E. Chessor, SOEH, UBC, Vancouver, BC, Canada; K. Johansson, Highland Valley Copper, Logan Lake, BC, Canada.
Highland Valley Copper is 90 km south of Kamloops, British Columbia, Canada. The company operates an open pit mine and the world’s third largest copper concentrator. The concentrator produces a million pounds per day of copper and 10 tons per day of molybdenum concentrate. Finely ground ore flows to a bank of bulk floatation cells that separates metal bearing minerals from waste minerals. The waste minerals are directed to a tailings impoundment. The bulk concentrate containing both copper and molybdenum bearing minerals is fed to the copper-molybdenum separation circuit. In the separation circuit, sodium hydrosulphide is added to depress the copper minerals. Molybdenum minerals are floated with nitrogen gas. Hydrogen sulphide gas can be generated during the separation process as a result of pH modification of the slurry by carbon dioxide. The molybdenum flotation plant was moved in 1988 from the Highmont mill to the Highland mill as a result of a partnership formation. The molybdenum floatation cells were covered and connected to an exhaust system. A wet scrubber and tall discharge stack disposed of the exhausted gases. In 2004, the plant operators became concerned about H2S odor that occasionally escaped from the floatation cells and regularly escaped from the copper concentrate slurry on its way from the flotation plant to the dewatering circuit. Ore flowing to the regrind circuit in the moly plant was also releasing H2S into the plant. Measurement of the H2S concentration in these areas confirmed that it would be prudent to upgrade the exhaust ventilation. A new monitoring and maintenance strategy, a new enclosure and replacement of three ducts with larger diameter ducts have eliminated detectable releases of H2S into the mill building. This report describes the investigation and design process that led to the changes, and the successful modifications to the system.
T. Hautalampi, M. Henriks-Eckerman, H. Koskela, Finnish Institute of Occupational Health, Turku, Finland.
Workers are still exposed to isocyanates and solvents in car body repair shops despite the implementation of water-based paints. The main target of this research project was to develop technical and industrial hygienic solutions for small car body repair shops to reduce workers’ exposure to chemicals during the painting process. Workers’ exposure to isocyanates and solvents was measured during the painting process with portable instruments in five car body shops of different ventilation and occupational hygiene levels. The Pimex method (combined video and real-time monitoring data) was used to assess the solvent exposure. Ventilation performance was studied by measuring airflow rate, air velocity, and smoke tests. Also, computational fluid dynamics was used to evaluate the flow patterns in the spray booth. Concentrations of isocyanates were high in the painter’s breathing zone when solvent-based paints were sprayed. Also, the varnish applied on water-based paints contains isocyanates and therefore the air concentrations were high during spraying. The highest solvent concentrations in the breathing zone were measured during the cleanup of the spray gun. Therefore, it is highly recommended to use the paint spray respirator and proper gloves when cleaning the spray gun. The use of a fume cupboard in paint mixing and spray gun cleanup is preferable. Primers were applied to car bodies in a poorly ventilated preparation room without the use of a proper breathing respirator, so personal exposure to solvents was often higher in the preparation room than in the spray booth. It is recommended that all painting should be done in the spray booth. It is essential to improve the workers’ awareness of the health hazards of the chemicals and the importance of using personal protective equipment.
K. Hankinson, KCH Engineered Systems, Forest City, NC.
Energy costs have risen dramatically in recent years. This issue has caused companies to focus more on operational costs when designing and selecting a ventilation system. Variable Frequency Drives have recently become more desirable due to their ability to control energy costs. The prices of Variable Frequency Drives have also become more affordable as maturing technologies. This paper will focus on the local exhaust ventilation of chemical processes and integrating mechanical covers with a VFD controlled exhaust system to reduce dilution air and ultimately reduce the cost to operate an exhaust system. An energy savings analysis will be performed by comparing the cost to operate an exhaust system ventilating open surface tanks without covers vs. operating a VFD equipped exhaust system ventilating tanks with covers.
J. Dessagne, J. Muller, J. L’Huillier, INRS, Vandoeuvre, France.
For more than 10 years, the occupational risk prevention departments of the CRAMs (French regional health insurance funds) and INRS (French National Research and Safety Institute) have been contributing to the reduction of operator exposure for the most polluting woodworking machines in common use, very often by installing more efficient exhaust devices. They developed a design methodology consisting of several phases: observation of dust source and characterization of emission during a machining operation, selection of type of capture device and position, layout of capture device, and sizing of aerodynamic characteristics. The methodology is described in a guidebook intended for manufacturers of new machines and reconditioners of existing ones. The major part of these guidelines have been discussed within a European working group in order to take them into account in EN standards for specific machines. This methodology was applied in the framework of studies carried out by INRS on some machines. The improvement of capture performances was assessed using as a criterion the decontamination index whose measurement method is described in standard EN 1093-11. Several exhaust device prototypes were constructed for a radial saw with manual feed. A pivoting device, following the direction of projection of particles over 360°, was developed for a DC router. It requires case-by-case studies to allow their integration into existing machines. In both cases, performances were greatly improved for lower airflow rates.
R. Huang, National Taiwan University of Science and Technology, Taipei, Taiwan Republic of China; C. Chen, C. Chang, T. Shih, Institute of Occupational Safety and Health, Taipei, Taiwan Republic of China.
Even though some special techniques, e.g., by-pass air, doorsill compensation, VAV, etc., have been employed by hood manufacturers to improve the containment efficiency, the inherent global and local recirculation flow structures induced by the boundary layer separation or the blockage effect of the traditional fume hood would inevitably induce more or less turbulent dispersion of contaminant. In order to remedy the difficulties of the traditional fume hood, a brand new design—the “air-curtain-isolated fume hood” is developed. The new hood applies a specially designed air curtain (generated by a push slot-jet and a suction flow) across the sash plane to isolate the inner cabinet and the outer environment. The hood constructed for study is full size and transparent. The flow characteristics and the contaminant leakage properties are diagnosed by using the laser-light-sheet-assisted smoke flow visualization method and the SF6 tracer gas concentration measurement, respectively. Results of the flow visualization reveal that the air-curtain-isolated fume hood has a much improved flow patterns when compared with those of the traditional ones. No flow recirculation areas are found in the hood and the boundary between the inner cabinet and the outer atmosphere. The in-hood released smoke particles are all drawn into the suction slot and are invisible in the outer atmosphere. From the point of view of the aerodynamics and mass transport, it indicates that the air curtain setup across the sash opening can separate efficiently the inner and outer flow fields and allow almost no sensible exchange of momentum and mass. Rigorous examinations by employing the tracer gas (SF6) concentration measurements of the ANSI/ASHRAE 110-1995, Invent/UK method, and EN14175 codes all show extraordinarily satisfactory results. Particularly, the robustness tests by simulating the moment of an object or a draft current across the sash opening show excellent resistance to the environmental interference.
A. Säämänen, J. Viitaniemi, K. Helin, VTT Technical Research Centre of Finland, Tampere, Finland.
Recent progress in designing occupied spaces has made it possible to predict the resulting indoor environment in advance. Computational fluid dynamics (CFD) is used to model indoor air quality and thermal conditions. Other simulations are made to improve the efficiency of production, production equipment, or working methods. However, the interaction of production and environmental conditions in work rooms is seldom simulated or even visualized concurrently. The aim of this study was to create a method for combining CFD modeling results and other work or production simulations in a virtual environment. This will allow end users to participate in developing their own job and work tasks. Component-based production simulation software was used as a platform. Also, external database of human operator’s basic motions and kinematical digital human model was used to simulate workers’ movements in the room. Visualization properties of the tool were developed to combine and present both production simulation and CFD results simultaneously. A section of an open plan office was chosen as a test case. A 3D model of the room was imported to the simulation software tool. The airflow characteristics, temperature distribution of the room, and the draft risk were calculated using a CFD code. The results of these calculations were also imported to the component-based production simulation software. Some basic office working operations were simulated to study the possibilities of, for example, draft risk. Notable benefits are offered to the industrial design and workplace development by combining (a) production simulations and models, (b) estimation of different indoor environment factors, and (c) work task simulation with digital human model. Especially, the indoor environment quality in relation to the work tasks can easily be presented for end users. This feature is beneficial when a collaborative design method is used, for example, for risk prevention.
R. Bresee, Unimin Corporation, Peterborough, ON, Canada.
Two types of design for dust control systems are utilized in the mining industry. Most familiar is the high velocity design, where air velocities in the ductwork are in the range of 3,000 to 4,000 feet per minute (FPM). The other, newer design is the low velocity system where transport velocities are less than 1,800 FPM. There are significant advantages to the low velocity transport design. A high velocity system carries all particles collected through ductwork to the dust collector. This system’s disadvantages are that maintenance costs are higher, product is lost to the dust collector, and the system requires more energy to operate. The ductwork is subjected to highly abrasive blasting from the coarser dust particles. A single hole worn in a high velocity duct can unbalance the whole system and dramatically reduce its effectiveness in controlling dust exposure. The low velocity design is a dust containment system where only the fine, primarily respirable size particles are moved to the collection device. Coarser particles, which are contained, rather than conveyed, are returned to the process stream. It is important to remember that low velocity does NOT mean low airflow. Pickup airflows, capture velocities, hood design, and static pressures at the pickup points are the same in either a low or high velocity transport system. The term “low velocity” refers only to that part of the ducting system downstream from the pickup point. The advantages of the low velocity system are lower maintenance costs, lower energy consumption, and more reliable dust control. The system is less likely to lose effectiveness due to wear. Although the low velocity system has a higher initial capital cost, over the life of the system this is offset by lower energy and maintenance costs.
M. Rollins, Thermo Electron, Waltham, MA.
There are numerous “good” references and examples available for those who want to design industrial ventilation systems. This presentation, however, focuses on the other aspects of ventilation system design, namely the “bad” and the “ugly.” Presented in an informal yet professional manner, the examples will show ventilation systems that have a host of potential problems ranging from location to construction materials. The presentation will also provide brief comments related to how best the examples could be fixed or modified to perform optimally.
H. Kubota, Hokkaido University, Sapporo, Japan; E. Curd, Consulting Engineer, West Kirby, United Kingdom; S. Nakajima, Kushiro National College of Technology, Kushiro, Japan.
This paper deals with the characteristics of a plane air curtain, discharging vertically downward from a high level slot to the floor without a suction opening. Its practical application is for the protection of internal rooms in a factory or laboratory test chamber, and, as such, the effect of wind forces is not considered. The aim of the research is to develop a model for the prediction of the air temperature and gas concentration inside the chamber in relation to that of the discharging air and that of the surrounding environment. The relationship of the slot width and the height of the slot from floor are considered. Calculations for the determination of the discharge velocity, temperature, and gas concentration for obtaining required inside-air conditions are based on the equations proposed by Y. Niitsu. The theoretical heat transfer coefficients results obtained by this model are compared with experimental data, and good agreement between theory and experiment is observed. By applying this model, the heat loads through air curtain are calculated when warm (or cool) air is supplied to the jet . The inside gas concentrations are calculated as a function of the surrounding environment when air of zero gas (pollutant) concentration is discharged as an air curtain. Finally, practical examples are given to determine the conditions of the discharged air.
Posted May 30, 2006