The SO2 and VOC emissions are of particular concern in refining and casting operations. Effluent from the vacuum degassing process also requires better control technology.

The major emissions during ingot casting, including iron and other oxides (FeO, Fe2O3, SiO2, CaO, and MgO), are controlled by collection devices.

Certain refining processes, including ladle metallurgy, generate particulate (and SOx if sulfur bearing compounds are used) emissions. These emissions are typically collected in baghouses as air pollution control dust. The EPA does not list any particulate emissions factors for continuous casting operations.

Of all the refining processes, only vacuum degassing uses process water and generates effluent. Principal pollutants contained in the effluent include low levels of total suspended solids (TSS) and metals (particularly lead and zinc, but also chromium, copper, and selenium) that volatilize from the steel. Standard treatment includes processing the total recirculating flow, or a portion of the flow, in clarifiers for TSS removal; cooling with mechanical draft cooling towers; and high-rate recycle. Blowdowns are usually co-treated with steelmaking and/or continuous casting wastewaters for metals removal.

Continuous casters usually include two separate closed-loop, non-contact cooling water systems for spray and mist cooling. The mold cooling water, the machine cooling water system and direct-contact water systems are to cool mold, machine and steel. The principal pollutants are total suspended solids, oil and grease, and low levels of particulate metals. As with vacuum degassing, chromium, copper, and selenium may be found in continuous casting wastewater. Wastewater treatment includes scale pits for mill scale recovery and oil removal, mixed- or single-media filtration, and high-rate recycle (EPA 2000).

Refining By-products:

Casting By-products

The major by-products of continuous casting are scale and sludge. The scale is usually recycled within the steelmaking facility at integrated mills that operate sinter plants. Scale may also be landfilled (particularly by stainless steel producers) or even charged to an electric arc furnace. Sludge generated during continuous casting is either processed and recycled on-site or landfilled.

There are no RCRA-listed hazardous wastes associated with refining or casting processes.

Ladle Refining Air Emissions. Emissions from these operations include:

Increased control of the particulate emissions from these sources may be required as part of the overall effort to reduce fine particulate emissions.

Ladle Refining Water Discharges. Process water is not normally discharged from these facilities. The exception is vacuum degassing. The vacuum for this process is normally generated by steam or water ejectors. Most steel contains low concentrations of zinc and lead. These elements are removed from the steel during the degassing process and end up in the ejector or quench water.

Ladle Refining Waste Discharges. Baghouse dusts collected from the electric arc or plasma-heated ladle refining furnaces contain mostly dusts from flux, ore and slags used in the process, and some metal oxides. Normally these dusts are not hazardous and can be disposed of in a conventional landfill. However, particulate wastes may contain enough lead to be characterized as hazardous, and, if so, must be disposed of or recycled as such. The industry anticipates continued pressure from regulatory agencies to minimize the generation and disposal of hazardous waste.

Casting Air Emissions. NOx may be from the fuel torches used to cut the steel sections to length. The steam emissions from the quenching and oiling sections of the caster contain VOCs from the leakage of lubrication systems used in the cooling sections. The NOx emissions, although minor, are the primary emissions of concern from fuel cutting torches. Particulate emissions are minimal at continuous caster operations. For facilities located in ozone non-attainment areas, additional controls may be needed to reduce emissions of NOx and VOCs.

Casting Water Discharges. The EPA is currently revising the water effluent guideline limitations for the iron and steelmaking industries, which may result in a reduction in the allowable limits for discharges from the continuous caster water treatment facilities. Such a reduction will probably be directed at reducing the discharge of metals such as nickel, chromium, lead, and zinc, and could well require additional water pollution control facilities for continuous casting operations.

Casting Waste Discharges. The primary wastes collected in a continuous caster are spent casting mold flux and coarse scale and sludges from the continuous caster wastewater treatment process. They are not hazardous wastes and are good candidates for recycling to the iron and steelmaking process. The fine particulate mill sludges collected from the caster wastewater treatment system are also not hazardous wastes, but contain larger amounts of water, oils, and greases. These sludge are normally landfilled. Drivers to increase the use of these caster wastes include the following:

None have been identified.

Summary

Small amounts of SO2 are emitted during electric-arc heated ladle refining. For new installations, these additional emissions could require controls in order to meet Prevention of Significant Deterioration requirements. Research into the mechanism of SO 2 formation during this ladle refining process may lead to ways to prevent these emissions.

The VOC emissions from lubrication oils and greases are transplanted in the steam that is vented to the atmosphere from the quenching and cooling section of the caster. Research is needed to develop oils and greases or alternative lubrication practices to reduce or eliminate such VOC emissions, if found to be significant.