Chlorine and sodium in Illinois coals as determined by neutron activation analyses

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.

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

Forthe past 25 years or more, coals that have high alkalichloride content have been recognized as likely to cause difficulties in high temperature steam boilers due to fouling and corrosion. The chlorine content of coal has been demonstrated to be an effective basis for estimating the degree of difficulty that may be expected. Mapping of the percentage of chlorine in Herrin (No. 6) Coal in Illinois generally shows an increase in chlorine content toward the deeper parts of the Illinois Basin. The chlorine values range from zero near the outcrop of the coal, to values in excess of 0.60 percent in the deeper part of the basin. Samples of both coal and groundwater associated with the coal were taken from 13 mines. The chlorine content of the coal was found to be more closely related to the chlorine content of associated ground water than to depth. The general correlation of chlorine in coal with depth is the result of the increase in salinity of the ground water with depth. Qualitative and semiquantitative tests demonstrating the evolution of chlorine have been made by heating chlorides at low temperatures in the presence of sulfur. Quantitative tests on total chlorine versus water soluble chlorine in coal and calculations of cation to anion mol ratios of both total and water soluble alkali chlorides have been made. No definite evidence of organically combined chlorine in Illinois coals has resulted from these investigations. It is the authors opinion that most, if not all, of the chlorine in Illinois coals occurs as inorganic chlorides, primarily sodium chloride. No Illinois coals are considered to be too high in chlorine for use as steam coals, although some may require special measures for their utilization.

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Chlorine in Illinois coal

The mode of occurrence and combustion characteristics of chlorine in British coal

Volatility of selected minor and trace elements in the low-temperature ash of an Illinois herrin no. 6 coal

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A. de Waele

Papers

The occurrence of chlorine in coal