Laboratory-scale study of the suppression of PCDD/F emission during coal and MSW co-incineration

The experimental test of co-incinerating Chinese raw municipal solid waste （MSW） and coal in a laboratory-scale tubular reactor was first reported in present study, and the emission of normal gas components and the effects of the S/Cl molar ratio or coal mixing percentages on polychlorinated dibenzo-p-dioxins and dibenzofurans （PCDDs/Fs） emission were investigated and discussed. The results indicated that OCDD was the only PCDD homologues since others like TCDD-HpCDD was hardly detected, while as the categories of PCDF homologues were comparatively much more general. The amount of PCDD was much larger than that of PCDF in all operating conditions. Since ZPCDF/∑PCDD〈〈1, the dominant role of the precursor formation was proven in our experimental conductions. With increasing the coal addition to MSW （from 0 to 16%）, PCDD and PCDF were reduced considerably. Coal and MSW may suppress the PCDD/F emissions efficiently （over 95%） during the MSW incineration process. The PCDD/F suppression results of the present study could be helpful guidance to the industrial application of Chinese MSW and auxiliary coal co-incineration processes. The PCDD/F stack emission data of two industrial incinerators using co-incineration technology in China seem to have a great positive reduction of PCDDs/Fs.

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

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 20e35 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 600C,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.