The process of forming anode/rod assemblies requires that the steel rod stub be coated with graphite powder. Until 1991 Alcoa's Rockdale operations used graphite powder suspended in 1,1,1 trichloroethane (Methyl chloroform or TCA) to coat steel anode stubs before they were attached to the carbon blocks to form the anode assembly. Due to the fact that methyl chloroform has become an environmental concern, an alternate method of graphite adhesion was needed.
Alcoa designed and built a device to electrostatically coat the steel stubs with graphite powder. The device sprays the carbon graphite through an electrically charged grid to positively charge the coating. Once charged, the material attaches itself to the opposite pole, the steel anode stub.
The electrostatic stub coater eliminated the use of more than 70,000 lbs of methyl chloroform annually. Eliminating the use of methyl chloroform in the rodding process decreased the employee exposure while eliminating the need to dispose of hazardous waste methyl chloroform. At the same time the new electrostatic system increased the ability to better maintain graphite coating thickness within a specific statistical range.
Details of Reductions
Additional Information :
Reduced cost of TCA and some reduction in disposal costs offset by additional operating costs of electrostatic system; therefore, no cost savings/benefit. Primary reason for installation was reduction of TCA emissions.