(52c) Energy Efficient Design In the Continuous Process Industries: From Nuisance to Necessity

A retrospective view of design for energy efficiency in the process industries reveals that there has been a fundamental change of thinking over the last 30 years. It is useful to review the change in order to understand its significance for process design in an energy-challenged future.

Chemical Engineers have always sought to use energy efficiently, but priorities in the investment boom up to the late 1970s in an energy-abundant world dictated an emphasis on scale, ?repeatability' and materials yield. The ?oil shocks' forced an abrupt change, and process energy efficiency, including revamps, received much greater attention. In this context, ?crossover' thinking from the power and cryogenics industries brought systematic thermodynamic analysis into general process design.

A key concept was to analyse process plants as integrated systems and to apply temperature interval analysis. From this flowed all the benefits of ?pinch' understanding in heat recovery systems, including the concepts of placing CHP and process units in relation to the pinch. Associated concepts were ?cross-the-boundary' thinking applied to adjacent units and even sites, and the inclusion of pinch design techniques within overall process synthesis methods. Systematic analysis of the capex-energy cost tradeoff in energy systems was introduced.

The drive for energy efficiency lost some impetus in the 1990s due to very cheap oil, but interestingly, improvements in process selectivity and in catalyst development brought reduced process energy consumption. Also, innovative separation technologies and new distillation systems including practical dividing wall columns were developed, improving energy demand. Meanwhile, computing power continued to grow and powerful optimisation methods allowed engineers to explore many more optimum process configurations.

Examples of energy efficiency improvement are given. For the future, the systems approach is being applied to the broader requirement for sustainability in process design, and the systems approach continues to be a focus of design research.