Analysis of unburned carbon in industrial ashes from biomass combustion by thermogravimetric method using Boudouard reaction

•The new thermogravimetric method for the determination of unburned carbon in ashes from biomass combustion is proposed.•For the determination, the strongly endothermic Boudouard reaction is used.•The method does not require acid treatment to remove carbonates.•The method may be used for samples containing a higher amount of portlandite and calcite.•Determination is not disturbed by mineral components typical for biomass-combustion ashes.

A novel thermogravimetric method for the determination of unburned carbon in industrial ashes from biomass combustion using the strongly endothermic Boudouard reaction is proposed. The method does not require acid treatment to remove carbonates; it may also be used for samples containing a higher amount of portlandite, calcite and other mineral components typical for biomass-combustion ashes and is utilizable in the wide range of the content of unburned carbon. The correctness of the proposed determination was verified by carbon mass balance in 10 samples of industrial ashes. The interpretation of the course of the TG curves obtained was corroborated by differential scanning calorimetry.