HEAT AND WATER RECOVERY FROM ALUMINA CALCINER STACK OFFGAS – A TECHNOLOGY REVIEW

In modern state-of-art alumina calciner operation, energy efficiency has been improved to a very high level by measures implemented within generations of calciner designs (e.g. Outotec´s CFB technologies). The measures started with intrinsic heat recovery in counter-current preheating/cooling of feed/products respectively to as well as extrinsic measures, such as section of fluid bed cooling coupled with heat recovery bundles for hydrate washing liquor preheating, and to include the latest Outotec hydrate drier, and digitalization tool such as calciner optimizer tool. Nevertheless, calciner stack offgas in a typical SGA alumina refinery remains a major heat and water loss for the complete alumina refinery operation, taking away about 2200MJ energy and 0.7 ton water per ton of alumina produced.
With a water content (vol frac) of generally higher than 50%, and a temperature ranging from 130 to 180°C, alumina calciner stack offgas poses itself as an ideal candidate to be exploited for heat and water recovery. The paper examines the technology routes published/practiced in the alumina industry.
The paper finishes with a techno-economic analysis of the studied WHR technologies and outlines key aspects to be addressed for implementation of such technologies.