This study examined the surface area degradation of kaolin, coal fly ash and the resulting impact on the alkali capture efficiency in a pilot-scale real flame combustion test rig using beech wood as fuel. Experiments in an electrically heated furnace revealed the thermal surface area evolution of kaolin with residence times between 30 and 3600 s and temperatures between 790 and 1400 °C under calcination conditions. Subsequent measurements of the resulting specific BET (Brunauer-Emmet-Teller method) surface area of the kaolin samples were carried out. The temperature profile in the top-down fired biomass combustion test rig (BoCTeR) was measured with a suction pyrometer when combusting natural gas and beech wood powder. Additional experiments were performed by injecting kaolin and coal fly ash particles directly into a natural gas flame at different reactor heights. Those kaolin particles exposed to high temperatures in the natural gas flame were collected and subsequently analysed for the specific BET area to evaluate the corresponding degree of surface loss. The main test series comprises a setup combusting beech wood with kaolin or coal fly ash injected at different positions of the combustion chamber. The alkali sorption capacity of the kaolin and coal fly ash used is indirectly measured by the combustion aerosol reduction performance determined with an electrical low-pressure impactor (ELPI). The goal of this work is to show the impact of surface area degradation phenomena of additives and the resulting optimisation potential when using Al/Si-based in-furnace additive during the pulverised-fuel combustion of biomass. The surface area development of the additives at high temperatures affects the most suitable temperature window for the additive injection. The results show an optimum for the kaolin injection. The coal fly ash reduced PM best when injected as early possible into the combustion chamber.     «

This study examined the surface area degradation of kaolin, coal fly ash and the resulting impact on the alkali capture efficiency in a pilot-scale real flame combustion test rig using beech wood as fuel. Experiments in an electrically heated furnace revealed the thermal surface area evolution of kaolin with residence times between 30 and 3600 s and temperatures between 790 and 1400 °C under calcination conditions. Subsequent measurements of the resulting specific BET (Brunauer-Emmet-Teller meth...     »