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Efficiency of recovery of packaging made of tinplate and steel

Summary and conclusions

The purpose of the project is to calculate the efficiency of recovery of packaging made of tinplate and steel. The focus of the project is to estimate the loss of metal from packaging made of tinplate processed with waste in the Danish incineration plants. In addition, the quality of the recovered metal for recycling from the slag from incineration plants is discussed.

The amounts of used packaging made of tinplate and steel divided on the different forms of treatment are estimated from data in "The Danish Supply of Packaging 2000", "The Danish Statistic for Packaging of Metal 2000" and supplementary information.

The supply of used packaging made of tinplate and steel in 2000 is calculated to 45,070 tons.

Packaging of steel is especially found among barrels and drums, containers of iron and steel for compressed gasses and cans and jars with a thickness above 0.5 mm.

The amounts of used packaging made of tin plate and steel for each treatment are calculated to:

Packaging of tin plate

Packaging of steel

As shown in the table, 90% of the packaging made of tin plate is incinerated with MSW and industrial waste while the rest is treated in the recycling industry.

The loss of metal based on iron in the shredders in the recycling industry is low, and therefore it can be assumed that nearly 100% is recovered in the recycling industry.

The loss from used packaging made of tin plate treated in the incineration plants for MSW and industrial waste was calculated from an experiment at Amagerforbrænding. In the experiment 203 marked halves of oval cans and 93 round cans for tomatoes passed the incineration plant together with the normal waste. Before the experiment the cans where emptied, dried, marked with a drilled 15-mm hole and weighed after removal of labels.

The cans where removed from the shaking conveyor where the slag from the incineration plant passes. All slag was inspected for cans, and cans with a recognisable hole were removed.

The plate thickness of the oval cans was 0.22 mm, and the thickness of the cans for tomatoes was 0.18 mm. From the slag were removed 128 recognisable oval cans and 23 tomato cans. The cans were divided into 3 classes after degree of disintegration. From each class was selected a representative can with maximum disintegration and one with minimum disintegration. The cans were cleaned down to pure metal by a rotating wire brush and a hammer to remove iron scales.

The mean loss for each class in the incineration process was calculated to:

The mean loss of oval cans and tomato cans, which was disintegrated so much that they where not recognisable, was estimated to 83%.

After the incineration experiment some of the oval cans from class 1 were stored in a pile of slag for 1½ months to simulate the normal treatment before metals were sorted out of the slag. During storing the iron oxidises which makes it easier to remove the slag in the mechanical separation process for metals and thereby reaches an acceptable quality of the metals for recycling.

After storing for 1½ months the cans was removed, and some was added to the sorting plant and retrieved after passing the sorting drum and over band magnet. Four representative cans where selected and the slag removed. The loss was 24.9% compared to the initial weight. The loss of cans after incineration, storing and sorting was then calculated to:

From correspondence with branch experts it has been estimated that more than 90% of the tin plate cans have material characteristics corresponding to the characteristics of the tomato cans. The losses from the tomato cans are therefore weighted with 90% and the oval cans with 10% in the final calculation of loss from used packaging of tin plate passing incineration plant and metal sorting:

When adding the amounts of recovered used packaging of tin plate in the recycling industry, a total efficiency of recycling for tin plate can calculated:

The calculated mean efficiency of 31% is lower than in a Norwegian study where the recovery efficiency for Norwegian packaging made of tin plate was calculated to 46%.

Loss in steel works has not been included but these losses are normally less than 4% of the pure metal, which is processed.

From the experiments with cleaning of cans after storing in slag and passing the sorting unit it was estimated that the amount of slag including iron oxides was significant (15-29%). This means that the costs for recycling in the steel works for this fraction is high as slag and iron oxides has to be melted. However, the packaging made of tin plate only constitutes a smaller amount of the iron scrap recovered from the slag where a significant number of large pieces like angle iron, rims, silencers and other heavy stuff is present. The other heavier iron pieces have a lower amount of slag, which reduces the total amount of slag to acceptable levels for recycling in steel works. In addition the smaller pieces passes the masks of the sorting drum and is typically cleaned for slag in a hammer mill thereby reducing the total amount of slag in iron exported for recycling

Concerning packaging made of steel (drums and containers for compressed gasses) the loss in the recycling industry is assumed low (ca. 0%) while the loss in connection with combustion of solid hazardous waste at Kommunekemi was 100%.

From the amounts processed in the recycling industry and Kommunekemi the recovery efficiency for packaging made of steel of 78% has been calculated.

The combined recovery efficiency for used packaging of tin plate and steel can be calculated to:

In the report a number of possibilities for increasing the recycling efficiency is mentioned.