Aughinish Alumina is located on Ireland’s south west coast, close to the mouth of the Shannon river and to Shannon airport and the city of Limerick. The refinery was built between 1978 and 1983 and produces in excess of 1.8 million tonnes of alumina per year from some four million tonnes of imported bauxite. The alumina is exported to aluminium smelters throughout Europe.
Aughinish has 500 permanent employees and some 200 contractors working in teams in what is a highly automated plant.
“This is the plant’s Operations Control Centre,” says Billy Dennehy. Like a spider in a web, he and his colleagues monitor how the plant’s processes are controlled. “From here I don’t interfere with the process,” says Dennehy, “but as the process is highly automated, the different sections of the plant work in their own teams and have their own control rooms. What I have here is a facility to see the entire plant and to respond to any requests for assistance or advice from any of the local control rooms.
“One of the most critical points of the production cycle is the Digestion Area. This is where caustic soda is mixed with the finely ground bauxite and heated to 250 degrees centigrade using high pressure steam. At any time, there are some 2,600 m3 of diluted caustic soda flowing around the plant. We recover the soda, so what actually comes out of this part of the process is alumina and the residues, such as mud and sand from the bauxite.”
Environment
“This plant is all about operational and environmental excellence. Although production has increased greatly and environmental standards have been enhanced, the actual workforce has decreased by some 200 employees due to optimising both the process and, more importantly, the organisation.
Making alumina is very much about process control, which is becoming more and more automated. We have ISO 9000 certificates as well as ISO 14001 for the environment,” says Capt. Kevin Cribbin, the port facilitator – in practical terms that means getting the bauxite in at the right time and in correct quantities and shipping the alumina back out.
Capt. Cribbin greets us at the main gate on a beautiful November day. The sun is out in a cloudless sky, and we are given a guided tour of the plant. We are impressed by the two huge bauxite storage sheds. Bauxite and rain do not go very well together, as bauxite will stick to any surface when wet. At one shed we see how the bauxite comes in by conveyor belt; it looks like a red-brownish waterfall as it falls down to the stockpile. From there it is taken by conveyor belt to the Digester, settling tank and on to the classifier. The aluminium hydroxide crystals are then calcined at over 1,100 degrees centigrade before the alumina (aluminium oxide) is exported by ship. Alumina is a very fine, white powder which needs to be kept dry at all times.
The plant consumes a constant 40 MW, all produced on site by a natural gas fired Combined Cycle power station. The capacity of the plant is some 150 MW, with the balance going to the Irish national grid.
A modern natural gas fired Combined Cycle power plant has a thermal efficiency of about 55% but, by using the steam generated for the plant, Aughinish increases the thermal efficiency of the Combined Cycle plant to more than 80%.
The Port
We move across the long approach arm leading out to the port itself. Along the driveway there are also the conveyor belts for moving in the bauxite and shipping out the alumina. The bauxite is lifted out of the vessels using a grab. “We need to keep our unloader in perfect shape all the time,” says Cribbin, “as we only have one. We also spend considerable time and money on training our crane operators as the unloader is such a key element when it comes to operating our plant. If the unloader should fail, then we would fail to deliver bauxite to the production process after a very short while.”
The Egypt-registered and manned Panamax bulk carrier Edfu was discharging bauxite from Kamsar in Guinea, West Africa when we visited.
The distance from land to the port is some 800 metres due to the shallow waters of the Shannon Estuary – also an important wild life reserve for birds and migrating birds. More than 100 species of birds have been identified, and the sanctuary is regularly visited by Birdwatch Ireland. Aughinish has established a nature trail network on the island, incorporating bird hides and observation areas along with butterfly and dragonfly sanctuaries. These areas are also open to the public.
“Aughinish is a subsidiary of Glencore of Baar, Switzerland and is the biggest alumina plant in Europe,” says Nelius Kennedy of the Aughinish Human Resources Department. “We moved a number of years ago to a flat organisation, where all the different production sections of our plant are organised in teams. Each team is responsible for its part of the production process, with only a limited amount of facilitation and coordination required between teams. We have a good partnership with our employees, who are primarily from the local area,” says Kennedy.
Refining bauxite to alumina
1. Preparation
Bauxite is crushed and ground and mixed with caustic soda solution and pumped into digester pressure vessels.
2. Digestion
Under high pressure and heat, the alumina (within the bauxites slurry) is dissolved by and combines with the caustic soda to produce sodium aluminate.
3. Clarification
The solid residues (red mud and process sand) in the digested bauxite slurry are separated by settling out of the sodium aluminate solution. The residues are washed and the red mud is thickened by vacuum filtration and pumped to the bauxite residue disposal area.
4. Precipitation
As the soluble sodium aluminate is cooled, it is agitated and seeded with aluminium hydroxide crystals. These form larger crystals which gradually settle out of solution. Seed crystals and sodium aluminate remaining in solution are recirculated.
5. Calcination
The aluminium hydroxide crystals are calcined at over 1100°C to remove the water of crystallisation. A fine white powder, alumina (aluminium oxide), is produced and this product is exported by ship to overseas smelters.
Date: 05 February 2008