Conveying has long been the preferred method to move large amounts of material from one fixed point to another fixed point. Belt conveyors allow a wide variety of materials to be moved safely and economically and result in the lowest environmental impact when compared to other available transport methods. Advancements and innovations in conveyor design have made it possible to use conveyors in places and terrain previously not possible. Some of these advancements include horizontal curves that allow the conveyor to shift side to side in much the same way as roads. This allows the conveyor system to follow terrain contours and avoid large obstacles.
A second innovation is intermediate drives. These allow multiple drives to power a long system making the conveyor easier to operate and maintain. Advances in technology mean that conveyors are now monitored from central control rooms that allow one person to operate one or more systems on a continual basis. The operator employs the use of computers, programmable logic controllers or PLCs and other technology to remotely monitor, adjust and make effective decisions regarding the system or systems without ever leaving the comfort of the control centre.
Safety considerations
Although conveyors have many moving parts and these parts present hazards, they are the safest available method to transport large amounts of bulk materials from one place to another.
Conveyors provide a stationary platform whereas other methods, such as haul trucks, provide mobile platforms.
In the case of conveyor systems one operator or technician can control multiple systems across a wide area from today’s advanced control room. In the case of haul trucks each vehicle has a single operator/driver and in most instances multiple vehicles are required to achieve the desired tonnage. Ergonomics, in this case, present a challenge in that each driver may be subject to stress and possible injuries in the course of completing their work. The haul truck operator must enter and exit as well as manoeuvre the vehicle throughout their shift subjecting the body to repeated stress. Whereas, the conveyor operator sits in a stationary platform monitoring systems via a computer monitor ensuring that the systems are performing correctly.
Intersections, in the case of haul trucks present particular dangers that are difficult to mitigate. On average, there are approximately 10 fatal haul truck accidents per year in the US. The most common causes for haul truck accidents include mechanical problems, inadequate training, and insufficient road/berm maintenance. According to the US department of transport (DOT) there are about 5,800 vehicle train crashes each year in the US, most of which occur at railroad crossings. These accidents result in roughly 600 deaths and injure about 2,300 people every year.
Limiting hazards
Both mobile and stationary options have a variety of hazards and dangers that are inherent. For the conveyor, proper guarding of exposed moving parts such as idlers and pulleys is important to help ensure the safety of those working on or around conveyors. This consists of a variety of options such as point, area and perimeter guarding. Each option is practical and economical and, when utilized correctly, these options adequately protect personnel from the potential of contact with the hazardous areas. The potential for material spillage off of the sides of conveyor also exists. In this case, falling material is dangerous to both foot and vehicular traffic. This hazard can be limited through the effective design of transfer points using impact beds, skirting and other equipment to help support and seal the conveyor at critical locations. Along the length of the belt conveyor covers may be used to add an additional level of protection from these hazards. According to the US department of labour there were four fatal accidents associated with powered conveyor systems in 2011.
When evaluating a mobile platform it is important to consider that this is a moving target. The truck itself is moving all the time and the pattern of traffic varies so it becomes more difficult to conduct a thorough hazard assessment. One must consider the traffic patterns, other vehicles and pedestrian activity. Other constantly changing factors must be periodically re-evaluated in order to ensure the accuracy and effectiveness of safety programmes. It is not possible to guard against the hazards created by a haul truck in the sense that guarding may be done for a conveyor system. Therefore, the safe operation of the truck by the operator is the number one consideration.
Traffic congestion and local opinion are also very serious considerations when considering the continual use of haul trucks and in some cases the use of rail cars. Often, the use of haul trucks results in a negative public opinion from the surrounding community.
Economic considerations
Base costs for both trucks and conveyors are relatively simple to obtain and should always include diesel fuel and electricity costs. When evaluating the options available during the planning phase of development it is clear that the hourly operating costs of the haul truck will be much higher than that of a conveyor system. Additionally, the rising cost of diesel fuel must be considered during this phase as inflation will undoubtedly increase the operating costs of the truck option at a much faster rate than that of the conveyor system.
Conveyors usually come with an upfront cost that is recouped over two or more decades. The structure will normally never need to be replaced even if the components require replacement at periodic intervals. Wear parts would include pulleys, idlers, belting, bearings and drive components predominantly. Conveyors usually have very high reliability rates approaching 98 percent. Electricity is the main source of power for conveyor systems and the cost of electric power, regardless of the method of generation, has been the most stable of any source of energy over the past 20 years.
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