Comparative study on ash characteristics of various high-alkali fuels using different ashing methods and temperatures

Abstract

The comparative study on ash characteristics of various high-alkali fuel helps to solve the ash-related problems. In this paper, the ashes of wheat straw (WS) and three high-alkali coals (LA, ZJ, and TC) were prepared using the plasma ashing method (at <200 °C) and the traditional ashing method (at 575 °C, 815 °C, and 1000 °C). The mineral matters close to the initial state in raw fuel could be elucidated by the plasma ashing method because it could remove organic material without converting the primary minerals. The traditional method was employed to study the ash characteristics at the following stages of fuel conversion. The ash samples, including plasma ash (PA), low-temperature ash (LTA), medium-temperature ash (MTA), and high-temperature ash (HTA), were subjected to a variety of analysis techniques. The results show that wheat straw has a large amount of potassium, while sodium is the main alkali in coals. The PA samples of wheat straw and coals contain little less sodium or potassium than the LTA samples, and the alkali contents decrease further in the MTA and HTA samples. The ashing procedure affects the phases of K-bearing mineral in WS ashes, Na-bearing and Ca-bearing minerals in LA coal ashes, Na-bearing, Ca-bearing, and Fe-bearing minerals in ZJ and TC coal ashes. During the thermal analysis, all PA samples exhibit significant weight losses due to the decomposition, volatilization, and oxidization of minerals. The MTA and HTA samples of WS present severe fused surfaces, while those of ZJ coal are slightly melted.