Effects of calcium, sodium and potassium on ash fusion temperatures of solid recovered fuels (SRF)

Various types of solid recovered fuels (SRFs) were investigated, then the waste was chemically leached and co-fired with coal and sewage sludge. Ashes with different properties and oxide compositions were used to explain the influence of various ash components (mainly sodium, potassium and calcium) on the Ash Fusion Temperatures (AFTs). Oxide compositions and empirical indices were determined and the effect of these data on the measured AFTs was investigated. An attempt to explain the effects of specific oxides on SRF melting temperatures using FactSage thermodynamic equilibrium software is presented. Thermodynamic equilibrium calculations are also used to predict the onset temperature of the molten phase, the percentage of molten phase at different combustion temperatures, and the possible solid phases that may exist at different temperatures. The mechanism of transformation of the inorganic substance of SRF turned out to be more complex than that of the mineral substance of coal, which resulted from the variable composition of the SRF. The character of temperature changes of the studied wastes after leaching in water and acetic acid in most cases is similar to the courses determined experimentally. For all investigated ashes from obtained the leaching of SRF wastes, the melting temperature decreases with the applied leaching. Potassium and sodium are the key elements causig the formation of low-melting silicates. Depending on the type of waste and leaching agent the lower the value of the B/A and α indices and the CaO content in ash, the lower the shrinkage temperature of the ash.

The effect of mineral additives on the process of chlorine bonding during combustion and co-combustion of Solid Recovered Fuels

The use of solid recovered fuels (SRF) is often associated with an increased risk of chloride corrosion because these fuels can be high in chlorine and alkali. One way to reduce the risk of chloride corrosion is the co-combustion of fuel mixtures in the presence of a mineral additive containing chemical compounds that bind the emitted chlorides. This paper concerns the influence of mineral additives - constituting waste material, on the process of the binding of emitted chlorides. One of these waste materials could be a halloysite, not yet used in power industry. The research has shown its high chloride binding effectiveness, comparable to that of kaolin (known in literature as a mineral additive effectively binding chloride). Moreover, the studies have shown that SRF combustion in the presence of stabilized, dried and granulated sewage sludge, with a 25% mass fraction of sewage sludge, allows reducing chloride emissions. Studies are based on tests in a calorimetric bomb.