Cupola (cupola furnace)

A cupola is a tall, vertical cylindrical shaft furnace used in iron foundries to melt scrap iron and pig iron. Alternating layers of metal, coke (fuel) and limestone (flux) are charged from the top while air is blown in through tuyeres near the bottom; the burning coke melts the descending metal, which collects at the base for tapping. It is the traditional workhorse of grey-iron casting and is widespread in India's foundry clusters such as Howrah, Rajkot, Coimbatore, Agra and Batala.

The cupola is a significant emission source. The burning coke and the metal charge release particulate matter (metal oxide fume and coke dust), carbon monoxide (from the oxygen-starved coke combustion), SO₂ from the coke's sulphur, and depending on the scrap's coatings, organic pollutants. Uncontrolled cupolas are a notorious source of black smoke and dust in foundry towns, and CPCB has driven a long programme of cupola emission control and conversion to cleaner divided-blast and induction furnaces.

For recyclers, the cupola matters because it is a major consumer of recycled ferrous scrap — foundries are an important market for the iron and steel fraction recovered from e-waste, ELVs, tyres (bead wire) and mixed metal recycling. The quality of recycled scrap (cleanliness, coating, contamination) directly affects cupola emissions: oily, painted or plastic-contaminated scrap produces far more smoke and VOCs when melted.

The control logic for cupolas is capture and afterburning: a capture hood at the charging door, an afterburner to combust the CO and organics, and a wet scrubber or baghouse for particulate, with divided-blast or recuperative designs to cut coke use and emissions. The cleaner-scrap point is the actionable one for recyclers — supplying clean, de-coated, de-oiled scrap to foundries reduces downstream cupola emissions and commands a better price.