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Life Cycle Assessment of a Pyrolysis / Gasification Plant for Hazardous Paint Waste

by Robert Jan Saft
International Journal of Life Cycle Assessment ()

Abstract

Goal, Scope and Background. Life Cycle Assessment (LCA) re- mains an important tool in Dutch waste management policies. In 2002 the new National Waste Management Plan 2002–2012 (NWMP) became effective. It was supported by some 150 LCA studies for more than 20 different waste streams. The LCA re- sults provided a benchmark level for new waste management technologies. Although not new, operational techniques using combined pyrolysis/gasification are still fairly rare in Europe. The goal of this study is to determine the environmental perfor- mance of the only full scale pyrolysis/gasification plant in the Netherlands and to compare it with more conventional tech- niques such as incineration. The results of the study support the process of obtaining environmental permits. Methods. In this study we used an impact assessment method based on the guidelines described by the Centre of Environmen- tal Science (CML) of Leiden University. The functional unit is defined as treatment of 1 ton of collected hazardous waste (paint packaging waste). Similar to the NWMP, not only normalized scores are presented but also 7 aggegated scores. All interven- tions from the foreground process (land use, emissions, final waste) are derived directly from the site with the exception of emissions to soil which were calculated. Interventions are accounted to each of the different waste streams by physical relations. Data from background processes are taken from the IVAM LCA database 4.0 mostly originating from the Swiss ETH96 data- base and adapted to the Dutch situation. Allocation was avoided by using system enlargement. The study has been peer reviewed by an external expert. Results and Discussion. It was possible to determine an envi- ronmental performance for the pyrolysis/ gasification of paint packaging waste. The Life Cycle Inventory was mainly ham- pered by the uncertainty occurred with estimated air emissions. Here several assumptions had to be made because several waste inputs and two waste treatment installations profit from one flue gas cleaning treatment thus making it difficult to allocate the emission values from the flue gasses. Compared to incineration in a rotary kiln, pyrolysis/gasifica- tion of hazardous waste showed better scores for most of the considered impact categories. Only for the impact categories biodiversity and life support the incineration option proved fa- vorable due to a lower land use. Several impact categories had significant influence on the conclusions: acidification, global warming potential, human toxicity and terrestrial ecotoxicity. The first three are related to a better energy efficiency for pyrolysis/ gasification leading to less fossil energy consumption. Terrestrial ecotoxicity in this case is related to specific emissions of mercury and chromium (III). A sensitivity analysis has been performed as well. It was found that the environmental performance of the gasification tech- nique is sensitive to the energy efficiency that can be reached as well as the choice for the avoided fossil energy source. In this study a conservative choice for diesel oil was made whereas a choice for heavy or light fuel oil would further improve the environmental profile. Conclusions. Gasification of hazardous waste has a better envi- ronmental performance compared to the traditional incinera- tion in rotary kilns mainly due to the high energy efficiency. As was determined by sensitivity analysis the differences in envi- ronmental performance are significant. Improvement options for a better performance are a decrease of process emissions (espe- cially mercury) and a further improvement of the energy balance by decreasing the electricity consumption for shredders and oxygen consumption or making more use of green electricity. Recommendations and Perspectives. Although the life cycle in- ventory was sufficiently complete, still some assumptions had to be made in order to establish sound mass balances on the level of individual components and substances. The data on input of waste and output of emissions and final waste were not compatible. It was recommended that companies put more emphasis on data storage accounted to particular waste streams. This is even more relevant since more companies in the future are expected to include life cycle impacts in their environmen- tal performance.

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