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New approaches benefit China's smelting operations

(China Daily)
Updated: 2008-06-30 14:04

The Anglesea power station is using a combination of real-time monitoring technology and operating protocols to manage ambient sulfur dioxide (SO2) levels. Real-time monitoring stations around Anglesea transmit information about ambient SO2 levels back to the power station control room. If these levels rise above a trigger point, the power station load is decreased with the objective of keeping ground-level SO2 concentrations below Environmental Protection Agency guideline levels.

In Western Australia, the Pinjarra refinery has reduced volatile organic compound (VOC), carbon monoxide and other emissions through the installation of a regenerative thermal oxidizer on the oxalate kiln. Improvements to its Wagerup refinery's calciner helped reduce formaldehyde emissions by 10 percent across the refinery and total VOC emission by 3 percent in 2004 and 2005. Wagerup's total VOC emissions have been reduced by 68 percent since 2001-02.

The installation of a low nitrogen oxide (NOx) burner in Wagerup refinery's power house contributed to a 36 percent cut in NOx emissions.

New emission reduction equipment has been installed on the Kwinana liquor burner, including an additional particulate filter, a three-stage wet scrubber, and a regenerative thermal oxidizer. This equipment, along with process control systems, will help reduce most emissions by more than 95 percent.

All of Alcoa's Australian operations report emissions to the National Pollutant Inventory, an Australian government database that reports emissions from a variety of sources.

US: new rolling method

Alcoa has also used technology to reduce emissions in its downstream rolling operations. Earlier this decade, Alcoa's Davenport, Iowa plant was nearly forced to abandon producing bright tread sheet - aluminum plate with diamond-shaped embossing - because of emission opacity concerns and high production costs. Due to the product's textured surface, significant coolant remained on the sheet as it left the cold rolling mill. This residual coolant caused the formation of visible emissions at the mill and required the sheet to be washed prior to further processing and shipment, significantly increasing costs and reducing productivity.

Davenport first looked at end-of-pipe treatment to reduce opacity by means of a $3 million air pollution control system. Instead, a small team pursued process changes that enable the line to run with only a very light coating of lubricant sprayed directly onto the sheet's surface. By introducing a new method for cold rolling this product, Alcoa's US plant was able to reduce visible emissions by 90 percent, increase finishing line speeds and save $3.5 million a year in production costs.

Benefits of the new process were good for both the environment and the business: the elimination of the need to use perchlorethylene to wash the product further reduced emissions and waste, purchase of expensive pollution control equipment was avoided and flow time for tread sheet was significantly reduced.

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