The dissolution of limestone, coal fly ash and bottom ash in wet flue gas desulphurization

dc.contributor.advisorRutto, H. L.
dc.contributor.authorKoech, Lawrence
dc.descriptionM. Tech. (Department of Chemical Engineering, Faculty of Engineering and Technology): Vaal University of Technologyen_US
dc.description.abstractStrict environmental regulation on flue gas emission has led to the implementation of FGD technologies in power stations. Wet FGD technology is commonly used because it has high SO2 removal efficiency, high sorbent utilization and due to availability of the sorbent (limestone) used. SO2 is removed by passing flue gas through the absorber where it reacts with the slurry containing calcium ions which is obtained by dissolution. This study presents the findings of the dissolution of a calcium-based material (limestone) for wet FGD process. This was done using a pH stat apparatus and adipic acid as acid titrant. Adipic acid was used because of its buffering effect in wet FGD process. The conditions used for this study are similar to what is encountered in a wet FGD process. The extent of dissolution was determined by analyzing the amount of calcium ions in solution at different dissolution periods. The dissolution kinetics were correlated to the shrinking core model and it was found out that chemical reaction at the surface of the particle is the rate controlling step. This study also investigated the dissolution of coal fly ash and bottom ash. Their dissolution kinetics showed that the diffusion through the product layer was the rate controlling step due to an ash layer formed around the particle. The formation of ash layer was attributed to pozzolanic reaction products which is calcium-alumino-silicate (anorthite) compounds were formed after dissolution. The effect of fly ash on the dissolution of rate of limestone was also studied using response surface methodology. Limestone reactivity was found to increase with increase in the amount of fly ash added and the pH was found to be strong function of the rate constant compared to other dissolution variables. The presence of silica and alumina in fly ash led to a significant increase in the specific surface area due to hydration products formed after dissolution.en_US
dc.format.extentxii, 134 leaves: illustrationsen_US
dc.subjectFlue gas emmissionen_US
dc.subjectPower stationsen_US
dc.subjectAcid titranten_US
dc.subjectAdipic aciden_US
dc.subjectShrinking core modelen_US
dc.subjectCoal fly ashen_US
dc.subjectCoal bottom ashen_US
dc.subjectPozzolanic reaction productsen_US
dc.subject.lcshCoal-fired power plantsen_US
dc.subject.lcshFlue gases -- Desulfurizationen_US
dc.subject.lcshFly ashen_US
dc.titleThe dissolution of limestone, coal fly ash and bottom ash in wet flue gas desulphurizationen_US
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