Disposal of waste-based fuels and raw materials in cement plants in Germany and Switzerland – What can be learned for global co-incineration practice and policy?

Abstract

Abstract The limit value for emissions of total organic carbon (TOC) for incinerators in the European Union (EU) is 10 mg/m3. However, clinker burning is a material conversion process during which TOC emissions from the fuels occur concurrently with the thermal decomposition of organic material from the raw material mixture (limestone, marl, shale, etc.) in the preheater, which alone can emit more than 10 mg/m3. Therefore, the German legislature has created an exemption that allows authorities to set higher limit values for cement kilns if the cause of the higher emissions is the natural raw material mixture and not the co-incinerated waste. Separating the effects requires a test to determine the baseline emission of the natural raw material or waste raw material. Up until now, these tests were only used internally by companies. By applying such tests, the emissions from the fuels, particularly from waste-based fuels, can be determined, restricted and controlled. TOC emissions from natural materials cannot be avoided. In Switzerland and Germany these emissions are on average around 20–35 mg/m3. Switzerland has recently set a high TOC limit value of 80 mg/m3 for cement kilns, independent of the source of organic emissions, and even allows the use of polychlorinated biphenyl (PCB) contaminated soils as raw material (up to 10 mg/kg). This limit is too high and can result in unnecessary emissions of carcinogenic benzene, PCBs and other pollutants. Both the natural raw materials and waste raw materials emit organic carbon. However, there is one major difference. The natural raw materials emit mostly aliphatic compounds at temperatures up to about 600 °C, whereas the organic compounds originating from waste-based raw material components can include hazardous pollutants like polychlorinated biphenyls (PCBs) and other persistent organic pollutants (POPs), which desorb in the preheater and are released into the environment. Therefore, waste raw materials such as soils contaminated with POPs or other semivolatile toxic chemicals cannot be introduced via the raw mill -(leading to desorption in the preheater) but need to be fed in the kiln inlet. Cement kilns treating POPs or raw materials with problematic semivolatile organics need strict control and possibly continuous monitoring for dioxins and other POPs.