Many industrial operations create fugitive dust. Because it can be airborne, fugitive dust is an environmental and a health hazard and in some cases, even a fire hazard. Airborne dust can also mean loss of usable material. Also, the airborne particles are highly pervasive and can enter the nose, lungs, eyes and even the pores of the skin. Industrial operations requiring dust prevention include dumping of material, transportation, transfer point operation, stockpiling, storage, reclaiming, conveyoring, shearing, continuous mining, crushing, screening and sifting, drying, packaging and filling.
All types of dust including soil particles, industrial products, by-products and waste, coal dust, road dust and many others present hazards. Some examples of particulate materials that produce dust include for example, ground limestone (10 to 1000 μm); fly ash (10 to 200 μm); coal dust (1 to 100 μm); cement dust (3 to 100 μm); carbon black (0.01 to 0.3 μm); and pulverized coal (3 to 500 μm).
For example, the high speed transportation of coal by rail may cause loss of fine coal particles. In fact, coal trains are known as “black snakes.” The name aptly describes the miles of uncovered rail cars bearing the black cargo as they slither along the tracks. During the journey from coal mines to their final destinations, coal trains shed plumes of coal dust from the tops of the train cars. As the dust spews from the rail cars, it fills the surrounding air with harmful substances such mercury, lead, cadmium, arsenic, manganese, beryllium, and chromium. When the dust settles, these substances are deposited in soil and water, harming plant, animal, and marine life.
Both train vibration and airspeed (from wind or due to the speed of train) can lift particles from exposed coal making them airborne and depositing them along the right-of-way and transporting them by wind considerable distances. In addition to environmental hazards, health hazards and product loss, coal dust lost during transportation can also damage transportation infrastructure. Environmental consequences from coal dust are also rooted in railroad safety concerns. Coal dust accumulation in the ballast can destabilize the tracks and contribute to derailments. Derailments impact the environment because the overturned train can spill locomotive fuel and dump thousands of pounds of coal and coal dust, resulting in soil and water contamination.
Fugitive dust problem avails itself to two solutions: (1) lowered dust creation; and (2) dust control through prevention, suppression, capture, or removal.
This invention relates to the second solution, that is, dust control. Dust control can be approached in four ways: (1) using wet systems that use water sprays to prevent dust or capture airborne dust; (2) using enclosures to contain dust; (3) using ventilation systems/exhaust systems to remove dust; (4) using a combination of these techniques. More specifically, this invention relates to novel asphalt-based emulsion formulations in wet spray systems that can assist in dust control.
Halide brines, comprising one or more dissolved or suspended salts in water, usually halide salts, especially chloride salts, particularly calcium chloride, magnesium chloride and other alkali metal and alkaline earth metal salts, are used extensively for inhibiting dust on a variety of surfaces including such uses as dust control of roadways, paved areas, bridges and the like as well as for inhibiting dust on surfaces of bulk materials, such as coal, coke, limestone and minerals. They are also used for dust control, especially during dry weather during the handling and transportation of dust-producing bulk materials, such as coal, coke and limestone.
Aqueous solutions of these halides are known to corrode metals and cause scaling or surface damage to concrete. For example, heavy use of road deicers can result in serious damage to steel, particularly autos and other vehicles, as well as rapid deterioration of steel reinforcing rods in poured concrete roadways and bridges. The halides used for dust control of bulk materials such as coal or other minerals often cause corrosive deterioration of the materials-handling equipment, rail cars and other container carriers.
In accordance with the present invention, it has been found that in one embodiment, a formulation comprising asphalt emulsions resists absorption into pores of coal and other mineral surfaces, including soil, so that after drying into a continuous or discontinuous film, the asphalt emulsion will provide later dust control, as well as exhibiting dust control and anti-corrosion properties upon later wetting with water.
The composition of the present invention addresses the above discussed problems of dust generation. The emulsion of the present invention comprising asphalt-based emulsion can be added to a water based spray system that can then be used for spraying on to the particulate material, for example, coal, to control the dust.