Anthracite for molten metal filtering is a hard coal of high quality that can be used in casting to filter the molten iron. Its pore structure and surface roughness help remove impurities from the molten metal before it is poured into molds. This reduces inclusions such as wall splatters, casting shrink, and wall splatter inclusions. Sand allows for a longer filtration run with less water and head loss.
Anthracite has a higher density than lighter media and can therefore remain on top of it during backwashing. This helps prevent premature failure. This is particularly important in order to prevent the costly wear of filter screens. Its angular structure is also more effective than sand in generating an efficient back wash which will dislodge particulate matter from the surfaces of the media. Good backwashing will result in long filtration run times and a more consistent treatment quality.
One of the major benefits of using anthracite in gravity sand filters is that it can easily be integrated. The municipalities can realize a lower cost by integrating anthracite into existing gravity sand filters. The anthracite filter will also offer a longer run time, less head loss and less backwash than sand.
This material requires less water and electricity to backwash due to its large porosity (large surface area), high adsorption capacities, and low polluting capacity. Backwashing water and electricity are saved. In addition, the hardness of this material makes it highly impact resistant and easy to reactivate.
Lignite coal does not filter as well as anthracite. This is because of its low microporosity. It is less reactivable than anthracite, and therefore will not perform as effectively in molten steel filtration. It is a good precursor for bituminous coal, which has been found to be the best reactivated charcoal for molten steel filtration.
Anthracite (or premium coal) is only available in a select few countries. It is mined according to its grade (standard grade, high grade, or ultrahigh grade) and primarily used in power generation. However, anthracite is also used by metallurgy for direct injection, sintering, and pelletizing. The fuel is also used in steam generation, and for domestic use as a non-smoking fuel.
Activated carbon is produced by subjecting carbonaceous materials to controlled oxidation under elevated temperatures. The oxidation increases pore surface area dramatically, increasing porosity. Normal carbonaceous materials may have between 10 and 15 square meters per gram. Activated carbon has a surface area of up to 1,200 sq.m. per gram. This is why it has such an impressive adsorption capacity. The high pore volume and surface area of the anthracite enables it to effectively filter the molten metals for metallurgical, thermoelectric, pharmaceutical, paper, printing and dyeing, and food industries. It can be used to make refractory materials. Due to its low permeability and high hardness, it is an ideal choice for hot metal filtering.
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