KX HEAT EXCHANGER WITH POTENTIAL TO ELIMINATE DIGESTION STEAM

The alumina industry is facing many challenges between now and 2050: environmental sustainability, climate change and carbon footprint, energy and resource efficiency, social and community impacts, technology advancements, etc. ALTEO Gardanne are faced with the increasing cost of energy and our commitment to meet “Net Zero by 2050”. We decided to engage Sahl Regen in August 2022 with the aim to eliminate steam utilisation and significantly reduce purchased energy in ALTEO Gardanne’s alumina refinery.
Usually the temperature pinch-point for heat recovery is in the Digestion section of the Bayer process in the first flash stage after the Digesters. This limitation in heat recovery is caused by the temperature drop in a flash stage plus the drop in the process steam condensing temperature, which are not recoverable. Sahl Regen’s KX heat exchanger technology not only eliminates this temperature loss, but can also recover heat across a negative temperature difference. Thus, it is possible to eliminate the use of steam in digestion and reduce purchased energy. The onus then becomes how to sufficiently reduce heat losses and increase the use of waste heat to reduce net heat requirements.
By June 2023, Sahl Regen with the assistance of KWA Kenwalt Australia (SysCAD) had completed conceptual engineering for a series of projects that will reduce purchased energy and digestion steam consumption in two phases: Phase 1 by 30% and 43% respectively, and Phase 2 by 70% and practically 100% respectively. Phase 1 includes replacing Altéo Gardanne’s traditional low temperature digestion that has 4 flash stages with a KX low temperature digestion. In Phase 1, spent liquor / pregnant liquor plate heat exchangers (PHEs) then become the practical limitation to further heat recovery. Phase 2 projects includes replacing these PHEs and recovering heat from the precipitators with KX heat exchangers. Purchased energy drops from 2.68 to 1.89 in Phase 1 and to 0.81 GJ/t Al₂O₃ in Phase 2. CO₂ emissions drop by 93% in Phase 2.
This paper describes the process modelling in SysCAD for the Phase 1 and Phase 2 projects that ALTEO Gardanne intend to implement over the next few years to reduce energy consumption and eliminate steam in digestion. A “game changer” in meeting “Net Zero by 2050” for energy intensive industries like the alumina industry.