Reductions in dust and gaseous emissions from sinter strands

The production of sinter is economically important for the integrated steelmaking route, and sinter plants also serve an environmentally useful function in allowing the convenient reprocessing of revert materials. However, sinter plant main stacks typically account for up to 30% of the mass of airborne pollutants from an integrated steelworks, largely because emissions are continuous and are associated with very large gas flows. Sintering operations are therefore the focus of considerable interest and effort in attempts to improve environmental performance, and are subject to environmental pressures for improved abatement of pollutants, both internationally and from national permitting authorities. Throughout Europe, sinter plant main stack emissions are controlled mainly by electrostatic precipitators. Typically these clean particulate material to around 100 mg/m 3 , and exceptionally to levels as low as 30 mg/m 3 . A step change is needed to achieve lower particulate emission levels and to mitigate other pollutants such as heavy metals and trace organic species. Best Available Techniques are currently centred on very expensive wet scrubbing technology or the use of bag filters. Although bag filters can provide enhanced dust removal, generally to levels of 10-20 mg/m 3 , and are suitable for the use of additives for control of other pollutants, they have drawbacks in terms of temperature performance and susceptibility to damage from moisture, sticky hydrocarbon components and abrasive particles. The problems are attributable to the properties of fabrics available at reasonable cost. A new technology, the KN Filter, offers the possibility of bag filter performance whilst avoiding the problems of fabrics. This device operates in a similar manner to the pulse jet bag filter but employs metallic filter screens of relatively coarse mesh, with apertures many times the size of the dust particles to be filtered. A cake can be built on this mesh from the particulate contaminants themselves, and this cake then acts as the filtration medium. The robust screens can be vigorously cleaned, have a long life, and are far less subject to the problems which can affect fabric media. In this project a specially designed KN Filter has been tested at small pilot scale (-1 m 3 /s flow) in industrial conditions. The device was a 4 chamber unit, with 3 chambers filtering at any particular time. Filter screens were of 316 grade stainless steel mesh. Initial tests on the direct (or 4th hole) extraction duct of an electric arc furnace confirmed the ability to give good filtration performance with very fine particles (largely sub-micron). Outlet dust concentration was -10 mg/m 3 stp during periods of intense furnace activity, and as low as 3 mg/m 3 stp over a full operating cycle. Inlet dust loading averaged 8 g/m 3 stp, so filtration efficiency was about 99.9%. Inlet gas temperatures of up to 270°C were accommodated, and substantially higher temperatures should not be problematic. Filtration velocity at 1.4 m/min and the pressure drop of 16 - 22 mbar were not dissimilar to the values encountered on fabric filters in EAF applications. Subsequent tests were performed on a side stream of the wind main of an operating sinter strand at the Scunthorpe Works of Corus UK.