Environmentalists say that “plans to protect air and water, wilderness and wildlife are plans to protect human kind”. In this light, dust and fume extraction systems are imperative not only in reducing air emission and green house gases, but also goes a long way in eliminating threats posed by pollution and reducing climate change.
The extraction of ferrous and non ferrous materials is a critical primary process in transformation and development of most products. Metallic and non metallic ores of copper, iron, aluminum, magnesium, and gold, silver are smelted using various furnaces. The final products are used for a wide variety of function in vehicles, trains, airplanes, electronics, construction, and manufacturing just to mention a few.
Cupola furnace smelting
The cupola and blast furnace is the oldest and most versatile smelters used for materials that require high temperatures such as copper, iron, lead and tin. The heater uses alternative stacks of ore, coal, coke, limestone and air. Most heating systems are cupola type and their fuel emits carbon dioxide, nitrogen dioxide, sulphur dioxide, carbon monoxide, ash and suspended particulate matter. All these materials are seriously harmful not only to environment but to human health.
Bag house are the most recommended air emissions control method in cupola furnace. In the bag house, the fumes are sucked from the equipment and pumped into the bag house where particulates accumulate in fabric filter. This method has been found to remove particulates ranging from 0.1 micrometers and 0.3 micrometers.
The heavy amount of gas from cupolas requires a long stack dust collection system that scraps excess gases, dust and ash. In addition, environmental protection agencies recommend the use of wet scrubbing method to remove the dangerous sulphur dioxide. Regulators recommend scrubber followed by a bag house. The wet scrubbers absorb sulphur dioxide which is highly soluble to form acid. In addition, these scrubbers absorb ash, dust and remove corrosive materials. The use of water also cools the waste gases and hence reduces volume of waste allowing easy settling.Electric and induction smelting
Electric furnaces use carbon electrode and resistor elements for melting. Induction furnace use heavy copper tubes with high frequency alternating current to induce heat on ores. These are suitable for materials with low melting points. Specially designed fume extraction system are used. The flue gases are extracted through rotating hoods cooled by water. The fumes are then directed to pulse jet or reverse air bag house to remove flue gases and dust. In addition, the system has an extra secondary line that extracts air in the workshop where the furnaces are installed and cleans them. This secondary system consists of suction duct, air bag cleaning, ID fan and chimney.
Hearth and reverberatory smelting
These are suitable for small scale melting processes. The hearth is heated using electric and natural gases and they produce small amount of products per operation. These produce hazardous wastes such as lead, zinc, cadmium as well as semi volatile and volatile wastes. Small bag house cleaners and fume extraction systems are used to remove particulates and wastes.