Livscykelanalys av behandlingsprocesser för flygaska från avfallsförbränning : jämförelse av Ash2Salt-processen med befintliga metoder

Sammanfattning: EasyMining Sweden AB, a subsidiary to Ragn-Sells AB, has developed a new process for treatment of fly ash from municipal solid waste incineration called Ash2Salt, which enables recycling of salts; sodium chloride, potassium chloride, calcium chloride and ammonium sulphate. To compare this new process with some of today’s fly ash treatment processes available for Swedish and European fly ash a life cycle assessment (LCA) was performed. The functional unit used for the comparison was “treatment or disposal of 1 ton of fly ash” and the environmental impact was compared through four different categories: climate change (kg CO2- eq), depletion of abiotic resources (kg Sb-eq), ecotoxicity (CTUe) and human toxicity (CTUh). The results showed that the Ash2Salt process had the lowest environmental impact considering all the studied environmental impact categories, which mainly depends on the assumption that the salts recycled from fly ash replaces conventionally produced salts. The treatment process with the highest environmental impact was the process of stabilising and refilling old salt mines in Germany, mainly because of the long distances of transport. Further on, the environmental impact from recycling the salts from fly ash using the Ash2Salt method was compared to conventional salt production processes. The functional unit used for the comparison was “production of 1 kg of salt”. Economic allocation was assessed between the salts from the Ash2Salt process. The results showed that for two of the impact categories (climate change and depletion of abiotic resources) the salts recycled from fly ash had lower environmental impact than the conventional production processes, but for both toxicity categories potassium chloride and ammonium sulphate had higher environmental impact than the conventional production processes. The reason for this mainly depends on the chosen principle of allocation and the fact that the production of ammonium sulphate in the Ash2Salt process demands more inputs than the other salts in the process.