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Abstract

This thesis examines the integrated control of a steel hot plate system consisting of a reheat furnace and a controlled reversing plate mill. Alternative multilevel techniques are proposed for the optimal control of the system where the objective is to minimise fuel consumption in the reheat furnace and minimise power consumption in the rolling mill. The alternative schemes are analysed, paying particular attention to their practical utility, resulting in a recommended feasible scheme based on the interaction prediction principle in which intermediate results from the iterative optimisation can be applied directly to the plant. In this scheme the temperature of the slab leaving the furnace is considered as an interaction variable and is under the direct control of the supremal coordinator. Infimal unit problems, which comprise the optimisation of the reheat furnace and rolling mill, respectively, are investigated in detail and simulation results are presented to illustrate the proposed control schemes.

The task of the reheat furnace subsystem is, with minimum fuel consumption, to heat the moving slabs to a defined exit temperature which is specified by the supremal coordinator. Control is performed in pre-heat, heat and soaking zones, taking account of interaction effects between the latter two zones. At a given push rate, steady state optimisation is performed using orthogonal search taking account of soaking zone entry gradient constraints.

The reversing plate mill subproblem of providing final plates of steel of given thickness, within a desired temperature range, at maximum throughput and minimum utilisation of energy is solved by dynamic programming with the constraint that there must be an odd number of passes during slab reduction.

In this thesis, emphasis is given to the practical on-line considerations of applying the multilevel optimisation scheme, including the effects of quantization. As well as presenting simulated results, the thesis describes a semi-pilot-scale plant investigation where the re heat furnace is represented by an electrically-heated travelling load oven and the rolling mill is simulated within a process control computer.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QA Mathematics > QA75 Electronic computers. Computer science T Technology > TJ Mechanical engineering and machinery T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments:	School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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