Effects of S and Al on K Migration and Transformation during Coal and Biomass Co-combustion

The co-combustion of biomass and coal has both environmental and economic benefits in terms of pollutants and greenhouse gas emissions. However, one of the key factors affecting the feasibility of this technology is the ash deposition and corrosion caused by the high alkali metal content of biomass, especially K. After the addition of elemental S to corn stalk/Xiaolongtan lignite blended fuel and Al2O3 to corn stalk/Datong lignite, combustion experiments were carried out in a tubular furnace to explore the effects of S and Al in coal on K migration and transformation. The experimental results show that when S/K < 6, an increase in the S/K ratio inhibited the release of K. When S/K > 6, the sulfation become saturated, and an increase in S promoted the release of K. When S/K = 6, the higher the temperature was, and the more obvious the inhibitory effect on the release of K was. Increasing the S/K ratio not only increased the CaSO4 content of the ash but also increased the content of water-soluble K compounds, such as K2SO4, and decreased the contents of acid-soluble K compounds and insoluble K compounds, such as KAlSi3O8. After Al2O3 was added, as the Al/K ratio increased, the K release rate gradually decreased. When the sample with Al/K = 2.5 and the original samples were burned at 600-700 °C, the difference in the K release rates of the two samples was relatively small. When the temperature was higher than 700 °C, the higher the temperature was, and the greater the difference in the K release rates of the samples was, which indicates that a high temperature promotes the formation of aluminosilicates containing K.