TECHNICAL ASSESSMENT OF STEAM RECOVERY FROM CALCINERS IN ALUMINA REFINERY

This study presents the technical assessment of recovering steam from alumina calcination via H2 or electric calciner. We proposed two steam recovery scenarios using steam ejectors or mechanical vapour recompression (MVR). Aspen Plus software was used to perform the mass and energy balances and to estimate the overall energy consumption of the overall process. In Scenario 1, using the proposed steam ejectors, the steam recovered from the calcination process, is expected to exceed the steam demand of the digestion by 23%-41% due to the additional steam required by the ejectors. Importantly, the estimated energy consumed by recovering per ton of steam is around 40% lower than that of fossil-fuel-fired boilers. In Scenario 2, the MVR demonstrated the highest energy efficiency, consuming only 0.6 GJ/tsteam in contrast with 2.93 GJ/tsteam for boilers. However, the predicted amount of steam which can be recovered from calcination can only meet 40-50% usage in the refinery. Another decarbonization technology considered in this study was an electric boiler. It potentially can achieve a reduction in energy consumption by 18% due to higher efficiency in low temperature refineries. Furthermore, it is noteworthy that utilizing renewable electricity in electric boilers and steam recovery can lead to the avoidance of approximately 0.3~0.6 tCO2/tAl2O3 emissions compared with boilers powered by fossil fuels.