The varying characterization of alkali metals (Na, K) from coal during theinitial stage of coal combustion

The first step in controlling alkali gaseous phase concentrations in flue g as is understanding their behavior during coal combustion. The behavior of sodium and potassium in coal during the initial stage of combustion was inv estigated. A series of tests were conducted under two combustion temperatur es (800 degreesC and 900 degreesC) and two atmospheres (21 vol % and 6.36 v ol % O-2) The data indicated that only a small portion of alkali metal in t he coal was released during the initial stage of combustion process (e.g., devolatilization and volatile combustion stage). The varying behaviors of d ifferent occurrence modes of alkali metals were also studied, that are iden tified by sequential extraction with the solutions of water, 1 M ammonium a cetate, and 1 M hydrochloric acid, respectively. In general, the water-solu ble (WS) alkalies in the burning residue decreased with an increase in expo sure time on high temperature combustion atmosphere, while the hydrochloric acid-soluble alkalies showed an opposite tendency. This result suggests th ere was conversion of the WS forms to the hydrochloric acid-soluble (HAS) f orms through aluminosilicates as inter-media. The possible pathway in the p rocess is that the WS alkali reacts with aluminosilicates to form chiefly a lkali aluminosilicates that can be dissolved in 1 M hydrochloric acid solut ion or partly as ion exchangeable alkali metals.