Nitrogen Oxides Control Research Articles

Real-time source contribution analysis of ambient ozone using an enhanced meta-modeling approach over the Pearl River Delta Region of China

The nonlinear response of O3 to nitrogen oxides (NOx) and volatile organic compounds (VOC) is not conducive to accurately identify the various source contributions and O3-NOx-VOC relationships. An enhanced meta-modeling approach, polynomial functions based response surface modeling coupled with the sectoral linear fitting technique (pf-ERSM-SL), integrating a new differential method (DM), was proposed to break through the limitation. The pf-ERSM-SL with DM was applied for analysis of O3 formation regime and real-time source contributions in July and October 2015 over the Pearl River Delta Region (PRD) of Mainland China. According to evaluations, the pf-ERSM-SL with DM was proven to be effective in source apportionment when the traditional sensitivity analysis was unsuitable for deriving the source contributions in the nonlinear system. After diagnosing the O3-NOx-VOC relationships, O3 formation in most regions of the PRD was identified as a distinctive NOx-limited regime in July; in October, the initial VOC-limited regime was found at small emission reductions (less than 22–44%), but it will transit to NOx-limited when further reductions were implemented. Investigation of the source contributions suggested that NOx emissions were the dominated contributor when turning-off the anthropogenic emissions, occupying 85.41–94.90% and 52.60–75.37% of the peak O3 responses in July and October respectively in the receptor regions of the PRD; NOx emissions from the on-road mobile source (NOx_ORM) in Guangzhou (GZ), Dongguan&Shenzhen (DG&SZ) and Zhongshan (ZS) were identified as the main contributors. Consequently, the reinforced control of NOx_ORM is highly recommended to lower the ambient O3 in the PRD effectively.

On-road emission measurements of reactive nitrogen compounds from heavy-duty diesel trucks in China

Emissions of major reactive nitrogen compounds, including nitric oxide (NO), nitrogen dioxide (NO2) and ammonia (NH3), from heavy-duty diesel vehicles (HDDVs) place substantial pressure on air quality for many large cities in China. To control nitrogen oxide (NOX) emissions from HDDVs, selective catalytic reduction (SCR) systems have been widely used since the China IV standards. To investigate the impacts of aftertreatment technologies and driving conditions on real-world emissions of reactive nitrogen compounds, a portable emissions measurement system was employed to test eighteen heavy-duty diesel trucks in China. The results showed that the China IV and China V HDDVs with appropriate SCR functionality could reduce NOX emissions by 36% and 53%, respectively, compared to the China III results, although their real-world emissions were still higher than the corresponding emission limits for regulatory engine tests. For these HDDVs, five samples were tested with NH3 emissions, ranging from 1.67 ppm to 51.49 ppm. The NH3 emission rates tended to significantly increase under high-speed driving conditions. The results indicate that the current SCR technology may have certain risks in exceeding the future China VI NH3 limit. However, five China IV/V HDDVs were found to have SCR temperature sensors that were intentionally tampered with, resulting in comparable or even higher NOX emissions and zero NH3 emissions. Increased NO2 emissions due to the adoption of diesel oxidation catalysts and diesel particulate filters were also found from our experiments. This study highlights the importance of enhancing in-use compliance requirements and eliminating aftertreatment tampering for China IV and China V HDDVs.

Optimization and control of NOx in coke oven vertical flue under flue gas recirculation

The orthogonal experimental design with CFD simulation was carried out to simulate combustion in the coke oven vertical flue at external flue gas recirculation. The control of nitrogen oxides (NOx) generation was analysed by different factors such as air excess coefficient, oxidant preheating temperature, flue gas recirculation and oxidizer inlet cross-sectional area ratio. The simulation results showed that the the orthogonal experimental design with CFD had a significant effect on the combustion process. The flue gas recirculation ratio effectively improved the temperature distribution uniformity in the vertical flue, and had a significant effect on NOx production in the vertical flue. Within the parameters of the orthogonal design, when the air excess coefficient was 1.1, the oxidant preheating temperature was 1200 K, the flue gas recirculation ratio was 30%, and the oxidant inlet cross-sectional area ratio was 0.5, the NOx production in the coke oven vertical flue was the smallest, lower than the industry emission standard.

Real-world gaseous emission characteristics of Euro 6b light-duty gasoline- and diesel-fueled vehicles

To accurately investigate vehicle emissions that have become major contributors to global air pollutants and greenhouse gases, test conditions have been transferred from laboratory type approval test cycles to real-world driving conditions. In this study, the real-world driving emissions of carbon monoxide (CO), total hydrocarbons (THC), nitrogen oxides (NOx), and carbon dioxide (CO2) from one gasoline and two diesel Euro 6b light-duty passenger vehicles were investigated by a portable emission measurement system (PEMS) in Lyon, France. NOx and CO2 emission controls remain critical to addressing the real-world driving emissions of Euro 6b vehicles. Notably, the tested gasoline vehicle emitted higher CO2 emissions than diesel vehicles on all types of roads, especially on the urban road with an excess of 29.3–48.3%. The highest emission factors of gaseous pollutants generally occurred on the motorway for the gasoline vehicle, while on the urban road for diesel vehicles. In particular, for high-speed driving conditions, the gasoline vehicle gaseous emissions, especially NOx emissions, were more affected by acceleration than diesel vehicle emissions. In addition, the CO emissions, especially THC emissions, for the gasoline vehicle, were more influenced by warm-start, especially cold-start, than those for diesel vehicles.

Controlling Nitrogen Oxide (NO x ) Emissions from Exothermic Nitrogen Generation Systems for Application in Subsea Environments.

A highly exothermic nitrogen generation system (NGS) can be achieved by mixing solutions of sodium nitrite and ammonium chloride, a process used by the oil and gas industry to dissolve paraffin wax and gas hydrates. Although its main products are nitrogen gas and a sodium chloride brine, the NGS has a side reaction that produces nitrogen oxides. To optimize this process to ensure the greatest and fastest heat generation with the lowest oxide production, this reaction was checked by infrared spectroscopy and calorimetry. The factors temperature, pH, and initial concentration of nitrite and ammonium were evaluated, and the optimal conditions of the NGS were determined by the constructed models to predict heat and NOx generation. These conditions were a ratio of ammonium/nitrite equal to 1 and a catalyst concentration of 0.07 mol·L–1 (for a case in which the temperature is 5 °C).

Multiple-objective optimization of methanol/diesel dual-fuel engine at low loads: A comparison of reactivity controlled compression ignition (RCCI) and direct dual fuel stratification (DDFS) strategies

Reactivity controlled compression ignition (RCCI) engines suffer from low thermal efficiency at low loads due to the high hydrocarbon and carbon monoxide emissions. Correspondingly, a direct dual fuel stratification (DDFS) combustion mode is investigated by directly injecting methanol and diesel into cylinder. Multi-objective optimization and detailed comparison are first conducted for the two engine strategies. Compared to RCCI, the optimized DDFS case shows higher thermal efficiency, lower emissions, lower demand for the in-cylinder initial temperature, and higher potential of energy recovery. Different from the single-stage combustion in RCCI, DDFS shows a two-stage combustion, the second stage of which is owing to its near-top dead center injection of methanol. Compared to RCCI, DDFS requires a lower initial temperature to retard combustion phasing, and a larger amount of exhaust gas recirculation rate to control nitrogen oxide and ringing intensity. The optimized methanol fraction and injection timings of diesel are similar for RCCI and DDFS, and they are determined in compromise of combustion efficiency and heat transfer loss. A large spray-included angle of diesel injector is preferable for RCCI to target diesel spray to the piston lip. In DDFS, a small spray-included angle of diesel injector is needed for more complete fuel oxidation, and a medium spray-included angle of methanol injector is required to avoid excessive heat transfer loss. Due to the non-sooting nature of methanol, DDFS produces as low soot emissions as RCCI. The present study shows that the co-optimization of operating parameters and fuel properties offers a promising approach to meet the more stringent regulation on efficiency and emission.

배기가스 조성에 따른 활성탄의 수은 흡착 특성

Activated carbon injection upstream of a particulate matter control device is a widely applied method for the control of mercury emission from the coal-fired plant and waste incinerator. Performance of activated carbon in mercury control depends on various factors such as flue gas composition, physical and chemical properties of fly ash and activated carbon, etc. This study was designed to investigate the effect of flue gas composition on the mercury adsorption efficiency of activated carbon. Commercial activated carbon was obtained, and a fixed-bed reactor system was used for the tests of its mercury adsorption at various simulated flue gas conditions. A baseline gas consists of 12% carbon dioxide (CO₂), 5% oxygen (O₂), 7% water vapor (H₂O), 60∼70 μg mercury (Hg)/m³ and balance nitrogen (N₂). Each of acidic gases such as sulfur dioxide (SO₂), nitrogen monoxide (NO) and hydrogen chloride (HCl) was added to the baseline gas and injected for the test to investigate the effect of each acidic gas on the mercury adsorption efficiency of activated carbon. In addition, the mercury adsorption efficiency of activated carbon was examined at the conditions of simulated flue gas (1) before air pollution control (2) after desulfurization and (3) after nitrogen oxides (NOx) control.

Bias in ammonia emission inventory and implications on emission control of nitrogen oxides over North China Plain

This study examined seasonal bias of ammonia (NH3) emission inventory over North China Plain (NCP) using the GEOS-Chem chemical transport model (NH3-standard simulation, SG1), and found that the MIX NH3 inventory overestimates winter NH3 by 31% and underestimates summer NH3 by 50%. NH3 emission from NCP is thus cut by 24% in winter and doubled in summer (NH3-corrected simulation, SG2) to match up with the observations. The corrected NH3 emission changes the surface PM2.5 and nitrate concentrations and is expected to impact the nitrogen oxides (NOx) emission control efficiency (relative changes of PM2.5 and nitrate concentration in response to 1% NOx emission change, βPM and βNO3). We then conducted sensitivity studies (SG3) by reducing 20% (S31) and 40% (S32) NOx emission based on NH3-standard and NH3-corrected simulation, respectively. Through comparing the NOx emission control efficiency under the two NH3 emission conditions (NH3-standard and NH3-corrected), we find that NH3 emission bias under the NH3-standard condition causes ~30% overprediction of winter βPM and ~35% underprediction of summer βPM. In addition, for the NH3-corrected simulation, βPM increases by 43% in winter and 7.7% in summer from S31 to S32. Taken together, these findings highlighted the importance of stringent NOx emission control throughout the year and NH3 emission control in summer as well. Moreover, it is critical to obtain a more accurate seasonal pattern of NH3 emission inventory in assessing emission control efficiency of PM2.5 precursors.

Passive SCR Performance Under Pseudo-Transient Cycle: Challenges and Opportunities for Meeting Tier 3 Emissions

The passive ammonia (NH3) selective catalytic reduction (SCR) system is a potential approach for controlling nitrogen oxide (NOx) emissions from lean-burn gasoline engines based on utilizing NH3 generated by a three-way catalyst (TWC) during brief periods of fuel-rich engine operation. NH3 generated by the TWC is stored and available to reduce NOx on a downstream SCR catalyst during subsequent periods of lean engine operation. Control of the overall passive SCR process can be more challenging than current urea-based approach because it depends explicitly on fuel-rich engine operation, which must be implemented in the context of transient engine operation. Under transient engine operation, significant variation in SCR temperatures is also to be expected. With NH3 storage capacity highly dependent on exhaust temperatures, proper system architecture and engine operating strategy are needed for effective NH3 utilization over the SCR catalyst. In this study, the performance of a passive SCR system was evaluated on a 2.0-l BMW lean-burn gasoline direct injection engine under 6-mode pseudo-transient cycle. The aim of this work is to understand how various engine operating strategies change the dynamics of NH3 generation and utilization, and NOx reduction in the passive SCR system. A 5.9% fuel economy improvement relative to stoichiometric-only operation with 0.018 g/mi of NOx + NMHC emissions were demonstrated over 6-mode pseudo-transient cycle; however, CO emissions were twice the emission standard. The results of this work reveal challenges and opportunities for meeting Tier 3 emissions and improving fuel savings benefits.

Summary of flue gas denitration technology for coal-fired power plants

With the rapid development of the economy, nitrogen oxide pollution has become a problem that cannot be ignored. Therefore, it is necessary to strengthen the control of nitrogen oxides in coal-fired power plants. This paper introduces the current denitration technology overview, including the selective catalytic reduction (SCR), non-selective catalytic reduction (SCNR), SCR-SNCR mixed denitration technology, including acid absorption, Wet denitration technology such as lye absorption method, oxidation absorption method and activated carbon absorption method, as well as coal-fired flue gas combined desulfurization and denitration technology were introduced. The process principle and characteristics were briefly described, and the development direction of flue gas denitration technology was introduced. The outlook was made.Introduction Nitrogen oxides (NOx) is an atmospheric pollutant that combines with water in the air to promote the formation of acid rain. It also produces photochemical smog under certain conditions with other pollutants. It also participates in the destruction of the ozone layer and oxidation. Nitrogen will destroy the ozone layer in the high-temperature stratosphere and increase the incidence of skin cancer. Therefore, while building a power plant to meet social energy needs, it should strengthen the effective control of nitrogen oxide emissions from coal-fired power plants, reduce air pollution, and reduce the serious damage caused by nitrogen oxides emissions to human living environment. The emission of nitrogen oxides from power plants. Denitration technology is particularly important.

Quick vaporization of sprayed sodium hypochlorite (NaClO(aq)) for simultaneous removal of nitrogen oxides (NOx), sulfur dioxide (SO2), and mercury (Hg0)

ABSTRACTSodium hypochlorite (NaClO) has been widely used as a chemical additive for enhancing nitrogen oxide (NOx; NO + NO2), sulfur dioxide (SO2), and mercury (Hg0) removals in a wet scrubber. However, they are each uniquely dependent on NaClO(aq) pH, hence making the simultaneous control difficult. In order to overcome this weakness, we sprayed low liquid-to-gas (L/G) ratio (0.1 L/Nm3) of NaClO(aq) to vaporize quickly at 165 °C. Results have shown that the maximized NOx, SO2, and Hg0 removals can be achieved at the pH range between 4.0 and 6.0. When NOx and Hg0 coexist with SO2, in addition, their removals are significantly enhanced by reactions with solid and gaseous by-products such as NaClO(s), NaClO2(s), OClO, ClO, and Cl species, originated from the reaction between SO2 and NaClO(aq). We have also demonstrated the feasibility of this approach in the real flue gases of a combustion plant and observed 50%, 80%, and 60% of NOx, SO2, and Hg0 removals, respectively. These findings led us to conclude that the spray of NaClO(aq) at a relatively high temperature at which the sprayed solution can vaporize quickly makes the simultaneous control of NOx, SO2, and Hg0 possible.Implications: The simple spray of NaClO(aq) at temperatures above 165 °C can cause the simultaneous removal of gaseous NOx, SO2, and Hg0 by its quick vaporization. Their maximized removals are achieved at the pH range between 4.0 and 6.0. NOx and Hg0 removals are also enhanced by gaseous and solid intermediate products generated from the reaction of SO2 with NaClO(aq). The feasibility of this approach has been demonstrated in the real flue gases of a combustion plant.

Global impacts of recent IMO regulations on marine fuel oil refining processes and ship emissions

This study presents an overview of the context and global impacts of recent International Maritime Organization (IMO) regulations on the marine fuel oil refining industry, future marine fuel mix and ship emissions. IMO limited marine fuel sulphur content in both Sulphur Emission Control Areas (SECAs) and Nitrogen Oxide Emission Control Areas (NECAs) to 0.1% (wt. %) by 2015, and to 0.5% globally by 2020. It is anticipated that the newly implemented IMO regulations will help to mitigate negative impact of ship emissions on public health and environment. IMO regulations require significant changes to refineries to increase the production of low sulphur fuels through a shift to distillates, use of novel deep desulphurization techniques, or fuel blending. Changes to the refinery processes can bring forth increases in greenhouse gas emissions and high capital investments. Alternative fuels will need to meet the required reduction of air pollutants and greenhouse gas emissions in coastal areas. Alternative marine fuels consisting of liquefied nature gas (LNG) and biofuel may be suitable fuels to meet both targets. These two fuels are predicted to account for 50% of shipping energy demand by 2050, while the remainder will still be supplied by conventional heavy fuel oil (HFO)/marine gas oil (MGO). Switching to low sulphur fuels as a results of the new IMO regulations has led to measureable reductions in ship emissions generally. This fuel switching also resulted in changes in engine emission characteristics, especially on particulate matter chemical composition.

Development of Fuel/Engine Systems—The Way Forward to Sustainable Transport

Abstract The global demand for transport energy is large, growing, and primarily met by petroleum-derived liquid fuels powering internal combustion engines (ICEs). Moreover, the demand for jet fuel and diesel is projected to grow faster than the demand for gasoline in the future, and is likely to result in low-octane gasoline components becoming more readily available. Significant initiatives with varying motivations are taking place to develop the battery electric vehicle (BEV) and the fuel cell as alternatives to ICE vehicles, and to establish fuels such as biofuels and natural gas as alternatives to conventional liquid fuels. However, each of these alternatives starts from a very low base and faces significant barriers to fast and unrestrained growth; thus, transport—and particularly commercial transport—will continue to be largely powered by ICEs running on petroleum-based liquid fuels for decades to come. Hence, the sustainability of transport in terms of affordability, energy security, and impact on greenhouse gas (GHG) emissions and air quality can only be ensured by improving ICEs. Indeed, ICEs will continue to improve while using current market fuels, through improvements in combustion, control, and after-treatment systems, assisted by partial electrification in the form of hybridization. However, there is even more scope for improvement through the development of fuel/engine systems that can additionally leverage benefits in fuels manufacture and use components that may be readily available. Gasoline compression ignition (GCI), which uses low-octane gasoline in a compression ignition engine, is one such example. GCI would enable diesel-like efficiencies while making it easier to control nitrogen oxides (NOx) and particulates at a lower cost compared with modern diesel engines. Octane on demand (OOD) also helps to ensure optimum use of available fuel anti-knock quality, and thus improves the overall efficiency of the system.

Analysis of the high instantaneous NOx emissions from Euro 6 diesel passenger cars under real driving conditions

In real-world driving, most Euro 5 and 6 diesel passenger cars exceed the nitrogen oxides (NOx) emission limits of type approval procedure. The emission factors of the fleet of Euro 6 vehicles show high variability, irrespective of the NOx control technology. This comprehensive study focused on the events of high instantaneous NOx emissions produced under real driving, to assess their impact on emission factors. Additionally, the relationships of these events with different parameters measured using portable emissions measurement system (PEMS) were determined. Three Euro 6b diesel passenger cars with exhaust gas recirculation (EGR), lean-burn NOx trap (LNT) and selective catalytic reduction (SCR) were tested based on the real driving emissions (RDE) regulation.The results show that high instantaneous NOx emissions represent a large amount of total NOx emissions, although they are produced in a small percentage of driving time. A theoretical constraint of these high NOx emissions could reduce emission factors by 30–82%. The emission of high instantaneous NOx emissions are related to characteristic speed modes of urban, rural and motorway sections, and are primarily produced in a narrow engine speed range of approximately 700 rpm. In general, the probability of producing high instantaneous NOx emissions increases as the engine speed, the exhaust gas temperature or the vehicle speed is increased. Finally, regarding driving severity, speed per positive acceleration (v⋅a+) observations above the maximum values of the new European driving cycle (NEDC) and the world-harmonized light-duty vehicle test cycle (WLTC), have a strong probability to yield high instantaneous NOx emissions. These findings could be useful in the design of low emission policies, optimization of NOx control strategies, and the improvement of micro/meso emission models.

Evaluation of Operating and Design Parameters of Pressurized Flue Gas Systems with Integrated Removal of NOx and SOx

This study investigates the operating and design parameters of product gas compression and integrated control of nitrogen oxides (NO x ) and sulfur oxides (SO x ) in large-scale oxy-fuel and chemical looping combustion processes. A process model that includes a comprehensive description of nitrogen and sulfur chemistry and mass transfer is developed. The results show that the fraction of NO oxidation into NO 2 will be 10-50% in a multistage compressor to 30 bars (1-4% O 2 in the gas) depending on the residence times in intercoolers and pressure levels. At lower O 2 concentrations (>0.1% O 2 in the gas), the oxidation is limited but still active. Nitric acid formation in the compressor condensate is, thus, inevitable, although limited, as most water is condensed in the early stages, whereas the acid gases are formed in the later stages. The NO 2 /NO x ratio has an important effect on the total amount of NO x absorbed and extra residence time should be added after the compressor to increase this ratio. Evaluation of the process behavior in relation to simultaneous absorption of SO 2 and NO x revealed that increased SO 2 /NO x ratio and bottom liquid recycling enhanced the total NO x absorption. In addition, maintaining the pH in the absorbing solution above 5 improves the removal efficiencies of NO x and SO 2 . NO x removal rates of up to around 95% can be achieved for SO 2 /NO x > 1 in the flue gas with appropriate design of the absorber. For SO 2 /NO x < 1, increasing the packing height or addition of S(IV) solutions could enhance the NO x removal rates to 95% or more. The model predictions are compared with the experimental data from a laboratory-scale absorber. The process model developed in this work enables design studies and techno-economic evaluation of absorption-based NO x and SO x removal concepts.

Experimental Research on NOx Emission Characteristics During Coal Combustion in the Stoker-fired Boiler

In this paper, the combustion stability and nitrogen oxides (NOx) emissions test were made in two coal-fired chain grate boilers with hot water supplies of 29MW and 46MW. The investigations aim to clarify the key characteristics of NOx emission, e.g.instability of NOx emission, temperature and gaseous components profiles and the unsteady variation of NOx emission with power level changing. Main conclusions include: 1) In the process of stable combustion, NOx emissions still have±5% fluctuations, it is not stable. 2) The furnace temperature distribution show double temperature peaks. One peak (~1500°C) is located on the burning solid-fuel surface on the chain grate, and the other (~1050°C) is ~5.6m above the arch. 3) With increasing the thermal power, NOx emission shows a dramatic increase, higher around 1.25 times, as due to the rapid adjustment of coal feeding in grate furnace. Those above show the NOx control difficulty and the proper injector location of SNCR (selective non-catalytic reaction), which is key data collected for further NOx reduction retrofits.

Measurement of atmospheric oxides of nitrogen and a preliminary investigation of their source

Abstract Introduction Maintenance of a breathable atmosphere is a core tenet of dived submarine operations, and the responsibility for this falls to the medical department. Nitrogen oxides (NOx) are atmospheric contaminants from a currently unconfirmed source. If not controlled, these contaminants can act as respiratory irritants and asphyxiants which may endanger health and threaten sustained dived operations. Methods Using the issued Dräger Short Term Detection Tubes (STDTs) to sample strategic locations, the relationship between atmospheric contaminants and NOx was investigated in an attempt to determine the source of NOx formation. Interventions were implemented to reduce NOx by reducing leakage of monoethanolamine (MEA) from carbon dioxide (CO2) scrubbing equipment, a known potential source of NOx if oxidised (combusted). Dräger STDTs for NH3 demonstrate cross-reactivity with MEA, these levels being referred to as NH3/MEA. Results A relationship was demonstrated between elevated readings for atmospheric NH3/MEA and elevated readings for NOx, with a variable lag period. Findings suggest that NOx production may be reduced by control of atmospheric NH3/MEA. Of the control measures examined, replacement of resin filter bags was noted to reduce atmospheric NH3/MEA, while replenishment of CO2 scrubber MEA was noted to increase it, with a resultant increase in NOx production. Conclusions Elevated NH3 atmospheric readings may in fact be due to MEA from CO2 scrubbers. This, when catalytically oxidised by CO/H2 burners, produces NOx. Management of MEA egress from CO2 scrubbers (carryover) represents a potential target for NOx control interventions. Specific MEA detection equipment is required to demonstrate whether MEA or NH3 is the progenitor species for NOx. Furthermore, controlled trials are required to prove a definitive relationship between MEA and NOx and to evaluate the best control measures.

Experimental analysis of NOx reduction through water addition and comparison with exhaust gas recycling

The diesel engine requirements regarding the reduction of exhaust emissions, especially nitrogen oxide (NOx) and particulate matter (PM) are becoming more stringent year by year. A current method used for NOx control is exhaust gas recirculation (EGR). However, this approach significantly increases the production of soot for medium and high rates. Water addition can also be used for NOx control, achieving 50% NOx reduction rates in relation to EGR with a lower production of soot and without additional carbon monoxide (CO) and hydrocarbons (HC) substantially. This paper analyses the weaknesses and the strengths of adding water into the intake manifold with a flow-blurring injector for NOx reduction on a current technology diesel engine with multiple injection thorough a proprietary tool for heat release rate that considered real gas properties. A reduction of NOx emissions around 60–70% was achieved with water injection at different loads and speeds. Besides, a clear relationship was established between the minimum attainable NOx emission and the thermal capacity of the load (air plus water), this result stablish the hard relationship between NOx formation and combustion chamber temperature and therefore shows the strong dependence of the Zeldovich mechanism.

The weekday/weekend ozone differences induced by the emissions change during summer and autumn in Guangzhou, China

Weekday/weekend mixing ratios of ozone (O3) and the O3 precursors of non-methane hydrocarbons (NMHCs) and nitrogen oxides (NOx) were recorded at the Guangzhou Panyu Atmospheric Composition Station (GPACS), a suburban site in Guangzhou, during the summer (June, July, and August) and autumn (September, October, and November) of 2011. In both summer and autumn, weekday/weekend O3 differences in the morning and at midday largely depend on how much the O3 precursors are affected by anthropogenic emissions. In the mornings (6:00–9:00 LT), pollutants (i.e. NOx and NMHCs) were more strongly influenced by vehicular emissions in autumn than in summer. In autumn, O3 titration and lower NOx on weekends in NMHCs-limited regimes lead to more rapid O3 production, which resulted in the O3 weekend effect during autumn morning. No O3 weekend effect occurred on summer mornings because O3 formation was in a NOx-limited regime, although O3 titration still existed. At midday (10:00–16:00 LT), the increase of biogenic NMHCs emissions reversed the sensitivity of O3 production from NMHCs-to NOx-sensitive. The weekday/weekend diurnal pattern of vehicular sources was the same at midday, more intense other human industrial activities in autumn not only gave rise to the higher mixing ratios of high-reactive anthropogenic NMHCs (e.g. aromatics) on weekdays, but also could affected the temperature in the city, leading to higher isoprene mixing ratio on weekdays. All these factors are likely to contribute to the O3 weekday effect in autumn. Meanwhile no weekday O3 effect occurred in summer due to the low-intensity industrial anthropogenic activities. Our results show that high-reactive NMHCs and NOx control can be effective for reducing peak O3 mixing ratios in Guangzhou. Further investigation based on numerical models is required to reach more robust conclusions.

Experimental study on dioxin formation in an MSW gasification-combustion process: An attempt for the simultaneous control of dioxins and nitrogen oxides

A gasification-combustion conversion process has been proposed for MSW disposal, and the positive effect of “homogeneous conversion” and “staged combustion” on the stabilization of Cl atoms and the rupture of CCl has been proved previously in fundamental experiments. To verify and evaluate their inhibition effect on dioxin generation, a bench-scale experimental system of the proposed process was established in the present work and an experimental study on the formation of dioxins in the process was carried out. Since both dioxins and nitrogen oxides should be strictly controlled while applied in industry, the simultaneous control of nitrogen oxides was also considered. Results indicated that “homogeneous conversion” has a clear inhibition effect on dioxins in both the syngas from gasification and the flue gas from combustion, which is a very important process in the stabilization of Cl atoms and the control of dioxins. During the “staged combustion” of the syngas, the increase of SR1, the rise of temperature and the extension of residence time all have a clear inhibition effect on dioxins in the flue gas. The extension of residence time seems to be more efficient, and while increasing SR1 and temperature, the regeneration of active chlorine species and the increase of NO need to be concerned. By the combination of “homogeneous conversion” with a temperature of 700 °C and “staged combustion” with a SR1/SR2 ratio of 0.7/0.4, a temperature of 900 °C, a residence time of 241 ms, a satisfactory simultaneous control of both dioxins and nitrogen oxides was obtained in the experiments of the present work.