Sponsored by HWIMay 9 2011
The roof of an electric arc furnace, which was used for melting stainless steel and operated at 2850-3000°F, was coated with Emisshield STG-2 (US Patent 7,105,047).
The Problem
A water-cooled roof could be typically used to nearly 500 heats of steel after which it has to be removed and rebuilt. Between rebuilds, a typical roof requires about two repairs. In the roof of an electric arc furnace that was cooled with exposed water tubes, signs of scaling and corrosion were observed. Corrosion was severe around water tubes due to occasional water leaks and the roof had to be repaired. The temperature of water used for cooling the roof was measured at entry and exit points. The temperature difference varied from 11 to 13° F.
The Solution
Prior to the application of Emisshield STG-2, the roof and water tubes were shot-blasted for removing slag and scale. Pressure testing of the water tubes was done, following which the furnace roof was cleaned using DIRL-LUM 603. Four gallons of Emisshield STG-2 were sprayed. The input and output temperatures of cooling water were determined. It was observed that the temperature difference ranged from about 2 to 5°F. When put into service, the roof lasted for 940 heats before it had to be rebuilt. No water leaks were reported during the service of the coated roof.
The Benefits
Installing Emisshield STG-2 high emissivity coating increased the time between rebuilds, lowering rebuild costs by 88%. The coating completely eliminated water leak repairs usually required during service, resulting in significant downtime and maintenance savings. The heat energy lost through the roof was reduced, saving 2 MW/h of electric power. The arc time that was required for melt was reduced by three minutes, thus saving electric costs during the roof’s service life. The amount of heat energy dissipated to the cooling water was found to be constant, clearly demonstrating that Emisshield STG-2 was strongly bonded to the roof and its emissivity properties did not vary with time during service.
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This information has been sourced, reviewed and adapted from materials provided by ANH Refractories Europe.
For more information on this source please visit ANH Refractories Europe.