DESIGN, START-UP AND OPERATIONAL ASPECTS OF THE NEW DIGESTION PROCESS AT COMALCO ALUMINA REFINERY, GLADSTONE, QUEENSLAND

de Boer, D.J., Edwards, M. and McIntosh, P.

The Digestion section of the new Comalco Alumina Refinery in Gladstone, Queensland utilizes a new design developed in a joint venture between Kaiser Engineers, Lurgi and VAW (KLV).

Operational complexities and process inefficiencies experienced with conventional digestion plants, together with the very high pressure-temperature conditions required for a high yield and efficient alumina refinery for processing Weipa bauxite, caused Comalco to investigate a tube-in-tube heating arrangement for their Gladstone refinery project. Tube flow is essentially plug-flow and ensures a uniform holding time for bauxite heating and extraction. Other advantages include capital, operating and maintenance cost benefits.

The main problem confronting Comalco in choosing the tube-in-tube option was that most of the existing tube heating designs were conceptually limited to capacities of about 200,000 tons per annum. Comalco’s alumina production target of 1,400,000 tons per annum would therefore require a multiplicity of operating units, which made these arrangements uneconomic.

An arrangement of 4 digestion units developed and operated by VAW at the AOS refinery in Germany had a total capacity of 650 000 tons per annum. Each of these units employed a single train of tube-in-tube heaters and had limited scale up potential, but VAW had the advantage of around 30 years operational experience with processing different bauxites, including Weipa bauxite. Lurgi had experience with the design and construction of the AOS refinery.

The KGCC chemical alumina refinery in Korea, completed in 1993 utilized a multiple tube heater arrangement developed and patented by Kaiser Engineers (now Hatch Associates). While the capacity of that plant was only 175 000 tons per annum, the multiple ‘tube heater’ design was capable of scaleup to much higher capacities.

The KLV Joint Venture between Kaiser Engineers, Lurgi and VAW was contracted by Comalco to design the new digestion system for the Gladstone project.

This paper reviews the unique design and operating solutions developed as well as the operating experiences and plant performance since commissioning of the Comalco refinery commenced September 2004.