Molten Metal Treatment by Salt Fluxing with Low Environmental Emissions

Sahai, Yogeshwar

The Ohio State University Research Foundation Columbus OH

关键词: Corrosion;    Aluminium;    Particulates;    Hydrochloric Acid;    Chlorides;   

DOI  :  10.2172/912766
RP-ID  :  DOE/ID/14400-1
RP-ID  :  FC36-02ID14400
RP-ID  :  912766

美国|英语

来源: UNT Digital Library

【 摘 要 】

Abstract: Chlorine gas is traditionally used for fluxing of aluminum melt for removal of alkali and alkaline earth elements. However this results in undesirable emissions of particulate matter and gases such as HCl and chlorine, which are often at unacceptable levels. Additionally, chlorine gas is highly toxic and its handling, storage, and use pose risks to employees and the local community. Holding of even minimal amounts of chlorine necessitates extensive training for all plant employees. Fugitive emissions from chlorine usage within the plant cause accelerated corrosion of plant equipment. The Secondary Aluminum Maximum Achievable Control Technology (MACT) under the Clean Air Act, finalized in March 2000 has set very tough new limits on particulate matter (PM) and total hydrogen chloride emissions from aluminum melting and holding furnaces. These limits are 0.4 and 0.1 lbs per ton of aluminum for hydrogen chloride and particulate emissions, respectively. Assuming new technologies for meeting these limits can be found, additional requirements under the Clean Air Act (Prevention of Significant Deterioration and New Source Review) trigger Best Available Control Technology (BACT) for new sources with annual emissions (net emissions not expressed per ton of production) over specified amounts. BACT currently is lime coated bag-houses for control of particulate and HCl emissions. These controls are expensive, difficult to operate and maintain, and result in reduced American competitiveness in the global economy. Solid salt fluxing is emerging as a viable option for the replacement of chlorine gas fluxing, provided emissions can be consistently maintained below the required levels. This project was a cooperative effort between the Ohio State University and Alcoa to investigate and optimize the effects of solid chloride flux addition in molten metal for alkali impurity and non-metallic inclusion removal minimizing dust and toxic emissions and maximizing energy conservation. In this program, the salt metal interactions were studies and the emissions at laboratory scale at OSU were monitored. The goal of the project was to obtain a fundamental understanding, based on first principles, of the pollutant formation that occurs when the salts are used in furnaces. This information will be used to control process parameters so that emissions are consistently below the required levels. The information obtained in these experiments will be used in industrial furnaces at aluminum plants and which will help in optimizing the process.