Enhanced cascade table analysis to target and design multi-constraint resource conservation networks

Abstract

Process Integration tools have served the process industries by identifying resource conservation solutions that minimise process waste, reducing the environmental impacts and costs. For dealing with water and wastewater minimisation, Pinch-based targeting and network design approaches are well established to handle single-quality water conservation problems. The Cascade Table Analysis, which has been an extension of the method used for targeting and designing single-quality material recycling networks, has evolved to handle multiple qualities. Based on previous analysis, multiple cascades with individual contaminant/quality indicators are analysed sequentially. Each contaminant is assigned a cascade table. Each sink is classified into the proper contaminant cascade based on their limiting contaminant, and the sources are prioritised based on the contaminant. This work also proposes a new way of arranging the Cascade Table streams to adapt for the multiple contaminants, which is by determining whether they belong to the high quality (Below the Pinch) region and the probable Pinch-causing source. The overall framework has been first identifying preliminary resource targets for each sink, followed by specific heuristics for additional reduction of the fresh resource. The proposed algorithm could yield an accurate minimum resource target and the associated network design. This work also explores the water-using processes with fixed load and fixed flowrate operations. An illustrative study and a real case study from a Brazilian paper mill are used to demonstrate the approach. The fresh water resource identified for the case study is 2,822 kg/h. The developed approach provides an informative interface to the user for the exact allocation of sources to the sinks. The numerical approach also shows directly the location of the Pinch Point(s), the overall fresh resource intake and the waste generation.