La-Na-Co-Mn-O系钙钛矿型催化剂同时去除柴油机碳颗粒和NOx性能的研究

采用低温燃烧法制备了Na+部分取代La3+的La1-xNaxCo0.5Mn0.5O3系钙钛矿型复合氧化物催化剂。利用程序升温反应(TPR)技术,对催化剂应用于柴油机常规排放物中的碳微粒(soot)和氮氧化合物(NOx)的同时催化脱除性能进行了研究。     

Polycyclic aromatic hydrocarbons, black carbon, and molecular markers in soils of Switzerland

Polycyclic aromatic hydrocarbons (PAH) were analysed in 23 soil samples (0–10 cm layer) from the Swiss soil monitoring network (NABO) together with total organic carbon (TOC) and black carbon (BC) concentration, as well as some PAH source diagnostic ratios and molecular markers. The concentrations of the sum of 16 EPA priority PAHs ranged from 50 to 619 μg/kg dw. Concentrations increased from arable, permanent and pasture grassland, forest, to urban soils and were 21–89% lower than median numbers reported in the literature for similar Swiss and European soils. NABO soils contained BC in concentrations from 0.4 to 1.8 mg/g dw, except for two sites with markedly higher levels. These numbers corresponded to 1–6% of TOC and were comparable to the limited published BC data in soil and sediments obtained with comparable analytical methods. The various PAH ratios and molecular markers pointed to a domination of pyrogenically formed PAHs in Swiss soils. In concert, the gathered data suggest the following major findings: (1) gas phase PAHs (naphthalene to fluorene) were long-range transported, cold-condensated at higher altitudes, and approaching equilibrium with soil organic matter (OM); (2) (partially) particle-bound PAHs (phenanthrene to benzo[ghi]perylene) were mostly deposited regionally in urban areas, and not equilibrated with soil OM; (3) Diesel combustion appeared to be a major emission source of PAH and BC in urban areas; and (4) wood combustion might have contributed significantly to PAH burdens in some soils of remote/alpine (forest) sites.     

Modeling polychlorinated biphenyl sorption isotherms for soot and coal

Sorption isotherms (pg-ng/L) were measured for 11 polychlorinated biphenyls (PCBs) of varying molecular planarity from aqueous solution to two carbonaceous geosorbents, anthracite coal and traffic soot. All isotherms were reasonably log-log-linear, but smooth for traffic soot and staircase-shaped for coal, to which sorption was stronger and more nonlinear. The isotherms were modeled using seven sorption models, including Freundlich, (dual) Langmuir, and Polanyi-Dubinin-Manes (PDM). PDM provided the best combination of reliability and mechanistically-interpretable parameters. The PDM normalizing factor Z appeared to correlate negatively with sorbate molecular volume, dependent on the degree of molecular planarity. The modeling results supported the hypothesis that maximum adsorption capacities (Q_max) correlate positively with the sorbent’s specific surface area. Q_max did not decrease with increasing sorbate molecular size, and adsorption affinities clearly differed between the sorbents. Sorption was consistently stronger but not less linear for planar than for nonplanar PCBs, suggesting surface rather than pore sorption.     

Thermal radiation from vapour cloud explosions

The current study estimates the radiation flux emitted from hot extended gas clouds characteristic of vapour cloud explosions along with the corresponding level of irradiance posed on particles suspended in the unburnt part of the cloud ahead of an advancing flame front. The data presented permits an assessment of the plausibility of combustion initiation by such particles due to forward thermal radiation. The thermal radiation will depend on the emissivity of the burned volume, which relates to the concentration of gaseous and particulate combustion products. A sensitivity analysis has been carried out to account for variations in the equivalence ratio, mixture pressure and radiative heat losses. The spatial distribution of irradiance ahead of the flame front has been computed by introducing appropriate geometrical factors to explore the impact of cloud size. Using fuel rich ethylene-air mixtures it has been shown that high flame emissivities can be achieved at path lengths of order 1 m even in the presence of very low soot volume fractions. The emissivity of gas-soot mixtures will hence be mainly determined by the soot concentration and to a lesser extent by the mixture temperature. Our analysis suggests that the role of forward thermal radiation as a contributing factor to flame propagation in large scale vapour cloud explosions can not currently be ruled out.     

浅谈油烟的危害以及相关标准的修订

伴随着经济的繁荣和人民物质生活质量的提高,餐饮业日益繁荣起来,再结合中国素来"民以食为天",传统饮食文化的特殊性及复杂性,导致烹饪过程复杂,同时也带来了各种各样的油烟污染问题。油烟已经成为继噪声、尾气、沙尘之后的又一大污染问题,并且成为百姓环保投诉的热点问题之一。《饮食业油烟排放标准》(GB18483-2001)是目前我国环保行业监测饮食业油烟的唯一标准方法,在实际工作中存在一定的局限性和不完备性,对现行标准进行修订势在必行。     

Competitive diesel engine emissions of sulphur and nitrogen species

NO_x, nitrate and sulphate emissions from a typical European passenger car diesel engine have been measured testing eight different fuels under five steady operating conditions (reproducing modes of the European transient urban/extraurban certification cycle). It is confirmed that nitrogen species compete with sulphur compounds to be adsorbed by diesel particulate matter (DPM) before being emitted into the atmosphere. This competition is found to increase with engine load, and is explained on the basis of the different specific surface and adsorption capacity of soot particles under different operating modes. When a high specific surface is available, as occurs in low load modes, both nitrates and sulphates are adsorbed by soot particles. On the contrary when a small surface is accessible, like in high load modes, sulphates are selectively adsorbed. This is specially important since sulphates are responsible for hydrocarbon retention in DPM due to the scrubbing effect.     

低压下典型可燃液体层流扩散火焰碳烟分布规律研究

对正己烷、正庚烷、正辛烷三种不同含碳量的可燃液体进行了燃烧实验,利用一台压力范围为40 kPa～101kPa的低压燃烧设备,分析了其在低压下的火焰高度、宽度及其与压力的关系,发现上述3种可燃液体的火焰高度均随压力升高而增加,火焰宽度随压力增加而减小。利用激光诱导炽光法研究了压力对三种可燃液体碳烟浓度分布的影响,包括不同高度下的径向碳烟浓度、轴向碳烟浓度和碳烟浓度峰值,结果表明低压下可燃物含碳量越高、压力越大,碳烟浓度越高;碳烟浓度峰值与压力成指数关系。     

An experimental-computational study of DPF soot capture and heat regeneration

ABSTRACT

A diesel particulate filter (DPF) can effectively reduce the exhaust emissions of particulate matter (PM) and meet emission regulations. We report herein an experimental-numerical study to investigate the soot capture and regeneration behavior in a commonly used DPF. Simulations are performed using the AVL FIRE software that considers a fairly detailed DPF model. The model is validated using measured pressure drop history during soot capture, and temperature history during regeneration from a parallel experimental study using a diesel engine equipped with a DPF. Then, a detailed numerical study is performed to examine the soot capture and heat regeneration processes, and characterize the effects of various parameters on these processes and on DPF performance. Results indicate that the pressure drop during soot loading can be reduced by increasing the CPSI (channels per square inch), minimizing the amount of residual soot in each regeneration cycle, and using moderate gas flow rates. The DPF regeneration performance is characterized in terms of the rates of temperature rise and soot oxidation. Results indicate that these rates are enhanced, as the oxygen content in the exhaust stream is increased to about 12%, the rate of thermal heating is moderately increased, and as the exhaust gas flow rate is increased. Thus, the regeneration efficiency can be significantly improving by optimizing these parameters.     

The effect of temperature on PAHs emission from incineration of acrylic waste

Incineration of acrylic waste solution in a lab scale quartz tube vertical incinerator showed the presence of 12–15 polycyclic aromatic hydrocarbons (PAHs) from a list of 16 priority pollutants at 700–1100^˚C after an interval of 50^˚C. The amount of total 16 PAHs at 900 and 1100^˚C was about 8.5 and 1.25 times higher than those at 700^˚C (739.48 μg g⁻¹) respectively. The amount of total probable (2A) and possible (2B) human carcinogenic PAHs was minimum at 700^˚C.     

Effects of black carbon on bioturbation-induced benthic fluxes of polychlorinated biphenyls

It is unknown whether carbonaceous geosorbents, such as black carbon (BC) affect bioturbation by benthic invertebrates, thereby possibly affecting sediment-water exchange of sediment-bound contaminants. Here, we assess the effects of oil soot on polychlorinated biphenyl (PCB) mass transfer from sediment to overlying water, for sediments with and without tubificid oligochaeta as bioturbators. PCB levels were so low that toxicity to the oligochaeta played no role, whereas soot levels and binding affinity of PCBs to soot were so low that pore water PCB concentrations were not significantly affected by binding of PCBs to soot. This setup left direct effects of BC on bioturbation activity as the only explanation for any observed effects on mass transfer. Mass transfer coefficients (K_L) for benthic boundary layer transport were measured by a novel flux method using Empore™ disks as a sink for PCBs in the overlying water. For the PCBs studied (logK_ow 5.2-8.2), K_L values ranged from 0.2 to 2 cm × d⁻¹ in systems without tubificids. Systems with tubificids showed K_L values that were a factor of 10-25 higher. However, in the presence of oil soot, tubificids did not cause an increase in mass transfer coefficients. This suggests that at BC levels as encountered under field conditions, the mechanism for reduction of sediment-water transfer of contaminants may be twofold: (a) reduced mass transfer due to strong binding of the contaminants to BC, and (b) reduced mass transfer of contaminants due to a decrease in bioturbation activity.