Effect of Dust Concentration Upon the Gas-Flow Capacity of a Cyclonic Collector

The flow rate through an industrial gas-cleaning cyclone at a fixed pressure drop is greater when the incoming gas is dusty than when it is clean. This observation by Briggs for a single cyclone tube was extended to multiple tubes, and ike results compared to observations by Soo and Trezek that the fraction factor for turbulent flow in a pipe is less for dusty gas than for clean. Empirical considerations indicated tJtat both of these observations should be connected with a rather large reduction in gas viscosity due to the dust. This predicted viscosity decrease was later observed. A physical theory accounting for viscosity reduction by a dust cloud is proposed. This effect also offers a means for increasing the heat, transfer coefficient in gas heat exchangers.     

Numerical studies of the heterogeneous combustion of char using detailed chemistry

The oxidation of graphite is used as a model system for the combustion of char. In order to understand this oxidation process a stagnation-point flow of an oxygen stream on a graphite surface is investigated numerically. The chemical reactions in the gas phase as well as on the surface are modelled by a series of elementary steps. The surface reactions take into consideration the different surface complexes formed, the influence of the geometry of the graphite surface and the interaction of gas-phase molecules with surface complexes. The rate coefficients used are estimated by applying methods of the microkinetic analysis of heterogeneous catalytic reactions. The mechanism is used to simulate the combustion rate of a graphite surface and the ratio of CO to CO2 formed on the surface. The simulation results are compared with experimental data and a good agreement is achieved. Furthermore, the fraction of char-bound nitrogen converted to N2 and N2O is calculated.     

Environmental Persistence of Chemicals

- DOI: http://dx.doi.org/10.1065/espr2006.01.008 Background The hazard criterion of persistence as it applies to chemicals in the environment is reviewed and discussed. This quantity can not be measured directly in the environment, thus it must be estimated using models that synthesise information on chemical half-lives and partitioning properties, the nature of the environment and how the chemical is released into the environment. Main Features It is suggested that the preferred criterion is the average residence time of the chemical in the environment, i.e. conceptually the sum of the life-times of all molecules (attributable only to losses by degrading reactions) divided by the number of molecules. If all chemical fate processes are first order, this persistence is independent of the quantity of chemical introduced and whether introduction is steady- or unsteady-state in nature. It is shown that in a multimedia environment persistence is affected not only by degradation kinetics, but also by mode-of-entry and partitioning. For screening level purposes a Level II equilibrium model may be adequate but a Level III model is generally preferable for estimating the average persistence. If a distribution of persistences is required a dynamic Level IV model must be used. Discussion The implications for regulating chemicals on the basis of persistence are discussed. Conclusion It is concluded that the preferred strategy is to use Level II, III, and IV models and that the use of only degradation kinetics or media-specific half-lives can be misleading and uneconomical.     

造纸废水混凝处理中SFT助凝替代性研究

中小造纸厂废水处理常用PAC作混凝剂 ,PAM作助凝剂。由于PAM成本很高 ,影响了处理设备的投运率。用超细滑石粉 (SFT)替代PAM助凝 ,与混凝剂PAC配合 ,其混凝处理效果基本相当 ,但是处理成本降低 0 .10元 /m3 。由于SFT属环境无害材料 ,不会给排泥带来二次污染     

Evaluation of a simplified top-down model for the spatial assessment of hot traffic emissions in mid-sized cities

Traffic emission estimation in developing countries is a key-issue for air pollution management. In most cases, comprehensive bottom-up methodologies cannot be applied in mid-sized cities because of the resource cost related to their application. In this paper, a simplified emission estimation model (SEEM) is evaluated. The model is based on a top-down approach and gives annual global hot emission. Particular attention is paid to the quality of the input traffic data. The quality of results is assessed by application of the SEEM model in the Chilean Gran Concepción urban area and by comparison with a bottom-up approach that has been led for the year 2000. The SEEM model estimates emissions with an accuracy of about $20\%$ and is related to important resource savings. The results of the SEEM model are then distributed in space with a disaggregation approach and using GIS techniques. The relevancy of the disaggregation approach is evaluated among several possibilities through statistical methods. A spatial disaggregation using principal roads density gives the best results in terms of emissions repartition and gives a globally accurate image of the distribution of hot emissions in a mid-sized city.     

Analysis of chemical and physical effects of ultraviolet bulbs on cooking emissions

There is a growing recognition of the risks to health, fire hazard, and air quality from cooking emissions. Recent research has identified what is emitted when foods are cooked. Some of the emitted mass is captured in the exhaust system. The balance is expelled into the atmosphere. The outlet of the exhaust system is a demarcation point-upstream the captured mass is the operator or building owner's concern, whereas downstream into the atmosphere, it affects air quality. Building codes have long required operators to deal with the upstream section. More recently, regulations are being placed on what kitchens can emit to the atmosphere. The industry is responding to this challenge with product innovations. Recently gained understanding of cooking emissions supports much of the innovation-but not all. This paper evaluates the purported benefit of adding better filtration and ultraviolet C (UVC) bulbs in kitchen hoods. A "UV hood" claims a two-step process to reduce emissions: better filters capture more emitted mass, and UVC photons and ozone drive photo-decomposition and oxidation reactions of some of the remaining greasy constituents. Adding UV to a hood at least doubles the cost compared to an equivalent non-UV hood. There is evidence that UV hoods do reduce some emissions. The essential question is whether improved performance is due to UV or relatively inexpensive, improved filters. Experimentation exposed an oleic acid aerosol, representative of cooking emissions, to UVC energy and ozone at higher concentrations and for longer exposure times than can occur in a UV hood. Particle-size and chemical changes were measured on samples collected with UV bulbs off and on. Results strongly indicate little change is happening and most emission reductions are caused by better filtration and not UV. The conclusion is that UV hoods fall short of claimed performance, and unreacted ozone may increase air pollution.     

Study of microbes having potentiality for biodegradation of plastics

Plastic is a broad name given to the different types of organic polymers having high molecular weight and is commonly derived from different petrochemicals. Plastics are generally not biodegradable or few are degradable but in a very slow rate. Day by day, the global demand of these polymers is sharply increasing; however, considering their abundance and potentiality in causing different environmental hazards, there is a great concern in the possible methods of degradation of plastics. Recently, there have been some debates at the world stage about the potential degradation procedures of these synthetic polymers and microbial degradation has emerged as one of the potential alternative ways of degradation of plastics. Alternatively, some scientists have also reported many adverse effects of these polymers in human health, and thus, there is an immediate need of a potential screening of some potential microbes to degrade these synthetic polymers. In this review, we have taken an attempt to accumulate all information regarding the chemical nature along with some potential microbes and their enzymatic nature of biodegradation of plastics along with some key factors that affect their biodegradability.     

加压溶气气浮设备理论溶气量的计算

本文通过对加压溶气过程的分析 ,建立了理想加压溶气过程模型 ,在此基础上推导出新的理论溶气量计算公式 ,并与现有的计算公式进行了比较。     

Determination of the required surface area of a final clarifier for an activated-sludge system.

A generic methodology for determining the required surface area of a final clarifier is presented. Clarification and thickening requirements are integrated to form a unified procedure for final clarifier design. The new method is based on results obtained by Yuen (2002) on the solids flux theory for a secondary clarifier; it does not require the specification of recycle rate, which is computed as an output of the method. The author shows that there is a minimum required surface area (A(m)) for a final clarifier under the thickening requirement when the designed recycle rate is set at the maximum allowable value (FR)m (at the critical state). The designed surface area and the return activated sludge pumping capacity can be determined by applying a safety factor to A(m) and (FR)m, respectively. The method is shown to conform to conventional design criteria under typical design conditions.     

Assessing the environmental fate of chemicals of emerging concern: a case study of the polybrominated diphenyl ethers

It is suggested that assessments of chemicals of emerging concern can be rationally structured around a multistage process in which fate and risk are evaluated with increasing accuracy as new data become available. An initial tentative and approximate assessment of fate and risk can identify key data gaps and justify and direct further investigations, which progressively improve the reliability of the assessment. This approach is demonstrated for a class of chemicals, the polybrominated diphenyl ethers (PBDEs), which is of increasing concern, but about which there is presently a lack of comprehensive data on properties, sources, fate and effects. Specifically, 20 PBDE congeners are investigated using the suggested approach and research needs are identified.     

Eulerian derivation of the fractional advection-dispersion equation

A fractional advection-dispersion equation (ADE) is a generalization of the classical ADE in which the second-order derivative is replaced with a fractional-order derivative. In contrast to the classical ADE, the fractional ADE has solutions that resemble the highly skewed and heavy-tailed breakthrough curves observed in field and laboratory studies. These solutions, known as alpha-stable distributions, are the result of a generalized central limit theorem which describes the behavior of sums of finite or infinite-variance random variables. We use this limit theorem in a model which sums the length of particle jumps during their random walk through a heterogeneous porous medium. If the length of solute particle jumps is not constrained to a representative elementary volume (REV), dispersive flux is proportional to a fractional derivative. The nature of fractional derivatives is readily visualized and their parameters are based on physical properties that are measurable. When a fractional Fick's law replaces the classical Fick's law in an Eulerian evaluation of solute transport in a porous medium, the result is a fractional ADE. Fractional ADEs are ergodic equations since they occur when a generalized central limit theorem is employed.     

The foundations of environmental decision-making

An account of judgement is developed, which is used to show that deliberative procedures can provide a substantially different input to environmental decision-making from that afforded by cost-benefit analysis and, specifically, by the method of contingent valuation. It is argued that environmental concern typically invokes values, which are in turn formed and expressed through the exercise of judgement – itself the outcome of a deliberative rather than a calculative process. It is concluded that environmental concern is more effectively articulated through deliberative procedures than through the method of cost-benefit analysis.     

Control of Photochemical Smog by Alteration of Initial Reactant Ratios

This paper is an endeavor to show how several experimenters have quite closely equaled the results of the other, and how the results from these various laboratories can, by a change of coordinate system, be related to each other in a systematic manner. Only after demonstrating where the Los Angeles Civic Center atmosphere is in relation to these coordinates and the contours, or gradients, of these various effects, eye irritation and oxidant, is it possible to predict the photochemical effect of a reduction of olefins (hydrocarbons) or the reduction of nitric oxide. In addition, a study of the variation in eye irritation with irradiation time, demonstrates that the time at which eye irritation measurements are taken is important in understanding the entire photochemical mechanism underlying the “smog” problem in the summertime in Los Angeles     

Thermally assisted mechanical dewatering (TAMD) of suspensions of fine particles: analysis of the influence of the operating conditions using the response surface methodology

Thermally assisted mechanical dewatering (TAMD) is a new process for energy-efficient liquid/solids separation which enhances conventional-device efficiency. The main idea of this process is to supply a flow of heat in mechanical dewatering processes to favour the reduction of the liquid content. This is not a new idea but the proposed combination, especially the chosen operating conditions (temperature <100 degrees C and pressure <3000 kPa) constitutes an original approach and a significant energy saving since the liquid is kept in liquid state. Response surface methodology was used to evaluate the effects of the processing parameters of TAMD on the final dry solids content, which is a fundamental dewatering parameter and an excellent indicator of the extent of TAMD. In this study, a two-factor central composite rotatable design was used to establish the optimum conditions for the TAMD of suspensions of fine particles. Significant regression models, describing changes on final dry solids content with respect to independent variables, were established with regression coefficients (usually called determination coefficients), R(2), greater than 80%. Experiments were carried out on a laboratory filtration/compression cell, firstly on different compressible materials: synthetic mineral suspensions such as talc and synthetic organic suspensions such as cellulose, and then on industrial materials, such as bentonite sludge provided by Soletanche Bachy Company. Experiment showed that the extent of TAMD for a given material is particularly dependent on their physical and chemical properties but also on processing parameters.     

Diffusion of an instantaneous cluster of particles in homogeneous turbulence

In this work we study the diffusion of instantaneous puffs vs the diffusion of continuous plumes. The model which we use is a Lagrangian model for the motion of N particles suggested by Kaplan and Dinar (1988, J. compt. Phys. 79, 317–335). This model is based on the approach of Richardson to the relative diffusion which states that the instantaneous relative velocity of particles is a function of their instantaneous separation. Results show that the diffusion of a puff is slower than that of a continuous source. We find that the puff evolves more slowly than in the analytic model of Lee and Stone (1983, Atmospheric Environment17, 2477–2481), since in their model diffusion is influenced only by the initial conditions. The effect of the source size on the diffusion rate is studied as well.     

Assessment of the sustainability of technology by means of a thermodynamically based life cycle analysis

Life cycle analysis is one of the tools in the assessment of the sustainability of technological options. It takes into account all effects on the ecosystem and the population which may endanger the possibilities of current and future generations. However, the main bottleneck in current LCA methodologies is the balancing of different effects, being all quantified on different scales. In this work, a methodology is proposed, which allows one to quantify different effects of the production, consumption and disposal of goods, and services on a single scale. The basis of the methodology is the second law of thermodynamics. All production, consumption and disposal processes affecting the ecosystem and the population, are quantified in terms of loss of exergy. The exergy content of a material is the maximum amount of energy which can be transformed into work at given environmental conditions. Next to the elaboration of the methodology, the new approach is illustrated by examples of the production of synthetic organic polymers, inorganic building insulation materials and different waste gas treatment options.     

Assessment of bioconcentration and secondary poisoning of surfactants

The relevance of the bioconcentration behaviour of surfactants for the secondary poisoning assessment and for the risk characterisation in the bird and mammalian food chain has been investigated. The approach used is described in the recently revised EU Technical Guidance Document for the Risk Assessment of Substances. The results demonstrate that, based on experimentally derived bioconcentration factors, environmental concentrations and effects in animals, there is a clear level of safety for both linear alkylbenzene sulphonate (LAS) and alcohol ethoxylates (AE), the most important surfactants by volume. To assess other surfactants used in detergents, a bioconcentration factor that would need to be attained for secondary poisoning to be of concern has been estimated from predicted environmental concentrations and known long-term effects data in animals. Based on the known structural similarity of these surfactants to LAS and AE and the ubiquitous nature of the enzymatic systems that are present in biotransformation processes in organisms, it is concluded that bioconcentration of these surfactants to these levels is highly unlikely. Therefore the potential for secondary poisoning effects of these surfactants is extremely low.     

Determination of aromatic hydrocarbons in submicrogram quantities in aqueous systems by means of high performance liquid chromatography

One liter of the water sample is extracted with 1,1,2-trichlorotrifluoroethane. This non-polar solvent with a low boiling point is then concentrated and a portion of the concentrated extract is injected in a high performance liquid chromatography system. Polar material is separated from the hydrocarbons by means of a silica gel column. The detector measures the UV absorbance at 254 nm at which wavelength aromatic compounds absorb especially well. The quantitative values are given as phenanthrene equivalents and amounts as small as 20 ng/l can be detected. The standard deviation of the method is ± 50 ng/l. Both these values can be improved with a limited amount of difficulty. A concentrated sample extract can be injected and evaluated in less than 6 minutes, and the method is simple enough to have been used at sea.     

Co-injection of air and steam for the prevention of the downward migration of DNAPLs during steam enhanced extraction: an experimental evaluation of optimum injection ratio predictions

When steam is injected into soil containing a dense volatile non-aqueous phase liquid contaminant, the DNAPL vaporized within the heated soil region condenses and accumulates ahead of the steam condensation front. If enough DNAPL accumulates, gravitational forces can overcome trapping forces allowing the liquid contaminant to flow downward. By injecting air with steam, a portion of the DNAPL vapor remains suspended in equilibrium with the air, decreasing liquid contaminant accumulation ahead of the steam condensation front, and thus reducing the possibility of downward migration. In a previous work, a theoretical model was developed to predict the optimum injection ratio of air to steam that would eliminate accumulation of DNAPL ahead of the temperature front and thus minimize the potential for downward migration. In this work, the theoretical model is summarized, and an experiment is presented in order to evaluate the optimum injection ratio prediction. In the experiment, a two-dimensional water saturated sand pack is contaminated with a known mass of TCE (DNAPL). The system is then remediated by co-injecting air and steam at the predicted optimum injection ratio, calculated based on the average contaminant soil concentration in the sand pack. Results for the co-injection of air and steam are compared to results for the injection of pure steam or pure air. Injection at the predicted optimum injection ratio for a volumetric average NAPL saturation, reduced accumulation of the contaminant ahead of the condensation front by over 90%, as compared to steam injection alone. This indicates that the optimum injection ratio prediction is a valuable tool for limiting the spreading of DNAPL during steam-enhanced extraction. Injection at the optimum injection ratio resulted in earlier recovery of contaminant than for steam injection alone. Co-injection of steam and air is also shown to result in much higher recovery rates than air injection alone.