Experimental Investigation of Mineral Sorbents for Alkali Removal during the Combustion of Solid Biomass

Additives like kaolin and coal fly ash (CFA) can reduce problems caused by alkali species during the combustion of solid biomass. In this work, a two-staged thermobalance is used to investigate the parameters of the alkali sorption process of kaolin and CFA. The two-staged thermobalance consist of two connected thermogravimetric analysis (TGA) systems with independent heating zones. In the upstream TGA, alkali salts like potassium chloride or potassium sulfate are evaporated to create a defined alkali concentration in the gas stream. The sorption process can then be observed accurately by the mass change of the sorbent sample in the downstream TGA. In the course of the measurements, the sorbent behavior of kaolin is investigated for alkali concentrations in the gas stream between 40 ppm and 645 ppm, as well as temperatures in the sorption zone between 800 °C and 1400 °C. The sorption efficiency increases with increasing temperature independent of the alkali concentration in the gas stream. At 1300 °C and 1400 °C, sorption efficiencies above 30 % can be observed at low potassium chloride concentrations, which is close to the theoretical maximum intake. For higher potassium chloride concentrations, the sorption efficiency decreases. The location of the additive introduction, the amount of additive, as well as the limitations of an alkali removal system can be assessed with the results. Additionally, this work shows that the novel two-staged thermobalance concept is capable of investigating gas-solid reactions at high temperatures. Especially the capability of creating stable atmospheres with minimal alkali concentrations stands out.     «

Additives like kaolin and coal fly ash (CFA) can reduce problems caused by alkali species during the combustion of solid biomass. In this work, a two-staged thermobalance is used to investigate the parameters of the alkali sorption process of kaolin and CFA. The two-staged thermobalance consist of two connected thermogravimetric analysis (TGA) systems with independent heating zones. In the upstream TGA, alkali salts like potassium chloride or potassium sulfate are evaporated to create a defined...     »