Absorption of HCl and HF by Ca-based sorbents at FBC conditions

In fluidized bed combustion of S-​contg. fuels, adding limestone or dolomite to the bed is a widely applied method to control SO₂ emissions.  In this work, HCl and HF adsorption by Ca-​based sorbents was studied in the lab. at different temps. from concns. inside the boiler furnace to those in the second pass (850-​650°)​.  The effect of temp., absorbent quality, and gas atm. on HCl and HF removal by Ca-​sorbents was examd.; special emphasis was placed on studying the effect of molten-​phase formation in HCl absorption.  Expts. were conducted isothermally using a thermogravimetric app. specially designed to study solid-​gas reactions.  Two limestones and 1 dolomite absorbent were tested; the effect of gas compn. was examd. by varying CO₂, water, and SO₂ concns. in a simulated flue gas mixt.  Absorbent conversions were calcd., and SEM- and energy dispersive spectrometry-​observations were conducted to study the reaction pattern inside the absorbent particles.  HF was very reactive, and conversions to CaF₂ were close to 100​%.  CaCl₂ was also formed at 650° and 850°, but the conversion was highly dependent on water and SO₂ concns.