Screening of potential mineral additives for use as fouling preventatives in Victorian brown coal combustion

Abstract Laboratory tests have been undertaken on a suite of 12 mineral samples to ascertain their effectiveness as fouling alleviating additives to coal during combustion. Two samples of Victorian coal from the Loy Yang and Yallourn coal mines were used in the investigation. The laboratory tests include measuring the total chemisorption capacity of the minerals for different Na compounds (NaCl, NaOH and Na2SO4) using a simple thermogravimetric technique. The second method involves ashing mixtures of the minerals and coal in air. Chemical analysis of the Na content within the mixtures (before and after ashing) is used to determine the effectiveness of the different additives, with a high Na retention indicating good potential for fouling mitigation. Minerals containing both alumina and silica were found to be the best sorbents for NaCl in the chemisorption experiments. They are also found to be the best additives for retaining sodium within the coal ash (for both coal types) as well. In contrast, minerals exhibiting high NaOH and Na2SO4 retention were not necessarily good candidates for use as coal additives. This indicates that the sodium released from the coal during combustion is primarily in the form of NaCl, agreeing with thermodynamic modelling of the combustion process. The best additive candidates are kaolin, bentonite, miclay (micaceous clay), diatomite, pumice, pyrophyllite and overburden. On a cost basis kaolin mineral types and overburdens (provided there are sufficient reserves) appear to be the best candidates for use as fouling preventative additives during the combustion of Victorian low-rank coal.