The importance of dust control
Dust emissions can have a range of environmental implications for the operators of a port. The main issues dust can cause in ports include: • A dirty and potentially hazardous working environment for port operators and ship crews. Conditions such as these can affect staff morale • A loss of productivity. Dust emitted affects operations, there are also costs involved in cleaning and controlling dust • Employee health problems • Abrasive public relations: dust emissions can drift beyond the port arena and generate unpleasant or even hazardous living /working conditions for neighbours • Explosions: dust emissions generated at ports are potentially combustible
Dust control measures
When a port operator is faced with a dusty material that must be unloaded and handled, there are five potential approaches that one can utilise. These approaches are:
Prevention at source
This method focuses on reducing the levels of dust present in materials shipped into a port. To effect changes here, this requires the control of, or an ability to influence: • Material purchasing decisions. One must investigate the possibilities of changing supplier with a view to find the same material with less dust, or with a coarser particle size • Material manufacturing. Options for changing the particle manufacturing process to reduce dust by granulation, removal of fines, or the addition of liquid should be explored • Material handling techniques. Correct practice can reduce particle attrition and dust generation
Prevention during handling
This approach concerns the reduction of the level of dust generated during handling operations at ports when loading / unloading ships or silos. A further key area is at the transfer points between conveyors. Regarding ship unloading there are a range of different approaches which provide different material transfer rates, levels of particle breakage and dust generation. A grab crane generates a low level of attrition as the number of particles in contact with a moving grab jaw surface is relatively low when corresponded with the total volume of material transported. However, the containment is poor. Bucket wheel and screw elevator continuous ship unloaders provide better containment once in the conveyor tube, however, they subject a large number of particles to contact with the moving buckets or screw flights relative to volume of material moved. In this instance, breakage is moderate. For blanket elevators, the conveying action of compressing material between two belts is very gentle, but the containment is poor. Finally, for pneumatic conveyors the containment is excellent both at the pickup point and during transport, but the conveying velocity at the end of the line can be very high, which results in the material being subjected to large impacts at the bends causing severe particle attrition and dust generation.
