Cornelis Klett

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.

Alumina Calcination: A Mature Technology Under Review from Supplier Perspective

Calcination is the last step in the production of alumina from Bauxite. In modern refineries this step is carried out in stationary calciners, such as Circulating Fluidized Bed (CFB), Gas Suspension (GSC) or Fluid Flash (FF) Calciners. These technologies have been available for over 40 years, and are thus very far matured. The technologies have developed substantially and many boundaries have been pushed, sometimes close to the theoretical limit. Yet the development has not stopped and new concepts and technologies are being explored. In this paper the authors discuss, from a supplier perspective, what was driving the design in the past, at present and possibly in the future, and also what the challenges typically encountered are.

Energy in Alumina Refining: Setting New Limits

Enormous emphasis is placed on the specific energy consumption from the refining of alumina from Bauxite. The current spread of specific energy consumption of the industry varies from 7 GJ/tonne to 21 GJ/tonne. Energy consumption is highly technology specific with digestion and calcination accounting for sixty percent of refinery thermal energy consumption. With Greenfield projects placing a high importance on fuel consumption in order to make their projects viable, careful selection of the technology will have an immediate impact on the energy consumption and in turn the fuel consumption which could ultimately determine the financial viability of the refinery throughout the lifetime of the project. This paper seeks to analyze the energy consumption requirements for different digestion and calcination configurations, such as single vs split stream digestion along with alternative methods of final stage heating; as well as calcination technology options and also their impact on the financial viability of the refinery itself.

Two Perspectives on the Evolution and Future of Alumina

Over the 125 year history there have been a number of step-changes in the Hall-Heroult process, despite a remarkable adherence to the original concepts of the invertors. In addition to the steady increment in scale, most noteworthy perhaps have been the introduction and impending disappearance of Soderberg technology, the introduction of magnetically compensated cell design, changes in dynamics of alumina feeding and the introduction of dry-scrubbers for HF control and fluoride recovery.

Increased Operational Flexibility in CFB Alumina Calcination

Operational flexibility with regards to production rates and fuel usage in alumina calcination is becoming increasingly important in today’s market. Outotec has a range of technologies, which can be retrofitted in old plants, or offered as options in new developments, that are aimed at improving the plant flexibility and performance, while maintaining product quality.