Migration and Transformation of Alkali and Alkaline Earth Metals during Co-gasification of Biomass and Coal

(2) Gas-solid reaction and ash formation stage: The reaction rate in this stage was relatively slow, during which the occurrence forms of alkali (earth) metal elements such as K, Ca, Na, Mg in semi-coke underwent significant changes when contacting with air (or CO2). Under air atmosphere during 5-120 min residence time: water-soluble K, insoluble K, and ammonium acetate-soluble K in cotton stalk transformed into HCl-soluble and volatile phases; In coal/elm blends, the HCl-soluble Ca content decreased from 35% to 13% under air atmosphere, while the volatile phase increased from 11% to 27%.

Water-soluble, ammonium acetate-soluble, and insoluble Na all transformed into volatile phases; Mg mainly existed in ammonium acetate-soluble form (55%) with little change during residence time. Prolonged residence time caused K and Ca to combine with S, Al, Si under air atmosphere forming CaSO4 and KAlSiO4; CO2 atmosphere increased components such as CaCO3, CaS, MgS.