Energetic valorisation of automotive shredder residue by co-incineration in a fluidized bed combustor

Over the last decades, cars have become one of the most important consumer products in industrialized societies. In Europe (EU 15) for example, ca. 14.4 106 new passenger cars are registered every year and as a consequence the total number of end of life vehicles (ELVs) is also quite elevated: 11 106/year. Currently around 75% of the total weight of ELV’s is recycled in European countries. This is accomplished by a combination of several successive steps: removal of hazardous fluids (motor oil, gasoline, cooling liquids,…) and hazardous or reusable parts (batteries, catalysts, tires,…), shredding of the dismantled ELV, magnetically removal of ferrous metals and eddy current removal of non-ferrous metals. In Belgium this remaining shredder residue is commonly further separated by flotation and hand sorting to obtain recycle rate of ca. 90%. The remaining fraction (10 to 25%) is a heterogeneous mixture of both inert and combustible materials including plastics, rubber, textiles and fiber material, wood, glass, … which is in general contaminated with metals, oils and hazardous substances. This fraction is called Automotive Shredder Residue (ASR) and because of its complexity and hazardous characteristics it is usually landfilled. The European directive 2000/53/EC on ELVs, sets very stringent recycling targets by the year of 2015. To comply with this directive, minimum “reuse and recycle” rates of 85% and minimum “reuse and recovery” rates of 95% have to be reached. To make this possible, further treatment of the ASR is necessary. Co-incineration in a fluidized bed combustor (FBC) with energy recovery can be seen as a complement to intensive dismantling and recycling activities in order to further increase the recovery of the ELV. The aim of this research was to investigate the environmental impact of co-incinerating ASR with waste water treatment sludge and refuse-derived fuel in a fluidized bed combustor. Data were obtained from full scale experiments in the SLECO FBC (Europe’s largest FBC), Antwerp. The fluidized bed combustor in which the eight days experiments took place, normally co-incinerates high calorific refuse derived fuel (RDF) from mechanical biological treatment of municipal solid waste with waste water treatment (WWT) sludge, in order to dry and incinerate the latter. During the experiment, which took place from the 17th till 24th of November 2008, the waste feed consisted of 25% RDF, 25% ASR and 50% WWT sludge instead of the normal 70% RDF and 30% WWT sludge mix. During the experiments, all input and output streams were sampled and further analyzed in order to make an inventory of the most important pollutants. These results were compared with the emissions during normal working conditions of the FBC (co-incineration of the sludge with RDF). Based on the inventories, the environmental impact of both situations was compared, using the CML-characterization factors, for the environmental impact categories: global warming, acidification, photochemical ozone creation, eutrophication, human and ecotoxicity. Also the expected environmental impact when co-incinerating ASR with only WWT sludge in the fluidized bed combustor were calculated. To ensure the continuity of the process, specialized waste incinerators require a certain average calorific value to be satisfied by the input. In this way complete burnout of all the waste and continuous production of steam and electricity can be ensured. For the SLECO fluidized bed combustor the input stream must satisfy an average calorific value of 8.7 MJ/kg. Therefore, the comparison of the environmental impact of the different cases is compared per ton of input stream, consisting respectively of 70% RDF and 30% WWT sludge, 25% RDF, 25% ASR and 50% WWT sludge or 39% ASR and 61% WWT sludge. Due to the higher heating value of ASR (19.2 MJ/kg) compared to RDF (11.6 MJ/kg), more WWT sludge can be destroyed when co-incinerating ASR in the FBC. A maximum of 61 wt% WWT sludge in the input stream can be destroyed, when being co-incinerated with only ASR. Since practically all the carbon in the WWT sludge is of biogenic origin (having a global warming potential of 0), a reduction in non-biogenic CO2-emission and subsequently a decrease in environmental impact on global warming, can be realized when co-incinerating WWT sludge with ASR [Figure 1]. Process heat is recovered and transformed into steam and electricity that is partly delivered to the electrical grid and partly reused in the process itself. When electricity is delivered to the electrical grid, emissions, that would occur elsewhere when the same amount of steam or electricity is produced in natural gas or coal fired units (the marginal power source in Belgium), are avoided. Since all considered input streams have approximately the same calorific value (8.7 MJ/kg), the avoided emissions are the same for all cases. No significant changes were found for the nitrogen oxide emissions (NOx) and the sulphur dioxide emissions (SO2); the environmental impact on acidification, photochemical ozone creation and eutrophication remained thus approximately constant. The emissions of Persistent Organic Pollutants (PCDDs, PCDFs, PCBs, PAHs, …) did not increase significantly when co-incinerating ASR, despite the increased input of PCDD/F. Indeed, the Persistent Organic Polutants (POPs) in the input streams are almost completely destroyed during the incineration process; other POPs are newly formed in the flue gas cleaning system. Several of our studies pointed out that the FBC serves as a sink for these toxic components. As ASR has a higher heavy metal content than the replaced RDF, the concentrations of heavy metals in the flue gas and solid residues are slightly higher than without the co-incineration of ASR, resulting in an increased environmental impact on human and exotoxicity. Also more bottom-ash is formed, due to the higher ash content of ASR (up to 48% more bottom ash). This research proves that co-incineration of ASR with WWT sludge in a fluidized bed combustor is a valid method to increase the reuse and recovery rate of ASR, as demanded by the European directive for 2015. This way ASR can be used as a fuel in a FBC, facilitating the destruction of WWT sludge; a part of its metal content can be recovered from the bottom ash formed during combustion.status: publishe