What can we learn from ecological valuation of processes with the sustainable process index (SPI) — the case study of energy production systems

The Sustainable Process Index is an ecological evaluation system specially developed for the requirements of process engineering. It allows reliable as well as convenient and quick valuation of processes on the base of data available to a process engineer even in the early stages of planning. The paper will discuss the application of this index in practical examples of interest to many process engineers. Energy systems are of great importance for almost any process, as they cause a considerable part of investment, as well as operating costs. From the ecological point of view, they may be even more influential as they cause direct emissions (e.g. SO2, NOx) as well as contributions to global ecological problems, most prominently global warming. The right decision about energy systems within a process therefore is of considerable importance for any process engineer. A comparison of different energy systems with the SPI will reveal the most important ecological features of energy systems using different conversion technologies as well as different raw materials and energy sources. The various pressures exerted by these systems on the environment will be discussed. However, the most important information derived from a valuation with the SPI is the relative size of these pressures. This bases the decision about the right energy system on an equal footing for all technological contenders. It allows also the setting of engineering and optimisation priorities.