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Title: Modelling of non-catalytic gas solid reactions : application in flue gas desulphurisation
Author: Elgarni, Mohamed M.
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 1997
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There is an ongoing interest in the use of metal oxides as regenerable sorbents for the removal of sulphur dioxide from flue gases. Cerium oxide on alumina has been suggested but few experimental data are available, particularly for the regeneration process. It has been shown that the overall stoichiometry of regeneration with hydrogen can be split into twelve reaction steps. These were deduced from an inspection of rate data and analysis of partially reduced samples by volumetric methods and using Fourier transform infra red spectroscopy. Below about 828 K, the hydrolysis of intermediate sulphides is rate limiting whilst, above that temperature, it is the formation of sulphides and/or the reduction of oxysulphates to cerium oxide which are important. The sulphation process has been investigated in the range 695 - 880 K. Observed reaction rates were interpreted both in terms of simple rate laws and using an adsorption/reaction mechanism. The latter was shown to be the most satisfactory for describing the reaction giving an activation energy of 46.5 kl/mol. The original diffuse - interface model for gas solid, non - catalytic reactions has been presented in dimensionless form and applied to reactions with various orders. This model was discussed in relation to the sharp - interface model. The effects of assuming different concentration profiles within the reaction zone were examined. Initial assumptions regarding the distribution of reactants in the reaction zone - whether linear or sigmoidal had little affect on the predictions of zone thicknesses and gaseous concentration profiles. No such agreement was found when exponential profiles were assumed. A new grain model has been developed in which it is assumed that a diffuse reacting interface, rather than a sharp - interface exists within the grains. Model equations were solved numerically and the effect of various reaction parameters on model predictions investigated. Some of the simplified techniques used previously to solve the grain model have been extended to the new model. A comparison of these with the numerical solution differed by a maximum of 12 %. Data relating to the regeneration in hydrogen of cerium sulphate on alumina, and also for the better known reaction with sulphur dioxide of copper oxide on alumina were analysed using the diffuse - interface shrinking core model and, for comparison, the volume reaction model. Both models provide a fairly good fit of the regeneration data. Energies of activation are in the range 190 to 210 kJ/moI. Both models fit data on the sulphation of copper oxide on alumina with reasonable accuracy with energies of activation ranging from 28 to 31.6 kJ/mol.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available