Browsing by Author "Petrie, James"

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    The catalytic reduction of nitric oxide over copper doped aluminosilicates
    (1993) Hwang, Gerard; Petrie, James
    With the object of greater energy efficiency, a role has been identified for a facility capable of the simultaneous removal of NOx, SO₂ and particulates from flue gas at high temperature. This project forms the initial phase of the development of such a high temperature flue gas cleaning facility and is limited to the study of catalytic NOx reduction over aluminosilicates. A copper ion-exchanged zeolite (Cu-ZSM-5) and copper oxide were studied as catalysts for the Selective Catalytic Reduction (SCR) of nitric oxide in the temperature range 250-530⁰ C. Ammonia was employed as the reducing agent. The intention of this investigation was to work towards an examination of the potential for obtaining an active SCR catalyst by doping amorphous aluminosilicate fibres (which are used as high temperature particulate filters), with copper. The direct decomposition of nitric oxide over Cu-ZSM-5 was investigated in order to validate the experimental rig and procedures by duplicating published results. An activation energy of 29 kcal/mol was determined and a reaction order with respect to nitric oxide of 1.2 was obtained at 500⁰ C. Both values compare well with published data. Cu-ZSM-5, CuO supported on silicalite and CuO physically blended with the fibrous aluminosilicate were investigated as SCR catalysts. It was found that: The rate of the SCR reaction was three orders of magnitude higher than the rate of the direct decomposition reaction over Cu-ZSM-5. CuO supported on silicalite yielded higher reaction rates than unsupported CuO and the rates of the former approached those for the reaction over Cu-ZSM-5. An activation energy of 14 kcal/mol was obtained for the SCR reaction over Cu-ZSM-5 and a value of 9 kcal/mol was obtained for reaction over CuO (supported and unsupported). The ability of supported CuO to catalyse the SCR reaction at a rate comparable to that found with Cu-ZSM-5 suggests that the use of CuO should be investigated further, both in its own right as a NOx reducing catalyst since little has been published in this regard, and as a simultaneous NOx/SO₂ removal sorbent/catalyst. The intrinsic catalytic activity of copper oxide and the success with which it has been dispersed/supported on the porous silicalite structure, suggests that a suitably active SCR catalyst form may be obtained if a high dispersion of copper oxide may be achieved on the non-porous aluminosilicate fibres.
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    Sulphur sorbent particle effects in fluidised combustion
    (1988) Petrie, James
    An overall process model is presented for the capture of sulphur dioxide by calcareous sorbents in a fluidised bed combustor for a feed of arbitrary size distribution. The description of sorbent sulphation kinetics, particle attrition and elutriation effects incorporated in this model is supported by experimental data for a wide range of South African sorbents. The sulphation of sorbent particles is described by a simple, two-parameter, kinetic model. No loss in physical relevance is incurred when the decrease in reaction rate with time is given by a negative exponential term. Both sulphation rate and capacity are shown to be functions of sorbent type. The sulphation propensity of the 16 South African samples is correlated against their geologic description. Sorbent properties such as porosity, crystallinity and topography, which affect sulphation capacity directly, are functions of geologic age. It is possible to make a first order assessment of sorbent potential simply from this geologic data. Sorbent attrition, caused by the continuous movement of particles within the combustor, is greatest for deep beds of soft friable material. Most of the attrition takes place in the distributor region where jetting action is important. The attrition model reflects an explicit dependence on fluidising velocity, bed depth, particle diameter, topography and structural strength. Measured values of attrition rate decrease with time to a steady state value, which, under normal FBC operating conditions, is attained after a time in the bed of 6 - 10 hours. The elutriation model considers the effect of fines, generated by attrition, on the carry-over of coarse particles from the bed. The overall process model confirms that choice of sulphation kinetics exerts the greatest influence on attainable sulphur capture,. although bed fluid dynamics, sorbent attrition and feed size distribution all play a role. The model is substantiated by extensive data from the performance of three dissimilar sorbents in a 10 MWth FBC. The contribution of sorbent attrition to the solids loading of downstream gas cleaning equipment is highlighted.
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    The use of life cycle assessment in the evaluation of environmental performance in the base metal refining industry
    (1999) Forbes, Patricia Belinda Crosby; Gaylard, Peter; Petrie, James
    In the last decade, life cycle assessment has come into consideration as an environmental decision support tool for the design and operation of industrial processes. The usefulness of this technique for the purpose of environmental management was assessed by means of a case study carried out at the base metal refinery of impala Platinum Limited. An assessment was first carried out on the historic performance of the process. This was then extended to evaluate some possible impacts of future changes in operating practice and technology.