The work presented in this thesis, in general, involves preparation and characterization of sorbents for SO2 and NOx removal using waste carbonaceous materials. The specific objectives of this project are to fundamentally investigate into
(1) the feasibility of utilization of coal washery reject m preparation of an effective sorbent for toxic gas removal from flue gases;
(2) structural and adsorptive properties of coal reject-derived sorbents;
(3) mechanisms and kinetics of the preparation processes as well as the sorption of SO2 and NOx onto the sorbents.
A series of experimental and theoretical studies were carried out to fulfill the objectives of this work. These studies are mainly on the preparation processes such as pyrolysis in inert atmosphere and activation in oxidative gases, and also on the sorption and reaction of SO2 in the carbonaceous sorbent developed. The principal experimental techniques used include (a) Thermogravimetric Analyzer (TGA) for kinetic studies, (b) Accelerated Surface Area and Porosimetry (ASAP 2000) system for surface area and pore structure characterization, (c) fixed bed high temperature reactors for pyrolysis and activation, (d) other characterization techniques such as XRD, SEM and Hg Porosimeter. The approach to the theoretical aspects of this project is essentially mathematical modelling of the kinetics of pyrolysis and activation reactions and dynamics of adsorption and reaction of SO2.
The results of the forementioned investigations show that coal reject can be converted into an effective sorbent for SO2 and NOx removal with considerable adsorption capacities. Pyrolysis of coal reject in inert atmosphere and activation of its pyrolyzed char with CO2 or steam have been established as two important processing steps in preparing the sorbent. Pyrolysis temperature, heating rate and residence time and temperature of activation are found to be important factors in controlling the pore structure of the resultant char sorbent from coal reject. Physical structural changes of coal reject during pyrolysis such as thermoplastic softening have been identified through kinetic modelling as important phenomena which affect the ultimate structure of the sorbent. The gas-solid reaction model simulations have provided a greater insight into the kinetics and structural evolution of coal reject char during activation. A better understanding of the SO2 sorption and reaction in carbonaceous sorbents is also achieved from the studies in this thesis.