Biomass ash modification in development of sustainable binders

Over one million tonnes of combustion waste was generated in 2015 in Finland, 40% of which was landfilled. Renotech Oy developed a concept which allows for the transformation of some of the combustion waste into a reactive... [ view full abstract ]

Over one million tonnes of combustion waste was generated in 2015 in Finland, 40% of which was landfilled. Renotech Oy developed a concept which allows for the transformation of some of the combustion waste into a reactive binder. The concept does not only contribute to circular economy by closing the loop but also reduces the energy consumption from cement production. In the concept the energy intensive cement production step is replaced by in situ modification of ash with the use of combustion additives, e.g. limestone. The biomass ash is modified directly during the combustion process of biomass. The combustion tests were performed at a biomass combustion unit (240 MWth). The tests comprised three cases: reference, lower additive level, and higher additive level. Fly ash samples were collected in all cases and saved for analysis. The fuel and additive feeding rates during the test were recorded together with sulphur emissions. The elemental composition of collected ashes was performed by means of SEM/EDX but also the changes in the crystalline structure of the ashes were followed by means of XRD. The potential use of ashes as a binder was determined based on their 7-, 14-, 28-, and 90-day compressive strengths. The compressive strengths were tested according to standard EN 196-1.  The modified ashes have shown increased compressive strengths. The 28-day compressive strength increased from 1.5 MPa for reference ash to 16 MPa for the modified ash (higher additive level).