Recovery of valuable elements from municipal solid waste incineration ashes

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Characterization of Ash Melting of Reed and Wheat Straw Blend

This work was supported by the European Regional Development Fund and the programme Mobilitas Pluss grant MOBTP112, Estonian Ministry of Education and Research (IUT19-4), as well as the European Regional Development Fund through the project TK141 “Advanced materials and high-technology devices for energy recuperation systems.” Peter Backman, Linus Silvander, and Arvo Mere are acknowledged for their help on the characterization of materials and for valuable comments and discussionsAsh melting could cause severe problems in boiler operation, such as agglomeration of the fluidized bed. Our previous work has shown that the ash melting behavior of the blend of reed and wheat straw is complex and needs further investigation. The ash melting behavior was studied using different laboratory methods such as simultaneous thermal analysis, heating microscope, scanning electron microscopy with energy dispersive X-ray (SEM/EDX) analysis, and X-ray diffraction (XRD). In the thermodynamic modeling, we used FactSage software, which supplements well the results obtained by other methods and vice versa. The results indicated that melting started at 660-680 °C when Na and K salts were melted and molten K2SO4 covered the ash material; the content of liquid mass fraction was 13.8%, revealing that the studied ash blend could already be sticky at 680 °C. Intensive melting took place in the temperature range of 800-980 °C. The rapid melting between 950 and 980 °C was caused by the melting of SiO2 and K2MgSi5O12; the ash material became glassy and amorphous. We propose an alternative distribution of ash melting stages for the studied blend.Peer reviewe

Application of bipolar electrochemistry to accelerate dew point corrosion for screening of steel materials for power boilers

Maximized energy recovery in power boilers lowers the flue gas temperature. However, lowering the temperature too much may lead to problems with corrosion. The lowest operational temperature is often limited by the presence of sulphuric acid in the flue gas. Condensation of sulphuric acid may lead to severe corrosion of pre-heaters and flue gas duct parts. In this study, an experimental setup for accelerated dew point corrosion testing of steels using a concept of bipolar electrochemistry was developed. The bipolar electrochemistry was for the first time applied to study corrosion at conditions of condensing vapours of acid on the steel surface. The method allows simultaneous testing of several samples at both oxidizing and reducing conditions. In the present work, several commercial boiler steels were tested for their resistance to the dew point corrosion. It was found that bipolar electrochemistry can easily be used to accelerate corrosion for fast screening of different steel materials in simulated, dew point corrosion conditions as present in the boiler's cold-end. The electron microscopy (SEM/EDX) analyses showed that corrosion was accelerated on carbon and high alloy steels with the use of bipolar electrochemistry. Generally, stainless steels showed very good corrosion resistance and no adverse effects caused by hot H2SO4 vapours were observed.The Åbo Akademi University Foundation is acknowledged for a travel grant to visit and perform experimental work at the Nanyang Technological University, Singapore