Installation and commissioning of a magnetic compensation loop and booster rectifier circuit by means of reliable and economically efficient bolted joints

Abstract

ALCOA’s Deschambault Smelter has been operating AP30 cells for more than 25 years, having crept its potline far beyond the original technology nameplate amperage. In order to validate the industrial performance of ALCOA’s internally-designed technology upgrade enabling the operation of these pots at even higher amperage, a magnetic compensation loop and a new booster rectifier and circuit were installed in early 2017. Working in a brownfield environment where the magnetic field could exceed 13 mT, the Integrated ALCOA-HATCH Alliance Project Team decided to assemble the 3 km of total equivalent linear length of prefabricated busbars modules without welding, resorting only to bolted connections. While most of the design and installation effort was based on proven methods employed in past successful experiences, a new tightening procedure for the assembly of bolted joints was developed based on the insights gained from both bench testing and numerical analyses. Furthermore, the Project Team developed a new contact resistance testing protocol to validate the quality of each one of its 170 connections in pre-operational verifications without having the busbars energized. This helped to streamline the equipment commissioning, which was successfully completed under budget and on schedule, including a 48 h existing booster shutdown, but no potline outage. Finally, an economic analysis based on Project’s total costs showed that the usage of reliable bolted connections can be cost-effective compared to traditional construction strategies using commercially available arc-welding methods subjected to the aforementioned conditions.