The behavior of methane/hydrogen/air premixed flame in a closed channel with inhibition

Hydrogen enriched natural gas (HNG) is a promising alternative fuel. But the blended fuel will inevitably have different ignition and combustion characteristics as compared to natural gas. The extent of the resulting difference depends on the percentage of hydrogen addition. It may affect the compatibility of combustion systems and have safety implications. The present study was aimed at enhancing the safety of HNG through inhibition by inert gases. Laboratory tests were conducted for methane/hydrogen/air premixed flame propagating in a closed channel with either nitrogen (N2) or carbon dioxide (CO2) as the inhibitor. Mixtures with different hydrogen volumetric fractions in fuel, including 0%, 20%, 50% or 80% were investigated. The flame shape evolution and the overpressure in the channel were recorded by high-speed Schlieren photography and pressure sensor, respectively. The flame shape was found to change in various ways depending on the inhibitor and hydrogen content. The pressure wave had remarkable impacts on flame and pressure dynamics. The effect of buoyancy on the flame deformation was observed and discussed. Both N2 and CO2 were found to have considerable inhibiting effect on the flame speed and overpressure build-up in the channel while the inhibiting effect of CO2 was stronger. The inhibition mechanisms of either N2 or CO2 were revealed from thermal and kinetic aspects

Characteristics of Volatile Organic Compound Leaks from Equipment Components: A Study of the Pharmaceutical Industry in China

Leak detection and repair (LDAR) plays an important role in controlling the fugitive emission of volatile organic compound (VOC) from chemical enterprises. At present, many policies and standards issued in China have set clear requirements for implementing LDAR in the pharmaceutical industry. In this study, the LDAR work of nine typical pharmaceutical enterprises was selected for analysis to allow investigation of the characteristics of VOC emissions from leaking equipment components. Some suggestions for controlling VOC are proposed to provide a reference for managing the fugitive emissions of VOC from pharmaceutical enterprises. The results showed that the number of equipment components used by the pharmaceutical enterprises ranged from several thousand to more than 20,000, which is lower than that in oil refining and coal chemical enterprises. The predominant leaky component was the flange, which accounted for 56.31% of the total, followed by connectors (21.51%) and valves (18.53%). Light liquid medium components accounted for the largest proportion of equipment (52.83%) on average, followed by gas medium components (45.52%, on average). Heavy liquid medium components, which are rarely used in pharmaceuticals, accounted for only 1.65%. The average leak ratio of the components in the pharmaceutical industry was approximately 0.99%. The leak ratio of the open-ended line was much higher than that of other types of components, reaching an average of 5.00%, while that value was only 0.92% for the flange, despite the numbers and proportion of them that were in use. The total annual VOC leakage from the nine pharmaceutical enterprises studied in this work was 20.11 tons, with an average of 2.23 tons per enterprise and an average of 0.22 kg/a per equipment component. Flanges, connectors, and valves were the top three contributors to leakage, generating 39.17%, 38.72%, and 16.79% of the total, respectively, and a total proportion of 94.68%. Although the number of pumps accounted for only 0.15% of the components, it generated 1.94% of the leakage. In terms of different production processes, the greatest unit product leakage came from the bulk production of chemicals used for pharmaceuticals, reaching 0.085 t/a. The production from traditional Chinese medicine enterprises was the lowest (0.011 t/a), which was only 12.80% of the leakage from the bulk production of chemicals for drugs. The leakage of VOC from the equipment components in the nine enterprises was reduced, to varying degrees, using LDAR. The overall reduction ratio was between 23.55% and 67.72%, with an average of 44.02%. The reduction in leakage was relatively significant after the implementation of LDAR; however, there is still room for improvement. Pharmaceutical enterprises should improve their implementation of LDAR and reduce VOC leakage by reducing the number of inaccessible components used and increasing the repair ratio of leaky components. Controlling the source of component leakage, which should be emphasized, can be realized by cutting down the number of components used, adopting low-leakage equipment, and putting anti-leakage measures in place

Online Measurement of PM2.5 at an Air Monitoring Supersite in Yangtze River Delta: Temporal Variation and Source Identification

To comprehensively explore the transport of air pollutants, one-year continuous online observation of PM2.5 was conducted from 1 April 2015 to 31 March 2016 at Dianshan Lake, a suburban junction at the central of Yangtze River Delta. The chemical species of PM2.5 samples mainly focused on Organic carbon (OC), Elemental carbon (EC) and Water-Soluble Inorganic Ions (WSIIs). The annual average of PM2.5 concentration was 59.8 ± 31.7 µg·m−3, 1.7 times higher than the Chinese National Ambient Air Quality Standards (CNAAQS) (35 µg·m−3). SNA (SO42−, NO3− and NH4+) was the most dominated species of PM2.5 total WSIIs, accounting for 51% of PM2.5. PM2.5 and all of its chemical species shared the same seasonal variations with higher concentration in winter and spring, lower in autumn and summer. The higher NO3−/EC and NOR occurred in winter suggested that intensive secondary formation of nitrate contributed to the higher levels of PM2.5. Cluster analysis based on 72-h backward air trajectory showed that the air mass cluster from nearby inland cities, including Zhejiang, Anhui and Jiangxi Provinces contributed mostly to the total trajectories. Furtherly, potential source contribution function (PSCF) analysis revealed that local sources, namely the emissions in the Yangtze River, were the primary sources. During haze pollution, NO3− was the most important fraction of PM2.5 and the heterogeneous formation of nitrate became conspicuous. All the results suggested that the anthropogenic emissions (such as traffic exhaust) was responsible for the relatively high level of PM2.5 at this monitoring station

Experimental study of hydrogen/air premixed flame propagation in a closed channel with inhibitions for safety consideration

An experimental study of hydrogen/air premixed flame propagation in a closed rectangular channel with the inhibitions (N2 or CO2) was conducted to investigate the inhibiting effect of N2 and CO2 on the flame properties during its propagation. Both Schlieren system and the pressure sensor were used to capture the evolution of flame shape and pressure changes in the channel. It was found that both N2 and CO2 have considerable inhibiting effect on hydrogen/air premixed flames. Compared with N2, CO2 has more prominent inhibition, which has been interpreted from thermal and kinetic standpoints. In all the flames, the classic tulip shape was observed. With different inhibitor concentration, the flame demonstrated three types of deformation after the classic tulip inversion. A simple theoretical analysis has also been conducted to indicate that the pressure wave generated upon the first flame-wall contact can affect the flame deformation depending on its meeting moment with the flame front. Most importantly, the meeting moment is always behind the start of tulip inversion, which suggests the non-dominant role of pressure wave on this featured phenomenon

Validation of the Application of Solid Contact Ion-Selective Electrode for Off-Body Sweat Ion Monitoring

The solid contact ion-selective electrode (ISE) is a promising skin-interfaced monitoring system for sweat ions. Despite a growing number of on-body usages of ISE with fancy new materials and device fabrications, there are very few reports attempting to validate ISE results with a gold standard technique. For this purpose, this work uses inductively coupled plasma-optical emission spectrometry (ICP-OES) as a reference technique to conduct a direct evaluation of the sweat sodium and potassium ion levels obtained by ISE in an off-body approach. Eight healthy male subjects were recruited to collect exercise-induced sweat. It was found that sweat sodium and potassium ions present a rather wide concentration range. The sweat sodium concentration did not vary greatly in an exercise period of half an hour, while the sweat potassium concentration typically decreased with exercise. Mineral drink intake had no clear impact on the sweat sodium level, but increased the sweat potassium level. A paired t-test and mean absolute relative difference (MARD) analysis, a method typically used for evaluating the performance of glucometers, was employed to compare the results of ISE and ICP-OES. The statistical analysis validated the feasibility of ISE for measuring sweat ions, although better accuracy is required. Our data suggests that overweight subjects are likely to possess a higher sweat sodium level

Temporal and Spatial Variation of PM2.5 in Xining, Northeast of the Qinghai–Xizang (Tibet) Plateau

PM2.5 was sampled from January 2017 to May 2018 at an urban, suburban, industrial, and rural sites in Xining. The annual mean of PM2.5 was highest at the urban site and lowest at the rural site, with an average of 51.5 ± 48.9 and 26.4 ± 17.8 μg·m−3, respectively. The average PM2.5 concentration of the industrial and suburban sites was 42.8 ± 27.4 and 37.2 ± 23.7 μg·m−3, respectively. All sites except for the rural had concentrations above the ambient air quality standards of China (GB3095-2012). The highest concentration of PM2.5 at all sites was observed in winter, followed by spring, autumn, and summer. The concentration of major constituents showed statistically significant seasonal and spatial variation. The highest concentrations of organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and water-soluble inorganic ions (WSIIs) were found at the urban site in winter. The average concentration of F− was higher than that in many studies, especially at the industrial site where the annual average concentration of F− was 1.5 ± 1.7 μg·m−3. The range of sulfur oxidation ratio (SOR) was 0.1–0.18 and nitrogen oxidation ratio (NOR) was 0.02–0.1 in Xining. The higher SO42−/NO3− indicates that coal combustion has greater impact than vehicle emissions. The results of the potential source contribution function (PSCF) suggest that air mass from middle- and large-scale transport from the western areas of Xining have contributed to the higher level of PM2.5. On the basis of the positive matrix factorization (PMF) model, it was found that aerosols from salt lakes and dust were the main sources of PM2.5 in Xining, accounting for 26.3% of aerosol total mass. During the sandstorms, the concentration of PM2.5 increased sharply, and the concentrations of Na+, Ca2+ and Mg2+ were 1.13–2.70, 1.68–4.41, and 1.15–5.12 times higher, respectively, than annual average concentration, implying that aerosols were mainly from dust and the largest saltwater lake, Qinghai Lake, and many other salt lakes in the province of Qinghai. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was utilized to study the surface components of PM2.5 and F− was found to be increasingly distributed from the surface to inside the particles. We determined that the extremely high PM2.5 concentration appears to be due to an episode of heavy pollution resulting from the combination of sandstorms and the burning of fireworks

Printed Circuit Board Integrated Wearable Ion-Selective Electrode with Potential Treatment for Highly Repeatable Sweat Monitoring

Wearable chemical sensors have recently received great attention, especially on monitoring ion concentration in sweat. However, challenges still remain, such as the nonnegligible potential deviation of the ion-selective electrode (ISE) based potentiometric sensor after multi-use. Herein, we propose an easily prepared and highly integrated wearable solid contact-ISE (SC-ISE), allowing multiple measurements with repeatable open circuit potential (OCP), which is achieved by applying a positive potential on the working electrode. It's believed that the positive potential alters the oxidation-reduction state of the conducting polymer. The integrated SC-ISE sensor is fabricated on a printed circuit board (PCB) substrate, eliminating external hardware. Preparation of the sensor electrode adopts a standard route, i.e. employing the electroless nickel immersion gold (ENIG) process for plating gold layers. Dual working electrodes have been designed to measure either sodium or potassium ion. This wearable platform has been validated through on-body tests by monitoring ion levels in the real sweat.</p

Sources and vertical distribution of PM2.5 over Shanghai during the winter of 2017

Shanghai, a metropolitan city in China, has suffered from severe air pollution, especially PM2.5, in the last few years. Up to now the contribution of local emission and regional transport to the formation of haze in Shanghai remains unclear. With an aim to characterize the mechanism of haze formation in Shanghai, the present paper attempted to provide an overview of a tethered balloon-based field campaign. According to the backward trajectories, the air mass traveling slowly from Jiangsu province accounted for the highest PM2.5 concentration (66 ± 20 μg/m3). Seventy vertical profiles of PM2.5, NO, NO2, SO2 and O3 within 1000 m were obtained, through which a comparison study on the characteristics of the vertical distributions of air pollutants on clean days and haze days was conducted. When altitude increased, clearly decreasing pattern of PM2.5, NO, and NO2 was observed during the field campaign. Due to the low atmospheric boundary layer, the diffusion of air pollutants was suppressed, which favored the formation of haze. The results of the generalized additive model revealed NO2 could the most significant factor influencing the vertical distribution of PM2.5 in both clean and haze days. This study provides new insight into the sources and vertical distribution of PM2.5, which could offer references for air pollution modeling.</p