Mixing Of Chemicals Research Articles

Application of ZW-1000 membranes for arsenic removal from water sources

The quality of the drinking water supply has become more important with Hungary's entry into the European Community. In some regions of the country, similar to many parts of the world, arsenic removal from drinking water is an urgent task to supply water with an arsenic content under 10 μg/l. We have worked out a new technology for arsenic removal using a membrane technique. Measurements on site were performed in a pilot plant with equipped with a pre-treatment system and a ZW-1000 (Zenon) membrane module. Before expanding the technological process, experiments on laboratory scale were done to find out which kind of pre-treatment and membrane configuration are needed. These experiments were performed with water from deep wells, among them with a high arsenic concentration (200–300 μg/l). The steps of the pre-treatment process were: oxidation with potassium permanganate (KMnO4), coagulation with ferrous(III) sulphate (Fe2(SO4)3), fast mixing of chemicals with a mixer, coagulation with slow mixing and settlement. Following membrane separation, the arsenic concentration was under the permitted value (10 μg/l). Results of experiments on site proved that the new technology was successful and is suitable to produce drinking water at the required quality from raw water with a high arsenic content in a pilot plant.

A COMPUTERIZED, SMALL-PLOT SPRAY EVALUATION SYSTEM WITH VARIABLE PIPETTER

A small plot pesticide evaluation system is described that includes a computer-controlled tractor-mounted spray system, an automatic pipetter for filling bottles used on the spray tractor, and a computer program for computation of amounts of adjuvants and pesticides to be added to a pre-set volume of carrier to result in a specific mixture concentration. Benefits of the system include fast, accurate mixing of chemicals in replicate, precise spraying of pesticide, computer-controlled rinsing of the system, and reduced operator fatigue.

Mixing and geometry of advected, chemically reactive scalar fields: Application to chlorine deactivation over the midnorthern latitudes

The mixing and reaction properties of advected chemicals are determined by the fractal dimension (or Kolmogorov capacity) D′ of a cut through the interface between the chemicals. We show that the amount m of reacted chemicals scales like where κ is diffusivity of the chemicals. If interscale transfer produced by the advecting flow has a linear time dependence, then the reaction rate of chemicals scales like with time t. Both relations are valid in a range of times and diffusivities where the diffusive length scales of the chemicals are within the range of scales where the interface between the chemicals has a well‐defined fractal dimension. We apply both relations to the problem of chlorine deactivation, ClO + NO2 → ClONO2, over the midnorthern latitudes. We determine numerically the Kolmogorov capacity of the interface between polar air which is comparatively rich in ClO and midlatitude air which is comparatively rich in NO2. Additionally, we show empirically that interscale transfer by the advecting flow can be well interpreted as having predominantly linear interscale transfer in the range of times under consideration. We can therefore explain diffusivity and time dependencies previously observed in numerical simulations. Furthermore we can extrapolate the results of such simulations down to realistically low diffusivities.

Measuring intense rotation and dissipation in turbulent flows.

Turbulent flows are highly intermittent--for example, they exhibit intense bursts of vorticity and strain. Kolmogorov theory describes such behaviour in the form of energy cascades from large to small spatial and temporal scales, where energy is dissipated as heat. But the causes of high intermittency in turbulence, which show non-gaussian statistics, are not well understood. Such intermittency can be important, for example, for enhancing the mixing of chemicals, by producing sharp drops in local pressure that can induce cavitation (damaging mechanical components and biological organisms), and by causing intense vortices in atmospheric flows. Here we present observations of the three components of velocity and all nine velocity gradients within a small volume, which allow us to determine simultaneously the dissipation (a measure of strain) and enstrophy (a measure of rotational energy) of a turbulent flow. Combining the statistics of all measurements and the evolution of individual bursts, we find that a typical sequence for intense events begins with rapid strain growth, followed by rising vorticity and a final sudden decline in stretching. We suggest two mechanisms which can produce these characteristics, depending whether they are due to the advection of coherent structures through our observed volume or caused locally.

Diffusivity dependence of ozone depletion over the midnorthern latitudes.

The mixing and reaction properties of advected chemicals (and passive scalars) are determined by the fractal dimension D of the interface between the chemicals. We show that the scaling of the amount m of reacted chemicals with diffusivity kappa is m(0)-m(kappa) proportional, proportional to kappa(1-D/2) in the two-dimensional case. This relation is valid in a range of times and diffusivities where the diffusive length scales of the chemicals are within the range of scales where the chemical interface has a well-defined fractal dimension. We apply the relation to the problems of chlorine deactivation and ozone depletion over the midnorthern latitudes. We determine numerically the fractal dimension of an interface advected by stratospheric winds. This allows us, first, to explain the diffusivity dependence of chlorine deactivation and ozone depletion that was previously observed in numerical simulations (Tan et al., J. Geophys. Res., [Atmos.] 103, 1585 (1998)) and, second, to extrapolate the results of such simulations down to realistically low diffusivities.

Mixmaster exposure to dust during mixing of wildland fire retardant chemicals

A study was performed at two air tanker/retardant bases to determine the mixmaster’s exposure to dust derived from mixing dry fire retardant compounds. Personal sampling for both inhalable and respirable dust was conducted while the mixmaster mixed fire retardant compounds to form a retardant slurry. Personal samples were also analysed for a colorant in the retardants and hydrogen cyanide. Hazard quotients were calculated for average and upper-end use scenarios using a risk assessment model from Labat-Anderson, Incorporated. The exposure analysis revealed that the 8-h time weighted average (TWA) concentrations were within applicable occupational exposure limits for the inhalable and respirable dust fractions as well as for the colorant and hydrogen cyanide. When the mean inhalable exposure concentration was used to calculate chemical intake, hazard quotients were above 1 at both retardant bases, indicating a potential for non-carcinogenic health effects. Exposure control methods recommended from this study include substitution of a liquid concentrate fire retardant, installation of local exhaust ventilation systems, good housekeeping and personal hygiene. We also recommend the use of personal protective equipment including a filtering facepiece, half-mask respirator; eye protection, and protective clothing such as gloves and coveralls.

Mixing with multiple circular turbulent jets

This paper presents the results of a laboratory study investigating chemical mixing in an open channel with multiple circular turbulent jets. The experiments were carried out for a, which is the ratio of the velocity of the jets to that of the crossflow, varying from 8 to 16, with a combination of coflowing and crossflowing jets and only crossflowing jets. The number of ports for the jets was varied for 20 to 36 and the spacing between the ports was varied from 12d to 24d where d is the diameter of the ports. Concentration measurements covered the relative distance x/d=2000, where x is the longitudinal distance from the diffuser. The dimensionless mixing distance cum/d at which the standard deviation of the concentration field reached a value of 5% was equal to 25000 where xm is the mixing distance. The results indicate that a diffuser with turbulent crossflowing jets could be an alternative to mechanical methods for achieving mixing of chemicals in open channels in water treatment plants.

CESAM: A code for stellar evolution calculations

The code CESAM is a consistent set of programs and routines which performs calculations of 1D quasi-static stellar evolution including diffusion and rotation. The principal new feature is the solution of the quasi-static equilibrium by collocation method based on piecewise polynomials approximations projected on their B-spline basis; that allows stable and robust calculations and the exact restitution of the solution not only at grid points. Another advantage is the monitoring by only one parameter of the accuracy and its improvement by superconvergence. An automatic mesh refinement has been designed for adjusting the localizations of grid points according to the changes of unknowns, each limit between a radiative and a convective zones being shifted to the closest grid point. For standard models, the evolution of the chemical composition is solved by stiffly stable schemes of orders up to four; for non-standard models the solution of the diffusion equation employs the Petrov-Galerkin scheme, with the mixing of chemicals in convective zones performed by strong turbulent diffusion. A precise restoration of the atmosphere is allowed for. CESAM computes evolution of stars from the pre-main sequence to the beginning of the 4He burning cycle. In this paper a detailed description of the algorithms is presented.

Effect of food type and placement on earthworm (Aporrectodea tuberculata) burrowing and soil turnover

Subsurface-dwelling Aporrectodea tuberculata, a common earthworm in Upper-Midwest (USA) agricultural fields, may be a significant component of agroeco-systems with regard to soil mixing and preferential transport of water and chemicals. In this study we looked at effects of food residue placement and food type on A. tuberculata burrowing and soil turnover in two-dimensional Evans box microcosms. Four food residue placements mimicked patterns induced by primary tillage and two food types, readily available and natural food sources, with no food as a control. An average earthworm population of 100 earthworms m-2 was calculated to generate 1058 km ha-1 of new burrows and turnover 7.9 Mg ha-1 of soil in 1 week of activity at 20°C. Burrowing was random until food sources were encountered, at which time burrowing appeared to center around the food source.

Determinants of safe behaviour in farmers when working with pesticides.

Despite stringent regulation, accidents occur in the use of pesticides. To explore the factors which might influence farmers' approaches to safety when handling chemicals, we interviewed 84 agricultural workers from south-west Hampshire who reported having worked with pesticides in the previous 12 months. Most of those interviewed claimed that they always followed manufacturers' instructions regarding indications for use, method of application, mixing of chemicals, cleaning up and washing hands, but compliance was lower for recommendations about personal protective equipment and disposal of containers. Only 38% of subjects said that they always read all of the manufacturer's label when using a product for the first time. The main determinant of safe behaviour was the person's approach to safety in other situations, but formal training in the use of pesticides was also associated with more frequent use of personal protective equipment. Possession of a certificate of competence in pesticide use appeared to have less influence on working methods. Future efforts should be directed at changing farmers' handling of pesticides.

Interfacial Mixing of Urethane Foam Chemicals

Interfacial Mixing of Urethane Foam Chemicals

Enhancing Thermal Hazard Awareness with Compatibility Charts

Abstract Compatibility (or Inter-Reactivity) charts provide a rapid and straightforward approach to the plant-wide dissemination of hazards associated with the inadvertent mixing of chemicals. This paper will describe The Dow Chemical Company's approach to the building and use of these charts. Incorporation of compatibility charts in safety and routine process chemistry training and for hazard evaluation will also be described. The benefits of using a personal computer to generate uniform charts will be addressed.

Complex mixtures in industrial workspaces: lessons for indoor air quality evaluations.

Acceptable occupational exposure levels for hundreds of airborne concentrations of dusts, vapors, fumes, and gases have been set by consensus organizations and regulatory bodies for decades. These levels have established tremendous precedent and are tempting reference values in the relatively new field of indoor air quality evaluations where validated criteria are greatly needed. The American Conference of Government Industrial Hygienists (ACGIH) has been the most visible and productive group setting these guidelines for industrial exposure. The ACGIH Chemical Substances Committee has published an annual list of threshold limit values (TLVs) for more than 40 years. Currently the list covers more than 400 substances. In 1989, the Occupational Safety and Health Administration (OSHA) published updated permissible exposure limits (PELs) for approximately 600 substances. Most PELs before this update were adopted from the 1968 ACGIH list of TLVs and consensus standards of the American Standards Association. This OSHA update has resulted in reductions of 212 PELs and the addition of 164 new levels. The magnitude of the problem of protecting workers can be seen by the small fraction that the OSHA PELs represent of the more than 60,000 entries in the National Institute for Occupational Safety and Health's Registry of Toxic Effects of Chemical Substances. None of these levels, whether guidelines or regulatory requirements, are established based on any possible synergistic effect with other chemicals. The only guidance given by the ACGIH for synergistic effects is that such cases must be determined individually. Clearly, there are major drawbacks in using occupational standards and guidelines for evaluating the health effects of chemical agents that can be found in office settings, often in concentrations orders of magnitude less than what is routinely measured in the workplace. These guidelines are even less valuable when the concern is the complex mixing of chemicals in nonoccupational environments.

Automatic Coagulation Control at Water‐Treatment Plants in the North‐West Region of England

North West Water has evaluated several automatic coagulation control systems covering a range of raw waters and treatment facilities.The experiences have shown that streaming‐current type systems are effective in controlling coagulant dose automatically, provided that appropriate plant conditions exist. In particular, rapid fluctuations in flow or poor mixing of chemicals can lead to unstable signals. Recent investigations indicate that for some waters streaming‐current voltage is sensitive to small changes in pH, and precise control of pH is therefore necessary.The main observed benefits have been treated water of a more consistent high quality, together with improved security of service, as the systems will respond reliably and effectively over long periods. Significant savings in coagulant usage can be obtained in certain cases.

Chemical process hazard identification

Abstract The impact of unwanted chemical reactions in the chemical process industry has been investigated. The approach used to answer the basic questions of origin, occurence and importance of unwanted chemical reactions was a study of accident case histories. In total 190 accident case histories were analysed. The most important reasons for unwanted chemical reactions were found to be: impurities, contaminations and stray catalysts (20%), mixing of wrong chemicals (19%), mischarging, incorrect process conditions (19%), and insufficient mixing (13%). A checklist for identifying unwanted chemical reactions is proposed. The checklist comprises 18 tables in all and is structured in four main groups: materials, reaction mixture, unwanted reactions, and standard methods.

Risk analysis of a warehouse for the mixing, repackaging and distribution of organic chemicals

Abstract The EEC directive on ‘Major Accident Hazards of Certain Industrial Activities’ has been implemented in Denmark. This means that risk analyses of some activities must be made before July 1989. One of the first plants that was analysed was a warehouse for the mixing, repackaging and distribution of organic chemicals. The analysis was performed as a commercial contract by Riso National Laboratory. The report has been submitted to the authorities but the plant has not yet been approved due to submission of a large amount of analyses of other plants. This paper illustrates how a risk analysis of a chemical plant can be made.

Occurrence and impact of unwanted chemical reactions

Abstract The impact of unwanted chemical reactions in the chemical process industry has been investigated by analysing 190 accident case histories. Accidents in batch reactors were reported more frequently than those in continuous process plant: 57% and 10%, respectively. A remarkable result was that a relatively large percentage of the accidents (24%) occurred during a holding or storage operation. The most important reasons for unwanted chemical reactions were found to be the presence of impurities, contaminations, stray catalysts (20%), mixing of wrong chemicals (19%), mischarging, incorrect process conditions (19%), and insufficient mixing (13%). In 55% of the cases, it was found that the accident probably could have been foreseen by applying risk analysis methods (hazard and operability study, action error analysis, etc.). and in 32% by use of laboratory tests (differential scanning calorimetry, differential thermal analysis, etc.). In 15% of the cases, it was not possible to suggest a method which could have pointed out the hazard. These cases involved impurities and contaminations or lack of thermochemical knowledge.

Hazards of inadvertent mixing of chemicals used in the Bachmann processes for manufacturing the military explosives RDX and HMX

Reactivity tests were conducted and a CHETAH diagram constructed to evaluate the hazards of inadvertent mixing of chemicals used at Holston Army Ammuni certain combinations of Bachmann chemicals, initially at ambient temperatures, were found to generate fires spontaneously. Other combinations spontaneo

Survey of the presence and methods of control of wild oat, black grass and couch grass in cereal crops in the United Kingdom during 1977

SUMMARYIn summer 1977 a random survey was made of 2250 fields on 1153 farms selected throughout the United Kingdom. Wild oat, Avena spp., was surveyed in all countries; black grass, Alopecurus myosuroides, was surveyed in England and Wales; and couch grass, including Agropyron repens and other perennial grasses, in Scotland and N. Ireland.Wild oat was reported by farmers on 95% of farms in England, 34% in Wales, 65% in Scotland and 30% in N. Ireland; the areas of infestation in the different countries were 67, 13, 37 and 16% respectively. The majority of wild oat was A.fatua. Only 6% of the cereal area of U.K., including sprayed and unsprayed fields, contained more than one wild oat seed head/m2 (10000/ha), the majority had less than one/20 m2. Black grass was reported on 50% of farms in England (22% of cereal area) mainly in East and South, and on 2% of farms in Wales. Couch grass occurred on 92% of farms in Scotland and 68% in N. Ireland: areas of infestation were 88 and 67% respectively. Most of the infestations of all three weeds had been present for longer than 5 years.Most farmers intended to eliminate or reduce wild oat and few proposed to hold the weed at its present level or do nothing. Herbicides were used against wild oat on approximately half of the infested area in England and Wales, with proportionately more use in Wales and much less in Scotland and N. Ireland. A third of the black grass infested area of England was treated with a herbicide. There was little spraying against couch grass in Scotland and N. Ireland. Details of dose, time of application and mixing of chemicals were obtained. Wild oat was subsequently found on most of the area treated against this weed, similar observations were made of black grass and couch grass. Most farmers considered herbicide performance good or excellent and those in East and South England believed wild oat to be decreasing as a problem; farmers elsewhere thought the problem to be increasing.Hand pulling of wild oat (roguing) had occurred on only one tenth of the infested area but a greater area was intended to be rogued after the survey visit. Much of the land that had been rogued was found subsequently to contain few wild oats.The survey provided information on associations between weed presence, soil type and cropping system, the types of herbicide used and farmers’ impressions of their performance. Comparisons are made with previous surveys in 1972, and information on the disposal of the 1976 crop of straw and on types of cultivation used in different regions is provided. The implications of the results are discussed.

Patent Office: Progress and Change

Patent Office: Progress and Change