排序方式: 共有26条查询结果,搜索用时 0 毫秒
11.
《环境科学学报(英文版)》2023,35(3):427-442
Volatile organic compounds (VOCs) have attracted much attention for decades as they are the precursors of photochemical smog and are harmful to the environment and human health. Vacuum ultraviolet (VUV) photodegradation is a simple and effective method to decompose VOCs (ranging from tens to hundreds of ppmV) without additional oxidants or catalysts in the air at atmospheric pressure. In this paper, we review the research progress of VOCs removal via VUV photodegradation. The fundamentals are outlined and the key operation factors for VOCs degradation, such as humidity, oxygen content, VOCs initial concentration, light intensity, and flow rate, are discussed. VUV photodegradation of VOCs mixture is elucidated. The application of VUV photodegradation in combination with ozone-assisted catalytic oxidation (OZCO) and photocatalytic oxidation (PCO) systems, and as the pre-treatment technique for biological purification are illustrated. Based on the summary, we propose the challenges of VUV photodegradation and perspectives for its future development. 相似文献
12.
Ammonia (NH3) is ubiquitous in the atmosphere, it can affect the formation of secondary aerosols and particulate matter, and cause soil eutrophication through sedimentation. Currently, the use of radioactive primary reagent ion source and the humidity interference on the sensitivity and stability are the two major issues faced by chemical ionization mass spectrometer (CIMS) in the analysis of atmospheric ammonia. In this work, a vacuum ultraviolet (VUV) Kr lamp was used to replace the radioactive source, and acetone was ionized under atmospheric pressure to obtain protonated acetone reagent ions to ionize ammonia. The ionization source is designed as a separated three-zone structure, and even 90 vol.% high-humidity samples can still be directly analyzed with a sensitivity of sub-ppbv. A signal normalization processing method was designed, and with this new method, the quantitative relative standard deviation (RSD) of the instrument was decreased from 17.5% to 9.1%, and the coefficient of determination was increased from 0.8340 to 0.9856. The humidity correction parameters of the instrument were calculated from different humidity, and the ammonia concentrations obtained under different humidity were converted to its concentration under zero humidity condition with these correction parameters. The analytical time for a single sample is only 60 sec, and the limit of detection (LOD) was 8.59 pptv (signal-to-noise ratio S/N = 3). The ambient measurement made in Qingdao, China, in January 2021 with this newly designed CIMS, showed that the concentration of ammonia ranged from 1 to 130 ppbv. 相似文献
13.
Satoshi Saitoh Albrecht Melber Hiroshi Ohbayashi Satoshi Nakai Masakuni Matsuoka Masaaki Hosomi 《Journal of Material Cycles and Waste Management》2008,10(1):71-78
We discuss the use of the Schmidt graphical method to calculate the time required to heat a polychlorinated biphenyl (PCB)-contaminated
capacitor in the vacuum thermal recycling process to the processing temperature of 400°C, and we evaluate the results of the
heating time calculation by comparing the calculated values with the corresponding experimental values. The thermal conductivity
and specific heat of the insulating paper and the carbonized paper in the capacitor were unknown, so we determined their values
from experimental data obtained during the vacuum thermal recycling process. The capacitor element is a multilamination of
aluminum foil and insulating paper, so we used an equation for a multilayer plane wall to calculate the value of the thermal
conductivity. For the thermal conductivity and specific heat of the insulating paper impregnated with PCBs, we used values
calculated from the mass ratios and thermal conductivities and specific heats of the individual materials. In addition, the
physical properties vary according to the treatment because of the evaporation of PCBs and the carbonization of the insulating
paper, so we modified the values of the thermal conductivity, specific heat, and density at the boiling point of the PCB and
the carbonization point of the insulating paper before performing the calculations. Our calculated heating times were almost
the same as, or were above, the experimental values, so we concluded that our method can be used as a simple calculation of
the heating time. 相似文献
14.
Effects of vacuum levels,carbon dioxide,and structural sizes of linked vessels on dump vessel vented
The method of explosion venting is widely used in industrial explosion-proof design due to its simple operation, economical and practical features. A dump vessel vented platform was built. By changing the vacuum level and the gas in the dump vessels and the structural size of linked vessels, the pressure in the explosion vessel and the dump vessel was compared, and the influencing factors of explosion venting investigated. The main conclusions are as follows: In the explosion venting process, the higher the vacuum in the dump vessel, the smaller the pressure peak of the explosion vessel and the dump vessel, and the faster the explosion pressure is lowered. When the dump vessel is under the same vacuum level and the gas in the dump vessel is CO2, the maximum pressure of the explosion vessel and the dump vessel is less than the maximum pressure when the containment medium is air. Under the same vacuum condition, the larger the volume ratio of the dump vessel and the explosion vessel, the smaller the pressure peak of the explosion vessel, the faster the explosion pressure drops, and the volume of the dump vessel reaches or exceeds the explosion vessel. Increasing the volume ratio of the containment vessel to the explosion vessel facilitates protection of the explosion vessel and the containment vessel. Under the same vacuum condition, when the gas explosion in 113 L vessel vents into 22 L vessel, the longer the length of the pipe, the greater the maximum pressure in the spherical vessel. When the gas explosion in 22 L vessel vents into 113 L dump vessel, as the pipeline grows, the maximum pressure in the two vessels decreases, but the reduction is not significant. In practical application, it is recommended to use a vacuum of 0.08Mpa or more for the dump vessel vented, and the containment medium is CO2.In terms of the structural size of the container, it is recommended that the ratio of the receiving container to the explosion container be as large as possible, and the pipe length be as long. 相似文献
15.
16.
旅客列车真空集便器便盆污物冲洗排空效果受诸多因素影响,各影响因素间相互作用.为实现以较低冲洗水量达到良好冲洗排空效果、提高系统洁净性能,对便盆曲面、冲洗流型进行分析设计,对旋流和扇面2种不同冲洗流型特点进行比较,分析不同设计参数及安装位置对冲洗排空效果的影响,最终通过试验研究验证冲洗喷嘴的安装位置、旋流喷嘴的射流方向等... 相似文献
17.
Perfluorooctanoic acid (PFOA) has long been an environmental contaminant of concern owing to its potential health risk. However, exposure to perfluorinated carboxylic acids (PFCAs) other than PFOA is not well understood. In this study, we investigated the concentrations of PFCAs in vacuum cleaner dust in Japan to measure the PFCAs contamination in an indoor environment. Most of the 77 samples contained PFCAs with 6-13 carbon atoms. The median concentration of perfluorononanoic acid (PFNA, 23.2 ng g−1) was highest among PFCAs, followed by PFOA (20.8 ng g−1) and perfluoroundecanoic acid (PFUnDA, 12.9 ng g−1). The 90th percentile concentrations of PFNA, PFUnDA and perfluorotridecanoic acid (PFTrDA) were 948, 283 and 110 ng g−1, respectively, and these were detected at greater concentrations than neighboring, even-numbered PFCAs. The proportion of long-chain PFCAs in vacuum cleaner dust from Japan was relatively higher than those reported for other countries. Factor analysis showed three independent factors. Odd-numbered long chain PFCAs (PFNA, PFUnDA and PFTrDA), which can correspond to factor 1, were major components of PFCAs in vacuum cleaner dust. Short chain PFCAs (factor 2) and even numbered long chain PFCAs (factor 3) were also statistically separated. These findings suggest that there are several sources of PFCAs with different origins in indoor environment. Further investigations into the origins of PFCAs are needed to evaluate indoor contamination with PFCAs. 相似文献
18.
The lead removal from the metallic mixture of waste printed circuit boards by vacuum distillation was optimized using experimental design, and a mathematical model was established to elucidate the removal mechanism. The variables studied in lead evaporation consisted of the chamber pressure, heating temperature, heating time, particle size and initial mass. The low-level chamber pressure was fixed at 0.1 Pa as the operation pressure. The application of two-level factorial design generated a first-order polynomial that agreed well with the data for evaporation efficiency of lead. The heating temperature and heating time exhibited significant effects on the efficiency, which was validated by means of the copper–lead mixture experiments. The optimized operating conditions within the region studied were the chamber pressure of 0.1 Pa, heating temperature of 1023 K and heating time of 120 min. After the conditions were employed to remove lead from the metallic mixture of waste printed circuit boards, the efficiency was 99.97%. The mechanism of the effects was elucidated by mathematical modeling that deals with evaporation, mass transfer and condensation, and can be applied to a wider range of metal removal by vacuum distillation. 相似文献
19.
20.
In this study, we introduce a jet-type foam preparation device for use in mine dust control, which can enhance the reliability and applicability of the foam production process compared with conventional foam generators. In order to elucidate the foaming agent self-suction properties of this novel foam generator, we used a self-built experimental setup to investigate the effects of the working pressure and outlet pressure on negative pressure (vacuum degree) during foaming agent suction, as well as the functional relationship between negative pressure and the foaming agent by adding parameters. We also studied the effects of the valve opening degree on the foaming agent flow rate and addition ratio. The results showed that the working pressure and outlet pressure affected the formation of negative pressure in a positive linear manner and a negative linear manner, respectively. Thus, the negative pressure increased linearly as the working pressure increased, whereas it decreased in a linear manner as the outlet pressure increased. There was also a quadratic relationship between the vacuum degree and foaming agent quantity with the piecewise characteristics of the growth process, where they increased slowly with a lower vacuum degree but increased rapidly with a higher vacuum degree. After creating a moderate negative pressure with the water jet, the foaming agent could be added automatically at a low flow rate with a low ratio via the regulating valve on the liquid suction hose. This study provides basic information that should facilitate the application of this novel foam preparation technique. 相似文献