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BAYER CALCINATION WASTE HEAT RECOVERY

Ilievski D, Hay P, Mills G, Bauer G, Ünal A

Alcoa has been investigating methods for reducing energy consumption and, hence, GHG emissions in alumina refining. This paper reports the results of two studies into methods for recovering the energy used in calcination.

The first study considered using low grade waste heat from calcination to drive a power cycle for generating electricity. The Kalina cycle and the Organic Rankine cycle were considered. The study focussed on the Kalina cycle because of its higher efficiency at lower heat source temperatures. A feasibility study was conducted at Alcoa’s Jamalco refinery by Siemens & Recurrent Engineering. The findings of the study will be discussed.

The second study developed and evaluated innovative new flowsheets for using low grade waste heat from calcination to evaporate spent liquor. The circuits use readily available process equipment in a configuration not previously utilised (to our knowledge) by the alumina industry. The study showed significant capability to reduce plant steam generation requirements and therefore reduce refinery energy use.