Dust is unavoidably produced when coal is transported on belt conveyors. Loading, unloading, transfer points and belt returns generate a majority of the dust and is the basis for the following discussion.

When properly designed, a dust control system can be cost-effective both in capital commitment and operating expenses. We believe the entire production process should be evaluated so that dust control becomes an integral part of the overall materials handling operation. The traditional approach has been to view dust control as an "add on cost". This attitude has resulted in systems that are very expensive to operate because they are, as the term implies, "add-on" systems. A fine example is the typical large bag house collector usually positioned next to a conveyor transfer house. This "add-on" unit is necessarily capable of processing the entire volume of contaminated air in the transfer enclosure. The power required to operate these systems is often in the range of 50-250 horsepower. Maintenance is correspondingly significant as a large area of bags is required to accommodate the volume of contaminated air. I am not suggesting that these systems will not function as designed but rather offer these facts to establish a basis for comparison.

If the "unavoidable" dust could be contained in a much smaller volume or collected directly and immediately from the site of generation it's control would be far more cost effective and provide a much safer working environment for plant employees. A fine example of Hudco's approach has recently been demonstrated by the installation of the C-2 conveyor. The Hudco Air Supported Conveyor provides a totally enclosed transfer of coal from the stockpile to the crusher house. The only area from which dust can escape is on the return side of the conveying belt. Hudco has the technology to clean this belt return to a level of 99% efficiency. The power requirements for controlling the dust from the C-2 return would be in the range of 3-10 horsepower. When contrasted with the "add-on" bag house described in the previous paragraph, the advantage of small area containment becomes apparent. The additional benefits of providing a cleaner and safer working environment for plant employees' further supports this technology.

 As you are likely aware, the Occupational Safety and Health Administration regulations regarding Permissible Exposure Limits (PELS) are constantly being updated. Currently,the Air Contaminants Standard, 29 CFR 191 0. I 000, lists coal PEL limits as 2 mg/m3 for coal with less than 5% quartz and. I mg/m3 for coal with greater than 5% quartz content. The long-term exposure predictions suggest a 10% probability of Pneumoconiosis with Fibrosis after 35 years exposure. Considering our litigious society, prudence with regard to these maters could prevent a multitude of "asbestos" styled lawsuits in the future.
The transfer of coal by the HudcoAir™ Air Supported Conveyor ... is virtually dust-free for the entire length. Dust from the multiple load points has been eliminated by seating the conveyor cover to the vibratory chutes. This is not possible with a conventional conveyor. Actually, dust from the loading operation is still being generated; it is simply contained by the unique design of the HudcoAir™ Air Supported Conveyor. Another of the many advantages of the conveyor is that it solves the dust problem while operating with far less cost than the previous conveyor. 

Furthermore, production rates are higher than before while maintaining excess drive capacity. Hence, the benefit of dust control is provided at a lower cost than no dust control with the previous system. Hudco can convert most ... existing conveyors by installing air-supported plenums and with dust-tight covers provided the existing support structure is intact. The capital recovery of a retrofit is quite fast when the total operational savings and dust control objectives are considered.

Transfer points contribute significantly to dust generation. As coal is deposited from the transporting conveyor the tumbling action creates a major dust problem. Here again, we recommend enclosing the receiving chute or hopper to make it "dust tight". When transfers are made dust tight, it is important to use a long term lining material to resist the abrasive wear caused by the material flow. Short term wear liners requiring frequent replacement and repair compromise the entire effort and are simply too expensive to maintain. Hudco's Wearspan is a patented composite panel designed to yield a minimum of 10 years service life in coal handling operations without repair. ... We have installed Wearspan in Southern Company plants in the Southeast since the early 90's with 100% success. All of the original installations are still in service today.

We are confident that greater than 95% of the dust generated from ... coal-handling facilities ... can be contained within the conveyors, chutes and hoppers. The installation of the specifically designed equipment can be made in stages congruent with capital forecasts. For example, it is not necessary to install a HudcoAir™ Air Supported Conveyor to seal the transfer points or install the Hudco Return Belt Cleaning System. These measures could be utilized with existing conveyors to greatly reduce the dust currently generated. The transfer can later be optimized by retrofitting the conveyor with the totally enclosed HudcoAir™ Air Supported unit.

OTHER FACTORS TO BE CONSIDERED
Caution is the order of the day when considering a dust control system. Coal dust is very combustible and can explode when ignited from a low-grade ignition source. Hudco has conducted exhaustive research on methods and techniques available to resist the potential of dust explosions. The design of all the equipment offered ... would employ the latest technology to insure safe and carefree operations.