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The behaviour of a pilot scale tubular fixed bed catalytic reactor for the catalytic oxidation of SO<SUB>2</SUB> under non-reactive and reactive conditions for both steady-state and unsteady-state regimes is analysed by means of heterogeneous, pseudo-heterogeneous and pseudo-homogeneous models. The equations involved are solved by double orthogonal collocation employing both global and finite element approaches. Steady-state and unsteady-state non-reactive experiments have been performed in order to estimate heat transport parameters. A Smith predictor scheme was implemented for the control of the reactor inlet temperature and its performance compared with that of a conventional PID controller. Radial heat transfer parameters are estimated from the steady-state experimental information and axial heat transfer parameters from dynamic experimental data. Individual heterogeneous heat transport parameters are evaluated by employing equivalence relationships and the estimated effective parameters. Radiant heat transport (a mechanism rarely included) is considered throughout and an average value of 0.9 has been obtained for the particle emissivity. Four different methods were employed to determine the contribution of radiant heat transport to the effective parameters. Although the predicted steady-state behaviour of the system shows good agreement with experimental data and the dual stage parameter estimation strategy yields fair equivalence between the three model representations, the values of the estimated heat transfer parameters are outside normal ranges (viz. effective axial conductivities around 4x10<SUP>-2</SUP> W m<SUP>-1</SUP>K<SUP>-1</SUP>, an asymptotic fluid Peclet number of 3 and a solid-wall Biot number of 4.7x10<SUP>6</SUP>). The transient behaviour of the reactor under non-reactive conditions is predicted well enough in terms of shape but exhibits an offset in the final steady-state in relation to the experimental measurements. The predicted dynamic response under reactive conditions is compared to experiments reported by other workers. The heterogeneous model gives a good qualitative prediction of the transients involved, whilst the other structures fail to reproduce the observed behaviour. The physical meaning of the values obtained for the estimated parameters are considered doubtful and it is recommended that the models employed should be considered as predictive structures. The finite element approach showed better numerical stability and speed of convergence than global collocation, especially in parameter estimation (where it had not been applied previously) and in the prediction of dynamic reactive behaviour as it updates the element boundaries to follow the movement of the reactor hot spot.

This thesis describes a study of catalysed steam methane reforming. A microreactor of 3 mm bore, operated and controlled by computer has been used. The catalyst employed was an industrial type steam reforming nickel oxide-alumina catalyst containing 15% nickel. The experiments were performed at temperatures of industrial interest in the range of 600-840°C. The pressure range was 2.5-9 bar, at hydrogen to methane ratios of 0.5-2 and steam to methane ratios of 2-3.1. The catalyst was initially activated at 700°C in a flow of steam and hydrogen (7:1) for 16 hours. Initially, the activity of the catalyst was very high then after 16 hours of operation it started to decline to reach its lowest level after 60 hours of operation despite reactivation. Subsequent activation methods including hydrogen reduction and temperature treatment were found to have dynamic effects on catalyst activity. An important improvement in the activity of the catalyst at lower temperature was established by incorporating a dynamic sequence of temperature changes that included some experiments at temperatures within the range 750-850°C. The dynamics of several such experiments were measured and recorded. The improvement in activity at lower temperature following a high temperature experiments gradually declined at a rate that was much slower than the dynamics of mass transfer and heat transfer in the system. The experimental results were used to examine a dual reaction mechanism for the reforming process. The reaction velocity coefficients established by non-linear parameter estimation were studied as function of temperature, pressure and composition.

The steady-state and dynamic behaviour of multicomponent packed distillation columns has been simulated using two film plug flow and back-mixing models. The model solutions have been obtained employing orthogonal collocation on finite elements. The use of Jacobi, Legendre or Hermite polynomials within the finite element procedure are compared with an approach employing the Galerkin criterion. Results from the three polynomial procedures are very similar. However, in cases where more than three collocation points are required the incorporation of cubic Hermite polynomials gave the most efficient routine in terms of CPU time on a VAX 8820 computer. The Galerkin procedure proved to be the least efficient. A number of comparisons are made with results obtained both theoretically and experimentally by previous workers. In the majority of cases the predictions of column behaviour using the finite element procedures of this work give better agreement with experiment than analytical and finite difference solutions reported by other researchers. Orthogonal collocation is seen also to give stable solutions with similar CPU times to those of the finite element procedures but it is not possible to place the grid points at desired locations. Single and two variable control of overheads and bottoms compositions is examined both for a simulated industrial scale column and for a column situated at B.P. Chemicals, Baglan Bay, South Wales. Perturbations in feed composition are utilised as the disturbance with reflux and vapour flowrates as the manipulated variables. Conventional PID feedback control is applied using previously published tuning algorithms as well as a new criterion (the 'decrease gain' procedure) based upon a method due to Yuwana and Seborg (1982).

A chemical process plant control software support system aimed at simplifying the task of designing and implementing complete digital computer chemical plant control systems was designed, and partially implemented on an 8-bit microcomputer. The bulk of the system (excluding the program development environment) was designed and fully specified, as was the application programming language. The system was designed with the aim of reducing the number of faults present in a finished application system. Consequently ease of use, conceptual simplicity, flexibility and reliability were its main design goals. The system was broken into two major components. These were the software support system and the application programming system. The software support system provided a mechanism to fully configure the system structure to match that of the controlled plant, a comprehensive menu driven operator interface, and a run-time execution control environment. The application programming system comprised a module interface type application language with message based inter-module communication and a very high level event and data interface to the controlled system. The application programming language compiler and editor were not implemented, due to the constraints imposed by project timescales. The attached appendices contain full details of the design and implementation work carried out, whilst the thesis itself illustrates the more general issues which underlie the system design.

Recent developments in excess oxygen trim for boilers have resulted in more efficient and economic operation. Comparable developments have, however, not been applied to furnaces, although close control of combustion would be beneficial for both energy efficiency and product quality. One possible reason for the slower progress is the increased complexity of the automatic control system required for the dual control of furnace temperature and excess oxygen levels. Consideration of the probable control behaviour led to the need for a study of the dynamic behaviour of the furnace. This in turn led to the development of a mathematical model to predict the responses of various furnace temperatures to disturbances in air and/or fuel flow. The model is based on the balance of radiative heat transfer from the combustion gases to the walls and stock of the furnace and the conduction of heat within the walls and stock. The resulting non-linear equations are solved by computer to predict the required transient behaviour. Dynamic behaviour in a combustion gas control loop is likely to be dominated by the instrumentation characteristics and this was not included in the model. Tests on a slab reheating furnace at the Port Talbot works of the British Steel Corporation were used as part of a model validation exercise. Although much useful information was obtained these tests highlighted the difficulties in using operational plant for such experimental purposes and it was found that further model development is required to give an acceptable correlation between predicted and recorded results. Tests on combustion gas analysis equipment have indicated the dynamic behaviour likely to be met in this part of the control system and have also shown that non-linear effects, present in the current control system, are likely to be important in the design of the dual input/dual output temperature/excess oxygen control system.

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