Investigation of Cu and Zn interactions with ilmenite during waste incineration

Examensarbete för masterexamen
Borgman, Elin
In 2018, approximately 2.01 billion tons of waste was generated in the world. By 2050, this number is expected to increase drastically to 3.40 billion tons of waste annually as lower income countries develop and the world population increases (Kaz, Yao, BhadaTata, & Van-Woerden, 2018). Some of the waste can be combusted to produce heat and power, leaving residual ash behind. This also decreases the volume of the waste flow by 90 % (Lam, Ip, Barford, & McKay, 2010). As waste generation is expected to increase while the land available for landfilling decreases, it is of interest to recycle as much as possible from waste, as well as from ash, and move towards a more circular economy in which no new raw materials are needed. One technology that can be used for waste incineration is Oxygen Carrier Aided Combustion (OCAC). OCAC is a type of fluidized-bed combustion, in which the conventional inert bed material is replaced fully or in part with metal oxides, called oxygen carrier. The oxygen carrier is reduced in fuel rich parts of the reactor and oxidized in oxygen rich parts during the combustion, thereby improving the distribution of oxygen in space and time. This improves the combustion efficiency. The interaction between the oxygen carrier and fuel ash can lead to an uptake of certain elements such as zinc, copper, potassium, calcium and phosphorous among others. The aim of the thesis was to investigate how major ash components (Si, Al, Fe, Mg, Ca, K, Na and Cl) and the minor ash components Cu and Zn interact with the oxygen carrier bed material ilmenite (FeTiO3) during waste incineration. A focus on Cu and Zn was chosen since these usually have the highest concentrations out of the trace metals that can be valuable for recycling, as they are high-cost metals and energy intensive to produce. The investigation was carried out by simulating different boiler conditions and performing thermodynamical equilibrium calculations (constructing phase diagrams) using the software FactSage 7.2. The simulations indicated that ilmenite interacts with Al2O3, CaO/CaCO2, Na2O, K2O, MgO, ZnO and Cu/Cu2O but does not interact with SiO2. The compounds formed from interactions between ilmenite and ash which could be relevant for OCAC applications are FeAl2O4, CaTiO3, (Na2O)(TiO2)3, (Na2O)(TiO2)6, ZnFe2O4, (ZnO)2TiO2, (Cu2O)(Fe2O3) (s2) and (CuO)(Fe2O3) (s3). Experimentally, potassium has been found as KTi8O16 in ilmenite particles rather than as K2Ti3O7 and K2Ti6O13 as indicated by the simulations. The compound KTi8O16 is missing in the software database, therefore giving inconclusive results not corresponding to experimental findings.
FactSage, copper, zinc, major ash elements
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