Thesis for the Degree of Master of Science


Year 2004
Anna Kesti

Energy Efficiency Control in Distillation Part of Hydrodesulfurization Unit

Distillation is one of the most important separation methods in the chemical industry. The majority of costs arising from operating a distillation column are energy-related. Hence, improving efficiency in energy consumption will result in significant savings. Illustrative key figures of distillation columns are required to enable operators to run distillation as energy efficiently as possible. The literature, however, is concentrated on plant wide key figures, which can not be used to control single distillation columns.

The aim of this thesis was to improve energy efficiency in the distillation part of the hydrodesulfurization unit and develop practical key figures by which the unit could be operated as close to energy optimum as possible. The aim was to integrate product quality, savings and energy efficiency into the developed figures. Industrial plant tests were organised to find the real process constraints, and to verify the benefits of operating the column close to its actual operating constraints.

The literature part of the thesis presents key figures relating to operating distillation columns available from the literature and reviews distillation process control theory. The study also addresses different methods used for decreasing energy consumption in existing distillation columns. In this thesis, distillation focuses only on two product columns with trays.

In the experimental part, industrial plant tests were planned and executed. The tests identified process constraints of condenser output temperature and column pressure, on the basis of which key figures were developed. During the plant tests column process control was monitored and improvements in configuration control were presented.

The energy-efficient operation of distillation columns presented in this work will achieve significant reduction in operating costs. Operating energy efficiently requires functional control of the process unit as well as motivation on the part of operators, who are to utilize the models developed in this thesis. Efficient process control of the hydrodesulfurization unit distillation part requires further development of pressure compensated temperatures, greater utilization of analyzers and reconfiguration of model matrixes.

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