Overall site optimisation by Pinch Technology

The importance of integration in process plant design has long been recognised. This is evidenced for example, by the existence of complex heat and power networks in modern production sites. These networks represent site-wide integration. They usually allow process heating duties in several processes to be effected at low cost by using turbine pass-out steam after obtaining a credit for power generated in a central turbine. When looking for energy saving in retrofit projects, an installed heat and power network of this type usually introduces a counter-productive element. A reduction in steam heating duties leads to a reduction in turbine pass-out steam which, in turn, leads to a reduction in power generation. This makes optimisation of the process alone and optimisation of the process in the site context two rather different tasks. More complications are given through other more general reflections across a site. A modern processing plant such as ethylene, for instance, is usually linked into the overall site and interacts with other plants through several utilities, not just back pressure steam. This makes it necessary to not only understand the fundamental process demands but also to analyse these demands in the site context. Process licensors will usually prefer to consider standard designs for individual processes. The best project, on the other hand, will almost invariably be site dependent. This article highlights the distinction between the application of process integration techniques—in particular pinch technology—within an individual process and their wider application in the overall site context. The “counter productive” aspect of heat savings in the context of isntalled heat and power networks is given attention. In addition to energy, the article discusses yields, flexibility and capital cost savings.