Pinjarra alumina refinery

The Pinjarra alumina refinery is located near the town of Pinjarra, a 30 minutes drive from the popular coastal town of Mandurah, south of Perth in Western Australia. It is a major employer in the district employing more than 1,000 people. The Pinjarra refinery is one of the largest alumina refineries in the world being able to refine 4.2 million tonnes of alumina a year.

The Pinjarra Alumina Refinery Uses the Bayer Process

The Pinjarra alumina refinery is owned by Alcoa which uses a process known as the Bayer process to refine alumina from bauxite ore. The Bayer process was devised by Karl Bayer of the Bayer Chemical Company and is commonly used in alumina refineries throughout the world.

Pinjarra Alumina Refinery Benefits From the Cogeneration Partnership With Alinta

Alcoa has entered into a co-generation partnership with power producing company Alinta to improve and create a more cost efficient and environmentally friendly operation of the Pinjarra alumina refinery. This cogeneration partnership involves the installation of two combined cycle gas fired turbine units to create efficient power generation as well as providing for the Pinjarra refinery's low pressure steam requirements. The first gas turbine was constructed at the Pinjarra refinery in 2004. Alinta sells off the excess electric power it produces into the regional grid.

The Bayer Processing System Used at the Pinjarra Alumina Refinery Requires Four Steps

Alcoa operate a triple refinery system in Western Australia, all located over a 200 kilometre stretch from Perth to Bunbury in the south. The refineries are at Wagerup, Kwinana and Pinjarra. The Bayer refining process used requires four stages to be undertaken to extract alumina from bauxite ore. These steps; digestion, clarification, precipitation and calcination are carried out as follows:

Digestion †ñ Digestion involves the red coloured finely ground bauxite being mixed into a solution of hot caustic soda. This dissolves the alumina from the bauxite. It takes six tonnes of bauxite to produce two tonnes of alumina.
Clarification †ñ Clarification requires the insolubles in the solution, such as mud and sand, to be settled before being filtered out. This leaves a solution of dissolved alumina hydrate.
Precipitation †ñ At this stage the liquid alumina hydrate is cooled in open top tanks where seed crystals are added. This causes the alumina to crystallise out of the solution.
Calcination †ñ This last stage in the process requires the alumina hydrate to be washed and heated until the water is removed. This leaves behind pure dry alumina as a fine white powder. The powder is cooled and placed into storage before it is taken to aluminium smelters for further processing.

Alumina is a white granular substance, much like table salt but not as coarse, its technical term is aluminium oxide. Aluminium doesn't occur in nature as a metal, it has to be refined from bauxite ore in its oxide state and then smelted.

The Pinjarra alumina refinery was commissioned in 1972 and expanded to contain five units by 1976. The adjoining power house consists of back pressure turbines and medium pressure boilers that provide the refinery's processing power and heating needs. In 2006 the cogeneration plant created an environment where the converting of gas into electricity proved to be 75 percent efficient compared to the previous coal fired plant that was between 30 and 35 percent efficient. The plant produces two outputs, steam and electricity from the gas input. It produces 140 megawatts of†electricity and 240 tonnes an hour of steam. The new cogeneration infrastructure allowed Alcoa to retire a number of its old inefficient boilers.