并流旋转床气体出口压降数值分析

气体出口是旋转床的重要组成部分,对旋转床流场与气相压降有着重要的影响。研究并流旋转床结构、构建气体出口物理模型,利用RNG k-ε湍流模型,探索不同气体出口结构对并流旋转床流场的影响。模拟结果表明:具有4个切向气体出口的DCRPB3615型旋转床有利于旋转床内速度分布均匀、降低湍动能,减小气相压降。模拟与实验对比表明,DCRPB3615压降比单一径向出口的CRPB3615型旋转床降低10%左右。     

催化型微粒捕集器的再生与压降数值研究

采用新的再生机理对催化型微粒捕集器（CPF）深床捕集微粒的氧化再生过程进行了建模,并将微粒捕集器中的压降分成5个部分分别计算,对其压降特性进行了数值研究。结果表明,新模型对深床捕集微粒的氧化再生计算与实验值吻合良好,比原模型更能反映微粒沉积的实际过程,深床捕集微粒的压降计算值也更精确。在排气流量大、温度高的工况下,深床捕集微粒的压降先迅速增大再减小的现象明显。研究结果能为工程应用提供验证手段,为CPF的优化设计提供依据。     

孔道结构对柴油机DPF压降及再生特性的影响

针对微粒捕集器(DPF)内部碳烟及灰分颗粒特征,运用AVL-Fire软件建立了六边形孔道结构柴油机微粒捕集器模型。针对不同排气流量、进口温度、孔密度、碳烟和灰分沉积量,对六边形孔道及四边形孔道DPF压降特性和碳烟再生特性进行分析,并研究灰分分布形式对不同孔道形状DPF的影响。结果表明:排气质量流量越大,进口温度越高,不同孔道结构的压降敏感性增大;与传统四边形孔道DPF相比,当碳烟沉积量较低时,六边形孔道DPF压降损失较高;随着碳烟沉积量的增加,六边形孔道DPF压降损失较低,且碳烟承载量较大;灰分在DPF孔道表面层状分布可以有效阻止碳烟深床捕集模式,降低压降损失;六边形孔道DPF能够有效提高碳烟及灰分容量,且碳烟捕集及再生效率较高,再生速率较快,热应力较小,可以降低DPF主动再生频率,延长使用寿命。     

基于GT-Power柴油机颗粒捕集器捕集性能的仿真研究

利用GT-Power软件建立了柴油机颗粒捕集器(DPF)仿真模型,进行了仿真计算。研究了颗粒捕集器本身结构参数对其捕集效率与压降的影响。结果表明,影响颗粒捕集器捕集效率的主要参数有通道密度(CPSI)、过滤体孔隙率、过滤体微孔直径以及过滤壁厚度;影响颗粒物压降的主要参数有通道密度、过滤体渗透率、过滤体孔隙率以及过滤壁厚度。     

可旋转径向式微粒捕集器消声特性影响因素灰色关联分析

为降低可旋转径向式微粒捕集器中的排气噪声,采用有限元法建立可旋转径向式微粒捕集器声学特性模型,分析得到了其消声特性和传递损失曲线,并采用灰色关联分析方法研究可旋转径向式微粒捕集器结构参数对消声特性的影响程度。结果表明,可旋转径向式微粒捕集器具有降噪能力,且对高频噪声消声效果明显好于低频噪声,平均消声量为20 dB左右;直径比和扩张管锥角是影响可旋转径向式微粒捕集器消声特性的2个主要因素,适当选用小的直径比和扩张管锥角,有利于提高可旋转径向式微粒捕集器的消声性能。     

循环流化床烟气脱硫系统内压降的建模

循环流化床烟气脱硫系统中的压降是保证反应器安全运行的重要参数,了解反应器内的气固流动状况以及压降分布并对其加以调节是系统稳定运行的关键.通过分析循环流化床内气固两相的流动状态,基于一维轴向流动模型,研究循环流化床烟气脱硫系统内的压降轴向分布特性.模型预测结果表明,压降受烟气流速和循环流量影响下的变化趋势与实验结论一致,证明了模型的有效性.可以用于循环流化床内脱硫传质研究,以及为反应器的设计与运行提供指导.     

移动颗粒床除尘器的除尘性能

为进一步了解移动颗粒床除尘器的除尘性能,首先解决了除尘器中容易出现的流动静止区域的消除问题,并实验研究了除尘效率及压降与表观过滤风速和滤料质量流率之间的关系,结果表明当表观过滤风速为0.3 m·s~(-1),滤料质量流率为300 g·min~(-1)时,除尘效率高达99.8%,压降最大还不及180 Pa。另外,通过数值仿真得到了滤料床层内部气体的流场分布以及灰尘粒子在床层中的运行轨迹,发现除尘器结构部件对气体流场分布以及灰尘粒子轨迹有重要影响。对仿真过程中逃逸出滤料床层的灰尘粒子进行统计,并与实验数据相比较,验证了尘饼对增强细微灰尘捕集能力的重要性。     

伞罩型除尘脱硫塔内除雾器性能研究

除雾器是湿法烟气脱硫(WFGD)系统内重要的设备之一,其性能对WFGD系统运行的可靠性有重要影响.利用Fluent6.2软件对新型伞罩型除尘脱硫塔内的三维两相流场进行数值模拟,气相采用RNG湍流模型,液相采用离散相模型,选择SIMPLE算法进行计算,分析塔内的折板除雾器和旋流板除雾器的速度场、压力场和液滴的分布情况.结果表明,烟气经过折板除雾器,产生了明显的压降,且在拐角区域湍流耗散强烈,是实现气液分离的关键区域;烟气经过旋流板除雾器,速度和压强分布具有良好的对称性,液滴被气流旋转抛向壁面实现气液分离.模拟结果对新型的WFGD除雾器的设计和运行具有一定的理论指导意义.     

城市生活垃圾在机械炉排炉内焚烧过程研究及数值模拟

研究城市生活垃圾在机械炉排炉内焚烧过程,建立了垃圾在炉排炉移动床内燃烧过程中垃圾体积变化、水分蒸发、挥发分析出及燃烧、垃圾颗粒的移动、气-固两相热传递、焦炭燃烧等各个反应阶段的热化学模型,采用一维非稳态模型分别建立了床层内气固两相介质控制方程。通过对炉排上垃圾焚烧过程的数值模拟研究,获得料层中温度分布、料层高度、炉床机械负荷、气相中反应物组分和污染物浓度分布。利用建立的模型对某大型垃圾焚烧炉的燃烧过程进行数值仿真,对燃烧过程、烟气成分进行预测,为垃圾焚烧炉排炉的设计和燃烧控制提供理论依据。     

错流式生物滴滤床净化甲苯废气

采用焦化厂污泥为菌源驯化甲苯降解菌,接种错流式生物滴滤床,净化含甲苯废气。研究了生物滴滤床的挂膜启动和长期运行情况,填料和营养液对滴滤床去除能力的影响,并对长期运行的压降进行了观察分析。反应器挂膜启动需要6 d时间,稳定运行的平均去除效率为95％,单位体积最大去除负荷为251 g/(m³·h)。结果表明,采用错流式生物滴滤床可以有效去除甲苯废气;以比表面积大的生物陶粒作为填料以及定期适量更换营养液,均有助于提高生物滴滤床的去除能力;错流式生物滴滤床具有压降小、气液分布均匀的特点。     

Chloroaromatic pollutants in mussels incubated in two finnish watercourses polluted by industry

Concentrations of different chlorinated compounds were measured in mussels incubated in two polluted watercourses, a river (the River Kymijoki) and a lake (Lake Vanaja) for four weeks in summer 1995. The sum concentrations of polychlorinated phenols (PCP) and biphenyls (PCB) were both about 1 μg/g lipid weight (lw) in Lake Vanaja mussels, while in the River Kymijoki mussels PCPs were non-detectable and PCBs were measured 120 ng/g lIw. The concentrations of toxic polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) congeners ranged between <17 and 370 pg/g Iw in Lake Vanaja mussels and between <38 and 11,000 pg/g lw in the River Kymijoki mussels. Polychlorinated diphenyl ethers (PCDE) were detected in the mussels incubated in the River Kymijoki (0.4–1.1 ng/g Iw), but not in those incubated in Lake Vanaja. Polychlorinated phenoxyanisoles (PCPA) were measured 33 ng/g lw and polychlorinated phenoxyphenols (PCPP) 300 ng/g lw in the mussels incubated in the River Kymijoki. PCPAs were also detected in reference samples, which were sediment and pike from the River Kymijoki and Baltic salmon, seal and white-tailed sea eagle.     

Radionuclides and trace elements in fish collected upstream and downstream of Los Alamos national laboratory and the doses to humans from the consumption of muscle and bone

Abstract

The purpose of this study was to determine radionuclide and trace element concentrations in bottom‐feeding fish (catfish, carp, and suckers) collected from the confluences of some of the major canyons that cross Los Alamos National Laboratory (LANL) lands with the Rio Grande (RG) and the potential radiological doses from the ingestion of these fish. Samples of muscle and bone (and viscera in some cases) were analyzed for ³H, ⁹⁰Sr, ¹³⁷Cs, ^totU, ²³⁸Pu, ^239,240Pu, and ²⁴¹Am and Ag, As, Ba, Be, Cr, Cd, Cu, Hg, Ni, Pb, Sb, Se, and Tl. Most radionuclides, with the exception of ⁹⁰Sr, in the muscle plus bone portions of fish collected from LANL canyons/RG were not significantly (p<0.05) higher from fish collected upstream (San Ildefonso/background) of LANL. Strontium‐90 in fish muscle plus bone tissue significantly (p<0.05) increases in concentration starting from Los Alamos Canyon, the most upstream confluence (fish contained 3.4E‐02 pCi g^‐1 [126E‐02 Bq kg^‐1]), to Frijoles Canyon, the most downstream confluence (fish contained 14E‐02 pCi g^‐1 [518E‐02 Bq kg^‐1]). The differences in ⁹⁰Sr concentrations in fish collected downstream and upstream (background) of LANL, however, were very small. Based on the average concentrations (±2SD) of radionuclides in fish tissue from the four LANL confluences, the committed effective dose equivalent from the ingestion of 46 lb (21 kg) (maximum ingestion rate per person per year) of fish muscle plus bone, after the subtraction of background, was 0.1 ± 0.1 mrem y^‐1 (1.0 ± 1.0 μSv y^‐1), and was far below the International Commission on Radiological Protection (all pathway) permissible dose limit of 100 mrem y^‐1 (1000 μSv y^‐1). Of the trace elements that were found above the limits of detection (Ba, Cu, and Hg) in fish muscle collected from the confluences of canyons that cross LANL and the RG, none were in significantly higher (p<0.05) concentrations than in muscle of fish collected from background locations.     

Book review

The Pesticide Manual ‐ A World Compendium, 8th Edition, C.R. Worthing, Editor and S.B. Walker, Assistant Editor, British Crop Protection Council, BCPC Publications Sales, Bear Farm, Binfield, Bracknell, Berkshire RG12 5QE, England. 1987, 1100 pp., UK £50; Overseas £56. ISBN 0–948404–01–9.     

Patterns of volatile metabolites and nonvolatile trichothecenes produced by isolates of <Emphasis Type="Italic">Stachybotrys,Fusarium, Trichoderma,Trichothecium</Emphasis> and <Emphasis Type="Italic">Memnoniella</Emphasis>

We reported previously that trichodiene, a volatile trichothecene derivative, was produced by a Stachybotrys isolate, also known to produce highly cytotoxic, non-volatile, macrocyclic trichothecenes (satrotoxins). We investigated the relationship between the production of trichodiene and various non-volatile trichothecenes for several molds. Volatile metabolites were concentrated by adsorption on Tenax TA and analyzed by GC/MS, while non-volatile metabolites were separated by HPLC, derivatized and analyzed by GC/MS. Stachybotrys chartarum isolates producing macrocyclic trichothecenes secreted significantly larger amounts of trichodiene and other sesquiterpenes than isolates which only produced simple trichothecenes. The amounts of secreted trichodiene were relatively small in all cases. With the exception of Memnoniella, which excreted small amounts of sesquiterpenes, the other isolates produced varying amounts of sesquiterpenes, including trichodiene, as well as simple tricothecenes, no detectable trichodiene, but large amounts of griseofulvin derivatives. In Stachybotrys there is apparently a correlation between trichodiene and macrocyclic trichothecene production. In the remaining isolates, there was no simple relationship between trichodiene and non-volatile trichothecene synthesis. Trichodiene is produced in larger amounts by Stachybotrys isolates, which also produce satratoxins, but it will be difficult to utilize this metabolite to detect toxic isolates in buildings due to the relatively small amounts excreted.     

Observations on the influence of water and soil pH on the persistence of insecticides

Abstract

The pH‐disappearance rate profiles were determined at ca. 25°C for 24 insecticides at 4 or 5 pH values over the range 4.5 to 8.0 in sterile phosphate buffers prepared in water‐ethanol (99: 1 v/v). Half‐lives measured at pH 8 were generally smaller than at lower pH values. Changes in half lives between pH 8.0 and 4.5 were largest (>1000x) for the aryl carbamates, carbofuran and carbaryl, the oxime carbamate, oxamyl, and the organophosphorus insecticide, trichlorfon. In contrast, half lives of phorate, terbufos, heptachlor, fensulfothion and aldicarb were affected only slightly by pH changes. Under the experimental conditions described half lives at pH8 varied from 1–2 days for trichlorfon and oxamyl to >1 year for fensulfothion and cyper‐methrin. Insecticide persistence on alumina (acid, neutral and basic), mineral soils amended with aluminum sulfate or calcium hydroxide to different pH values and four natural soils of different pH was examined. No correlation was observed between the measured pH of these solids and the rate of disappearance of selected insecticides applied to them. These observations demonstrate the difficulty of extrapolating the pH dependent disappearance behaviour observed in homogeneous solution to partially solid heterogeneous systems such as soil.     

The chemical stability of formulations of some hydrolyzable insecticides in aqueous mixtures with hydrolysis catalysts

Abstract

The active ingredients in commercial formulations of malathion, oxamyl, carbaryl, diazinon, and chlorpyrifos diluted to “spray tank”; concentrations with buffered distilled or natural water of pH 4–9 were stable for at least 24 hr. Formulations of trichlorfon were not stable at pH 7 or above but disappearance rates were slower than for the pure chemical in homogeneous solution. Cupric ion was observed to be an effective catalyst for the hydrolysis of a variety of pure organophosphorus insecticides but did not catalyze hydrolysis of the active ingredients of the formulations examined. Increasing the dilution of the formulation increased the susceptibility of malathion, oxamyl, and carbaryl to hydrolysis.     

Organochlorine compounds in a three-step terrestrial food chain

The concentrations of 15 organochlorine chemicals (PCBs and pesticides) were studied in a Central European oak wood food chain system: Great tit (Parus major), caterpillars (Tortrix viridana, Operophtera brumata, Erannis defoliaria), and oak-leaves (Quercus robur). Juvenile tits receive organochlorines from the mother via egg transfer and, eventually to a greater extent, from the caterpillar food source during nestling period. The concentrations of PCB 153 (2,2′,4,4′,5,5′-hexachlorobiphenyl, the most abundant in this study) was found in leaf material at ca. 1 ng/g, in caterpillars 10 ng/g, and in bird eggs 170 ng/g on an average and on a dry mass basis.     

Radionuclides in deer and elk from Los Alamos national laboratory and the doses to humans from the ingestion of muscle and bone

Abstract

This paper summarizes radionuclide concentrations (³H, ⁹⁰Sr, ¹³⁷Cs, ²³⁸Pu, ^239,240Pu, ²⁴¹Am, and ^totU) in muscle and bone tissue of mule deer (Odocoileus hemionus) and Rocky Mountain elk (Cervus elaphus) collected from Los Alamos National Laboratory (LANL), Los Alamos, New Mexico, lands from 1991 through 1998. Also, the committed effective dose equivalent (CEDE) and the risk of excess cancer fatalities (RECF) to people who ingest muscle and bone from deer and elk collected from LANL lands were estimated. Most radionuclide concentrations in muscle and bone from individual deer (n = 11) and elk (n = 22) collected from LANL lands were either at less than detectable quantities (where the analytical result was smaller than two counting uncertainties) and/or within upper (95%) level background (BG) concentrations. As a group, most radionuclides in muscle and bone of deer and elk from LANL lands were not significantly higher (p<0.10) than in similar tissues from deer (n = 3) and elk (n = 7) collected from BG locations. Also, elk that had been radio collared and tracked for two years and spent an average time of 50% on LANL lands were not significantly different in most radionuclides from road kill elk that have been collected as part of the environmental surveillance program. Overall, the upper (95%) level net CEDEs (the CEDE plus two sigma for each radioisotope minus background) at the most conservative ingestion rate (50 lbs of muscle and 13 lbs of bone) were as follows: deer muscle = 0.22 mrem y^‐1 (2.2 μSv y^‐1), deer bone = 3.8 mrem y^‐1 (38 μSv y^‐1), elk muscle = 0.12 mrem y^‐1 (1.2 μSv y^‐1), and elk bone = 1.7 mrem y^‐1 (17 μSv y^‐1). All CEDEs were far below the International Commission on Radiological Protection guideline of 100 mrem y^‐1 (1000 μSv y^‐1), and the highest muscle plus bone net CEDE corresponded to a RECF of 2E‐06, which is far below the Environmental Protection Agency upper level guideline of 1E‐04.     

Radionuclides in pinon pine (Pinus edulis) nuts from los alamos national laboratory lands and the dose from consumption

Abstract

One of the dominant tree species growing within and around the eastern portion of Los Alamos National Laboratory (LANL), Los Alamos, NM, lands is the pinon pine (Pinus edulis). Pinon pine is used for firewood, fence posts, and building materials and is a source of nuts for food—the seeds are consumed by a wide variety of animals and are also gathered by people in the area and eaten raw or roasted. This study investigated the (1) concentration of ³H, ¹³⁷Cs, ⁹⁰Sr, ^totU, ²³⁸Pu, ^{239, 240}Pu, and²⁴¹ Am in soils (0‐ to 12‐in. [31 cm] depth underneath the tree), pinon pine shoots (PPS), and pinon pine nuts (PPN) collected from LANL lands and regional background (BG) locations, (2) committed effective dose equivalent (CEDE) from the ingestion of nuts, and (3) soil to PPS to PPN concentration ratios (CRs). Most radionuclides, with the exception of ³H in soils, were not significantly higher (p < 0.10) in soils, PPS, and PPN collected from LANL as compared to BG locations, and concentrations of most radionuclides in PPN from LANL have decreased over time. The maximum net CEDE (the CEDE plus two sigma minus BG) at the most conservative ingestion rate (10 lb [4.5 kg]) was 0.0018 mrem (0.018 μSv); this is far below the International Commission on Radiological Protection (all pathway) permissible dose limit of 100 mrem (1000 μSv). Soil‐to‐nut CRs for most radionuclides were within the range of default values in the literature for common fruits and vegetables.     

Degradation and sorption of imidacloprid in dissimilar surface and subsurface soils

Degradation and sorption/desorption are important processes affecting the leaching of pesticides through soil. This research characterized the degradation and sorption of imidacloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine) in Drummer (silty clay loam) and Exeter (sandy loam) surface soils and their corresponding subsurface soils using sequential extraction methods over 400 days. By the end of the incubation, approximately 55% of imidacloprid applied at a rate of 1.0 mg kg^?1 degraded in the Exeter sandy loam surface and subsurface soils, compared to 40% of applied imidacloprid within 300 days in Drummer surface and subsurface soils. At the 0.1 mg kg^?1 application rate, dissipation was slower for all four soils. Water-extractable imidacloprid in Exeter surface soil decreased from 98% of applied at day 1 to > 70% of the imidacloprid remaining after 400 d, as compared to 55% in the Drummer surface soil at day 1 and 12% at day 400. These data suggest that imidacloprid was bioavailable to degrading soil microorganisms and sorption/desorption was not the limiting factor for biodegradation. In subsurface soils > 40% of ¹⁴C-benzoic acid was mineralized over 21 days, demonstrating an active microbial community. In contrast, cumulative ¹⁴CO₂ was less than 1.5% of applied ¹⁴C-imidacloprid in all soils over 400 d. Qualitative differences in the microbial communities appear to limit the degradation of imidacloprid in the subsurface soils.