Conclusion
This work has formulated a Pinch-Based simultaneous targeting and
synthesis procedure for multi-contaminant material recycle-reuse
networks, on the example of water networks. It involves the methods to
determine the source prioritisation sequence for each sink,
classification of sinks to Below/Above Pinch, and determine the limited
flowrate of the sources that can be assigned. The allocated sinks and
sources are then arranged with ascending order of their concentrations.
After the assignment of the sinks and sources to each contaminant
cascade, the typical PA can then be performed for each contaminant
cascade and for each sink sequentially. If the Pinch Point occurs at the
non-limiting contaminant of the sink, a source reduction can be
performed to further reduce the freshwater target for that sink. The
proposed method is validated with an illustrative example and two real
case studies from the paper mill and starch industry. The obtained
freshwater targets for both cases studies are 39,836 kt/d and 47.36
kg/h. The results agree well with the solution from the literature and
the solutions obtained by solving the superstructure model. The
consistent solutions obtained compared with optimisation method and
previous works prove the accuracy and legitimacy of the method.
Note that the freshwater requirements determined in this work represent
the resource requirement ignoring the interaction between the sinks and
sources are. The data used in this work are the maximum flowrates and
concentrations of the sources and sinks. Certain sink’s maximum
concentration limit might not be reached, and this could affect the
concentration of the sources from the same operation of the sink. If
fixed contaminant load is assumed for each unit operation, the
concentration of the source might be reduced as well, and the overall
fresh requirement can be reduced. For fixed load operation, the
flowrates of the sink and source can be reduced, as long as the fixed
mass load is guaranteed. This could lead to a reduction in a fresh
resource. However, future research should incorporate the realistic
relationships between the inlet and outlet contaminant concentrations.
The interaction between multiple contaminants in either inlet or outlet
streams should be taken into account as well. Future research can be
focused on a Multi-Contaminant Cascade Table Analysis. It can be
developed for automated resource targeting. Water regeneration potential
and multiple fresh resources with prioritised objectives should be
incorporated into the analysis as well.