Methods to Reduce Operating Costs in Circulating Fluidized Bed Calcination

The calcination of gibbsite or hydrate to alumina is one of the most energy consuming process steps in every alumina refinery based on the Bayer process. Approximately 30% of the thermal energy input is used for the calcination process step. Over the years new technologies such as Circulating Fluidized Bed (CFB) Calciners by Outotec (formerly Lurgi) have reduced the energy consumption for the calcination step significantly (see also recent Energy Efficiency Award, given in 2010 by the German Energy Agency). The CFB technology was introduced as early as 1961. Up till then rotary kilns were the standard technology for the calcination of alumina. This innovation reduced the consumption of fuel by up to 30%. Since then, CFB calciners have been constantly improved, and methods have been developed to reduce fuel consumption even further. Not all, but some, of the methods to reduce fuel consumption have resulted in increasing process complexity and operator and maintenance demand. However, a number of measures have also been introduced to mitigate the negative effects of the increased process complexity and to even improve on operability and maintainability. In this paper the different options and methods introduced for reduction of fuel consumption, but also to increase of operability and maintainability are compared and evaluated with regard to their effects on installation and operating costs.