Definition of a Robustness Indicator for Assessment of Heat Exchanger Network Performances

Due to process variabilities and operational modifications, operation parameters of the HEN may alter its output temperatures. Flexibility of HEN refers to the ability of a system to operate for a finite number of points. The first level of flexibility concerns the robustness (ability of the system to absorb disturbances without changing utility flowrates). Assuming that some parameters p vary with a normal distribution characterized by its mean value pmean and standard deviation psd, a linear system is solved where the left-hand term involves matrices representing the HEN (fluctuations of the HEN characteristics, except topology) and right-hand side involves fluctuations of input temperatures of the HEN. Due to this linear formulation, the normally distributed inputs also propagate along a normal distribution output temperatures. A robustness criterion is then defined evaluating the probability of a selected critical value output distribution to fall within a predefined interval. This robustness criterion can only be significant when a thorough data analysis is carried out to identify the relevant perturbations and their frequency of occurrence