GALCO Case Study
The reduction and subsequent recovery of Galvanising Pickling Acid.
Galco Steel Ltd. is the largest hot dip galvanizer in Ireland with plants located in Dublin, Cork and a recently acquired plant in Waterford. They employ approximately 240 people between the Dublin, Cork and Waterford. The Dublin site has 2 galvanizing baths with the Cork and Waterford sites each having one bath and Galco are in the process of establishing a new plant at Kilcock, Co. Kildare.
Hydrochloric acid is used as a pickling solution for steel, i.e. it removes rust, prior to galvanizing. During the process the acid is consumed and the iron content increases until the solution is no longer suitable for pickling. Pilot plant microfiltration trials were carried out on site to investigate cleaning up the spent pickle and extending the life of the pickling bath. While the trials showed some benefits in terms of water use, acid use and waste reduction, costing showed it to be commercially unviable. At this stage of the project Galco focused their investigations on how to extend the lifetime of the pickling solution using the knowledge gained.
This project at a hot dip galvanising plant originally aimed to investigate the feasibility of an acid recovery process and production of an iron solution more suited for use in the waste water treatment industry in Ireland.
However as a result of the extensive investigations undertaken by Galco as part of this project, an alternative solution has been implemented which is in fact further up the waste prevention hierarchy. Increased analysis of spent pickle made Galco more aware of the chemistry of their process and they are now moving to implement simpler solutions which will improve the quality of their spent pickle.
Galco is implementing modifications to produce a spent pickle by-product which will be more acceptable for use in municipal waste water treatment plants. The steps involved will be:
- Implementing acid degreasing, replacing the current caustic degreasing system, giving reduced sludge and better pickling efficiency.
- Pickling at a higher temperature giving a lower acid solution with a higher iron content (increased energy use is compensated by reduced energy use in the degreasing step).
- Adding iron oxide to the spent pickle in a controlled reaction to boost the iron content and reduce the acid content of the pickle.
In Galco’s new plant, zinc will be practically eliminated from the spent pickle through the design of the plant equipment and layout. This is a classic case of cleaner production - i.e. do not create a waste stream in the first place. Galco has continued cleaner greener production work in other areas – water usage has been reduced throughout the plant by 36% between 2005 and 2006 (about 3000 m3) through increased controls and collection and reuse of drips and spillages.
The full environmental impact of the changes currently being introduced in Galco has not yet been quantified; however there will be improvements in the following areas:
- Zinc reduction at source - in the new plant there should only be minimal zinc content in the spent pickle.
- Reduced acid and water use due to pickling at a higher temperature.
- Extended productivity from pickling acid, less sludge for disposal.
- Less tankers off-site for disposal, tankers that are going off-site will only be within Ireland, not for export.
- Spent pickle will be of improved quality having lower acid content and higher iron content as a result of pickling at a higher temperature and iron enrichment.
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