Development of carbonaceous adsorbents from coal reject for acidic gases removal

Abstract

Studies on the preparation of carbonaceous sorbents from coal reject, a waste material generated in coal preparation processes, by pyrolysis and activation, and their applications to acidic gases removal are reviewed. The kinetics of coal reject pyrolysis and structural changes of coal reject as well as activation of coal reject chars are studied by both experiment and modelling. It is demonstrated that coal reject can be converted to effective adsorbents for NO_x and SO₂ removal. A two-consecutive-reaction model developed in this work can well describe the pyrolysis kinetics and confirm the softening effect on pore structure development during carbonization of coal reject. Structure-based kinetic models for the activation reactions are developed and validated by experimental data. Experimental and modelling studies of adsorption and reaction of sulfur dioxide on activated coal reject char are summarized. A macropore and surface diffusion model is successfully used to describe and predict the dynamic adsorption and desorption behaviour of SO₂ on coal reject-derived adsorbent. It is found that sorption of SO₂ in the presence of water vapour and oxygen enhances the capacity owing to sulfuric acid formation.