To optimise the energy utilisation in the processes (and in particular in the chemical industry) it is useful to identify (when possible) process configurations in which the driving forces are uniform and the entropy generation approaches zero when the size of the plant increases. Such ideal configurations can be used as references and, to obtain practical plant flow diagrams, they have to be modified, according to the peculiar features of the process and the plant, the economical factors and the safety and environmental requirements. This paper presents, after a short methodological introduction, a vinyl chloride plant optimisation, based on such concepts and realised in the Porto Torres plant by the European Vinyl Corporation. Vinyl chloride monomer (VCM) is obtained by ethylene dichloride (EDC) cracking; furnace effluents containing VCM, EDC, hydrogen chloride (HCl) and chlorinated byproducts are processed through quench towers and a distillation train in oder to separate the various components. The key of the new technology is the distillation sequence, which is adjusted to make it similar to the thermodynamically optimal configuration. Due to the new temperature levels of reboilers and condensers, a better heat cascading and a reduction of the steam consumption are obtained. The modification of the existing plant with a nominal capacity of 150,000 t/a has been realised using mainly the existing columns and exchangers; a HCl distillation column and three heat exchangers have been added; a new screw compressor allows the use of the existing cooling system,In a 10-day test run carried out at 50% capacity after the modification of the plant a reduction of the steam consumption of 50% was achieved.