TABLE OF CONTENTS So far, we have dealt exclusively with continuous processes. However, pinch analysis can also be applied to batch processes, with suitable modifications. This type of analysis has been largely neglected, because batch processes are in general less energy intensive than continuous bulk systems. However, the techniques are worth studying for several reasons:
Existing batch processes often have little or no heat recovery and there can be easy energy saving opportunities.
The analysis often gives useful non-energy operational benefits, such as debottlenecking identifying rate-limiting steps and reducing cycle times.
Many continuous processes incorporate semi-batch sections, which must be included in the analysis to give the overall picture.
The methods can be applied to other situations where the stream data varies with time, for example, during start-up and shutdown, or day/night variations.
Although continuous processes reign supreme for the production of bulk chemicals, there are many batch plants in existence. Indeed, their use is increasing in many countries because of the trend towards high-value, low-tonnage products such as specialty chemicals, fine chemicals and pharmaceuticals. However, the throughput and energy use of these processes is low, and therefore energy and cost savings from heat recovery are also limited.
For batch systems, both pinch analysis and practical heat recovery projects are much more difficult than for continuous processes, for a number of reasons. Many streams are present for only certain time periods, which restricts the possibilities for heat exchange. Also, they may not run between constant temperatures with constant heat capacity...
