Digestion Screen Boxes & Vessels.

Digestion screen boxes in an alumina refinery screen hot, caustic process slurry following digestion, removing oversized particles, scale, debris and other unwanted material before the slurry continues to downstream flashing, clarification and separation stages. Their purpose is to maintain stable process flow, protect downstream equipment from blockages and damage, and improve the consistency of the slurry entering the next stage of the refinery.

The screen boxes must withstand high temperatures, caustic liquor, abrasive solids, continuous slurry flow and frequent thermal cycling while maintaining effective screening and reliable discharge of retained material.

MEA was engaged by Rio Tinto and Bechtel to undertake the fabrication, testing and thermal stress relief of digestion screen boxes, scale traps and associated process piping and vessel assemblies for the Rio Tinto Yarwun Refinery Expansion Project. The project involved a substantial fabrication program requiring MEA to operate both day and night shifts across its boilermaking, fitting and quality teams.

The assemblies incorporated heavy fabricated sections, pressure-retaining welds, flanged piping connections, internal components and accurately positioned interfaces required to integrate with the refinery's digestion process equipment. Fabrication was completed under controlled welding and inspection procedures, with close attention to material traceability, weld preparation, dimensional accuracy and distortion control.

Each screen box, scale trap and vessel assembly underwent air-leak testing and hydrostatic pressure testing in accordance with the approved inspection and test requirements to verify the integrity of the pressure boundary, welded joints and piping connections. The completed assemblies were also thermally stress relieved within a controlled furnace cycle to reduce residual stresses introduced during heavy fabrication and welding, with final inspections, dimensional checks and quality documentation completed before delivery to the Yarwun site.