This paper reviews the scale and nature of the decarbonisation challenge faced by the alumina refining industry globally and provides a technical assessment of potential retrofit pathways to reduce carbon emissions associated with the Bayer process. Three aspects of this challenge are considered. Firstly, the energy footprint of the industry is considered both from a global perspective, as well as detailed mapping of the energy flow through the Bayer process to highlight key areas of energy consumption and waste. Secondly, emerging and established technologies are investigated that have the potential to support decarbonisation through process electrification, low-grade energy recovery, and the reduction/elimination of cooling water requirements. Methods are proposed for the recovery and reuse of each low-grade energy loss from the process. A refinery-wide retrofit case study is then detailed, which applies a selection of these methods to eliminate the requirement for boiler generated steam during normal operation. The resulting Bayer energy footprint, CO2 abatement achieved, economics, practical considerations, and challenges are discussed. Lastly, technologies are reviewed that have the potential to eliminate the residual fossil fuel requirement including green calcination, electrified steam generation, and on-site thermal energy storage.

In line with the Greenhouse Gas Protocol (scopes 1 and 2 emissions), Hydro aims to reduce its CO2 emissions by 30 % in 2030. Alunorte, Hydro’s alumina refinery in Para, Brazil, will make a significant contribution to this goal, reducing its direct and indirect CO2 emissions by 70 %. Alunorte burns approximately 720 kt/year of mineral coal in three fluidized bed boilers to produce high-pressure steam for energy generation and subsequent use in its thermal processes. The objective of this work was to show a way of decarbonization by replacing coal with local biomass, acai seed (Euterpe oleracea). Acai seed is a locally abundant agroforestry residue, with an availability of 1,4 Mtpy. Using such residue as boiler fuel fits the circular economy concept and will benefit the local community in the environmental, economic, and social spheres. The methodology consisted of acai seed energy characterization in the laboratory, computer simulation of the combustion, and industrial test execution with biomass and coal cofiring, in which the biomass contributed up to 20 % of the boilers' overall energy input. The results contain boiler operational parameters, ash properties, and atmospheric emissions. Besides the avoided emission of 52 000 t CO2 up to this phase of tests, this work shows the feasibility of using acai seed as fuel regularly and safely for bubbling fluidized bed boiler operation. These activities are part of the ongoing development stage to gather technical knowledge to support the conversion studies of the coal-fired boilers for exclusively biomass feeding and prepare the supply chain for this new raw material with the future quantity and quality needed for 2030.

The patented KX heat exchanger, supplied by Sahl Regen, in combination with reduction of environmental heat losses, can reduce energy consumption at ALTEO’s Bayer process by 70% and reduce CO₂ footprint by 93%; as reported at the AQW conference in April 2024 [1]. Since then ALTEO Gardanne and Sahl Regen have completed preliminary engineering with two equipment suppliers to improve the cost estimate of the project and establish how to conduct a pilot project to finalise design parameters, such as reboiler design heat transfer coefficient (HTC). This paper provides details on how ALTEO and Sahl Regen scoped and delivered the preliminary engineering to replace the existing Digestion section with a new KX low temperature digestion (KX LTD) and reduce environmental heat losses.

Waste heat recovery is a crucial aspect of sustainable industrial processes, offering both environmental and economic benefits. This study investigates the potential to recover energy from waste/ low quality heat that is released to exhaust in an alumina refinery. Alumina refining process involves digestion of bauxite ore at high temperatures and pressure. After digestion, pressure is released using a series of flash vessels and the evaporative flash steam is optimally used for regenerative heating of caustic liquor. The blow-off slurry still possess temperature of about 104 °C, i.e., above boiling point. Thereby, produces flash steam which is generally unutilized for its relative low energy content and vent through the relief tanks. In alumina refineries, steam is the major source of energy used in digestion (46 %) and any efforts to recover waste heat and utilize for other applications will be of great scope to reduce steam consumption.

Utkal Alumina International Ltd. (UAIL) Refinery being a modern alumina plant operates with 3 low temperature digestion circuits to support overall production requirement. The digestion circuit consumes steam at a rate of 75 t/h. Blow off slurry remains at ~104 °C approximately 6 t/h per train of vapor (waste heat) is being released to relief tank at atmospheric pressure and about 100 °C. Venturi condenser technology was applied to assess its feasibility and effectiveness for waste heat recovery. With this system, it is demonstrated to recover 1.24 MJ/day of waste heat that can be able to reduce 15 t/h of low-pressure (LP) steam from wash water heating in mud wash circuit ultimately saves 430 m3/day of water from vaporization. Waste heat recovery emerges as a viable and sustainable solution for improving energy efficiency and reducing environmental impact in alumina refining processes.