow field, temperature field, and component fraction in the precalciner are studied and analyzed using numerical simulation methods. Based on this, the influence of the reductant injection height and amount on the SNCR was studied by simulating the selective non-catalytic reduction (SNCR) process in the precalciner. The effect of natural gas on the NOx emissions from the precalciner was also investigated. The simulation results showed that, with the increase in height, the NOx concentration in the precalciner decreased, then increased, then decreased, and then increased again. The final NOx concentration at the exit position was 531.33 ppm. In the SNCR denitrification process, the reductant should be injected in the area where the precalciner height is 26–30 m so that the reductant can fully react with NOx and avoid the increase of ammonia escape. The NSR represents the ratio of reductant to NOx, and the results show that the larger the NSR is, the higher the denitrification rate is. However, as the NSR approaches 2, the denitrification rate slows down and the ammonia escape starts to increase. Therefore, according to the simulation results, the NSR should be kept between 1 and 1.6. The denitrification rate reached the maximum value of 42.62% at the optimal condition of 26 m of reductant injection height and 1.6 of NSR. Co-firing of natural gas with pulverized coal can effectively reduce the NOx generation in the furnace. The denitrification rate reached the maximum value of 32.15% when the natural gas injection amount was 10%. The simulation results of natural gas co-combustion and SNCR combined denitrification showed that combined denitrification was better than natural gas co-combustion or SNCR denitrification. Under the condition of NSR of 1 and natural gas injection of 10%, the denitrification rate increased by 29.83% and 31.64% compared to SNCR-only or co-combustion-only denitrification, reaching 61.98%, respectively. Moreover, less reductant is used in co-denitrification, so the problem of excessive ammonia emissions can be avoided. The results of this study provide useful guidance for denitrification process development and NOx reduction in cement production.

Experimental research on direct expansion heat pump flue gas waste heat recovery and humidification nitrogen reduction system

In order to solve the heat loss and the pollution of gas boilers, a synergistic system consisting of waste heat recovery tower and air humidification tower is proposed. Increasing in moisture content of the air can inhibit the generation of nitrogen oxides and increase the dew point of the flue gas, which is beneficial to the utilization of the waste heat from the flue gas. More heat is absorbed by the humidification water at the fin heat exchanger after the flue gas enters the waste heat recovery tower, which enhances the heat and mass exchange process in the air humidification tower. But the performance of the heat pump was found to show a downward trend, indicating a competitive relationship between nitrogen oxides reduction and waste heat recovery. Under the optimal condition, the experimental system can reduce nitrogen oxides emissions by 62.35%, and the exhaust gas temperature can be reduced to 24.46 °C. The heat pump can recover 6.94% heat while maintaining a minimum nitrogen oxides emission of 39.66 mg/m3. The heat pump makes more heat from the fuel to enter the heating network, which improves the heating efficiency of the boiler system. The system can meet the high-efficiency and clean production requirements of the energy system at the same time.

Gasification of uric acid in supercritical water: Reaction characteristics, nitrogen transformation mechanisms, and kinetics analysis

Supercritical water gasification (SCWG) of biomass waste as a new clean waste conversion technology is increasingly valued worldwide attributable to the unique properties of supercritical water (water: T > 374 °C, P > 22.1 MPa). However, the fate of conventionally contaminated elements such as nitrogen in this process still warrants further research to control potential contamination. In this work, uric acid was used as the model compound of nitrogenous components in chicken manure to investigate the transformation mechanism of nitrogen during the SCWG process. The effects of different temperatures (550–650 °C) and residence times (2–30 min) on the gasification characteristic of uric acid and the behaviour of nitrogen were experimentally explored. The results indicated that the higher temperatures and longer residence time significantly facilitated the uric acid gasification and nitrogen transformation. The maximum nitrogen conversion efficiency was 84.83%, and the maximum yield of NH3, H2, and CO2 reached 20.20 mol/kg, 23.78 mol/kg, and 20.10 mol/kg at 650 °C and 30 min, respectively. Subsequently, the reaction pathways of nitrogen in uric acid were proposed in detail according to the product analysis. Finally, a kinetic model was developed to describe the SCWG process, especially the reaction kinetic of nitrogenous products. The results revealed that the hydrolysis reactions of uric acid led to a rapid increase in NH3 yield in the initial stage of the SCWG process. As the process continued, the increase in NH3 was mainly due to the deamidation reaction of small-molecule nitrogenous intermediates. Notably, NOx, NO2−, and NO3− were not detected in products, validating the inhibitory effects of the reducing environment of supercritical water on the generation of nitrogen oxides.

Causal analysis of nitrogen oxides emissions process in coal-fired power plant with LiNGAM

Coal has been an important energy source worldwide; however, it is the largest source of nitrogen oxide (NOx) emissions because the amount of nitrogen in coal is larger than that of other fossil fuels. Precise control of NOx emissions is required in operations of coal-fired power plants from the viewpoint of air pollution control. Although theoretical analyses of NOx generation from a coal-fired power plant have been conducted, it is difficult to precisely predict NOx generation in an actual plant. NOx generation is affected by various factors, such as furnace design and operating conditions, and there are complicated relationships among them. Thus, it is necessary to identify important operating factors that affect NOx generation in actual coal-fired power plants. A linear non-Gaussian acyclic model (LiNGAM) is an exploratory causal analysis method that identifies a causal ordering of variables and their connection strengths without any prior knowledge of causal relationships among variables. In this study, we analyzed real operation data collected from a coal-fired power plant using LiNGAM to identify factors of NOx generation. The causal relationship between process variables and NOx generation was estimated by means of LiNGAM, and the connectional strengths of the variables on NOx generation were derived. The analysis results agreed with previous reports on NOx generation mechanisms, such as combustion air temperature, steam temperature on a specific side of the furnace, and air flow rate of forced draft fans. In addition, we found the steam flow rate and the furnace pressure as new candidate factors of NOx generation through causal analysis using LiNGAM, which heretofore has not been suggested. Our analysis result should contribute to reducing NOx emissions from coal-fired power plants in the future.

Spectroscopy of Laser-Induced Dielectric Breakdown Plasma in Mixtures of Air with Inert Gases Ar, He, Kr, and Xe.

The generation of ozone and nitrogen oxides by laser-induced dielectric breakdown (LIDB) in mixtures of air with noble gases Ar, He, Kr, and Xe is investigated using OES and IR spectroscopy, mass spectrometry, and absorption spectrophotometry. It is shown that the formation of NO and NO2 noticeably depends on the type of inert gas; the more complex electronic configuration and the lower ionization potential of the inert gas led to increased production of NO and NO2. The formation of ozone occurs mainly due to the photolytic reaction outside the gas discharge zone. Equilibrium thermodynamic analysis showed that the formation of NO in mixtures of air with inert gases does not depend on the choice of an inert gas, while the equilibrium concentration of the NO+ ion decreases with increasing complexity of the electronic configuration of an inert gas.

Numerical study of combustion and nitrogen oxide generation for recycled flue gas distribution in supercritical carbon dioxide coal-fired boiler with double furnace

Numerical study of combustion and nitrogen oxide generation for recycled flue gas distribution in supercritical carbon dioxide coal-fired boiler with double furnace