Slag processing at the waste-to-energy plant Schwandorf

Modern processing technology captures metals (ferrous and non-ferrous) almost completely

ZMS

The Schwandorf Waste-to-Energy Association in southeastern Germany recycles the household, bulky and commercial waste of almost 1.9 million inhabitants from a disposal area of around 15,000 square kilometers every year. Each year, the waste-to-energy plant's four incineration lines thermally recycle around 450,000 tons of waste into steam, heat, and electricity. The slag produced during incineration has been treated on site for further processing since 1982. Now it has been renewed.

 
In 2019, after an operating period of almost 40 years, the old processing plant of the waste-to-energy plant was dismantled and replaced by a new plant from the same manufacturer. Thanks to the modern slag processing plant, metallic raw materials and, now also, valuable non-ferrous metals can be recovered from the slag (material recycling).
 
Performance
 
The new processing plant handles 110,000 tons of slag per year. This corresponds to 13 tons per hour. The following results were achieved in the first months of operation:
 
 
 

If the quantities are roughly related to approx. 1.9 million inhabitants, this is 4.36 kg/inhabitant and year (1.84% of 450,000 Mg = 8,280 / 1,900,000).

According to the Bavarian waste balance sheet from 2021, the per capita volume of scrap metals was 8.1 kg. Residues from thermal treatment were 3.5 kg per inhabitant.

Regarding residues from waste incineration slags, the waste balance sheet states:
 
 
 

The share of metal from the post-treatment of ashes across all plants in Bavaria was 46,262 t in the balance year (graph: LfU). This corresponds to a value of 3.5 kg per inhabitant. The amount collected decreased slightly compared to the previous year. The above figure is the amount of metal that is (arithmetically) attributable to treated waste from households. This quantity does not yet include scrap metal delivered directly to the transfer points or to the cogeneration plant.
 
Summary
 
The quantities of ferrous and non-ferrous metals collected at ZMS could be increased by about one third compared to the average of the Bavarian plants due to the modern processing plant.

From a comprehensive household waste analysis of a partial quantity (District of Neustadt a. d. Waldnaab) at the ZMS in 2020/2021, it was determined that the amount of scrap metal was of a similar magnitude (1.9%).
 
 
It can be noted that a modern treatment plant for separating metals from the waste incineration slag - as in the ZMS - can collect almost all metals and forward them for recycling. The recycling revenues change constantly and are of a similar order of magnitude for the ferrous metals and the non-ferrous metals.  According to ZMS, the investment in the plant is amortized in approx. 2.5 years.

The fascination of this processing plant becomes even more apparent, however, when one brings to mind the quality of the processing results based on the detailed views of individual fractions (Pictures ZMS).
 
   

The treatment process
 
In the first step, coarse slag and coarse iron are removed from the slag using a bar screen and magnetic drum. Further steps in the processing include the discharge of fine iron with the aid of an overbelt magnet and a high-speed drum. Non-ferrous metals are separated from the slag using an Eddy-current separator. The separated fractions are fed to their planned discharge position via several conveyor belts. At the end of the treatment process, the various grain sizes of the individual fractions are available for further use.

Space conditions
 
The new slag preparation plant was installed in an existing silo which, along with three other adjacent bunkers, is used for the intermediate storage of slag and scrap. With the required floor space of approx. 510 m², the installation was a real challenge. The plant is continuously supplied with slag via an 80-meter-long ascending conveyor belt. The slag preparation plant was installed at a height of between 12 meters (lowest level) and 23 meters (top level) above the silo floor on a new steel structure. By means of an assembly lifting device, also planned, and supplied by the manufacturer, it was possible to place all components with millimeter precision. The crane system will also be used in the future for maintenance and inspection work.
 
Emissions
 
Since the waste-to-energy plant is located about 100 meters from a residential area, care was taken to reduce noise emissions and that the vapor fumes, generated by the warm and moist slag, are extracted in the silo.
 
Manufacturer and supplier
 
The processing plant was supplied and put into operation by Loibl Förderanlagen GmbH, Straubing.
The company has kindly provided the following pictures of the processing plant.