Dust Control Suppression method overview Presented by GFM Engineering Solutions
Basic Principles of Dust Suppression Water spray does not suppress airborne dust. Atomised Water particles attract dust. Atomised droplets attract dust particles because of lower surface tension and if the water is ionised prior to atomisation positive-negative attraction is possible. Water Spray repel dust particles. Large water droplets repel dust particles due to high surface tension.
Water Spray Systems Why then do these types of systems work in mining applications for reducing dust? Water spray system work by increasing the Dust Extinguishing Moisture (DEM) level of the ore rather that treating the airborne dust. Advantages: Low Capital Cost Low Operating Cost Maintenance of equipment Low quality water acceptable for use Disadvantages: When ore is conveyed close to or over its DEM level most ores become sticky resulting in chute blockages, conveyor overloading etc. This normally result in operating downtime cost that far out way the cost of a well designed dust suppression system. High water consumption. Mud flush down that can relate to product loss (Gold Mining) Increase drainage requirements through out the plant Increase wash down labour requirements
Atomised Spray Systems Why is there an industry perception that these systems do not work? Maintenance of these systems, like any other piece of mining equipment is vital for efficient operation. Atomised Spray alone is not effective, the system need to be designed to take into account various other aspects like wind effect, dust flow velocity etc. Advantages: Lower Water Consumption than Water Spray System Higher dust suppression efficiency than Water Spray Systems Water conservation lower water consumption. Disadvantages: Increased Operating and Maintenance Cost over Water Spray Systems Robustness some types of system are easily damaged in a harsh mining environment Larger Capital Expenditure than Spray Water Systems Require potable quality water
Chemical Spray Systems What is the differences between these system and other water only spray system? Chemical additives (surfactants) are added to the water to break the droplet surface tension, which will allow the droplet to attract dust particles much like Atomised Spray. Foam System spray and cover the surface area of the ore (eg. On Overland Conveyors) and cap the top surface which encapsulate any dust particles. Advantages: Efficient on controlling airborne dust Water conservation lower water consumption. Robust nozzle design Disadvantages: Increased Operating and Maintenance Cost over Atomised Spray Systems Continues operating cost Chemical additives and surfactant purchase Larger Capital Expenditure than Atomised Water Systems Require potable quality water Sole source chemical supplier once equipment is installed Steelwork corrosion and paint staining possible
Client Requirements One system is normally not the solution for the diverse mining industry. In many cases a combination of the discussed method are required to provide a solution for each case of dust emission source. Air atomised system are normally not very effective at stockpile stacking, open air dust generation like uncovered overland conveyors. The best solutions are normally a combination of systems. Haul truck dumping, uncovered overland conveyor and stacking systems can be covered with an additive that bind with the ore and reduce dust generation. These additives are normally Environmentally benign. These systems need to be supplemented at crushing and transfer point with a well designed fogging system to reduce OPEX cost for chemical additives.
Expertise Fogging systems are extremely versatile when applied in the correct environment. The need for chemical additives are reduces if air/dust flow is understood and correctly suppressed. Atomised spray system can effectively work from ROM tipping stations through to Stacking, reclaiming and Train Load Out. The largest challenge for fogging is stacking into open air. Dust need to be handled in three steps called the 3 C s: Capture Dust particles need to be directed to a containment area Contain Dust particles need to be contained where fogging can interact with the dust laden air Condition Dust particles need sufficient contact time with atomised droplets. In the case of stackers and any other open air dust source wind is the largest threat to allow for the 3 C s to occur. The Dust cannot be contained and can therefore not easily be conditioned. In the case of static stackers, the use of Rill towers have been used, but the use of atomised spray was not always introduced making these just another transfer point. With some minor modification the towers can be efficiently used to suppress dust by introducing atomised fogging inside the tower.
Observations Air Atomised Systems are normally used for conveyor transfers, but industry have largely rejected these types of system as efficient. There are a number of reasons for this: Initial installation is normally done with no further OEM training, service agreements or assistance. Therefore the correct maintenance and operational practices are not employed. Air atomisation systems make use of plant air and water pressure to create a fogging profile much like in a car injector system. Air and water (fuel in the case of a car) is mixed at a exact ratio. If the pressure for one drop suddenly the other does not react. Thereby reducing the fogging efficiency. GFM designed a system that is reactive, but due to economics of the system and the benefits of High Pressure atomisation systems this prototype was never developed further. The nozzles and tubing are prone to damage. One of the most effective air atomising systems used in many cases in Australia is the German VSR system. The system operate extremely efficient with very low water consumption and efficient atomisation. The problem with the system in a mining environment is damage to the nozzles and tubing regularly occur. The nozzles have a ultrasonic head which vibrate to allow atomisation. Conducting route course analysis for these system normally identify three items. Nozzle Damage Hose Damage Incorrect Air/Water ratio settings
Observations High Pressure Systems are normally not used. There are a number of reasons for this: High Pressure is a term sometimes misunderstood, 10 Bar is classified as high pressure in the industry. The need to therefore procure a booster pump is considered unnecessary and water sprinklers are installed. In atomised spray 10 Bar water pressure would be regarded as Low pressure. Most fogging nozzles start atomising particles around 30-40 Bar. The higher the pressure the smaller droplet size is achieved. After 80 Bar the percentage of reduction in droplet size and cost of equipment is in many cases not feasible. Project history: Harbour Coal Loading Terminal - Single Rail Car Dumper Water Suppression System (10 Bar) Water Usage 320 l/min to contain single car dumper. Pump Power: 7.5kW Capital Cost: Estimate AUD converted $75,000.00 Coal Unloading System Dual Rail Car Dumper Water Suppression System (70 Bar) Water usage 30 l/min to contain both car dumper. Pump Power: 4kW Capital Cost: Estimate AUD converted $70,000.00
Examples of Case Studies Air water atomise nozzles and tubing damage. Nozzle tip damage due to ore contact Blocked nozzles resulting Solution: Nozzle Replacement with robust nozzle. Tubing installed inside conduit.
Case Studies Project Completed Low pressure system vs High Pressure High Pressure Dual Car Dumper Low pressure- Single Car Dumper System Pressure 10 Bar - 70 Bar Water Usage 320 l/min - 30 l/min Pump Power 7.5kW - 4kW Capital Cost: Estimate AUD converted $75,000.00 - $70,000.00
Case Studies Project Completed Robust High Pressure System Design Silica Mine Truck Dump (Xstrata) South Africa Installation: 2006 Failure: 2009 Reason for Failure: Water Source Contaminated with mud. Investigation: Client operated system for 3 years without any failure. Mud was pumped through the system. The pump diaphragm plate failed after the mud could not passed through the nozzles. Investigation revealed the pump still contained the original factory filled oil. It was therefore concluded that no maintenance was done on the system since commissioning. Total cost of repair: $3000 including labour to clear mud from system.
Advancements Air Water Systems Air/water atomising capabilities and advancements that will increase system performance. Nozzle capabilities include a fully automated cleaning system. Further development of a re-active air/water pressure system.
High Pressure Water Systems Full 3D design capabilities Robust piping design Robust nozzle design including internal strainers Simple installation Service Backup available and recommended Fully operational portable Demo unit available
Further dust mitigation measures available Centralised Vacuum Systems Vacuum Trailers Vacuum Belt Cleaning System Vacuum Transfer Systems