An Enhanced Tool for Heat Exchanger Network Retrofit Towards Cleaner Processes

The individual stream temperature versus enthalpy plot (STEP) is a graphical tool that can be used to simultaneously diagnose and retrofit existing heat exchanger networks (HEN). The Modified Energy Transfer Diagram (ETD) utilises the Grand Composite Curve (GCC) to provide insights on the scope for HEN retrofit and to pinpoint retrofit alternatives based on the Bridge Analysis method. Both the STEP and the Modified ETD methods are based on graphical representation of individual process streams that enable users to visually identify the potential scope for improvement in an existing HEN. It is found that, using the distance of the horizontal gap between the stream pairs of the STEP diagram can simplify the construction of the Modified ETD. The Modified ETD can help monitor the progress of HEN retrofit. This paper shows through a case study that, combining the use of STEP-ETD methods can simplify, facilitate and enhance the simultaneous targeting, diagnosis and retrofit of a HEN toward achieving cleaner processes, while yielding the same final retrofitted structure like those produced by using only the Modified ETD.