A Method for the Quantification of Chlorine in Low-Rank Solid Fuels

This study reports a method for quantifying total chlorine (Cl) in low-rank solid fuels such as biomass and brown coal. It is a two-step method that separates fuel Cl into Cl released in volatiles and that retained in char via slow pyrolysis at 500 °C. The Cl in volatiles is converted to gaseous chloride (e.g., HCl) via in situ volatiles combustion at 950 °C, followed by subsequent collection and quantification. The Cl in char is quantified via conventional Eschka method. The total Cl content in fuel is then calculated as the sum of the Cl in volatiles and that in char. The method is validated using five standard samples (i.e., a high-purity polyvinyl chloride sample, an inorganic-free cellulose char, and three NaCl-loaded cellulose chars of different chlorine-loading levels). The two-step method was then used to quantify the Cl contents in three typical low-rank solid fuels (i.e., a mallee bark, a brown coal, and a water-washed brown coal), benchmarking against those analyzed using the conventional water-washing and Eschka methods. The results suggest that the water-washing method gives similar Cl content in the bark compared to that from the two-step method because all Cl in the bark is water-soluble. However, the water-washing method substantially underestimates Cl content in the brown coal due to the presence of water-insoluble Cl. The conventional Eschka method is capable of quantifying Cl in the brown coal. However, it substantially underestimates Cl content in the bark due to the loss of Cl during Eschka combustion. It is therefore noted that in using the two-step method, the choice of 500 °C as the pyrolysis temperature is essential. This temperature is sufficiently high to avoid Cl loss in char during Eschka combustion and sufficiently low to avoid Cl loss during in situ volatiles combustion.