Increasing O2 Concentration Research Articles

Interactive Effects of Ozone and Drought on Antioxidant Enzyme Activities of Poplar Leaves

Ground-level ozone (O3) pollution and drought have become major environmental factors that threaten the normal growth of plants. In this study, we determined the effects of three O3 concentrations (charcoal-filtered air, CF, non-filtered air, NF and non-filtered air+40 nmol·mol-1, NF40), two water treatments (well-watered, WW, and mild drought, MD, 60% of WW in volumetric soil water content), and their interactions on the light-saturated photosynthesis rate (Asat) and on the activity of antioxidant enzymes and soluble proteins of the poplar '546' (Populus deltoids cv. 55/56×P. deltoides cv. Imperial). Results showed that Asat significantly decreased with elevated O3, and with interactions between O3 and drought. Drought significantly reduced the activities of catalase (CAT) and superoxide dismutase (SOD) but did not affect the activities of peroxidase (POD) or ascorbate peroxidase (APX). Reduction ranges in CAT and SOD increased with drought duration. APX activity significantly decreased with increasing O3 and drought, but soluble protein content did not. Activities of antioxidant enzymes were not significantly affected by elevated O3 and their interactions. Results provide a scientific basis for protection of poplar plantations in response to increasing O3 concentrations and drought under environmental changes.

Unburnt Carbon From Oxygen-Enriched Combustion of Low-Quality Fuels at Low Temperatures

This paper investigates the effectiveness of oxygen-enriched combustion process at low temperatures to avoid the unburnt carbon that remains in ash during conventional burning process. For this, thermal treatment of low-quality fuels such as olive pomace and Turkish lignite (Afsin-Elbistan) under oxygen-enriched conditions was tested in a tube furnace at temperatures between 400 and 700 °C under O2/N2 mixtures containing O2 ratios in the range of 25–50 vol %. The calorific value and the unburnt carbon content of the residues from these tests were used to investigate the combined effects of temperature and O2 concentration on unusable part of fuels. Thermal reactivity of untreated parent samples and the residues obtained from oxygen-enriched combustion was also compared based on differential thermal analysis (DTA) and derivative thermogravimetry (DTG) profiles. It was determined that oxygen-enriched conditions are able to remove the organic part of the fuels at low temperatures easily as O2 concentration increases and the oxygen-enriched conditions shifted complete burning temperature to lower values.

The effect of carbon dioxide on flame propagation speed of wood combustion in a fixed bed under oxy-fuel conditions

This paper presents an investigation of wood combustion in a laboratory-scale fixed bed with an aim of establishing the effect of CO2 environment on flame propagation speed and flame structures. Different oxy-fuel combustion atmospheres in which the composition of O2 in CO2 was varied from 21% to 50% by volume were tested and compared to air-fuel condition. Euler-Lagrange (Computational Fluid Dynamics - Discrete Element Method, CFD-DEM) approach which captures information of individual particle processes is used to model wood conversion in a packed bed. Results show that flame front propagation speed in oxy-fuel atmosphere reduced to 78% of that of the air-fuel condition with similar O2 concentration. For oxy-fuel conditions, propagation speed increased with increase in O2 concentration. The CFD-DEM model agrees very well with experimental values for mass loss, propagation speed and flame front positions. However, peak temperatures are poorly predicted at lower oxygen concentrations. The accuracy of temperature prediction improves at higher oxygen concentrations. During initial and devolatilization stage, mass fraction of tar predicted in CO2 environment are smaller than in N2 environment, while the amount of CO predicted is almost equal in both environments. However, during char combustion stage a high amount of CO is observed in oxy-fuel conditions.

MnII-Doped Cesium Lead Chloride Perovskite Nanocrystals: Demonstration of Oxygen Sensing Capability Based on Luminescent Dopants and Host-Dopant Energy Transfer.

The design of photoluminescence-quenching probes for molecular oxygen (O2) is always a large space to explore. Luminescent semiconductor nanocrystals (NCs) have been proposed as emerging oxygen-responsive probes, but the inherent O2 sensing of phosphorescent semiconductor NCs has not been reported so far. Here, we demonstrate the O2 sensing capability of MnII-doped CsPbCl3 nanocrystals (Mn:CsPbCl3 NCs) and reveal the role of O2 on the optical de-excitation process of such perovskite nanocrystals (PNCs). By adjusting the amount and distribution of MnII dopants, as well as the host-dopant energy transfer process in PNCs, we highlight that O2 can reversibly quench the MnII emission due to the temporary disturbance to the ligand field of near-surface MnII dopants in PNCs. In phosphorescence mode, the photoluminescence intensity of the Mn:CsPbCl3 NCs is quenched by 53% on increasing O2 concentration from 0 to 100%. The Stern-Volmer plot shows a good linear in the 0-12% O2 concentration range. High sensing reversibility and rapid signal response are also achieved. In our perception, the mechanism study makes our PNCs candidates for the optical probes of O2, and it is enlightening to explore more possibilities of the inherent O2 sensing based on the semiconductor-doped NCs (not restricted to MnII-doped PNCs) with phosphorescence emission.

Mode Transition of Filaments in Packed-Bed Dielectric Barrier Discharges

We investigated the mode transition from volume to surface discharge in a packed bed dielectric barrier discharge reactor by a two-dimensional particle-in-cell/Monte Carlo collision method. The calculations are performed at atmospheric pressure for various driving voltages and for gas mixtures with different N2 and O2 compositions. Our results reveal that both a change of the driving voltage and gas mixture can induce mode transition. Upon increasing voltage, a mode transition from hybrid (volume+surface) discharge to pure surface discharge occurs, because the charged species can escape much more easily to the beads and charge the bead surface due to the strong electric field at high driving voltage. This significant surface charging will further enhance the tangential component of the electric field along the dielectric bead surface, yielding surface ionization waves (SIWs). The SIWs will give rise to a high concentration of reactive species on the surface, and thus possibly enhance the surface activity of the beads, which might be of interest for plasma catalysis. Indeed, electron impact excitation and ionization mainly take place near the bead surface. In addition, the propagation speed of SIWs becomes faster with increasing N2 content in the gas mixture, and slower with increasing O2 content, due to the loss of electrons by attachment to O2 molecules. Indeed, the negative O2− ion density produced by electron impact attachment is much higher than the electron and positive O2+ ion density. The different ionization rates between N2 and O2 gases will create different amounts of electrons and ions on the dielectric bead surface, which might also have effects in plasma catalysis.

Effects of CO2 gasification reaction on the combustion of pulverized coal char

Although numerous studies on CO2 gasification during coal char combustion have been documented, the effects of CO2 gasification on high-temperature carbon oxidation, which is important for evaluation of carbon conversion during pulverized coal combustion under oxy-fuel and flue gas recirculation conditions, are unclear. Thus, the char conversion characteristics at various contents of O2 and CO2 were studied in a drop-tube furnace at 1373 K. Due to the cumulative effects of CO2 gasification, which can not only suppress carbon conversion due to endothermicity but also consume part of carbon directly, there exists a minimal carbon conversion point around the CO2 content of 9–13 vol%, where the growth of promotion effect with CO2 content catches up with the suppression effect, and an inflection point around the CO2 content of 17–25 vol%, where the promotion effect of the direct gasification reaction on carbon consumption surpasses the suppression effect. Increasing O2 shifts both points towards high CO2 contents, whereas increasing combustion gas temperature decreases the values. A mathematical formula including oxidation, effect of gasification on oxidation, and CO2 gasification, is presented, which gives well prediction on high-temperature carbon conversion. With increasing CO2 content, the reduction degree of CO2 gasification on oxidation rate increases, and the synthesis oxidation rate slightly decreases, whereas there always exists a minimal point for gasification rate, gross carbon conversion rate, and gasification weightiness. With increasing O2 content, the oxidation rate, reduction degree of CO2 gasification on oxidation rate, and gross carbon conversion rate increase; the gasification rate increases below the minimal point, whereas decreases above the minimal point; the gasification weightiness decreases. Combustion gas temperature shows positive effect on all abovementioned parameters. The results derived here provide meaningful guidelines for practical application and kinetics research on pulverized coal combustion.

CB&I announces joint development agreement with Saudi Aramco

The ozone (O3) hypersensitive species Nicotiana tabacum Bel W3 was used to assess the impact on O3 contamination profile by a natural gas-powered thermoelectric plant (TP) that provides power to an oil refinery at Cubatão (SE-Brazil). An increase in O3 levels would represent an even more harmful effect to the Atlantic Rainforest present in the region. The biomonitoring study was performed along TP pre-operation, transition and TP post-operation phases. Tobacco plants were biweekly exposed at urban, industrial and forest areas at different altitudes. O3-induced leaf injuries were evaluated at the end of each exposure. N. tabacum plants at forest sites at mountain slope were usually more affected by O3, especially at higher layers. As TP started operating, nitrogen dioxide (O3 precursor) mean concentrations increased considerably (6 ppb to 16 ppb). The contamination of the Atlantic Rainforest by high levels of N created a favourable scenario for an increase in O3 concentrations. In fact, F200, F300 and F350 sites (forest sites at 200, 300 and 350 m.a.s.l.) had plants showing a significant increase in O3-induced leaf injuries. Phytotoxic levels were similar to those found at F700 site (forest site at 700 m.a.s.l.), which were high for the whole study period. The new O3 contamination profile persisted for F200 and F300 sites during TP post-operation phase. Although slightly lower levels than those seen on transition phase, the intensity of O3-injuries remained higher compared to the original conditions. The use of Nicotiana tabacum Bel W3 allowed to see the negative impact on the air quality after TP started operating, contributing to an increase in O3 concentrations and phytotoxic levels at forest sites at mountain slope. Plant community were then exposed to an even higher harmful effect compared to the first phase. The stability and fitness of the Atlantic Rainforest influenced by the pollution coming from Cubatão are still under potential risk. However, how the vegetation will behave at this new scenario is unknown and requires time.

Physiological and biochemical responses of two sugarcane genotypes growing under free-air ozone exposure

Biomass accumulation, physiological and biochemical responses of sugarcane to ozone (O3) were evaluated in two genotypes (IACSP94-2094 and IACSP95-5000) in a realistic free-air O3 exposure system. Our aims were to investigate the mechanisms involved in O3 detoxification and verify whether such mechanisms are genotype-dependent. Plants were exposed to ambient air (Amb.) and ambient air plus 40% increase in O3 concentration (x1.4) for 90 days. Plants at x1.4 O3 showed reductions in leaf gas exchange and biomass production with consistent differences between the genotypes. Photosynthesis of IACSP95-5000 was more sensitive to elevated O3 as compared to IACSP94-2094. As a primary response, IACSP94-2094 showed reductions in stomatal conductance due to elevated O3, thus avoiding oxidative stress and maintaining CO2 assimilation for longer. As a consequence, IACSP94-2094 produced more biomass, and stalks had more soluble sugar concentration than IACSP95-5000. Leaf concentrations of O2− and H2O2 in plants exposed to x1.4 O3 were not enhanced, with such unexpected result suggesting that sugarcane plants have an effective antioxidant system to avoid O3-induced damage. In both genotypes, increases in ascorbate peroxidase activity was directly related to decreases in leaf H2O2 concentration. In IACSP94-2094, however, catalase pathway was also stimulated for detoxifying H2O2. We concluded that sugarcane sensitivity to O3 is genotype-dependent and then it is possible to reduce the deleterious effects of high O3 levels on sugarcane physiology and biomass production by growing tolerant genotypes in polluted areas.

Ash and Flue Gas from Oil Shale Oxy-Fuel Circulating Fluidized Bed Combustion

Carbon dioxide emissions are considered a major environmental threat. To enable power production from carbon-containing fuels, carbon capture is required. Oxy-fuel combustion technology facilitates carbon capture by increasing the carbon dioxide concentration in flue gas. This study reports the results of calcium rich oil shale combustion in a 60 kWth circulating fluidized bed (CFB) combustor. The focus was on the composition of the formed flue gas and ash during air and oxy-fuel combustion. The fuel was typical Estonian oil shale characterized by high volatile and ash contents. No additional bed material was used in the CFB; the formed ash was enough for the purpose. Two modes of oxy-fuel combustion were investigated and compared with combustion in air. When N2 in the oxidizer was replaced with CO2, the CFB temperatures decreased by up to 100 °C. When oil shale was fired in the CFB with increased O2 content in CO2, the temperatures in the furnace were similar to combustion in air. In air mode, the emissions of SO2 and NOx were low (<14 and 141 mg/Nm3 @ 6% O2, respectively). Pollutant concentrations in the flue gas during oxy-fuel operations remained low (for OXY30 SO2 < 14 and NOx 130 mg/Nm3 @ 6% O2 and for OXY21 SO2 23 and NOx 156 mg/Nm3 @ 6% O2). Analyses of the collected ash samples showed a decreased extent of carbonate minerals decomposition during both oxy-fuel experiments. This results in decreased carbon dioxide emissions. The outcomes show that oxy-fuel CFB combustion of the oil shale ensures sulfur binding and decreases CO2 production.

Influence of Conversion Conditions on Heavy-Oil Coking During in Situ Combustion Process

Coking of heavy oil plays a key role in in situ combustion, which is affected by conversion conditions. In this study, a fixed-bed reactor and a pressurized reactor were used to thermally transform a heavy oil sample from China into coke under different atmospheric conditions, heating rates, and pressures. Elemental composition and surface functional groups were studied by an elemental analyzer and diffuse reflectance Fourier transform infrared spectrometer, whereas oxidative activity and coke yield were characterized by a thermal gravimetric analyzer. Results showed that yields, characteristics, and oxidative activities differed between the cokes produced in inert and oxidizing atmospheres. Compared with an inert atmosphere, an oxidizing atmosphere presented lower coke formation temperature and higher yield. In comparison with inert atmosphere, the coke produced in oxidizing atmosphere contained more oxygen, thus increasing the amount of surface functional group, but its oxidative activity was poorer. In oxidizing atmosphere, conversion conditions influenced yield and characteristics of coke but exerted minimal influence on oxidative activity. Oxygen content increased, whereas coke yield decreased with increasing O2 concentration. Oxygen content decreased, and yield increased initially and then decreased with increasing heating rate. Temperature of coke formation and oxidation decreased, while oxygen content and yield increased with increasing pressure. Through analysis of elements and functional groups of residues produced at different holding temperatures, our study confirmed that the following processes occurred during low-temperature oxidation: evaporation, oxygen-adding reaction, dehydrogenation and dealkylation, polymerization, decarbonylation, and mild oxidation of coke. Conversion conditions, including heating rate, oxygen concentration, and pressure, affected conversion rate of these processes, thus influencing coke characteristics.

Release characteristics of semi-volatile heavy metals during co-combustion of sewage sludge and coal under the O2/CO2 atmosphere

Co-combustion of sewage sludge and bituminous coal in O2/CO2 atmosphere was carried out in a horizontal electric heating tube furnace. The effects of incineration temperature, mass ratio of sewage sludge to coal (Xs) and incineration atmosphere on the release characteristics of heavy metals (HMs, such as As, Cr, Ni and Pb) were investigated. The results indicated that incineration temperature can promote the release of As and Pb significantly, but it has little effect on the release of Cr and Ni. The release fractions of As, Cr, Ni and Pb in 21%O2/79%CO2 atmosphere are less than that in air atmosphere due to higher specific heat of CO2. With increasing O2 content in O2/CO2 atmosphere, the release fractions of Cr, Ni and Pb increase, but As release fraction decreases. With the increase in Xs, the release fractions of As and Pb increase, Cr release fraction decreases, but Ni release fraction is almost stable. It is infeasible to predict the release fractions of different HMs under co-combustion based on sewage sludge addition and their release fractions of mono-combustion. The co-combustion condition of sewage sludge with coal is suggested as: temperature of 800–900 °C, 30%O2 in O2/CO2 atmosphere, and about 30% sludge addition.

Arsenic Partitioning Behavior During Sludge Co-combustion: Thermodynamic Equilibrium Simulation

Using the computation method of thermodynamic equilibrium, effects of sewage sludge (SS) co-combustion conditions and interactions with Fe2O3, SiO2, CaO and Al2O3 on migration and transformation of arsenic (As) were simulated in oxy-fuel (CO2/O2) and air (N2/O2) atmospheres. Arsenic mainly existed as As(s), As4(g), As2O5(s), As4O6(g) and AsO(g) and volatilized more easily in reducing than oxidizing atmosphere. Increased O2 concentration slowed down the formation rate of AsO(g), thus reducing the volatilization rate of As. With the increased pressure, the conversion rate of As2O5(s) into As4O6(g) accelerated. In the multi-chemical system of SiO2, Al2O3 and CaO, As reacted with CaO and Al2O3 to form AlAsO4(s) and Ca3(AsO4)2(s) which inhibited As volatilization. SiO2 prevented As from reacting with CaO to generate Ca3(AsO4)2(s). Fe2O3 affected reactions between Al2O3(CaO) and As which inhibited As volatilization. In the whole SS co-combustion system, As reacted with O2 but had a weak affinity with Cl and with no arsenic chlorides observed.

Effect of CO2 and H2O on the combustion characteristics and ash formation of pulverized coal in oxy-fuel conditions

The combustion characteristics and ash formation of pulverized coal under different atmospheres (O2/N2, O2/CO2 and O2/H2O/CO2) were investigated using an isothermal thermal analysis system. The burning rate in O2/N2 was faster than that in O2/CO2 due to differences in the physical properties between N2 and CO2 at 800 °C. The effect of CO2 gasification was enhanced with increasing temperature; as a result, the overall reaction rate in O2/CO2 approached and exceeded the combustion rate in O2/N2. However, the effect of gasification was weakened by increasing O2 concentration, and the overall reaction rate in O2/CO2 decreased and eventually lagged the combustion rate in O2/N2. Because of the distinct physical properties of H2O, the burning rate in O2/CO2/H2O was lower than that in O2/N2 but higher than that in O2/CO2 at 800 °C. At a low O2 concentration, the influence of CO2 and H2O gasification was enhanced with increasing temperature; thus, the overall reaction rate in O2/H2O/CO2 was higher than that in O2/CO2. Moreover, the burning rate in O2/H2O/CO2 increased slightly with increasing H2O concentration. However, higher O2 concentrations weakened the effect of gasification, leading to similar burning processes under different atmospheres. The XRD analysis of the ash samples showed that CO2 and H2O had no significant effect on the transformation of main minerals.

Study on Elemental Mercury Oxidation by Non-thermal Plasma with Calcium Chloride Enhancement

Converting of elemental mercury (Hg0) into oxidized mercury compounds is considered to be an effective method for prompting mercury removal of conventional flue gas treatment systems. The technology of non-thermal plasma (NTP) with CaCl2 treatment was utilized to oxidize Hg0 in this paper. The effects of input energy and different flue gas components like O2, NO and SO2 on Hg0 oxidation were investigated. The results showed that the Hg0 oxidation efficiency with CaCl2 treatment was increased obviously compare with single NTP treatment, and would be more than 90% when the input energy was 120 J/L. The O2 in simulated flue gas played an important role for mercury oxidation. The Hg0 oxidation efficiency and O3 outlet concentration were increased with the increase of O2 content. However, both NO and SO2 inhibited Hg0 oxidation due to their competitive consumption of O3 and O. Compare with single NTP technology, the effects of NO and SO2 on Hg0 oxidation under NTP with CaCl2 treatment were decreased obviously. The technology of Temperature-Programmed Decomposition and Desorption was utilized to analyze the mercury speciation adsorbed or deposited on AC and CaCl2 surface. The results concluded that the main Hg0 oxidation products by NTP with CaCl2 treatment were HgO, Hg2O and HgCl2, which indicated that the chlorine of CaCl2 surface was the main reason for enhancement of Hg0 oxidation.

Comparative thermogravimetric analyses of co-combustion of textile dyeing sludge and sugarcane bagasse in carbon dioxide/oxygen and nitrogen/oxygen atmospheres: Thermal conversion characteristics, kinetics, and thermodynamics

Thermodynamic and kinetic parameters of co-combustion of textile dyeing sludge (TDS) and sugarcane bagasse (SB) were studied using thermogravimetric analysis in CO2/O2 and N2/O2 atmospheres. Our results showed that the comprehensive combustion characteristic index (CCI) of the blends was improved by 1.71–4.32 times. With the increased O2 concentration, co-combustion peak temperature decreased from 329.7 to 318.2 °C, with an increase in its maximum weight loss rate from 10.04 to 14.99%/min and its CCI by 1.31 times (β = 20 °C·min−1). To evaluate the co-combustion characteristics, thermodynamic and kinetic parameters (entropy, Gibbs free energy and enthalpy changes, and apparent activation energy) were obtained in the five atmospheres. The lowest apparent activation energy of the TB64 blend was obtained in oxy-fuel atmosphere (CO2/O2 = 7/3).

Amperometric glucose sensing with polyaniline/poly(acrylic acid) composite film bearing glucose oxidase and catalase based on competitive oxygen consumption reactions

For the purpose of avoiding interference with glucose biosensing caused by coexisting easily oxidizable compounds, the sensing was attempted with an enzyme electrode (PANI/PAA-GOx/Cat) that was fabricated by co-immobilizing glucose oxidase (GOx) and catalase (Cat) on polyaniline/poly(acrylic acid) (PANI/PAA) composite films. The glucose sensing was carried out by monitoring the decrease in the O2 reduction current resulted from competitive consumption of dissolved O2 caused by electrochemical O2 reduction and enzymatic glucose oxidation. It was found that the immobilized Cat reproduced O2 from H2O2 accompanying GOx-catalytic glucose oxidation. As a result, the enzyme electrode gave a wide linear range (up to 1.6 ± 0.0 mM glucose) and a high sensitivity (49.3 ± 0.6 μA cm−2 mM−1) in the glucose sensing due to increased O2 concentration in the vicinity of the enzyme electrode. The linear range and sensitivity of the electrode are obviously higher than those of the enzyme electrode without Cat (PANI/PAA-GOx). In contrast, despite the complexity of the electrode reaction, the detection limit of the PANI/PAA-GOx/Cat (26.5 ± 5.2 μM) was almost same as that of the PANI/PAA-GOx. Moreover, high glucose selectivity was achieved by adopting a bioelectrochemical system which functions at a low potential to avoid the interference of coexisting easily oxidizable compounds.

Photocatalytic ozonation of monuron over suspended and immobilized TiO2–study of transformation, mineralization and economic feasibility

The transformation and mineralization of monuron herbicide were investigated by heterogeneous photocatalysis, ozonation, and their combination (photocatalytic ozonation) at various ozone (O3) concentrations (0–20 mg dm‐3 in gas phase), using TiO2 in suspensions and in immobilized form.The applied AOPs were characterized by the transformation and mineralization rate of monuron, the concentration of dissolved O3, and the economic feasibility based on the values of Electrical Energy per Order related to the rate of decrease of monuron concentration and of the total organic carbon content. In the case of photocatalytic ozonation, the transformation and mineralization rate of monuron increased with the increase of O3 concentration. However, there was no significant synergistic effect. Electrical Energy per Order decreased with the increase of O3 concentration, and economical efficiency of the photocatalytic ozonation using TiO2 in suspensions highly exceed that of both ozonation and heterogeneous photocatalysis regarding the value determined for the decrease of total organic carbon content.

The chemical effects on the summertime ozone in the upper troposphere and lower stratosphere over the Tibetan Plateau and the South Asian monsoon region

We use the global three-dimensional Goddard Earth Observing System chemical transport model with the Universal tropospheric–stratospheric Chemistry eXtension mechanism to examine the contributions of the chemical processes to summertime O3 in the upper troposphere and lower stratosphere (UTLS) over the Tibetan Plateau and the South Asian monsoon region (TP/SASM). Simulated UTLS O3 concentrations are evaluated by comparisons with Microwave Limb Sounder products and net chemical production of O3 (NPO3) are evaluated by comparisons with model results in previous studies. Simulations show that the chemical processes lead to an increase in O3 concentration, which is opposite to the effect of O3 transport in the UTLS over the TP/SASM region throughout the boreal summer. NPO3 in UTLS over the TP/SASM region is the largest in summer. Elevated values (0.016–0.020 Tg year−1) of the seasonal mean NPO3 are simulated to locate at 100 hPa in the TP/SASM region, where the mixing ratios of O3 are low and those of O3 precursors (NOx, VOCs, and CO) are high. The high concentrations of O3 precursors (NOx, VOCs, and CO) together with the active photochemical reactions of NO2 in the UTLS over the TP/SASM region during summertime could be important reasons for the enhancement of $${\text{NP}}_{{{\text{O}}_{3} }}$$ over the studied region.

Conversions of fuel-N to NO and N2O during devolatilization and char combustion stages of a single coal particle under oxy-fuel fluidized bed conditions

The conversions of fuel-N to NO and N2O during devolatilization and char combustion stages of a single coal particle of 7 mm in diameter were investigated in a laboratory-scale flow tube reactor under oxy-fuel fluidized bed (FB) conditions. The method of isothermal thermo-gravimetric analysis (TGA) combing with the coal properties was proposed to distinguish the devolatilization and char combustion stages of coal combustion. The results show that the char combustion stage plays a dominant role in NO and N2O emissions in oxy-fuel FB combustion. Temperature changes the trade-off between NO and N2O during the two stages. With increasing temperature, the conversion ratios of fuel-N to NO during the two stages increase, and the opposite tendencies are observed for N2O. CO2 inhibits the fuel-N conversions to NO during the two stages but promotes those to N2O. Compared with air combustion, the conversion ratios of fuel-N to NO during the two stages are lower in 21%O2/79%CO2, and those to N2O are higher. At <O2> = 21–50% by volume, the conversion ratios of fuel-N to NO during the two stages reach the maximum values at <O2> = 30% by volume, and those to N2O decrease with increasing O2 concentration. H2O suppresses the fuel-N conversions to NO and N2O during the two stages. A higher coal rank has higher total conversion ratios of fuel-N to NO and N2O. Fuel-N, volatile matter, and fixed carbon contents are the important factors on fuel-N conversions to NO and N2O during the two stages. The results benefit the understanding of NO and N2O emission mechanisms during oxy-fuel FB combustion of coal.

An evaluation of neat biodiesel/diesel performance, emission pattern of NOx and CO in compression ignition engine

Oxides of nitrogen (NOx) and carbon (II) oxide (CO) emissions from engine running on pure biodiesel constitute one of the environmental challenges to its application as fuel. Verifying their sources and production pattern is an essential first step to tackling the challenge. 100% biodiesel derived from moringa, jatropha and waste oil along with petroleum diesel were evaluated in a single cylinder diesel engine. It was observed that oxygen concentration and combustion temperature are the primary drivers of a kinetically determined process. NOx emission trended with Zeldovich mechanism prediction and thus increases with increasing O2 concentration and temperature. CO2 dissociation at elevated combustion temperature in a suppressed O2 concentration regime governs CO production for normal diesel running at high load but, low temperature and high viscosity account for same effect in biodiesel runs. CO therefore increases with increasing temperature and decreasing O2 concentrations for petroleum diesel but for biodiesel, the reverse is the case. Novel exhaust gas recirculation (EGR) and low temperature combustion (LTC) engine therefore holds the key to unlocking biodiesel potential and remediating some of the difficulties observed with petroleum diesel.