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The application of computational fluid dynamic (CFD) models to improve the prediction of fugitive dust emission and dispersion within and from large open.

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Presentation on theme: "The application of computational fluid dynamic (CFD) models to improve the prediction of fugitive dust emission and dispersion within and from large open."— Presentation transcript:

1 The application of computational fluid dynamic (CFD) models to improve the prediction of fugitive dust emission and dispersion within and from large open pit mining operations Presentation delivered to 12 th US/North American Mine Ventilation Symposium Reno, Nevada 9 th -11 th June 2008 Ian LOWNDES, Stephen SILVESTER, Sam KINGMAN and David HARGREAVES Faculty of Engineering, University of Nottingham, Nottingham, UK Process and Environmental Engineering Research Group

2 Fugitive Dust Emissions Industrial Drivers Health and Safety Personnel & Operations Environment & Community Divided into near and far field effects respectively Near Field Personnel exposure In pit retention - poor air exchange - deep pits Site visibility Management of resources (water, efficient use for mitigation) Life, asset and production losses Far field Regulatory compliance – need to demonstrate compliance Nuisance dust Health hazards Public perception Process and Environmental Engineering Research Group

3 Introduction - Industrial Drivers Fugitive dust dispersion from and within open-pit mineral extraction sites are influenced by a number of complex factors – Meteorological Diurnal and seasonal wind variation Thermal stability effects Haul Road traffic movements Frequency Road conditions Changing pit terrain Processing Crushing/loading/stockpiling Surrounding topography Requires the development of an effective and well defined environmental management system Process and Environmental Engineering Research Group

4 Introduction- A Case Study Quarry Extraction Site A limestone extraction quarry – current reserves of 260 million tonnes – (extensive deposits of regular bedded consistent limestone) Chemical stone – 3M tpa, construction stone - 3M tpa Operates a typical blast and haul extraction method Operates in close proximity to densely populated residential areas and a national park Tunstead Quarry Process and Environmental Engineering Research Group Nottingham 

5 Introduction Monitoring & Modelling Strategy Old Moor Quarry site (highlighted) continuously monitored for peripheral dust deposition over a three year period Site dimensions – 1100m x 800m x 110 m deep (5 benches). Deposition on perimeter recorded by gravitational settling gauges (BS dust deposition frisbees) and continual real time dust monitors Later modified to investigate attenuation of dust deposition Meteorological data recorded via an on site weather station, operations data recorded (blasting location/tonnage, haul road usage) Samples collated on a monthly cycle – analysed for total mass (gravimetric) deposition, size distribution & mineralogy (SEM) Process and Environmental Engineering Research Group

6 In-Pit Dust Retention - Current status regarding the modelling of dust emissions from open pits Reference: Significant Dust Dispersion Models for Mining Operations NIOSH DHHS September 2005 A large number of regulatory approved models are in use: UK ADMS, TAPM CSIRO,AUSPLUME, SCREEN3, CALPUFF, ISC3…. Terrain effects are simplified or emissions from open pits modified using reduction factors – e.g. Shearer (1984) – a uniform reduction of 1/3 Cole & Fabrick (1984) suggested two reduction factor functions, one based on pit depth (H), the second based upon wind velocity at the top of the pit – both approximate to 1/3 –1/2 of in pit emissions More recently the US EPA (TRC Consultants 1995) evaluated several models based upon more advanced finite element methods, though no field validation was performed. Process and Environmental Engineering Research Group

7 In-Pit Dust Retention - Current status regarding the modelling of dust emissions from open pits * Significant Dust Dispersion Models for Mining Operations NIOSH DHHS September 2005 Operation specific models suggested by Wei et al (1999) to take into account face impaction/reflection during blasting. ISC3 Model modified by Reed (2003) to take into account dynamic effects of haul traffic. EPA studies (1995) confirmed over prediction of ISC3 model using EPA AP 42 emissions factors for surface mining operations, source of error – emission rate or terrain effects were not identified. Process and Environmental Engineering Research Group

8 In-Pit Dust Retention - Current status regarding the modelling of dust emissions from open pits CONCLUSIONS Traditional Gaussian plume dispersion model capabilities vary widely, many studies are inconclusive, field/scale validation is limited, in pit dispersion studies under-represented. Need to better define near field emission and dispersion characteristics and the influence of both in-pit meteorology and topography on the deposition, removal and dispersion of fugitive dust within pit. Clarification and best practice guidelines to be established for in/out pit environmental impact assessment and health and safety management (inc visibility assessments) Process and Environmental Engineering Research Group

9 Micro climate flow reversals that may influence dust dispersion, deposition and retention Process and Environmental Engineering Research Group In-Pit Dust Retention- The influence of in- pit topography and meteorology

10 Why is the in-pit topography and meteorology so important? A significant proportion of potential in-pit fugitive dust emissions may be retained in pit through: the impaction and deposition of the coarse fraction, and the retention of the fine fraction due to recirculation and stagnation flows created by the combination of mechanical shear flows created by the ABL and thermal buoyancy. Any increase of in-pit dust residence time creates potential visibility and exposure health and safety issues in- pit. Process and Environmental Engineering Research Group

11 CFD Case Study B5 bench blast modelling A bench blast was modelled as a velocity pulse, extracted from video of single event Oncoming wind profile (normal to blast face) Initially modelled as steady prior to blast event DPM emission defined on rubble pile over pulse duration Measured particles assumed spherical 2.5 µ m - 0.05 10 µ m - 0.45 30 µ m - 0.3 75 µ m - 0.2 B5 Rubble Pile Aspect Ratio Distribution – Taken from gauge results Process and Environmental Engineering Research Group Inlet of ABL

12 CFD Study- Improved bench blast fugitive dust generation and dispersion models B5 Bench blast modelled as a velocity pulse, extracted from video of single event Process and Environmental Engineering Research Group

13 Advanced Work – The influence of the ABL and in pit topography on the in pit microclimate The detail of the in pit and surrounding terrain extracted from detailed digital survey mappings of the site Process and Environmental Engineering Research Group

14 Advanced Work – 8 Wind Directions – 160 In Pit Emissions – Generic Characteristics Micro climate flow reversals that may influence dust dispersion, deposition and retention Process and Environmental Engineering Research Group

15 Advanced Work – The influence of the ABL and in pit topography on the in pit microclimate Gradual increase in resolution (from 200m post spacing to 2m post spacing) of quarry topography demonstrating development of in pit microclimate – contours of velocity magnitude Process and Environmental Engineering Research Group

16 Advanced Work – 8 Wind Directions – 5 In Pit Emission Locations – Generic Characteristics Micro climate flow reversals that may influence dust dispersion, deposition and retention Wind direction Regions of air flow reversal Dust emission source Process and Environmental Engineering Research Group

17 Advanced Work – The influence of in pit topography Gradual increase in resolution (from 200m post spacing to 2m post spacing) of quarry topography demonstrating development of in pit microclimate – Contours of in pit emission ground concentration Process and Environmental Engineering Research Group

18 In-pit dust emission, dispersion deposition and retention modelling studies 5 simulated bench blast dust emissions located at different elevations and locations within the quarry 8 different wind directions Neutral stability conditions Process and Environmental Engineering Research Group

19 In-pit dust emission, dispersion deposition and retention modelling studies Refinement of detail of bench model meshes Process and Environmental Engineering Research Group

20 Advanced Work: Neutral Stability conditions; 8 principal Wind Directions; Bench blast simulated dust emissions Dust dispersion and retention due to topography, wind direction and stability conditions N Process and Environmental Engineering Research Group

21 Advanced Work: Neutral Stability conditions; 8 principal Wind Directions; Source of dust emissions at 5 different elevations and locations within quarry Source 2: Third level of quarrySource 3: Second level of quarry Source 4: First level of quarrySource 5: Second level of quarry Process and Environmental Engineering Research Group

22 In-pit dust emission, dispersion deposition and retention modelling studies 5 simulated bench blast dust emissions located at different elevations and locations within the quarry 8 different wind directions Neutral stability conditions Process and Environmental Engineering Research Group

23 Advanced Work: Neutral Stability conditions; 8 principal Wind Directions; Source of dust emissions at 5 different elevations and locations within quarry Process and Environmental Engineering Research Group

24 Advanced Work: Neutral Stability conditions; 8 principal Wind Directions; Source of dust emissions at 4 different elevations and locations within quarry Process and Environmental Engineering Research Group

25 Advanced Work: Neutral Stability conditions; 8 principal Wind Directions; Source of dust emissions at 5 different elevations and locations within quarry The maximum in pit weighted average deposition is around 0.6 and the minimum is around 0.3. The calculated grand total weighted average in pit dust deposition for all sources and wind directions is 50% Process and Environmental Engineering Research Group

26 Future Model Studies- the adoption of a multi-scale modelling approach Process and Environmental Engineering Research Group

27 Future Model Studies- the adoption of a multi-scale modelling approach Simulation Validation Site wind measurement Validating microclimate models Dust monitoring Validating dispersion models Process and Environmental Engineering Research Group

28 The application of the combined CFD and Gaussian plume multi-scale predictive modelling approach The application of the combined CFD and Gaussian plume multi scale fugitive dust modelling approach Process and Environmental Engineering Research Group

29 Conclusions & Recommendations The enhanced capabilities of CFD in respect of ground source characterisation using equivalent emissions to a plume based model shows a substantial reduction in out of pit emission and deposition for a single event model at a high level within a typical UK surface extraction site Limited capabilities of k- ε turbulence models may adversely bias out of pit prediction due to divergence from the ABL – modified wall functions/methods for these purposes are under development at Nottingham The combined use of CFD for near source and long range Gaussian plume models for out of pit may prove to be a successful intermediate measure, following the execution of a greater number of validation case studies Process and Environmental Engineering Research Group

30 Conclusions & Recommendations Process and Environmental Engineering Research Group

31 The End…………. Process and Environmental Engineering Research Group

32 Benefits and Deliverables Generation of improved knowledge of the factors that influence in-pit generation, dispersion and retention. Development of improved predictive models to be incorporated within an Environmental Dust Management System (EDMS) Online environmental impact and hazard assessment tool to be used for: - Historical analyses (impact of prior events) - Incident investigation - Environmental complaint rebuttal/defence - Improved IPPC application fugitive dust modelling studies - Predictive analysis (impact of planned events/the impact of development sequences) - Confirmation of compliance with site/off site environmental and health and safety regulations - Early warning of potential problems - Flagging of high risk scenarios Process and Environmental Engineering Research Group

33 CFD Study- Improved haul truck fugitive dust generation and dispersion model Measured cross wind applied Dust concentration profiles taken at coincident roadside distances to sampling points Long term objective is to produce generic emission profiles under a range of conditions to construct multi- scale emission and dispersion models Process and Environmental Engineering Research Group

34 CFD Study- Improved haul truck fugitive dust generation and dispersion model Process and Environmental Engineering Research Group

35 In-Pit Dust Retention- The influence of in- pit topography and meteorology Example: Dispersion and retention of haul truck generated dust Process and Environmental Engineering Research Group

36 Development of an Environmental Management System (EMS) The development of an effective EMS for the control of fugitive dust emissions is dependent upon a continuous monitoring and interpretation of the relevant atmospheric, environmental and mine operational data, including: Global meteorological data – provided by on site weather stations (continuous real time data feed and historical records) In-pit meteorological data in the vicinity of extraction sites, loading operations, haul roads, primary crushing and stockpiling operations (continuous real time data feed and historical records) Planned truck schedule and actual truck haul road movements (continuous real time data feed) Process and Environmental Engineering Research Group

37 Development of an Environmental Management System (EMS) Road haulage surface conditions (truck/road mounted sensors) Fugitive dust emission data (truck/road mounted sensors; loading operations) Assessment of truck driver visibility on haul roads Assessment of the required frequency and efficacy of road wetting operations Process and Environmental Engineering Research Group

38 Future Model Studies- the adoption of a multi-scale modelling approach Near & Far Wake Mixing Limit of Source Influence Near source can account for dynamic source effects (wake mixing, blast turbulence) Fully dispersed emission from source passed as a flux to pit wide CFD model Flux from pit passed to far field Gaussian plume model Process and Environmental Engineering Research Group

39 In-pit dust emission, dispersion deposition and retention modelling studies 5 simulated bench blast dust emissions located at different elevations and locations within the quarry 8 different wind directions Neutral stability conditions Process and Environmental Engineering Research Group


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