Korvest Galvanisers is a publicly listed company and the largest hot dip galvaniser in South Australia. The company has been operating at its present site for the last 14 years and has a workforce of 55.
The company uses a galvanising method which has remained largely unchanged for 150 years. The process involves the application of a corrosion resistant coating of zinc to fabricated steel products.
The steelwork is dipped in a series of baths containing pre-treatment chemicals, followed by air drying and a dip in molten zinc. The hot galvanised steelwork is quenched in a post- treatment chemical with manual 'fettling' to remove unsightly barbs and run-off from the completed work.
The efficiency of the galvanising process is critically dependent on the level of ammonia in the bath containing the flux. A reduced level of ammonia decreases flux performance. By the end of each week, the flux was of very low quality. In an attempt to maintain flux quality, the baths were topped up at the end of each week with zinc ammonium chloride. Reworks were running at 3.5 percent, costing $100,000 per annum in lost production and rework costs.
The process resulted in considerable waste mainly due to the removal of paint and surface oxidation from the fabricated steel, but also in terms of spent acid, caustic rinse water and acid rinse water. Around 10-12 tonnes of spent acid was taken away each week by a licensed liquid waste contractor. Waste removal in 1995 cost the company in excess of $150,000.
Furthermore, the practice of continuous blowing of air into the flux bath (air sparging) to reduce iron content caused the ammonia to dissipate to the atmosphere.
Cleaner Production Initiative
A consultancy study into ways of reducing waste at source was carried out with a grant from the South Australian Environment Protection Agency under its Cleaner Industries Demonstration Scheme.
The changes recommended and subsequently implemented involved altering work practices and training staff.
The ammonia, zinc and chloride content of the flux is now analysed each week. Zinc ammonium chloride and ammonia solution is added daily in small quantities. The steelwork is dipped in the flux bath for longer duration to allow it to equilibrate with the bath temperature.
Work procedures have been altered to make sure that the jig holding the items to be galvanised does not become coated with zinc. This is necessary to prevent contamination at other stages of the galvanising process. Jig design has been modified to ensure that as little as possible of its surface is immersed in the process baths.
Modifications have been made to the acid rinse tanks to allow rinsing of larger items after the acid dip stage.
Initiatives recommended by the consultancy study but not yet implemented include the elimination of off-site waste treatment through reclamation of metals and recycling of clear liquor. The proprietary chemical Emag 75 has been successfully trialed to batch treat the metal contaminated acid wastes from the galvanising process. Treating the waste on-site will enable discharge of treated liquor to the sewer and appropriate disposal of sludge.
Advantages of the Process
The improved quality of the flux has increased the efficiency of the galvanising process and reduced the amount of zinc required. Waste produced has been reduced by 4.5 percent of the weight of zinc used. Quality of the product has improved and the rework rate has fallen from 3.5 percent to 1 percent, saving around $70,000 per annum..
A minimal investment in staff training, has resulted in total cost savings from all work practice changes of approximately $100,000 per annum, giving the company immediate payback. Apart from the cost savings which have resulted from staff training, the involvement of staff has lead to a discernible increase in morale.
The gains made in waste minimisation have enabled the company to be more competitive.
Treatment of acid waste on-site would reduce off-site disposal by 12 KL per week, with a saving of $96,000 per annum after treatment costs.
Cleaner Production Incentive
The primary aim of the changes was to reduce operating costs and improve product quality, thus decreasing the amount of rework required. The company was also keen to improve the awareness of staff in waste minimisation and to seek their input.
No significant barriers were encountered.
Case study coordinated by the South Australian Environment Protection Agency in association with the Environment Management Industry Association of Australia (EMIAA), July 1998.