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Preparation of bagasse Ash/MgO/ammonium acetate sorbent properties and modeling their desulphurization reaction

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Abstract

This work investigates the use of a siliceous material (bagasse ash) and a hydrating agent (ammonium acetate) as additives to enhance sulphur dioxide removal efficiency in low temperature dry flue gas desulphurization (FGD) process when magnesium-based sorbent is used. Response surface methodology (RSM) was used to determine the effects of hydration temperature, hydration time, amount of ammonium acetate and amount of bagasse ash on the surface area of the sorbent. A polynomial model was developed to relate the preparation variables to the sorbent surface area. The Brunauer-Emmet-Teller (BET) surface area results show that the surface area increased from 56 m2/g to 219 m2/g when bagasse ash and ammonium acetate was used at different sorbent preparation conditions. The desulphurization experiments performed using a Thermo Gravimetric Analyzer (TGA) showed that sulphur dioxide (SO2) removal efficiency of up to 99.9% at reaction time of 2 h was achieved. The surface area results were in excellent agreement with the results obtained from the desulphurization reaction. The unreacted shrinking core model was chosen to describe the desulphurization reaction kinetics between SO2 and the magnesium hydrated sorbent. The model shows that a non-porous shielding layer forms which stops further gas(SO2)-solid (magnesium sorbent) reaction from occurring and the product layer was determined to be the rate limiting. The scanning electron microscope (SEM) results illustrates that as the sulphation reaction takes place pores become plugged with reaction products resulting to a non-porous structure. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 23–31, 2015

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